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Tips for Selecting Smaller Trees to Leave During Pre-commercial Thinning

Q: What are some tips for selecting smaller trees to leave during pre-commercial thinning?

A: There are several considerations when thinning smaller trees to ensure that the fastest growing trees are left at a proper spacing.

1. Generally the larger trees, in an even-aged stand, are preferred since they have already expressed a sort of dominance. Needles are the driver of growth in conifers, so look for an abundance of healthy green needles that can generate good future growth.
2. Examine the bark of potential leave trees. Faster growing trees will show wider gaps in the bark as the tree diameter increase faster than new bark can be created. These gaps are generally lighter in color.
3. Spacing is usually determined by allowing enough distance between the live crowns (green foliage) that can be filled within a decade or two by crowns increasing horizontally. Horizontal growth of crowns is much slower than vertical crown growth. Be aware that too much space between crowns can be occupied by woody brush species which compete for moisture and nutrients.
4. It usually is best to utilize an “uneven” spacing that allows the very best growing trees to be left rather than a “set” spacing that resembles an orchard. Trees may be 4-14 feet apart in some instances depending solely on tree characteristics.
5. Try to allow diversity of species when possible. Insects and disease can decimate monocultures where one species forms a dominant part of the stand.
6. As a generality, we tend to leave forests too dense even after thinning because we dislike cutting live trees that are healthy. If the forest looks a little too dense after thinning, it probably is too dense.