Thanks for the feedback and the photos! I have plenty of boreal forest photos of my own, as well. The sketch isn't a mockup, it was me working out the scale and colours, and trying to get an idea of how many layers I'll need to get enough trees in the background xP I have been using colours from it as background colours to work on, but not putting my trees in because it's too much of a mess to be of real value. Once I have some more assets drawn, I can put together a "proper" mockup to serve as context for future assets.
The terrain will definitely be more varied and defined, there will be mossy rocks, bilberry shrubs everywhere, dead trees, slopes, tree roots just begging to be tripped on, etc, as much as I can figure out how to do in-engine. Ground cover in particular is something I went out and got a lot of ref of, because that's always missing in other people's photos, no one stops to photograph the ground they're standing on, everybody's always looking forward and up (quite the opposite of how people act in vidyas xP).