GYPSY MOTH DEFOLIATION EFFECTS ON WATERSHED HYDROLOGY

Forests insects and pathogens (FIPs) cause widespread disturbance in U.S. forests, affecting an area 45 times greater than wildfire and costing $1.5 billion dollars in damage each year. FIPs have important implications for ecosystem processes, including ecosystem-level water cycling. Disturbance and associated vegetation change can increase water yield in catchment basins. Magnitude of water yield increase varies significantly according type of disturbance and catchment vegetation. Gypsy moths are major defoliating insects of eastern North American forests. Since the 1980s populations in southern New England have been largely controlled by a parasitic virus, but a series of dry springs from 2014-2016 is thought to have contributed to an 2015-2018 outbreak. Large scale defoliation events, like the 2015-2018 outbreak can potentially impact evapotranspiration and runoff, critical for water resources in the Northeast. An advanced understanding of northeastern hydrologic systems requires knowledge of how disturbance events, including defoliation, can affect ecosystem hydrology. Prior modeling suggests that FIP disturbance by defoliators (like gypsy moths) causes a significant short-term increase in soil moisture. In this study, Landsat imagery are used to identify extent and location of the 2015-2018 outbreak. Data from Southern New England USGS stream gages are used to identify changes in stream hydrology associated with defoliation of the catchment basins. Initial results show that during defoliation events, the ratio of stream discharge to precipitation increases, supporting increased groundwater infiltration. Shifts in ecosystem hydrology have important implications for runoff, flood risk, and ecosystem stability (including dominant forest type).