Effects of natural warming and snow on grass phenology and fitness

Abstract: Organisms respond to changes in their environment using different strategies. Understanding how species deal with changes expected due to ongoing climate change is important for making accurate predictions about their effect on ecosystems. Geothermal areas provide a natural warming laboratory because the species present have been exposed to warming over generations. This study used geothermal areas in Iceland to study plant fitness and phenology in a common garden experiment. Additionally, plants were exposed to a snow manipulation treatment. In the experiment, 794 individuals of Festuca rubra were used; 375 originated from non-heated soil and, of these, 182 were exposed to ambient snowfall and 193 were exposed to snow removal treatment; 419 of the individuals originated from geothermally heated areas and, of those, 226 were exposed to ambient snowfall and 193 to snow removal treatment.  I expected both phenological and fitness differences, such that plants from geothermally heated areas; (1) develop slower, (2) have a lower chance of survival and probability to flower. However, I expected no difference in biomass between plants from geothermally heated soils and non-heated soils. For plants exposed to snow removal treatment I hypothesized the effects on fitness and phenology would depend on the winter condition. Results showed there were no overall differences between plants originating from geothermally heated soils and plants originating from non-heated soils in any of the recorded responses. Snow had an effect on biomass allocation, where plants exposed to ambient snowfall produced a larger proportion of reproductive biomass; there were also tendencies that the reproductive structures were more numerous and had a higher biomass overall. My results suggest F. rubra shows a plastic response to geothermal warming and that snow cover has a positive effect on fitness (reproductive biomass). The study is an important contribution to understanding the ways in which plants cope with changes in temperature and how they are affected by changes in snow regimes.