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Appendix SW. The Southwestern California Region


Contributing Authors: Frank Davis, Peter Stine, David Stoms, and Mark Borchert

Regional Character
Land Stewardship
Plant Community Types

Regional Character

The region includes 33,832 km² or roughly 8 percent of the area of California and is comprised of three subregions (not including the Channel Islands): South Coast, Transverse Ranges, and Peninsular Ranges (Figure SW-1). The Peninsular Ranges subregion includes one district, the San Jacinto Mountains. The Transverse Ranges subregion is subdivided into the San Bernardino Mountains, the San Gabriel Mountains, and the Western Transverse Ranges districts. The region is bounded by the transition to the Sonoran and Mojave Desert regions on the east and the Santa Ynez Mountains on the north. The boundary at the southern end of the region is defined as the Mexican border, although vegetation similar to that found in southwest San Diego County extends south into Baja California for roughly 300 km, where there is an abrupt transition to a more arid adapted flora (Westman 1981).


Figure SW-1. Shaded relief image of the Southwestern California Region.

Based on 1990 census data, 16,539,858 people (56% of California's total population) reside in the region. This region has experienced extraordinarily rapid population growth in recent decades. From 1980 to 1990, the population of San Bernardino and Riverside Counties grew at a rate of more than 50%, San Diego County grew at a rate of 30-40%, Orange and Ventura Counties expanded by 20-30%, and Santa Barbara and Los Angeles Counties grew 5-20% (Goodenough 1992). It is this rapid urbanization, particularly in the low-lying coastal regions, that is causing greatest loss of habitat in this region.

Land Stewardship

Figure SW-2 shows the management status of lands in the Southwestern California Region. Sixty percent is privately owned, whereas approximately 50% is privately owned statewide. The 40% of the region in public ownership is managed by the USFS (29.1%), BLM (3.1%), DoD (2.4%), Indian reservations (2.3%), USFWS (0.1%), NPS (0.2%), state parks (1.9%), CDF&G (0.2%), other state lands (0.2%), local governments (0.7%), and TNC and Audubon (0.1% each).

Southwestern Region Managed Areas

Figure SW-2. Management status of lands in the Southwestern California Region. See text for definitions of management levels.

Ten percent of the region was mapped as status 1 or 2 managed areas (Table SW-1). (Note: this slight increase from 9.8% reported previously [Beardsley and Stoms 1993, Davis et al. 1995] was caused be minor recent revisions in the stewardship coverage, primarily 1) the designation by the California Desert Protection Act of 1994 of portions of 3 new wilderness areas managed by BLM along the eastern edge of the region, and 2) the reclassification from three levels to the standard four levels for GAP). The area of status 1 and 2 managed areas is dominated by USFS Wilderness Areas. State park units, including reserves and wilderness areas, are the second largest category. In addition, BLM administers several ACECs and wilderness areas.

Table SW-1. Area and percentage of land surface by management status level of the Southwestern California Region.

Status Area (km²) %
1 2,707 8.0
2 670 2.0
3 9,217 27.2
4 21,239 62.8
Total 33,833 100.0

Lands below 500 m elevation account for nearly half of the region, yet the proportion that is managed for biodiversity is exceptionally small (Figure SW-3). Lower elevations are predominately private land and intensively converted to urban and agricultural use. In contrast, lands above 1000 m have a disproportionate share of the biodiversity management areas. Mid-elevations, between 1500 and 2500 meters are primarily public lands, with about 25 percent being status 1 or 2 management, but most being classified as status 3. More than 90 percent of the highest elevation zone is in status 1 management (usually National Forest wilderness areas).

Elevation Bias in SW Region

Figure SW-3. Comparison of the proportion of managed areas with all lands in the Southwestern California Region by elevation zones.

Plant Community Types

Ancillary information, especially air photos and VTM maps, was used to capture additional compositional changes in vegetation that were not visually obvious in the TM imagery. VTM maps were used to position landscape boundaries on vegetation gradients where no obvious break was visible on either the satellite imagery or in air photos. Two hundred-thirty polygons (excluding urban and agricultural areas) were checked in the field, primarily by roadside reconnaissance. There have been minor revisions in the species and community types data since the version reported in Davis et al. (1995) and so there will be some differences in mapped extent and management status results here from those reported previously.

