Love the inspiration you gathered Jake!! I think it really fits the area. I'll leave here some resources and images in regards to forest growth, iirc I saw a forest of yours that was very sudden, I think it was a birch forest. Forest growth is a lot like mold growing, it slowly creeps in in blobs or branches and starts small and as it grows it thickens and gets bigger.
You may find this disturbing idk if there's a phobia for this type of imagery, seems fine to me but just in case:
6e8e4d4584c38f83c13a61521a7a17e3.gif
This article explains well growth of forests and which plants would grow first and which come after
https://nature-mentor.com/how-forests-form/
This image shows that progress:
And this image I quickly did on photoshop I think translates well the differences between a forest near a settlement and a forest that has meadow space between itself and the human influence areas:
And some more images for reference, the one I did on photoshop is very simplified, forest borders tend to be very organic and random except when there's human influence. But be careful cuz most plantations and farming areas nowadays are very geometric and cut forest very suddenly, medieval times you wouldn't have such a perfect precision hence a certain distance from the forest and the crops as a buffer zone.
But even though forest borders are supposed to be very random, the borders you see in satellite are macro examples, in game and irl near these borders you wouldn't notice as much as you do in those images, so always keep in mind the scale of things. You have already some examples of gradual forest in-game such as Whitegrove, although I think in some areas the growth and height progression is a bit too regular, it's still a good example of this forest growth phenomenon.
Call me when the nuking begins, I want to make it go boom
-Seri