In temperate systems, winter is changing faster than any other season. Increasing temperatures and less precipitation falling as snow results in colder and more variable soil temperatures. In grassland systems, fire is an important management tool, but we know little about how decisions on fire timing may interact with climate change to affect prairie plant communities. For example, leaving plant litter over winter by burning in the spring instead of the fall may ameliorate the effects of snow loss. Here we examine how soil temperatures, prairie plant communities, and prairie plant growth and phenology respond to the combination of variation in fire seasonality and winter climate change in a 3-year field experiment. We addressed this question by installing an experiment where prairie plots are burned annually in either the spring or fall and snow depth was manipulated during the winter by shoveling snow following any accumulation. During the winter, we measured soil temperatures every two hours. During the growing season, we measured community composition and growth and phenology of individual plants. We also measured key plant functional traits related to tolerating freezing risk to predict which species are most at risk.
Results/Conclusions
The combination of fire timing and snow manipulation had substantial effects on winter soil temperature dynamics. During the winter, soils were coldest in the fall burn, snow reduction treatment (minimum temperature: -15°C) and warmest in the control, snow addition treatment (minimum temperature: -2°C). However, this varied by year and depended on the amount of snow that fell that year. Over the course of the experiment, plant diversity, richness, and grass/forb cover did not change significantly, but plant growth and phenology did and varied by species. While burning promoted flowering in some species regardless of snow treatment, snow removal resulted in lower growth rates in other species. Together, these results indicate that climate change and management practices do not have short term effects on plant community composition, but do affect individual plant responses, likely resulting in long-term community consequences. Future management of prairie systems with fire should account for how variation in fire timing might interact with changing winter conditions and potentially avoid removing litter before winter to reduce cold-related damage to overwintering plants.