Silviculture Can Reduce Losses from the Southern Pine Beetle
Southern Pine Beetle Handbook
United States Department of Agriculture, Combined Forest Pest Research and Development Program, Southern Pine Beetle Handbook, Agriculture Handbook No. 576 - Issued December 1980
Promote Stand Resistance
|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 stands.|
|Figure 5. - Slow radial growth is a
common measure of high-risk stands.
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.
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 forest management is required to obtain and maintain the mixed species composition best suited for a given location.
|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).
Minimize Logging Damage.- 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.
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.
Regenerate Overmature Stands.- 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.
|Figure 8. - Trees severely
damaged by logging
equipment should be
removed from the stand.
|Figure 9. - Stand should be
regenerated with pine most
resistant to SPB attack. (Photo
courtesy of the Mississippi
Developed by the University of Georgia Bugwood Network in cooperation with USDA Forest Service - Forest Health Protection, USDA APHIS PPQ, Georgia Forestry Commission, Texas Forest Service
and the Pests and Diseases Image Library - Australia
Last updated August 2018
www.barkbeetles.org version 2.0