The temperate and subtropical evergreen broadleaf forests and similar forests.
Man'en gannen no futtoboru (1967)
1 All shades of green
1. Relict climates, scattered biomes
1.1 A small and fragmented biome
What is a rainforest? When people think of a rainforest, they think of a tropical rainforest. Yet lush rainforests--the temperate rainforests--occur in regions far from the equator. Though they are not as rich in species as the tropical rainforests, the structure, outward appearance, complexity, and diversity of the temperate rainforests and the highly specialized adaptations and interactions of the species living there mean that the rainforests are more like the tropical rainforests than any other forests.
Fragmented and scattered
The characteristics of the planet's different biomes depend on their climate, soil conditions, and history. Other ecological factors may be decisive in the biome's development and its dynamics and heterogeneity in both space and time. These factors include disturbances, natural or anthropogenic, the relief and the interactions between the individuals of different species. Thus, in each region of the planet, ecological factors act as a filter selecting certain species from the local possibilities. Those that manage to survive over the course of history will form the regional flora or fauna (biota) of each zone. Thus, history is an important ecological factor. The current distribution of the temperate rainforests can only be understood in terms of their ecology and their history.
The temperate rainforests form a geographically dispersed biome, split into many fragments in regions that are far apart. In comparison with other biomes, such as the tropical rainforests or the boreal forest, the temperate rainforests do not cover a large area. Temperate rainforests are present in every continent and have a different evolutionary history. All these factors have led to the formation of a biome with a high diversity of species and plant formations.
The temperate rainforests are found in climates with mild temperatures, without dramatic changes, and where the relatively high rainfall is evenly distributed throughout the year. Obviously, outside the equatorial area, these conditions only occur in a few specific regions of the planet, where special wind patterns bring rain-laden winds that moderate extreme temperatures.
Temperate rainforests occur in the wet subtropical areas under the influence of the trade winds and the monsoons and in the rainy temperate zones under the influence of maritime winds from the west. The temperate rainforests either occur on islands or in coastal areas subject to maritime winds, on the eastern coastlines in the case of the subtropical areas influenced by the trade winds and monsoons, and on the western coastlines in the temperate areas. The main feature of their climate is that frosts and dry periods are almost totally absent, although differences between seasons may be quite significant.
A tropical origin in the remote past
The flora of each of the temperate rainforests belongs to the floristic region in which the rainforest is located. These floras include a noteworthy contingent of tropical species. These tropical species include tree ferns in New Zealand, palms and epiphytic bromeliads (Tillandsia usneoides) in the southeastern United States and in southeast Brazil, bamboos of the genus Chusquea in Chile and Brazil, species of Persea in Macaronesia, in North America, in the Sino-Japanese forests, etc. This characteristic, and others mentioned in the following paragraphs, suggest that the temperate rainforests are all of tropical-subtropical origin. In general, all forests can be derived from the primitive tropical rainforest.
However, the temperate evergreen broadleaf rainforests are remarkable because they are almost a tropical rainforest, but are located outside the tropics. The high temperatures, without sharp changes, have played a very important role over the history of the redistribution of the plant species and in their adaptations. It is no coincidence that the contemporary forests most similar to the forests of the mid-Tertiary period are located in areas with mild wet climates. This mild wet climate has remained unchanged in some areas for millions of years. This has favored the persistence of ancient floras in a few scattered areas, where some of the most ancient forms of conifers have also survived as relicts.
Many genera and families of plants now present in the temperate rainforests were very important in the Tertiary forests, as shown by the fossil record. However, the species are different because of their different evolutionary histories. Comparing the floras of the temperate rainforests, their affinities show that they have a common geographical origin but have evolved separately.
The temperate rainforests contain many paleoendemic species. These are relict species, isolated due to the extinction of their close relatives, and they usually have a very restricted distribution. This is shown by the relict species of podocarps (Podocarpaceae), the conifers in the temperate forests of the Southern Hemisphere, and the swamp cypress or bald cypress (Taxodium distichum) in the southeastern United States.
The limited influence of the glaciations
Some aspects of the appearance of the temperate rainforests reflect the fact that they arose in the tropical climatic conditions which prevailed until the mid-Tertiary. They can be considered relicts of a Tertiary forest that was much richer in species. The high diversity of species and their highly specialized interactions show us that the forests have evolved continuously under climates that we can also consider relicts, as they have remained more or less unchanged for millions of years.
In fact, apart from those located in areas at higher latitudes or altitudes, the temperate rainforests were almost unaffected by the Quaternary glaciations. The Valdivian forest, for example, was not drastically affected by the glaciations and was a refugium for many species. During the glaciations, ice covered the entire Andes to 44[degrees]S, and the eastern half of Chiloe Island, but at lower latitudes, the glaciers only covered the higher parts of the mountains. The fact that the Andes run north-south made it easier for plant species to migrate. The Valdivian zone was a shelter for many species that escaped the Pleistocene glaciations by migrating to lower, warmer, latitudes and acted as a refugium for many of these species.
Something similar happened in the Vancouverian forests, the temperate forests of northwest North America. The glaciations played an important geological role at the higher altitudes of the mountain ranges running from Alaska to Oregon. In the Pleistocene, the ice reached the south of Puget Sound, where Seattle, Washington, is located. However, temperate rainforest has been present in this region for at least two million years, and it contains vegetation that has changed little since the Mesozoic. The last glaciation, which only ended in southern Alaska about 4,000 years ago, scarcely reduced the biodiversity of these forests thanks to the existence of migration routes and numerous refugia. Some plant species are still dispersing from these refugia, and only recently reached the current northern limits of their range, such as the western red cedar or giant arborvitae (Thuja plicata) or the Nootka or yellow cedar (Chamaecyparis nootkatensis).
Many regions of New Zealand have river terraces, u-shaped glacial valleys, and alluvial plains left by the last period of glaciation, which was at its peak about 25,000 years ago and ended less than 15,000 years ago. There are still glaciers in the Southern Alps in New Zealand [the largest of them, the Tasman Glacier, is 18 mi (29 km) long]. Yet this isolated archipelago in the southern Pacific Ocean experienced a fall in temperatures of 7.2-10.8[degrees]F (4-6[degrees]C) during the last glaciation.
A similar drop of 7.2-9[degrees]F (4-5[degrees]C) occurred in Macaronesia (the Canary Islands, Azores, and Madeira). This is why species and entire communities from the Tertiary have survived there. Many fossils found in North Africa and in southern Europe belong to species that have now disappeared from both Europe and Africa and have only managed to survive in Macaronesia. Nowhere else in Africa or Europe have they survived, so the Macaronesian flora is of enormous biogeographical and ecological importance.
The high percentage of endemic species (for example, 81.1% of the flora of New Zealand, 46.6% of that of the Canary Islands, and 34.1% of that of Japan) shows these temperate forests have evolved independently. Even so, the temperate forests contain floristic elements very different from each other, which are the result of their geographical location. After the repeated fragmentation of continents, Laurasia and Gondwana, the different continents and islands separated, and their floras and faunas evolved independently. For example, the southern beeches (Nothofagus, Fagaceae) are characteristic of the temperate forests of the Southern Hemisphere, while evergreen and deciduous oaks (Quercus), and other genera of the beech family (Fagaceae), are typical of those in the Northern Hemisphere. Some of the main components of some temperate rainforests seem out of place in the local climate, such as the coniferous rainforest on the northwest coastline of North America.
1.2 Plate tectonics, the engine of history
The temperate rainforest biome is very complex, and the contribution of geographical and historical factors to this complexity makes its interpretation difficult and controversial. In the mid-nineteenth century, Joseph D. Hooker, Charles Darwin, and Alfred Russell Wallace argued over how to interpret the present distribution of species; why are they where they are? and how did they get there? A century later, the natural sciences have two fully accepted unifying theories: plate tectonics and evolution by natural selection, a framework in which to order field observations and to pose new questions.
Continental drift and the resilience of the flora
When the great continent Gondwana began to split in the early Jurassic, gymnosperms totally dominated the forests. Species of Araucaria (Araucariaceae) were cosmopolitan. Ginkgo spp. (Ginkgoaceae) were abundant in the Northern Hemisphere and podocarps (Podocarpus, Podocarpaceae) were abundant in the Southern Hemisphere. The first split created two supercontinents, Laurasia, consisting of what is now North America and Eurasia (except India), and Gondwana, consisting of what is now Africa, South America, India, Australia and Antarctica. Later, both supercontinents split again, and the pieces drifted apart (see vol. 1, pp. 40-41).
The climate during the Cretaceous period (118-105 million years ago) and the early Tertiary period was relatively hot. The temperature gradient toward the higher latitudes was gentle, and climatic zoning was not sharply defined, though there was a tropical zone (between 30[degrees]N and 30[degrees]S), a temperate zone and a smaller zone with a relatively dry climate, sandwiched between these two other zones in the western areas of the continents, at around 30[degrees]N and 30[degrees]S. The records of oxygen isotopes, pollen, and fossil plant remains indicate that the climate was also very wet. In this period, there were no steppes, deserts, or polar icecaps. The continents were very flat, and the average elevation of the land was much lower than today. There were no major geographical barriers, so the biota could disperse to relatively high latitudes, where the climate was free of frost.
In these environmental conditions, during the lower-middle Cretaceous, the angiosperms started their rapid evolution on Laurasia and Gondwana. The fossil record also shows that the high-latitude floras of the Northern and Southern Hemispheres were already quite different when they first appeared in the Cretaceous. Fifty million years later, in the early Tertiary period, there was an extraordinary diversity of flowering plants. The angiosperms marginalized the gymnosperms and pteridophytes, yet their rise and diversification is not related to any dramatic climate changes.
The dominant wet temperate climate favored the growth of extensive tropical and subtropical forests of angiosperms until well into the Miocene. In both hemispheres, there were representatives of a pan-tropical Arcto-Tertiary flora in which many families were abundant, such as the Lauraceae (Laurus, Persea, Machilus, Cinnamomum); Anacardiaceae (Rhus, Pistacia); Theaceae (Camellia); Moraceae (Celtis, Morus, Brousonnetia); Hamamelidaceae (Hamamelis, Liquidambar); Aquifoliaceae (Ilex); Ericaceae (Arbutus, Gaulteria); Fagaceae (Castanea, Fagus, Nothofagus, Castanopsis, Lithocarpus, Quercus); Fabaceae (Albizia, Acacia, Robinia, Cercis); and Saxifragaceae (Ribes, Hydrangea). Other tropical families that spread to the extratropical latitudes in the Northern Hemisphere included the Magnoliaceae (Liriodendron, Magnolia); Tetracentraceae (Tetra-centron); Juglandaceae (Carya, Engelhardia [=Engel-hardtia], Juglans); and Hippocastanaceae (Aesculus). The families of extratropical origin that spread throughout the temperate and cold temperate zones of the Northern Hemisphere included the Betulaceae, Platanaceae, and Trochodendraceae. Other families had a tropical and temperate distribution in the Southern Hemisphere, such as the Myrtaceae, Winteraceae, and Proteaceae. In the Southern Hemisphere, the typical components of the forests included conifers, such as members of the Podocarpaceae (Podocarpus, Saxegothea), and Araucari-aceae (Araucaria, Agathis, etc.).
However, this flora started to fragment and was restricted to marginal areas by geological and climatic factors. The mid-Tertiary saw the onset of the slow general cooling that culminated in the glaciations of the Quaternary (the last 1.6 million years). Temperatures started to fall sharply at the end of the Oligocene (about 25 million years ago). The major alpine orogenies (the rising of the Alps, Pyrenees, Himalayas, Andes, Rockies) ended in the Miocene, Pliocene, and Pleistocene. This substantially changed atmospheric circulation and the climate of the areas they influenced. During this period, some large water bodies, such as the Mediterranean Sea, dried up, and the climate became increasingly continental. All of this had enormous repercussions for the flora. The appearance of climatic and geological barriers encouraged geographical vicariance (fragmentation of the environment) in many elements of the Arcto-Tertiary flora and meant that their distributions became discontinuous.
The cooler climate caused the flora to retreat to lower latitudes and almost all the tropical and many thermophilic species (organisms growing at high temperatures) of the Arcto-Tertiary flora that could not find a refugium became extinct. In Europe, the fact that the mountain chains and the Mediterranean basin run east-west was an obstacle to north-south migration This is one of the main reasons why Europe's flora has less Arcto-Tertiary elements than that of North America or of eastern Asia. The discontinuous areas of distribution of many floristic elements, such as beeches (Fagus), magnolias (Magnolia), hemlocks (Tsuga), witch hazels (Hamamelis), or the only two species of the genus Apollonias, are signs of the progressive retreat of the Arcto-Tertiary flora that culminated in the Pleistocene, as are the distribution of relict endemic species, such as the maidenhair tree (Ginkgo biloba) or the bald cypresses (Taxodium).
During the Quaternary, there have been 24 glaciations, and temperatures have been, on average, much lower than in the Tertiary. In the glacial phases, large ice masses accumulated at high latitudes and on mountains. These ice ages ended abruptly and were followed by shorter interglacial periods, 10,000-20,000 years long. The rise and fall of the glaciations was accompanied by the beginning of the formation of the large desert zones in both hemispheres on the edge of the tropical zone. This divided the primitive forests into areas to the north and to the south of the tropics (see also vol. 1, pp. 62-65).
The most drastic changes in the distribution of the vegetation took place in the Pleistocene. The tropical rainforests were compressed toward the equator, and the subtropical vegetation dominated by Arcto-Tertiary elements only survived in the areas that did not undergo dramatic climatic changes (refugia). The tundra spread, and there was a general retreat of the forests. Many Tertiary species became extinct, and new species arose by hybridization and polyploidy. In general, there was a migration of species toward the equator in the glacial periods and away from it in the interglacial periods. As a consequence of the advances and retreats of the ice, the floristic components that could not resist the low temperatures died out over most of their range.
