Sunday, June 1, 2008

Landscape - Saving Trees in Construction Areas

We often are called to look at trees in decline in areas where construction occured. The following is some information on this problem and how to avoid tree loss from North Carolina State University.

Understanding the problem

Tree roots develop and survive where there is adequate oxygen and moisture. Most active tree roots are in the top 3 feet of soil; the majority are in the top 12 inches. The more compacted or poorly drained the soil the closer the roots are to the soil surface. Roots normally grow outward to about three times the branch spread. Only 50 percent of the trees root system occurs between the trunk and the dripline. Roots on one side of the tree normally supply the foliage on the same side of the tree. When the roots on one side of the tree are injured the branches on that side of the tree may die back or die. With some trees, such as maple, the effect may develop anywhere in the tree canopy.

You should decide which trees add value to the property and take necessary measures to protect them. Consider the location, species, size, age, and overall health. Will the tree provide needed shade in the summer? Is there too much shade to grow the plants you hope to install? Does the tree hide an undesirable view? Will roots pose a problem to sidewalks or driveway? Is it a high maintenance tree that will require frequent spraying for insect or disease control? Does it drop messy fruit pods or seeds? How adaptable is it to environmental changes?
Older trees do not adapt as well to changes in the environment as young trees. Some young trees may be replaced at a lower cost than trying to preserve them, especially if extensive treatment will be required to help them recover from construction damage. The length of annual twig growth and the size and color of leaves are indications of health and vigor. Examine the tree for dead wood and indication of decline.

Pre-construction care

Ideal, a tree protective plan is developed before construction begins. Many roots are destroyed when construction equipment pass over the root zone. Simply placing a barrier around the trunk of the tree does not protect most of the tree's root system. Place tall, conspicuous stakes and fencing at the ends of the branches on the sides where trucks or bulldozers will be operating. Groups of trees usually stand a better chance of survival than individual specimens.
Minimize construction traffic to a few paths which are covered with 6 to 10 inches of mulch and do not allow parking under desirable trees. Avoid storing construction material under trees. Do not store or spread soil beneath the canopy of trees which are to be saved. Be sure that grading changes do not cause water to be channeled towards the trees.

From Erv Evans, Consumer Horticulturist, NC State University. Go to for the full set of fact sheets

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