This is really cool! I just have some questions to help me understand the mod better (and a small suggestion that you're free to ignore :3 ). I was going to post this as a comment, but I thought it might be smarter to put it here in the Discussions area.

It was kind of hard for me to tell which trees are my old-growth at first. I think this is just because I only had 4 trees on the map I loaded that were truly massive, so I mostly chalk it up to not being sure what to expect.
I will say, I found myself looking for some sort of color/value change to help me "see" the forest/buff-affected trees, perhaps that could also add to the visual variety?

As I search for a map with a "good" forest, there are some things I'm not quite sure of: If I have only 4 oldgrowth trees in my map (for example), do the food spawn buffs only happen around those 4 trees, or is it a larger AoE?
Do you still need other trees to help the food to spawn? are other trees affected somehow?
I ask because in the vicinity of those 4 trees (but not their immediate area), I found an excess of food, but it was growing amongst stone and not many other trees around (not as many as you'd normally find with so much food). I wish I got a screencap, but I've since loaded a few other maps to see how the forests spawn.

Anyway I love forests in Banished, so I'm super excited to play more with your mod!