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The Transition from Mojave to Desert on the Test Site

D. J. Hansen W. K. Ostler D.B. Hall

Abstract— species and associations on the Nevada Test Site (Ostler and others 1999). Approximately 1,500 ecological land- are located along elevation and gradients. Associa- form units (ELUs) were delineated using aerial photography tions in the had the highest species diversity. and satellite imagery to distinguish ecological mapping sign and of annual are least in the lower types. The boundaries of each ELU were field verified. and higher elevations and most abundant in the mid-elevations. Landforms were selected because they are highly correlated Microbiotic crusts are most abundant in fine-textured soils and of with soil types in Nevada (Peterson 1981) and have been low abundance in soils with active erosional processes. Texture of used historically to help classify habitat types in the Mojave surface soils (0 to 5 centimeters [0 to 2 inches]) differs little among Desert ( 1979). Vegetation and other site parameters all associations except for a few that are correlated with playas and were sampled within representative areas of each ELU. steep mountain slopes. However, differences among associations Data were analyzed using cluster analyses and descriptive are observed for deeper substrates comprised of , basalt, statistics to help classify vegetation into 10 alliances and and tuff parent materials. 20 associations.

Results ______The Nevada Test Site (NTS) is located about 105 km (65 miles) northwest of in (see fig. 1 Results of the vegetation classification on the NTS are of companion paper, Ostler and others, 1999). The site was shown in table 1. About 23 percent and 37 percent of the created by a series of land withdrawals in the early 1950s for ELUs sampled on the NTS were located in the nuclear weapons testing. It comprises a total land area of and Great Basin Desert, respectively (table 2). The remain- 350,000 ha (1,350 square miles). Despite nearly 1,000 ing 36 percent of the ELUs were located in a Transition Zone atmospheric and below-ground nuclear tests, the area is between these two . About 4 percent of the 1,508 relatively undisturbed and offers an excellent location for ELUs sampled were classified as “miscellaneous” because biological studies. The area has had limited or no livestock they were unique vegetation types, burned, scraped, or since the 1950s and is designated as a National disturbed by nuclear testing. In the Mojave Desert the Environmental Research Park. / was the The NTS consists of three large valleys, , French- most numerous association representing about 19 percent of man, and Jackass Flats. It has two high mesas, Rainier and the ELUs on the NTS (18 percent of the total area). No other Pahute. It has a rough elevational gradient from south to association in the Mojave Desert represented more than north with the lowest point at 829 m (2,688 ft) in Jackass 4 percent of the total ELUs. In the Great Basin Desert the Flats and the highest point at 2,340 m (7,679 ft) on Rainier -Chrysothamnus viscidiflorus Mesa. The site straddles the Mojave and Great Basin Deserts Shrubland was the most numerous association representing and provides an excellent site to observe the transition about 11 percent of the ELUs on the NTS (7.5 percent of the between these two deserts. Numerous detailed studies have total area). No other association in the Great Basin Desert been conducted on NTS biota focusing primarily on invento- represented more than 7 percent of the total ELUs. In the ries and evaluating the effects of nuclear testing. Approxi- Transition Zone between these deserts, the mately 730 plant species occur on the NTS, of which several ramosissima- nevadensis Shrubland was the most are sensitive or protected. numerous association representing about 22 percent of the ELUs on the NTS (21.6 percent of the total area). No other association in the Transition Zone represented more than Methods ______6 percent of the total ELUs. of the NTS were classified using methods de- scribed in a companion paper presented in these proceedings Distribution of Plant Alliances on the Nevada Test Site

Figure 1 shows the distribution of plant alliances on the

In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999. NTS. Also shown are the generalized boundaries for the Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc. Mojave Desert, Great Basin Desert, and the Transition Zone RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service, between these deserts. Plant species that dominate associa- Rocky Mountain Research Station. D. J. Hansen, W. K. Ostler, and D. B. Hall are Biologists with Bechtel tions within the Transition Zone have been historically Nevada, P.O. Box 98521, M/S NLV-081, Las Vegas, NV 89193-8521.

