Hazard Tree Identification and Prevention

Trees should be inspected regularly for situations that may cause them to break or fall. When damage or injury occurs because of a defective tree, the law usually holds the property owner responsible. A tree is considered a hazard tree when it has a structural defect that may cause the tree or a portion of the tree to fall on someone or something of value. To look for hazardous conditions inspect the tree from top to bottom. First what kind of tree is it? Some species are more brittle than others.  Silver maple, box elder, willow and poplar are fast growing trees with weak wood. What is the condition of the crown? Are there dead limbs greater than 1” in diameter? Do some branches cross or rub? Does the tree have weak branches caused by previous topping? All of these conditions call for some cleanup pruning.

Forked trunks are often a weak point. Narrow-angled forks can be weakly attached and a site for infection. Pruning early in the life of a tree to promote a strong central leader will avoid these problems down the road. Leaning and lopsided trees present more of a hazard than those growing vertically, but if a tree has always grown off center, it generally is not an undue risk. The development of a sudden lean means the support roots have been weakened and requires immediate action. Check the trunk for cracks. Small cracks in the bark generally don’t affect the strength of the tree but wounds extending to the ground should be examined regularly. Vertical cracks on opposite sides of the tree can indicate root damage or internal damage and can be extremely dangerous.

 Decay can weaken the structural support of a tree. Any wound is an opening for disease organisms and decay. Trees resist decay by creating physical and chemical barriers. Wounds are not healed, they are compartmentalized. Topping and flush-cut pruning leaves the tree especially vulnerable to infection and decay because they remove the trees ability to compartmentalize the wound. Always make pruning cuts outside the branch collar and never top trees. Signs of internal decay are cavities, disfiguration (cankers) and the fruiting bodies of the fungus (conks).  

 Don’t forget the roots, the tree’s support system.  Trenching or construction within the root zone is a major cause of hazard trees. When roots are severed or damaged by compaction they lose the ability to support the tree and damaged roots are open to infection from decay organisms. The harm caused the tree may not appear for several years; then suddenly the tree falls over! Remember: A healthy, vigorous tree that receives regular care is much less likely to become a hazard. If you have concerns about the safety of your tree contact a certified arborist for a tree risk assessment.