US: The carbon sink capacity of forests in the contiguous US reduced by 36 percent due to natural and human-caused disturbances between 1992 and 2001, according to researchers from the University of New Hampshire and the US Department of Agriculture Forest Service.
Daolan Zheng and his colleagues used remote sensing data combined with ground-based inventory data and identified spatial patterns of carbon sink/source dynamics associated with three major disturbances – land cover change, forest harvesting and wildfires. They analysed the roles of growth, disturbance and land-cover change across the contiguous 48 states of the US, highlighting regional differences that are important both for ecological interpretation and policy implications.
“Although both the Southern region and the greater Pacific Northwest region of the US were large pre-disturbance sinks, (in the time period of our study) the Southern region was a small net carbon source whereas the greater Pacific Northwest region was a strong net sink,” said Zheng. “Our approach is to consider gross changes in forest cover, such as afforestation versus deforestation, rather than the net change approach currently used in the US forest greenhouse-gas inventory.”
According to Zheng, this was the first time that the carbon effects from these different disturbances had been determined using a consistent approach across the lower 48 states. The researchers estimated that forest-related land-cover change contributed 33 percent of the total effect of reducing the forest carbon potential sink, whereas harvests and fires accounted for 63 percent and 4 percent of the reduction, respectively.
“Because of the large influence of harvesting on forest carbon, these results also indicate the importance of following the fate of carbon in harvested wood when estimating forest carbon and forest carbon changes in US forests,” said Zheng. “However, more research is needed to reduce the uncertainty for the forest carbon estimates, as well as understanding the implications of defining forest by land cover versus land use.”
The researchers published their work in Environmental Research Letters (ERL).