Rooting out Construction-Related Tree Damage

Mary Ferguson  |  6/13/2018 2:50:16 PM

20180523_181714jpgWhen I see a tree that appears to be on the decline, one of my first thoughts is usually to consider whether some sort of construction-related activity has gone on in the area. Was a driveway laid over the root system? Did someone dig a trench for a utility line?

There are a variety of ways in which trees can be damaged during construction. Many of these involve injury to tree roots. This injury can be direct – a site may be graded or excavated so that roots are removed, or a utility trench may be dug, severing the root system. Injury to roots can also be indirect. Concrete for a foundation or driveway may be laid over part of the root system, or grading may result in additional soil on top of it. Vehicles may be driven or parked over the roots, or construction materials may be stored near a tree, so that soil is compacted. When concrete or too much soil is laid over the roots, or when soil is compacted, tree roots often die due to a lack of oxygen.

Tree damage can also result from changes in the surroundings. Some smaller trees are understory trees and may not do well if large trees around them are cut, exposing them to direct sunlight. Removal of other trees on the site can result in more wind exposure for trees that remain, making them more likely to be blown over in a storm. Trees may be stressed by higher temperatures that result from the presence of concrete patios, for example. Activities at the site might also result in changes to how wet or dry a particular area is.

So what can you do?

Consider what trees are present and which are worth making an effort to keep. If trees close to the planned site of the structure are already showing signs of decline (e.g., no leaves at tips of branches) or have sustained significant injury in the past, these should probably be removed. It’s likely to be less expensive to remove trees before a house or other structure is present, and it’s certainly preferable to remove a large tree before it falls on a new structure.

Sketch a map of the site plan, including trees. You may be able to adjust the location of buildings, driveways, utility trenches, etc., to maximize the chances that trees you want to keep will stay healthy. Keep in mind that construction crews must have room to work. Get input from those involved in building so that you’ll know how much room they will need for various activities.

Trees within 30 feet of planned structures are considered at high risk for construction damage. These can be removed, or a special effort can be made to protect them. In addition, other trees that are close to (within approximately 60 feet of) the construction site should be protected. Use temporary fences to define the areas that should not be disturbed. It’s recommended that a tree protection fence be no closer to the trunk than 15 times the width of the trunk. Another way to say this is to allow at least 1.25 feet from the trunk for every inch of trunk diameter. So, for a tree that is one foot in diameter, the temporary fence should be at least 15 feet from the trunk in all directions. Fences will need to be checked from time to time to make sure that they have not been removed and that construction materials are not being stored within the fenced areas.

If you’re interested in reading more about this topic, a couple of resources to look at are Tree Protection Standards in Construction Sites (http://fwrc.msstate.edu/pubs/treeprotection.pdf) and Construction and Tree Protection (www.ces.ncsu.edu/nreos/forest/pdf/ag/ag685.pdf). Tree care professionals may want to consult Conserving Trees During Site Development: A Training Manual, available here: https://www.warnell.uga.edu/outreach/publications.

An arborist can help make calls about the health of existing trees. A list of arborists licensed by the State of Louisiana can be found on this page: http://www.ldaf.state.la.us/ldaf-programs/horticulture-programs/louisiana-horticulture-commission/.

Dr. Mary Helen Ferguson is an Associate Extension Agent with the LSU AgCenter, with horticulture responsibilities in Livingston and Tangipahoa Parishes. For more information on these and related topics, contact Mary Helen at 225-686-3020 or mhferguson@agcenter.lsu.edu.

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