A diameter-based thinning-from-above reduces the stocking (again, to about 60 percent in this case) by removing all the trees larger than a calculated dimater. Those largest trees are selected on the basis of diameter alone, regardless of their location with respect to other trees. None of the diameter-based thinnings shown in this demonstration is rooted in sound forestry. The results are generally undesirable. Once again, when all similarly sized trees are removed, certain trees can be completely eliminated from the remaining stand, and in an even-aged stand (most in Pennsylvania are), the burden of ultimately regenerating the forest falls on the smaller and possible genetically inferior residual trees. Because the remaining trees are not younger, but instead are slower growing, damages, diseased, or less vigorous species, they may not be able to respond to the increased growing space made available to them by the thinning. This is a negative impact on long-term forest health and diversity. In addition, this treatment allows no consideration for wildlife habitat. A diameter-based cut from above probably yields the highest immediate cash return of any thinning, but the long-term financial yield is drastically reduced. The residual stand, dominated by low value and poor quality trees, is simply unable to generate more future income potential.

Key Points

• Also known as "high-grading"
• Generally not good forestry
• Immediate income, but harmful to long term profits and forest health