How to spot a dangerous tree

Advice from a Certified Arborist:

The recent tree-related tragedies in Atlanta have led many people to rightfully conclude that they must maintain their trees properly. Trees should be examined periodically for health and potential hazards, and there is no substitute for having a professional certified arborist perform tree inspections. But how do you know when to call an arborist? And, as a property owner, what can you do to preserve the trees you love, while protecting yourself and your home against an unhealthy or dangerous tree? Here’s a basic outline of where and what to look for to detect potential problems.

Ground Inspection. A tree is held up and fed by its root system. There are two types of tree roots. The anchoring roots support the tree, and are the most visible. The absorbing roots pull water and nutrients from the soil. When the anchoring roots rot and decay, the tree will have severe problems. The tree may appear healthy, and could be fully clad with foliage because the absorbing roots are still actively supplying the tree with nutrients. It may be completely vertical, or it may have a slight lean. In either case, if there are root problems, even a gentle wind or rainwater sitting on its leaves could cause the tree to topple without warning.

The ground and soil surrounding the base of the tree can provide clues to a serious problem. Cracked or raised soil can indicate root disturbances that could point to tree in the process of uprooting. Look carefully for signs of a tree beginning to fall over.

Fungal growth like mushrooms on or near a tree trunk is indicative of rot or decay. The presence of fungus is particularly serious if it is profuse. Fungus grows only on decayed wood. To determine if the tree is unsafe, you need to know how extensive the decay is. Call a certified arborist immediately if you see fungal growth around the base of a tree.

The most accurate procedure for detecting root rot or trunk decay makes use of tool called a resistograph. Here’s how it works: A tiny drill bit, less than of an eighth inch in diameter, is pushed into the tree with a gear. A scratch pin records on a wax paper strip the resistance to the drill bit as it enters the tree. This does not damage the tree, and it can tell the tester how decayed or hollow the tree is.

Trunk Inspection. The entire tree can break or split if there are cavities or cracks in its trunk. However, the presence of a cavity does not necessarily mean the tree needs to be removed. This depends on how extensive the cavity is, where the tree is growing, and the overall state of the tree’s health. The resistograph is valuable here, too, because it can precisely measure the depth of the cavity or hollow. Using those results, the arborist uses a mathematical formula to determine if there is enough trunk thickness to keep the tree upright.

Look for places on the tree’s trunk where there is no bark. This can indicate a dead section or a fungus attack. A long streak of missing bark coming down the tree usually means the tree was hit by lightning.

Insects often attack a sick tree’s trunk, leaving very fine sawdust shavings that are clearly visible because they are light in color. Ants boring into decayed wood leave coarser shavings. Pine bark beetles attacking a pine tree leave “pitch tubes” that resemble marble-sized balls of light colored sap.

If any of these conditions are present, call a certified arborist to find out if your tree is stable and healthy.

Multi-Stemmed Trees Trunks. Sometimes a tree grows two or more trunks. The points where the multiple trunks connect must be inspected for weakness or past storm damage. Stronger connections appear as a U shape at the crotch. A tight V shape usually evidences a weak connection. To prevent a double-trunk tree from splitting apart during high winds, a cable made of synthetic fiber can be installed high in the tree to provide mechanical support. Multiple trunk trees should be inspected by a certified arborist.

Branch Inspection. One of the most obvious tree dangers is the dead wood that can fall. You can spot dead wood easily: dead branches won’t have leaves. (A dead pine branch will have brown needles.) If they have been dead for a period of time, dead branches will be stripped of their bark. Also look for broken branches, especially after a strong storm. You might not even know a branch is broken after a recent storm until a month later, when the leaves turn brown. Pockets of decay or rot sometimes exist on the upper side of a branch, where they are invisible to a ground observer. This is where an aerial tree inspection by a certified arborist can be very helpful.

To protect yourself, your home, and the health of your tree, have weak, broken, or dead branches trimmed or removed.


To get the best care for your tree, hire a certified arborist. Arborists have an understanding of a tree’s needs. Unlike others who may want to profit from your lack of knowledge about trees and their care, arborists will do their best to protect and preserve your trees. They also will not recommend a removal unless it’s absolutely necessary.
If you are having work done on live trees, do not permit climbers to use leg spikes. Leg spikes injure and can sometimes kill a tree.
Expect to pay a fee for a tree inspection. You are paying for an arborist’s knowledge, experience and time.
The cheapest estimate may not always be the best deal! A cheap estimate might mean a terrible job awaits your tree by someone who is not qualified to perform the work.
Don’t wait for a tree to let you know it’s sick! Be proactive. Check out your trees. If you see something suspicious, call an arborist. A healthy tree is a safe tree!

Peter “Treeman” Jenkins, Certified Arborist
Treeman Inc.
(404) 377-9663