|Nature Gallery (Eco Regions)|
Temperate Deserts and Semi-Deserts
|The popular notion of a desert
includes heat, sand, and drought.
It is true that all deserts are dry, but not all are hot, at least not all
the time. All deserts grow cold at night, and the deserts of the temperate
zone grow cold in the winter as well. (Polar
deserts, of course, are always cold.)
Although a sandy substrate is a feature of some deserts, rocky, gravelly, and salty soils are also quite common. The climate of cold-winter deserts is similar to but more extreme than that found in the adjacent steppes. Precipitation is even lower and more irregular than in the grasslands, into which these cold-winter deserts grade via transitional zones called semi-deserts. Not only is precipitation scanty, but moisture loss from evaporation and transpiration is great.
of temperate deserts and semi-deserts is sparse. In the less arid
semi-deserts, the plant cover consists of grasses, shrubs, and occasional
trees distributed thinly but more or less evenly. In the true deserts, the
predominant shrubs are spaced widely over the mostly bare ground, and the
soil is often salty. The succulent
plants so typical of the deserts of warmer climates are generally lacking
in their cold-winter counterparts.
High mountains force humid air masses upward and cause them to release their moisture as snow or rain. In their lee, the mountains cast parched "rain shadows," and it is here that the deserts of the temperate zone develop. In the continental interior of Eurasia, the Karakum Desert, Takla Makan, Gobi, Ordos, and other deserts and semi-deserts occupy the country north of the great chain of mountains that stretches from the Caucasus in the west through Iran and Afghanistan to the Himalayas in the east. In North America, the Sierra Nevada, Cascades, and Rocky Mountains surround the cold-winter sagebrush deserts and semi-deserts of the Great Basin and the outlying northern Columbia Plateau and Snake River Plain.
In southern South America, a drying westerly wind blows constantly from the Andes across the plains of Patagonia. The semi-desert that results is vegetated with grasses and "cushion plants"-plants of different species that share a low, mounded, wind-resistant habit of growth.