Wednesday, August 5, 2009
Exhibit Hall NE & SE, Albuquerque Convention Center
Background/Question/Methods Understanding mechanisms underlying recovery following disturbance are essential for the accurate prediction of carbon and nitrogen dynamics in forest ecosystems. We studied the recovery of carbon (C) and nitrogen (N) cycling following three major disturbances in pine and oak-dominated forests on the Atlantic Coastal Plain; clearcutting, complete insect defoliation, and prescribed fire. We measured net ecosystem exchange of CO2 using eddy covariance and calculated ecosystem respiration (Reco) and gross ecosystem production (GEP), and tracked understory and overstory productivity, LAI and N dynamics using biometric measurements during and following disturbance events. Leaf, stem, litterfall, frass, litterbag, and soil samples were analyzed for N content.
Results/Conclusions At all stands, annual Reco varied by less than 16% pre- and post-disturbance, with the greatest increase associated with the most intense disturbance (+291 g C m-2 yr-1 following clearcutting). GEP closely tracked the recovery of leaf area of understory vegetation, which increased from an LAI of < 0.1 to 3.0 in 6 months following clearcutting, from < 0.2 to 0.8 in stands defoliated by Gypsy moth (Lymantria dispar L.), and from < 0.1 to 1.4 in burned stands, and accounted for 25 % to 100 % of total LAI within one year following disturbance. Disturbance also impacted internal N cycling; for example, defoliation increased N flux in annual litterfall by ca. 56%. However, N pools and N mineralization in mineral soil were nearly unaffected by defoliation, because of storage on the forest floor. Our results indicate the importance of rapid responses of understory vegetation and the stability of detrital pools in the recovery of C and N cycling following disturbance in these forests.
Results/Conclusions At all stands, annual Reco varied by less than 16% pre- and post-disturbance, with the greatest increase associated with the most intense disturbance (+291 g C m-2 yr-1 following clearcutting). GEP closely tracked the recovery of leaf area of understory vegetation, which increased from an LAI of < 0.1 to 3.0 in 6 months following clearcutting, from < 0.2 to 0.8 in stands defoliated by Gypsy moth (Lymantria dispar L.), and from < 0.1 to 1.4 in burned stands, and accounted for 25 % to 100 % of total LAI within one year following disturbance. Disturbance also impacted internal N cycling; for example, defoliation increased N flux in annual litterfall by ca. 56%. However, N pools and N mineralization in mineral soil were nearly unaffected by defoliation, because of storage on the forest floor. Our results indicate the importance of rapid responses of understory vegetation and the stability of detrital pools in the recovery of C and N cycling following disturbance in these forests.
