Trees are a valuable asset in home landscapes. Their shade makes summer living more pleasant and can significantly reduce air conditioning costs. In winter, they shield against wind and snow, reducing heating costs. Leaves act as air cleaners, filtering dust and removing airborne pollutants. Trees shelter wildlife, slow rainfall runoff, muffle noise and provide privacy. But perhaps the main reason people value trees highly is simply the beauty and grace they add to a community.
Because a tree takes many years to grow to maturity, wooded building sites command premium prices. All too frequently, however, the trees that make the site attractive are damaged during construction. Trees may decline and die soon after construction work is finished. The homeowner then faces the cost of tree removal in addition to the expense and time needed to grow replacement trees.
Trees around older, established homes also suffer from construction damage. Remodeling projects, sidewalk replacement, landscaping projects or utility work can cause injury to trees.
Damage to trees occurs directly from physical wounding or indirectly through change of environment around the tree.
Careless movement of construction equipment causes wounds to tree trunks and root collars, the area of the tree at ground line where the roots begin to spread out. A healthy tree is capable of sealing off small wounds, localizing injury. However, large wounds and those on stressed trees will not readily seal off, allowing decay to begin.
Improper pruning to create clearance for construction equipment and tree-removal techniques are other sources of physical injury to branches and trunks. As trees are removed for placement of a new building or driveway, they may scrape bark off trunks or break branches of trees that are to be saved, creating wounds that serve as entry points for diseases. Improper pruning leaves branch stubs that die and begin to decay. To prune properly, make clean cuts with a sharp pruning saw just outside the swollen branch collar. (For more information on pruning, see MU Extension publication G6866, Pruning and Care of Shade Trees.)
Below ground, root damage is common from excavation and grade changes. Roots may be torn by improper excavation, opening wounds for disease organisms to enter. Fine, absorbing roots are lost by topsoil removal, putting the tree under stress. Structural support is lost by trenching too close to major roots, creating a potential hazard. Bruising or crushing of roots by heavy equipment may not be apparent from above ground.
Soil compaction is a serious problem on many construction sites. Even when care is taken to avoid trunk and branch injury from equipment, trees may be damaged by equipment driving over root systems. The weight of the equipment compacts soil, reducing air space in the root zone. Limited oxygen availability to roots is also a problem when soil is stockpiled at the base of trees or paving is put over existing roots.
Excessive thinning of tree stands or removal of underbrush causes increased exposure to sun, wind and heat. Sunscald may develop on trees previously acclimated to shade. Increased wind and heat exposure increases moisture stress.
Also, moisture stress may develop from grade changes that lower the water table or divert drainage patterns away from the site. Excess soil moisture may develop from grade changes, as well. A rise in the water table, puddling from improper grading, or an increase in water flow through the area will decrease the amount of oxygen in the root zone and lead to tree decline.
Adding fill soil or cutting away excess soil alters the environment around tree roots. Hauling in fill reduces oxygen to the roots. Adding as little as 1 or 2 inches of heavy clay soil on top of the existing grade may damage sensitive trees such as oaks. The soil profile and soil pH are also altered. Topsoil is often more acidic than excavated subsoils spread on the surface. Trees adapted to growing in acidic topsoil will be stressed when forced to develop new roots in soil of a different pH and texture. The ability of roots to take up many micronutrients is reduced in high pH soils, leading to decreased growth rate and yellowing leaves. Construction material buried on-site also often raises soil pH.