Spotting Unhealthy Trees

Generally speaking, trees and shrubs are the most long-lived of all landscape plants. Some species can live for hundreds or, in some cases, even thousands of years, but as a tree reaches maturity it may begin to show signs of old age. To ensure the health of the tree, you'll have to monitor those signs.

"You need to get up close and personal with your trees and give them a thorough checkup at least once a year," says master gardener Paul James. "At first glance a tree may appear to be perfectly healthy. I've seen trees that look fine one day and topple to the ground the next day only to reveal a completely hollow interior or a tangled mass of rotten roots."

Here are a few things to check for:

Cracks and splits in trees are two of the most common and easily recognizable signs of potential problems. They typically occur where a branch joins a trunk or where a trunk divides somewhere up the tree. While they often appear for no reason, they can be caused by many factors — including weak branch angles, excessive weight from above, internal decay and even lightning. As the tree matures, these cracks, which are structural defects, will only get worse, especially if you live in an area where the weather includes high winds and snow and ice storms.

One of the surest ways to stabilize branches prone to cracking or splitting is to cable them or anchor the weaker branch to a stronger branch by attaching the two with a seven-strand, galvanized steel cable two-thirds to three-quarters of the way up from the defective area.

Cabling is something that should be done by an arborist. Alternatively, you can completely remove the branch that represents a potential hazard or you can selectively remove smaller branches from the main branch to lighten the load. James has cabled a large overhanging branch on a prized red oak, but every year he prunes a few smaller branches to eliminate excess weight without altering the tree.

James made a proper cut last year to one of his trees, and the wound has effectively healed. A cut on another tree was made flush to the trunk by someone else; the wound has failed to heal, exposing the interior of the tree to the elements; the tree is starting to rot.

Still another cut made properly a few years ago is developing a small hole, which indicates a hollow interior somewhere in the tree. Trees with hollow interiors can live for decades, but they can come crashing down suddenly and without warning.

A hollow at the tree's base can also mean a hollow interior. Most often a fungal disease causes these hollows. The fungus usually has entered the tree via bark damage caused by a lawnmower or string trimmer. For example, a cut by a mower may not look threatening, but it can serve as an entry for a fungus, resulting in a hollow tree.

Fungal diseases can also enter the tree in other ways, such as through the soil or leaves, or in the form of mushrooms, which, if found on or around the base of the tree, signal a serious problem in the roots or trunk. Because fungal diseases are difficult if not impossible to control, you should call an arborist immediately if you find evidence of fungal invasion.

Other holes in trees such as those created by woodpeckers or squirrels are further evidence of a potential hollow in a tree. Depending on their size, they may not cause a structural problem, but it's a good idea to have an expert examine them. An arborist will first inspect the hole visually, then he may drill a small hole in the tree to determine the extent of the hollowness. He may remove a core sample from the tree or may use a special device that measures the density of the wood. Based on his findings, he may recommend that you have the tree removed.

A hollow tree can be quite healthy, although structurally unsound. The vascular system of a tree (the vessels that carry water and nutrients up and down the tree) is contained within a relatively small area of wood just inside the outer bark (the small blue and red circle seen here). Even if a tree is rotten at its core, the tree can remain physiologically active. That's why girdling a tree (tying a wire around it) will eventually kill the tree by shutting down the flow of water and nutrients through its vascular system.

Tilting trees usually indicate some sort of decay within the root system, most often brought on by fungal diseases or improper planting. (Some trees, such as the river birch, have a natural tilt.) If the tree is truly tilting, and the tilt is so severe that it causes the ground to rise up in the opposite direction of the tilt and the roots have lost contact with the soil, you'll want it removed quickly before the next storm.

All trees occasionally have dead branches, often for no reason. They can be trimmed any time, but dying branches in the tops of healthy trees usually signal a problem in the tree's root system. You will probably need an arborist to help identify the source of the problem and recommend a solution. You may need help removing the branches; however, with a telescoping pole pruner you can reach a long way up in the tree, and you might be able to do the job yourself.