<p>Montane vegetation on the eastern Tibetan Plateau (TP) is highly sensitive to climatic variability, yet the scarcity of high-resolution archives has limited our understanding of vegetation dynamics, treeline behaviour, and peat development over the last two millennia. Here we present a ~ 2,100-year peat sequence from a small montane peatland situated near the modern treeline. High-resolution (~ 13 years) analyses of loss-on-ignition, pollen, and conifer stomata were conducted. The results show that vegetation evolution across the eastern TP exhibits broadly coherent patterns, as indicated by consistent long-term trends in arboreal pollen records. A progressive increase in arboreal pollen percentages since ~ 2 ka <span>bp</span> indicates sustained forest expansion, reflecting a temperature-dominated control on long-term vegetation trends. In contrast, centennial–decadal variability in arboreal pollen shows closer correspondence with both temperature and monsoon precipitation records, suggesting that short-term vegetation fluctuations were jointly regulated by temperature and precipitation, with temperature exerting the primary influence. A pronounced decline in arboreal pollen during the past ~ 90 years, despite continued warming and increased precipitation, points to the emergence of human impacts on vegetation. Temporal offsets between conifer stomata and arboreal pollen records indicate that treeline migration lagged regional forest and climatic changes by several decades, consistent with modern ecological observations of delayed treeline responses to temperature forcing. Peaks in organic matter content during cold-wet intervals further indicate that such conditions promoted peat preservation and enhanced peat accumulation. These findings provide new insight into the multi-scale controls on vegetation dynamics in the eastern TP mountains and offer long-term ecological evidence for assessing future responses of alpine forest and treeline to ongoing climate warming and increasing human disturbance.</p>