property line tree2If the trunk of the tree touches the property line, it's a "shared" tree.

Even if it's not a shared tree, however, any work you or your neighbor does that will impact the tree’s health must be approved by both sides. (This does not include occasional pruning over one of the houses.) Without that approval, either one of you could be held responsible for the appraised value of the tree if damage is done to the tree or it dies.