Socio-ecological drivers of long-term ecosystem carbon stock trend: An assessment with the LUCCA model of the French case

Land ecosystems can play a crucial role in climate-change mitigation by acting as sinks for carbon. Legacy effects of past land use, including land conversion and changes in land-use intensity, influence the capacity for future ecosystem carbon sequestration. These effects are hard to quantify, however, and the influence of changes in land-use intensity are still largely overlooked. This study assessed the long term dynamics (1850-2015) of the terrestrial carbon budget in France. We developed a new dynamic model: LUCCA (Land Use Change & Conversion Accounting) that robustly quantifies the dynamics of carbon stocks and fluxes. It allows disentanglement of land conversion from land management effects following a socio-ecological perspective. Carbon stocks in terrestrial ecosystems in France increased from 3.5 GtC in 1850 to 4.8 GtC in 2015 as a result of contrasting regional land-use trajectories. Based on five counterfactual scenarios, we unravel that changes in land-use intensity explained 46 % of the observed carbon stock changes since 1850, while land conversion was responsible for 30 %, and the rest can be attributed to changes in forest growth rates induced by both environmental and management changes. The effects of land conversion and changes in land-use intensity on carbon stock accumulation, however, would have been hardly possible in the absence of agricultural intensification and release of harvest pressure following wood-fuel substitution by fossil fuel. In fact, carbon emissions induced by fossil fuel consumption in France from 1850 to 2015 were 9 times the carbon sink in terrestrial ecosystems. These figures highlight the importance of considering long-term trajectories of ecosystem carbon fluxes and their relationship with emissions from other processes for climate action strategies. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

The study assessed the long-term dynamics of the terrestrial carbon budget in France from 1850 to 2015. It found that changes in land-use intensity and land conversion accounted for the majority of observed carbon stock changes, highlighting the importance of considering ecosystem carbon fluxes and their relationship with other emission processes for climate action strategies.