COS 110-5 - Climate sensitivity among co-occurring alpine plant species

Abstract: Plant sensitivity to climate conditions can impact the immediate fitness and long-term persistence of plant populations and species. Phenological records provide a means for comparing climate sensitivity among co-occurring plant species. Flowering phenology is especially useful in this context because of the availability of long-term records that make this a highly tractable trait and the link between flowering phenology and reproductive fitness. Highly sensitive plants that shift their flowering phenology in response to climate conditions may experience phenological mismatches with key pollinators, resulting in reduced fitness. Insensitive plant species may also be at risk if the inability to adjust to variable conditions results in a maladaptive strategy. Here, we analyzed plant phenological data from three alpine sites across natural climate gradients in Colorado (Mount Evans, Niwot Ridge, and Pennsylvania Mountain). Climate sensitivity was estimated for ten co-occurring plant species based on the slope of the relationship between average flowering time and site-specific climate conditions. We then compared the relationship between climate sensitivity and flowering traits known to influence overall plant fitness. Finally, for one of the sites we explored the relationship between climate sensitivity and plant functional traits to gain insight into potential mechanisms driving variation in climate sensitivity.

Average May temperature was the strongest predictor of flowering time at all three sites. Total winter precipitation was also a significant predicator of flowering phenology and partially buffered plants from the effects of warm May temperatures. The slope of the relationship between flowering phenology and temperature was consistently negative, indicating that warmer springs resulted in earlier flowering. Plants at Niwot Ridge exhibited the greatest average shift in flowering phenology, suggesting that these plant communities may be more sensitive to warming conditions. Climate sensitivity also varied significantly among co-occurring plants species at each site and was inversely correlated with average seasonal flower density at Mount Evans and Pennsylvania Mountain. This suggests that highly sensitive species experience greater fitness consequences of climate change. At Pennsylvania Mountain, our driest site, estimated climate sensitivity was negatively correlated with average leaf δ¹³C, a time-integrated measure of water-use efficiency. The more climate-sensitive plant species had both lower and more variable leaf δ¹³C, indicating reduced water-use efficiency. This suggests that plant-water relations are likely an important factor shaping species-specific responses to climate change. Overall, this work demonstrates how species-specific variation in climate sensitivity could impact population and community dynamics as temperatures continue to warm.