The Effects of Defoliation by the Larch Casebearer on the Radial Growth of Tamarack

Abstract

Tamarack (Larix laricina [DuRoi] K. Koch) was severely defoliated by the larch casebearer (Coleophora laricella) in most areas of Quebec during 1979 and 1980. Increment core samples were taken in late September 1982 from 20 tamaracks in each of two stands to determine the effect of defoliation on radial growth. In one stand, the trees were 80% defoliated in 1980 and during this year radial growth was reduced by 52%. Growth returned to predefoliation level the following year when the trees were not defoliated. In the other stand, trees were 60% defoliated in 1979 and 70% in 1980. During these years, radial growth was reduced by 48 and 70% respectively. Growth in this stand had not fully returned to predefoliation level two years after the collapse of the infestation. In both stands, variations in defoliation among trees did not exceed 10% of the average. Key Words: Coleophora laricella, larch casebearer, tamarack, larch, defoliation.