Vole-driven succession in experimental wet-prairie restorations

A challenge of experimental restoration is to determine the reasons why restored communities develop as they do. Divergent successions in plantings of 16 tallgrass prairie species sown in equal densities in Wisconsin (USA) revealed strong effects of vole (Microtus pennsylvanicus) herbivory on vegetation initially protected for an establishment period of over 24 months, by which time all principal species were flowering and fruiting. Half of the plots were then subjected to 48 months of vole access. An otherwise common legume (Desmodium canadense) and grass (Elyinus virginicus) were all but eliminated in 48 months of exposure: combined cover under protection was 43 +/- 6%, but plummeted to <1% cover when voles had access. Dicots not eaten by voles (Pycnanthemum virginianum, Rudbeckia subtomentosa) averaged 40 +/- 7% cover where voles were excluded, but 68 +/- 8% after 48 months of vole access. Repeated-measures analyses of variance revealed that net decreases (D. canadense, E. virginicus) or increases (P. virginianum, R. subtomentosa) in cover masked nonlinear effects reflecting vole-driven transient dynamics during divergent successional processes. Diversities diverged for three years after vole access; a dramatic convergence of diversities in the fourth year leaves grossly similar communities with similar numbers of species and similar levels of equity, but distinctly different species compositions. Vole-mediated effects on vegetation resemble those likely to occur in native prairies, without the catastrophic changes in cover and standing crop caused by rodents that occurred in some previous efforts of this research program.