From carbon sink to carbon source: evaluating Portuguese forest carbon dynamics under improved accounting methodologies

Portuguese forests are traditionally regarded as carbon sinks or carbon-neutral systems. However, this assumption is challenged by increasing wildfire activity, intensive harvesting practices, and shortcomings in current carbon accounting methods. This study proposes an improved model, based on the method adopted in the national greenhouse gas inventory, that explicitly incorporates post-fire succession and forest management effects of logging activities, to critically evaluate the carbon balance dynamics of Portuguese forests over the past three decades. While the official national inventory suggests a near-neutral carbon balance since 2010, the improved model indicates that Portuguese forests have become a net carbon source since the early 2000s, emitting on average approximately 2500 kt of CO₂ annually. Wood harvesting emerged as the largest contributor to forest-related emissions, and the underestimation of wildfire emissions further distorts the national carbon inventory. The study also highlights the lack of detailed forest data, which hinders the application of a higher-tier IPCC methodology. Overall, the results emphasize the need for improved forest monitoring, more accurate accounting practices, and the urgent adaptation of forestry practices to support climate mitigation and sustainable development objectives in fire-prone regions.