Impact of Invasive Insects and Fire on Forest Water Resources
Forest Service scientists quantified water use by forests that were defoliated by gypsy moth or burned by prescribed fire. Defoliation and prescribed fire initially had little effect on overall stand biomass but did reduce leaf area, which altered energy partitioning and reduced evapotranspiration. At the landscape scale, defoliation of about 20 percent of the forest increased ground water input by 7 percent.
Forest Service scientists quantified energy exchange and evapotranspiration in three representative upland forest stands in the New Jersey pinelands that were either defoliated by gypsy moth or burned in prescribed fires. Defoliation and prescribed fire reduced leaf area, altered the partitioning of available energy, and reduced water vapor flux compared with undisturbed periods at the same location.
For all years measured, leaf area accounted for 82 percent of the variability in daily evapotranspiration during the summer at an oak-dominated stand and for 80 percent of the variability at mixed and pine-dominated stands. When averaged across all stands and years, annual evapotranspiration was approximately one-half of incident precipitation (24 inches per year), similar to long-term averages reported in other studies in the New Jersey pinelands.
Gypsy moth defoliation reduced evapotranspiration in the heavily defoliated oak stands by 9 inches per year, and by about 1.5 inches per year across all upland forests, resulting in a 7.3-percent increase in groundwater recharge to the Kirkwood-Cohansey aquifer. This research indicates that nonstand replacing disturbances can have significant, but typically short-term effects on energy partitioning and evapotranspiration at the stand and landscape scales.
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