148 USDA Forest Service Proceedings RMRS-P-11. 1999 Table 1—Classification of vegetation on the Nevada Test Site. deciduous (e.g., blackbrush) or have essentially leafless, photosynthetic stems (e.g., Ephedra spp.), while the most Mojave Desert abundant dominant from associations in the Mojave spp. Shrubland Alliance Desert and Great Basin Desert are evergreen in habit (e.g., Lycium shockleyi- Shrubland Larrea tridentata/Ambrosia dumosa Shrubland Alliance creosote bush, big sagebrush, singleleaf pinyon, and Larrea tridentata /Ambrosia dumosa -Shrubland ). The evolutionary adaptation of reduction or Atriplex confertifolia - Ambrosia dumosa Shrubland Alliance abscission during drought and stress-induced dormancy Atriplex confertifolia - Ambrosia dumosa Shrubland may help maintain the abundance of blackbrush and Mor- mon tea () in these ecotones. While the Transition Zone Hymenoclea -Lycium Shrubland Alliance abundance of species other than blackbrush are relatively - Hymenoclea salsola Shrubland low in the Coleogyne ramosissima - Ephedra nevadensis Hymenoclea salsola - Ephedra nevadensis Shrubland Shrubland, they are frequently present in small numbers Ephedra nevadensis Shrubland Alliance being found in small patches where animals have disturbed spinescens - Ephedra nevadensis Shrubland the soil horizons or fire has reduced competition with - Ephedra nevadensis Shrubland blackbrush. Eriogonum fasciculatum - Ephedra nevadensis Shrubland Blackbrush occurs at intermediate elevations. At these Ephedra nevadensis - Shrubland elevations lightning strikes, associated with storms blowing Coleogyne ramosissima Shrubland Alliance from the south, are common during the summer and occa- Coleogyne ramosissima - Ephedra nevadensis Shrubland sionally fuel loading reaches levels high enough to support Great Basin Desert wildfires. Once burned these communities reestablish very Atriplex spp. Shrubland Alliance slowly; this phenomenon is also reported by Brown (1982). Atriplex confertifolia - Kochia americana Shrubland Atriplex canescens - Krascheninnikovia lanata Shrubland Chrysothamnus-Ericameria Shrubland Alliance Species Diversity Chrysothamnus viscidiflorus - Ephedra nevadensis Shrubland Ericameria nauseosa Shrubland Alliance Species diversity (richness or the number of species) of Ericameria nauseosa - Ephedra nevadensis Shrubland perennial and shrubs was greatest in the Great Basin Artemisia spp. Shrubland Alliance Desert associations (mean of 56 species) compared to asso- Ephedra viridis - Artemisia tridentata Shrubland ciations in the Transition Zone (mean of 49 species) and the Artemisia tridentata - Chrysothamnus viscidiflorus Shrubland Mojave Desert (mean of 36 species). Similar species diver- - Chrysothamnus viscidiflorus Shrubland sity patterns were also observed for all combined perennial Artemisia nova - Artemisia tridentata Shrubland /Artemisia spp. Alliance species on the NTS (table 2) (e.g., Great Basin Desert: 21.7 Pinus monophylla/Artemisia nova Woodland species per ELU, Transition Zone: 17.4 species per ELU, and Pinus monophylla/Artemisia tridentata Woodland Mojave Desert: 12.7 species per ELU).

Elevation and Precipitation associated with either desert, and in some cases, listed as a Plant associations within the Mojave Desert and Great minor species in both deserts. Basin Desert were ordered according to increasing elevation and precipitation (fig. 5). Mean annual precipitation was Associations that were considered typical or characteris- 2 tic of the Mojave Desert were those that contained a presence determined to be positively correlated (r = 0.85) with eleva- of Shockley’s desertthorn (Lycium shockleyi), rabbit thorn tion on the NTS, based on correlation modeling and actual (Lycium pallidum), creosote bush (Larrea tridentata), or weather recording data (French 1986; other detailed meteo- white bursage (Ambrosia dumosa), but lacked species char- rological data are presented by Fransioli and Ambos 1997). acteristic of the Great Basin Desert (table 3). The distribu- The importance of elevation, slope, and substrate in account- tion of creosote bush on the NTS (fig. 2) approximates the ing for statistical variance in species cover was also described for the Nellis Air Force Range consisting of boundaries for the Mojave Desert on the NTS. Associations 2 that were considered typical of the Great Basin Desert were 1,228,355 ha (7,432 mi ) of shrubland adjacent to the NTS those that contained a presence of sagebrush (Artemisia (Pritchett and others 1997). spp.), singleleaf pinyon (Pinus monophylla), or Utah juniper (), but lacked species characteristic Soils and Parent Materials of the Mojave Desert. The distribution of big sagebrush (Artemisia tridentata) on the NTS (fig. 3) approximates the Texture of surface soils (0 to 5 centimeters [0 to 2 inches]) boundaries of the Great Basin on the NTS. Associations appeared to differ little among all associations except for within the Transition Zone were considered to be those that two that were correlated with playas and steep mountain had a mixture of species, many species occurring in both the slopes. The plant associations associated with playas were Mojave and Great Basin Desert (table 3), such as Ephedra the Lycium shockleyi - Lycium pallidum Shrubland and the (Ephedra) spp. and blackbrush, (Coleogyne ramosissima). Atriplex confertifolia - Kochia americana Shrubland. Soil The distribution of blackbrush on the NTS (fig. 4) approxi- texture of these associations had a greater percentage of mates the boundaries of the Transition Zone on the NTS. clay than other associations. The most abundant soil tex- Associations that occur in the Transition Zone appear to tures for surface soils of the associations were comprised of be comprised of shrubs that are predominantly drought three textural types: sandy loam (30 percent), loamy sand

