Semidesert Zones of Temperate Belts

Semidesert Zones of Temperate Belts


natural zones in the temperate belts of the northern and southern hemispheres where semidesert landscapes predominate. The largest area of such zones is in the interior of Eurasia, where semideserts stretch for roughly 10,000 km from the Caspian Lowland in the west to the eastern margin of the Ordos Plateau in the east. The width of the band of semideserts, in which plains predominate, reaches 500 km in places. In North America the semidesert zones are located in the Rocky Mountain foothills, extending in a band from north to south, and in the depressions of the Great Basin, where they alternate in a mosaic pattern with desert landscapes. In the southern hemisphere these zones are found east of the Andes in the southern part of South America (Patagonia).

The climate of the semidesert zones of the temperate belt in the northern hemisphere is arid and continental, with cold winters and long hot and dry summers. The radiation balance is roughly 5 megajoules per sq m, or 120 kilocalories per sq cm a year, and evaporation is several times the annual precipitation of about 200–300 mm. The mean temperature is 22°–25°C in July, dropping to —20°C in January. In winter these zones usually have little snow and strong winds. In the southern hemisphere (Patagonia) the climate is less continental. The temperature averages 15°–20°C in summer and about 1°C in winter. The Andes block most of the moisture carried by the prevailing westerly winds, so that the annual precipitation is only 100–150 mm, increasing to 250 mm in places.

Surface runoff is poorly developed. Rivers are usually high only in the spring, during the thawing of snow, and many of them dry up in summer. Large areas have no surface runoff at all, and there are many brackish and salt lakes. The moisture deficit in the soil is permanent from the middle of the growing season.

Light chestnut and brown soils predominate, often combined with solonets soils. Solonchaks and meadow-solonchak soils occur in low areas. The soils are generally complex and contain little humus (1.5–3 percent). They often have a high gypsum and carbonate content and reflect solonets processes. They are often suitable for farming but require irrigation and, in some places, desalinization and the elimination of alkalinity.

The vegetation is xerophilous and often includes many different species. In the semideserts of the temperate latitudes of the northern hemisphere the predominant vegetation is grass and wormwood, with many ephemerals. Tree and shrub vegetation, including oleaster, birch, pine, Calligonum, and sand acacia, is usually found on sandy soils. In the southern hemisphere the vegetation of the semidesert regions is sparse, consisting chiefly of small undershrubs, with some grasses and succulents. The most common animals are desert and steppe species. The semideserts of the temperate latitudes are usually good pastures for year-round grazing.