The model behind this study uses climate-based multipliers of forest growth and mortality and aninventory-based diameter-class approach, where each year a share of trees in a given diameter classis “promoted” to the next one, and each diameter class has its own growth and mortality rates. Hencethe model recognises both the climatic influence (through the multipliers) and the effects of carbonaccumulation on forest ecosystems (through an ageing diameter class structure, with less growth andmore mortality), resulting in a concave pattern in the capacity of French forests to act as a carbon sink.