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Desert rocks as plant refugia in the Near East.

II. Introduction

I grew up in a suburb of Jerusalem named Bet Hakerem. As a child, each autumn I searched for the yellow flowers of Sternbergia clusiana, which was given the local vernacular name "karmit" after our neighborhood. In 1963 I participated in a project in which the vegetation of the Negev Highlands was mapped. My friends in the Negev asked me to explain how it was that these yellow flowers "of Jerusalem" are found in the desert. My studies of their habitat enabled me to discover later more than ten species that were new to science. The search for explanations of how mesophytes can survive in the desert brought me to the field of biogenic weathering and climatic changes in the Near East. The visit to the gigantic refugia of Edom, Jordan, after the peace treaty was signed between Israel and Jordan led me to summarize my 30 years of observations in this special habitat, which is found in deserts all over the world.

The Near East is a meeting zone of Asia and Africa and is well known for the richness and complexity of its botanical, zoological, anthropological, prehistorical, archaeological, cultural, and political issues throughout the ages. When focusing on a specific field one must utilize a broad background, which may help the reader to better understand the distribution of any given organism. In this section I provide the geographical, environmental, floristic, and vegetative background of the region.

The area of Israel and Jordan has been divided and redivided into geomorphological or geographical subdivisions since biblical times. There is no one subdivision of Israel that is agreed upon by all authors of geographical, geological, or biological books and articles. The subdivision of the Hashemite Kingdom of Jordan by European authors (Smith, 1931) follows the biblical subdivision as reflected in the maps of Eig et al. (1948) and Zohary (1966). Figure 1 combines for Israel and Jordan the map by Feinbrun-Dothan and Danin (1991) and for the Sinai that by Danin (1983a).


Each occurrence of the special habitat I examine is considered an "island" in a "desert sea" of the Near East. In this section I elaborate the general features of the Near Eastern countries in order to provide a framework in which to view the peculiar features of the special habitat of plant refugia.

1. Topography

The topography of Israel and Jordan can be best described as north-south topographic elements that are influenced by the geomorphological features of the area. The Mediterranean coastal plain is narrow in the north of Israel and becomes wide in the south. Low hills with gentle topography constitute the foothills. The mountainous area reaches elevations of about 1000 m at Judea and the Negev Highlands and 1200 m at the Galilee. Steep escarpments dissected by canyons typify the area east of the water divide, leading to the Jordan-Dead Sea-Arava rift valley. This valley is 400 m below sea level in the deepest part of the Dead Sea and ascends to 200 m above sea level northward and southward. Mount Hermon, situated east of the Jordan River at the common border of Israel, Lebanon, and Syria, reaches an elevation of 2800 m and terminates sharply at the basalt-covered plateau of the Golan to the south. This plateau descends gently from an elevation of 1200 m toward the Yarmouch River and toward the Kinneret (the Sea of Galilee) at 200 m below sea level. The Jordanian plateau starts south of the Yarmouch River. The escarpments that delimit the rift valley there are as steep as, and in many places steeper than, the escarpments in Israel. The Jordanian plateau has several peaks 1200 to 1600 m high. A few deep rivers dissect the plateau from east to west toward the riff valley. East of the water divide, which is close to the western edge of the plateau, the landscape becomes flat and gradually descends toward Mesopotamia.

The Sinai has a wide coastal area along the Mediterranean Sea that ascends gradually southward. The northern Sinai sand belt [ILLUSTRATION FOR FIGURE 1.15 OMITTED] reaches the anticlinal ridges of Gebel Maghara, Gebel Halal, and Gebel Yiallaq [ILLUSTRATION FOR FIGURE 1.16 OMITTED]. The central Sinai gravel plains are surrounded by crescentlike ranges of mountains or plateaus, dissected by a few valley passes such as those of Wadi Mitlah and Wadi Sidr. South of the gravel plains are two large plateaus that ascend gradually in a north-south direction. In Gebel el Igma are a 1600 m peak and a few lower ones; in Gebel et Tih are a 1400 m peak and a few lower ones. The erosion escarpments of the two plateaus are steep, and that of the latter descends to the sandstone belt. The morphology of the sandstone belt is highly diverse in different parts of the Sinai. The Southern Sinai Massif [ILLUSTRATION FOR FIGURES 1.25 & 1.26 OMITTED], built up of magmatic and metamorphic rocks, is highly dissected. The mountain peaks reach 2500-2600 m. The escarpments toward the Gulf of Elat-Aqaba are not as steep as those of the rift valley in Israel and Jordan. The coastal plain along this gulf is rather wide in the southern part of the Sinai, but in many other places the mountain slopes descend directly into the sea without any coastal plain. Most of the escarpments in the Gulf of Suez have a wide coastal plain.

2. Geomorphology and Edaphic Conditions

The most common substratum of the Mediterranean territories of Israel and Jordan is sedimentary limestones, dolomites, chalks, and marls of the Cretaceous and the Tertiary (Bartov, 1994). Terra Rossa soils occur in the mountainous areas on hard rocks; Rendzinas, on the soft ones (Dan & Raz, 1970; Dan et al., 1975). Basalt rocks typify much of the Golan plateau and the northeastern Galilee; both are covered with Basaltic Brown or Red Mediterranean soils. The Tertiary and Pleistocene rocks and derived soils fill up the small and large valleys and are typified by calcareous sandstones and sandy soils (Kurkar and Hamra) close to the coast and by deep clay soils (grumusols) far from the Mediterranean coast. Cretaceous and older sandstones typify the vicinity of the rift valley of the Jordan River, the Dead Sea, and Arava in Jordan. The edaphic conditions in northern Jordan and south to Amman are rather similar to those in the area west of the Jordan River.

The steppe and desert areas of Israel, Jordan, and the Sinai develop on much more diverse kinds of rocks. The main contributors are limestone, chalk, marl, chert, sandstone, magmatic and metamorphic rocks, and gravel of alluvial origin or rocks weathered in situ. Loess is an important aeolian sediment, composed mainly of silt and clay particles, which influences much the soils of the transition zone of the Mediterranean territory and the steppelands. Large flatlands south of that transition zone occur in the northern Negev of Israel and east of Irbid, Jarash, and Amman in Jordan. The poor moisture regime of loessial soils with low quantities of rainfall make the desert boundary rather prominent.

Soil maps of Israel are those by Dan and Raz (1970) and Dan et al. (1975); of Jordan, that by Al-Eisawi (1985, 1996); a detailed soil map of the Sinai is not available. The specific influence of each type of substratum on the vegetation is discussed in detail elsewhere (Danin et al., 1975; Danin, 1983a). The relationships among rock type, soil, and vegetation in the desert areas of Israel and the Sinai, discussed in Danin (1983a), fit rather well with the situation in much of Jordan. My discussion here is restricted to the distribution of hard rocks and their influence on the formation of smooth-faced outcrops.

3. Climate

a. Rainfall

The Mediterranean climate of Israel, Jordan, and the Sinai is characterized by warm, rainless summers and cold, rainy winters. Rainfall varies in two main directions: It decreases gradually from north to south, sharply from the water divide eastward in Israel, and gradually eastward in Jordan [ILLUSTRATION FOR FIGURE 2 OMITTED]. The north-south gradient is influenced mainly by the intensity and frequency of rain-contributing systems, whereas the west-east gradients are influenced by the topography. Thus the ascent of air masses toward the mountains of Judea and Samaria results in cooler air and therefore increased rainfall as elevation increases. Descending air bodies (toward the rift valley) become warmer and drier; hence deserts occur in the rain shadow of the Judean and Samarian mountains. The ascent to the Jordanian plateau displays a mirror view of the rainfall map, with maximum rainfall at the mountaintops. Mean annual rainfall descends gradually eastward with as distance from the Mediterranean increases. The increase in mean annual rainfall in Moav and Edom, situated south of the west-east section of the 300 mm isohyet in Israel, is related to the orographic influence of the high elevation of this area.

In cold, wet years winter snow may fall on the highest summits of mountains in Israel, Jordan, and the Sinai and stay there for a few days. The period of snow cover in the high peaks of the Sinai and Jordan is longer than that of the Negev.

b. Summer Rains

The driest and warmest parts of southern Israel, the Sinai, and southern Jordan are the ones that rarely experience local strong showers in the summer. These showers occur at unpredictable times and locations in the extreme desert parts of the study area, where mean annual rainfall is less than 100 mm. In the area of Elat most rains are convective (Sharon, 1972). Observing a flood at the northern Arava Valley in summer, in mid-June 1975, I became interested in the subject and searched for its impact on plant life. The indicator tree for these summer showers became Tamarix aphylla, which grows in wadis (Danin, 1981a). A species of Sudanian-to-tropical origin (Zohary, 1972), it grows in East Africa beside seasonal rivers in deciduous bushlands (Hunt, 1966). It blooms in summer, and, like other species of Tamarix, its minute, wind-dispersed seeds lose their vitality shortly after they are dispersed (Waisel, 1960). Germination and establishment take place only when the seeds land in a recently watered site that has a considerable quantity of water for a long time and is free of competition. Such habitats are found mainly in wadis that flood during the summer. Germination under simulated conditions was observed in agricultural areas in the desert, where Tamarix aphylla developed as a weed in places where trickle-pipe irrigation took place (Danin, 1981 a). Local summer rains that were recorded in Israel and the Sinai between 1925 and 1975 are presented in Table I. The distribution map of spontaneous Tamarix aphylla trees (Fig. 3) may serve as a climate map and indicate at least one recent, strong, summer shower that led to flooding in the watershed.

c. Dew and Fog

Dew and fog are important sources of humidity for the poikilohydric organisms that grow on rock outcrops. The measurement of dew by Duvdevani's (1947) dew gauge proved a rather high similarity with events of efficient dew when lichens imbibed on stones and rocks in the Negev Highlands (Danin & Garty, 1983). The mean annual number of nights with more than 0.02 mm of dew per night is 191 [+ or -] 22 for 15 years at Avdat. Of these, only 124 [+ or -] 28 nights annually have dew amounts of 0.11 to 0.5 mm (Evenari in Danin & Garty, 1983). Other aspects of dewfall were studied by Zangvil and Druian (1980). Similar measurements in other parts of Israel, Jordan, and the Sinai are not available. However, lithobiont communities in the area [TABULAR DATA FOR TABLE I OMITTED] where Evenari's measurements were carried out were used to extrapolate the regional distribution of dew (Danin, 1986b: [ILLUSTRATION FOR FIGURE 1.2 OMITTED]). The typical features of the Negev Highlands with precipitation like that in Avdat are detached stones covered by endolithic lichens that form a jigsaw puzzle-like pattern and north-facing rocks covered by epilithic lichens. These features are also found at the top of the northern Sinai anticlines and on limestone outcrops at the Jordanian plateau. I assume that the dew-and-fog regime is similar in the latter two areas to that of Avdat area, where real measurements of dew and rainfall were made.

d. Temperature

The temperature regime in the study area is greatly influenced by altitude and latitude. Mean annual temperature in the desert areas varies from 9 [degrees] C to 25 [degrees] C. The lowest temperatures prevail in the peaks of the southern Sinai and Jordan near Shoubak; the highest are those in the Dead Sea and Arava Valley, where the elevation reaches 400 m below sea level. Mean annual temperature maps of Israel are presented by Rosenan and Gilead (1985); of Jordan, by Al-Eisawi (1996).

e. Wind

Wind direction, especially where it blows strongly and constantly, is of great importance for plant life. Another aspect of wind direction is its impact on rainfall efficiency (Sharon, 1980; Danin, 1989c; Caneva et al., 1992). The amount of rainfall accumulated on windward slopes during a rain shower may be five times higher than that on the leeward slope (Sharon, 1980). Consequently, significant differences in the distribution of higher plants and of microorganisms is attributed to the direction of incident rainfall in the Judean Desert (Danin, 1989c) - as is their distribution on house walls in Rome (Caneva et al., 1992). Local influence of the constant wind direction was therefore expected in my study area as well.


Israel is home to 2682 plant species, as derived from the data on plant distribution in Feinbrun-Dothan and Danin (1991); this number includes some 200 species that occur only in the Mount Hermon area. The number of species in Jordan is 2078 in Al-Eisawi's list (1982). The combined list of plants of Israel and Jordan contains 2865 species (Danin, 1998). The high species richness in Israel, expressed as the parameter of species to area (Table II), is related mainly to three factors:

1. Its position in a meeting zone of plant-geographical regions, each with its typical flora.

2. The existence of many habitats needed to support these species. The wealth of habitats derives from the climatic transition between the relatively moist area in the northern parts of the countries and the desert in their southern parts. Topography is a second factor in creating the warm climates of the Jordan-to-Arava rift valleys and the relatively cold climate of Mount Hermon. In other highland and lowland areas of Israel and Jordan local climatic influences also increase the diversity of habitats and therefore of plant species. The geomorphological structures are relatively small, but the number of rock types is high. As a result, many soil types develop in a small area (Dan & Raz, 1970), increasing the diversity of habitats available for plants.

3. A long history of human activity of cultivation and grazing by domestic animals has led to strong stress on the existing flora and enabled the

introduction of many alien species. Many of the latter occupy synanthropic habitats; that is, they grow in habitats that have been created by human activity (Zohary, 1973; Danin, 1991a).

According to Eig (1931-1932), Zohary (1962, 1966, 1972), Feinbrun-Dothan (1978, 1986), and Danin and Plitmann (1987), the flora of Israel is divided into seven groups:

1. Mediterranean (M) species, which are distributed around the Mediterranean Sea.

2. Irano-Turanian (IT) species, which also inhabit Asian steppes of the Syrian Desert, Iran, Anatolia in Turkey, and the Gobi Desert.

3. Saharo-Arabian (SA) species, which also grow in the Sahara, the Sinai, and Arabian Deserts.

4. Sudano-Zambesian (S) species, typical of the subtropical savannas of Africa.

5. Euro-Siberian species, also known in countries with a wetter and cooler climate than that of Israel, which grow mainly in wet habitats and along the Mediterranean coast.

6. Biregional, triregional, and multiregional species that grow in more than one of the regions mentioned above.

7. Alien species from remote countries; these plants propagate without human assistance. The principal countries of origin are the Americas, Australia, and South Africa.

Four plant-geographical territories have been delineated in Israel (Eig, 1938; Zohary, 1962): Mediterranean; Irano-Turanian; Saharo-Sindian; and Sudano-Deccanian enclaves. Zohary (1966) renamed some of the phytogeographical regions; he regarded parts of Eig's Saharo-Sindian as Saharo-Arabian and Eig's Sudano-Deccanian as Sudanian. Eig's Sudano-Deccanian enclaves in the Dead Sea area became a "territory of Sudanian penetration" (Zohary, 1966).

A new plant-geographical map of the area was compiled as a result of analysis of a comprehensive database of the flora of Israel and the Sinai (Danin & Plitmann, 1987). In that map [TABULAR DATA FOR TABLE II OMITTED] the Mediterranean territory (see M in Danin & Plitmann, 1987) is rather similar in extent to that of Eig (1931-1932). All other territories are regarded as "complex territories" in which the second most frequent chorotype is in parentheses; for example, in M(M-IT) the most frequent chorotype is the Mediterranean (M) and the second is the biregional Mediterranean-Irano-Turanian (M-IT). These complex territories are: M(M-IT), SA(M), SA(IT), SA(S), IT(SA), and S(SA). On a large-scale map one can see two main domains in Israel: the Mediterranean, including M and M(M-IT); and the Saharo-Arabian, including SA(M), SA(IT), and SA(S). The area of IT(SA) and S(SA) is more prominent in the Sinai than in Israel.

Another phytogeographical analysis of Israel and Jordan is presented in Figure 4. The data used for this map are predominantly from Feinbrun-Dothan and Danin (1991). The flora of each of the 31 districts of Israel and Jordan is analyzed and presented in the bar diagram. Bar graphs of districts 1 through 5 display the distribution of chorotypes in the coastal plain. The percentage of Mediterranean (M) species decreases gradually from north (1) to south (5), the proportion of the M-IT chorotype remains relatively constant, and the desert (SA and IT) and thermophilous species increase.

Bar graphs of districts 6 through 12 and 17 through 20 are of the Mediterranean territory of Israel and display a rather similar phytogeographical spectrum, with M and M-IT chorotypes being most frequent. In most of these 11 districts the percentages of the IT, SA, and thermophilous species are negligible.

