Part 2 of a 3-part series
The key to preventing storm damage to your Portland home or property is to look for conditions that predispose a tree to damage and if possible, correct the issue before damage is done. We have listed the general areas of concern below along with explanations of them.
Form of a tree
Trees may have natural imperfections that make them weaker, such as the inclusion of bark at branch unions or the presence of co–dominant leaders.
There should be a rough, protruding branch bark ridge where 2 branches meet and if there’s not, it’s a common weak point that has an inclination to separate during storms or high wind.
Co–dominant leaders are when a tree has 2 or more branches (stems) competing for the center point of the tree and these co–dominant leaders usually show inclusion at their unions therefore making them weaker.
Decay is one of the most common reasons for tree failure because degraded tissue has very little strength. Where the decay is located is vital in determining the tree’s potential for failure. If the decay is isolated to a small branch, it’s probably not a critical situation as the small branch can easily be removed, therefore eliminating the threat.
The most dangerous situation is when the decay is located within the trunk of the tree. Of course, the extent of the decay plays a role and there is a test for establishing the strength loss within a branch or trunk. For every 3 inches of diameter (of the branch or stem), solid wood should make up at least 1 to 1.5 inches. Anything less and the branch, stem or trunk is more likely than not to fail during a storm.
Maintenance of a tree
Poor maintenance routines can foster decay in trees. For example, mechanical damage from lawnmowers or weed trimmers along with poor pruning can cause wounds. This ‘wounding’ can make it easier for decay organisms to enter.
Too much watering can over–saturate the soil which can aid in the tree developing a shallow root system and potentially unstable trees. Even piling excessive mulch against the trunk can lead to stem girdling roots or other dysfunctional root systems.
You should be aware that improper pruning techniques encourage decay or the growth of weak branches. These can include flush cutting (pruning too close to the lead branch/trunk), leaving long stubs or stripping bark off the tree.
It’s ok to put mulch around a tree but it should be coarse mulch, piled 2 to 4 inches high with none of it touching the trunk of the tree.
Stem girdling roots
These are roots at or below the soil surface that partially or completely encircle the trunk of the tree. While not a problem at first, over time they begin to stress the tree and affect its health, especially the root system. The girdling roots cause compression of the lower trunk, which initiates a weak point and we know that any weak point is usually where the tree will fail during windy conditions.
Stem girdling root problems can be prevented by pruning the roots of pot bound trees before planting them and planting them at the correct depth. The first branch roots should be just below the surface of the soil.
Red maples, silver maples, poplars and green ash are some of the trees which are prone to forming stem girdling roots, especially in urban environment where they are planted too deep. Also, trees that are native to floodplain areas have a tendency to form stem roots since they are often buried by floodplain material.
Common site problems that add to tree failure
- Shallow soils
- Compacted clay soils
- Saturated soils
- Confined rooting areas
- Inappropriate species for the area
All the things listed above are related to a lack of oxygen reaching the roots of a tree. Just like humans, trees (and their roots) need an adequate supply of oxygen and when they don’t have it, their root systems suffers and so does the tree’s stability.
That being said, it’s crucial to know your site situation (soil type, rooting volume) before choosing and planting trees in your yard. For example, if the soil in your yard is clay-like, don’t plant a tree that needs well-draining soil or don’t plant large trees in a small area since there won’t be adequate space for the roots to grow.
In Part 3 of the Prevent Storm Damage series, we’ll discuss the types of storm damage that can occur and ways you can limit damage to your precious trees and possibly your home.