Abstract
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.
Highlights
Understanding the carbon (C) balance in global forest is key for climate-change mitigation
We fill that gap by combining the most recent and consistent global forest dataset provided by the Forest Resource Assessment (FRA2)—an authoritative data source3,15—with the parsimonious forest C model CRAFT16 (CaRbon Accumulation in ForesT)
We calculate the temporal dynamics of managed and primary forest growth rates in 152 countries in 1990–2020 and couple counterfactual scenario development with a typology approach in order to answer the following question: Which role do the individual drivers changes in area, harvest, burnt area, and forest growth rate play for the observed C-stock changes in national and global forest biomass dynamics over the last three decades? Answering this question is essential for assessing the efficiency of various forest-based climate-change-mitigation strategies
Summary
The ranges of values in the attribution of main drivers result from the previously reported differences between the counterfactual and actual C budget estimates across sensitivity analyses (see Supplementary Tables 2–3) combined with some changes in the type of forest C-dynamics trajectory identified through the typology in countries with large forest biomass stocks: China, India, and Australia (Supplementary Note 1 and Supplementary Fig. 6). This result suggests that globally a reduction of forest use may have the potential to enhance growth rate, corroborating previous findings by Quesada et al.[14] These interpretations warrant a caveat that primary versus managed forest growth rate changes are derived from the FRA data and a state-of-the-art of the literature on changes in primary forest density (see “Methods” section and Supplementary Note 2), the latter being associated with higher uncertainties the corresponding sensitivity analysis testing suggests these uncertainties to have little impact on the figures displayed here Our results plead for a double strategy to enable future forest-based solutions for climate-change mitigation: in the Global South, ending deforestation is the main priority to reverse the net C source toward a net C sink, while in the Global North, lowering wood harvest has the strongest potential to immediately enhance the C sink in forest biomass
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