We compared the regional vegetation data to large scale vegetation maps that had been extensively field checked and were not used in preparing the CA-GAP map. For instance, we compared our Coastal Sage Scrub type to a map prepared with a 1 ha MMU by Regional Environmental Consultants (RECON) for coastal San Diego County (Stine et al. 1996). 99% of coastal scrub in patches larger than 100 ha was represented in both maps. We have also compared our map to very detailed vegetation maps (MMU < .25 ha) prepared for southwestern San Diego County as part of the Multi-Species Conservation Planning (MSCP) program. A comparison of 138 random points on the two maps shows 87% agreement (i. e. either Primary or Secondary designation of the Gap map is in accord with the MSCP designation) and only 5% are larger polygons (i. e. > 10 ha) that disagree. Another comparison with the MSCP map also showed relatively high overall agreement, with most disagreement being the result of generalization rather than error (Stoms 1996). Other sources of discrepancy arose from minor differences in interpretation. In summary, the vegetation database has inaccuracies but is generally in high agreement with other, recent vegetation maps.

The land cover database was delineated into 2,014 landscape units, averaging 1,678 ha in size. The average size of vegetated, undeveloped landscapes is 1,238 ha. Sixty-one plant community types were mapped, out of 89 described by the CNDDB (Holland 1986). Two more types were added for CA-GAP, Cercocarpus ledifolius Woodland and Southern Alluvial Fan Scrub (Magney 1992), making a total of 63 in the database. Distributional information is provided on 123 dominant canopy species, and 12 land use/land cover types without native vegetation.

Table SW-2. Percent area of each CNDDB community type at each management status level in the Southwestern California Region. * indicates an addition to the standard CNDDB classification (Holland 1986).

