Natural Areas Journal . . . to advance the preservation of natural diversity
A publication of the Natural Areas Association - www.naturalarea.org © Natural Areas Association
The San Joaquin Desert of California: Ecologically Misunderstood and Overlooked
David J. Germano1,6
1Department of Biology California State University Bakersfield, California, 93311-1022
Galen B. Rathbun2 Lawrence R. Saslaw3 Brian L. Cypher4 Ellen A. Cypher4 Larry M. Vredenburgh5
2Department of Ornithology and Mammalogy California Academy of Sciences Golden Gate Park, San Francisco c/o P.O. Box 202 Cambria, California 93428 3U.S. Bureau of Land Management Bakersfield, California 93308 4Endangered Species Recovery Program California State University-Stanislaus P.O. Box 9622 Bakersfield, CA 93389 5U. S. Bureau of Land Management Bakersfield, California 93308
6 Corresponding author: [email protected]; 661-654-2471
Natural Areas Journal 31:138–147 R E S E A R C H A R T I C L E ABSTRACT: The vegetation community of the San Joaquin Valley of California has been formally classified as a perennial grassland based largely on assumptions of past climax state. However, histori- cal records suggest that the region might be more accurately classified as a desert. The distinction is important in determining the appropriate management strategies for this ecosystem, particularly for the • many rare and endemic taxa that reside there. Abiotic and biotic factors–including low precipitation, arid soils, and desert-adapted plants and vertebrate–are consistent with conditions typical of desert ar- eas. We examined the distributions of these factors to define the extent of the San Joaquin Desert. We conclude that the San Joaquin Desert historically encompassed 28,493 km2 including the western and The San Joaquin southern two thirds of the San Joaquin Valley, and the Carrizo Plain and Cuyama Valley to the south- west. However, this ecosystem has been reduced by up to 59% from agricultural, industrial, and urban activities. The conservation of the unique biodiversity of this region is dependent upon this ecosystem Desert of California: being appropriately managed as a desert and not as a perennial or annual grassland.
Ecologically Index terms: biogeography, desert distribution, endemism, grassland, LoCoH analysis Misunderstood and Overlooked INTRODUCTION defining) desert habitats than only climate and geology data. Thus, we have used both Deserts are defined in many ways, but biotic and abiotic factors in defining the David J. Germano1,6 mainly they are regions with low precipi- extent of the San Joaquin Desert, which tation and high evapotranspiration (Meigs we believe provides much of the most 1Department of Biology 1953; Jaeger 1957; Budyko 1974; Mabbutt important information that will be needed California State University 1977; Daubenmire 1978). In the Whittaker to effectively manage and protect these Bakersfield, California, 93311-1022 (1970) classification of biomes, desert dwindling natural areas from the increasing areas usually receive less than 250 mm of adverse impacts of people. Galen B. Rathbun2 precipitation annually, whereas temperate Lawrence R. Saslaw3 grasslands that are in the same temperature Traditionally, four major deserts have regime generally receive greater than 635 been recognized in North America, with Brian L. Cypher4 mm. Low precipitation and vegetation all located in the southwestern part of Ellen A. Cypher4 biomass lead to characteristic soils that the continent (Shreve 1942; Jaeger 1957; Larry M. Vredenburgh5 are alkaline, calcareous, low in organic MacMahon 1979; MacMahon and Wag- matter, and weakly zonal or stratified ner 1985; Hafner and Riddle 1997). The 2 2Department of Ornithology and (Dregne 1984). This climatic regime also Great Basin Desert (149,000 km ) is the Mammalogy generally limits perennial vegetation to most northerly and is located mostly in California Academy of Sciences low shrubs, cacti, succulents, and a few Nevada and western Utah. The Mojave Golden Gate Park, San Francisco grasses and forbs (Jaeger 1957; Mabbutt Desert (140,000 km2) is just south of the c/o P.O. Box 202 1977; Daubenmire 1978). However, some Great Basin Desert and is mostly in south- Cambria, California 93428 desert areas receive so little precipitation eastern California. The Sonoran Desert 3U.S. Bureau of Land Management that no plants grow, while others receive (275,000 km2) extends southeasterly from Bakersfield, California 93308 enough precipitation to support small the Mojave Desert into southern Arizona 4 Endangered Species Recovery Program