Protecting Trees During Construction Activities
Jim Sellmer, Ornamental Horticulture Extension Specialist

We often forget that trees are required to adapt themselves to their surroundings to survive. We often reduce a tree's survival by making three very poor assumptions:

• Trees are elastic enough to adapt to abrupt changes to their environment.
• Our actions in and around our trees do not obviously and immediately impact the trees.
• The tree has been there for years, so nothing will affect it anyway.

In reality, established, mature trees are less tolerant of change to their surroundings than newly planted young trees. Furthermore, trees vary in their elasticity. Fast growing, colonizing, and stress tolerant plants (i.e., Mulberry, Boxelder, Silver Maple, Bur Oak, Willow and Poplar) are more readily adaptable to a change in their environment than slow growing, climax trees (i.e., American Beech, Red and White Oaks and Sugar Maple).

Construction activities in and around trees can change the environment of the tree in several ways both directly and indirectly. Common changes that affect established plants include:

• Change in grade due to the addition or removal of soil in and around the trees root system
• Soil compaction around the tree root system by heavy equipment, construction materials stored under the tree, vehicles being parked under the tree, extensive foot traffic over roots during wet periods, and lack of overall protection of the root system.
• Direct damage to the roots and trunk by equipment and vehicles during maintenance and construction process.
• Change in the overall environment including water drainage patterns, available light, pedestrian and vehicular traffic and activities, and other management practices (i.e., deicing salts).

Planning for Construction
As a Grounds Manager, you will likely be involved in the decision making on new construction. Either as a resource person regarding the site or as the person responsible for protecting the plantings and accommodating the construction crews. It is likely that you will play a part in both roles. For this reason, having a plan and information on all of the plantings can help you make decisions and provide responsible feedback on the construction planning process.

The first step in preparing for immediate or future change on a site is to begin with a plan of the site. Knowing what you have and plan to add will assure greater protection for the plants on the grounds. In order to protect the established trees on your grounds from changes in the landscape and new construction you must start with a plan.

• Acquire a plat plan with locations of existing buildings and projected construction.

• Identify and map the trees and shrubs on the grounds on a copy of the plat plan. This may seem tedious but when decisions on building or parking expansions or new construction occurs, you will have a base of information on the plants which will be affected. New employees and volunteers with assistance and supervision can readily do tree identification and mapping. This provides new employees with a sense of orientation to the site. Similarly, this provides projects for volunteer groups and public good will.

• Know your plants. Plants vary in their tolerance to construction and environmental change. Know their level of tolerance to root damage, soil compaction, moisture stress (ex. drought and flooding), insect and disease susceptibility, and overall health and vigor.

• Prioritize the plants based on health and on the overall landscape and monetary value. If you are uncertain of the health of a tree, contact an arborist that can evaluate the tree's health. Similarly, an arborist, landscape contractor, nursery personnel, or an extension agent can assist you in evaluating the monetary or replacement value of a landscape plant. Prioritizing the plants assures that those that should be removed or replaced are clearly identified and the unique, prized, and healthy plants on the site are marked for protection.

• Once identified for protection then a clear set of plans can be developed for the proper protection of these plants. Knowing the protection options for plantings can change the placement of structures, the site preparation techniques, and the traffic patterns of the construction equipment. Not reporting these needs can lead to increased replacement costs, unidentified costs, damage to the structure, and loss of desirable and prized plantings. In addition, the stage is set for future development of the protected plantings.

• Identifying the protected plantings and the proper methods for protecting the plantings can then be clearly and concisely recommended and explained to the administrators, architects, construction contractors, and utilities who develop the placement of the building and its supporting infrastructure. This includes the placement on walkways and driveways away from the established planting beds to avoid root system suffocation due to pavement and soil chemistry changes due to the placement of limestone gravel as a base for pavement.

Avoiding Construction Damage
Avoiding construction damage is paramount to the survival of the plantings and to reduce future costs to your landscape budget. Construction damage can occur both above ground and below ground. Below ground damage includes severing roots, soil compaction, grade change, drainage change, and change in soil chemistry. Above ground damage includes: breaking limbs, gouging and scrapping trunks, changes in light and exposure, and bark and cambial damage from chains and signs attached to trees.

A tree's feeder roots are within the top 6 to 18 inches of soil and most often extend beyond the drip line of the tree's branches. In many cases, the feeder roots are growing in the organic litter or mulch, which has accumulated under the tree. A tree’s roots develop at the soil depth, which provides the optimum conditions for absorbing nutrients, moisture, and oxygen, which are necessary for its growth and survival.

Methods for protecting a plant root system should include organizing the construction area and damage prevention strategies including:

