Land cover change in the Seattle metropolitan region: An examination of spatio-temporal changes and the carbon consequences of urbanization

Understanding the role humans play in modifying ecosystems through changing land cover is central to addressing our current and emerging environmental challenges. In particular, the consequences of urban growth and land cover change on terrestrial carbon budgets is a growing issue for our rapidly urbanizing planet. Using the Seattle urbanizing region as a sample case study, this paper explores the consequences of the past land cover changes on vegetative carbon stocks. Between 1986 and 2007, the amount of urban land cover within the lowland Seattle Metropolitan Statistical Area more than doubled, from 1,316 km2 to 2,798 km2 (from 17.3% to 37.4%), respectively. Virtually all of the urban expansion was at the expense of low elevation forests with the forest area declining from 4,472 km2 (58.9%) in 1986 to 2,878 km2 (38.5%) in 2007. The annual mean rate of urban land cover expansion was 1 ± 0.6 % year-1, with a mean population density change of 1.6% yr-1 between 1980 and 2000. A first order estimate of the impact of these regional land cover changes on aboveground carbon stocks is an average loss of 1.2 Mg C ha-1 yr-1 in terrestrial carbon stocks. These carbon losses from urban expansion correspond to nearly 15% of the lowland regional fossil fuel emissions making it an important, albeit typically overlooked, term in regional carbon budgets. Urbanization is an important driver of land use change and can result in significant emissions. As we plan for future urban growth and strive for more ecologically sustainable cities, it is critical that we understand the past patterns and consequences of urban development to inform our future land development and conservation strategies. Map of the lowland Seattle Metropolitan Statistical Area land cover in 1986 and 2007, with the change in total estimated aboveground carbon stocks between 1986 and 2007. Annualized carbon emission and change in terrestrial carbon stocks in Seattle MSA between 1986 and 2007 Annualized emissions estimates for the low land Seattle MSA (< 500m). MSA region based on Vulcan reported fossil fuel emissions (Gurney et al. 2009) and land coverchange analysis (average annual changes from 1986 to 2007).