About the tree and treeants, maybe add some special events like lumber jacks. Every x seconds they come and try to cut down the trees. Also maybe rain, increasing the water given to the trees, drought, making less water.
Also, you could make a simple system like this: the more the corrupted treeants attack the world tree, the world trees tinting would change, making it more violent every time attacked. Just like a simple way of telling if your trees are weak.
Also, you could make a simple system like this: the more the corrupted treeants attack the world tree, the world trees tinting would change, making it more violent every time attacked. Just like a simple way of telling if your trees are weak.