Except for the extreme desert districts (16 and 25), where the SA chorotype has the highest percentages, most of the desert districts display a rather mixed spectrum. This mixed spectrum indicates that the environmental conditions are neither too dry nor excessively moist, thus enabling the coexistence of species from various chorotypes. The high percentages of M and M-IT species in districts 13, 14, 21, 22, 23, and 24 may be explained by the geographical proximity of these districts to the boundary of the Mediterranean region. The high percentages of M and M-IT species in the Negev Highlands (district 15) were attributed by Danin and Plitmann (1987) to the presence of many relicts (Danin, 1972) of moister climates in crevices of smooth-faced outcrops of limestone and in wadis.

The districts east of the Jordan River display patterns that are similar to those of the area west of the Jordan. When comparing the bar graphs from north to south, the Mediterranean ones (26 through 28) display the predominant M and M-IT chorotypes. The highest peak in the study area, Mount Hermon, is rather exceptional, for it has a high percentage of Irano-Turanian species; I will discuss this anomaly later. As in the coastal plain of Israel, the north-south gradient is associated with moderate but clear changes in the flora. The percentages of the M and M-IT chorotypes decrease gradually, and those of the IT, SA, and thermophilous species increase. The nearly unimodal phytogeographical spectrum of the Mediterranean districts is prominently different from that of the desert ones, such as Edom (district 31).

Whereas the north-south gradients in the floristic composition in areas with small differences in mean annual rainfall are moderate, the gradients in west-east transects are much more abrupt. The floristic differences between the districts of the main mountain range and the area east of it display, floristically, the rain-shadow effect. This is evident when districts 6 or 7 are compared with 18, district 10 with 21, 12 with 22, and 15 with 16. In all of these cases the more drought-resistant species that belong to the IT and SA chorotypes and the thermophilous species display higher percentages in the rain shadow, whereas the M and M-IT chorotypes have lower percentages.

Another aspect of the phytogeographical setup of Israel is represented by Kadmon and Danin (1997), who analyzed floristic gradients in Israel, based on the same data used by Danin and Plitmann (1987), and arrived at a rather similar layout of phytochoria.


Depicted here for the first time in Figure 5 are a synthesis of the maps discussed below and, in the Jordanian section of the map, a visual representation of my own impressions. However, the reader can combine the general information on the vegetation of Israel (Danin, 1988a, 1995) with that on the Sinai (Danin, 1983a, 1996a) and of Jordan (Al-Eisawi, 1996). The features of the vegetation that may assist the reader in understanding the origins of the plants that have survived in the desert refugia are repeated here. The description of the vegetation follows the subdivisions and categories in the caption for Figure 5.

1. Vegetation of the Mesic Parts of Israel and Jordan

a. Maquis and Forests

The principal woodlands of Israel are found in the mountains of Judea, Carmel, Galilee, and at the foot of Mount Hermon; those of Jordan are north of Amman [ILLUSTRATION FOR FIGURE 5.1 OMITTED]. Forests or maquis dominated by the sclerophyllous evergreen Quercus calliprinos and the deciduous Pistacia palaestina on hard limestone with Terra Rossa soil are still common in the Upper Galilee and Mount Carmel and Jebel Ajlun area in Jordan (the mesic aspect) and in the Judean mountains (the xeric aspect). The companions of Q. calliprinos vary according to edaphic and climatic conditions. In the Upper Galilee, where the climate is the moistest in Israel, the mesophytic companions are the following: Rhamnus alaternus, R. punctatus, Eriolobus trilobatus, Acer obtusifolium, Crataegus azarolus, C. monogyna, Arbutus andrachne, Laurus nobilis, the vines Clematis flammula and Hedera helix, and many geophytes and herbaceous species. Mesophytic components rarely occur in the maquis of the Judean mountains. In the driest maquis stands, Rhamnus lycioides subsp. graecus is the only arboreal companion of Q. calliprinos. Typical vines in these maquis are Rubia tenuifolia, Lonicera etrusca, Asparagus aphyllus, and Ephedra foeminea.

Marly chalk is a common rock type; it has a high moisture-holding capacity and is covered with Light Rendzina soil. The aeration of the rhizosphere of trees and shrubs that penetrate into the soft rock is poor; thus only specially adapted plants develop there. Much of the nitrogen in this soil is in the form of ammonium ions, whereas in the Terra Rossa it is in the nitrate state. The vegetation cover of the Light Rendzinas on marly chalk is poor when compared with Terra Rossa. Only a few annual companions are found in the maquis stands on this substratum. At sites in which the clay content of the rocks is high and aeration is low, Arbutus andrachne is dominant. Symbiosis of tree roots and fungi (mycorrhiza) seems to enable the success of A. andrachne. The only arboreal companion of A. andrachne is Pinus halepensis; its mycorrhizal fungus (Suillus granulatus) is the most common edible winter mushroom species in Israel. P. halepensis grows on marly chalk without A. andrachne in sites with low clay content. Similar spontaneous pine stands cover the mountaintops in the southern parts of Ajlun and southeast of the town. Near Bet Jan, the Upper Galilee, is the only known slope (in Israel) with marly chalk where Juniperus oxycedrus accompanies P. halepensis and A. andrachne.

In most of the area cultivated plants have replaced spontaneous trees. A few thousand years ago, people in the eastern Mediterranean countries began to clear the natural vegetation to create agricultural land. Trees such as olives (Olea europaea) and almonds (Amygdalus communis) have been domesticated from the spontaneous flora of the area. The timber derived from the forests and maquis was used for the construction of houses, for agricultural tools, and for fuel. For the last few millennia shepherds have burned large woodland areas in order to open paths for domestic animals, and the pasture quality has been improved through the replacement of trees and shrubs by palatable herbaceous plants.

After cultivated ground is abandoned, the area becomes populated for dozens of years by low lignified and herbaceous plants. This vegetation formation of Mediterranean semishrubs covering the entire area has been locally known since biblical times as "batha" (phrygana). At present, after thousands of years of deforestation and agricultural and urban development, large parts of these areas look like mosaics of seral communities. These are semishrub communities dominated by Sarcopoterium spinosum, Coridothymus capitatus, and Cistus spp. Formations of taller shrubs (garigue), such as Calicotome villosa and Salvia fruticosa, replace the Sarcopoterium-dominated bathas.

b. Quercus calliprinos Woodlands on Basalt

These differ from woodlands on Terra Rossa by their rich, herbaceous vegetation and the absence of semishrub communities from the early successional stages after destruction and abandonment. Remnants of this community are found in the northern Golan and in the northeastern Galilee [ILLUSTRATION FOR FIGURE 5.2 OMITTED]. The gentle, north-facing slope of the ancient volcanic cone of Har Odem, in the Golan near Masada, at an elevation of 900-1000 m, is covered by a dense maquis of Q. calliprinos. It is accompanied by Q. boissieri, Crataegus monogyna, C. aronia, and Prunus ursina. Among the trees, the rich, ephemeral vegetation includes some 20 species of Trifolium. The herbaceous plants may be prevalent because the soil is rich in available phosphorus (Rabinovitch, 1981).

c. The Montane Forest of Mount Hermon

The montane forest [ILLUSTRATION FOR FIGURE 5.3 OMITTED] stretches from 1300 to 1700 m, and its dominants are deciduous trees, such as Quercus boissieri, Q. libani, and Acer microphyllum, and several species of Crataegus, Amygdalus, and Prunus. Their companions are mainly perennial grasses and other herbaceous plants. No representative areas of this category exist in Jordan because the northern part of the country has no mountains of this elevation; southern Jordan does have such high mountains, but, owing to their drier climate, woodlands of this kind are missing. However, a few of the representative shrubs that are common in Mount Hermon also occur in crevices of smooth-faced rocks in the southern Sinai, as well as in southwestern Jordan (see section II.C.1.i below).

d. Open Forests of Quercus ithaburensis

The Tabor oak is often accompanied by Styrax officinalis, sometimes by Pistacia atlantica, and always by many herbaceous plants. The few semishrubs found in this community where it develops on chalky ground are mainly Majorana syriaca (but not Sarcopoterium spinosum). This type of forest, which once dominated the Sharon Plain, is now restricted in the Sharon [ILLUSTRATION FOR FIGURE 5.4 OMITTED] to single, sporadic Tabor oak trees and one reserve between Haifa and Tel Aviv. Large woodlands of the Tabor oak are found in the Lower Galilee and in the Golan, below 500 m. The Tabor oak woodlands in northwestern Jordan are well preserved and cover considerable areas of rocky terrain west of Irbid, at the western escarpments of the Jordanian plateau, from sea level to 500 m.

e. Open Forests of Ceratonia siliqua and Pistacia lentiscus

This type of vegetation [ILLUSTRATION FOR FIGURE 5.5 OMITTED] occupies Terra Rossa soils at the lower elevations of the main mountain ranges, below 300 m on both sides of the central mountain range, Rendzina soils in the foothills of the Judean mountains, and light soils in the Sharon Plain (the littoral aspect). Generally, the community is more drought and heat resistant than are the communities dominated by Quercus calliprinos and has a position in the aridity sequence of communities similar to those that are dominated by the Tabor oak. One of the important companions in rocky sites at Mount Carmel and the Galilee is the wild olive, Olea europaea var. sylvestris, which resembles the cultivated olive but has much smaller fruit. In Jordan this category is almost missing. However, scattered carob trees occur m the open woodlands of Quercus ithaburensis in the Gilead, mainly in the transition zone from the belt dominated by the Tabor oak to that of Q. calliprinos, at elevation of 500-600 m.

As to the biogeography of the carob tree, which probably originated in East Africa, there are various theories. The main companion of the carob at the southern Judean foothills is Rhamnus lycioides subsp, graecus. The latter totally replaces all the other arboreal components in dry habitats.

f. Ziziphus lotus with Herbaceous Vegetation

Grasslands of wild wheat, barley, and oats cover the relatively dry and warm area of basalt hills in the southeastern Galilee and the slopes around the Sea of Galilee down to the Samarian desert [ILLUSTRATION FOR FIGURE 5.6 OMITTED]. A similar formation covers the west-facing slopes of the Gilead below the Tabor oak belt. In drier and warmer sites Stipa capensis becomes the dominant plant. However, a better indicator of such conditions is the lignified and spiny shrub Ziziphus lotus, which spreads as green patches all over the area. This category is presented as a mosaic with that of the "savannoid Mediterranean vegetation" [ILLUSTRATION FOR FIGURE 5.7 OMITTED] in the steep topography in the vicinity of the rift valley north of Jericho and up to north of the Sea of Galilee.

g. Mediterranean Savannoid Vegetation

Ziziphus spina-christi, a low, spiny tree with edible fruit, is the principal component in grasslands of annuals with large seeds, such as wild wheat, barley, and oats. These develop on the warm, stony-rocky slopes of the Galilee, the Golan, Gilead, and Samaria, descending to the rift valley [ILLUSTRATION FOR FIGURE 5.7 OMITTED] at and below sea level. Z. spina-christi dominates in true savannas in Africa, where its companions are Sudanian perennial grasses. Therefore, the vegetation here is named "savannoid." Stands of this tree are also established along the transverse valleys on heavy soils and on the Sharon Plain, where it grows on sandy-loamy soils together with the grass Desmostachya bipinnata.

h. Semisteppe Batha

The communities dominated by semishrubs at the boundary of the Mediterranean zone [ILLUSTRATION FOR FIGURE 5.8 OMITTED], where mean annual rainfall is 300-400 mm, are regarded as semisteppe bathas. Several of the communities are dominated by such Mediterranean plants as Sarcopoterium spinosum, which dominates bathas in the more mesic parts of the country. Others, such as Artemisia sieberi and Noaea mucronata, dominate steppe areas in the Negev, the Sinai, Jordan, and eastward to Afghanistan. Many plants that play an important role in the seral communities in fallow fields at the center of the Mediterranean region grow here in their primary habitats. No anthropogenic disturbance assists or enables their growth. Sarcopoterium spinosum, which becomes ethiolant and dies in the shade of trees and shrubs in the course of plant succession in the mesic maquis and forests, has no such competitors. In southwestern Jordan the semisteppe bathas extend farther south of the regional boundary of the maquis than do those in Israel.

i. Tragacanth Vegetation of Mount Hermon

The most prominent formation of vegetation that has developed on the windward slopes of the peaks (above 1900 m) of Mount Hermon [ILLUSTRATION FOR FIGURE 5.9 OMITTED] is dominated by shrubs that look like spiny cushions. This formation is also known as tragacanth vegetation, a name derived from a large group in the genus Astragalus-section Tragacantha (regarded at present as the independent genus Astracantha Podlech). Many species of this group and of the genus Acantholimon are components of the cushion-plants formation all over the Middle East. The spiny cushion seems to have some biological advantages that allow it to adapt to the harsh conditions of this habitat: cold winters with high winds; precipitation mainly in the form of snow; dry summers; and high grazing pressure by domestic animals. Because of the short growth season and the harsh environment only very few annual plants accompany the cushion plants.

Wind velocity on the slopes that are in the wind shadow of small, local ridges or crests is rather low. Consequently, snow accumulates there and covers the soil as a layer that may reach a depth of 10 m for a few months. Water drainage from the slopes of this area is through karst systems and not through wadis, as in many parts of the country.

Several species of tragacanth Astragalus occur in areas that are far from Mount Hermon and the Anti-Lebanon Mountains. A. bethlehemiticus is a typical companion of steppes and rock vegetation in the shrub-steppes of the Negev Highlands and southwestern Jordan; A. echinus is a representative of this group at the high elevations of the southern Sinai.

2. Vegetation of the Dry Parts of Israel, Jordan, and the Sinai

The two principal distribution patterns of vegetation in the dry parts of the Near East are related to wadis. Where plants grow all over slopes and depressions the pattern is regarded as "diffused" ("mode diffus," sensu Monod, 1954). In extremely dry deserts, where vegetation is restricted to wadis that receive additional water, the pattern is "contracted" ("mode contracte," sensu Monod, 1954). At a detailed scale, edaphic conditions are the main predictors of vegetation patterns in the deserts of Israel, Jordan, and the Sinai. In an area where the climatic conditions enable the development of diffused vegetation on most soil types, relatively dry soils, such as silty or clayey ones, will locally support contracted vegetation. The opposing situation, when plants that demand high quantities of moisture occur in special habitats outside wadis in zones of contracted vegetation, is also found in many desert areas. In hard and fissured limestone, dolomite, granite, and metamorphic rocks, much of the rainfall is available to the semishrubs growing there because water infiltration is good and the soil in the rock fissures is leached. Accumulated deep in the soil and the weathered rock, this water is protected by rocks and stones from direct evaporation. Trees that grow on slopes in the Mediterranean zone with 500-700 mm annual rainfall also occur in desert areas with 100 mm or less in proximity to outcrops of smooth-faced hard rocks. These rocks do not absorb much water, and their crevices receive large amounts of water through runoff (Danin, 1972; Yair & Danin, 1980).

a. Shrub-steppes

Semishrubs grow in a diffused pattern in most of the Negev Highlands, the Judean Desert, the Sinai, and southwestern Jordan with 80-250 mm mean annual rainfall, thus forming shrub-steppes [ILLUSTRATION FOR FIGURE 5.10 OMITTED]. The most common dominants in these steppes are Artemisia sieberi, Noaea mucronata, and Gymnocarpos decander. The phytomass produced by annuals in the plant communities that develop on stony-rocky shallow soils is always rather small when compared with that on fine-grained and deep soils. The latter types hold much of their water close to the soil surface, thus losing much of it through direct evaporation. The minute quantities of salts (8 ppm) carried by clouds and later by rain from the Mediterranean Sea climate systems remain in the soil and accumulate there (Yaalon, 1963). The soil may be too dry or too saline for the growth of annuals in regular or dry years. Nearly monospecific communities of semishrubs exist, each of them best adapted to the specific local saline conditions (Danin, 1978). The most common dominants under these conditions are Reaumuria hirtella, R. negevensis, Salsola vermiculata, Bassia (Chenolea) arabica, and Atriplex glauca on chalk- and marl-derived soils; Anabasis syriaca and Haloxylon scoparium are the shrubby dominants on loess-derived soils. However, in moist years there is a rich development of annuals, although in patches with high salinity there are monospecific patches of salt-resistant annuals. Showy geophytes such as species of Tulipa, Iris, Ixiolirion, Ranunculus, and Anemone may bloom in high quantities in the shrub-steppes in moist years.

Outcrops of smooth-faced hard limestone support plants that may differ greatly from those on the other soil types. This vegetation is typically characterized by Chiliadenus iphionoides, C. montanus, Globularia arabica, Stachys aegyptiaca, Polygala negevensis, Tanacetum sinaicum, and Capparis aegyptia. Isolated populations of dozens of Mediterranean relicts and many rare desert plants are found in this habitat in the Negev, the Judean Desert, the Sinai, and Jordan. The semishrub Sarcopoterium spinosum and the geophytes Narcissus tazetta and Sternbergia clusiana are representatives of this phenomenon in the Negev (Danin, 1972, 1983a). Several newly discovered species and many species that had not been collected before in the steppe areas of the Near East are confined to this habitat.

