!forest! under mountain (how to...?)

I’ve got problem. I’d like to make forest under mountain and i don’t know how. Howe to make good forest. It’s a big area and my computer is always suspended. What is the best way to make it - that must look like real. It is to film.
Thank you in advance

If It’s going to be a background forest you could simply make sprites, that is pictures of trees with an alpha channel for transparency. If you want more detailed trees you can check out L-system tree generating python script or the tree-from-curves-script in 2.49.
There are also online libraries with models of trees and plants, for example ngplant.

ok, I’ll try