trees and tall columnar cacti, such as the and northwestern Mexico. The Chihuahua California State University-Stanislaus Sonoran Desert in North America (Shreve Desert (453,000 km2) covers southern New P.O. Box 9622 Bakersfield, CA 93389 1942; Turner and Brown 1982). Depending Mexico, southwestern Texas, and north 5U. S. Bureau of Land Management on the rainfall regime, deserts periodically central Mexico (Shreve 1942; Jaeger 1957; Bakersfield, California 93308 can also produce dramatic blooms of native MacMahon 1979; MacMahon and Wagner annual plants (Minnich 2008). Because 1985; Hafner and Riddle 1997). All receive • plants and animals are often adapted to less than 350 mm of precipitation per year, deserts, they have been used to delineate and although they differ considerably in boundaries of deserts (Shreve 1942; Lowe elevation and seasonal temperatures, they 6 Corresponding author: 1955; Morafka 1977; MacMahon 1979). share many of the same species of plants [email protected]; 661-654-2471 Indeed, MacMahon and Wagner (1985) and vertebrates. However, each also has its believe that climate factors alone are too own characteristic flora and fauna (MacMa- variable to define the limits of deserts in hon 1985; Hafner and Riddle 1997). North America. It also can be persuasively argued that the ecology and behavioral Much of the non-forested or non-shrubland Natural Areas Journal 31:138–147 traits of arid-adapted plants and animals habitat west of the Sierra Nevada in Califor- are much better at “selecting” (and thus nia historically has been considered native
138 Natural Areas Journal Volume 31 (2), 2011 grassland (Clements 1920; Biswell 1956; perennial or annual grassland. Rather, an- The scrub habitats likely were dominated Küchler 1995). This is particularly true nual wildflowers of numerous species were by saltbush (Atriplex spinifera and A. poly- of the San Joaquin Valley, which except the dominant cover (Minnich 2008) for a carpa) with a few other low-stature shrubs for marshes, riparian habitats, and a small short time during the spring. Because of the (Griggs et al. 1992). According to Vasek area of alkali sink habitat on the valley extreme aridity of much of the San Joaquin and Barbour (1995) and Axelrod (1995), floor, has been classified as a bunchgrass Valley, the herbaceous layer of vegetation saltbush scrub is typical in basins and val- prairie (Heady 1995; Küchler 1995; Baker would have dried and disintegrated by leys of the Mojave Desert and occurs at 1978). The implication is that this region, May, leaving barren ground dotted with the western edge of the San Joaquin Valley which is currently dominated by exotic bushes throughout the summer (Minnich from Panoche southward. Also shared by annual grasses and forbs and has large 2008). Thus, without the exotic species, the both the Mojave Desert and the southern areas devoid of shrubs, was historically physical and biotic characteristics of most San Joaquin Valley is halophytic alkali native perennial grassland. of the San Joaquin Valley are consistent sink scrub that occurs on playas, sinks, with conditions typical of a desert, albeit and near seeps (Vasek and Barbour 1995). Recent evidence casts doubt on the histori- one that is under a Mediterranean climate Several vertebrates typical of the Mojave cal habitat classification of the southern regime (Dallman 1998), which receives no Desert also occur in the San Joaquin Valley. San Joaquin Valley, and the adjacent Car- meaningful summer rainfall. Before the widespread invasion of exotic rizo Plain and Cuyama Valley (Figure 1), annual plants and the conversion of vast as perennial grassland. Based on writings Most of the southern San Joaquin Valley areas to human use, the desert in the San of Spanish explorers and missionaries, a was desert scrub habitat on the upland sites Joaquin Valley would have been a unique convincing argument has been made that, and alkali sink habitats on the valley floor. North American habitat, with extreme in fact, none of the pre-European herba- There were riparian corridors along rivers arid areas infused with three large but ceous cover in the San Joaquin Valley that carried runoff from the Sierra Nevada shallow lakes with associated rivers and (D’Antonio et al. 2007; Schiffman 2007; into seasonal wetlands that surrounded wetlands, which supported a remarkable Minnich 2008) was ever dominated by shallow lakes (Figure 1; Griggs et al. 1992). abundance of waterfowl (Griggs 1992). The area would have been reminiscent of the desert of southern Iraq that supports a vast marshland.
