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3 Humans in the hot deserts and subdeserts.

1. Human settlement of the hot deserts and subdeserts

1.1 Technological and social adaptations to a difficult environment

The scarcity of resources in the hot deserts and, to a lesser extent, in the hot subdeserts has forced most humans living there to lead a nomadic life. Over the centuries, different human populations have survived in arid lands by making use of what is offered by their environment and by learning to organize their seasonal transhumance so as to anticipate the seasonal changes.

Thus, they have traveled to sites where there was food and water for them and their herds, taking advantage of the abundant water in the rainy season and staying near poorer but safer permanent sources of water in times of scarcity and drought. Sedentary populations have only occurred where water was not a limiting factor, for instance, at an oases or on the banks of some large rivers bearing water that fell as rain in distant mountains.

Sedentary life and the control of water resources

Many deserts have not always been as dry as they are today. The Sahara, now the textbook example of a hot desert, was very dry at the peak of the last glaciation (about 18,000 years ago), but the melting of the glaciers made it a very rainy region (though there continued to be a dry season) with large lakes. The deserts of Arabia also show traces of past wetter periods some 9,000-6,000 years ago, when the fauna of the lakes in what are now the Rub' al-Khali and An Nafud deserts included hippopotamuses. Little is known about Arabia's archeology in comparison with the Sahara's, and it is still not known for sure if any human populations lived there, although in light of known later population movements it seems likely that some did. Remains of pre-Neolithic settlements are also very scarce in the other hot deserts (apart from those in Australia, where the Paleolithic lasted until British colonization of the nineteenth and twentieth centuries).

Colonization of the deserts requires technological adaptations beyond the reach of the bands of Paleolithic hunter-gatherers, who preferred to live in less inhospitable areas anyway. In fact, hunter-gatherers have, in almost all cases, only colonized deserts and subdeserts when more powerful and aggressive populations--or technologically more advanced ones--have forced them to take refuge in lands unsuitable for agriculture; this is true of the San of the deserts of southern Africa. Most of the world's hot deserts (except those in Australia) were really only colonized when irrigation-based agriculture and nomadic pastoralism developed.

Irrigating crops and traveling with herds in search of pastures help make food supplies more regular in harsh arid environments, and the oldest (and almost contemporary) traces of both techniques seem to come from the same region: the northern desert and subdesert areas of the Syrian Desert and Mesopotamia adjacent to the Fertile Crescent. In this area, about 8,000 years ago, some human groups were experimenting with irrigation by gravity using water from artesian springs, while others started to travel across the deserts with their herds in search of grazing. Since then, these two economic and social systems have been put to the test, either complementing each other or ending up as irreconcilable opponents.

Irrigation for agriculture started to take off in Mesopotamia 7,000-8,000 years ago, in Egypt about 6,500 years ago, and in the Indus Valley roughly 6,000 years ago. Irrigation provided the basis for the first great historical civilizations and the first city-states in which power was centralized and a significant part of the population held posts that were not related to food production (jobs in administration, warfare, manufacturing, sciences, or the arts).

Not all traditional irrigation-based agriculture has utilized surface or underground water. Some desert farming cultures have been based on the use of rainfall. The Nabataeans and the Peruvians developed elaborate, but different, techniques to make use of the slightest rainfall.

Between 400-200 b.c., the powerful Nabataean kingdom occupied the Syrian Desert as far as the Negev, along the eastern bank of the Jordan and the Dead Sea. They prepared a reasonably large water catchment basin (about 20 ha for each hectare [1 ha=2.5 acres] to be irrigated) and channeled the rain falling anywhere in the basin to the plots they wanted to irrigate. This was an area of 1-3 ha, at the outlet of the catchment basin with a margin that acted as a dam to retain the topsoil and the incoming water. The water permeated into the soil and supplied the soil water reserve. If there was any water leftover (after heavy rainfall), it could flow to the next plot at a lower level and then to others at even lower levels. Less is known about the techniques used by the ancient coastal inhabitants of Peru, but they certainly included terrace systems and systems to use rainwater. In the Arequipa region, the recurrent fog at the altitude of the lomas seems to have been used in a sort of dry farming that did not rely on rain.

Irrigation agriculture is now widespread in all the world's arid and semiarid regions, even in the Mediterranean areas (see vol. 5, pp. 275-279), but nowhere is irrigation as important for human settlement as in the hot deserts. Irrigated areas create concentrations of high population density in a small area. Most humans living in hot deserts--in Mesopotamia, the Peruvian coastline, the Nile Valley, the Colorado Valley, the Saharan oases, and the villages of the Chihuahua Desert--in fact live outside the desert in areas that irrigation has transformed into market gardens and orchards

Nomadic life and control of routes through the desert

The strategy of extensive exploitation of both water and grazing resources in the immense hot desert lands seems to have originated in the deserts of southwestern Asia at almost the same time as irrigated agriculture. Contemporary Bedouins are probably the direct descendants of those first nomadic herders of about 8,000 years ago, whose lifestyle must have been very different, as the ass or camel had not been domesticated and horses were unknown until they arrived in the area already domesticated.

The first nomadic herders thus traveled on foot with their herds from water hole to water hole, just as the desert hunter-gatherers had done before them--and just as some Australian Aborigine peoples (such as the Pilbarras) continued doing until the twentieth century. Later, some started to ride cows, as shown in many Saharan rock paintings from the cattle phase; cow riding was still practiced in the early twentieth century by Khoikhoi herders in southern Africa. The decisive step was the domestication of the camel, "the ship of the desert," by the Arabs 5,000-6,000 years ago and the subsequent development of the first caravan routes from Syria and Mesopotamia to Egypt and southern Arabia.

The nomads of the hot deserts have not always confined themselves to extensive stockraising. Once they had beasts of burden and animals to ride, the nomads also controlled the routes crossing the deserts. Nomadic trading was a natural complement to the economy of the sedentary inhabitants of the oases: the nomadic herders supplied the sedentary populations with livestock products (wool, leather, milk products, horns) and could transport their goods reliably across the desert. In turn, the sedentary peoples supplied the nomads with plant foodstuffs and all the manufactured objects necessary for life in the desert (knives, textiles, cooking utensils, and weapons). Sometimes, this complementary relationship soured, leading to confrontation and hostility. It is important to note that the two sides have deep differences in their social organization and outlook. Nomads have been stereotyped as barbarous, violent, dangerous people with unlimited territorial ambitions, troublemakers who are envious of the good life enjoyed by people who have settled down. Sedentary peoples have been stereotyped as greedy tricksters, jealous of the nomads' freedom and lacking in both strength and resolve.

Individual ownership of land makes no sense to the nomads of the deserts of Africa and Asia; for them, personal wealth takes the form of livestock, slaves, servants, and easily transportable valuable objects (jewels, decorations for tents, harnesses, weapons, clothing). Pastures and water holes, however, are the collective property of the different groups of each nomadic society and sometimes give rise to disputes between them, disputes that often end in bloodshed. Violence and aggression, together with an overriding sense of honor, can set off a chain of killings and revenge killings between families and clans. This aggression, when directed outward and exercised collectively by a large enough group of nomads, may turn a minor quarrel with the sedentary population of an oasis into a series of attacks on caravans with pillaging, slaughters, the imposition of tributes, or even an outright war (which the nomads have always tended to win, as they are better prepared for combat).

The crisis arising from the spatial and functional division of resource usage

In the end, the fascination of the cities has historically conquered the nomads, or at least their leaders, who have settled in cities and eventually adopted a sedentary lifestyle. The cities of the desert have always been surrounded by legends, intense fascination, and even religious worship. Islam was born in Medina, though it needed the help of the Bedouins to conquer Mecca and to begin the irresistible expansion of the first centuries of the Hegira. Islam made its cities of origin into centers of pilgrimage and developed a civilization in which cities from Cordoba to Delhi and from Timbuktu to Samarkand were the centers of power and the creation and diffusion of culture. Cities, as fourteenth-century Arab philosopher, historian, and sociologist Ibn Khaldun (1332-1406) commented, have been the necessary condition for civilization; wherever it has taken root, Islamic civilization has transported the city model based on Mecca and Medina.

Ibn Khaldun was highly critical of nomads, especially Bedouins, and pointed out that when nomads conquered a city, their leaders initially maintained their nomadic identity and remained in close contact with their warriors. Local authorities were responsible for all aspects of civil administration. Later, however, the nomad leaders integrated into the old sedentary aristocracy and adopted their values, so the nomad state became sedentary and urban.

Throughout the twentieth century, the implantation of a system of nation-states throughout the Old World hot deserts has completely changed the relationship between nomads and sedentary peoples. (It seems to have tipped the balance even further in favor of the latter.) The states--even those ruled by a dynasty with nomadic origins (Saudi Arabia, Jordan, Kuwait) and those mainly controlled by peoples from a nomadic tradition (Mauritania, Libya)--sooner or later (and generally sooner rather than later) become sedentary; the city-dwellers inevitably seek to preserve their sovereignty, expressed by maintaining the integrity of their frontiers. This leads to the establishment of policies to encourage permanent settlement, the construction of new capital cities from scratch, and ongoing conflicts between many nomads (especially the Tuaregs) and the governments of the states where they live because of the incompatibility of their system of use of space with the frontiers imposed by colonization. The nomads who do not accept settlement tend to be marginalized by their new society, but those who settle down are also in marginal situations, especially if they practice agriculture; those who respond best to this change are those whose activities are more in line with their cultural tradition (soldiers, haulers, traders, and the like).

The discovery and exploitation of oil fields has completed the total change in the socioeconomic relationships of all the populations--both nomadic and sedentary--in oil-producing countries. Involvement in oil production stimulates widespread migration to the cities and oilfields and results in the abandonment of traditional economic activities. Conversely, the Saharan countries where no oil has been found are among the countries with the world's lowest per capita income and where a high percentage of the population is employed in traditional economic activities.

1.2 Humans in the hot North African deserts

Humans settled the Sahara long ago (see vol. 3, pp. 250-252). What is now an immense desert must have had a higher population in ancient times, when the prevailing climate was much wetter and supported a richer flora and fauna. There was, then, a wider range of resources when human groups arrived in this now-desert zone either from the Mediterranean coastline or from the southern savannahs.

The ancient settlers of the Sahara

The first settlers were hunter-gatherer peoples living in relatively permanent settlements near the banks of lakes, where there was plentiful food and water, or in the rainier strip to the south. The oldest archeological deposits yet found (estimated to be 10,500 years old) show the existence of encampments inhabited by fishermen (fishhooks made of shell have been found) and hunters of hippopotamuses and crocodiles. The people also collected grain from the wild grasses. Sites dating back 9,000 years have yielded evidence of the use of pottery made with barbel bones and decorated with wavy lines. Such finds indicate that the settlements were by this time more stable, though they did not have a Neolithic economy. The distribution of the pottery coincides closely with the current distribution of the languages of the Nilotic-Saharan family. Individuals who speak these languages are thought to be descendants of the groups of Saharan fishermen who made up the aqualithic culture.

The first traces of the domestication of cattle appeared about 8,500 years ago, and, within 500 years of that, some farmers were cultivating sorghum and millet. As the region's climate became drier, the people retreated to the oases in the Sudan, the Nile Valley, and the desert's northern and southern edges, except for the stockraisers, some of whom continued entering the desert during the rainy season with their herds, beasts of burden, and steeds. About 2,000 years later, desert herders could still find fodder for their horses, but horses were eventually replaced by dromedaries.

One of the greatest civilizations of antiquity, the ancient Egyptian civilization, arose about 6,500 years ago in the Nile Valley and Nile Delta and lasted until the time of the Romans. Egyptian civilization was based on agricultural irrigation methods that used the Nile's floodwaters to fertilize the land as well as irrigate it. The flooding of the Nile is highly regular, always occurring at the end of summer. This regularity allowed the Egyptians to develop a calendar system and made planning for the future easier. Once the waters had returned to their normal level, the Egyptian farmers planted grain; the crops grew without needing additional water until the harvest in April-May. After harvesting the grain, the fields were left fallow for a few months, until the following flood brought new water and nutrients (see vol. 10, p. 424). The period of the Roman empire, the advent of Christianity, and the later conversion to Islam hardly modified the living conditions of the Egyptian farmers, though each invasion brought new crop species.

The Tuaregs and other current inhabitants

The Tuaregs, a Berber-speaking people, are nomadic herders. Specialized in trans-Saharan trade, they have traditionally raised camels and asses for use as beasts of burden on their long journeys. They also raise sheep, goats, and cows in the Sahel-Sudan region. In the rainy season, they usually head toward the interior of the Sahara to find good grazing for their herds; at this time of year, the very rich milk is the herders' basic foodstuff. Different Tuareg groups often coincide in the grazing areas, and intertribal events are held--the naming of newborn children, camel dances, and weddings among them. It is also the time when wild millet is collected and stored for the dry season. When the dry season arrives, the Tuaregs return south, where they remain until the rains are due and it is once again time to set off into the desert. If the rains do not arrive on time, many of their cattle may die.

The Tuaregs' good technical and social adaptations to the harsh conditions of the desert have allowed them to maintain their own language (Tamashek) and script (Tifinagh) despite the adverse circumstances. Tamashek is a language of the Afro-Asian family that belongs to the now highly fragmented group of Berber languages spoken in the Maghreb (see vol. 5, pp. 186-187) and much of the Sahara.

The traditional Tuareg society is so highly stratified that one can talk of the existence of castes or social strata. The highest caste is represented by the immagaren or nobles, who avoid mixing with the members of the other strata and whose genes have thus been relatively isolated. The imraud are vassals owing allegiance to one of the noble families, but they can own slaves. The iklan, or servants, are descendants of slaves taken prisoner on raids against sedentary farmers and kept in the service of a lord from one of the higher castes. The inadan or blacksmith class are craftsmen who make weapons and jewelry and are usually avoided by the rest of the population. (They are considered dangerous due to their relationship with the supernatural through the use of fire.)

Finally, there is the caste of inislimen or wandering priests, who supply amulets to all the different strata within the groups. The Tuaregs are Muslims but retain many pre-Islamic traditions; for example, unlike Arabs and Bedouins, their society is matrilineal and they are monogamous. Much of their social organization was broken down by French colonization and later by the socioeconomic policies of the states where they live, especially by the abolition of slavery and of feudal systems of allegiance. There are now about one and a half million Tuaregs living in the five African states in the region, Algeria, Burkina Faso, Libya, Mali, and Niger. Since these states' independence, the Tuaregs have been increasingly marginalized and have been in permanent conflict with the always distant and often authoritarian governments of the new states. The drawing up of frontiers has restricted their movements and has been one of the main causes of conflict with the governments. Freedom of movement is essential for the Tuaregs, even though they are able to find alternative solutions to the irregularity of the climate.

To the west of the Tuaregs, in the Saharan areas of Algeria, Mauritania, and the Western Sahara, live the Moors, who are also of Berber origin, but with greater Arabic and Islamic influences. They are also mainly nomadic herders, although their social organization is not so stratified and as a result of their conflict with Morocco has become even more egalitarian among the Reguibat and other tribes of Western Sahara, now better known as Saharans. Farther east, in Chad and Sudan, there are populations who speak Nilotic-Saharan languages, especially the Tedes or Tebus, the Daza, Zaghawa, Messalits, and Nubians. The Saharan populations of Egypt, Libya, and Sudan are mostly Arabicized, though it seems that the sedentary rural populations of the Nile Valley have not received external genetic inputs since the stabilization through unification of Upper Egypt and Lower Egypt in the times of the pharaohs.

In the Horn of Africa, the Saho, Afar, and Somali are mainly nomadic herders of goats, sheep, and camels, though there are some areas with sedentary populations along the rivers, especially in southern Somalia and in the former city-states on the coastline. In the less dry regions of northwestern and southern Somalia and southern Ethiopia, some people live as stockraisers--the Boran of southern Ethiopia, for example. They do not have as highly a developed caste system as the Tuaregs, but some craft trades (such as blacksmiths and tanners, who are also hunters) are associated with highly inbred castes. With few exceptions, all these peoples of the Horn of Africa are repelled by the idea of eating fish; even on the coast, only the nonnative population eats fish. Only a few groups of Somalis, among them the Midjurtin at the eastern tip of Somalia and the Rer Magno on the coast north of Moqdiisho (Mogadishu), are mainly fishers.

1.3 The humans of the hot deserts of southern Africa

The deserts and subdeserts of southern Africa are inhabited mainly by populations that have settled there relatively recently and who were often forced there by hostile peoples. The first human settlers, at an unknown date, lived by hunting and gathering roots and fruits (except for those living on the coast, who collected marine molluscs) and sheltered in caves. Nowadays, the most characteristic inhabitants are the Khoisan, whose morphology and languages are sharply different from those of all other Africans, but there are also Bantu-speaking peoples such as the Herero and Himba.

The Khoisan peoples

The Khoisan live in the deserts, subdeserts, and savannahs of southern Africa (Botswana, Zimbabwe, Namib-ia, and South Africa). Until recently, the roughly 55,000 San, or Bushmen, lived in the dry savannahs and the subdesert thickets of the Kalahari as hunter-gatherers, but very few now live their ancestral lifestyle.

The roughly 30,000 Khoikhoin, or Hottentots, are nomadic herders who breed herds of cattle, sheep, and goats; the milk of these animals is their basic foodstuff. Both groups speak variants of the Khoisan linguistic family, the "click languages" that are the only languages using unusual aspirated velar sounds known as clicks. Both the San and the Khoikhoin are descended from an ancestral group that occupied vast areas of Africa in the past. The invasion of the Bantu peoples from the north, starting about 2,000 years ago, pushed them farther south, and then the expansion of the European population after the founding of the Cape Colony 300 years ago gradually deprived them of the best grazing grounds in southern Africa. The Bantu and the Europeans drove them to the most arid regions of southern Africa, where they still live, as they could not defend themselves from the Bantu people's superior iron tools and weapons or the Europeans' firearms. The confrontation of the Khoisan with the invaders led to the extermination of some (such as those who used to live in the area of the Cape of Good Hope), the enslavement of others (such as the Nusan, servants of the Tswana, the majority Bantu tribe in Botswana), or marginalization (the !Kung of Botswana and Namibia). Many were recruited by whites to work in mines, in agricultural and stockraising installations in South Africa, and more recently as guides for the South African Army during the Namibian independence war.

The Khoisan are short; their average height is 5 ft (1.6 m). One unusual characteristic of these peoples is steatopygia in the women--the tendency to accumulate fat reserves on the buttocks and thighs without developing generalized obesity in the rest of the body. It starts to develop at puberty, increases with age and successive pregnancies, and is accentuated by the highly curved lower spine of Khoisan women. It has been suggested that steatopygia is a physical adaptation to dry environments--a molecular water reserve. Yet the Khoisan only occupied these environments recently, and some of the rock paintings by their ancestors, found in wetter or formerly wetter regions from the Sahara to southern Africa, already show this feature. Sexual selection is another possible explanation for steatopygia, because in these societies large buttocks are a highly valued female characteristic.

Two additional morphological characteristics further distinguish the Khoisan from other native populations in southern Africa: their epicanthic fold (a fold of skin on the inner angle of the upper eyelid) and light skin pigmentation. The epicanthic fold makes the Khoisan look rather Asian and led early anthropologists to consider a hypothetical Asian origin, but this is now rejected. Their light skin coloring leaves the Khoisan at risk of sunburn after excessive exposure to the sun. This insufficient pigmentation seems to confirm that the Khoisan have not occupied the desert environment until the last few centuries and evolved in conditions of less intense sunshine in the temperate regions of the southern tip of Africa or even in regions now occupied by the Sahara before they dried out over the last few millennia.

The Bantu peoples

The earliest remains suggesting human occupation of the Namib Desert are about 2,000 years old. At that point in time, nomadic stockraising was already established in the area. The Zemba or Himba--"the ochre people of the dry river beds," one of the peoples of the Herero group--say they are the descendants of those first inhabitants. The area is also inhabited by other peoples of the Herero group, who belong to the Bantu tradition. The Himba are experienced in using the desert's resources and follow a semi-nomadic strategy. They are governed by the principle of double descent, which is found in few other areas of the world and consists of membership in two clans, the patriarchal and the matriarchal: they are said to inherit spiritual and social goods from their father, and material goods from the mother and her brothers. Now independent, Namibia is forcing the Himba to abandon their nomadic lifestyle and accept school education and Christianity. Modern Namibians show little interest in or respect for the indigenous cultures. School-educated children are rejecting the ancestral culture and customs, so the maintenance and future of the traditions are not ensured.

The Herero are nomadic herders who live in the center of Namibia on the edge of the Namib and Kalahari. Originally from regions farther to the north, they are possibly the descendants of herders from Angola who settled in southern Africa in the fifteenth century, and, like the other Bantu peoples, knew how to work iron. When the Germans started to colonize Namibia in 1883, they broke up the nomadic stockraising system. This led to the outbreak of the Herero rebellion in 1893. Combat continued for a period of 15 years in a genuine war of extermination that left more than 65,000 dead. The survivors were expelled to the most arid regions of the Kalahari or kept in virtual slavery to work on the land the colonists had appropriated.

When World War I (1914-1918) broke out, the South African Army invaded Namibia; the Germans surrendered in 1915. The Herero population was under less pressure during the South African occupation than it was during the period of German domination, and they were able to recover somewhat despite successive rebellions against the new occupants, who controlled Namibia until its independence (1990). The Herero now number about 400,000, making them one of the most influential minorities in Namibia, where they occupy numerous secondary positions in the administration. Their traditions, however, have been lost.

European colonists

The successive waves of colonization by Germans (1883-1915) and Afrikaaners (1915-1990) left about 80,000 whites in Namibia, more than half of Afrikaans origin and almost one-third of German origin. They represent only about 6.4% of the population, but they are extremely influential. The Afrikaaners are more numerous in the South African Karoo and in the rest of South Africa.

1.4 Humans in the hot deserts of Asia

The desert and subdesert zones of the Near East were settled by humans during the Paleolithic, and this important crossroads has been the site of some of the defining events in human history. The northwest edge of the Asian hot deserts, the Fertile Crescent, saw the beginning of the change from a Paleolithic hunter-gatherer economy to a Neolithic economy based on domesticated animals and plants and voluntary food production. Recent hypotheses suggest that the Neolithic was spread about 10,000 years ago by separate migrations northwest to Europe, southwest to Arabia and Africa, and southeast to Iran and India. These migrants were the origin of the populations that would later speak Indo-European, Afro-Asiatic, and Dravidian languages. Two cultural traditions started in the regions of the Syrian Desert closest to the Fertile Crescent: one linked to irrigated agriculture in oases and on riverbanks, and one linked to nomadic pastoralism. These two traditions have shaped human life in deserts for the last 8,000 years.

The hydraulic civilizations and the nomadic herders

The alluvial plains of Mesopotamia, though their climatic conditions are comparable to those of the neighboring deserts, receive water in rivers coming from rainier regions. These plains were the birthplace of irrigated agriculture, the basis for the appearance of the first urban cultures. From 8,000-6,000 years ago, many city-states arose, first in Lower Mesopotamia, then in Upper Mesopotamia and on the plains at the base of the Zagros Mountains, and then in the wider surrounding area. The wealth of the Mesopotamian city-states boosted the rise of other regional powers, which, in turn, left the subdesert periphery or the desert itself in an effort to take over the city-states. The Akkadian empire was populated by a Mesopotamian people speaking a Semitic language. These people were the first to unify Mesopotamia and start expansion towards Syria, Anatolia, and Iran around 2350 b.c. The Akkadian empire fell to the Elamites, a Proto-Dravidic-speaking people whose capital was Susa (now in the Khuzistan region of Iran). Two centuries later, the Elamites were replaced by the Amorites, marking the first expansion of the nomadic Semitic-speaking populations from the north of the Arabian desert.

