Planning to build an addition? Maybe you're thinking about adding a new bedroom or that dream workshop you've wanted since moving in.
Take some time during the planning process to think about the impact your project will have on nearby trees.
The impact may go beyond your individual yard.
Urban forests, composed of native-forest remnants and the planted landscapes in our cities, provide a vast array of benefits, including clean air and water, lower crime rates, even higher residential and commercial property values.
Trees remove particulates, nitrogen dioxide and other pollutants from the air. They slow water runoff and ensure ground-water supplies are continually replenished. Their mere presence raises the property values of adjacent homes, and the shade they provide lowers energy bills in summer. Studies even show social benefits, such as less crime in tree-filled neighborhoods and shorter recovery times for hospital patients with views of trees.
What are the more common ways trees become damaged during construction, and what simple measures can we take to protect them?
Protect bark and branches
Trucks, graders and equipment can injure a tree by tearing bark, wounding the trunk and breaking branches. These injuries often prove fatal later on. To prevent trucks and machinery from injuring trees' crowns or trunks, plan ahead by talking to all workers on site about tree protection.
Compaction of soil can be a severe problem where trees are concerned because their roots need oxygen, nutrients and water to grow. If soil becomes compacted around a tree, it's only a matter of time before the tree will decline and die. Placing 4 to 6 inches of mulch or wood chips into the "drip zone" around trees will help, as will placing construction fencing around all trees that are to remain.
The drip zone is the circle that could be drawn on the soil around a tree directly under the tips of its outermost branches.
Another pointer is to make sure any protective fencing is placed as far away from the trunks of trees as feasible, and require the fence to remain in place for the life of the development project. Also, protect soil horizons in the surrounding landscape by avoiding soil disturbance as much as possible. Maintaining early communication with the builder and workers is key.
Protect the tree's roots
A tree's roots are found mostly in the upper 6 to 12 inches of the soil and, in a mature tree, extend far from the trunk; in fact, roots can be found growing a distance of one to three times the height of the tree. Cutting or disturbing a large percentage of a tree's roots increases the odds of the tree's failure or death; the amount of damage a tree suffers from root loss depends in part on how close to the tree the cut is made. Also, remember that tree roots larger than 4 inches in diameter are usually structural roots, and cutting them creates a potential for the tree to fall over later on.
Be careful not to smother tree roots by adding soil. Tree roots need air to breathe and grow, and it takes only a few inches of added soil to kill a sensitive, mature tree.
Sometimes, when laying irrigation pipes and doing other yard projects, cutting through a tree's roots will be unavoidable. If this is the case, use sharp tools and never tear the roots with a backhoe. You can place damp burlap on roots that are left next to a trench; also, after a lot of root disturbance, be sure to give the tree extra watering on a regular basis.
After root disturbance, don't prune your tree for at least a year — your tree will need all of its leaves to regenerate its roots.
Protecting trees during remodel, construction or development projects saves money on long-term tree maintenance and replacement costs, provides aesthetic benefits and generates positive response from neighbors and the community. However, it's not usually wise or feasible to try to save every tree. If in doubt, consult with your city forester or a certified arborist to help you with the evaluation process.
Cynthia Orlando has a degree in forest management and is a certified arborist and public-affairs specialist with Oregon Department of Forestry.