The decisive role of mountain formation
In Europe, as previously stated, the east-west alignment of the mountain ranges and the Mediterranean basin prevented the species from migrating north-south, as did the arid regions of the Sahara. Even so, some floristic element, such as oaks (Quercus), extended their areas of distribution by spreading into the tropics, though they did reach as far as the temperate forests of the Southern Hemisphere. The Arcto-Tertiary flora was restricted to refugia. Thus, for example, some species in Europe and southwest Asia, such as the Serbian spruce (Picea omorika) were restricted to the Balkans and the shores of the Black Sea and Caspian Sea. Macaronesia was one of the best refugia for many elements of the Arcto-Tertiary flora. These islands conserve many relict communities that combine elements of this flora with many elements from other floristic regions whose distributions are now discontinuous, such as the genus Apollonias, which has two species: the Canary ebony (A. barbujana) in the Canary Islands and another species in India. At the other end of the area of the Mediterranean basin in the broadest sense [the northeastern shoreline of the Black Sea and the southwestern shoreline of the Caspian Sea (see p. 46)], Arcto-Tertiary elements have also survived, though they form part of a flora that has undergone much greater modification.
India had a tropical vegetation in the early Cenozoic (65 million years ago), when the Himalayas started to form. The Indian landmass separated from southeast Africa and moved toward southern China at a rate of about 4 in (10 cm) per year and collided with it during the Tertiary. This immense collision caused the Himalayas to rise, though this was not completed until the Pliocene. These orogenic (mountain-building) processes caused drastic changes in the vegetation, and most of the original flora was replaced. At the present, the forests consist of species that were established there in the Pleistocene (and have survived), while the tropical vegetation is restricted to the eastern zone.
In the Southern Hemisphere, the flora was fragmented due to geological and climatic changes. The cooling process led to the total covering of Antarctica with ice and the destruction of its flora, which was very possibly temperate. Fossil remains (leaves, pollen) of southern beech (Nothofagus) have been found in Antarctica; however, fossil remains of this genus have not been found in Africa or India. Nothofagus evolved in the Southern Hemisphere independently of the other genera of its family (Fagaceae) in the Northern Hemisphere, and everything seems to indicate that its center of diversity was in an area at high latitudes with violent tectonic and volcanic activity during cold periods. The flora could migrate through Antarctica, which was still connected to Australia and South America in the upper Cretaceous (about 100 million years ago).
The fossil record shows that Antarctica played a key role in the redistribution of the flora of the Southern Hemisphere. Australia, New Zealand, and Antarc-tica separated in the late Paleocene. Since that time, their forests have evolved separately. This is shown by the fact that the many genera they share have evolved into many endemic species. In the Southern Hemisphere, apart from Antarctica, the effects of glaciation were most pronounced in the mountains, but in general, temperatures only fell a few degrees Celsius. Migrations and extinctions occurred, especially among conifers, but these extinctions were not as massive as those in the Northern Hemisphere.
Rainforests covered the whole of Australia during the Tertiary, but in the Oligocene, the drier climate favored the spread of the genus Eucalyptus throughout the Australian continent. The tropical rainforest was restricted to the northeast and the temperate forests to southeast Australia and Tasmania.
The domination of conifers in the northwest United States and neighboring areas of Canada is due to the special history of the region and to its relief. An Arcto-Tertiary flora of mixed temperate rainforests of broadleaf trees and conifers also covered all this region until the Eocene. The gradual cooling of the climate and the elevation of mountain systems between the Oligocene and Pliocene caused almost all the local Arcto-Tertiary flora to die out and a more xerophytic vegetation to spread. This flora was displaced shortly afterward by the conifers, as they rapidly recolonized the areas from which they had been eliminated by the Pleistocene glaciations. The local mountain ranges run north-south and acted as migration routes for the plants, which were forced to migrate to lower latitudes as a result of the cooler and increasingly continental climatic conditions in the Tertiary. The most thermophilic species, such as the genus Sequoia, remained in restricted sites at these lower latitudes, while others were eliminated during the Pliocene and Pleistocene. To the contrary, the pine family (Pinaceae), some genera of which (such as Picea and Abies) are important elements of the Vancouverian rainforests, became dominant during the Miocene and continued to spread throughout the Pliocene, as the climate became colder.
2. Moisture from the oceans and a benevolent climate
2.1 The mild climate
The temperate rainforest region is characterized by its benign climate. The temperatures are mild, and the fluctuations are small or moderate. Rains are abundant and distributed evenly throughout the year. There is never a water deficit in any season. Although some forests undergo short periods of water stress, on average, water lost by evapotranspiration never exceeds that provided by rainfall or horizontal precipitation. It is easy to see why vegetation growing in these conditions has developed a complex structure that can only be compared to the tropical rainforests.
The influence of the trade winds on the eastern coastlines
In the Northern and Southern Hemispheres, between 20[degrees] and 35[degrees] latitude, the eastern areas of the land masses are influenced by tropical maritime air masses proceeding from the western edges of the high pressure cells over the oceans at latitudes between 30[degrees]N and 30[degrees]S. These air masses move to the low pressure centers over the equator. This movement generates winds-the trade winds-which are moving toward the equator to replace the hot air masses that rise to the upper atmosphere as a consequence of the greater heating of the equatorial zone. As they move southward and northward to the equator, the trade winds are moved by the Coriolis effect-toward the right in the Northern Hemisphere and to the left in the Southern Hemisphere--as they blow from the northeast and southeast, respectively. These air masses are originally very dry, but on their journey over the oceans toward the equator, they become saturated with moisture. The air masses warm (to about 75[degrees]F [24[degrees]C]) and become wet (about 17 g of water vapor/kg air). The trade winds persist throughout almost the entire year and are most intense in summer, which is the rainiest period.
In summer, there are abundant convective rains in the regions exposed to the influence of the trade winds. Occasionally, there are tropical storms with short downpours. Further inland, the air masses become increasingly dry and rainfall diminishes. Thus, the normal north-south gradient in vegetation is replaced by an east-west gradient. The influence of the trade winds on the eastern zones of the continents counteracts the latitudinal gradient in rainfall, which tends to increase toward the equator. This is why these eastern coastal regions are occupied by subtropical temperate rainforests rather than by deserts, savannahs, and sclerophyllous vegetation, as is found at the same latitudes on the western sides of the continents. This is clearly seen by comparing the coast of the western Sahara and of southwest Morocco with those of China and Japan, which are at the same latitudes, or comparing the Californian Peninsula with Florida and Georgia.
The situation of the islands of Macaronesia is less typical. They are located on the western coast of Africa, between 18[degrees]N and 38[degrees]N, at the latitudes of the Sahara Desert. The unusual conditions that have allowed the survival of the ancient temperate rainforest are largely due to island's mountainous relief (reaching a height of 13,000 ft /3,718 m, in Teide Peak) and to the dominant trade winds from the northeast. The trade winds collide with the northeastern faces of the mountain, where the temperate rainforests have survived. Temperate rainforest only occurs in the Canary Islands (between 27[degrees]37' and 29[degrees]23'N) on the western islands (El Hierro, La Palma, Gomera, Tenerife, and Gran Canaria), at altitudes between 1,082-1,640 ft (330-500 m) and 2,985-3,937 ft (910-1,200 m) above sea level, depending on the island and the site, while the southern and western slopes are covered by a very different vegetation. The evergreen broadleaf rainforest grows at this altitude 1,640-2,952 ft (500-900 m) because of a temperature inversion. When the warm hot air masses hit the mountains, they rise up the sides. As they rise, they cool (following a dry adabiatic gradient) and become denser than the air layers above them, which do not cool very quickly and are less dense and more stable. The rising air masses hit this barrier, but cannot cross it, and tend to descend. The presence of this barrier of warm air in the higher layers lowers the altitude at which dew condenses, causing the accumulation of clouds below the height of the temperature inversion. This is known as the "sea of clouds" and the altitude at which it occurs varies over the course of the year (being higher in winter). The "sea of clouds" is very important for the plants, since it provides water directly (as condensation, i.e., horizontal precipitation) in amounts that may exceed rainfall, especially during July and August. If this were not so, the evergreen broadleaf forest would probably be unable to survive because during the summer, it undergoes the long dry period typical of the Mediterranean climate (see figures 5, 7, and 22).
Mild temperatures and abundant precipitation
The temperate rainforest biome's climate is typically mild with abundant rain year round. Despite their discontinuous distribution, the set of conditions where temperate rainforests occur lie within a clearly defined range of rainfall and temperature parameters; average annual precipitation is between roughly 69 in (1,750 mm) and 128 in (3,250 mm), and average annual temperatures between 36.5[degrees]F (2.5[degrees]C) and 68[degrees]F (20[degrees]C). Though average temperatures and the total average annual rainfall are important, the vegetation's response to climatic conditions also depends on many other factors, such as the distribution of precipitation over the course of the year (which determines the availability of water and allows temperate rainforests to grow in areas where rainfall is lower than indicated above), oscillations in the air and soil temperature, the seasonal patterns of sunshine, runoff, and potential evapotranspiration.
The subtropical temperate rainforests on the eastern coasts of the continents, which in both hemispheres are between 18-20[degrees] and 30-35[degrees], occupy an intermediate position between the tropical rainforests and the wet areas of the middle latitudes. Toward the tropics, they are bounded by the tropical rainforest and the seasonal tropical forests; the limit is marked by the 64.4[degrees]F (18[degrees]C) isotherm for the coldest month. Toward the temperate regions, the limit is the 41[degrees]F (5[degrees]C) isotherm on the coast and the 35.6[degrees]F (2[degrees]C) isotherm in the more continental zones. Further inland, precipitation gradually decreases, and the subtropical rainforests are replaced by a transition zone several kilometers wide that eventually ends in savannah or sub-desert.
In summer, sunshine is very strong, and temperatures are high in these temperate rainforests. These conditions are comparable to those in the seasonal tropical zones, although the fact that humidity is high year round (80% on average in the Mission forests and 72% in the Araucaria forests in Brazil) is more similar to the wet tropics. The climate can be defined as wet subtropical, with average annual precipitation of 39.3-98.4 in (1,000-2,500 mm). It also rains abundantly in winter. During this season, the precipitation, which sometimes falls as snow, is mainly due to storms that originate in the mid-latitudes. This happens when cold dry continental polar air arrives and causes temperatures to fall. The absolute temperature may sometimes fall below 32[degrees]F (0[degrees]C), but the average winter temperatures are above zero, usually above 41[degrees]F (5[degrees]C).
In the temperate and subtropical rainforests of the Parana region, the hot wet climate is relatively uniform. There is no dry season although the climate is clearly seasonal. The annual average temperature in the region as a whole is 50-64.4[degrees]F (10-18[degrees]C), and the difference between the average temperatures of the coldest month and the hottest month is very small (about 14.4[degrees]F [8[degrees]C] in the eastern zone and about 17.6[degrees]F [9.8[degrees]C] in the western, more continental, part). Only in the southern tip of the region, due to the arrival of cold air masses from the south, do temperatures sometimes fall below zero (to 24.8[degrees]F [-4[degrees]C], or lower). The number of days with frost is low, and they only occur above an altitude of 3,282 ft (1,000 m).
In the southeast of North America the average winter temperatures are similar, although they show greater annual oscillations, about 30.6[degrees]F (17[degrees]C), which is because the summer temperatures are higher, with an average of 82[degrees]F (27.8[degrees]C) for the region as a whole. The average temperature in January is between 43.7[degrees]F (6.5[degrees]C) and 51.6[degrees]F (10.9[degrees]C). In this area, the presence of the Gulf Stream and the Appalachian Mountains modify the climate as a whole. The Gulf Stream transports heat northward along the Atlantic coastline, so the temperature regime of northern Florida occurs along the coastline as far north as Cape Fear in North Carolina. The Appalachian Mountains divert the Arctic air masses blowing down through central North America toward the Gulf of Mexico. (Occasionally, they may reach as far south as the Tehuantepec Isthmus in southern Mexico.) Thus, the species of pines with a southern distribution (Pinus elliottii, P. glabra, P. palustris, P. taeda), the evergreen broadleaves and most wetland broadleaves, all occur further north on the Atlantic coastline than in the alluvial plains of the Mississippi.
The climatic regime of Southeast Asia is greatly influenced by the monsoons, so that in summer, the rains are much more abundant, especially in the coastal regions. The result is a hyper-wet climate, with average rainfall greater than 78.7 in (2,000 mm). Further inland, for example, in some areas of the Himalayas, precipitation is scarce, especially in the winter, and there may even be dry periods. In these areas, the winter weather is dominated by dry air masses originating in central Asia, which are responsible for sharp temperature changes, up to 39.6[degrees]F (22[degrees]C), though the average winter temperatures are above 42.8[degrees]F (6[degrees]C).
The effect of the moist, wet air
The temperate forests of the middle latitudes of the western regions of North and South America, New Zealand, Tasmania, and southeast Australia enjoy a maritime western coastal climate. This type of climate is due to the winds from the west which bring cold air masses, with a temperature of about 39.2[degrees]F (4[degrees]C) when they start. Heavy rainfall due to cyclonic storms is frequent. These cyclones originate as a result of low-pressure systems moving from the Pacific (the Indian Ocean, in the case of Tasmania and the adjacent coast of Australia) toward the coasts. The winds from the west blow air masses over the oceans (which are warmer than the air) that become laden with moisture as they cross. When these air masses reach the land, they cool down and soften the extreme temperatures. These air masses lose heat by radiation to the land, and this causes the formation of clouds almost year round.
All the areas where temperate rainforests grow have large mountain chains running north-south that act as huge barriers blocking the passage of the maritime air masses. Moisture condenses from these air masses as they rise up the sides of the mountains, causing abundant precipitation on the western slopes of the mountains and a rain shadow on their eastern slopes. At higher altitudes, precipitation falls as snow. For example, in New Zealand, the mountains act as a barrier to the winds from the west, the dominant winds, and in the western areas and highlands, this often gives rise to intense and prolonged precipitation. In these areas, annual precipitation may exceed 393.7 in (10,000 mm), and above an altitude of 3,282 ft (1,000 m), the heavy snowfalls in the winter provide a long-lasting snow cover. The eastern part of New Zealand, however, suffers from the rain shadow of the mountain barrier, which is particularly severe in some inland watersheds between the main ranges and the exterior ones. In the center of the Otago Peninsula, in the south of South Island, the local climate is semiarid, and average annual rainfall barely reaches 11.8 in (300 mm).
