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A forest inventory of Baxter State Park, Maine, was done during the summer and fall of 1983 to study the patterns of mortality in balsam fir and in the red-black spruce complex during an uncontrolled spruce budworm outbreak. The volume of trees that died during the outbreak was estimated at 40% of the original quantity. Fir mortality was consistently greater than that of spruce. The percentage mortality of spruce was always greater in the higher elevation zone than in the lower elevation zone. Percentage mortality of fir and spruce showed inconsistent patterns in relation to the proportion of hardwood species basal area and to the proportion of fir basal area in a stand. However, those mortality patterns tended to be pronounced when the overall tree mortality was relatively high. Hypotheses on the mechanisms producing the tree mortality patterns during a budworm outbreak were summarized and observed tree mortality patterns were then interpreted according to those hypotheses. Most observed patterns could be explained by more than one hypothesis. It was suggested that complex processes were responsible for developing certain tree mortality patterns, and a deductive method based on the simple observations would not reveal the true mechanisms.
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Maine Agricultural Experiment Station
spruce budworm, Baxter State Park
Osawa, A., C.J. Spies III, and J.B. Dimond. 1986. Patterns of tree mortality during an uncontrolled spruce budworm outbreak in Baxter State Park, 1983. Maine Agricultural Experiment Station Technical Bulletin 121.