Abstract:Exurbia (rural low-density residential development) is one of the fastest growing types of land-use and can result in habitat fragmentation and loss of farmland. Local zoning restrictions and farmland protection are the most common ways of controlling low-density development in rural areas. While planners have recognized the utility of landuse change models for decision-making, most models do not effectively forecast exurban expansion. To rectify this problem, a spatially explicit model called UPlan that projects exurban development was adapted for Sonoma County California, where an estimated 27% of the people live at low densities (< 1 unit/0.8 ha [2 acres]). The projected pattern and extent of development resulting from three alternate agricultural land protection policies were compared, and the likely impact on natural areas and farmland was assessed. The results reveal that if current farmland is not protected from exurban development, 73% of all Sonoma County’s remaining core forest could be comprised of edge habitat (within 500m of development) by 2010, and as much as 12% of existing farmland will be developed. We demonstrate that some farmland protection policies can have unintended consequences for forest conservation due to increases in exurban residential development. This research represents a real-world application of a new model that can assist planners to assess the impact of zoning and subdivision controls on land conservation where exurban expansion is a concern.