Precipitation is more abundant in winter, when the water in the coastal marine currents is much warmer than the land. This ensures temperatures remain mild. It has been estimated that in Tasmania, New Zealand, the Valdivian forest of Chile, and the conifer forests of the northwest coastline of North America, to a latitude of about 45[degrees]N, there are 43 days a year with frost (less than 12%). At higher latitudes, frost is not very frequent though temperatures do fall to zero more often. Thus, for example, in many zones of New Zealand's South Island and at higher inland elevations on the North Island, the average temperature over the course of the winter is low, but not freezing, but severe frost does occur. Note that the changes in temperatures over the course of the year are very similar to that prevailing from the Cretaceous to the mid-Tertiary. In southern Chile, between 43[degrees]S and 47[degrees]S, the dominant influence is the winds from the west. The distribution of rainfall over the course of the year is more regular than further to the north, and conditions of high humidity prevail throughout the year. The average annual rainfall varies between 118.1 and 196.9 in (3,000 and 5,000 mm), and even in the driest month, rainfall is usually more than 3.9 in (100 mm).
In summer, the land warms more quickly than the oceans, and precipitation is less abundant, so summers are relatively cool and dry. In summer, rainfall declines toward the equator, and from about 38[degrees]N, sclerophyllous vegetation is abundant within the temperate rainforests. This is particularly clear in the Valdivian region of Chile (central-southern Chile), between 37-38[degrees]S and 43[degrees]S, where the climate is temperate maritime, very rainy and with Mediterranean influences, with less rainfall in summer (January-March) and a rainfall maximum in winter (June-August). In the Depressio Central (the intermediate depression between the Cordillera de la Costa-the coastal ranges-and the Andes), the rain shadow of the Cordillera de la Costa means precipitation is low, and snow usually only falls above 2,625 ft (800 m). In winter, cyclonic storms cause strong gusts of wind (galernas), which are also frequent in summer, when the high pressure center is located in southern Argentina.
In the northwestern coast of North America, between 38[degrees]N and 60[degrees]N, temperatures only fall below 32[degrees]F (0[degrees]C) for short periods (eight days at most). By the sea, the summer temperatures range between 39.2[degrees]F (4[degrees]C) and 80.6[degrees]F (27[degrees]C) and the average monthly temperatures of the summer months vary between 43.7[degrees]F (6.5[degrees]C) and 62.6[degrees]F (17[degrees]C), though inland they may reach 78.8[degrees]F (26[degrees]C) or more. In Alaska and British Columbia, the climate is cool, and rain falls year round, but in northern California, it only rains in the winter, the season when winds from the west reach furthest to the south. At sea level, snowfalls are habitual in the northern part of this area of the biome, but they are rare and short south of Vancouver Island. At higher altitudes, snowfalls are more frequent, and 6.6-9.8 ft (2-3 m) of snow may accumulate in the region's subalpine forests.
The climatic gradient along the latitudes and east-west variations
Briefly, at higher latitudes, rainfall is higher, and temperatures are lower. Conditions of high humidity prevail all year round. The climate changes from temperate to very wet temperate-cold. In the Magellanic region of southern Chile, to the south of 47[degrees]S, the climate is temperate-cold and hyperwet; the temperatures gradually fall and the daily and seasonal changes in temperature become smaller. Precipitation becomes more regular, and as a whole, it is lower than in the Valdivian forest. Snow may fall at any time of year but is scarce at sea level.
In these zones, the growing season is very short. The plants enter true winter dormancy, except in New Zealand, which only reaches 47[degrees]S and is strongly influenced by winds from the west, except at its northern tip, which is dominated by the trade winds. There, as in the regions of the Americas where temperate rainforests develop, the climate is determined by the successive movement of depressions and anti-cyclones with their associated fronts. This pattern is, however, modified with some regularity by occluded warm fronts and by the cyclones that originate in the tropical zones, to the northwest of the archipelago. These masses of air especially affect the northern part of North Island and cause torrential rains. As in the temperate forests of South and North America, these forests in New Zealand may experience periods when the air is very dry at any time of year, though they are most severe in summer, when evaporation is greatest.
In all the temperate forests at middle latitudes, the most important gradient is the east-west gradient created by the presence of mountain ranges. In the Valdivian region in Chile, average annual rainfall may reach 157.5 in (4,000 mm), and in New Zealand, there are places where it reaches 393.7 in (10,000 mm). On the leeward side, on the eastern slopes of the mountains, precipitation is much less abundant as a result of the rain shadow. When the air masses cross the mountains and descend, they have lost almost all their moisture, meaning that they are dry, and cannot give rise to rainfall. This type of situation often gives rise to what are known as rain-shadow deserts, which begin at the base of the mountains: the Patagonian steppe grasslands and the deserts of the western United States are deserts precisely because they lie in the rain shadow of mountains.
On the eastern slopes of the mountains of South America, Araucaria forests grow in sites with widely different average annual rainfall, between 74.8 in (1,900 mm) in the rainiest sites and only 23.6 in (600 mm) in Lake Alumine in the Argentinean province of Neuquen, where most of the precipitation falls as snow, while the summers are relatively dry. In New Zealand, the average annual precipitation in the eastern zones (brought mainly by the fronts arriving from the south) varies between 19.7 and 29.5 in (500 and 750 mm). Precipitation is lower in the zones between the mountains, where it totals only 13.8 in (350 mm).
2.2 The dark side of these favorable climates
The very favorable picture apparently presented by the above description of these climates, is sporadically disturbed by catastrophes, especially cyclones and occasional cold spells.
Repeated destruction by cyclones and hurricanes
In 1969, the 199 mph (320 kph) winds and torrential rain carried by Hurricane Camille devastated an entire strip from Mississippi to Virginia. The waves reached a height of more than 19 ft (6 m), 292 people died, and material damages were estimated at one billion dollars. It was one of the most devastating hurricanes to affect the southeast United States, but by no means the only one. Much earlier, in 1900, the Galveston hurricane caused great damage to the forests, and in 1990, Hurricane Carla brought down a large number of great trees.
Tropical cyclones such as these, varying only in their intensity, occur with some frequency in the southeast United States and in many subtropical islands and coastal regions. Tropical cyclones have different names in the different regions they affect. They are known as hurricanes in the western Atlantic; in Southeast Asia, they are known as typhoons; and in Australia, they are known as "willy-willy" (see also vol. 2, pp. 28-31). Tropical cyclones are deep depressions that move from tropical regions to subtropical and temperate zones. They are accompanied by strong winds and intense rains. The depressions known as tornadoes are smaller, but their winds are more intense and destructive. Although they are infrequent, hurricanes and cyclones always have devastating effects, such as destroying vegetation and causing floods and intense erosion. In many cases, they travel hundreds of kilometers inland before they dissipate.
Tropical cyclones affect coastal tropical and subtropical zones. Tornadoes seem to be typical of the Americas, although they also hit Australia with some degree of regularity. Tornadoes are small depressions that are very intense. They mainly form in spring and summer from a dense cumulonimbus cloud preceding a very turbulent cold front. They look like a chimney with a base up to 1,641 ft (500 m) in diameter and are darkish in color, because of the dust borne by the wind. The winds associated with a tornado are much faster than, in a hurricane, and they may reach a speed of 249 mph (400 kph), those causing them to be extremely destructive. Like hurricanes, the destruction caused by tornadoes is due to their high wind speed and the high-pressure gradient they create.
Disturbances caused by cyclones usually affect large areas. The degree of destruction depends, among other things on: the size of the cyclone; the frequency with which they occur; the intensity of the wind and rain; and the condition and phenological state of the vegetation. This type of disturbance has many ecological consequences for the species in the area affected and the landscape as a whole. Many studies of the effects of cyclones have shown that they increase the diversity of the vegetation and landscape by creating patches of different sizes at different stages of succession. Their destructive effect is influenced by the local topography and the local biota's physiognomy and its stage of succession. The larger trees of a mature forest are more likely to be blown over than the smaller, younger trees of a forest in the early stages of succession. Furthermore, not all the effects of a cyclone are visible or negative as part of the damage is rapidly mended; cyclones are an agent of natural selection forcing species to adapt and evolve.
Occasional catastrophic cold spells
The survival of the species typical of each plant formation is closely related to the changes in temperature over the course of the year and the extreme values reached. The natural limits of the distribution of many species are set by the stress due to low temperatures, so the mechanisms acquired by different species of plants to survive the low temperatures are comparable, in terms of their ecological and evolutionary importance, to adaptations to drought. The evergreen species of the laurel family (Lauraceae), for example, which are very important elements in the temperate and tropical rainforests, are not at all resistant to frosts and are confined to regions with a climate with mild winters. In general, the limits to the distribution of many woody plants correspond well to the minimum temperature their tissues can withstand. Cold temperatures probably also limit the latitudinal distribution of many species of bamboo.
For example, in the conifers that resist temperatures below freezing point in winter, the water potential of the leaves falls at a rate of 1.2 MPa/[degrees]C when the air temperature falls below 32[degrees]F (0[degrees]C), and this situation is more critical than that occurring during the summer. Many species of trees that are frost resistant, because they supercool their wood, have been able to colonize areas where the annual minimum temperature may reach as low as -40[degrees]F (-40[degrees]C).
The temperate rainforests are restricted to regions with a climate that is favorable year round. Their distribution in Japan is related to the climate and shows the importance of temperatures in determining vegetation type. The different parts of the Japanese archipelago have very different climates. The climate is cold in the north, with very severe winters, whereas the south is subtropical. Rainfall is abundant in all these zones, but temperatures are not uniform. At higher latitudes, the winter temperatures fall, and evergreen species (except in the understory) decrease rapidly in number and diversity, and deciduous species increase until they are dominant, in the islands' middle and high latitudes. The limit of the evergreen broadleaf species coincides with the strip where the average temperature of the coldest month is between 33.8[degrees]F (1[degrees]C) and 35.6[degrees]F (2[degrees]C), in keeping with the ability to survive absolute minimum temperatures of 5[degrees]F (-15[degrees]C) and -0.4[degrees]F (-18[degrees]C).
The occasional cold spells are rarer in the Southern Hemisphere temperate rainforests, which explains why they reach such high latitudes at the southern tip of South America. Even so, the extreme temperatures show greater variation in the temperate rainforests further inland in Australia and in the Parana region, where excessive frequency of frosts is a factor limiting the range of many temperate rainforest species. In these areas, where cold spells are not at all unusual in winter, often because they are at high elevation, the forests are dominated by conifers, such as Araucaria.
3. Deep washed soils
3.1 Diverse, complex, soils
It is hard to describe the dominant soil types in the temperate rainforests, because they occur on a mosaic of very different soil classes. Many soil formation factors (climate, parent material, organisms, relief, time) are at work, but none completely dominates the soil formation processes in the temperate rainforests.
The absence of a single factor dominating soil formation
The influence of the climate on these soils is shown by the fast and extensive weathering of the parent material as a result of the excess precipitation they receive. The temperature and humidity regimes also affect the rate and scale of the accumulation and recycling of organic matter. Accumulation is greatest in cold, wet climates.
The geology of the zone occupied by the temperate rainforests includes all sorts of parental materials, such as coastal sands, quartzitic sandstones, metamorphic rocks and plutonic rocks (such as granites) and even volcanic rocks. The volcanic rocks, especially basalts, are important as they are the parent material in much of the temperate rainforest area.
The role of the living organisms is decisive, as the microorganisms are responsible for the recycling of nutrients between the soil and the plant cover, on which maintenance of the forests depends. The temperate rainforests are, from this point of view, "top heavy" ecosystems, as the nutrients are mainly stored in the vegetation. In "top heavy" ecosystems, the soil fauna is specialized in decomposing plant remains as quickly as possible, thus making the nutrients available to the plants again.
The form of the landscape affects the degree of in situ development of soils before they are transported and deposited by natural erosion processes. Conceptually, we can divide positions within the landscape into three broad types: residual source positions, dominated by weathering; transport positions, in which there is a balance between weathering and the lateral soil movement down slopes; and deposition positions, where the eroded soil material accumulates and weathering is less important.
The importance of time as a factor
Unlike the situation in other regions of the world, time has played a very important role in soil formation in the temperate rainforest biome, where soil formation processes have not been interrupted by ice ages or severe droughts. As a result, the soils formed on coherent rocks in the most stable positions, may be very ancient, on the order of tens of millions of years old. This explains why temperate rainforest soils are highly washed, even in areas where rainfall is not particularly high. In other words, in sites where rainfall is moderate and where washing has been slow and continuous over millions of years, the soil may be as completely washed as in sites with a much more tropical climate.
3.2 The mosaic of soils in the temperate rainforests
No one type of soil can be considered typical or dominant in the temperate rainforest area. The following is a description of the most important soils, the ones that form on basalts (ferralsols and nitosols), those soils derived from recent volcanic rocks (andosols) and those formed on quartzitic sands (podzols), and a general description of the others.
The wide range of soils
The most developed temperate rainforests, in terms of species diversity and tree height, grow on soils derived from basalts. The most common soil types on basalt-derived materials are ferralsols and nitosols. They only occupy a small part of the temperate zone, but occur along a broad climatic gradient and are the soil medium that most favors the development of productive and diverse temperate rainforests. These soils include the characteristic red ferralitic soils of the Parana region.
There are also temperate rainforests on other less mafic types of rock, such as volcanic rocks, plutonic rocks (granites) and metamorphic rocks. In the southern Andes, for example, most soils are derived from multiple recent postglacial volcanic deposits, less than 2,000 years old in some cases, and consist of layers of pumice stone, which is extremely porous and variable in size, and layers of fine andesitic ash. The high allophane content of these volcanic deposits makes them particularly prone to landslides, which occur frequently and rejuvenate the soils. In both the Andes and the Cordillera de la Costa in Chile, the soils that form on granitic and metamorphic substrates are usually shallow, sandy, acidic, and well drained. In the northern half of the Northern Hemisphere temperate zone and the southern half of the Southern Hemisphere temperate zone, the distribution of the temperate rainforests is determined to a greater extent by the orientation of the slopes (north-facing in the Northern Hemisphere, and south-facing in the Southern Hemisphere) than by the type of soil. The most sheltered positions within the landscape, such as narrow valley bottoms, sheltered from winds and from excessive evaporation, are also favorable sites for the development of temperate rainforests.
