Aliso: A Journal of Systematic and Evolutionary Botany Volume 35 | Issue 2 Article 2 2017 The egetV ation and Flora of Edwards Air Force Base, Western Mojave Desert, California David Charlton Jacobs Engineering, Pasadena Philip W. Rundel University of California, Los Angeles Follow this and additional works at: http://scholarship.claremont.edu/aliso Part of the Botany Commons Recommended Citation Charlton, David and Rundel, Philip W. (2017) "The eV getation and Flora of Edwards Air Force Base, Western Mojave Desert, California," Aliso: A Journal of Systematic and Evolutionary Botany: Vol. 35: Iss. 2, Article 2. Available at: http://scholarship.claremont.edu/aliso/vol35/iss2/2 Aliso, 35(2), pp. 51–68 ISSN: 0065-6265 (print), 2327-2929 (online) THE VEGETATION AND FLORA OF EDWARDS AIR FORCE BASE, WESTERN MOJAVE DESERT, CALIFORNIA DAV I D CHARLTON1 AND PHILIP W. RUNDEL2,3 1Jacobs Engineering, Pasadena, California 91101 ([email protected]); 2Department of Ecology and Evolutionary Biology, University of California, Los Angeles, California 90095 3Corresponding author ([email protected]) ABSTRACT Edwards Air Force Base extends over 121,000 ha in the Antelope Valley of the western Mojave Desert, with much of the area part of a closed endorheic basin that held the Pleistocene Lake Thompson. Notable topographic features are Rogers, Rosamond and Buckhorn dry lakes, while rounded domes and scattered hills are present to the north and east. Elevation gradients are limited, ranging from a low of 690 m to 1044 m near the eastern margin. Diverse communities of saltbush scrub dominate the lower plains, while creosote bush scrub and Joshua tree woodlands are present away from the old lake basin. In many ways EAFB is a biogeographic crossroads with the broader central Mojave Desert to the east, Owens Valley and Great Basin to the north, and cismontane Central Valley and foothills to the west. The flora as currently known contains 403 vascular plant taxa, with 324 (80%) of these native. The eight largest families comprise more than 68% of the flora, led by the Asteraceae with 84 taxa (72 native). Annual plants make up over two-thirds of the total flora. Key words: creosote bush scrub, flora, Mojave Desert, non-native species, saltbush scrub. INTRODUCTION (5589 ha), Buckhorn Dry Lake (739 ha), and playa complexes north and northeast of Buckhorn Dry Lake (690 ha). In the late Edwards Air Force Base (EAFB) lies in the Antelope Val- Pleistocene, Lake Thompson rose to 710 meters above sea level ley, a low-lying basin at about 700 m elevation that occupies and covered 950 km2 (95,000 ha) of the Antelope Valley (Orme the western edge of the Mojave Desert. The Antelope Valley is 2008). The lake slowly desiccated following the Pleistocene and roughly triangular in shape and bordered on the southwest by the the old lakebed is today represented by Rogers, Rosamond and San Gabriel Mountains and on the northwest by the Tehachapi Buckhorn Dry Lakes. Beyond these playas the former lake basin Mountains (Fig. 1). This western valley is a closed endorheic is characterized by exposed lake beds and beach ridges as well basin that was the site of the large Pleistocene Lake Thompson as areas mantled by aeolian and fluvial deposits (Orme 2008). (Orme 2008). The boundaries of EAFB include approximately Rogers Dry Lake has a long history of aviation use ranging from 121,000 ha of the Antelope Valley, extending over portions of the development of special aircraft for the U.S. Air Force to its Kern, Los Angeles and San Bernardino counties. Geographi- service as a recovery site for early Space Shuttle landings. cally, EAFB is approximately 160 km northeast of Los Angeles, The second region is an upland area in the northwest portion 140 km northwest of San Bernardino and 130 km southeast of of the base north of Rosamond Dry Lake and west of Rogers Bakersfield. Dry Lake. This area is characterized by low, rounded hills, in- The topography of EAFB can be characterized by broad ex- cluding the Rosamond and Bissell Hills, with elevations ranging panses of flat to gently sloping plains interspersed with broad, between 690 and 975 m. The third physiographic area is formed rounded domes and a scattered occurrence of steeper, more by the highlands to the east of Rogers Dry Lake and extending rugged hills that rise sharply above the surrounding plains. The to the eastern boundary of EAFB. This upland area is similar domes and hills consist mostly of outcrops of granite and quartz in landform to that in the northwestern corner of the base ex- monzonite, with non-granitic volcanic rock forming some of the cept for two prominent relief features. Leuhman Ridge in Kern smaller features (EAFB 2008). Limestone is absent. Elevations County reaches 1034 m in elevation, and Haystack Butte in San on base range from 690 m at Rogers Dry Lake to 1044 m at Red Bernardino County has an elevation of 1030 m. Buttes