Stem Girdling Root Syndrome: Causes and Prevention
Trees can slowly decline and die as a result of the stress and dysfunction induced by stem girdling roots. A tree may appear healthy and normal, until one day, you notice that the tree’s crown does not look as full and you start seeing dead branches.
Stem Girdling Root Syndrome (SGRS) is often misdiagnosed as other tree disorders because the problem is often hidden just beneath the soil line. The symptoms produced by stem girdling roots may be characteristic of several different and unrelated problems.
A trained and knowledgeable arborist will be able to recognize symptoms associated with SGRS, leading to an accurate diagnosis. Once diagnosed, few options exist from simply removing the SGR during the root collar examination to the removal of trees that pose a stability risk.
Planting new trees near affected trees in anticipation of their death would be appropriate.
What Are Stem Girdling Roots?
Stem girdling roots are roots found growing around or circling the stem or trunk of a tree. Stem girdling roots act like a tourniquet, slowly strangling the tree.
How Do They Develop?
Stem girdling roots develop when roots are given the opportunity to grow around the tree’s stem due to the presence of soil above the root flare. Seldom in nature do roots girdle the stem. As tree seeds and nuts fall to the ground, they germinate into the leaf litter and soil or are shallowly buried by squirrels or chipmunks. Stem girdling root problems are initiated by humans in a few ways. Directly or indirectly, through our actions, excess soil ends up surrounding the trunk above the root flare.
Many of the trees we plant come from the nursery with the tree root collar or buttress root flare, covered with several inches of soil. The tree root flare must be visible at the top of the root ball when planting.
Facts Concerning the Stem and Roots
Roots prefer to grow in loose, porous soil or rooting medium.
Roots cannot grow through the air to encircle the stem.
Roots grow where they find the path of least resistance.
Roots prefer the well-aerated, moist soils containing organic matter found near the surface.
When clay soils are glazed or compacted, roots will find it difficult to grow through.
When roots are forced to grow in a circular pattern as they do in a plastic nursery container, they will remain growing that way unless they are cut and redirected.
Tree roots growing together in the soil overlap with one another and graft together. This happens all the time with no apparent harm to the tree.
Tree roots are adept to growing under ground in moist to wet soils. Tree stems and bark are not.
How Do We Predispose Trees to Stem Girdling Roots?
Listed below are the ways in which we directly or indirectly place soil around a tree’s stem above the root flare.
As field-grown trees are cultivated in the nursery, additional loose soil builds up at the tree’s base.
When bare root seedlings are potted at the nursery, the top-heavy seedling is placed in the very bottom of the container before it is filled with soil. This is done because it provides additional support for the plant.
Mechanical tree planters and tree spades, if not used properly, will set the plants too deep.
Trees are deliberately planted too deep.
Trees placed on top of loose soil in the planting hole, later settle deeper into the hole as the tree is watered in.
Trees planted at the proper initial depth have all the excess backfill soil placed around the trunk instead of being hauled away.
Additional soil is added around the base of trees when a soil grade change takes place.
How Does This Harm the Tree?
Stem girdling root syndrome develops slowly over time. It may take years for the first symptoms to appear. In the early stages, minimal damage is done to the tree. As the stem and offending root or roots continue to grow in circumference, they begin to exert pressure upon one another. The stem is adversely affected more than the root. As new sapwood continues to develop year after year, the size and number of vessels begin to diminish causing stress to the tree. Eventually the pressure is so great that the growth layer just beneath the bark, called the cambium is killed. Without the cambium, the tree trunk would quit growing. The annual growth rings are no longer being added and the bark dies and falls off. This leads to the starvation and death of the root system, which in turn leads to the death of the trees crown. It is all a very slow but predictable process. Eventually the whole tree may die.
Before the cambium is killed, growth is slowed. It is at this time that if the girdling root or roots are discovered and removed, the tree stands a chance of recovering. It is important to note here, that in effect, trees grow a whole new tree over the old one each year. With the strangling roots removed and the cambium released from its compressive pressures, the tree can now attempt to resume normal growth again.
Girdling roots can cause another problem for trees. At times, circling roots will prevent other roots from developing properly, leading to stability problems. A healthy tree will typically develop 5-7 healthy buttress roots radiating out away from the tree, providing a very stable base.
What Can Be Done About Stem Girdling Roots?
A knowledgeable arborist can perform what is termed a “root collar examination”. This will expose the root collar area and any SGRs that might exist. In most cases, the excavation is only inches deep and extends out about a foot from the tree.
If the problem is severe and the trees stability is in question, the arborist may very well recommend removal of the tree.
In cases that are caught early enough, the girdling root or roots are cut with a bypass pruner or a small pruning saw and removed. The excavation is dished out, rather than filled back in again. This prevents the same condition from developing again. Remember that roots do not grow through the air. A thin layer of organic mulch is carefully placed over the exposed roots and soil to help conserve moisture. In a situation like this, the trees long-term survival is considered good. There are never any guarantees.