Legal Question in Real Estate Law in California

There are two (at least) causes of action (civil complaints) that could be brought against the neighbor, perhaps in Small Claims Court. First, you probably have a cause of action for trespass to land. Second, I'd suggest a claim be made for 'wrongful injury to trees,' a tort for which the Civil Code provides (in many cases at least) treble damages. See Civil Code section 3346, either on line or at your county law library. A lawyer analyzing your case would also want to ask you more questions about whether the neighbor's conduct is accidental (doesn't know where the property line is, perhaps) or malicious, whether he has a claim of some kind against you (the trees block his view), and so forth.