Fire Ecology and Fire-Adapted Ecosystems

Fire requires three ingredients, commonly diagrammed as the "fire triangle": fuel, oxygen, and a heat source sufficient to ignite that fuel. In wildland settings the heat source is most often lightning, which strikes the Earth roughly eight million times a day worldwide, though human ignition, whether accidental or deliberate, now accounts for a large majority of wildfire starts in most inhabited regions. Fire scientists describe the resulting pattern of burning in a given landscape as its "fire regime," a concept popularized by the environmental historian Stephen Pyne, characterized by frequency (how often an area burns), intensity (the heat energy released), severity (the ecological damage caused), seasonality, and typical spatial extent. Regimes range from frequent, low-intensity surface fires that creep through grass and litter to infrequent, high-intensity crown fires that consume entire forest canopies, and a single biome can shift between these states depending on fuel structure and climate.