DIEBACK AND GROWTH LOSS OF SUGAR MAPLE ASSOCIATED WITH DEFOLIATION BY THE FOREST TENT CATERPILLAR

Sugar maple (Acer saccharum Marsh.) stands in southwestern Ontario experienced a forest tent caterpillar (Malacosoma distria Hbn.) infestation in the mid 1970s. The defoliation was considered a key factor that accounted for an upsurge in the amount of dieback damage that occurred in 1977 and 1978 in the area affected by the caterpillar. Growth loss, dieback and food reserve relationships were examined. In the years 1977-1979 defoliated maples grew at a reduced rate that averaged 39.5% less than that for maples in stands adjacent to the infestation. Trees that recovered from the influence of defoliation were compared with those that died or continued to experience dieback. Those that recovered had greater food reserves in 1978 and 1979, on the basis of sapwood starch content, than did maples that declined. Stands showed good recovery from dieback. Dominant and codominant maples that had less than 40% branch mortality in 1978 generally recovered to good vigor and crown shape by 1980.