About 4,000 years ago, a new hydraulic culture emerged in the Indus Valley--the Harappan culture (or Indus Valley civilization), which appears to have lasted until 3,7503,500 years ago, probably coinciding with the invasion of the Indo-Europeans. (Some authors, however, suggest that the decline of these civilizations can be explained by natural causes such as climate change, changes in the course of rivers, or the massive salinization of irrigated lands as a result of insufficient drainage.) The Harappan culture left far fewer remains than those of Egypt and Mesopotamia but appears to have reached a similar technical level. It disappeared 3,000-3,500 years ago, possibly due to climatic causes or due to the military superiority of the Indo-Europeans who had horses, war chariots, and iron weapons. (Warfare would have occurred shortly before the Aryan civilization imposed its control on the whole of northern India.)

While the Indo-Europeans were also taking control of the cold deserts and subdeserts of Iran and Anatolia, a succession of empires arose and declined in Mesopotamia. The Babylonian dynasty (Amorite), mainly under King Hammurabi I, saw another unification about 3,800 years ago that lasted until about 3,600 years ago. Around 1400 b.c., Assyria emerged as the main regional power, reaching its peak from 900-700 b.c. It formed the first true empire of antiquity, as it included all Mesopotamia and the Fertile Crescent, part of the interior of Anatolia, Cyprus, and Egypt. Later, the Chaldeans (Aramaeans living in Babylon) installed a short-lived dynasty that lasted less than a century, until 2538 b.p., when the Persians, an Indo-European people settled in the highlands of Iran, conquered Babylon and divided Mesopotamia into two satraps or provinces: Assyria (Upper Mesopotamia) and Babylon (Lower Mesopotamia).

Two thousand years ago, after Persian conquest and then Hellenic domination following the conquests of Alexander the Great (see p. 384), Mesopotamia and the Arabian deserts marked the eastern frontiers of the Roman Empire. In Iran, there was a revival of the former Persian empire under the Sassanian dynasty (the Sasanids), and, farther to the east, the Indo-Scythian Kushan empire dominated the area from middle Asia to northern India. The scene was totally disrupted in the third and fourth centuries mainly by the arrival of nomadic populations from the steppes and cold deserts of Asia. The hot deserts were more influenced by Islam, which arose precisely in the Arabian deserts. In the seventh and eighth centuries, the Muslim Arabs took their new religion west beyond the Pyrenees and east as far as the Punjab, establishing the basis of an empire that was soon politically fragmented, though it showed remarkable religious unity throughout the area under consideration (and beyond). The Mongol and Turkish invasions were the last contribution to the populations of the hot deserts and subdeserts of southwest Asia. In the twentieth century, especially since the creation of Israel in 1948, Jewish immigration has led to the return to the promised land of many groups of Jews from around the world.

All the actual populations of the hot deserts and subdeserts of southwest Asia are Caucasoids and clearly differentiated from those of northern and eastern Asia and from those of southern Asia and northeast India. They can be separated by linguistic criteria into two large groups: the peoples speaking Indo-European languages (Baluchi, Punjabis) and those speaking Afro-Asiatic languages (Arabs, Israelis, Druze, Yemeni).

The Indo-European peoples

The deserts and subdeserts of the Near East are home to many peoples (Baluchi, Punjabis) who speak Indo-European languages. They occupy the easternmost part of this desert and subdesert area and are mainly descendants of settlers who arrived from the steppes and the central Asian steppes and subdeserts about 3,500 years ago.

The Baluchi form the core of the population of Baluchistan, now split between Iran and Pakistan, and have interbred with the neighboring populations: Punjabis and Sindh to the east; Turks to the north; Arabs to the south; and Farsi to the west, though they consider themselves descendants of Arab populations from Aleppo. The medieval invasions by Turks and Mongols forced them to retire to the desert zones, both the hot deserts (the coastal regions) and the cold deserts (the plateaus) where they became nomads, expert horse trainers, and camel drivers.

The Punjabis and Sindhi form most of the population of Pakistan and are also numerous in India. (The Punjab was divided in two at the India-Pakistan frontier when the two countries became independent in 1947.) Other populations of Indo-European origin also form the majority of the population in the desert and subdesert regions of Gujarat (Gujaratis) and Rajasthan (Marwaris).

The Semitic or Afro-Asiatic populations

The peoples who speak Afro-Asiatic languages (traditionally known as Semitic languages) seem to have arisen in the hot deserts and subdeserts of Asia, either in the southern branch of the Fertile Crescent or on the northern periphery of the deserts of Arabia. Afro-Asiatic languages are now spoken from Mesopotamia and Arabia to the Atlantic coastline of the Sahara and as far south as the equator in eastern Africa. The distribution of this linguistic family has varied little over time, though the relative importance of its different languages has changed. Languages thousands of years old that were spoken by the populations of large empires have disappeared (such as Ancient Egyptian and Akkadian), while others that were originally spoken by a few small tribes have become major world languages (for example, Arabic). Some of the languages of this family were among the first to leave written traces; the alphabet used to write this book is derived from the Phoenician alphabet. Afro-Asiatic languages are spoken by the Hebrews, Copts, Arabs, Berbers, Ethiopians, and other peoples.

Like the Sahara, the Arabian Peninsula had a more benign climate after the last ice age, though both are now total deserts. The increasingly dry climate caused major migrations northward to more welcoming sites, especially toward Mesopotamia. The successive waves of migration were by Akkadians (5,000 years ago), Amorites (4,000 years ago), Aramaeans (about 3,000 years ago), and Arabs (in the seventh century). Roughly 3,000-4,000 years ago, the Hebrews and Canaanites settled in the area of Palestine and Syria.

The term Arab is used to designate all the inhabitants of the Arabian Peninsula, but it is necessary to distinguish the inhabitants of southern Arabia (or Arabia Felix), who are mainly urban and sedentary with an agriculture-based economy, from the inhabitants of central and northern Arabia, who are mainly nomadic herders, although there are also sedentary farmers, known as fellah, in the oases. The origin of the Arab nomads goes back 3,000 years. When the domestication of the dromedary and the techniques related to its use as a beast of burden or as a steed became widespread in the Arabian desert, the peoples living in the north of the peninsula (Edomites and Nabataeans) could travel and colonize the desert region (the Nabataeans excelled in their low-water-consumption irrigation and agricultural techniques). They soon controlled trade between Arabia Felix and Mesopotamia. The Assyrians knew of these warrior peoples around 2,850 years ago. By about 2,000 years ago, the Arab herders had reached Arabia Felix and had assimilated the groups of hunters that still lived there, establishing castes that still exist and pushing south the pre-Bedouin tribes of herders, who spoke non-Arabic Semitic languages. Arabia was reached first by Judaism and then by Christianity, and some Arabs converted to these faiths, but the typical religion of the Arabs is Islam, preached by the Prophet Muhammad after his divine revelation, which is recorded in the holy book of Islam, the Koran.

Muhammad's Islam spread very quickly, and within a century Islam stretched from the Iberian Peninsula to central Asia, creating a corridor with a common language, along which merchandise and culture could circulate freely from the Atlantic to China. After 623 a.d., the history of the Arab peoples is inseparable from that of their religion, which, in turn, is inseparable from the history of their language. The true Arabs, who claim to be the direct descendants of the Arabs of the times of the Koran, are Bedouins. They represent all the camel-riding tribes of Arabia (and some areas of northern Africa). These groups are now mainly sedentary, but some are still nomads who live by stockraising and trade or form units in the region's armies, just like the warriors in the past who ensured the security of the sedentary Arabs in return for tributes. The conversion of the Near East to Islam spread the Arabic language throughout the region; thus the Palestinians and the Druze are also Arabic-speaking groups.

An Old Testament tale states that about 4,000 years ago, Abraham, the patriarch of several seminomadic tribes, led his people from Ur to the Land of Canaan, east of the Dead Sea, in search of better pasture for their herds. Later, possibly forced by the Hyksos, most migrated to Egypt, where they remained until Moses organized their return during the reign of Rameses II. On their way back, they spent 40 years in the desert of the Sinai Peninsula, living as seminomadic herders. When they returned to their land, they had to struggle with the people who lived there. Then they formed a confederation of seminomadic tribes, united by their common faith in Jehovah and commanded by temporary leaders known as judges. They survived conflicts with the different neighboring peoples (Canaanites, Moabites, Ammonites, and Philistines). The persistent threat from the Philistines led them, about 3,000 years ago, to adopt a monarchic system, which reached its greatest splendor in the days of King David and his son Solomon.

The fall of Jerusalem to the Babylonians in 586 b.c. led to the first diaspora of the Hebrews, which lasted for less than a century. Their social and religious links, together with the Jews' faith that they were the chosen people of God, has helped them to maintain their identity as a people, despite the migrations and persecutions (though the destruction of Jerusalem by the Romans in 70 a.d. and the banishment of the Jews from their land led to their spread throughout the world for 2,000 years). In the late nineteenth century, the Zionist movement arose and sought the Jews' return to the land of Israel. Throughout the years preceding and following the Nazi Holocaust in World War II (1939-1945), during which roughly six million Jews died, tens of thousands of Jews arrived in Palestine and demanded the creation of an independent Jewish state there. (At the time, Palestine was under British administration.) The Jewish state came into existence on May 14, 1948, a few hours before the end of the British occupation of Palestine, with the approval of the United Nations Organization. The first Arab-Israeli War started immediately, leading to defeat for the Arabs and the exodus of nearly a million people of Arabic descent. Four million Jews and nearly a million Arabs now live in Israel.

1.5 The humans of the hot Australian deserts

It is widely accepted that humans arrived in Australia 60,000-50,000 years ago, but there is no proof that they lived in the desert until 20,000 years ago; the oldest archeological remains are sites in the Cleland Hills in the Hamersley Range and in the Nullarbor Plain in the south of the Victoria Desert. The zone, which must also have been arid then, supported a human population that lived as hunter-gatherers.

The Aborigine population

At the height of the last glaciation (20,000-16,000 years ago), humans seem to have abandoned the Australian deserts and did not return until about 10,000 years ago. By the time of the arrival of the European colonists, the Australian Aborigines had acquired a great deal of information about the climate, plants, and animals of the areas where they lived. The flowering of the Grevillea trees indicated that the kangaroos were fat enough to be hunted, and the fruiting of Eremophila (emu bush) indicated that the emu would soon arrive at the water holes to drink. The rains provided the Australian Aborigines with different and more varied foodstuffs such as flowers, seeds, and insect larvae. Like other hunter-gatherer groups, they did not store foodstuffs but rather led a hand-to-mouth existence. Gathering was done by women, who searched for insects (and their larvae and eggs), worms and slugs; roots of the wild yam (Dioscorea); water-lily (Nymphaea stellata) seeds; purslane (Portulaca); fruits of sedge; some parts of Eucalyptus trees; and the wood, resin, roots, and flower buds of Xanthorrhoea. The men hunted emu and kangaroos. They fished with nets or bone or thorn harpoons, or they encircled the fish and caught them by hand or after stunning them with blows. There is evidence to show that they planted grass seeds, mainly different species of Panicum, and cuttings of some roots, especially yams. The fact that agriculture did not prosper is surely due to the lack of incentives to plant or tend plants that would have been no more abundant or predictable than spontaneous ones. The low productivity of land in Australia has led the people living there to use the widest variety of food resources. But, despite this wide range of food resources, many Aboriginal songs refer to hunger, an ever-present danger, especially in the most arid areas.

There have never been many Australian Aborigines, and they have surely never exceeded 200,000-300,000. When British colonization began in the late eighteenth century, they were probably split among many tribes, about 40 of them desert-dwelling. They used tools of wood, stone, bone, and occasionally even shells. They had boomerangs, but not pottery or bows and arrows. Using the hair from their own head and beards, which they spun with spindles, they made resistant ropes, and several tribes had complex rules governing hair donation by group members. The old men gave up the hair from their moustache and beard, and their clean-shaven head was a mark of respect.

The European colonists

Europeans arrived in Australia in the eighteenth century but did not enter the desert areas until much later and have never been numerous except in the small urban centers. To learn about the interior and to explore it, they used natives as guides. Cattle stations and population centers arose in the desert, some of which have grown into small urban centers, though only Alice Springs (founded 1871), which, as its name suggests is next to a spring, has more than 10,000 inhabitants. Many Australian Aborigines were attracted to urban life and decided to abandon their traditional ways of life and live in populations such as Balgo, Jiggalong, Lake Nash, Ernabella, and Papunya in the center of Australia, or in Wiluna, Oodnadatta, and Alice Springs.

The many problems created by their rapid urbanization-mainly unemployment, alcoholism, and other forms of drug abuse--has led to a return to traditional lifestyles, especially where their routes and other infrastructure have been restored. The Aboriginal Land Movement (ALM) emphasizes that the Aborigines' links to the land led to improvements in education in communities living in deserts. The ALM is now managed by a community committee, which employs teachers and has a right to express its opinion on the program. Thus, thousands of people maintain their languages because education is bilingual. There are also radio and television stations controlled by Aborigines broadcasting in several languages to the people living in the desert. Even so, access to a suitable sanitary system is a problem for communities living in the Australian desert. Legal conflicts often arise between Aboriginal territorial councils and mining companies wishing to exploit their sacred sites, but in some cases agreements have been reached that satisfy the Aborigines, the government, and the geological exploitation services, since they represent work for the Aborigine community.

1.6 The humans of the hot deserts of North America

Since the first settlers crossed the Bering Strait, human population movements in the Americas have been very complex. In different places and at different times, the Amerindians have formed groups and tribes related to each other by their language or by the different techniques used to extract natural resources, depending on the climate and terrain. The high mobility of the groups and the varied contacts between them split the indigenous population of the Americas into a complex mosaic of neighboring tribes with widely different degrees of relationship. Linguistic features seem to reflect genetic relationships more closely than cultural or geographic ones do, though some groups are left out and there is no unanimity among historical linguists. One of the more recent interpretations, that of Joseph H. Greenberg, seeks to bring together the three main families established by American anthropologist and linguist Edward Sapir (1884-1939) in 1929; Amerindian, Na-Dene and Eskimo-Aleutian. The indigenous peoples living in the hot deserts and subdeserts of North America can be divided into three main linguistic groups: the Uto-Aztecan, North Amerindians, and Na-Dene. They all used to occupy areas much larger than the hot deserts and subdeserts.

The Uto-Aztecan peoples of the Mojave Desert and northern Mexico

Some Uto-Aztecan speaking peoples used to occupy much of the Mojave Desert in California and much of the hot desert and subdesert land west of the Rio Grande, in the area now on the frontier between the southwestern United States and northern Mexico. Their survival strategies were very diverse: some of the more southerly groups had learned the agricultural techniques of the Neolithic centers of Meso-America and lived in stable settlements, while the more northerly groups were hunter-gatherers. The Mojave Desert-and the desert and subdesert areas of southern California in general-was home to the most southerly Paiute, whose main area of concentration was farther north, in the Great Basin (see also p. 393). Their main tribe in this area was the Chemehuevi. The desert character of the zone forced them to live a precarious nomadic life as hunter-gatherers using a very limited range of tools, but they had a wide range of baskets and receptacles that they used for very diverse purposes. They gathered roots (the reason why they are known as "digger Indians"), herbs, and fruit and captured fish and small game (mainly cottontails), though they also hunted bigger game (deer) when they could.

The Pima lived farther to the southeast in the Sonoran Desert. They formed numerous tribes that developed into a very advanced agricultural society. The Pima grew maize in terraces that they irrigated with systems of channels. They hunted small game, fished, and gathered; they also obtained food and alcoholic drinks from agaves and cacti. Tribal ceremonies sometimes called for the ritualistic use of peyote, a small cactus with hallucinogenic effects (see p. 192). The Pima became known for their skilled craftspeople who wove and dyed cotton, fashioned excellent baskets, and made ceramics. Members of the tribe had small Chocho dogs and succeeded in domesticating hawks and eagles, fed by the children with snakes, lizards, and leeches. For transport, the people used bags made of bundles of reeds; the women used nets to carry extra-heavy loads. Their social regime was patriarchal, and the village unit was ruled by a chief. There are now about 10,000 Pima in reserves in Arizona and about 3,000 in Mexico.

The Hokan peoples of the Lower Colorado and Baja California

The lower valley of the Colorado River and the entire Baja California Peninsula (and the coastline of the State of California as far as San Diego) was inhabited by Hokan-speaking tribes. Those in the lower valley of the Colorado (Yuman, Mojave, Maricopa) had highly developed irrigated agriculture, related to that of the neighboring Pima, but they also fished with nets in the river, hunted, and collected wild grains (grasses, which they sometimes sowed, and fruits, often those of different species of mesquite). The Hokan of the Californian coastline and Baja California (Diegueno, Cochimi) were often specialized gatherers, and there were intertribal subdivisions: the coastal groups caught fish and collected seafood, and the inland groups did more hunting and collected plant foodstuffs.

Both were bellicose (warring) peoples who valued war as a means of spiritual enrichment for the tribal collective and submitted to strict rule by their chiefs in times of war (which they did not do so readily in times of peace). The social status of women was subordinate, and they performed much of the agricultural labor. By 1910 there were less than 4,300 Hokan-speaking Indians, and many of their groups are now practically extinct; about 1,500 Mojave survive in reserves in California and Arizona (less than half of them still speak their language), along with about 400 Maricopa (only 100 of whom still speak their language) and a few representatives of other tribes.

The southern Athabascan peoples

The Athabascans (or Na-dene) tribes show clear linguistic uniformity despite their wide geographic distribution throughout Alaska, much of western Canada, and some of the states of the southwestern United States. The center of origin of the Athabascans seems to have been close to Lake Athabasca, where they arrived from Alaska, possibly in the second wave of humans to cross the Bering Strait. However, the most culturally interesting and the best known (because of their prolonged contact with Europeans) are the southern groups, the Apache and Navajo, who stopped their migration in the sixteenth century when they came up against the Spanish. The Apache were of great historical importance, and the Navajo culture showed great vitality. The Navajo live in an area at an altitude and in conditions comparable to that of the Great Basin and, thus, the cold deserts (see p. 394). Some of the Apache lived in the Chihuahua Desert, though their culture is generally more like that of the Plains Indians.

The recent arrivals

The expansion of the Europeans meant that the Indians of the hot deserts and subdeserts of North America came into contact with people with very different customs-the Spanish colonists and missionaries. These arid regions initially attracted only hunters and trappers, later followed by prospectors for gold and other valuable minerals. Colonists also arrived to settle there, made possible by the wealth of the subsoil. Development, especially during the twentieth century, has been due to this wealth, in conjunction with the expansion of irrigation systems, industry, and tourism. Large cities have thus grown up in the hot North American deserts such as Las Vegas (Nevada) and Phoenix (Arizona). The highly-mixed native populations of the desert areas of North America, which ceased to be Mexican in the mid-nineteenth century and became part of the United States, have maintained a strong Hispano-American influence, greatly accentuated in the last few years by the intense and largely clandestine migration into the United States across the frontier formed by the Rio Grande. The heavy Chicano influence is contributing to the development of a creole culture on the frontier.

1.7 The humans of the South American hot deserts

The coastal desert regions of modern-day Peru and Chile are among the most important areas of Neolithic development in the Americas. Roughly 7,000-4,000 years ago, resources caught by hunting became less important than the exploitation of marine resources and of plants in river valleys.

The peoples of the Peruvian coastline

The 5,500-year-old archeological sites in Chilca and Ancon (on the central Peruvian coast) contain evidence of the cultivation of cotton, which was used for fishing nets as well as textiles. The bottle gourd was also grown, and for 5,000 years bottle gourds are known to have been used as receptacles and also as floats for fishing nets. The first villages, one of the most important of which was Las Haldas, were established on the coast, but 4,500 years ago the settlements moved to the river valleys, near the fertile silt of the seasonal floods. Systems to irrigate the fields soon developed. The most important archeological sites are at Aspero, Sechin Alto, Huaca de los Reyes, and Garagay, where stone and peat constructions had appeared by 2600 b.c.

Around this time, thousands of tons of earth and stone were moved to build large tumulus temples, indicating considerable technical and organizational ability. Archeological finds from the Peruvian coastline and plateau dated 5,000-4,000 years ago suggest the progressive establishment of the long-distance trade of colored seashells for tubers from the Andes or brightly colored feathers from Amazonia. Ceramics and the spread of maize cultivation reached the Peruvian coastline 4,000 years ago, though farther north in Colombia and on the Ecuadorian coastline remains of pottery a thousand years older have been found. The richest and most complex civilizations of South America (Chavin, Nazca, Moche) also arose along Peru's desert coastline and the Peruvian plateau.

The Atacaman peoples

In the Atacama Desert, a pre-Columbian culture developed that spread to cover a vast area. The territory of the Atacaman people covered the puna de Atacama (the inland high plateaus) and as far as El Huasco and Jujuy. They were displaced from these regions by the attacks of the Diaguita and the Incas (Inca Yupanqui). Archeological sites in the Atacama Desert show there were relations between the Andean cultures in Peru, Bolivia, and northern Chile. Contact with the Peruvians led the Atacamans to adopt agriculture and become sedentary. About 5,000 years ago, the Chinchorro mummified the corpses of children and decorated them with clay and paint; they buried their adults with textiles, baskets, hunting tools, and other items of significance. The San Pedro site, 2,600-3,000 years old, contains ceramic pieces with similarities to those found in Tiahuanaco, near Lake Titicaca. Finds at other necropolises include stone tools (balls for bolas, harpoons, and tips for lances and arrows), wooden and bone tools, and interesting geometrically painted pottery.

From the tenth century onward, there is evidence of the existence of cities-Caserones (Tarapaca, Chile)-with an economy based on advanced agriculture and with fortifications and rectangular buildings that bounded public squares and spaces. From 1480 a.d. onward, Inca influence in the region was very strong, as is clearly shown by the types of burial.

The Atacamans are remnants of former populations that were displaced by later population movements into the area. They are presumed to have been related to the Diaguita and the Changos and may have had a common origin with them. They call themselves lincan-antai (village dwellers), or Lipas, and speak Cunza. The Atacaman people are short-statured: the men are a little more than 5 ft (1.6 m) tall, and the women are not quite 5 ft (about 1.45 m). They were nomadic hunters who traded with tribes from farther north and from the interior and with the Changos on the coast. Present-day Atacamans live by agriculture, stockraising, and fishing.

1.8 Sickness and health in the hot deserts

For a human population to exploit the resources of an environment as hostile as the desert, it must acclimatize to the environmental conditions. This is achieved by a series of homeostatic responses in the individual or group. Individual responses are acclimatization, while responses by groups are adaptations, as they do not depend on individual plasticity but the effects of natural selection on the group. Migrations, nutrition, and general state of health contribute greatly to help or hinder acclimatization and adaptation.

Acclimatization phenomena

To avoid the most serious threats to humans in a hot desert-dehydration and overheating-the body brings a series of heat-losing (thermolytic) mechanisms into operation when temperatures are too hot. When ambient temperatures are below 91[degrees]F (33[degrees]C), the human body radiates heat by convection. But temperatures are often much higher than this, and then sweating is needed to reduce body temperature, though no sweat may be noticeable if the skin remains dry as a result of evaporation. However, the lost water must be replaced in order for the body to maintain its fluid balance. The amount of water lost depends on the ambient temperature and humidity, diet, and activity. Basal metabolism in the shade requires the replacement of some water, the amount of which varies from individual to individual. In sunshine, even more water is required, and if a person is walking any distance, still more is needed. If the necessary water is not replaced, the body is forced to draw on its tissue reserves, leading to dehydration and thermostatic imbalance.

After the body has acclimatized, the sweat is less salty, reducing the risk of ionic imbalance and thus the risk of cramps in the limbs and cardiovascular disturbances. It seems to take an individual about two weeks to be able to move about and work in the desert, and few differences have been found between the natives of desert areas and recent arrivals. (Their responses were statistically similar.)

