Biology » Ecology and the Biosphere » Terrestrial Biomes

Subtropical Deserts

Subtropical Deserts

Subtropical deserts exist between 15 ° and 30 ° north and south latitude and are centered on the Tropics of Cancer and Capricorn (see the figure below). This biome is very dry; in some years, evaporation exceeds precipitation. Subtropical hot deserts can have daytime soil surface temperatures above 60 °C (140 °F) and nighttime temperatures approaching 0 °C (32 °F). In cold deserts, temperatures can be as high as 25 °C and can drop below -30 °C (-22 °F). Subtropical deserts are characterized by low annual precipitation of fewer than 30 cm (12 in) with little monthly variation and lack of predictability in rainfall. In some cases, the annual rainfall can be as low as 2 cm (0.8 in) in subtropical deserts located in central Australia (“the Outback”) and northern Africa.

 This world map shows the eight major biomes, polar ice, and mountains. Tropical forests, deserts and savannas are found primarily in South America, Africa, and Australia. Tropical forests also dominate Southeast Asia. Deserts dominate the Middle East and are found in the southwestern United States. Temperate forests dominate the eastern United States, Europe, and Eastern Asia. Temperate grasslands dominate the midwestern United States and parts of Asia, and are also found in South America. The boreal forest is found in northern Canada, Europe, and Asia, and tundra exists to the north of the boreal forest. Mountainous regions run the length of North and South America, and are found in northern India, Africa, and parts of Europe. Polar ice covers Greenland and Antarctica, which the latter is not shown on the map.

Each of the world’s major biomes is distinguished by characteristic temperatures and amounts of precipitation. Polar ice and mountains are also shown.

The vegetation and low animal diversity of this biome is closely related to this low and unpredictable precipitation. Very dry deserts lack perennial vegetation that lives from one year to the next; instead, many plants are annuals that grow quickly and reproduce when rainfall does occur, then they die. Many other plants in these areas are characterized by having a number of adaptations that conserve water, such as deep roots, reduced foliage, and water-storing stems (see the figure below). Seed plants in the desert produce seeds that can be in dormancy for extended periods between rains. Adaptations in desert animals include nocturnal behavior and burrowing.

 This photo shows a sandy desert dotted with scrubby bushes. An ocotillo plant dominates the picture. It has long, thin unbranched stems that grow straight up from the base of the plant and radiate out slightly. The plant has no leaves.

To reduce water loss, many desert plants have tiny leaves or no leaves at all. The leaves of ocotillo (Fouquieria splendens), shown here in the Sonora Desert near Gila Bend, Arizona, appear only after rainfall, and then are shed.

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