We used eddy covariance and meteorological measurements to estimate net ecosystem exchange of CO<sub>2</sub> (NEE<sub>c</sub>), gross ecosystem production (GEP), evapotranspiration (Et), and ecosystem water use efficiency (WUE<sub>e</sub>) in three upland forests in the New Jersey Pinelands that were defoliated by Gypsy moth (<i>Lymantria dispar</i> L.) or burned using prescribed fire. Before disturbance daytime NEE<sub>c</sub>, daily GEP and daily WUE<sub>e</sub> 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 WUE<sub>e</sub>, 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 WUE<sub>e</sub>. Overall, our results indicate that WUE<sub>e</sub> during recovery is dependent on both the type and time since disturbance.
Clark, K. L., Skowronski, N. S., Gallagher, M. R., Renninger, H., & Schäfer, K. V. R. (2014). Contrasting effects of invasive insects and fire on ecosystem water use efficiency. Biogeosciences, 11(23), 6509–6523. https://doi.org/10.5194/bg-11-6509-2014