Morphological and cultural adaptations

Natural selection seems to have intervened in those cases where body morphology seems designed to favor heat loss. Tallness, long limbs, and scarce adipose (fat) tissue all make heat loss easier, by increasing the surface area/volume ratio. The most frequently cited example is the Nilotic peoples of the Sudan. Yet it can be argued that this body shape also favors water loss, though this can be compensated by suitable clothing or shelter.

Clothing is important in protecting the body from sunshine. In principle, the clothing worn should be loose and lightweight. If very active labor is required, though, it may have to be done in the nude, as sweat-soaked clothing does not protect from the heat. Clothing is also needed as protection against the hot desert winds. (The Tuareg and Moors are famous for covering their faces.) These winds cause great stress and increase the risk of dehydration, as they greatly increase the loss of body water. The inhabitants of the Sahara wear loose, light clothing, including turbans, and wear sandals that are about 1 in (2 cm) longer than the soles of their feet.

Dwellings are another type of cultural adaptation. To prevent heat from entering homes and other structures, building materials such as peat, mud, or stone with a high specific heat capacity are used, measures are taken to favor reflection of sunlight, and ventilation is reduced, as it would lead to the entry of hot air. The shape is usually compact, and many dwellings are usually built side by side to maintain a suitable microclimate. In very hot sites, underground dwellings are built to keep the rooms cool, making use of the high specific heat capacity of the ground. Desert nomads who live in tents, however, have to ensure ventilation to cool the environment during the daytime. The high specific heat capacity of the ground means they are also more comfortable at night, when the temperature may be low in deserts.

Hunter-gatherers who do not have stable dwellings have to defend themselves from the large temperature changes in other ways. The Khoisan of the Kalahari, for example, make fires and sleep together around them in a circle and under a blanket, with their feet near the fire, creating a steady temperature of about 77[degrees]F (25[degrees]C). Australian desert Aborigines can withstand frosts without stress and are not affected when nighttime temperatures fall, even though they are naked.

Recurrent famine

Famines are by no means restricted to hot deserts, though the precarious and unforeseeable nature of production in deserts means they are more likely to occur there than in other richer and more predictable environments. Yet famines are often the result of social and political inequalities and an unfair distribution of wealth, not just a simple shortage of food. Local or regional famines may be the direct result of failures in the production or distribution of foodstuffs due to natural catastrophes (flooding, eruptions, earthquakes, drought, frosts, epidemics, pests) or they may be seasonal and restricted to the time before the harvest when reserves from the previous year are finished. More often, however, they are due to social or political factors (wars, revolutions, mistaken planning, debt, corruption, speculation, or hoarding).

In reality, it is hard to establish when there is an episode of generalized famine, as it usually becomes highly political, making it difficult to ascertain the truth; sometimes it is convenient to hide bad policies or marked social inequalities or to receive aid with the excuse that the population is going hungry. In a generalized situation of famine, there is a clear increase in mortality (in the absence of any previous epidemic) that mainly affects the marginal or subordinate groups, coinciding in time with a fall in the birthrate and, of course, with increases in the price of foodstuffs. The increase in the death rate may be due to several factors: 1) malnutrition, 2) the associated social disorders, due either to the lack of food or to the resulting mental disorders, or 3) the accompanying infectious diseases, as malnourished people are more susceptible to infection by pathogenic agents.

The threshold for the clinical symptoms of hunger is a loss of about 10% of the body weight before an episode of starvation. Weight loss affects all body organs except the brain, but weight loss by other organs is unequal: the liver, intestines, and skin lose most, while the kidneys and heart lose least.

In any human group affected by famine, those who suffer most are the most physiologically vulnerable individuals, especially children. Children are the first to show the classic symptoms of the protein-energy deficiency diseases, kwashiorkor and marasmus. Kwashiorkor, often called infantile pellagra, is a dietary deficiency disease, essentially a lack of protein (and not carbohydrates), that mainly affects children 1-3 years old and usually takes the form of anemia, edema, weight loss, and a characteristic loss of pigmentation in the skin (which looks pellagrous). Some types of marasmus are linked to little or no calorie intake (often due to excessively early weaning and feeding with excessively diluted milk powder), and the clinical symptoms are major weight loss, up to 40%, and extreme wasting of the fat and muscle.

Malnutrition often begins even before the child is born. In areas where famine is endemic, the children of malnourished mothers usually have a lower-than-normal weight at birth and reduced defenses that make them easy victims to many parasitic infections. Death in childbirth is even more common among malnourished mothers who cannot breastfeed. Even when infants are breastfed, though, they start to fall victim to malnutrition as soon as they are weaned. Malnutrition affects the growth of the central nervous system when it occurs so early in life; the earlier this occurs, the harder it is for the affected child to develop correctly. Children suffering chronic malnutrition grow less than those with a normal diet, so the age/height ratio is a significant indicator of the problem. Episodes of acute malnutrition are more clearly shown in the weight/height ratio.

In adults, the first clinical symptoms of malnutrition are weakness, muscle pains, slow movement, nocturnal insomnia (though there is a gradual increase in the hours of sleep), sensitivity to noise, and fragility of the skin, which is easily bruised. The blood pressure and heartbeat decline, there are episodes of diarrhea due to atrophy, as well as digestive disorders and edema. The brain is not directly affected by these physiological responses, but they are associated with emotional upsets, including alternating episodes of apathy and extreme irritability. Concentration is poor, memory lapses become more common, and conversation is slower. Scalp and pubic hair is lost in both sexes; women grow hair on their face, and beard growth stops in men. Women cease menstruating and men stop producing sperm, and there is also a loss of interest in sex. Eventually, the appetite is lost altogether. The body's resistance to periods of starvation is very variable, and individuals not performing any physical activity have survived for up to two months. The loss of 40% of the body's weight is the critical point that usually leads to fatal consequences.

There are also social responses to worsening famine. The alarm phase is characterized by hyperactivity, due to the urgency of the matter; people show solidarity, helping and assisting each other. Gradually, markets become more and more chaotic. During the second phase, resistance, the group turns its attention to food sources that are normally ignored or considered inedible. Social relationships become less frequent, visits from family and friends are considered suspicious, provisions are hidden, and food is prepared and eaten secretly. When weight loss among the members of a group reaches an average of 20%, serious social disturbances cease. The third phase, exhaustion, leads to the disintegration of the family and inequality in the division of foodstuffs that had not occurred previously; food is withheld from the weakest, the old, and the young. Children are sold or abandoned, people may kill for food, and there may even be cases of cannibalism.

Eye infections

The different forms of ophthalmia are inflammations of the eye, especially of the conjunctiva, the thin membrane covering the front of the eyeball and behind the eyelids. Granular conjunctivitis, or trachoma (also known as Egyptian ophthalmia), is an infection of the cornea and conjunctiva produced by a microorganism (Chlamydia trachomatis). It is characterized by marked photophobia and granular inflammations of the inner part of the eyelids, which may either heal or develop into serious purulent infections that cause blindness. Chlamydia infections are sexually transmitted diseases that can be transmitted from mother to child at birth, and this is why trachoma is the most serious ophthalmia among newborns. Adults can also be infected in conditions of poor hygiene and high population density. It is spread by direct contact, infected clothing and water, and sexual transmission. Dry climates seem to favor the disease, and the countries with the highest rates of infection are in the hot deserts of northern Africa, the Near East, Australia, and several countries in the New World. But the disease is also present at lower levels in the countries of south and southeast Asia, Russia, Japan, New Zealand (where it affects the Maoris), and the Pacific Islands.

2. The use of plant resources

2.1 Harvesting without planting

Many plants growing wild in deserts can be used by humans in a wide variety of ways. Some can be used directly as shade, shelter, or fencing, while others are sources of foodstuffs or grazing for livestock. Still others provide water, fuel, or building materials or materials for a huge range of articles such as arms, tools, textiles, baskets, furniture, and artistic or ornamental objects. Some wild plants are the sources of active ingredients in various medicines, especially psychotropic drugs, or raw materials for industrial processes.

The desert larder

Hunter-gatherers and nomadic herders have had to rely on native plants to feed themselves. The seeds of wild grasses, for example, have been widely used to obtain flour in Australia, the Americas, Africa, and the Near East. Unfortunately, the nutritional value of most edible wild desert plants is unknown, though considerable efforts are now being made in South Africa and Australia to remedy this. Recent studies of the traditional food plants of the Australian Aborigines have shown that the pods of many species of Acacia are highly nutritious, with a high content of protein (17-25%), fat (4-16%), and carbohydrates (30-40%). The hard impermeable seed covering means they can be stored almost indefinitely without deteriorating, making them a good food reserve for times of scarcity.

One of the most promising species for plantation agriculture in the western Sahel is Acacia colei, a recently described species formerly included within A. holosericea. The edible plants of the Namib and Kalahari deserts include several species of cucurbits with fruits that are full of water: among them are the nara (Acanthosicyos horridus), a phreatophytic species that grows on dunes, the African cucumber (Cucumis africanus), and the wild Tsama watermelon (Citrullus lanatus); C. naudinianus also stores a lot of water in its roots, while other members of the same family--Coccinia rehmannii and Corallocar-pus bainesii--store water in their tubers.

One fruit that is of great importance in the diet of San hunter-gatherers is the mongongo nut, the fruit of Ricinodendron rautanenii (Euphorbiaceae). Other subdesert plants with edible fruits include marula (Sclerocarya birrea subsp. birrea,Anacardiaceae), whose fruits are sometimes sold by the name marula plums; snot (Thaspesia [=Azanza] garckiana, Malvaceae); kei (Dovyalis caffra, Flacourtiaceae), whose fruit is the size and color of an apricot; Mimusops zeyheri (Sapotaceae); and Strychnos cocummoides (Loganiaceae), which, unlike the well-known highly toxic species of the same genus, produces an innocuous and tasty fruit. The sand truffle (Terfezia pfeilii,) is also greatly appreciated and collected for sale.

An important food for the nomadic herders of southeast Somali and Ogaden is Yeheb (now spelled jicid in Somali; Cordeauxia edulis, Leguminosae-Caesalpinoideae), a little known species endemic to the area. A small tree that reaches a height of 10 ft (3 m), it has many stems and branches, a taproot up to 10 ft (3 m) deep, and small secondary rhizomes near the surface. The youngest roots produce the nitrogen-fixing nodules typical of the Leguminosae. Care must be taken when growing it in nurseries to avoid breaking the taproot, as the plant might die.

Jicid, formerly widespread and even locally abundant, now grows in areas with average annual rainfall of 3-8 in (85-200 mm), with sandy or loose soils, though it also tolerates slightly saline soils. It cannot withstand flooding, but it can survive two years without rainfall; its leaves curl up and may fall off in extreme droughts. The young trees flower and fruit after three or four years. The fruit of C. edulis takes 10-14 days to ripen, after rainfall; if it does not rain, however, the fertilized ovaries can delay development until the next rains arrive. The seeds do not last for long, and they germinate rapidly, though the plant grows slowly. Jicid can also be grown from cuttings.

Jicid has an edible fruit with a shell that is easily removed. These delicious fruits, which taste similar to chestnuts, can be eaten raw, roasted, or even boiled; they might even be a good table fruit if it were possible to establish plantations. Locally, the tree's fruit are so important that they are often collected unripe to make sure no one else takes them. Production is about 11 lb (5 kg) per shrub per year. The young jicid shoots and leaves are covered in numerous red or purple scaly glands that contain 0.7-0.8% cordeauxiaquinone (the only naphthaquinone found in any member of the Leguminosae), a magenta pigment derived from naphthazarine. This coloring agent, which rapidly forms insoluble combinations with many metals, can be dissolved in boiling water and is used to dye some textiles (7 oz [200 g] of powdered leaves can dye almost 10 m2 of cotton fabric). This dye is also the reason why goats that browse on jicid leaves end up with patches of bright red or orange on their teeth--and even their bones. Pigment deposition in the bones may directly or indirectly stimulate the hematopoietic (blood-forming) tissues to produce more red blood cells. Jicid leaves are used to make an infusion, and the liquid left after boiling the seeds is used to make a sweet liqueur. The wood is used as fuel. The species is now being cultivated experimentally in Israel to improve production and introduce the fruit into the food industry.

In the subdesert wastelands of northern Africa, parts of many plants are eaten, as is a fungus, the African white truffle (Terfezia ovalispora). A starch-rich lichen (Lecanora esculenta) is eaten mainly by livestock. The many plants eaten include the Malta mushroom (not a fungus, but the parasite Cynomorium coccineum, Balanophoraceae), which is greatly appreciated as a condiment. As in other deserts, the seeds of wild grasses are consumed, in this case the seeds of wild millets such as Panicum turgidum. The tender shoots of asparagus (Asparagus) and the hearts of the dwarf fan palm (Chamaerops humilis) are savored by the people of the northern African deserts; the flower shoots of broomrapes (Cistanche phelypaea [Orobanchaceae] and C. violacaea) are especially popular among the Tuaregs, who eat them whole, like asparagus. They are also eaten in times of scarcity throughout northern Africa. The roots of some scorzoneras such as Scorzonera undulata (Asteraceae) are also highly edible. Many more plants are used as condiments, especially Lamiaceae such as capitate thyme (Thymus [=Coridothymus] capitatus), Apiaceae such as Ridolfia segetum, and Asteraceae such as safflower (Carthamus tinctorius).

In the Sahel, two of the best-known species that are appreciated for their fruits are 1) the baobab (Adansonia digitata), whose leaves are also eaten (and the water stored in its trunk is sometimes consumed; see vol. 3, p. 76), and 2) the karit or shea butter tree (Vitellaria [=Butyrospermum] paradoxa; see vol. 3, p. 315). Less well-known species include kutunkuri (Lannea acida, Anacardiaceae) and other members of the same genus, and the above-mentioned marula (Sclerocarya birrea), which is eaten fresh or used to make alcoholic drinks. Other fruit-producing species of interest include: botsu (Carissa edulis, Apocynaceae); the tamarind (Tamarindus indicus, Leguminosae), of African origin despite its specific name; Combretum aculeatum (Combre-taceae); Diospyros mespiliformis (Ebenaceae), one of the western African ebonies; Parkia biglobosa (Leguminosae-Mimosoideae), known locally as duaga; the jujube Ziziphus spina-christi (Rham-naceae); Feretia apodanthera, Canthium, and Gardenia (all three Rubiaceae); Salvadora persica (Salvadoraceae), whose leaves and twigs are also used in oral hygiene; Celtis integrifolia (Ulmaceae); and Vitex doniana (Verbenaceae). Both the fruit and the tender hearts of some species of palms are eaten, among them Borassus aethiopum and Hyphaene thebaica.

In the North American deserts, the hearts of some palms such as the Sonora palmetto (Sabal uresana) are also eaten. The fruit of the Californian desert fan palm (Washingtonia filifera) can be consumed as well, and this palm provided the Coahuilteco Indians and their neighbors in the Sonoran and California deserts with materials for construction and basket making. The fruits of the mesquite (Prosopis chilensis [=P. juliflora], Leguminosae-Mimosoideae) and the screw bean (P. pubescens) were also eaten by many of these peoples. Mescal, or pulque, is a greatly appreciated alcoholic drink made by fermenting and distilling the sap of the inflorescence of several species of Agave (see p. 210). The sweet fruit of prickly pears (Opuntia), known as tunas in Mexico, are popular as well, both in their area of origin and in northern Africa and the many areas of the Mediterranean Basin where the prickly pear (O. ficus-indica) has become naturalized.

Curative, poisonous, and aromatic plants

Countless medicinal plants grow in the deserts and subdeserts. About 40% of the known plant species of the subdesert wastes of northern Africa are used in traditional medicine, and they still represent a major contribution to the region's economy. In 52% of these species, the organs used are stems and leaves, in 33% fruits, seeds and flowers, and in 15% roots and bulbs. Most are also common in the Mediterranean Basin (Ajuga iva, Marrubium vulgare, Peganum harmala, Teucrium polium, Lavandula multifida). The tar obtained from the resin of the arar (Tetraclinis articulata) is used against mange in camels and also as a varnish. Deverra [=Pituranthos] tortuosa (Apiaceae) prevents contamination within cisterns. The Apiaceae includes species such as the visnaga (Ammi visnaga), whose fruits act as diuretics and vasodilators; aniseed (Anethum graveolens) and fennel (Foeniculum vulgare), used as condiments in cookery and for a variety of therapeutic purposes; and giant fennel (Ferula communis) and turpeth root (Thapsia garganica), whose roots are used as pain relievers, powerful purgatives, and antidotes to poisons, although at high doses they are toxic.

The poptato family (Solanaceae) includes many species with medicinal properties, especially the henbanes (Hyoscyamus), which contains alkaloids that when consumed give a feeling of weightlessness. Apart from its toxic properties, and its uses as a hypnotic and against all sorts of convulsions, henbane is also used against asthma, toothaches, and in creams that relieve muscle and joint pains. Similar properties are possessed by thorn apples (Datura stramonium, D. metel) and mandrake (Mandragora autumnalis), to which very many other properties have been attributed. Withania (Withania somnifera) is a narcotic. Castor oil, extracted from the seeds of the castor oil plant (Ricinus communis) is used as a purgative, while the highly toxic root of Atractylis gummifera has traditionally been used by murderers to poison people.

Noteworthy plants of the deserts and subdeserts of southern Africa include the grapple plant (Harpago-phytum procumbens, Pedaliaceae), which is used to treat kidney stones and arthritis. The tuber of the Bauhinia [=Tylosema] esculenta (Leguminosae), the morama bean, is a source of starch. The medicinal plant Vangueria infesta (Rubiaceae), as well as Lippia jaranica (Verbenaceae) and L. scabra, are taken as herb teas, as is Artemisia afra, which produces a tea that helps digestion (Boer tea).

The different species of the genus Opuntia are abundant in the hot deserts and subdeserts of Mexico and the southwestern United States, and their fruit and stem pads contain pectin, which soothes coughs and lowers cholesterol levels. This has been confirmed in clinical studies, which have shown that these species affect tolerance to glucose, insulin, serum lipids, and beta cholesterol, and lower blood sugar levels. Though they are not strictly curative, it is also worth mentioning the aromatic frankincense trees Boswellia frereana and B. carteri (Burseraceae). They grow in the subdeserts of the Horn of Africa in the fog zone from 2,297-5,577 ft (700-1,700 m) on the escarpment in Somalia that dominates the coastal plains of the Red Sea.

Dye and tannin producing plants

The biochemical properties of a large number of desert plants make it possible to obtain a wide range of different natural products--from pigments to mordants for tan skins and hides. Mention has been made of the use of the leaves of jicid as a dye, though it is only important locally. Henna and anchusine are much more important dyes.

Henna is obtained from Lawsonia inermis (Ly-thraceae), originally from northern Africa and southwest Asia but now widely cultivated throughout the tropics and even the Mediterranean Basin. The finely ground dried leaves are mixed with water to prepare a paste to dye the skin, hair, eyebrows, and nails a reddish color; when mixed with indigo (extracted from species of Indigofera) before application, henna makes the hair a shiny black. As it is fast-acting, it was formerly used to dye textiles and skins. The mummies of the ancient Egyptians were wrapped in cloth dyed with henna. In traditional medicine in Islamic countries, henna has been used to reduce fever and as an astringent. The leaves were placed in the armpits as deodorants; mixed with Acacia leaves to cure cuts on the hands and feet; and mixed with vinegar to get rid of headaches. It is also thought to have abortion-inducing properties.

Anchusine, a scarlet coloring agent, is obtained from the roots of the herbaceous perennial dyer's alkanet (Alkanna lehmannii [=A. tinctoria], Boraginaceae). Anchusine is used to color oils, cosmetics, medicines, thermometer fluids, and low-quality wines. It is also used in microscopy to detect oils and fats in tissue sections. It has, however, been replaced for most of these uses by synthetic coloring agents such as Sudan IV (a diazocompound that is bright red).

Major sources of tannins are found in plants that grow in the wastelands and thyme scrubs of North Africa. Among these plant parts are the roots of sumacs (Rhus pentaphyllum, R. tripartitum) and mastics (Pistacia lentiscus, P. atlantica) and the leaves and stems of the storksbill Erodium glaucophyllum (Geraniaceae), whose tubers are a greatly appreciated foodstuff.

Fibers and wickerwork

Basketwork has been important in many desert and subdesert cultures, as a nomadic lifestyle discourages carrying too many belongings, especially those that are heavy or fragile. In these cultures, woven baskets are not easily displaced or replaced by ceramic ones. Even after becoming sedentary, the shortage of fuel discourages making things that consume too much fuel. Many peoples of the hot deserts and subdeserts, not just the famous Anasazi (or Basket Maker Indians), have made excellent baskets with the materials provided by the desert flora.

The subdesert steppes of northern Africa, for example, are dominated by species of perennial grass, among them two esparto grasses (Stipa tenacissima and Lygeum spartum) that have played an important role in craft production of basket and mats in the region, and also in some areas of the Mediterranean Basin, where this tradition still survives, though not as vigorously as in the past. Stipa tenacissima grows wild in the most arid areas of the Iberian Peninsula. A robust clump-forming perennial with shallow roots, it has been introduced to many areas of the world. Its fiber has traditionally been used in local crafts as ropes for boats (esparto rope is highly durable but so light it floats on water), more everyday types of rope, harnesses for draft animals and beasts of burden, mats, curtains, and other objects, but it was also exported (after collection and baling) for the manufacture of high quality paper, especially cigarette papers.

The exploitation of esparto grass was abandoned many years ago in Libya and Morocco and is dying out in Algeria and Tunisia. This is because productivity has declined greatly and mechanization cannot be introduced. But the decline in area and yield are not only caused by overexploitation.

In the countries where esparto has not been traded for years, there is continuous degradation as a result of overgrazing, fires set by herders, trampling, erosion, and especially plowing to cultivate cereals, even though the harvest is highly uncertain. Once destroyed, esparto cannot regenerate, as in these desert areas it can only disperse vegetatively by its outward-spreading rhizomes. (Sexual reproduction requires the slight shade of open grasslands.) Steppes of the other esparto grass, albardine (Lygeum spartum), sometimes occupy a dynamic stage intermediate between esparto scrub and shrubland.

Unlike S. tenacissima, it can regenerate from seed in its actual habitat. Its fiber has traditionally been used in local crafts for the same purposes as esparto, but the way it is used and valued has only been studied from the point of view of ethnography and art. Craft production using esparto is rapidly declining because of the appearance of plastic fibers.

Other species of grass such as the giant reedor Spanish cane (Arundo donax) and common reeds (Phragmites spp.) are also used in basketmaking, as are the fronds of the date palm (Phoenix dactylifera), the dwarf fan palm (Chamaerops humilis), and, in the North American deserts, the desert fan palm (Washingtonia filifera). Basketmakers in the North American deserts obtained most of their materials from water holes or dry river beds where the water table was near the surface and where there were abundant trees producing suitable shoots (Salix, Chilopsis linearis), cattails (Typha), and several species of sedge and grass. They were plaited into a spiral and woven on a wicker frame then dyed a range of colors with coloring agents also obtained from plants.

Timber and firewood

Trees are scarce in deserts, but where they are present they grow slowly and produce hard long-lasting wood. Overlogging has considerably reduced their populations and has modified the distribution of age classes, and thus size, of the desert trees. The largest trees (the oldest) have now disappeared. In the northern tropical arid regions of the Old World, it is possible to find the giant tamarisk (Tamarix aphylla, Tamaricaceae) whose wood has been used in carpentry since the times of the ancient Egyptians. (The largest trunks were made into sarcophagus lids.) Overexploitation means it is no longer possible to find such large trunks; the giant tamarisk trees, or at least the specimens now growing, no longer live up to their name.

Conocarpus lancifolius (Combretaceae) is another tree from this region whose trunks are no longer large enough for their traditional use, the construction of boats (dhows). This tree grows on the alluvial terraces of wadis and areas where springs emerge or where there is a shallow water table near the coast. It is now used to build houses and fences, in carpentry, turnery, and in carvings, as well as for good firewood and excellent charcoal.

