Forest-Steppe Zones, Subtropical

natural zones characterized by alternating forest and steppe landscapes and located in the subtropical regions of North America (the western Central Plains and the Mexican Lowland) and South America (the southern Brazilian Plateau, the area between the Uruguay and Paraná rivers, and the eastern Pampas). Small areas of subtropical forest-steppe zones are found in Africa (in the southeast and in the interior valleys of the Cape Mountains) and in Australia (the eastern end of the Murray Basin). Because the subtropical areas of Eurasia are mountainous, subtropical forest-steppe zones are poorly developed there.

The climate of the subtropical forest-steppe zones is subtropical monsoonal, with warm winters and hot summers. The radiation balance is 210–250 kilojoules per cm² (50–60 kilocalories per cm²) a year. The average atmospheric temperature during the coldest month ranges from 4° to 12°C, and that of the warmest month, from 20° to 24°C. In the winter, intrusions of cold air sometimes cause brief frosts and snowfalls. The total annual precipitation is 600–1,200 mm, with the greatest precipitation occurring in the summer in most regions. The growing season lasts all year, but the rate of growth is slowed by low atmospheric temperatures in winter and by drought in summer. Characteristic of soil formation is a combination of humification and ferralit-ization, which contributes to high natural fertility. The vegetation consists of a grass cover (primarily cereal grasses with a considerable number of weed grasses), thin forests, a few trees (leafless during the dry season), and shrubs. Arboreal vegetation prevails in the river valleys.

In North America the subtropical forest-steppe zones are characterized by widely distributed, low-growing trees (chiefly oak and hickory) and by abundant grass stands (primarily beard grass species) on calcareous soils. The arboreal vegetation in South America is most highly developed on the periphery of the subtropical forest-steppe zones, where it consists of mimosa, acacia, and some palm species. The interior regions are occupied by treeless savannas and pampas. Characteristic of Africa is a combination of treeless water divides covered with dense grass stands and river valleys covered with trees (chiefly acacia). In Australia the vegetation of most of the subtropical forest-steppe zones is savanna-like. Arboreal vegetation (chiefly eucalyptus) is well developed primarily in the river valleys and hollows. Steppe or savanna species dominate the wildlife.

The land of the subtropical forest-steppe zones is widely used for farming (cereal crops, forage grasses, and cotton, for example). Some areas are used for grazing. Artificial irrigation is necessary in some regions during the dry season.

Subtropical forest-steppe zones are divided into savanna subzones characterized by an arid climate. Grasses prevail, with isolated trees or groups of trees in some places. There are also prairie subzones with a more humid, cooler climate and natural vegetation dominated by tall steppe grasses.