1. Use Signs, flags, and flexible snow fencing to mark plants to be saved, identify vehicle throughways, parking sites and material storage areas.
2. Stake out utility lines. Group and route these lines carefully to avoid severing roots. Where routing around a planting is not feasible, recommend tunneling lines under trees rather than trenching through the root zone.
3. Use high visibility flexible snow fencing barriers to protect individual and groups of plants during construction. Remember that barrier areas should be larger than the planting zone to protect established feeder roots.
4. Where traffic patterns can not be controlled, then other options for reducing soil compaction should be employed. These protective options include spreading several inches of wood chips over traffic zone to reduce compaction, bridging root areas with steel plates or boards, using conveyor pipes and belt systems to reduce driving heavy trucks (ex. concrete trucks) over tree roots. Where excess mulch is used to reduce compaction, remember to remove the mulch to avoid suffocation of the plants once the traffic pattern has changed.
5. To avoid trenching and severing roots, recommend the use of pit, post, pier, and pillar construction methods instead for the building of some structural features.
6. Changes in grade are one of the most common and destructive causes of damage to plants. Grade changes come in the form of adding or removing soil from an area. Adding soil buries the roots and thus deprives them of oxygen and water. Removing soil damages feeder roots and subjects the roots to drying out due to loss of its protective soil covering. If soil must be added around the tree, start by adding a porous soil (ex. sandy loam) or gravel layer to insure air and water movement. Do not use crushed limestone over the root zone before adding soil. Another option is to plan the grade change to occur outside of the root zone and use a retaining wall to protect the root system. Small circular pits dug around the trunks of trees do not adequately protect the trees because the added soil still acts to suffocate the fine feeder roots. If soil must be removed, plant the grade change outside of the root zone to prevent root damage. Do not allow soil to be removed from more than one side of the planting to assure that the tree can adapt in other directions to reduce root area loss in one direction.
7. Drainage changes due to grade changes can include the loss of water from the planting bed or an increase in water due to the development of a pond or low area. Drainage or tiling may be necessary in areas where increased water collects around the root system. Future planting choices for the area should consider the increased water. On sites, which are now drier than before due to the grade, change may require irrigation to maintain the existing trees. In addition, future plant choices should take into consideration the new microenvironment of the area.
8. Changes in soil chemistry can take many forms. In established stands of trees, consider the natural environment of the plants. Oak trees prefer an acidic soil and if their leaves have remained under the trees up until the construction, then removing them will change the pH of their soil over time. Changing their natural undergrowth will likely affect their survival over time. Similarly, construction activities can change the soil pH of a planting bed. Protect the soil under plantings from the alkalinity attributed to the mixing of concrete and cutting of sheet rock. Heavy plastic tarps on the ground can provide this protection. Paint brushes and tools should not be cleaned over the roots of trees. Dispose of all chemical wastes properly.

Protecting the trunk and branch structure of a plant requires care and diligence.

1. Removing, moving, and tagging trees will help to avoid future problems. Hazard and leaning trees should be the first to go from a construction site. Trees within five feet of the new construction will likely be damaged and should be removed to avoid problems. Consider transplanting trees that are less than two inches in diameter and ten feet tall. Check the other trees for low branches that may be damaged by construction equipment and vehicles. If the traffic routes cannot be modified, prune up the low hanging branches that are in the traffic pattern. Barriers around the trees should help in reducing trunk damage.
2. Trees often become signposts, fence posts, and fulcrum arms for pulleys on construction sites. Do not allow this to happen. Nails, screws, and other fasteners provide openings for insect and disease problems. Wires and chains can girdle trees especially if let after construction. Attaching pulleys to trees for use in lifting construction materials invite insect problems, branch breakage, and undue stress on a tree.

Repairing Construction Damage
Signs of breakage and tree wounds become immediately apparent upon examination of the trees closest to the construction site. On the other hand, symptoms from construction damage may appear the next growing season or may take several years to appear. Common symptoms of root damage include:

• Branch die back in affected trees.
• Yellowing foliage occurs in some trees due to nutrient deficiency.
• Reduced leaf size and sparse leaf cover in future years.
• Growth slows over consecutive years based on branch tip elongation.

If left alone trees stressed from construction damage will continue to wither and are open to disease and insect attack. Unless an effort is made to remove the stress or revitalize the tree, then the tree should be removed before it becomes a hazard tree. As mentioned earlier some trees that are more tolerant to construction stress than others so efforts to revitalize may not be affective. Some methods of revitalizing a tree suffering from construction damage include:

• Thinning the Crown of the Tree
  This may be the most effective way of helping a declining tree. A tree with a damaged root system can not sustain all of its branches. Removing dead or dying branches will help to bring the crown to root ratio back into balance. Do not remove healthy, growing branches.
• Applying Mulch Over the Root System of the Tree
  Organic mulches (wood chips or shredded bark) encourage the growth of fine feeder roots.
• Fertilize the Tree
  This is especially true if fertilizer has not been applied recently. The reality is that fertilize will stimulate luxuriant growth but fertilizer alone will not save a tree with a severely damaged root system.
• Increase Care and Observation of Trees
  Extra care should be given to trees in construction areas whether they are showing stress symptoms or not. Water the trees well during dry periods and fertilize once a year in the early spring or late fall.
• Broken Branches Should Be Removed
  Prune back to a branch intersection or to the branch collar using the three cut method. This will reduce invasion by insects and disease while promoting the compartmentalizing process.
• The Ragged Edges of Gouges and Ripped Bark Can Be Repaired with a Chisel or Sharp Knife
  Remove the bark back to its point of attachment to the tree. Shape the wound in the form of a narrow ellipse with rounded ends. This will promote wound closure of the wound, look good, and will reduce die back and pest entry. Do not expose more cambium.

CALENDAR OF PROGRAMS

JULY 15 1998
Grounds Managers Field Day
Westtown School, Westtown, PA
Contact: Scott Guiser, Bucks County Cooperative Extension at 215-345-3283

JULY 27-29 1998
Penn Allied Nursery Trade Show (PANTS '98)
Fort Washington Expo Center
Fort Washington, PA
Visit the http://www.pantshow.com for more information

JULY 28-29 1998
1998 Cutflower Short Course
Ag Progress Days Ground
Contact: Steve Bogash, Blair County Cooperative Extension at 814-693-3265

Information provided by Rob Berghage and Jim Sellmer Penn State Department of Horticulture, Ornamental Horticulture Extension Specialist, 103 Tyson Building, University Park, PA 16802, (814) 863-2571

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