I really don't see any other way you can do it if you don't own the property. Additionally, those species you mentioned are not really worth anything commercially. The nut pines could be worth something if you can get them to produce but as of yet I don't know anyone that ever got a crop off them. I have talked to growers who have planted thousands of those but they mostly all died, are very slow growing. Honey Locust has almost no commercial value and does not make forage grow enough to offset the expense of planting and maintaining them, most silvo pasture is done in the Southeast with pecans trees because of the value of the timber and nuts and also there is a fair amount done with black walnut trees.. So maybe considering some other tree species might also be important, especially something that has been shown to work.
Is there a legal framework that would allow someone to own trees on land owned by another? (For higher value plantings that would be worth ensuring continued access to.
In the end, I think the best way to maintain control through a change in ownership is to give people something that they value, be honest, and be nice. You might not get a legally binding contract. But let's be honest, even a legal framework isn't going to protect you from a new owner who doesn't want you on their property. They can easily destroy decades of your work and the only recourse you'd have is trying to put a monetary value to your work and fight them in court (spoiler alert: that isn't going to end well for you). But if you're the nice man who does forest management for the property in trade for practicing his curiosity… they'll probably want to keep you around.