No refuge : decline of a northern forest herb, Clintonia borealis, at multiple sites along a broad elevational gradient suggests impacts of recent climate change

Recent climate change has impacted the performance and distribution of species around the globe. In the Northeast U.S., declines and local extirpations of several northern plant species have already been recorded. However, only a few studies have documented these impacts in a controlled, longitudinal study. In this study, we surveyed populations of the northern forest herb Clintonia borealis (Bluebead Lily) in permanent plots located along an approximately 1000-m elevational gradient in western Massachusetts in 2010-11 and 2019. We predicted that plant performance would be positively correlated with elevation due to its close relationship with climate, and that performance would have declined at lower elevations between 2010-11 and 2019 because of the climate warming near the species’ warm-edge distribution limit. As predicted, plant performance was significantly positively correlated with elevation in 2010-11, with ramets at higher elevation being significantly larger and populations having a higher rate of flowering. However, in the longitudinal comparison of populations between 2010-11 and 2019, we found that all populations had declined in at least two measures of plant performance, even those at higher elevation sites. These results suggest that C. borealis populations across the region are being negatively by climate change and that even populations at cooler, higher elevation sites might have seen conditions deteriorate over the course of the study. Our results suggest this common northern forest herb might decline and disappear from many locations in the near future, as has already been documented for rarer northern plant species in the area