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EXTENSION REPORT

Alabama Cooperative Extension System/ Baldwin County Office
302A Byrne Street   
Bay Minette, AL  36507   

Beau Brodbeck
Regional Extension Agent
Forestry, Wildlife & Natural Resources
Febuary 6, 2007

Protecting your Trees from Construction Damage; a Necessity for Tree Survival

            Trees add value to real estate and the urban landscape.  Research has indicated that large urban trees can increase property value by 15% or more.  That’s one reason homeowners and builders should consider protecting and saving trees prior construction.  It not only ensures a healthier tree but it can save money spent on dead or dying trees later.

            Poor construction techniques damage trees.  The most visible damage happens by way of physical injury to the trunk or branches of the tree.  This is often referred to as mechanical damage and is the result of machinery, equipment, or construction materials wounding the cambial tissue (this is the growing tissue of the tree located just underneath the bark). 

            Mechanical damage causes several problems, including reduction of nutrient and water flow up and down the tree, reduced structural integrity of the tree, and most devastatingly the introduction of decay and disease.  Mechanical damage also provides an easy entry point for decay and disease to infect trees and reduce their vigor and health, but more importantly their structural strength and integrity.  If allowed to spread, decay wounds may become hollow and structurally unsound making affected trees a liability and a safety hazard.

            While mechanical damage above ground is important to avoid, the most common injury to trees during construction occur below ground.  Roots are vital to tree survival and because we don’t see them, we tend to ignore them.  This is a recipe for failure and all too often is the cause of tree mortality during and after construction.  There are several ways in which roots can be damaged during construction, renovations or even during sprinkler installations.

            The first and most obvious is root removal.  Roots are often removed to make way for foundations, sidewalks, garden walls, or even sprinkler systems.  According to Dr. Ed Gillman with the University of Florida the removal of roots greater than 1 inch in diameter can be a problem.  Removing roots reduces the tree’s capacity for absorbing nutrients and water critical for survival, and in extreme cases where 50% or more the roots are lost, a tree can loose structural stability (during hurricanes, trees which have lost large structural roots are more likely to blow over).

            The second problem is soil compaction.  The use of heavy equipment, vehicles, and the storage of construction materials over a trees root system will compact soil and damage fragile feeder roots.  Ninety percent of a trees root system is located within 12-18 inches of the soil surface making soil compaction a serious problem.  The loss of feeder roots is critical especially when combined with a soil’s reduced capacity to absorb water or air by compressing macro-pores necessary for water and air permeability and retention. 

            The third problem found on construction sites is raising the natural ground level.  Filling or adding layers of soil on site will bury a tree's roots.   Contrary to some beliefs roots require air in the way of carbon dioxide and do not delve deep because of reduced carbon dioxide and water availability.  When the ground level is raised roots are often unable to get carbon dioxide and water, causing mortality in the fragile feeder roots.  In most cases this causes tree decline and mortality.

            There are several rules of thumb used in the industry today to identify the region inside which roots should not be disturbed, if tree survival is desired.  One common rule is protecting roots inside the tree’s “drip line”.  The “drip line” is a line encircling a tree corresponding to the furthest extension of the branches of the tree.   A second method developed by Dr. Kim Coder at the University of Georgia is the “critical root zone”.  This method is a simple formula composed of multiplying the tree’s “diameter at breast height” (or 4.5 feet above ground level) by 2.5 feet to derive a diameter inside which roots should not be disturbed. 

            Regardless of the method you use to protect a tree’s root system it is important to consult with a Certified Arborist before construction begins and work cooperatively with architects and contractors.  It is important to include trees in your pre-construction plan by selecting and protecting the trees you desire saving before the project begins.  A common method to enforce the “critical root zone” is erecting fences protecting root zones around the trees you wish to preserve on your prized piece of real estate. 

            For additional information contact Beau Brodbeck at the Baldwin County Extension Office in Bay Minette Alabama by email at brodbam@auburn.edu or by phone at 251-937-7176.

Email address: brodbam@auburn.edu
Phone: 937-7176 or 943-5611, ext. 2222

Issued in furtherance of Cooperative Extension work in agriculture and home economics, Acts of May 8 and June 30, 1914, and other related acts, in cooperation with the U.S. Department of Agriculture. The Alabama Cooperative Extension System (Alabama A&M University and Auburn University) offers educational programs, materials, and equal opportunity employment to all people without regard to race, color, national origin, religion, sex, age, veteran status, or disability.

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