Carbon sink was strengthening in Yunnan’s vegetation: findings from trained eddy flux data with gradient boosting machine

Yunnan Province, a key forest region in China, plays a crucial role in the nation’s terrestrial carbon sink. Understanding the spatiotemporal dynamics and driving mechanisms of vegetation carbon sinks in this topographically complex and ecologically diverse region is essential for guiding regional carbon neutrality policies. Using Gradient Boosting Machine (GBM), integrating FLUXNET eddy covariance data, remote sensing products, and climatic variables to simulate net ecosystem production ( NEP ) across Yunnan from 1999 to 2021. Model validation was performed against independent solar‑induced chlorophyll fluorescence (SIF) data, Random Forest predictions, and national forest inventory reports. The results identified significant spatial heterogeneity in NEP across Yunnan, characterized by a west–east gradient of decreasing sink strength, with western Yunnan acting as the primary carbon sink while the eastern region exhibits weaker sink capacity or even carbon sources. Over the past two decades, provincial NEP showed a consistent upward trend (0.103 tC ha − 1 yr − 1 ), primarily driven by faster growth of gross primary production ( GPP ) relative to ecosystem respiration. Key factors contributing to this enhancement include the growth of middle‑aged forests from economic plantations, afforestation, and secondary growth in protected areas, as well as the existence of an optimal GPP range (8–17 tC ha − 1 yr − 1 ) that supports the fastest NEP growth, a condition met by most vegetation in Yunnan. Our findings, validated against multiple independent datasets (SIF, Random Forest, and national forest inventories), highlight the importance of growth of middle‑aged forests and moderate‑productivity ecosystems in driving regional carbon sink dynamics. These results offer critical insights for optimizing forest management and afforestation strategies to enhance carbon sequestration in support of China’s climate mitigation goals.