Functional trait shifts along temperature and precipitation gradients in the light of trait driver theory

Background Climate projections for western Norway predict warmer and wetter conditions in the future, a change that has already started. Such changes are affecting plant communities in different ways. They may be affected by extinctions, colonization, shifts in species abundance, or plasticity and adaptive changes within species. Functional traits affect ecological functioning of species, and are good tools used to investigate the responses of species and communities to climate change. Methods In this study, we collected functional traits of grassland plants along temperature (6.5-10.5 °C mean summer temperature), and precipitation gradients (600-2700 mm/year). In total, 2780 leaves from 88 species were collected for measuring the functional traits; specific leaf area (SLA), leaf dry matter content (LDMC), leaf thickness, carbon-to-nitrogen-ratio and vegetative height. We use trait driver theory to investigate our plant communities. We use the community weighted means and variance along the gradient to investigate the long-term climate change effects. To see the directional changes to climate change within a site we use the skewness of the trait distribution. To find which species are more sensitive to these changes we use the kurtosis of the trait distribution. Findings Our results show that the plant communities have a less resource conservative trait syndrome as the temperature increases, and that there is an interaction with precipitation. Both intraspecific variability and species turnover effect are important for these trends. Plant communities within sites are responding to climate change through directional trait shifts, in compliance with the recent changes in climate. The species with trait values that the plant communities are moving away from are more sensitive to climate change. Conclusion We use functional traits to understand how plant communities and species will be, and are, affected by climate change. This is important for nature management, and understanding our future plant communities. Key words: functional traits, climate change, functional ecology, grasslands, trait driver theory.