Regulate Stocking. - High-hazard stands are characterized
by dense stocking and slow radial growth (fig. 5). Thinning will stimulate
growth and vigor in young stands and reduce the likelihood of future losses
from the SPB (fig. 6). Low thinning or "thinning from below"
is recommended to reduce competition and remove slow-growing trees, which
are most subject to SPB attack (fig. 7). The poorer crown classes suppressed
and intermediate trees are cut first. Dominant and codominant trees with
large five crown ratios and desirable phenotypic traits should be favored
as crop trees. They are most likely to respond to thinning and to provide
the greatest number of silvicultural options in the management of residual
Figure 5. - Slow radial growth is a common measure of high-risk
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Thinning schedules depend on the close relationships between site quality,
stand age, stocking, live crown ratio of individual trees, and growth
rate. Root and crown competition among individual trees develop at ages
10 to 15 years on most sites. Crowding can occur earlier than age 10 on
better-quality sites that contain a large number of trees. Initial thinning
should be scheduled before live crown ratios drop to 40 percent. Delay
will reduce stand vigor to levels unfavorable for growth but attractive
to the SPB.
Figure 6. - Thinning promotes the rapid growth and vigor
of your stands. (Photo courtesy of the Texas Forest Service.)
Figure 7. - Low thinning will remove small, slow-growing
trees that are susceptible to SPB attack (top). Healthy dominant and codominant
trees should be favored as crop trees (bottom).
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Degree of thinning is determined
by the intensity of management, the kind of product desired, available
markets, and natural conditions particular to each location. Depending
on site quality, basal areas of 80 to 100 ft2/ acre are recommended to
reduce the potential for SPB attacks. The risk of beetle attack in most
instances will increase considerably when stocking levels exceed 100 ft2/acre.
Wide spacings distribute growth on fewer stems, resulting in the production
of small sawlogs by age 35 to 40 years on good sites. Close spacings are
recommended for high yields of wood fiber. Thinnings should be scheduled
as needed to maintain desired stocking levels and stand vigor.
Mix Pine and Hardwood.-The
SPB prefers pure pine stands. A mixture of pine and hardwood species
reduces the potential for spot incidence and growth. Stands composed of
pines and hardwoods may be suited to owners of nonindustrial woodlands
managing for products other than or in addition to timber; such stands
often support diverse wildlife populations, are esthetically pleasing,
and contribute to soil improvement. However, intensive
Minimize Logging Damage.
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Damage from recent logging (within the past year) favors SPB infestations.
Careless cutting, skidding, and hauling often cause severe mechanical
injury to above- and below-ground portions of residual trees (fig. 8).
Moderately to severely damaged trees are high-hazard trees and should
be removed from the stand as soon as possible.
Figure 8. - Trees severely damaged by logging equipment
should be removed from the stand.
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Use of small harvesting equipment and removal of short roundwood are
recommended for intermediate cuttings. Heavy equipment and tree-length
logging generally increase the amount of damage to residual trees. Equipment
operators and ground crews should be trained to minimize damage to residual
trees and thus reduce the likelihood of bark beetle attacks.
Figure 9-Stands should be regenerated with pine most resistant to SPB
attack. (Photo courtesy of the Mississippi Forestry Association.)
Figure 9. - Stand should be regenerated with pine most
resistant to SPB attack. (Photo courtesy of the Mississippi Forestry Association.)
Regenerate Overmature Stands.
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Susceptibility of trees to SPB attack increases with age. Mature and
overmature trees usually have slower radial growth, flat-topped crowns,
and sparse foliage. These trees seldom respond to intermediate cuttings
and should be replaced with the most resistant host species or a species
mix suited to the area (fig. 9).
Many overmature pine stands throughout the South are being intentionally
preserved for ecological, wildlife, or esthetic reasons. These stands
are extremely susceptible to attack and should be monitored regularly
to detect the buildup of SPB populations early, when remedial action can
save the pine component.