Native woodlands of the genus Quercus play an essential role in biodiversity conservation and climate change mitigation, functioning as carbon reservoirs and providing high-value ecosystem services. However, anthropogenic pressure, progressive climate change, and the structural degradation of forests compromise the ecological stability of these systems, making it essential to identify their regulating factors. This study analyzes carbon sequestration dynamics in forest stands dominated by Quercus faginea Lam. and Quercus pyrenaica Willd., distributed across regions of mainland Portugal under distinct edaphoclimatic conditions. The Q. faginea plots are located in Ansião (NUTS III - Região de Coimbra), while the Q. pyrenaica plots are located in Sabugal (NUTS III - Beiras e Serra da Estrela) and Valpaços (NUTS III - Terras de Trás-os-Montes). The central objective is to identify and quantify how physiological, edaphic, climatic, and structural factors determine carbon retention capacity in these ecosystems. The methodology is based on continuous monitoring of instrumented plots over a one-year period, with systematic collection of dendrometric, ecophysiological, and edaphoclimatic data, complemented by floristic inventories. This functional approach prioritizes analysis at the individual tree scale and its interactions with the environment. The results reveal water availability as a determining factor in carbon fixation efficiency: in Ansião, the higher soil field capacity translates into greater carbon sequestration and a denser understory. In Sabugal and Valpaços, the stands are at distinct successional stages: Valpaços exhibits high canopy density and species diversity, constituting a suitable study stand for assessing the ecology of the target species. Sabugal exhibits moderate density but is subject to grazing, with a sparse shrub understory. Based on these results, the aim is to: (i) systematically quantify the main determinants of carbon sequestration potential; (ii) propose integrated metrics of ecological quality and carbon fixation capacity, applicable in forest management; and (iii) contribute to close-to-nature silviculture models that reconcile productivity, biodiversity conservation, and ecological resilience. Occupying only 2% of mainland Portugal's forested area, oak woodlands respond in an integrated manner to challenges of profitability, fire regime, and nature conservation, which underlies the relevance of this study.

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This work is funded by Agenda Transform, project no. C644865735-00000007, following the Mobilization Agendas for Business Innovation (Notice No. 02/C05-i01/2021), supported by the Recovery and Resilience Plan (PRR) and European Funds NextGeneration EU.