Is Your Tree a Risk to You?

By Jeneen Wiche

Leaning Tree
Leaning Tree by Chris_parfitt

Trees are wonderful assets in landscapes that add a lot of value to a property. But sometimes trees are perceived as threatening. People often worry about trees potentially damaging their property or themselves, even though the trees may pose very little actual risk. So, how do we determine if a tree is a risk to us?

The Arborist’s Certification Study Guide (published by the International Society of Arboriculture) contains a chapter on Tree Assessment and Risk Management which outlines the three main components to risk assessment. These factors include potential to fail, the environment that may contribute to failure, and the potential target (of that failure).

Potential Failure

Potential to fail encompasses many factors: the species, growth habit, branch structure (co-dominate, multi-stemmed or included bark), the apparent health of the root system, and any obvious defects like cracks, splits, wounds, or decay. Decay can be present but unseen. Arborists look for things like fruiting bodies (mushrooms), cracked or loose bark; and bees, carpenter ants or birds and other animals using cavities.

Poor pruning in the past can contribute, too. One significant cause of failure is the practice of topping trees. Topping should always be avoided. In fact, topping can greatly increase failure potential. A topped tree has difficulty compartmentalizing improper pruning wounds, increasing the chances of decay at the individual pruning sites. Topping also encourages weakly attached rapid new growth and it reduces the tree’s ability to photosynthesize and take in nutrients. Rapid, weak growth increases the potential of future partial canopy or complete canopy failure.

Environmental Factors

Environmental factors that may contribute to failure include things like heavy irrigation (where uprooting may be more likely), drought, soil compaction after construction, pollution and the history of the tree (wind, ice and mechanical damage to mention a few).

Potential Targets

Tall Vehicles Beware Leaning Tree Trunk by brownpau
Tall Vehicles Beware Leaning Tree Trunk by brownpau

Potential targets include things like structures, heavy traffic areas, driveways, roads, and people. When assessing a tree, the likelihood of damaging such targets should be taken into consideration. For example, a tree out in the middle of a field poses little threat to people and none to structures, so pruning is a viable option, or it may be the case that no action is necessary. However, a tree near a house which has lost half of its main branches, is multi-stemmed and has included bark may need to be removed.

A Certified Arborist can do restorative pruning to coax a damaged tree back into shape. Restorative pruning techniques can prolong the life of a tree that experiences significant damage. This restorative technique may require several years of selective pruning by a qualified arborist.

Another option to mitigate potential failure is to have a Certified Arborist install a cable or brace system into the canopy or trunk of your tree. If you install such a system, or currently have one in a tree, it is recommended that you have a Certified Arborist inspect the system annually.

If you have concerns about the safety of your trees, these guidelines can help you understand the risk involved in your situation. If you are concerned, it is best to contact a Certified Arborist for expert advice.

If you have any questions or concerns about trees around your property, please contact Limbwalker at 502-634-0400.