Impacts of historical land cover changes on carbon stocks in the Itacaiúnas River Basin, eastern Amazon

Quantifying the long-term impacts of land use and land cover (LULC) change on carbon stocks is critical for guiding climate change mitigation strategies in tropical forest frontiers. In this study, we assessed the spatially explicit carbon balance of the Itacaiúnas River Basin (IRB), located in the Amazon arc of deforestation, from 1985 to 2021. To achieve this, we combined annual LULC maps with estimates of biomass and soil carbon stocks and burned area data to quantify carbon losses from deforestation, carbon gains from secondary forest regrowth, and direct fire emissions. Over the 36-year period, the IRB lost 335 Mt-C (40% of its original stock), mainly due to biomass loss associated with the conversion of primary forests to pasture. Protected areas, which cover 29% of the basin, contained 51% of the remaining carbon stock in 2021 and contributed only 4% to the net carbon loss. Fire emissions accounted for up to 12% of annual carbon losses during prolonged drought years. Secondary forests stored 23 Mt-C in 2021, although current regrowth rates remain insufficient to offset ongoing deforestation. These findings reinforce the importance of protected areas, forest restoration, deforestation control, and improved pasture management in supporting climate change mitigation and sustainable land management strategies across the Amazon.