This file was created by scanning the printed publication. Errors identified by the software have been corrected; however, some errors may remain. Spatial Distribution of Desert Tortoises (Gopherus agassi'ii) at Twentvnine Palms. californib: ~rn~~icatidns for Relocations1 Ronald J. Baxter2 The desert tortoise (Gopherus agassizii) is a species whose future is uncertain. Increased use of the deserts by man (Luckenbach 1982) has led to the point where the tortoise was officially listed as "threatened" in the state of Utah (Dodd 1980).The U.S. Fish and Wildlife Service stated in 1985 that "...listing [of the desert tortoise as a threatened or endangered species] is warranted but precluded by other pending proposals of higher priority" (Federal Register. 50(234): 49868-49870,1985). In California, the desert tortoise is the official state reptile, and is fully protected under law. The tortoise is also protected in Arizona and Nevada. As part of a larger population study (Stewart and Baxter 1987) at the Twentynine Palms Marine Corps Air Ground Combat Center (MCAGCC), the spatial distributions of tortoise captures and burrows were analyzed and compared against randomly generated distributions. Questions asked were: (1)Are tortoise captures and burrows randomly located across the landscape Paper presented at symposium, Management of Amphibians, Repti!es, and Small Mammals in North America. (Flagstaff, AZ,July 19-21 , 1988). 2RonaldJ. Baxter received his master's degree in biology for working on the desert tortoise while at California State Polyfechnic University,Pomona. He is currently completing his doctorate a t the Department of Bi~logicalSciences, Northern Arizona University, Flagstaff, AZ, 860 1 1-5640. Abstract.-The spatial distribution of desert tortoises in relation to plant communities was compared against randomness. Tortoise captures (n = 120) and tortoise burrows (n = 160) exhibited nonrandom distributions across a 1.29 square kilometer study plot at Twentynine Palms, ~alifornia. Results imply high diversity plant ecotones and communities, and possibly soil characteristics are important in determining tortoise densities. Nonrandomness in tortoise populations dictates that relocation sites must include specific vegetafioml, topographic and edaphic habitats used by the parental populations. and/or are they associated with certain habitat types or site characteristics, and if so, (2) what implications do these distributions have for future management decisions? Methods Twentynine Palms MCAGCC is Ioca ted approximately 5 kilometers north of Twentynine Palms, San Bernardino County, California, in the southwestern extreme of the Mojave Desert. All fieldwork was performed in the Sand Hill Training Area which is in the southwest corner of the MCAGCC. Elevations ranged from 865 meters atop Sand Hill to about 730 meters in the bottom of Surprise Springs wash. Data were collected Monday through Friday, 14 April through 18 July, 1986. Systematic searching methods for tortoises and tortoise burrows were a derivation of procedures described by Berry (1984). A 1.29 square kilometer permanent study plot was established, with its approximate center being the NE 1/4, SW 1/4, NE 1/ 4, of S7, T2N, R7E (San Bernardino Base Meridian) This site offered a wide variety of habitats including washes, sandy basins, rolling hills and alluvial bajadas. The plot was divided into 64 equal sized "grids" of 142 meters on a side, with grid corners marked by posts. Grids were searched in parallel belts until the entire plot had been searched twice; once with the belts running northsouth, and once with the belts running east-west. The plot was also randomly searched. \'?hen an active tortoise was encountered, it was marked, weighed, sexed, measured and photographed. Each tortoise was assigned a unique number, and rmaa~ginalscu tes were notched with a small triangular file for relatively permanent identification. The precise location of the capture was noted by its distance (meas-. wed by rangefinder) and compass aspect to the nearest grid past. Data collected at each capture site included plant community, temperatures at the ground, 1 centimeter, and 1 meter, cloud cover, wind speed and direction, closest burrow, closest plant, and any unusual behavior. Precise location of tortoise burrows were similarly detern:ine$ by rangefinder and compass. Data collected at each bumow included planl. community, distance and identification of nearest ecotone, distance to nearest wash, distance to nearest HiIaria rigda, slope aspect and steepness, opening compass aspect and position, length, depth, and tunnel characteristics. In this study area, it was difficult to determine if a burrow high on a slope above a wash was part of the wash "system." Therefore, it was arbitrarily decided to include burrows in the wash plant community only if they were actually found the wash bed. Six visually identified plant communities (Latr/ Amdu, Hiri/ Amdu, Mixed, Wash, Sparse Wash and Meadow) were mapped within the study plot, and seven 15-meter line transects (total of 105 meters) were measured which included bare ground as a species. Transects were 1:LATWAMDU 2:MIXED 5 :MEADOW :BURROW 3:SPARSE WASH #:WASH 4:HIRI/AMDU u I NORTH 100 METERS Figure 1 .