Understanding how climate change influences succession is fundamental for predicting future forest composition. Warming is expected to accelerate species succession at their cold thermal ranges, such as alpine treelines. Here we examined how interactions and successional strategies of the early-successional birch (Betula utilis) and the late-successional fir (Abies spectabilis) affected treeline dynamics by combining plot data with an individual-based treeline model at treelines in the central Himalayas. Fir showed increasing recruitment and a higher upslope shift rate (0.11 ± 0.02 m yr⁻¹) compared with birch (0.06 ± 0.03 m yr⁻¹) over the past 200 years. Spatial analyses indicate strong interspecies competition when trees were young. Model outputs from various climatic scenarios indicate that fir will probably accelerate its upslope movement with warming, while birch recruitment will decline drastically, forming stable or even retreating treelines. Our findings point to accelerating successional dynamics with late-successional species rapidly outcompeting pioneer species, offering insight into future forest succession and its influences on ecosystem services.

了解气候变化如何影响演替是预测未来森林构成的基础。预计变暖将加速其寒冷热区（如高山林线）的物种演替。在这里，我们通过将绘图数据与喜马拉雅山脉中部林线的基于个体的林线模型相结合，研究了早期演替桦树 （Betula utilis） 和晚期演替冷杉 （Abies spectabilis） 的相互作用和演替策略如何影响林线动态。在过去 200 年中，与桦树 （0.06 ± 0.03 m ^yr-1） 相比，冷杉的补充增加和更高的上坡位移率 （0.11 ± 0.02 m ^yr-1）。空间分析表明，当树木年轻时，物种间竞争很激烈。各种气候情景的模型输出表明，随着变暖，冷杉可能会加速其上坡运动，而桦树的补充将急剧下降，形成稳定甚至后退的林线。我们的研究结果表明，演替动态加速，演替后期物种迅速超过竞争性先锋物种，为未来的森林演替及其对生态系统服务的影响提供了见解。