West Mojave Plan FEIR/S - Desert Managers Group

NAWS China Lake 1993). As discussed above, there is concern that sandy habitats resultingfrom new Army maneuvers in the Superior Valley may favor round-tailed ground squirrels at theexpense of the MGS, which tends to prefer relatively coarser sands. Gustafson (1993) also notedthat the residential areas of Edwards AFB, China Lake, and Fort Irwin (often referred to ascantonment areas) directly and indirectly affect MGS.Military maneuvers and their observable impacts vary dramatically. Edwards AFB hascantonment areas west of Rogers Dry Lake, and logistical support facilities occur west of Rogersand east of the northern end (Leuhman Ridge facilities) that have resulted in MGS habitat loss.China Lake has a limited cantonment area (Ridgecrest serves that function) and office area, sosupport facilities have resulted in minimal impacts to either the northern or southern ranges.Given that both installations practice air-to-ground maneuvers, with limited day-to-day grounddisturbance, most of the habitats are still intact and potentially occupied.At Fort Irwin, mechanized vehicles and ground troops create new ground disturbancesduring each exercise (albeit in previously degraded areas). Gustafson (1993) reported thatmilitary training had affected approximately 130,000 acres (203 mi 2 ) in the known range. Mostof the impacts are limited to areas below about 20% slope (LaRue and Boarman, in prep.), whichcoincides with the substrates most preferred by the MGS, where about 90% of 102 MGS recordshave occurred (LaRue, 1998 unpublished data). Approximately half of Fort Irwin [i.e., 353,644acres (552 mi 2 ) of the 1,000 mi 2 ] installation within the MGS range is below 20% slope, and istherefore susceptible to some of the heaviest maneuver impacts. Krzysik and Woodman (1991)noted heavy shrub losses from the main maneuver corridors at Fort Irwin.“Natural” Predators: Recently Dr. Leitner (pers. comm. 2000) indicated that commonravens might also prey on the MGS, although the evidence is anecdotal. He indicated that ravensare known to prey on Townsend's ground squirrels. In their Coso studies, the Leitners havefound radio collars of several of their study animals at known raven perch sites. The extent ofraven predation on the MGS is unknown. Although ravens are identified as a “natural” predator,they have also been referred to as a “subsidized predator” (Boarman 1993), and would probablynot occur at current population levels in the absence of human resources. No data were found inthe literature to indicate to what extent other predators (e.g., raptors, kit fox, coyote) may prey onthe MGS.Off Highway Vehicles: Off-highway vehicles may pose a threat to the MGS by crushingindividuals or burrows, and degrading habitats (Gustafson 1993, Laabs 1998). With time, theplant diversity and abundance decreases in areas with intense OHV use (Laabs 1998), whichreduces cover needed by the species for shade and forage. Gustafson (1993; citing Bury andLuckenbach 1977), reported that even light OHV use in the Mojave Desert can result in lost orcompacted topsoil, unavailability of seeds for birds and mammals, and disrupted soil mantles.Gustafson (1993) reported, “…it is known that the squirrel is run over by vehicle[s],” but did notprovide any specific reports.There is anecdotal evidence that the MGS may be killed on both paved and dirt roads,although it has been suggested that they are too quick for this to happen. For example, duringtortoise surveys conducted near Water Valley, northwest of Barstow, in 1998, LaRue crushed aChapter 3 3-161