Sevenless wrote:Magicman posted that jorb stated trees use a "generic forest biome". I don't think I've actually ever seen it in game.
Safish bet to say you'll probably need to "grow" it yourself.
If you run a custom client the "biome" they spread is named Wald - which is German for forest.
All trees that i tried (fir, beech, mullbery) seem to spread it, and trees growing on seem to grow MUCH faster.
From my observation it will appear randomly in 5x5 tiles around a tree and can spread outwards from that.