Preserving Boulder's Roots Some strategies for avoiding construction damage to trees
by Fred Berkelhammer
This text appeared as a Guest Opinion in Boulder Colorado's Daily Camera in March 2002.
Spring has arrived, a season when many Boulder County residents plan and initiate major building or landscape construction projects. The number and scale of these projects seems to be increasing. The resulting damage to large, old, established trees, whether caused by poor planning, carelessness, or both, is clearly on the rise. Contractors cause much of this damage, but ultimately homeowners must take responsibility, and therefore should undertake to learn some basic principles and precautions.
Most construction damage to trees involves roots. Some unadvisable practices include: severing and shredding of roots, compacting the soil, changing the grade, and disrupting drainage patterns. Most tree roots are found in the top foot of soil; most extend out beyond the "dripline." Injury to roots, whether from new excavation, sprinkler or utility trenching, soil roto-tilling
or installation of metal garden edging, reduces a tree’s ability to absorb water, oxygen and other vital elements. Trees become stressed, and thus more susceptible to harmful insects and disease. They often die as a result of such damage.
Roots also serve to anchor trees in the ground; when major roots are removed, it can cause a tree to fall over. This may be intuitively obvious to most people, but for some reason, such potential hazards are being created all over the county.
Soil compaction, usually caused by heavy machinery, closes the pore spaces in the soil, and deprives tree roots of oxygen. This is a condition that is very hard to correct. Adding soil to the grade has the same effect, and resulting "suffocation" causes trees to lose vitality and often die. Finally, large trees in our semi-arid climate may come to depend on existing drainage patterns; changing these can be detrimental or fatal.
Though most construction-related tree damage occurs below ground, workers also frequently harm trees above ground. Most common among these injuries are wounding of the trunks and branches, and over-pruning of the crowns. Backhoe operators are notorious for bashing into trunks; concrete trucks break low branches; framers and roofers tend to remove large branches or entire leaders improperly and unnecessarily.
Luckily, most of these problems largely can be avoided if they are anticipated during the planning stages of a project. Quite simply: Design the site so that construction activity occurs at a good distance from valued trees. This advice applies to many landscape projects as well. You also may want to consult an arborist at the very beginning of any project. The arborist can formulate a tree preservation plan as an integral part of the site plan. From the outset, inform all the relevant contractors that wounding of certain trees will not be tolerated. Penalties for unnecessary damage to trees can and often should be written into contracts.
If it’s "too late," and the planning phase can’t be revisited, there are a number of steps that can be taken to lessen the impacts. Where roots have been or must be disrupted, they should be cut cleanly just prior to backfilling. The backfilled soil should then be watered, in similar fashion to that around a newly transplanted tree. This will help the severed roots to regenerate.
Many projects include excavations that are alarmingly close to the trunks of trees. If a tree has been rendered hazardous due to major root damage, it should be removed. With a little foresight, the decision to remove can be made before excavation begins; this is a safer and less expensive approach.
To avoid soil compaction, the use of heavy equipment should be minimized, and traffic should be limited to lanes that circumnavigate vital root systems. This can be enforced by placing sturdy fencing around trees at as wide a radius as is practical. Dirt and construction materials should not be permitted to be stored under trees. Where heavy traffic over roots is unavoidable, a thick covering of wood chip mulch (about eight to ten inches), should be laid down to cushion the load. Mulch helps create a moist, aerated root environment; it therefore should be retained in the landscape (in a thinner layer), after the project is completed.
If branches need to be removed, hire someone who knows how to make proper cuts, and who understands how extensively a tree can afford to be pruned. Finally, monitor the site diligently: For all the expressed good intentions of contractors, the attitudes and habits of the workers are what matter most.
Some of the trees in this area are approaching 100 years of age; many are now magnificent specimens. Most of us love these trees deeply. The old methods and mentalities of the construction trades must adapt to this changing reality. Unfortunately, some of Boulder County’s grand old trees are needlessly dying or already dead. With a little care and effort on our part, others can be preserved for future generations.