"Forestry for the Future"
Harvesting Techniques
Single-Tree Selection
The single-tree selection method removes individually selected trees throughout all diameter classes, creating small gaps in the canopy to facilitate regeneration. This method is generally the most expensive method of harvesting and requires the greatest amount of care and skill on the part of the forester and logger. Advanced regeneration established before the harvest must be of shade-tolerant species that are known to grow well in the low-light conditions that persist even after harvest.
Thomas C. Croker, USDA Forest Service, www.forestryimages.org
Group Selection
The group selection method removes trees in a number of 0.1 to 1-acre areas to create openings in the forest canopy. The larger the opening, the more likely that regeneration of sun-loving (shade-intolerant) species will develop and persist in the openings. Shade-tolerant species are more likely to sprout and survive near the edges of the opening and in the uncut forest between the openings. For shade-tolerant species to compete successfully, with shade-intolerant species in the openings, they should be present as advanced regeneration before the harvest.
Shelterwood Method
The shelterwood method leaves a large number of trees standing long enough to establish and protect "advanced regeneration" sites until the seedlings and saplings are well established. (Because the residual trees also serve as a continuing seed source, the shelterwood method is desirable when when insufficient advanced regeneration is present.) After regeneration is well established, the sheltering trees are harvested, permitting the advanced regeneration to occupy the site fully.
Seed Tree Method
The seed tree method leaves a few of the best trees standing to become the parent trees of the new forest. This method has limited application in Pennsylvania forests.
Robert F. Wittwer, Oklahoma State University, www.forestryimages.orgClear-Cut Method
The clear-cut method, in its pure form, removes all of the trees in a multi-acre area in a single cut. However, as management plans have evolved to include multiple objectives, it is not unusual to find that even in a clear-cut area, some tree species are reserved in the interests of biodiversity, wildlife habitat, or aesthetics. These include rare or slow-growing species, good mast producers, and wolf trees, den trees, and some snags. This method is the most controversial harvesting method and is often the target of public outcry. However, there are biologically based justifications for clear-cutting, given that the requirements for regeneration have been satisfied. Clear-cutting may be the best way to promote early successional forests that are essential for numerous plant and wildlife species. Clear-cutting is the best method for regenerating those tree species (such as black cherry, aspen, and yellow poplar) that require full sunlight, at least in their early life.
High-Grading
High grading is the harvest of only those trees that will give the highest immediate economic return. There is concern among all sectors of the forestry community that high-grading may lead to a widespread decline in forest resource quality. Two practices, diameter-limit cutting and selecting cutting, generally fall into this category. In diamter-limit cutting, all sellable trees trees above a certain diameter are harvested. Selective cutting usually removes the largest, most valuable trees and may leave large-diameter, poor-quality, low-value trees. In each case, most of the trees that remain after the harvest are genetically inferior or physically defective. Neither method gives any thought to the composition of the future forest.
Chris Schnepf, University of Idaho Extension, www.forestryimages.org
In even-aged forests such as those in Pennsylvania, smaller-diameter trees are not necessarily younger trees.. It is more probable that these smaller trees are:
1. slow-growing species of the same age as different, fast growing species;
2. the same species of the same age but growing on an inferior Microsite; or
3. the same species of the same age but genetically inferior to their larger-diameter counterparts
Because slower-growing and poorer-quality trees are retained, high-grading diminishes the diversity and economic value of the future forest. Landowners may agree to high-grading because of a lack of knowledge about the practice and its undesirable consequences. High-grading also can be driven by short-term economic considerations. Immediate cash flow may be higher with high-grading, but potential environmental degradation and decreased future timber values will more than cancel the immediate cash advantage.Stewardship requires that landowners consider the future consequences of high-grading when making a decision whether or not to accept the use of the practice on their land. Resource professionals and harvesters also have an obligation to look beyond the present when recommending forest management practices to landowners.
* Above information provided by the Pennsylvania DCNR Bureau of Forestry.
Crop Tree Management
Crop Tree Management is a system of forest resource management that offers private, non-industrial forest landowners a means of accomplishing single or multiple stewardship goals. It focuses on releasing individual trees that have been selected to produce benefits consistent with stand-specific landowner objectives. This system is based on application of the crown-touching release technique researched and developed by the Timber Management Research Project at the Fernow Experimental Forest near Parsons, West Virginia. Basically, any competing trees whose crowns are touching the crowns of the designated crops trees are harvested. This "releases" the crop trees and allows them to develop more rapidly when exposed to more sunlight.
To determine which trees must be removed to release a crop tree, simply look up into the crop tree crown and envision it divided into four separate quadrants, or sides (Figure 1). Evaluate each of these four sides for interference from neighboring crowns. A crop tree that has only one or two feet between its crown and a neighboring crown is not free to grow in that quadrant. If there is any doubt about whether an adjacent tree is touching or competing, cut it.
The crop tree crown in the center of this illustration has been separated into four quadrants, or sides. As free-to-grow rating is determined by evaluating each side for competition from neighboring crowns. This crop tree is free to grow on three sides.
The crop tree crown in the center of this illustration has been separated into four quadrants, or sides. As free-to-grow rating is determined by evaluating each side for competition from neighboring crowns. This crop tree is free to grow on three sides.
A crown-touching release essentially involves removal of all trees with crown that interfere with, or touch, the crop tree. However, in the event of two crop trees occurring close together with adjoining crowns, it is acceptable to to consider the two as one crown, and then release fully around the dual crown (Figure 2). This means the two crop trees each receive three-sided release rather than a four-sided release, as otherwise recommended.
The only exception to the four-sided crown-touching release rule is the occurrence of two crop trees with adjoining crowns. When this is the case, consider the two crop tree crowns as one, and release fully around the entire perimeter of the dual crown.
The only exception to the four-sided crown-touching release rule is the occurrence of two crop trees with adjoining crowns. When this is the case, consider the two crop tree crowns as one, and release fully around the entire perimeter of the dual crown.
*Information provided by the US Forest Service "Crop Tree Management: Quick Reference" by Brenda L. Wilkins, Jan. 1994.
Timber Harvesting, a 20 page document that provides guidelines for reducing negative impacts, protecting sensitive areas, such as wildlife habitat and wetlands, and minimizing erosion.
Sustainable Forest Harvesting: An Economic Perspective compares diameter-limit cutting and crown thinning from the perspective of long-term economic sustainability.
Timber Harvesting and Logging Practices for Private Woodlands suggests many woodland owners are not familiar with timber harvesting or the appearance of the residual forest following harvesting. This publication will discuss woodland ownership objectives, the steps involved in timber removal, alternatives for harvesting residue, and timber harvesting considerations.
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