Contrasting Approaches to the Restoration of Diverse Vegetation in Herbaceous Wetlands

Abstract

Undisturbed fens, bogs, and sedge meadows have high plant species diversity (Verhoeven and Bobbink 2001;Amon et al. 2002).High diversity is associated with a combination of features - a dependable water source, water with low nutrient concentrations, low nutrient influxes (which prevent any one species from developing high biomass), and a lack of dominance (allowing many oligotrophic species to co-exist). Fens and sedge meadows remain low in nutrients due to ample discharges of high-quality groundwater; the more speciesrich fens are continuously leached by groundwater, while sedge meadows show a seasonal pattern (wet in spring, followed by a late-summer drawdown). Bogs, in contrast, are supplied primarily by rainwater, which is typically low in nutrients. Diverse natural plant communities can shift to species-poor vegetation when either the water supply or the nutrient regimes change in response to human activities within the watershed (Day et al. 1988; Bedford and Godwin 2003) or when invasive species establish and subsequently outcompete native species (Galatowitsch et al. 1999; Kercher et al. 2004). Nutrient addition and altered hydroperiods can act alone or in combination to reduce wetland plant diversity (Wilcox and Meeker 1991;Verhoeven et al. 1993; Kercher and Zedler 2004).While we know that shifts in hydroperiod toward more flooding or less frequent inundation can shift diversity (Mack et al. 2000), such effects are less well known than the effects of nutrient addition. One reason is that changes in hydroperiod are difficult to separate from other impacts (such as nutrient/sediment influxes); another is that nutrient addition experiments are easier to conduct.