Shrubs of Retama raetam and Achillea fragrantissima are the dominants in wadis of the terrain of hard limestones. Atriplex halimus prevails in this habitat where the catchment area is built up from the salty soils on chalk, clay, or marl. At lower elevations Acacia raddiana, A. pachyceras, Tamarix nilotica, and T. aphylla occur as well. Many small springs exist in the limestone hills of the western Sinai and the sandstone hills of southwestern Jordan. Most of these springs can be detected from afar by the presence of date palms (Phoenix dactylifera), which are confined to sites with a high freshwater table. Date palms are accompanied by Nitraria retusa, Juncus arabicus, Phragmites australis, and Cressa cretica. Many wadis contain canyons, which may have long-lasting water pools supplied by floods and may thus support rich flora of hydrophytes, such as Zannichellia palustris and Potamogeton spp., and green algae, such as Chara spp.

b. Shrub-steppes with Trees

Most of the area of this category [ILLUSTRATION FOR FIGURE 5.11 OMITTED] is covered by steppes in which the dominants are Artemisia sieberi, Noaea mucronata, and Gymnocarpos decander. Subunit 11a, in the Negev Highlands and the eastern Sinai, differs from unit 10 because it contains some 1400 adult trees, most of which are Pistacia atlantica and some which are Amygdalus ramonensis or Rhamnus disperma (Danin & Orshan, 1970; Danin, 1983a). These trees are found in affinity to outcrops of smooth-faced rocks. The high yields of runoff water from the rock outcrops to their crevices enable the successful germination and establishment of seedlings even outside wadis. Where outcrops of limestone are large enough, the seedlings may develop into trees, some of which are several hundred years old. Wadis with such outcrops in their catchment area support large trees [ILLUSTRATION FOR FIGURE 5 OMITTED]. Rare relicts, such as the vines of the Mediterranean maquis Prasium majus and Ephedra foeminea, and endemic plants, such as Origanum ramonense and Ferula negevensis, also occur in these rocks.

The tree of subunit 11b is Juniperus phoenicea, which grows on three anticlinal ridges in the northern Sinai. The richest in trees and accompanying rare plants is Gebel Halal (Danin, 1969). The junipers occur here in crevices of smooth-faced limestone outcrops and in wadis [ILLUSTRATION FOR FIGURE 6 OMITTED]. Rare Mediterranean relicts are the companions. Such species growing in the rock crevices are Ephedra foeminea, Rubia tenuifolia, and Astoma seselifolium. A rare endemic component of the rock vegetation is Origanum isthmicum, the world distribution area of which is but a part of Gebel Halal. The closest relative of this species, Origanum jordanicum, was discovered recently in Jordan, near Petra (Danin & Kunne, 1996). The populations of Juniperus phoenicea of Gebel Maghara (Shmida, 1977) and Gebel Yiallaq grow mainly in wadis.

Subunit 11c is richer both in nondesert trees and shrubs and in companions. The large outcrops of smooth granite and the high elevation of the Southern Sinai Massif influence the occurrence of the many habitats in which the rare species can survive. The typical trees of the rocky environment in 11c are: Pistacia khinjuk, Crataegus sinaicus, and Ficus pseudosycomorus. The west-facing escarpments of Gebel Serbal are rich in Moringa peregrina, which grow on rocky slopes near springs. In this habitat dozens of Moringa trees occur in the vicinity of the Wadi Feiran oasis. The typical shrubs of the rocky habitat of 11c are Rhamnus disperma, Rhus tripartita, Cotoneaster orbicularis, Periploca aphylla, and Sageretia thea. Most of the endemic and rare species of the Sinai occur in the rocks that also support trees.

The Quercus calliprinos and Juniperus phoenicea woodlands in Edom, Jordan, are marked 11d on the vegetation map. The climatically controlled belt of the arboreal Mediterranean vegetation terminates some 120 km north of the Dana-Tafila area. Large areas of shrub-steppe and steppe-forest typify the western ridge of the Jordanian plateau between At Tafila and Petra. These are dominated by Artemisia sieberi, Noaea mucronata, and spiny species of Astragalus, with occasional arboreal components such as Pistacia atlantica, Crataegus aronia, Juniperus phoenicea, and Quercus calliprinos. These formations develop on fissured limestone, basalt, and chalk rocks. The smooth-faced hard sandstone outcrops of the Dana-Petra area support the richest relict arboreal flora in the Near East. The trees and shrubs growing there are Quercus calliprinos, Pistacia atlantica, P. palaestina, P. khinjuk, Crataegus aronia, Juniperus phoenicea, Amygdalus korschinskii, Ceratonia siliqua, Olea europaea, Arbutus andrachne, Rhamnus punctata, R. lycioides, R. disperma, Ficus carica, F. pseudosycomorus, and Sageretia rhea. Typical semiparasites of the Mediterranean maquis, such as Osyris alba, Thesium bergeri, and Viscum cruciatum, occur in the rock crevices, together with typical vines of the maquis. These are: Rubia tenuifolia, Ephedra foeminea, Hedera helix, Bryonia cretica, and Lonicera etrusca, which are represented by a higher number of individuals than other Mediterranean vines in any other refugia in the Near East. The rich Mediterranean flora with many endemics may be regarded as existing in a successful refugium that functions for a long time in the evolutionary history of the region.

c. Desert Vegetation

In this category shrubs and trees are confined to wadis. However, on the broad boundary between the desert and the steppes [ILLUSTRATION FOR FIGURE 5.12 OMITTED], Anabasis articulata and Zygophyllum dumosum, the typical semishrubs of the desert, grow in a diffused pattern. Chalk and marl outcrops are populated with the halophyte communities of Suaeda asphaltica, Salsola tetrandra, and Haloxylon negevensis. The nearly monospecific communities of semishrub halophytes are accompanied by a diverse assemblage of herbaceous plants that grow on the leached soil only in rainy years. A lower section of the wadi receives higher quantities of water and supports small and short-lived semishrubs, such as Pulicaria incisa, which may locally function as an annual. Farther down, larger and long-lived semishrubs, such as Anabasis articulata, grow. A section dominated by shrubs, such as Retama raetam, which may become 3 m high, prevails farther down the wadi system. In the lowest section of the wadi system trees, mostly acacias or tamarisks, may be found. The nature of plant communities and the sequence of their occurrence along the wadis are in close affinity to rock and soil types, which greatly influence the moisture, salinity, and nutrient regime in the wadi systems (Lipkin, 1971). There are different plant communities in wadis on alluvium composed of flint pebbles, flint rocks, limestone outcrops, magmatic rocks, or marl. An example of the diversity of plant communities in such an area near Hazeva, in the Arava Valley [ILLUSTRATION FOR FIGURE 1.8 OMITTED] is discussed by Rudich and Danin (1978). The patterns of wadi ramification and the color of the land among the wadis are the main features by which the heterogeneous area is divided, using aerial photographs, into homogeneous units.

The most common dominant shrub in the large desert area south of Ma'an to the Saudi Arabian border is Anabasis articulata, accompanied by Acacia pachyceras trees at the fifth-order section of the wadi system. The rocky terrain between the escarpments of southwestern Jordan and the rift valley of the Arava supports diverse communities in a way that is similar to that of the Sinai. In the southern desert of Jordan gravel plains with extremely poor vegetation cover of category 12 are mixed with sandstone and derivative sand of category 13.

d. Sand Vegetation

Sand dunes or sand sheets occur in Israel [ILLUSTRATION FOR FIGURE 5.13 OMITTED] on the Mediterranean coastal plain, in the western Negev as a continuation of the northern Sinai sands, in a few valleys in the northeastern Negev, and in the Arava Valley. Each of these areas has a different climatic regime and sand texture, and the vegetation and its development differ accordingly. Much of this vegetation was discussed in earlier publications (Danin et al., 1964; Danin 1988a, 1995, 1996a, 1996b), so some background concerning the sand vegetation of southern Jordan is presented.

The sands of the Arava Valley are derived from weathering of Nubian Sandstones in Edom. The relatively high water table in the valley enables the tall shrub Haloxylon persicum to develop successfully where sand is sufficiently deep. Most stands of this plant in Israel became intensively irrigated agricultural areas. However, large areas of Haloxylonetum persici cover considerable parts of the Arava Valley and the desert of southeastern Jordan (Al-Eisawi, 1996). Sand mobility is high in a few places, but most of the sandy areas are stable. The common semishrubs growing in the sandy areas are Haloxylon salicornicum and Salsola cyclophylla. In the wadis that cross the sandy areas are large Haloxylon persicum plants, as well as occasional Tamarix aphylla trees covered by sand mounds that may reach a height of about 5 m.

Steep and isolated sandstone hills that project from large, flat valleys, filled up with stable sand, typify the Wadi Rum area of southern Jordan (see section V.E below). Huge areas of sand sheets are dominated there by Haloxylon salicornicum, Anabasis articulata, and occasional patches of Haloxylon persicum where the sand is slightly mobile and deeper than in the areas dominated by the two other species. The sandstone hills support many relict Mediterranean species and have particularly interesting vegetation in the vicinity of the contact zone between the sandstone and the Precambrian crystalline rocks (Barsotti & Cavalli, 1989).

e. Oases with Sudanian Trees

The main features of the environment in the oases of the rift valley [ILLUSTRATION FOR FIGURE 5.14 OMITTED] are their high temperatures and the large quantities of fresh water that are available throughout the year. Most of the springs in the dry part of Israel, Jordan, and the Sinai that are not marked on the map may be recognized from afar by the presence of date palms (Phoenix dactylifera), which are regarded as part of the typical flora of this habitat (Danin, 1983a). Many more tree species typical of the Sudanian savannas are found in these oases: Acacia raddiana, A. tortilis, Calotropis procera, Moringa peregrina, Balanites aegyptiaca, Cordia sinensis, Maerua crassifolia, Dalbergia sisoo, Capparis decidua (in Jordan), and Ziziphus spina-christi. The long and continuous existence of these freshwater springs, and the additional springs that existed along the riff valley in the past, may have helped the development of this northern extension of many species for which the main area of distribution is farther south. In many freshwater springs and oases near the Dead Sea in Israel and Jordan and in the southern Sinai, Adiantum capillus-veneris grows on dripping water in shady places with the orchid Epipactis veratrifolia. A prominent species of the freshwater springs in the Jordanian Desert, Nerium oleander, is missing from the desert springs of Israel and the Sinai.

f. Desert Savannoid Vegetation

Savannoid vegetation where acacia trees are accompanied by desert semishrubs is the main feature of large parts of the Arava and the Dead Sea Valleys [ILLUSTRATION FOR FIGURE 5.15 OMITTED]. In wadis the upper soil layers support typical desert vegetation, with Anabasis articulata, Haloxylon salicornicum, Zygophyllum dumosum, Retama raetam, and Lycium shawii as the principal contributors. Acacia pachyceras is confined to the areas that are at a relatively high elevation, such as the upper tributaries of Nahal Paran in Israel, Wadi Jirafi in the Sinai., and large areas of gravel plains in Jordan south of Ma'an. Acacia raddiana, which is less resistant to low temperatures, is the dominant at lower elevations, and Acacia tortilis, which has the greatest need for high temperatures, grows in the southern Arava Valley and below sea level in the northern Arava and Dead Sea Valleys (Halevy & Orshan, 1972). Maerua crassifolia and Capparis decidua are rare Sudanian trees that occur in a few places as components of the savannoid vegetation on the Jordanian side of the Dead Sea area. In a few places between Wadi Watir and Sharm el Sheikh in the eastern Sinai are rare trees of Capparis decidua, which is an important component of the savanna vegetation in southern Egypt and the Sudan.

g. Swamps and Reed Thickets

The large areas of swamps with diverse vegetation that existed in Israel at the beginning of the 20th century have been drained, and only small nature reserves, such as that of Huh Lake, remain [ILLUSTRATION FOR FIGURE 5.16 OMITTED]. Freshwater springs still flow, and a small number of species that produce high quantities of phytomass are rather prominent throughout the country. The most common indicators for the flowing water are Phragmites australis, Arundo donax, Arundo plinii, and Typha domingensis. Large areas of swamps in the Hula Valley supported Cyperus papyrus, which had reached its northernmost station there. Several rivers in the coastal plain that supported riparian vegetation in the past have now become sewage canals, and their polluted water has destroyed most of the rivers' vegetation.

h. Wet Salinas

Wet, salty soils occur where springs of salty water rise and where the water table is close to the surface and the evaporating water leaves salt in the upper soil layers [ILLUSTRATION FOR FIGURE 5.17 OMITTED] (Danin, 1981b: 269). In arid regions a salt crust may be formed at the soil surface, and plants may grow only in small wadis where leaching takes place. Most of the plants in the desert salt marshes are perennials that establish themselves in the rare events of leaching. The typical plants of desert salty soils are Suaeda monoica, S. fruticosa, S. vermiculata, Nitraria retusa, Seidlitzia rosmarinus, and a few species of Tamarix.

i. Synanthropic Vegetation

The category of synanthropic vegetation [ILLUSTRATION FOR FIGURE 5.18 OMITTED] is further divided in Israel into three subcategories according to the remnants of trees found in the intensively cultivated areas: in 18a, Quercus ithaburensis; in 18b, Ziziphus spina-christi; and in 18c, Acacia raddiana and Ziziphus spina-christi (Danin, 1988a: 129). The synanthropic vegetation of Jordan and the present status of the synanthropic vegetation in the Sinai need further investigation.

j. Mangroves

The mangroves of Nabq, in the eastern Sinai [ILLUSTRATION FOR FIGURE 5.19 OMITTED], which typically grow in the muddy soils of the tidewater, constitute the northernmost population of Avicennia marina on earth, at 28 [degrees] 10 [minutes] N. This species was recorded even farther from the equator in southern Australia, at 37 [degrees] S (Walsh, 1974). The only population found in the Gulf of Suez is the one that shares its water, and possibly warmth, with the Gulf of Elat at Ras Mohammed.

III. Smooth-faced Rock Outcrops in Deserts, Their Distribution, and Their Significance as a Habitat for Plants

The principal habitat discussed here is outcrops of smooth-faced hard rocks and their pediment. These outcrops are rather large and continuous, with only a few fissures and crevices, and have no soft layers in their typical sequence of component rocks. The pediment is a gentle slope formed in bedrock, which occurs below a substantially steeper slope and is separated from it by a relatively rapid change in angle (Young, 1972). The first accounts of the special features of this habitat in Near Eastern deserts were published in the context of their special flora (Danin, 1967a, 1967b, 1969, 1972, 1977a, 1977b, 1978, 1980, 1983a, 1986a, 1988a, 1988b, 1990, 1991b; Danin & Ganor, 1991; Danin & Kunne, 1996; Danin & Orshan, 1970; Danin et al., 1975).Yair and Danin (1980) studied the special moisture regime of smooth-faced limestone rocks of the Negev Highlands. They proved that the large areas of bare rocks contribute great amounts of water to the soil of the few crevices, bedding planes, and joints within and at the base of steps. The proportion of the area of the runoff "contributing phase" (rock outcrops) and the area of the water "receiving phase" (crevices, joints, interbedding plans) is high. The quality of the rock outcrop as contributing runoff is greatly influenced by the fine morphology of its surface. The sum of water needed to fill up all the depressions in the contributing surface is termed "depression storage." The smoother the surface the lower the depression storage and the higher the potential runoff yields from the surface under consideration. After the water arrives at the receiving phase of the substratum, rock blocks protect it in the few crevices from desiccation by direct solar radiation.


Soil in the crevices and fissures of smooth-faced rocks in deserts is rich in fine-grained particles that result from how it accumulates and its diagenesis. Being hard rocks, the clay content is negligible, and the contribution of fine-grained particles as the residual, insoluble component of the rock is minute, even in areas with much more rainfall (Danin et al., 1983). The main contributor of fine-grained components to soil in desert and shrub-steppe areas in Near Eastern deserts is airborne silt and clay (Ganor & Yaalon, 1974; Danin & Ganor, 1991, 1997). Many studies of the composition of the dust in Israel proved a similar composition in various parts of the country (Mamane et al., 1982). The three components carried out by winter winds are calcareous material, quartz, and clay minerals in particles with a diameter smaller than 50 [[micro]meter]. They are derived from weathering of rocks in the Middle Eastern and North African deserts. The sedimentary origin of the calcareous components is proved by the presence of coccoliths, fossils of marine algae that lived in past geological eras but not at present (Danin et al., 1989). The dust is deposited on the entire landscape at a layer about 100 [[micro]meter] deep in the semiarid and arid parts of the region (Yaalon & Ganor, 1975). A portion of the sedimented dust is removed by rain and wind, but some of it is trapped in the canopy of plants and washed into the ground by rainwater. Small plants such as mosses, which form cushion-like patches, may function as an efficient trap (Danin & Ganor, 1991, 1997). Poa eigii is a perennial grass that forms lawnlike populations in the Judean Desert and grows slowly above the dust that is deposited among its leaves (Danin & Ganor, 1997).

