West Mojave Plan FEIR/S - Desert Managers Group

There are places, such as one lightly used road in the Copper Mountain Mesa area, where15 active tortoise burrows were found in the berms of a 1.5-mile long stretch of this road.However, this may be an exception. For example, only 1 occupied burrow of 202 found duringsign count surveys was recorded as occurring in the berm of a road.Lovich and Bainbridge (1999) reported that increased water availability from pavementrunoff and increased retention of moisture under the pavement are probably responsible for theobserved increase in plant vigor along roadsides. Vollmer et al. (1976) reported thatproductivity, diversity, and cover of Mojave Desert vegetation have been found to increase alongroadsides. One problem associated with these “greenbelts” is that tortoises may be attracted tothe vegetation and be crushed by normal use of the road, primarily, but also occasionally bymaintenance activities. Boarman et al. (1996) indicated that tortoises are probably attracted to theedges of highways because increased water from rain collects along the shoulder facilitatinggrowth of plants, some of which are species preferred by tortoises. Nicholson (1976) reportedthat tortoises might be attracted to roadsides, especially during a dry year, by the denservegetation growing there.Indirect Anthropogenic Mortality Factors: By their nature, indirect mortality factorsare more difficult to quantify, and are in effect extensions of direct mortality factors.Cattle and sheep grazing, cross-country OHV travel, blading rights-of-way for newconstruction, and agriculture (direct mortality factors) promote soil conditions that favor plantspecies that are not native to the desert, such as European weed species. Poor nutritionalqualities of weeds may result in physiological conditions that leave tortoises more susceptible todisease and drought. Jennings (1997) summarized impacts of exotic plants as follows: (a) exoticplants are spread by roads and along utility lines; (b) exotic plants may pose threats to deserttortoises by competitively reducing or excluding important native forage species, compromisingnutrition and health, and by contributing to the frequency and severity of fires in a region wherefire was previously rare; (c) annual exotic grasses, Schismus sp., may be relatively deficient inkey nutrients and may contain higher levels of metals than native plants.Avery (1998) has found, during experimental tortoise foraging studies, that sometortoises prefer Schismus, an exotic, to all other native and non-native species he provided.Avery (1998) further found that dietary nitrogen in exotic plants was assimilated at significantlylower rates; tortoises were physiologically more capable of utilizing native vegetation comparedto exotic vegetation; tortoises fed exotic plants lost body mass; and native vegetation was morenutritionally beneficial to desert tortoises than exotic vegetation [(see also Nagy et al. 1998, andHazard et al. 2001)]. Johnson and Belnap (1996) found that shifts in vegetation resulting inexotic dominated stands could alter soil biota compositions and create conditions unfavorable tonative plants.Not all studies have found that tortoises prefer non-native forage. Jennings (1992) foundthat tortoises he studied at the DTNA preferred native species. Avery et al. (1997, 1998) foundthat tortoises consumed some exotic annuals (i.e., Schismus barbatus and Erodium cicutarium)but did not prefer them. Krzysik (1994) concluded that tortoises forage on exotic annuals, butthe impact of these exotics on native ecosystems is unknown, and may remain unknown becauseChapter 3 3-100