Many people purchase a house with large, existing shade trees expecting them to live forever. Other perspective home owners purchase a wooded lot with plans to build a new home among the trees. During the home construction process, however, many trees are destroyed or injured.

The damage that occurs during construction may not at first be obvious unless the tree's trunk was damaged. In most cases the tree appears healthy but produces little new growth. Stress symptoms caused by tree root damage may take 5 to 10 years to fully develop. The tree initially lives off of its stored reserves --- after the reserves are depleted and the tree is exposed to hot, dry weather the tree declines or dies rapidly. Often insects and disease will invade the weakened tree and lead to a gradual deterioration. During periods of stress (high temperatures and drought) the trees may go through a rapid decline and die.

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.

Root damage by trenching
Digging trenches for installation of water, sewer, telephone, cable, gas lines, or for building foundations can damage the root system of nearby trees. The percentage of the total root system affected, the overall health of the tree, time of year, and the type and age of the tree will influence the survival and recovery rate of the tree. To minimize potential damage, attempt to locate trenching in areas that will cause the fewest roots to be damaged or near areas that have already been trenched. If possible, designate one general area for trenching.

Roots covered by pavement
Roots which are covered by pavement may be deprived of air and moisture which are essential for growth. If the covered area involves only a small portion along one side of the tree, satisfactory growth should continue. If a large area around the tree is paved, the surface should be porous to allow water and air to penetrate. If brick or flagstone is used, joints should not be mortared. When pavement is nonporous, an opening should be left around the trunk of the tree. This opening should be at least 6 feet in diameter for small trees. The opening should be larger for mature trees unless the roots extend beyond the pavement into uncovered soil.

Changes in soil grade
Even a few inches of fill or soil removal can cause extensive root damage. If possible, never remove soil from or add large amounts of soil within the drip line. When soil air is decreased by filling, certain gases and chemicals increase and become toxic to roots. Symptoms may appear within months or years after filling has occurred.

The extent of injury from filling varies with the species, age, and condition of the tree; the depth and type of fill; and drainage. Beech, dogwood, most oaks, pine, sugar maple, spruce, tulip popular, and walnut are the most easily injured. Elm, locust, pin oak, sycamore, and willow are the least effected. Clay soils cause the most damage because the fineness of the soil shuts out air and water more than a gravelly or coarse soil. Three to four inches of soil can be added to small areas under the tree provided the soil texture is coarser than the native soil. Finer textured soils should not be used for filling.

If a tree well is to be constructed, built a wall no closer than the dripline and grade the soil outside of the tree well so it drains away from the tree. Success has been reported in some cases where gravel was spread over the existing grade and vertical pipes were installed every 10 feet before the area was covered with a coarse-textured fill soil. Building a tree well several feet from the trunk of a tree before adding several feet of soil will do little to prevent root death.

Care After Construction
Damage to the trunk
Bruised and peeled bark should be treated to promote rapid healing. Trim around the wound to sound tissue on each side. Use a sharp knife and do not cut any deeper than necessary. The top and bottom should be rounded instead of forming a sharp point. This will facilitate movement of moisture and nutrients around the damage area. When done properly, healing should occur completely around the wound.

If the damaged area is less than 25 percent of the circumference of the trunk, the wound should gradually heal over and no permanent injury should result. If the damage involves more than 50 percent of the circumference, the tree may be seriously reduced in vigor. It may lose branches and become quite unsightly. However, the corrective procedures of pruning, irrigation, and fertilization should be practiced until the tree recovers or until it is evident that the tree should be removed.

Damage from filling
The base of a tree at the soil line should flare out (be wider than the tree trunk a foot above the soil line). If the tree does not have a flare, but enters the ground in a straight line, fill dirt has been added. Digging will reveal the depth of the fill. Other visible symptoms include small leaves, many dead twigs, and the presence of numerous suckers along the main trunk and branches. If the filling was recently done and roots have not begun to regrow into the fill, efforts should be made to restore the soil to its original level.

Damage to roots
Damage to trees during construction usually involves impairment of the water and nutrient supply system. Therefore, three corrective procedures should be applied: thinning branches to reduce water requirements; irrigating as needed to maintain an adequate moisture supply, and applying fertilizer to help stimulate new root growth (avoid excessive nitrogen). Limited or no tilling should be done under damaged tree until they have had adequate time to recover.

A moderate application of fertilizer may be beneficial. Use 2 pounds of 5-10-5 per inch of trunk diameter measured three feet above the ground. Excessive applications of nitrogen will promote new foliage growth that the tree can not support with its reduced root system. The easiest and most practical method of application is to broadcast the fertilizer over the area of greatest concentration of feeder roots. These are located in a band around the tree starting about two feet from the trunk and extending several feet beyond the ends of the branches. Scatter fertilizer evenly over this area, and apply water liberally to wash it into the ground.

Keep the tree mulched and well watered during stress periods. Gradually prune and reshape the tree for balance and general appearance over a period of 3 to 5 years. Control devitalizing conditions such as sucker sprouts, insects, and diseases.

Prepared by: Erv Evans, Consumer Horticulturist, NC State University

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