Identifying the southern and western San Joaquin Valley as a true desert is not novel. Based on the plant and animal species of this area, Hawbecker (1953) considered this part of the Valley as a desert. In his book on birds of California, Small (1975) has a section on the “San Joaquin Valley Desert” and maps its boundary. Hafner and Riddle (1997) also treated this area as a desert, equal in status to other North American deserts, and were the first au- thors to name this area the “San Joaquin Desert.” Axelrod (1995) notes species such as the San Joaquin kit fox (Vulpes macrotis mutica) and the blunt-nosed leopard lizard (Gambelia sila) that “inhabit saline Kern Desert [italics ours] in Kern and southern Kings Cos.” Commenting on the amount of moisture necessary to recharge soil ca- pacity in various parts of California, Major (1995) said, “In general, in cismontane California winter precipitation is sufficient to fully recharge soil water. Where it is not, the area can properly be termed a desert. South of Fresno with a rather dry, but otherwise typical Californian Mediter- Figure 1. The area receiving an average of 229–279 mm (9–11 in) of precipitation per year, and the oc- currence of aridic soils, in the San Joaquin Valley and surrounding central California. The precipitation ranean climate, the southern San Joaquin polygon completely overlays the aridic soil distribution. Valley is such a desert, as at Bakersfield,
Volume 31 (2), 2011 Natural Areas Journal 139 and so is its west side as far north as Los the 229-279 mm isohyets to define desert We used vertebrates endemic to the San Baños to Newman.” areas because this encompasses the typi- Joaquin Valley, plus some that occur in the cal highest amount of rainfall that deserts other North American deserts but that are Although deserts of the world are usually receive. also found in the Valley. However, we ex- identified and named when they cover cluded vertebrates with desert affinities that relatively large areas, smaller areas that The soils data we used were obtained occur in the Valley if they also are found have climatic and biotic characteristics of from the U.S. Department of Agriculture’s in adjacent non-desert montane or coastal deserts should also be formally identified Natural Resources Conservation Service habitats (e.g., coast horned lizard, Phryno- and named so that the general public and (available online at http://websoilsurvey. soma coronatum; black-tailed jackrabbit, resource managers correctly recognize the nrcs.usda. gov/app/HomePage.htm) for Lepus californicus; greater roadrunner, landscapes in which they reside and work, Madera County, Fresno County (western Geococcyx californicus) because, similar and which they impact and manage. For ex- part), Kings County, Tulare County (central to plant species, we did not want to have ample, a recently published popular review and western parts), Kern County (north- habitat generalists distort our analyses. of the deserts of California (Pavlik 2008) western and southwestern parts), Carrizo Location information for all mammals, makes no mention of the suite of unique Plain, and Santa Barbara County (northern the blunt-nosed leopard lizard, and the plants, animals, and habitats found in the part). For the analysis, we selected “Aridic Le Conte’s thrasher (Toxostoma lecontei) southern San Joaquin Valley, thus providing Soil Moist” and ”Xeric Soil Moist” sub- were assembled by the Endangered Spe- the public and land managers no insights class units. These moisture regimes refer cies Recovery Program, Fresno, California into the importance of this arid area of to the presence or absence of water held (U.S. Fish and Wildlife Service 1998). great biodiversity and endemism. at a tension of < 1500 kPa in the soil or Location data for reptiles were provided in specific horizons during periods of the to us by Robert Hansen (Editor, Herpeto- Although portions of the San Joaquin Val- year. These aridic soils in normal years logical Review), which we supplemented ley (and adjacent valleys to the southwest) are dry in all parts for more than half of with museum records from the Museum have been recognized by some as desert in the cumulative days per year when the soil of Vertebrate Zoology and the California general terms as outlined above, the extent temperature at a depth of 50 cm from the Academy of Sciences. of the desert has not been quantified and soil surface is above 5 °C and are moist in the desert is still not widely acknowledged. some or all parts for less than 90 consecu- We used point data for eight plants, four In this paper, we propose boundaries of the tive days when the soil temperature at a reptiles, one bird, and five mammals (Table San Joaquin Desert using the distribution of depth of 50 cm is above 8 °C. 1) to construct utilization polygons rep- several factors typical of deserts, including resenting their distributions (Fortin et al. precipitation, soils, plants, and vertebrates We selected plants that occur in the San 2005). The utilization polygons were con- (MacMahon and Wagner 1985). We then Joaquin Valley and are characteristic of structed by the localized convex hull (Lo- assess the current status of this desert in the following desert communities: Mo- CoH) method of Getz and Wilmers (2004) terms of anthropogenic changes to habitats jave Creosote Bush Scrub, Mojave Mixed and Getz et. al. (2007) using ESRI ArcMap and the implication of these changes to the Woody Scrub, Mojave Mixed Steppe, Mo- 9.2 GIS software with a downloaded map conservation of this unique ecosystem. jave Wash Scrub, Desert Saltbush Scrub, template (Lyons et al. 2009) for LoCoH or Desert Sink Scrub (Holland 1986). We analyses. We subjectively chose the most representative polygon, rejecting those METHODS then further restricted the list (Table 1) by excluding those plants that also occurred in with obviously unreasonably fragmented non-desert mountainous or coastal areas of distributions, for each species after apply- To define the approximate boundary of ing several different K factors (number of the region (e.g., Allenrolfea occidentalis, the San Joaquin Desert, we examined the nearest neighbors) to each data set. The Eriogonum fasciculatum var. polifolium, distribution of precipitation, soils, plants, complexity of the resulting polygons was Frankenia salina, and Isomeris arborea) and vertebrates typical of desert environ- dictated by the distribution of occurrence ments. We obtained rainfall data from the because these plants would unreasonably points available for each species (Table Fire and Resource Assessment Program, exaggerate the boundaries of the desert. 1). Precipitation and soil data already California Department of Forestry and Fire We also included several San Joaquin existed as polygons, as indicated above. Valley endemics with close relatives in the Protection. The precipitation isohyets we To determine the extent of the San Joa- Mojave Desert (e.g., Bakersfield cactus, used (polygon shape files available online quin Desert, we overlaid (unioned) all 20 Opuntia basilaris var. treleasei). Loca- at http://frap.cdf. ca.gov) are based on a polygons. This resulted in 1653 polygons tion coordinates were obtained from data from which we determined the number of 60-year (1900–1960) annual average from provided by the Consortium of California coincident (overlapping) distributions and approximately 800 stations maintained by Herbaria (2008). Those locations without the area contributed by each overlap (Figure the U.S. Geological Survey, the California coordinates, but with adequately detailed 2). Even though 20 distribution polygons Department of Water Resources, and the descriptions, were georeferenced using were used, there was only a maximum of California Division of Mines. We used Google Earth (2008). 16 coincident polygons. We looked for
140 Natural Areas Journal Volume 31 (2), 2011 Table 1. Plant and animal species used to define the San Joaquin Desert (see text for criteria for choosing taxa). The number of locations refers to the number of georeferenced locations used to determine the distribution polygon. The K value for the LoCoH analysis is the variable used to determine the size of the hulls that the software uses to construct distribution polygons (see Getz and Wilmers 2004). An asterisk denotes species listed by either the California Department of Fish and Game or the U.S. Fish and Wildlife Service, or both, as threatened or endangered.
