Stem Girdling Roots - April 8, 2009
Jeff Schalau, Associate Agent, Agriculture & Natural Resources
University of Arizona Cooperative Extension, Yavapai County
Some trees appear to commit suicide by self strangulation. This is caused by stem girdling roots (SGRs) that encircle or run tangential to a tree’s stem, eventually compressing the woody and non-woody tissues of the stem. The degree to which trees are negatively impacted varies with severity of root encirclement, growing conditions, tree species, weather, age, size, and, very likely, genetics. As most of us are aware, urban trees are subjected to a range of natural and unnatural stresses and/or suboptimal growing conditions.
Trees commonly fail (die and/or fall over) for structural and physiological reasons. In Arizona’s residential and commercial landscapes, improper tree staking is often a leading cause of tree failure. SGRs appear to be another causal factor for tree failure. Tree failure translates to economic and environmental losses: labor and materials to maintain trees; labor to remove and replace trees; cost of new trees; damage to personal and public property; and loss of shade, wildlife habitat, noise attenuation, and other benefits. Woody plant researchers are currently working to gain a greater understanding of SGRs.
Published accounts of SGRs first appeared in the 1930s. It was 40 years before any scientifically valid research began to substantiate the impacts of SGRs. Early research documented morphological characteristics of Norway maple trees with SGRs in Ann Arbor, Michigan. It was observed that trees with SGRs often lacked a normal root flare, had flattened stems, and had smaller leaves. However, they did not detect differences in survival, diameter, or crown density between trees with and without SGRs. Subsequent research has gathered increasing evidence that supports the hypothesis that SGRs are responsible, at least in part, to urban tree failure.
In some cases, SGRs can be visible on the soil surface and diagnosed without excavation. However, SGRs are not always at the soil surface and easily noticed. Some professional arborists have received professional training in root collar examinations. As an Extension Agent, I am often called to look at dead and dying trees and shrubs. In my experience, the SGRs are often discovered only after tree or shrub failure.
The best solution to SGRs is prevention which begins at planting. For bare-rooted nursery stock, closely examine the root system and remove encircling roots or 'J' roots (those that have reversed the normal outward growing pattern). For containerized trees, inspect the root systems for encircling woody roots and depth to the root collar flare. A common cause of SRGs in containerized nursery stock is waiting too long before transplanting to a larger container. If woody roots are encircled, straighten or prune them prior to planting. If the root collar flare is buried more than 1 to 2 inches, remove the excess soil to expose the flare areas prior to planting. If the root collar flare and stem are above the soil surface, developing SGRs will be easily detectable and treatable long before they cause stress to the tree.
Established trees suspected of having SGRs should be examined. A common symptom is the absence of a visible root flare (the buttress-like appearance where the trunk meets the soil). Sometimes light excavation is required. Obvious SGRs can be removed where they have caused minimal stem compression. Removal may be done with wood gouges, saws, or pruners during the examination process. Remember to sanitize your tools in isopropyl alcohol if you consider trying to remove SGRs. In more severe cases, where complete removal would incur excessive damage, the SGR can be cut at both ends and left to decay over time. Regardless of treatment, do not backfill the examination area. Lightly mulch the exposed roots but not the root collar flare or stem area. Remove adjacent competing plants (including lawns), maintain optimum soil water through irrigation and monitor the tree for signs of stress.
Some certified professional arborists also have experience with SGR inspection and removal. For more information on and photos of SGRs, consult the University of Minnesota publication A Practitioner’s Guide to Stem Girdling Roots which is available on-line at: www.extension.umn.edu/distribution/naturalresources/DD7501.html.
The University of Arizona Cooperative Extension has publications and information on gardening and pest control. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 ext. 14 or E-mail us at firstname.lastname@example.org and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site: http://cals.arizona.edu/yavapai/anr/hort/byg/.
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Last Updated: March 31, 2009
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