Belowground bud bank response to grazing under severe, short-term drought

Benjamin L. VanderWeide, David C. Hartnett

While the effects of drought and grazing are often studied separately, these disturbances co-occur in grasslands worldwide and interactively influence population, community, and ecosystem processes. The effects of drought and grazing on the belowground bud bank may dictate the trajectory of community recovery because new shoots arise from belowground buds after disturbance in perennial grasslands. We therefore investigated the separate and interactive effects of severe drought and grazing on the belowground bud bank and aboveground vegetation in the tallgrass prairie of northeast Kansas, USA. Contrary to our expectations, we observed changes in community structure and declines in species richness both above and below ground in response to drought and grazing. We also hypothesized that drought would reduce bud bank density of all taxonomic groups, but found that grass bud and shoot densities remained constant across all drought and grazing treatment combinations. While sedge and forb bud and shoot densities were reduced by drought, only sedge bud density declined to a greater extent when grazed under drought conditions. Live rhizome biomass did not vary by treatment and was highly correlated with bud bank density, suggesting that bud demography is tightly linked to the production and senescence of rhizomes. Despite the effects of drought and grazing on aboveground net primary productivity and community structure, our work suggests that grasses stabilize tallgrass prairie plant communities because their rhizomes and associated buds persist through co-occurring disturbances.