Regional Arboreal Pollen Input and Its Millennial-Scale Variability Recorded in an Alpine Lake in the Hengduan Mountains, China

The Hengduan Mountains are a major hotspot for lake-sediment research, but regional vegetation responses to Holocene climate variability remain incompletely understood. Here, we analyzed pollen assemblages and concentrations from Dinggongniang Co (4633 m a.s.l.) to investigate regional vegetation-related changes over the past approximately 4.7 ka. Pollen percentage and concentration analyses were combined with ensemble empirical mode decomposition (EEMD) and Lomb–Scargle spectral analysis. Despite being located above the modern tree line, the lake sediments are dominated by arboreal pollen (89.5%), particularly Pinus, indicating substantial pollen input from lower-elevation forests. Total pollen concentrations were relatively low around 4.2 ka, increased markedly during the Roman Warm Period, and remained relatively elevated during the Medieval Climate Anomaly, suggesting changes in regional arboreal pollen input potentially associated with Asian summer monsoon-related hydroclimatic variability. Furthermore, time-series analyses identified a possible millennial-scale oscillation at approximately 1.3–1.4 ka, broadly consistent with variability documented in North Atlantic and Asian monsoon records. This finding highlights the value of high-altitude lake pollen records for tracing regional arboreal pollen input and suggests possible connections between Asian monsoon variability and broader Northern Hemisphere climate fluctuations. Although chronological uncertainties and multiple factors influencing pollen concentrations introduce some limitations, the observed patterns offer valuable insights into long-term vegetation-related environmental variability in the Hengduan Mountains.