Biological Resources !
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3. Biological Resources ! For a complete discussion of the City’s Biological Resources, see the The Biological Resource Report for the City of San Marcos Revised July 11, 1996. Sweetwater Environmental Biologists. Portions of this document are excerpted below. All references cited in Section 3.1 – 3.4.5 can be found in the “Biological Resource Report”. 3.1 Methods The vegetation and sensitive species data within the City were mapped and incorporated into SANDAG's Geographic Information System (GIS). The vegetation classification scheme employed was based upon a modified (San Diego) Holland Vegetation Classification System that was designed to merge the different mapping efforts within the County (City of Carlsbad HMP, County of San Diego, MSCP, Metropolitan Water District of Southern California (MWD), and Camp Pendleton. 3.1.2 Existing Information Specific information on the vegetation and sensitive species sightings within the City was gleaned from several sources including over 30 biological resources reports (EIR's, biotechnical reports, etc.); the CNPS's Inventory of Rare and Endangered Vascular Plants (Smith and Berg 1988); Beauchamp's (1988) Flora of San Diego County, California; Bauder's (1986) San Diego Vernal Pools; Recent and Projected Losses; Their Condition; and Threats to Their Existence, Vols. 1 and 2; the San Diego Biodiversity Project's (1991) San Marcos Vernal Pool report; and discussions with local experts. 3.1.2 Biological Surveys Field surveys were conducted to verify areas that had been previously mapped, or areas where the vegetation could not be determined from the aerial photographs. These field surveys were limited due to time and were also limited to areas that were easily accessible to the public. 3.1.3 Vegetation Mapping The vegetation within the City and its' Sphere of Influence was mapped on laminated infrared aerial photographs at a scale of 1:24,000 (1 "=2,000') utilizing the following sources. For areas where there was prior vegetation information (EIRs, etc.), this information was incorporated onto these photographs. The vegetation and sensitive species data were then entered into SANDAG's GIS, generating a biological resource map. This map was then reviewed by John Brown from Dudek and Associates and Fred Sproul from the County of San Diego, as both of these biologists were involved in various mapping projects that overlap with areas within both the City limits and Sphere of Influence of San Marcos. 061401 26 San Marcos Subarea Plan Public Review Draft 3.2 Vegetation Communities There are 12 vegetation communities within the City and the City's Sphere of Influence (Figure 2). The classification scheme used in this report is based upon Holland's Vegetation Classification System modified for San Diego County. The classification system used for San Marcos is consistent with the classification system used for the MHCP. Since much of the information within this report was compiled from other environmental and biological documents, some vegetation types were reclassified so as to be consistent with the MHCP. These decisions were based on the information within these documents and also on site visits by SEB 3.2.1 Scrub Communities Diegan Coastal Sage Scrub Coastal sage scrub is one of the two major shrub types that occur in California. This habitat type occupies xeric (dry) sites characterized by shallow soils. Sage scrub is dominated by subshrubs whose leaves abscise (fall off) during summer drought and are replaced by a lesser amount of smaller leaves. This adaptation of drought evasion allows these species to better withstand the prolonged drought period in the summer and fall in areas of low precipitation. Sage scrub species have relatively shallow root systems and open canopies. This last trait allows for the occurrence of a substantial herbaceous (non-woody) component in coastal sage scrub. Four floristic associations are recognized within coastal sage scrub plant formation and these occur in distinct geographical areas along the California coast with the Diegan association occupying the area from Orange County to northwestern coastal Baja California (O'Leary 1990). Coastal sage scrub occurs on a variety of soil types, both chemically and physically, from sandy lithosols on siliceous sandstone to clay-rich chernozems on volcanic ash. Coastal sage shrubs have shallow, fibrous root systems, in contrast to the deep penetration root systems of most of the chaparral species dominant in adjacent areas. Water is less likely to penetrate to depth in clay soils than in siliceous soils. Clay soils generally lose more moisture through runoff, have lower infiltration rates, store more moisture in an equivalent depth of soil, and are likely to lose a greater proportion of moisture through capillary action and transpiration (water loss) from shallow-rooted species than siliceous soils. Thus, in areas of relatively low precipitation, fine-textured soils are more likely to favor the success of shallow-rooted species rather than