Appendix MOJ. The Mojave Desert Region

Contributing Authors: Kathryn Thomas, David Stoms, and Frank Davis

Regional Character
Land Stewardship
Plant Community Types

The Mojave Desert Region is located in the eastern side of California north of the Sonoran Desert Region (Figure MOJ-1). The region is roughly the shape of a diamond. Mountain ranges form the southwest and northwest borders (on the southwest border the Little San Bernardino Mountains, the San Bernardino Mountains, the San Gabriel Mountains; on the northwest border the Tehachapi Mountains, the southern Sierra Nevadas, and the base of the Inyo Mountains). The California-Nevada state line forms the northeast border. The southeast border is formed partially by the Colorado River and a somewhat vaguely determined boundary based on elevational and floristic differences between the Mojave and Sonoran deserts.

Figure MOJ-1. Shaded relief image of the Mojave Desert Region. Heavy white lines delineate the subregions used in the vegetation analysis. Bold letters indicate sites for consideration as conservation priorities.

Thomas (1996) undertook an analysis of the floristic variation in community types within the California portion of the Mojave Desert to determine how well they could serve as a coarse-filter for representing plant species in conservation strategies. Using a Jaccard's similarity coefficient to measure the homogeneity of the CNDDB communities based on approximately 1150 species in an existing database (Lum 1975), Thomas (1996) distinguished two subregions of the Mojave (western and easternsee Figure MOJ-1) in order to describe systematic geographic variation in floristic composition in some widespread vegetation types. erefore, separate gap analyses were conducted in the two floristic divisions. Therefore, separate gap analyses were conducted in the two floristic divisions.

The Mojave region is characterized by basin and range topography as illustrated in Figure MOJ-1. The basins often contain dry lakes or playas. The lowest point in the Mojave and the United States is -86 meters in the Death Valley basin. Nearby is the highest point in the Mojave, Telescope Peak, at 3368 meters. Numerous other ranges exist; the highest being the New York Mountains (2296 m), Kingston Mountains (2232 m), Clark Mountains (2417 m) and Providence Mountains (2186 m).

Geologically the Mojave consists of a variety of substrates and geomorphic features. Faults are common, notable ones being the Garlock Fault and the San Andreas Fault near the southern boundary of the region. Historic lake beds and volcanoes have left their imprint on the region in the form of unique landforms and substrate material. A typical geomorphic sequence that can be observed is the hill or mountain upland eroding onto bajada or piedmont which slopes down to a dry lake. Soil formation is often minimal compared to regions with higher vegetation cover and more rain.

The Mojave climate dominates the rate and direction of many physical and biotic processes in the desert. Diurnal temperature differences may be extreme (up to 25 °C ; Rowlands et al. 1982). Heat in the summer is an overriding factor (47°C mean July maximum at Death Valley; Rowlands et al. 1982). Winter may bring snow or frost. Rainfall is sparse and highly variable on a seasonal and annual basis (mean annual of 41 to 136 mm/yr depending upon the weather station; Rowlands et al. 1982). Windstorms contribute to erosional factors and increase the desiccation rates to which plants and animals must adapt.

Land Stewardship

Over three quarters of the Mojave is in federal jurisdiction (77%). The three main federal land administrators are the BLM (34%), National Park Service (28%) and Department of Defense (14%). The 4 large DoD basesEdwards Air Force Base, China Lake Naval Weapons Center, Fort Irwin, and Twentynine Palms Marine Corps Basewere categorized as status level 3 because much of their lands are unused. The USFS administers 0.3% of the land, primarily along the western edges of the region. The California Desert Protection Act of 1994 (CDPA) changed the administrative composition of federal land (14.2% less BLM land and 14.1% more NPS land) and added a small amount of state land (plus 0.1%). The California Department of State Lands administers 0.2% of the land area, CDF&G 0.1%, and other state lands comprise 2.0%. Private land, comprising 21% of the Mojave, are mostly located in the western portion in Antelope Valley and along the southwestern border, including Morongo and Yucca Valleys. Urbanization has exploded in these areas, with the communities serving in a sense as extensions of the greater Los Angeles economic center. Private and state lands occur in a checkerboard pattern embedded in a matrix of federal properties, a pattern established in the 19th century as a result of federal policy of land allocation during the homesteading and railroad development period. The checkerboard pattern of land management has resulted in a situation where the management levels occur in fragmented matrices; this is particularly evident across the central Mojave along the Interstate 40 corridor (Figure MOJ-2).

