The Solitary Tree

What is a Solitary Tree?
The obvious definition would be a tree that stands alone, possibly out in a field or pasture. Why did it survive the axe while the others did not?
Another meaning may simply be that this tree stands out for some unique reason. They all seem to have a human story that is associated with them.

“I think that I shall never see
A poem lovely as a tree.”
~ Joyce Kilmer