On the Global and Regional Ecological Significance of Southern Orange County: Conservation Priorities for a Biodiversity Hotspot

Executive Summary

October 2001

This report summarizes available scientific information establishing the crucial role that Southern Orange County could play in efforts to conserve biodiversity at both global and regional scales. The report outlines a conservation framework for the area, using principles of conservation planning to delineate four core biological resource units. These four resource units must be conserved essentially intact, without further internal fragmentation by development, to continue supporting key species and ecosystem processes. We present this information in support of the Natural Community Conservation Planning (NCCP) program for the Southern Orange County NCCP subregion.

South-coastal California is a biodiversity "hotspot" of global importance. Hotspots are those areas harboring the greatest concentrations of living species, especially those species found nowhere else on Earth (endemics). Together, 25 global hotspots identified by leading conservation scientists support more than 60 percent of the Earth's total species diversity, on only 1.44 percent of its surface. Concentrating conservation efforts in these relatively small areas therefore gains the greatest biodiversity value from limited conservation funds.

Much of Southern California's unique biodiversity is concentrated in the foothills and terraces along the Pacific coast, from Orange County to the Mexican border. Having thus far escaped the urban sprawl that has reduced and fragmented natural habitats throughout southern California, southern Orange County supports the last best representation of this globally unique ecosystem. In concert with adjacent federal lands (Cleveland National Forest and Marine Corps Base Camp Pendleton), this large undeveloped block of natural habitat supports the broadest remaining array of natural environmental gradients and ecosystem processes in the south-coastal landscape. Southern Orange County and adjacent preserve areas support core populations of many imperiled wildlife species. The area's outstanding biological attributes include the following:

• Seven federally threatened or endangered species and critical habitat (areas designated by the U.S. Fish and Wildlife Service as essential to species survival and recovery) for three of these.
• Approximately 65 to 85 percent of the total remaining population of coastal cactus wrens--the single most important breeding area for this rare endemic bird.
• Approximately 25 to 34 percent of the California gnatcatchers in the U.S.--the country's largest contiguous population of this threatened species.
• The last remaining undammed and undiverted major drainage in all of southern California--San Mateo Creek is the most pristine coastal stream south of the Santa Monica Mountains.
• The southernmost population of endangered steelhead trout--and the only one south of Malibu Creek--which is considered essential to species recovery.
• A tremendous diversity of nesting raptors (hawks, owls, eagles, and falcons)--with over 330 recorded nest sites and 15 species--including a critical foraging area for one of the last remaining golden eagle pairs in Orange County.
• Significant areas of native California grasslands, an imperiled vegetation community that exists here in natural mosaic with other diverse habitats--as much of south-coastal California once appeared.
• Healthy populations of mountain lions and mule deer, which require large and intact wildlands to survive.
• Some of the largest remaining populations of certain narrow endemic plant species within some of the last and best examples of such rare ecological communities as southern alkali marshes and grasslands.

Based on these biological facts, principles of conservation biology and planning, and guidance provided by the Southern Orange County NCCP Science Advisors, we mapped those areas most critical to retaining these resource values in the region. Four core biological resource areas (Arroyo Trabuco, Chiquita, San Juan, and San Mateo) must be conserved essentially intact, without further internal fragmentation, significant reduction in size, or degradation by development, to retain these resources and the ecosystem processes they depend upon. Conserving private lands within these four areas would consolidate a large ecosystem reserve in conjunction with adjacent existing protected areas, such as the San Mateo Canyon Wilderness Area, Cleveland National Forest, Caspers Wilderness Park, Rancho Mission Viejo Conservancy, and Audubon Starr Ranch Sanctuary.

The findings and recommendations of this report should help guide NCCP planning for the Southern Orange County NCCP subregion, which is the last best hope to conserve a large, ecologically intact representation of the globally unique coastal foothills and terraces ecosystem. This hope can be achieved through the NCCP process as long as society agrees that these resource values are irreplaceable.

For more information, contact Jerre Stallcup or Mike White in the CBI San Diego office (phone: 760-634-1590).