USDA Forest Service Proceedings RMRS-P-11. 1999 149

Chrysothamnus viscidiflorus-Ephedra Nevadensis viscidiflorus-Ephedra Chrysothamnus

Atriplex canescens-Krascheninnikovia lanata canescens-Krascheninnikovia Atriplex

Atriplex confertifolia-Kochia americana confertifolia-Kochia Atriplex

Coleogyne ramosissima-Ephedra nevadensis ramosissima-Ephedra Coleogyne

Ephedra nevadensis-Grayia spinosa nevadensis-Grayia Ephedra

Eriogonum fasciculatum - Ephedra nevadensis Ephedra - fasciculatum Eriogonum

Hymenoclea salsola-Ephedra nevadensis salsola-Ephedra Hymenoclea

Lycium andersonii-Hymenoclea salsola andersonii-Hymenoclea Lycium

Krascheninnikovia lanata-Ephedra nevadensis lanata-Ephedra Krascheninnikovia

Menodora spinescens-Ephedra nevadensis spinescens-Ephedra Menodora

Atriplex confertifolia-Ambrosia dumosa confertifolia-Ambrosia Atriplex

Larrea tridentata/Ambrosia dumosa tridentata/Ambrosia Larrea Lycium shockleyi-Lycium pallidum shockleyi-Lycium Lycium 4 287 51 42 29 11 44 14 93 325 17 38 76

11 49 49 50 34 23 50 36 66 84 53 87 61 43 42 73 56 47 54 47

8.8 13.2 16.2 19.4 17.6 12.8 15.2 20.4 19.7 16.9 9.2 11.9 21.4 17.1 27 20.8 24.7 29.1 27 28.6

0.8 5.7 13.6 8 3.6 2.3 3.8 36.3 8.8 8.5 2.7 3.5 7.1 6.9 18.2 5.9 6.4 8.6 8.1 14.3

941 1,080 1,153 1,198 1,258 1,263 1,263 1,292 1,413 1,385 1,208 1,237 1,485 1,563 1,719 1,776 1,805 1,831 1,985 2,054

14.8 16 16.9 17.5 18.2 18.3 18.3 18.7 20.2 19.8 17.6 18 21.1 22.1 24 24.7 25.1 25.4 27.3 28.2

32.5 63.2 57.4 65 58.1 55.5 47.6 17.5 57 68.2 34.1 41.1 57.2 62.8 49.8 52.5 66.7 47.8 53.5 47.8

Mojave Desert Transition zone Great Basin Desert

Parameters

—Parameters associated with associations in the Mojave and Great Basin Deserts and Transition Zone on the Nevada Test Site.

Number of stands Number of shrub species Mean number of perennial species/ELU Mean elevation (m) Mean precipitation (cm) Mean slope (degrees) Mean rock pavement (percent)

Table 2

150 USDA Forest Service Proceedings RMRS-P-11. 1999 Figure 1—Vegetation alliances on the Nevada Test Site. (1 = Pinus monophylla/Artemisia spp. woodland; 2 = Artemisia spp. shrubland; 3 = Atriplex spp. shrubland; 4 = Chrysothamnus-Ericameria shrubland; 5 = Coleogyne ramosissima shrubland; 6 = Ephedra nevadensis shrubland; 7 = Lycium spp. shrubland; 8 = Hymenoclea-Lycium shrubland; 9 = Atriplex confertifolia-Ambrosia dumosa shrubland; 10 = Larrea tridentata/Ambrosia dumosa shrubland; 11 = Miscellaneous; 12 = Playa/Disturbances).

