Important role of forest disturbances in the global biomass turnover and carbon sinks

Forest disturbances leading to replacement of whole tree stands are a cornerstone of forest dynamics, with drivers including fire, wind-throw, biotic outbreaks and harvest. The frequency of disturbances may change over the next century, impacting the age, composition and biomass of forests. However, the variation in disturbance return time, i.e. the mean interval between disturbance events, across the world's forested biomes remains poorly characterised, hindering quantification of their role in the global carbon cycle. Here we present the global distribution of stand-replacing disturbance return time inferred from satellite-based observations of forest loss. Prescribing this distribution within a vegetation model with a detailed representation of stand structure, we quantify the importance of stand-replacing disturbances for biomass carbon turnover globally over 2001-2014. Return time varied from less than 50 years in heavily-managed temperate ecosystems to over 1000 years in tropical evergreen forests. Stand-replacing disturbances accounted for 12.3% (95% confidence interval, 11.4-13.7%) of annual biomass carbon turnover due to tree mortality globally, and in 44% of forested area biomass stocks are strongly sensitive to changes in disturbance return time. Relatively small shifts in disturbance regimes in these areas would substantially influence the forest carbon sink, that currently limits climate change by offsetting emissions.