-Approximate distribution of plant communities and tortoise burrows across the study plot. See text for explanation of plant community names. randomly located in each of these six communities. Standard transect statistics (density, coverage, frequency, relative density, relative coverage, relative frequency and importance values; Brower and Zar 1984) were computed for each community. Simpson's diversity indices (Simpson 1949) were computed and compared with Student's t-tests (Keefe and Bergerson 1977).Available annuals as well as perennials were used to give the best estimate possible for diversity. In addition, seven soil samples were taken in each community, and analyzed for soil separates (Brower and Zar 1984) and soil calcium (Hach 1983).Finally, nine "sand scats" were collected during the field work and tested for calcium. A random model for capture and burrow locations was formed by combining a number of statistical tests. First a master map of the plot was constructed from actual field data at a scale of 1:2000. All capture positions, burrows and plant community boundaries were plotted on this map and checked against aerial photographs. The area covered by each plant community was then determined by the use of a planimeter. An X-Y scale ranging from 0 to 8 was plotted on the sides of the map, and a list of 328 random numbers was generated by computer. These numbers were paired, and the pairs be- came the X-Y coordinates of random positions against which observed capture and burrow locations were compared. Distances to the nearest wash and ecotone were determined for these random locations by measuring them on the map, and csmpared against observed by Student's t-tests (Zar 1974). Observed capture distances were sometimes combined with previous data recorded in this area (Baxter and Stewart 1986). A lack of habitat preference may be suggested if burrows and captures were found in the same relative abundance as the plant communities. In addition, if the expected plant abundance distribution differed significantly from random an extrapolation of observed distributional characteristics could be accomplished. An assumption of this test was that a distribution of randomly generated locations (with randomness confirmed) produced a random frequency distribution. Expected frequencies for burrows and captures were generated by multiplying the total number of actual burrows or captures by the percent of the plot encompassed by each plant community. These values were compared by a goodness-of-fit chi-square test (Zar 1974).In addition, the number of burrows or captures per grid were compared against expected values as derived from the Poisson distribution by a goodness-of-fit test. Results Plant Communities and Soils Vegetation analyses revealed six distinct plant assemblages (table 1; fig. 1). Plant community distributions generally reflected the relief of the plot. The higher, more well-drained hills were dominated by an association of Larrea tridentata and Ambrosia dumosa, which encompassed plot area the most ("Eatr / Amdu"; table 1) and exhibited relatively high plant diversity. Found on 37.2%of the plot area was the "mixed" community that generally occupied intermediate areas between the Latr/Amdu and either washes or areas of high Hilaria rigida density. It was characterized by the association of L, iridenfata, A. dumosa and H. rigida, and was found most often on the slopes above, and narrow linings next to washes. The edge, or ecotone, of this community with the Latr/Amdu community is extensively discussed bebw. A highly diverse plant community was found in the washes (table 1; appendix 1).Such areas not only contained these perennial species, but also a significant number of other species found only in this cornmunity, giving it the highest species richness of any community. Small uplifts within wash channels seemed to support a more open type of wash vegetation, "sparse wash." Such areas had many species common to the washes (appendix 1), yet much of this community was essentially pure stands of the opportunistic grass, Schismus barbatus. A community ("Hiri/Arndu") consisting primarily of H. rigida and A. dumosa was located in upland basins where L. tridentafa was not found. Such areas were low in habit and diversity, and very sandy. Finally, near the south boundary of the plot, a small "meadow" of mostly Baileya multiradiata was found. Since no tortoises or tortoise burrows were found there, it was eliminated from further analyses. Bare ground, when treated as a species in transect analyses, had overriding importance values and dominance in all communities (appendix 1). This is often the case in desert environments. Likewise importance values of S. barbatus were extremely high in all communities, pointing to the generally disturbed nature of the site. Comparisons of Simpson indices for the communities revealed significant differences (p < 0.05) in diversity for all communities except two. The htr/Arndu and wash communities were not significantly different (p > 0.50) in their diversity. Soils were found to be somewhat similar in constituency (table 21, each being composed to a large degree of sand. Soil calcium levels (table 3) were shown to differ significantly. No detectable calcium was found in any of the sand scats tested. Tortoise Burrows A total of 164 tortoise burrows was found on the study plot (fig. 1).Seventy-five percent were found under bushes, 14%with the opening under a bush but the tunnel proceeding into an open area, 8% with entrances in the open but the tunnels proceeding under a bush, and 3%entirely in an open area. Thus, almost all of burrows (97%)were associated with shrubs. Of these, '71% were associated with L. tridentata, 13%each with H. rigida and A. durnosa, and another 3%with other species. Neither the distribution of observed or random burrows differed significantly from the Poisson expected frequencies (table 4). Likewise, when the distribution of observed burrows was compared against the distribution of random burrows, no significant difference was found (chi-square.= 2.224; DF = 5; p > 0.50). Thus, when the entire plot area is considered, tortoise burrows exhibited a random pattern across the landscape. However, this was a relatively large scale test of burrows per arbitrary unit area, and says nothing about the pattern of tortoise burrows in relation to plant communities. The abundances of tortoise burrows (both observed and random) in each plant community were compared against expected frequencies generated by the abundances of the plant communities (table 5). Burrows were sparse in the.Hiri/Amdu and wash communities. Observed burrow frequency distribution did not differ significantly (p > 0.25) from the expected frequency distribution. The observed frequency distribution differed significantly from the random distribution (chi-square = 11.74; DF = 5; p < 0.051, as did the expected distribution (chi square = 158.9; DF = 5; p < 0.001). Mean observed burrow distance to the closest wash was compared to the mean distance from the randomly located burrows (table 6). Comparisons for the sparse wash and Hiri/Amdu communities were not done because they would be biologically meaningless or had too low a sample size, respectively. For all burrows, and for burrows found in either the Latr/Amdu or mixed communities, no significant differences between random and observed wash distances were detected. Thus, observed tortoise burrows were not located closer to washes than a set of random points predicted. However, examination of the spatial pattern (fig. 1) reveals a lack of burrows deep within Latr/Amdu and Hiri/Amdu areas which were furthest away from any possible wash influence. Fast observations seemed to indicate a correlation between burrow location and the presence of the edge of the H. rigida distribution (Baxter and Stewart 1986).The approximate distribution of observed burrows to this edge may be seen in figure 1. Mean edge (ecotone) distance of observed burrows was compared to that of random sites (table 7). Highly significant differences in ecotone distances were found in both communities, and also when combined. Thus, burrows were found closer to tkie ecotone than a set of random points. Tortoise Captures Similar analyses were performed for tortoise capture sites. There were a total of 120 tortoise captures and recaptures of 41 individual tortoises. The observed captures per grid, along with the randomly located capture frequencies (same points used for random burrow sites) were compared against expected values derived from the Poisson distribution (table 8). Observed capture sites showed a statistically significant departure from Poisson expected frequencies by the goodness-of-fit test (p < 0.05). Frequencies of capture sites in each plant community were compared against expected values gener- ated by community abundance (table 9). Observed distributions for both all captures, and for captures of active tortoises (those found outside of burrows) differed significantly from expected. These two observed distributions did not differ from each other (chi-square = 0.5385; DF = 5; p > 0.99), yet differed significantly from the randomly generated distribution (chi-square = 18.957 and 19.556, respectively; DF = 5; p < 0.005). Thus, tortoise captures were not found across the plot in a random fashion as would be predicted by a set of randomly generated points. Habitat preference for washes was seemingly indicated, as was a lack of preference for Hiri/Amdu areas. These results also gave further support to the