摘要
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.
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.
