Wildlife Corridors -- A Need of Nature
(The following article was excerpted from Linkages, a periodical of the Institute for Ecological Health. It is presented here because the northernmost portion of the Santa Clara Watershed touches on the Tehachapi-Grapevine ecotone, an area now threatened with large-scale development.)
Wildlife corridors have become a popular concept over the past few years. People usually think of small scale situations--a corridor of a few miles or less connecting two hatitat areas to allow mobile species to move between the two areas.
Very large scale connections also play important roles, particularly over very long time periods. The most important example in California is the Tehachapi Mountains-Grapevine region between the San Joaquin Valley and the Los Angeles Basin. This area is a huge ecotone where five major biological regions--Sierra Nevada, Central Valley, Mojave Desert, Transverse Range and the Los Angeles Basin--come together. It provides for species movement as climatic conditions change or other factors cause species to extend their ranges. Examples are movement of desert species into the southern San Joaquin Valley, and of southern species from Mexico up into central and northern California--movements that have occurred in the past and will need to occur in the future.
The Tehachapi-Grapevine ecotone also provides for important medium-term connectivity needs. It is one of two connections between oak woodlands of the Sierra Nevada foothills and Coast Range, and also provides for movement of individual animals from the Sierra to the southern Californian and coastal mountain ranges.
Much of this region is federal land. However, several key areas include extensive private lands. One is the Antelope Valley, a V-shaped valley separating the Liebre-Sawmill Mountains portion of the Angeles National Forest from the Tehachapi Mountains. This valley broadens slowly from a point near the I-5/Highway 138 junction to a wide connection with the Mojave Desert proper in the Lancaster-Rosamond area. A second is the Tehachapi Mountains, which include the huge Tejon Ranch. A third is the I-5 corridor over the Grapevine from the San Joaquin Valley to the Santa Clara River Valley.
Current and future land use planning in Los Angeles and Kern Counties must address the ecological needs of this ecotone. Otherwise we risk severing or degrading the connections between bioregions, with immense long-term consequences. For example, development along the Lancaster-Rosamond Highway 14 corridor, or along with Highway 138 corridor in western Antelope Valley, could block the connection between the Mojave Desert and the center of the ecotone. Development in the foothill areas that form the southern rim of the San Joaquin Valley, or in critical spots along I-5, could also cause major long-term biological impairment.
Development pressures are building in this region, as the Los Angeles metropolitan area spills over onto the edge of the Mojave Desert and along the I-5 corridor into the southern San Joaquin Valley. At the end of August, the Tejon Ranch Company, owner of 270,000 acres in the Tehachapi Mountains, filed plans to construct a 23,000-home new town in Los Angeles County. The proposed community of Centennial would be just east of I-5 on Highway 138--about the center of the five bioregions ecotone area. Construction of Centennial could easily lead to further development along the Highway 138 corridor in Antelope Valley, the last remaining undeveloped valley in Los Angeles County. There are also proposed commercial tracts along I-5. It is noteworthy that Tejon Ranch, the largest single private landowner in the state, sold off all its cattle a year or so ago, and now leases its land to other ranchers.
County and city planners and development companies normally do not think about issues like long-term movements between bioregions. But decisions made in Kern and Los Angeles Counties over the next few decades will have huge impacts for as long as our civilization, with its cities and highways, is present in California. This is a critical time to think about bioregional connectivity and plan for the Needs of Nature.