PB1774 Technical Guide to Crop Tree Release in Hardwood Forests

Crop tree release (CTR) is a widely applicable silvicultural technique used to enhance the performance of individual trees. It offers flexibility in that it can be applied on small or large properties, and with certain modifications, it can be applied as a precommercial or commercial operation. By favoring the development of selected crop trees within a hardwood stand, the landowner can meet a variety of area-wide management objectives such as wildlife habitat, recreation, timber value, aesthetic beauty and species diversity.

CTR can be applied at various stages of development, including sapling, pole and sawtimber stands, depending on the specific opportunities to improve stand conditions. In some cases, it may be advisable to apply CTR more than once during the rotation. As forest managers gain experience with CTR, many come to realize that it is a versatile silvicultural technique that can be effective in many situations (Houston et al. 1995; Perkey et al. 1994; Perkey and Wilkins 2001; Singer and Lorimer 1997). CTR is not consistently defined in forestry literature and is often assumed to be synonymous with thinning, improvement cutting or timber stand improvement. CTR is an intermediate silvicultural treatment intended to provide increased growing space to selected trees through the removal of crown competition from adjacent trees (Figure 1). Although CTR could be considered a special type of thinning, traditional thinning techniques are intended to reach a desired area-wide residual stand density or remove specific sizes or crown classes of trees. CTR differs from traditional thinning in that it assures that most site resources are focused on a small number of selected trees rather than being widely distributed to all residual trees. CTR can be applied in both even-aged and uneven-aged stands; it is applicable in any situation where the forest manager intends to reallocate site resources to selected crop trees. While the term “crop tree” suggests a tree that has been selected for future harvest, CTR can be applied to trees that will be either harvested or retained for any number of years, depending on how they provide desired benefits or meet management objectives.

Although CTR is relatively simple to apply, two key concepts are important to consider for optimal use of the technique. These concepts are understanding how crop trees help meet management objectives and how reducing competition for site resources around crop trees enhances their vigor and development. This publication provides forest managers and landowners with guidelines for applying CTR in hardwoods and technical information based on published research. Several mechanical and chemical methods for releasing crop trees are described, and useful references are provided for more in-depth coverage of specific topics.