Divergent asymmetric responses of regional forest aboveground biomass carbon dynamics to climatic factors under different ENSO events.

Forest aboveground biomass carbon (AGBC) represents one of the largest terrestrial carbon reservoirs and is highly sensitive to climate variability. However, the responses of forest carbon dynamics to climate exhibit spatiotemporal heterogeneity, resulting in inconsistent conclusions across different spatial and temporal scales. In particular, the mechanisms through which El Niño-Southern Oscillation (ENSO) events influence AGBC dynamics remain insufficiently understood. This study aims to elucidate the climatic response of forest AGBC in Zhejiang Province across different ENSO events. We distinguished El Niño and La Niña events from 2002 to 2021, and collected forest AGBC datasets, meteorological data, and drought indices to investigate the responses of AGBC to climatic factors using partial correlation analysis and the geographical detector method. Our results showed that (1) AGBC exhibited an overall increasing trend during the past two decades, with an average growth rate of 12.07%. (2) Forest AGBC exhibited divergent asymmetric responses to climatic factors under different ENSO events. The responses of interannual AGBC change (ΔAGBC) to climatic factors under different ENSO events displayed stronger spatial non-stationarity. (3) Geographical detector analysis revealed the Pre showed the strongest individual explanatory power, while climatic interactions consistently exceeded individual factors. During El Niño, the explanatory power of Tmean increased, with the Pre-SC-PDSI interaction reaching the highest explanatory value among all scenarios. During La Niña, Tmean weakened markedly, while moisture-related interactions became dominant. This study provides a new perspective on the climatic responses of forest ecosystems.