Tallgrass prairie recovery following persistent grazing depends on response measured

The dynamics of tallgrass prairie plant communities have historically been driven by the interacting effects of grazing by large ungulate herbivores, frequent fire, and a variable mid-continental climate.  The effects of grazing on tallgrass prairie are well known, and include decreased C₄ grass abundance, increased forb abundance, increased species diversity, and increased spatial heterogeneity. However, the short- and long-term legacy effects that persist after grazing is removed are not well known, and may differ above- and belowground.  These legacy effects may have important implications for land managers, biodiversity conservation, and understanding of ecosystem function.  In this study we examine above- and belowground responses of the plant community following release from persistent grazing by comparing the responses of ungrazed, currently grazed, and recovering areas of upland tallgrass prairie (last grazed in 2007).  Aboveground we measured productivity, stem density, and cover, while belowground we measured bud bank density and seed bank density. Following grazer exclusion, aboveground plant productivity is consistently greater in recovering areas than long-term ungrazed areas.  C₄ grass cover and stem density in recovery areas are not different from ungrazed areas, but densities of C₄ grass buds remain low compared to ungrazed areas. Overall bud bank densities of grazed areas are consistently lower than bud bank densities in ungrazed areas, while bud bank densities of recovering areas tend to be intermediate between grazed and ungrazed densities. Seed bank density in the recovery areas is greater than seed bank density in both the grazed and ungrazed areas. Aboveground plant species richness in recovering areas is intermediate between species richness of ungrazed and grazed areas, but belowground in the bud bank both recovery and grazed areas have greater species richness than ungrazed areas.  These results suggest that after release from grazing, the plant communities of tallgrass prairie do not quickly return to the state of long-term ungrazed prairie. Furthermore, perceptions of plant community recovery depend on the response variable used, suggesting that multiple metrics will be need to assess recovery from grazing.