Protecting Trees

Douglas L. Airhart & Guy Zimmerman III

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[ Up ] [ What Will Damage Trees? ] [ Protecting Trees During Construction ] [ Tree Decline Symptoms ]

Protecting Trees- Protecting Trees During Construction:

Construction damage to existing trees may occur even when the contractor is trying to save the trees. Supervision is just not available each and every minute that machinery is being operated near trees.

Tree Decline:

Trees have stored reserves that help them survive stressful situations. It may take months or possibly even years for a tree to begin showing symptoms of decline due to prior construction activities. Here are examples of tree decline.

But a little prevention can save many trees. We suggest you contact a certified Arborist to assist you in this regard. Their job would include supervising the site parameters and explaining these procedures to the site workers. The arborist would be expected to visit the site at least weakly.

Soil compaction, dropping the grade in root zones, changing the grade and leveling, changing the drainage patterns, excavating and trenching with heavy equipment, disposing of chemicals, burning debris, and the stockpiling of topsoil are typical construction activities. The types of damage to trees can occur in four main ways:

	root zone compaction;
	mechanical damage to trunks and branches;
	mechanical damage to roots; and
	chemical and material spillage at some sites.

Some trees are highly susceptible to construction damage and should be considered for removal unless strict attention to protection details is possible. In general, young trees can adapt to construction changes better than old trees.

Susceptible trees are: beech, yellow poplar, hickory, birch, some oaks, most maples, and all conifers.

Tolerant trees are: elm, poplar, willow, plane tree, and locust.

Site parameters to consider for protecting trees are:

1. Select and flag the trees to be saved.

2. Select and prominently mark the trees to be removed. However, some of these trees may make a natural barrier for trees to be saved. You can let them remain until after construction.

Trees to be removed that are growing near trees to be saved should be cut off flush with the soil or their stumps ground out rather than pulling them or digging them with a backhoe. Using a backhoe may compact the soil around the trees to be saved. Because the roots will be entwined, pulling out the stumps would damage the roots of trees to be saved.

Trunks of deciduous trees to be saved may need a thin coat of whitewash to protect them from the possibility of sunscald from new amount of sunlight.

3. Build a barrier around the protection zone of trees to be saved.

Allow NO storage, NO heavy equipment, NO machinery, NO trenching, NO digging, NO driving, NO lounging of workers in this area. Nothing should happen within the drip line of the trees to be saved.

Usually, the barrier should be placed just at the drip line. Fitzpatrick (2002) recommends a tree protection root zone calculated as one foot of radius for each inch of tree diameter at breast height. For specimen trees larger than 30 inch diameter, the ratio is 1.5 foot radius per inch diameter. This is a lot of space, but if the tree is valuable, it deserves protection. If you want to protect the lower branches, the barrier must be just outside the drip line.

The barrier must be sturdy enough to prevent equipment and machinery from entering the protection zone, in case the operator “forgets” about the barrier. The strength of the barrier depends on the type of equipment being used. Heavy equipment may require a chain link fence; tractors may need 4x4 posts and 2x4 railing (Figure 9-6a); pick-up trucks may need metal posts and welded wire or snow fencing (Figure 9-6b,c).

Used with permission of Tennessee Tech University, (Photo courtesy of J. Plant, 2002).

(Figure 9-6a) Sturdy Wooden Barrier.

Used to mark the tree protection zone (partly within the drip line).

Wooden stakes and 2-foot plastic mesh perimeter netting is not satisfactory. Suitable barriers cannot be omitted. If in doubt, over-build the barrier.

4. In some cases, activity must take place within the drip line. Move the barrier no closer than 5 feet to the trunk to allow access.

If vehicles must continually drive across the root zone, drive mats or steel plates can be placed on the soil to prevent compaction.

Used with permission of Tennessee Tech University, (Photo courtesy of D. Airhart, 2000).

(Figure 9-6b) Metal Pole / Welded Wire Fence Barrier.

It is placed at the drip-line to delineate the tree protection zone.

(Figure 9-6c) Close up of Welded Wire Fence Barrier.

For temporary traffic over the root zone, we suggest vertical mulching and then covering the traveled area with at least eight inches of bark or wood chips to make a buffer to prevent compaction by construction traffic. In addition, we recommend vertical mulching or at least core aerating that part of the root zone and pruning any branches that would be hit by traffic.

(Figure 9-7) Wood Chip Buffer over Tree Roots.

When construction is finished, half of the depth can be removed and spread out over the area under the drip line as mulch.

5. Avoid changing water drainage patterns near tree colonies or individual trunks. Surface barricades, tile drains or gravel-filled trenches may be needed to divert the water to natural drainage ditches.

6. Contact a certified arborist. Look drivers and operators in the eye and tell them “no damage to trees, or no job”! Strict supervision and expectations to follow your instructions are mandatory.

7. We suggest that the construction contract include a clause about tree protection, and that monetary penalties be applied for each infraction encountered, each day.

(Figure 9-7a) Yellow Flag Designations Yellow flags shown in these two photographs trace the trench used to install electric utility lines.
(Figure 9-7b). Yellow Flag Designations The contractor was instructed to stay outside the drip line! This is why we suggest that you construct a sturdy fence to mark the tree root protection zones before construction begins.

(Figure 9-8) Backhoe Damage to Scaffold Branches.

A tree protection clause in contracts could require a contractor to pay to repair these damages.

A penalty would apply for each and every point of damage, or infringement of the rules (resting within the barrier, overnight storage, any “little thing” that occurs).

Benches for resting areas can be placed in the shade without being within the barrier. A $500 fine per item of infraction should be a deterrent. Loss of job or contract may be another suitable deterrent. Do no be afraid to enforce the very first and slightest infringement of the rules.

8. Do not pile soil onto root zones and trunks of trees. Areas under trees are needed for moisture absorption and aeration of roots, not for storing topsoil.

Any new piles of stored soil will compact the existing soil and will restrict roots from vital air passages. Equipment needed to move the piles in or out will damage the trees or the roots.

9. Any pruning or any digging within root zones must be approved by the arborist in charge.

10. Do not fertilize the trees during construction. Root zone moisture and prevention of soil compaction are more critical factors to ensure tree survival.

11. Any requested changes in these specifications must be evaluated and approved by the arborist in charge. Failure to consult the arborist should result in fines or termination of contract, or both.

(Figure 9-8a) Block Tree Well Distant.

The soil grade has been raised in this yard in an attempt to eliminate a drainage gully.

(Figure 9-8b) The tree well was installed in an effort to save the tree, but the proper subsurface aeration system was not installed. This effectively suffocated the roots of the tree, forcing the tree into decline. (The tree has since been removed.)

(Figure 9-8c)

Partial Tree Well Construction

This diagram demonstrates proper treatment when only partial filing is required. A proper subsurface aeration system would also be required within the partial filling zone.

One Treatment for Soil Compaction:

A process called vertical mulching may be used to overcome or partially eliminate the effects of soil compaction. Two-inch holes are drilled about 12- 18" deep on a grid system about 2.5 feet apart. The hole is refilled with sandy soil or pure sand in order allow air and water penetration.

(Figure 9-8d)

Vertical Mulching Technique

This diagram demonstrates the technique of vertical mulching to increase soil aeration and water penetration into compacted root zone soils.

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TLCforTrees.info is maintained by: Douglas Airhart, Ph.D. Certified Arborist & Jeff Plant, Ph.D, Last Updated on: 07/11/03