By Linda Summers, Master Gardener
I never thought too much about what trees might be considered hazardous until last spring. A silver maple bordering our driveway had lost a few limbs already. However, a strong wind tore a large branch off of the tree and carried it into the side of our car. The cost of repairing the car totaled over $2,500. I noticed other trees after that that definitely would rank high among hazardous trees. So what exactly do you look for in identifying what might present a safety hazard to you or your property?
First of all, a tree is considered to be hazardous if it is structurally unsound and there is a possible target. If a tree with decayed or rotting branches is located out in the middle of a pasture and there is no target that the limbs might fall on, then the tree is not considered a hazardous tree.
Trees become structurally unsound due to their weak structure (an inherent characteristic of the tree species), trunk or branch decay, cankers and canker rot, and root loss or root decay. Trees, or large shrubs for that matter, can obstruct street signs or intersections that might result in serious accidents. Roots might crack pavement that can cause injury. Property can be damaged and people injured or killed when trees or their branches fall.
Most tree failures occur during storms when strong winds, rain-saturated soil, or the weight from snow and ice damage the tree. It is wise to inspect evergreens in the spring after they’ve been exposed to winter weather. Deciduous trees can be inspected during leafing out, when dead branches or tops stand out. However, look for defects any time you are working in your yard or garden during the spring and fall. The Tree Hazard Checklist, as recommended by the ISA (International Society of Arboriculture) and National Arborist Association includes the following:
Check the base of the tree at the soil for heaving or partial uprooting, which might have occurred during a windstorm.Look for cracks or splits on the trunk or branches that can form from twisting or bending during a severe storm. Cracks dry out and can lead to decay and rot.
Look for large pieces of deadwood or hangers, which are branches that have torn or broken and are hanging in the tree canopy.
Look for cavities or wounds which compromise tree strength. Also, cankers, caused by fungi or bacteria, are seen as sunken, dead areas of the bark on the trunk or branches. They are a sign of decay.
Look for fruiting bodies, such as mushrooms, which are a sign of rot and decay.
Check for decay and rot because they affect the structural integrity of the tree. One common sign of decayed wood is carpenter ants.
Look to see if the tree has proper trunk flare and taper. If the tree has been planted too deep, it will look like a pole stuck in the ground. If there is poor taper to the tree, then quite possibly the grade has been changed around the tree.
Look for a tree with a girdling root problem. It will have a sunken or indented trunk on the side where the root is being girdled. This is a common problem with Norway maples.
Look for trees with co-dominant stems, poor crotch angles (such as with silver maples), “included bark” (which is bark that has been buried or pinched between two branches), and multiple branch attachments at one point. These are all defects, some of which can be corrected through proper pruning.
Recognizing tree defects allows you to take corrective measures before the tree becomes hazardous. There are instances when tree removal becomes the best option, such as in the case of our silver maple!
If you’re not sure whether your tree is hazardous or not, you might consider having a certified arborist look at the tree. For more information on certified arborists, check out the Illinois Arborist Society webpage at www.illinoisarborist.org.
For more information on hazardous trees, please ask any Master Gardener or call or visit your local University of Illinois Extension Office.