non-randomness exhibited in the Poisson analyses. To further examine this apparent non-random distribution of capture locations, the mean observed cavture distance to washes was compared to that of the randonlly located sites (table 10).When all capture sites, or captures within the mixed community were considered, a significant A difference between random and observed locations was demonstrated. However, mean distance to washes within Latr/Amdu sites was not significantly different from the random set of points, possibly because the Latr/ Amdu communities were generally located further away from washes, as well as the high variation in observed Latr/Amdu distances. These results, along with the results of the community analysis above, seemed to indicate a high degree of tortoise activity near the washes. Distances to the edge of the H. rigida were compared between randomly generated and observed capture locations (table 11).Highly significant differences in mean distances were demonstrated for both the Latr/Amdu community, and for captures found in the mixed and La&/ Amdu communities combined. Cap- tures within the mixed community alone were not significantly different from randomly generated locations. It seems then that captures, like burrows, were generally not found far within Latr/ Amdu areas, but tended to be near its edge with the H. rigida distribution (i.e. the mixed comrnunity). Because there was no difference within the mixed community alone, differences from random for captures within the mixed and Latr/ Amdu communities combined were probably significant due to the higher number of observations within the La&/ Amdu community biasing the sample. Thus, it seems that tortoises tended to stay either near the washes, the mixed community, or its ecotone with the Latr/ Amdu community, and generally were not going far within the Lab/ Amdu community. Discussion Since the establishment in 1975 of the Desert Tortoise Council, the amount of literature published on the desert tortoise has been considerable. Oddly enough, only a few papers may be found that attempt to say what exactly makes good tortoise habitat. A paper by Schwartzmann and Ohmart (1978) quantified the frequency of use by tortoises in a number of "habitat types." Their study took place in the Picacho Mountains of Arizona's Sonoran Desert, where tortoises are known to frequent rocky hillsides and are absent from valley bottoms (Fritts 1985). Habitat preferences are just the opposite in the Mojave Desert, and thus their results may not be applicable. Likewise, Walchuck and Devos (1982) studied tortoise habitat, but this was also in the Sonoran Desert of Arizona. In a draft report, Weinstein et al. (1986) performed several multivariate analyses on the large Bureau of Land Management tortoise database. Several attempts were made to correlate abundance with habitat characteristics. Not only were many of these characteristics derived from the extrapolation of large scale map data, but the best fit analysis was found by designating "corrected sign" of the transects (the dependent variable; not actual population numbers) into arbitrary categories. Indeed, one of the authors (Berry and Nicholson 1984) has shown that roughly onethird of population estimates (7 out of 20 and 4 out of 6) based on sign transects did not agree with intensive plot censuses. Also, Turner et al. (1982) stated that sign transects "...cannot provide the accuracy and precision needed. .." In addition, Fritts (1985) stated that such transects are "...subject to error." Thus the accuracy of sign transects are open to serious debate, and although the discriminant analysis showed some promise as a method for accessing regional abundances, the nature of the analysis and the underlying assumptions of both the data acquisition and techniques leave much to be desired. When viewed from the larger scale of regional or even plot area, these data seem to indicate that burrows were found in a random fashion when predicted by burrows per unit area. However, different results may have been obtained by changing the size and shape of the grids. For example, 32 larger rectangular grids may very well have produced different results than the 64 smaller square grids used in this study. In addition, such an analysis said nothing about distributions in relation to habitat characteristics. Therefore, such a test should be used as a starting point and/or support for other tests, and locally is of limited use by itself for describing ecologically meaningful patterns which may exist. With closer examination, these data also indicate that burrow locations were assembled in a pattern similar to the non-random distribution of plant communities. Withincornmunity examinations revealed patterns of burrow site utilization, and such patterns were strongly nonrandom. At Sand Hill then, while a majority of burrows were not found in washes, they were often found within easy walking