We have lots of trees with curved trunks on our property. The trunks curve, then straighten out, and the trees grow to full height. What causes this?—Bent Out of Shape
Trees, no matter where they are or what trauma they’ve had to endure, will always attempt to grow towards the light. In a group of trees, “there’s competition for sunlight, and a tree will try to gain any advantage that it can,” explains Michael J. Mills, a certified arborist in Gibsons, B.C. So if one tree surrounded by many others finds a gap in the canopy, “it’ll grow away from what it’s competing against, and reach for the light.”
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Your wonky trees may also be compensating for something that’s caused the trunks to curve; this is called “corrected lean.” Insect damage and rough weather—strong, persistent wind or pressure from ice and snow—can do this, says John Stewart, a senior consulting arborist with the Davey Resource Group.
After Canada’s 1998 ice storm, Stewart recalls seeing trees with bent trunks. “The ice load on the tips of the trees caused the trunks to bend permanently, but any new growth that occurred after was vertical.”
Finally, trees growing on an unstable slope—say, a bank that’s slipping down into a river—can sometimes have curved trunks. Trees with root systems near the surface can be pushed downhill as the top layer of soil moves faster than the layer below. An inanimate object, such as a fence post, would tilt. But because the tree continues to grow up despite the forces pulling it down, it develops a curve near the base of the trunk.
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This article was originally published in the Winter 2015 issue of Cottage Life magazine.
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