A versatile tree, it also provides food for goats and other livestock (in times of drought, the branches are cut to obtain fodder for livestock) and wild herbivores, and an alcoholic drink is made from its fragrant flowers. In cities like Mogadishu and Khartoum, it is planted along the avenues and is also used in windbreaks to stabilize the soil and to reforest former limestone quarries. The ground-up leaves are used as a fishing poison and the gum resin is traditionally used to treat people and animals for stomachache and lung disorders.

Surprisingly, some cacti also provide valuable timber. The central woody skeleton of several columniform cacti (known as cardones in Argentina and Chile), including the Atacama pasacana (Tri-chocereus atacamensis) and the pasacana proper (T. pasacana) of the puna and monte, is widely used to make beams, doors, and furniture. The woody skeleton of the saguaro (Carnegiea gigantea) from the Sonoran Desert is used for the same purposes, as are other cacti of the North American deserts such as the Mexicangiant or cardo pelon (Pachycereus pringlei) of the Sonoran and Vizcaino deserts. The ocotillo (Fouquieria [=Idria] columnaris) is frequently used to build wooden huts, which are then roofed with clay and straw. In Africa, the cactuslike spurges (Euphorbia abyssinica, E. candelabrum, E. tirucalli,) have traditionally been used to construct palisades and fences. The bushman's candle (Sarcocaulon malothii, Geraniaceae) is used in a remarkable way by the San of southern Africa. This pachycaul shrub's bark contains a hydrocarbon-rich wax, which they burn as a torch.

Ornamental plants

Many trees from the Sahel subdeserts are greatly appreciated as street trees because they are attractive and require very little water. Examples include members of 1) the Meliaceae, including the or neem tree (Azadirachta indica), also valued for its natural pesticides with few of the undesirable side effects of synthetic insecticides; 2) the Tamaricaceae, including the phraetophyte Tamarix stricta from Pakistan and Tamarindus indica from Africa; 3) the Combretaceae, including hodeti (Conocarpus lancifolius) from Somalia; and 4) the Leguminosae, including shishamor sissoo (Dalbergia sissoo), the kassod tree (Cassia siamea) from India, the Jerusalem thorn (Parkinsonia aculeata) of the American deserts, the mesquite (Prosopis chilensis [=P. juliflora]), the jhand (P. cineraria [=P. spicigera]), the babul (Acacia nilotica subsp. indica) from India, and kad (A. [= Faidherbia] albida).

The deserts of southern Africa are home to a large number of ornamental plants, mainly from the families Proteaceae, Geraniaceae, and especially succulents and nonsucculents from the families Aizoaceae and Asteraceae. The contribution of the American deserts includes their great diversity of cacti (Cactaceae) and agaves (Agavaceae).

2.2 Grazing in arid areas

The secondary production of the pastures of the arid and semiarid tropical regions is very low, as the grasses are of little nutritional value--except for the few weeks before flowering--and therefore cannot support the livestock. These poor pastures of grass that can be grazed or scrub and shrubs that can be browsed by livestock are, however, the most important grazing resource in the hot deserts.

The deserts and subdeserts of North Africa

As far as plant resources--and especially grazing resources--are concerned, probably the world's best-studied areas of hot desert are those of North Africa. Extensive grazing areas and fallow ground occupy most of the subdesert scrub in the region. Of a total of 630,000 [km.sup.2], pastures occupy 70%, about 440,000 [km.sup.2]. Pastures also occur in the depressions and the vegetated areas of the Sahara, about 5% of the desert's area (430,000 [km.sup.2]; of a total of 8.6 million [km.sup.2]).

These formations are the basic food supply for almost 50 million sheep equivalents, roughly one sheep per hectare (1 ha=2.5 acres), and the many types vary greatly depending on the site's climate, soil, and management. Each type has its well-established floristic composition, with its dominant species, some of them especially sought out by the livestock and thus considered to be preferentially grazed. The bulk of the food supply for these animals is now based on grains, straw, cane, and a wide range of agricultural residues (leaves and twigs of fruit trees, olive stones, rejected dates, bran, and other residues from milling and flour mills), as well as the produce from some sylvo-pastoral plantations. Even so, approximately one-third of the total plant species of these scrublands regularly form part of the livestock's food supply.

The average annual epigeal production of the thyme scrubs of northern Africa is about 3 kg dry matter/ha per year and per mm rainfall, though in practice this varies from 1-6 kg, depending on the conditions, and is about 100-300 kg dry matter/ha on the edge of the Sahara and 400-1,200 kg dry matter/ha per year on the edge of the semiarid zone. The aboveground perennial plant biomass is closely linked to the extent of cover by the perennial layer. Each 1% of plant cover corresponds to a plant biomass of 30-60 kg. The aboveground plant biomass of the annual species corresponds, by definition, to their annual production, and this is highly variable. In the less degraded thyme scrubs, it represents an average of 25% of total primary production. The annual species' share of the total plant biomass, however, increases as the scrub is degraded and may reach almost 100% in the areas that have been turned into deserts. This relationship between the epigeal plant biomass and the extent of perennial plant cover does not apply to other types of subdesert formations.

The Sahel

The ecological region known as the Sahel lies south of the Sahara, between the 4 in (100 mm) and the 24 in (600 mm) annual rainfall isohyet. It occupies a strip 373 mi (600 km) wide (from north to south) and 3,107 mi (5,000 km) long (from west to east) and thus occupies roughly 3 million [km.sup.2]. It is a stockraising area with subsistence crops such as pearl millet (Pennisetum glaucum), sorghum (Sorghum bicolor), and cowpea (Vigna unguiculata), some industrial crops such as peanuts (Arachis hypogaea) and cotton (Gossypium hirsutum), and a few irrigated crops, including sugarcane (Saccharum officinarum), on the southern edge.

Despite the dominance of the herbaceous layer, the woody species are very important in the Sahel pastures, as they are the main source of protein for the herbivores during the nine-month-long dry season. In this period, the herbaceous layer consists of nothing more than dry straw left over from the previous wet season; it is relatively rich in energy but contains almost no phosphorus, protein, or carotene (precursor of vitamin A). In theory, these woody plants could be replaced by concentrated feeds, seeds (cottonseed), or urea. But this replacement is not economically viable, taking into account the current terms of exchange, especially the huge cost of transport and the low price of meat. The woody plants are such essential sources of proteins, phosphorus, and carotene during the dry season that their disappearance would inevitably lead to the end of grazing in the area outside the short rainy season (one-to-three months long).

In the northern Sahara or Saharo-Sahelian zone, the area between the 4 in (100 mm) and 8 in (200 mm) annual rainfall isohyets, there are pastures dominated by perennial grasses (Panicum turgidum, Aristida pallida, A. papposa, Lasiurus scindicus, Cymbopogon schoenanthus) and some sedges (Cyperus conglomeratus [=C. jeminicus]). The average primary production of these pastures is 100-200 kg dry matter/ha per year, that is to say a rainfall efficiency use coefficient of 1-4 kg dry matter/ha per year and per mm rainfall, and a carrying capacity of 1 TLU (tropical livestock unit) per 45-275 ha. One TLU corresponds to the unit equivalent to a bovid with a live weight of about 550 lb (250 kg) that neither gains not loses weight, consuming 6.25 kg dry matter per day (2.5% of its live weight or 10% of its metabolic weight [metabolic weight equals: of its live weight]). This represents annual consumption of 2,280 kg dry matter (an estimated 25-30% of plant cover is consumed). The different livestock species reared in the Sahara can be given the following values in TLUs: cattle 0.81; sheep 0.18; goats 0.16; asses 0.53; and camels 1.16 (values based on the ratio of the mean metabolic weight and body weight for the population of each species).

The Sahel zone is characterized by a vegetation consisting of slightly or very spiny woody plants (Acacia ehrenbergiana, A. laeta, A. nilotica, A. senegal, A. tortilis, Guiera senegalensis, Maerua crassifolia, Balanites aegyptiaca, Commiphora africana, Boscia senegalensis, Cordia sinensis, Ziziphus mauritania, Grewia bicolor, and Euphorbia balsamifera). These are more or less regularly scattered above a herbaceous layer dominated by annual grasses (Aristida funiculata, A. mutabilis, A. adscensionis, Cenchrus biflorus, Eragrostis tremula, Pennisetum mollissimum, Dactyloctenium aegyptium, Schoenefeldia gracilis, Panicum laetum, and Tragus racemosus). The number of stems of woody plants per hectare varies from 0-500, though normally there are 20-80 stems/ha, with a canopy cover of 5-20%. The leaves, shoots, and even the branches may be an important addition to the livestock's diet when the highly variably production of the grass layer does not provide enough for the livestock to feed upon. The aboveground primary production of the herbaceous layer may be 1,000-2,000 kg dry matter/ha per year (or as high as 3,000 kg/ha per year in silty depressions with plenty of water). Average annual aboveground production is about 1,200 kg dry matter/ha. The average number of days of grazing per year is about 50, representing a load of 1 TLU per 7.3 ha. The apparent consumption would be 25-30 kg per day, though the real figure is 6.25.

The Sudano-Sahelian region receives an average annual rainfall of 16-24 in (400-600 mm). The Saharo-Sahelian zone and the Sahel sensu stricto are totally covered by sand, the result of the southward spread of the Quaternary Saharan ergs, especially the Ogolien erg (10,000-20,000 years ago). The soils of the Sudan-Sahelian zone are, however, very diverse, as is land use. The deepest and most favorable soils and the floodable depressions are used for agriculture. On sandy soils, millet and groundnuts can be cultivated; sorghum can grow on loamy and clay soil; on the southern edge of the zone, cotton may grow on the soils with plenty of water. The pastures of the Sudan-Sahel are distinguished from the true Saharan ones by the presence of the perennial grasses (Andropogon gayanaus, Hyperthelia dissoluta) and of several woody species (Acacia [=Faidherbia] albida, A. seyal, A. ataxacantha, A. mellifera, Bauhinia rufescens, Pterocarpus lucens, Terminalia avicennoides). The average aboveground primary productivity of this type of pasture is 800-5,000 kg dry matter/ha per year, and the average number of days of grazing per year is about 40, equivalent to a grazing load of 1 TLU per nine hectares. In silty and clay depressions, primary productivity is about 3,000 kg/dry matter per ha per year with about 160 days of grazing per year, equivalent to 1 TLU per 2.3 ha, but in the floodable grasslands of Echinochloa stagnina this figure is doubled. The zone's average is about 1,800 kg dry matter/ha per year with about 90 days of grazing, equivalent to a grazing load of 1 TLU per 4 ha.

The deserts and subdeserts of southern Africa

The deserts and subdeserts of southern Africa occupy about 2 million [km.sup.2] in South Africa, Botswana, Namibia, and a small part of Angola. About 310,000 [km.sup.2], the Atlantic coastlines of Angola, Namibia, and South Africa, can be considered authentic desert, the Namib Desert. The arid zones include much of Botswana and Namibia, 50% of South Africa, and a small area of southwest Angola. About 80% of this area is at an elevation of 3,281-4,921 ft (1,000-1,500 m). The region's flora (9,000 species) shows remarkable diversification, as does the vegetation, which includes scrub and shrubland (comparable to those of the Mediterranean Basin) on the other side of the African landmass and arid savannahs comparable to those of the Sahel. The scrub and shrubland of the Karoo occupy almost 550,000 [km.sup.2] in South Africa (most of it) and Namibia. There are about 20 types of scrub that can be classified into three major groups: grassy, chamaephytic, and succulent. The first two form what is known as Nama Karoo.

Grassy scrub is especially common in the northern Karoo, between the Orange River, the Namib, and the Kalahari. Average annual rainfall is 5-12 in (120-300 mm). The soils are sandy and covered with a very hard, dense, calcareous crust. They are dominated by perennial grasses (Stipagrostis uniplumis, S. namaquensis, S. amabilis, Themeda triandra, Heteropogon contortus, Eragrostis curvula, E. lehmanniana, Aristida difusa, A. congesta, Schmi-dtia pappophoroides). When the calcareous crust is at the surface, the shrub Rhigozum trichotomum (Bignoniaceae) tends to become dominant. There are also some trees such as the shepherd's tree or witgat (Boscia albitrunca), the camel thorn (Acacia erioloba), the umbrella thorn (A. tortilis subsp. heteracantha), and other species of the same genus (A. mellifera subsp. detinens, A. hematocarpa, A. hebeclada). The limited potential of the pasture means that their carrying capacity is about one sheep per 4-6 ha (1 ha=2.5 acres).

Chamaephytic scrub occupies most of the Karoo, where average annual rainfall is 8-16 in (200-400 mm). This type is similar to the Mediterranean and subdesert thyme scrub of northern Africa in physiognomy, but the floristic composition is totally different. The soils are usually sandy-silty or silty and shallow, overlying a very hard, thick, calcareous crust of Pleistocene origin. Every 3-4 ha of this scrub can support on average one 45 kg ovineunit (the average consumption of plant biomass is 200 kg dry matter/ha per year, and the total plant biomass is 800-1,000 kg dry matter/ha per year). The precipitation-efficiency index is 3-4 kg dry matter/ha per mm rainfall. The dominant species are chamaephytes belonging to the family Asteraceae such as ankerkaroo (Pentzia incana) and other species of the same genus, pteronias (Pteronia), etc. There are also some succulent chamaephytes belonging to the Aizoaceae and Crassulaceae, as well as several perennial Poaceae.

A coastal strip extends the Namib to the south from the latitude of Luderitz (Namibia) to Lambert Bay (Cape Province), then expands inland of the province between the Mediterranean fynbos and the Karoo proper (or Nama Karoo); this is known as the succulent Karoo and consists of dry subdesert to desert pastures. Average annual rainfall is 3-10 in (80-250 mm). The dominant species are chamaephytes belonging to the families Aizoaceae (Galenia, Drosanthemum), Crassulaceae (Cotyledon orbiculata and species of Crassula, Andromischus, and Cotylecodon), with the occasional presence of chamaephytes of the family Asteraceae. There are also some annual or short-lived perennial grasses. The soils of these succulent scrublands are generally superficial and often salty and/or sodic, which explains the frequent presence of members of the Zygophyllaceae (Zygophyllum, Augea) and Chenopodiaceae (Salsola, Atriplex). The carrying capacity of these scrubs is very low, roughly one sheep per 10 hectares.

2.3 Sylvo-pastoral plantations

A significant part of the plant resources exploited by the herders of desert and subdesert Africa are not derived from the natural vegetation but from new pastures deliberately created by reinforcing the woody species. They are known as sylvo-pastoral plantations and cover almost a million hectares in the arid zones of northern Africa alone. Promoted and subsidized by state governments, they aim to provide fodder to complement the pastures during the episodes of shortage following droughts and are also an effective way of rehabilitating degraded areas.

African repopulated pastures

The strategy against the effects of drought adopted by the farmers and herders of the Karoo subdeserts is to plant drought-resistant fodder shrubs: cacti such as prickly pears (Opuntia ficus-indica) and other species of the same genus (O. robusta, O. fusicaulis), agaves (Agave americana), and saltbush (Atriplex nummularia). The total planted area is about 800,000 ha (1 ha=2.5 acres), about 500,000 of them planted with cacti, 200,000 with saltbush, and 100,000 with agaves. The productivity of these plantations is about three to five times greater than that of an area planted with nonresistant species. Production of the cacti can be left to accumulate for two to three years, the saltbush for six to nine months, and the agaves for 5-7 years. This allows the farmer and the herder to store substantial fodder reserves for when the drought arrives.

A similar strategy is practiced in the subdesert pastures of northern Africa, especially in Tunisia. The main species used in the upper layer are acacias, originally from the arid regions of Australia, mainly Acacia saligna, A. salicina, and A. cyclops, while the main species in the lower layer are saltbushes of different origins (Atriplex nummularia from Australia, A. halimus from the local flora) and prickly pears (Opuntia ficus-indica). Each hectare of these plantations provides as much fodder as 3-5 ha of undegraded natural pastures, with a pluviometric efficiency-index of 8-10 kg dry matter/ha per year per mm rainfall within the 4-16 in (100-400 mm) rainfall interval. The Acacia and Atriplex also provide firewood that is greatly appreciated by the local people.

The Australian mulga

Mulga (Acacia aneura) is a small Australian tree up to 46 ft (14 m) tall that grows in areas with annual rainfall of 8-15 in (200-380 mm). The last 4-12 in (10-30 cm) of the branches bear phyllodes (modified petioles) that are narrow and flattened or cylindrical. The root system is extensive, consisting of long radial roots that anchor it to the substrate and other much more branched roots that penetrate at an angle in search of water. This root system is so effective that there is little or no ground cover, and mulga normally forms single-species forests or very open scattered patches. The summer and winter rains, despite their scarcity, are vital to the survival of the mulga, which can grow and flower at any time of year when there is rain.

The mulga is a highly variable species that adopts four different growth forms in Australia. Low mulga, consisting of small shrubs or subshrubs, is the result of constant browsing by sheep and cattle and is a very important source of fodder during droughts. Whipstick mulga consists of immature trees with thin straight branches that only bear leaves at the tips; these leaves are not available to the livestock without the use of heavy machinery. Umbrella mulga consists of mature shrubs with thin upright branches covered with leaves that respond very well to pruning; although its nutritional value is not very high, it forms the main standing reserve for browsing by sheep during long periods of drought. Mulgacopses with 175-200 trees/ha, when pruned, provide the best combination of grazing and browsing during the dry season. Leaf palatability varies greatly, but 1.4 kg of leaves per day is enough to feed a sheep, as long as its diet is complemented with sulfur and phosphorus. Finally, high mulga consists of forests of old trees with bare trunks that only bear leaves on the highest stems. These leaves are usually palatable but inaccessible to the livestock. Furthermore, these trees do not tolerate pruning, so that they cannot be cut for fodder without killing them. The trees of the high mulga usually produce large quantities of seed.

2.4 Agricultural activity

Agricultural activity is impossible in true deserts and occurs only in oases or on riverbanks, where irrigation is possible. In the subdeserts, some unproductive dry farming is possible, but it is unreliable and the fallow periods have to be long.

Dry farming

In general, dry farming is possible if average annual rainfall is greater than 16 in (400 mm). If rainfall is a little greater, it is also feasible in areas where the climate is bimodal; in regions with average annual rainfall of only 8 in (200 mm), in some years it is possible to get crops to grow. In any arid or semiarid region, however, soil stabilization and the application of water conservation techniques are essential if agriculture is to be sustainable. In any case, herbaceous crops have little chance of growing well in these regions, due to their superficial roots.

Dry farming of trees produces better results in the subdesert regions of northern Africa. Unirrigated fruit trees occupy about 1,600,000 ha, most (1,400,000 ha) in Tunisia, about 150,000 ha in western Libya (Tripolitania), and about 50,000 ha on the northwestern coastline of Egypt to the west of Alexandria. In Tunisia and Libya, 80% of these crops are olive trees, while in Egypt, figs account for 80% of the area cultivated. In both cases, the remaining 20% of dry farming tree crops consists of secondary species such as almonds, pomegranates, apricots, peaches, table grapes, date palms, and, of course, figs in Tunisia and Libya and olives in Egypt. Unirrigated tree crops are usually grown on deep, relatively coarse, sandy soil, and so productivity is generally satisfactory, 600-1,200 kg olives/ha per year. When the soil is finer-textured (fine sands and silt), hydraulic techniques have to be used to control and make use of the runoff. Among these water-saving strategies are the use of the tabia (a sort of ridge between two furrows that runs perpendicular to the direction of the runoff, thereby slowing it down and increasing the infiltration of water into the soil) and jessur (building dry walls along the course of a wadi for the same purpose).

When the soil is sandy, the distance between the trees is very large, 66-82 ft (20-25 m) for olives and 33-39 ft (10-12 m) for almonds and other members of the rose family (Rosaceae). This means a single hectare can only support 16-25 olive trees and 70-100 trees of other species. In crops that use runoff, the density is variable, but on average they may be twice the densities given above and four times in the case of vines (up to 400-600 stems/ha). In central Tunisia, where annual rainfall is 8-12 in (200-300 mm), average annual production is about 35 kg per tree, about 700 kg of olives/ha or 160 kg of olive oil/ha per year. Such a high production, despite the low rainfall and sandy soil, is easily explained. Of the 8 in (200 mm) of rainfall per year, 4 in (100 mm) is lost through evaporation, while the other 4 in (100 mm) infiltrates into the soil, protected from evaporation but available to the trees. The cover of the canopies of the olives, about 1,000 m2/ha, or 10%, loses the infiltrated water by evapotranspiration. If the cover were 100%, the evapotranspiration would be 39 in (1,000 mm), a value corresponding to the water consumption of an irrigated crop or a crop in the Mediterranean zone with a wet climate.

Irrigation-based agriculture

In the regions where rainfall is too scarce for dry farming, certain types of agricultural production are possible if the water table is quite high and irrigation is possible. The high rates of evaporation, however, may cause problems of soil salinization; agricultural land has been lost all over the world through excessive soil salinity, which is more or less related to irrigation of crops. Irrigation considerably increases crop production and guarantees a harvest in years of little or no rainfall. The Papago of the Sonoran Desert managed to cultivate the tepary bean (Phaseolus acutifolius, Leguminosae), a species of desert origin, with the water from a single summer shower channeled to their vegetable plots using a system of ridges and strengthened dams. Typical desert irrigation is practiced in oases, growing vegetables and greens, fruit crops (citrus fruits, bananas, apricots, olives, avocado pears, guavas, palms, and pomegranates), and even industrial plants such as cotton, beetroot, fodder plants, and cereals. In northern Africa, the value of these harvests is about $2 billion a year, representing 31% of the entire local agricultural sector. On river banks, especially on the larger rivers such as the Nile, Tigris, Euphrates, and Colorado, more land is suitable for agriculture and communications are better, so that most of these fruits and vegetables can be cultivated commercially.

Palms

The date palm (Phoenix dactylifera), probably originally from Arabia, has been cultivated for 5,000 years in all the Saharan oases in Arabia, in the Nile Valley (in northern Sudan and Egypt), and along the rivers Tigris and Euphrates. It has recently been successfully introduced as a commercial crop into California, Arizona, and Queensland. As date palms are dioecious (male and female flowers are borne on different plants), production is greatest when the number of male plants is kept as low as possible. Natural wind pollination is enhanced by placing pieces of the male inflorescence in close contact with the female one. Ritual fertilization of date palms is known to have been practiced by the civilizations of ancient Mesopotamia.

The date palm has more than 800 different uses, making it a true multipurpose species. The fruit can be eaten fresh or dried and can be made into a syrup and an alcoholic drink called arrack. The palm's heart can also be eaten, as can the flowers and pollen, and the roots can be fed to livestock when the stem is cut. The stem is widely used in coverings for buildings, pillars, roofing, small bridges, and irrigation channels, while the date stones are made into a high quality charcoal used by silversmiths. The fibers are used to make rope, and a wide range of baskets and the leaves are woven into bags and baskets (see vol. 5, pp. 278-279).

The African palmyra palm (Borassus aethiopium), with its characteristic swollen stem topped by a tuft of fan-shaped leaves, is widespread throughout the more arid regions of tropical Africa, while its relative the palmyra palm (B. flabellifer) occurs throughout the drier tropical zones of Asia as far as eastern Malaysia. Both species have multiple uses, though the African species is not used as much as the Asian one. Their fruits are edible but are not commercially exploited. The petioles of B. flabellifer are also a source of fibers.

Safflower and other industrial crops

Cotton is the most important industrial crop in the oases of the African deserts, but other major crops include cereals (wheat, sorghum, and millet), legumes such as kidney beans (Phaseolus vulgaris), the pigon pea or arhan (Cajanus cajan), the cow pea (Vigna unguiculata [=V. sinensis]), and oil crops such as the sunflower (Helianthus annuus), peanut (Arachis hypogaea), sesame (Sesamum indicum), and especially safflower.