There are also temperate rainforests in protected valley bottoms on quartzitic sandstones, for example, in the Sydney region of Australia. Temperate rainforests can grow in these sites because they receive an input of nutrients, organic matter, and moisture from the sides of these valleys. Temperate rainforests, like the Australian wet sclerophyllous Eucalyptus forests, are also present on coastal sands, in zones with higher rainfall and a cooler climate, as in southwest Western Australia and in Victoria and Tasmania.
Soils derived from basalts: ferralsols and nitosols
The most developed temperate rainforests with the highest species diversity grow in areas of basalt-derived soils. These soils also occur in other climatic environments in the temperate zone, from the coldest areas to the edges of the tropical zone, and form on basalts and other mafic rocks. In the temperate zone, it can be considered that these soils are the only ones that are almost completely occupied by rainforests and other types of wet forest, regardless of the other factors controlling the distribution of the vegetation, such as orientation and fires. This is not true of the other soils present in the biome (andosols, podzols).
The most developed soils on basalts are, in the FAO terminology, ferralsols and nitosols. Although the Australian and Russian classification systems include them as krasnozems (red soils), the FAO system divides them into two groups: soils with aggregates whose faces are red (ferralsols) and those with smooth-faced aggregates (nitosols). The two units are described together because their properties and uses are very similar. These soils only occupy a small area of the temperate area (less than 5%), but they are very important because of the high productivity of the forests growing on them, and they are at the final stage of their development.
Both ferralsols and nitosols are the product of intense weathering and washing of the basalt. The basic cations are rapidly washed, and the soils become unsaturated; less than 50% of the ion exchange sites are occupied by bases. The silica, aluminium, and iron oxides that remain combine together to form kaolinite and large amounts of hematite and hydrated iron oxides, which are present throughout the soil, giving it a strong structure. The low clay content of the upper soil horizons is due to the clay's destruction by weathering (in ferralsols) or its loss by illuviation (in nitosols).
Ferralization is the main process leading to the formation of both ferralsols and nitosols. This consists of the gradual release and loss by washing of the silica, potassium, sodium, magnesium, and calcium from the soil profile, leaving only the most insoluble components, such as the oxides and hydroxides of iron and aluminium. As basalt largely consists of minerals that can undergo weathering, the ferralitic remnant retains few primary minerals and consists of a clay matrix rich in iron and aluminium.
Nitosols are also characterized by the illuviation of clay and nitosolization, which consists of the formation of strong angular blocks that break up into smaller angular aggregates or polyhedral aggregates with smooth shiny faces. Both ferralsols and nitosols are subject to active bioturbation, the mixture of the surface and subsurface horizons by the activities of the soil fauna. This mixture is the cause of the formation of thick transitional AB horizons, which are due to the action of invertebrates, such as termites and ants in the middle latitudes, and earthworms on the colder edges of the biome.
Soils subject to wetting-drying cycles contain concentrations of iron and aluminium oxides known as plinthite (see also vol. 2, p. 36). Plinthite is often present as continuous layers or a layer of nodules at the level in the soil where the water table rises and falls. Plinthic ferralsols and nitosols, where the plinthite is deeper than 49 in (125 cm), mainly occur in the hottest areas of the temperate zone.
The typical profile of ferralsols and nitosols consists of a dark A horizon (about 12 in [30 cm] thick and with a strong crumb structure), a transitional AB horizon (12-24 in [30-60 cm] thick), a B horizon (between 24-114 in [60-290 cm] thick, with either a crumb or angular structure, which is ferralic [Bws] in the case of ferralsols, and argillic [Bt] with nitic properties in the case of the nitosols, and a transitional BC horizon 138 in [350 cm]) or more thick. In highly altered residual sites, the soil may reach a depth of 33 ft (10 m).
The high content in sesquioxides of these soils means that the clays are highly aggregated (flocculated), even in conditions of waterlogging. As a result, ferralsols and nitosols are moderate-to well-drained, and their hydrological properties are similar to those of loamy soils. Most of them have a high water retention capacity but retain a great deal of water at the permanent wilting point. This is because the clays tightly bind part of the water, making it unavailable to the plants.
Ferralsols are highly productive when they are cultivated for the first time after the rainforest has been cleared, as they contain abundant organic matter and their structure provides good drainage and makes them easy to cultivate. These soils' chemistry is dominated by their pH-dependent cation exchange capacity, which is due to the presence of organic matter and iron oxides and aluminum oxides in the A and AB horizons. The B horizons are usually moderately to highly acidic, which may cause aluminum toxicity and immobilization of phosphorus. Once the organic matter has been lost from these soils, the remaining constituents (kaolinitic clays) have a low cation exchange capacity, and this accentuates the problem of the washing of cations.
Due to their properties, these soils have been intensely used for agriculture and stockraising. The decrease in productivity that they usually show is directly related to the loss of their organic matter as a result of deforestation. In the long term, the continued use of these soils depends on maintaining their organic matter content and correcting their acidity by liming. In addition to the loss of organic matter, the erosion of the surface horizons as a result of clearing the forest for agricultural use is a serious problem in plinthic ferralsols and nitosols, because the plinthite is exposed at the surface and turns into a hard ferruginous crust that the roots cannot penetrate. On the southwestern shores of the Caspian Sea and on the Black Sea coast of western Georgia, the ferralsols and nitosols have been thoroughly deforested and cultivated. To prevent erosion, terraces have been built in many places and cover crops have been planted.
Sand-derived soils: podzols
Podzols support a wide range of vegetation types. They are of great importance because they support the nutrient-rich and species-diverse temperate rainforests and wet sclerophyllous forests, which is very surprising taking into account that the soils are nutrient poor. The wet sclerophyllous Eucalyptus forests of western Australia are the best example of this. These forests grow on podzols, and the trees, especially the karri (Eucalyptus diversicolor), may grow more than 328 ft (100 m) tall. Temperate forests also covered a large area of the podzols of the northern coast of New Zealand before human settlement. Podzols are also present in the southeastern United States, where they are often gley podzols with a surface water table to which the organic compounds lose iron and aluminum. In the northwest, podzols mainly occur in the highlands of the Cascade Range and the Okanogan Highlands. The temperate rainforests are present on podzols because these forests are the climax of the succession rather than because the soils are naturally fertile. The development of the climax vegetation of temperate rainforests takes much longer on podzols than on other soils, because of their low nutrient content. It takes a long time for the process of recycling of nutrients in these soils to accumulate enough carbon to support these forests.
The process of podzol formation (see vol. 8, pp. 258-259) involves the formation of a spodic Bhs horizon. These are subsurface accumulation horizons of organic matter, illuviated from the surface horizons in the form of chelates with a variable content of oxides of iron and of aluminum. They are often under an eluvial E horizon that is whitish (ash-like) as a result of the loss of organic matter. Podzols characteristically have, in all the horizons, an extremely high content of quartz sand of wind-borne or fluvial origin, though the E horizons consist almost entirely of this sand. Their drainage is usually good in the A and E horizons, but it may be blocked at these levels due to the accumulation and cementation of sesquioxides and organic matter in the spodic horizons.
Unlike the European podzols, those of the Southern Hemisphere are deeper and lack a well-developed organic O horizon. A typical temperate rainforest podzol consists of an Ah horizon (up to 24 in [60 cm] deep), that is dark, sandy-loam and with a high content of organic matter. Below this is the eluvial E horizon, consisting of whitish or gray washed sands, which may be up to 79 in (200 cm) thick. Below this, there is a Bh horizon (79-102 in [200-260 cm] thick) that is dark brown to black and the result of the accumulation of illuviated organic matter, which covers the sand grains and may cement them together. Just below this is another darkened horizon, but with yellowish streaks due to the presence of iron oxides in addition to organic matter. The total thickness of the spodic B horizons in areas of Pleistocene sands may exceed 33 ft (10 m), and, in some cases, may reach 66 ft (20 m).
Podzols are not very fertile. They are moderately to highly acidic and because they are dominated by sands their cation exchange capacity is low. The nutrients are mainly recycled by mycorhhizae and insects, and they are concentrated in the Ah horizon, almost exclusively in the organic matter. The maintenance of nutrient levels depends on the input of leaf litter, and they rapidly decrease after deforestation. Much of the area occupied by podzols in Australia, New Zealand, and Florida has been cleared for agriculture and stockraising. However, their productivity drastically declines within a few years, and they become unproductive. Continued use of these soils requires the input of large amounts of fertilizers and treatment with lime to correct their acidity.
Soils derived from volcanic ashes: andosols
Soils derived from volcanic ash occur in many sites that have suffered recent volcanic action, and these are the soils on which many temperate rainforests grow. The most typical are the andosols, whose name comes from the Japanese phrase "an-do," meaning black soil. Unlike other soil classes, which are defined by their lack of development (such as regosols and lithosols) or by the compounds they accumulate (calcisols, gypsols), andosols are defined by possessing characteristic properties that are called "andic." The presence of volcanic glass or amorphous oxides of iron and aluminum gives andosols their unique properties. They are highly porous and have a low apparent density, show thixotropy (the ability to change from a gel to a sol), show anion exchange capacity, retention of phosphates and the presence of highly stable organo-mineral compounds. All these features have to be present to a depth of 13.8 in (35 cm) or more for a soil to be an andosol. In addition, there also has to be a mollic, umbric, or cambic horizon that shows some degree of development. The formation process starts from the material ejected by volcanoes, small porous fragments that are weathered rapidly due to their very large surface area. Immediately after deposition, the materials start to lose silica and basic cations in large amounts, while the content of volcanic glass decreases and that of organic matter increases. As the soil ages, A horizons gradually differentiate as a result of accumulation of organic matter, and B horizons as a result of the formation of amorphous clays. The degree of differentiation reflects the length of time the pyroclastic materials have undergone weathering. In Japan, studies of the relationship between the two factors suggest that the B horizons start to differentiate after 500 years but are only fully developed after about 1,500 years. This is really extremely fast when compared to the rate of formation of other soils, which may take thousands or even millions of years to develop fully.
When there is a volcanic eruption, the entire landscape is covered by a layer of ashes, the thickness of which affects the water regime of the new soils. If the layer of ash is thin, the water regime will be similar to that of the underlying soil, but if it is thick, the soil will develop under drier conditions and will be little affected by the former moisture regime of the underlying soil. Depending on the age of the deposit and the environmental conditions at the time of the deposition, these underlying sediments will undergo greater or lesser disturbance, so the soils that form on them may be immature or completely developed. Generally, the particle size of the ash increases with depth; if the deposit is thick, initial weathering occurs slowly, as a result of the limited water retention capacity of the sandy material (pumice stone). As the process progresses, amorphous allophane-type clays form, and this increases the soil's water retention capacity. The colonizing species adapted to dry environments are replaced by those adapted to moister environments.
In southern Chile, there are two types of andosols that occur at the extremes of the range of climates and plant formations. The waterlogged Zadis occur in the hyperwet southern zone. In these conditions, an allophane gel develops that, because of its ability to retain large amounts of water in the soil, controls the amount of water in the soil. The trumaos occur in the subhumid zone, are more permeable, and form because of the effects of the dry period of several months in the summer; the amorphous allophane turns into crystalline clays (gibbsite) and stratified clays (halloysite).
The most common profile of a mature andosol consists of an A horizon 8-20 in (20-50 cm) thick that is dark and loose, with large quantities of organic matter, and a brown Bw horizon above a transitional BC horizon. Depending on the age and the degree of washing, accumulation horizons of silica (duripan) or of iron oxides (plinthite and ferruginous crusts) may occur. In the youngest soils, the B horizon is often absent. In many cases, the soils are altered by erosion or the deposition of other soil materials, or covered by recent pyroclastic deposits. Polygenetic soils are thus often present, as the result of the repeated covering of soils by new layers of ash.
Andosols contain high levels of organic matter because organic matter forms very stable compounds with the allophanes. The solid phase of the soil occupies only 20-30% of the apparent volume. Thus, the apparent density is very low (500-1,000 kg/m3), and its porosity and water retention capacity are high. These properties partly explain andosols' high fertility, why they weather very rapidly, and why they are so severely affected by erosion.
Andosols are generally acidic. In these conditions, the cation exchange capacity is low, and the vegetation may suffer problems due to aluminum toxicity and the immobilization of phosphates. This immobilization is because at low pH values the allophones can adsorb anions like nitrates and phosphates, which would be washed from the soil profile in other soils. This represents a reserve of nitrogen for the roots, but the phosphates are so tightly bound that they are totally immobile in the soil and unavailable to the plants, which may thus suffer phosphorus deficiency. Improving these soils requires a combination of suitable techniques, such as treatment with lime and adding organic matter, and the application of large amounts of phosphates. Despite these problems, andosols are considered to have a high natural fertility, and they have been extensively cleared and cultivated in the temperate rainforest biome.
In the temperate rainforest biome, there are andosols on the coasts of southern Chile, on the North Island of New Zealand, in Japan, and in the archipelagoes of Macaronesia (the Canary Islands, Madeira, and the Azores). On andosols, as on podzols, the temperate rainforests are the result of the plant succession to climax rather than the result of soil fertility. Other types of vegetation can grow on these soils in the temperate zone. On the other hand, andosols also occur in almost all the other biomes. In many cases, the presence of forests on andosols is more closely related to orientation and microclimate than to soil type.
4. The world's temperate rainforests
4.1 The variations in physiognomy of the temperate rainforests
Unlike the deciduous forests and the taiga, where there is usually a single, or a few, dominant species, the temperate rainforests usually consist of a large number of different tree species, showing a level of biodiversity only exceeded by the tropical rainforests. It should be pointed out that there are also low-diversity temperate rainforests dominated by a few species, mainly at higher latitudes with cooler climates. As a whole, temperate rainforests are less diverse and less dense than the tropical rainforests, and both the trees and their leaves are usually smaller. Because the temperate rainforest biome consists of many small fragments scattered far apart, there are great differences between the temperate rainforests. Some temperate rainforests are dominated by evergreen broadleaf trees with slightly coriaceous shiny leaves (laurel forests), while others are dominated by needle-leaved conifers, and others combine the two in different proportions, and some deciduous species may even be present.
