Different scenes with dynamic lighting, the first one intend to achieve a realistic view on an open vista of top trees, the second one is a foggy alpine view of a small pines, and the last one is a night view with some kind of UFO over the trees being affected by the light casting and wind.
None of this uses volumetric fog, but a custom material to fake it.
Each tree were edited using Blender with a base mesh created on TreeIt and a whole normals and leafs overhaul inside Blender.