distance to a wash. Very often, burrows were on slopes high above washes, and possibly within its area of influence. They were not found far within either the Latr/ Amdu or Hiri/Amdu communities, but were tied strongly to the edge of these communities with the mixed community. Washes are sometimes cited as being of great importance to tortoise populations (Burge 1978, Hohman 1977, Lowe 1964).However, results of this study indicated that tortoise burrows were not significantly closer to washes than a set of randomly selected sites. Burge (1978) found 207 (26%) of 783 burrows and pallets were associated with washes. Of these, 56 (27%)were actually within a wash bed. However, Burge apparently eliminated some burrows from the analysis due to their physical characteristics. The discrepancy may be due to the definition used. In this study, wash burrows were defined as such, only if they were actually within the sandy wash bottoms. In this way, burrows which were on wash banks, were counted as being in the plant community of the bank. Burrows located on wash banks, and even further away, may have been associated with the wash, and a reclassification of these burrows may show washes to have a more important influence in burrow analyses. Examinations of the actual burrow distribution (fig. 1) seemed to indicate that they were mostly absent from areas highly isolated from wash influence. The significance of capture locations in relation to the washes also seemed to refute the burrow/wash results. Washes clearly supported a disproportionate amount of activity in relation to their abundance on the plot. Preliminary investigations of tortoise communities near Kramer Junction, San Bernardino County, have also shown tortoises are probably localizing their activities in the vicinity of washes (Baxter, unpub. data). Several things may explain the disproportionate amount of captures in the washes. Greater visibility of tortoises in the washes may be a factor. Utilization of highly diverse plant resources there may also contribute to the localization of activity. Finally, washes may simply serve a natural highways for tortoise movements. For instance, several relocated tortoises at Kramer Junction abruptly turned and followed trails and washes upon their release (Baxter, unpub. data). Regardless, these data seem to support washes as an important habitat characteristic for tortoises at Sand Hill. If this population is representative of other Mojave populations, the importance of washes in potential relocation sites will be highly significant in assuring the best chance of survival for the relocates. Further, impacts to washes may have highly significant impacts on a population if it is localizing its activities there. These data support the importance of large woody shrubs (i.e., L. tridentata) for successful burrow construction at this site. Similar results have been reported by Burge (1978) who found 72% of "cover sites" associated with shrubs. Berry and Turner (1984) found 75% of juvenile burrows associated with bushes. Support for the burrow roofs and added protection from predators are likely reasons for this association. Regardless, the absence of L. tridentata from the Hiri/ Amdu community is probably a major reason for the tortoises not utilizing those areas. Unsuccessful burrow construction by virtue of the sandier soils is another possibility. This latter assumption is supported by the Weinstein et al. (1986) analysis which showed "soil diggibility" as a highly significant regression variable. However, the lack of burrows deep within Latr/ Amdu communities is not explained by the spatial abundance of L. tridentata. The high frequency of burrows and captures point out that something is being sought there by the tortoises. Yet, deep ventures within these areas apparently d o not provide resources that are unavailable at their edges. Perhaps the higher levels of soil calcium found there are being utilized. Tortoises must support a massive, ossified shell, as well as lay eggs, and calcium may be a very important nutrient. Tortoises have been observed eating dirt (geophagy) and then producing "sand scats," and calcium levels have been hypothesized as an explanation for this behavior (Sokol 1971).The lack of calcium in the sand scats tested seems to support this hypothesis. In contrast, such deep ventures would take the tortoises away from the distribution of H. rigzda, and the frequented and diverse washes. Although detailed scat analyses were not performed, field examination of hundreds of scats seemed to suggest that H. rigida is a significant dietary component. Turner and Berry (1986) found H. rigida as a part of the diet of tortoises near Goffs, California. It would seem then that tortoises in this area are exhibiting some characteristics similar to "edge" species. That is, tortoise activity is centered on the two communities with the highest vegetational diversity that border extensive