I'm as guilty as most in usually spending lots of time on models but not the accompanying terrain. I found these trees in a Man Cave clean up this week which I got from Glynn at Fernvale Speciality Scenics (see them here). I realised I had gotten them at Cancon almost a year ago and hadn't done anything with them - time for action!
I cut the bases from mdf with a hole saw and used my typical basing technique. They came out pretty good I think. The tall light green ones are very nice indeed, and this large number is a beauty. They are probably best suited for 28mm gaming, but wont look too out of place in 15mm.