If you daily pick fruits from a tree, do you own the tree or only the fruits? What do you think and what is your explanation for it?
if you come to an unowned land and find a tree, to homeasted it you have to improve it somehow, I suppose. Take care of it. Trees "come" with the land around it, so you can't own a tree but not land where it grows. That's my reasoning.
(english is not my native language, sorry for grammar.)