Abstract
Fossil fuel burning and deforestation have driven dramatic increases in atmospheric CO2 since the industrial revolution. However, forests in the northern temperate region sequester a substantial (~0.6 Pg?yr–1) amount of carbon (C), largely through the regrowth of secondary forests that were originally cleared for timber over one hundred years ago. In the United States, however, some regions are approaching a maximum regrowth as forests are cleared again, this time for suburban and exurban development. Here we explore the effects of such development on C stocks in King County, WA, an area with high forest cover but rapid suburban expansion. We measured soil and biomass C on 18 paired-house/forest lots, and found house lots stored ~80 Mg?C?ha–1 less soil C, and between 130 and 280 Mg?C?ha–1 less above-ground biomass C than adjacent forest lots. Combining soil C losses with estimates of C emissions from forest products yields average C emissions of 130 - 280 Mg?C?ha–1, with the majority of losses occurring at the time of lot conversion. As a comparison, suburban dwellers drive ~30% more than city residents, but this increase in annual emissions from increased driving is 1% - 2.5% of the losses of C associated with converting forests to house lots. If forestland conversion in the Seattle area continues apace, in the coming decades C emissions each year from that land-use conversion will equal ~4% of King County’s 2008 C emissions.
Highlights
Land-use change and the burning of fossil fuels have dramatically increased atmospheric carbon dioxide (CO2) concentrations since the industrial revolution, to a level not seen during the past 650 thousand years (IPCC 2007)
Our data suggest that a pulse of C is released from the soils of a house lot during development that does not re-accumulate over time
The soil C loss associated with lot development is large, roughly 30% - 60% of the aboveground C loss
Summary
Land-use change and the burning of fossil fuels have dramatically increased atmospheric carbon dioxide (CO2) concentrations since the industrial revolution, to a level not seen during the past 650 thousand years (IPCC 2007). As reforestation in some areas reaches a peak, and suburban and exurban development begins to reverse forest regrowth (Wienert 2006; Dwyer et al, 2000), rates of C sequestration may slow. The effects of suburban development on soil and biomass C has only recently been assessed in several regions of the US (Pouyat et al, 2002). Similar results from Larimer County, CO suggest that surface soils in urban lawns can contain as much as 65% more C than shortgrass steppe soils (Kaye et al, 2005), which is not surprising given low organic C in semi-arid systems and the increased growth on lawns in response to water and fertilizer. Whether changes in soil carbon content translates to emissions to the atmosphere is less well understood. The emission C from these soils to the atmosphere may be quite different
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