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Effects of aspen budbreak phenology and leaf chemistry on levels of defoliation during a forest tent caterpillar outbreak.
Donaldson, Jack*,1, Lindroth, Rick1, 1 University of Wisconsin-Madison, Madison, Wisconsin
ABSTRACT- Early successional forests of northern Wisconsin experience periodic eruptions of forest tent caterpillars (FTC) (Malacosoma disstria), during which expansive areas of aspen- (Populus tremuloides) dominated forest experience nearly complete defoliation for up to 3 successive years. Previous observations have shown aspen clones to vary in susceptibility to defoliation during FTC outbreaks. In 2001, coincident with a major FTC outbreak in much of northern Wisconsin, we conducted an observational field study in an effort to link clonal variability in defoliation with budbreak phenology and leaf chemistry. Thirty-four clones were identified based on phenology and leaf and bark morphology. Early in the season, clear differences in percent defoliation were apparent among clones. Budbreak phenology varied by as much as three weeks and explained 23 percent of the variation (R2 = 22.9). The relationship was quadratic, with clones developing both early and late relative to egg hatch showing significantly less defoliation. Defoliation levels were not related to leaf chemical constituents including nitrogen, condensed tannins, and phenolic glycosides. By mid-June, during the final instar of FTC development, all but one clone were completely defoliated. During intense episodic eruptions of outbreak folivores such as FTC, aspen chemical resistance mechanisms appear to break down. Mechanisms such as tolerance to herbivory, which allow recovery from defoliation, may be particularly important during such events.
KEY WORDS: aspen, forest tent caterpillar, resistance, outbreak