Relating jack pine budworm damage to stand inventory variables in northern Michigan

Abstract

Stand-level mortality and top kill from a 1991–1993 jack pine budworm (Choristoneurapinuspinus Freeman) outbreak were surveyed annually in the Raco Plains area of the Hiawatha National Forest in Michigan's Upper Peninsula from 1992 to 1994. Defoliation was visually estimated and percentage of trees killed or top killed was determined in 104 stands. In 1994, tree mortality attributable to the outbreak averaged 8% and 17% of trees had dead tops. Current stand inventory data, including age, site index, basal area, and size, were acquired from the Hiawatha Forest. Stands were grouped on the basis of inventory variables used for jack pine management in the Lake States region of the United States. Differences in tree mortality and top kill between groups, and associations between tree mortality and inventory variables, were evaluated. Tree mortality was greater in overmature stands and in overstocked stands, but stand size had little effect. Contrary to expectations, mortality was lower on poor sites with low site index values than on better sites with higher site index values. Mortality was not related to abundance of open-grown, full-canopied wolf trees or to abundance of trees infected with pine gall rust (Endocronartiumharknessii (J.P. Moore) Y. Hiratsuka (=Peridermiumharknessii J.P. Moore)). Amount of top kill was related to defoliation severity and was higher in overmature and understocked stands. Top kill was not strongly associated with amount of tree mortality or with inventory variables.