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Biogeosciences An interactive open-access journal of the European Geosciences Union
Biogeosciences, 11, 6509-6523, 2014
https://doi.org/10.5194/bg-11-6509-2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
01 Dec 2014
Contrasting effects of invasive insects and fire on ecosystem water use efficiency
K. L. Clark1, N. S. Skowronski2, M. R. Gallagher1, H. Renninger3, and K. V. R. Schäfer3 1Silas Little Experimental Forest, USDA Forest Service, 501 Four Mile Road, New Lisbon, NJ 08064, USA
2Northern Research Station, USDA Forest Service, 180 Canfield St., Morgantown, WV 26505, USA
3Rutgers University, Dept. of Biological Sciences, 195 University Ave., Newark, NJ 07102, USA
Abstract. We used eddy covariance and meteorological measurements to estimate net ecosystem exchange of CO2 (NEE), gross ecosystem production (GEP), evapotranspiration (Et), and ecosystem water use efficiency (WUEe; calculated as GEP / Et during dry canopy conditions) in three upland forests in the New Jersey Pinelands, USA, that were defoliated by gypsy moth (Lymantria dispar L.) or burned using prescribed fire. Before disturbance, half-hourly daytime NEE during full sunlight conditions, daily GEP, and daily WUEe during the summer months were greater at the oak-dominated stand compared to the mixed or pine-dominated stands. Both defoliation by gypsy moth and prescribed burning reduced stand leaf area and nitrogen mass in foliage. During complete defoliation in 2007 at the oak stand, NEE during full sunlight conditions and daily GEP during the summer averaged only 14 and 35% of pre-disturbance values. Midday NEE and daily GEP then averaged 58 and 85%, and 71 and 78% of pre-defoliation values 1 and 2 years following complete defoliation, respectively. Prescribed fires conducted in the dormant season at the mixed and pine-dominated stands reduced NEE during full sunlight conditions and daily GEP during the following summer to 57 and 68%, and 79 and 82% of pre-disturbance values, respectively. Daily GEP during the summer was a strong function of N mass in foliage at the oak and mixed stands, but a weaker function of N in foliage at the pine-dominated stand. Ecosystem WUEe during the summer at the oak and mixed stands during defoliation by gypsy moth averaged 1.6 and 1.1 g C kg H2O−1, representing 60 and 46% of pre-disturbance values. In contrast, prescribed fires at the mixed and pine-dominated stands had little effect on WUEe. Two years following complete defoliation by gypsy moth, WUEe during the summer averaged 2.1 g C kg H2O−1, 80% of pre-disturbance values. WUEe was correlated with canopy N content only at the oak-dominated stand. Overall, our results indicate that WUEe during and following non-stand replacing disturbance is dependent on both the type and time since disturbance.

Citation: Clark, K. L., Skowronski, N. S., Gallagher, M. R., Renninger, H., and Schäfer, K. V. R.: Contrasting effects of invasive insects and fire on ecosystem water use efficiency, Biogeosciences, 11, 6509-6523, https://doi.org/10.5194/bg-11-6509-2014, 2014.
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Eddy covariance and biometric measurements were used to contrast the effects of defoliation by gypsy moth and prescribed fire on net CO2 exchange (NEE) and ecosystem water use efficiency (WUEe) in three forests in the New Jersey Pinelands, USA. Defoliation reduced long-term NEE and WUEe, while prescribed burning had little effect. Our results suggest that WUEe following disturbance is dependent on its impact on the N status of canopy foliage, in addition to time since disturbance.
Eddy covariance and biometric measurements were used to contrast the effects of defoliation by...
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