USDA Forest Service Proceedings RMRS-P-11. 1999 151

Atriplex confertifolia-Kochia americana confertifolia-Kochia Atriplex

Coleogyne ramosissima-Ephedra nevadensis ramosissima-Ephedra Coleogyne Ephedra nevadensis-Grayia spinosa nevadensis-Grayia Ephedra

0.1 0.4 0.7 0.2 0.8 15.0 0.6 0.3 0.9 0.8 0.3

0.3 0.9 0.0 1.0 0.5 1.9 67.9 33.8 55.4 5.4

0.1 0.0 0.0 0.2 0.1 0.6 1.4 0.6 1.2 5.9 7.3 0.0 0.4 0.2 0.6 0.2 0.2 1.7 7.9 0.0 0.2 0.1 0.7 2.2 0.9 1.3 14.1 27.5

Eriogonum fasciculatum - Ephedra nevadensis Ephedra - fasciculatum Eriogonum Hymenoclea salsola-Ephedra nevadensis salsola-Ephedra Hymenoclea

0.5 0.3 0.2 0.5 0.3 0.3 51.7 0.2 0.9 0.3 0.8 0.0 0.3

0.6 0.6 0.3 0.2 0.4 1.3 8.9 0.8 0.3 0.1 1.1 1.4

Lycium andersonii-Hymenoclea salsola andersonii-Hymenoclea Lycium

Krascheninnikovia lanata-Ephedra nevadensis lanata-Ephedra Krascheninnikovia

Menodora spinescens-Ephedra nevadensis spinescens-Ephedra Menodora Atriplex confertifolia-Ambrosia dumosa confertifolia-Ambrosia Atriplex

0.0 0.1 0.2 1.3 1.4 0.3 5.0 6.0 15.7 56.1 14.3 25.1 2.6 22.8 0.0 0.2 0.4 0.2 0.1 4.5 3.3 2.7 7.5 1.7 1.5 Larrea tridentata/Ambrosia dumosa tridentata/Ambrosia Larrea

6.6 3.8 4.5 0.8 0.4 0.3 5.0 1.0 0.8 0.0 0.2 0.0 0.1 1.3 1.8 13.9 2.2 0.4 0.0 1.6 0.5 5.8 2.6 0.4 0.0 0.0 2.1 0.6 1.1 8.3 5.3 1.9 3.7 2.1 8.1 0.2 3.2 5.1 0.1 0.8 1.9 2.0 1.9 0.5 0.1 3.0 6.4 4.5 8.0 51.8 4.5 3.4 3.2 5.9 5.4 5.0 4.7 0.5 0.1 0.7 0.6 0.3 0.0

0.4 0.8 0.5 0.1 0.1 28.1 0.8 1.7 0.1 0.4 6.0 0.4 0.0 0.3 0.0 0.6 3.6 4.7 1.9 2.6 1.6 0.7 56.3 4.1 0.1 1.8 1.8 5.3 1.8 0.5 0.2 1.8 0.1 0.6 0.2 0.5 1.2 0.4 2.3 0.7 4.9 0.0 0.8 0.7 0.0 0.2 0.1 0.1 0.7 7.1 8.9 11.8 12.3 6.4 8.5 16.4 9.6 22.8 0.1 2.9 11.4 11.1 2.1 7.1 4.3 3.1 0.8 1.0

0.1 0.5 2.7 2.2 0.6 5.4 2.2 1.5 5.3 0.8 1.0 36.7 4.4 1.9 8.1 5.2 4.8 3.7 2.8

0.0 0.2 0.5 3.0 1.0 1.5 0.9 0.4 1.5 2.3 21.0 2.0 1.7 2.2 2.3 1.1

0.0 0.0 0.0 0.3 0.0 0.0 0.3 1.5 2.9 0.7 3.6 2.3 4.1

12.4 4.2 3.4 2.4 2.4 1.6 0.3 1.9 0.6 0.1 0.9 0.1 0.0 Mojave Desert Transition zonepallidum shockleyi-Lycium Lycium Great Basin Desert

