Wind gust not only cause of branch failure

KENNEWICK -- I'd call it limbs falling out of trees, but the technical term is "branch failure".

The winds last week in our region and elsewhere in the state led to a number of branch failures. When wind gusts blow and twist about tree tops, there's always the chance of limbs and branches breaking.

Rarely do limbs drop from trees for no reason. When the bough breaks and falls in wind storms, there are three very predictable reasons.

Past tree topping is at fault for many limbs that break from trees. When trees are topped the regrowth that develops are called water sprouts.

These water sprouts are not strongly attached to the stem or branch on which they form. As they grow larger and heavier, they're more and more prone to breakage in windstorms because their weak attachment can't hold their weight.

This type of failure can be avoided by not making topping cuts on large tree branches and major limbs.

If needed, tree height and crown density can be reduced with thinning cuts that retain a tree's natural form and don't leave stubs. With thinning cuts, branches are cut back to side or lateral branches that are at least one-third the diameter of the ones being removed.

The growth that is stimulated by thinning cuts will be evenly distributed around the crown, in contrast to the vigorous, weakly attached water sprouts that result from topping cuts.

Wood rot is another problem that results from topping. A branch stub left from a topping cut never closes over, leaving the branch wood exposed and prone to invasion by wood rot fungi. Once rot invades the heart wood of a branch or trunk, it loses its structural integrity.

Decayed branches are very vulnerable to wind breakage. Also, decayed branches provide poor support to branches that developed from water sprouts.

Wood rot is best avoided by making proper pruning cuts at the base of a branch, but outside what is called the branch collar. Treating pruning wounds with pruning paint or "wound dressing" materials will not prevent wood rot. In fact, these materials can actually encourage wood rot by sealing in moisture and excluding light, creating a better environment for wood decay organisms.

The third common reason for branch or limb failures are narrow or V-shaped crotch branch angles.

These narrow angles are weak connections between two branches or limbs. The narrower the angle, the more poorly they're bonded together. Stress put on these weak attachments by wind or ice can cause them to split. This is particularly true as the branches or trunks grow in girth, pushing against each other.

Certain trees, such as Bradford pear, green ash, and silver maple, are prone to developing narrow branch angles. However, other trees may also have narrow crotches due to poor training as a young tree. The best way to avoid problems is to refrain from buying trees that have already developed narrow crotch angles or trunks with forks. Forks are "co-dominant leaders" or competing leaders that have developed instead of a single trunk or "leader."

When buying a tree, look for ones with good branch angles of 60 to 75 degrees. Avoid any trees with trunks that already have forks. Also, branches should be evenly distributed around the trunk, not all on one side or with multiple branches arising from one point.

Protect yourself from falling branches by never topping trees and by buying well-structured trees that won't set you up for failure in th future.