Figure MOJ-2. Management status of lands in the Mojave Desert Region. See text for definitions of management levels.

As reported for the Sonoran Desert region in Appendix SON, the wilderness designations and expansions of National Parks in the California deserts legislated in the CDPA were incorporated into the final stewardship for CA-GAP. The data were primarily obtained from a preliminary digital version of the 1991 version of the bill, but excluding areas that were omitted in the final version of the bill. Some boundaries may have been adjusted by Congress between these two versions, and thus there may be small errors in the reported area by management levels and the management status of plant community types and vertebrate species.

Table MOJ-1. Area and percentage of land surface by management status level of the Mojave Desert Region of California.
(The table compares management levels before and after the passage of the California Desert Protection Act of 1994)

Pre-bill Status Current Status

Status Area (km²) % Area (km²) %

1 10,414 14.0 26,851 36.3

2 1,016 1.4 1,747 2.4

3 46,219 62.5 29,149 39.4

4 16,340 22.1 16,242 21.9

Total 73,989 100.0 73,989 100.0

The CDPA increased the proportion of status 1 lands in the Mojave region by approximately 150%, from 14 to 36% (Table MOJ-1, Figure MOJ-2). Fifty-seven status 1 managed areas were mapped for the region, including those established by the CDPA. Of these, BLM manages 41 wilderness areas. There are also 5 USFS wilderness areas, 3 national park units, 3 TNC preserves, 2 CDF&G ecological reserves, 1 state reserve, and 2 UC natural reserves. The vast majority of status 1 land area is managed currently by the NPS, with over 20,000 km², followed by BLM with over 6,000 km², mostly in wilderness areas. Other status 1 areas total less than 100 km² per agency.

The management profiles of the two floristic subregions are quite different (Table MOJ-2). The majority of the status 1 managed area is in the eastern subregion, with very little status 4 land. The western Mojave, on the other hand, has a more modest amount of status 1 and 2 land with nearly half in status 3 and a third in status 4. The western portion is where the military bases and most private ownership occurs in the Mojave Desert.

Table MOJ-2. Area and percentage of land surface by management status level of the two floristic subregions of the Mojave Desert Region of California.

West Mojave East Mojave

Status Area (km²) % Area (km²) %

1 5,074 13.4 21,777 60.5

2 1,594 4.2 153 0.4

3 18,370 48.4 10,763 29.9

4 12,911 34.0 3,329 9.2

Total 37,950 100.0 36,021 100.0

There are 42 status 2 managed areas within the Mojave Region. The majority (27) are BLM Areas of Critical Environmental Concern or wilderness planning areas. There is one national wildlife refuge (Havasu), 7 state wildlife areas, and 2 state parks.

Of the 99 status 1 and 2 managed areas, 35 are larger than 10,000 ha in size (ignoring adjacencies among areas). Mean size of status 1 areas is 47,100 ha while status 2 is 4,160 ha. The largest are the NPS units, while most of the remainder are newly designated BLM wilderness areas. At the small end of the scale, 26 areas are less than 1,000 ha, although some of these are small portions of large managed areas from adjoining regions.

Elevation Bias in Mojave Region

Figure MOJ-3. Comparison of the proportion of managed areas with all lands in the Mojave Desert Region by elevation zones.

As with most other regions in the state, management is not uniform across elevation zones (Figure MOJ-3). The proportion of status 1 and 2 lands increases steadily with elevation, with a peak in the 501-1000 m zone. On the other hand, 70% of the lands in the region are in the 1-500 m zone where only 16% of protected lands occur.

