Elevational demographic differences of two alpine cushion plants indicate divergent responses to climate changes

Juvenile proportions of A. polytrichoides increased at higher elevations at one site but remained uniform elsewhere, whereas A. oreophila generally had higher proportions of older individuals at higher elevations, with some site-specific variation. These patterns suggest that A. oreophila is more sensitive to warming, and thus exhibits faster population dynamics. Controlled experiments showed that warmer temperatures promoted seedling growth and biomass accumulation but reduced survival in both species, with optimal survival at intermediate temperatures (10/15 °C and 15/20 °C).

Most growth responses did not differ between species. Microhabitat type strongly influenced seedling performance: bare ground supported higher germination and growth than grass- or shrub-covered habitats but reduced seedling survival. The two species showed species-specific responses to microhabitat, especially in combination with other environmental factors.

Experimental warming using open top chambers alone did not significantly affect seedling growth. Together, these results reveal that divergent population responses to climate change are already emerging between co-occurring alpine cushion species. This divergence is shaped primarily by species-specific microhabitat use and population structure, likely driven by die-off of older individuals, rather than by differences in early life-stage sensitivity.

Our findings have critical conservation implications, demonstrating that effective management in rapidly warming mountain regions must account for the interplay between microhabitat heterogeneity and broad-scale climatic drivers.