Saturday 9 July 2005

Trees and Summer Flooding

This strange weather we are having may be fatal to your trees!

While it’s true that trees need water to survive, too much water can injure your trees roots.

The top six inches of normal soil is composed of almost equal parts of soil, water and air.

When the soil becomes saturated with water, air is excluded and roots will become stressed.

The amount and extent of damage to the roots depends on several factors. Different species of trees react to flooding differently. The time of year that the flooding occurs also has a direct relationship to the damage it will cause. Another factor is the depth of the flood water and how long it sticks around. These are just a few of the factors to consider.

Flooding in spring along streams and rivers is a normal process and in most years, takes place before the trees have leaves. This type of flooding usually causes little damage for two reasons. The trees are not actively growing so their roots don’t require large amounts of oxygen. The second reason is most river bank, or riparian trees as they are called, have adapted over millions of years to survive this type of flooding. Willows actually have air passages in the tissues of their roots to allow them to survive and even thrive in flooded soils. Damage to trees flooded at this time is often mechanical injury from floating ice, debris or deposition of top soil over their roots. Ash trees will sometimes loose all of their bark up to the high water mark when spring flood waters rise. These types of injuries are often fatal to the trees but are not wide spread. Injuries may go unnoticed as the trees often take several years to ultimately succumb to this damage.

Once the trees have leafed out and are actively growing they are much more susceptible to serious injury from flooding. Temperatures are higher and roots are actively respiring using oxygen in the process of converting carbohydrates to energy. Waste gasses are also lost to the atmosphere and this process is interrupted by flood waters. The roots then start to operate with out oxygen. In this anaerobic state, roots will start to rot quickly if the soil remains saturated. Trees respond by shedding fine feeder roots and shutting down life processes in the larger roots. This in turn prevents the normal uptake of water and the top portions of the tree. The tree will start to exhibit drought symptoms. Leaves will curl and drop and the tree may become completely defoliated. Even though there is plenty of water around none of it is available to a tree without roots. Just as a stranded sailor in a life boat is surrounded by the salty ocean, no water is available to quench his thirst. Trees may die suddenly following this type of flooding or may become weakened and fall prey to other diseases or insects. Trees that are able to survive this type of flooding include, black and green ash, and willow. Trees that may be injured from this type of flooding include, cedars, poplars, cottonwood, birch, Manitoba maple, American elm, hackberry, honey locust, silver maple, bur oak, basswood, buckeye, crabapple, sugar maple, and most pines or spruces. Keep in mind it may take several seasons for the damage to become evident.

Trees that are in shallow depressions may need to be pumped out or drained.

Also when you are pumping out your basement take care that you’re not flooding your valuable trees and shrubs just outside the window.