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Life at the top: Long-term demography, microclimatic refugia, and responses to climate change for a high-elevation southern Appalachian endemic plant

Abstract:

Plants existing in small and isolated populations often depend on microclimatic refugia that create local environments buffered from macroclimatic conditions. Currently much effort is devoted toward identifying features that create refugial conditions in the expectation that they will continue to serve as refugia into the future. However, the ability of a refuge to resist macroclimatic change is a biological question, not an abiotic one, since species can persist in these conditions while suffering slow decline. Here we test the ability of current refugial habitats of Geum radiatum, a narrowly endemic perennial herb specializing in cool, humid, high elevation sites, to continue to serve as refugia under present and future climatic conditions. We constructed integral projection models to characterize demography, and macro- and topoclimatic niche models to pbkp_redict dynamics given climate change through 2070. This species' demography is characterized by high adult survival (about 97% annually), variable growth, frequent flowering, and rare seedling recruitment. Site relative humidity affected survival and reproduction, but pbkp_redicted population growth rates under current conditions were similar for dry, wet, sheltered, and exposed sites (λ = 0.994-0.998). Augmentation by planting 20-70 seedlings annually would raise population growth rates to 1. Demographic modeling under future lower relative humidity pbkp_redicted further reductions in population growth. Models of the species' macro- and microclimatic niche indicated that all populations had reduced climatic suitability by 2050 or 2080, with 58-83% falling below minimum suitability levels, depending on the climate scenario. G. radiatum's stable demography and habitat protection mean that, barring catastrophes, most populations are not facing extinction under current conditions. However, this species is extremely vulnerable to projected climate change even within its current refugial habitats. This study demonstrates that climate refugia that currently buffer rare species from macroclimatic extremes may not be able to do so under anticipated climate change.