The Wargame Terrain Blog has a photo tutorial on making jungle terrain.
trees
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.
Modeling Forest For Lord of the Rings
The video that follows is full of inspiration and instruction for making forest terrain In this instance, the idea is to create “Lord of the Rings” style terrain.