Green trees grow on bare ground, and a tree catches fire when a neighbor is burning or, rarely, when lightning strikes it. A fire burns for one step and leaves bare ground, where trees slowly grow back. The two sliders set how fast the forest regrows and how often lightning strikes. Press Play and watch fires of all sizes sweep through. Click or drag to plant trees or start a fire.

This is the Drossel-Schwabl forest-fire model, a classic example of self-organized criticality: the forest settles at a density where small fires are common and huge ones are rare but not impossible, without anyone tuning it. In my test (a 128-cell square, 1 percent growth and 10 lightning strikes per million cells per step) about 40 percent of the cells were trees, with fires burning in under one percent. Lower the growth or raise the lightning and the forest stays sparse; with a lot of growth and little lightning it grows dense, and a single strike burns a huge area. The grid does not wrap around.

This page was created with Claude Code.