Here are five common sticking points when it comes to neighbors and trees:
Fallen trees. If your neighbor's tree falls onto your property and causes damage, your neighbor may be liable for negligence, if it can be shown that he failed to properly maintain the tree or remove it when it became a hazard. However, property owners are not typically liable for damages caused by purely natural conditions.
Cutting down trees. When it comes to cutting down trees that may straddle both your and your neighbor's property, the general rule is that the owner of the property where the tree's trunk is located is considered the "owner" of the tree. However, branches that hang over property lines can generally be trimmed by the property owner as long as the trimming does not destroy portions of the tree on the neighbor's property.
Blocked views. Generally, you can't force a neighbor to cut down a tree that may be blocking your view, unless there are prior agreements that apply to your property (such as an easement) or specific laws such as view ordinances. There may, however, be different laws in different cities and states. In San Francisco, for example, billionaire Larry Ellison was able to settle a dispute with neighbors whose trees were blocking his view, in part because of a local ordinance that requires arbitration of tree disputes before lawsuits can go to trial.
Picking fruit. What about picking fruit off your neighbor's tree? If it requires crossing onto your neighbor's property it may be criminal trespassing, theft, or both. Even if done from branches that are hanging onto your property (which would, in theory, force you to pick up the fruit that drops off the tree anyway), it's probably still a good idea to run it by your neighbor first.
Leaves in your yard. Although leaves that blow or fall onto your property from a neighbor's tree may be a pain in the neck, they probably won't be a sufficient basis for a nuisance lawsuit. You can, however, trim any portion of the tree that is on your property or erect a fence to block the spread of leaves onto your property.
To learn more about legal disputes between neighbors over trees, head over to FindLaw's section on Neighbors and Trees.