areas of H. rigida. Since burrows are closely associated with L. tridentata, they in turn are found primarily along the only highly diverse ecotone of the H. rigida distribution where L. tridentata importance is the highest. This importance of H. rigida and L. tridentata is further shown in appendix 1. The two communities where tortoises were not found (i.e., deep Latr/ Amdu and Hiri/Amdu) each lack one of these species. The assumption that they are focusing on high diversity areas is further supported by Weinstein et al. (1968) which shows "food availability" as the single most significant regression variable. Finally, Spealce (1986) reports that for the gopher tortoise (G. polyphemus), "Edge habitats or ecotonal areas appear important to tortoises. In each habitat type except oldfields tortoises tended to cluster near the edges. In general, the more edge availability in a given hahitat, the higher the tortoise density." In summary, tortoises utilized the environment at Sand Hill in a mostly non-random fashion. Tortoise captures were spread out between two communities of highly diverse resources, with clustering occurring at either edge. Tortoises frequented washes and the ecotonal edge of the Latr/ Amdu community, with many found in the intermediate mixed community. Tortoises were not found deep within Latr/Amdu or Hiri/Amdu areas. Burrows were found close to the ecotone of the mixed and Latr/Amdu communities. Burrows were not found closer to washes than randomly located burrows, although this point is far from clear. Burrows were located close to the one highly diverse edge of tortoise activity area where the importance of L. tridentata and soil calcium were the greatest, and were not found in Hiri/Amdu areas where L. fridentata was absent; and soils were the most unconsolidated. Non-randomness in tortoi.~poplalations is especially important for the management considerations of relocation. Clearly, despite the best efforts of concerned managers, the use of the deserts will continue to increase and the frequency of tortoise relocations will also undoubtedly increase. If tortoise distributions are random, relocation management essentially becomes a search for safe relocation sites roughly similar to the "parental" area. No special consid erations of unique habitat types are required. If on the other hand they are not, then the relocation sit&) must include such high-use habitats as those found in the parental site. In addition, severe disturbance of such favored habitats will in turn have severe impacts on the populations, particularly if small. This study indicates that the nonrandomness exhibited by the Sand Hill tortoises is probably a function of the non-randomness of highly diverse plant assemblages and edaphic characteristics. Thus, the presence of diverse land forms and their asswiated plant communities and diverse edges within future relocation sites should be of significant importance to the manager. Areas which "look good" to the relocation manager may not supply the needed resources for the relocates. These data are in need of further support however. If such patterns are exhibited in other populations, biologists and managers may use such techniques to successfully determine possible habitat requirements, and help insure the survival of one of the Mojave's most enigmatic species. The author wishes to express sincere thanks to Dr. Glenn R. Stewart of Cal Poly, Pomona for physical help and moral support during the fieldwork, and for his abiding friendship. Many thanks also to the entire staff at the MCAGGC for logistical support. Finally, t h a n k to K. Berry, D. Speake and R. Szaro for their constructive reviews of this manuscript. This work was supported by United State Navy contract N6247484RPOOV48, which was administered by the Cal Poly Kellogg Unit Foundation. Additional equipment support was supplied by graduate research funds of Cal Poly, and monies received from the Chuck Bayless and Tim Brown memorial scholarship funds. 'Travel funds were supplied by Sigma Xi, The Scientific Research Society. Literature Cited Baxter, Ronald J ., and Glenn R. Stewart. 1986. Report of the continuing fieldwork on the desert tortoise (Gopherus agassizii) at the Twentynine Palms marine corps base. Proceedings of the symposium, [Palmdale, Calif., March, 19861. The Desert Tortoise Council, Long Beach, Calif [in press]. Berry, Kristin H. 1%4. A description and comparison of field methods used in studying and censusing desert tortoises. Appendix 11. In The status of the desert tortoise (Gopherus agassizii) in the United States. Kristin Berry, editor. Report to the U.S. Fish and Wildlife Service, Sacramento, Calif. Order NO. 11310-0083-81. Berry, Kristin H., and Lori L. Nicholson. 1984. The distribution and density of desert tortoise populations in California in the 1970's. In Kristin Berry, editor. The status of the desert tortoise (Gopherus agassizii) in the United States. Report to the U.S. Fish and Wildlife Service, Sacramento, CA. Order No. 11310-0083-81. Berry, Kristin H., and Frederick B. Turner. 