Safflower (Carthamus tinctorius, Asteraceae) is not known in the wild but seems to have originated in Arabia. It was cultivated in ancient Egypt, and since then it has spread throughout the Mediterranean and east to China. More recently, the Spanish introduced it into Mexico. In Egypt, the Middle East, and India, the dried flowers were used to obtain carthamin, a red textile dye and food coloring agent. Safflower is sometimes still used as a substitute for saffron or to adulterate it. Now mainly grown for the oil extracted from the seeds, safflower has been cultivated on a large scale in the United States since the 1950s, and production may exceed 4,500 kg/ha. The world's largest producers are India (about 450,000 tons), where the oil pressed from safflower seeds is used in cooking, in lighting, and to make soap, followed by Mexico (25,0000 tons) and the United States (100,000 tons). Safflower oil is very healthy and tastes good, but outside India it is mainly used in paints and therefore is not an important human foodstuff.

The hopes raised by jojoba plantations

The jojoba (Simmondsia chinensis) is the only member of its family, the Simmondsiaceae. It is a dioecious, semideciduous, plant with a shrubby growth-form that can grow to a height of 10 ft (3 m), and produces a fruit resembling an acorn, containing a single seed or occasionally two. The fruits ripen in early autumn and shed their oily brown seeds onto the ground, where they are greatly appreciated by sheep and goats, as well as humans, especially children, who gather them at the base of the tree. The Mexicans make a nutritious and tasty drink with the seeds of the jojoba: they are toasted and ground with the yolk of hard-boiled eggs, then the paste is boiled with water, and milk and sugar are added.

The jojoba (Simmondsia chinensis) is originally from the hot North American deserts. Its specific name, a misinterpretation by the botanist who described it, resulted from a mix-up between collections from California and China. It was first mentioned in the diaries of the Jesuit priest Eusebio Kino, who in a letter to Philip V of Spain referred, together with the other resources used by the Pima Indians, to the medicinal jojoba fruit. Later, in 1789, Francisco Clavijero stated in his Storia della California that this fruit was valuable for its medicinal properties and was widely used to ease childbirth, to heal wounds, and to cure difficulty in urination due to mucus concretions. The oil extracted from the seeds was also considered an excellent remedy against cancer; it is so tasty that some people in California use it in salads instead of olive oil.

Jojoba oil was analyzed for the first time in 1895 by Leon Diguet of France who recommended jojoba cultivation to the French colonists in northern Africa for its edible fruit. The interesting molecular structure of jojoba oil was not discovered until 1933. Jojoba oil, in reality a liquid wax, is a fatty acid molecule joined to a long-chain alcohol. No other plant is known to produce an acid-alcohol ester of this type in its fruits. The fruit contains 40-60% oil, which is of great economic importance as a lubricant for delicate instruments and in industrial processes involving high temperatures and pressures. It might also be a good chemical intermediary for products used as wetting agents and high-pressure additives. It is now cultivated commercially in several desert regions, but production is mainly for the cosmetics industry, as it does not turn rancid like other oils and its similarity to sperm oil (see vol. 10, p. 263) has given rise to hopes that increasing jojoba production will help to conserve the sperm whale. In traditional cosmetics, it has been used to stimulate cell and hair growth. The rapid increase in production, especially in the United States, has brought the price of jojoba oil down to about half a dollar a kilo, well below the $60 a kilo it cost in 1975 or $30 dollars in 1985. Even so, it is a profitable crop with great potential for expansion to meet the huge market.

3. The use of animal resources

3.1 The exploitation of the native fauna

Potentially a major resource, the fauna of large mammals and birds was decimated in the first half of the twentieth century and now is only of secondary economic importance in the subdeserts of northern Africa, the Sahara, Sahel, and the deserts and subdeserts of southwestern Asia. Some species from hot deserts have been domesticated extremely successfully. Two of the most important domesticated animals--the ass (Equus asinus) and the dromedary (Camelus dromedarius)--are originally from deserts. The wild fauna includes major fisheries in some large rivers of external origin that cross deserts.

Fishing in the middle of the desert

It may seem absurd to include a section on fishing in deserts, but the large rivers that cross hot deserts provide abundant and varied fishery resources. One particularly well-studied case is the inland delta of the River Niger, on the edge between the Saharan and Sahelian regions in Mali. The Niger's source is on the northern slopes of the Guinea Highlands. It then flows broadly northeast to Tombouctou, where it turns east to the Tosaye, then turns southeast and continues in this direction until it joins the Benoue. From there it flows south toward its delta, which flows into the Gulf of Guinea.

One of the most interesting features of the course of the Niger is the presence in its middle stretches of a large flood plain more than 311 mi (500 km) long and nearly 62 mi (100 km) wide. It is known as an inland delta because, as in a delta, the river splits into countless branches as soon as the volume of flow increases slightly, as the gradient in the area barely exceeds 2 cm/km (there is only a drop of 39 ft [12 m] between Ke-Macina and Dire, which are 342 mi [550 km] apart). This region is located precisely where the river enters the most arid part of its basin, with low average annual rainfall (for example, in Tombouk-tou, less than 8 in [200 mm], and even at Mopti, right in the heart of the lake region, barely more than 16 in [400 mm]). As the average annual rainfall is much greater upstream (more than 79 in [2,000 mm] in the upper headwaters of the basin), and this is largely seasonal, the rivers receive major surges at the end of the summer which cause a long period of high water, when fishing activity is intense. For the rest of the year, fishing is limited to the permanent stretches of the Niger, its tributaries, and the permanent lakes.

The size of the fish catch in this delta area varies greatly (45,000-100,000 tons per year) from one year to the next, depending on the size of the summer surge, or the total rainfall in the basin. Roughly 200,000-300,000 people live by fishing in the area, and it represents 3% of Mali's gross national product (GNP). This fishing is entirely a craft activity using a wide range of methods such as harpoons and three-pronged spears to catch relatively large fish, especially in pools that are drying out or on the flood plains, as well as large sand barriers called dien that close off entire branches of the river.

The fish caught vary greatly, but many species of fish are caught in small numbers. About 85% of the catch consists of just 17 species, the ones that are regularly present in the markets, either fresh, dried, or smoked. The most appreciated fresh fish is Auchenoglanis occidentalis (together with A. biscutatus), a bottom-feeding species of muddy river bottoms found mainly in flooded areas rather than stretches of the river. It only represented 2.7% of the catches in 1990-1991 but accounted for 7.7% of market sales during the period 1982-1991. This presence in the markets is exceeded only by a few other species: 1) the tilapias (the commercial name for several species of cichlid fish), which for the same periods represented 26.6% of the catch and 22.5% of the sales; 2) the Nile perch (Lates niloticus), known locally as capitaine, which represented 3.8% of the catches and 8.7% of the sales; and 3) synodontids or lizard fish (a name for 15 species of catfish belonging to three genera in the family Mochokidae), which used to be caught in abundance but now have declined to less than 1% of catches, though they represented 9% of fresh sales during the period considered.

The drought suffered by the Sahel and the southern Sahara since 1973 and reservoir construction on some of the Niger's tributaries has led to 1) a decline in the area flooded every year on the Niger's inland delta and 2) the appearance of irregular surges during the summer low water due to discharges of water from reservoirs to compensate the insufficient volume of flow. This has led to an overall decline in catches but also a qualitative variation in the fish caught, with an increase in the catch of opportunistic species such as tilapias, and clariids or air-breathing catfish, and a decline in the catches of other more valuable fish such as synodontid catfish.

The seasonality of production explains the tradition of conserving part of the catch either dried, smoked, or grilled. The tinameni (Alestes leuciscus) is the source of an oil, which is extracted by boiling. Some species such as the air-breathing catfish (family Clariidae, catfish with gill chambers that allow them to breathe atmospheric oxygen for a while when they are in oxygen-poor water), especially Claris anguillaris and to a lesser extent C. grandisquamis, are almost only eaten smoked. The production of dried and smoked fish is a craft industry carried out in family installations. The installations for smoking the fish consist of one or more ovens where the fish are placed (after cleaning and removing the scales) on a sort of mesh grill over firewood and dry dung (dung smoke appears to improve the color of the fish being smoked). Fish to be dried are first left to ferment slightly in pottery or metal vessels or even in a hole in the ground. After this fermentation, the fish are placed flat on a surface exposed to the sun and a (natural or artificial) preservative is added to prevent insect infestation. Apart from the small internal trade circuits within the delta itself, most production is sent to the city of Mopti, and from there it is distributed to the rest of Mali and even to some neighboring countries, mainly the Ivory Coast and to a lesser extent Burkina Faso and Ghana, which was until recently the main client.

In Lake Nasser, the situation is very different. This lake was created when the Aswan Dam was built on the Nile River. There has always been fishing activity on the Nile, but on the stretch now occupied by Lake Nasser the increase in catches has been spectacular. The catch increased 24-fold between 1966-1977 (from 750-18,000 tons). The fisheries are based on 15 species. Tilapias (Sarotherodon niloticus, S. galilaeus), which like all plankton-eating fish have increased spectacularly in number and size, are the most abundant, followed by characins (family Characidae) such as Hydrocynus forskalii, Alestes nurse, A. dentex, A. baremose) and the Nile perch (Lates niloticus).

Hunting activity

Large-scale hunts are still organized in some Saharan countries for potentates from the oil-producing Arab countries who can no longer hunt antelopes, gazelles, and bustards in their own countries. Yet, most hunting is due to the perception--deeply rooted among nomadic herders--that wild herbivores compete with their herds and that carnivores threaten them. The scarcity of resources in the desert regions of Africa and much of southwest Asia means that hunting is a significant complement to the economy of many families.

Unlike the precarious subsistence of most countries of Saharan Africa and the Sahel, in southern Africa there are more than 100,000 [km.sup.2] of game farms, large estates where wild animals are raised in the wild but managed to some degree with the intention of hunting them for several purposes: meat production, big game trophy hunters, photo safaris. There are also large areas dedicated to intensive or extensive ostrich rearing. The fauna thus plays a major role in the economy--much greater than in the countries of eastern Africa such as Kenya and Tanzania. Parks represent 5% of the area of southern Africa, but game farms represent 8.3%, though not all are in desert or subdesert areas. In Namibia, for example, there are about 400 game farms, most of them with an excellent management of their animal populations, and they occupy almost 25,000 [km.sup.2]. Almost all of them combine wildlife management with the exploitation of domesticated livestock.

The domestication and rearing of the ass

The deserts near the major centers of civilization of antiquity, Egypt and Mesopotamia, were the site of the domestication of two of the most important species of animal whose muscle power has long provided humans with additional energy to plow the ground, transport heavy loads, and sometimes aid in war efforts: the ass and the dromedary.

The ass (Equus asinus) is the only domesticated large mammal originating in the African continent. It comes from the deserts of Egypt and Libya. Its wild ancestor was probably the Nubian wild ass (E. asinus africanus), which now seems to be extinct, although in some areas (Somalia, Maghrib) it may have been involved in the domesticated offspring of other wild subspecies of ass. The domestication of the Nubian wild ass seems to have occurred in pre-dynastic upper Egypt more than 5,500 years ago. Some rock carvings in the western Egyptian desert dated from the Gerzean culture (about 5,500 years ago) support this idea, and relief carvings on slate tablets from a period soon afterward (Naqadah II, about 5,400 years ago) confirm it. The ass was the most important beast of burden for the ancient Egyptians; all their land trade was based on caravans of asses. It was only rarely used as a mount, and if used to transport people this was done with a sort of bed or chair suspended from two asses harnessed side by side. The ass spread from Egypt to all the areas that traded with the Egyptians, from Ethiopia to Mesopotamia and Iran. Later, in the Roman period, the ass spread throughout the Mediterranean Basin and much of Europe and to the edges of the Roman Empire.

The introduction of the domesticated ass into Mesopotamia, where there was another member of the horse family, the onager (Equus hemionus onager), led about 5,000 years ago to the first attempts at hybridization. The results were good, as the hybrids were stronger and more resistant than their parents. They were further improved upon later, when the onager fell out of favor and the asses were crossed with horses to produce mules, animals the size of a horse and with the stamina and strength of the ass. Mules are the most widely used working animals and beasts of burden in much of the world. The colonization of the Americas was a new opportunity for asses and mules, which were the most efficient means of transporting heavy loads over long distances on bad roads. Catalan stud asses were particularly successful and helped to supply mules for most of Spanish colonies, and during the nineteenth century they also played an indispensable role in the conquest of the west in the United States. Throughout the twentieth century, the mechanization of transport has displaced horses and their relatives as draft animals or beasts of burden except in very inhospitable regions or steep areas, where asses and mules are still extremely useful.

Though available statistics are unreliable, throughout the world there are an estimated 40 million asses (more than 10 million of them in China and about as many in Africa) and about 15 million mules (about five million in China, more than three million in Mexico, and about two million in the countries of the Andes and Central America). Despite popular opinion in developed countries, the number of asses is increasing, especially in Africa, where the use of animal traction for transport and agricultural work is, in many areas, an innovation when compared to agricultural practices using no energy inputs other than human labor.

The domestication and breeding of the dromedary camel

The ass was domesticated in Egypt and then spread to Asia, but the common camel or dromedary (Camelus dromedarius) was domesticated in southern Arabia. It spread westward from there to Africa and east to the hot deserts of Iran and the Indian subcontinent. The dromedary was domesticated 5,000-6,000 years ago and led in the following centuries to the appearance of nomadic pastoralism based on camels as a means of transport and as a mount, a lifestyle still followed by the Bedouins. Northward migration by Semitic nomads introduced the domesticated dromedary into Mesopotamia and Palestine 3,000-4,000 years ago. The Assyrians rode camels into battle, as shown in several reliefs of the palace of Ashurbanipal in Nineveh, which is about 2,700 years old. The camel seems to have been introduced to Africa around the time when Egypt was conquered by Ashurbanipal, arriving not only from the north with the invading armies but also from the south accompanying immigrants from the Arabian Peninsula, though it does not seem to have spread widely through Africa's Mediterranean coastline until the Roman period. The camel's spread to Iran and India was very slow, too, although the Persian emperors incorporated nomadic camel-riding Arabs into their armies from 2,600 years ago onward. Herodotus mentions how the camels were kept at the rear because their smell frightened the horses, though this was also sometimes used to break the enemy cavalry. Camels do not, however, seem to have reached India until the Arabic invasion in the eighth century. In the fifteenth century they were introduced by Spanish colonists into the Canary Islands, then into Peru in the sixteenth century, but it was only successful in the Canary Islands. In the mid-nineteenth century they were introduced into the deserts of the southwest United States and Australia.

Some nomadic herders in the Sahara and the Arabian Desert live mainly by raising camels. The Moors of Mauritania, for example, graze an area of half a million [km.sup.2] (about twice the size of the state of Michigan) between Jbel Bani Mountains and the Adrar Oasis, more than 620 mi (1,000 km) apart, with more than 40,000 head of camel. Normally, however, camels are an essential help to nomads whose herds consist of other animals or are used as transport (almost one-third of all trans-Saharan transport is still on camel back). Camel milk is also consumed. The world's camel population is not very large, little more than 1.5 million animals, a million of them in Africa and almost half a million in Somalia alone.

3.2 Stockraising activity

Livestock production systems in the African hot deserts, the hot deserts where agricultural and stockraising activity is most intense, include nomadic pastoralism and seasonally migrating stockraising, mostly of camels and small livestock (sheep and goats) and occasionally cattle. These animals drink water from rivers with sources outside the desert, as in the Danakil Desert. Transhumance is the name for seasonal movements between the desert and the subdesert or between low areas and the mountains, while nomadic pastoralism is based on random movements depending only on the rainfall. Seasonally migrating pastoralism normally occurs on the edge of the deserts or in mountainous regions, while nomadic pastoralism occurs strictly within the desert, often covering large distances of 620 mi (1,000 km) or more.

Until recently, apart from life in oases, nomadism was almost the only lifestyle in most of the deserts of Africa and Asia. In the hot deserts in the Americas and Australia, despite exploiting huge areas totally dominated by sheep, stockraising only requires the shepherds--not the entire population--to travel.

In general, as pastures become increasingly degraded (especially in Africa and Asia), the percentage of cattle and sheep declines and that of camels and goats increases. The consumers of woody plants increase at the expense of consumers of grass. Certain eastern African ethnic herder groups (Rendile, Samburu, Booran) have adapted their tradition of cattle raising to raising camels.

Northern Africa

In the arid areas of northern Africa, stockraising is restricted to sheep, goats, and dromedaries. There is hardly any cattle in unirrigated arid zones. Since the 1970s, raising sheep has developed into a form of speculation that is highly dependent on subsidized feeds and grains, and the sheep are increasingly fed stubble, straw, and agricultural and food industry residues. The raising of dromedaries is clearly declining, while that of goats is stagnant. The infectious diseases that affected the livestock have disappeared thanks to vaccinations, leaving only parasitic infections such as infections of the lung and stomach (strongyloidiasis) caused by strongylid nematodes or tapeworm infestation caused by Taenia.

Average consumption of meat is about 40 lb (18 kg) per person per year, half of it commercially raised poultry. Poultry consumption increased from zero in 1960 to 750,000 tons in 1990, growing at a constant rate of 7% per year for 30 years. Beef and lamb production per person has remained stable, and so has the sheep/human ratio, at one sheep per person. This ratio has stayed stable for the last 50 years, though total consumption of meat per person has doubled over this time. Production per person of beef and lamb together is about 8.5 kg/year, and that of poultry is about the same.

The Sahel

In 1990 the livestock population of the Sahel countries was about 55 million Tropical Livestock Units (TLU), after almost tripling in the last 40 years. Cattle account for about 60% of the biomass of livestock. Stockraising used to be limited regularly by the death of many animals due to infectious diseases, especially rinderpest, contagious peripneumonia, anthrax, brucellosis, epizootic abortion (vibriosis), and foot-and-mouth disease. These sanitary constraints have largely been solved by a vigorous preventive program, especially vaccination campaigns.

Diseases transmitted by ticks are not a major problem in the Sahel, unlike in eastern Africa, probably due to the extreme dryness of the air from November to May, which prevents these arachnids from reproducing. All this has led to the exponential growth of the number of head of cattle, at a rate of 2.2% per year. Traditional pastoral practices, virtually unchanged apart from these sanitary improvements, have changed little, and pastures have been greatly degraded by the increased number of cattle, plowing, and competition for land between stockraisers and farmers. The rearing of small ruminants (sheep and goats) is restrained by an as-yet incompletely understood disease, small ruminant plague, and also by parasitic infections of the respiratory or digestive tracts.

Livestock productivity is very low in the Sahel, especially due to feeding problems and traditional stockraising practices. The main direct causes for this low productivity are: the long time between births, low fertility, the low percentage of reproductive females, the high percentage of males, inadequate and unbalanced feeding, parasitic infections, and diseases.

Eastern Africa

In 1980 eastern Africa contained about 78 million TLU and had a human population of 110 million (0.7 TLU per person). The constraints on stockraising are the same as those in the Sahel, though there are some differences. Fodder availability is slightly better, as there are two rainy seasons a year; therefore, fresh food is available for more of the year and the animals' diet is more balanced. There are, however, two factors that are less favorable than in the Sahel: disease and the threat of predators.

One major group of livestock diseases are the different forms of piroplasmosis (or babesiasis), parasites that destroy the red blood cells. They are piroplasmids (protoctists of the apicomplex group, also known as sporozoans) transmitted by ticks. East Coast fever, caused by the piroplasmid Theileria parva, takes the form of long periods (15 days) of high fever, followed by an apparent improvement, and then the cattle's sudden death due to lung edema; cattle tick fever caused by Babesia bigemina destroys the red blood cells, leading to symptoms of fever and blood in the urine. Other diseases transmitted by ticks include anaplasmosis, which is often fatal and is caused by Anaplasma marginale, an aphragmabacteria or mycoplasma that takes the form of fever, jaundice, and intense destruction of the red blood cells, which show a characteristic sickle shape. There is also the rickettsia infection known as heartwater, caused by Cowdria ruminantium. These tick-transmitted diseases are prevented by anti-tick baths and dusting.

Predation by large carnivores (lion, laughing hyaena, jackals) is a second problem that is worse in eastern Africa than in the Sahel, as predators may locally take 10% of the herds, mainly the young animals. Unlike the Sahel, eastern Africa has a modern productive livestock sector, but not in the arid area, which is entirely dedicated to traditional grazing and whose productivity is comparable to that of the Sahel.

Southern Africa

Unlike the other arid zones of Africa, stockraising in southern Africa is highly diverse, mainly sedentary, and extensive, but at the same time modern and commercial. The tropical savannahs of Botswana, Namibia, and the Transvaal are essentially used for cattle ranching, while the grasslands of the Karoo and Namibia are dominated by small ruminants, especially sheep. The total herd in southern Africa is about 31 million TLU, of which about 50% are located in the arid zones (sensu lato). Of this total, cattle represent about 70% in terms of metabolic weight (1.7 lb [0.75 kg]), sheep about 22%, and goats about 8%. The number of cattle represents 30%, sheep 54%, and goats 16% of the total number of head of livestock.

The cattle of southern Africa are heavier than the average African zebu (1.2 TLU/per head); a high proportion are animals for fattening that belong to selected breeds such as the local Afrikaner zebu cattle, or the Indo-Pakistani brahman zebu, or are the product of a variety of crosses (for example, Afrikaner crossed with humpless cattle of European origin and the bonsmare breed, or Afrikaner crossed with short-horned Durham). In Botswana and Namibia, the tswana and its crosses are the dominant breed. The breeds of zebus (Bos taurus indicus) and crosses with humpless breeds, mainly of European origin, are a necessity, given the zebu's relative tolerance of tick-borne diseases like piroplasmosis. There are three main breeds of sheep: merinos for wool, dorper for meat, and karakul for leather, of which South Africa has the world's second largest flock. There are two main breeds of goat: the Boer goat, a large, robust, animal reared for its milk and flesh, and the Angora goat, which produces mohair wool.

Southwest Asia

Stockraising in the Arabian Desert is similar to the model in the Sahara, with nomadic Bedouin stockraisers who raise herds of sheep and goats. Farther north and east, from Anatolia to India, high-altitude nomadic stockraising is more common, and this exploits the mountain pastures in the summer and those of the subdesert plain in the winter. This is similar to seasonally migrating stockraising, but in this case the entire community moves. The Paichu nomads of Afghanistan, who travel from the Indus Valley to the peaks of the Hindu Kush with thousands of head of sheep, goats, camels, asses, and horses, are perhaps the most typical example. Turkey, Iran, and India have the largest number of sheep in the area, 35-55 million each; only Australia, China, and New Zealand have more. Pakistan has the largest number of goats, with 25 million head (exceeded only by China), followed by Turkey and Iran with 15-20 million head.

The North American and Argentine deserts

Dominated by extensive cattle ranching and sheep raising, the North American deserts are an extension of the high prairies of the plains east of the Rocky Mountains. Sheep dominate in New Mexico, where the Navajo have become the most important raisers of sheep, while cattle dominate in northern Mexico and in Arizona, where varieties of British origin have replaced the former criollo cattle even on large estates in Mexico. They are essentially raised for their flesh, which is fattened locally, or they are bred to be fattened in farms elsewhere. One distinctive feature, especially in Mexico, is the relative abundance of horses and their relatives, with more than four million horses, almost three million asses, and nearly three million mules.

The Argentinean monte is an area of extensive stockraising, mainly of sheep, but also of cattle, in large estates enclosed by wire fencing. Though they are not as large as the huge sheeprearing estates of Patagonia, they are still very large, often owned by stockraisers of British origin, who have replaced the merino with British breeds that produce wool (Romney Marsh) or flesh (Lincoln). Cattle are bred in the area but tend to be fattened in the wetter pampas regions.

