West Mojave Plan FEIR/S - Desert Managers Group

The 1998 vegetation data were independently assessed to determine if these three regionsof MGS trapping success, compared to lower trapping success areas south of Highway 58,supported above-average occurrences of winterfat and hopsage 26 . The three regions and areassouth of Highway 58 are listed in the first column of Table 3-33. Regional averages were thendetermined (see footnote) to be 33 winterfat/transect and 28 hopsage/transect where at least oneof the two species was observed (as given in the footnote, transects without either of the plantswere excluded from the analysis; the number of transects with at least one of the plants are givenin the first column). The number and percent of transects reported in the second and thirdcolumns indicates the relative occurrences of these two species within each of the regions ofcomparison. MGS trapping success rates for the four areas were provided in Dr. Leitner’smemo, and are listed in the fourth column. Data are presented in descending order of theprevalence of the two plants, as expressed in percentages in the second and third columns.REGION (NO. OFTRANSECTS SURVEYED)Coolgardie Mesa/SuperiorValley (23 transects)Little Dixie Wash(15 transects)Cuddeback Lake/Pilot Knob(59 transects)South of Highway 58(117 transects)Table 3-33Comparisons Among Four Regions for Occurrence ofAbove-Average Numbers of Winterfat and/or HopsageNO. (%) TRANSECTSWITH MORE THAN 33WINTERFATNO. (%) TRANSECTSWITH MORE THAN 28HOPSAGE2002 TRAPPINGSUCCESS WITHINEACH REGION13 (56% of 23 transects) 15 (65% of 23 transects) 4 of 4 sites (100%)5 (33% of 15 transects) 4 (26% of 15 transects) 2 of 3 sites (67%)6 (10% of 59 transects) 15 (25% of 59 transects) 6 of 7 sites (86%)14 (12% of 117 transects) 3 (2% of 117 transects) 1 of 9 sites (11%)Vegetation sample sizes may be too small for meaningful statistical comparisons, but onecan see that these two plants were relatively more common in the three regions where more MGSwere trapped north of Highway 58 than to the south. When percentages are combined for thetwo plants within each region (in respective order given in the table), these plants were found on60.5%, 29.5%, and 17.5% transects in the three regions north of Highway 58, compared to only7% of the transects surveyed south of Highway 58. Dr. Leitner reported that MGS was capturedat 13 (56%) of the 23 sites listed in the table. Importantly, of the 13 sites where MGS wastrapped, 12 (92%) were located in the three regions north of Highway 58. MGS was trapped ononly 1 (11%) of the 9 sites located south of Highway 58.The average trapping success rate for the first three regions, which correspond to highincidences of winterfat and hopsage, was 84% compared to only 11% at the 9 sites surveyedsouth of Highway 58. This does not appear to be a sampling bias, as about 40% of the 2002trapping effort occurred south of Highway 58, where the lower success rate was observed.26 The methods used for this analysis were similar to those used to determine above-average tortoise concentrationsand vehicle-based disturbances. Using the 310 transects surveyed in 1998 within the range, all transects where nowinterfat or hopsage were found were dropped; the average numbers of these two species were then determined.The prevalence of these two plants within the two regions was then compared. Data were used for transects shownon Map 3-18, and included the three regions of higher trapping success and all transects south of Highway 58.Chapter 3 3-152