A mish-mash of trees.
It’s hard to call this part of the level a forest: it’s as if they took a handful of every tree asset in the game and tossed them in here. It’s a bit hard to tell on some of these - especially the swaying trees - but I’m fairly sure these are 2D cards with 3D renders (or maybe even paintings) of the plants. The swaying and rustle of the grass or trees is done by moving the vertices of the cards that make up the foliage.
The reason I can’t quite tell if these are 2D renders of plants on cards is that the game is using an orthogonal or isometric camera that doesn’t have any angular distortion towards the edges of the scene. As far as I remember, the game never once rotates the camera, though my recollection of the endgame is fuzzy. I remember some level geometry gets rotated, but the benefit of the orthogonal camera is that you can mix-and-match 2D and 3D assets.