General Number of K Value for Area in San Joaquin Common Name Scientific Name Distribution Locations LoCoH Valley, km2 Shrubby Alkali Arida carnosa North American 7 10 2,189 Aster deserts Arrowscale Atriplex phyllostegia North American 22 8 10,517 deserts Allscale Saltbush Atriplex polycarpa North American 32 15 16,209 deserts Spinescale Atriplex spinifera Mojave & San 36 10 8,203 Saltbush Joaquin deserts Jackass Clover Wislizenia refracta North American 25 10 17,330 deserts San Joaquin Monolopia congdonii San Joaquin 87 15 8,250 Wooly-threads* endemic Kern Mallow* Eremalche parryi San Joaquin 21 15 1,282 ssp. kernensis endemic Bakersfield Opuntia basilaris San Joaquin 38 15 1,481 Cactus* var. treleasei endemic Blunt-nosed Gambelia sila San Joaquin 548 35 21,106 Leopard Lizard* endemic Desert Spiny Sceloporus magister North American 22 10 5,602 Lizard deserts San Joaquin Masticophis San Joaquin 71 12 31,319 Coachwhip flagellum endemic ruddocki Glossy Snake Arizona elegans North American 53 12 26,586 deserts Le Conte’s Toxostoma lecontei Mojave & San 48 10 2,390 Thrasher Joaquin deserts San Joaquin Ammospermophilus San Joaquin 349 20 13,580 Antelope nelsoni endemic Squirrel* Tulare Onychomys torridus San Joaquin 40 15 12,338 Grasshopper tularensis endemic Mouse Giant Kangaroo Dipodomys ingens San Joaquin 366 25 8,155 Rat* endemic San Joaquin Dipodomys nitratoides San Joaquin 578 20 19,698 Kangaroo Rat* endemic San Joaquin Kit Vulpes macrotis San Joaquin 2604 50 20,904 Fox* mutica endemic
Volume 31 (2), 2011 Natural Areas Journal 141 bound by the Sierra Nevada to the east and Transverse Range to the south.
The map of coincident distributions shows a core area of high overlap in the southern end and western side of the San Joaquin Valley, which includes the Carrizo Plain and Cuyama Valley (Figure 4). With each category of less coincidence the area in- creases, especially to the north, but also creeps into mountainous habitats. The areas of high, medium, and low coinci- dence are, from the core outward: 5061; 28,493; and 55,360 km2; respectively. The area encompassed by just the precipitation isopleth is 37,620 km2 and that of the arid soil polygon is 16,174 km2.
