GROWTH REDUCTION AND MORTALITY OF SPRUCE CAUSED BY THE EUROPEAN SPRUCE SAWFLY, GILPINIA HERCYNIAE (HTG.) (HYMENOPTERA: DIPRIONIDAE)

Abstract

The severe outbreak of the European spruce sawfly, Gilpinia hercyniae (Htg.), in the Gaspe Peninsula (3) , continued for about ten years following its discovery in 1930. During this period other outbreaks of shorter duration developed in other regions of Quebec and in New Brunswick. The general extent of the damage has been reported in several papers (1, 2, 3, 5,). The purpose of this paper is to show how the defoliation affected the growth of surviving white spruce, Picea glanca (Moench) Voss, and of black spruce, P, mariana (Mill.) B.S.P., and to indicate the final extent of the damage several years after the end of the outbreak. As some of the stands investigated had been affected by a previous outbreak of the spruce budworm, Cbo~istoneura fumiferana (Clem.), comparisons are made of the injury caused by the two defoliators. Reference is also made to the eastern spruce beetle, Dend~octonus piceaperda Hopk., since an outbreak of this species occurred simultaneously with that of the sawfly in the Gaspe. This study is based principally on observations in three districts: the Cascapedia and Ste. Anne watersheds in the Gaspe Peninsula; Park Reserve Township, Kamouraska County, P.Q.; and Young's Brook, York County, N.B. Data on defoliation and mortality were obtained by annual observations on 73 semi-permanent cruise lines, totalling 32 acres, and on 23 permanent D ~ O ~ S. I The lines were cruised annually at about the same points on five drainages near the centre of the Gaspe Peninsula from 1932 to 1938. In 1938 permanent lines were established by marking every tree over 4.5 inches D.B.H. These trees were re-tallied each vear until 1947. Thev ran across the vallevs and up the slopes as far as the dhite spruce extended. The plots ranged In size from 0.2 to 2.8 acres and were established between 1932 and 1938 in both white spruce and black spruce types. All trees above 3.5 inches D.B.H. I were numbered and examined annually. Estimates of defoliation were made from the ground and these were checked by a Inore critical examination of felled trees. The increment loss of surviving trees was determined by measuring the width of annual rings of sections and cores. Thirty trees were sectioned at lo-foot intervals fro& 2 feet above the butt swell to about 7 feet from the