Is My Tree Prepared for a Windstorm?
Trees are buffeted by the wind all the time. The 10-15 mile per hour variety can create angst in a tree owner as they watch their tree sway back and forth in the billowy gusts. The tree may even bang against the house and produce spooky creaking sounds as branches rub against one another. These are easy fixes. A few pruning cuts can create more space between the tree, and the house, and removal of crossing branches can eliminate the spooky creaking! But what about the really fierce winds? What effect does that have on a tree?
What is wind?
Wind is air in motion. Air moves from a region of high pressure to low pressure, the difference due to unequal heating of the atmosphere. The really fierce winds, such as tornados, hurricanes, and gale-force winds, can devastate a landscape by ripping off branches and uprooting whole trees, especially if the ground is saturated with water. Fortunately, living in California, we don’t have to contend with tornados or hurricanes. But we can learn from trees that survive those types of winds.
How trees protect themselves
First off, trees don’t want to fall over or lose giant limbs any more than we want them to. Trees have developed traits that help minimize wind damage. Palms trees are probably the most adaptable trees for extreme winds. The next time they show palms trees blowing in a hurricane, notice how the palm fronds fold up into cones and minimize the fronds surface to winds. Other species, such as maples and sycamores, have leaves with long petioles that roll up into a cone and act as a windsock, funneling the wind through the canopy. Trees that grow in the face of prevailing or steady winds, such as trees near the ocean, adapt by putting on more growth in their roots and stems than in height and therefore tend to be short and stocky.
Wind helps trees develop a strong root system.
A tree stem must be free to move or flex for proper development. The diameter of the lower trunk is greater in free-swaying trees than in those prevented from moving. Free-swaying trees also are shorter than those held rigidly or protected. Trees that are properly staked at planting and allowed to move in the wind develop a better and stronger root system (assuming there are no girdling roots) than those not allowed to move.
However, all trees can be uprooted when subjected to certain levels of wind velocity. Barring uprooting, when push comes to shove, trees will snap at the weakest trunk juncture. Barring that, the crown may break and split apart, leaving nothing but a tree trunk behind. In strong winds, the tree trunk acts as a lever between the fulcrum root structure and the canopy. As trunk height increases, the lever effect becomes increasingly powerful, leading to trees being uprooted.
Proper pruning can reduce wind failure potential
Studies of trees after a hurricane have shown that trees that were properly pruned before the storm survived 25% more than trees of the same species that were not pruned. The emphasis here is on “proper” pruning. Trees that have been topped, excessively thinned or lion tailed (where the hard to reach foliage at the end of the branch is left) have NOT been properly pruned!
Lessons learned from hurricanes
The University in Florida studied all the hurricanes between Andrew (1992) and Katrina (2005) to answer the question: what makes a tree more wind resistant? Here is what they discovered.
- The higher the wind speed, the more likely trees will fail.
- Trees in groups survive winds better than trees growing individually.
- Trees suddenly exposed to the wind due to adjacent trees being removed are more prone to failure.
- Some species resist wind better than others.
- Older trees are more likely to fail.
- Unhealthy trees are predisposed to damage.
- Trees with poor structure or included bark are more vulnerable in the wind.
- Trees with more rooting space survive better
- Good soil properties, such as adequate soil depth, deep water table, and no compaction, help wind resistance.
- Damaged root systems make trees vulnerable in the wind.
As always, having a Certified Arborist inspect your tree in person is the best way to answer the question, “Is my tree prepared for a wind storm?”
By John Traverso, Traverso Tree Service