that's why you purchase an easement, and yes, it would be enforceable. I mean, it would be as enforceable as making sure no one poached your trees on your vast swaths of remote, distributed acreage. In my scheme, because the revenue is recurring, the owners would have every incentive to prevent poaching, thus potentially relieving you of some extra costs.

I suppose a tree hating owner could sign up and then chop down your trees, but luckily, you can probably sue him for breaking a contract, or just not let him have another tree.