The Australian subdeserts

The large sheep raising areas are not so much in the deserts and subdeserts as in the savannah and prairie regions, though they partly affect the subdesert regions surrounding the central deserts, which are too inhospitable for any type of stockraising activity. In these subdesert areas, the main stock animals are merino sheep raised for their wool. They graze extensively in large herds. The low productivity of these pastures means that more than 5 ha (1 ha=2.5 acres) is often needed to support a single animal.

4. Management conflicts and environmental problems

4.1 The human contribution to desertification

The desert biome, unlike all the other biomes, seems to be expanding. This is due partly to climatic factors, but, as has already been pointed out, it is also due to thousands of years of human actions. Two centuries ago, the romantic French writer FrancoisAuguste-Rene de Chateaubriand (1768-1848) wrote: "Forests precede people, but deserts follow them." Perhaps this is not always true, but it expresses very clearly the decisive role of human beings in spreading the world's deserts.

Like the sea, deserts are commonly but wrongly thought to be a limitless dumping ground. One major difference between them, however, is that in the sea, wastes are dispersed by waves and currents; in deserts, they are only dispersed by the wind. What is dumped in the desert and is not gradually blown away by the wind stays there, or--if the substrate allows it--seeps down to contaminate the aquifers. These hard facts do not prevent many people from considering deserts as ideal sites to install or dump anything and everything that may be bothersome or dangerous, including contaminating industrial waste, radioactive waste, and garbage from secret military installations and nuclear test sites. Much of the industry recently established in many petroleum-exporting countries (Saudi Arabia and Libya), or that which has recently grown up in connection with mining (such as that of phosphates in Morocco and, to a lesser extent, in Tunisia), is highly contaminating. In the oil-producing countries, it is mainly the petrochemicals industry, although there is a desire for some diversification by adding other industries to make use of several locally available raw materials (for example, iron and steel works in Saudi Arabia and Libya). In Morocco and Tunisia, the emphasis has been on phosphate fertilizer production, often in industrial plants that do not fulfill the minimum conditions demanded of similar industries in developed countries.

The uncertain effects of the current climate change

The currently available global atmospheric circulation models (about 20 have been proposed in the last 15 years) have defined hypotheses about climatic change due to the increasing levels of carbon dioxide and other pollutants. All these hypotheses foresee, with some differences, an increase in the global temperature of 3-5[degrees]C in the lower atmosphere by 2050. This increase would not be homogeneous but would increase with latitude by 0-1[degrees]C at the equator and by 6-9[degrees]C at the poles. Yet these hypotheses disagree on the changes in rainfall patterns; some envisage a small increase in rainfall at the latitude of the arid regions, while others predict a slight decrease.

In the worst foreseeable case for the hot deserts, given that a temperature increase of 1[degrees]C causes an increase in the potential evapotranspiration of about 70 mm/year (i.e., an increase of 2-7% in the arid areas) and supposing that rainfall did not vary, then the rainfall effectiveness or precipitation/evaporation index (P/PE) would decline in the hot arid areas by about 4-5% per [degrees]C increase in temperature. The climate would thus get worse: aridity would increase. The increase in temperature would also cause a shift to more thermophilous communities in the vegetation at given latitudinal and altitudinal zones.

Obviously, these changes will not be sudden. Paleontology and palynology show that a rapid change can occur in a century or even less, while a slow change may take a thousand years. There will thus be an indeterminate delay between the predicted physical changes and the biological responses to them. This delay would depend on the capacity for change of the ecosystems, an aspect that has not yet been thoroughly investigated. It is, however, generally considered that this ability to respond is low. It might thus be expected that rapid changes would occur over a period of a few decades, and that these changes might be locally slowed down or speeded up by climatic fluctuations (periods with rainfall greater or lower than the long-term averages).

In the worst case, the bioclimatic zones might be displaced by about 10% toward the neighboring, more arid areas. Thus, within a period of 50-100 years, the hyperarid area might spread to cover 10% of the arid zone, the arid zone might spread to cover 10% of the semiarid zone, and so on. This hypothesis is far from being confirmed, as some physiological mechanisms tend to attenuate the impact of these changes. In the first place, the increasing CO2 concentration in the atmosphere would cause a carbon fertilization effect because photosynthesis would be increasingly effective. Carbon fertilization caused by a doubling of carbon dioxide in the atmosphere to 700 ppm by volume by the year 2050 might cause an increase in primary production of 10-30% (the combined result of simulations carried out in greenhouses or growth chambers) or perhaps only 8-10% (the combined result of open air experimental data in air enriched with carbon dioxide). The increase in atmospheric carbon dioxide will tend to decrease stomatic conductivity, thus reducing transpiration and water consumption by 10%. Current knowledge does not allow us to say which mechanism will prevail, the increase in the climatic demand for water (potential evapotranspiration) or the saving of water due to the lower stomatic permeability and the increased photosynthetic efficiency.

The inevitability of human desertification

Whatever the consequences of the climate changes, people are the main cause of recent desertification. A prolonged drought is neither necessary nor sufficient to start desertification. Climatic variability is one of the characteristic features of the arid lands, and there are many convincing examples and much evidence that natural ecosystems can resist a prolonged drought with almost no damage, as long as the impact of human beings and their herds of livestock is slight. When subject to a moderate grazing pressure (measured in terms of their carrying capacity), the pastures of the Sahel, for example, can resist droughts of up to 15 years without major alterations, despite the apparent contradiction that millions of hectares of overgrazed land have become desertified.

Desertification can start (and has in many cases started) in periods of moderate aridity--and even in periods that are less arid than average. All that is necessary is for the fragile and unstable ecosystems in question to be subject to especially intense pressure from people and their animals. In the best of cases, the native perennial species are replaced by annual plants or perennial weeds, unpalatable to the livestock and useless to human beings except as protection from erosion for the soil surface. In the worst case, the elimination of all the plants leaves the soil totally bare and subject to the unchecked action of the agents of erosion--the impact of the drops of rain, the force of the freshets (that are no longer slowed down by the vegetation), the wind and the particles it bears, etc.

Anthropogenic desertification--the apparently irreversible degradation of a relatively arid space to conditions of little or no biological production (bare soil, sand dunes, rock pavements) as a result of human intervention--affects immense areas of the planet, according to the most reliable calculations. About 60,000 [km.sup.2] of arid land turn into deserts every year. On the northern edge of the Sahara, an estimated 0.5-0.7% of the area of arid land turns into desert every year. These figures are considerably lower in the North American and Australian deserts, but they do not escape this scourge entirely.

The impact of the various ways that humans degrade the soil and vegetation in the world's arid areas varies greatly from one area to another with the standard of living and lifestyles of their human populations. Two main activities--the cultivation of subdesert steppe and scrub for dry farming, and deforestation due to firewood collection and charcoal production--are typical causes of deforestation in rural societies with low incomes or with very high rates of population growth. They mainly occur in developing countries in northern Africa, the Near East, the Sahel, eastern Africa, and the Indian subcontinent.

Other equally dangerous activities, including the destabilization of sand dunes by fourwheel-drive vehicles, some types of tourist development, urban and industrial pollution of air, water, vegetation and soils, as well as uncontrolled fires, are more likely to occur in societies with high incomes.

Some activities that have an effect on the overexploitation of resources may be shared by poor countries (where much of the population lives in arid areas and depends on the meager resources for survival) and by rich countries (where only a very small percentage of the population lives in the arid areas and is only marginally dependent on the resources). Overgrazing is an example: in most (but not all) developing countries, high grazing pressure coincides with a high population density, leading in turn to some of the other destructive activities described above. However, high, and even excessive, stock levels may also occur in countries without this demographic pressure (United States, Argentina, Australia). Rich and poor countries also share extractive activities whose location depends only on the location of the mineral deposits, but they receive very different treatments, depending on the environmental legislation in a given country. The way that rich countries and poor countries cause desertification may be different, but the end result is always the same: more desert.

4.2 The impact of wild-gathering

The current climate change is not the first to affect the hot deserts in the last few millennia. There is plenty of evidence that people used to live permanently in areas that only nomads now visit (and only seasonally); humans even lived in some areas that these nomads now avoid because of their extreme aridity.

The hot deserts we know have formed gradually over the last 10,000 years, independent of human pressure, which was relatively moderate before the expansion of irrigated agriculture (initially only in Mesopotamia and Egypt) and the spread of nomadism that followed the domestication of the camel. There are also testimonies of anthropogenic desertification; dune fields or salt pans in areas that were once cultivated, cities buried under the sand, and networks of channels that have silted up and are now dry.

From balance to risk

In the desert, gathering resources requires a great deal of knowledge. The Aboriginal tribes of Australia's desert regions were perhaps the pre-Neolithic human group best adapted to life in hot deserts because of their exact knowledge of the area's resources and their ability to use them over the seasons of the year.

The Walpiri (or Walbiri) are one of the best-studied cases. They used to live in a desert region in the southwest of the Northern Territory, near its border with Western Australia, and did not come into contact with the British colonists until the second half of the nineteenth century. Throughout the year, the Walpiri traveled throughout their territory hunting and gathering all sorts of animals and plants.

Their use of the flora and fauna was quite remarkable, and their diet consisted of more than a hundred animals and about 40 plants. In autumn, when the springs were full and the game and edible plants were abundant, they came together in large groups and moved leisurely from one spring to the next; as the water became insufficient for the entire group, the group subdivided and dispersed into smaller groups until the springtime. When the resources had declined to a minimum and life was getting difficult, the groups were split up into single family groups. During this period, their thorough knowledge of the way of life of all the organisms they ate allowed them to find roots, tubers, or lizards hidden underground. Only in cases of exceptional drought was any group left totally without any resources, and then they had to cross the frontier of the neighboring tribes, whose lands had more resources, rather than die of starvation.

An exceptional drought from 1924-1927, 50 years after the Walpiri had come into sporadic contact with the colonists, caused the surviving Walpiri to disperse; most settled in the region of Alice Springs and on different cattle ranches.

The increasing consumption of firewood

About 90% of the energy needs of most of the peoples living in the hot deserts and subdeserts are met by firewood extracted from the few trees and shrubs that grow locally; all traces of woody vegetation have now disappeared in a radius of 4-8 km (19-77 mi2 [50-200 [km.sup.2]]) around most villages in the Sahel.

International organizations estimated the average rate of deforestation for the period 1981-90 was about 0.7% per year. This rate corresponds to a reduction of 10% of the area covered in 15 years, 20% in 30 years, 30% in 50 years, 40% in 70 years, and 50% in 100 years (a logarithmic regression). But the rate of deforestation is growing in parallel with the increasing population (2.7% per year), so the chances are that the entire Sahel will be almost totally deforested by the middle of the twenty-first century.

There have been some remedial measures, such as the local introduction of cooking fires with a greater energetic yield than the traditional simple fire on the ground between three stones. Still, they are insufficient, despite surprising success on a local scale. (In the Agades Department of Niger, an estimated 600 trees a day have been saved by the spread of these simple devices.)

In a similar manner, but in clearly different social and economic conditions, overexploitation of the patches of algorrobales in the Argentinian monte (phraetophytic thickets of Prosopis flexuosa, known as algorrobo dulce to the Argentinians) has made this species rare. It is felled for timber for building houses or service buildings on cattle ranches, to plant vineyards, and of course for fuel. Mining uses timber for construction and firewood for fuel and has also been highly destructive in the monte, as well as in many other deserts.

In the deserts of northern Chile, the indiscriminate use of the vegetation by the mines since colonial times and by contemporary human settlements has been one of the causes for increasing desertification. In the last 20 years, intense state-funded efforts have been made to reverse the loss of plant cover by creating artificial plantations of different shrub and tree species, both native and introduced, of the genera Prosopis, Acacia, Atriplex, and Eucalyptus.

In some regions, western Africa among them, gathering medicinal plants and other useful plants may, like gathering firewood, lead to the disappearance of the woody plant cover that protects the soil from erosion and supplies it with organic material.

4.3 Minimal agriculture

Though it may seem incompatible with the current climatic conditions of the deserts and subdeserts, most of the Neolithic centers where humans first practiced agriculture were located very close to the edge of arid regions. The secret of their success was almost always their use of an additional resource, water, which is vitally important in deserts.

Water is the limiting resource in the world's arid and semiarid regions, as it is absolutely essential for life and has many other uses (drinking water, sanitation, irrigation, transport routes, industrial uses, treatment--or simply transport--of sewage). Water management, including management of surface waters, underground waters, and rainfall, leaves much to be desired.

Water exploitation systems can, however, easily turn into a double-edged weapon: they may become a curse rather than a blessing, especially if proper preliminary studies are not performed, if usage and management rules are ignored, or if the legal provisions are unrealistic and thus not enforced.

In some areas, water is not necessary, as the low rainfall, or even the fog, is sufficient. This is shown by the techniques of the ancient Nabataean culture, now successfully copied in the Negev Desert, based on capturing the runoff water from a large area; similar methods have been successfully developed in the northern Sahara and in the Sonoran Desert, where the Papago Indians excelled at this type of agriculture. In the arid coastal regions of Peru and Chile, which are frequently covered by fog, ingenious devices with large condensation surfaces are used to obtain significant quantities of water from the fog.

Subsistence dry farming

Very few of the hot deserts are fortunate enough to receive heavy condensation. In many of the world's subdeserts, the natural vegetation is being destroyed, partly for the establishment of subsistence crops, especially cereals that are on the borderline of viability.

The reasons for this senseless agricultural activity lie in poverty and population pressure, as the population of these relatively poor regions has been growing exponentially for the last half century, and the legitimate desire for increased income or the need to feed a large family stimulate this type of agriculture.

This is subsistence, or even survival, agriculture. These extensive crops are cultivated with very low inputs, without fertilizers or pesticides, and no more labor than plowing and sowing with a disc harrow; the amount of seed used is very low, only about 30-50 kg/ha for barley, and so the crop obtained by the farmer is about 200 kg/ha of grain (while in commercial cultivation, the yield is 1,000-1,200 kg/ha of grain). Thus, any grain production above 200 kg/ha is profitable.

Yet not even this small yield is reliable. In the subdesert wastelands and scrubs of northern Africa, which since the Second World War (1939-1945) have been subject to episodic exploitation of this type, the chance of obtaining a harvest is 10-40%, and when there is a harvest it may range from 100-1,000 kg/ha of grain.

The most widely cultivated grain is barley (Hordeum vulgare) and then durum wheat (Triticum durum). Despite the unreliability of the harvest and the low yields obtained, cereal crops and the associated fallow ground represent 30-50% of the area of the wastes and scrubs of northern Africa. To put it another way, all the soil soft enough to be worked, except dunes and excessively saline soils, are cultivated in the agricultural years when the autumn rains are favorable. The result is an authentic ecological catastrophe: soil erosion, the formation of large areas of sand dunes, and desertification.

Large areas are cultivated sporadically in favorable years (these occur anywhere from one year in three to one year in ten) and may cover 60-70% of the surface area of the subdeserts of some parts of northern Africa and the Near East. In other areas such as the Sahel, eastern Africa, and the edges of the Kalahari, degradation is equally clear, but the area affected is smaller.

Barley is the most widely cultivated cereal in the Mediterranean edges of the Old World deserts, but on the tropical edge of the deserts of both the Old World and the New World the commonest cereals are pearl millet (Pennisetum glaucum) and sorghum (Sorghum bicolor).

These randomly grown crops are present even in the arid areas of developed countries (United States or Australia) but do not evolve. In developing countries, as the population expands, larger areas of ground have to be cultivated to obtain sufficient food; if there is no more land to clear, the fallow period is shortened or eliminated, thus reducing the fertility and therefore the yield, so that larger and larger areas are needed to obtain the same harvest. This worrying spiral of desertification is self-accelerating.

In many countries, especially in the Sahel, laws have been passed banning the plowing of land in areas with rainfall below a defined annual average (normally 14-16 in [350-400 mm]), but these laws are not enforced. Niger, as part of its policy to preserve natural resources, passed laws in 1961 and 1962 establishing a northern limit to dry farming (the 16 in [400 mm] average annual rainfall isohyet).

North of this limit, an area was established exclusively for livestock exploitation, and laws were also passed to regulate the herders' use of wells and other water points; the government regulated vaccination campaigns and prevented the burning of scrub around the new wells that had been dug, thus establishing crucial elements of livestock policy; Niger also created a new public-sector body responsible for monitoring wells and enforcing national livestock policies. This law fixed a northern limit to dry farming, but it was never applied; in fact, millet cultivation spread farther and farther north, to the 10 in (250 mm) and 8 in (200 mm) isohyets, even in the major drought that began in 1969. The farmers lack training, and their desperate need to grow the food they eat leads them to overexploit the land.

The salinization of irrigated ground

Desert agriculture relies on irrigation, either with surface waters or underground water. Yet even this form of agriculture has its problems; desertification can also be started by incorrect use of water resources. There are about 250 million ha of irrigated land in the world, and roughly 0.4-0.6% of this area is lost every year, becoming unproductive or completely sterile due to excessive salinization, sodication, or waterlogging.

If they continue at their present rate, in 140 years one-half of all the land currently irrigated will become unproductive. This would have disastrous effects on the world food production, as irrigated land is the most productive. (Though it only represents 18% of all cultivated ground, irrigated land produces one-third of all humanity's food and therefore benefits from investment of up to $20,000 per hectare.)

Some traditional irrigation systems have shown themselves to be very efficient and sustainable. Egypt, for example, lived for thousands of years by its agricultural irrigation based exclusively on the regular flooding of the Nile, until little more than a century ago, when the first major hydraulic transformations were put in place. The inland delta of the Niger contains the most important concentration of agriculture in the Sahel. On the Pacific coastal slopes of the Peruvian Andes, there are series of terraces surrounded by marls on which cotton, alfalfa, sugar cane, and maize are grown. In this area, most of the native vegetation, including the Prosopis thickets, has been felled for timber and for charcoal and has been replaced by small plantations of olives, pears, apples, and plums; all that remains, shading the edges, are a few specimens of willow (Salix humboldtiana), pepper tree (Schinus molle), and the reed jabonero or uva grass (Gynerium sagittatum). Some ambitious projects seek to channel water from the upper slopes of the Andes in order to extend the area of agriculture in the region.

The undesirable consequences of irrigating arid areas are by no means new. The ancient Sumerians had problems of salinization due to their crops' intense evaporation in the summer, and by 4,000 years ago the previously balanced proportion of wheat to barley started to swing heavily in favor of barley, which is more resistant to salt. Wheat totally disappeared within a century, while the yield of barley per unit area diminished 4,0003,500 years ago. These changes were related to the gradual movement northward of the centers of power in Mesopotamia, and the region's definitive decline with the fall of Babylon to the Persians 2,600 years ago. The Persians renovated the irrigation and drainage network, but only in conflict-free periods of highly centralized power did it function regularly. When the Sassanid dynasty collapsed in the face of the Arab advance, this network had deteriorated greatly due to silting up of the channels. The thirteenth century Mongol conquest ended the legendary wealth of Mesopotamia, which it has still not totally recovered.

Secondary salinization may be due to several causes. Excessively saline soils are unsuitable for irrigation due to their bad drainage, as are those that have unbalanced proportions of cations. But soil degradation is often due to incompetent management, lack of maintenance of drainage systems, excessive irrigation, or the application of inappropriate agricultural systems. The most frequent cause is inadequate drainage for whatever reason (because it was not included in the preliminary studies, because adequate drainage was not built to save on investment, because the project was badly planned from the beginning, or because it was never brought into operation in order to save money). Furthermore, instead of low levels of salinity, the water used may have an unbalanced cationic composition.

Salinization affects a very large area: 4.5-9 million ha in Pakistan, 15 million in India, 750,000 in Egypt, and 4 million in the United States. An estimated 5% of the 5.2 million [km.sup.2] of arid land that have become desert did so because of salinization. These losses are the most important economically, as they are potentially the most productive areas in the world.

Large hydraulic schemes

The twentieth century has seen many drastic transformations in the longest-lasting of all irrigation systems, the traditional Egyptian system. The construction of the Aswan High Dam, which retains the immense Lake Nasser, makes it possible to regulate the flow of the Nile, without surges or droughts, and to supply water year-round to the two million ha of preexisting irrigated land in Egypt, as well as to an additional 500,000 ha (1 ha=2.5 acres). Much of this land produces more than one harvest a year, which is very necessary in a country with one of the world's highest rates of population growth. The Aswan High Dam, like almost all the large dams built since the late nineteenth century, not only meets irrigation requirements but also produces hydroelectric power, enough to meet much of Egypt's energy needs.

However, retention of sediments by the dam (silting) has caused a series of undesirable problems. The most serious is probably the retreat of the front of the Nile Delta, and attempts are being made to prevent this by building large cement dykes to avoid erosion. There has also been a drastic decline in fisheries, both in the Nile itself and along the coastline of the southeast Mediterranean, as well as an increase in the incidence of schistosomiasis. Flood-derived silt used to provide a regular input of organic matter and minerals for the croplands (now it's replaced with fertilizers) and was also a source of mud for making pottery and bricks (but the mud is now taken from good arable land). Furthermore, excess irrigation accompanied by deficient drainage has created so many problems due to the rising water table and the salinization of land that, in the mid-1970s, an estimated 80% of Egypt's cultivated land needed improved drainage.

When the first Spanish colonists reached the lower basin of the Colorado, there was already a dry farming tradition among the agricultural Indian peoples living there. The Spanish brought their own experience from Andalusia and created new irrigated areas, especially along the Santa Cruz River, a tributary of the Gila, from the mid-eighteenth century onward. In 1902, the U.S. government began an ambitious scheme to develop the entire Colorado Basin, mainly by providing urban infrastructure and irrigation throughout the hot desert regions of the lower basin.

The project that definitively changed the river was the construction of the Hoover Dam (1928-1935) in Boulder Canyon and the related schemes (especially the All-American Canal) that allowed the irrigation of more than 642,471 acres (260,000 ha) in southern California and southwestern Arizona, and more than 395,367 acres (160,000 ha) in Mexico, without summer drops in level or catastrophic surges. At the same time, the dam can produce 4,000 million kWh (kilowatt-hours) of electricity every year. The Hoover Dam impounds Lake Mead, which initially had a capacity of 40 billion m3, almost double the river's annual volume of flow. It ensured efficient regulation of the river, completed by other major dams on the upper basin and a series of smaller dams in the lower basin, beginning with the Imperial Dam (the starting point of the All-American Canal) and some others on the Colorado River itself (Davis, Parker, Headgate, Rock, Palo Verde, Laguna, Morelos dams) or on its tributaries (Coolidge Dam on the Gila River, Roosevelt Dam on the Salt River). Downstream, the effect of the Hoover Dam on the Colorado River (in Spanish, colorado means red, the color of the sediments transported by the river) is equivalent, but on a smaller scale, to that of the construction of the Aswan High Dam. Before 1930, the Colorado transported an average 125-150 million tons of sediments (more than the roughly 100 million tons transported into the Mediterranean by the Nile before the construction of the Aswan High Dam), but since 1934, when Lake Mead began to fill up, the sediment transported fell to minimum values and declined to almost nothing after the mid-1950s.

In the 1970s, construction began on the Granite Reef aqueduct to bear water from the Parker Dam to the city of Phoenix and the surrounding area and to the irrigated fields of the Salt River's valley. The aqueduct, the first of the schemes in the Central Arizona Project, was finished in 1986 and supplies irrigation water to more than 988,417 acres (400,000 ha) of new irrigated land and more than 600 million m3 for domestic, urban, and industrial use in the areas of Phoenix and Tucson. Use of the Colorado's water has now reached an upper limit that can only be exceeded by very rigorous measures to save water or to reuse it; there are now more legal disputes in the Colorado Basin than in any of the world's other river basins.

