Any wound to the roots, stem or main branches of a tree, caused during construction, is considered construction damage. These wounds can occur during any building activities around trees that cover the soil, disturb the soil, or simply driving near the tree with heavy equipment. Construction damage can occur on projects as small as paving a patio.
Why are construction activities so hard on trees? Trees get into trouble when they become low on energy reserves, when their roots can't get enough oxygen or water or when more than 40% of their root system is lost. As you can see from the list above, most of the damage due to construction happens to the root system. Developing a site is seldom possible without hurting tree roots to some extent. Roots are one of the most vital parts of the tree. They are responsible for nutrient, oxygen and water uptake and anchoring the tree in the soil. In addition, energy rich chemicals are stored in the roots. Trees draw on these energy reserves to get them through emergencies like drought, defoliation, insect attack or construction damage.
Because of their location, roots are more easily wounded than you would think. Fifty percent of the root system is in the top one foot of soil and over 90% of the root system is in the top three feet. The root system extends well beyond the tree's dripline, often extending a distance equaling two to three times the tree's height. A single pass by a cement truck or dump truck can sever or crush the roots.
Diagnosis Conspicuous symptoms of construction damage may occur within weeks of the damage but are more likely to take years to appear. The long term delay causes landowners to attribute losses to other causes or to remain unknown. Most of the time there is no obvious damage to the stem or the branches! Damage remains hidden under the soil in the root system.
Wilted or scorched leaves or needles and drooping branches are usually the first symptoms of construction damage. In deciduous trees, these symptoms may be followed by early fall coloration and premature leaf drop. Damaged conifers will drop excessive amounts of inner needles. In later years, there may be yellowed and dwarfed leaves, low leaf density, twig and branch die back. Other indicators might include massive branch die back, epicormic branches (suckering on the main stem), flowering out of season or production of an abnormally large amount of seed. These responses are defense mechanisms for ensuring species survival and often indicate that the individual tree is experiencing extreme stress and is near death.
Damage: causes and possible remedies The best way to avoid losing trees to construction damage is prevention. However, if the damage is already done, you may still have time to take some remedial actions.
Scraped trunks, broken branches and wilted leaves are symptoms that appear quickly. Small wounds to the trunks are not serious but may act as entry points for fungi which cause decay later on. Wounds exceeding 50% of the tree's diameter are serious. There may not be enough tissues left to conduct food down or water up and the tree will decline and may die. The strength of the stem may also be weakened. A tree with a stem wound destroying more than 50% of the wood diameter, is hazardous and should be cut down. Broken branches should be pruned back to their main branches using the proper pruning techniques. Painting wounds or pruning scars actually increases decay organism activity, so it isn't recommended except for oaks to prevent oak wilt disease infection in May and June.
Severed roots can be the result of lowering the grade, new construction or trenching. This type of damage has few remedies. Severing roots reduces water and nutrient uptake, eliminates stored energy and may compromise the stability of the tree. When the grade is lowered by more than two inches, vital feeder roots are eliminated, nutrient rich topsoil is removed and the remaining root system is severely wounded. If enough of the root system is destroyed or detached, the tree will die. As a general rule, 20% of the root system can be destroyed before the tree will show signs of injury. If 40% of the root system is lost, the tree will probably die. It should also be removed because it is hazardous.
For all types of digging operations, cleanly cut exposed or severed roots to promote rapid wound closure. Vibratory plows and chain trenchers leave cleaner cuts than bulldozers and backhoes. When working inside the dripline, use only hand tools. Instead of trenching, tunnel under the root system when it is necessary to work inside the dripline. Minimize the impact of root severing by avoiding construction during hot, dry weather, keeping trees well watered before and after digging and covering exposed roots with soil or mulch as soon as possible.
Smothered roots have their oxygen supply cut off. The most common method of smothering roots is through changing the grade, that is, adding more topsoil or fill dirt to the existing contour of the area. This cuts off the water supply, too. For some tree species, like red oak, only a few inches of fill is enough to do serious damage. Roots can also be smothered by "temporary" piles of soil placed inside a tree's dripline or by pools of water impounded by construction activities.
