Avoiding Construction Damage
By Paul Martin, Growing Earth Tree Care
Editing by Bonnie Appleton, VA Tech

One of the most neglected items in planning a new construction project -trees-are the hardest to replace. The damage caused by construction is often fatal to even the hardiest. It can take up to ten years before a tree finally succumbs to a slow, agonizing death. The length of time depends on several factors including extent of damage, level of stored energy and nutrients in the tree and species' hardiness. To the untrained eye, a tree may appear to be healthy and vibrant. This is because the tree is living off the energy and nutrients it stored prior to the damage. But the root system that has been crippled by compaction and butchering may not be able to replenish the tree.

All too often, the purchasers of new homes are in for a rude awakening when they find the beautiful trees on their lot dying a few years after they move in. Although the builder caused this damage, its the homeowner who usually must pay for expensive removals. This can be very frustrating because the value of their home goes down along with the trees.

A while ago, we were called to "save" a large elm tree that had 90 percent of it's root system cut. The builder also piled up bricks and backfill over the few remaining roots. The owner actually had the house designed around this tree, but waited until the slate roof was being put on to call us. It's too bad, because if we had been called in at the architectural stage, the tree could have survived. Instead, the owner will have to pay for the tree to be taken down. This will be expensive because the slate roof and the proximity of the building will require the costly services of a crane and operator.

The first consideration in the planning stage is to determine which trees to save and which to cut down. A good rule to remember is that it is easier, cheaper and safer to remove future problems before construction begins. The current and future health of the tree are extremely important. Some species growing in shade may do poorly if changes result in more sunlight. Often the largest and/or oldest trees are not the best to save. Each species also differs in how well it can withstand root cutting, or how susceptible it is to local insects and disease. Have an I.S.A. Certified Arborist do a tree inventory and survey.

Whenever possible, trees should be moved to a temporary nursery at a safer location on the property. Tree spades can move specimens with a diameter up to ten inches. Smaller ones can be dug up and moved in a basket or balled and burlapped. When construction is complete, these trees can then be placed back into the landscape around the building.

Larger trees that can't be moved must be protected from construction damage with proper planning. The first step is to set a physical barrier, such as fencing, around the tree. The barrier should prevent construction activity over as much of the root area as possible. Remember, roots can grow out two to four times the drip line. This barrier should be clearly marked with signs as a "Tree Save Area".

It is very important to work with the construction crew. Make sure they understand that they are not to encroach on the "save area." A good way to enforce this rule is to levy a fine for each violation. Have that written into the contract whenever possible, and make frequent inspections to ensure compliance.

When barriers are not possible to keep away vehicles and foot traffic, other protective methods can be used. They include spreading several inches of wood chips to reduce soil and root compaction and increase water absorption and bridging root systems with steel plates. Have cement pumped through conveyor pipes, instead of letting the truck drive over roots.

Some root cutting near construction is inevitable, but much is avoidable. For example, the routing of underground utilities does not have to follow a straight line from the street to the structure. Careful route selection often can avoid important trees. When that is not possible, tunneling is a good way to lesson damage. To reduce root-cutting trenches for foundations, posts and pillars can be substituted for footers and walls. If roots must be cut, it should be done with a trencher or by hand to avoid the damage caused by bulldozers ripping and tearing.

Many times construction projects will result in a change in terrain and how water drains from the land. If flows are created that add too much moisture to a wooded site, a drainage system may be needed. It is imperative to maintain the previous amount of moisture which provided the natural growing conditions for the existing trees.

Adding toxins or otherwise altering the soil can result in weakened trees, making them more susceptible to insects and disease. To prevent adverse effects on soil chemistry, spread a heavy plastic tarp where concrete or sheet rock will be cut. The alkalinity of these materials can change soil pH. Read labels. Do not use wood products containing pentachloraphenol which is deadly to roots (CCA-treated timber (greenish in color) is a safer alternative).

Subsurface fertilizing a construction-damaged tree has several functions. The first is to aerate the compacted soil to allow the suffocating roots to absorb water, oxygen and nutrients. The second is to provide the necessary nutrients that are often displaced with backfill. The third is to reduce the susceptibility of the tree to certain diseases and pests, and help reverse declining health.

Mulching the area above a root system is one of the best ways to protect it. It keeps nutrient-robbing grass and weeds at bay, while providing valuable humus as the mulch decays. Mulching will aid in regulating soil temperatures and helps to reduce soil erosion prevalent around most construction sites. Mulching decreases evaporation by trapping water and making it more readily available when needed. It is important to know what the tree's pH level should be since mulch varies in the amount of pH it has. Fresh woodchip mulch is very acidic and should not be used around a tree that requires a high pH. An I.S.A. certified arborist can help you determine which type of mulch to use and how much.

A generous supply of water is necessary for any tree to be healthy, but it is vital for a construction-damaged tree. Although you want a well watered tree, don't want to drown it and make sure there is proper drainage so you don't have standing water.

Trees that have suffered physical damage above ground may require corrective pruning or wound sculpting.