GIMME SHELTER- Root of the matter: Protect trees during construction

Adam Downing
Virginia Cooperative Extension, Forestry & Natural Resources Agent

Q: I'm a local developer proposing a project, and I want to make sure beautiful trees on the property are properly protected. What are the steps I should take?

A: Whether it's a development in an existing forest, a sidewalk replacement, or a building addition, trees are most likely part of the landscape. Unfortunately, trees aren't always factored into the planning phases of development or construction. Kudos to you for making it a priority.

Construction damage to trees can result in sudden death or, years later, to a weakened tree that finally succumbs to insect pests or disease. Through decent planning and proper tree protection measures, the story can have a much happier ending.

Protecting trees begins before the first piece of equipment goes to work. The initial planning should include trees in the drawings; even better– include an arborist or forester in the planning phase.

Where will construction take place? Can that be modified? Which specific trees are valuable?Reasons may include historical significance, size, uniqueness, location, beauty, and energy conservation. How much space is needed for storing equipment and materials? Where does the access to the construction site fit into everything?

Make the tough calls at the beginning. Perhaps changes to the site can be made or specific measures can be put into place early on to protect certain trees. 

Protection applies to all tree parts, include leaves, branches, trunk, and roots. Protecting the above-ground parts is rather simple: Don't run into or over a tree, don't build large burn piles under a tree, and don't cut branches without proper pruning techniques. However, the most ignored measure is often the most important– protecting the roots.

Roots function to keep plants upright and to take up water and nutrients from the soil. To accomplish this, roots need to "breath." Roots uptake oxygen and discharge carbon dioxide (just the opposite of leaves) to enable cellular respiration. Roots need soil that has nutrients and structure. Soil with good structure has space for air and water. When soil structure is destroyed, a roots' ability to take up nutrients, air, and water is compromised. 

Soil structure is most commonly destroyed by compaction, which limits infiltration of rainwater and increases runoff. This results in even less water for plant growth. Depending on the texture, soil is easily compacted. That's good news when it comes to building roads, but bad news for roots. Compaction can result from a number of above-ground activities, but most notably from heavy vehicle traffic. Amazingly, due to the mechanics of soil, full compaction actually occurs on the first pass. Therefore, "just driving under this tree once" can be fatally damaging.

Establishing a tree protection zone (TPZ) is the most effective measure. It protects the tree above and below. The size of the zone will vary depending on tree size, species, and health. Larger trees need larger zones as do species more sensitive to disturbance. 

When fencing off the TPZ, place it underneath the drip line (the outer circumference where the rain is shed to the ground) for broad-canopied trees. Understand, however, that most roots extend well beyond the drip line. One other way is to base the TPZ on trunk diameter. First, measure the diameter of the tree (at 4.5 feet above ground) in inches. Then make a circle around the tree in feet equal to the number of inches the trunk measured.

In the TPZ zone, no equipment or material storage, no parking, no refuge dumping, or anything else that would result in compaction or soil pollution should occur. If possible, a sign should be posted explaining the purpose and consequences of tampering. If there's not enough room for an effective TPZ, temporary ground covers like mulch and geotextile fabric can also be used.

Adam Downing
PHOTO COURTESY ADAM DOWNING

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