The development of appropriate tools to quantify long-term carbon (C) budgets following forest transitions, that is, shifts from deforestation to afforestation, and to identify their drivers are key issues for forging sustainable land-based climate-change mitigation strategies. Here, we develop a new modeling approach, CRAFT (CaRbon Accumulation in ForesTs) based on widely available input data to study the C dynamics in French forests at the regional scale from 1850 to 2015. The model is composed of two interconnected modules which integrate biomass stocks and flows (Module 1) with litter and soil organic C (Module 2) and build upon previously established coupled climate-vegetation models. Our model allows to develop a comprehensive understanding of forest C dynamics by systematically depicting the integrated impact of environmental changes and land use. Model outputs were compared to empirical data of C stocks in forest biomass and soils, available for recent decades from inventories, and to a long-term simulation using a bookkeeping model. The CRAFT model reliably simulates the C dynamics during France's forest transition and reproduces C-fluxes and stocks reported in the forest and soil inventories, in contrast to a widely used bookkeeping model which strictly only depicts C-fluxes due to wood extraction. Model results show that like in several other industrialized countries, a sharp increase in forest biomass and SOC stocks resulted from forest area expansion and, especially after 1960, from tree growth resulting in vegetation thickening (on average 7.8 Mt C/year over the whole period). The difference between the bookkeeping model, 0.3 Mt C/year in 1850 and 21 Mt C/year in 2015, can be attributed to environmental and land management changes. The CRAFT model opens new grounds for better quantifying long-term forest C dynamics and investigating the relative effects of land use, land management, and environmental change.

中文翻译：

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森林长期碳固存的建模和实证验证（法国，1850-2015）。

开发适当的工具来量化森林转型（即从毁林到造林的转变）后的长期碳（C）预算，并确定其驱动因素，是制定可持续的基于土地的气候变化减缓战略的关键问题。在这里，我们基于广泛可用的输入数据开发了一种新的建模方法 CRAFT（森林碳累积），以研究 1850 年至 2015 年区域范围内法国森林的碳动态。该模型由两个相互关联的模块组成，其中集成了生物量库和流量（模块 1）与凋落物和土壤有机碳（模块 2），并建立在先前建立的气候-植被耦合模型的基础上。我们的模型可以通过系统地描述环境变化和土地利用的综合影响来全面了解森林碳动态。将模型输出与森林生物量和土壤中碳库的经验数据（近几十年来可从清单中获得）以及使用簿记模型的长期模拟进行比较。CRAFT 模型可靠地模拟了法国森林转型期间的碳动态，并再现了森林和土壤清单中报告的碳通量和库存，这与广泛使用的簿记模型形成鲜明对比，该模型仅严格描述因木材采伐而产生的碳通量。模型结果表明，与其他几个工业化国家一样，森林生物量和有机碳储量急剧增加是由于森林面积扩大，特别是 1960 年之后，由于树木生长导致植被增厚（整个时期平均每年增加 7.8 吨碳） ）。簿记模型之间的差异（1850 年为 0.3 吨碳/年，2015 年为 21 吨碳/年）可归因于环境和土地管理的变化。CRAFT 模型为更好地量化长期森林碳动态以及研究土地利用、土地管理和环境变化的相对影响开辟了新的基础。