Steppe Zones, Temperate
Steppe Zones, Temperate
natural zones occurring on continents within the temperate belts of the northern and southern hemispheres and characterized by a dry continental climate, an absence of forests in watersheds, and the predominance of grassy vegetation on chernozem, dark-brown, and brown soils. Temperate steppe zones are particularly common in Eurasia and North America (where they are known as prairies); such zones are also found in South America (where they are called pampas).
The annual total solar radiation on the surface of steppe zones of the temperate belts usually varies from 500 to 580 kJ/cm2 (120 to 140 kcal/cm2), and the annual radiation balance varies from 145 to 190 kJ/cm2 (35 to 45 kcal/cm2). The sunny, moderately hot summer with infrequent rains rapidly changes to a relatively cold winter with a light snow cover. In the northern hemisphere the average July temperature varies from 20° to 24°C, and the average January temperature from 0° to - 30°C (in the southern part of Central Siberia and in Central Asia). The mean annual precipitation is between 200 and 450 mm. The precipitation regime is unstable, with relatively wet years alternating with arid years. Strong winds are frequent, resulting in snowstorms during the winter and dry winds and dust storms during the warm period of the year.
The river network in temperate steppe zones is poorly developed, and the surface runoff is insignificant, with its maximum flow occurring during the spring. The widespread occurrence of friable and easily eroded loess-like rocks leads to the rapid development of gullies and ravines, which is usually the result of destruction of the natural vegetative cover. Flat watersheds are characterized by shallow sinkholes, some of which retain water throughout the summer.
Chernozem soils in temperate steppe zones contain a large amount of humus and carbonates and have a high natural fertility. The dark-brown and brown soils have a lower natural fertility, owing to a lower humus content and frequent salinity. Solonetzes are frequently encountered.
A significant area of the steppe zones of the temperate belts is under cultivation. The remaining natural vegetation is composed of grassy steppes with feather grass, fescue, Koeleria, bluegrass, and wheat grass. Snakeweed grows in the steppes of Transbaikalia and Central Asia, and grama and buffalo grass grow on the prairies of North America. Forbs play a subordinate role in typical steppes, and rather substantial areas in arid regions are occupied by Artemisia. Scrub communities (blackthorn, ground cherry, dwarf almond, and spirea) are found in some places. Forests occur along river floodplains and along streams. Steppes do not have a continuous plant cover; between patches of sod there are areas of bare soil, on which annual and perennial ephemerals grow during the spring. Steppe plants include species of tumble-weed.
The reliefs of temperate steppe zones have been markedly transformed by man, and a substantial area is under crop cultivation. On the Eastern European Plain virgin steppes have remained only in preserves. Soil improvement is necessary owing to periodically recurring droughts, the retardation of water, and wind erosion. In the USSR artificial irrigation is widely used in steppes, and a system of protective forest strips has been established. The natural terrains of steppes have been best retained in the intermontane basins of Southern Siberia and in the mountains of Central Asia, where the pasturing of lifestock plays an important role.
REFERENCESSee references under STEPPE.
F. N. MIL’KOV