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Lucash ESA 2012 Abstract

posted Apr 20, 2012, 7:18 AM by Melissa Lucash   [ updated Apr 20, 2012, 7:35 AM by Robert Scheller ]

Nitrogen Cycling in the New Jersey Pine Barrens as a Consequence of Insect Outbreaks and Wildfire

Contributing authors: Melissa Lucash,, Robert M. Scheller, Alec Kretchun, Kenneth Clark, John Hom and Samantha Chapman

Disturbances, like insect outbreaks and wildfire, can cause large reductions in forest productivity and carbon sequestration in the short term, but it is unclear how these disturbances interact over the long-term.  Both fire and insect defoliation affect productivity and alter species composition, but they also affect nitrogen cycling through changes in litter quality and quantity, uptake, retranslocation and leaching.  In this study, we estimated the effects of gypsy moth defoliation and fire on above- and belowground biomass, carbon cycling and nitrogen cycling of vegetation and soil in the New Jersey Pine Barrens (NJPB) over the next 50 years.  To forecast these changes in ecosystem processes, we used the LANDIS-II succession and disturbance model combined with the CENTURY extension to simulate changes in seven forested ecoregions.  The model was calibrated and validated using net ecosystem exchange and aboveground productivity from three eddy flux towers in the NJPB.  Our results suggest that gypsy moth defoliation decreased total biomass but increased the rate of above- and belowground production when compared to prescribed fire.  Gypsy moth defoliation increased total ecosystem N since both leaf and soil N increased with defoliation.  Though total N increased, the amount of available N declined with defoliation.  Declines in available N were probably due to leaching, since N leaching doubled with defoliation, while N mineralization only increased by 25%.  Though average rates of N uptake and retranslocation were unaffected by defoliation, the variation in N uptake and retranslocation were significantly higher with gypsy moths.  Overall, defoliation by gypsy moths lowered tree biomass and had a significant effect on N cycling in the NJ Pine Barrens.  Disturbances, like insect defoliation and wildfire are important for understanding long-term changes in nitrogen cycling and forest productivity under a changing climate.  
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