Effect of throughfall variability on recharge: application to hemlock and deciduous forests in western Massachusetts

Vegetation canopies intercept and redistribute precipitation in space. Although throughfall patterns are challenging to correlate with plant characteristics, many studies have shown that the spatial patterns persist through time. This persistence leads to wet and dry spots that can affect recharge, transpiration, and other nonlinear ecohydrologic and biogeochemical processes. A stochastic framework is used to determine the effect of throughfall variability on hydrologic fluxes. Throughfall variability increases and concentrates recharge, and the magnitude of the effect depends on the character of throughfall variability along with characteristics of climate, soil, and vegetation. This framework is also used to explore specific differences in summertime recharge between stands of deciduous trees (birch, maple, and oak) and eastern hemlock (Tsuga canadensis). Throughout the eastern United States, the invasive hemlock woolly adelgid poses a significant threat to hemlock forests, and replacement of hemlock forests by other species has the potential to alter hydrologic fluxes and other processes. Field investigations in 2009 and 2010 indicate that, relative to deciduous stands, hemlock canopies intercept more water and tend to produce dry rather than wet spots. Although deciduous stands produce more throughfall, model results indicate that differences in canopy interception are outweighed by large differences in peak transpiration rates, and predictions of summertime recharge are lower in deciduous forests than in hemlock. Copyright (C) 2011 John Wiley & Sons, Ltd.