Plant Community Types

The Mojave Region land-cover database was developed using existing maps as baseline source data, including the East Mojave Resource Inventory from Southern California Edison, the BLM West Mojave map (Clark, personal communication), CALVEG (Parker and Matyas 1981), Edwards Air Force Base, Twentynine Palms Marine Corps Base, Joshua Tree National Monument (Leary 1977), and a BLM/USGS map derived from MSS imagery. Maps were updated and refined using Thematic Mapper satellite imagery, a current 1:150,000 road atlas (to identify areas of residential or industrial development), and extensive reconnaissance level field survey (see Thomas 1996 for details). Seven expert reviewers made comments on a draft version, and the map was revised accordingly. The revisions made by the Bureau of Land Management for their Northern and Eastern Colorado Desert planning area (Dorweiler 1997) included a small part of the southern Mojave Desert region. The revisions were incorporated into the final CA-GAP land-cover as described above for the Sonoran Desert region. Because these existing sources could only reliably determine community types, information on dominant species was generally not recorded for map units in this region. While logistics and resources prevented an extensive, quantitative accuracy assessment, an evaluation was made in the eastern Mojave region using a set of 462 transects collected for BLM in 1975. Overall accuracy of the map based on these plots was 84%, with class accuracies ranging from 65-100% (Thomas 1996). A confidence rating was applied to each map unit and summarized for each cover type. Cover types with the most questionable reliability are Mojave Mixed Woody Scrub, Mojave Mixed Steppe, Mojave Mixed Woody and Succulent Scrub, Blackbush Scrub, Shadscale Scrub, Desert Native Grassland, Transmontane Freshwater Marsh, Foothill Pine-Oak Woodland, and Bristlecone Pine Forest. Cover types of questionable reliability occur mainly on lands administered by China Lake Naval Weapons Center and Death Valley National Park and to some extent Fort Irwin Military Reservation, Mojave National Preserve, and Joshua Tree National Park.

The Mojave land-cover database contains distribution information on 33 natural vegetation communities and 8 land use or non-vegetated types. Three new community types were described for gap analysisBlack Sagebrush Scrub (35213), Desert Holly Scrub (36150), and Desert Native Grassland (42160). Three vegetation types contribute to 75% of the land cover in the Mojave region. The most prominent vegetation community is Mojave Creosote Bush Scrub which contributes 57%. Mojave Mixed Woody Scrub contributes 13% and Desert Saltbush Scrub contributes 5%.

Not all cover types were evaluated for protection status. Cover types eliminated were those: 1) with less than 25 km² total area, 2) cultural and barren in nature, 3) characterized by non-native or disturbance following species, and 4) widespread outside the Mojave and not characteristic of the desert. The size constraint was imposed because the minimum mapping unit employed in gap analysis is not sensitive to highly localized cover types or extensive types that may occur in small patches. Also because of differences in cover type definition between the source data, localized cover types may not be representatively mapped across all source data.

Fifteen (unshaded rows of Table MOJ-3) of the 33 original vegetated land-cover types were eliminated from further evaluation. These include 9 cover types with less than 25 km² distribution: Black Sagebrush Scrub, Bristlecone Pine Forest, Foothill Pine-Oak Woodland, Desert Greasewood Scrub, Modoc-Great Basin Willow Riparian Forest, Mojave Desert Wash Scrub, Transmontane Alkali Marsh, Transmontane Freshwater Marsh, and Wildflower Field. Two cover types characterized by invasive exotic species, Non-native Grassland and Tamarisk Scrub, were eliminated as was Rabbitbrush Scrub, a disturbance maintained cover type (Holland 1986). Three cover types that are extensive outside of the Mojave region were eliminated, those being Interior Live Oak Chaparral, Chamise Chaparral and Sonoran Creosote Bush Scrub. The chaparral areal occurrence in the Mojave is relatively small (114 km² and 57 km² respectively) and may be an artifact of boundary placement between the Mojave and Southwest regions. Likewise, Sonoran Creosote Bush Scrub with 779 km² is more extensive in the Sonoran region and may occur in the Mojave due to imprecise nature of the southeast boundary of the Mojave. Despite the fact that 15 plant community types were eliminated from further evaluation, the remaining 18 cover types contribute 92% of the Mojave area.

Table MOJ-3. Percent area of each natural plant community type at each management status level in the Mojave Desert Region. * indicates addition to the standard CNDDB classification.

CNDDB Code CNDDB Community Name (Holland 1986) CNDDB Rank Status 1 % Status 2 % Status 3 % Status 4 % Total Mapped Distribution (km²) Status 1+2 %

