Effects of Wildland Fire on Regional and Global Carbon Stocks in a Changing Environment

Every year tens of millions of hectares of forests, woodlands, and grasslands burn globally. Some are burned intentionally for land conversion, pasture renewal or hazard reduction, or wildlife habitat improvement, but most are burned by uncontrolled wildfire. Estimates of burned area available in the literature vary widely, but satellite-based remote sensing data are increasing the accuracy of monitoring active fire and estimating burned areas. Recent data suggest that global wildfire emissions vary substantially from year to year. Nonetheless, average annual carbon emissions from wildfire are 20–40 % of those from fossil fuel combustion and cement produc-tion. Results of field studies and modelling efforts indicate that changing climate is likely to increase the extent and frequency of wildfires, highlighting the importance of accurately quantifying the regional and global effects of wildfire on carbon stocks and on atmospheric carbon compounds. The nature and strength of feedbacks between fire and climate will depend not only on changes in the area that is burned annually, but perhaps more importantly, on how those fires burn and how ecosystems respond and recover. Changes in burn severity can result in large differences in the amount of fuel consumed, emissions to the atmosphere, and the capacity of ecosystems to recover carbon after a fire. Recent work also indicates that even low-severity surface fire may cause significant changes in soil respiration, and these changes may either increase or decrease the net effects of fire on atmospheric carbon. Postfire recovery to a different vegetation type—which may occur in response to changing climate, unusually high burn severities, or other factors—also has the Corresponding author