Data from: Mountain building, climate cooling and the richness of cold-adapted plants in the northern hemisphere

Aim The summits of mountain ranges at mid-latitude in the Northern Hemisphere and the Arctic share many ecological properties including comparable climate and similar floras. We hypothesise that the orogeny during the Oligocene-Miocene combined with global cooling allowed the origin and early diversification of cold-adapted plant lineages in these regions. Before establishment of the Arctic cryosphere, adaptation and speciation in high elevation areas of these mountains ranges may have led to higher species richness when compared to the Arctic. Subsequent colonisation from mid-latitude mountain ranges to the Arctic may explain similar but poorer flora. Location Arctic-Alpine regions of the Northern Hemisphere. Methods We mapped the cold climate in the Northern Hemisphere for most of the Cenozoic (60 Ma until present) based on paleoclimate proxies coupled with paleoelevations. We generated species distribution maps from occurrences and regional atlases for 5464 cold-adapted plant species from 756 genera occupying cold climates. We fitted a generalised linear model to evaluate the association between cold-adapted plant species richness and environmental as well as geographic variables. We performed a meta-analysis of studies, which inferred and dated the ancestral geographic origin of cold-adapted lineages using phylogenies. Results We found that the subalpine-alpine areas of the mid-latitude mountain ranges comprise higher cold-adapted plant species richness than the Palearctic and Nearctic polar regions. The topo-climatic reconstructions indicated that the cold climatic niche occurred first in mid-latitude mountain ranges (42-38 Ma), specifically in the Himalayan region, and only later in the Arctic (22-18 Ma). The meta-analysis of the dating of the origin of cold-adapted lineages indicated that most clades originated in central Asia between 39 and 7 Ma. Main conclusions Our results support the hypothesis that the orogeny and the progressive cooling in the Oligocene-Miocene generated cold climates in mid-latitude mountain ranges, before the appearance of cold climates in most of the Arctic. Early, cold mountainous regions likely allowed for the evolution and diversification of cold-adapted plant lineages followed by the subsequent colonisation of the Arctic. Our results are in line with Humboldt's vision of integrating biological and geological context in order to better understand the processes underlying the origin of arctic-alpine plant assemblages.

研究目的：北半球中纬度山脉的山顶与北极区域拥有诸多共通的生态特征，包括相似的气候条件与相近的植物区系。我们提出假说：渐新世-中新世的造山运动与全球变冷共同促成了上述区域内耐寒植物支系的起源与早期分化。在北极冰冻圈形成之前，这些山脉高海拔区域的适应性演化与物种形成，可能使其物种丰富度高于北极区域；而后续从中纬度山脉向北极的拓殖事件，则可以解释北极植物区系与前者相似但物种更为贫乏的现象。

研究区域：北半球北极-高山区域。

研究方法：我们基于古气候代用指标与古海拔数据，重建了新生代大部分时期（60 Ma至今）北半球的寒冷气候分布。我们针对756个属、共计5464种耐寒植物，结合物种记录与区域分布图集，生成了其物种分布地图。我们构建了广义线性模型（generalised linear model），以评估耐寒植物物种丰富度与环境及地理变量之间的关联。我们还开展了一项元分析，整合了利用系统发育树推断并定年耐寒植物支系祖先地理起源的相关研究。

研究结果：我们发现，北半球中纬度山脉的亚高山-高山区域，其耐寒植物物种丰富度高于古北界与新北界的极地区域。地形-气候重建结果显示，寒冷气候生态位最早出现于中纬度山脉（42~38 Ma），尤其是喜马拉雅地区，直至较晚时期才出现在北极区域（22~18 Ma）。针对耐寒植物支系起源定年的元分析表明，绝大多数演化支起源于距今39~7 Ma的中亚区域。

主要结论：我们的研究结果支持如下假说：在北极多数区域形成寒冷气候之前，渐新世-中新世的造山运动与逐步加剧的全球变冷，已在中纬度山脉区域催生了寒冷气候。早期的高海拔寒冷山地区域可能促成了耐寒植物支系的演化与分化，随后这些支系才向北极区域完成拓殖。我们的研究结果与洪堡的学术理念相符——即整合生物学与地质学背景，以更好地理解北极-高山植物群落起源背后的演化过程。