22000 Desert Dunes-East S2.2/3.2 88.2 0.2 8.1 3.6 675.9 88.4

22000 Desert Dunes-West S2.2/3.2 46.0 0.0 43.1 10.8 199.5 46.0

33100 Sonoran Creosote Bush Scrub-Mojave S4 88.6 0.0 4.3 7.0 778.6 88.6

34100 Mojave Creosote Bush Scrub-East S4 49.4 0.6 35.5 14.5 15,202.3 50.0

34100 Mojave Creosote Bush Scrub-West S4 16.6 0.6 54.2 25.1 27,269.1 17.2

34210 Mojave Mixed Woody Scrub-East S3.2 71.2 0.7 23.2 4.9 4,472.9 71.9

34210 Mojave Mixed Woody Scrub-West S3.2 49.6 3.8 29.0 17.6 4,969.8 53.4

34220 Mojave Mixed Steppe-East S2.2 74.0 0.0 1.6 24.4 527.2 74.0

34220 Mojave Mixed Steppe-West S2.2 96.6 0.0 0.7 2.7 116.5 96.6

34240 Mojave Mixed Woody and Succulent Scrub-Mojave (only occurs in East) S3.2 68.3 0.0 22.3 9.4 521.7 68.3

34300 Blackbush Scrub-East S3.2 56.3 0.9 38,8 4.0 385.1 57.2

34300 Blackbush Scrub-West S3.2 70.5 1.0 20.0 8.5 963.2 71.5

35210 Big Sagebrush Scrub-East S4 91.2 0.0 1.4 7.4 353.1 91.2

35210 Big Sagebrush Scrub-West S4 5.7 16.4 58.8 19.1 4.3 22.1

35213 Black Sagebrush Scrub * -- 96.7 0.0 3.3 0.0 18.2 96.7

35400 Rabbitbrush Scrub S5 0.0 0.0 0.1 99.9 31.9 0.0

36110 Desert Saltbush Scrub-East S3.2 38.2 0.2 47.2 14.5 1,130.3 38.4

36110 Desert Saltbush Scrub-West S3.2 5.3 1.6 37.4 55.6 2,780.8 6.9

36120 Desert Sink Scrub-East S3.1 64.9 0.0 27.8 7.3 132.0 64.9

36120 Desert Sink Scrub-West S3.1 1.4 4.4 74.9 19.4 158.2 5.8

36130 Desert Greasewood Scrub S3.2 0.0 0.0 0.1 99.9 1.7 0.0

36140 Shadscale Scrub-East S3.2 93.5 0.0 6.2 0.4 1,762.1 93.5

36140 Shadscale Scrub-West S3.2 43.4 11.2 34.3 11.1 677.1 54.6

36150 Desert Holly Scrub-East * -- 45.9 0.0 51.5 2.6 303.9 45.9

36150 Desert Holly Scrub-West * -- 71.0 1.5 25.5 2.0 1,144.1 72.5

37200 Chamise Chaparral S4 0.0 0.0 35.4 64.6 57.0 0.0

37400 Semi-Desert Chaparral-East S3.2 0.0 0.0 64.5 35.5 0.9 0.0

37400 Semi-Desert Chaparral-West S3.2 8.3 0.1 20.0 71.7 450.6 8.4

37A00 Interior Live Oak Chaparral S3.3 0.0 0.0 51.8 48.2 113.7 0.0

42160 Desert Native Grassland-East * -- 0.0 0.0 92.0 8.0 208.2 0.0

42160 Desert Native Grassland-West * -- 0.0 1.7 41.0 57.3 92.1 1.7

42200 Non-Native Grassland S4 4.1 3.6 0.8 91.5 278.0 7.7

42300 Wildflower Field S2.2 0.0 0.0 31.5 68.5 7.0 0.0

46000 Alkali Playa-East S3.2 59.9 0.1 35.5 4.6 398.2 60.0

46000 Alkali Playa-West S3.2 1.4 4.4 75.0 19.2 889.2 5.8

52320 Transmontane Alkali Marsh S2.1 0.0 43.0 0.0 57.0 2.5 43.0

52420 Transmontane Freshwater Marsh S2.2 100.0 0.0 0.0 0.0 3.0 100.0

61610 Modoc-Great Basin Cottonwood-Willow Riparian Forest S2.1 52.2 12.4 7.0 28.4 2.0 64.6

61700 Mojave Riparian Forest-East S1.1 9.4 3.0 56.8 30.8 27.5 12.4

61700 Mojave Riparian Forest-West S1.1 0.0 18.5 5.0 76.5 31.3 18.5

61820 Mesquite Bosque-East S2.1 72.4 0.0 18.4 9.2 210.7 72.4

61820 Mesquite Bosque-West S2.1 0.0 43.9 2.6 53.5 18.3 43.9

62200 Desert Dry Wash Woodland-East S3.2 5.6 1.4 67.0 26.1 205.2 7.0

62200 Desert Dry Wash Woodland-West S3.2 83.4 0.0 5.3 11.2 94.1 83.4

63700 Mojave Desert Wash Scrub S3.2 0.0 0.0 44.6 55.4 2.0 0.0

63810 Tamarisk Scrub S4 4.6 6.3 39.2 50.0 52.1 10.9

71410 Foothill Pine-Oak Woodland S4 0.0 0.0 1.7 98.3 7.7 0.0

72200 Mojavean Pinyon and Juniper Woodlands-East S3.2/4 67.7 0.0 29.8 2.5 911.1 67.7

72200 Mojavean Pinyon and Juniper Woodlands-West S3.2/4 33.0 2.4 21.2 43.3 901.9 35.4

86400 Bristlecone Pine Forest S2.3 100.0 0.0 0.0 0.0 3.8 100.0

Region Total - Natural Communities in Mojave

69,530 (94.0%)

Region Total - Natural Communities in East Subregion

35,203 (97.7%)

Region Total - Natural Communities in West Subregion

34,315 (90.4%)

Region Total - All Lands in Mojave
36.3 2.4 39.4 22.0 73,981 38.7

Region Total - All Lands in East Subregion
60.5 0.4 29.9 9.2 36,021 60.9

