Construction practices often kill trees. The top 12 inches of soil holds approximately 90% of the fine roots that provide water and oxygen for the tree. Heavy equipment such as excavators and vehicles driving on top of the root system cause compaction of the soil. Water has difficulty penetrating the compacted top soil and gas exchange is impaired. The damage to the trees is often not visible until many years after construction. Initial symptoms include wilting or shedding of leaves, often leading to the death of the tree years later. Unfortunately, if the soil is severely compacted, there are no real practical solutions to restore the trees health.

It is important to get an arborist to evaluate the trees prior to construction and devise a tree preservation plan that clearly indicates which trees should be preserved and which ones should be removed. It requires the skill of a certified arborist to decide which ones are of greater value, which ones are practical to retain, and which ones are likely to survive the construction process. The arborist may recommend changes to the building plan if a particularly valuable tree can be saved. New construction results in a major change for the trees' environment. Even minor lot grading can severely affect water absorption. Some trees will not survive a significant change of grade as an excess or a shortage of water may result. Both problems (too much water and not enough) can kill a tree.

Many cities now require that an arborist report be submitted prior to construction, and some cities insist that the site be supervised during the course of construction. Even if city bylaws do not require arborist reports for construction, they should be done. Prior to construction, the arborist creates a tree protection plan. Those trees which are to be retained require protective fencing to protect the root zone. This protective fencing must be erected before construction begins and stay erected during construction, right to the final landscaping phase. The distance of the fencing from the trunk is determined by root diameter and the species of tree. Even with protective fencing, trees may be significantly stressed. The arborist must often reach a balance between what is ideal for the health of the trees and what is practical for construction.

Physical wounds:

Construction equipment, such as excavators, can cause physical damage to trees. Broken branches and large wounds to tree trunks do not heal properly and become entry points for disease. Once the decay sets in, decline in the tree's health is usually irreversible. Often construction workers remove branches that are in the way, using incorrect pruning techniques. Stubs left by such inexperienced trimmers do not heal properly and endanger the future health of the tree. In new construction, trenching can kill up to one third of a trees roots if the trench is dug too close to the trunk. A much better alternative is tunneling underground which does minimal damage.

These are only a few of the many things to consider when new construction is occurring close to mature trees. Again, it is important to use the services of a qualified certified arborist for consultation.