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Carl E. Crisp
budworm (Choristoneura pinus Freeman) have lost 55-61% of their timber
volumes compared to noninfested trees. Heavy defoliation of forests in New
Brunswick by spruce budworm can cause volume losses of 33-50% in 10 years.
One year of light defoliation has little or no impact on long-term growth (Kulman,
1971; Fettes and Buckner, 1976).
In the forests of the northwestern United States, where the western spruce
budworm is the major defoliator, the greatest damage is (1) reduction in height
and radial growth, and top-killing and tree-killing in regeneration, sapling, and
some pole-size stands; (2) growth reduction and top-killing in older growth
stands; and (3) damage to cones and seeds (Fellin, 1980). The effect of defoliation
by gypsy moth on eastern hardwood forests is a 24-37% reduction in volumedepending on the tree species (Kulman, 1971).
Defoliation as a stress factor in forests is not the same as in agriculture
(NAS, 1975b). Because the rotation times for mature trees are much longer, the
general effect of defoliation by most insects is usually not tree mortality but
retardation of growth and in some cases lengthening of the rotation time.
The loss on commercial forest land attributable to all insects totals 1.3
billion board feet per year (Johnson and Lawrence, 1977). The total dollar value
of agricultural crop losses due to insects has been estimated at 18% of the
potential crop value (Pimentel et al., 1978). With the use of insecticides, this
loss was reduced to 13%. And for every cost unit invested in pest control, four
units of profit were returned in additional agricultural products. A similar study
needs to be done on losses in timber production caused by insects.
The effect of a major insect outbreak and the resulting defoliation on esthetic
resources and wildlife can be both positive and negative depending on the value
judgment assigned to the forest unit under management (McGuire, 1976). Spruce
budworm attacks not only kill balsam fir and white spruce trees in 3-5 years of
extreme defoliation but also increase the fuel load, with threat of vast fires as
an aftermath to epidemics (Fettes and Buckner, 1976).
Aerial surveys presently estimate defoliator boundaries and defoliation intensities (Krebs, 1976). Results from aerial surveys show that 52.8 million
hectares in Canada and the United States are infested with spruce budworm each
year.
Not all infested areas surveyed will be treated chemically, because they are
not all managed under extensive or intensive silvicultural practices (NAS,
1975b). As future demands for forest resources increase, a trend toward intensive
management appears likely. With such management, the application of insecticides usually increases as part of the pest management program (NAS, 1975b).
But this may not be true if sound prevention practices are part of the overall pest
management plan. Then the use of insecticides may actually decrease. Most
forests in North America are extensively managed. Intensive management should
reduce the losses attributed to insects.
Carl E. Crisp
budworm (Choristoneura pinus Freeman) have lost 55-61% of their timber
volumes compared to noninfested trees. Heavy defoliation of forests in New
Brunswick by spruce budworm can cause volume losses of 33-50% in 10 years.
One year of light defoliation has little or no impact on long-term growth (Kulman,
1971; Fettes and Buckner, 1976).
In the forests of the northwestern United States, where the western spruce
budworm is the major defoliator, the greatest damage is (1) reduction in height
and radial growth, and top-killing and tree-killing in regeneration, sapling, and
some pole-size stands; (2) growth reduction and top-killing in older growth
stands; and (3) damage to cones and seeds (Fellin, 1980). The effect of defoliation
by gypsy moth on eastern hardwood forests is a 24-37% reduction in volumedepending on the tree species (Kulman, 1971).
Defoliation as a stress factor in forests is not the same as in agriculture
(NAS, 1975b). Because the rotation times for mature trees are much longer, the
general effect of defoliation by most insects is usually not tree mortality but
retardation of growth and in some cases lengthening of the rotation time.
The loss on commercial forest land attributable to all insects totals 1.3
billion board feet per year (Johnson and Lawrence, 1977). The total dollar value
of agricultural crop losses due to insects has been estimated at 18% of the
potential crop value (Pimentel et al., 1978). With the use of insecticides, this
loss was reduced to 13%. And for every cost unit invested in pest control, four
units of profit were returned in additional agricultural products. A similar study
needs to be done on losses in timber production caused by insects.
The effect of a major insect outbreak and the resulting defoliation on esthetic
resources and wildlife can be both positive and negative depending on the value
judgment assigned to the forest unit under management (McGuire, 1976). Spruce
budworm attacks not only kill balsam fir and white spruce trees in 3-5 years of
extreme defoliation but also increase the fuel load, with threat of vast fires as
an aftermath to epidemics (Fettes and Buckner, 1976).
Aerial surveys presently estimate defoliator boundaries and defoliation intensities (Krebs, 1976). Results from aerial surveys show that 52.8 million
hectares in Canada and the United States are infested with spruce budworm each
year.
Not all infested areas surveyed will be treated chemically, because they are
not all managed under extensive or intensive silvicultural practices (NAS,
1975b). As future demands for forest resources increase, a trend toward intensive
management appears likely. With such management, the application of insecticides usually increases as part of the pest management program (NAS, 1975b).
But this may not be true if sound prevention practices are part of the overall pest
management plan. Then the use of insecticides may actually decrease. Most
forests in North America are extensively managed. Intensive management should
reduce the losses attributed to insects.