Global warming is changing plant communities due to the arrival of new species from warmer regions and declining abundance of cold-adapted species. However, experimentally testing predictions about trajectories and rates of community change is challenging because we normally lack an expectation for future community composition, and most warming experiments fail to incorporate colonization by novel species. To address these issues, we analyzed data from 44 whole-community transplant experiments along 22 elevational gradients across the Northern Hemisphere. In these experiments, high-elevation communities were transplanted to lower elevations to simulate warming, while also removing dispersal barriers for lower-elevation species to establish. We quantified the extent and pace at which warmed high-elevation communities shifted towards the taxonomic composition of lower elevation communities. High-elevation plant communities converged towards the composition of low-elevation communities, with higher rates under stronger experimental warming. Strong community shifts occurred in the first year after transplantation then slowed over time, such that communities remained distinct from both origin and destination control by the end of the experimental periods (3-9 years). Changes were driven to a similar extent by both new species colonization and abundance shifts of high-elevation species, but with substantial variation across experiments that could be partly explained by the magnitude and duration of experimental warming, plot size and functional traits. Our macroecological approach reveals that while warmed high-elevation communities increasingly resemble communities at lower elevations today, the slow pace of taxonomic shifts implies considerable colonization and extinction lags, where a novel taxonomic composition of both low- and high-elevation species could coexist for long periods of time. The important contribution of the colonizing species to community change also indicates that once dispersal barriers are overcome, warmed high-elevation communities are vulnerable to encroachment from lower elevation species.

中文翻译：

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定殖和灭绝滞后推动了北半球山地植物群落对变暖的非线性反应


由于来自温暖地区的新物种的到来和适应寒冷的物种丰度下降，全球变暖正在改变植物群落。然而，通过实验测试对群落变化轨迹和速率的预测是具有挑战性的，因为我们通常缺乏对未来群落构成的预期，而且大多数变暖实验未能纳入新物种的定殖。为了解决这些问题，我们分析了北半球沿 22 个海拔梯度的 44 个全群落移植实验的数据。在这些实验中，将高海拔群落移植到低海拔地区以模拟变暖，同时也消除了低海拔物种建立的扩散障碍。我们量化了变暖的高海拔群落向低海拔群落的分类组成的程度和速度。高海拔植物群落向低海拔群落的组成收敛，在更强的实验变暖下，速率更高。移植后的第一年发生了强烈的群落变化，然后随着时间的推移而减慢，因此到实验期结束时（3-9 年），群落仍然不同于起点和目的地控制。新物种定植和高海拔物种的丰度变化在类似程度上推动了变化，但实验之间存在很大差异，部分原因可能是实验变暖的幅度和持续时间、小区大小和功能性状。 我们的宏观生态学方法表明，虽然变暖的高海拔群落与当今低海拔地区的群落越来越相似，但分类学转变的缓慢步伐意味着相当大的定植和灭绝滞后，低海拔和高海拔物种的新分类学组成可以长期共存。定殖物种对群落变化的重要贡献也表明，一旦克服了扩散障碍，变暖的高海拔群落就容易受到低海拔物种的侵占。