3.5 3.3 4.4 3.6 28.5 7.3 2.5 3.7 1.4 3.3 2.8 10.8 5.3 0.0 0.1 1.0 0.6 0.5 0.0 0.0 0.0 1.7 1.2 2.7 3.7 9.6 51.5 1.3 2.6 7.9 0.2 3.9 1.6 0.2 0.0 0.0

1.0 0.1 0.7 0.6 5.2 1.5 0.2 0.2 0.9 6.6 0.8 2.6 0.3 0.1 0.1 1.8 7.5 2.7 31.3 8.2 4.7 0.5 3.0 1.4 0.7 49.8 3.3 3.9 0.2 0.8 0.0 0.0 0.3 0.5 0.1 0.0 22.1 0.9 0.3 0.0 9.0 0.4 0.3 0.8 2.5 6.4 4.6 0.4 0.8 8.0 2.4 57.8 6.6 5.2 3.5 1.9 1.4 2.0 0.5 0.0

47.5 0.5 0.2 0.0 17.0 5.5 0.4 0.1 1.0 0.1 12.5 43.4 15.6 10.3 4.0 1.1 2.2 5.3 3.5 0.5 0.6 0.4 0.6 0.1 0.1

Parameters

—Percent abundance of dominant species found in associations in the Mojave and Great Basin Deserts on the Nevada Test Site.

Lycium shockleyi Lycium pallidum Ambrosia dumosa Larrea tridentata erecta Menodora spinescens Grayia spinosa Krascheninnikovia lanata Lycium andersonii Hymenoclea salsola Eriogonum fasciculatum Coleogyne ramosissima Ericameria cooperii Ephedra nevadensis Artemisia spinescens Atriplex confertifolia Kochia americana Atriplex canescens Chrysothamnus viscidiflorus spp. Ericameria nauseosa Ephedra viridis Purshia stansburiana Artemisia tridentata Artemisia nova Chrysothamnus viscidiflorus spp. Leptodactylon pungens Juniperus osteosperma Purshia tridentata Pinus monophylla

Table 3

152 USDA Forest Service Proceedings RMRS-P-11. 1999 Figure 2—Distribution and percent abundance of creosote bush on the Nevada Test Site.

USDA Forest Service Proceedings RMRS-P-11. 1999 153 Figure 3—Distribution and percent abundance of big sagebrush on the Nevada Test Site.

154 USDA Forest Service Proceedings RMRS-P-11. 1999 Figure 4—Distribution and percent abundance of blackbrush on the Nevada Test Site.

USDA Forest Service Proceedings RMRS-P-11. 1999 155 —Average elevation and precipitation of vegetation associations on the Nevada Test Site.

