Vole‐driven Succession in Experimental Wet‐prairie Restorations

Abstract

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 (Elymus 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.

Reversal of fortune: plant suppression and recovery after vole herbivory

“…The experiment was established on seasonally Xooded ground in 1995 (details in Howe and Lane 2004). A total of eighteen 4 £ 4-m plots were delineated in a 3 £ 6 east-west grid, with each plot separated from others by a 3-m lane planted with Kentucky bluegrass (Poa pratensis L., Poaceae).…”

“…Voles, for instance, may alter forest succession by eliminating seedlings of some tree species more than others (Ostfeld et al 1997;Manson et al 2001), may change competitive interactions between herbaceous species (e.g., Batzli and Pitelka 1970;Olofsson et al 2002Olofsson et al , 2004Olofsson et al , 2005Hambäck et al 2004), and may alter genetic composition of plant populations (Prittinen et al 2006). Adaptation of techniques used in experimental restoration (Jordan et al 1987) is enlightening because herbaceous grasses and forbs that rarely if ever achieve dominance in nature do so in plantings when protected from voles, sometimes reaching 80% cover in individual plots (Howe and Lane 2004). The implication is that top-down eVects of rodent herbivory collectively shape the species composition of herbaceous plant assemblages (Howe and Brown 1999;Howe et al 2006;Olofsson et al 2004Olofsson et al , 2005del-Val and Crawley 2005).…”

“…Earlier studies found that the response of an experimental wet-mesic plant assemblage to vole herbivory depended on the responses of three key species to vole herbivory (Howe and Lane 2004). These included the direct reduction of rye (Elymus virginicus) and tick-trefoil (Desmodium canadense) from herbivory.…”

Ecosystem structure in disturbed and restored subtropical seagrass meadows

“…Herbivores are capable of altering ecosystem structure and function (Milchunas et al 1988;Parker et al 2006) through interacting effects of stress from grazing and release from competitive exclusion (Paine 1971;Grime 1973;Connell 1978). In terrestrial grasslands, the success of restoration and recovery trajectories in restoration projects that target rehabilitation of plant communities may be influenced by selective herbivory (Howe & Lane 2004;Fraser & Madson 2008).…”

“…In these projects, an early successional, faster-growing seagrass species (e.g., H. wrightii and/or S. filiforme in the subtropical western Atlantic region) is transplanted under the assumption that they will colonize more quickly than slower-growing climax species (e.g., T. testudinum), which in time, will reestablish dominance in the restoration area. Experimental evidence exists that that transplanted, early-successional seagrasses may be preferentially consumed through selective herbivory (Howe & Lane 2004;Fraser & Madson 2008;Prado et al 2010). However, despite the literature record as well as cautionary notes of the potential impact of herbivory to planting unit survival (Fonseca et al 1998), the impacts of herbivores on transplanting success in seagrass meadows remains largely unstudied.…”