Life at the top: Long-term demography and responses to climate change for a high-elevation southern Appalachian endemic plant
Plants existing in small and isolated populations may be particularly vulnerable to disturbance and changing climatic conditions. We analyzed the demography of Geum radiatum, a narrowly endemic and federally endangered perennial herb, at 20 locations in North Carolina and Tennessee. This perennial herb is found only at high elevations and primarily on wet cliffs and grassy balds. We collected annual demographic from 2003-2013 and constructed integral projection models to characterize demography and test scenarios related to potential threats. As a size measure, we used the product of canopy area and number of rosettes, the best predictor of vital rate variation. We collected temperature and relative humidity data from study sites for three years. The fact that this species grows on the coldest, wettest, highest elevation sites means that future climate change could pose a significant threat. Accordingly, we modeled the species’ macro- and topoclimatic niche in relation to expected climate change through 2050.
This species’ demography is characterized by very high survival (about 97% annually), variable growth, frequent flowering, a lack of a seed bank, and rare seedling recruitment. Weather data indicated cool and humid conditions but variation in weather did not consistently affect vital rates. Population growth rates were nearly one, with only minor differences among sites varying in wetness and exposure. Predicted population growth rates were slightly higher for dry sheltered (0.997) and wet exposed (0.997) than dry exposed (0.992) and wet sheltered (0.993) and did not differ significantly. Augmentation by planting 20-70 seedlings, depending on the habitat, would be required to balance population growth. Physical disturbances of the precipitous, wet substrates supporting G. radiatum populations could result in both mortality and recruitment opportunities, but we did not observe any of these events during our study. G. radiatum’s stable demography and habitat protection mean that, barring catastrophes, most populations are not facing imminent extinction. Nearly all populations would suffer reduced climatic suitability in the next 35 years, though only a quarter would experience severe declines. The limited capacity of this species to recruit seedlings and its likely problems with future climate change paint an uncertain future.