Unit 3:Peoples and The Environment

Semiarid Desert

The major deserts of this type include the sagebrush of Utah, Montana and Great Basin. They also include the Nearctic realm (North America, Newfoundland, Greenland, Russia, Europe and northern Asia).

The summers are moderately long and dry, and like hot deserts, the winters normally bring low concentrations of rainfall. Summer temperatures usually average between 21-27° C. It normally does not go above 38° C and evening temperatures are cool, at around 10° C. Cool nights help both plants and animals by reducing moisture loss from transpiration, sweating and breathing. Furthermore, condensation of dew caused by night cooling may equal or exceed the rainfall received by some deserts. As in the hot desert, rainfall is often very low and/or concentrated. The average rainfall ranges from 2-4 cm annually.

The soil can range from sandy and fine-textured to loose rock fragments, gravel or sand. It has a fairly low salt concentration, compared to deserts which receive a lot of rain (acquiring higher salt concentrations as a result). In areas such as mountain slopes, the soil is shallow, rocky or gravely with good drainage. In the upper bajada (lower slopes) they are coarse-textured, rocky, well-drained and partly "laid by rock bench." In the lower bajada (bottom land) the soil is sandy and fine-textured, often with "caliche hardpan." In each case there is no subsurface water.
The spiny nature of many plants in semiarid deserts provides protection in a hazardous environment. The large numbers of spines shade the surface enough to significantly reduce transpiration. The same may be true of the hairs on the woolly desert plants. Many plants have silvery or glossy leaves, allowing them to reflect more radiant energy. These plants often have an unfavorable odor or taste. Semiarid plants include: Creosote bush, bur sage (Franseria dumosa or F. deltoidea), white thorn, cat claw, mesquite, brittle bushes (Encelia farinosa), lyciums, and jujube.

During the day, insects move around twigs to stay on the shady side; jack rabbits follow the moving shadow of a cactus or shrub. Naturally, many animals find protection in underground burrows where they are insulated from both heat and aridity. These animals include mammals such as the kangaroo rats, rabbits, and skunks; insects like grasshoppers and ants; reptiles are represented by lizards and snakes; and birds such as burrowing owls and the California thrasher.

by:MARIATI BINTI MOHD

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