. Insect and disease conditions in the United States, 1979-83 : what else is growing in our forests?. Forest insects United States; Trees Diseases and pests United States; Plants Disease and pest resistance. 1982 1983. O Areas of visible western spruce budworm defoliation ing beneath mature trees. Larvae disperse from the overstory and feed on the small trees below. Small trees have relatively few needles and shoots and can be seriously deformed or killed by only a few larvae. The mortality of these new trees, coupled with the damage to the cones, can significantly delay natural regeneration,
. Insect and disease conditions in the United States, 1979-83 : what else is growing in our forests?. Forest insects United States; Trees Diseases and pests United States; Plants Disease and pest resistance. 1982 1983. O Areas of visible western spruce budworm defoliation ing beneath mature trees. Larvae disperse from the overstory and feed on the small trees below. Small trees have relatively few needles and shoots and can be seriously deformed or killed by only a few larvae. The mortality of these new trees, coupled with the damage to the cones, can significantly delay natural regeneration, particularly when partial cutting methods leave host trees in the residual overstory. Some small trees sur- vive, however, probably because many larvae dispersing to the forest floor are eaten by insects and small mammal predators. Timber Yield. After 3 or more years of sustained feeding, young stands of Douglas-fir, true firs, and spruce can be almost entirely defoliated, reducing growth both in diameter and height. The tops of some trees are killed, which often results in stem deformity, multiple leaders, or death of the entire tree. In young western larch stands, several years of defoliation deforms the trees' crowns and reduces their height growth by as much as 30 percent. In mature stands, budworm defoliation also reduces growth. Repeated defoliation sometimes kills the tree's crown or the tree itself. Recent studies in Idaho and Washington showed that radial growth of defoliated trees declined about 25 percent over a 5-year period, whereas radial growth of undefoliated, nonhost trees in the same stand declined only 2 percent. Larger, dominant trees can be so severely defoliated that the tops die, but the trees re- main alive because they produce adventitious buds, that is, buds growing in abnormal positions on the branches or main stem (fig. 4). In both young and mature stands, trees severely defoliated by the western spruce budworm may be predisposed to one or. Please no
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