Hazardous Trees: How To Spot Dangerous Or Declining Trees

Safety-conscious homeowners and municipal officials, ever-vigilant of deep potholes and cracked sidewalks, often ignore hazardous situations that are hiding in plain sight -- aging or declining trees.

Many accidents involving falling trees or branches can be prevented by inspecting trees each year and by prioritizing and performing any maintenance as soon as possible, according to William Elmendorf, instructor and coordinator of the urban and community forestry program in Penn State's School of Forest Resources.

"Ignorance is not bliss when it comes to tree safety," Elmendorf points out. "Municipalities and homeowners are responsible for safe streets. Avoiding a tree management decision isn't going to make the problem go away."

Elmendorf says detecting hazardous trees can be tricky. "A tree can look healthy and beautiful, but it might have decay or structural problems within the roots or other areas that are hard to detect," he says. Elmendorf recommends hiring a professional arborist to perform an in-depth examination of the tree before taking any action.

Still, there are some danger signs that untrained homeowners or municipal officials can watch for.

• Cracks. Watch for deep, open cracks in the trunk or branches. Any tree wound is an opening for decay. Vertical cracks on opposite sides of the trunk can be a sign of severe injury.
• Forked trunks. Forked trunks are signs of potential weakness, particularly if the fork is narrow with bark growing between the trunks.
• History. Unexplained loss of large branches can be a sign of internal problems. "If a tree loses a big branch one year and it happens again the next year, you should question the safety of the tree," advises Elmendorf.
• Root Rot. Look on or near the base of the tree for fungal growth or mushrooms, which can weaken or decay roots. Construction can cause root injury or severed roots.
• Limbs and branches. Dead limbs can fall at any time, even in the slightest wind, Elmendorf says. Crossed or rubbing branches can lead to weak spots and should be pruned immediately. Long, heavy, horizontal limbs often can be weak spots, even on large trees. Oddly shaped branches with kinks or curves should be examined.
• Architecture. Trees that lean or exhibit unbalanced growth should be monitored and examined every year, Elmendorf advises.

In some cases, older trees cannot be removed for historical or sentimental reasons. Elmendorf suggests that homeowners or communities eliminate hazards by landscaping or removing the "targets" of a possibly hazardous tree. "It's a bad idea to put a swing set or a picnic table underneath an older tree," he says. "You can plant hedges or reroute walks to avoid the tree or you can plant groundcovers that would make resting under the tree uncomfortable."

Elmendorf emphasizes that the best way to avoid hazardous trees is to provide consistent care when the tree is young. Young trees should be pruned to help develop a strong branch structure. In addition, homeowners and community foresters should inspect the root systems of new trees before they are planted, checking for circling, kinked or stunted roots.

"People also should plant the right tree in the right area," Elmendorf says. "Big trees need large areas in which to grow. For instance, you shouldn't plant an oak right next to your house or in a small sidewalk soil bed."

Homeowners can perform preliminary inspections by standing back from the tree and walking all the way around it, noting any abnormalities. "You should look at the canopy of the tree first, using binoculars if necessary," Elmendorf explains. "You also can estimate the height of a tree, if it might fall near the house, by comparing it to nearby houses."

Aging or declining trees can be supported by cables, but Elmendorf emphasizes that such support systems should be professionally designed, installed and maintained. "Even then, cable supports are no guarantee against failure," he warns.