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Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

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October 2002

Building for growth

Trees on construction sites need protection to ensure they survive and thrive in the years to come.

Don Kissinger

Additional sources of information
Advice to assure trees thrive
A wider tree protection area is better
Protecting your trees now for tomorrow

A four-year-old home sits neatly amid 30 or so trees; the remains of a once-thriving maple forest now subdivided into half-acre lots. Although it's July, it looks like the last days of fall: What leaves are left have turned a dull, sickly yellow. The trees are dying, and the homeowner who shelled out $80,000 for a wooded lot wants to know why.

An arborist could spot the problem halfway down the block. The telltale signs of a grade change are evident: The trees look like telephone poles stuck into the meticulously leveled-and-groomed lawn. Few will survive, and the homeowners drawn to the lots precisely because of the trees will be disappointed for a long, long time.

The problems begin below:

Careless handling of building materials and equipment above ground can damage branches and tear tree bark. The real damage, however, occurs below ground. Soil compaction and altered grade within a tree's large rooting area are the two primary causes for tree decline and death years after a development or home has been completed.

Compaction is caused by equipment and people. Trucks, bulldozers, stockpiled materials and the constant battering of soil by wheelbarrow or foot traffic can be detrimental. This compaction not only impacts the current trees, but can jeopardize the success of plantings yet to come, by creating a medium which new trees' roots may not be able to penetrate, thus it is the combination of weight and repetition of traffic that damages roots.

The weight squeezes the air spaces from the soil and by repeatedly traveling over the same area, the air spaces become smaller and smaller until in some cases you have a soil medium similar to concrete. The resulting decreased oxygen to the roots is not adequate for the tree to sustain itself. This will cause the tree to shut down and shed limbs it cannot maintain. This can occur sporadically throughout the crown of the tree or in entire sections. The hardened soil can no longer absorb water. Instead of soaking into the ground where roots can take it up, water runs off and trees become dehydrated, and the runoff results in soil erosion and pollution.

Road expansion makes a deep cut into this tree's roots. Damage and disruption from construction activities can be minimized or eliminated with careful planning.© John Van Ellis
Road expansion makes a deep cut into this tree's roots. Damage and disruption from construction activities can be minimized or eliminated with careful planning.

© John Van Ellis

Grade changes also can be fatal. Dropping the grade cuts exposes a tree's root system, most of which is within the top 18 inches of soil. On the other hand, adding (or as builders call it loosing) fill on top of tree roots, even as little as three inches, can literally smother roots. The telltale signs of added fill are a tree trunk coming straight out of the ground like a telephone pole without the normal flare at the base where typically the trunk changes over to roots.

Additional symptoms of grade change damage to trees are newly formed smaller sucker limbs protruding from the trunk of the tree and growing mostly vertical. These sucker limbs are the tree's way of trying to produce additional food to compensate for the damage done by the increase of soil or decrease of roots.

Protecting your trees now for tomorrow

You can have a beautiful home and trees, but it requires planning and some work. The process begins well before any earth is moved.

Hire a reputable arborist for assistance, then between the two of you inventory all trees of landscape size or larger on the lot. Record the location, size and species in tabular form and on a map. Include comments on each tree's overall form and health. Use this information to help determine which trees should be saved and where the home or building will be situated.

In some cases, to truly preserve the desired trees, the home or building plans may need to be altered. Next, go to the lot with the builder and arborist to mark or stake the proposed location of the house or building. Determine how much room is needed for machinery, to maneuver reasonably during construction activities. Allow for a single entrance and exit corridor for all machinery, equipment and material deliveries – preferably the location of the future drive or parking lot.

With the building footprint determined select the trees to be saved, thinking carefully about future landscaping needs. Saving groups of trees is far more beneficial and will allow a better chance of surviving and thriving into the future than just single specimens. Contact the utilities involved to encourage a single corridor for the electric, gas, phone, water and sewer lines. Placing these alongside the driveway is an excellent idea. If you must cross the yard where savable trees are located, curve the lines or tunnel under the tree roots to sever as few roots as possible.

A wider tree protection area is better

After clearing the agreed-upon trees to accommodate the home or building, driveway or parking lot and construction activity area (but before any dirt is moved), meet again with the arborist, builder and all subcontractors to outline the parameters for the fenced "tree protection" areas.

