A four-year community bud bank record reveals belowground disturbance legacies in tallgrass prairie

Background/Question/Methods

Much research has been devoted to understanding immediate, aboveground responses to disturbance in plant communities. For example, in tallgrass prairie we have devoted plenty of time to understanding responses to three key processes: fire, grazing, and drought.  The short-term effects of grazing on tallgrass prairie are well known, and include decreased C₄grass abundance, increased forb abundance, increased species and diversity. Drought causes an immediate decline in productivity, with plant community structure and composition changing more slowly. Few studies, however, have determined if these effects persist in the years after disturbance is removed. The research we present here explores the legacy effects of grazing and drought on plant productivity, demography, and diversity. To study legacy effects of grazing, we compared recovery areas with grazed and ungrazed areas for 4 years after grazers were removed from the recovery areas. To study legacy effects of drought, we experimentally reduced precipitation 75% from ambient levels for 2 years, and compared the response to ambient control plots and irrigated plots during the 2 years of drought and 2 years of recovery. In both grazing and drought studies, we measured belowground bud bank density and aboveground stem density, cover, and productivity.

Results/Conclusions

We found that after both drought and grazing ceased, the aboveground plant community recovered quickly, becoming more like undisturbed sites, while belowground bud bank densities responded more slowly.  Following removal of grazing animals, the aboveground plant productivity, stem density, and diversity quickly become more like reference ungrazed areas than grazed areas. Belowground, however, the plant community represented by the bud bank remains more like grazed areas, both in terms of composition and density.  During and following a 2-year severe experimental drought, we found no differences in bud bank density and stem density in drought plots compared to un-manipulated controls. The bud bank density and stem density of paired irrigation plots, however, was greater than both drought and control plots during two years of recovery.  Our work demonstrates that lagged effects of drought and grazing are present in tallgrass prairie plant communities, persisting both above- and belowground.