Trees, Forests, LIFE!

Um, I’ve been wanting to make a natural scene for some time. But I’m curious if there is a shortcut to modeling the trees (not the leaves, but the trunks/branches). Currently all I can think of is make one, then make duplicates that have small changes in each one, but that seems like the hard way, and I think it wont lend itself to enough realism, so, could anyone suggest a better way? Sorry if this question has an obveous answer or it’s been asked before!

There is a script out there for making trees. Its called L-system.

http://www.geocities.com/blenderdungeon/lsystem/index.html