Your neighbor owns the tree. It is accepted law in all states that a tree whose trunk stands wholly on the land of one person belongs to that person.
If the trunk stands partly on the land of two or more people, it is called a boundary tree, and in most cases it belongs to all the property owners. All the owners are responsible for caring for the tree, and one co-owner may not remove a healthy tree without the other owners' permission. As for who owns any fruit from the tree, however, that's another matter.
Yes. The basic rule is that someone who cuts down, removes, or hurts a tree without permission owes the tree's owner money to compensate for the harm done. You can sue to enforce that right, but you probably won't have to, once you tell your neighbor what the law is.
You can trim back branches to your property line, but that might not solve the problem if you're worried about the whole tree coming down.
City governments often step in to take care of, or make the owner take care of, dangerous trees. Some cities have ordinances that prohibit maintaining any dangerous condition, including a hazardous tree, on private property. To enforce such an ordinance, the city can demand that the owner remove the tree or pay a fine. Some cities will even remove such a tree for the owner.
You might also get help from a utility company, if the tree threatens its equipment. For example, a phone company will trim a tree that hangs menacingly over its lines.
If you don't get help from these sources, and the neighbor refuses to take action, you can sue. The legal theory is that the dangerous tree is a "nuisance" because it is unreasonable for the owner to keep it and it interferes with your use and enjoyment of your property. You can ask the court to order the owner to prune or remove the tree. You'll probably have to sue in regular court (not small claims court) and have proof that the tree really does pose a danger to you.
Whether you are liable for damages to your neighbor's property caused by the spreading roots of a tree on your property depends on what state you live in. In most situations, a neighbor who is bothered or worried by encroaching branches or roots of a healthy tree won't be able to successfully sue the tree owner. Instead, the neighbor can go ahead and trim the tree himself. In some states, however, neighbors may sue under certain conditions, including:
In many other states the law is unclear. In these states, a case might be successful if the tree:
In addition to finding out what the laws are in your state, there are other questions to answer in getting to the roots of this dilemma. What's the cost of the damage to the neighbors' septic system? Do you like these neighbors and want to keep a good relationship? How about splitting the cost? If you love your tree, how about your having the roots cut back professionally so that the neighbors don't damage the tree if they exercise their right to trim back the roots to your property line?
Sometimes, no matter what the law dictates, it's better to spend money to fix a situation instead of paying the same money to a lawyer and losing a neighbor.
You have the legal right to trim tree branches up to the property line. But you may not go onto the neighbor's property or destroy the tree itself.
Welcome to the club—neighbors who have a dispute about trees. To avoid an unpleasant dispute (or your neighbor trimming your tree on their own—and possibly botching the job), talk with your neighbors and find out exactly how much tree trimming would do the trick.
If it's not too much, and doesn't affect the health or aesthetics of your tree, consider making the trim. Your neighbors might be willing spring for the cost of the tree trimming (or at least split it). But you should hire a professional tree service to do the work , to assure a quality job that keeps your tree healthy and aesthetically pleasing.
If you are firmly opposed to trimming your tree—perhaps it screens your view of your neighbors' unsightly back yard—check your local tree ordinance to make sure the law is on your side. You might be violating local law if your tree (no matter how beautiful) presents a hazard to your neighbor (for example, if dangerous limbs hang over the neighbor's property), violates any height limits or view ordinances, or straddles the property line. If you're breaking the law by refusing to trim your tree, the results might be more than a bad relationship with your neighbor; you could find yourself in court if your neighbors sue you for interfering with the use and enjoyment of their property,
You can find out local tree rules by contacting your building or planning commission or checking local ordinances online. If your house is part of a homeowners' association with CC&Rs, make sure you check these rules, such as restrictions on tree heights.
See these articles on Neighbors and Trees for advice on handling tree disputes with neighbors. The book Neighbor Law, by Attorneys Emily Doskow and Lina Guillen, provides extensive advice on tree-related law and liability issues involving invading branches, damage from an unsound tree, boundary trees, and more, including how mediation or small claims court can help resolve tree disputes.