The Myth of “Windsail Reduction”

“Should I have my trees ‘wind-sailed’?”

In recent years, one of the most common requests I get as an arborist is to ‘wind-sail’ or ‘wind-thin’ a tree. You may of had a door-to-door salesperson from another company knock on your door and try to sell you on this fabricated notion.

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This may sound reasonable and may even seem to have some logic behind it. But beware, the truth is that there is really no formal scientific study that definitively shows thinning to increase resistance during a windstorm.

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This pruning technique is marketed to make trees ‘safer’ in the wind by allowing wind to pass through the canopy of a tree, thus reducing movement and strain on a tree. This is done by indiscriminately removing branches throughout the canopy to reduce it’s overall foliage mass. This may sound reasonable and may even seem to have some logic behind it. But beware, the truth is that there is really no formal scientific study that definitively shows thinning to increase resistance during a windstorm.

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In fact, many studies have shown that the outside limbs can actually divert some wind from the center of the tree and act as a buffering shield. The more limbs a conifer has from bottom to top, the more of a ‘shield’ they provide.

Aggressive thinning can also make the remaining branches more vulnerable to failure now that they are isolated and must take on the elements alone. Thus, the idea of removing a major portion of the trees live canopy for the sake of not falling over during a windstorm is in fact harming most trees in the long run. Especially healthy conifers, which beyond necessary deadwood removal, crown-raising and/or end-weight reduction, do not require much if any crown-thinning.‍

Remember, trees need leaves and needles to produce food for its survival.

Furthermore, and this is a topic in and of it’s own, but trees do not heal from wounds. Trees only have the ability to compartmentalize and seal themselves off from a wound. So removing live branches actually depletes the energy already stored in the tree by forcing it to compartmentalize the areas around pruning cuts rather than growing new wood in areas that will stabilize the tree. Therefore, aggressive pruning takes away a trees ability to produce food for itself and as a result causes unnecessary stress. This stress can be an invitation to disease, bacteria, insect and sapsucker damage, and general decline due to ‘starvation’.

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“What do I do if I am concerned about my trees falling in a windstorm?”

Trees have been around a very, very long time. For the most part, they have figured out how to react to wind. The reality is that all trees move. It is crucial that they bend. Movement is what creates growth. By moving in the wind, a tree figures out where to add wood to strengthen weak areas (compression and tension wood). When a tree is aggressively wind-sailed, it no longer bends or moves and thus no longer builds up holding wood or necessary anchoring roots. Wind-sailing can create a false sense of stability.

Most trees that have not been damaged by human interference or affected by root rot are more than capable of withstanding our regions fiercest windstorms. It is the trees that do not fit into this category that we should be most concerned about. While our goal and many of our clients goal is to preserve their trees, some may need selective pruning or even complete removal. Techniques such as end-weight reduction of branches and selective crown-thinning of canopies has been shown to reduce limb breakage but has not been proven to necessarily prevent whole tree failure. The only sure way to prevent trees from falling is to reduce the overall canopy or to completely remove the tree. This reduction is called ‘topping‘. The only time this practice should be applied is in extreme circumstances where removal is not wanted but prescribed with the understanding that once you top a tree you have basically given it a death sentence. Often times, it is better to remove the tree and replace it with a more suitable tree that is appropriate for it’s surroundings.

We always strive to listen to our clients concerns and consider as many factors and options as we can before giving recommendations. We understand that trees are a long term investment both to your property value and to everyone’s basic survival. In the end, we always encourage our clients to think about the benefits and/or risks to any tree care decision. If you feel that your tree is a hazard, please contact us. Our arborists approach each task with a basis of understanding tree biology. If your tree is unstable there may be methods to keep it safe and improve its health. Pruning, cabling, crown reduction or complete removal may be necessary. Whichever course is best, we can help with your decisions and carry them out in a safe and effective manner.

To read other recent articles posted by the Washington State Department of Natural Resources click here: “Windsail Reduction: a Northwest Controversy” Also, “Trees don’t windsail, do they?”

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