Full Professor University of Wisconsin-Madison Madison, Wisconsin, United States
Abstract: The climate is changing faster in winter than in other seasons in temperate regions. Shorter winters, precipitation as rain rather than snow, and more freeze-thaw events are reducing snow accumulation and insulation, increasing temperature variability in the soil. In long-lived perennial ecosystems, this may reduce fitness of plants that resprout from winter-dormant bud banks. Fire management may be an important tool to increase the resiliency of these often disturbance-adapted habitats, since litter accumulation is another form of soil insulation. Here, we use a replicated field experiment to ask whether management alters plant community responses to winter climate in a restored Wisconsin tallgrass prairie. We combine plant community responses to experimental treatments with functional trait data to understand what life history characteristics predict persistence. Our experiment – ongoing since 2016 – consists of three snow manipulation treatments (snow reduction, snow addition, unmanipulated) nested within four fire management treatments (fall burn, spring burn, fall mow, undisturbed). Within this design, we measured percent cover of each species present annually in late summer to estimate plant richness, diversity, and abundance. We used changes in abundance to determine the response ratio for the 20 most abundant species present in the experiment by quantifying how treatment combinations altered abundance. We also measured a suite of functional traits (vegetative height, specific leaf area, leaf dry matter content, percent leaf carbon and nitrogen, plant clonality, perenniality) for each of these 20 species to calculate species-specific trait means. We found minimal changes to herbaceous plant community structure with respect to winter climate but did find some response to management. Both burning and mowing, regardless of timing, resulted in greater plant richness and diversity compared to undisturbed controls, and spring burning in particular increased the abundance of flowering forbs and reduced the abundance of cool season grasses. We also found that functional traits predicted the response ratio – that is, changes in abundance – as functional diversity changed, again, more so from management than climate treatments. Annual, non-clonal species decreased in unmanaged treatments, and short species with high leaf carbon to nitrogen ratios decreased with spring burning in particular. Long-term investigation is needed to further understand the interaction that observed community changes with management may have with changing winter climate. The potential of fire management to increase tallgrass prairie resilience under global change will help us better conserve and restore these imperiled ecosystems now and into the future.