Driving mechanisms of forest age and climate on carbon sinks in Xinjiang forests

Net ecosystem productivity (NEP) is a key indicator of the carbon sink function of forests, reflecting the combined influence of forest structural characteristics and climatic factors. However, the relative contributions of climate variables to carbon sink formation remain uncertain. This study focuses on forest ecosystems in Xinjiang, China, and develops a statistical regression model relating NEP to forest age over the period 2000-2020. Through residual analysis, the dominant influence of forest age on carbon sinks was effectively isolated. A linear regression model was then applied to quantify the relative contribution of climatic factors to the residual NEP, enabling the decoupling of different driving factors in this region. The results indicate that: (1) Forest age contributes 45-49% to NEP in Xinjiang, confirming its dominant role. (2) The contribution of climatic factors varies with vegetation type, mean annual temperature (MAT) explains a larger proportion of variance (R²= 0.401) in coniferous forests than mean annual precipitation (MAP), whereas broadleaf forests show the opposite pattern, with MAP explaining more variance (R²= 0.399) than MAT. Overall, climatic factors account for 24.52% of the annual total NEP in Xinjiang forests. (3) Decoupling analysis reveals that neglecting forest age may lead to an overestimation of climatic contributions to NEP by approximately tenfold. This approach provides a reliable framework for accurately quantifying the independent effects of different drivers. Considering that younger forests currently constitute a substantial portion of Xinjiang’s forests, they are expected to exhibit a stronger carbon sequestration capacity under current climatic conditions. These findings provide a scientific basis for the precise assessment of forest carbon sink functions in arid regions.