Abstract. We used eddy covariance and meteorological measurements to estimate net ecosystem exchange of CO2 (NEEc), gross ecosystem production (GEP), evapotranspiration (Et), and ecosystem water use efficiency (WUEe) in three upland forests in the New Jersey Pinelands that were defoliated by Gypsy moth (Lymantria dispar L.) or burned using prescribed fire. Before disturbance daytime NEEc, daily GEP and daily WUEe during the summer were greater at an oak-dominated stand than at mixed or pine-dominated stands. Both defoliation and prescribed burning reduced stand leaf area and canopy nitrogen content. At the oak stand, daily GEP during the summer was only 35% of pre-disturbance values during complete defoliation in 2007, and then averaged 71% and 78% of pre-defoliation values one and two years following complete defoliation. Prescribed fires conducted in the dormant season at the mixed and pine-dominated stands reduced daily GEP during the summer to 79 and 82% of pre-disturbance periods during the following growing season. Daily GEP during the summer was a strong function of N content in foliage at the oak and mixed stands, but a weaker function at the pine-dominated stand. Ecosystem WUEe, calculated as GEP/Et during dry canopy conditions in the summer, was reduced to 60% and 46% of pre-disturbance values at the oak and mixed stands during defoliation, while prescribed fire had little effect on WUEe. Overall, our results indicate that WUEe during recovery is dependent on both the type and time since disturbance.
Response of gross ecosystem productivity, light use efficiency, and water use efficiency of Mongolian steppe to seasonal variations in soil moisture
