Legal Question in Real Estate Law in California

Re: neighbor planting

If you're sure the trees are on your property, you may remove them. If you want to keep them, your downhill neighbor gave you a gift of trees. Send the neighbor a thank you letter for such a thoughtful and enduring gift of lovely trees. Keep a copy. You will have to maintain them, though.

Re: neighbor planting

Mr. Cohen is right. The way to prevent a prescriptice easement is to make the use permissive. Accepting the trees as a gift is one way to create the permissive atmosphere. Another, somewhat more formal way would be to write up and send him a revocable license granting him permission, revocable at any time, to plant trees on your land, also stating that the trees, upon planting, will become part of your land. Under the law of licenses, the revocability and tree-ownership aspects would happen automatically, but just to be sure they could be written in.

You can write it yourself: "I, X, hereby grant you, Y, a revocable license to plant trees on my side of the joint retaining wall; upon planting, such trees will become fixtures upon the land. This license is not coupled with an interest."

Re: neighbor planting

If you do not want your neighbor coming on your property any more, sue him for tresspass in small claims court. You also could get an injunction against him in Superior Court.