Tree Storm Damage: Prevention and Wound Care

We just had some serious storms come through Cortez and the surrounding county. Several trees received serious damage while other had nothing. Why is that?

Here are some answers:

Which way was the wind blowing?

Usually our winds come out of the west. Trees, like humans, can respond to a load (weight or any force exerted on a tree) by reinforcing cell walls and tissue structure to strengthen parts of the tree. A consistent wind from the west will cause the tree to reinforce the tension side (the west side) of deciduous trees, and the compression side (the east side) of conifer trees. You may be able to see this by looking at the large basal roots coming off the trunk and going into the ground. 

Unfortunately, if a strong wind comes from a different direction than what the tree usually experiences, the tree is not braced for this and can fail. 

For many of the trees we cleaned up, they failed towards the west, meaning the wind came from the east. Their roots had not been reinforced in this direction because of our normal winds from the west. In addition they had shallow root systems that are often found in a turf setting. 

There are simple physics behind a tree blowing over. Two main components to consider are the “sail” factor and the “lever” factor. The sail is the amount of foliage and canopy that will catch the wind in the event of a big wind storm. The bigger the sail the stronger the load on the tree. 

The second factor is the lever arm. The taller the tree the longer the lever arm and the stronger the load on the tree. 

So, you may be thinking "We should be topping our trees!" Not exactly. The main reason is you may kill the tree when you top it and the regrowth from topping a tree often fails because it is poorly attached. 

Furthermore, trees have evolved to stand upright. They’ve been doing this a long time! One of their strategies is wind buffering. This means that when one branch is being blown east, the neighboring branches are rebounding and coming west. These branches run into each other and the overall load on the tree is dampened. This is why when trees are improperly pruned and all of their interior branches are removed the branches are more likely to fail. This research comes out of the University of Florida and their hurricane research. 

So how do we prune trees to withstand big storms or do we leave them alone?

Great question! We prune trees in the urban environment because although branch failure is not a high consequence event in the forest, but when it happens over a vehicle or playground it can be. Furthermore, trees usually grow in forests. We like to plant them in wide open spaces where their growth habits change in ways that aren’t always structurally sound. Therefore, we as stewards of the trees, must be proactive in our management. 

So how do we prune? From the outside in. We want to reduce the lever arm, and reduce the sail, without changing the buffering dynamic of th

e interior branches. Understanding how branches shift in the wind, how their foliage catches the wind, what makes a strong branch union, what their normal loads are, are all important factors in deciding how to prune your tree for storm damage mitigation. 

At the end of the day, some of these things are hard to predict.

What do you do if the damage has already occurred and the tree has a large wound?

Again, trees have evolved over millions of years, have survived multiple mass extinctions, they usually don’t need our help. If you read my blog on CODIT, you would know that trees put up walls to compartmentalize decay. They do this automatically and don’t require our help. What we can do is prune off the tearing, but still attached, branch to minimize overall damage. ISA has encouraged “bark tracing” in the past, which is the practise of cleaning up the wound to maximize healing. At this point, I personally feel more damage is done trying to clean up the wound then if it was just left alone. Therefore, I usually will cut off the tearing branch, maybe cut off loose bark or wood and then let the tree do the rest. Wound dressing is no longer encouraged as this can trap in

moisture or prevent the tree from performing its natural CODIT processes. 

The good news is the tree will respond to the break by sending out new growth. Dormant buds on the sides of the wound will be “released” because the subordinating hormonal signals that were coming from the branch are no longer detected, and the void in the canopy is now exposing the trunk or stem to sunlight. The new growth from a large wound is called epicormic growth, and you’ve seen it if you’ve ever seen the regrowth from topping a tree. Epicormic growth is not well attached the first few years but over the course of many years it will eventually fill the void that was created by the broken branch. 

The next time you see a large broken branch, cut off the excess wood or tearing branch and measure how many years it takes until you can’t even tell there was ever a break in the first place.