Floods and Trees

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Published on: Aug. 2, 1995

Last revision: Oct. 20, 2010

home free. At the least, many trees were under severe stress for several months. Evidence of stress could be seen in the yellowing leaves, crown dieback and peeling bark.

Some roots died or suffered mechanical injury from sediment and objects carried by floodwaters. Sprouting often occurs along the stems of wounded trees. The early coloration seen on flooded trees during late summer was a stress symptom, too.

Stress sets the stage for invasion of trees by insects and disease organisms. These "secondary attackers" prey on weakened trees, presumably because the defense systems of the trees are impaired. Stem borers are an important group of insects to be concerned with after a flood or other severe stress event. Borers affect the water and food conducting systems in trees and weaken stems, leading to later breakage.

Diseases most likely to occur are root rots and cankers. This is because root systems are stressed, and stems and branches have wounds providing easy entrance for diseases.

What will happen in future years as a result of the 1993 flood is still unknown. We have limited experience with floods of this duration and timing. Experts seem to agree that we haven't seen the last effects of this flood, however.

To help us learn more about what happens following a flood of this magnitude, the Conservation Department has begun several studies to monitor the aftermath. One is a study of trees in urban areas. The objectives of this study are to determine how different species respond to floods and what secondary attackers are common. Another study is concerned with the effects of the floods in natural bottomland settings. Both involve several states and are cooperatively funded by the U. S. Forest Service.

We can be certain more trees will die over the next five growing seasons, as secondary pest organisms victimize stressed trees. But is this good or bad?

The mortality is viewed as a problem by loggers and tree farmers interested in using a crop. Dead trees need to be salvaged quickly to avoid defects that will soon occur because of rotting. Surviving trees and saplings may be prone to poor form because of mechanical damage and sprouting.

Dead and dying trees in urban areas can present hazards and cost dollars to replace. And there is the fear that the loss of mast species, such as pin oak, will reduce waterfowl, turkey and deer numbers.

On the other hand, flooding is a natural occurrence.

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