Comment on bg-2022-35

Abstract

To become carbon neutral by 2050, the European Union (EU27) net carbon sink from forests should increase from the current level of about −360 Mt CO2e yr−1 to −450 Mt CO2e yr−1 by 2050. Reaching this target requires additional efforts, which should be based on a strategic view of the realistic evolution of European forests within the next decades, considering the current age-class distributions, the effect of forest management practices and the expected impacts of future climate change. However, modelling the combined effect of these drivers is quite challenging since it requires a mechanistic assessment of climate impacts on primary productivity and a detailed representation of the forest age structure and of the management practices across the entire EU. To achieve this goal, in this study we combined the output provided by four land-climate models – run under two different representative concentration pathway scenarios (RCP 2.6 and RCP 6.0) – to parameterize the input data used in an empirical forest growth model. This hybrid modelling approach aims to quantify the impact of climate change and forest management on the long-term (i.e., to 2100) evolution of the EU27+UK forest carbon budget, under a Business-as-Usual scenario, based on the continuation of the management practices applied by EU member states within the historical period 2000–2015. Our results highlight that, under the continuation of the current management practices, the EU27+UK forest C sink would decrease to about −250 Mt CO2e yr−1 in 2050 and −80 Mt CO2e yr−1 by 2100. The main driver of the long-term evolution of the forest C sink is the ongoing ageing process of the European forests, mostly determined by past management. In addition, climate change may further amplify or mitigate this trend. Due to the large uncertainty of climate projections, in 2050 the net C sink may range from −100 to −400 Mt CO2e yr−1 CO2e yr−1 (RCP 2.6) and from −100 to −300 Mt CO2e yr−1 (RCP 6.0). This suggests that, while a change in management practices is needed to reverse an otherwise declining trend in the sink, climate change adds a considerable uncertainty, potentially nearly doubling or halving the sink associated to management.