• Removal of Trees. The first concern is selecting which trees to leave. Younger trees will stand the stress of the removal of surrounding trees better than older trees. Removal of a few trees from a group exposes the remaining trees to greater wind velocities. As trees growing in large stands do not develop root anchorages as strong as individual ones, the removal of trees can increase the hazard of topping of trees by wind.
• Modifying Grade. Either raising or lowering the grade around a tree can cause significant damage. Lowering the grade as little as 6 to 8 inches can remove a significant amount of the feeder roots on trees and greatly weaken the tree, making it more susceptible to diseases and death from various causes. The loss of topsoil reduces nutrient availability, and the remaining feeder roots are exposed to drying out and low-temperature injury as a result of removing the topsoil, natural mulch and ground vegetation. Raising the grade as little as 6 inches can suffocate the roots by reducing the exchange between soil gases and air. In addition, it is also possible for the roots to suffer damage from excesses of toxic gases and chemicals released by soil bacteria. Raising the grade may also cause the water table to rise. Although not evident at the surface, a rise in the water table can cause drowning of the deeper roots.
• Trenching. Trenching or excavating through a tree’s root zone can result in the elimination of as much as 40 percent of a tree’s root system with each cut. Trees suffering such severe root damage usually do not survive, with mortality generally occurring within two to five years after the completion of construction. Underground wires and water systems must be planned carefully to avoid damage.
• Compaction. Compacting the soil around the base of a tree due to heavy equipment operation, material storage or paving can prevent moisture and air from reaching the tree’s feeder roots and ultimately kill the tree. Even parking vehicles in the shade for lunch can do significant damage.
Before ConstructionIf you are serious about saving trees, it is critical that you start before any work is done. Work with your architect or home designer to locate all trees on the site plan, then gradually eliminate those that must be removed for construction. Mark those that will be damaged due to installation of water and wires and by proximity to the movement of heavy equipment. If particularly valuable trees are involved, consider relocation of construction elements or taking a longer route for installation of underground utilities. Inspect and discuss all planned changes to the topography. Grading, even at a distance from a tree to be saved, could result in excessive drainage to the location and needs to be corrected before such a thing occurs. Develop a plan with the contractor and worker to protect the trees. Reach a written agreement about methods that will be used, and either have the contractor post a bond or put financial penalties in the contract.
This story ran longer and with more pictures in the March 2008 issue of Log Homes Illustrated.
Diane Relf is an extension specialist in environmental horticulture at Virginia Polytechnic Institute and State University. She is also editor of The Virginia Gardener Newsletter, where this article appeared in slightly different form.
For further information, check out the Virginia Cooperative Extension website: (http://www.ext.vt.edu/resources).
For additional information about tree maintenance, visit the International Society of Arboriculture website: (http://www.ag.uiuc.edu/~isa/).