|As aspiring homesteaders contemplate a wooded lot, they usually imagine their dream home surrounded by healthy, vigorous trees that shade the summer sun and whisper with every breeze. After the home is built, however, the trees that made the location desirable often are either gone or dying, the victims of damaging construction work.
The conflict between land development and tree protection seems to be a losing battle. Often times, a building site has been chosen because of the presence of mature trees. These trees, however, have difficulty surviving the construction process. Although most developers would prefer to save trees on a property, they are often discouraged by past failures or regulations that force them to remove trees to locate utilities. Communication and cooperation among all participants involved in the building process (landowner, contractors, architect, landscape architect, arborist, etc.) is essential to ensure a successful tree-protection plan.
No matter how good our intentions, any construction work near trees will have some impact on them, because of the close relationship between a tree and the soil surrounding it. Trees are much more than the visible trunk, branches and leaves.
How Trees Are Harmed by Construction
Trees can be harmed by construction work in several ways. Any break or tear in a tree's bark disrupts the flow of vital fluids and exposes wood to invasion by disease and decay microorganisms, which the tree must then expend energy to deal with. A trunk wound does not always cause corresponding loss of branches or foliage, so the consequences may not be fully apparent. But a large wound in the trunk of a tree is serious-it cannot be repaired and will almost certainly result in future decay and loss of stem strength.
Just as serious, although not as visible, is damage to the root system. Roots can be severed by excavation or smothered by earth fill or compacted soil.
Compaction, the loss of tiny air spaces within the soil from foot or vehicle traffic, is especially insidious. Not only will existing tree roots be affected, but future root growth also will be impaired. Symptoms of root damage from compaction include slow growth and branch dieback in the top of the tree. Soil compaction may kill trees, although no other damage occurs. New trees, shrubs or ground covers planted in the dense soil also will suffer.
Injuries are cumulative. Construction work will compound problems trees may have received from earlier drought, insects or other natural causes. This means that trees in poor condition before construction work are not as likely to tolerate further damage. It also means that trees that do not succumb to construction disturbance may be left weakened after the work is finished.
How to Protect Trees During Construction
Are we just lucky if trees survive construction? Not at all. We can greatly increase the chances of keeping trees healthy by using these strategies:
Survey the entire construction site well before work begins to determine where trees are and what condition they are in. It is best to plot all trees on a scaled drawing, but this also can be done on the ground, especially for small construction projects. Healthy, vigorous trees with solid stems and a full complement of live branches are the best candidates for saving. Large, old trees may not tolerate much disturbance. Don't overlook smaller, under-story trees, such as dogwood, redbud, serviceberry and ironwood. If you are working with builders, inform them of your desire to save trees.
Develop a construction plan that blends the buildings with the trees on the site. This is the time to decide which trees will be removed and which will remain. Consider alternate locations for footings, walks, drives and changes in the ground line to save the best trees.
Keep in mind that it may be necessary to remove some good trees simply because there is not sufficient space for them. It is much easier to make these choices before the construction work begins. The plan can be drafted on a layer that overlays the survey plan, or mark the ground with stakes or flags. Remember that you need to keep a relatively large undisturbed area around each tree to help protect it. The larger the tree, the larger the area needed surrounding it.
Establish tree protection zones around individual trees or groups of trees to be saved. Exclude any type of construction disturbance, including grade changes, vehicle parking or storage of materials around protected trees. Set steel fence posts with flexible, snow-fence-type fabric around the perimeter of each protection zone.
Route trenches as far away from trees as possible. Utilities that may require trenching include sanitary sewer, water, gas, electricity and telephone or television cable. Some utilities may be advantageously placed in the same trench. Placement of some utilities is flexible, while others are not. If a trench cannot be placed by the builder to avoid coming close to a valuable tree, consider going under it. Dig the trench directly up to a tree trunk on both sides. Then bore or force a tube or line through the soil below the tree. Rerouting or tunneling for utilities may add to the cost of the project, but also will increase the chances of saving trees.
