1. Habitat Description, Status and Importance

The Mohave Desert is the smallest of the four North American desert biomes and lies between the Great Basin and Sonoran deserts. Little of the Mohave Desert proper is in Arizona, but enough of Arizona lies adjacent to it and is intermediate in vegetation, soil type, and rainfall patterns to make it a significant biome in the state. The Mohave Desert is found only in the northwest corner of Arizona, but the areas along the Colorado River are in a transition zone between Sonoran and Mohave and are difficult to separate.

There are 18 - 26 days of annual precipitation in these areas, most occurring during winter and early spring and averaging approx. 35-130 mm (1.5-5.5 in) (MacMahon 1979; McKell 1985). Brown (1982) cites an annual precipitation of 46 mm (1.85 in) at Death Valley and as high as 253 mm (10 in) at Pierce Ferry, AZ. The elevational range of the Mohave Desertscrub biome is broader than other desertscrub biomes; 75% of the area lies between 610-1220 m (2000-4000 ft), with a biome range of 300-1675 m (985-5495 ft), hence the term "high desert".

Dominant plants of the Mohave include creosotebush, all-scale, brittlebush, desert holly, and white burrobush. The Joshua tree is the most famous endemic, having a near circular range around the edges of the Mohave Desert.

In Arizona, the Mohave Desert can be difficult to separate from Sonoran Desertscrub. Plant species characteristic of Sonoran desertscrub include ironwood, blue palo verde, and chuparosa. Other Sonoran plants are bitter condalia, emory dalea, smoketree, longleaf ephedra, crucifixion thorn, western honey mesquite and jojoba. The northern limits of these species in eastern California coincide with a shift to Mohave species. These include spiny menodora, sages, desert senna, Mohave dalea, Fremont dalea, goldenhead, and scalebroom.

Cacti are well-represented in Mohave Desertscrub. Many are widely distributed, but some endemics include Engelmann hedgehog, silver cholla, Mohave prickly pear, beavertail cactus, many-headed barrel cactus, and Neolloydia johnsonii. Subspecies of the following cacti are restricted to Mohave Desertscrub: Buckhorn cholla (var. multigeniculata), Parish cholla (var. parishii), and Coryphantha vivipara (var. desertii).

Approximately 80-90 annuals are endemic to Mohave Desertscrub, most being winter annuals. Of the few summer annuals, most germinate in response to rain in August and September (monsoon season). Winter annuals germinate in response to rain between late September and early December. The critical rainfall arriving in one storm should exceed 24 mm (.96 in) to produce abundant germination.

Brown and others (1979) named five major series within the Mohave Desertscrub. The creosotebush series is mostly below about 1220 m (4000 ft) where Larrea occurs on the bajadas and well-drained sandy flats. The most prevalent co-dominant in this series is Ambrosia dumosa. Other co-dominants are Anderson thornbush, spiny hopsage, paperbag bush, and shadscale. Diamond cholla occurs only in this Larrea-Atriplex confertifolia community.

The Shadscale series is dominated by Shadscale. This transitional community between Great Basin desertscrub and Mohave is tolerant of most extremes in temperature and rainfall and various other extreme conditions including salt content of the soil.

One or more species of Atriplex characterize the Saltbush community. In addition, there is a common association with other salt-tolerant plants from the family Chenopodiaceae, such as pickleweed and alkali weeds. In the southern areas of the Great Basin and northern areas of the Mohave, plant associations are dominated by blackbrush, considered a community transitional between these two biomes.

The Joshua Tree series is perhaps best known in the Mohave, but because of its limited occurrence it is not used to characterize most of the biome. Except for the southeastern margin, this species is found along the edges of almost the entire Mohave Desert on cooler, moister upslopes. The Joshua Tree is found in sandy, loamy or fine gravelly soils with minimal runoff, indicating its requirement for increased moisture.

Several bird species use the habitat of Mohave Desertscrub but perhaps some of the most common Arizona birds found in this habitat are Bendire’s Thrasher, Le Conte’s Thrasher, Costa’s Hummingbird and Scott’s Oriole. All of the above species are currently stable in Arizona. Since only a small portion of Mohave Desertscrub falls in Arizona, these species should be watched more closely in both California and Nevada, where more of this habitat occurs. For a more detailed description of this habitat and a list of the priority species that use it, see the state Partners in Flight Bird Conservation plans of California and Nevada.