Ecological Outcomes and Evaluation of Success in Passively Restored Southeastern Depressional Wetlands

Abstract

Depressional wetlands may be restored passively by disrupting prior drainage to recover original hydrology and relying on natural revegetation. Restored hydrology selects for wetland vegetation; however, depression geomorphology constrains the achievable hydroperiod, and plant communities are influenced by hydroperiod and available species pools. Such constraints can complicate assessments of restoration success. Sixteen drained depressions in South Carolina, USA, were restored experimentally by forest clearing and ditch plugging for potential crediting to a mitigation bank. Depressions were assigned to alternate revegetation methods representing desired targets of herbaceous and wet-forest communities. After five years, restoration progress and revegetation methods were evaluated. Restored hydroperiods differed among wetlands, but all sites developed diverse vegetation of native wetland species. Vegetation traits were influenced by hydroperiod and the effects of early drought, rather than by revegetation method. For mitigation banking, individual wetlands were assessed for improvement from pre-restoration condition and similarity to assigned reference type. Most wetlands met goals to increase hydroperiod, herb-species dominance, and wetland-plant composition. Fewer wetlands achieved equivalence to reference types because some vegetation targets were incompatible with depression hydroperiods and improbable without intensive management. The results illustrated a paradox in judging success when vegetation goals may be unsuited to system constraints.

Response of Aquatic Invertebrates to Ecological Rehabilitation of Southeastern USA Depressional Wetlands

“…Among the macroinvertebrates, baetid mayflies exhibited the strongest response to rehabilitation. As algal feeders the nymphs may have benefitted from the reduction in shade, increased nutrients from decaying tree-slash, and a proliferation of herbaceous plants (De Steven et al 2010) associated with rehabilitation. In 2006, Taylor and Batzer (2010 used stable isotopes to assess diets of non-predaceous chironomid midge larvae in one rehabilitated (#5204) and one control (#118) wetland, and found that larvae in the rehabilitated site relied almost solely on algae for food, while larvae in the control site relied on an assortment of detrital and algal foods.…”

“…1, Table 1). Vegetation in most of the wetlands was dominated by facultative wetland trees (e.g., sweetgum Liquidambar styraciflua, loblolly pine Pinus taeda, longleaf pine P. palustris, and water oak Quercus nigra), although wetlands #5011 and #5204 were dominated by upland hardwoods (Barton and Singer 2001;De Steven et al 2010). Only wetland #5 contained marsh with obligate wetland herbaceous species.…”

“…Finally, the rehabilitation involved both a change in hydroperiod and a change in vegetation. Logging converted the post-rehabilitation sites from forested to herbaceous wetlands (see De Steven et al 2010), and this kind of vegetative change can affect invertebrates even if hydrology remains the same (e.g., Batzer et al 2005). Macroinvertebrates (insects, malacostracan crustaceans, mollusks, annelids) were sampled using a D-frame sweep net (30 cm width, 1 mm mesh).…”

“…Both physical (hydrology, soils; Barton et al 2008) and vegetative (De Steven et al 2010) measures indicated a considerable level of success for this effort. This paper examines the response of aquatic invertebrates, and contrasts those findings with the results from hydrology, soil, and plant monitoring.…”

“…As such, restoration or rehabilitation of degraded wetlands is premised on the idea of first restoring natural hydrology, with the assumption that appropriate biota will then reestablish (Barton et al 2008;Galatowitsch and Zedler 2014). For restoration projects, vegetation response is the biotic variable most often measured (Aronson and Galatowitsch 2008;De Steven et al 2010). While plants are crucially important to wetland ecology, restoration efforts are meant to develop suitable conditions for the full suite of organisms found in wetland habitats (microbes, invertebrates, amphibians, birds).…”