Roots of trees can extend outward two to three times the height of trees and further in some cases depending on soil and trees species. A good rule of thumb for designating a tree protection area is a 1 -foot radius from the tree trunk for every inch of diameter measured at breast height 4 feet above ground level, with a six-foot minimum, regardless of trunk diameter.

Fence the tree protection area off with sturdy posts and hefty chain-link fence. Designate one staging area, away from trees, where building materials can be located along with refueling machinery, mixing compounds, or washing off equipment.This will lessen adverse impacts to tree roots. It's advisable to fence this area also. Adhering large weather resistant signs stating "TREE PROTECTION ZONE," "NO ENTRY" and "MATERIALS STAGING AREA" to the appropriate fences will emphasize the magnitude of your concern and may educate others.

Prior to backhoe or bulldozer use in digging basements or foundations within the building area, it is a good idea to use a vibrating plow to cleanly sever any roots at the perimeter of the tree protection zone. In essence, this acts a form of root pruning, which allows for a quicker and more complete recovery to the tree roots than if they were still attached and were being crushed and exposed by machinery. Require that all excavated soil be moved off site, as mounds of soil will smother tree roots by limiting available oxygen.

Include a landscape protection clause in all contracts stating agreed upon definitions and the penalties to be paid by the builder if damage occurs to trees, or fences are moved or removed during the building process. Make sure the builder understands that he or she is responsible for all subcontractors' actions taken against any tree. Emphasize that the builder is ultimately responsible for the successful completion of the project. Monitor the construction process once it has begun. Visit the site regularly to inspect and take pictures or videotape. Your presence will alert workers of your concern. Should damage occur, notify the builder immediately, and take action to ensure continued health of the affected trees.

Snippets of advice to assure trees thrive

Remember, the existing trees add a great deal of monetary and aesthetic value, along with benefits such as wind reduction in the winter and shading of homes and air conditioners to run more efficiently in the summer. Shading also improves durability and extends the life of asphalt roofs, painted surfaces and vinyl siding. It may take decades to replace the trees should they die. Keep the following points in mind to ensure your trees are thriving long after construction is finished:

  • Before construction activities occur, mulch from the dripline (or perimeter of branches) to near the trunk of the tree. This will help conserve moisture and regulate soil temperatures, as well as adding nutrients back to the soil for the tree to use. If the root zone of preserved trees must be traveled across, adding six inches of wood chip mulch or four inches of gravel can substantially reduce compaction. Using a geotextile material under the gravel will help in its removal upon completion of the project. Do not use limestone or dolomite gravel as this could dramatically alter the pH of the soil to the detriment of the tree.

  • Prior to any building activities taking place, prune any large dead or live limbs that may be damaged by machinery or the structure being built. Be particularly aware not to prune oak trees during late spring and early summer as they are highly susceptible to the deadly oak wilt disease during that time.

  • Supply trees with adequate moisture before, during and after construction.

  • Tolerances to construction activity vary by tree species. Some trees can handle root severance but not compacted soil; know a tree's constraints.

  • Competition with a grass lawn in areas that were once a naturally large litter layer will negatively impact preserved trees. Having a smaller grass area to maintain and more natural vegetation will be less time consuming for the property owner and make for better long-term tree health.

  • The micro-climate change to preserved trees due to others trees being removed will lend them to a higher wind-throw exposure, an increased amount of light and fluctuating air temperatures, which are all realities that must be considered when deciding what tree species to preserve along with future plantings.

Additional sources of information

The National Arbor Day Foundation (NADF) in cooperation with the National Association of Home Builders (NAHB), presents the Building With Trees recognition program to recognize and award builders and developers who protect trees during building and land development.

Since the 1990s, hundreds of homes have been built following program guidelines, helping thousands of trees to survive and thrive after home completion. The Building With Trees program provides two opportunities for builders and developers to receive recognition for their efforts – one following the planning and design phase of a project, another following project completion. Contact the NADF at (402) 474-5655.

This article is a good primer for homeowners, builders and developers. To learn more, get a copy of a free 25-page booklet with diagrams and tables produced by Penn State College of Agricultural Sciences Cooperative Extension. Additional copies are $1.45 each. The title of the publication is "A Guide to Preserving Trees in Development Projects," publication code number UH122. To order a copy call (877) 345-0691.

Additional information:

Trees & Home Construction – Minimizing the impact of construction activity on trees; Ohio State University Forestry Extension, bulletin 870-99.