Old man willow...

[Bêthberry]

The animosity of the trees in the Old Forest to hobbits is said to be due to the battle between the trees and the hobbits over the Hedge, with the hobbits starting a fire at what became known as the Bonfire Glade. The Old Forest is not quite so much evil as . . . more aware and thus perilous. It is the Barrow Downs where real evil lurks.

Originally Posted by LotR, "The Old Forest", Merry

But the Forest is queer. Everything in it is very much more alive, more aware of what is going on, so to speak, than things are in the Shire. . . . In fact long ago they [ie, the trees] attacked the Hedge: they came and planted themselves right by it, and leaned over it. But the hobbits came and cut down hundreds of trees, and made a great bonfire in the Forest, and burned all the ground in a long strip east of the Hedge. After that the trees gave up the attack, but they became very unfriendly. There is still a wide bare space not far inside where the bonfire was made.'"