Estimated biomass and carbon committed to decomposition in a north Georgia 2011 tornado swath

Background/Question/Methods

Forest disturbances constitute one of the major challenges to projections of future carbon cycling in North America.  If, as some predictions suggest, rates or sizes or intensities of forest disturbances increase under a warmer climate, the current carbon sink in eastern U.S. forests could become a carbon source to the atmosphere.  Consequently, both regional and global carbon cycle estimates need better knowledge of biomass and carbon committed to decomposition after major forest disturbances.  We have initiated a stand and landscape-scale study of forest damage in two out of the hundreds of tornadoes that struck the southeastern U.S. in late April, 2011.  Data in hand thus far is focused on a 600-ha section of a tornado swath across Chattahoochee National Forest in northern Georgia.  We surveyed individual tree sizes and types of damage in 35 plots (0.04 ha each). 

Results/Conclusions

In these plots, treefall biomass (i.e. trees uprooted or snapped) ranged from 85 to 27,630 kg; converted to carbon and scaled up to hectares, damages ranged from 1.26 to 345.4 Mg ha^-1, with a mean of 91.76 Mg C ha^-1.  Landscape-scale analyses of aerial photos are ongoing, but rough estimates indicate the tornado damage swath was generally ~ 500 m wide, and was ~ 45 km long (totaling approximately 2,250 ha).   If forest damage was similar to that of the study site across just half of the tornado track (allowing for ‘skipping’), we estimate that 0.103 Tg of carbon was committed to decomposition by this tornado.  Further scaling up to consider the entire tornado outbreak of April 2011 will require landscape-scale analyses of multiple tornado tracks, but will provide the first quantitative estimate of how tornado wind disturbance to forests may impact carbon cycling, and allow comparison to the well-studied impacts of Hurricane Katrina.