Analysis of soil trapped by lichens and mosses in southwestern Jordan was performed in the following way. The texture of soil trapped in a bulk of the moss Grimmia mesopotamica in Wadi Barra, Dana Nature Reserve, southwestern Jordan, was compared with that of the supporting sandstone and with that of the soil in a crevice supporting Origanum petraeum. Another sample was taken from the soil trapped in a horizontal rock surface covered by soil lichens mixed with mosses. Yet another set of samples was taken from soil trapped in a moss cushion on a vertical rock surface and its supporting sandstone in a rock outcrop 13 km south-southwest of Petra. The results of the texture analysis are presented in Table III. It is clear that the coarse texture of the sandstone has only a partial influence on the texture of the soil in the crevices. The moss and lichen traps lead to enrichment of the soil by fine-grained particles and thus to the improved moisture regime of the habitats in the smooth-faced rocks.

The thallus of epilithic crustose lichens is rich in fissures when dry. The fissures may be 50-200 [[micro]meter] wide and 0.5-2 mm deep and constitute a system of polygons. In many thalli occasional polygons, each a few millimeters square, may be missing, thus forming depressions in the thallus. The natural events that may lead to such an absence are trampling by various passing animals, grazing by snails or slugs, and local death of the lichen portion. Dust particles deposited in the fissures and in the depressions are protected from removal by even strong winds. When wetted by rain, dew, or mist the thallus imbibes, sealing the trapped dust from the reach of transporting agents. When the lichen thallus grows, the dust is trapped within, as if incorporated in the thallus. When dying or being removed by trampling animals, the lichen parts are transported by the runoff water to crevices and to the pediment of the rock outcrop. Deterioration of the organic matter of the dead lichens leaves in the crevices the inorganic particles trapped in that material. The flux of water through soil pockets and pediments is higher than that of the soils surrounding the rock outcrop, so leaching of the soluble components is more rapid and efficient in these sites. The carbonate components are leached, and the proportion of clays increases (Yair & Danin, 1980; Danin et al., 1983). Thus the soil in the crevices and pediment of the smooth-faced rocks is richer in fine-grained particles and therefore has a higher moisture-holding capacity than do other soil types in the vicinity. The many showers every year contribute not only enough water to fill up the crevices in the smooth rock but also runoff from the rocky slope to its pediment. Consequently, in desert areas the rock outcrops and their pediment should be considered as habitats that contain microhabitats with high water-holding capacity and are rich in available water.



Limestone and dolomite are the most common rock types in the mountainous part of the Negev Highlands and the northern Sinai (Bartov, 1994) [ILLUSTRATION FOR FIGURE 7 OMITTED]. Most geological formations of the sedimentary sequence of this area are bedded limestone and dolomite from the Cretaceous and Tertiary (Eocene). These are composed of thin layers of hard, massive calcareous rocks interbedded with chalk or marl. The soft components weather faster than do the hard ones, so the landscape is slopes of hills composed of natural steps. Such steps are made of a small outcrop of densely fissured hard rock, a small cliff as tall as the hard rock is thick, and a fiat area with shallow, stony Brown Lithosol (Dan et al., 1975; Danin et al., 1975) in place of the soft rock layer. The densely fissured rocks do not contribute much runoff because of the high depression storage of the Lithosol. The proportion of the runoff-contributing phase to the water-receiving phase is much lower in this substratum than in the smooth-faced rock outcrops; the same amount of rainfall per unit area is shared by a large number of crevices, soil pockets, and soil patches free of rocks. Much of the water-retaining component of this substratum is not protected well from direct solar radiation, so each volume unit of the receiving phase offers less water to plants than does the water-retaining component of the smooth-faced rocks. Under special geomorphological situations even bedded limestone and dolomite may constitute smooth-faced outcrops; these positions are steeply inclined strata where stones and soil are easily removed by rolling or by erosion from the rock outcrop, leaving relatively smooth faces.

A few formations of the Cenoman, Turon, and Eocene are of massive limestone or dolomite, which constitute large outcrops bare of any soil cover. The layers of these formations are of crystallized limestone or dolomite not interrupted by soft layers. They do not weather into steps and constitute continuous, hard outcrops. A part of the vegetation map of the Negev Highlands at a scale of 1:100,000 in the vicinity of Yeroham and Dimona displaying only the patches of the smooth-faced rock vegetation (Origano dayi-Chiliadenetum iphionoidis) (Danin & Solomeshch, 1999) is shown in Figure 8. The higher density of patches in the oblique area (the anticline) northwest of the Yeroham-Dimona line than in the anticline southeast of that line calls for an explanation. The rock types in both anticlines are marked as the same in the geological maps of the area. It seems that this difference is related to the impact of climatic factors on the agents of the biogenic weathering and consequently on the density of the smooth-faced rock outcrops.

1. Weathering Processes Leading to the Formation of Smooth Calcareous Rocks

In the study area there is hardly any place where rock surface is not populated by one or another kind of organism (Danin et al., 1982; Danin & Garty, 1983; Danin, 1986b). Most of these organisms are poikilohydric. When dry, their thallus is dormant but in a latent, reversible state. When wetted they rapidly become physiologically active. Cycles of wetting and drying can take place many times without affecting their viability. Although most organisms are microscopic, their constant impact on the processes of weathering leads to the formation of predictable forms of rock surfaces at certain geomorphological and microclimatic positions. I believe that, at least in the desert, much of the weathering is influenced or caused by organisms living at the rock surface or a few millimeters below the surface. I have been studying it over large areas and have participated in many publications concerning biogenic weathering (Danin et al., 1982, 1983, 1987; Danin, 1983b, 1983c, 1984, 1985, 1986c, 1986d, 1989a, 1989b, 1992a, 1992b; Danin & Garty, 1983; Hungate, et al., 1987; Danin & Caneva, 1990; Caneva et al., 1992, 1994). I therefore deal here with the important biogenic causes for weathering and not with physical processes, which have been thoroughly reviewed in the geomorphological literature.

a. The Role of Epilithic Lichens

The north-facing slopes of the massive limestone of Shivta Formation (Turonian) (Bartoy et al., 1981) on Har Halukim are totally covered by epilithic lichens (Danin & Garty, 1983). This living crust, up to 2 mm thick, prevents direct contact of raindrops with the rock. The water reaching the rock is enriched with C[O.sub.2] resulting from respiration of the lichens and probably with additional constituents released from the lichens' thallus. The rock surface undergoes a spatially homogeneous process of dissolution. Most lichens in this habitat cause a process of weathering that is of the same order of magnitude as neighboring lichens do. In other words, no pits or microelevations occur beneath a certain species of lichen as a result of a faster or a slower rate of weathering than its neighbors. Joints in the rock are sites of weakness; at the exposed rock surface they often form lines of local depressions that result from faster deterioration of the soft material in the joint. However, many of these joints cannot be seen when they are covered by crustose lichens because the lichens prevent the removal of rock material by water or wind. As a result, there are very few sites of local weakness that may start faster deterioration, and the relatively homogeneous rate of weathering leads to the formation of smooth-faced outcrops [ILLUSTRATION FOR FIGURES 9 & 10 OMITTED]. The distribution of smooth-faced limestone outcrops [ILLUSTRATION FOR FIGURE 8 OMITTED] in a representative part of the Negev Highlands reflects the distribution of the combination of hard rock formations and epilithic lichens. The boundary of the area in which epilithic lichens totally cover limestone rocks on north-facing slopes (Danin, 1986b: [ILLUSTRATION FOR FIGURE 1.2 OMITTED]) runs 7-10 km east of the Yeroham-Dimona line.

Endolithic lichens that grow on hard limestone or dolomite and induce a jigsaw puzzle-like pattern of weathering (Danin et al., 1982) [ILLUSTRATION FOR FIGURES 11 & 12 OMITTED] are restricted in Israel and in Sinai desert areas to detached stones that are frequently wetted by dew (Danin & Garty, 1983; Danin, 1986b). This weathering pattern, under living lichens, is not found on in situ large rocks in areas with less than 400 mm mean annual rainfall; it typically occurs on south-facing hard rocks in areas with rainfall higher than 400 mm (Danin, 1986b). However, remnants of the jigsaw-puzzle pattern on south-facing rocks in the dry areas do occur and are interpreted as fossils from periods with higher quantities of rainfall (Danin, 1986b). When found as a remnant on rocks of north-facing slopes, as in Har Halukim below the crust of epilithic lichens (Danin & Garty, 1983), this jigsaw pattern indicates that sometime in the past a climate drier than that of the present prevailed in the area. In conclusion, the weathering induced by endolithic lichens has no bearing on the surface morphology of smooth-faced rock outcrops in the desert.

b. The Role of Chasmoendolithic Cyanobacteria

The surface of hard and massive limestone and dolomite on south-facing slopes in the Negev Highlands and in other places with similar climatic conditions is populated by fungi of the Lichenothelia group and by lichenized and nonlichenized cyanobacteria. Members of these three kinds of organisms cause minute or large pits in the rock surface (see sect. III.B.1.c). Under these climatic, microclimatic, and substratum conditions chasmoendolithic coccoid cyanobacteria may occur in exfoliating surfaces (Danin & Garty, 1983: Photograph 9; Danin, 1986b, 1992b). In these microsites the cyanobacteria develop beneath in situ, undetached, thin rock parts that are almost parallel to the rock surface. When detached from the rock, flat stones a few millimeters thick and look like thin flakes of rock are derived. I use the term "flakes" later in reference to this kind of weathering product. The cyanobacteria receive the moisture they need when it rains and water is soaked through all the fissures in the upper layers. When the rock is wet, its light conductivity increases (Nienow et al., 1988). Some populations of cyanobacteria may use the light that directly penetrates the thin rock. The situation in rock fissures below the surface soaked with water was compared by Dr. Bloch (1965, pers. comm.) to the optic fibers that are commonly used in scientific and other kinds of equipment. Light that penetrates an optic glass fiber runs in one direction because of the perfect reflectance of the fiber peripheral walls, no matter what the outer morphology of the fiber is. In a similar way, light that penetrates water-filled capillary fissures in the rock is conducted inward and supplies the cyanobacterial cells with the light energy they need. Dr. Bloch used to say that when the soil or rock becomes wet it is also illuminated in all the capillaries that become wet.

When the cyanobacteria multiply in crevices two cleavage forces are produced inside the rock. One is that of the organisms themselves, which imbibe water and thus push the rock to open. Recall how the ancient Romans used the considerable force created by imbibing plant mucilages in their quarries: Pieces of dry wood were put into narrow artificial fissures that had been chiseled into the rock. Wetting of the wood caused the imbibition of its mucilaginous components; the wet wood expanded and cleaved the rock block in the desired location.

The second cleavage-inducing force is the sediments that accumulate in the rock near the organisms. Chemical sediments are produced near the organisms due to their biochemical activity. When a molecule of C[O.sub.2] is fixed by the photosynthesizing cyanobacteria a molecule of CaC[O.sub.3] is sedimented at the site. The gradual opening of fissures by the imbibition force of the cyanobacterial mucilages and the wedging effect of the sedimented CaC[O.sub.3] are accompanied by penetration of airborne silt and clay into the fissure. These grains have both wedging and imbibition effects, which further promote the cleavage of the rock flakes in the exfoliation microsites. As a result of prolonged activity of the microorganisms and other components of this microecosystem, flakes are detached from the rock. Relatively smooth and hardly weathered new faces of the rock are exposed in these sites. Smooth-faced outcrops associated with exfoliation were observed in dry slopes that are not facing north and in steeply inclined hard layers, such as the folding escarpments of anticlines, monoclines, and domes or tilted blocks. Naturally, the extent of continuous outcrops is smaller here than in the rocks crusted with epilithic lichens because there is no protection of the joints from further weathering and because of the local nature of the exfoliating faces. Depression storage of the exfoliating faces is higher than that of lichen-encrusted rock outcrops, so the runoff yields are smaller. Many of the southeasternmost patches of smooth-faced rocks illustrated in Figure 8 have exfoliating surfaces; the rest is lichen-encrusted limestone.

c. The Role of Euendolithic Fungi, Cyanobacteria, and Cyanophilous Lichens

Several microorganisms are capable of growing on the bare rock and changing its surface micromorphology by inducing biogenic weathering; penetration of the rock as a result of their activity makes them "euendolithic" (Golubic et al., 1981). The three kinds of organisms discussed here dissolve the rock parts that are in direct contact with them. This dissolution may be a result of the release of C[O.sub.2] into the water that surround the organism during its respiratory activity. The organisms may also release additional kinds of dissolving agents, such as the chelating compounds that have been reported for lithobiont activity elsewhere (Lange, 1974). Thus the shape of the organism's thallus influences the morphology of the depression it induces. Fungi from the genus Lichenothelia (Ascomycetes) (Henssen, 1987) often function as pioneers on newly exposed hard limestones (Danin, 1992b). They dissolve microscopic, funnel-shaped pits in the rock [ILLUSTRATION FOR FIGURE 13 OMITTED]. L. intertexta, which grows on rock outcrops in many parts of Israel, multiplies by spores and vegetatively by propagation (Danin, 1992b). In time the micropits of more than one thallus join together, thus producing microsites that may contain more water than is needed for L. intertexta and enough for the growth of coccoid cyanobacteria and cyanophilous lichens. The microorganisms of the latter community induce weathering at a rate faster than that of the former and thus occur in lower places [ILLUSTRATION FOR FIGURE 14 OMITTED]. The "spongy" rock structure derived from the dissolution activity of many small organisms at a layer 100-200 [[micro]meter] thick of the free and lichenized cyanobacteria [ILLUSTRATION FOR FIGURE 15 OMITTED] is further illustrated by Danin (1986b: [ILLUSTRATION FOR FIGURES 1-5 OMITTED]). The rate of weathering is higher here not only because the free-living and lichenized cyanobacteria directly dissolve the rock in contact with their body but also because all of the microorganisms (including unstudied fungi and bacteria) release C[O.sub.2] during respiration. The high concentration of C[O.sub.2] in the water of the pit promotes CaC[O.sub.3] dissolution in the contact zones of rock crystals. When becoming relatively free these crystals or larger rock particles are easily detached from the rock by splashing raindrops. The only process of weathering in the Lichenothelia community is the direct dissolution of the rock CaC[O.sub.3] by rainwater or at a slightly higher rate near the sparse thalli. In the cyanobacterial and cyanophilous lichen faces it is enhanced by the denser biomass of C[O.sub.2]-releasing organisms and by the splashing of the raindrops. The rate of weathering by Lichenothelia intertexta was estimated as 1 mm per 3000 years (Danin, 1992b); that of cyanobacteria with cyanophilous lichens, as 1 mm per 200 years (Danin, 1983c).

As a result of the prolonged activity of these organisms the rock surface populated by them becomes pitted. The pits are sites where the cyanobacterial community grows for a long time and induces weathering that occurs more rapidly than weathering in surrounding sites. The longer a patch of this community lives and induces weathering, the deeper and larger is the pit (Danin & Caneva, 1990; Danin, 1992a). The depression storage of the pitted surface is higher than that of the smooth-faced rocks, so the number of events during which the rock contributes runoff to its crevices is lower than that of the north-facing crusted and smooth slopes.


Magmatic and metamorphic rocks build up the main bulk of mountains in the Southern Sinai Massif (Bartov, 1994). Granite mountains are among the most spectacular of the southern Sinai, especially those of Gebel Musa, Gebel Serbal, Gebel el Deir, Gebel Umm Shomar, and Gebel el Beida [ILLUSTRATION FOR FIGURE 16 OMITTED]. All of these peaks are made up of smooth granite in long, steep slopes [ILLUSTRATION FOR FIGURE 17 OMITTED]. One of the most common micromorphological kinds of surface in the granites of the southern Sinai is the smooth face, where crystals do not project and are difficult to remove. The second, more common in the southern Negev and in southwestern Jordan, is the arkosic surfaces, where crystals project, are easy to remove, and thus leave depressions at the surface. The common type of biogenic weathering in the smooth surfaces is exfoliation. Thin flakes of granite can easily be removed from the rock outcrops, leaving patches of cyanobacteria or their induced calcitic sediment. The soil at the pediment and in the crevices is often rich in such flakes.

