Learn how to use particle systems to create volumetric trees in this video tutorial. .blend file is included.
During the course of creating my “Bag End” scene for The Nature Academy competition one of the things I knew would be a challenge would be the sheer number of trees that would need to be created for the mid-ground landscape.
The obvious solution would have been to use an array of various 2D trees mapped to planes, seeded via a particle system on the lanscape. While this would have worked, I wanted to try my hand at something I had seen on the BlenderArtists forum. The following video is a time lapse of the creation process for the volumetric trees.