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I live in Wausau, Wisconsin. Our city planted small maples two years ago near the street. They are now about 8-10 feet tall. Both of ours show some encircling roots above the surface of the ground under the mulch. The roots are about 1/2 inch diameter in one case and a bit larger in the other. Is it too late to prune these away? Any other suggestions?
The answer to your question will depend, to some extent, on the type of maple tree you are growing. Silver maple will tolerate root-pruning, but sugar maples are intolerant of it, and can be more likely to break in windstorms if roots are pruned. There is always some risk of loss involved in root-pruning a tree. Source: Iowa State Extension.
Since encircling roots are not good for the tree, you probably will need to prune, but it would be best to consult a certified arborist in your area to make sure this is done correctly. University of Minnesota has a guide called "Stem Girdling Roots: The Undergound Epidemic Killing Our Trees" by Gary Johnson. Excerpt:
Removal is the most common treatment of encircling roots or SGRs that have caused minimal stem compression. Roots may be removed with wood gouges, saws, or pruners during the examination process.
When SGRs have caused extensive stem compression and are fully or partially embedded in the stem, modify the removal treatment to avoid damage to the stem. Embedded and severely compressing SGRs are often left in place when they cannot be safely removed; there is some belief that SGRs reduce the typically short life span of urban trees by only a few years, and the potential damage associated with SGR removal is not justified (Watson et al. 1990; Tate 1981). A compromise is to prevent the SGR from growing and further compressing stem tissues by severing it at the edges of the stem. Remove the remaining root to a distance where it no longer poses a threat to the stem and allow the severed SGR to decay with time. Annual examination of the stem to assess for decay is recommended.
The season during which SGRs are removed might influence the success of the treatment. Smiley (1999a) found that summer removal resulted in better diameter growth over two years than did fall removal or a combination of summer and fall removal for red maple trees under an irrigation system.
Regardless of treatment, do not backfill the examination area. Lightly mulch the exposed roots but not the root collar flare or stem area. Subsequent examinations will not require the time-consuming removal of soil.
Ohio State University Extension's information on stem-girdling roots says that removing the encircling root is a wound from which the tree may or may not heal, but doing nothing about it will likely result in the death of the tree, so it is better to take a chance and deal with the problem.
To find a certified arborist in your area, you can search your local chapter of the International Society of Arboriculture.
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July 29 2016 16:04:17