Biogeography of the Earth

The Desert Biome 

The desert biome has the lightest cover of plants of any biome. Lack of moisture prevents plants from establishing themselves in this harsh climate. Many unique adaptations to the extreme heat and lack of moisture enable some plants to survive. Plants adapted to drought are called xerophytes. Aridisol soils, common to deserts, are typically coarse, lack much organic material, and are often weakly developed.

Dry Desert

The dry deserts are typically found in subtropical latitudes and are produced by subsidence associated with the eastern sides of the subtropical high. These are extremely dry regions, some places hardly receiving any measurable precipitation during the year. Plant cover is non-existent over much of the dry desert.

Figure BE.40 Grand Erg Occidental Desert,  Algeria
(Photo credit: J.Van Acker, FAO Used with permission)

Like many dry deserts, a layer of coarse material blankets the surface. This "desert pavement" protects the underlying surface from erosion. When disturbed, wind easily dislodges particles and transports them away in a process called deflation. This makes the establishment of plants very difficult.

Figure BE.41 Desert encroaching on desert oasis  (Photo credit: Mauritania. I.Balderi,

Plants occur only under the most favorable microclimatic settings like those surrounding an oasis. Oases are created where the water table is near the surface. Groundwater can be easily extracted to support vegetation and wildlife.

Plant growth and reproduction are quite slow under desert conditions. Surface erosion by wind or water restricts the establishment of plants. Infrequent storms causes water to sweep across the barren surface carrying away massive amounts of material along with plants. The rapid movement of sand dunes covers and prevents the establishment of a plant cover too.

Shrub Desert

The Shrub desert of the midlatitudes supports a more diverse community of plants and animals. Associated with the midlatitude desert climate, more precipitation and cooler temperatures help support a more complete ground cover.  This is especially true along dry stream beds where moisture is often more plentiful. Large cacti like the Saguaro cactus, and xerophytic shrubs are found in the Shrub desert of  North America.

Figure BE.42 Typical vegetation of shrub desert in Arizona. (Photo Credit: McKee, E.P. 1967, USGS Digital Data Series DDS-21. Used with permission)

Some xerophytic vegetation are widely spaced, and have extensive root systems to capture moisture in the soil. Others have waxy leaves or fleshy tissues to store moisture. Enlarged green stems like those found on cacti take over the function of leaves in photosynthesis. Some desert vegetation may shed parts of branches during extreme drought.

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