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
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.
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
in soil grade
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
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
Damage to roots
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
First decide if the tree is worth saving. Does the tree serve a needed function or does it have sentimental or historical value? If over 30 to 50 percent of the main branches or trunk are severely split, broken, or mutilated, the benefit of extensive repairs is questionable. You probably would not want to save less desirable trees, such as black locust, Siberian elm, box elder, mulberry, poplars, and silver maple. More desirable trees, such as oak, maple, pecan, pine, magnolia, holly, and beech may be worth saving unless severely damaged. If the trees are close to power lines, building or other structures, the tree should be removed by a professional. Extremely old, low-vigor trees might not have the ability to recovery.
Small trees which are uprooted should be straightened and staked immediately. Left exposed to sun and wind will severely damage any upturned roots. Remove any damaged roots or branches. Some staking or cabling may be necessary.
Cut off broken and split
branches but delay pruning to reshape the tree. Too much removal of
wood in one season can create such problems as sunscald, weak branching
habits, and sucker growth. Reattach trunk bark to the inner wood with
galvanized nails if healing seems possible or trim the wound edges to
promote healing. Promptly remove all debris such as broken branches
and prunings to help eliminate breeding grounds for insects and diseases.
Do not be in a hurry to prune to correct plants bent out of shape by snow or ice. Often the plants will straighten up in a few days by itself. Broken branches, however, should be pruned as soon as possible. Proper pruning is effective in minimizing potential damage from ice and snow. Particularly important is the removal of weak, narrow-angled, v-shaped crotches.
Traditionally, homeowners have attempted to clean decay from the cavity and to add a material, such as concrete, to fill the empty space. Cavity treatment is an exacting process that if done incorrectly can shorten the life of the tree. The hard rim of tissue, Wall 4, surrounding the decayed wood must not be broken or decay could spread to the wood produced after the initial injury. If you chose to remove decayed wood, only remove wood that comes out easily.
Benefits from filling the cavity are questionable at best. Since the fill material will expand and contract at a different rate than tree wood it can create problems of its own. The strength of a hollow tree comes from the new wood produced after the injury, not from material used to fill a cavity. Remove hollow trees that appear weak and are likely to fall.
Sometimes the cavity will
contain water. The old recommendation was to drill holes below the cavity
so the water could drain. However, drilling holes will break the barrier
that keeps the decay from invading healthy wood. If water has been present
for one or more growing seasons, the tree has already adjusted. You
can cover hollow openings with a piece of tin or window screen filled
with plaster to keep out animals, water, and to form a surface that
allows new tissue to grow over the opening.
A condition known as leaf scorch can develop on plants, such as dogwood, maple, beech, ash, and elm when their root systems can not replenish moisture as fast as it is lost from their foliage. This disorder can be caused by a limited or damaged root system, drought, and hot, windy conditions. The leaf tissue on the edges and between the main veins dies and turns brown. Eventually the entire leaf except for a narrow band along the veins die. Plants can be affected uniformly or only on one side. Plants growing near reflective surfaces such as roads and patios, as well as, recent transplants are more likely to be affected.
A similar condition can develop during the winter from desiccation. It is particularly important to provide relatively high soil moisture for evergreen plants prior to a severe freeze.
Bruised and peeled bark
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.
Lawn mower and weed-trimmer
Wounds are serious enough by themselves, but the wounded tree must also protect itself from pathogens that invade the wound. These microorganisms often attack the injured bark and invade adjacent healthy tissue, greatly enlarging the affected area. Trees can be completely girdled from microbial attack following injury. Decay fungi also become active on the wound surface, and structural deterioration of the woody tissues beneath the wound will often occur.
Prepared by: Erv Evans, Consumer Horticulturist, NC State University
© 2000 NC State University - All Rights Reserved