Legal Question in Real Estate Law in New York

Yes, provided they are on his property and there is no local prohibition against cutting without a permit. Any trees on your property would involve him trespassing.

If the tree is "on" the property line, then neither owner may cut down the tree or stump it. Horticultural/arboral work is permitted if reasonable. If the tree is not on the line, but branches spread accross the line, the other owner nay remove growth that is in his airspace so long as he does not "crown" the tree.

If you get the idea that tree disputes are fact-dependent and may need input from experts, you begin to grasp how much trouble and expense you are in for.

There are civil and potential criminal penalties for cutting down another person's tree. And as a prior poster observed there are environmental protection laws that may regulate trees above a certain size.