The Corbania Prime Blog has a nice illustrated tutorial on making heavy — jungle — foliage terrain pieces.
trees
Making Jungle Trees
The Wargame Terrain Blog has a photo tutorial on making jungle terrain.
Modeling Swamp Trees / Cypress
Here’s a video on modeling cypress trees / swamp trees.
Making Stands For 10mm Trees
Tim’s Wargaming Blog has an illustrated tutorial on making stands for 10mm trees.