Steppe Zones, Subtropical
Steppe Zones, Subtropical
natural zones occurring on continents within the subtropical belts of the northern and southern hemispheres and characterized by a hot, arid climate and a predominance of grassy and scrub vegetation. Subtropical steppe zones are generally located far from seas and oceans in relatively small areas in both hemispheres between 25° and 40° lat. In North America such zones, commonly called prairies, are encountered in the Central Valley of California, the Colorado Plateau, the southern part of the Great Plains, and the interior region of the Meseta Central. In South America subtropical steppe zones include the pampas of the La Plata depression and the eastern foothills of the Andes. Such zones are also found in the plains of southern and southwestern Australia and in the foothills near the Kura-Araks Lowland in Transcaucasia (USSR).
The solar radiation on the surface of steppe zones of the subtropical belts varies from 580 to 790 kJ/cm2 (140 to 180 kcal/cm2) per year, and the radiation balance varies from 210 to 290 kJ/cm2(50 to 70 kcal/cm2) per year. Winters are warm and without snowfall. The average atmospheric temperature in the coldest month is between 5° and 12°C; frosts occur infrequently. Summers are hot, with the average temperature in the hottest month ranging from 20° to 25°C. Severe droughts, which limit the vegetative period to three or four months, are frequent. The annual precipitation is between 500 and 600 mm. In the eastern parts of continents the maximum precipitation occurs during the summer, whereas in the western parts the maximum precipitation occurs during the winter. The surface runoff is insignificant, and the rivers have low water capacity and often dry up in the dry season.
The soils in subtropical steppe zones have a high iron and aluminum-oxide content, which results in a brown or reddish color. Mineralization of the soils is seasonal and halts or is severely inhibited during the dry period. In many regions saline soils form. The predominant vegetation consists of sparse sod grasses, with an alternation with scrub in places. Fringing forests occur along river valleys. Trees are sometimes encountered in interfluvial regions, where steppes undergo transition to savannas. The animal life includes numerous rodents known for their complex burrows, swift-running ungulates, reptiles, and orthopterons.
Steppe zones of the subtropical belts are used mainly for livestock pasturing and irrigated crop cultivation.