West Mojave Plan FEIR/S - Desert Managers Group

mi 2 within the planning area supported vegetation communities that may still support tortoises.The remaining 135 mi 2 were developed for residential, industrial, commercial, and agriculturalpurposes, and no longer constituted suitable habitats. Table 3-17 reports the prevalence of thedisturbances listed above in Table 3-17 that were observed on 72 mi 2 in the Lancaster sphere oninfluence (2 nd column) and 18 mi 2 within Lancaster’s city limits (3 rd column), which comprisedthe 90 mi 2 of potential tortoise habitat.Table 3-17Disturbances Observed in the Lancaster Planning Area in 1991DISTURBANCECATEGORYPERCENT OCCURRENCE IN THESPHERE OF INFLUENCEPERCENT OCCURRENCE WITHIN THECITY LIMITSCross-country OHV travel 81% 88%Dumping 92 100Domestic dog sign 77 72Dirt roads 60 72Shotgun shells 97 89Misc. ground disturbance 7 16Evidence of sheep grazing 100 100Several attempts have been made to determine if there is a statistical relationship betweenincreased human disturbances and decreased numbers of tortoises, with limited success (Dr. RossKiester, pers. comm. 2000). Fifty-eight of LaRue’s 78 surveys recorded the total number ofhuman disturbances observed on each transect, and either the presence or absence of tortoisesign. Tortoise sign was found on 25 project sites (43%) and absent from 33 (57%) of them.Table 3-18 shows the average number of disturbances observed (of the 10 categories given) pertransect for each of these categories.Table 3-18Human Disturbance Levels Observed25 Sites Where Tortoise Sign Was Found and 33 Sites Where Sign Was Not FoundDISTURBANCE CATEGORYPREVALENCE OF DISTURBANCES PER TRANSECTTortoise Sign Present(25 sites)Tortoise Sign Absent(33 sites)Cross-country OHV travel 2.40 2.83Domestic dog sign 1.37 2.59Dirt roads 1.56 2.04Dumping 0.72 1.50Shot gun shells 0.63 0.57Evidence of sheep grazing 0.59 0.44Misc. ground disturbance 0.40 0.26These data show that cross country travel, domestic dogs, dirt roads, and dumping wererelatively more prevalent on urban sites where tortoise sign was absent. Both direct and indirectimpacts associated with these human uses result in degraded habitats and loss of tortoises.In Table 3-19, data collected between 1998 and 2002 on 1,572 transects in the Fremont-Kramer and Superior-Cronese DWMAs are compared to disturbances observed on the 78 urbanChapter 3 3-98