Chasmoendolithic cyanobacteria grow beneath large crystals of light-colored minerals, such as quartz and feldspars, in the arkosic weathering surfaces. These crystals are either transparent or become transparent to a certain extent when wetted. The particles of rock that become detached from the surface are single, large crystals that form coarse-grained soil rich in feldspar and quartz and known as "arkose." The surface of the weathered rock is rough and has much higher depression storage than does the exfoliated surface. The relatively loose crystals leave large volumes of capillaries among them, capable of absorbing water. Consequently, runoff yields from granite with smooth faces is much higher than from granite with arkosic surfaces. The geologic differences between granites of the two kinds are beyond the scope of the present discussion. However, a general tendency of their distribution is that smooth-faced granites in the Sinai and southwestern Jordan occur at high elevations, whereas arkosic weathering is more typical in lowlands. Low elevation in the latter is associated with extreme desert conditions, whereas the higher mountains support shrub-steppes. The small area of magmatic rocks in Israel is in the driest part of the country, and smooth-faced granite is practically absent there.

The reader of recent articles on the vegetation of granite outcrops (e.g., Alves & Kolbek, 1994; Porembski et al., 1994; Porembski, 1996; Fleischmann et al., 1996) may think of inselbergs as the main biotope discussed here. In-depth studies of inselbergs and bornhardts ("bare surfaces, domelike summits, precipitous sides becoming steeper toward the base," according to Willis [1936]) were carried out by several geomorphologists (Willis, 1934, 1936; Twidale & Bourne, 1974; Thomas, 1978; Ollier, 1978). These studies focus mainly on their origin and on the mechanisms of their formation, and several theories on each component of the system have been put forward. My main goal here is to predict what a botanist will find in the microhabitats of bare, hard rocks. All of the inselbergs and bornhardts are included in the category of smooth-faced bare rocks, but not all of the bare rocks are parts of inselbergs or bornhardts.

Most metamorphic rocks exposed in the Southern Sinai Massif and the magmatic Precambrian outcrops of southwestern Jordan (Bartov, 1994) do not constitute smooth-faced rock outcrops. Many kinds of metamorphic rocks are highly fissured and do not form continuous, large outcrops. This may be because of their internal structure and joint system, which is mostly perpendicular and not parallel to the surface. The dark color of many kinds of metamorphic rocks influences the poor colonization by chasmoendolithic cyanobacteria and the resulting kind of weathering. Although exfoliation is found in metamorphic rocks, it does not produce large, smooth outcrops as granites of high elevation.


Sandstones that function as refugia in desert areas of the Sinai and Jordan are hard and tend to form cliffs or concave slopes. Even sandstones in the most extreme desert areas are inhabited by one or several life forms of microorganisms. The kind of weathering that the rock undergoes and that influences its surface architecture is strongly affected by the microorganisms that inhabit it. The kind of lithobiont populations is strongly correlated with the climatic conditions. In an extremely dry area of Timna, the Arava Valley, Israel and slopes along the highway between Tafila and Safi, Jordan (mean annual rainfall 50-70 mm), are two principal lithobiont communities on hard white sandstones. These are manganese- and iron-oxidizing bacteria that commonly form a continuous brown-to-black crust of rock varnish on the surface and a layer of cryptoendolithic coccoid cyanobacteria at a depth of 1-3 mm (Friedmann et al., 1967).

Rather similar sandstone in Wadi Barra area, Dana Nature Reserve, Jordan (250-300 mm mean annual rainfall and higher air humidity) supports a different assemblage of lithobionts. Most of the sandstone surface in this site is covered by epilithic lichens, with a dominance of those with Chlorophyceae as phycobiont; cyanophilous lichens grow as well. There are also various kinds of cryptoendolithic organisms (see sect. III.D.2).

1. Rock Varnish

The main sandstone formations that constitute large, smooth-faced outcrops are of light-colored rocks. In the extreme desert areas where these sandstones are exposed - for example, close to the Israeli-Jordanian border in Jordan, in southern Israel, and at lower elevations of the sandstone outcrops in the Sinai - a dark layer of manganese and iron oxides is present at the sandstone surface. This layer, known as rock varnish (Hungate et al., 1987), has in association manganese-oxidizing bacteria. The bacteria affix airborne clays to the quartz grain surface and constitute a layer 10-100 [[micro]meter] thick (Dorn & Oberlander, 1981; Dorn, 1982). Because the process of darkening by the clays and by the oxides of manganese and iron is the color of accumulated materials, the hue of a particular surface may indicate its relative age. The varnish crust, even when well developed and old, does not prevent the penetration of water into the rock. Hence the varnish may protect the sandstone from direct deterioration but does not add runoff to the crevices. Higher plants rarely grow in crevices of sandstone in these extreme desert areas.

2. Cryptoendolithic Cyanobacteria and Green Algae

Cryptoendolithic organisms constitute a green layer a few millimeters below the sandstone surface. Various aspects of such a thin green layer in the sandstone rocks of the cold desert of Antarctica were the subject of a rich literature published in the past two decades by E. I. Friedmann and his collaborators. The literature concerning this habitat in the warm desert of the Near East is rather scant (Friedmann et al., 1967). The study by Nienow et al. (1988) shows that the cryptoendolithic organisms receive light energy when the rock is wetted. Thus, when the poikilohydric organisms that live inside the rock imbibe and start their biotic activity, they also have the light they need for photosynthesis. In the dry climate of the extreme desert, water is available only for a few days following strong showers. It was assumed by Danin (1986d) that water penetrating the permeable sandstone remains there, protected from direct evaporation. After the surface becomes dry, water vapor begins to diffuse through the rock capillaries toward the surface. At night the cooling of the rock surface may lead to condensation of the water and to prolonged activity of the cryptoendolithic organisms.

Preliminary observations of the green cryptoendolithic layer in the sandstone from elevations of 200 m below sea level near Wadi Mujib, the Dead Sea area, Jordan, revealed coccoid cyanobacteria in south-facing slopes and coccoid and filamentous cyanobacteria in north-facing sandstones.

3. Epilithic Crustose Lichens and Their Role in Smooth-face Development

Some lichen species cover entire rocks with a layer 1-2 mm thick. When such lichens are detached naturally or artificially, they leave a brownish patch of sandstone that has resulted from the layer of dust trapped and deposited on the rock surface by the preexisting lichen. Propagules of epilithic lichens occur among the quartz grains. The ratio of sand grains and lichen thalli changes as the established lichens grow and cover more and more quartz particles. Many thalli of lichens that cover the entire surface still display a few projecting quartz grains. A mature rock surface with epilitic lichen displays mostly the lichen thallus. Therefore, rainfall drops and other weathering agents come into contact with the lichens and not with the rock particles, thus protecting the rock. The chemical constituents of the surface layer also change over time. The epilithic lichens trap airborne dust, which contains about 40 percent CaC[O.sub.3] in the Near East (Mamane et al., 1982). Dust trapped in the fissures of the thallus becomes incorporated into the upper layers of rock. Cycles of wetting and desiccation, common in the area with poor rainfall, together with the chemical impact of the lichen thallus on the overlaid layers, lead to recrystallization of the calcium carbonate component of the dust at the sandstone surface. No sandstone layer of the heartstone displayed effervescence with dilute hydrochloric acid, whereas most of the surface samples studied displayed strong effervescence, thus indicating the trapped calcium carbonate. The result of lichen development is the formation of smooth faces that are protected from weathering. In some parts of the sandstone domain in southwestern Jordan, north-facing slopes are totally covered with epilithic lichens, whereas the south-facing ones are devoid or almost devoid of such cover. The differing slope angle, gentle in the north-facing and steep in the south-facing, indicates the impact of lichens on weathering.

4. Mosses and Their Role in the Sandstone Ecosystem

Although mosses are small organisms with leaflike appendages that are 1-2 mm long, they are capable of contributing much to the moisture regime of plants in the rocky terrain. They grow and produce new leaves above the sand that is produced as sandstone deteriorates and as airborne fine particles cover it (Moore & Scott, 1979; Danin & Ganor, 1991, 1997). Spores of mosses can survive desiccation for 6 months to 3 years, and some species even up to 10 years; thus spores of many moss species are capable of long-term dispersal (Zanten, 1978, 1984). Spores of many fungi, lichens, and mosses, asexual diaspores of lichens (soredia and isidia) and thallus fragments of cyanobacteria are 1-50 [[micro]meter] in diameter and can be dispersed as components of aerosols (Akers et al., 1979) and carried by winds for thousands of kilometers. Chatigny et al. (1979) provide data about the dispersal distances of small particles from volcanic eruptions which are capable of changing light infiltration through the atmosphere at distances of thousands of kilometers from the volcano. Particles with a radius of 10 [[micro]meter] or more may be washed out of the air by raindrops or may fall directly; smaller particles eventually coagulate in clouds and reach the ground in raindrops (Newell, 1971). Therefore, every point on earth may theoretically receive showers of such diaspores. The development of mosses or other kinds of microorganisms on the rock surface is therefore not limited by the supply of diaspores or propagules. It is a function of the fitness of the lithobiont component of the local environment. The role of mosses in determining the composition of soil in crevices of sandstone in southwestern Jordan is dealt with in section III.A above.


Chert (flint) rocks of the Mishash formation (Senonian) (Bartov et al., 1981) form relatively smooth outcrops in a few places in the study area, but they are too small to be drawn on a map at the scale of Figure 7 or Figure 8. In anticlines and anticlinal steep flanks are continuous layers of chert that are hardly interbedded with chalk or other soft rock; in synclines most of these formations are interbedded with much chalk and hence form only small outcrops of hard rocks. When strongly inclined, as in the southeast-facing slopes of the anticlinal ridges of the northern Negev, the chert layers form patches of smooth rocks with a few joints, fissures, and crevices that follow the general "terms" of the desert refugia in that a large area contributes runoff water to the small area of soil pockets that become a rhizosphere for special plants.

IV. The Impact of Rock, Soil, and Climate on Floristic Parameters

Following floristic investigations of the vegetation of granite outcrops in tropical countries (Alves & Kolbek, 1994; Porembski et al., 1994; Porembski, 1996; Fleischmann et al., 1996), researchers have concluded that the most important environmental factor in the existence of endemic plants in these rocks is insolation. Plants that cannot stand shade are disadvantaged in the arboreal vegetation that surrounds the granite inselbergs they investigated. Hence, plants that may stand or demand high solar radiation become confined to rock outcrops that offer low resources for trees and support smaller plants. A comparative study of the impact of rainfall and substratum type on the number of perennial species, the numbers of their individuals, species richness, phytogeographical affinity, and additional parameters was carried out in the Negev in the summer of 1996. The working hypothesis was that moisture regime is the most important factor in the vegetation of rocks and soils. In order to test the hypothesis, four study areas were selected at various positions along a moisture gradient in the Negev Highlands. In each location seven quadrates or circles 100 [m.sup.2] each on smooth-faced bare limestone or dolomite rocks and seven quadrates or circles on Brown Lithosol (Dan & Raz, 1970) in their vicinity were selected. Each individual of all the perennial plants that could be seen in summer was recorded. My database of the flora of Israel, Jordan, and the Sinai was used to evaluate quantitatively several features of the plants recorded in each quadrate or circle. Figures 18-21 present the average for several parameters in each of the eight habitats studied. The distribution of the various parameters indicates the number of niches available for plants in each habitat, their quality from the viewpoint of moisture regime, and their phytogeographical affinity. The study sites were:

1. The Hazera mountains, the driest site, 17 km southeast of Dimona, altitude 400 m;

2. The Hathira mountains, a slightly moister site in the outlet of Makhtesh Hathira, 14 km southeast of Dimona, altitude 310 m;

3. Near Sde Boqer, altitude 500 m; and

4. Nahal Elot, the moistest site, 20 km southwest of Mizpe Ramon, altitude 900 m. Although all four sites are in the 100-mm-isohyet zone, their vegetation varies significantly. At sites I and 2 the sparse vegetation belongs to the class of desert vegetation known as Anabasietea articulatae (Danin & Solomeshch, 1999). The most common association in that area is Reaumurio hirtellae-Zygophylletum dumosi: At site 2 it covers all of the slopes with Brown Lithosol, but at site I it is restricted to outcrops of fissured hard rocks and to the pediment of smooth-faced rock outcrops. At the latter site the soft substratum, such as alluvium or colluvium with fine-grained soil, is devoid of semishrubs and is partially populated by annuals only during rainy years. Sites 3 and 4 are in the area of shrub-steppe class Artemisietea sieberi (Danin & Solomeshch, 1999). The most common association at site 3 is Gymnocarpo decandri-Artemisietum sieberi, whereas that near site 4 is Moricandio nitentis -Artemisietum sieberi. The smooth-faced, hard rock outcrops of site I are Cenomanian rocks (Hazera formation); those of sites 2 and 3, Turonian (Shivta formation); and those of site 4, Eocene (Nitzzana formation).


In this study the average number of individuals per quadrate [ILLUSTRATION FOR FIGURE 18 OMITTED] indicates the number of niches that may support perennial plants and enable their survival even in extremely dry years. In the area of Anabasietea articulatae more such niches occur in the smooth-faced rock outcrops than in the Lithosol. The aridity of this area clearly decreases the microsites in which plants can survive. The moister conditions in the Hathira mountains provide more niches for plant growth than do the Hazera mountains in both the Lithosol and the rocky habitats. In the area of Artemisietea sieberi more niches are available for plant survival in the lithosol habitat than in the rocky one. The quality of these niches, as indicated by plants growing there, is discussed further below. The large number of individuals in the soil quadrates at Sde Boqer may be related to the fact that the Brown Lithosol is rich there in outcrops of hard and fissured limestone. The hard rocks contribute water to their fissures, and the soft beds that retain the water protect it from direct evaporation.


The distribution of the number of species per 100 [m.sup.2] [ILLUSTRATION FOR FIGURE 19 OMITTED] shows clearly that at all sites more species are found in the rocks than in the Lithosol quadrates. The gradual increase in the number of species in the rocks from the driest site to the most mesophytic one means that more different niches in the rocks become available for colonization by plants as moisture availability increases. Species diversity is presented in Figure 20 by three parameters:

d = (S- l)/log N;

H = the Shannon-Wiener index = -[Sigma] [P.sub.i] In [P.sub.i]; and

[e.sup.H] = Hill (1973) index,

where N = number of individuals in the sample, [N.sub.i] = number of individuals of the ith species, [P.sub.i] = [N.sub.i]/N, and S = number of species.

The three parameters demonstrate the distribution of individuals (N) in the different species (S) at the different sites and habitats. The model of S of the rock vegetation being much larger than that of soil vegetation repeats itself throughout the whole range also with the parameters of species diversity. Species diversity in rock vegetation increases along the humidity gradient, except for that at the Nahal Elot site, which is nearly as high as that at the Sde Boqer site.


Based on information gathered over many years of recording and collecting plants in Near Eastern deserts, I have developed a scale of rarity for plant species in the desert rocks. The parameters are: 0, not growing in natural desert habitats; 1, steppe or desert species; 2, common rock-inhabiting species; 3, rare rock-inhabiting species; 4, very rare rock-inhabiting species; and 5, extremely rare rock-inhabiting species. This evaluation sounds subjective but represents conclusions drawn from thousands of observations; transforming the parameters to absolute objectivity would be an unreasonably time-consuming operation. The average frequency of the first four rarity types at the four sites is presented in Figure 21. All of the rocks have three classes of rarity, whereas the Lithosols have mostly steppe or desert plants and only a few common rock plants. The rocky nature of the Lithosol at the Sde Boqer site is reflected in the high proportion of common rock plants, in comparison with that of the Lithosols at the other sites. The proportion of rare rock plants increases gradually along the climate gradient, with the maximum at the Nahal Elot site.


The average phytogeographical spectrum of the rock and Lithosol vegetation of the four sites is presented in Figure 22. In each site the number of chorotypes that contribute to the vegetation covering the Lithosols is 2-3, whereas in the rocks it is 5-6 chorotypes. This means that there are many more kinds of niches available for plant habitation in the rock outcrops. The flora at the four sites sampled is exemplified by the relative proportions of the Saharo-Arabian and the Irano-Turanian chorotypes in all soil types. The Hazera mountains site has the highest percentage of Saharo-Arabian individuals and the lowest of Irano-Turanian, whereas the Nahal Elot site has an almost reciprocal situation. There are Mediterranean and M-IT species in all rock sample areas, with the highest score in the rocks at the Nahal Elot site. These two chorotypes are absent from all of the Lithosol quadrates at all of the sites. Species of the biregional chorotypes M-SA and IT-SA occur in the rocks but are almost absent from the Lithosol quadrates at all sites.


