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Name: Roderick
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Why do bark and tree rings show greater growth on the north and northeast sides of the tree?

I posed this question to an licensed arborist. Here is his response:

In general, this isn't true. Tree rings do show greater growth on certain sides of leaning trees because the tree is trying to compensate (wind does make trees lean) for the lean. There can also be additional growth on the bottom of branches for the same reason.

As for prevailing winds: they would have to be very strong and continuous, which is something usually found on a local or maybe regional scale. For example, central Nevada is a windy, open and exposed place where 15+ mph winds are common for the majority of the year. I think that trees could show those winds in their rings (trees growing in central Nevada already show a visible lean).

I have never heard of bark being thicker on one side over another, but again, at a micro climate level, it could be feasible. But certainly not common nor true for generalization.

Vince Calder

They do not! Tree rings will vary in width depending on a large number of environmental conditions from year to year and tree to tree. It would be very rare to find uniform rings on any tree, but the variations can be caused by competition from nearby trees, moisture, damage, fires, any number of causes.

J. Elliott

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