Question: Do regional species pools, landscape isolation or on-site constraints cause plants from different guilds to vary in their ability to colonize restored wetlands?
Location: Iowa, Minnesota, and South Dakota, USA.
Methods: Floristic surveys of 41 restored wetlands were made three and 12 years after reflooding to determine changes in local species pools for eight plant guilds. The effect of landscape isolation on colonization efficiency was evaluated for each guild by plotting local species pools against distance to nearby natural wetlands, and the relative importance of dispersal vs. on-site constraints in limiting colonization was explored by comparing the local species pools of restored and natural wetlands within the region.
Results: Of the 517 wetland plant taxa occurring in the region, 50% have established within 12 years. The proportion of the regional species pool represented in local species pools differed among guilds, with sedge-meadow perennials, emergent perennials and floating/submersed aquatics least represented (33-36%) and annual guilds most represented (74-94%). Colonization-to-extinction ratios suggest that floating/submersed aquatics have already reached a species equilibrium while sedge-meadow and emergent perennials are still accumulating species. Increasing distance to nearest wetlands decreased the proportion of the regional species pool present in local pools for all guilds except native annuals and woody plants. The maximum proportion predicted, assuming no distance constraint, was comparable to the lowest-diversity natural wetlands for most perennial guilds, and also lower than what was achieved in a planted, weeded restoration.
Conclusions: A biotic constraints seem to limit the colonization of floating/submersed aquatics into natural or restored wetlands, whereas all other guilds are potentially constrained by dispersal or biotic factors (i.e. competition from invasive species). Using species pools to evaluate restoration progress revealed that immigration potential varies considerably among guilds, that local species richness does not necessarily correspond to immigration limitations, and that some guilds (e.g. sedge-meadow perennials) will likely benefit more than others from being planted at restoration sites.