The temperate evergreen broadleaf forests, laurisilvas
The true laurel forests, the most typical temperate rainforests, are normally dominated by evergreen broadleaf trees with large, coriaceous, shiny green leaves, like those of magnolias (Magnolia, Magnoliaceae) and laurels (Laurus, Lauraceae). In Japan, this type of forest is known as shoyoju-rin ("shiny forest"), because the smooth surfaces of the leaf cuticles reflect the sunlight, making them look shiny. These forests are evergreen, though they show greater variation in color in spring, when the new leaves are produced and replace the old ones. The senescing leaves of many species of the Lauraceae turn red, and the new leaves and shoots replacing them also have a reddish tinge. Their broad flat leaves have a greater surface area for photosynthesis, but they also lose more water by transpiration. To prevent and slow down excessive water loss in the brief periods of water stress, the leaves are covered with thick cuticles and some species are rather sclerophyllous. Leaves of this type are relatively thermophilic, and so they do not resist sudden drops in temperature very well, meaning that the species bearing them can only grow in sites with a mild climate.
The term "laurel forest" was first applied to the temperate rainforests of the Canary Islands by the English botanist Philip Barker Webb (1793-1854). The term was soon extended to include the comparable rainforests in other parts of Macaronesia, and later to those of southern Japan and other regions of Asia, where this type of temperate rainforest is widespread. It is now used for all the temperate rainforests that are clearly dominated by evergreen broadleaves, both in the Northern Hemisphere (where they occur from the Canary Islands to Japan and from the northern shores of the Black Sea to southern China) and in the Southern Hemisphere (in Tasmania, in southeast Australia and in New Zealand).
Temperate rainforests dominated by broadleaf species occur in the Northern and Southern Hemispheres. In the Northern Hemisphere, they occur in central China, in southern Japan, on the eastern coasts of the Black Sea, and at some heights in the Himalayas. In the Southern Hemisphere, the broadleaf species cover a large portion of New Zealand, Tasmania, and southern Australia. Species of Eucalyptus that are drought-resistant now occupy much of this area. Broadleaf evergreen forests can also occur in South America (Mission forest) and in southern Africa. Although these are not treated in this volume, they are similar to the African cloud forests (or Afromontane forests, see vol. 2, pp. 361-362). In many evergreen broadleaf forests, such as the subtropical ones, the trees are deciduous-they shed their needle leaves in the winter, indicating a seasonal climate.
The temperate conifer forests
Temperate rainforests may be dominated by conifers. Usually, these trees are associated with open forests or areas with a scarce plant cover. The needle leaves of conifers are more resistant to drying by the cold or high temperatures than those of broadleaves. Thus, temperate rainforests of conifers prosper in areas with more extreme conditions, such as frequent frost and more frequent droughts, which occur throughout the year. In the temperate rainforests of conifers, the leaf density is very high, and the leaf area index (LAI-the ratio of the area of leaves to the area of soil on which they grow, for example, 2 [m.sup.2] of leaf/[m.sup.2] of soil) are among the highest, with values between 8 and 18.
Many different types of leaves can be found in the temperate rainforest. Some species have flattened linear needles, such as the yews (Taxus, Taxaceae); the hemlocks or hemlock spruces (Tsuga, Pinaceae); the China firs (Cunninghamia, Taxodiaceae); the firs (Abies, Pinaceae); and the Japanese umbrella pine (Sciadopitys verticillata, Taxodiaceae). Others have flattened scale leaves, such as the arbor-vitaes (Thuja, Cupressaceae) and the false cypresses (Chamaecyparis, Cupressaceae) or small awl-shaped leaves with a decurrent base, such as the sugi or Japanese red cedar (Cryptomeria japonica, Taxodiaceae). Still others have both needle leaves and awl-shaped leaves, such as the coastal redwoods (Sequoia sempervirens, Taxodiaceae). The leaves of the two species of Araucaria (Araucariaceae) are more flattened than those of the species previously mentioned.
The temperate rainforests dominated by perennial needle-leaved conifers are located in the North and South America-both in the temperate zone (the Vancouver rainforests and the Chilean-Argentinean Araucaria araucana forests) and in the subtropical zone (the Mesoamerican pine and oak forests and the Araucaria angustifolia forests of the Parana region).
The mixed temperate rainforests
All temperate rainforests cannot be considered as either evergreen broadleaf or conifer forests. In many areas of the world, the two types are mixed together, and in some cases, there are also deciduous species more typical of deciduous forests. This occurs in southeast North America; in the mountains of Mesoamerica; the southern tip of South America; and in much of Australia, Tasmania, and New Zealand. Rather than mixing, the pine and evergreen broadleaf forests are sometimes distributed as a mosaic within the landscape depending on the local variations in environmental conditions.
4.2 The temperate rainforests of western coastlines and the connected formations
The temperate rainforests of the western coastlines are the temperate forests par excellence. They occur at the middle latitudes on the Pacific coastlines of North and South America, the south of Australia (including Tasmania), and New Zealand. The conifers play a major role in them, and their composition is diverse, as are their geographical locations. The Chilean-Argentinean Araucaria araucana forests, which occupy the driest areas of the biome in South America, are related to them. They are temperate rainforests with high rainfall, and they occur next to the other temperate rainforests of the southern tip of South America. Also, the drier Australian and New Zealand forests, which are discussed, are comparable because they are associated with wetter ones in their respective geographic areas.
The temperate rainforests of Vancouver and similar areas
The world's tallest forests occur along the Pacific coastline of North America, in a broad strip 37-75 mi (60-120 km) wide, running from 38[degrees]20'N (in northern California) to 60[degrees]N in southern Alaska. These forests are unique for their great diversity of species, the density of trees, the height of the trees (reaching an average of 164-246 ft [50-75 m]), the mass of wood that accumulates (4,525 tonnes/ha in the coast redwood forests), and the trees' longevity (500 years). Unlike other forests at middle latitudes, the forests of the Pacific coastline are almost totally dominated by conifers, with a floristic diversity decreasing from south to north until the formation completely disappears north and west of the Seward Peninsula and Kodiak Island, in Alaska. These forests are of great economic importance because the Douglas fir (Pseudotsuga menziesii) is one of the world's most important timbers.
These forests' great height and accumulation of biomass can largely be attributed to the dominant wet climate, which is the result of the strong westerly winds from the Pacific Ocean. The winds move cold air from Asia over the relatively warm ocean, where they pick up moisture, and then flow onto North America. The progress of the winds is halted when they hit the mountain ranges running roughly north-south and parallel to the Pacific coastline. The average annual precipitation varies from about 39 in (1,000 mm) to about 197 in (5,000 mm). For example, at Little Port Walter, Alaska, precipitation is 226 in (5,730 mm). Inland, the limit of these forests coincides with the isoline for 120 frost-free days a year. Where precipitation patterns permit, from British Columbia to Oregon, some species that are widely distributed in this coastal strip form forests as far inland as the Rocky Mountains. This is due to the existence of low-level westerlies bearing moisture-laden clouds across the coastal range, following three main routes. The two broadest passes are between 45[degrees]N and 50[degrees]N, the latitudes where the westerly winds are strongest, and the third is the Columbia River-Snake River-Wyoming Basin gap.
Generally, these forests of large conifers are confined to the two mountain ranges running parallel to the coast: the Coast Ranges and the Cascade Range. They occur in the northern tip of the Coast Ranges (Pacific Coast Ranges) in California and Oregon and in their northern continuations, the Olympic Mountains and the Insular Belt of British Columbia and southern Alaska. These tall conifer forests occur on the Cascade Range and its northern prolongation, the Coastal Belt in British Columbia and southern Alaska. Although they are generally drier than the other coastal ranges, the Klamath Mountains of Oregon support tall forests with some endemic species of conifer. In addition, the northern Rocky Mountains support high temperate conifer rainforests in Idaho and in western Montana, along a series of mountain ranges running from the Selkirk Mountains and the Purcell Mountains in the north to the Palouse Mountains, the Bitterroot Range, and the Clearwater Mountains in the south. In Oregon and Washington, coast-type forests grow in the region of the Blue Mountains, on a series of relatively low mountains connecting the Cascade Range with the Rocky Mountains. The Okanogan Highlands, on the border between Washington State and British Columbia, are divided by river valleys. At low and middle elevations in these mountains, in the area of Lake Quesnel and in the valleys of the Kootenay River, Fraser River, and the upper Thompson River, there are patches of coast-type coniferous forest (known as "Columbian Forest"). The coast-type coniferous forest reaches further inland in the transition area between the basins of the Skeena River and the Nass River in northwest British Columbia.
The mixed Valdivian, northern Patagonian, and Magellanic forests
The Valdivian forests cover most of southwest South America, between the Pacific coastline and the Andes and are known as the "Nothofagus forest region." The different species of southern beech (Nothofagus, Fagaceae), together with other evergreen and deciduous angiosperms and conifers, form very impressive mixed forests that long ago attracted the attention of naturalists and geographers for their unique biogeographic characteristics. They belong to the Antarctic floral kingdom, as do the southern beech forests of New Zealand, Australia, and Tasmania, to which they are closely related (see p. 22). Their composition includes many elements from the neotropical floral kingdom that are widely distributed in other regions of South America.
The Valdivian rainforest, which grows in the north of this region, is the most highly developed temperate rainforest in South America and is effectively a tropical rainforest growing outside the tropics. Its physiognomy, its high diversity, and the highly specialized adaptations of many of the species reflect a long uninterrupted history under very favorable climatic conditions. As temperatures gradually fall toward the south, the diversity decreases, although these evergreen forests are still impressive. They continue through southern Chile, from 37[degrees]45'S to 55[degrees]S, with some incursions into Argentina. To the north, they are bounded by the Chilean Mediterranean region and the deciduous forests of the roble pellin (Nothofagus obliqua, also known as coyan, hualle, and roble beech) and rauli (N. procera). To the south, they reach Tierra del Fuego and the many islands off the Chilean coastline (the "Magellanic Archipelago"). Geographically, the region's most significant features are its great length from north to south and the presence of the Andes, which act as a barrier preventing westerly winds from progressing eastward.
These rainforests occur on the western slopes of the Andes, where the precipitation is most abundant, running a total of 1,367 mi (2,200 km) along the coast. In the northern part of their range, from 37[degrees]45'S to 43[degrees]S, the Cordillera de la Costa reaches an altitude of nearly 3,300 ft (1,000 m). Between this range and the Andes is the Central Plain, a structural depression that only reaches a maximum altitude of 984 ft (300 m), and runs into the sea at 41[degrees]30'S. From here onward, the peaks of the Cordillera de la Costa take the form of an island chain, and the Andes rise sheer from the sea, indicating that the coastline has some very spectacular cliffs, numerous fjords reaching inland, and is bordered by a fringe of many small islands.
From north to south, in response to the lower temperatures, there are three different variant forms of the Valdivian rainforest: the true Valdivian forest, between 37[degrees]45'S and 43[degrees]20'S; the north Patagonian rainforests between 43[degrees]20'S and 47[degrees]30'S; and the Magellanic evergreen forests, between 47[degrees]30'S and 55[degrees]S.
The Chilean-Argentinean Araucaria araucana forests
In the southern Andes, near the latitudes corresponding to the Valdivian forests, there are forests of the monkey puzzle tree (Araucaria araucana, Araucariaceae), also known as Chile pines. This very attractive species of Araucaria is of great cultural importance and is economically important for its edible seeds. Some trees grow to a height of 147-162 ft (45-50 m) and a diameter of 6.6 ft (2 m) and may live for thousands of years. (Specimens about 1,500 years old are frequent.) They form pure and mixed forests, in which the specimens of A. araucana are conspicuous because their crown resembles an umbrella (see p. 85). Both pure and mixed forests are exceptionally beautiful in their natural setting of the snow-covered mountains and the glacial lakes of the Andes.
The forests of A. araucana have a limited and scattered range, from 37[degrees]20'S to 39[degrees]30'S in Chile, and from 37[degrees]30'S to 40[degrees]20'S in Argentina. These relict enclaves in the Andes are the only surviving modern representatives of the forests of different species of Araucaria that were widely distributed during the Tertiary. Other species of the genus grow in tropical or subtropical areas. Now they occur in three zones. The main area is along the ridge of the Andes between Chile and Argentina, with the two smaller areas in the Cordillera de la Costa in Nahuelbuta (Chile). In the Andes, they occur at altitudes from 1,969 ft (600 m) (in the Argentinean part) to the timber line (about 5,906 ft [1,800 m] in the north of this area and about 4,921 ft [1,500 m] in the southern part). In the coastal mountains, A. araucana forests grow at 3,281-4,593 ft (1,000-1,400 m) in the northern part, and above 1,969 ft (600 m) in the southern part. This contemporary distribution is due to its exploitation since the arrival of Europeans in the sixteenth century. Note that its distribution corresponds to that of many volcanoes in the Andes that were active until recently.
The temperate Australian and Tasmanian forests
In Australia, the temperate rainforests show great variation, depending on their geographical location and the local relief. The Australian floral kingdom consists of the entire continent plus Tasmania and a few adjacent islands. It can be subdivided into two subkingdoms: the central or desert area (i.e., arid Australia) and the Eucalyptus. The latter includes the most mesic peripheral areas of the continent and the adjacent islands. This second group's name is a reflection of one of the most distinctive features of Australia's flora: its total domination by the genus Eucalyptus, which has no equivalent elsewhere.
The temperate rainforests, the tropical forests, the monsoon forests, the savannahs, and the areas with Mediterranean climates occur in the second subkingdom. The temperate rainforests are located in the southeastern and southwestern tips of Australia and in Tasmania. The southeastern ones extend inland to about the 19.7-in (500 mm) isohyet (i.e., they grow where annual rainfall is above 19.7 in [500 mm]), and as isolated patches in appropriate environments, such as gallery forests even in areas where average annual rainfall barely reaches 11.8 in (300 mm). Typically, they are dominated by southern beech (Nothofagus) or associations of species in which this genus plays a relevant role. The temperate rainforests of southwestern Australia are located in the wettest areas. They are in contact with areas with Mediterranean climates and occur in areas with an average annual rainfall of more than 47.2 in (1,200 mm). These southwestern forests are dominated by species of Eucalyptus and have an understory similar to the temperate rainforests of southeastern Australia, except that tree ferns are absent.
The New Zealand temperate rainforests
About 60% of New Zealand still retains substantial native elements and a plant cover that is essentially the same as when the first human beings arrived. The rest is highly modified and is mainly used for extensive agriculture, pastures, cultivation of introduced tree species, or for urban uses.
