Comparing and predicting forest stand susceptibility to gypsy moth

Abstract

One hundred and sixty-eight forest stands in the northeastern United States with different histories of defoliation and responses to defoliation by the gypsy moth were compared by principal-components analysis (PCA) ordinations. The ordinations were based on tree structure-feature variables. PCA ordinations separated stands into meaningful groups that historically have been either susceptible or resistant to prolonged gypsy moth infestation. The best separation of resistant and susceptible stands occurred when the structure-feature variables were measured separately for tree species in different gypsy moth food-preference classes. Tree mortality after defoliation often was greater in the resistant wet bottom and mesic slope and ridge stands than in the susceptible dry ridge and sand stands. Our ordinations suggest that some stands, as a consequence of high oak mortality, may now be more resistant than before.