At what density does the fire cross the forest? The orange front moves one patch per tick through touching trees and goes out where it runs into empty ground.
Try this Set density to 60 and press Reset (density is only read at setup). Run it a few times; the fire reaches the right edge in roughly half the runs. At 56 it almost never does, and at 62 it does about nine times in ten.
About this model Where it ends up
Uri Wilensky's Fire model (NetLogo Models Library, 1997). Fire spreads through a randomly planted forest, and whether it gets across depends sharply on tree density: the switch sits near 59.3%, the site-percolation threshold of the square lattice.
Each patch is empty, tree, burning or burned. Setup makes each patch a tree with probability density/100 and sets the trees in the leftmost column burning. Each tick updates every patch from the previous tick's state: burning patches become burned, and a tree with a burning neighbor to its north, south, east or west starts burning. The front moves one patch per tick, and the run stops when nothing is burning. density is read only at setup.
NetLogo's version sets the whole left column alight, empty patches included; here only the trees in that column are lit. The grid is 121 × 89 patches with hard edges.