near the eastern boundary. The climate of EAFB is typical of the western Mojave Desert The base can be divided into three distinct physiographic with a precipitation regime dominated by winter rainfall (Run- sections. The first physiographic area occupies the central and del and Gibson 1996). The presence of the San Gabriel and southwestern lowlands of the base. This region extends from Tehachapi Mountains to the southwest and northwest of the the southern to the northern boundary of the base and has a low Antelope Valley limits, but does not prevent, the passage of relief of approximately 120 m, with elevations ranging from moist air from the Pacific Ocean. Cyclonic winter storms bring 690 to 815 m (EAFB 2008). The greatest portion of this area is the majority of precipitation, with 80% falling from November composed of Rogers Dry Lake (11,453 ha), Rosamond Dry Lake through March. A summer weakening of the subtropical high pressure center of the eastern pacific, however, can occasionally allow low pressure systems from the Gulf of Mexico or tropi- C 2017, The Author(s), CC-BY. This open access article is distributed under a Creative Commons Attribution License, which allows unrestricted cal storms from the subtropical Pacific Ocean to penetrate and use, distribution, and reproduction in any medium, provided that the orig- bring August or September rains. Mean annual precipitation at inal author(s) and source are credited. Articles can be downloaded at Rogers Dry Lake was 122 mm for 1933–1989 (Londquist et al. http://scholarship.claremont.edu/aliso/. 1993) or about 125 mm for 1944–2003 (EAFB 2008). Figure 2 52 Charlton and Rundel ALISO Fig. 1. Location of Edwards Air Force Base in Antelope Valley in the western Mojave Desert, California. Base boundaries are indicated by a dot-dash line. illustrates the annual precipitation at EAFB from 1944 to 2003 forms the dominant vegetation on EAFB in the areas around and demonstrates the large amount of inter-annual variation. Rosamond, Buckhorn and Rogers dry lakes (Fig. 3A; Lichvar Seasonal temperature variation is high, with mean summer high and Sprecher 1996; Lichvar et al. 2004). A complex interac- ◦ ◦ temperatures of 36 C, but record extremes up to 45 C. Winter tion of topography, geology and soils creates special microsite ◦ ◦ lows at night average −1 C, but record lows are −15 C. conditions with a diverse set of identifiable associations includ- ing sand fields, various dune types, beach ridges and bare clay pans (Fig. 3B; Sharifi et al. 2017a). Dominance by Atriplex canescens (four-wing saltbush) is generally associated with deep VEGETATION sand along washes or on dunes. In contrast, stands dominated Saltbush scrub with a dominance of single or multiple species by Atriplex confertifolia (shadscale) occur in areas of deflated of Atriplex is widespread in the western Mojave Desert and dunes with sandy hummocks and pans. Associations of Atriplex VOLUME 35(2) Vegetation and Flora of Edwards Air Force Base 53 Fig. 2. Long-term calendar-year precipitation from 1944 to 2003 at Edwards Air Force Base, California. Long-term mean annual precipitation is 215 mm (EAFB 2008). spinescens (spinescale) are limited to areas of the Pleistocene low and high species diversity. The portions with low species bed of Lake Thompson that have been eroded by flood events richness are dominated by L. tridentata and/or Ambrosia du- to produce shallow sands over the soil surface. Clay drainages mosa (burrobush). The more species-rich communities include exhibit associations of Atriplex torreyi (Nevada saltbush) with Ephedra nevadensis (Nevada tea), Grayia spinosa (spiny hop- Ericameria nauseosa (rabbitbrush), Gutierrezia microcephala sage) and Krascheninnikovia lanata (winterfat) as important (matchweed) and Artemisia tridentata subsp. parishii (Parish’s associated shrubs. These are the same species that make up the sagebrush) as co-dominants. Atriplex parryi (Parry saltbush) is understory shrubs in the Joshua tree woodland. The annuals are restricted to depressions and small pans. Associations domi- much more diverse than in the saltbush scrub and are most com- nated by Atriplex polycarpa (allscale) are typically found in less monly observed in the sandy soils on the flats near the Rosamond saline transitional ecotones between playa, oligotrophic soils Hills and slopes of the west range. and upland plant communities. Allscale also occurs on rhyolitic Rocky slopes on the base support shrub communities with Eri- outcrops and clay pans disturbed by trenching. ogonum fasciculatum var. polifolium (bush buckwheat) and Ly- The edges of clay pans in the southwestern portion of the cium andersonii (desert tomato), along with Ericameria cooperi base where there is a thin veneer of sand that has been sorted (Cooper’s goldenbush) and E. teretifolia (round-leaf golden- into the pan and dune habitat are dominated by stem succulent bush).