Aggravated forest fragmentation undermines productivity stability and amplifies climate impact

African tropical forests have undergone extensive fragmentation, with an increasing proportion of previously intact forests now influenced by edge effects. It has become a pressing necessity to develop a comprehensible index to assess forest fragmentation and its interplay with climate factors influencing forest ecosystem productivity (FEP). Using high-resolution forest cover maps, we developed Forest Fragmentation Gradient Index (FFGI), a novel metric derived from a two-dimensional framework incorporating landscape configuration and edge-to-interior gradient distance. Results reveal that from 2000 to 2023, 76.03% of forests exhibited increased fragmentation, particularly in Central Africa and the Congo region. Statistical analysis of FEP under different fragmentation levels shows that low fragmentation forests are more conducive to FEP accumulation, indicated by kNDVI values of 0.617 ± 0.118 in 2000 and 0.669 ± 0.102 in 2023. With the increase of static fragmentation, the interaction of temperature variation and wind speed to explain FEP gradually increased. Over the past 20 years, in addition, under the corresponding degree of fragmentation, the effects of temperature variations and radiation coupling on FEP all show an increasing trend. Furthermore, as dynamic FFGI (ΔFFGI) intensified, the stability of FEP progressively declined. Thus, curbing further forest fragmentation and moderately restoring afforestation are imperative for sustaining forest ecosystem stability and mitigating climate change impacts.