One feature of irrigated agriculture in the Lower Colorado is the sharp contrast between the Mexican and American sides of the frontier (which is clearly visible in satellite pictures). The American side, where sprinkler irrigation systems have been widely used since the 1960s, uses a lot of high technology and is highly productive. Recently, laser leveling and automatic sluice-gate control have been introduced. Unlike in the Nile, the water is not distributed free by the federal government but is distributed by profit-making private enterprises. Water is expensive, so the American farmers of the Lower Colorado have to seek the most profitable strategy by carefully following market developments, depending on which they may change crops (sugar beet, long-staple cotton, fodder for penned livestock, etc., though fruit and vegetable production is also important). Even so, there are problems. The spread of irrigation in the Gila Valley since the 1950s has increased the salinity of the waters of the Colorado River, which led to legal claims by Mexico (whose internationally recognized usage rights were negatively affected) and forced the construction of desalinization plants. Heavy use of fertilizers and pesticides means that any excess, like the breakdown products, ends up in the rivers or the aquifers.

Irrigation with fossil water

Some oil-exporting countries have decided to invest part of their huge profits from oil and gas in huge hydraulic projects to use the large fossil aquifers below the Sahara and the Arabian Desert. These very deep aquifers formed in the geological past receive no water at all, and so like oil, they are not renewable resources. The reserves are enormous, with 3,400, 4,800 and 10,000 km3 in the Libyan aquifers of Kufrah, Murzuq, and Sarir respectively.

In 1971, a development project in the Al-Kufrah oasis in Libya to irrigate 24,710 acres (10,000 ha) of cereal crops began the construction of what has been called the Great Desert River, a huge pipeline made for carrying water from Tazirbu (in the middle of the desert, about 500 mi [800 km] from the Mediter-ranean coastline) and from Sarir (485 mi [780 km]) to the coastal cities of Surt and Benghazi in Cyrenaica. The project was completed in 1992. A similar design will bear water from the aquifers of Fezzan to the coasts of Tripolitania and will ensure the food supply of 300,000 sheep in the north of the Fezzan region. Saudi Arabia now also exploits fossil water resources in order to become self-sufficient in food production, and surprisingly, since 1990, Saudi Arabia has been a net exporter of wheat and other food products.

4.4 Grazing in adverse conditions

The decline of nomadic pastoralism began in the Near East in the 1920s with the discovery and exploitation of the first oil fields in the region. After the Second World War (1939-1945), this decline spread to all the hot deserts in the Old World. In the early 1960s, for example, about 1.75 million people lived as nomads in the 10 countries surrounding the Sahara. Today, there are only half a million nomads. In centuries past, the nomads of the African deserts controlled the oases that were cultivated by their serfs and slaves; they also controlled the trans-Saharan caravan trade between central Africa and the Mediterranean coastline, as well as the salt trade between the central Sahara and the ecological zones to the south (the Sudan, Guinea, and Sahel). These lifestyles have become extinct, except in the case of the Kababish in Sudan, who have adapted their activities very well to motorized transport. Most of these nomads have been forced to emigrate to the cities and now survive on international food aid, join the army, the police, or other government service, or work in the oil fields or mines.

Traditional subsistence nomadic lifestyles have incorporated new ways of using pastures, that, as a whole, have even further increased the impact of the already poor vegetation of the African and Asian deserts. On the edges of the desert, especially in northern Africa and in the Near East, seminomadism or transhumance is practiced, combining a precarious cultivation of cereals that relies on the winter rains with grazing in the mountains in the summer; in seminomadism, the entire camp (or duar) moves as a collective, but in seasonal migration only the herders travel. Anyway, in the last half century, the number of head of cattle in the deserts in the developing countries has grown at 1-2% a year, half the rate of growth of the human population. The area of grazing has declined at almost the same rate due to clearance for agriculture, so livestock density has increased roughly fourfold in the last half century.

Overgrazing around water points

The increase in stock density has not been compensated by improvements in production techniques and practice, and some modern technologies have unfortunately made the problem worse. The drilling of wells with pumping stations that can supply 4 l/s, paradoxically, in the subdesert pastures in the Niger Republic, led to the rapid destruction of the grazing within an area of 12 mi (20 km) around these water points, due to the lack of adequate planning and management criteria.

Theoretically, the number of animals with access to the wells should be controlled by opening and closing the pumping stations, but in practice the local representatives of the government were never able to manage this, and during the dry season many animals concentrated around the wells, perhaps 20,000-30,000 TLU per well for 8-10 months a year, far exceeding (by up to three times) the carrying capacity of the grazing land.

In this area, the carrying capacity was 8-10 TLU/ha before the wells were drilled, but now it is less than 4 TLU/ha. In an area of 124 acres (50 ha) around the wells, the density reached 20 TLU/ha a day. In two or three sites, the final result was the destruction of all the grazing within an area of 12-19 mi (20-30 km) around each well, between 126,000 and 283,000 ha (1 ha=2.5 acres). In the extreme 1970-1973 drought, the many animals that died next to the wells died of hunger not thirst.

This example shows that a policy designed with the best will in the world can lead to disaster if it is not based on realistic assessments of the situation. But not all the different ways of managing water have had the same results. The wells drilled in the Ferlo region of Senegal, despite creating some problems, did not destroy the food resources of the herds or create an anthropic desert. This was due largely to the fact that the area belonged to a homogeneous group of pastors, the walo or dieri Fulani, who prevented the entry into the area of other herders and thus converted the area into a forest and grazing reserve.

Throughout the Sahel, free access by livestock to wells and large pools and rivers has, in general, had the same results: the destruction of grazing lands and desertification. The impact on the woody vegetation of the Sahel has been especially well documented by at least a dozen scientists. The woody layer is in most cases declining, by about 1% a year. In the stockraising areas of eastern Africa, specifically northern Kenya, southern Ethiopia, and Somalia, exploitation of water in pools, without any control on grazing, had the same results as in Niger, and the several million dollars invested by the World Bank had the same effect.

Agro-pastoral degradation of oasis margins

Likewise, irrigated areas are often surrounded by a strip of extremely degraded arid land-land degraded by dry farming, permanent grazing, or firewood collection.

The money obtained from irrigated crops is usually invested in livestock that graze freely in a radius of 3-4 mi (5-6 km) in the case of small animals and 12-16 mi (20-25 km) in the case of cows and horses, the distances these animals can travel in a day while grazing.

A study was performed on the periphery of the central zone of the inland delta of the Niger (see map on p. 237) in Mali; comparison of two sets of 1:50,000 aerial photographs taken in 1952 and 1975 showed that during this period, the area of intensely degraded ground increased from less than 200,000 ha to 1.2 million ha, from 4% of the area in question to 26%. During the same period, the area dedicated to dry farming increased from 130,000 ha to 255,000 ha, almost doubling to 5.5% of the area.

Many recently developed irrigation systems have also caused similar degradation of their surroundings, but the old oases remaining in the northern and southern Sahara have probably been surrounded since time immemorial by dry zones, just as they were described by late nineteenth-century and early twentieth-century explorers.

4.5 The exploitation of mineral resources

The hot deserts and subdeserts contain many mineral resources. In many desert areas, minerals are by far the most important economic resource-and virtually the only ones in countries like Kuwait, Qatar, or the United Arab Emirates, whose economy is based almost entirely on oil extraction.

Extractive activity

Some extractive activities in deserts are very old; the saltworks in the Sahara, the Thar Desert, and other deserts are as old as the development of the caravan trade routes and, in some places, even older. The extraction of caliche or Chilean saltpeter (sodium nitrate) from the desert areas of contemporary northern Chile dates back to pre-Colombian times. Whether ancient or modern, mineral extraction is exceptionally destructive, especially opencast mining, which is increasingly common. Low local populations, ground that costs little or nothing, and the difficulty of access for potential observers mean that mines in deserts are less likely to be well managed and monitored. On the other hand, the difficult access and transport, together with the difficult working conditions, mean that in most hot deserts it is only worth extracting high-value minerals, mainly precious stones, valuable metals, uranium and other rare metals, and those that can be highly mechanized (such as deposits of oil or natural gas).

Historically, precious metals were the first minerals to attract the most daring and ambitious prospectors to some deserts: gold from the Sahara (which, in fact, was not extracted from but only crossed the Sahara in caravans) stimulated the medieval imagination and was one of the main motives spurring Portuguese explorers to follow the African coastline, where they gave the name Rio de Oro (River of Gold) to the coastline of the western Sahara; in the Americas, silver attracted the first colonists to the Mexican and Chilean deserts; in Australia, gold was found in 1892 in Coolgardie, a desert region about 311 mi (500 km) east of Perth, and attracted more than 100,000 men in four years. In Death Valley (California), so much borax was extracted that, after 1880, columns of up to 20 mules pulled cart trains of it for more than 125 mi (200 km).

Petrol is now by far the most important mineral product extracted from deserts. The largest reserves (more than half the world's known reserves) are found around the Persian Gulf, mainly in Saudi Arabia, though there are also large deposits in northern Africa (especially in Libya and Algeria). Oil (and natural gas) drives the economies of these countries and may be their only source of foreign currency. This source, however, is now highly productive and has made the beneficiary countries among the richest countries in the world, causing deep changes in their societies. It has also given rise to countless frontier conflicts, the most serious of which led to the Iran-Iraq War (1980-1988), Iraq's invasion of Kuwait (1990) and the Gulf War (1990-1991). Pollution, a major problem in the Gulf even before these wars, has worsened considerably in the last 15 years, especially during the Gulf War and the following months, when the Iraqi army left behind more than 500 burning oil wells, a slick of 4-6 million barrels of oil in the waters of the Gulf, and discharges of 150 million barrels on dry land. All of these seriously contaminated soil, vegetation, and aquifers.

The environmental impact of mining

The impact of large opencast mines is spectacular. When the exploitation is fully operational, immense craters are dug tens or even hundreds of meters below the original ground level, and huge quantities of waste accumulate; though as much of the mineral has been removed as is profitable, enough remains to contaminate large areas of land and the related aquifers, and it gives rise to dust with high levels of heavy metals. The large copper mines in the Atacama Desert and some in Nevada (United States)-among the largest in the world-are major sources of direct and indirect pollution.

Mining, by definition, is the exploitation of a nonrenewable resource in a given site until it is exhausted. Therefore, except in extraordinarily rich or large deposits, this activity is limited in time but potentially generates great wealth. In the case of the deserts (and the developing countries in general), though, this wealth does not have beneficial effects on the local economy; rather, it accrues in the distant financial centers that provided the original investment to make efficient exploitation of the resource possible.

Thus, little of the wealth created by uranium mining in the Republic of Niger or diamond mining on the coast of Namibia has benefited these countries, although the landscape has been destroyed with toxic slag heaps and contaminated aquifers. Even in developed countries, there is an unequal distribution of benefits and costs; because the mines are in relatively unpopulated areas, the companies always come from outside and employ more labor from outside than from the local labor pool, and they rarely reinvest in the same site, seeking a new site when the mine has been exhausted.

90 Camels (Camelus) have played a major role in human adaptation to the desert. The camel was domesticated long ago--about 5,000 years ago--and has since become vital for the nomadic populations of the Old World's deserts and subdeserts because of its many uses in these hostile climates. The camel provides food, leather, and fuel (its dung) and is an excellent beast of burden and mount; it has long been used in warfare and for other military purposes. The existence of camel markets such as the one in the photo in Pushkar (Rajasthan, India) is therefore quite basic, and the deals struck there are of great importance.

[Photo: DPA / Images of India]

91 The large lakes in the Sahara during the Quater-nary climatic optimum, roughly 10,000-12,000 years ago, were a reflection of the high prevailing levels of humidity and had abundant flora and fauna. They have all since disappeared, except for Lake Chad (limited to the most tropical part of the region and now much smaller than in the past) and a few sebkhas or chotts. In fact, the Saharan region has been occupied since the early Pleistocene by a mosaic of deserts, subdeserts, and less arid areas that have expanded and contracted with climatic fluctuations. The map only shows one of the wetter periods through which the region has passed. The names correspond to the areas that the lakes would now occupy, when identification is reasonably certain.

[Drawing: IDEM, based on Lay, 1991]

92 The construction materials and architecture used in desert villages are often lessons in optimizing the use of natural resources. Ait Arbi, in the Valley of the Dades (Morocco) is one of the many examples of multipurpose design, adapting the architecture to the desert environment while making the most effective use of space. In the southern Atlas, where the population is mainly Berber, there are many ksars, fortified villages typical of the preSaharan zone in the valleys of rivers like the Dra, Dades, Gheria, and Ziz. In these traditional constructions made of stone, adobe, and mud, the dwellings are designed to occupy the maximum possible space by limiting the exposure of the external walls to the rays of the sun. The upper stories and internal courtyards are also orientated so that they are protected from the light, and the inhabitants move from room to room over the course of the day. During the daytime, the ground floor is coolest, but at night inhabitants prefer to sleep on the flat terrace roofs, where during the day fruit and grains are dried in the sun. The materials used in the construction of the ksars are the best to achieve this balance between architecture and environment. The dry mud covering the external walls heats up very slowly during the day and releases the accumulated heat at night. The internal rooms stay at an agreeable temperature during the day thanks to their high roofs. This magnificent adaptation to their environment has not, unfortunately, prevented many of these traditional settlements from suffering gradual population loss, as many of their inhabitants prefer the comfort of modern buildings.

[Photo: Adolf de Sostoa]

93 The term blue men often applied to the Tuareg refers to the color of their clothes and above all to their veil, or litam, perhaps their most typical item of clothing (see figure 104). This intense dark blue is obtained by dying clothing with indigo, a coloring agent obtained from several legumes of the genus Indigofera, mainly I. tinctoria, I. arrecta, and I. articulata. As the traditional dying method is rudimentary, the color runs, often giving the wearers' skin the bluish color for which they are named. (Many Tuareg are melanoderms, but those with lighter skin show the blue more clearly.) The photo shows Tuaregs riding through the streets of Djanet (Algeria) on their typically arrogant-looking camels. The Tuareg, whose weapons include a sword and a dagger hanging from their arm, have always sought to distinguish themselves from the other Saharan peoples, whom they have often subjected or at least attacked on their journeys through the desert.

[Photo: Sandra Prato / Bruce Coleman Limited]

94 The Afar of the Danakil Desert in Ethiopia are strong, tall, thin and dark-skinned and accustomed to the harshest desert conditions. They are nomadic herders who herd goats and sheep, like the group shown in the photograph, and they also raise some camels. The Afar usually set up tents, which they take down to transport on their travels, making their caravans look very unusual, with the long tent struts forming curved bundles. Though their economy is based on stockraising, they sometimes trade with other tribes. Also known as Danakil after the region where they live, the Afar are Muslim Cushites, but they still maintain many of their ancient animist traditions.

[Photo: Dieter & Mary Page / Survival Anglia / Oxford Scientific Films]

95 The !Kung are San hunter-gatherers, like these two people photographed in the Kalahari Desert. An African people with a culture well-adapted since ancient times to the hostile desert environment in which they live, the !Kung used to live in the western and southern savannahs of Africa, but since the early twentieth century they have been restricted to the Kalahari Desert in Botswana and Namibia. Only about 5,000 of the remaining 50,000 San retain their traditional hunter-gatherer lifestyle. The women and children go out to find plants and small invertebrates, while the men are responsible for catching animals for extra protein in their diet.

[Photo: Anthony Bannister / NHPA]

96 The great civilizations of ancient Mesopotamia developed in the hot deserts of western Asia between the Tigris and the Euphrates. About 12,000 years ago, hunter-gatherer groups in the area took up agriculture and turned part of this arid area into fertile oases that were later envied by nomadic groups such as Hurrians, Kassites and Guti. The most important civilizations, the Sumerian, Babylonian, and Assyrian, were at their height 5,500-2,600 years ago. Other peoples such as the Elamites or the Semites had a huge influence on the development of these cultures. The Sumerian civilization is the oldest of all known civilizations. It appeared 5,500-5,000 years ago, when several separate settlements came together in walled cities. In 2340 b.c. the Sumerians were conquered by the Akkadians arriving from the northwest. The Akkadians assimilated many Sumerian features into their culture, among them the organization of their cities, their laws, and their monumental architecture. Sumer and Akkadia were unified under Babylonian law and had a highly organized administrative system. During the Babylonian period, commerce, art, and science flourished. Later, Babylonian culture spread under the Assyrian empire from the Persian Gulf to the Mediterranean. The Urartians from the mountainous regions of Lake Van were for a long time the greatest enemies of the Assyrians, but much of their culture came from the Assyrians. The Assyrian empire collapsed about 2,600 years ago due to the pressure of the peoples on their northeastern border.

[Drawing: IDEM, based on GEC]

97 On the edge of the Thar Desert, the medieval walled city of Jaisalmer (India) has many beautiful temples and a sophisticated ancient system used to extract water and store it in an area where water is very scarce. Other cities in the area, like Jodhpur, also have similar systems. The presence of wells, large deposits, and water distribution systems that are in many cases architecturally stunning and highly beautiful suggest that the desert peoples planned their use of water resources very carefully. Unfortunately many of these large deposits (often situated within the city the walls, so the water could not be poisoned by an enemy) have been converted into garbage dumps and are no longer cleaned regularly. In the last few decades, due to irrigation and especially excessive pumping of underground water, the Thar Desert's already low water table has fallen alarmingly. This shows that deposit systems are both cheaper and less damaging than modern pumping and channeling methods.

[Photo: Josep Pedrol]

98 This drawing shows the links between the Afro-Asiatic languages proper (HamitoSemitic) and Omo-tic languages. Until recently, the Omotic languages were considered a subgroup of the Cushitic languages, but most linguists now consider them a separate but closely related branch of the Afro-Asiatic languages. The Afro-Asiatic languages contain five main families: ancient Egyptian, Semitic, Berber, Cushitic, and Chadic. It is difficult to classify the languages in each of these five branches, and the method proposed here is only one of many possibilities. There are written traces of ancient Egyptian more than 6,000 years old; this gave rise to Coptic, which is now used only in the liturgy of the Coptic church. The Semitic group is perhaps the most widespread, including the whole of northern Africa and reaching southwest Iran; it is also spoken in the areas where Islam has arrived. In addition to Arabic and Hebrew--the best-known Semitic languages--the family also includes Aramaic, some Ethiopic languages, and Ge'ez, now used only in the Ethiopian church. There is written evidence of Aramaic dating from more than 3,000 years ago. About 2,000 years ago, Aramaic was the dominant language from Mesopotamia to Palestine, but it was later replaced by Arabic. It is still spoken by some peoples in northern Syria, Iraq, Iran, and south of the former Soviet Union, though the number of Aramaic-speakers does not exceed 100,000. The diverse Berber dialects were spoken in a continuous strip across northern Africa, but Berber-speakers are now divided into separate groups. The different languages of the large Cushite group, are scattered throughout Somalia, Ethiopia, Kenya, Tanzania, and Sudan, while the Chadic languages, the best known of which is Hausa, are spoken in Chad, Nigeria, Cameroon, and the central African Republic.

[Drawing: IDEM, based on Junyent, 1989]

99 Islam is present throughout the Old World's hot deserts, as is shown by their decorative arts and the most common expressions of their culture. This house of a Muslim in Luxor in the Valley of the Kings (Egypt) is decorated with scenes from his pilgrimage to Mecca, telling the world he has performed the hajj. The details shown include the sacred spaces, the means of transport, the environment, the animals and plants, the prayers and the camel transporting the kiswah, and the sacred black brocade cloth that covers the Black Stone (the Al-Kabah or Kaaba shrine), which in the past was woven in Egypt. The journey is in the first 15 days of the month Dhu'l-Hijja, after Ramadan. Over a period of four days, several complex rituals must be performed while walking around the sacred space of the Kabah, the cubic temple said to have been built by Abraham. For Muslims, it is the house of God on Earth. Every year Saudi Arabia receives about two and a half million pilgrims from all over the world who come to fulfill one of the five precepts of Islam. In the times of Muham-mad, Mecca was a stopping point visited by caravans from distant regions in search of water from its well. Once a year, it became a center of trade and exchange. Muham-mad's religious discourses, attacking the huge proliferation of divinities and defending the existence of a single god, came into conflict with the interests of the city's merchants. In 623 a.d. Muhammad and his followers had to abandon Mecca and take shelter in Medina. This journey, the Hegira, was the beginning of the century that saw Islam become a huge empire.

[Photo: Rosa Carvajal]

100 The personal nature of body decoration in Australian Aborigenes is shown by this man's work painting his skin to participate in the Butterfly Dance in Arnhem Land. The Aborig-ines developed a very close relationship with the materials of their surroundings; their highly complex totem culture was linked to the land and landscape. The ochre they adorn themselves with also has a symbolic importance. Obtaining it, grinding it, and using it has become a ritual process, which sometimes forms part of ceremonial acts. The drawings depend on the occasion and on each individual's totemic rights. Good quality ochre used to be greatly appreciated and was a valuable item for barter between different tribal groups.

[Photo: Jean-Paul Ferrero]

101 The decorated pottery of the Mimbres Indians, with a profusion of shapes and drawings, is one of the most representative elements of this former agricultural culture of the southwest United States. The earliest designs are simple geometric forms decorating the outside of globular receptacles such as saucepans, cups, and jars. Descriptive motifs appeared later, as seen in these black-and-white designs from a bowl 2,900-3,500 years old, now in the Maxwell Museum at Taos (New Mexico). In the most southern area, the decoration also included animist representations. The Mimbres Indians adopted pottery late, and for a long time objects for personal use were made mainly of wickerwork (the origin of the Castillian Spanish term mimbre) and were also decorated.

[Photo: John Cancalosi / Auscape International]

102 When the Spanish conquistadors reached the hot deserts of North America, there were about 100,000 indigenous inhabitants divided among about 40 different peoples. They all lived in a similar arid environment, but each people had its own language and culture. The Rancheria Indians lived in small, scattered agricultural settlements, while the Pueblo Indians founded agricultural cities along the Rio Grande and on the plateau drained by the Colorado River. Other peoples such as the Apache, Ute, and Comanche were nomadic hunter-gatherers. The Spanish arrived around 1540 in search of the fabulous treasures rumored to be in possession of the local peoples. They explored the entire southwest region of North America in search of gold but returned empty-handed. Catholic missionaries followed them on the same route in search of souls to convert. After the missionaries came the colonists who built farms and cities; colonial authorities installed barracks and courthouses. Several Indian tribes tried to resist the invaders, but these uprisings were harshly repressed. In 1680 the Pueblo Indians managed to expel the Spanish from the region of Santa Fe, but 13 years later the Spanish destroyed the city and executed 70 Indian chiefs in retaliation. The indige-nous population declined, while that of Spanish colonists increased. About 20,000 people of Spanish descent lived in the area by the late eighteenth century, when the Spanish empire began to collapse in Europe and its overseas possessions became vulnerable. Mexico's independence in 1821 opened the way for the Anglo-Americans, and the Spanish definitively lost the arid areas of North America.

[Drawing: IDEM, from several sources]

103 The extremely realistic pottery of the Mochica people, much of which still survives, has made it possible to reconstruct the lifestyle of this agricultural and warrior people who settled the deserts between the Andes and the Pacific Ocean. Each piece of pottery shows a person or a scene from Mochica daily life; the pot in the picture (2,800-2,200 years old) represents a woman kneeling. The documentary importance of Mochica pottery is even greater because the pre-Columbian populations of South America did not develop any system of writing; thus, the main features of their culture can only be reconstructed from archeological material.

[Photo: Museo del Oro, Lima / Giraudon]

104 The clothing of desert dwellers is especially important in preventing dehydration. The Tuareg in the photo are wearing clothes that cover almost their entire bodies, protecting them from the desert sun and sand. Air can circulate in the space bet-ween the clothes and the skin, thus preventing excessive water loss through transpiration. When they have to perform heavy physical exercise, they take off the outermost layer of clothing so that they are cooled by the sweat evaporating from their skin. Their clothing is usually dark, because dark colors provide better insulation and the dust of the desert is less obvious than on light colors. Women in nomadic groups do not usually wear a veil, but most men of the nomadic groups of Arabia and northern Africa wear something to cover their head, especially the Tuareg men. The veil covering the man's face (see photo 93) protects it from the desert wind and from the evil spirits that live in dark lonely places. The Tuaregs' blue clothing is the origin of the name blue men, though the Tuareg call themselves kel tagilmust, which means the people of the veil.

