Currently, the Plateau operates as an integral part of the larger Santa Ana Mountain ecosystem. Natural features and compatible land uses protect the habitat areas and their respective fauna. An escarpment to the north, the Cleveland National Forest to the west, and Camp Pendleton to the southwest have provided separation from the suburban development that has typified growth in this part of southern California for the past decade. Now, however, ongoing development on the escarpment and the lower plateau threatens the long-term viability of the Reserve as an element in the larger and connected landscape patterns that support the region's high biodiversity. Rural residential development is increasing on the northeast and sizable orchards have been established to the south. These orchards are shown as bright purple in the JERS 1 image. If this pincer-like development trend continues, the Reserve will become isolated from the other wilderness areas and may no longer have access to the sufficient influx of genetic diversity that is necessary for long-term species survival.
Figure 106 illustrates the 1990+ development on the Plateau. Shown in dark green are the Santa Rosa Reserve and the San Mateo Wilderness Reserve of the Cleveland National Forest, the principal biological reserves of this section of the study area. In lighter shades of green are other protected or managed properties including the remaining lands of the Cleveland National Forest and San Diego State University's reserve land. Camp Pendleton's military maneuver and impact areas are shown in light blue and purple respectively. Densely developed areas are shown in red, and slopes greater than 25% are shown in yellow. Potentially developable land is shown in gray.
To maintain the connections between these natural areas and thereby help to maintain the area's biodiversity, wildlife corridors must be identified and managed. The word corridor in this instance is equivalent to its usage in the landscape ecological pattern model: a linear strip of natural vegetation that provides linkage between natural patches. Strips may be along riparian corridors, but may also be comprised of grassland, sage, chaparral, or other native plant communities. It is also possible that a corridor may be comprised of several vegetation communities.
The planning and design of a wildlife corridor is, in part, a function of the goals of the conservation effort. Corridors may be designed for a single species, such as is being done in Florida for the panther, or for several species, as is done in parts of northern Europe. In identifying possible movement linkages for biodiversity on the Santa Rosa Plateau, it is advisable to maintain at least two representative stands of each native vegetation type, in the event that one is lost to disease. This is consistent with the noted relationship between habitat and biodiversity and will also contribute to the continuity of the pattern of vegetation across the landscape.
The planning and design of a wildlife corridor is also a function of land availability, landowner interest in participation, and land management. All of the land between the Reserve and the natural lands to the west is already subdivided for house lots. It is also possible that some larger lots may be further subdivided to a zoned density of one house per 2 hectares. While the existing parcelization and potential re-parcelization of this land may create some difficulties in establishing corridors, it does not create insurmountable obstacles.
The siting of houses within the parcels, and not the parcel lines themselves, is in this case the most important consideration in creating the corridors. It is known, for example, that cougars avoid artificial light. Siting houses so that evening lights are not evident from the surrounding landscape will contribute to successful wildlife corridors. Also, architectural design elements such as roof overhangs, low exterior lighting, and special light retarding window glass can greatly contribute to the success of a corridor design. Locating houses so that driveways are shared will reduce the amount of vegetation displaced by impermeable surface and lessen the effects on the hydrologic cycle and thereby the long-term impact on habitat communities.
Homes should also be sited to allow active fire management. Fire is both necessary and inevitable in this landscape and the current practice of fire suppression in areas of rural residential development threatens both homeowners and the native plant communities. Periodic controlled burning reduces fuel loads and lessens the threat of destruction to life and property by catastrophic fire events and also simulates the natural fire patterns that allow many native plant species to regenerate. Fire related guidelines for siting houses include avoiding the middle of slopes and using existing and new roads as fire breaks. Prevailing winds in this area often direct fire toward the northeast, so extreme care should be taken if homes must be sited on south or southwestern slopes. Figure 107, from the Plan for the Santa Lucia Preserve (1995), near Monterey, California, shows several general guidelines for siting homes within such conserved habitat areas.
Lastly, the use of exotic plantings around houses should be avoided. Beyond the direct displacement of habitat by non-native plants, there is the risk that these species will become naturalized in the landscape and out-compete the native plants. The eucalyptus trees imported to California from Australia in the last century provide an example. Steep hillsides are the most likely areas for conversion to non-native species, because while they are difficult and expensive to develop for housing, they are easily planted with orchards that have minimal habitat value.
Maintaining connected natural vegetation could be the first step toward developing a working network of corridors between the Reserve and the nearby natural landscape without unduly limiting possible house sites. The combination of development opportunities and landscape conservation should result in both economically enhanced development and the maintenance of biodiversity.