|
back
| home
University
of Rhode Island GreenShare Factsheets
Protecting
Trees During Construction
The conflict between land development and tree protection
seems to be a losing battle. Oftentimes, 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.
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.
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.
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.
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.
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.
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 often killing trees on the property. To prevent adverse
effects on construction site soils:
• Spread heavy plastic tarp
where concrete is to be mixed or sheet rock will be cut.
These materials raise
the pH, causing alkaline soils.
• Do not clean paintbrushes and tools over tree roots.
• Dispose of chemical wastes (paint thinner, oil, etc.) properly. Do not
drain these wastes on site.
Adapted from Debbie Shaughnessy and Bob
Polomski, Clemson University Cooperative Extension Service,
2001
Pesticides
are poisonous! Read and follow all safety precautions on labels.
Handle carefully and store in original containers out of reach
of children, pets or livestock. Dispose of empty containers
immediately, in a safe manner and place. Pesticides should never
be stored with foods or in areas where people eat.
When trade names are used for identification, no product endorsement
is implied, nor is discrimination intended against similar materials.
Be sure that the pesticide you intend to use is registered for
the state of use.
The user of this information assumes all risk for personal injury
or property damage.
For more
information, call the URI CE Gardening and Food Safety Hotline
at 1-800-448-1011 or (401)874-2929 from outside Rhode Island;
Monday-Thursday between 9 am and 2 pm.
University
of Rhode Island Cooperative Extension provides equal program
opportunities.
|