If the tree is already showing symptoms of advanced decline, it probably cannot be saved. If it appears mostly healthy and there is more than ten inches of fill anywhere inside the dripline, restore the area to its original contour by removal of all the fill. Avoid soil compaction, only use hand tools to remove the last ten inches of fill.
Soil compaction is by far the most common way construction damage can harm and kill trees. Tree roots need crumbly, well-aerated soil to grow and to obtain oxygen, water and nutrients. Lacking good soil aeration, roots suffocate and tree health declines. Leaf wilt, early fall coloration, branch die back, overall decline and tree death are symptoms of soil compaction. Diagnosing compaction can be difficult because it can take quite a while for symptoms to appear; trees can die five years after the original damage.
Most soil compaction is caused by construction equipment. One pass by a heavy tractor or truck is all it takes. Compaction can also be caused by stockpiled building materials and excessive foot traffic. By controlling equipment traffic patterns, soil compaction can be prevented. Reroute traffic away from trees, put up protective fences and signs, mulch the equipment routes with several inches of wood chips and locate materials storage areas well away from the dripline of the trees you want to save.
Compaction can be partially alleviated by drilling a series of two inch diameter holes to a depth of 12 to 18 inches. Begin three feet from the trunk and continue drilling holes at two foot intervals in concentric rings around the tree and continue to at least the dripline. Each hole may be refilled with sand, peat moss or mulch. Don't recap the hole with a sod plug. There are other alternatives, such as soil injections of air or pressurized water, available from some professional tree care services.
Poisoned roots occur from improper handling, disposal or spills of materials used during construction. Chemical spill damage can be prevented by filling gas tanks, cleaning paint brushes and repairing equipment well outside the tree dripline. Debris and chemical waste should be hauled away, not burned or buried on the site. Cement trucks should never be rinsed out over root systems.
Exposure to new conditions occurs to the remaining trees when removing a large number of trees around them. Heavily wooded sites should be thinned gradually over a two to three-year period to reduce exposure shock. Save groups of trees, rather than individuals. Tree crowns can act like sails with winds from new directions and if not securely anchored by the roots, the trees can topple over. Prune away branches that act like sails.
Prevention is the key
Nearly everyone recognizes the value of trees in providing shade, ornament and protection. All too frequently, the trees that make a site attractive are damaged or killed during construction by inadequate protection or carelessness. Sometimes it is possible to remedy the situation, but it is always better and more economical to prevent damage than to remedy it. Here is a short list of prevention activities to consider:
PLAN - Formulate a plan. Select which trees can be saved and which trees should be removed. Try to save islands of trees rather than individuals. Talk about your plans with contractors/workers. Make a map so plans are clear to everyone. Control traffic patterns by fencing off areas to be protected. Post signs that say "Off limits." Water trees regularly before, during and after construction activities. Visit the construction site and monitor for signs of tree damage.
TIMING - Cut trees down during the fall and winter because the "saved" trees are extremely vulnerable to wounding during the spring. Use chainsaws to fell trees near the trees you want to save. Avoid felling trees into the trees you want to save. Avoid pushing trees over with bulldozers because it rips up neighboring trees' roots. If you want to keep the wood for firewood (from elms, oaks, pines or birches), keep it covered tightly during the first growing season.
ROOTS - Avoid trenching inside the dripline by going around the tree rather than under it. Use tunneling rather than trenching inside the dripline. Use porous paving materials such as brick or flagstone rather than concrete or asphalt. Don't raise the grade more than a few inches inside the dripline. Avoid lowering the grade more than two inches inside the dripline. Never pile soil or construction materials inside the dripline, even temporarily. Don't limit root growth by "boxing" in an average sized tree.
AFTERWARDS - Monitor for damage and take remedial actions. Use proper pruning techniques to remove dead and dying branches. Don't wound trees by topping, tipping or pruning with flush cuts or stub cuts. Wait two years before fertilizing damaged trees, then use a low nitrogen product. It's a waste of time to paint tree wounds (except oaks in May and June). Water trees regularly.