Ecological Foundations of Selection Silviculture
While it may not be necessary to fully understand all of the ecological foundations of selection silviculture in order to apply the system efficiently, background knowledge about several issues will allow the practitioner to appropriately modify the default values in the Pro-B method so that it is best suited to their unique situation. More detailed information is available by following the links in the headers below.
- Depletion Curve
In selection silviculture, this refers to the structure of the diameter distribution. While a stereotypical even-aged distribution is bell-shaped (a normal distribution), the most commonly envisioned uneven-aged distribution is a reverse J-shaped distribution (negative-exponential distribution). - Shape of the curve (q-value)
The q-value refers to the diminution coefficient, or ratio at which the number of trees declines with each subsequent diameter class. It is defined as the number of trees in diameter class i divided by the number of trees in diameter class i+1. While only directly applicable to the negative-exponential distribution, the concept is useful even if the depletion curve for the stand you are managing is irregular or follows some other form. - Height of the curve (residual stand basal area)
A common misconception is that selection silviculture is only applicable for shade-tolerant tree species. This is assuredly not the case. The system has been successfully applied in moderately tolerant species mixes (upland oaks) and intolerant forest types such as longleaf pine. While there are situations where the site conditions or the species composition may be unsuitable, or at least challenging, for the application of selection, in many cases success is only a matter of selecting the appropriate residual basal area and length of cutting cycle.
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