The effects of future urban development on habitat fragmentation in the Santa Monica Mountains

A site suitability model of urban development was created for the Santa Mon ica Mountains in southern California, USA, to project to what degree future development might fragment the natural habitat. The purpose was to help pr ioritize land acquisition for the Santa Monica Mountains National Recreatio n Area and examine to what extent projected urban development would affect distinct vegetation classes. The model included both environmental constrai nts (slope angle), and spatial factors related to urban planning (proximity to roads and existing development, proposed development, and areas zoned f or development). It implemented a stochastic component; areas projected to have high development potential in the suitability model were randomly sele cted for development. Ownership tracts were used as the spatial unit of dev elopment in order to give the model spatial realism and not arbitrarily `de velop' grid cells. Using different assumptions and parameters, the model pr ojected the pattern of development from similar to5 to similar to 25 years hence (based on recent development rates in the area). While < 25% of the r emaining natural landscape is removed under these scenarios, up to 30% of c ore (interior) habitat area is lost and edge length between natural vegetat ion and development increases as much as 45%. Measures of landscape shape c omplexity increased with area developed and number of patches of natural ha bitat increased four- to nine-fold, depending upon model parameters. This i ncrease in fragmentation occurs because of the existing patterns of land ow nership, where private ('developable') land is interspersed with preserved park lands.