deep-rooted species (Kirkpatrick and Hutchinson 1980). Diegan coastal sage scrub may be dominated by a variety of species depending upon soil type, slope, and aspect. Diegan coastal sage scrub may be classified into several sub-associations based on the dominant species. The largest contiguous block of Diegan coastal sage scrub within the City occurs on the hills west of Twin Oaks Valley Road, east of Neighborhood One of the College Area Plan and north of Palomar College and San Marcos Junior High School. The sage scrub within this area is dominated by black sage (Salvia mellifera), California sagebrush (Artemisia 061401 27 San Marcos Subarea Plan Public Review Draft californica), and laurel sumac (Malosma. laurina). Other sub-associates include flat-top buckwheat, white sage, and coast monkey flower (Diplacus puniceus). Some of the low lying areas and drainages support dense stands of coyote bush (Baccharis pilularis ssp. consanguinea) (ERCE 1990; JPF 1988). A semi-contiguous band of Diegan coastal sage scrub occurs along the slopes that extend from the developed area to the east of Lake San Marcos Country Club, eastward past Discovery Lake and southeast from Discovery Lake to Mt. Whitney. The sage scrub is interrupted by patches of development (the cement plant on Rancho Coronado South and residential development near Mt. Whitney). The component species of this community include California sagebrush, black sage, toyon (Heteromeles arbutifolia), flat-top buckwheat, and coast monkey flower (MBA 1990a). From Discovery Lake to South Lake (Rancho Coronado South) this community is dominated by black sage and laurel sumac with coyote bush dominant in the sage scrub that is highly disturbed SEB 1992c). In the southwest comer of the limits of the City (located on and near the University Commons project) there are disjunct patches of Diegan coastal sage scrub. These patches occur from east of Rancho Santa Fe Road and north of San Marcos Creek southeast along Questhaven Road to the San Marcos Landfill. The component species of this community include California sagebrush, flat-top buckwheat, black sage, white sage, laurel sumac and coyote bush (ERCE 1991). This patch was once contiguous with the sage scrub on the southern portion of San Elijo Ranch project. Much of the sage scrub on San Elijo Ranch has been cleared of brush after project certification pursuant to CEQA. The remaining sage scrub habitat is now disjunct from the sage scrub on University Commons. The sage scrub on San Elijo Ranch occurs on the southeast facing slopes of Double Peak. There is also some disturbed sage scrub in the western portion of San Elijo Ranch. California sagebrush, flat-top buckwheat, black sage, and laurel sumac are the dominant species within the sage scrub on San Elijo Ranch (PSBS 1989). Small disjunct patches of sage scrub on the Cielo Azul project and west of Rancho Santa Fe Road along the Carlsbad border are also a part of the sage scrub mosaic in the southwestern comer of the City. Other small disjunct patches of Diegan coastal sage scrub occur in the central portion of the City (Walnut Hills II; Discovery Hills; the hill between Amorlite Drive and Knoll Road; the hill just east of the intersection of Twin Oaks Valley and Mission roads; and Twin Oaks Valley Ranch. In the northern Sphere of Influence, a large patch of Diegan coastal sage scrub occurs on the hillsides north of Buena Creek Road, east of Tamara Lane and south and west of Twin Oaks Valley Road. Diegan coastal sage scrub represents the second largest vegetation community within the BRMP Study Area. 061401 28 San Marcos Subarea Plan Public Review Draft Diegan Coastal Sage Scrub/Chaparral -Ecotone This community has components of both Diegan coastal sage scrub and southern mixed chaparral. The largest block of this community within the City occurs on the south-facing slopes directly north of Deer Springs Road in the northeastern comer of the City's Sphere of influence. This community is dominated by sage scrub species but has chamise as a dominant component. Most of the habitat described on the San Marcos Landfill Expansion site is classified as this ecotone. The component species of this community are chamise (Adenostoma fasciculatum), coast white lilac (Ceanothus verrucosus), California sagebrush, laurel sumac, flat-top buckwheat, and black sage (MBA 1990b). Chapparal Chaparral is the most prominent vegetation type within the regions of California which experience a Mediterranean climate. Chaparral communities are dominated by evergreen shrubs with small, sclerophyllous ("hard leaved") leaves, which are thick and heavily cutinized to reduce evapo-transpirational water losses. The shrub species characteristic of chaparral communities share other morphological traits including a rigid branching structure and a dual-root system composed of both deep-tap roots and a shallow lateral root system (Rundel 1986). The deep-root systems of chaparral species appear primarily adapted to obtaining moisture from deep recesses, often penetrating into unweathered bedrock (Kirkpatrick and Hutchinson 1980).