It is not unusual to find a hole full of rotten wood in the trunk of a living tree or even to find a completely hollow space just inside.
Formerly, homeowners believed that in such a case, you could save the tree by scraping away the rotten wood and digging into healthy wood to “eliminate the rot.” However, we now know that trees are able to protect themselves from rot. They do this by forming stronger, more resistant cells around the wound. This is called compartmentalization. By cutting into healthy wood in an effort to clean the wound, you’ll actually be removing the tree’s natural protection and may even cause the rot to expand.
Neither is it necessary either to fill the hole with concrete, bricks, etc., or to paint it with wound dressing, two outdated techniques that cause more harm than good.
Dear or Alive
It’s important to understand that the heartwood of a large tree is dead anyway. It is only the bark and a thin layer under the bark (the sapwood) that is alive. Healthy heartwood may, in some cases, help the tree to better withstand wind, but not always. You often see hollow trees that are very strong. And a hollow trunk certainly doesn’t mean the tree is dying! It can sometimes survive another 20, 40 or 60 years, even a century, depending on the species, as long as it is structurally sound.
To check that out, you’ll need the opinion of an experienced arborist. If they deem the tree to be structurally unsound and if, because of its placement, it could do damage when it falls, you’ll have to have it removed. Otherwise, just leave it alone.
Holes in trees often host all sorts of interesting animals and birds (a hollow Norway maple at my former residence was once home a family of flying squirrels, much to the delight of my kids!). And hollow trees are part of a normal and healthy environment.
So in most cases, when you realize that one of your trees is hollow, just let Mother Nature do her job. She knows better than you do what to do!
Regardless of the material, a tube is always stronger than a solid cylinder. It’s like that in many fields, and in nature too. It’s the case with bones, quills, tusks, horns. Plus, most plants are also an illustration of this, such as the common reed, for example.
The cavity itself is not a problem. It’s simply not a factor when it comes to strength. That being said, there are limits. The opening itself should not be too large or extend too far up and down, like a slit. The tree takes care of reinforcing the circumference of the hole with scar tissues. They begin to appear as soon as the missing branch responsible for the hole is dead, or broken, or cut. Thus, before the wound even becomes a hole, the tree is already taking care of itself.