Charles T. Smith wrote:
We bought and planted a tree that was called an "American Oak" about 3
years ago. It's currently about 3 - 4 cm (2 - 3 inches) in diameter.

A few days ago, I discovered a hole in the trunk, about 170 cm's from
the ground (under 6 ft). The hole itself is about 1.5 cm's in diameter
(just under an inch). A wire detected that it went about 15 cm up and 4
cms down (about a foot up and a few inches down).

After probing with the wire, I looked away for an instant, and then had
the distinct impression that I saw something out of the corner of my
eye pop its head out of the hole for a fraction of a second. I wasn't
able to get it again. It looked like a huge worm or something. Or maybe
it didn't happen. But something made that hole.

The hole occupies about 20% of the diameter of the trunk.

My question: will the tree grow in respect to the size of the hole, so
that the hole becomes insignicant, or will the hole "grow" with the tree?

Should I cut it down now instead of pealing it off my house later?

Should I fill the hole with anything?

Any thoughts will be appreciated.

I would be concerned that a hole that size would substantially weaken
the trunk. Even as a small tree, it might easily break in the next wind
storm. Thus, I would remove and replace it.

First, however, I would consult a local aborist or horticulturist to
identify what pest made the hole. Then, you might be able to either
plant something that does not attract such a pest or else be able to
block it from damaging anything else.

The "World Book of Trees" and Sunset's "Western Garden Book" list many
oaks (genus Quercus) with common names indicating European and Asian
nations as well as states within the U.S. However, neither work lists
an "American oak". Was it possibly an "Armenian oak" (Q. pontica)?

--
David E. Ross
Climate: California Mediterranean
Sunset Zone: 21 -- interior Santa Monica Mountains with some ocean
influence (USDA 10a, very close to Sunset Zone 19)
Gardening pages at http://www.rossde.com/garden/