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Bill Pramuk: Trees and People: Do tree wounds heal?
Trees and People

Bill Pramuk: Trees and People: Do tree wounds heal?

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“Every wound a tree receives in its lifetime is recorded in the wood,” Alex Shigo said in his “New Tree Biology Dictionary” (Shigo and Trees, Associates, 1986). I would add: Wounds are also recorded in the loss of wood.

Dr. Shigo was a remarkable leader in examining tree anatomy and understanding tree biology. He did this by opening trees with a chain saw and observing the results of old wounding and decay. And he was insistent on using appropriate terms and concepts about trees. For example, he wrote: “Wounds close, not heal… (they) wall off, or compartmentalize, injured and infected wood.” He advised, if we must use the term, we should distinguish between “animal healing” and “tree healing.”

Look closely at older trees that have a history of severe pruning wounds. You might notice wound closure as a layer of wound wood covering the site of an old wound. But the inert inner wood exposed by the wound will typically be in a state of advancing decay while the outer layers of living cells generate new tissues.

We people have a strong tendency to equate tree systems with our own and invest them with qualities they do not necessarily possess. Many times, I have heard folks refer to valued monecious trees – having both male and female flowers — as “she” or “he”. And then there are questions like: “Will pruning off that limb hurt the tree?” In response to that question I once responded: “I don’t know if it will hurt but it will injure it.”

On the other hand, too many people regard trees as static objects. We see this all too often where new construction meets existing trees. A tree that has spent, perhaps, 100 years establishing a dynamic system of roots and physical connections in the soil to beneficial organisms and neighboring trees, is expected to shrug off sudden grade changes, compaction, trenching, paving over its root system and loss of “associates”.

They may be big and strong, but they are vulnerable —some more than others. Species vary in their response to wounds. Some tend to invest energy in defense while others invest in rapid growth.

For example, about 20 years ago, I examined and made recommendations for the care (or removal) of and old weeping willow with a trunk diameter of about 4 ½ feet. Now surrounded by backyards, a sidewalk and a busy boulevard, the tree is reputed to be over 100 years of age, planted in what was then a rural setting.

The tree sustained some severe wounds long ago, perhaps when a large, weakly attached limb split off. The exposed inner wood decayed away, as is typical of this weak compartmentalizing species, leaving a thin shell of trunk with bands of living tissue partially surrounding a large cavity.

At some point, the load of foliage and wood weight becomes too much for the shell of a hollow trunk to support. The truism applies: Failure occurs when load exceeds strength.

What are the options when you are faced with a potentially hazardous, but historically significant, tree? Remove it? Move or exclude potential targets? Do something with the tree to make it less likely to fail? The owner chose the latter for this particular tree and location. It was was drastically reduced in overall size, leaving the hollow trunk and no significant limb structure.

The tree sprouted new shoots on the trunk, the sprout response being an inherent survival mechanism of this species. Depending on your personal point of view, you might see the short trunk and weeping shoots as “Cousin It”, a living monument to local history, or a tree owner’s appreciation of an old friend.

Bill Pramuk is a registered consulting arborist. Visit his website, email questions to or call him at 707-363-0114.

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