Figure 5

156 USDA Forest Service Proceedings RMRS-P-11. 1999 (18 percent), and loam (14 percent). Soil samples from the Rodent Activity remaining 38 percent of associations were classified into more than 30 different textural types. The Eriogonum The absence of sign indicating burrowing and the fasiculatum - Ephedra nevadensis Shrubland was located on low abundance of sign (e.g., burrows and excavated soils) the steepest slopes (36 degrees) with all other associations were found to be correlated with increasing elevation. For averaging slopes less than 18 degrees, with a mean slope of example, the Mojave Desert was observed to have 45 percent 7 degrees. of the sites with none to low sign. The Transition Zone was Despite little difference in soil texture near the soil sur- observed to have 59 percent of the sites with none to low sign, face, associations were observed to differ in the type of and the Great Basin Desert was observed to have 80 percent substrate upon which they most commonly appeared. The of the sites with none to low sign Both the moderate rodent Coleogyne ramosissima - Ephedra nevadensis Shrubland sign and the high to very high rodent sign were inversely and Atriplex confertifolia - Ambrosia dumosa Shrubland correlated with elevation. For example, the Mojave Desert appeared frequently on shallow soils of limestone-derived had 39 percent moderate sign and 16 percent high to very parent materials, while most of the associations in the Great high sign. The Transition Zone had 30 percent moderate sign Basin Desert occurred in the basalt or tuff formations. and 11 percent high to very high sign. The Great Basin Remaining associations occurred in alluvial soils. Creosote Desert had 14 percent moderate sign and 6 percent high to bush appeared to be limited by shallow soils or the presence very high sign. The Mojave Desert sites may have deeper of a layer. Lunt and others (1973) suggest that big soils that are more conducive to burrowing, while the rockier sagebrush and creosote bush have unusually high oxygen soils of the Transition Zone have fewer burrows. The Great requirements, while roots of white bursage appear to require Basin Desert sites have shallow soils and more severe less oxygen. winters that may also reduce burrowing or abundance of animals likely to burrow. Microbiotic Crusts Species Correlations The presence of microbiotic crusts on the soil surface (i.e., nonvascular microorganisms such as algae, fungi or lichens Pairwise comparisons of species abundance at a statistical that are frequently important for enhancing soil fertility and level of significance of α = 0.05 of the 718 species observed to surface stabilization) was noted during the field surveys. occur on the NTS indicate that there were 447 positive Within the NTS 58 percent of the ELUs sampled had no interspecific associations between species and only 271 visual evidence of microbiotic crusts, 28 percent had low negative interspecific associations. This general trend is in visual evidence of crusts, 11 percent had moderate visual agreement with earlier studies conducted using 25 circular evidence of crusts, and only 4 percent had high visual plots of 30.5 m (100 ft) in diameter during the late 1960s at evidence of microbiotic crusts. Visual evidence of crusts were the NTS (Wallace and Romney 1972). Using Chi-squared observed to decrease with increases in elevation. For ex- analyses, Wallace and Romney reported a great many more ample, no microbiotic crusts were observed in 31 percent of positive than negative measures of association. sites within the Mojave Desert, 43 percent of sites within the Transition Zone and 50 percent of sites within the Great Basin Desert. Associations with high abundance of crusts Vegetation and Climate of the Last 45,000 also had higher percentages of soil fines (clays or silts). Low Years presence of crusts or their absence was associated with Vegetation patterns in response to changing climatic active soil erosional processes (e.g., along washes and steeper conditions have been studied extensively on the NTS and unstable slopes). documented through the analyses of several packrat-midden sites (Spaulding 1985). Vegetation patterns suggest that Productivity of Annual Vegetation about 45 thousand years before present (k yr BP), the NTS had cooler and wetter conditions than currently; dominant The presence of annual vegetation and its relative abun- plants included littleleaf mountain mahogany (Cercocarpus dance were not randomly distributed across the three areas ledifolius), Utah juniper, sagebrush, and horsebrush (Mojave Desert, Transition Zone, and Great Basin Desert) (Tetradymia spp). By 35 k yr BP, limber () based on Chi-square analyses (58.6, P < 0.001, df = 4). and four-wing saltbush (Atriplex canescens) had established Associations in the Mojave Desert and the Transition Zone at the site. By 25 k yr BP, shadscale (Atriplex confertifolia), tended to be over-represented in the moderate category (41 snowberry (Symphoricarpos longiflorus), and Utah and 35 percent respectively) and underrepresented in the Fendlerbush (Fendlerella utahensis) became more common. low-very low category (43 and 43 percent respectively) By 10 k yr BP, limber pine was no longer found in packrat- while associations in the Great Basin Desert tended to be midden samples and was replaced by the presence of singleleaf overrepresented in the low-very low category (60 percent) pine and increase in the abundance of Utah Juniper. and underrepresented in the moderate category (22 per- Goldenweed (Haplopappus nanus), Dorr’s sage (Salvia cent). Levels within the high-very high category were simi- dorii), and grizzlybear pricklypear ( erinacea) be- lar for all three areas. This is consistent with regional floras came more prevalent. which show a greater number of annual species in drier and During the past 5 k yr BP, creosote bush, white bursage, hotter deserts of the Southwest compared to the colder and other species characteristic of the Mojave Desert Great Basin Desert.

