Preventing Construction Damage to Trees
Wooded lots are an added value when selecting a site for building a home, just as mature trees add appeal to an already existing home. Homes that are constructed in the midst of trees take advantage of the aesthetic and environmental value of the property. The cost and care of preventing tree damage during construction protects those assets. Careful planning and preparation before construction begins may help to preserve and protect existing trees from unnecessary damage.
Trees vary in their ability to tolerate damage. Among the most sensitive are red oak, white oak, and sugar maple. These species will require more protection during construction. More tolerant trees include bur oak, silver maple, poplars, and willows. In general, younger trees are able to withstand the changes of construction better than larger, mature trees.
The key to tree preservation is protecting the root system from damage. The roots of trees are concentrated in the top several inches of soil. They spread at least as far as the branches, often much further. Disturbing the soil around a tree will cause serious damage to the root system, resulting in decline or death of the tree. Excavation, grade changes, traffic, and material storage (including soil) can all damage roots. Even when trees are protected from direct disturbance, building in a wooded area imposes many indirect changes in the environment. These changes result in increased stress on the trees.
BEFORE CONSTRUCTIONS BEGINS
Take a tree inventory. In order to choose the best location for a house, pavement, and utilities, the exact location and condition of each tree must be determined. In some cases, the foundation shape and position may have to be selected specifically to avoid certain key trees.
Draw the plan on paper. Confine the sidewalks, driveway, construction vehicle access, work areas, grade changes, and utility trenches into the smallest area possible. All trees with significant portions of their roots in the disturbed areas should be removed prior to construction. Unless the lot is very large, most of the trees in the front of the house may have to be removed.
Choose the right contractors. Before you build, work with the builder to prevent damage to valuable trees. Tree protection will require that work be restricted to certain areas of the property, which may constitute additional costs but could be worth the expense.
PROTECTION DURING CONSTRUCTION
Clearly mark the ‘root protection zones’ before construction begins. The root systems of all trees to be saved should be well protected. An area of soil around each tree should be fenced off and protected from all disturbances. The protected root zone should include one foot of radius for each inch of trunk diameter. This circle of protection need not be exactly equal around the tree, but it should be positioned so that no disturbance will occur closer to the tree than one-half the radius of the circle. Individual zones should be joined into a larger “conservation area” wherever possible.
Mulch the “root protection zones” with wood chips. Trees and heavy construction equipment do not mix. A single pass by a vehicle or piece of construction equipment can irreparably damage the soil and roots. Ask your contractor to keep heavy equipment away from trees. For times when temporary heavy traffic over a root system cannot be avoided, apply a heavy layer of mulch or gravel, which will minimize compaction but not prevent compaction entirely. Mulch also helps insulate the rooting environment from changes imposed by opening the forest canopy. (See Mulching Trees and Shrubs leaflet.)
Watering during dry periods is important, both during and after construction. Shallow tree roots are sensitive to drought stress. Mulch will help reduce evaporation, but watering will be required during periods of scarce rainfall. Water the entire root zone slowly until the upper 8-12 inches are thoroughly moist.
Occasionally, special techniques are warranted to preserve a tree. A temporary soil excavation, such as for a utility installation or repair, may result in significant root loss, but if the soil is replaced soon afterwards there is opportunity for recovery. Augering under tree root systems, rather than trenching through them, or installing special aeration systems at the original soil surface below fill soil, are costly, but can be the difference between saving and losing a tree. (See Watering Trees and Shrubs leaflet.)
WHAT TO DO IF CONSTRUCTION DAMAGES TREES
Symptoms of trees suffering from construction damage may appear the next growing season or may take two to three years to appear. When roots are damaged, the tree is not able to take up enough water and nutrients to feed all the branches. This results in dieback in the top of the tree and near the ends of the branches. Some trees develop yellowing foliage as a result of nutrient deficiencies. The tree’s overall health and vigor are slowed, resulting in small or sparse foliage.
Prune the crown to compensate for stress. A tree with a damaged root system is not able to sustain all of its branches and leaves. Reducing the number of leaves and branches will counterbalance the changes imposed on the root environment. All trees should be pruned by a qualified arborist who can remove the dead wood and selectively thin the live branches without disfiguring the tree. Regular pruning may be required every 3-5 years. (See Pruning Trees leaflet.)
Mulch with organic material, such as woodchips or shredded bark, to encourage fine roots, which absorb nutrients, water, and oxygen. Ideally, extend a three to four inch layer of mulch as far out from the tree as practical, keeping mulch away from the base of the tree.
Fertilizing mature trees is not usually recommended as long as growth is adequate and nutrient deficiencies are not evident. Mulch recycles nutrients naturally. Heavy fertilization may stimulate excessive growth in the top and could counteract pruning intended to reduce the crown size. (See Fertilizing Trees and Shrubs leaflet.)
Water. Even if no symptoms appear, give extra care to trees following construction. Water well during dry periods.