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| Introduction |
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A closer look at thinning Often, trees in windbreaks are planted too closely. Even if trees were planted at the correct spacing, their growth will eventually bring them together to the point where trees are competing with each other for light, water, nutrients and space. Thinning provides an opportunity to lower windbreak density without losing overall windbreak function. The trees that remain after thinning have less competition, less stress and their growth rates will increase within two years of the procedure. Additionally, these trees should be able to fight insect and disease infestations better because of their better growth conditions.
The number of trees to remove depends on the starting density and the desired final density. Some general guidelines are to remove 33% (every third tree), 40% (every second and fifth tree), or 50%. Because tree crowns often grow together and overlap each other, thinning by 50%, for example, does not necessarily mean that density will decrease by 50%. Figure 3-5 shows before-and-after photos of a thinned single-row field windbreak of golden willow near Carrington, ND. The windbreak is about 150 yards long, the trees are approximately 50 feet tall and were overhanging into the nearby fields. There was a thick understory consisting of chokecherry, boxelder, green ash, red-osier dogwood and honeysuckle. Many dead and broken trees were cluttering up the stand. A more thorough discussion of this project, including the amount of time spent on this project, is available.
Figure 3-5. Before-and-after photos of a thinned windbreak near Carrington, N.D. The majority of material removed consisted of stems and branches that were overhanging the field, reducing the density of the bottom part of the windbreak. Photos by Joe Zeleznik.
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