Before the arrival of the first human beings, an estimated 70-80% of New Zealand was covered by temperate forests, but by 1990, the forests occupied less than 40% of the area and only 14.8 million acres (6 million ha) of native forest remained. The rest (3.2 million acres [1.3 million ha, approximately]) was occupied by plantations of introduced species. Even so, temperate rainforests occur from sea level to the timber line. In many zones, they are discontinuous, but at least in the western region of South Island, the rainiest and most rugged region, the temperate rainforests grow continuously from the shore to the subalpine layer. On the main islands, the temperate rainforests consist of up to 48 large and medium-sized tree species, and about 70 species that normally do not exceed 33 ft (10 m).
The distribution of the rainforests in New Zealand does not follow a regular pattern along defined environmental parameters. There are two types of forests: mixed forests and dominant forests. Each type shows preferences for certain environmental conditions. In the lowlands and the low to middle elevations of the mountains, in the western part of South Island and also in North Island, where many of them have been largely cleared, mixed forests occur. They have a high canopy of gymnosperms, mainly podocarps, and a lower layer of broadleaf trees. In general terms, these forests occupy the low-lying areas, where rainfall is higher, and soils are better, however, there are numerous exceptions. Rising from sea level to the tree line, the dominant forests are the southern beeches (Nothofagus), all of them evergreen species, even the mountain beech (N. solandri var. cliffortioides), which occupied the entire subalpine layer at the tree line in the high mountain areas of New Zealand. These forests of mountain beech occupy the highest areas, where rainfall is lower and the soils are poorer. However, as in the mixed forests, there are many exceptions.
The evergreen broadleaf forests and pine forests of Macaronesia
The Macaronesian archipelagoes (Canary Islands, Azores, Madeira) are not entirely subtropical nor do they occur on the maritime eastern facade of a continent. Thus, they are atypical temperate rainforests, as these evergreen broadleaf forests grow on sites exposed to the trade winds, which do not always provide enough rainfall, but provide the moisture they need in the form of horizontal precipitation (see p. 24). Of the three archipelagoes that are usually considered to form Macaronesia, temperate evergreen broadleaf forests only occur on the Azores, the western Canary Islands, and the island of Madeira. On the Cape Verde Islands, some of the more thermophilic species of these rainforests have survived, such as Sideroxylon marmulano (Sapotaceae). There are no temperate rainforests on the eastern Canary Islands, on the Selvagens (or Salvage Islands), or on the island of Porto Santo, both of them in the Madeira archipelago.
Currently, the evergreen broadleaf forests occur in the moist wettest zones of each of these archipelagoes, where rainfall decreases from north to south (from more than 118 in [3,000 mm] in the Azores to a little over 39 in [1,000 mm] in the most favorable sites in the Canary Islands). These forests are directly subject to the influence of the water-laden trade winds, which arrive from the north, northwest, and northeast, and provide significant amounts of moisture. Moisture is deposited by horizontal precipitation in relatively large amounts, varying with the site and the relief from 12 to 98 in (300 to 2,500 mm). This phenomenon is particularly important in the Canaries, as it allows the rainforests to survive and to recharge the aquifers.
Ninety-five percent of the Azores are below 4,265 ft (1,300 m), meaning that their climate is stable and favorable year round. Most of the archipelago was formerly covered by evergreen broadleaf forest. The evergreen broadleaf rainforest, locally known as monteverde, is highly degraded and restricted to small areas on some of the islands. It occurs on both north-facing and south-facing slopes from sea level to more than 3,281 ft (1,000 m). This distribution is possible because of the high average annual rainfall that is often greater than 79 in (2,000 mm).
On the Madeira archipelago, which consists of Madeira Island, Porto Santo Island, the Desertas Islands, and the Selvagens (Salvage Islands), the evergreen broadleaf rainforest might have occupied 60-70% of the land area and was only present on Madeira and Porto Santo. On the other islands, only a few species typical of the dry evergreen broadleaf forest have been able to survive, such as Heberdenia excelsa (Myrsinaceae). On the southern slopes of Madeira, the average annual rainfall is lower and prevents this type of vegetation from growing at lower altitudes (below 984-1,312 ft [300-400 m]), while on the northern slopes, they reach down to sea level. Now the archipelago's evergreen broadleaf forests occur only on the island of Madeira. About 30% of the island remains undisturbed forest. The small and uninhabited Selvagens Islands between the Canary Islands and Madeira are very low and do not possess any type of vegetation related to the temperate rainforest formations.
On the Canary Islands, the evergreen broadleaf rainforest covers only about 30% of the land area, indicating that the climate is not favorable for its development. In addition, the forest is limited by the low total precipitation and by its distribution during the year. Only the most thermophilic forms of the evergreen broadleaf temperate rainforest can grow close to sea level, occurring at a few points on the northern coasts on the islands with the highest rainfall (La Palma, Tenerife, and Gomera).
These forests do not occur in the southern part of the islands because this area is occupied by Canary pine (Pinus canariensis) and sclerophyllous forests, except for a few localized sites favored by their special orientation or by the presence of low surrounding mountains (such as the Ghimar Valley in Tenerife, the Cumbre Nueva on La Palma, etc.). Evergreen broadleaf forest used to be present in a few sites on the eastern islands of Lanzarote and Fuerteventura. Today, all that remains are a few isolated floristic elements. In addition, the forest used to cover a large area of Gran Canaria, where it has been almost annihilated by overexploitation and is now reduced to a handful of sites or to secondary thickets of myrtle-heath. Myrtle-heath is a heathland dominated by myrtle, or bayberry, Myrica faya and white heath (Erica arborea), or patches of heath dominated by white heath alone. Now the main stands of Canary evergreen broadleaf forest occur in the western islands (Tenerife, Gomera, El Hierro, and La Palma) and still occupy a considerable area, altered to a greater or lesser extent, with abundant secondary forests and significant examples of climax forest.
The evergreen broadleaf forests of the Black Sea and Caspian Sea
At the eastern end of the Black Sea and the south of the Caspian Sea, there are evergreen broadleaf forests, the Euxinic and Hyrcanian forests (see map). The Euxinic forests (a term derived from Pontos Euxinus, which means "hospitable sea," the classical name of the Black Sea) are of exceptional historical, floristical, and ecological interest. They grow in the region known in ancient times as Colchis (now Kolkhida), in the southern Caucasus, on the eastern coast of the Black Sea, and are also known as the Colchic forest. The Hyrcanian evergreen broadleaf forests are similar and occupy a section of the southwestern shoreline of the Caspian Sea, in northern Iran and southeastern Azerbaijan (Gilan-Mazandaran Lowlands, the maritime faces of the Talish Mountains, the Lenkoran Lowland, and the floodplain of the Kura and Aras [or Araxes], the Kura-Aras Lowland).
The Euxinic evergreen broadleaf forests have only survived in the gorges and valleys of the southern faces of the Greater Caucasus Range on the edge of the Black Sea, in the districts running from Tuapse in southern Russia through the republics of Abkhazia, Georgia, and Ajaria (Adzhariya), to Batumi, the capital of Ajaria, which is almost on the frontier between Georgia and Turkey. In addition, Euxinic evergreen broadleaf forests occur in Turkey in the mountains of Anatolia near the shores of the Black Sea, adjacent to Georgia. In the mountain areas, they occur at altitudes between 656 ft (200 m) and 3,281-3,937 ft (1,000-1,200 m).
Although the general climatic conditions of the Colchic area are relatively moist, only a few valleys and gorges have retained the same plant cover since before the glaciations, which occurred more than 30 million years ago. The valleys and gorges have provided an unchanging climate for these evergreen broadleaf forests and their exceptional flora because the air humidity of these valleys and gorges is high and regular throughout the year, even during the dry periods. This is a result of the relief or the elevations of the landscape: the valleys descending from the Caucasus range or the mountains in Ajaria are short, steep, and almost perpendicular to the coast, which favors the entry of moist sea air and clouds. Another factor is the abundant flow of surface and underground water down these valleys, the evaporation of which greatly increases the atmospheric humidity, especially in the lower part of these valleys. Finally, the cool moist conditions on the sides at the bottom of the valley, which only receive a few hours a day of direct sunlight, or none at all, provide a favorable environment for the conservation of hygrophilous elements of the Tertiary flora.
In addition, the Hyrcanian evergreen broadleaf forests have survived in scattered patches on the plains next to the Caspian Sea, which are now cultivated. Generally, the climatic conditions are cool and moist, with average monthly temperatures of 57.2-60.8[degrees]F (14-16[degrees]C), and average annual precipitation (mostly in winter) of 35-55 in (900-1,400 mm), with only one or two relatively dry months in the summer.
4.3 The subtropical evergreen broadleaf and mixed formations of eastern coastlines and similar formations
The most typical evergreen broadleaf forests are those of subtropical Asia. The northernmost forms occur at about 39[degrees]N, on the Japanese island of Honshu. In China, however, only the most northerly ones reach about 30[degrees]N because inland the climate is drier and cooler. The same thing happens in the Parana region, which is in subtropical latitudes, but whose relatively high altitude and inland location means it has a climate relatively cooler than the strictly maritime southeast coast of Brazil, where the Mata Atlantica tropical rainforest grows (see vol. 2, p. 52). In many regions, the evergreen broadleaf forests are associated with formations dominated by conifers, which occupy ecologically different sites from those completely occupied by the evergreen broadleaf forest: for example, in the pine forests in the Canary Islands and of the Araucaria forests in the Parana region. In other cases, broadleaves and conifers are associated in mixed formations, as happens in the southeast United States and in the mountain areas of Mesoamerica.
The evergreen broadleaf and pine forests of the southeast United States
On the coastal plains of the southeast United States and northern Florida is a life zone of forests of three different physiognomic types: deciduous dicot trees ("hardwoods"), broadleaf evergreens, and conifers (most of them evergreen). They are known by the initials D (deciduous dicots), E (evergreen dicots), and C (coniferous). U. S. botanists have created the DEC terminology, which is often used to describe this region. The American naturalist Clinton Hart Merriam (1855-1942) called it the "Austroriparian Life Zone," a reference to its location next to the southern coastline of the United States along the Atlantic and Gulf of Mexico and in the lower valley of the Mississippi. Other authors, such as German Heinrich Walter (1898-1989), considered it an ecotone between the deciduous forest biome and the evergreen broadleaf temperate rainforests.
The three physiognomic types are represented, not only in the upper tree layer, but also in the lower tree layer, the shrub layer, and the herbaceous layer. The understory contains evergreen shrubby monocotyledons (palms). The evergreen conifers are prominent on dry, sandy, upland sites. Deciduous trees, as long as there are no fires, become increasingly important on better soils. Moist well-drained and nutrient-rich sites are dominated by evergreen broadleaves, especially toward the southern limits of the area. The alluvial swamps are characterized by the presence of a deciduous conifer-the bald cypress or swamp cypress (Taxodium distichum, Taxodiaceae)-though swamp hardwoods and broadleaf evergreens are also important in large areas where climatic and ecological conditions allow it.
However the DEC area of the southeastern United States is classified, it is usually shown in broad terms on the maps as a u-shaped area occupying the Atlantic and Gulf coastal plains and extending northward along the Mississippi Valley to Indiana. Redefining the southern mixed hardwood forest to include representation of the three different physiognomic types of the canopy, its northern limit is on the Atlantic coast in the southeast tip of Virginia (about 37[degrees]N), although some authors believe it extends along the coast to the Pinelands of New Jersey. It occurs to the south near to the coastline and on the barrier islands to Cape Hatteras and then spreading inland southward to northern Florida (about 30[degrees]30'N) and westward across the northern half of the Florida panhandle to about 95[degrees]W in eastern Texas. Inland from the Gulf of Mexico, on the western Gulf Coastal Plain, this community only reaches north to 31[degrees]N. It gradually spreads northward on the eastern Gulf Coastal Plain toward south-central Georgia, where it reaches approximately 32[degrees]N, before it veers to the north, parallel to the Atlantic coast. On the Atlantic Coastal Plain, this community reaches about 99 mi (160 km) inland in Georgia and about 87 mi (140 km) inland in South Carolina and southern North Carolina: Then, it veers east to within about 37 mi (60 km) of the coast at the border with Virginia and continues northeast to Virginia Beach, with outlying areas to the north around Chesapeake Bay.
The bald cypress (Taxodium distichum) swamps and forests of southern pine (Pinus elliottii, P. glabra, P. palustris, and P. taeda) extend north beyond this region, in the Mississippi Valley and along the Atlantic coast, and are considered to represent different soil factors (pedobiomes). As a result of their ability to compete with deciduous trees in this favorable "maritime" climate, they penetrate in the deciduous forests zonobiome. In addition, they extend into the prairie biome in the coastal prairie zone of southern Texas (see vol. 8, pp. 41-43 and 80), where they are interspersed with different types of open forests that have as many species of evergreen broadleaves as deciduous broadleaves. Further west, on the vertical walls of canyons and cliffs of the Balcones Escarpment, to the east and south of the Edwards Plateau and in the gorges in the mountains of Guadalupe, there is a series of open forests and mixed forests consisting of representatives of the three DEC physiognomic types.
The Mesoamerican forests of conifers and oaks
Further south, between northern Mexico and the Nicaragua Depression, there is a large mountainous area with vegetation dominated by a forest of pines (Pinus) and oaks (Quercus, including marcescent or deciduous species), as well as some more northerly conifers, such as oyamel (Abies religiosa, Pinaceae); cypresses (Cupressus); junipers (Juniperus, Cupres-saceae); Picea and Pseudotsuga (pinabetes). These forests are estimated to have occupied about one fifth of Mexico before human intervention, about 154,000 [mi.sup.2] (400,000 [km.sup.2]) at altitudes between 4,921 and 13,123 ft (1,500 and 4,000 m) (although they may occur locally as low as 3,281 ft [1,000 m]) and where average annual rainfall is 24-47 in (600-1,200 mm).
The axis of the main mountain chains of mesoamer-ica run northwest-southeast for 2,796 mi (4,500 km), with two large gaps where the mountains fall almost to sea level. One of these gaps, the Tehuantepec Isthmus (in southern Mexico) is not a major biogeographical barrier to the plants. However, the other gap, the Nicaragua Depression, acts as an important barrier to many Andean plants, which only reach as far as the highlands of Costa Rica, and for an important contingent of boreal lineages that do not reach beyond the mountain ranges of Honduras and northern Nicaragua.
