Cellular Automata has featured on this blog before - Conway's Game of Life. Whilst on the Rosetta Code site I stumble upon the Forest Fire model. Of course, a Dart version was soon underway - specifically designed to fit nicely on my phone's screen.
The model's rules are straightforward:
"A burning cell turns into an empty cell A tree will burn if at least one neighbor is burning A tree ignites with probability f even if no neighbor is burning An empty space fills with a tree with probability p"