CNDDB Code CNDDB Community Name CNDDB Rank Status 1 % Status 2 % Status 3 % Status 4 % Total Mapped Distribution (km²) Status 1+2 %
31200 Southern Coastal Bluff Scrub S1.1 0.0 13.9 0.5 85.6 22.6 13.9
32300 Venturan Coastal Sage Scrub S3.1 2.3 4.1 9.3 84.2 1,470.8 6.4
32500 Diegan Coastal Sage Scrub S3.1 4.0 1.8 27.6 66.6 1,316.9 5.8
32700 Riversidian Sage Scrub S1.1/3.1 3.7 3.6 19.5 73.2 744.3 7.3
34100 Mojave Creosote Bush Scrub S4 17.5 4.8 48.2 29.4 88.2 22.3
35100 Great Basin Mixed Scrub S4 28.5 0.0 21.7 49.8 34.4 28.5
35210 Big Sagebrush Scrub S4 6.1 2.2 50.2 41.5 335.5 8.3
35500 Cercocarpus ledifolius woodland * NR 92.1 0.0 0.2 7.8 2.1 92.1
37110 Northern Mixed Chaparral S4 5.3 1.4 47.8 45.4 1,173.7 6.7
37120 Southern Mixed Chaparral S3.2/3.3 2.1 1.7 18.8 77.5 219.4 3.8
37200 Chamise Chaparral S4 9.7 1.6 27.4 61.3 1,431.7 11.3
37300 Red Shank Chaparral S3.2 5.6 4.9 37.3 52.2 957.2 10.5
37400 Semi-Desert Chaparral S3.2 11.6 6.4 49.6 32.4 1,252.9 18.0
37510 Mixed Montane Chaparral S4 45.9 3.0 39.5 11.6 186.0 48.9
37520 Montane Manzanita Chaparral S4 2.8 2.2 57.8 37.1 13.7 5.1
37530 Montane Ceanothus Chaparral S4/3.3 9.9 1.3 57.5 31.3 357.3 11.2
37810 Buck Brush Chaparral S4 13.9 2.8 37.8 45.5 716.8 16.7
37830 Ceanothus crassifolius Chaparral S3.2 14.6 0.9 46.5 38.0 2,091.1 15.5
37840 Ceanothus megacarpus Chaparral S3.2 1.3 17.3 24.9 56.5 578.9 18.6
37900 Scrub Oak Chaparral S3.3 20.7 0.9 53.0 25.5 1,660.7 21.6
37A00 Interior Live Oak Chaparral S3.3 24.5 0.6 59.8 15.2 1,189.7 25.1
37B00 Upper Sonoran Manzanita Chaparral S4 3.7 2.6 67.9 25.8 388.8 6.3
37E00 Mesic North Slope Chaparral S3.3 58.6 2.7 37.6 1.1 14.6 61.3
37G00 Coastal Sage-Chaparral Scrub S3.2 0.1 3.3 14.7 81.9 193.1 3.4
42110 Valley Needlegrass Grassland S3.1 6.1 0.0 0.7 93.1 3.4 6.1
42200 Non-Native Grassland S4 1.7 4.9 19.5 73.9 1,205.5 6.6
47000 Pavement Plain S1.1 0.1 0.9 66.8 32.2 11.3 1.0
52120 Southern Coastal Salt Marsh S2.1 21.6 12.1 16.6 49.6 11.0 33.7
52200 Coastal Brackish Marsh S2.1 0.0 0.0 0.0 100.0 1.1 0.0
52410 Coastal and Valley Freshwater Marsh S2.1 4.3 1.0 6.9 87.8 40.4 5.3
61310 Southern Coast Live Oak Riparian Forest S4 16.2 0.0 45.6 38.1 26.0 16.2
61320 Southern Arroyo Willow Riparian Forest S2.1 4.4 3.2 26.4 65.9 37.7 7.6
61330 Southern Cottonwood-Willow Riparian Forest S3.2 1.6 5.8 44.8 47.8 59.9 7.4
61510 White Alder Riparian Forest S4 17.1 0.0 35.7 47.1 8.4 17.1
62400 Southern Sycamore-Alder Riparian Woodland S4 6.6 0.0 27.7 65.7 18.1 6.6
63310 Mule Fat Scrub S4 2.5 8.3 27.8 61.4 45.8 10.8
63320 Southern Willow Scrub S2.1 0.0 0.0 11.7 88.3 1.6 0.0
63330 Southern Alluvial Fan Scrub * NR 0.0 0.0 2.3 97.7 13.2 0.0
71130 Valley Oak Woodland S2.1 0.0 3.4 2.8 93.8 36.6 3.4
71140 Blue Oak Woodland S3.2 0.0 0.0 10.5 89.5 4.9 0.0
71150 Interior Live Oak Woodland S3.2 0.0 0.0 100.0 0.0 14.2 0.0
71160 Coast Live Oak Woodland S4 0.8 1.4 24.6 73.2 60.4 2.2
71182 Dense Engelmann Oak Woodland S2.1 3.2 0.3 20.7 75.9 234.8 3.5
71210 California Walnut Woodland S2.1 0.4 2.5 8.4 88.7 58.5 2.9
71322 Non-Serpentine Foothill Pine Woodland S4 0.0 0.0 0.0 100.0 4.9 0.0
71410 Foothill Pine-Oak Woodland S4 0.0 0.0 24.4 75.6 10.0 0.0
72200 Mojavean Pinyon and Juniper Woodlands S3.2/4 12.8 0.6 66.4 20.2 1,447.0 13.4
72300 Peninsular Pinyon and Juniper Woodlands S3.2 71.1 1.5 5.6 21.8 14.8 72.6
81310 Coast Live Oak Forest S4 6.3 1.7 14.9 77.1 175.7 8.0
81320 Canyon Live Oak Forest S4 29.7 1.5 46.7 22.0 178.2 31.2
81330 Interior Live Oak Forest S4 0.0 0.0 99.4 0.6 40.6 0.0
81340 Black Oak Forest S4 6.6 9.5 48.2 35.7 208.9 16.1
83210 Knobcone Pine Forest S4 0.0 0.0 91.8 8.2 5.1 0.0
83330 Southern Interior Cypress Forest S2.1 0.0 7.2 70.3 22.4 17.8 7.2
84140 Coulter Pine Forest S3.2 12.3 2.4 50.7 34.6 310.2 14.7
84150 Bigcone Spruce-Canyon Oak Forest S3.2 46.6 0.1 45.7 7.6 320.4 46.7
84210 Westside Ponderosa Pine Forest S2.1 38.4 5.5 30.6 25.5 322.5 43.9
84230 Sierran Mixed Coniferous Forest S4 27.9 2.5 55.7 13.9 216.3 30.4
85100 Jeffrey Pine Forest S4 21.9 0.2 65.1 12.7 235.2 22.1
85210 Jeffrey Pine-Fir Forest S4 23.9 0.0 63.3 12.8 354.8 23.9
85320 Southern California White Fir Forest S4 33.5 1.3 52.7 12.6 38.1 34.8
86100 Lodgepole Pine Forest S4 51.7 0.0 34.6 13.7 4.7 51.7
86500 Southern California Subalpine Forest S3.3 92.3 0.0 7.7 0.0 52.4 92.3

