The asynchronous rise of Northern Hemisphere alpine floras reveals general responses of biotic assembly to orogeny and climate change

Understanding how biotic assembly processes responded to past geo-climatic
changes is key to explaining the origins of mountain biodiversity and the
causes of regional disparities in species richness. Here, we jointly
reconstructed geographic ranges and biome-niche evolution for 34 diverse
plant clades across five major Northern Hemisphere mountain systems and
quantified how late Neogene cooling increased arctic-alpine habitat
connections across regions. We reveal that, while alpine floras originated
asynchronously and were assembled through distinct evolutionary processes
over the past 30 Ma, general biological responses to orogeny and
environmental change are apparent. Across regions, in situ diversification
was consistently elevated during heightened phases of tectonic activity.
Over the past 5 Ma, enhanced arctic–alpine connectivity facilitated biotic
interchange and positioned the boreal–arctic region as a major
biogeographic crossroads linking Eurasia and North America.