Desert

With its spacious, rainless interior, Eurasia is home to the northernmost deserts in the world. Located entirely outside the tropics, the deserts of Central Asia have all the usual desert features, including sand dunes, desert pavement, rock formations, small saline lakes and playas, and very little vegetation. However, the northern, boreal elements of their flora and fauna are unique. The main deserts in North America are found at latitudes between 25? and 35?N, whereas in Eurasia they occur between 38? and 44?N. The four main deserts of Central Asia are the Kara Kum in Turkmenistan, south of the Aral Sea; the Kyzyl Kum in Uzbekistan, southeast of the Aral Sea; the Moyynqum in Kazakhstan, east of the Aral Sea; and the Saryesik Atyrau, south of Lake Balkhash. There is also a small desert north of Makhachkala and west of the Caspian Sea in Russia, in Kalmykia (the only true desert in Europe). Altogether, the Central Asian deserts occupy 3.5 million km2—an area as large as Saudi Arabia and Iran combined.

Deserts generally form in areas with potential evaporation exceeding precipitation by a factor of 10 or more. In temperate deserts, the average rainfall is <250 mm per year. The sandy desert is the most common type, with large dune fields of various shapes. The most famous dune form is the crescent-shaped “barkhan,” with horns pointing downwind. Barkhans form in areas with little vegetation. Parabolic dunes, star dunes, and longitudinal dunes are also common. Some dunes may be 30–40 m high. Most of the Kara-Kum is sandy desert (“black sand”). East of the Caspian Sea is the gravelly Ustyurt desert. There are also stony and salty deserts in Central Asia. When soils are present, they are of the desert type (“aridisols”). In the United States, such soils are common in parts of the western Great Plains and much of the Southwest.

Plants of the deserts are “xerophytic,” which means they are adapted to very dry conditions. Typically they lack leaves and have extensive but shallow root systems, capable of catching whatever moisture may be available on short notice. There are no cacti, because those are native only to the Americas. Instead, Artemisia forbs and small shrubs (Atriplex, Salsola, Tamarix, and Anabasis) are widespread. One genus, saxaul (Haloxylon), grows into a small-sized tree. Unique communities develop on saline flats that are flooded during the rain period, the so-called takyrs (similar to the playas of North America). Many desert plants are adapted to tolerate severe salinity. Along the seasonal watercourses, gallery forests or tugai develop, with poplar and willow species. Reeds develop around isolated saline desert lakes.

The fauna of the deserts can be surprisingly diverse, but elusive. Animals spend most of the day underground, avoiding heat; at night they are everywhere. Unfortunately, some of the most spectacular representatives of large desert mammals are now extinct (wild tarpan horses and tigers), while others are endangered (Asiatic wild donkeys, Przhevalsky horses, saiga antelopes, Persian gazelles) and are confined to a few prserves or zoos. The most common mammals are rodents (22 species); also common are insectivores, including long-eared hedgehogs, and carnivores, including weasels and wildcats. Birds are represented by eagles, Asian pheasants, sand grouse, pratincoles, desert jays, crested larks, and desert wheatears. Reptiles thrive in this biome, with monitor lizards, agamas, skinks, epha vipers, cobras, and others. There are some spectacular butterflies, beetles, cicada, and spiders in the deserts as well. Gerald and Lee Durrell (1986) provide some excellent descriptions of the ones they found in the Repetek preserve of Turkmenistan.