Carbon loss and removal due to forest disturbance and regeneration in the Amazon

Highlights: • Twenty-year estimates of carbon loss from deforestation and degradation in the Amazon • Total net carbon loss totaled 5 Pg C from 1996 to 2017 • Emissions due to degradation highest in periods of drought • Disturbance in the Amazon causes 2% of global carbon emissions • Approximately 30% of forest-related carbon loss due to degradation The forest carbon flux is the difference between the total carbon loss from deforestation, forest degradation, and natural disturbance and removal of atmospheric CO₂ due to photosynthetic activity. The Amazon rainforest accounts for approximately a quarter of global emissions from land use change, due in part to its' immense size, carbon storage, and recent history of land use change. Large area estimates of carbon exchange in forests are highly uncertain, however, which reflects the pervasive challenges in estimating carbon flux parameters, such as disturbance area and forest carbon pools. In this study, we use a new dataset with characterized uncertainty on deforestation, degradation, and natural disturbances in the Amazon Ecoregion to estimate carbon loss from disturbance and removals from regeneration at biennial intervals from 1996 to 2017. Using the gain-loss approach to estimating carbon flux in a Monte Carlo analysis we found that carbon loss from degradation and deforestation averaged 0.23 (±0.09) Pg C biennium⁻¹ and 0.34 (±0.16) Pg C biennium⁻¹, respectively. While deforestation contributed the most to carbon loss overall, there were two biennial periods in which degradation and natural disturbance resulted in more carbon loss. Regeneration partially offset these emissions, but our results show that loss is occurring much more rapidly than removal, resulting in a total net carbon loss of 4.86 to 5.32 Pg C over the study period. With the compounding effect of drought and fires in addition to continued deforestation it appears certain that forest disturbance in the Amazon will continue to be a significant factor in the terrestrial carbon cycle.