Few studies investigate the interactive effects of temperature, precipitation and grazing on temperate grasslands. Though previous studies show warming can decrease or increase grassland productivity, with the average response near zero, temperature will not be the only factor affecting these grasslands in the future. As climate change is predicted to both increase temperature and change precipitation patterns, it is imperative that these factors be investigated interactively. Another factor that could act synergistically with temperature and precipitation is grazing, as grasslands will continue to support wild and domestic ungulate populations. A particular geographic area of concern is the Canadian prairies, where plant communities are at the edge of their bio-geographic range, and thus may be especially vulnerable to climate change effects. We conducted a manipulative experiment in Canadian native prairie to determine the potential impacts of warming, altered precipitation, and grazing on primary productivity and community composition. The study used a factorial design of warming, precipitation, and defoliation (simulated grazing) treatments, based on variability predicted for the system. The abiotic and biotic conditions of the plots were extensively surveyed, including monthly plant cover estimates and the harvest of a subplot at peak biomass for vegetation biomass data, analysed by vegetation type. Results presented here are from the second year of the experiment.

Results/Conclusions

Primary productivity and community composition were most sensitive to modifications in precipitation and defoliation, and less sensitive to warming. Specifically, total productivity declined with increasing defoliation and decreasing precipitation. Temperature did not affect total productivity, but it did affect forb productivity. Under drought conditions, warmed plots had higher forb biomass than unwarmed plots. However, this increase in forb productivity was not reflected in changes to community composition. Ordinations indicated changes in community composition due to the precipitation and defoliation treatments, but community composition was robust to warming. These results suggest that plant communities and productivity in northern grasslands will be affected by grazing and precipitation, with potential for interactions with climate warming, and that vegetation type will play a role in determining how plants respond.