It can, but doing that for a whole forest would require a lot of voxels!
Yes, especially as not all trees are the same age, and the older trees were grown defined by even older trees that are now gone.
yeah, and them having different rules for growth given different species
All their growth models do involve light, however. So it probably does make sense to have a common light representation - ideally some sort of sparse cone storage though, not a voxel grid the size of a forest.
it would be nice to be able to place different light sources and have a basic ray tracing sim, so you could simulate trees growing in cave entrances etc