I just purchased property that has 2 large trees with concrete in them. One, a large oak, has a basketball size spot where a large limb may have been. The other tree has a section from ground level up about 3 feet. It is about 18 inches across at the base.
How do I repair/remove this eyesore without damaging the tree? Was this a common thing to do 30+ years ago? Why was it done?

Don-
This was a common procedure years ago. It was thought that the tree would be less likely to rot and collect water and debris if the hole were filled. We now know it is harmful to the tree.
I think you will do more damage to the tree trying to remove it since the tree has had some growth. Can you paint or stain the concrete to disguise it?
Tony M

Cement is bad, bad, bad.

I think any attempt to correct this/remove cement would be worse for the tree than the cement itself.

One of the best things we can do to help trees is just leave 'em alone.

Agreed.

Only remove it, if there's clear signs fo rot around it and/or it looks like it will fall out due to the wood around it deteriorating to the point that nothing but gravity is holding it in.

Are the trees in good health otherwise?

_________________
Shepherd of the Trees
It is not our part to master all the tides of the world, but to do what is in us for the succor of those years wherein we are set, uprooting the evil in the fields we know so that those who live after may have clean earth to till.