Variation in the impact of climate change on flowering phenology and abundance: An examination of two pairs of closely related wildflower species

Abstract

Variability in plant phenological responses to climate change is likely to lead to changes in many ecological relationships as the climate continues to change. We used a 34-yr record of flowering times and flower abundance for four species (two Delphinium [Ranunculaceae] species and two Mertensia [Boraginaceae] species) from a subalpine plant community near the Rocky Mountain Biological Laboratory to test the hypothesis that the phenologies of early-flowering species change more rapidly in response to climatological and other abiotic cues than do late-flowering species, a pattern previously found in plant communities in North America and Europe. We also explored a related hypothesis, that flower abundance of late-flowering species is more responsive to changes in climate than that of early-flowering species. The Delphinium species did not support these hypotheses, but the Mertensia species did. The difference between the peak flowering times of the early and late Mertensia species is expanding, leading to a period of diminished resources for pollinators that specialize on this genus. Mertensia ciliata populations are already severely declining in our study area, possibly as a result of earlier snowmelt. Together, these results show that the reported differences between early- and late-flowering species may be widespread, but they are not ubiquitous.