If branches or roots must be severed, cut them with care. Generally, remove entire limbs or branches at their origin. Use the 3-cut method to avoid stripping bark below the limb and to promote proper wound closure. Roots should be cleanly cut with a saw to maximize root regeneration and minimize chances for decay. Do not leave ragged ends. Dig carefully around large roots and allow them to pass through a trench. Place utility pipes or lines below the roots. Backfill trenches with loose soil placed on top.
Because leaves manufacture food for a tree, removal of more than one fourth of the live branches threatens a tree. Weak trees, or trees with root damage, for example, may tolerate less. Removing dead limbs will not hurt a tree.
Pruning your trees before construction could be the difference between saving that beauty and losing it! These recommended guides will give you the instructions you need to keep those trees healthy!
Use wood chips as a protective blanket over the ground. A layer 4 inches or more deep will help prevent soil compaction, especially where construction work near trees cannot be avoided. Chips help protect soils anywhere on the site where new trees, shrubs or turf will be planted. Replenish chips as they deteriorate or wear thin.
Avoid post-construction activities which could further stress weakened trees. Refrain from adding topsoil around trees, installing underground irrigation pipes or using herbicides within tree rooting areas. Do not prune trees heavily, until normal growth rate returns.
Plan for new trees, shrubs, and ground covers, which are compatible with a wooded environment. Plant shade tolerant shrubs and small trees around saved trees to maintain a wooded appearance and help preserve the original root environment. Retain and expand the natural forest floor with bark mulch. Plant turf grasses in more open, sunny areas where they will grow better and compete less with tree roots.
Building homes or other buildings on wooded sites requires taking precautions to preserve the trees. Consider tree needs before construction begins. Find the best trees and concentrate on saving them. You may wish to protect small trees that have the potential to grow into shade trees.
During construction, protect as much undisturbed area around each tree as possible, remembering to take into account both the visible and the fragile underground parts of the trees. Finally, continue to care for your trees after construction is finished. Your efforts on behalf of the trees will make your dream home in a woodsy setting a reality.
No two trees will react the same to disturbance because of differences in soil type, species, age and condition. Healthy trees generally can tolerate limited injury if they have a good growing environment for recuperation. The more severe the damage and adverse the growing conditions, the higher the risk.
Understanding where roots are.
How close to the tree can a tree's roots be cut?
An easily recognizable limit for root disturbances is the ground outside the branch spread, or drip-line. Soil excavation inside this point may result in some root loss. But if damage is not done on all sides, a healthy tree can likely tolerate it. If roots are exposed, cut them off cleanly with a saw to promote better re-growth.
Understanding where roots are and the roots' need for oxygen can help us properly protect trees during construction. To prevent construction damage, a sturdy barrier fence must be erected around the root protection zone before any construction activity begins. Furthermore, the fence must be monitored to assure that it remains standing during construction.
Once you have selected the trees to remain on the property, consider their location in deciding placement of the house, garage, driveway, walks and patio. Simply changing the angle of a building or curving a walk can preserve the essential root space of a prized tree. It is important at this point to be in close communication with your architect, who can help by locating buildings to harmonize with the natural terrain.
The key to the survival of trees in the years following construction is protection of the roots during construction. The three main causes of tree death during construction are soil compaction, grade changes and root severing. Decline and tree mortality usually show up two to three years after the home is completed. Many people still believe tree roots grow deep and extend only to the drip line. We now know roots do not grow that way.
Tree roots can grow three times beyond the drip line.
Tree Basics - the root of most tree problems......Out of sight...out of mind
But continuing research has demonstrated time and again that 95 % of most tree roots are in the top 12-16 inches of soil. And tree roots extend far out beyond the drip line usually about as far as the tree is tall. That could extend three times beyoud the drip edge. Feeder roots are shallow because living roots require oxygen as well as moisture. Tree roots want to receive moisture and nutrients as soon as possible following a rain. Imagine... the area under a tree is like a fresh piece of baked bread. The capillaries contain all the gases, moisture and nutrients the tree needs, Flatten this root zone out like a tortilla and materials are no longer available to the tree. The consequences of this treatment can cause mortality within two to three years. The unseen killer. Imagine if someone stood on you foot all day! That has got to HURT!.
