Effects of birds and rodents on synthetic tallgrass communities

We used a bird and mammal exclosure design on plowed ground to rest for the effects of granivory and herbivory by small vertebrates on early stages of tallgrass prairie succession. Seed predation by birds and browsing by rodents had major and additive impacts. In high- and low-density plantings, respectively, seed-eating birds reduced plant densities by 20% and 23% and grass biomass by 24% and 34%. Meadow voles did not affect plant numbers but reduced forb biomass by 35% in high- and 57% in low-density plantings. In high- and low-density plots, respectively, birds reduced species richness by 3% and 17% without influencing diversity; selective browsing by voles on two legumes and one coneflower left species number unaffected but reduced diversity by 4% and 25% by accentuating dominance of already-prominent species. Bird effects were more pronounced in high-density plantings, while vole effects were most pronounced in low-density plantings. Results suggest that opportunistic finches and doves that seek out high seed concentrations depress tallgrass plant densities on open ground, while voles, which selectively forage on emerging vegetation, alter community structure, especially when their home ranges include low-density plant assemblages. Both results are likely to be relevant to native prairies after burns or other disturbance, and ro ecological restoration.