Region Total - All Lands in West Subregion
13.4 4.2 48.4 34.0 37,950 17.6

Due to the floristic dissimilarity between the eastern and western subregions, the 18 remaining cover types were subdivided by the two floristic regions into two subtypes each, an eastern and western subtype. One of the cover types only occurred in the eastern floristic region ( Mojave Mixed Woody and Succulent Scrub). This gives a total of 35 natural vegetation subtypes that were given conservation evaluation (shaded rows in Table MOJ-3). Following is analysis of the distribution and conservation status of each cover type:

Desert Dunes (22000) can be found in association with Alkali Playas or as discrete landform features. The dune associated vegetation may occur in mosaics with Mojave Creosote Bush Scrub and Desert Saltbush Scrub. Desert Dunes also are well represented in status 1/2 management (79% in the region, 88% in the East and 46% in the West) and is almost entirely in public ownership (95%).

Mojave Creosote Bush Scrub (34100) is the most extensive cover type in the Mojave Desert region, covering 57% of the land surface. Over most of its mapped distribution (81%) it is the only vegetation type in a map unit but it can occur in mosaics with urban and agricultural cover types (5% of occurrence). It's combined status 1/2 management (Table 7-2) is lower than the current regional level (31% for the type compared to 39% for the region). When regionalized, Mojave Creosote Bush Scrub in the western floristic subregion has only 17% status level 1 and 2 protection, while 50% of the type in the eastern subregion was protected. While the total protected acreage is large, the pattern of management is highly fragmented between management status 1 and 4 or status 3 and 4 due to the checkerboard pattern of land ownership.

Mojave Mixed Woody Scrub (34210) covers 13% of the Mojave. It is found in mosaics with any of the upland scrub or woodland cover types, except the halophytic saltbushes. Over 62% of its area is managed at status 1 or 2, regionwide. In the western subregion it has 53% status 1 and 2 protection (Table MOJ-2), much of which occurs in Joshua Tree National Park. In the eastern subregion, the percentage of protection is 72%. Mapping for this cover type is of low reliability (Thomas 1996).

Mojave Mixed Steppe (34220), Mojave Mixed Woody and Succulent Scrub (34240), Desert Holly Scrub (36150) and Blackbush Scrub (34300) are similar in that they each contribute 1-2% to the total Mojave cover and are well represented in status 1 or 2 management (67 to 78% regionally, 46 to 97% in subregions). Of this group, mapping is considered reliable only for Desert Holly Scrub (Thomas 1996).

Big Sagebrush Scrub (35210) occurs mostly in the northern Mojave, with some patches in the central and western Mojave. Although it is well represented in status 1 and 2 management (90%), its protection is fragmented in the central Mojave. A small amount of the cover type (344 ha) occurs in the western floristic subregion. This type is also widespread throughout the Great Basin.

Desert Saltbush Scrub (36110) often intergrades at lower elevations with Alkali Playa and Desert Sink Scrub, and at higher elevations it is often found in mosaics with Mojave Creosote Bush Scrub, Desert Native Grassland or urban/agricultural cover. Sixteen percent of the cover type is in status 1 or 2 management regionwide. In the western floristic subregion, this drops to 7%, and that occurs in highly fragmented patches with both status 3 and 4 managed lands. It was observed that a high proportion of associated species in Desert Saltbush Scrub - West Region are invasive exotics (Thomas 1996).

