HAH HAHAHAHAHAHAHAAAAA
I accidentally set fire to a whole forest once. I laid a brick of netherrack down and lit it as a light, but it was too close, like 4 blocks away from the tree, really quite far but obviously too close, and then it burnt the forest down.
I was disappointed because I was going to chop the whole forest down for myself, but I got knack all for that =/ Fun to watch though I guess.