LAUSR

Significance Scientists and the public alike are gaining an increasing appreciation for the role of fire in the Earth system. Understanding and predicting fire behavior has become increasingly critical in the face of changing constraints on fire behavior. Here, we show that fires in grassy ecosystems are subject to threshold behaviors—widely hypothesized in theory, but rarely applied—which should be included in mechanistic models of fire behavior. We link these thresholds explicitly to fuel and weather conditions to facilitate their broad adoption in applied contexts, bridging the sizeable divide between theoretical and applied fire models.