Tuesday, August 3, 2010
Exhibit Hall A, David L Lawrence Convention Center
Background/Question/Methods Gypsy moth (Lymantria dispar L.) is an abundant invasive insect in North America, and currently occupies only ca. 23% of its potential range. Climate change will potentially result in a large range expansion of Gypsy moth, thus defoliation and subsequent mortality will likely affect large forested regions in the future. We used biometric, eddy covariance, and nitrogen (N) deposition and throughfall measurements to evaluate the impacts of Gypsy moth on carbon, hydrologic and N cycles in an Oak-pine stand in the New Jersey Pine Barrens that was completely defoliated in 2007 and partially defoliated in 2008. This stand occurs on sandy, low N status soils, and is typical of many Oak-pine stands on the Atlantic Coastal Plain.
Results/Conclusions Nitrogen flux to the forest floor as frass, unconsumed leaf fragments, and unretained N in throughfall during complete defoliation of the Oak-pine stand from June 1 to July 15th 2007 totaled 29 kg N ha-1, representing 35% of the annual aboveground N requirement. Mass loss from frass and leaf fragments in litterbags was 60 ± 5 % and 45 ± 13% over a 3-month period, respectively, and N release was equally rapid. Decomposition rates of these substrates were ca. 6 and 4.5 times greater than mass loss from typical overstory Oak litter. Evapotranspiration (ET) during the defoliated period was only 92 mm, and compared to an average ET of 193 mm during the same period in previous, undefoliated years, results suggested that twice the amount of water drained to subsurface soil layers and the water table. Although maximum seasonal leaf area (LAI) recovered to 3.4 ± 0.7 and 4.5 ± 0.8 in 2008 and 2009, respectively, N content of foliage was reduced post-defoliation. Considerable mortality of overstory oaks occurred, and by late 2009, 15% of the individuals and 25% of oak basal area were dead. Although the ultimate causes of oak mortality are unknown, our data indicate that N stress potentially contributes to the high levels of tree mortality observed in heavily defoliated stands.
Results/Conclusions Nitrogen flux to the forest floor as frass, unconsumed leaf fragments, and unretained N in throughfall during complete defoliation of the Oak-pine stand from June 1 to July 15th 2007 totaled 29 kg N ha-1, representing 35% of the annual aboveground N requirement. Mass loss from frass and leaf fragments in litterbags was 60 ± 5 % and 45 ± 13% over a 3-month period, respectively, and N release was equally rapid. Decomposition rates of these substrates were ca. 6 and 4.5 times greater than mass loss from typical overstory Oak litter. Evapotranspiration (ET) during the defoliated period was only 92 mm, and compared to an average ET of 193 mm during the same period in previous, undefoliated years, results suggested that twice the amount of water drained to subsurface soil layers and the water table. Although maximum seasonal leaf area (LAI) recovered to 3.4 ± 0.7 and 4.5 ± 0.8 in 2008 and 2009, respectively, N content of foliage was reduced post-defoliation. Considerable mortality of overstory oaks occurred, and by late 2009, 15% of the individuals and 25% of oak basal area were dead. Although the ultimate causes of oak mortality are unknown, our data indicate that N stress potentially contributes to the high levels of tree mortality observed in heavily defoliated stands.
