Premises on CSS Ecology

  1. CSS vegetation is dominated by a characteristic suite of shrub species in southern California. The composition of coastal sage scrub vegetational subcommunities may vary substantially depending on physical circumstances and the successional status of the habitat. An explicit definition of CSS and a description of its constituent species has been prepared by the SRP. (See Special Report No. 2, March 1992.) A generalized map of CSS and a summary description is included in Attachment A

  2. While a variety of species are characteristic of CSS, no single animal or plant species readily serves as a consistent and entirely reliable indicator of CSS conditions across the entirety of the distribution of the habitat in southern California. Rather, many species dependent on CSS are found in only certain subsets of the community, and, conversely, many nominal CSS species are widely distributed in non-CSS habitats. Nonetheless, a suite of "target" species has been identified by the SRP that is useful as a surrogate for planning purposes. Species other than target species that have been identified as deserving special consideration on account of possible rarity or endangerment are referred to as species of concern. These are state or federal candidates for listing. (See SRP Survey Guidelines, February 1992.)

  3. Target species are three vertebrates that are among the community's most visible imperiled organisms: California gnatcatcher, cactus wren, and orange-throated whiptail lizard. Their distributions embrace the majority of the geographic range of southern California CSS.

  4. Many species that depend on coastal sage scrub exhibit transitory habitat occupancy, along with short lifetimes, high potential rates of reproduction, limited home ranges, dramatic population fluctuations, and great susceptibility to local extirpation.

  5. Because of population fluctuations and routine local extirpation and recolonization events, a single point-in-time appraisal of the presence or absence of a species on an individual parcel of land does not reliably indicate the parcel's long-term potential value or importance as habitat.

  6. CSS may convert to chaparral or grassland, depending on slope, aspect, climate, Fire history, and other physical factors and biological phenomena; conversely, chaparral or grassland areas may convert to CSS.

  7. CSS is a naturally patchy vegetation community. Over a scale of several miles, it is found in diverse habitat mosaics with other ecological communities. While there are species dependent on coastal sage scrub, these species do not always exhibit a clear tendency to occupy areas of continuous coastal sage scrub. Rather, vegetation components of coastal scrub habitat in mosaics with other habitat types may provide habitat for target species and other species of concern.

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