Carbon consequences of land cover change and expansion of urban lands: A case study in the Seattle metropolitan region

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 lowland Seattle Statistical Metropolitan Area (MSA) region as a case study, this paper explores the consequences of the past land cover changes on vegetative carbon stocks with a combination of direct field measurements and a time series of remote sensing data. Between 1986 and 2007, the amount of urban land cover within the lowland Seattle MSA more than doubled, from 1316 km2 to 2798 km2, respectively. Virtually all of the urban expansion was at the expense of forests with the forested area declining from 4472 km2 in 1986 to 2878 km2 in 2007. The annual mean rate of urban land cover expansion was 1 ± 0.6% year−1. We estimate that the impact of these regional land cover changes on aboveground carbon stocks was an average loss of 1.2 Mg C ha−1 yr−1 in vegetative 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 emissions budgets. 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 future land development and conservation strategies.

► Between 1986 and 2007, the amount of urban land cover within the lowland Seattle Metropolitan Statistical Area more than doubled from 1316 km2 to 2798 km2, respectively.
► The impact of the regional urban expansion on aboveground carbon stocks is an average loss of 1.2 Mg C ha−1 yr−1 in vegetative carbon stocks.
► The vegetative carbon losses from urban expansion correspond to nearly 15% of the lowland regional fossil fuel emissions.