Tree canopies often overhang property lines, creating benefits and conflict. Tree owners are responsible for maintenance of the tree so that it doesn't harm neighbour's property; but clean up of fallen leaves is the responsibility of the property owner.
Fallen leaves are considered a natural product, and as such, are the responsibility of the property owner. If the leaves block gutters or pipes, the property owner may have a legal claim against the tree owner in the United Kingdom, but, probably not in the United States.
In all states, the property owner has the right to cut branches reaching over the property line. However, the tree owner can make a claim for damage caused to the structure of the tree or its aesthetic appearance by overenthusiastic pruning.
State law governs trees and can vary. For example, fruit belongs to the owner of the tree and can't be eaten without permission even if the branch overhangs the property line. But, fallen fruit could be a windfall for the property owner.