West Mojave Plan FEIR/S - Desert Managers Group

Table 3-20Prevalence of Tortoises in the Six Plant Communities Where ObservedPLANT COMMUNITY% PLANNING AREAOCCUPIED BY PLANTCOMMUNITYNO. SIGN COUNTTORTOISESOBSERVED 1998-2002% TORTOISESDIVIDED BY% COMMUNITYMojave Creosote Bush Scrub 63% 242 (92.7%) 1.5Desert Saltbush Scrub 9% 14 (5.4%) 0.6Mojave Desert Wash Scrub 0.3% 2 (0.7%) 2.3Mojave Mixed Woody Scrub 11% 1 (0.4%) 0.4Shadscale Scrub 0.5% 1 (0.4%) 0.8Stabilized, Partially Stabilized Sand0.3% 1 (0.4%) 1.3DunesTotal 84.1% 261 (100%) N/AThe data indicate that 261 observed tortoises occurred in six plant communities, whichcover about 84% of the planning area. About 98% of the tortoises (256 of 261) occurred increosote bush and saltbush scrub, which encompass 72% of the area. The key observation (andreason these data are given in this section) is that two tortoises were observed in Mojave DesertWash Scrub, which occupies only 0.7% of the planning area. One can see in the fourth column,where the percent of tortoises is divided by the percent occurrence of each plant community, thatthe highest ratio (2.3) was observed in Mojave Desert Wash Scrub. This may suggest thattortoise occurrence in wash scrub is relatively more common when one considers how little ofthe planning area is occupied by this plant community.There may be compounding circumstances, or synergistic effects, between the impacts ofdrought and the use of desert washes by both tortoises and recreational users. In relatively dryyears it is common to see a wide swath of green shrubbery growing along washes in an otherwisegray-brown landscape. A creosote bush growing alongside a wash may be bright green andtwice the size of all the creosote bushes within 100 feet of the wash. There are times when theonly place where annual germination occurs is along the margins of washes (LaRue, pers. obs;Dave Morafka, pers. comm.). Tortoises have been documented to use washes as travel corridorsseeking what appeared to be preferred, native forage (Jennings 1997). Wash resources supportboth sensitive bird and bat species. Water is nearest to the surface where washes and dry lakesoccur. As a drought progresses, the last places remaining green in the absence of supplementalrainwater are along washes.Recent evidence suggests tortoises may concentrate along washes in time of drought. Forexample, in the southeastern California desert, near Blythe, all tortoises found during one surveywere restricted to several large tributaries along McCoy Wash and adjacent upland areas out toseveral hundred feet (Circle Mountain Biological Consultants 2000). Importantly, much of thesite was below 600 feet elevation, which is about 400 feet below the “typical” 1,000 feet lowerelevation threshold observed in many places for tortoises. Circle Mountain concluded that thewash, with its thick palo verde growth, provided sufficient resources for several animals to livein an otherwise inhospitable environment.Chapter 3 3-109