Predicting Hemlock Woolly Adelgid Winter Mortality in Connecticut Forests by Climate Divisions

Abstract

Abstract Hemlock Woolly Adelgid (HWA) is a devastating non-native pest of North American Tsuga canadensis (Eastern Hemlock) and Tsuga caroliniana (Carolina Hemlock). I analyzed 15 years of data collected during the period 2000–2015 to determine important winter variables influencing HWA mortality in the 3 Connecticut climatic divisions. Absolute minimum daily winter temperature, the number of subzero days (temperature drops below -17.8 °C [0 °F]), and a new interaction variable—negative degree days (NDD)—were identified as significant predictors of HWA winter mortality. The absolute minimum daily winter temperature was the most critical factor. Minimum daily winter temperatures of -24 °C, 5.5 subzero days, and -130 NDD in Division 1(Northwest); -22.4 °C, 6 subzero days, and -100 NDD in Division 2 (Central); and -21.2 °C, 2.6 subzero days, and -45 NDD in Division 3 (Coastal) resulted in 90% HWA mortality. Patterns of HWA winter mortality in coastal Division 3 were distinct from the interior and suggest col...