Most desert areas of the world experience relatively little human disturbance, but the San Joaquin Desert supports vast areas of intensively irrigated agriculture, oil extrac- tion, and urban development (Figure 5). The area (km2) of relatively undisturbed habitat that remains within each of the three polygon categories of coincidence, Figure 2. The relationship between the contributed area and number of coincident distributions of soil, from high to low coincidence, is: 2910; 2 rainfall, plants, reptiles, birds, and mammals in California. There is a natural break in contributed 12,458; and 29,752 km . Based on these area at about 5 to 12 coincident distributions. data and the total area for each of the coincidence polygons, 43.3%, 59%, and natural breaks in the graph comparing the the Cuyama Valley and the Carrizo Plain 35.5%, respectively, of the desert habitat in number of coincident distributions with the (Figure 1). the San Joaquin Valley has been modified area each coincident distribution contrib- beyond recognition (Table 2). uted (Figure 2); and using the coincident Desert plant distributions are almost all in distribution polygons, we merged data the San Joaquin Valley, Carrizo Plain, and DISCUSSION into ranges of 1 to 4, 5 to 12, and 13 to Cuyama Valley, similar to the rainfall and 16 coincident distributions. soils distributions. Similarly, the distribu- Precipitation and temperature regimes tions of reptiles, mammals, and the Le in the San Joaquin Valley are largely Conte’s thrasher are confined mostly to RESULTS dependent on the direction and timing of the southern and western areas of the San winter (November-March) storms out of Joaquin Valley, the Cuyama Valley, and the The polygon representing the 229-279 the northern Pacific, resulting in a Medi- Carrizo Plain (Figure 3). That these distri- terranean climate with hot, dry summers mm mean annual rainfall isopleth covers butions are so well defined in the southern the southern two thirds of the San Joaquin and cool, moist winters (Biswell 1956; San Joaquin Valley is not surprising given Twisselmann 1967; Griggs et al. 1992; Valley and extends up the Salinas Valley that 10 of the 19 taxa are endemic (Table 1). Major 1995). These regimes result in two on the west side of the inner coast range Jackass clover (Wislizenia refracta) and decreasing moisture gradients in the Valley: of mountains nearly to Monterey Bay, and the San Joaquin coachwhip (Masticophis north to south and east to west. The inner to the south includes the Cuyama Valley flagellum ruddocki) have occurrences and Carrizo Plain (Figure 1). The arid on the edge of the Salinas Valley, which coastal mountain range forms the western soils polygon is largely coincident with considerably expands the distributions of boundary of the valley and creates a rain the rainfall isopleth (Figure 1), but is more these species to include vast areas with no shadow (Major 1995), while rainfall on restricted to the southern end of the San likely occurrences. The San Joaquin kit fox the eastern side increases because of the Joaquin Valley, where it is tightly bound has an extensive range that encompasses orographic effect of the Sierra Nevada. by the Sierra Nevada, Transverse Range, many mountainous areas on the west side Thus, on the west side, yearly average and Inner Coastal Mountains, similar to of the San Joaquin Valley, although, like all precipitation decreases from Panoche (230 the rainfall. Arid soils are also found in the other plants and vertebrates, it is tightly mm) in the north to Taft (117 mm) in the
142 Natural Areas Journal Volume 31 (2), 2011 south and increases to the east of Taft at Bakersfield (145 mm) and east of Panoche at Fresno (269 mm; Twisselmann 1967; Western Regional Climate Center 2010). These two gradients have an impact on the distributions of plants and vertebrates within the Valley, presumably resulting in those species that are tolerant of more mesic conditions having the widest distributions and conversely those most adapted to xeric conditions being restricted to the western and southern portions of the Valley (Figure 3). Interestingly, the same Mediterranean weather patterns and geological features found in the southern San Joaquin Valley are found in the long and thin Atacama and Sachura deserts of Chile and Peru, which are bound on their western and eastern sides by coastal mountains and the Andes (Dallman 1998). There is also a latitudinal aridity gradient, as in the San Joaquin Val- ley, but in the opposite direction.
For determining the distributions of the plants and vertebrates of the San Joaquin Valley, we have used the best available loca- tion information. These are historical data for the most part and may not reflect where the species currently occur because much of their habitat, along with the species, has been destroyed by human activities. Also, certain attributes of these data may provide inaccurate representations of spe- cies’ ranges. For some species, the sample sizes are small (i.e., < 30 locations, Table 1), and some species have a few “outlier” occurrences that are geographically distant from the main areas of occurrence. These small sample sizes and outlier occurrences expand some distributions so that they include areas of likely unsuitable habitat, as we observed for the jackass clover and San Joaquin coachwhip. The low number of locations for some species also results in distribution polygons characterized by relatively long, straight lines, which may not accurately reflect a more complex distribution. On the other hand, some distributions with large numbers of oc- currence points, such as the San Joaquin kit fox and San Joaquin kangaroo rat (Dipodomys nitratoides), also have rela- Figure 3. The distribution of desert plants (top), desert reptiles (middle), and desert mammals and tively simple polygons, even though the LeConte’s thrasher (bottom) in the San Joaquin Valley and surrounding central California. shape of these polygons probably reflects their true distributions because of the large sample sizes and overall dispersion. The
Volume 31 (2), 2011 Natural Areas Journal 143 is the area represented by the 5-12 coinci- dent distributions polygon. Our unbiased method of boundary determination includes non-desert mountainous habitat on the western edge of the desert; but, otherwise, we think that the 5-12 polygon defines well the relatively sharp southern and western edges of the desert with a broad ecotone grading into grassland and woodland to the north and east. The boundaries we suggest are similar, although more defensible on methodological grounds, to those described by Hawbecker (1953), Small (1975), Axel- rod (1995), Major (1995), and Hafner and Riddle (1997).
