aesthetic is kinda unclear but wow thats a detailed prod plan haha. cool concept, I was thinking that if the tree grows healthy it can start weakening the towers around it, forcing player to move them further out or smth as radius increases cuz an old tree in a house i previously lived in was trying to eat away wall and floor lol. but this is just an idea, may not be suited to your theme.
Also since you mentioned solarpunk, I'd love to see inspirations from this video: