Trees fail when the force (gravity, wind or both) applied to them is too strong. Structural defects predispose a tree to failure, even under normal weather conditions. There are seven groups of defects/conditions arborists look for when assessing for a likelihood of failure. These are:
- dead parts/dying tree
- broken/hanging branches
- weakly attached branches/co-dominant stems
- architectural issues such as lean
- root/soil problems
Some of these problems are relatively easy to spot. Just looking at a tree, a property owner might notice that it is leaning, that a branch is hanging or that there is a crack. The severity of the defect may or may not be apparent at that time.
Some defects like internal decay or root decay are not readily visible. Root problems like girdling roots may also be hidden under soil or mulch.
A visual examination of the tree by a certified arborist is the best way to identify if a tree is at risk of failure. Remember, solutions other than removal may be an option in some cases. Depending on the defect, pruning may be an effective strategy for reducing the risk of failure. Support systems (cables, braces, guys, props) also work well to address a number of structural issues.