Legal Question in Real Estate Law in California

If it's really your neighbor's tree, he/she is responsible. If it could be argued that the tree trunk is on the boundary line, then possibly you co-own the tree and there's no one to hold liable.

If the neighbor is responsible, a successful suit could probably be brought for trespass, private nuisance, or both. Whether removal of the tree or repair of the fence is a preferable remedy would be the real issue. A court could require removal of the tree.

Since loss of a tree could be a rather harsh outcome, perhaps a negotiated settlement where the fence is moved or a jog is built into it, at the neighbor's expense, would be more equitable. Such a solution should be in writing and state that it is a license and no easement or lot-line change is created.

Negotiated solutions between neighbors are preferable to going to court.