The impact of frequent wildfires during the Permian-Triassic transition: Floral change and terrestrial crisis in southwestern China

Wildfires are considered to have played an important role in the land plants crisis during the Permian–Triassic (P-T) transition. However, the nature of, and the impact of wildfires in the P-T terrestrial extinction crisis remains unclear. Organic petrology and geochemical data from a terrestrial sequence from southwest China indicate that wildfires were a frequently occuring phenomenon of low-latitude tropical rainforests during the P-T transition. Abundant inertinite and Hg/TOC peaks in earliest Triassic strata support the co-existence of wildfires and volcanism at that time. Volcanic emissions were potentially lethal for plants and volcanism made vegetation more liable to combustion. Volcanism is also a possible source of ignition. Inertinite reflectance values are used to estimate wildfire combustion temperatures, themselves a function of wildfire type. Crown fires with high combustion temperatures were prevalent in wetland settings in the latest Permian. However, surface fires with lower combustion temperatures became dominant during the major terrestrial extinction phase as a result of the sparse, scrubby vegetation that dominated at that time. The subsequent spread of gymnosperms resulted in the reoccurrence of high-temperature crown fires in the earliest Triassic. Wildfires associated with the early stages of volcanism in the late Permian likely contributed to ecological disturbance in terrestrial settings, which occurred notably earlier than that seen in marine environments. Thus, enhanced wildfire activity destabilized wetlands and increased ecological stress in the late Permian. Wildfire activity on land potentially had devastating consequences for late Permian marine environments via a complex cascade of terrestrial denudation, runoff, and nutrient flux.