Oxford, MS (January 1, 2004)- Although trees and people enjoy a mutually beneficial relationship, human activity that changes the environment can often be devastating to trees. Many of these activities are construction related, such as building fountains, sidewalks, sewer lines, and roads. However, most trees can survive construction if they are separated from the construction activity. Therefore, all phases of construction must include the protection of trees.
Common construction activities that are involved in building includes trenching, soil compaction, soil clearing, and grading. The stress from these activities can slowly kill healthy shade trees in a “mortality spiral” in which the tree spirals from healthy to stressed to declining to dead. The downward spiral begins when one stress weakens a tree and sets the tree up to be injured by another stress that wouldn’t normally cause damage. As stresses accumulate, a tree becomes weaker and weaker. Once a declining tree displays many dead branches and twigs, most restorative treatments are ineffective.
Before beginning construction, tree evaluations should be done. In a tree evaluation, the tree condition, size, and species are important factors determining which trees to save. Some trees will need to be removed. Determining factors generally include: the distance trees are from building foundations, the overall health of the tree, and the tree species. This way money is not wasted saving trees that should be removed. The decision to preserve or remove a tree can rely on comparing costs with the likelihood of survival.
Construction activities most often damage a tree’s root system because it is unseen, large, and very close to the soil surface. Roots cover two to three times more land area than the visible parts of the tree. Since roots are so large and so close to the soil surface they are the hardest to protect and usually the cause of death in a tree. Additionally, if the construction activities negatively impact soil characteristics, they will cause the roots to suffer.
The ideal soil texture is a loam, composed of approximately 40% sand, 40% silt, and 20% clay. Additionally, pedons, or small soil blocks, give soil structure and hold open small cracks and pore spaces. The pores and cracks between pedons provide air and water movement to support the roots. If construction activity causes the soil composition to change or to become to compacted, the roots will suffer and can even be crushed, causing the tree’s health to decline.
In order to protect trees from injury, a tree protection zone should be established using protective fencing. Additionally, improving the soil conditions within the tree protection zone can cause new roots to move away from the unprotected zone and into the protected one. The tree protection zone should be measured so as to protect the “critical root area.” Tree survival is close to 100% when the entire critical root area is protected.
Preserving Trees in Construction Sites