West Mojave Plan FEIR/S - Desert Managers Group

A relatively small number of introduced wildlife species (excluding insects) is found inthe western Mojave Desert. A few of these species have very significant effects on the nativeenvironment, particularly feral burros, bullfrogs, and brown-headed cowbirds. In addition, feraldogs are a problem in several areas, where they may kill desert tortoises or Mohave groundsquirrels. Although common ravens are “natural” predator of tortoises, population levelsapparently increased by as much as 1,500% between 1968 and 1988 (BLM 1990). Increasedraven populations are likely associated with new water sources (cattle troughs, agricultural fields,wildlife guzzlers), increased scavenging potential (refuse in urbanizing areas, animal carcassesfound along highways), and more nesting substrates (transmission lines and a multitude ofhuman structures like houses, abandoned vehicles). The number of invasive introduced plants ishigher and in many respects more of a threat to the natural ecosystem. Riparian pests includetamarisk, Russian olive and Phragmites, which consume a lot of water and crowd out nativewillows and cottonwoods. Weedy annuals such as storksbill, several species of brome grass,Sahara mustard and others compete with native wildflowers and provide a nutritionally deficientfood plant for the desert tortoise.Following is a description of the natural communities of the western Mojave Desert, andthe life history and status of the desert tortoise, Mohave ground squirrel, and other speciesaddressed by the West Mojave Plan. The summaries of species other than the tortoise andground squirrel are based on the Species Accounts prepared for this planning effort in 1998 plussubsequent information. Copies of the full species accounts are included on the compact diskattached to this final EIR/S.3.3.1 Natural CommunitiesThe western Mojave Desert comprises a distinct area of the Mojave Desert biome, wherethe flora and fauna has adapted to the local conditions and formed distinct natural communities,including species found nowhere else (i.e. “endemics”). It also incorporates the transitionalecotones from the Sierra Nevada, Tehachapi, San Gabriel, and San Bernardino Mountains andthe Colorado Desert.The predominant aspect of the West Mojave is a flat, sparsely vegetated regioninterspersed with mountain ranges and dry lakes. The area is a part of the high desert, largeportions of which lie at elevations between 2500 and 4000 feet. Freezing temperatures arelimited to a few days in the winter in most of the region, while summer temperatures regularlyexceed 100 degrees Fahrenheit. The characteristic creosote bush and saltbush plant communitiesare covered with wildflowers in years of above-normal winter rainfall, and up to 90% of the floraare composed of annual plants.The central and southeastern regions reflect the Pleistocene history of the Mojave River,which flows from the San Bernardino Mountains north to Barstow, then east to Silver Lake andthe Mojave National Preserve. In the last Ice Age, extending from 30,000 to 10,000 years ago,the Mojave River discharged to the south into the Mojave Valley, Lavic Lake, Dale Lake, BristolLake, and other playas extending nearly to the Colorado River. The river (now dry) and playassupported species of invertebrates, fish, amphibians, and pond turtles, and attracted migratoryChapter 3 3-65