Monday, 15 August 2011

Circled Roots

I spend the majority of my time examining trees. And I really like that! However lately I have been noticing more and more trees with circled or girdling roots. The outward expression of this condition can be very obvious, a large root or group of roots circling a tree above the surface of the soil quite clearly strangling the life out of the tree above. Or it can be practically un-noticeable, a buried root that circles around below the soil level choking the life out of a seemingly healthy tree. And the signs can also include thinning tree crown and eventually die back. Trees generally have a pronounced widening at the point where they enter the ground, called the basal flare. The tissue at the base of the tree is a mixture of trunk tissue and root tissue that is very tough and resistant to insects and decay. If you have ever burned piece of a stump it takes forever. If you have tried to chop a stump out with an axe you will know how tough this tissue is. In fact one of the most common ways to remove a stump is to grind it out like you would grind a rock.

Root tissue is different from this transitional trunk flare tissue and will not join or graft to it when they come in contact. When the root tissue tries to grow over the trunk tissue, the tissues continue to expand compressing the trunk tissue. The phloem in the trunk tissue, the outermost layer of living cells is responsible for transporting sugars back down to the roots from the leaves where it if produced. The phloem becomes blocked and compressed by the root pressing against it and results in further swelling above the blockage. This continues until the tree completely blocks itself or the root is removed.

This past weekend I purchased a Japanese black pine on a standard, while I was planting it I discovered several girdling roots. Fortunately they were small and I was able to remove them with a pair of pruners while I was planting it.

The lesson learned is that even small trees can have potentially large problems. You must carefully examine their roots and take corrective actions. Roots should move away from the trunk in a pattern resembling the spokes of a wheel. If they circle back or cross other roots sideways to the trunk, problems may be looming.

Three seasons ago we were able to identify a potentially fatal root conflict on a Dawn redwood. We were able to excavate the root collar with high pressure air and carefully remove the root. Typically the results are slow to show, however this particular redwood made such a remarkable recovery, you can barely see where the root was circling the trunk. If appropriate timely action is taken the problem can be averted and the trees life extended.

If you have trees with troubled roots contact your ISA Certified Arborist to develop a root recovery plan.