Climate change has shifted reproductive timing in many plant species. The goal of this project is to better understand the environmental cues that drive plant reproductive cycles and how they are expected to shift under climate change. Observational studies in alpine and subalpine systems have found that both rising temperatures and earlier snowmelt lead to earlier phenological events. However, observational studies are unable to determine the relative effects of these two environmental factors because they tend to be correlated. This project examines the effect of rising temperatures and early snowmelt on the timing of flowering and fruiting in subalpine wildflowers, as well as the reproductive consequences of these changes. The experiment manipulated both the ambient air temperature and the timing of snowmelt in a factorial design in a subalpine meadow at the Rocky Mountain Biological Laboratory (RMBL) in Gothic, Colorado. We tracked the reproductive stages of individual plants of three species (Valeriana edulis, Potentilla pulcherrima, and Delphinuim nuttallianum) three days a week for three months. We counted flowers and seeds to determine both potential and realized
Results/Conclusions
Snow melted on average 9 days earlier in the early melt treatments compared to the controls. Warming treatments increased air temperatures by an average of 1.9°C. As expected, both earlier snowmelt and warmer temperatures led to earlier flowering and fruiting in all three species. We did not find evidence for interactions between snowmelt and temperature. Snowmelt date had a consistently larger effect than temperature on the timing of peak flowering (2–4 times larger, depending on the species). Snowmelt date also had a larger effect on the timing of peak fruiting, and in one species (Potentilla), the timing of peak fruiting was not affected by temperature at all. The treatments had minimal effect on durations of flowering and fruiting, with only one species (Valeriana) increasing the length of its flowering and decreasing the length of fruiting in response to the climate treatments. We also found that the treatments had small and inconsistent effects on reproductive output of these species. This study suggests that the timing of snowmelt may be the primary driving climatic factor behind phenological change in subalpine and alpine plants. These results also show that shifts in phenology and duration can occur without loss of reproductive fitness.