Changes in growing season length alter population dynamics and community-level phenology

Background/Question/Methods

Climate change is causing widespread shifts in phenology, the timing of life cycle events such as flowering and spring leaf out. While these patterns have been fairly well characterized for plants using experiments and observational studies, the consequences of phenological shifts for demography, population dynamics and interactions in a community are not well understood. Understanding these consequences is critical for developing a predictive understanding of the effects of climate change on species and communities. Doing so is difficult, however, due to the high variability observed among species in their phenological responses to climate.

In this study, we investigated the demographic consequences of changing season length using experimental manipulations of snowmelt dates in sub-alpine plant communities in Switzerland. We used two years of extensive field work to address two overall questions:

1. 1.    What are the consequences of changing season length for individual species’ demography and population dynamics?
2. 2.    How does changing season length affect the degree of overlap in phenological phases for the whole community?

Results/Conclusions

Our study contributes to a growing picture of the important ecological implications of variability in how individuals and species respond to climate change. Across species, some phenological stages were more plastic than others, suggesting particular life history pressures due to changes in snowmelt date. Similarly, some species were more phenologically sensitive than others. These differences were explained in part by species traits, offering hope of building a predictive understanding of how communities may respond to climate change. Further, by comparing the breadth of species’ phenophases within control plots to the phenological shift under manipulated season length, we also found that more variable species were also more plastic year to year. Overall, these results have important implications for understanding how plant communities will respond to further climatic variability in the future. The demography and population dynamics of individual species can be greatly affected by changes in the date of snowmelt. However, the variability among species will affect community level patterns of phenology, with important implications for multiple trophic levels.