Controls over Fire Characteristics in Siberian Larch Forests

Fire is the major forest disturbance in Siberian larch (Larix spp.) ecosystems, which occupy 20% of the boreal forest biome and are underlain by large, temperature-protected stocks of soil carbon. Fire is necessary for the persistence of larch forests, but fire can also alter forest stand composition and structure, with important implications for permafrost and carbon and albedo climate feedbacks. Long-term records show that burned area has increased in Siberian larch forests over the past several decades, and extreme climate conditions in recent years have led to record burned areas. Such increases in burn area have the potential to restructure larch ecosystems, yet the fire regime in this remote region is not well understood. Here, we investigated how landscape position, geographic climate variation, and interannual climate variability from 2001 to 2020 affected total burn area, the number of fires, and fire size in Siberian larch forests. The number of fires was positively correlated with metrics of drought (for example, vapor pressure deficit), while fire size was negatively correlated with precipitation in the previous year. Spatial variation in fire size was primarily controlled by landscape position, with larger fires occurring in relatively flat, low-elevation areas with high levels of soil organic carbon. Given that climate change is increasing both vapor pressure deficit and precipitation across the region, our results suggest that future climate change could result in more but smaller fires. Additionally, increasing variability in precipitation could lead to unprecedented extremes in fire size, with future burned area dependent on the magnitude and timing of concurrent increases in temperature and precipitation.