Crow’s Nest: Sometimes we nail it.

February 15, 2015

By Daniel Barringer, Preserve Manager

We have a hazard tree management program on our preserves. It’s not something we talk about much, but just something that we do as part of our routine land management.

Twice a year we survey the trees near targets such as buildings, wires and roads. Trees with defects are entered into a database that we forward to Tom Kershner, our Arborist, who oversees the program. We monitor these trees until they are rated high enough that we think they need to be removed or pruned.

Every tree dies someday, that’s reality. We would like to manage how and when trees along roads fall. One cannot eliminate risk, only manage it. Sometimes a tree with no outward defect fails, but often there are signs we look for to evaluate a tree’s decline. Our preserve managers have received training on evaluating tree health and proper chainsaw operation for felling trees.

Sometimes it’s obvious why a tree is on the list. If it’s dead and near a target, it needs to be removed. Sometimes woodpeckers excavate the trunk, indicating insect damage and likely rot. And sometimes a tree falls due to “soil failure,” where saturated soils can’t hold the roots of a tree with a tall crown. Trees near roads suffer many stresses: physical damage from cars or road maintenance, road salt, reflected heat from the road surface, nails from boundary signs, and their roots don’t typically grow well under the pavement—a surface that is impervious to water and deprives roots of the oxygen they need.

The red maple below didn’t look like an imminent hazard—and it wasn’t. But it had experienced some storm damage from ice accumulation—small broken limbs still dangling above, but not big enough themselves to be a hazard. And it had lost a couple branches entirely but the bark had failed to grow over the holes leaving open cavities. It wasn’t a huge tree, and it was tempting to put off any management until the tree was larger and really looked like a hazard. After all, as I’ve said before, I prefer my trees standing. But this one really wasn’t thriving and would only be more difficult to remove when larger.


So although I had no idea this tree was so hollow I wasn’t surprised to find that it was. There are tests you can do, and even tapping the trunk lightly can sometimes reveal that there is a cavity inside. I am glad I made the call that this one should go. By the way, a hollow tree is also more difficult to safely take down because it lacks much of the material used to create a hinge for the felling.

There are some good books out there for learning about tree defects. Here are three I like:

Tree Decay: An Expanded Concept by Alex Shigo, USDA Forest Service Bulletin 419, April 1979.

The Body Language of Trees: A Handbook for Failure Analysis by Claus Mattheck and Helge Breloer, translated by Robert Strouts and edited by David Lonsdale, United Kingdom Stationary Office, 1998.

Evaluation of Hazard Trees in Urban Areas by Nelda P. Matheny and James R. Clark, International Society of Arboriculture, 1994.