Baskin and Baskin (1988), working on endemism in rock-outcrop plant communities in the eastern United States, assume that moisture regime is not the important factor in the rock as a habitat for endemics. They suggest that, under the conditions they studied, "endemics are not restricted to rock outcrops because soil moisture is higher there than elsewhere during the growing season." After dealing with several environmental factors they conclude that most endemics in the rock outcrops of the eastern United States demand high light intensities. In that area the soils surrounding the rock outcrops are covered by deciduous forest, and only in the bare rocks can the endemics grow without being in the shade of their competitors. At the four Negev sites I found eight species endemic to Israel, the Sinai, and Jordan. Origanum dayi and O. ramonense (with rarity-index scores of 2 and 3, respectively) are confined to a relatively small area. The rock vegetation shares with the Lithosol quadrates two endemic species, Zygophyllum dumosum and Reaumuria negevensis (with a rarity-index score of 1), which grow in great quantities in much of the desert and steppe areas of Israel, the Sinai, and Jordan. Astragalus amalecitanus is also shared by the rocks and Lithosol sites and has the lowest rarity-index score for rocks (2). The other three endemic species are confined to rocks and have a rarity-index score of 3 (Dianthus sinaicus and Micromeria sinaica) or 4 (Haplophyllum poorei). These facts are in agreement with all indications that the important environmental factor in desert rocks is their better moisture regime, which seems true for the endemic species as well.


The main influence on the occurrence of endemic and other rare plants in desert rocks is humidity. All of the rock outcrops and their surroundings are fully exposed to insolation. However, humidity seems to control the number of available microhabitats for rare plants. Unlike the flora of rocks in moister areas, where light intensity seems to be the limiting factor (Alves & Kolbek, 1994; Porembski et al., 1994; Porembski, 1996; Fleischmann et al., 1996), moisture regime seems to be the limiting factor in steppe and desert areas. The improved moisture regime in the smooth-faced rock outcrops seems to be "provided" either by higher elevation, which increases the efficiency of the available water (low temperature and so forth), or by the increasing smoothness of the rock outcrops owing to lithologic or geomorphological reasons.

V. Major Refugia in Near Eastern Deserts

For this section I selected a typical transect for each of the desert types in Israel, the Sinai, and Jordan: one in the Negev Highlands, one in the northern Sinai anticlines, one in the southern Sinai granite mountains, one from the rift valley to the Jordanian plateau, and one in the extreme desert of southwestern Jordan. Description of the relationships between the flora and vegetation of the refugia and that of the steppes or deserts around them highlights the special situation of the refugia.


The Nahal Elot site, at one of the highest peaks in the Negev Highlands, was selected because it displays the special features of the relict flora of the highlands and for the questions it raises. The center of the study area, represented in Figures 23 and 24, point II on the transect, is at 36 [degrees] 30 [minutes]E / 32 [degrees]. The vegetation analysis of Nahal Elot (see section III above) was carried out in the vicinity of point III, on the north-facing slope of the Pistacia atlantica-Chiliadenus iphionoides plant community (habitat 2, at the right-hand side of [ILLUSTRATION FOR FIGURE 24 OMITTED]). The vegetation of the Brown Lithosol at that site (Moricando nitensis-Artemisietum sieberi) was sampled at the far north-northeastern side, on bedded limestone. The vegetation of all the edaphic types is discussed by Danin et al. (1975), Danin (1983a), and Danin and Solomeshch (1999). The north-facing rocky slope on peak I is light colored, a result of the epilithic crustose lichens that cover the entire rock surface. The dark area below habitat 2 is a belt dominated by Artemisia sieberi (habitat 3). The high density of shrubs in that belt testifies to the large amount of water that runs off from the smooth-faced rocks and is therefore available to the plants. This north-facing rock outcrop is a real "island of botanical treasures" in the relatively monotonous shrub-steppe dominated by Artemisia sieberi and Moricandia nitens. The phytogeographical analysis of the vegetation recorded in the rock outcrops near peak III is displayed in Figures 22 and 25. The prevalence of the Irano-Turanian chorotype in the rock flora reflects the fact that the rocks are surrounded by shrub-steppes dominated by Irano-Turanian plants. The high percentages of Mediterranean, M-IT, and M-SA species mirror the local amelioration of the moisture regime in the crevices of the smooth-faced rocks. Most of these relative mesophytes are regarded as relicts of moister periods. I discuss below a similar situation in the other refugia presented in Figure 25.

The first prominent feature of the long and wide outcrop of smooth-faced limestone is the presence of seven large Pistacia atlantica trees where the I-II line passes the layer below peak I. P. atlantica specimens vary greatly in form, from a small nonflowering shrub to a large flowering and fruiting tree, depending on the moisture regime of each specific habitat. The way in which the moisture regime affects P. atlantica may be used to explain the form, size, and density of trees in deserts. How much water is available to each plant depends on the mass of substrate associated with the roots (rhizosphere), the size of the catchment area, the annual rainfall, and the amount of water that eventually reaches the rhizosphere. This last factor depends on the properties of the catchment area that contributes runoff. Smooth-faced rock outcrops contribute much more runoff than do most other substrates. Runoff from smooth rocks may begin after the first millimeter of rain. The running water first saturates the soil pockets in the rocks and then, if the rain continues, wets the pediment of the rock outcrop. After strong showers the runoff may reach the wadis. When compared with that of smooth rocks, the "yields" of runoff from stony slopes or slopes with highly fissured rocks is much lower, and heavier showers are needed to initiate runoff. Small catchment areas of stony slopes in the Negev Highlands contribute runoff only after at least 4 to 6 mm of rainfall within a short period of time (Evenari et al., 1982). Large catchment areas contribute runoff only after strong rains of 10 to 15 mm (Shanan et al., 1958). Light showers are much more common than strong showers (Shanan et al., 1967). Thus, in stony slopes, the larger the catchment area the fewer the number of days in which runoff occurs. The following habitats of P. atlantica in the Negev Highlands are listed in order of decreasing frequency of days in which rain causes runoff: crevices in smooth-faced rock outcrops; pediments of rock outcrops; small wadis with smooth rocks in their catchment area; small wadis with stony soil or fissured rocks in their catchment area; and large wadis.

Based on aerial photographs, the size of the catchment area of individual P. atlantica trees was measured (Danin & Orshan, 1970). When measuring the catchment areas, the only tree studied in a given wadi or slope was the one closest to the ridge. The mean area for nine catchments with stony slopes was found to be 250,000 [m.sup.2]; the mean area for seven catchments with smooth-faced rocks, only 1500 [m.sup.2]. This illustrates the superiority of smooth rocks as a habitat for trees in the desert. In addition to about 1400 large trees recorded in the Negev Highlands (Danin & Orshan, 1970), thousands of dwarf P. atlantica plants aged 2 through 150 years were found in small soil pockets and crevices. Their age was found either by counting their annual rings or by estimating the age from the mean width of their annual rings. These findings mean that reproduction of P. atlantica from seeds occurs in the Negev Highlands even today but that conditions for the germination and establishment of seedlings are not everywhere favorable in each year.

Many well-developed P. atlantica trees grow in the large wadis ([ILLUSTRATION FOR FIGURE 24 OMITTED], point II). Their number is higher in wadis that drain areas with smooth-faced limestone outcrops in their catchment. Wadis with only bedded rocks in their catchment hardly support trees.

Rhamnus disperma, which rarely reaches a height of 3 m, is a common shrub companion of P. atlantica in Nahal Elot rock outcrops. It does not grow in the Mediterranean parts of Israel, but it does in many of the smooth-faced rock outcrops represented in Figure 7 for Israel, the Sinai, and Jordan.

In addition to P. atlantica, which grows in the Mediterranean woodlands of the moister parts of the country, a few other woodland species are found at Nahal Elot. Prasium majus is a typical vine of those woodlands. So far fewer than 100 individual plants of this species have been discovered in rock crevices of smooth-faced limestone in the vicinity of Nahal Elot. The closest population of P. majus was recorded about 100 km north of the site, in the southern Judean mountains, or at about the same distance, in Edom. The occurrence of one individual Ephedra foeminea, another typical Mediterranean vine, in rocks in the catchment of Nahal Elot should be accepted in the same context. Both have fleshy diaspores that are dispersed by small birds. They also testify to the former continuity of the Mediterranean woodlands to the Negev Highlands, thus constituting a bridge of dispersal for these short-distance dispersed plants.

Sternbergia clusiana is a typical Mediterranean geophyte found on Mount Meiron, the highest peak in the Upper Galilee, where the mean annual rainfall is 800 mm. It grows in Nahal Elot close to the transect line near peak I, where the mean annual rainfall is 80-100 mm. Having an elaiosom on its seeds, S. clusiana is dispersed by ants and must have had a "dispersal bridge" to cover the long distance in terrain that is now too dry for it to grow in a pattern that may enable ants to transfer it. Astoma seslifolium is another geophyte confined to deep brown soils in the semisteppe bathas at the boundary of the Mediterranean territory. The diaspore is a 1.5 x 2 mm spherical mericarp that does not have any specific way of dispersal except for falling from the mother plant. It is found in many isolated rock outcrops like those illustrated in Figure 8 and thus further indicates that a dispersal bridge once existed from the southern Judean mountains to the Negev. Delphinium ithaburense is another Mediterranean geophyte, less frequent than A. seselifolium, which is dispersed by spherical seeds 2 mm in diameter.

Crepis pterothecoides is an annual relict that grows at Nahal Elot, mainly in habitats 2 and 3 below peak I [ILLUSTRATION FOR FIGURE 24 OMITTED]. The closest population in the Mediterranean part of Israel is the woodlands of the northern Golan, about 320 km north of Nahal Elot. A similar disjunction is represented by Scrophularia xylorrhiza, a perennial chasmophyte with a lignified basis, which grows in cliffy section of habitat 2 below peak l [ILLUSTRATION FOR FIGURES 23 & 24 OMITTED] and in the cliffs of Arbel, by the Sea of Galilee north of Tiberia, 265 km north of Nahal Elot.

Endemic species confined to the Negev Highlands are Ferula negevensis, Origanum ramonense, and Amygdalus ramonensis. The latter two are named after Mount Ramon, the highest peak (1033 m) in the Negev, situated 5 km southeast of the transect [ILLUSTRATION FOR FIGURE 24 OMITTED]. The area in which Ferula negevensis has so far been found is a 15 x 15 [km.sup.2] square, mainly on north-facing slopes of stony-rocky ground. Origanum ramonense is a low chamaephyte that is confined to smooth limestone rocks in the Negev Highlands. It is one of six endemic members of section Campanulaticalyx, found only in the Near East (Danin, 1967b: Iestwaart, 1980; Danin & Kunne, 1996). Its closest relative is O. dayi, which is endemic to the northern and lower part of the Negev Highlands (Danin, 1983a: Fig. 99). Amygdalus ramonensis is another local endemic, with fewer than 200 specimens (Danin, 1980), that grows in crevices of smooth-faced rocks, in the pediment of smooth rock outcrops, and in wadis where with smooth rocks in their catchment area. Browicz and Zohary (1996) regarded this species as synonymous with Amygdalus communis L. subsp. "microphylla (Post) Browicz et D. Zohary; their opinion should be verified by a substantial taxonomic investigation. The closest population of Amygdalus, related in the same way (according to Browicz & Zohary 1996) to A. communis subsp. microphylla, occurs in Israel in the southern Judean mountains, 13 km northwest of Arad and 100 km north-northeast of Nahal Elot.


Gebel Halal, a large anticlinal ridge in the northern Sinai, is surrounded by a desert more extreme than that of the Negev Highlands. Whereas steppes dominated by Irano-Turanian species typify the Negev Highlands, contracted vegetation dominated by Saharo-Arabian species predominates in the gravel plains and sand sheets around most of the Gebel Halal (Danin, 1983a). The vegetation of Gebel Halal is presented [ILLUSTRATION FOR FIGURE 5 OMITTED] by the patch of 11b closest to the Israeli-Egyptian border. A typical transect in this mountain is presented and discussed by Danin (1983a: 57-58). The large areas of smooth-faced limestone outcrops are on the northwestern flanks of the anticline. The smooth outcrops occur on north-facing slopes covered by a continuous crust of epilithic lichens. The prominent feature of one of the tributaries of Wadi Abu Seyal (named after Acacia pachyceras, which grows from the outlet of this wadi to the sandy plains north of the mountain range) is Juniperus phoenicea. These trees grow in three main habitats [ILLUSTRATION FOR FIGURE 26 OMITTED]: crevices and large soil pockets in the smooth-faced limestone outcrop; where the smooth-faced outcrop meets the bedded limestone at its pediment; and in a small wadi that drains the catchment with habitats I and 2. Figure 6 displays a large tree farther down the wadi that is shown in Figure 26. A preliminary study of the annual rings of one of the four trunks of the tree near the number I in the upper center of Figure 26 revealed 862 rings, which make it one of the oldest trees ever studied in the Near East. In contrast, one-year-old seedlings were found in rock crevices. The juvenile leaves of this species are not scale-shaped, like Cupressus leaves, but needle shaped, like Cedrus leaves. As with Pistacia atlantica, there are thousands of small trees that may be a few years to hundreds of years old, as revealed from preliminary ring analysis (Danin, unpubl.).

Several rare companions of the Mediterranean maquis still grow in rock crevices of the smooth-faced rocks in Figure 26. Rare individuals of the Mediterranean vines Ephedra foeminea and of Rubia tenuifolia were found, as were the herbaceous Mediterranean species Asterolinon linum-stellatum and Astoma seselifolium. Another disjunct species is the cliff chasmophyte Rosularia lineata, which has a gap of about 80 km to the population at Nahal Hava, in the Negev Highlands, then 60 km to near Arad, in the northeastern Negev, and then 90 km to eastern Samaria. Several typical desert rock species are shared with the Negev Highlands and southwestern Jordan: Haplophyllum poorei, Dianthus sinaicus, Micromeria sinaica, and Centaurea damascena.

The most prominent botanical feature of the slope in Figure 26 is its being the type locality of the narrow endemic Origanum isthmicum, confined to an area of 5 x 10 [km.sup.2] of Gebel Halal (Danin, 1969). Its closest relative is a narrow endemic of southwestern Jordan, Origanum jordanicum (Danin & Kunne, 1996); the two share several morphological and fragrance features.


Gebel Serbal, the upper (northwestern) patch of 11c on the vegetation map in Figure 5, is surrounded mainly by desert and steppe vegetation. Its five peaks are smooth-faced granite [ILLUSTRATION FOR FIGURE 27 OMITTED] and support rich vegetation. The phytogeographical spectrum of the rock vegetation [ILLUSTRATION FOR FIGURE 25 OMITTED] resembles that of Gebel Halal, where the most frequent chorotype is the Saharo-Arabian. The role of the Irano-Turanian species is lesser, whereas the M and M-IT chorotypes are more frequent. The shrub-steppes on nonrocky ground are dominated by a species of Artemisia from A. herba-alba group. Whether it is A. sieberi, which dominates in the Israeli steppes and eastward, or A. inculta, which dominates in the North African steppes, is not yet clear. A few of the most prominent companions of this Artemisia are Ephedra pachyclada, Atraphaxis spinosa, Tanacetum sinaicum, Centaurea scoparia, Echinops glaberrimus, and Gymnocarpos decander.

The principal relict tree at Gebel Serbal is Pistacia khinjuk, represented by hundreds of specimens, growing mainly on the western escarpments. A few Crataegus sinaicus and Ficus pseudosycomorus trees occur on the northern escarpments and in the valley among the peaks at the top of the mountain. Moringa peregrina, a tropical tree, grows in rock crevices in the lower part of the western escarpments. Of the Mediterranean relicts found in the rock crevices, Scrophularia libanotica represents a group of species that penetrated the Sinai during a cold period. The closest populations are in Mount Hermon, part of the southern Anti-Lebanon Mountains, 530 km away (11c from 9 in [ILLUSTRATION FOR FIGURE 5 OMITTED]). Ballota saxatilis is a Mediterranean relict lithophyte of Gebel Serbal that also grows in the rocks of Wadi Rum and is separated from its closest population in the Mediterranean territory of Israel by 340 km of mainly desert, where it does not grow. Similarly, a relict lithophyte of Gebel Serbal, disjunct by a similar distance but not yet found in Jordan, is Arenaria deflexa. A chasmophyte that represents an almost 300 km disjunction from the Mediterranean bathas is Majorana syriaca. It occurs also as a relict in the vicinity of Nahal Elot, 220 km away from Gebel Serbal.

