Comparison of Alternatives

A Comparison of the Regional Alternative Futures

Each of the alternatives has been assessed by each model for the impacts of changes between 1990+ and 2010, and between 1990+ and Build-Out. These are summarized in figure 132, which compares the six alternatives: Plans Build-Out, Spread, Spread with Conservation 2010, Private Conservation, Multi-Centers, and the New City.

Soils

In the Plans Build-Out scenario, half the potentially productive agricultural soils listed by the NRCS or the State of California will be lost to development. The protection of the other half is not through any new conservation strategy, but rather through the stewardship for other reasons by the current owners and managers: the Metropolitan Water District, the Bureau of Land Management, and MCB Camp Pendleton.

All of the alternative scenarios do better than Plans Build-Out. The New City and both Spread alternatives urbanize considerable areas of prime agricultural soils. The Multi-Centers and Private Conservation proposals lose the least amounts.

Hydrology

The Plans Build-Out and Spread scenarios both cover considerable areas of permeable soils with impervious land uses or compacted soils. This will lead to more run-off and less retention and more severe flooding. Development in currently unprotected land in the eastern portion of the study area will change the runoff in the headwaters area, reducing soil moisture and altering the vegetation pattern in both the Multi-Centers and New City alternatives. The Private Conservation scenario spreads small disturbance widely so soil runoff will be increased, but not as severely as in the other alternatives.

In Plans Build-Out nearly 5000ha of upland soils will change from very dry to dry or mesic as more water runs off developed uphill land. Much of the change will occur within typically dry vegetation types. About 2% of the total area of coastal sage scrub and about 13% of the total area of chaparral will become wetter which may change the vegetation.

Fire

The Plans Build-Out, both Spread alternatives, and the New City late-stage (after 2010) alternative enable rural residential development which will place both houses and the native vegetation communities at risk and make fire management difficult. While the Multi-Centers alternative protects some large areas in the northern half of the study area, fragmented conservation land in the southern half will also prove difficult to manage for fire. The Private Conservation alternative's strategy of clustering small numbers of houses at the edges of wide bands of conservation land affords a spatial distribution suitable for fire management within developed areas.

Landscape Ecological Pattern

Both the Plans Build-Out and Spread alternatives seriously impact the large natural areas in the eastern half of the study area. Even though one Spread alternative calls for conservation of available land after the year 2010, the landscape is expected to be so fragmented by that date that only the protection of small patches will be possible. The Multi-Centers, and to a slightly lesser extent the New City alternative, maintain smaller but contiguous patches of natural vegetation. The Private Conservation alternative, by privately protecting large natural areas and wide corridors at an early stage, best maintains the ecological pattern of the region. However, this alternative assumes that about 20% of the study area will fall within its policy proposals.

Single Species Potential Habitat

In general, the Private Conservation alternative best protects the single species potential habitats. In some cases, it expands potential habitats. The Spread alternatives and Plans Build-Out alter the patterns of habitat the most. It should be noted that several of the species will significantly expand their habitat because of the growth of rural residential development and its accompanying change to upland vegetation. Whether or not the great increase in cowbird habitat is good for biodiversity is questionable.

Species Richness

While suburbanization may only slightly change the total number of vertebrate species in the region, the habitat communities with the highest species richness will decrease significantly. The scenarios differ in the amount of that decrease, with the New City and Private Conservation proposals maintaining relatively more species richness than the others. All of the alternatives except Private Conservation decrease the number of species having at least 500 home range patches.

While species richness declines in all of the future scenarios, much is retained in the rural residential areas. This is especially true where smaller patches encompass species' home ranges. The definition of rural residential development posits an average of 25% conversion from native vegetation to structures, paving, and other land cover, and the retention of the remaining 75% of the natural vegetation. The analysis results are strongly dependent on strict adherance to this definition. Rural residential development that converts the remaining 75% to ornamental gardens, avocado orchards, or horse pastures would not maintain the predicted levels of species richness.

Visual Preference

The Plans Build-Out scenario will effectively destroy most of the highly preferred visual qualities of the area. Perhaps even more alarming, the Spread scenarios anticipate that some of the most visually attractive areas will be the first to be developed. The Private Conservation alternative, which is primarily directed at conserving the landscape ecological pattern, also protects exposed areas near roads. The New City alternative anticipates protecting some of the same areas after the year 2010, but the region will have lost much of its scenic value by then from development and fragmentation. The Multi-Centers alternative is the only one that substantially protects a continuous circuit of scenic views, but its proposed development in highly accessable areas still decreases the region's overall visual value.