Thinning overcrowded stands improves the growth rate, quality, health and survival rate of the remaining trees. Large, high-quality, favored species trees are more valuable than small, poor quality, or off-species trees. Thinning can substantially increase the yield of these trees for production of lumber, plywood, poles and veneers.
Pre-Commercial Thinning
This management cut involves removing numerous small trees from a young over-stocked stand. This method is typically performed when the trees are between 2 to 5 years old. An acre of land can optimally support only a certain number of trees, when this amount is exceeded, the overall growth rate will slow dramatically. Nature will eventually take care of this situation, however, a pre-commercial thinning can yield better results much faster. It is termed "Pre-commercial" since the value of the small trees removed often falls short of the costs to conduct the thinning operation. When completed, the remaining trees should be of good form and spaced 6' to 8' apart. There will be a dramatic visual difference after the cut is finished. In many cases, a timberland owner may perform the thinning by hand or use a tractor and brush-cutter to mow 6' to 8' swaths through the stand if the trees are below 2 ½" diameter. On large plantations, a harvester may be available to perform the operation using a mechanical chipper. The chips produced can be sold to offset the costs of the operation.
Thinning
Thinning has the same intentions as "Pre-Commercial" thinning, it just occurs later in the growing cycle. Thinning can first be considered once the trees reach pulpwood size (4" diameter by 10' long). If thinning at this stage is not absolutely necessary, it is better to wait until the trees reach an average diameter of 6" or larger to ensure a profitable operation. The objectives are to remedy any overcrowding conditions and remove any trees that are poorly formed, diseased, or otherwise inferior. The remaining trees will grow at a faster rate and develop into higher value products. A thinning should provide income to help recover any costs associated with site preparation, planting or management activities conducted earlier. Thin only enough to match your improvement goals as any financial return is a bonus at this point. You will not notice quite as dramatic a change in aesthetics as compared to a pre-commercial thinning.
Improvement Thinning
Improvement cutting is typically performed on mixed stands to help favor growth of the higher valued species present in the mix. As trees develop naturally, competition occurs between all trees for available moisture and sunlight. In a mixed pine & hardwood stand, an improvement cut can be performed to remove the lower valued products from impeding the growth of higher value products. In the Southern Forests, this would most likely involve removing low value hardwoods such as gum or scrub oak to allow pines to mature at a faster rate. In the forests of the North or Northeast, this may not hold true. In this case, the pines may be removed to release quality hardwoods such as maple, cherry, walnut and others from competition. Determining which timber products are marketable for the highest value in your area should dictate which species to remove. Depending on the quality and volume removed, this operation may yield a profit as well. Aesthetics should be improved having a slightly thinner forest containing better quality trees.