Species assemblages of mammals and reptiles of the southern San Joaquin Val- ley are composed similarly to those of the Mojave, Great Basin, and Sonoran deserts (Hafner and Riddle 1997). Of the total number of non-volant small mammal species in the San Joaquin Valley, 73.3% are considered xeric-adapted (Hafner and Riddle 1997). This is lower than in the Mojave (85%) or Sonoran deserts (76%), but higher than in either the Great Basin Figure 4. Areas of coincident distribution shown in Figs. 1 and 3, which we used to define the boundar- (63.4%) or Chihuahuan (48.3%) deserts ies and ecotones of the San Joaquin Desert of California. We believe the 5-12 polygon area best defines (Hafner and Riddle 1997). Fossil remains the desert (see text for details). of plants and vertebrates from the McK- ittrick tar pits at the southern end of the similarity in complexity of all the species desert-adapted (McGrew 1979); and, al- San Joaquin Valley indicate that the area polygons probably reflects the overall though not depicted on our maps, all known has been a desert for thousands of years relative coarseness of the distribution persistent populations of the San Joaquin (Brattstrom 1953). Of special interest are data, but also reflects the uniformity of kit fox occur within the 229 mm rainfall Pleistocene remains of both the long-nosed the desert habitat and the highly selective isopleth (B. Cypher, unpubl. data). leopard lizard (Gambelia wislizenii) and the nature of the arid-adapted species. In the desert tortoise (Gopherus agassizii), which spirit of reducing subjective interpretations, Ecotones can vary from well to poorly currently are only found in the deserts to we have not altered the distributions as defined regions, and the San Joaquin Desert the east, including the Mojave. determined by the impartial quantitative illustrates both extremes. If the ecotonal methods described above. Despite these region of the desert is defined as that area Accurately defining the appropriate eco- limitations, however, we believe that the between the outer edge of the innermost system classification for the southern San utilization polygons are more than suffi- polygon and the outer edge of the outer Joaquin Valley is not merely an academic cient to define the desert with considerable polygon (Figure 4), it can be seen that exercise, but has important conservation accuracy, especially given that we have the transition between desert habitats and implications as well. The true composition used 18 different species distributions with foothill or mountainous habitats is quite of this community is masked by anthropo- a total of 4947 locations, in addition to the narrow in the southern and southwestern genic alteration and the prevalence of non- soil and rainfall polygons. region of the valley, but the transition be- native plants, particularly exotic grasses tween desert and woodlands and grassland (Twisselmann 1967; Heady 1995; Germano The inclusion of the kit fox in our analysis to the north and east is very broad. et al. 2001; Minnich 2008). The erroneous may seem odd given that it has an extensive classification of this region as a perennial range, a good portion of which does not Despite the variation in the width of the grassland de-emphasizes its uniqueness and overlap other species. This is partly due to ecotone, it is useful for the purposes can lead to mismanagement, both of which the ability of kit foxes to move relatively of further analyses and also developing could jeopardize the region’s biodiversity long distances (> 120 km, Schwartz et management actions to define a specific – particularly its 10 endemic plants and al. 2005). However, kit foxes are indeed area that is mostly desert. We believe this vertebrates. For example, if this region
144 Natural Areas Journal Volume 31 (2), 2011 squirrel (Ammospermophilus nelson). It is imperative that management strategies strive to reduce the density of non-native plants, especially persistent non-native annual grasses, to levels suitable for des- ert-adapted species, which prefer a more sparse vegetation cover with areas of bare ground. Managing for a desert, rather than grassland attributes, would better meet these species’ habitat requirements. Eight species inhabiting the San Joaquin Desert are already listed as endangered or threatened federally or by the state of California (U.S. Fish and Wildlife Service 1998; Table 1); and with the continuing impacts to this ecosystem, focused con- servation efforts and appropriate habitat management practices are necessary to prevent the loss of species.
