Large mammal grazing and fire are considered important processes that structure tallgrass prairie plant communities. After a fire, large bison or cattle grazing is typically intense as these animals selectively feed on higher nutritional grasses that regrow after a burn. This selective grazing has important consequences for plant community structure. Over time, as nutritional quality declines, bison or cattle will reduce grazing intensity, which allows grasses to grow vigorously and eventually create conditions again conducive to fire. While herbivorous arthropods are important consumers in terrestrial systems, sometimes having herbivory rates comparable to large mammals, their interaction with large mammal grazing is poorly studied. We performed a 2 X 2 factorial experiment manipulating bison grazing and herbivorous arthropod abundance in a tallgrass prairie and monitored the plant community for 15 months following a prescribed burn.
Results/Conclusions
Total plant biomass was unchanged by the end of the experiment, but individual biomass of forbs and grasses was altered by the treatment interactions. Forb biomass in the bison-grazed/arthropod-reduced plots was two to three times higher than other treatment combinations, while grass biomass was higher where arthropods were unmanipulated. Plant species richness was only affected by bison grazing and only for the first season. Our results suggest that bison grazing and arthropod herbivory work synergistically; bison reduce grass biomass, allowing forbs to increase, while arthropods reduce forb biomass, allowing grasses to increase. We argue arthropod herbivory is an additional important process structuring tallgrass prairie plant communities and should be investigated in other grassland systems. Arthropod abundance and diversity is likely an important factor in management strategies for the conservation of tallgrass prairies, one of the most endangered bioregions on Earth.