Distribution and Effects of Jack-pine Budworm Defoliation
A defoliation classification in which new and old needles were considered separately was devised for studies on the distribution and effects of defoliation in Minnesota by the jack-pine budworm (Choristoneura pinus Free.). During periods of light defoliation, regressive trees were more heavily defoliated than progressive and provisional trees. During medium defoliation all crown classes were affected about equally. Expressed in area of the annual rings, the summerwood ring area for the defoliation year 1956, and both the springwood and summerwood rings in 1957 and 1958 were correlated with the 1956 defoliation. Growth was reduced in light, medium, heavy, and very heavy defoliation classes in the 1956 summerwood by 32, 60, 83, and 99 percent; the 1957 springwood by 54, 76, 99, and 99 percent; and the 1957 summerwood by 27, 44, 73 and and 91 percent. In 1958, in the heavy and very heavy defoliation classes springwood was reduced by 52 and 86 percent and summerwood by 20 and 86 percent. Top defoliation causes trees to develop rounded or flat tops. Medium and heavy defoliation in a young pole-sized stand caused 2 to 6 percent mortality in progressive and provisional trees and 9 to 13 percent in regressive trees during the first 2 years after defoliation. From 29 to 44 percent of almost completely defoliated trees died. Budworms often severely damage male and female cones. Trees heavily defoliated in 1957 produced almost no male cones for 1959 whereas 30 to 60 percent of the tips of non- or lightly-defoliated trees produced 1959 male cones.
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Document Type: Journal Article
Affiliations: Professor of Forestry, Univ. Minnesota, St. Paul.
Publication date: 1963-06-01
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