Region Total - Natural Communities


Region Total - All Lands
8.0 2.0 27.2 62.8 33,827 10.0

Based on the GAP classification of management status, communities restricted largely to the lower elevations , such as Non-Native Grasslands and coastal sage scrub types, are at considerable risk (Table SW-2). Roughly 88% of areas below 500 m are in status 4 management (i.e. primarily privately owned). A majority of the lands at these elevations have already been converted to agricultural or urban uses and most of the remaining lands are threatened with future urbanization. We summarize the data for widespread types (mapped distribution > 25 km²) in Table SW-2 in four categories of protection. A comparison of management status with the ranking of communities in the Natural Diversity Data Base indicated that communities with greater than 70% of their distribution in status 4 lands or less than 10% in status 1 and 2 lands are most vulnerable (Davis et al. 1995).

1. Plant community types occurring mainly on status 4 lands. Many of the community types characteristic of lower elevation areas near the coast fall into this category. Valley Needlegrass Grassland and Valley Oak Woodland were mapped with over 90% of their distribution on lands with essentially no formal protection. Other widespread types include Venturan Coastal (32300) and Riversidian (32700) Sage Scrub, Coastal Sage-Chaparral Scrub, Southern Mixed Chaparral, Non-Native Grassland, Coastal and Valley Freshwater Marsh, Coast Live Oak (both woodland and forest), California Walnut Woodland, and Dense Engelmann Oak Woodland.

2. Scrub, chaparral, and herbaceous types mainly located in unprotected areas. Many of the types listed in category 1 above, also have less than 10% of their area in status 1 or 2 lands: all four sage scrub types, Southern Mixed Chaparral, grasslands, and Coastal and Valley Freshwater Marsh. Big Sagebrush Scrub, Northern Mixed Chaparral, and Upper Sonoran Manzanita Chaparral are additions to the list.

3. Forest and woodland types mainly located in unprotected areas. Many of the tree-dominated community types listed in category 1 are repeated here as well, such as the oak types (Valley, Coast Live, and Engelmann) and California Walnut Woodland. Additional woodlands of note here are two riparian forests (Southern Cottonwood-Willow and Southern Arroyo Willow), Interior Live Oak Forest, and Southern Interior Cypress Forest, although the last type was only mapped over 17.8 km².

4. Community types that appear well-protected. Communities at higher elevations, especially montane chaparral and coniferous forest types, are generally well represented (> 25% in status 1 or 2 areas). Included are the montane forest types, several of which are more typical of other regions: Canyon Live Oak Forest, Bigcone Spruce-Canyon Oak Forest, Westside Ponderosa Pine, Sierran Mixed Coniferous, Jeffrey Pine-Fir, Southern California White Fir, and Southern California Subapline Forests. Another well-represented group are the desert types that are widespread in adjacent regions such as Mojave Creosote Bush Scrub and Great Basin Mixed Scrub.