Desert Sink Scrub (36120), found at the upper edges of Alkali Playa Vegetation, has 33% status 1/2 representation, although this drops to 6% in the western floristic subregion. Both Alkali Playa and Desert Sink Scrub occur in discrete patches due to their association with the actual dry lake basins.

Shadscale Scrub (36140) covers 3% of the Mojave and occurs mainly in the northern floristic region. It can be found intergrading with Mojave Creosote Bush Scrub as well as Mojave Mixed Woody Scrub, Blackbush Scrub, and Mojave Mixed Woody Steppe. A high proportion is in status 1/2 management both for the entire region (83%) and for the west and east floristic subregions (55 and 94% respectively). Mapping reliability for this cover type is considered low (Thomas 1996).

Semi-Desert Chaparral (37400) is found along the south-western borders of the Mojave. It has low representation in status 1/2 (8%) and is mainly under private ownership (72%). It is often found intergrading with Mojavean Pinyon and Juniper Woodlands and Mojave Mixed Woody Scrub.

Desert Native Grassland (42160) occurs in discrete patches in the Mojave (<1% of the total land area), has very low representation in status 1 or 2 managed areas (0.5%), but does have high representation on status 3 lands (76%). It can be found in mosaics with Mojave Creosote Bush Scrub and Desert Saltbush Scrub. In the western floristic subregion, it has low acreage in total protection, around 150 ha. In the eastern floristic subregion, the cover type is entirely in status 3 or 4 management.

Alkali Playa Vegetation (46000) occurs at the edges of closed basins throughout the desert at lower elevations. Approximately 60 playas or playa complexes are mapped on the Mojave vegetation coverage. Over the entire region Alkali Playa has 23% distribution in status 1/2 management but only 6% in the western floristic subregion.

Mojave Riparian Forest (61700) is found along the Mojave River with varying density from the Mojave River Forks to downstream of Afton Canyon. It is also found in small patches along Little Rock Wash and Big Rock Wash and along the Amargosa River. It's total coverage is small (5,880 ha, 0.08% of the land area) and 16% is in status 1/2 management. Field observations of Mojave Riparian Forest revealed that tamarisk, an invasive exotic, has often heavily invaded and degraded its quality (Thomas 1996).

Mesquite Bosque (61820), a streamside thorn forest often found in association with Alkali Playas or Desert Dunes, has an overall status 1/2 representation of 70%. Status 1/2 representation in the western floristic subregion is 44% but the total acreage in protection is only slightly more than 800 ha (all in status 2).

Desert Dry Wash Woodland (62200) was mapped by BLM (Dorweiler 1997) over a small area in the southern portion of the region. The type is well-represented in status 1/2 managed areas (31% in the whole region) but this is unevenly distributed between subregions (83% status 1/2 in the western subregion, only 7% in the east). This type is more widespread in the Sonoran Desert region.

Mojavean Pinyon and Juniper Woodlands (72200) cover 2% of the Mojave. It occurs along the western and southwestern borders of the Mojave and in discrete patches in the interior. In the western floristic region it occurs in mosaics with Semi-Desert Chaparral or Non-native Grassland. In the interior of the region, the cover type can be found in mosaics with Mojave Mixed Woody Scrub or Blackbush Scrub. For the entire Mojave it has 52% status 1/2 management. It has 35% status 1/2 management in the western floristic region and 68% in the east.

Ten land-cover types were identified as most vulnerable in the Mojave Desert region from the evaluation: Desert Native Grassland (both east and west), Mojave Riparian Forest (both east and west), Desert Saltbush Scrub - West, Semi-Desert Chaparral - West, Alkali Playa - West, Desert Sink Scrub - West, Mojave Creosote Bush Scrub - West, and Mesquite Bosque - West.

Of the 10 cover types identified as vulnerable in this analysis, five have been rated as very threatened by the Natural Heritage Division (NHD) of California Department of Fish and Game (Alkali Playa, Desert Sink Scrub, Mesquite Bosque, Mojave Riparian Forest), two as threatened (Desert Saltbush Scrub, Semi-Desert Chaparral), one as not threatened (Mojave Creosote Bush Scrub) and two with no rating (Desert Native Grassland, both subregions). These types were selected as vulnerable based on GAP criteria which are largely separate from those of the NHD. The NHD identified two additional cover types as very threatened; however, both these cover types were not evaluated in this gap analysis because they were mapped on less than 25 km². Gap analysis has revealed Mojave Creosote Bush Scrub in the western region to be under-represented, while it is rated as not threatened in the NHD ratings.