USDA Forest Service Proceedings RMRS-P-11. 1999 157 established within the NTS area as temperatures increased References ______and precipitation decreased. It was estimated that many Great Basin Desert trees and shrubs were displaced about Berry, K. H. 1979. The East Mojave Desert: An example of Inven- 457 to 610 m (1,500 to 2,000 ft) upward in elevation to what tory design and habitat analysis. In: Classification, inventory, they historically had been as the climate changed (Spaulding and analysis of fish and wildlife habitat—the proceedings of a national symposium; January 24-27, 1977; Phoenix, AZ; Allan 1985). This climate change opened new niches for coloniza- Marmelstein, General Chairman. Biological Services Program, tion by other species such as blackbrush. Ecotonal species PB 299240, FWS/OBS-78/76, U.S. Fish and Wildlife Service, are often adapted to a wide change in climatic conditions Washington, D.C. such as freezing temperatures as well as hot, droughty Brown, D. E. 1982. Biotic communities of the American South- west— and . Tucson, AZ: The University of climate. . Desert Plants. 4(1-4): 151. French, R. H. 1986. Daily, seasonal, and annual precipitation at the Nevada Test Site, Nevada. Desert Research Institute Summary and Conclusions ______University of Nevada System, Water Resources Center Publica- tion #45042, DOE/NV/10384-01, U.S. Department of Energy, Vegetation of the NTS is diverse and relatively protected Nevada Operations, Las Vegas, Nevada. from the effects of livestock grazing. Plant communities Fransioli, P. M.; Ambos, D. S. 1997. Engineering design climatol- ogy and regional meterological conditions report. TRW appear to respond to moisture and temperature gradients Environmental Safety Systems Inc. B00000000-01717-5707- associated with elevation gradients at the site. Other sec- 00066 REV00, October 2, 1997, U.S. Department of Energy, ondary patterns of plant distribution are associated with Yucca Mountain Site Characterization Office, North Las adaptation to unique substrates such as playas, steep rocky Vegas, Nevada. slopes, and novel substrates comprised of limestone, basalt, Lunt, O. R.; Letey, J.; Clark, S. B. 1973. Oxygen requirements for root growth in three species of desert shrubs. Ecology. 54( 6): tuff, and alluvium. Changes in temporal species patterns on 1356-1362. the NTS have been correlated with changing climate during Ostler, W. Kent; Hansen, D. J.; Hall, D. J. 1999. The classification the past 45 thousand years. Position of species along the of ahrublands on the Nevada Test Site. In: McArthur, E. Durant; elevation gradient on the NTS under current climatic condi- Ostler, W. Kent; Wambolt, Carl L. comps. 1999. Proceedings: Shrubland Ecotones. 1998 August 12-14, Ephraim, UT. Pro- tions creates a Transition Zone characterized by a diverse ceedings RMRS-P-000. Ogden, UT: U.S. Department of Agricul- mixture of species. This assemblage of species is not recog- ture, Forest Service, Rocky Mountain Research Station. nized as a regional vegetation type, but appears to be shaped Peterson, F. F. 1981. Landforms of the Basin & Range Province, by climatic extremes present in both the Mojave Desert and defined for soil survey. Technical Bulletin 28. Reno: University Great Basin Desert. The width of this zone is dependent on of Nevada, Nevada Agricultural Experiment Station, Max C. Fleischmann College of Agriculture. 52 pp. the steepness of the elevation gradient, slope aspect, and Pritchertt, D.; Knight, T.; Smith, F. 1997. An inventory for rare, moisture retention characteristics of the substrate. Indi- threatened, endangered, and endemic plants and unique com- vidual species appear to be independently distributed across munities on Nellis Air Force Bombing and Gunnery Range, the NTS within both deserts and the Transition Zone. This Clark, Lincoln, and Nye Counties, Nevada. The Nature Conser- vancy, U.S. Department of Defense, Legacy Resource Manage- distribution is based on species growth requirements, al- ment Program, Nellis Air Force Base, Nevada. though assemblages of species that have similar biological Spaulding, W. G. 1985. Vegetation and climates of the last 45,000 and physiological needs are found together consistently years in the vicinity of the Nevada Test Site, South-Central enough to be considered as distinct plant communities (i.e., Nevada. U.S. Geological Survey Professional Paper 1329. U.S. alliances and associations). A better knowledge of the veg- Department of the Interior in cooperation with the U.S. Depart- ment of Energy. 83 p. etation and the environmental conditions within the Mojave Wallace, A.; Romney, E. M. 1972. Radioecology and ecophysiology Desert and Great Basin Desert helps us better appreciate of desert plants at the Nevada Test Site. TID-25954. United the transition between these deserts with its varying tempo- States Atomic Energy Commission, Office of Information ral and spatial characteristics. Services, Library of Congress Catalog Card Number: 72-600110.

158 USDA Forest Service Proceedings RMRS-P-11. 1999