Plant communities, populations and individuals have distinct responses to short-term warming and neighbour biomass removal in two montane grasslands

Aims Climate change will impact plant communities and populations but also individual plant performance. Most predictive models of community responses to climate change ignore individual-level biotic interactions despite their known importance for community diversity and functioning. Here, we consider plant fitness and diversity responses to climate change associated factors at three organisational levels: communities, populations and individual plants, to increase our understanding of how plant communities respond to climate change. Location Montane grassland, Tasmania, Australia. Methods In two plant communities, we manipulated temperature using open-top chambers and removed random and dominant species biomass. Two years after experimental manipulations, we assessed the impact of treatments on species diversity, community- and population-level functional traits and individual plant fitness. Results Species diversity was affected by warming in one of the two communities, while community-level functional trait diversity metrics were unaffected by treatments. Mean community trait values were strongly impacted by dominant species biomass removal in both communities, notably increasing specific leaf area (SLA) and specific root length. SLA showed the strongest population-level trait response, with higher values found in warmed plots and lower values found in dominant species biomass removal plots. Neighbours had a stronger competitive effect on individual plant fitness in warmed compared to unwarmed conditions at the higher-elevation site and facilitation was common in both communities. Conclusions We demonstrated that over short time scales, plant communities respond to experimental warming and biomass removal across multiple organisational levels. Competitive and facilitative interactions played a significant role in determining fitness outcomes, but competitive interactions dominated under warmed conditions. We highlight the importance of local-scale biotic interactions in mediating individual responses to warming and recommend their inclusion in future studies of how climate change will impact the long-term structure and function of plant communities through short-term impacts on individual plant fitness.