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Harvard Forest Symposium Abstract 2007

• Title: Carbon dynamics of a temperate forest five years after selective logging
• Primary Author: Frances O'Donnell (Harvard University)
• Additional Authors: John Budney (Harvard University); Daniel Curran (Harvard University); Elizabeth Hammond Pyle (Harvard University); Lucy Hutyra (Boston University); Kathryn McKain (Harvard University); J. William Munger (Harvard University); Steven Wofsy (Harvard University)
• Abstract:

  Rising atmospheric carbon dioxide levels are mitigated by carbon sequestration in the terrestrial biosphere, including temperate forests in the northern hemisphere. Many of the second-growth mixed hardwood forests that cover large parts of eastern North America are significant carbon sinks and are under management that includes harvesting for economic gain. This study examines the effect of a timber harvest typical of the North Quabbin region in north central Massachusetts on the carbon source-sink dynamics of the stand, both annually and cumulatively since the time of harvest. We used plot-based biometric measurements to estimate annual fluxes in the live and dead aboveground carbon pools from 2000 through 2006 in a tract of forest that was selectively logged in 2001. As a control, these measurements were compared to analogous biometric measurements done on an adjacent tract of forest in the footprint of an eddy flux covariance measurement site. We estimated coarse woody debris (CWD) respiration with a linear regression model to compare the dynamics of this pool on the two sites, and tracked the fate of harvested wood by species and timber grade to estimate the annual return of carbon to the atmosphere from removed wood products. Annual carbon storage due to tree growth was reduced after the harvest but has increased steadily since, largely due to increased uptake by trees in smaller diameter classes. There were no significant changes in the coarse woody debris (CWD) pool on the control site, but both the decay class distribution and standing-downed distribution of harvest site CWD were altered. Together, the aboveground carbon pools on the harvest site were a net carbon source in 2001 and a slight sink in 2002-2003. By 2004 the aboveground carbon pools were a sink with a magnitude similar to that on the control site. Cumulatively between 2001 and 2006 the harvested forest was a carbon source of 2.9 MgC/ha. 60% of the harvested wood was sold as firewood, resulting in an immediate flux of carbon to the atmosphere. The carbon released by burning wood for energy is largely offset if it is considered as a substitute for fossil fuels. 3.7 MgC/ha was stored in wood products and landfills, though this storage is partially offset by fossil fuel use in harvesting, transport, and production of wood products. We found a net carbon sink of 8.4 MgC/ha in relation to the atmosphere five years after the harvest when we considered wood products and on-site carbon pools together, compared to a net uptake of 16.3 MgC/ha on the control site over the same time period.

• Research Category: Forest-Atmosphere Exchange