RIPARIAN HABITATS

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Riparian environments are river-bank environments, but in deserts the water courses are usually temporary - desert washes or arroyos that receive flood water draining from higher ground after seasonal heavy rains but contain no water for most of the year. Nevertheless, the soils in these washes often are moister than in the surrounding desert and thus support a lusher vegetation. The image above shows a typical wash in the Sonoran Desert of Arizona. The edges of the wash support mesquite and paloverde sub-trees. [For more images see Pinacate Desert wash]

In many parts of the arid southwestern USA, the dry or temporary river courses are marked by conspicuous lines of cottonwood trees (Populus freemontii), as seen in this image, taken from the site of "Biosphere 2" near the town of Oracle, in the Arizona Upland region. Note the typical high desert vegetation of saguaro, cholla and prickly pear cacti on the slope in the foreground.

Willows and giant reeds on the banks of the Rio Grande

The banks of the more permanent rivers such as the Colorado River and the Rio Grande typically support a range of trees and subtrees, such as willows and fan palms. However, these riverbanks are increasingly becoming dominated by exotic species, many of which have reached the status of bioinvaders which are suppressing the native species. Tamarisk is a classic example of this.

Thick growth of tamarisk on flood plains of the Colorado River