Thinning Practices in Southern Pines - With Pest Management Recommendations

T. Evan Nebeker – Respectively, professor, Department of Entomology,
John D. Hodges – Professor, Department of Forestry, Mississippi State University, Mississippi State, MS,
Bob K. Karr – Assistant professor, Department of Forestry, Mississippi State University, Mississippi State, MS, and
David M. Moehring – Professor (deceased), Department of Forestry, Mississippi State University, Mississippi State, MS.

United States Department of Agriculture, Forest Service, Technical Bulletin 1703, December 1985.

Discussion

Stocking, carrying capacity, and stand dynamics are the concepts that form the biological basis for spacing and thinning to achieve management objectives. A thorough understanding of the positive and negative impacts of thinning operations much be taken into account in the development of appropriate management recommendations.

Growth Factors

If thinnings are properly performed, they will have beneficial effects, not only in the form of increased product values and increased stand utilization, but in terms of increased resistance to damage by both biotic and abiotic agents as well as genetic improvement. Increased values and resistance are largely due to increased growth rates and improved vigor of the residual stand. The end result is increased economic gain. In addition, the changed forest environment resulting from thinnings is usually considered beneficial for wildlife habitat management, watershed management, recreational uses, grazing, and other amenities.

Damage Factors

Conversely, poor thinning practices can result in direct damage to residual trees in the form of stem breakage, limb breakage, bole wounding, and/or root damage. Indirectly, site damage may result in growth reduction and increased susceptibility to damaging agents. The kind and amount of damage will depend on felling methods and equipment used, spacing, and time of thinning.

The type of equipment used is the single most important factor in the extent of direct damage, with mechanized felling of any type generally causing more damage than hand felling.

Mechanized felling equipment can also damage the site. Site damage includes soil compaction, puddling, and rutting, conditions that all influence both tree growth and soil erosion. Variables that determine the intensity of such damage are equipment used, soil moisture, soil type, slope, presence of an herbaceous layer, and slash distribution. In general, damage to the site and residual stand increases as equipment size increases.

Regardless of the type of equipment used, damage is usually greater on wet than on dry soils because wet soils are more susceptible to compaction and puddling. Erosion damage is greater on sloping ground.

Thinning may also subject the residual stand to indirect damage from abiotic factors such as wind and ice. This type of damage is most closely related to the thinning method employed, with damage potential greater after a mechanical thinning than after a selective-type thinning.

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