A special word should be stated about Joshua Tree Woodland (73000). This type was not mapped as a specific plant community type in the GAP land-cover database. The presence of Joshua Tree (Yucca brevifolia) was recorded as a dominant or special interest species where possible. Frequently, however, the density of Y. brevifolia is so low (or unknown) that the community must be classified as a scrub type. From the information in the GAP database, Joshua Tree occurs in approximately 15% of the Mojave, and it appears to be well represented in protected areas. The Natural Heritage Division rates Joshua Tree Woodland as very threatened. Due to the high uncertainty regarding Joshua Tree Woodland, we are unable to evaluate its current management status reliably at this time.

We have not yet applied formal siting models to identify priority areas in the Mojave Region. Based on the gap analysis of plant community types, Thomas (1996) identified 7 areas with high potential for improving representation of under-represented types (Figure MOJ-1). Areas in the Mojave were selected that support vulnerable cover type(s) that have one or more of the following characteristics: 1) a high (70% or more) coverage of vulnerable cover types in map units occurring in the area, or with vulnerable cover types occurring in adjacent map units, and 2) with open space or unknown zoning, if on private land, or 3) some indication that management changes could be facilitated if on federal land. Zoning designation for Los Angeles and San Bernardino counties was provided by the Southern California Association of Governments (SCAG) from their general plan (Crowe 1996). The zoning categories in the SCAG general plans were aggregated into four zoning categories: open space, urban developed, agriculture, and unknown. These 7 areas are only suggested as areas for more detailed consideration in region wide conservation planning in the Mojave.

The West Antelope Valley site (Area A, Fig. 7-1) occurs at the base of Tehachapi Mountains in parts of Winters Ridge, Liebre Twins and Willow Springs 7.5' topographic quads. Semi-Desert Chaparral and Desert Native Grassland occur in this area. Land ownership is predominantly private; zoning is unknown.

Another area supporting Semi-Desert Chaparral is in a strip of land along the base of the San Gabriel Mountains (Area B). This strip occurs east of Highway 14, south of Hwy. 138 and west of I15 and is contained in parts of Lancaster East, Pacifico Mountain, Hi Vista, Valyermo, and Phelan 7.5' quads. Mojave Riparian Forest that occurs around Lake Palmdale and Little Rock Wash occur also within the strip. Mojave Riparian Forest occurring in Big Rock Wash is found downslope of the strip in Hi Vista quad. Much of the land is privately owned, zoned for open space. Along the southern border of the strip, some National Forest lands occur.

The area including and surrounding the Rosamond, Buckthorn and Rogers Playa complex (Area C) supports Mojave Creosote Bush Scrub - West Region, Desert Saltbush Scrub - West Region, Desert Sink Scrub - West Region as well as Alkali Playa. This area is contained within the Bissell and Rogers Lake North topographic quads. It is predominantly administered by Edwards Air Force base under status 3 management.

The Koehn Lake area (Area D), centered around a playa north of the Rosamond Playa complex contains the same vulnerable cover types. Land ownership in the area includes status 1 managed lands to the east, status 3 managed lands in and immediately adjacent to the playa, and status 4 lands to the west. Koehn Lake is found in the Garlock quad.

A small, apparently unnamed, playa (Area E) west of Hwy 395 in the Boron NE quad is surrounded by Desert Saltbush Scrub. The land management in this area is fragmented with BLM status 1 and 3 management in a checkerboard pattern with private (status 4) lands.

Two other candidate areas occur around Harper Lake and the Superior Lake complex (Areas F and G), both Alkali Playas. Both support Desert Sink Scrub - West Region and Desert Saltbush Scrub - West Region, as well as Alkali Playa. North, and adjacent to the Harper Lake playa is Desert Native Grassland. Desert Native Grassland is also mapped to the east of Superior playa complex on the Fort Irwin military reservation. Status 1 BLM land in a checkerboard pattern with private land occurs between the two playas. Status 3 BLM land fragmented with private land occurs around each playa. Fort Irwin status 3 land occurs north of the Superior playa complex.

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