Print PageUnderstanding the impacts of disturbance and recovery on evapotranspiration and productivity is essential for the accurate prediction of water yields and carbon storage in forest ecosystems. We used eddy covariance and meteorological measurements to quantify energy exchange, evapotranspiration (Et), gross ecosystem production (GEP) and water use efficiency (WUE) in three representative upland forest stands in the New Jersey Pinelands that were either defoliated by Gypsy moths (Lymantria dispar L.) or burned in prescribed fires during the study period. Ecosystem WUE was estimated as GEP/Et during dry canopy conditions in the summer.
Results/Conclusions
Seasonal changes in leaf area display had a major effect on the partitioning of available energy (Rnet – G) into latent (LE) and sensible heat fluxes, and the effects of defoliation, prescribed fire, and drought were all observed in the relationship between LE and Rnet - G. Summer daily Et averaged 4.1 ± 1.5, 3.7 ± 1.4 and 4.1 ± 1.5 mm day-1 at the oak-pine, pine-oak, and pine-scrub oak stands during undisturbed periods, but only 2.2 ± 0.9 mm day-1 during defoliation at the oak-pine stand, and 2.4 ± 0.9 and 3.0 ± 0.9 mm day-1 following spring fires at the pine-oak and pine scrub oak stands, respectively. WUE was still lower than pre-defoliation periods two years after complete defoliation of the oak-pine stand. In contrast, WUE was greater than pre-disturbance periods one year following the prescribed fire at the pine-scrub oak stand. Averaged across all stands and years, annual Et was 608 mm yr-1, ca. 53% of incident precipitation, which is similar to long-term averages reported in other studies of the Pinelands. Maximum seasonal LAI explained 77 % of the variation in annual Et and 86% of the variation in annual GEP across all stands and years.
