Cavity Filling

When we were at The Greenbrier, we did stumble upon something interesting. A lot of their Weeping Mulberry trees had their holes filled in with cement.

A Weeping Mulberry… filled with cement

This perked my curiosity enough to do some Internet research when I returned home. It turns out this is a practice called “Cavity Filling”. It was invented by a tree surgeon named John Davey. The idea was to fill in hollow trees or crevices with cement to stabilize the tree and give it a chance to grow around the filling and heal itself. In 1901, the practice made multiple appearances in Davey’s book, The Tree Doctor.

(Photo from John Davey’s The Tree Doctor, published in 1901)

Modern research has indicated that all trees do not in fact heal when properly filled. Here’s an excerpt from Greensboro, North Carolina’s “Tree Myths” page:

Filling of hollow trees, a process called “cavity filling,” was practiced by arborists for many years. Thanks to modern research, it has been discovered that cavity filling is not needed to support or improve the health of hollow trees.

Tree experts have found that cavity filling with cement can actually damage a hollow tree. According to Bob Rouse, Staff Arborist at the National Arborist Association, “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 further damages the tree.”

Decay organisms, such as rot fungi, that created the hollow in the first place are able to take advantage of the new injuries created by the rubbing and invade the healthy tissue of the tree. Rouse adds, “If that wasn’t bad enough, the cement holds moisture, creating a favorable environment in the filled cavity for the decay organisms!”

Research contradicting conclusions from the past didn’t strike me as odd– that happens every day. What did surprise me about cavity filling was that it had been a common practice by arborists for over 100 years. In recent times, I’ve paid quite a bit of attention to trees. How have I not seen this before?!?

And then I remembered… The hollow trees and the trees riddled with deep crevices I run across are typically in the woods!  Looking at them, Bob Rouse from the National Arborist Association may be correct. These trees don’t have the luxury of cement and they are managing to get along.

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Andy Layne Trail – Tinker Cliffs	Appalachian Trail – Brush Mountain
Appalachian Trail – Petite’s Gap	Appalachian Trail – Kelly’s Knob