[Photo: Charlie Nairn / The Hutchison Library]

105 The classic tents of desert nomads, such as the ones in this Bedouin camp in Jordan, consist of thick goat or camel leather raised above the ground on four posts. Sometimes this cover is of a material finer than cotton or of sewn goat skins (10-100 animals are needed to make a single tent). Other tents similar to those of sedentary peoples are built with blinds covering a wooden framework. Inside, the ground is always covered with a carpet. Some tents are rectangular, while others are circular or relatively elongated, and the largest are 33- 39 ft (10-12 m) wide.

[Photo: Tony Morrison / South American Pictures]

106 Kwashiorkor is a condition caused by an unbalanced diet that mainly affects children between six months and three years of age. It is due to a diet deficient in protein but rich in starches, which provide sufficient calories. Bacterial and parasitic illnesses may aggravate the problem. A protein deficiency might suggest that children affected by kwashiorkor would be very thin, but in fact they are rather distended, like this Somali boy. The deficiency takes many other forms, including major behavioral disturbances and general listlessness. Attempts to supply the protein needed through milk powder have been a waste of time and money--in many regions of the Third World children who are malnourished cannot tolerate lactose.

[Photo: Christine Osborne Pictures]

107 The collection of fruit and other succulent plant materials containing abundant water is of great importance for the San tribes of the Kalahari Desert, as in such a dry habitat the limiting factor is not food intake but water intake. Wild squashes (Cucur-bitaceae), such as this Gems-bok cucumber (Acanthosicyos naudinianus) about to be harvested by a woman, are very important (see figure 55). Though the rain falling in the Kalahari is not enough to maintain a minimum grass, shrub, or even tree cover, permanent bodies of water are extremely scarce, and the rains dry up quickly. For the San, it is thus essential to know the rhythms of the seasons and to keep track of water sources, including plants that can provide water.

[Photo: John Downer / Planet Earth Pictures]

108 The small desert trees known as incense trees (Boswellia carteri, upper photo) and myrrh trees (Commiphora myrrha, lower photo) played, and still play, an important role in many religions. They produce gum resins (incense and myrrh, respectively) burned to spread their essential oils in the air and perfume their environment. The religious use of these two products began in funeral ceremonies to disguise the smell of the body and later acquired a purificatory, liturgical, and sacrificial meaning. As incense and myrrh were also closely associated, the plants that produced them were also confused. Both belong to the family Burseraceae but are different from each other, as shown by these plates from the first volume of Medicinal plants by R. Bentley and H. Trimen, published in 1880. Myrrh and incense are still used for similar purposes in the cosmetics industry, perfumery, and the pharmaceutical industry, and also as fumigants.

[Photos: Board of Trustees of the Royal Botanic Gardens, Kew]

109 Body decoration with henna (Lawsonia inermis) paste. Henna is one of the oldest known dyes for skin and hair. According to tradition, the prophet Muhammad (570-632) used it to dye his beard red, and it has long been a popular natural dye. Women use it to color their cheeks, hands, and feet and paint their nails, and in India the custom is for the bride's hands to be painted with complicated designs using henna. Berbers also use henna in marriage ceremonies because they believe it has seductive properties. For the Berbers, henna has a mystic and religious significance as well, and they feel it strengthens the link between mankind and nature. The coloring agent is a symbol of youth; they paint their entire bodies with it.

[Photo: The Hutchinson Library]

110 The manipulation of sisal fibers in a Mexican workshop. Sisal fibers are extracted from the leaves of Agave, dried, and used to make rope. Several species of Agave, all of them from the arid and semiarid regions of the Western Hemisphere, produce good fibers. One of the most important is sisal (A. sisalana), originally from Mexico, the name of which is taken from the port of Sisal in Yucatan, the first port to export the fiber in the nineteenth century. It is now mainly cultivated in Brazil (annual production is about 20,000 tons) and in some countries in eastern Africa such as Kenya, Tanzania, and Madagascar. Sisal cultivation and processing the fiber require a great deal of labor and a lot of water. The leaves are cut, their tips are removed by hand and then mechanically washed (consuming 38,041-47,551 qt [36,000-45,000 l] of water per hour), meaning the future does not look very good for the sisal industry.

[Photo: Edward Parker / Still Pictures]

111 The woody structure of some columnar cacti is a good source of wood for building purposes. These include the saguaro Carnegiea gigantea, upper photo, which has large cylindrical rods running from bottom to top (see also photo 39). This is very different from the prickly pear Opuntia fulgida (see middle photo), whose woody structure is reticulate. The best trunks are those of the pasacana (Tri-chocereus pasacana), used as planks for all sorts of purposes, including this door to the bell tower in Tocanao in the Atacama (Chile).

[Photos: Ramon Folch / ERF]

112 Changes in the area of esparto grass in northern Africa and the esparto plant biomass in the arid areas of Algeria under a grazing regime. The industrial use of the leaves of esparto grass (Stipa tenacissima) to make high-quality paper has led to overexploitation of the areas of esparto grass in northern Africa (upper diagram). In less than 100 years, the area occupied by esparto grass has declined by 62.5% and is still declining at a rate of 1.2% per year. The biomass of this plant has decreased, as shown by the changes in the biomass of esparto grass in Algeria from 1976-1986 (lower graph). Esparto production has been seriously affected. In the early twentieth century, annual trade was almost one million tons a year. This declined to 400,000 tons by the 1950s and to about 100,000 tons in 1995. Therefore, the esparto trade has declined by about 90% in this century.

[Drawing: IDEM, from data provided by the author]

113 Goats browsing in the treetops are a typical image of tropical arid and semiarid grazing areas, shown by the goats in the photo taken in southwest Morocco. (They have clim-bed up an argan [Argania spinosa, Sapo-taceae].) In desert zones, the vegetation is so poor that herbivores are forced to browse on woody plants. Their great ability to browse has made goats one of the main causes of the spread of deserts in North Africa and Asia. One remedy might be to replace them with camels, which would be mo-re productive and would allow for more rational use of grazing.

[Photo: Daniel Heuclin / NHPA]

114 The number of stems of woody plants is inversely proportional to the diameter of their crowns, as shown by this graph of the grasslands in the Sahel in Africa. The greater the density of trees and shrubs, the less space they have, so that the percentage plant cover corresponding to each tree is also lower. Note that in arid regions, the appearance of each plant and of the woody cover in general is not only determined by the area's microclimate but also by the intensity of grazing and the livestock's type of food. Large herds of browsing animals such as goats and camels can considerably reduce the woody cover by eliminating all the young shoots. If browsing is intense and continuous, it can lead to desertification in the long term.

[Drawing: IDEM, from data provided by the author]

115 The grassy scrubland of southern Africa that forms on sandy substrates contains other plants as well as grasses. This photo of the Karoo shows a flowering specimen of Hoodia bainii, (Asclepiadaceae), a perennial plant whose succulent stems are protected by rows of spines. The spines are very useful, protecting it from herbivores and reducing water loss due to evaporation by creating a thick layer of air saturated with water vapor next to the plant's surface. Spines also reflect and disperse the sun's rays. This plant stores its seeds, which are like parachutes, within pods that only explode and release the seeds under certain conditions. Once released, the seeds are dispersed by the wind.

[Photo: Peter Steyn / Ardea London]

116 The mulga (Acacia aneura) has very diverse applications. This species, represented here by a specimen in western Australia, is planted to stabilize soils and as an ornamental; it also provides timber, firewood, fodder, and food. The timber, with a narrow light band of softwood and a darker heartwood, is celebrated for being tough, heavy, and resistant. It is used for carvings, to make fencing and props, and as a fuel. The large succulent galls, known as mulga apples, are a good way to quench thirst, and the pods contain small seeds with a high protein content (23.3%), which are consumed in large quantities. These seeds could be used to make bread, and the food industry could surely find some use for the proteins from the seeds. Other mulga products consumed by Australian Aborig-ines include its gum and lerp, a sweet substance secreted by the honey ant (Austrotat-achardia acaciae). The smoke of burning mulga leaves is also used as a therapy after childbirth or to induce sweating in the sick.

[Photo: Jan Taylor / Bruce Coleman Limited]

117 The system known as qanat, falaj, or foggara--an ancient system for obtaining water and channeling it--is still widely used in the desert regions of the Old World. The engineering and final purpose are almost identical in the karez in the Turpan Basin, Xinjiang (China; see photo 229). The system consists of a series of underground galleries sloping gently onward and bringing water from the mountain slopes to the valleys, where springs are scarce or excessively salty. The engineering is simple: a few vertical wells are drilled down to the water table, and from there a tunnel with a slight slope that goes down to the plain is excavated. Along the route of these galleries, every 33-66 ft (10-50 m), are other vertical wells that give access to the water in the qanat, ventilate it, and make cleaning and maintenance easier. Its crater-like form is due to the piling of the earth removed when the well is dug; the shape protects the opening from the solid objects that might fall in. The system of underground aqueducts reaches the surface near the cultivated fields, and the water is divided and flows along irrigation channels to a large area. Qanat are usually a few hundred meters long, but some are several kilometers long. The system of channels does not require pumping and reduces losses by evaporation. Qanat are cheap and safe, and they are widespread in Iran (which has 200 active ones), but there are also many in other arid areas from western China to the Maghreb. The Spanish introduced them to South America, and in the Atacama Desert (Chile) there are about 15 (known as socavones) that are still in use and collect water from the foothills of the Andes.

[Drawing: Jordi Ballonga, bas-ed on several sources]

118 Most oases have been turned into irrigated vegetable gardens, with a very wide range of herbaceous crops. This oasis is in Tinerhir in the High Atlas (Morocco). It is dominated by palms, which are put to many uses. Palms provide protection from the heat of the sun and the desert winds. Some fruit trees can be planted under palms, among them figs (Ficus carica), pomegranates (Punica granatum), apricots (Prunus armeniaca), peaches (P. persica), oranges (Citrus sinensis), and lemons (C. limon). The ground left free under these trees is used to grow vegetables. Palms have many other uses. Date palms (Phoenix dactylifera) not only provide dates but also material for construction and for making furniture; the leaves yield fibers to make rope and twine and the juice of the shoots is used to make a sweet, milky, alcoholic drink.

[Photo: Cyril Ruos / Bios / Still Pictures]

119 There are many different varieties of dates on the market. The most appreciated is the degla date, which is grown, for example, in the Taghit Oasis in the Great Western Erg (Algeria). This variety is exported and is an important source of wealth. The degla palm requires water that is not very salty, but other varieties, such as those producing ghar dates, grow where the water is salty. Ghar dates are stored in baskets as a long-term food reserve, but they are not exported. Dates are an essential component of the diet of oasis dwellers, as this nutritious fruit meets many of the body's food requirements, and date palms produce large amounts of dates. A date palm can grow to a height of 98 ft (30 m) and live for 200 years. It reaches maturity at an age of about 15 years and then produces about 198 lb (90 kg) of dates a year.

[Photo: Josep Pedrol]

120 The seeds of the jojoba (Simmondsia chinensis, Simmondsiaceae) yield a liquid wax that is used to make shampoo and soap, lubricants for machinery, and many other uses. Jojoba oil is similar to sperm oil and may well replace it, which would help whale conservation. It is also thought that jojoba oil could replace most of the fuels derived from petroleum. Jojoba is now cultivated commercially in large areas of deserts, since it can grow with very little irrigation water. These are not, however, the only uses of jojoba seeds. The Indians of the Sonoran Desert have long used them for medicinal purposes, and in Mexico they are used as a good substitute for coffee.

[Photo: P. Morris / Ardea London]

121 Falconry is still very important in Arab culture, and falcon markets, such as this one in Riyadh (Saudi Arabia). The Bedouin of the Sahara Desert and the Moroccan kaid (high officials) use these birds of prey to catch hares and thus take great care of their peregrine falcons (Falco peregrinus). They are kept in the owner's house or within a tent, their heads covered by black hoods, and they are caressed and fed by hand. When the hunter sets out on horseback, the falcon is borne on his shoulder or turban with its hood still on. As many as 30 riders may hunt together, each with his own bird. When they see the prey, the falcon's hood is removed and it is freed to hunt the prey. The falcon's hunting abilities are extraordinary. Its eyesight is incredibly good, and these daring birds can fly very fast and for relatively long periods. They can kill creatures almost as large as themselves, swooping down on their prey at speeds of up to 155 mph (250 km/h); most prey die immediately in their talons before having a chance to react.

[Photo: Erik Bjurstrom / Bruce Coleman Limited]

122 The fishermen of the inland delta of the Niger River use different types of net, depending on the time of year and the characteristics of the waters they are fishing. Traps consist of a framework of branches, varying greatly in size and shape, covered by a net of nylon or some other material. The ones in this photo of a stretch of bank in Mali are known as durankoro and were introduced in the 1980s. Durankoro are traps that are left in position all year-round in single file, perpendicular to the flow of the current, in shallow water (usually in channels and on river arms). Normally, the women are responsible for setting them up.

[Photo: Chris Dodwell / The Hutchison Library]

123 The Somali ass (Equus asinus somalicus) is one of the two subspecies of wild African asses still found in scattered areas in southern Sudan, Ethiopia, and Somalia. The original habitat of this animal was the rough stony desertland of northern Africa, but once it was domesticated, the Somali ass was introduced into many of the world's other hot biomes. Asses are surefooted, with strong hooves that are well adapted to rocky terrain. They are able to resist dehydration and have been a great help to the inhabitants of arid regions. An ass can carry a load of hundreds of kilos for several days with very little food, and can work in asphyxiating heat. In arid regions, only camels are better than asses as beasts of burden and mounts.

[Photo: Jean-Paul Ferrero / Auscape International]

124 The increase in the number of Tropical Live-stock Units and the area under cereals matches the growth of the human population in the countries of the Sahel between 19501990 (and shows estimates for the year 2000 based on different hypothesis proposed in the 1990s). The censuses used to draw up this graph were from Burkina Faso, Chad, Mali, Mauritania, Niger, Senegal, and Sudan. The increasing growth of livestock in the Sahel since 1950 has been the result of, among other things, a reduction in livestock mortality by a veterinary program that eliminated many diseases. In 1961 and 1962, laws were passed to prevent farmers from occupying grazing land. The increase in the number of head of cattle is not inconsistent with an increase in dry farming, as the cereals are grown for use in animal feeds. During the droughts in the Sahel since 1968, the fodder available for the herds was greatly reduced and many animals died. The survivors concentrated around the wells, where they exerted excessive pressure on the scarce productive grazing. Yet these droughts did not have much effect on the long-term trend toward the increasing number of livestock.

[Drawing: IDEM, based on data provided by the author]

125 The number of sheep in Algeria over the last hundred years has been irregular. Until the 1920s, despite the large fluctuations, there was an average of seven or eight million head of sheep; that decreased to about five million between 1920-1970. In the 1970s, changes in feeding sheep, together with a vaccination program, caused a steep increase; by the mid-1980s, there were about 10 million sheep.

[Drawing: IDEM, based on data provided by the author]

126 Sedentary stockraising is the main activity of the Hazara tribe of the central plateau of Afghanistan. The region they occupy is rich in natural grazing, and there is no shortage of places with water for the animals to drink; as a result, their land has always been coveted by other Afghan peoples, and there are still rivalries between them. The Hazara are of Mongol origin and, according to tradition, are direct descendants of Genghis Khan (1167-1227). They zealously defended their pastures, and for a long time no nomadic herders dared to enter their territories. By the late nineteenth century, the Hazara were dominated by the terrible ruler 'Abd ar-Rahman, and during his time in power their livestock economy was impoverished. They still follow their traditional lifestyle, and their herds of goats can often be seen grazing below their villages, as in this valley of the southeastern Hindu Kush.

[Photo: Richard Waller / Ardea London]

127 Raising sheep is the main stockraising activity in the drier areas of southern Africa. The first farms in this area were almost self-sufficient, and the shepherds bartered livestock for the products they needed. During the nineteenth century, the industrial revolution led to increased demand for animal products, especially wool, and the former subsistence stockraising spread to meet demand from foreign markets. Demand for wool increased greatly after 1830, and in the next 20 years exports of this raw material increased two hundred-fold. During this period the number of sheep increased fourfold. The arid pastures had to support greatly increased grazing pressure, which led to major degradation and soil erosion. Despite this, stockraising is still considered a good way to make a living, and large herds--such as these karakul sheep in the southwestern Kalahari in Botswana--can still be seen searching for grazing.

[Photo: Anthony Bannister / NHPA]

128 Riyadh, the capital of Saudi Arabia, is in the Hanifah wadi, in an area where several drainage systems meet. This geographical location has made it possible to build this modern city in the middle of the desert. West of Riyadh, there is a highly eroded sandy plain, and there are similar outcrops to the east. To the northeast is the railway joining the city with Damman, the center of the oil industry. The growth of the oil industry has boosted rapid improvements in transport throughout the country's eastern province, where there are communication links to Kuwait, Qatar, and the United Arab Emirates.

[Photo: Bernard Gerard / The Hutchison Library]

129 Motor rallies through the desert, such as the Paris-Dakar Rally, the Rally of the Pharaohs, and other smaller ones, are increasingly common, and though they are localized they have a great environmental impact. The problem with this and other leisure-related activities lies in the visitors' lack of respect for the desert environment, which they often consider to be empty, a no-man's-land, and thus not deserving special care. The risk of pollution in the rest areas is particularly high, especially when several hundred people gather to watch the end of a race. Because the rest sites are at the water points, there are only a few and they are always the same on all the different routes. These competitions have an even greater social impact, due to scandalous waste of fuel and money concentrated for a few days in an area of extreme poverty.

[Photo: Denize-Francolon / Gamma]

130 The cities and housing developments that have grown up in the deserts of the United States, like this one in the Coachella Valley in southern California, have caused major environmental disturbances. Bringing water to these centers of population is expensive; it has to be extracted from aquifers, which then become exhausted, or from the neighboring agricultural areas. The water reserves needed for the farmers' crops are then used to irrigate luxurious green spaces. In the complex United States economy, many different types of settlements have grown up in the desert, ranging from industrial and agricultural cities (Phoenix, Arizona) to large sports or recreational centers (Las Vegas, Nevada) to residential developments for retired people.

[Photo: Stephen Krasermann / NHPA]

131 Small urban vegetable gardens around a well in Tombouktou (Mali), on the edge of the Sahara. The gardens are watered by hand with water that is hauled up the stairs. Humans have not always respected the world's arid and semiarid zones and have often degraded them so far they cannot be recovered. Yet when people manage water supplies well, they can make these areas much more productive than would be expected on the basis of the climatic conditions. Unfortunately, use of surface or underground water in the desert has often been irrational, and in the long term this has made the land cultivated even more unproductive.

[Photo: Timothy Beddow / The Hutchison Library]

132 The retreating isohyets and decrease of the flooded areas of the inland delta of the Niger. These floodable areas are of great biological richness and have been retreating little by little since the late 1950s, especially after the major drought that began in 1969 (clearly shown on the map by the difference between the isohyets before and after 1969). During the same period, the population increase necessitated an increase in cultivated ground and a reduction in fallow periods, which caused the soil's production to decline greatly and encouraged desertification. In order to preserve natural resources, laws passed in the early 1960s banned agriculture where average annual rainfall was less than 16 in (400 mm; the 400 mm isohyet). The areas north of this line were intended to be used for stockraising, which was to be thoroughly regulated. These laws, however, were never enforced, and crops spread as far as the areas with annual average rainfall below 8 in (200 mm). In the central delta of the Niger, like many other arid areas, the climate normally shows large variations in rainfall, so good long-term planning is the only way to deal with these changes without greatly diminishing the land's productivity.

[Drawing: Jordi Corbera, bas-ed on Quensiere, 1994]

133 The flow regime of many of the large rivers that cross deserts has been greatly altered by human activities since the mid-twentieth century. The construction of large dams and reservoirs, such as the many regulating the variable waters of the Nile (upper diagram), has made crop irrigation possible, while providing water supplies to the large cities. Huge amounts of hydroelectric power are also generated, but there is a great reduction in the amount of water in the lower stretches of the river. The Colorado River in the United States is another very clear example, as its flow has declined drastically since the beginning of the twentieth century (lower left diagram). The low flow from 1935-1939 was due to the construction of the Hoover Dam in 1935. This reduction became especially severe after 1960, and since then almost every drop in the Colorado has been used, so that very little reaches the river's mouth. In 1979-1980, exceptional flooding in the lower stretches caused the volume of flow to increase, but floods like this are very uncommon. Logically, the quantity of sediment in suspension borne by the river has declined proportionately with the decline in the volume of flow (lower right diagram). These sediments are of great importance for the cycling of nutrients and biological productivity in the estuary ecosystem. Before 1930, the Colorado carried about 125-150 million tons of suspended sediments a year to its delta in the Gulf of California. When the Hoover Dam was completed, the sediment input declined to 100,000 tons per year. Something similar is happening to the Nile, which used to bear 100 million tons a year of sediment to the Mediterranean, now reduced to 30 million tons.

[Drawing: Jordi Corbera, bas-ed on several sources]

134 Experimental crops in the middle of the Sahara Desert, in Kufrah (Libya), where irrigation allows cereals and alfalfa (Medicago sativa) to be cultivated. The climate is favorable to plant growth all year-round, and these fields may produce 14 harvests of alfalfa a year. Irrigation functions even with salty water; the soil has to be suitable, the drainage system adequate, and excess water has to be used to wash away the saline deposits. This project is not very cost effective, though. The water has to be pumped from very deep deposits and at great expense from fossil aquifers; eventually they will be exhausted because they are not replenished with new water. In the late 1980s, these projects seeking to transform the desert sands into croplands were complemented with other more effective projects.

[Photo: Derek Bayes / Aspect Picture Library]

135 The construction of artificial drinking troughs for livestock reduces pressure on former water holes. This means more animals can be raised. These new drinking points are normally constructed by digging wells and hafirs, artificial lakes to store rainwater. Around each water point, herds of goats, sheep, and camels anxiously await their turn to drink, as shown by the herds in the picture, taken in Kordofan, southern Sudan. But as there is more water, the number of animals can increase considerably, and the resulting overgrazing contributes to erosion and the spread of deserts. If there are too many animals, complications will arise when the rains become scarce: grazing will be insufficient and many animals may die. In such cases, grazing, not water, limits the number of head of livestock.

[Photo: Mark Edwards / Still Pictures]

136 The immense areas of salt in the Danakil Desert, at the bottom of the basin of the Ethiopian subsidence (see also figure 36), have been mined since prehistoric times. These open-air mines produce about 20,000 tons of salt a year. The mining techniques are sometimes very simple and have little environmental impact. Some-times, however, large-scale salt extraction has great environmental impact. The salt mined in Danakil is transported to the mountain areas of Ethiopia in very long caravans of camels, mules, and asses of up to 20,000 animals.

[Photo: Mary Plage / Bruce Coleman Limited]

137 Oil wells have only been present in deserts for a short time, but their future may be equally short. By the middle of the twenty-first century, most of the oil reserves of the world's desert regions will be exhausted. Only the oil fields in Saudi Arabia, Iran, Iraq, and Kuwait have a long-term future. The industry's short history is in stark contrast to its huge ecological impact. The oil industry has contributed to the development of very poor regions, replacing small villages of herders and hunter-gatherers with fast-growing modern cities that have filled the deserts with garbage. The Gulf War (1990-1991) and other disasters have often led to the release of huge quantities of oil on land or sea that polluted large areas. For many years natural gas, a by-product of oil extraction, was simply burned, as in the Bu Hasa oil field (Abu Dhabi, United Arab Emirates) shown in the photo, which generates large amounts of air pollution.

[Photo: Jacques Burlot / Gamma]
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Publication:Encyclopedia of the Biosphere
Article Type:Report
Geographic Code:60AFR
Date:Apr 1, 2000
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