This is an mountain biome whose flora and physiognomy is close to that of the DEC area of the United States. Sometimes this biome is defined as the Mexican Holarctic forest. Usually, the upper tree layer of these temperate rainforests has a canopy about 66 ft (20 m) above the ground (though it can reach 131 ft [40 m]) and is dominated by a mixture of deciduous broadleaves, evergreen broadleaves, and conifers. In the lower tree layer, there are many smaller trees belonging to a wide variety of botanical families, including tree ferns. There are many vascular epiphytes, shrubs, lianas, and other climbing plants; there is also a very rich herbaceous layer, which includes abundant ferns, clubmosses (Lycopodium), and spike mosses (Selaginella). The climate is warm to hot, very temperate and wet; the growing season lasts 205-260 days and less than 0.1% of the hours in the year show temperatures below freezing point.
The Chinese-Japanese and Himalayan evergreen broadleaf forests
Evergreen broadleaf forests also occur in Asia, from the southern slopes of the Himalayas (Nepal, Sikkim, Bhutan) to the temperate zones of southwest Japan (Japan, Korea, and central-eastern China) and the subtropical regions of southern Japan, Taiwan, and southern China. All southwest Japan and the southern coastal face of the Korean Peninsula are within the area of evergreen broadleaf forests, which, towards the north of the Japanese Archipelago, is limited to the lowest areas, until it reaches its northern limit about 39[degrees]N at sea level on the shores of the Pacific, at latitudes slightly lower than the Sea of Japan, where the climate is colder. This large area has a climate with summer rains in which evergreen broadleaf forest grows naturally and would constitute a well-defined vegetation zone if it had not been almost totally replaced by crops and forest plantations of economically important species.
On the slopes of the Himalayas, which run more than 1,243 mi (2,000 km) northwest-southeast between Eurasia and Indian subcontinent, the dry western floristic realm is connected to the wet eastern one. Over the length of the Himalayas, there is a gradient in precipitation from average annual values of more than 98 in (2,500 mm) in the eastern Himalayas in Assam to less than 24 in (600 mm) in the Punjab in the west. In addition, there is a temperature gradient on the southern slopes, which varies with altitude. The mountains rise 26,247 ft (8,000 m) above the surrounding area creating a temperature gradient of more than 90[degrees]F (50[degrees]C) from the base of the mountains, where the vegetation is subtropical or tropical, to alpine tundra and frozen peaks. The forested zone is below 13,123 ft (4,000 m) and can be divided into four or five different altitudinal layers.
At the extreme eastern tip of the Himalayas, the wet evergreen forests form an altitudinal layer about 4,921 ft (1,500 m) wide (between 3,281 and 8,202 ft [1,000 and 2,500 m]) that gradually becomes narrower toward the west. The wet evergreen forest of the eastern Himalayas is very similar in appearance to the tropical montane forests of the high mountains of Southeast Asia (see vol. 2, pp. 364-365). Toward the northeast of the Himalayas, the tropical evergreen montane forests lose their accompanying species, and their floristic composition becomes poorer, while its altitudinal limits gradually descend to the valley of the Chang (Yangtze) River in China. From east to west, along the southern slopes of the Himalayas, these moist forests are replaced by sclerophyllous forests that are subject to dry summer conditions. The northwestern region of the Himalayas is dry, with a subdesert-type vegetation, more closely related to the vegetation of central Asia than that of the tropics. The tree vegetation is restricted to the cloud belt at middle altitudes, where conifer forests are dominant, and to the wetter areas with high local precipitation or along water courses, where deciduous trees may also occur. In the eastern Himalayas the temperate conifer forest is also the vegetation layer immediately above the evergreen broadleaf forest.
The subtropical Mission forest
The subtropical rainforest of South America forms part of the Parana floristic province in southeast Brazil. In Brazil, it is known as selva higrofila (hygrophilous forest) to distinguish from the dry and the deciduous subtropical forests. It is also commonly known in Brazil as mata branca (white forest) to distinguish it from the mata preta, the Araucaria forests of the region, dominated by the emergent Araucaria angustifolia, the Parana pine, which is known locally as kuri'y. In Argentina, it is also known as "Mission forest." It is considered an evergreen broadleaf forest because it is dominated by species of the Lauraceae and other trees with similar leaves, although there are deciduous trees in variable proportions.
The Mission forest is subtropical rather than temperate and is similar to an equatorial rainforest, although it differs in the composition of its flora and fauna. The cold winter keeps the regional intertropical biota from living there. The Mission forest extends from the western edges of the Serra do Mar to the center of Rio Grande do Sul, the northeast tip of Argentina and eastern Paraguay, from 40[degrees]W to 58[degrees]W. From north to south, it runs from 18[degrees]S, on the edge of the tropical zone, to 30[degrees]S or 34[degrees]S, if the gallery forests along the Parana River and Uruguay River are included. Large areas of the Mission forest have disappeared and have been replaced by meadows (campos). As a result, even the best conserved forests give little idea of the original flora and vegetation structure, about which little is known.
The Brazilian Araucaria forest
The Serra do Mar runs down Brazil's Atlantic coastline and reaches a maximum height of 6,306 ft (1,922 m). The eastern slopes are abrupt and border a coastal strip, a few dozen kilometers long, where the Mata Atlantica grows. To the west, the relief consists of three stepped mesetas, known as planaltos, which gently descend to 656 ft (200 m) on the banks of the Parana River. The subtropical forest, without Araucaria, rarely grows above 2,625 ft (800 m). It forms the matrix for the forests of Parana pine (Araucaria angustifolia), with a different floristic composition and characterized by the dominance of this majestic evergreen conifer.
The Parana pine (Araucaria angustifolia), forms (or used to form) the largest forests dominated by a single species of conifer in South America. The presence of the Araucaria forests in the Parana subtropical region is in contrast to the vegetation of the rest of the zone. This is because this species is ancient. It belongs to a group of conifers more than 200 million years old that was very widespread in the past. The presence of forests of this species in southeast Brazil is due to the migrations from the southern Andes toward what is now southern Brazil, rather than the other way round. The flora of the Andean-Patagonian region is very closely related to that of the Araucaria forests of Brazil. In both of these regions, the conifers (which are uncommon in South America) are important elements in some forests. In the forests of Parana pine, apart from the dominant species, the common species include podocarps (Podocarpus) and shrubs like Drimys, barberries (Berberis), and fuchsias (Fuchsia).
Forests of Parana pine cover much of the planalto of southern Brazil (the above-mentioned stepped mesetas that descend gently to the west, from the Serra do Mar to the banks of the Parana) at altitudes greater than 1,640 ft (500 m) between the 18[degrees]S and 30[degrees]S and between 44[degrees]W and 54[degrees]W but do not reach the coast. Not even isolated patches occur within 12-25 mi (20-40 km) of the sea. In Brazil, its area of distribution includes four states: Rio Grande do Sul, Santa Caterina, Parana, and Sao Paulo and also enters the Argentinean province of Misiones and eastern Paraguay. There are also isolated forests of this type in the south of the states of Rio de Janeiro and Minas Gerais. The growth of Araucaria angustifolia forests is closely related to altitude. In the southern localities, the lower limit is above 1,640 ft (500 m) and the upper limit above 3,609 ft (1,100 m), while in the northern zone, the lower altitudinal limits vary between 2,625 and 3,937 ft (800 and 1,200 m), and the upper limits between 5,906 and 7,546 ft (1,800 and 2,300 m). The highly fragmented shape of its area of distribution is because the Parana pine prefers sites with a low slope, rolling landscapes, so it occupies the edges of the planaltos and the edges of all the deep canyons formed by the rivers flowing down from the meseta.
1 The lush vegetation of the temperate rainforests, as shown by this photo of the forest in the Otway National Park in Victoria, Australia, is comparable to that of the tropical rainforests growing near the equator, the "jungles." The similarities between these two types of rainforest do not finish there because they share a wet, damp, climate; abundant fog; an evergreen canopy layer; vegetation with a complex structure; and a high diversity of plant species with abundant ferns, climbers, and epiphytes. The temperate rainforests tend to have much cooler climates and, depending on the area, much more seasonal climates. Another feature distinguishing temperate from tropical rainforests is their geographical distribution. The tropical rainforests all occur in a relatively continuous strip along the equator, but the distribution of the temperate rainforests is broken up into many little patches (see figure 7). This is because the temperate rainforests, unlike the other biomes, are highly conditioned by the recent geological (and thus biological) history of the planet, especially the events of the Quaternary.
[Photo: Jean-Marc La Roque / Auscape International]
2 The Emerald Lakes in New Zealand's Southern Alps, were formed in the last Pleistocene glaciation, which was at its height 25,000 years ago. In each glaciation, low temperatures led to the accumulation of snow and ice on mountaintops, the growth of glaciers, and their descent to the valleys, which they made deeper and wider. Every time an ice age finished, the ice retreated leaving piles of moraine deposits that blocked the valleys, damming rivers and streams, and causing their waters to accumulate. New Zealand is one of the Southern Hemisphere regions with most lakes of glacial origin, and the Emerald Lakes were formed when the Tasman Glacier retreated. The Tasman Glacier, the largest in the Southern Alps, 18 mi (29 km) long, can be seen in the background of the photo. The glaciations were not very intense in New Zealand, and temperatures did not fall enough to affect the temperate rainforests, which still covered most of New Zealand at the end of the last ice age, 10,000 years ago.
[Photo: Photobank Image Library New Zealand]
3 The latitudinal distribution of some tree species from southern South America helps to distinguish between the different types of forest in the area but is mainly a reflection of the climatic events of the late Tertiary and Quaternary. Confers like Fitzroya cupressoides and Araucaria araucana have been restricted to small areas. Some species of Nothofagus occur over a wider range of latitudes. In the north of this area, the southern beeches usually occur at higher altitudes than in the more southerly areas, where they grow almost at sea level.
[Drawing: IDEM, based on Hueck, 1978]
4 Mountain formation has played a major role in the current distribution of the temperate rainforests. During the Cenozoic, mountain formation caused temperature rainforests to disappear from most of the areas they had occupied, as the rising of mountain ranges dramatically affected the circulation of the atmosphere and the local climate. The elevation of the Himalayas greatly changed the circulation of the atmosphere of the surrounding area. Mountain ranges also act as barriers to the spread of plant species. The temperate rainforests often occupy areas of intense volcanic activity (whether now or in the geologically recent past), further strengthening this biome's links to mountains and to geological processes. The rainforests of Macaronesia occur on volcanic islands, and on the other side of the planet, New Zealand's active volcanoes play a major role in ecological succession in temperate rainforests (see also figure 37). The photo shows the Three Sisters mountains (in the background), seen from Mackenzie Pass in Oregon. The area in the foreground is a relatively recent lava flow covering 66 [mi.sup.2] (170 [km.sup.2]) that has only been colonized to a limited extent by the vegetation.
[Photo: Charlie Ott / Bruce Coleman Collection]
5 The dominant winds in the Canary Islands are the trade winds from the northeast and northwest, the result of the breakdown of the anti-trade winds from the equator into two streams. The trade winds from the northeast, the true trade winds, are temperate winds laden with moisture. The large quantities of water they bear cannot condense unless they cool as a result of being forced to rise. This is what happens on islands with high mountains; when the air masses hit the mountain, they cannot advance and are forced to rise up the mountain. As the air rises, it cools, and the water vapor condenses (see also figure 6). One might expect this to lead to rainfall; however, this does not happen in the Canary Islands. The trade winds blowing from the northwest, which are hot and warm, are present at altitudes above 4,921 ft (1,500 m) and cause the clouds to dissipate without any rain falling. The arrival of maritime air masses from the pole at lower altitudes prevents the clouds from descending below 2,461 ft (750 m). For all these reasons, on the islands with the highest relief, such as Tenerife, the cloud belt is always between 2,461 and 4,921 ft (750 and 1,500 m), roughly halfway up the slope, and in Gomera and the other islands that do not reach an altitude of 4,921 ft (1,500 m), the cloudbelt is in the highest areas. In the low-lying islands, such as Lanzarote, the cloud belt never forms.
[Drawing IDEM, from several sources]
6 The "sea of clouds" generated by the trade winds on the northeastern slopes of Gomera (Canary Islands). When the clouds hit the mountain, they start to rise, but the warmer, less dense layers prevent them from rising, causing this type of accumulations and providing the plants with abundant water all year round through the condensation of droplets (horizontal precipitation). This supports the growth of the temperate rainforests on the northeast-facing slopes of Gomera and the other western Canary Islands (Tenerife, La Palma, and El Hierro), where precipitation alone would be insufficient. In many of these sites, the quantity of rainfall is less than the amount of horizontal precipitation. The photo shows the "sea of clouds" above the division separating the north of the island from the south, and it also shows the aridity of the slopes that are not affected by the clouds. The shrub in the foreground is a sweet tabaiba (Euphorbia balsamifera), a plant that forms relatively large scrubs in the coastal and arid regions in the south and west of the Canary Islands.
[Photo: Thomas Dressler / Planet Earth Pictures]
7 The temperate rainforest biome is fragmented and consists of small areas that are distant from each other. All these areas have a mild climate. Temperatures never reach extreme values or show marked changes over the course of the year. There may be frost in winter in some sites, but there is not a single month when average daily temperatures are below 32[degrees]F (0[degrees]C). Rainfall varies between relatively high and very high (and is rarely below 3.9 in [100 mm] of rain per month) and is distributed regularly over the course of the year. However, as shown by the temperature and rainfall diagrams for Seattle, Washing-ton, and La Laguna (Tenerife, Canary Islands), some sites may have a relatively long dry period (colored yellow). This period is only relatively dry, as the permanent clouds covering both sites provide the vegetation with the water it needs (see also figures 5 and 6).
