Sugar Maple Decline Following Defoliation by the Forest Tent Caterpillar.

Defoliation has been suggested as a significant stressor of forest stands that may incite decline disease of sugar maple (Acer saccharum: Marsh; Manion 1991; Houston 1992). The recent outbreak (2002-2007) of forest tent caterpillar (Malacosoma disstria: Hübner; FTC) in the northeastern U.S. offered the opportunity to test if defoliation exacerbated forest damage (dieback, mortality, and loss of vigor), and to determine the site variables that predisposed the stands to damage. We measured 51 North American Maple decline Project (NAMP) stands in New York and Vermont in Summer 2007. Mortality (p=0.04) and poor vigor (p=0.01) were significantly higher in stands defoliated by FTC, and dieback neared significance (p=0.07). Growing-season soil moisture during the outbreak, indicated by Palmer’s Z-index, and defoliation measured in 2006 were the most significant predictors of forest damage. Mean annual temperature during the outbreak and site microrelief were also important predictors. We present the results of our multiple regression equations for stand dieback, mortality, and vigor in tables that can be used by forest managers to evaluate the vulnerability of their sugar maple stands to decline following defoliation by FTC.