We were unable to distinguish herbaceous plant species and community types beyond very general classes. For example, we classified practically all grasslands as "Non-native" despite the fact that many of these areas contain sizeable populations of native grasses and forbs. Thus our estimate of the extent of the Valley Needlegrass community is undoubtedly too low. Keeley (1990) provides a much more detailed assessment of the distribution and conservation status of native grasslands. However, we would call attention to the fact that nearly three-fourths of non-native grassland in the region is privately held, and only 6.6% is in status 1 or 2 areas. Although dominated by exotic species, these grasslands can be rich in native plant species and are habitat to many animal species. Recent efforts to preserve grassland habitats for the Stephens' kangaroo rat (Dipodomys stephensi) in the Riverside Basin attest the ecological significance of this community type. However, annual grasslands in other parts of the region are generally not considered a conservation priority. Our data suggest that from a regional perspective Non-Native Grasslands appear to be at risk.

All coastal sage scrub communities (or soft chaparral) occur predominantly on private lands. Soft chaparral in California is largely confined to this region, although variations with different species composition extend north along the coast to beyond the San Francisco Bay. Once very common and widespread, the type has been fragmented and its extent reduced severely by development of coastal habitats (O'Leary 1990). Much conservation effort is focused on areas in Orange, Riverside, and San Diego Counties that are habitat for the threatened California gnatcatcher (Polioptila californica) (Brussard and Murphy 1992). Our analysis highlights the need to consider more northerly elements as well. For example, practically all landscapes dominated by Salvia leucophylla are in the western Transverse ranges, north of the current range of the gnatcatcher.

Big Sagebrush Scrub, although widespread elsewhere in California, appears vulnerable in this region. Plant communities dominated by Artemisia tridentata, Chrysothamnus nauseousus or C. parryi occur along northern and northeastern margins of the region, and are concentrated in the upper Cuyama Valley, Lockwood Valley, eastern San Bernardino Mountains, locally in the Anza Valley, and in the extreme southeastern corner of the region. It appears that nearly all sagebrush scrub in the region is subject to grazing. Roughly 50% of the area occupied by sagebrush is multiple-use (status 3) public land, so conservation concern for this community can probably be adequately addressed by the public land managing agencies. Within the sagebrush community near Baldwin Lake in the northeastern San Bernardino Mountains, there is an edaphic community known as Pavement (or Pebble) Plains. These small plains, the remnants of a Pleistocene lake, are habitat to candidate endangered species such as Castilleja cinerea and Astragalus leucolobus, and to the greatest concentration of endemic plants in the state (Schoenherr 1992). Because this type occurs in patches below our minimum mapping unit, our assessment of its extent and land ownership and management patterns are only approximations. Nevertheless, this type appears to be deserving of more conservation research and management.

There are five major hardwood woodland types characteristic of this region. Coast Live Oak (Quercus agrifolia) is distributed throughout the region and in association with a number of other co-dominant species. Most communities types and the overall distribution of this species are poorly represented in protected areas, and conversion to urban land use appears to be one of the major causes of decline in these types (e.g., Scheidlinger and Zedler 1980). Quercus engelmannii is endemic to this region and is also significantly under-represented in status 1 and 2 areas. Recently Scott (1991) analyzed the geographic distribution of this species based on 1:24,000 maps that he prepared from air photos. He estimated that Q. engelmannii occurs over 31,500 ha, compared to our estimate of 23,480 ha. The discrepancy appears mainly due to the differences in map scale rather than classification, given that his mapped stands fall almost entirely within our mapped landscapes. Scott called attention to the poor representation of the species in existing reserves, a pattern that we also observed (3.5%), despite the recent establishment of significant new reserves such as The Nature Conservancy's Santa Rosa Plateau Reserve. Additional aquisitions, subsequent to the database compiled for CA-GAP, have extended the protection for this type to an unknown degree.

More localized woodland species include Quercus lobata, Quercus douglasii, Quercus wislizenii, Arbutus menziesii, and Juglans californica. While most of these species are more widely distributed in other regions of California, the southern California black walnut (var. californica) is almost entirely restricted to this region. The current distribution of this species is highly fragmented and reduced compared with its original distribution. It is almost entirely (89.3%) on private land, with remnant populations in the Santa Clara River drainage, Simi Hills, Santa Susana Mountains, Santa Monica Mountains, San Jose Hills, Puente Hills and Chino Hills. Quinn (1990) provides a detailed analysis of the distribution, ecology and conservation status of this type, and emphasizes the need for immediate conservation action in the face of iminent urbanization of many remaining habitats. Quercus chrysolepis, and to a lesser extent Quercus kelloggii, are widely distributed in the region and throughout California, and generally well represented in managed areas.

