Altered growth conditions more than reforestation counteracted forest biomass carbon emissions 1990-2020

Understanding the carbon (C) balance in global forest is key for climate-change mitigation. However, land use and environmental drivers affecting global forest C fluxes remain poorly quantified. Here we show, following a counterfactual modelling approach based on global Forest Resource Assessments, that in 1990-2020 deforestation is the main driver of forest C emissions, partly counteracted by increased forest growth rates under altered conditions: In the hypothetical absence of changes in forest (i) area, (ii) harvest or (iii) burnt area, global forest biomass would reverse from an actual cumulative net C source of c. 0.74 GtC to a net C sink of 26.9, 4.9 and 0.63 GtC, respectively. In contrast, (iv) without growth rate changes, cumulative emissions would be 7.4 GtC, i.e., 10 times higher. Because this sink function may be discontinued in the future due to climate-change, ending deforestation and lowering wood harvest emerge here as key climate-change mitigation strategies. We combine data from global forest resource assessments with a forest model to quantify the role of major drivers of net carbon fluxes from global forest biomass at national resolution between 1990 and 2020. We find that growth-condition changes, more than reforestation, counteracted forest biomass carbon emissions mostly driven by deforestation.

Automated summary

This study reveals that deforestation is the main driver of carbon emissions in global forests between 1990 and 2020. Without changes in forest area, harvest, or burnt area, global forest biomass would become a net carbon sink instead of a carbon source. Actively ending deforestation and reducing wood harvest are essential strategies for climate-change mitigation due to the potential discontinuation of the carbon sink function in the future.