You need to Broaden Your Horizon fellas ... get it ... Broaden Your Horiz....ah forget it.
Have a look at this:
http://www.gamedev.net/community/for....asp?jn=263350
This is terrain generation procedural style. It is CPU intensive but way less expensive on storage space i.e. RAM, but with multi core CPU's pretty much main stream now who cares. So with the saving in RAM bounding boxes could be cached to aid in collision detection between tree and planes.