Forest-Steppe Zones, Temperate

Forest-Steppe Zones, Temperate

 

natural zones of the northern hemisphere characterized by a combination of forest and steppe areas. In Eurasia the forest-steppes extend in a solid band from west to east from the eastern foothills of the Carpathians to the Altai. West and east of this band the forest-steppe is broken up by mountains. Forest-steppe regions are located on the Central Danubian Plain, in a number of intermontane hollows in Southern Siberia, in the Mongolian People’s Republic, and in the Far East. They also occupy part of the Sungliao Plain in northeastern China. In North America forest-steppes stretch from north to south through the Great Plains to 38° N lat. There are no forest-steppe zones in the temperate region of the southern hemisphere.

Cold, snowy winters and warm, relatively humid summers are characteristic of the temperate forest-steppe zones. The surface receives 420–545 kilojoules per cm2 (100–130 kilocalories per cm2) of solar radiation a year (67–75 percent in the warm half of the year). The average January temperature ranges from — 2° to — 20°C. In continental Siberia it is as low as — 35°C. The average July temperature ranges from 18° to 25°C. The total annual precipitation on the plains usually ranges from 400 to 1,000 mm; most of it falls in the summer. Because of the high rate of evaporation, the soil may dry out during the summer, causing the plants to wilt. The snow cover lasts for a long time in the winter. In the winter, low temperatures stop plant growth and many biogeochemical processes in the soil.

The rivers overflow in the spring because of the thaw and melting snow. They are low in the summer, when parts of some small rivers dry up. There are numerous small depressions, some of which are filled with salt water.

The soil cover of the temperate forest-steppe zones is highly varied. The main groups are gray forest soils with signs of pod-zolization, leached and podzolized chernozems, and meadow-chernozem and chernozem-like prairie soils. Alkaline and solonets soils are widespread in regions with a continental climate (Western Siberia, the Great Plains). A high humus content, slow mineralization of the leaf-fall, and stable structure are characteristic of forest-steppe soils. They are very fertile and can, therefore, be cultivated intensively. Excessive plowing of the land has resulted in severe soil erosion in many regions.

The natural vegetation of temperate forest-steppe zones consists of small forests alternating with areas of steppe-like meadows and meadow-steppes. In the European forest-steppe zone oak and linden prevail. In the west, ash and hornbeam are also important; in Siberia, birch, aspen, larch, and pine; and in northeastern China, oak and other broad-leaved species. In North America birch and aspen prevail in the forest-steppes of the Great Plains, and oak and hickory in the western part of the plains. The natural grassy vegetation is preserved mainly in national parks. It is characterized by considerable species diversity (about 70–80 species of higher plants per sq m), abundant rhizomatous grasses, and weed grasses. Meadow grass, fescue, reed grass, hair grass, and feather grass, as well as beard grass, are very common in North America. The annual increment in the plant biomass is about 200 centners per hectare (ha) in the wooded areas and about 130 centners per ha in the meadows. Biogeochemical processes occur more intensively in the forest-steppe zones than in the other zones of the temperate region. The biological cycle of minerals on the meadow-steppe parts of the European forest-steppe is estimated to be 550–700 kg per ha.

Both forest and steppe fauna are found in the temperate forest-steppe zones. Typical forest animals of the European forest-steppe are squirrels, European hares, and in some areas, elk. The large jerboa and spotted suslik are among the steppe animals found in the European forest-steppes. Susliks and hamsters are common in the Siberian forest-steppe, and prairie dogs, murids, hares, woodchucks, and rattlesnakes, in the American forest-steppe.

The natural conditions of the temperate forest-steppe zones have been substantially altered by man. The number of forests declined as the area of plowed land expanded. A large area is plowed up regularly. The main crops are winter and spring wheat, oats, corn, potatoes, and sugar beets.

Subzones of broad-leaved forest steppes, coniferous small-leaved forest steppes, and prairies are encountered in the temperate forest-steppe zones. The prairies are distinguished from the forest-steppes by a number of characteristics, including a warmer, more humid climate and greater quantity and productivity of the plant mass.

REFERENCES

Berg, L. S. Geograficheskie zony Sovetskogo Soiuza, 3rd ed., vol. 1. Moscow, 1947.
Mil’kov, F. N. Lesostep’ Russkoi ravniny. Moscow, 1950.
Ignat’ev, G. M. Severnaia Amerika. Moscow, 1965.
Rodin, L. E., and N. I. Bazilevich. Dinamika organicheskogo veshchestva i biologicheskii krugovorot zol’nykh elementov i azota v osnovnykh ti-pakh rastitel’nosti zemnogo shara. Moscow-Leningrad, 1965.

G. M. IGNAT’EV

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