Their root systems, close to the surface and wide spreading, are easy to damage, even far from the trunk. Trees cannot be repaired or restored to their original condition after a construction project is finished. Therefore, it is better to prevent construction injuries to trees, rather than attempt to treat them after the fact.
Soil compaction cuts off air and water to the tree roots. The damage caused by soil compaction occurs slowly, sometimes not becoming evident for several years. To prevent vehicular and foot traffic around the roots of protected trees, erect physical barriers beyond the dripline of individual trees, or better yet, groups of trees. When this is not possible, other protective methods can be used: (1) spreading several inches of wood chips in the root zone area; (2) bridging root areas with plates of steel. Work with the builder to locate and mark (with signs or flagging) all parking places for workers, construction roads, and areas for storage of building materials, soil and gravel.
Raising The Existing Grade
How much soil can be added over the roots? Preferably, none. Added soil can suffocate roots from lack of oxygen. If soil must be added, use the thinnest possible layer of loose soil over the smallest possible area. Think in terms of inches rather than feet. Willows or cottonwoods can tolerate more fill, ashes less and white oaks little, if any, added soil.
Grade changes are often necessary during construction of a new building. When the grade around an established tree is being raised, consider methods of preventing injury to the tree before the fill is made rather than attempting to take corrective measures after the damage has been done. While the initial cost may be high, prevention is always cheaper and more effective than attempting to correct the situation after damage has been done.
Remove all vegetation, including underbrush and sod, beneath the branch spread of the tree. Break up the top 3 to 6 inches of soil carefully so as to disturb the least possible amount of roots. This allows better contact between the fill and soil surface. Apply fertilizer at recommended rates.
Construct an open-joint wall of shell, brick, rock or masonry in a circle around the tree trunk, with at least 1 to 2 feet between the wall and trunk. This wall should be as high as the top of the new grade. This opening is commonly referred to as a tree well. Construct an aeration system using 4-inch agricultural clay tile or 4-inch perforated plastic pipe arranged in five to six horizontal lines radiating from the tree well like spokes in a wheel to a point beyond the branch spread. Allow excess moisture to drain away by installing the radial lines so they slope away from the trunk. Connect the outer ends of the radiating system with a circle of tile or perforated plastic pipe. (See Figures 1 and 2.)
To provide vents, place 4- or 6-inch plastic pipe or bell tile upright over the junction of the radial lines with the circle. They should extend to the surface of the planned grade level. Extend the lower end of the aeration system to a curb or storm drain to carry excess moisture away from the root system.
Cover the exposed soil and tile system with rock or coarse gravel to a depth of 6 to18 inches, depending on the amount of fill. Follow this with a covering layer of gravel. Place a thin layer of straw, woven plastic or other porous material over the gravel to prevent soil from filtering into the gravel and stone. Fill with good topsoil to the desired grade.
To discourage rodents, fill the tree well with enough coarse gravel to cover the ends of the lines opening into the well. Also fill the upright bell tile and cover with a screen or grill. The tree well can be left open, covered with a metal grill or wooden deck, or filled with a mixture of coarse sand and charcoal (50 percent each, by volume) to within several inches of the top. If filled with the sand/charcoal mixture, cover with pea gravel, decorative bark or other attractive material to allow air circulation through the tile system. An alternate method can be used if 30 inches or less fill will be used. No tile or pipe is used - only gravel. Again, remove all sod and underbrush, break up the soil surface above the roots and apply fertilizer at recommended rates.
