West Mojave Plan FEIR/S - Desert Managers Group

populations, partly because there are probably relatively few tortoises in most open use areas.[OHVs] damage and destroy vegetation. Density, cover, and biomass are all reduced inside versusoutside of [OHV] use areas, particularly following multiple passes by vehicles. Split grass(Schismus barbatus), a weedy introduced grass, in particular appears to benefit from [OHV]activity. Very light, basically non-repeated, vehicle use probably has relatively little long-termimpact. Soil becomes compacted by vehicles. The compaction increases with moisture content ofthe soil, weight of vehicle (particularly high weight to tire surface area ratio), and soil type.Cohesionless sand, such as in sand dunes and washes, [is] largely immune to compaction whilemoist soils are much more susceptible than dry ones. Compaction, lower infiltration rates, loss ofplants and cryptogamic soils all contribute to increased wind and water erosion and fugitive dust,particularly when such areas are several meters in width. More research is needed to understandthe effect light [OHV] use has on tortoise populations and habitat.Boarman (2002) reported that tortoise densities have been reduced through (a) directeffects, including crushing of tortoises and burrows, and (b) indirect effects of (i) compaction ofsoil, (ii) destruction of cryptogamic soils, (iii) changes in vegetation, (iv) erosion and loss of soil,(v) light OHV use, and (vi) human access to tortoise habitat.The USFWS (2002) indicated that the degree of threat posed to desert tortoises byrecreation increases with the speed, weight, and numbers of recreational units involved. Theyindicated, for example, that a small group of hikers posed much less threat to the desert tortoiseand its habitat than a race that involved numerous all-terrain vehicles.Positive Benefits of Motorized Vehicle Routes: Haskell (2000) reported that roadsprovided benefits to society such as opportunities for recreation and natural resource extraction.The USFWS (2002) felt that recreational use of the desert might benefit the desert tortoise in anindirect manner. They concluded that many people viewed the California desert as a uniqueplace to enjoy nature and solitude, and that the enjoyment of the desert could promote privatecitizens to assist in volunteer projects to restore habitats, clean up trash, report problems to theBLM, and educate other users. The BLM’s existing educational programs were identified asstriving for these goals (USFWS 2002).3.3.2.6.2 Direct Impacts of OHVs on Desert Tortoise PopulationsAs of 1980, the USFWS (2002) reported that OHV activities had affected approximately25% of desert tortoise habitat in California. In 1986, Dodd (1986) concluded that nearly 70% ofthe remaining high-density tortoise populations in the California desert were subject to OHVimpacts. In 1990, Chambers Group, Inc. (1990) found that 413 square miles (2.9%) of theplanning area had been directly disturbed by OHVs, and that much of the disturbance hadoccurred in open areas or in unauthorized OHV-use areas.Sign count data collected between 1998 and 2002 indicate that vehicle-based impacts areprevalent throughout tortoise habitats, including DWMAs. Within the Fremont-Kramer andSuperior-Cronese DWMAs, cross-country travel was observed on 833 of 1,572 (53%) transectsand roads were observed on 702 (45%) transects. There were 447 mi 2 with higher tortoise signcounts, 159 mi 2 (36%) of which overlapped with above-average vehicle-based impacts (see Map3-14).Chapter 3 3-120