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)
If I had asked people what they wanted, they would have said faster horses - Henry Ford. Tiny ad:
Getting ready for the Better World Book kickstarter - February 2019https://permies.com/t/99513/ready-World-Book-kickstarter-February