Protecting trees during construction
Trees may decline, become hazardous, or die as a result of construction-related damage unless adequate, protective steps are taken.
Assess which trees are worth saving and are likely to survive construction. Examine trees regularly to ensure that they are
- receiving proper cultural care
- being protected from injury to limbs, trunks, roots, and root-zone soil
- not hazardous
See recognizing hazardous trees for a list of some signs that indicate a tree may be hazardous. Be aware that some hazards are difficult to detect, such as internal decay and unhealthy roots.
Forests, oak woodlands, and urban lots with large trees are often developed because mature trees make these sites desirable to people. Construction-related damage can increase a tree’s susceptibility to many disorders and pests. Negligent or thoughtless activities may wound limbs, roots, and trunks.
Injuring roots by crushing or cutting them or by compacting soil are very serious problems that construction commonly causes. Wet soil is especially susceptible to compaction by heavy equipment. Compaction or changes in soil grade or drainage can deprive roots of oxygen, water, or both. Changes belowground promote root and crown diseases and predispose trees to attack by bark beetles and wood-boring insects.
In constructing buildings and roads and while installing amenities and utilities, trees are often killed outright or their lives are greatly shortened. Damaged or unhealthy trees may be hazardous if located where dropping limbs or tipping trunks are likely to injure people or damage property. The adverse effects of construction damage to trees may not become apparent until several years after the injury or stress.
Consider tree preservation during the planning stage of development projects. For help consult a tree-care professional, such as an arborist who is certified by the International Society of Arboriculture or registered with the American Society of Consulting Arborists. Check city or county ordinances before working around mature trees as they may be publicly owned or protected by ordinances.
How to Protect Trees. Fence off individual trees or groups of trees around the drip line or beyond to provide protection zones that prevent equipment and activities from damaging roots and trunks and compacting the soil near trees. Most roots are near the soil surface and many extend much farther than the tree canopy spread.
If soil must be driven on or temporarily used to store heavy materials, apply and maintain a 6-inch-thick layer of coarse, organic mulch to reduce soil compaction. Minimize changes in soil grade and drainage; compaction and changes in soil contour alter surface and subsurface water flow on which established vegetation may depend. If roots have been crushed or cut, monitor the root zone in the undisturbed area and ensure that the soil is appropriately irrigated.
Use engineered soil mixes. In areas that will include both landscape and paving, such as commercial parking lots where shade trees will be planted, consider using special, structural, soil mixes. These engineered mixes can be compacted to the density required to ensure pavement integrity while still providing the air- and water-holding properties vital for root growth and health.
Do not place fill around trunks. If the grade must be elevated, construct a stone or concrete well around each trunk. Before placing the fill, installing a drainage system on top of the existing soil may help provide oxygen and appropriate water to established roots once the original soil level is covered.
If the grade must be lowered, construct retaining walls to preserve as much of the original grade, roots, and soil as possible, at least within the drip line of established trees. If soil is undisturbed on one side and adequate cultural care is provided, a tree may survive if soil on the other side is removed no closer to the trunk than about halfway between the trunk and drip line. If the grade must be lowered near trunks, consider removing the trees as they are likely to become diseased and hazardous and die prematurely.
Assess the situation. Be realistic in assessing which trees are worth saving and likely to survive construction. When large roots are cut or injured, the tree becomes more likely to be blown over by wind, especially if the soil is wet.
Remove declining or severely injured trees rather than leaving them to become a hazardous and expensive problem after sites are occupied; trees can be left to protect other trees during construction, then removed soon afterward. Consider removing trees if the drainage, root zone, or soil grade will be seriously disturbed or if species with incompatible cultural needs will be planted nearby, such as planting frequently irrigated turfgrass near native oaks.
Protect roots. Avoid crushing or cutting roots, especially those larger than about 2 inches in diameter. Trench for utilities away from roots, combine utilities in a single trench, and tunnel beneath roots instead of cutting them. Instead of digging around roots, use hydroexcavation or pneumatic excavation (e.g., Air Knife or Air Spade) that remove soil but leave roots intact.
Locate septic systems away from trees. Chemicals used in septic systems may leach and damage roots or roots may grow into the systems and cause damage.
Use partially permeable materials (e.g., bricks instead of concrete) if extensive areas near trunks must be paved. Use caution when applying wood preservatives; they may kill nearby vegetation through direct contact or by leaching.
Landscape thoughtfully. Be aware of fire hazards from natural or planted vegetation around buildings. Use good judgment by planting species with compatible water requirements in an existing landscape.
For more information, consult How to Save Trees during Construction and Living Among the Oaks: A Management Guide for Landowners and Managers.
Adapted from Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide, University of California Statewide Integrated Pest Management Program (UC IPM).