[Drawing: IDEM, from several sources]
8 Snow is not a rare phenomenon in the temperate rainforests as shown by this photograph taken in the Tierra del Fuego National Park, near Ushuaia, in Argentina. This area of the biome is at high latitudes, so temperatures often fall below 32[degrees]F (0[degrees]C), and precipitation falls as snow. In other temperate rainforests at lower latitudes, frosts may also occur during the winter, but much less frequently (usually no more than 50 days a year). The temperate rainforests of the wet subtropical regions enjoy a much milder climate, with average temperatures that are always above 32[degrees]F (0[degrees]C), and with occasional frost when masses of cold air arrive from the poles. In general, the temperate rainforest biome enjoys mild temperatures that vary little over the course of the year. Another important feature of their climate is that average annual rainfall is very high 70.9-126 in (1,800-3,200 mm) and evenly distributed over the course of the year, which is vital to support the lush vegetation, almost as lush as that of the tropical rainforests. Very few of the temperate rainforests undergo a regular period of water stress, and when one does occur, it is usually very short. The climate may be very seasonal, with rainier summers than winters.
[Photo: Richard Coomber / Planet Earth Pictures]
9 The cold resistance of some trees from the Southern Hemisphere temperate rainforests. As temperatures are mild in the temperate rainforests, the trees are not particularly cold resistant. Many species of conifers from the Southern Hemi-sphere temperate rainforests are no more cold resistant than their relatives from hot tropical climates; most of them cannot survive temperatures below -4[degrees]F (-20[degrees]C). The angiosperms of the temperate rainforests, which bear their leaves all year round and whose buds are totally unprotected (something that is particularly typical of the species of Eucalyptus), are even less resistant.
[Source: Sakai et al., 1981]
10 The soils of the temperate rainforest biome, exemplified by this andosol from New Zealand (see also figure 12), are quite varied, as they are not the result of the vegetation cover but of many different factors, such as the parent material that they develop on. It is extremely difficult to determine which soil types are typical of the temperate rainforests be-cause they occupy small areas and are scattered in many different countries, which do not always use the same soil classification systems. Broadly speaking, four soil types are of most importance in this biome: ferralsols and nitosols (formed on basalts), andosols (derived from recent volcanic materials), and podsols (formed on quartz sands). Many other soil types are also present in the temperate rainforest biome, and the only information that can be given about them is the dominant soil type in each zone. For example, acrisols are the most abundant soils in the temperate rainforests of China, podsols are more typical of Florida, and andosols are the most frequent in the Canary Islands.
[Photo: L.P. van Reeuwijk / ISRIC, Wageningen]
11 Podsols, like this one in southeast Queensland (Australia), form in wet climates on parent materials poor in weatherable components. They are the most common soils in the temperate rainforest biome and contain three different horizons: a blackish surface O horizon; a grayish E (elluvial) horizon; and a Bh accumulation horizon that, as the photo shows, is often reddish in color. Podsols are acidic soils where the organic matter undergoes chelation and eluvation with the oxides of iron and aluminium. The low nutrient content of podsols (almost all of it in the A horizon) means they are not very suitable for agriculture, as they require large fertilizer inputs.
[Photo: Robert Banks]
12 Andosols, like this one on Sao Miguel Island (Azores), are dark because they have developed from volcanic ash, as well as other amorphous materials. The photo shows an andosol that has formed on alternating layers of clay and volcanic ash (pyroclastic materials). Andosols form much faster than other types of soil, as these volcanic materials are easily weathered. In less than a thousand years, there may be a clear, deep and dark A horizon of organic matter, below which is a brown illuviation B horizon. New volcanic eruptions may deposit a layer of ash on top of them, and then, soil formation processes slow down. There may be some problems cultivating these soils (such as phosphorus deficiency), but they have a reputation for being very fertile, and in many zones, they have largely been cleared for cultivation.
[Photo: Antoni Agelet]
13 Some temperate rainforests are dominated by evergreen broadleaf trees and shrubs. Their large, dark green leaves are held perpendicular to the rays of the sun and provide a large photosynthetic area. However, since they lose a lot of water by transpiration, they are covered by a protective cuticle that makes them look shiny, as can be seen in this photo of a specimen of vinatigo (Persea indica, Lauraceae) in fruit, taken in the Macaronesian evergreen broadleaf forest. The temperate rainforests dominated by broadleaf trees occupy only a small area now, being largely restricted to coastal areas and islands with an oceanic climate, but they were widespread in the wet subtropical areas at the end of the Tertiary, before the Quaternary glaciations caused them to retreat.
[Photo: Antoni Agelet]
14 Some temperate rainforests are dominated by needle-leaved conifers, such as the Japanese umbrella pine (Sciadopitys verticillata, Taxo-diaceae), which is shown in the photograph. Their long narrow evergreen leaves mean that these species can continue photosynthesizing outside their active growing season and that they are resistant to drought and cold conditions. Thus, the temperate rainforests that grow at high altitudes or latitudes or in areas subject to periods of water stress are usually dominated by trees and shrubs with needle leaves. In other regions, however, conifers grow mixed with broadleaf species to form mixed temperate forests.
[Photo: John Mason / Ardea London]
15 Temperate rainforests of conifers are common on the northern Pacific coastline of North America, where the moist temperate climate, dominated by oceanic influences, allows the growth of forest formations like this one on Johnstone Strait, in Vancouver, southwest British Columbia. These rich dense forests are among the most productive in the world. The biomass they accumulate per unit area is greater than that in the tropical rainforests. The dominant species are tall conifers that are very long-lived and include the Douglas fir (Pseudotsuga menziesii), western hemlock (Tsuga heterophylla), western red cedar or giant arborvitae (Thuja plicata), Sitka spruce (Picea sitchensis), and the coast redwood (Sequoia sempervirens). All these species live for many centuries.
[Photo: David Parer & Elizabeth Parer-Cook / Auscape International]
16 The temperate rainforests of the northwest coastline of North America, occur in a long narrow strip running down the Pacific coastline from the Gulf of Alaska to northwest California. To the west, they reach sea level, while their eastern limit is determined by the ridge of the Coast Mountains in Canada and the Coast Ranges and Cascade Range in the United States. This region's wet highly maritime climate is characterized by mild rainy winters and relatively dry summers. The fact that this strip of forest occurs over a range of almost 20[degrees] latitude and grows in a mountainous area next to the coast introduces variations in climate due to altitude and latitude. The temperate rainforests of northwest North America, the most northerly of all the temperate rainforests, are large conifer forests that are not dominated by a single tree species, but by several (see also figure 15). Angiosperm trees only occur in a few marginal habitats and never in large numbers.
[Drawing: IDEM, from several sources]
17 The southern beeches (Nothofagus) are the dominant trees of the temperate rainforests of the southwest coastline of South America, as shown by this oblique aerial photograph of a forest in Tierra del Fuego, in Argentina. The growth of temperate rainforest in this area is the result of the presence of the Andes Mountains, which run down the western coastline of South America, almost parallel to the coast between 70[degrees]W and 71[degrees]W. Maritime air masses from the Pacific cannot pass this high range of mountains and they discharge their moisture on the western slopes, allowing the growth of lush forests.
[Photo: Thierry Thomas / Bios / Still Pictures]
18 In South America, the temperate rainforests are concentrated in a long narrow strip near the Pacific coastline. There are four types of temperate rainforest in South America: the Valdivian rainforests (between roughly 37[degrees]S and 43[degrees]S), the Patagonian evergreen broadleaf forests (43-48[degrees]S), the Magellanic evergreen broadleaf forests (south of 47[degrees]S), and the Chilean-Argentinean Araucaria forests (east of the Valdivian rainforests, roughly 37-40[degrees]S). The limits between these formations are not always very clearly defined because forests are transitions between the four types. The species typical of the Valdivian forests gradually disappear out in the southern part of their range, so that this formation often merges into the Patagonian evergreen broadleaf forests.
[Drawing: IDEM, from several sources]
19 Eucalypts (Eucalyptus spp.) are the dominant trees in the rainforests of southwestern Australia. The species present there include the marri or red gum (E. calophylla), the gum-top stringybark (E. delgatensis), the bullich (E. megacarpa), and the wandoo (E. wandoo). The species that is dominant in a given area depends mainly on the soil conditions and the rainfall. Fertile soils formed from quartz material often support forests of karri (E. diversicolor), like the one shown in the photograph, near Pemberton in Western Australia. The temperate rainforests of southeastern Australia are dominated by southern beeches (Nothofagus), which together with other evergreen broadleaf species, tree ferns, and some palm trees form lush forests.
[Photo: Jaume Altadill]
20 The distribution of temperate rainforests in Oceania, showing the largest areas are in southeast Australia. They occur along the coastline, but also reach many kilometers inland. The dominant trees are the southern beeches (Nothofagus), unlike the much smaller area of temperate rainforests in the southeast tip of the continent, which are dominated by species of Eucalyptus. Temperate rainforests are the most abundant forest formation in New Zealand. Before human colonization, they covered the entire North Island and the western part of South Island, but in many areas, they have been cleared. The dominant trees are southern beeches, as they are in the temperate rainforests of Tasmania, which occupy much of the island.
[Drawing, IDEM, from several sources]
21 The evergreen broadleaf forests grow in the wettest sites on the islands of Macaronesia. They consist of tall trees (easily exceeding 66 ft [20 m] in height), and their crowns form a dense evergreen canopy that prevents light from reaching the ground level. The understory consists largely of ferns, mosses, and lichens, shrub species; and some climbing plants and epiphytes that grow on the trunks. These forests have a rich flora. Because of their high degree of insularity, they contain more endemic species than most other temperate rainforests. One of these endemic species is the taginaste or arrebol (Echium brevirame, Boraginaceae), which only occurs on the island of La Palma, in the Canary Islands. As can be seen in the photo, this spiny-leaved plant produces violet flowers on tall spikes that may be quite conspicuous in some sites in these forests.
[Photo: Arnoldo Santos]
22 The geographical location of Macaronesia and the location of the evergreen broadleaf forests in the Canary Islands. The archipelagoes that form Macaronesia lie in a large area of the northeast Atlantic Ocean, between 27[degrees]N and 40[degrees]N, and between 13[degrees]W and 31[degrees]W. The evergreen forests only occur in the Azores, Madeira, and on the northeast slopes of the western Canary Islands (La Palma, El Hierro, Gomera, Tenerife, and Gran Canaria) and not on all the islands in the area.
[Drawing, IDEM, from several sources]
23 The distribution of the Euxinic and Hyrcanian temperate forests, in the western Caucasus, on the eastern coast of the Black Sea, and on the southern coast of the Caspian Sea, respectively. The evergreen broadleaf forests on the shores of the Black Sea are called Euxinic (derived from the Black Sea's name in antiquity), and those on the shores of the Caspian Sea are known as the Hyrcanian forests. Both used to occupy much larger areas but are now confined to a few sites.
[Drawing, IDEM, from several sources]
24 In southeastern North America, temperate rainforests occur in the plains of the Atlantic coastline and of the Gulf of Mexico (except southern Florida) and the alluvial plains of the Mississippi. These temperate forests consist of broadleaves, both evergreen and deciduous, and conifers. Broadleaves dominate toward the south and at lower altitudes; evergreens dominate toward the north, at middle altitudes in the Appalachians and on the banks of the Mississippi, where pine forests with deciduous trees merge into deciduous forests.
[Drawing: IDEM, from several sources]
25 The distribution of the temperate rainforests in Mesoamerica. In Mesoamerica, temperate rainforests grow at altitudes between 3,281 and 13,123 ft (1,000 and 4,000 m) in the Sierra Madre and in most of the mountainous regions. These forests are dominated by a range of conifers and members of the beech family. The most important conifers are the pines (Pinus), though many species of other genera are present (such as Abies, Picea, and Pseudotsuga). The most abundant members of the beech family are the different species of oak (Quercus). The very diverse temperate rainforests of Mesoamerica are similar in appearance to those of the southeastern United States, and this area contains endemic species.
[Drawing: IDEM, from several sources]
26 The Sino-Japanese and Himalayan temperate rainforests cover a large area in eastern Asia and on the nearby islands. They spread along the southern slopes of the Himalayas, at lower heights further to the west. Much of southern China, the southern half of Japan and part of the island of Formosa, lie within the temperate rainforest biome, as does part of the southern coast of the Korean peninsula.
[Drawing: IDEM, from Masahiko Ohsawa, 1993]
27 Originally, southern Japan was covered with evergreen broadleaf forests known in Japanese as shoyoju-rin (shiny forest), which used to occupy large areas on the islands of Shikoku and Kyushu. Since antiquity, farmers have cleared the forests for rice paddies and agricultural fields. Only the forests on a few small islands remain intact; many species of plants grow in these forests. The most distinctive tree species are: the camphor laurel (Cinnamomum camphorum, Lauraceae); several Japanese evergreen oaks (Quercus subgenus Cyclobalanopsis); podocarps (Podocarpus); and Albizia. This great diversity of trees is the reason for the wide range of shades of green in the canopy, as shown by this photograph, taken on Yakushima (Yaku Island), at the southern tip of Japan.
[Photo: Norizo Higeta / Nature Productions]
28 The subtropical Mission forest is a broadleaf formation 82-98 ft (25-30 m) tall with a variable number of deciduous species. The understory is dense, with many climbing plants and epiphytes. Palms also grow in some areas, the most abundant including the queen palm (Arecastrum romanzoffianum), locally known as coco, geriba, and pindo, which can grow to a height of 66 ft (20 m). The photograph, taken in the Iguazu National Park in Argentina, shows how dense the canopy is and its similarity to a tropical rainforest. The area in the photo contains bamboos (Guadua) and palms, most of which cannot be distinguished among the canopy (see left edge in center).
[Photo: Xavier Ferrer & Adolf de Sostoa]
29 Temperate rainforests grow in eastern South America, in southeastern Brazil and the adjacent area of Argentina and Paraguay (between roughly 20[degrees]S and 30[degrees]S and between 42[degrees]W and 57[degrees]W). Two different types of temperate rainforest grow in this area: the subtropical Mission forest and the forests of Parana pine, or kuri'y (Araucaria angustifolia). The Mission forest occurs at lower altitudes, below 2,297-2,625 ft (700-800 m), while the Parana pine forest grows above this. The climate of the area where the Mission forest grows has relatively high rainfall, only exceeding 55 in (1,400 mm) in a few sites. The seasonal changes are not very well marked. The winters are mild, and the summers are hot. In the Araucaria forests, the average annual rainfall usually exceeds 55 in (1,400 mm), and the winters may be cold.
[Drawing: IDEM, based on several sources]
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|Publication:||Encyclopedia of the Biosphere|
|Date:||Jun 1, 2000|