Many of the endemic species of the Sinai are confined to smooth-faced rock outcrops (Danin, 1978) dominated by Chiliadenus montanus, and at least ten of them are found in Gebel Serbal. The first to be listed is Micromeria serbaliana, named after the first place it was collected. It grows in a few additional peaks in the southern Sinai (Gebel el Deir, Gebel Umm Shomar). Others are Ballota kaiseri, Galium sinaicum (also in southwestern Jordan), Hyoscyamus boveanus, Nepeta septemcrenata, Phlomis aurea, Polygala sinaica, Silene leucophylla, S. odontopetala, S. schimperiana, and Thymus decussatus.


The sandstone and limestone outcrops between Tafila and Ras en Naqb, southwestern Jordan, represent a unique situation in the entire Mediterranean area. It is a gigantic refugium of Mediterranean flora in the transition between desert and shrub-steppe. The occurrence of large outcrops of smooth-faced hard sandstone and limestone at elevations from sea level to 1200 m enabled the long existence of diverse kinds of habitats that supported Mediterranean relicts from periods when the climate was moister. The vegetation map of Jordan, Israel, and the Sinai shows that the climatically controlled belt of Mediterranean woodland vegetation terminates 120-140 km north of Tafila, or some 100 km northwest of it in Israel [ILLUSTRATION FOR FIGURE 1.1 OMITTED]. The west-facing steep escarpment of the Jordanian plateau is associated with considerable environmental changes over a short horizontal distance. A floristic, geomorphological, ecologic, and vegetation transect is presented in section V.D.1. Vegetation diversity in the sandstone and limestone terrain at 1000-1600 m elevation in the Dana-Shoubak area is discussed in section V.D.2. A comparison of the relict trees, shrubs, and vines in the desert refugia of Israel, the Sinai, and Jordan is made in Section V.D.3.

1. A Transect across Southwestern Jordan

The following west-east transect, a simplification of the transect presented by Baierle (1993) and following Kurschner (1986), illustrates plant-soil relationships between the extreme desert of the Arava Valley (Wadi Araba), through the rocky escarpments of the Jordanian plateau, and to the loessial plains and the desert east of Ma'an [ILLUSTRATION FOR FIGURE 28 OMITTED]. In order to include the oak steppe-forest south of Shoubak, the transect is not a straight line. All of the species I recorded in four squares, each 100 [km.sup.2], were used to analyze the floristic changes along the transect. The center of the squares in the geographical grid and the number of species (S) are marked in the abscissa of Figure 29. The percentage of the Saharo-Arabian species (SA) decreases from the Arava Valley along the escarpment and rises again toward Ma'an. The contribution of Irano-Turanian (IT) species rises prominently eastward, and the Mediterranean (M) and M-IT have their peaks in the upper section of the escarpment. The percentage of thermophilous species decreases eastward from its maximum at the vicinity of the Arava Valley.

a. The Arava Sands

The sands of the Arava Valley [ILLUSTRATION FOR FIGURE 28.1 OMITTED] are derived from weathering and disintegration of sandstones in the Jordanian escarpment. They cover, at varying depths, the alluvium that typifies much of the Arava. The persistent vegetation of the sands is dominated by sparse shrubs of Haloxylon persicum, which is occasionally accompanied by Calligonum comosum and Haloxylon salicornicum. In the spring of rainy years the sparse shrubs may be accompanied by dense, colorful carpets of Eremobium aegyptiacum, Anthemis melampodina, Rumex vesicarius, and Plantago cylindrica. The distribution of plants on a sand dune of this area was studied in detail by Jenny and Smettan (1991).

b. The Alluvial Fans Bordering the Arava

Alluvial fans derived from the accumulation of alluvium of the Jordanian plateau at the outlet of large wadis in the Arava Valley typify the foothills below the escarpment of the Jordanian Plateau [ILLUSTRATION FOR FIGURE 28.2 OMITTED]. This landscape is covered by contracted vegetation that resembles the gravel plains of the Arava near Hazeva (Rudich & Danin, 1978). Common dominants of small wadis in the area of Wadi Musa are Anabasis articulata and Haloxylon salicornicum, whereas in larger wadis Acacia raddiana and A. tortilis constitute desert savannoid vegetation. These trees enjoy the underground water and high temperatures of the riff valley. Where the water table is relatively high, the trees are taller and denser than in other places.

c. Vegetation of the Limestone Outcrops

Blocks of fissured limestone at the margins of the Arava Valley are covered with diffused vegetation where the limestone is hard and contracted vegetation where the rock is soft [ILLUSTRATION FOR FIGURE 28.3 OMITTED]. The dominant in both edaphic types is Zygophyllum dumosum, accompanied by Reaumuria hirtella. This kind of vegetation typifies large areas of limestone outcrops in southern Israel and the Sinai.

d. Vegetation of the Magmatic Rock Outcrops

The lower section of the escarpment is built up of magmatic rocks that are covered by sparse, diffused vegetation [ILLUSTRATION FOR FIGURE 28.4 OMITTED]. The dominants here are the Saharo-Arabian semishrubs Anabasis articulata, Agathophora alopecuroides, and Gymnocarpos decander, which are accompanied by very few companions at lower elevations, 200-300 m. At higher elevations plants of the steppes and the rock crevices accompany the dominants in rocky habitats.

e. Diverse Steppe-forests on Sandstone

Hard sandstone is the thickest rock sequence along a considerable part of the escarpment between Tafila and Ras en Naqb [ILLUSTRATION FOR FIGURE 28.5 OMITTED]. The exceptionally mesic moisture regime in crevices of rock outcrops and in wadis is exemplified by the Mediterranean trees, shrubs, and herbaceous plants found here. The following trees and shrubs have been recorded, in decreasing quantity, in these rocks: Quercus calliprinos, Juniperus phoenicea, Pistacia khinjuk, P. atlantica, P. palaestina, Amygdalus korschinskii, Rhamnus lycioides, R. disperma, R. punctata, Daphne linearifolia (endemic), Ceratonia siliqua, Olea europaea, and Arbutus andrachne. Semishrubs and shrubs of Mediterranean origin growing in these rocks are Sarcopoterium spinosum, Fumana thymifolia, F. arabica, Cistus salviifolius, Teucrium capitatum, Calicotome villosa, Ononis natrix, and the root parasites Osyris alba and Thesium bergeri. Plants that function as vines in Mediterranean maquis and grow in these rocks are Rubia tenuifolia, Lonicera etrusca, Ephedra foeminea, Bryonia cretica, B. syriaca. Herbaceous plants of the Mediterranean maquis area that are very rare or not found in other refugia of the Near East are Arena sterilis, Hordeum bulbosum, Aegilops geniculata, and Anchusa strigosa. Many semishrubs are endemic in these rocks, some of which were described recently; these include Origanum petraeum, O. punonense, O. jordanicum, Kickxia petrana, Micromeria danaensis, and Silene danaensis. Many Irano-Turanian semishrubs, which dominate drier habitats of the steppes that surround the sandstone refugium, grow in rock crevices as well: Artemisia sieberi, Astragalus bethlehemiticus, Argyrolobium crotalarioides, and Noaea mucronata. Wherever colluvium or alluvium covers the sandstone outcrop at a depth of more than half a meter, the nature of vegetation totally changes. Layers of such colluvium near the visitors' center of the Dana Nature Reserve are dominated by Artemisia sieberi or Noaea mucronata steppe or a community dominated by Retama raetam and Noaea mucronata. In places closer to the cliffs or rock outcrops there are also semisteppe bathas dominated by Phlomis brachyodon and Sarcopoterium spinosum

f. Juniper Steppe-forest

A steppe-forest, in which Juniperus phoenicea trees are prominent against a background of a steppe of Artemisia sieberi and its companions, occurs in various habitats in the upper section of the escarpment [ILLUSTRATION FOR FIGURE 28.6 OMITTED]. The junipers use habitats in which the water supply seems to be ameliorated in comparison with that in the other soil types (excluding the smooth-faced sandstone). Many junipers are growing on the alluvium-covered, soft sandstone rocks, but none exist in the steppes at sites where the alluvium more than approximately 2-3 m deep. Springs are found in a few places where the soft sandstone is exposed. One such spring is Ain Gaygab, northwest of the Dana visitors' center and east of the Dana campsite, on the steep escarpment at the head of Wadi Dana. This spring is named after Arbutus andrachne ("gaygabkaykab" is its local vernacular name), which grows together with Ceratonia siliqua in the spring water. The many additional small springs along that escarpment can be recognized by the patches of Adiantum capillus-veneris. Many Quercus calliprinos trees grow on this escarpment, together with the junipers. The oak and juniper steppe-forest may indicate a moisture regime that is better than that in the juniper steppe-forest on the escarpments. My preliminary assumption is that the arboreal components of the steppe-forest obtain their water from reserves in the sandstone, reached by the roots, and not necessarily from direct infiltration of rainwater. A unique and somewhat different situation is that in the Cupressus sempervirens reserve between Dana and Buseira. Its substratum is soft sandstones on a gentle, northwest-facing slope where the escarpment is not as steep as it is in Wadi Dana. Some of the C. sempervirens trees [ILLUSTRATION FOR FIGURE 30 OMITTED] are several hundred years old (Dr. A. Bensada, pers. comm.).

Scattered junipers occur also on bedded limestone at the escarpment, even where no soft sandstones exist. Near the road from Tafila to the Dead Sea, such junipers grow in small wadis that look from afar as if they form a diffused pattern and constitute a steppe-forest.

g. Limestone Cliff Vegetation

Cliffs of hard limestone and dolomite also support junipers and other trees, such as Pistacia atlantica [ILLUSTRATION FOR FIGURE 28.7 OMITTED]. This is the main habitat of the endemic shrub Rubia danaensis, a morphological relative of the Mediterranean vine Rubia tenuifolia, which commonly grows on trees in the various refugia of southwestern Jordan. R. danaensis was found in undisturbed habitats only in limestone cliffs. It blooms about a month after Rubia tenuifolia stops flowering, and it does not have the minute, curved appendages on leaves and stems that help Rubia tenuifolia climb trees. The chamaephyte Kickxia petrana and the hemicryptophyte Silene danaensis are also endemic, common to sandstone and limestone cliffs in southwestern Jordan. No less interesting is the isolated population of Hypericum sinaicum, which had been considered endemic to the southern Sinai until it was recently discovered on limestone cliffs near old village of Dana (Danin, 1997). The distance between the disjunct populations is about 270 km. Many species listed for the sandstone portion of the transect grow in this portion as well.

h. Oak Steppe-forest

Most oaks (Quercus calliprinos) that grow in southwestern Jordan and not in the smooth sandstone are found in the following types of steppe-forests. At elevations of 1000-1200 m - at the Dana Nature Reserve, for example - well-developed oaks grow at the foot of limestone cliffs, accompanied by steppe plants. The releves (vegetation records) of this habitat were recorded at the periphery of the Dana Nature Reserve and are probably much influenced by cutting and grazing. The trees may obtain water from deep layers and, as discussed above, may not represent the moisture regime of the surrounding steppe.

The second landscape is the steppe-forest on the hard and fissured limestone south of Shoubak, at elevations of 1500-1600 m [ILLUSTRATION FOR FIGURE 28.8 OMITTED]. Although the area contains the highest places along the top crest of the Jordanian plateau, the oaks do not occur all over it; there is a sharp boundary of the woodland on the road from Shoubak to Petra through the escarpment. The boundary coincides with that of a hard limestone layer that supports the steppe-forest where almost no tree other than Q. calliprinos grows. This oak woodland near Shoubak [ILLUSTRATION FOR FIGURE 31 OMITTED] differs from all other associations dominated by Q. calliprinos in Jordan and Israel in its steppe companions. It is possible that even the Q. calliprinos that grows in southwestern Jordan is not identical physiologically and thus ecologically with that of the more mesic parts of the Near East. The nearly spiny margin, typical in juvenile leaves of seedlings and of stems that sprout from the rootstock of the mesic populations after fires, is found all over the adult trees in southwestern Jordan. The status of this association is further discussed below, in section V.D.2.

i. Atlantic Pistachio Steppe-forest

East of the King's Highway the oaks disappear even on the hard limestone, and an Artemisia sieberi steppe is accompanied by scattered huge and old Pistacia atlantica trees and small Crataegus aronia trees [ILLUSTRATION FOR FIGURE 28.9 OMITTED]. The trees occur mainly in the vicinity of large, smooth-faced rock outcrops. Such rocks could presumably have supported the establishment of tree hundreds of years ago, as they did in Nahal Elot. The endemic shrub Daphne linearifolia and the Irano-Turanian shrub Colutea istria occur here as depauperate, 0.5-1.5-m-tall occasional shrubs "shaped" by overgrazing and cutting. In rock crevices both may reach a height of 3-4 m and look like trees. The way in which the composition of the steppes varies must be investigated further. In such a steppe, from 10 kilometers north of Wadi Musa to Shoubak, at elevation of 1600 m, the following cold-resistant shrubs and semishrubs were noted: Astragalus bethlehemiticus, A. deinacanthus, Argyrolobium crotalarioides, Cerasus microcarpa, and Cotoneaster racemiflorus var. nummularia.

j. Shrub-steppes

A considerable area of a north-south belt, a few kilometers wide and east of the scattered trees discussed in section V.D.1.g, is dominated by Artemisia sieberi, Noaea mucronata, and their companions on stony soils. Loessial soils in this area are dominated by the xerohalophytes Anabasis syriaca and Peganum harmala. The grazing and cutting pressure in this area is rather great, so it is difficult to discover additional species except during the spring in rainy years.

k. Contracted Desert Vegetation

The desert south of Ma'an and toward the Saudi Arabian border becomes an extreme desert as one moves southward. A few kilometers south of Ma'an the vegetation of the gravel plains becomes restricted to wadis, where the dominant plants are the semishrubs Anabasis articulata and Gymnocarpos decander. The trees that grow in higher-order wadis are Acacia pachyceras, the most cold-resistant species of the three acacia species of savannoid desert vegetation in Israel and the Sinai.

2. Analysis of Three Associations in the Dana-Shoubak Area

The three most significant tree-supporting plant communities in southwestern Jordan were discussed above, in sections V.D.1.e, V.D.1.g, and V.D.1.h. Full vegetation records, each on 10 x 10 [m.sup.2] were recorded on 13-14 May 1996: for the Polygala negevensis-Juniperus phoenicea plant community, 9 releves on the sandstone outcrops 300 m southwest of the forester's station, elevation 1100-1200 m; for the Achillea aleppica-Juniperus phoenicea plant community, 9 releves on limestone outcrops above and 400 m north of the Dana Nature Reserve visitors' center, elevation 1100-1300 m; and for the Artemisia sieberi-Quercus calliprinos plant community, 8 releves on fissured limestone at Jebel Umm Suwana, elevation 1600 m. The names used for these associations were not published in a legitimate manner according to the Code of Phytosociological Nomenclature (Barkman et al., 1986); describing them legitimately is beyond the scope of this paper. The summary of the three association tables is presented in Table IV, where the percentage of presence of each species in the releves of each plant community are presented. The species are listed in alphabetical order within each of the two basic growth-form groups: persistents, or those with active organs that remain aboveground all year long (mainly phanerophytes and chamaephytes); and ephemerals, or [TABULAR DATA FOR TABLE IV OMITTED] those that shed their aboveground parts during the harsh season (therophytes and most hemicryptophytes and geophytes).

a. Polygalo negevensis-Juniperetum phoenicei

The number of species in this association is 120:80 persistent species, 10 of which are trees or shrubs, and 40 ephemeral species. The phytogeographical analysis of the list of species [ILLUSTRATION FOR FIGURE 32 OMITTED] reveals the prevalence of the Mediterranean chorotype. The second in importance is the Irano-Turanian, and the third is M-IT. Of the 9 endemic species in the vegetation records of the present study, 6 occur in this association.

b. Achilleo aleppici-Juniperetum phoenicei

The number of species in this association is 106:69 persistent species, 7 of which are trees or shrubs, and 37 ephemeral species. The phytogeographical spectrum of this association strongly resembles the Polygalo negevensis-Juniperetum phoenicei association. Of the 9 endemic species in Table IV, 4 occur in this association.

c. Artemisio sieberi-Quercetum calliprini

The number of species in this association is 34:24 persistent species, 5 of which are trees or shrubs, and 10 ephemeral species. The phytogeographical spectrum of this association differs from that of the two previous ones by the prevalence of the Irano-Turanian chorotype. There are 9 differential species (26.5%) that occur in this association but are absent in the other associations. Most of these differentials are steppe plants; none is a Mediterranean woodland species. None of the 9 endemic species listed in Table IV occurs in this association.

d. If a Long and Continuous Drought Begins

Only three Arbutus andrachne trees remain in southwestern Jordan (Danin & Hedge, 1998): two at springs in the Dana Nature Reserve and one, in Jebel Bayda, in sandstone like that found in the Polygalo negevensis-Juniperetum phoenicei association. The bedouin who showed me the latter tree, Mr. Haroun Jamada, knows that it is the only tree in that area but does not know its name. The bedouin who live in the surrounding environment know a great deal about the local flora, so Haroun's statement means that it is the only individual tree that has existed there for two or more generations. He also showed me a spontaneous olive tree (Olea europaea) in the same area. These observations, the large number of trees and shrubs, the endemic species, and the high percentages of Mediterranean species in the phytogeographical spectrum of the Polygalo negevensis-Juniperetum phoenicei association indicate that the survival value of mesophytic plants is higher in this habitat than in the other habitats. I observed dead juniper trees in the Dana Nature Reserve on colluvium covering soft or hard sandstone. I assume that because these trees are not supplied in rock crevices by large water-contributing rock outcrops, their water supply may drop to limiting levels in drought years. I have seen many dead juniper trees in Gebel Halal, in habitats that are not rich in outcrops of smooth-faced limestone. Because the oak steppe-forest in the Artemisio sieberi-Quercetum calliprini association has developed at high elevations, which receive more rainfall than do areas at lower elevations, the oaks could easily die in a period when the total rainfall drops. However, the same species will continue to survive in the rocky habitat of the sandstone in the Polygalo negevensis-Juniperetum phoenicei association, even when the quantity of rainfall decreases. An example of this is the last Arbutus andrachne, which lives with less than 200 mm of annual rainfall in a sandstone crevice in Jebel Bayda, whereas the closest trees of this species live with 500-600 mm of annual rainfall in northern Jordan and the Judean mountains of Israel.

