The urbanization of second-growth forests in the Pacific Northwest: Land-use change, fragmentation, and policy implications

This dissertation discusses three related studies that examine the effects of urbanization in King County, Washington, in the context of Urban Ecology. The first study quantified land cover change and explored the effects of growth management policies on urban fringe areas. Results showed that from 1974-1998, 23% of the study area was converted from agriculture and forests to suburban and exurban development. The land cover study verified the conceptual model of Alberti et al. (2003) that describes the interaction of human and natural systems in human-dominated environments: primary drivers of observed changes in landscape pattern were policies of low-density residential development outside cities. Although urban density increased, low-density residential development outside urban areas constituted 72% of land developed. The effects of these changes were substantial: wildland forest decreased by 19%; forests in residential areas were reduced to isolated fragments too small to contain interior habitat.;To examine effects of fragmentation on forests, the second study compared understory vegetation, forest structure, and effects of fragment size and time since isolation in 52 fragments of second-growth forest in urban, suburban, and exurban landscapes. The fragmentation study confirmed the presence of an urban to exurban gradient of effects: composition of understory vegetation and forest structure changed gradually from urban to exurban areas. The fragmentation study confirmed expected impacts of fragmentation and urbanization on forests: effects were most pronounced in urban fragments. Urban fragments had significantly more exotic species, exotic cover, and exotic tree seedlings, and were structurally simpler, than exurban fragments. However, there were few effects of fragment size or time since isolation.;The third study explored management of forest fragments in parks by analyzing comprehensive park and vegetation management plans (VMPs) for five cities. Forest management policies described in comprehensive park plans focused on enhancement and restoration of natural vegetation and control of exotic species, generally ignoring forest structure. VMPs had only general goals for forest management and were not consistent between or within cities. VMPs discussed control of exotic species, enhancement of native forest species (mainly trees and shrubs) and forest structure, and post-restoration maintenance/monitoring. Level of detail varied among plans.