Holes in Trees: Hazardous or Harmless?

Hazardous trees pose a danger to people and property. When storms or high winds hit, limbs – and often whole trees – fall to the ground.

“Many fatal accidents and millions of dollars in property damage can be averted if homeowners heed the warning signs of a hazardous tree,” explains Tchukki Andersen, BCMA, CTSP* and staff arborist for the Tree Care Industry Association (TCIA). “By not paying attention to your trees, you are potentially placing your property, even your life, in jeopardy.”

Tree defect clues

Fortunately, one can often read the clues that indicate a tree is prone to failure. For instance, if a tree has large branches attached with tight, V-shaped forks, those attachment points are often weak and could break or fail during strong weather events. However, those branches can be removed or reduced in length to reduce the risk while maintaining the tree’s aesthetic appearance.

Other warning signs of structural instability include cracks in the trunk or major limbs, hollow and decayed areas or the presence of extensive dead wood. Mushrooms growing from the base of the tree or under its canopy may be a sign of root decay, which could cause the entire tree to fail. Remember to be thorough in your evaluation; the absence of fungus growth does not necessarily mean the tree is healthy.

“It also pays to be highly suspicious of any tree that has had construction activities performed near it – such as cable or utility trenching, addition or removal of soil, digging or heavy equipment movement – anywhere under the spread of its branches,” says Andersen. These activities can cause root death, which in turn, again, could lead to the structural instability of the tree.

Holes in trees

The indicator most people recognize is a hollow in a tree. But even a large hollow does not always imply that a tree has become hazardous. Nor does it mean the hollow should be filled. Filling of hollow trees, a process called “cavity filling,” was practiced by arborists for many years. However, thanks to recent research, it has been discovered that cavity filling is not needed to support or improve the health of hollow trees.

Tree experts found that cavity filling with cement can damage a tree. According to Andersen, “The column of cement created in the tree by a cavity fill doesn’t move, just like a column on a building, but the tree is always moving. It sways with the wind constantly. The rubbing created by the swaying tree and the solid column of cement can further damage the tree.”

Wood decay fungi that created the hollow tree defect may take advantage of new injuries created by the rubbing. They could invade the remaining healthy tissue of the tree. When cavity filling is desired for aesthetic reasons, synthetic foams can be applied by professional arborists. These materials will bend with the swaying tree, reducing injury. However, there is really no reason to fill a cavity other than for aesthetic reasons; it doesn’t improve the tree’s health and doesn’t offer extra support. If structural support of a tree is required, a professional arborist will recommend alternative options. Cabling, bracing, propping, tree guying or removing the tree are preferred.

What can you do?

Find a professional. A professional arborist can work with you to determine the best course of action to care for and maintain your landscape.

*Board Certified Master Arborist, Certified Treecare Safety Professional