Wind Sail Reduction

I must talk about wind sail and trees. It seems that this is the focus of many tree pruners now. Wind sail reduction, reducing the sail, wind thinning, and any other way that it is called has not been demonstrated to reduce failure of trees due to wind. It sounds good, and on some level seems logical, so what might be the truth behind tree strength and wind resistance?

• Trees need leaves to get stronger.
• Over pruning causes a tree to be stressed.
• Thinning a tree does not increase resistive bending moment.
• Reduction of a tree's height and spread can decrease resistive bending moment.
• Reduction can cause a tree to be stressed.

Trees move. Pretty basic stuff, here, but it is true that as trees move around in the wind, they are stimulated to grow. The practice of pruning out a substantial portion of the trees canopy to improve a trees ability to stay upright during a wind storm is in reality harming most trees. Trees need live branches to gather sunlight energy and convert it into, among other things, more wood. The vast majority of trees that I look at are more than strong enough to withstand the strongest storms that we experience in the Northwest. So what is the answer?

Now for the most interesting part of this subject. A tree that is marginally strong, or perhaps just barely able to withstand an average storm, is the trees that we are most concerned about. What do we do with these trees? Some of our clients are interested in tree preservation, while others are interested primarily with risk abatement. For the folks who have a marginally strong tree, it may be best to remove the tree and replace it with a more desirable species. But how can we make a tree stronger as to trunk failure? In a word - REDUCTION. Yes, reduction, or as some would call it, topping. Reducing a trees overall dimensions is the only demonstrable way to increase resistive bending moment. So when do we know if this is the right call to make for a tree?

We take into account as many factors as possible when giving recommendations to our clients. In the end, we encourage our clients to think about the long term benefits or risks to any tree care procedure. If the tree is generally vigorous, a prescriptive reduction might enable the tree to grow a dense, but shorter canopy. It may be that the tree is not healthy enough to recover from a reduction, in which case, removal might be the better option. In many cases, guying a weak tree to a stronger tree can be accomplished without significantly changing the status of either tree.

 

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