ACKNOWLEDGEMENTS
We thank Scott Philips of the Endangered Species Recovery Program and Robert Hansen (Editor, Herpetological Review) for providing us with location data for vertebrates in the San Joaquin Valley. We Figure 5. Current land use in the San Joaquin Desert of California. Polygon boundaries are the same also thank Robert Hansen and L. Maynard areas of coincidence shown in Fig. 4. Moe for reviewing a draft of the paper and providing helpful suggestions. is viewed as floristically similar to more needed to promote native annual grasses northern grasslands, this could dilute con- and forbs (Corbin et al. 2007; Huntsinger servation efforts, such as habitat acquisi- et al. 2007; Jackson and Bartolome 2007; tion. Conservation efforts are critical, given Reiner 2007). Of particular importance, David J. Germano is a Professor of Biology that at least 59% of the natural habitat in non-native grasses have been identified as at California State University, Bakersfield the San Joaquin Desert has already been a threat to several rare species (U.S. Fish specializing in the life history and conser- lost to agricultural, urban, and industrial and Wildlife Service 1998; Germano et al. vation of reptiles and small mammals in activities. This estimate is likely higher as 2001) including Kern mallow (Eremalche western North America. the desert boundary that we suggest and parryi ssp. kernensis), Bakersfield cactus, have used includes an extensive area of blunt-nosed leopard lizard, giant kanga- Galen B. Rathbun is a retired federal re- non-desert mountains on the western edge roo rat (Dipodomys ingens), San Joaquin search biologist who has focused on the that are relatively undisturbed. Fortunately, kangaroo rat, and San Joaquin antelope behavioral ecology and conservation of some significant actions have been taken to protect biodiversity within the San Joa- quin Desert, most notably the creation of Table 2. The total area, undisturbed area, and percentage of habitat disturbed of high (13-16), the ca. 100,000-ha Carrizo Plain National medium (5-12), and low (1-4) number of coincidence polygons of the San Joaquin Desert in Monument. California. Disturbance to natural habitat in the desert is to a large extent due to agricultural, industrial, and urban activities. Management of the San Joaquin Desert, including the Carrizo Plain, as a peren- coincidence total area (km2) undisturbed area (km2) % disturbed nial grassland could result in unfavorable high 5061 2910 43.3 habitat conditions for the native plants and animals, especially those that are en- medium 28493 12458 59.0 demic. Management strategies that favor low 55360 29752 35.5 perennial grasses often differ from those
Volume 31 (2), 2011 Natural Areas Journal 145 mammals and their habitats in Africa and 2007. Competitive interactions. Pp. 156-168 mammals. Pp. 39-68 in T.L. Yates, W.L. the Americas. in M.R. Stromberg, J.D. Corbin, and C.M. Gannon, and D.E. Wilson, eds., Life Among D’Antonio, eds., California Grasslands: the Muses: Papers in Honor of James S. Lawrence R. Saslaw is the regional Wildlife Ecology and Management. University of Findley. Number 3, Special publication of California Press, Berkeley. the Museum of Southwestern Biology, The Biologist for the Bureau of Land Manage- University of New Mexico, Albuquerque. ment in Bakersfield, California. Dallman, P.R. 1998. Plant Life in the World’s Mediterranean Climates. University of Hawbecker, A.C. 1953. Environment of the California Press, Berkeley. Nelson antelope ground squirrel. Journal Brian L. Cypher is a Research Ecolo- D’Antonio, C.M., C. Malmstrom, S.A. Reyn- of Mammalogy 34:324-334. gist with the California State University, olds, and J. Gerlach. 2007. Ecology of Heady, H.F. 1995. Valley grassland. Pp. 491- Stanislaus Endangered Species Recovery invasive non-native species in California 514 in M.G. Barbour and J. Major, eds., Program. grassland. Pp. 67-83 in M.R. Stromberg, J.D. Terrestrial Vegetation of California. Special Corbin, and C.M. D’Antonio, eds., Califor- Publication Number 9, California Native Ellen Cypher is currently the Botanist nia Grasslands: Ecology and Management. Plant Society, Sacramento. for the Central Region of the California University of California Press, Berkeley. Holland, R.F. 1986. Preliminary Descriptions Department of Fish and Game. She has Daubenmire, R. 1978. Plant Geography with of the Terrestrial Natural Communities of been involved in research and conservation Special Reference to North America. Aca- California. California Department of Fish efforts for plants and natural communities demic Press, New York. and Game, Sacramento. in California’s Central Valley and southern Dregne, H.E. 1984. North American deserts. Huntsinger, L., J.W. Bartolome, and C.M. in Sierra Nevada foothills since Pp. 145-156 F. El-Baz, ed., Desert and D’Antonio. 2007. Grazing management on Arid Lands. Martinus Nijhoff Publishers, California’s Mediterranean grasslands. Pp. 1990. The Hague. 