Starting at the dripline, apply from 3 to 6 inches of crushed stone or coarse gravel. Gradually increase the depth towards the trunk of the tree until it is 8 to 12 inches or deeper within 2 feet of the trunk. The gravel can reach the surface of the fill in the area extending 2 feet around the trunk of the tree. Cover the gravel with a thin layer of straw, woven plastic or other porous material to prevent soil from filtering into the gravel and sealing the air spaces. Spread good topsoil over the area to the desired depth. Use good, well-drained topsoil in making the fill in order to provide adequate aeration for normal root activity and tree growth. (See Figure 3.)
Lowering The Existing Grade
There will likely be less damage to a tree when the grade is lowered, unless a great amount of the root zone is exposed or removed. Removing 1 to 2 inches of soil normally will not affect the growth of a tree, especially if steps are taken to ensure that drought damage does not result from loss of roots. Use retaining walls or terraces to avoid excessive soil loss in the area of greatest root growth. When possible, spread mulch over the exposed area to help prevent soil erosion, reduce moisture loss and keep soil temperatures lower. Provide adequate water in the event of a prolonged drought.
Corrective Steps After A Fill Is Made
If a fill has been in place long enough that the tree is already showing symptoms of deterioration, there is little that can be done to save the tree. If the fill was made recently, or if serious damage has not occurred, steps can be taken to correct the problem.
If the increase was greater than 12 inches, it will be necessary to install a tile and gravel aeration system as described above, excavating the soil to the original grade. If the increase is less than 12 inches, remove the soil around the trunk, down to the original soil level, for a radius of 2 feet beyond the tree trunk. Install a dry well around the trunk to hold the fill soil in place. Drill or dig holes every 2 feet beneath the branch spread, starting about 2 feet from the well. Insert a 6-inch tile or plastic pipe and fill with coarse gravel to allow free air and gas exchange to the roots.
Although some cutting of roots near construction is inevitable, much of it can be avoided with good planning and cooperation. It is not necessary to route underground utilities in a straight line from the street to the house. Careful route selection can often avoid the root systems of important trees. If this is not possible, reduce damage by tunneling beneath the roots. To reduce trenching for foundations, substitute posts and pillars for footers and walls.
Often when grade changes are made the terrain is altered, and there may be a change in how water drains from the land. If too much water drains into a wooded site, trees in that area may eventually die from lack of oxygen. It may be necessary to build a drainage system to maintain the previous amount of moisture that provided natural growing conditions for the existing trees. If sites are deprived of water, irrigation may be necessary to maintain existing trees.
Watch for equipment damage to limbs and trunks, and repair promptly. Chemicals and other products that are often dumped on a construction site can change the soil chemistry, weakening and oftentimes killing trees on the property. To prevent adverse effects on construction site soils:
Do Not clean paint brushed and tools over tree roots. Dispose of chemicals wastes (paint thinner,oil, etc.) properly Do Not drain these wastes on site. Spread heavy plastic tarp where concrete is to be mixed or sheet rock to be cut. These materials raise the pH, causing alkaline soils.
The Sturdy Barrier Fence
As the new homeowner ijnsist on this with your contrasctor,it is most important to the survival of your trees. To prevent construction damage, THE FENCE must be erected around the root protection zone before any construction activity begins. Furthermore, the fence must be monitored to assure that it remains standing during construction. Work with the builder to locate and mark all parking places for workers, construction roads, and areas for storage of building materials, soil and gravel. Your trees are a very valuable asset to your new home.
Boring In Utilities In The Way To Protect Tree Roots
Trenching cuts important roots. Boring under the critical root zone causes little or no damage to the treee roots. This methor will ensure a healthy tree for the life of your home.
HOME & GARDEN INFORMATION CENTER
http://hgic.clemson.edu Illustrations taken from Protecting Existing Landscape Trees from Construction Damage
Due to Grade Changes, by Everette E. Janne and Douglas F. Welsh, Texas Agricultural Extension Service.
Reproduced with permission. Prepared by Debbie Shaughnessy, HGIC Information Specialist, and Bob Polomski ,
Extension Consumer Horticulturist, Clemson University.