I don't know a lot about growing trees, do you mean you're grafting them onto any old tree? How does that work?
It's owned by the county... I guess asking first is the best way to start.
I can't really see them saying no to a proposal to create an exotic-looking, drought-tolerant forest, especially when no funding is expected.
My wager is that they would say no because of liability concerns (it sounds totally crazy but thats unfortunately how municipalities work)