233-253 in M.R. Stromberg, J.D. Corbin, Fortin, M.J., T.H. Keitt, B.A. Maurer, M.L. and C.M. D’Antonio, eds., California Grass- Larry M. Vredenburgh is a geologist with Taper, D.M. Kaufman, and T.M Blackburn. lands: Ecology and Management. University the Bureau of Land Management, Bakers- 2005. Species’ geographic ranges and of California Press, Berkeley. field. During his 30-year career with BLM, distributional limits: pattern analysis and Jackson, R.D., and J.W. Bartolome. 2007. Graz- he has worked throughout California. statistical issues. Oikos 108:7-17. ing ecology of California grasslands. Pp. Germano, D.J., R.B. Rathbun, and L.R. Saslaw. 197-206 in M.R. Stromberg, J.D. Corbin, 2001. Managing exotic grasses and con- and C.M. D’Antonio, eds., California Grass- LITERATURE CITED serving declining species. Wildlife Society lands: Ecology and Management. University Bulletin 29:551-559. of California Press, Berkeley. Axelrod, D.I. 1995. Outline history of California Getz, W.M, S. Fortmann-Roe, P.C. Cross, A.J. Jaeger, E.C. 1957. The North American Deserts. vegetation. Pp. 139-193 in M.G. Barbour Lyons, S.J. Ryan, and C.C. Wilmers. 2007. Stanford University Press, Stanford, Calif. and J. Major, eds., Terrestrial Vegetation LoCoH: nonparametric kernel methods Küchler, A.W. 1995. The map of the vegeta- of California. Special Publication Number for constructing home ranges and utiliza- tion of California. Pp. 909-1002 in M.G. 9, California Native Plant Society, Sacra- tion distributions. PLoS ONE 2(2): e207. Barbour and J. Major, ed., Terrestrial Veg- mento, Calif. DOI:10.1371 /journal.pone.0000207. etation of California. Special Publication Baker, H.G. 1978. Invasion and replacement in Getz, W.M., and C.C. Wilmers. 2004. A local Number 9, California Native Plant Society, California and neotropical grasslands. Pp. nearest-neighbor convex-hull construction Sacramento. 368-384 in J.R. Wilson, ed., Plant Relations of home ranges and utilization distributions. Lowe, C.H. 1955. The eastern limit of the in Pastures. Commonwealth Scientific and Ecography 27:489-505. Sonoran Desert in the United States with Industrial Research Organization, Mel- additions to the known herpetofauna of New bourne. Griggs, F.T. 1992. The remaining biologi- cal diversity of the San Joaquin Valley, Mexico. Ecology 36:343-345. Biswell, H.H. 1956. Ecology of California California. Pp. 11-15 in D.F. Williams, S. Lyons, A., W. Getz, and S. Roe-Fortmann. 2009. grasslands. Journal of Range Management Byrne, and T.A. Rado, eds., Endangered and LoCoH (Local Convex Hull) Homerange 9:19-24. Sensitive Species of the San Joaquin Valley, Generator for ArcGIS 9. Available online Brattstrom, B.H. 1953. Records of Pleistocene California. California Energy Commission,
146 Natural Areas Journal Volume 31 (2), 2011 MacMahon, J.A., and F.H. Wagner. 1985. The – United States and Mexico. Transactions Turner, R.M., and D.E. Brown. 1982. Sonoran Mojave, Sonoran and Chihuahuan Deserts and Proceedings Series No. 3, U.S. Depart- desertscrub. Pp. 181-221 in D.E. Brown, of North America. Pp. 105-202 in M. Eve- ment of the Interior, National Park Service, ed., Biotic Communities of the American nari, I. Noy-Meir, and D.W. Goodall, eds., Washington, D.C. Southwest – United States and Mexico. Hot Deserts and Arid Shrublands. Elsevier Pavlik, B.M. 2008. The California Deserts: Desert Plants, Vol. 4. The University of Scientific Publishers, Amsterdam. an Ecological Rediscovery. University of Arizona, Tucson. Major, J. 1995. California climate in relation California Press, Berkeley. Twisselmann, E.C. 1967. A flora of Kern to vegetation. Pp. 11-74 in M.G. Barbour Reiner, R.J. 2007. Fire in California grasslands. County, California. Wasmann Journal of and J. Major, ed., Terrestrial Vegetation of Pp. 207-217 in M.R. Stromberg, J.D. Corbin, Biology 25:1-395. California. Special Publication Number and C.M. D’Antonio, eds., California Grass- U.S. Fish and Wildlife Service. 1998. Recovery 9, California Native Plant Society, Sacra- lands: Ecology and Management. University plan for upland species of the San Joaquin mento. of California Press, Berkeley. Valley, California. U.S. Fish and Wildlife McGrew, J.C. 1979. Vulpes macrotis. Mam- Schiffman, P.M. 2007. Species composition at Service, Region 1, Portland, Ore. malian Species 123:1-6. the time of first European settlement. Pp. Vasek, F.C., and M.G. Barbour. 1995. Mojave Meigs, P. 1953. World distribution of arid and 52-56 in M.R. Stromberg, J.D. Corbin, and desert scrub vegetation. Pp. 835-867 in semi-arid homoclimates. Pp. 203-209 in C.M. D’Antonio, eds., California Grass- M.G. Barbour and J. Major, eds., Terrestrial Reviews of Research on Arid Zone Hydrol- lands: Ecology and Management. University Vegetation of California. Special Publication ogy. UNESCO, Paris. of California Press, Berkeley. Number 9, California Native Plant Society, Minnich, R.A. 2008. California’s Fading Schwartz, M.K., K. Ralls, D.F. Williams, B.L. Sacramento. Wildflowers: Lost Legacy and Biological Cypher, K.L. Pilgrim, and R.C. Fleischer. Western Regional Climate Center. 2010. His- Invasions. University of California Press, 2005. Gene flow among San Joaquin kit fox torical climate information. NOAA and Berkeley. populations in a severely changed ecosys- Desert Research Institute. Available online tem. Conservation Genetics 6:25-37. Morafka, D.J. 1977. Is there a Chihuahuan
Volume 31 (2), 2011 Natural Areas Journal 147