By Island County Extension Agent, Donald B. Meehan
CONSTRUCTION DAMAGE TO TREES
Living on an island that has one of the fastest-growing populations in the state, we all see tremendous growth in housing to accommodate that growth. This change in our natural environment has its costs. One of them is the damage done to trees adjacent to building sites.
Most people try to plan their new home site to include some of the existing trees which were present. In some cases this can be accomplished, but in many cases the result is short-term. Builders confronted with saving a tree often overlook the damage they do to the root system during the building process.
Following the construction phase a damaged tree which was close by the home site can survive for 2-8 years. At the beginning of the 2 to 8-year period the tree appears normal. However, if the damage during construction was serious it will begin showing symptoms such as stunting, browning leaves, thinning foliage and branch dying.
What are the causes of construction damage? There are several. One of the most common ones is CHANGE OF GRADE. Soil moved in to level a site can suffocate tree roots. The degree of suffocation will depend on the tolerance of the particular tree species to lower oxygen levels, the depth of fill and the soil texture used as fill material. Soil which packs tightly, having a significant amount of clay and silt, will not allow air to move through it. Placing concrete or asphalt over a trees root zone will have the same damaging effect.
Lowering the grade around a tree can be equally serious. Most feeder roots are located in the top 6-8 inches of soil. Removal of soil to this depth will result in a loss of roots. Roots provide the means for trees to get adequate water and nutrients. Large roots removed by lowering the grade can cause an anchoring problem, subjecting the tree to falling in heavy winds.
Grade changes often affect the water table. Raising the grade generally raises the water table and lowering the grade lowers it. This can create too much water or insufficient water. Grade changes in other areas which cause the moisture content in the soil to change at the root zone can pose a problem. Sloping driveways or patios towards a tree may create enough extra moisture in the root zone to suffocate the roots.
SOIL COMPACTION by heavy equipment driving over a tree's root zone can be another type of problem. Compacted soil reduces the movement of air and water to roots. Sandy or highly organic soils compact less than heavy clay-type soils.
MECHANICAL INJURY created by bulldozers and other equipment may gouge the bark off tree trunks or major roots. This type of injury can be serious because these injuries leave the tree more susceptible to attack by decay organisms.
TREE THINNING in a building site to create a better view or reduce the amount of shade causes the remaining trees to be subjected to greater stress. This stress comes in the form of wind stress. It is also the major reason for the ailment we call sunscald, which is a pulling of the bark away from the tree cambium layer. This is caused because the tree is exposed to greater levels of sun in the wintertime. The bark absorbs the sun's energy and expands, causing cracking.
There are some obvious things you can do to lessen construction damage. The most important is proper planning which incorporates trees and their root zones. When thinking about root zones, it is important to recognize that zones extend beyond the traditional drip-line of the tree. In recent studies of tree roots of conifer trees, it was found that roots can extend as far as 150 feet from the tree. However, if you tried to use this as a guiding figure, you would not have room for the house, only the trees. I think a good rule of thumb is consider the root zone radius to be about half the height of the tree. This is still going to create some damage to the tree, but most trees should be able to recuperate.
Pruning a tree which has had too many roots removed or damaged will help balance the branch and root system. Prune as soon as possible after the root damage has taken place. Remove whole branches and strive to maintain the tree's shape.
Trees that have been injured by heavy equipment need first aid. This can be given by cutting away the dead or loose bark in the wound area with a sharp knife so there is a clean margin left. Old wounds which have begun to heal should be left alone. Cutting into the callus formation will only harm the healing process. Spraying wounds with wound dressings have not been proven beneficial by researchers, on the contrary, they seem to create problems.
All trees have some degree of wound healing capability. However, there is great variability of tree species to seal off the damaged area completely. Conifers are typically poor and accounts for the many heart-rot problems seen.
Two publications about dealing with construction damage are available. One is geared for helping people recognize hazard trees near homes. They are called EB 1157, "Construction Damage to Trees" published by Washington State University, and "How to Detect and Correct Hazard Trees Near Your Home" published by the Department of Natural Resources. Both are available from our office for a small fee..
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