Sedimentary pollen evidence for Estuarine vegetation shifts: Climate-dominated drivers in the Yellow River Delta, China

The Yellow River Delta, as a typical land-sea interaction zone, is crucial for understanding regional environmental evolution and predicting biological feedbacks of estuarine wetlands via reconstructing past vegetation history. In this study, we reconstructed the Holocene vegetation succession of the Yellow River Delta based on the pollen records from the Kenli (KL) core. Five successive vegetation evolutionary stages were identified in accordance with palynological variations. The early Holocene (9.28–8.15 cal ka BP) featured regional woodlands under cold, arid conditions. From 8.15 to 7.37 cal ka BP, hygrophytic wetlands expanded with a warming, humid climate. During the Middle Holocene (7.37–3.19 cal ka BP) saw dense forests peak under climatic optimum. The late Holocene (3.19–0.82 cal ka BP) witnessed forest degradation and the transition to open woodlands in response to cooling and aridification. Since 0.82 cal ka BP, coniferous forests and steppes have coexisted under persistent cooling and drying. Principal component analysis (PCA) reveals a moisture-related ecological gradient as the primary dimension of pollen assemblage variation. Redundancy analysis (RDA) further indicates that regional temperature and precipitation, broadly consistent with East Asian Summer Monsoon (EASM) evolution, explain a significant portion of the pollen variance. These results suggest a close association between monsoon-modulated hydroclimate and long-term vegetation changes. Superimposed on this climatic framework, coastline migration and frequent Yellow River channel avulsions sequentially shifted local habitats from shallow-water wetlands to salt marshes and tidal mudflats, eventually evolving into terrestrial alluvial plains. Additionally, the mid-Holocene sea-level highstand may have partially influenced coastal moisture conditions through groundwater recharge and wetland expansion, though this interpretation remains tentative. These findings advance the understanding of wetland ecological responses to compound climatic and geomorphic disturbances in monsoon-affected coastal delta regions.