Effects of white-tailed deer exclusion on the plant community composition of an upland tallgrass prairie ecosystem

Questions: Grasslands support ecosystem services, promote diversity, and assist in carbon sequestration. However, grasslands worldwide are diminishing in area, and understanding the drivers shaping the remaining grasslands is critical for their maintenance. The North American tallgrass prairie covers approximately 13% of its historical range and is shaped by fire and herbivory. Fire frequency negatively correlates with plant species richness, while bison (Bos bison) — the historical grazers — offset this effect. However, bison populations have declined, and large browsers are increasing in density. Few studies though have examined the role of large browsers — particularly white-tailed deer (Odocoileus virginianus) — and their interaction with fire frequency in tallgrass prairies. Here, we addressed two questions: (a) What are the impacts of deer on plant diversity, species identities, and relative abundances; and (b) is there an interactive effect between the pressures exerted by deer and the well-documented effects of fire in driving plant community responses?. Location: This study took place at the Konza Prairie Biological Station in northeastern Kansas, USA. Methods: Using a 22-year deer exclosure experiment, we examined differences in plant species richness, evenness, and plant community composition between plots that were either accessible or inaccessible to deer, in areas burned annually or once every four years. Results: We did not find significant effects of deer or interactive effects between deer and burning frequency on any metric of the plant community measured, including plant species richness, evenness, and plant community composition. Conclusions: Contrary to the impact that deer have in other ecosystems (e.g. forests), our results indicate that deer do not affect the plant community of herbaceous-dominated tallgrass prairies. These results indicate that while the loss of bison-grazers has shifted tallgrass prairie plant communities to C₄ grass-dominated systems, the shift to browsing-dominated herbivore pressure from deer has a minimal effect on the plant community.