Anyone know of a good tutorial on creating distant forests? Or better yet, any tips on how to do it?

ONe technique that has been used here is to create a grouping of four or five trees, render against a solid background, then use that image on a 2d plane with appropriate transparency. Then multi-replicate the 2d plane and scatter as needed in the distant parts of the scene.

Yep... If you're going for a lot of trees, then using 2D planes is the way to go. Unless of course, you don't plan on doing anything else with your computer for a good while.

Attached Link: http://www.renderosity.com/viewed.ez?galleryid=266155&Start=19&Artist=Rayraz&ByArtist=Yes

If you need very distant trees you can use a terrain with spikes added. a bit of fiddling with soften and spikes should get you very far. Check this image: http://www.renderosity.com/viewed.ez?galleryid=266155&Start=19&Artist=Rayraz&ByArtist=Yes The trees next to the river are Bryce-trees, but the mountains behind are terrains with softened spikes for trees. As you can see, there's very little difference between the mountain and the foreground trees. The trees in the foreground are all native bryce trees and with 3128 of them it still rendered at 1280x960 in only 54 minutes. Terrains are the way to go on very distant trees. For semi-distant trees 2D-planes are best and for close-up you should just stick to 3D-ones for better detail and shadows.

thanx folks, I'll give your suggestions a try. The "spikes on terrain" trick I knew already, and is nice for makes scenes with trees creeping up the sides of mountains.