3. A Comparison of the Relict Trees, Shrubs, and Vines in Near Eastern Desert Refugia

The refugia discussed above differ in the amount of relict Mediterranean species that have survived in them. Their relative efficiency as refugia can be demonstrated by the number of drought-sensitive species they harbor. The record presented in Table V considers the total area of refugia in Israel, the Sinai, and Jordan. A rough estimation of the relative efficiency of the refugia can be calculated by comparing the number of x and/or + signs in each area. Those in Israel amount to 24.2 percent and those of the Sinai to 27.4 percent of the marks for Jordan. This comparison is only qualitative, in values of presence or absence; quantitative analysis of the vegetation could reveal much greater differences. Although Israel and the Sinai experienced the same climatic fluctuations as did Jordan, neither of them has areas of potential refugia as large as those in Jordan.


Wadi Rum is situated in an area of extreme desert. The wide valleys among the mountain peaks west of the wadi are covered with poor contracted vegetation dominated by the Saharo-Arabian Anabasis articulata and Haloxylon salicornicum, with scattered Acacia tortilis and Acacia raddiana trees. East of the Precambrian crystalline rock terrain [ILLUSTRATION FOR FIGURE 33 OMITTED] are mountains with peaks of sandstone. In these areas and near Wadi Rum, among the sandstone hills, sand covers or is mixed with alluvium. Haloxylon salicornicum and Anabasis articulata are the dominants here as well, but the wadis are not as prominent as they are in nonsandy areas. Local sites where mobile and deep sand is available are dominated by Haloxylon persicum. The number of companions in these valleys is low, even in rainy years. The most interesting ecological feature of this area is the layer of the contact zone between the sandstone and the magmatic rocks; this layer marks the Cambrian peneplain. This special habitat supports Mediterranean species, some of which may be regarded as relicts (Barsotti & Cavalli, 1989). The plants near the small springs are unexpectedly rather similar to springs in the middle of the Mediterranean territory of Israel or Jordan: Dittrichia (Inula) viscosa, Samolus valerandi, Saccharum ravennae, Cynodon dactylon, and Nasturtium officinale. These can be dispersed over a long distance, but it is rather surprising to find them so far from the Mediterranean region in the extreme desert. The smooth-faced sandstones above the contact with the Precambrian rocks support relicts like those in the Ras en Naqb-Tafila area, but in smaller quantities. In addition to a few Juniperus phoenicea I observed, Barsotti and Cavalli (1989) report finding one Olea europea tree. Additional Mediterranean relicts in the rock crevices are Galium incanum, Rubia tenuifolia, Ephedra foeminea, Ononis natrix, Ballota saxatilis, Hyoscyamus aureus, Piptatherum miliaceum, and Urginea maritima. The endemic Jordanian [TABULAR DATA FOR TABLE V OMITTED] new species Silene danaensis and Satureja nabateorum (Danin & Hedge, 1998) were collected in this area as well. In this extremely dry Saharo-Arabian desert even the occurrence of such Irano-Turanian plants as Noaea mucronata, Colutea istria, and Bituminaria flaccida is worth mentioning. I regard these plants as relicts of the invasion of mesophytes into the extreme desert.

VI. Concluding Remarks


I assume here that the populations of oak and juniper in southwestern Jordan should be regarded as a kind of metapopulation in the way determined by Hanski and Gilpin (1991). I wish to apply this model to the arboreal components of southwestern Jordan on a local basis but not to the overall distribution. Following the above model, the "source populations" (sensu Hanski & Gilpin, 1991; Simberloff, 1996) of the oak and of the juniper are those of the sandstone [ILLUSTRATION FOR FIGURE 28.5 OMITTED]. The populations of the oak in the steppe-forest [ILLUSTRATION FOR FIGURE 28.8 OMITTED] and those of the juniper [ILLUSTRATION FOR FIGURE 28.6 OMITTED] fit the "sink populations." The size of the source populations remains constant over time. It is rather difficult to find dead oak or juniper trees in the source areas. Many seedlings of varying ages are found there. However, the sink populations or the extensions expand and contract according to climatic fluctuations. One can see evidence for that in tree deaths, which can occur in high numbers where the habitat is not large, smooth-faced rock outcrops. I observed dead junipers in various places in the Dana Nature Reserve and at Gebel Halal. Other species of the Mediterranean assemblage of relicts in the steppe bioclimatic zone of southwestern Jordan are so sensitive to dry habitats that they are found in that region only in the source populations; that is, in the sandstone or limestone refugia. Hence, the narrow endemic species of the limestone cliffs, Rubia danaensis, is found in a local sink population of the roadside near the ancient castle at Shoubak, owing to the runoff contributed by the asphalt road and the destruction of its natural competitors at the roadside. Peltaria angustifolia is a perennial herbaceous plant of the northern Golan and Hermon grasslands. It grows in crevices of sandstone near Dana village [ILLUSTRATION FOR FIGURE 28.6 OMITTED] in a source population and, occasionally, as a weed in the irrigated fields of Dana village, in human-disturbed habitat. These extensions should be regarded as sink populations.


Climatic oscillations in Africa left their impression on the flora and vegetation of mountains where smooth-faced rocks occur, in a similar way to that discussed above for the Near East. The profound investigations in the high central Saharan mountains (Maire 1933, 1940; Quezel, 1965; White, 1983; Le Houerou 1995) enable evaluation of the similarities in the flora and processes that took place in the evolutionary history of the two areas.

1. Climatic Changes in Africa and Relicts in the Central Saharan Mountains

In his comprehensive review of the vegetation of the Sahara, Quezel (1965) notes that, at elevations above 1800 m, special vegetation rich in endemics and Mediterranean flora exists. Our model of the penetration of Mediterranean flora into the desert and of the existence, in rocky refugia, of relict and endemic species related to Mediterranean ones repeats itself. A wet period, termed "interpluvial" (Quezel & Martinez 1961), prevailed in the central Sahara between 12,000 and 4800 years ago. Pollen grains of Pinus halepensis, Quercus ilex, Juniperus phoenicea, J. oxycedrus, Olea laperrinii, Cupressus duprezziana, and Cedrus atlantica, found at various locations in the Jebel Ahaggar area, are examples of the flora that grew in that vicinity before it turned into an extreme desert. Many taxa that can be regarded as relicts similar or identical to those in Jordan, the Sinai, and Israel occur in the central Saharan mountains. However, the distances of disjunction of the Saharan mountains from the Mediterranean coast are one order of magnitude larger than those of the Near East. The Ahaggar mountains are 1400 km south of the Mediterranean coast; the Tibesti mountains, 1900 km south; and the Air mountains, 2000 km south. Olea laperrinii, an endemic related to the Mediterranean Olea europaea, occurs in the Ahaggar and Air mountains; and Myrtus nivelli, an endemic related to the Mediterranean Myrtus communis, occurs at the Ahaggar and Tibesti mountains (Maire 1933, 1940; Quezel 1965). Olea laperrinii grows, together with Rhus tripartita and Atriplex halimus, in granite outcrops at high elevations (Maire, 1940). Cupressus duprezziana is a central Saharan endemic species related to the Mediterranean Cupressus sempervirens, found living in Tibesti mountains and, as dead trunks and pollen grains, in the Ahaggar mountains (Quezel & Martinez, 1961; Quezel 1965). A few additional interesting Mediterranean or Irano-Turanian relicts in these mountains are: Clematis flammula, Conyza stricta, Nerium oleander, Osyris alba, Piptatherum miliaceum, P. blancheanum, Pistacia atlantica, Rhus tripartita. Some of the latter are common to the sandstone refugium of southwestern Jordan. The central Saharan mountains harbor relicts from additional floristic regions in a similar way to those in the Near Eastern refugia.

Climatic changes and the shifting of climatic belts in Africa during the past 20,000 years are presented by Wickens (1975, 1976) for the Sudan. The climate in that area was very dry between 20,000 and 15,000 years B.P., and the rainfall belts were 450 km south of where they are now. Between 12,000 and 4500 B.P. it was wet, and the rainfall belts were 400 km north of their present location. Between 6000 and 4000 B.P. the rainfall belts shifted 250 km north of where they are now. The present-day conditions prevailed for the past 2000 years. In addition to the changes in the Sudan, Wickens (1976: 56-57) portrays the climatic changes in several areas of Africa and Europe over the past 33,000 years.

In conclusion, climatic oscillations that could cause Mediterranean plants to shift into areas that are now extreme deserts are well documented for northern and central Africa. Similarly, documented climatic fluctuations in the Near East seem to have caused a shift of climatic belts that left Mediterranean relicts in deserts.

2. Climatic Oscillations in the Near East since the Pleistocene

A wealth of literature reports oscillations of climatic conditions in the Near East over the past million years. An excellent "climate gauge" in the study area is the Dead Sea and Lisan Lake (Neev & Emery, 1967; Begin et al., 1974). Its watershed includes considerable parts of districts 1-12 and 18 [ILLUSTRATION FOR FIGURE 1 OMITTED]. The fluctuations of its level, as recorded directly in the present century, was correlated with the amount of rainfall (Klein, 1981) and became a tool for evaluating the past climates in the area. Sedimentary rocks are used to investigate the extent of the climatic record provided by the lake for older periods. Finding conglomerates at the lowest portions of the Dead Sea and Lisan Lake prove that a climate much drier than that of the present enabled wadis to carry pebbles to an area that was otherwise covered with lake water (Neev & Emery, 1967). However, finding freshwater sediments at a level of approximately 220 m above the present level of the Dead Sea prove that the existence of a period wetter than that of today.

I do not claim an exact correlation between these oscillations and the distribution of one or another plant species. Rather, I wish to present some examples of climatic changes during the past 780,000 years in the Near East. Wet periods could have allowed mesophytic taxa to penetrate into the desert, and dry periods could have destroyed the mesophytic components that grow outside the refugia. Periods wetter than today's were recorded in Gesher Benot Yaakov excavations, the Upper Jordan Valley, from approximately 780,000 years ago (Prof. N. Goren-Inbar, pers. comm.). Climatic fluctuations in the level of the Samra Lake, which preceded Lisan Lake and existed between 350,000 and 63,000 B.P., are discussed by Kaufman et al. (1992). Alternating wet and dry periods were recorded at Lake Lisan, the precursor of the Dead Sea (Neev & Emery, 1967), from 100,000 to 10,000 B.P. Between 100,000 and 70,000 B.P. it was mostly dry; between 70,000 and 20,000 B.P., wet ("pluvial"); and after 10,000 B.P. became mostly dry. Begin et al. (1974) also studied that area. The dating of Lisan Lake by Kaufman et al. (1992) is from 63,000 to 18,000 B.P. Pluvial records for the northern Golan, drawn from pollen diagrams at Birkat Ram (Horowitz, 1979), suggest the following climatic fluctuations when compared with the present climate: from 50,000 to 45,000 B.P., cool and very humid; from 45,000 to 32,000-28,000 B.P., warm and humid; and from 28,000 to 22,000 B.P., cold and humid. Accurate measurements and new dating techniques used to analyze cave deposits derived from 20 km west of Jerusalem have enabled Bar-Matthews et al. (1997) to estimate mean annual rainfall (P) and temperature (T) over the past 25,000 years. At present, P = 500 mm and T = 18 [degrees]-20 [degrees] C. The Glacial period, 25,000-17,000 B.P., was colder and drier: T = 12 [degrees] -16 [degrees] C and P = 250-400 mm. The rest of their data are presented in Table VI. Tchernov (1998) indicates that the climatic regime changed between 12,000 and 9000 B.P. He adds that during the period between 10,000 and 8000 B.P. the area could have enjoyed a significant amount of summer rainfall, as all the faunal assemblages from excavations of that period clearly indicate.

As discovered in the central Saharan investigations, pollen grains from the Negev Highlands from about 11,000-8000 B.P. (Horowitz, 1976, 1992) are of Quercus, Cupressus, Olea, Pistacia, and Amygdalus trees. Only individuals of the latter two species grow there at present. Two additional extinct species that grew in the Negev Highlands at the end of the Pleistocene are Juniperus and Paliurus, judging from archaeological charred wood remains (Baruch & Goring-Morris, 1997). In his reconstruction of the pluvial vegetation zones of Israel from pollen data, Horowitz (1992: 380) draws a continuous Mediterranean oak forest, all along the Jordanian Plateau to as far south as Ras en Naqb, but without information on the sources.


In Near Eastern deserts, outcrops of smooth-faced rocks function as refugia for plants that do not fit the present local climate, plants that have survived from periods when the continuous extensions of moister climate allowed them to penetrate from the Mediterranean zone.


The Near Eastern model repeats that of the northern and central Sahara, where a moister climate dozens of thousands of years ago, permitted the growth of Mediterranean species of Quercus, Pinus, Cedrus, Olea, and Juniperus. Desiccation of the climate has left relicts and endemic species in the high central Saharan mountains more than 1500 km south of the Mediterranean coast.

A similar situation, but with a 100-300 km disjunction distance, is that of the refugia in the Near East. Periods with a climate moister than today's have been recorded in many geological investigations. The isolated Mediterranean relicts in small refugia in the deserts of Israel and the Sinai were reported in the past. In this article I claim that the entire flora of the sandstone outcrops of southwestern Jordan should be regarded as an assemblage of many Mediterranean relicts and narrow Edom endemics. These remained in the large outcrops of smooth-faced sandstone and limestone that function as an efficient refugium for many components of the rich Mediterranean flora. Plants that play diverse roles in the vegetation of the Mediterranean territory grow here sympatrically as relicts, surviving in the refugium. A few components, such as oaks and junipers, succeed under the present climatic conditions in having extended populations in additional habitats that enable the growth of only a few Mediterranean companions. These trees, together with the shrub-steppe species, constitute the steppe-forests. It is assumed that trunks of dead trees in these stands indicate their temporary nature as opposed to the more permanent status of the oaks and junipers in the sandstone refugia. Most endemic species in the desert areas of the Near East are confined to the refugia of the smooth-faced rock outcrops.

VII. Acknowledgments

I dedicate this article to my wife, Drora, who more than 30 years ago began to assist me in my work on these rocks and plants - and has never stopped. I thank all my students and colleagues whose questions and interest promoted my search for answers concerning relicts in the desert. I thank Prof. N. Goren-Inbar for information on her excavations in the Upper Jordan Valley and Prof. E. Tchernov for sharing with me his "in press" manuscript. I thank Mr. P. Grosmann for drawing most of the illustrations and Mrs. Tamar Soffer for preparing the vegetation map and a few other maps; Prof. U. Motro for his help with methodological and statistical issues; Dr. Ilana Hernnstadt, who determined the mosses; Prof. Dr. A. Henssen for determining Lichenothelia intertexta; and Mr. H. Seligmann for translating the abstract into French. I thank the staff of the Royal Society for Conservation of Nature in Jordan for helping me during my fieldwork at the Dana and Wadi Mujib Nature Reserves, especially Dr. A. Bensada and Mr. T. M. Abul Hawa, director of the Dana Nature Reserve.

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Date:Apr 1, 1999
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