The various riparian woodland types are usually found in patches too small to be detected with the techniques employed by the GAP. Nevertheless some of these types appear to be poorly represented in biodiversity management areas.

Bigcone Spruce (Pseudostuga macrocarpa) and, to a lesser extent, Coulter Pine (Pinus coulteri) are largely restricted to and characteristic of this region. They generally occur between 500m and 1500m, but P. macrocarpa is concentrated in canyons and steep north-facing slopes, whereas P. coulteri occupies a range of topographic sites. Forty-seven percent of the mapped distribution of Bigcone Spruce-Canyon Oak Forest is in status 1 or 2 areas. Fifteen percent of the mapped distribution of Coulter Pine Forest is in protected areas.

Pinyon and Juniper Woodlands are prominant at the region boundaries adjoining the desert and Great Central Valley regions. They appear to be reasonably well represented and occur primarily on public lands.

Two endemic conifers, Cupressus forbesii , and C. arizonica ssp. arizonica are restricted to very local sites and difficult to detect using our methods. Both are worthy of conservation attention based on existing information (Oberbauer 1990).

Table SW-3. Zoning status of natural communities identified as vulnerable using Gap Analysis criteria in the Southern California Association of Governments planning region. Asterisks indicate community types whose mapped distribution totals less than 25 km².

CNDDB Code CNDDB Community Name

(Holland 1986)

% zoned for development % zoned for agriculture % zoned for open space or unknown
32300 Venturan Coastal Sage Scrub 19 1 80
32500 Diegan Coastal Sage Scrub 32 0 68
32700 Riversidian Sage Scrub 18 0 82
35210 Big Sagebrush Scrub 15 0 85
37120 Southern Mixed Chaparral 20 0 80
37B00 Upper Sonoran Manzanita Chaparral 2 0 98
37G00 Coastal Sage-Chaparral Scrub 32 0 68
42110 Valley Needlegrass Grassland * 0 7 93
42200 Non-Native Grassland 30 1 69
47000 Pavement Plain * 0 0 100
71130 Valley Oak Woodland 49 0 51
71160 Coast Live Oak Woodland 0 0 100
71182 Engelmann Oak Woodland 9 0 91
71210 California Walnut Woodland 34 0 66
81310 Coast Live Oak Forest 13 0 87
83330 Southern Interior Cypress Forest * N/A N/A N/A

In 1993, the CA-GAP data were used to assist the Southern California Association of Governments (SCAG) develop the open space element of their comprehensive regional plan (Crowe 1996). The distribution of vulnerable plant community types were compared with the pattern of land use zoning in the combined general plans of the jurisdictions in the 6 county area. (The only significant land areas not covered by the SCAG plan are Santa Barbara and San Diego Counties). This information was used to highlight plant communities that were not only vulnerable because of land management status but also because of permitted land uses. Here we update that information using the final version of the CA-GAP land-cover map and list of vulnerable types. Table SW-3 shows the types considered vulnerable from the analysis summarized above and the proportion of each that is zoned for development, agriculture, open space/unknown. Public lands such as National Forests are often zoned in the last category by counties, although the actual land uses are determined by planning conducted by the public land management agency. Worth noting in the table are the relatively large proportions of several types zoned for development (coastal scrub types, Big Sagebrush Scrub, Southern Mixed Chaparral, Non-Native Grassland, and Valley Oak Woodland, California Walnut Woodland, and Coast Live Oak Forest). These types, particularly the coastal scrub and the walnut woodlands which have already suffered serious losses, become of more immediate conservation concern because the pressure for conversion is already authorized. Southern Interior Cypress Forest was only mapped in San Diego County and therefore outside the SCAG jurisdiction. Figure SW-4 shows the pattern of vulnerable communities in relation to zoning.

Vulnerable Communities in SCAG

Figure SW-4. Vulnerable plant communities in the Southern California Association of Governments portion of the Southwestern California region and current zoning status.

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