Ecologists have recently come to recognize that natural disturbances are an inherent part of the ebb and flow of forests, yet understanding of forest response to natural disturbances is patchy at best. There exists a good understanding of forest responses to fire, insect outbreaks, and hurricanes, but a poor grasp of forest response to ice storms, floods, and tornadoes. This project will examine forest damage caused by three long-track tornadoes that were part of the record-setting April 27-28, 2011 tornado outbreak. One tornado passed through the western section of Great Smoky Mountains National Park in southern Tennessee, and the other two through Chattahoochee National Forest in northern Georgia. The core goals of the project are to develop detailed inventories of the forest damage severity along these tornado tracks, and use that severity information to test three ecological models that hypothesize about how forests respond to different severity of disturbance. The study needs to begin promptly in order to accurately measure the severity of the disturbance and to identify the tree species that were blown down before they are salvage-logged or decompose. Once forest damage severity has been characterized along the tornado tracks, the recovery of the forests will be monitored, to see which model most accurately predicted the recovery of the forest. The model whose predictions are most accurate will be confirmed as the best understanding of how forests respond to wind disturbance.
Knowledge of how forests respond to disturbance is important to society for a number of reasons: 1) guide management decisions, such as whether or not to log downed timber after disturbance; 2) project the likely future species composition after disturbance, i.e. will the tornado blowdown areas in 50 years be mostly cherry and maple, or mostly birch and hemlock?; 3) improve projections of carbon fixation in regrowing forests, a vitally important service provided by forests in a high-CO2 atmosphere; and, if future climate change brings increases in extreme weather events, 4) allow forecasts of how forests will change under the altered disturbance regime.
for DEB-1143511, "Topographic variation in tornado blowdownseverity and consequences for forest reorganization" Awarded July 2011 Grantee: Chris J. Peterson, University of Georgia This RAPID grant allowed the PI to conduct benchmark sampling soon after a catastrophic windstorm to Southern Appalachian forests, and establish inventory locations that will be monitored for years to come, to test theories of the impact of disturbance on forest succession. The two major theories being tested are called the Cusp Catastrophe Theory (originating with Lee Frelich and Peter Reich), and the Legacies or Complexity theory (mostly based on work by Jerry Franklin). These theories predict that forest species composition is strongly related to severity of disturbance. This research is testing the theories by using numerous inventory plots established in 2011 shortly after a tornado passed through mixed pine-oak forest of Chattahoochee National Forest in northern Georgia, and pine-oak forest of the western Great Smoky Mountains National Park in eastern Tennessee. In >100 plots of 20 m x 20 m, we have measured pre-disturbance forest composition, as well as quantified disturbance severity in each plot as the proportion of pre-disturbance basal area (the cumulative area of cross sections at the base of all trees in the plot). This initial severity estimation will allow us to henceforth monitor the recovery of each plot for many years to come; the test of the theories will be to record species composition during this process of recovery, to see if the predictions of the Cusp and Legacy theories actually happen. The Broader Impacts of this work have several components. First, the detailed assessment of severity of damage from the 2011 tornado adds to a growing knowledge of the severity of natural disturbances; forest managers in the large areas of public forest land in the Southern Appalachian can use the natural severity we document as guidelines to limit the severity of impacts of management actions (e.g. harvesting, thinning, etc.). Second, this work will provide a snapshot of the current picture of forest wind disturbance and initial recovery, for comparison in coming decades under a changing climate. Third, human resource development has been substantial; this project has involved > 15 undergraduates in various aspects of field work, data analyses, and presentation of findings at scientific meetings; these undergrads have included 5 minorities and 7 women. Several have subsequently continued on to graduate work in science. A different but equally valuable aspect of human resource development has been the forging of links and collaborations; this work has allowed us to work closely with personnel from three federal agencies (U.S. Forest Service, National Park Service, and U.S. Fish and Wildlife Service), and to establish a continuing collaboration with a collague at University of North Carolina – Asheville. Finally, our research results are of particular interest to Great Smoky Mountains National Park scientific staff because the park scientists are stretched thin and do not have time for their own detailed studies of wind disturbance and are thus keenly interested in any of our studies of the recovery of Park forests following the 2011 tornado.
