Forest Zones, Temperate
Forest Zones, Temperate
natural zones of the continents in the northern and southern hemispheres, characterized by the presence of forest vegetation (chiefly coniferous and deciduous species) and by the prevalence of podzols and brown earth. Many forms of glacial and periglacial terrain have been preserved in the northern temperate forest zones of the northern hemisphere.
The temperate forest zones of Eurasia occupy most of Western Europe, with the exception of the extreme northern and southern regions. They prevail on the Eastern European Plain, in the Urals, in Western Siberia, on the Central Siberian Plateau, and in the Far East, where they extend to the North China Plain and occupy the northern parts of the Korean Peninsula and the island of Honshu. In North America the forest zones stretch from the Pacific to the Atlantic, extending south along both coasts to 36°-40° N lat. In South America the temperate forest zones are found only in the west in the Andes, south of 38° S lat. A small section of the temperate forest zone is found on New Zealand’s South Island. There are no forest zones in the temperate belts of the other continents.
The temperate forest zones receive comparatively little solar heat. The total solar radiation is 290–420 kilojoules per cm2(70–100 kilocalories per cm2). In most of the temperate forest zones 70–90 percent of the radiative heat is received in the warm half of the year. The average atmospheric temperature in the coldest months ranges from −40° to 5°C, and in the warmest months, from 10° to 20°C. Much of the temperate forest zone in the northern hemisphere is penetrated by arctic air masses from the north. Plant growth slows markedly and in many places ceases because of insufficient warmth during the winter. Perennially frozen rocks are widespread in the intracontinental regions. Snow covers much of the area in winter. The total annual precipitation ranges from 300–1,000 mm on the plains to 2,000–3,500 mm in the mountains and in regions subject to monsoons. The greatest precipitation generally occurs in the summer. In almost every part of the temperate forest zones, more precipitation falls than evaporates. Consequently, the rivers have abundant water which, for the most part, freezes over in winter. Vast stretches of the plains are swampy.
The vegetation of the temperate forest zones is distinguished by its comparative lack of variety. There are usually no more than five to eight types of forest trees, and in regions with the most extreme continental climate the trees of a single species often prevail. Species diversity increases in places where forests and meadows, forests and swamps, or forests and steppes interpenetrate. Coniferous forests of spruce, fir, pine, and larch, often mixed with small-leaved species such as birch and aspen, are widespread in the interior and eastern parts of continents in the northern hemisphere, in regions that have freezing winters. Mosses, grasses, and bushes are well developed in temperate forest zones. Broad-leaved forests, which are common along the coasts of the continents, are more varied in composition and complex in structure than forests of the interior. Beeches, oaks, lindens, and maples predominate in the coastal forests. The undergrowth and grass cover are well developed. Mixed forests occupy an intermediate position between the coniferous and deciduous forests. The most widely distributed of the broad-leaved species are the oaks, maples, and lindens, and of the coniferous species, the spruces, pines, and firs. Small-leaved species are also very common.
The average above-ground plant mass is 900 centners per hectare (ha) on the northern taiga and 3,700 centners per ha in the broad-leaved forests; the annual increment varies from 70–200 centners per ha. The density and diversity of the plant cover, the density of the animal population, and the intensity of biogeochemical processes are greater in the broad-leaved than in the coniferous forests. The biological cycle of minerals is 80–230 kg per ha a year in coniferous forests and 300–450 kg per ha in broad-leaved forests. Cryogenic-taiga and podzolic soils prevail under coniferous vegetation, and brown forest soils under broad-leaved forests. Brown forest soils, which have the most valuable agronomic qualities of all the soils in the temperate forest zones, contain a substantial quantity of humus, are chemically neutral, and have a high absorption capacity. Acidity and a low humus content are characteristic of most soils of the temperate forest zones. Forest vegetation and permafrost retard soil erosion in many regions.
In mountain regions (the Scandinavian upland, the Alps, Carpathians, and Urals, the mountains of Eastern Siberia and the Far East, and the Cordilleras, Appalachians, and Andes, for example), the natural features of the forest zones change with altitude. For example, in mountains situated among broad-leaved forests, as the altitude increases the broad-leaved forests give way to mixed and subsequently, to coniferous forests, and then to subalpine and alpine meadows. In taiga regions coniferous forests usually give way to mountain tundra as the altitude increases.
The fauna of temperate forest zones consists mainly of forest species. The animals are found at different stories (levels) of the forest. Many species have adapted to the seasonal rhythm of natural processes. In addition to forest species, there are animals usually associated with the steppe, meadows, and bogs.
There are three subzones of the temperate forest zones: the taiga (sometimes considered a separate zone), mixed forest, and broad-leaved forest. The taiga is found primarily in Eurasia, where it stretches 12,000–13,000 km from west to east. The subzone of broad-leaved forests is most highly developed in western Eurasia. At the eastern end of the continent the cold winter monsoon and prevailing mountain terrain push the taiga and mixed forests to the south.
In North America the temperate forest zones occupy a substantially smaller area than in Eurasia. Strongly developed coniferous forests with considerable species diversity (Sitka spruce and Douglas fir, for example) prevail in the maritime regions. Landscapes of mixed and broad-leaved forests are quite pronounced southeast of the Great Lakes, where they cover a large area. The flora and fauna of this region are very abundant and extremely diverse. A subzone of the mixed forest prevails in South America and in New Zealand, where climatic conditions favor the development of evergreens, as well as coniferous and deciduous species. Beech (southern) and coniferous-deciduous forests prevail on brown forest soils.
The vast natural resources of the temperate forest zones promoted the settlement and exploitation of these regions. Large areas, especially those once covered with broad-leaved and mixed forests, are now farmlands. Forestry and hunting are well developed in the taiga.
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G. M. IGNAT’EV