The full Unreal Engine 4.24 project files for my Birch Forest | UE4 environment.
All the vegetation in the project was modeled exclusively in SpeedTree, from high to low poly. The assets and textures in the scene are built using my own personal scanned data, processed in Agisoft Photoscan, while certain elements such as rocks, clutter and terrain materials were built using a mix of my own personal scanned data, Substance, ZBrush, and traditional modeling & texturing techniques.
All assets were roughly built to the higher end of current video game budgets, minus the LODs, but since I was just having fun with the project I didn't bother to optimize it further. (For example, the trees range from 13k - 30k triangles, rocks range from 2k - 5k triangles.)
I've uploaded this project in hopes that it might be of help to see how things were constructed and put together.
Before you can open and navigate the project, you will need to activate Light Propagation Volumes in your Unreal Engine directory.