Twenty-five years of sprawl in the Seattle region: growth management responses and implications for conservation

To study the effects of growth management efforts on urban fringe areas in Washington State’s Puget Sound region, USA, this study documents and quantifies transformations in land cover and land-use from 1974 to 1998 for a 474 km2 study area east of Seattle. Geo-referenced aerial photographs (orthophotos) were digitized, then classified, to compare patch patterns (clustered versus dispersed vegetation, remnant versus planted vegetation), size, development type (single-family housing, multi-family housing, commercial) and percent vegetative cover between 1974 and 1998 images. Changes in interior forest habitat and amount of edge were also calculated. The study showed that suburban and exurban landscapes increased dramatically between 1974 and 1998 at the expense of rural and wildland areas. Settled lands became more contiguous while rural and wildland areas became more fragmented. Interior forest habitat in wildland areas decreased by 41%. Single-family housing was the primary cause of land conversion. Current growth management efforts prioritize increasing housing density within urban growth boundaries (UGBs), while limiting densities outside these boundaries. The study demonstrated that housing density has indeed increased within these boundaries, but at the same time, sprawling low-density housing in rural and wildland areas constituted 72% of total land developed within the study area. Therefore, policies to reduce the density of settlement outside urban centers, in part to protect ecological systems, may have unintended environmental consequences. This has implications for those urban areas, both in the United States and in other countries, considering growth management strategies.