Mojave National Preserve - Deserts

Deserts are the driest of all terrestrial biomes, characterized by low and unpredictable precipitation, on average less than 10 inches per year. The dry climate of deserts may be caused by several factors, including the rainshadow effect, remoteness from oceanic moisture, and global air circulation patterns. The density of vegetation, which is sparse and consists mainly of widely scattered drought-resistant shrubs and cacti, is determined by the frequency and amount of the precipitation, soil composition, slope, elevation, and temperature. Deserts may also be classified as either hot or cold. Hot deserts experience high daytime temperatures during a long summer and have large daily fluctuations in temperature. In addition, much of the plant life is evolutionarily affiliated with the subtropical plant communities further to the south. Cold deserts on the other hand are somewhat cooler, and the dominant plant life is not subtropical in origin. Seed-eating animals such as ants, birds, and rodents, are common in deserts, as are reptiles. Both animals and plants of the desert are consummately adapted for life in the harsh environment in which they live.

Of the four major deserts in North America, Mojave National Preserve contains elements of three: the Mojave, the Sonoran, and the Great Basin. Located in southeastern California, the majority of the preserve occupies a portion of the eastern Mojave desert, the smallest of the North American deserts. Common plants of the Mojave include creosote bush ( Larrea tridentata ), white bursage ( Ambrosia dumosa ), and yucca ( Yucca spp.). Joshua tree ( Yucca brevifolia ) is an indicator species for this desert, although it is only found at middle elevations. Mojave desert is considered a hot desert, with average summertime highs over 100ºF, wintertime lows near freezing, and an average yearly precipitation of less than 5 inches. In fact, freezing temperatures and a lack of predictable summer precipitation are some of the factors which distinguish the Mojave desert from the Sonoran desert. The Mojave desert is a rainshadow desert, a result of its location on the leeward side of the Tehachapi, San Gabriel, San Bernardino, and San Jacinto mountain ranges.

The southern portion of the preserve serves as a transition between the Mojave desert and the Sonoran desert, which in California is sometimes called the Colorado desert. Sonoran desert is found in south central California and southern Arizona. The presence of many spring annuals is one Sonoran desert element found within the preserve. However, one of the most conspicuous elements of Sonoran desert, the saguaro, is not found here. Predictable summer precipitation and lack of freezing temperatures in the winter, missing from the Preserve, provide ideal conditions for this giant cactus and other showy succulents of the Sonoran desert. Sonoran desert, like the Mojave desert, is considered a hot desert.

At the higher elevations of the preserve there is a conspicuous Great Basin desert influence. The largest of the deserts found in the United States, it is found primarily in northern Nevada, southern and western Utah, southern Idaho, and southeastern Oregon. The Great Basin influence is perhaps most easily observed in the Mid Hills area, where Piñon-Juniper woodland and sagebrush scrub dominate the landscape. Considerable stands of juniper ( Juniperus spp.) are also present in the Clark and New York Mountains. Big sagebrush ( Salvia dorii ) is an indicator species for the Great Basin desert. The temperatures at these higher elevations are slightly cooler than the surrounding area. Great Basin desert is typically thought of as being a cold desert.