1984. Notes on the behavior and habitat preferences of juvenile desert tortoises (Gopherus agassizii) in California. Proceedings of the symposium, [Lake Havasu City, Ariz., March, 19841. The Desert Tortoise Council, Long Beach, CA. Brower, James E. and Jerrold Zar. 1984. Field and laboratory methods for general ecology. William E. Brown, publishers. Dubuque, Iowa. Burge, Betty. 1978. Physical characteristics and patterns of utilization of cover sites used by Gopherus agassizii in southern Nevada. Proceedings of the symposium, [Las Vegas, Nevada, 19781.The Desert Tortoise Council, Long Beach, CA. Dodd, C. Kenneth. 1980. Endangered and threatened wildlife and plants: listing as threatened with critical habitat for the Beaver Dam slope population of desert tortoise in Utah. Federal Register 45(163): 55654-55666. Fritts, Thomas H. 1985. Ecology and conservation of North American Tortoises (genus Gopherus). 11. Evaluation of tortoise abundance based on tortoise sign detected in field surveys. Prepared for: U.S. Fish and Wildlife Service, Denver Wildlife Research Center, University of New Mexico, Albuquerque. NM. Hach Company. 1983. Soil calcium and magnesium test kit (model 14855)instruction manual. Hach Company, Inc., Loveland, CO. Hohrnan, Judy P. 1977. Preliminary investigations of the desert tortoise on the Beaver Dam slope in Arizona. Proceedings of the symposium, [Las Vegas, Nev., March 19771. The Desert Tortoise Council, Long Beach, CA. Keefe, T. J. and E. Bergerson. 1977. A simple diversity index based on the theory of runs. Water Resources 11:689-691. Lowe, Charles. 1964. The vertebrates of Arizona. The University of Arizona press, Tucson, Ariz. Luckenbach, Roger A. 1982. Ecology and management of the desert tortoise (Gopherus agassizii) in California. In R. Bruce Bury, editor. North American tortoises: conservation and ecology. U.S. Fish and Wildlife Service, Wildlife research report No. 12, Washington, D.C. Schwartzmann, James L., and Robert D. Ohmart. 1976. Quantitative vegetational data of desert tortoise (Gopherus agassizii) habitat in the lower Sonoran Desert. Proceedings of the symposium, [Las Vegas, Nev. March, 19781 The Desert Tortoise Council, Long Beach, CA. Appendix 1 Summary of Importance Values1From Plant Transect Data. Plant Community2 Species Bare Ground 128.2 Schismus barbatus Larrea tridentata Ambrosia dumosa Hila ria rigida Erodium texanurn Malacothrix spp. Eriogonum spp. Wyrnenoclea salsola Amsinckia spp. Oenothera del toides Baileya mu1tiradiata Abronia villosa Bromus rubens Langloisia Mat thewsii Langloisira Palmeri 0yzopsis hymenoides Eriophyllum Wallacei Menodora spinescens Lesquerella Palrneri Salazaria rnexicana Dalea Fremontii Cucurbita foetidissima Euphorbia polycarpa Isomeris arborea Prunus fasiculata Spheralcea am bigua Salvia columbariae Phacelia spp. Petalonyx Thurberi Unknown composite #1 Unknown composite #2 iImpotfance value = relative density + re/,domin. + re/. ireq. 2Plantcommunity: See texf for description of community names; Meadow and bare areas not listed; I = Sparse Wash; 2 = Hiri/Amdu; 3 = Mixed; 4 = Latr/Amdu; 5 = Wash. Simpson, E. H. 1949. Measurement of diversity. Nature 163:466-467. Sokol, 0.M. 1971. Lithophagy and geophagy in reptiles. Journal of Herpetology 5:69-71. Speake, Daniel W. 1986. Gopher tortoise density in various south Alabama habitats. Alabama Cooperative Fish and Wildlife Research Unit, Research Information Bulletin 86-105,l p. Auburn, Alabama. Stewart, Glenn R., and Ronald J. Baxter. 1987. Final report and habitat management plan for the desert tortoise (Gopherus agmsizii) in the West and Sand Hill training areas of the Twentynine Palms MCAGCC. Report prepared for the U.S. Department of the Navy, San Bruno, Calif. Contract number N6247484RPOOV48. Turner, Frederick B., and Kristin H. Berry. 1986. Population ecology of the desert tortoise at Goffs, California, in 1985. University of California, Los Angeles publication number 12-1544. Turner, Frederick B., and Carl Thelander, Daniel Pearson, and Betty Burge. 1982. An evaluation of the transect technique for estimating desert tortoise density at a prospective power plant site in Ivanpah Valley, California. Proceedings of the symposium, [Las Vegas, Nev., March, 19821. The Desert Tortoise Council, Long Beach, CA. Walchuck, Sandra L., and James C. devos, Jr. 1982. An inventory of desert tortoise populations near Tucson, Arizona. Proceedings of the symposium, [Las Vegas, Nev., March, 19821. The Desert Tortoise Council, Long Beach, CA. Weinstein, Michael and Frederick B. Turner and Kristin H. Berry. 1986. An analysis of habitat relationships of the desert tortoise in California. Draft report prepared for Southern California Edison Company, Los Angeles, Calif. Zar, Jerrold H. Biostatistical analysis. 1974. Prentice-Hall, Inc., Englewood Cliffs, NJ.