Diane De Steven

VEGETATION OF UPPER COASTAL PLAIN DEPRESSION WETLANDS: ENVIRONMENTAL TEMPLATES AND WETLAND DYNAMICS WITHIN A LANDSCAPE FRAMEWORK

Reference wetlands play an important role in efforts to protect wetlands and assess wetland condition. Because wetland vegetation integrates the influence of many ecological factors, a useful reference system would identify natural vegetation types and include models relating vegetation to important regional geomorphic, hydrologic, and geochemical properties. Across the U.S. Atlantic Coastal Plain, depression wetlands are a major hydrogeomorphic class with diverse characteristics. For 57 functional depression wetlands in the Upper Coastal Plain of South Carolina, we characterized the principal vegetation types and used a landscape framework to assess how local (wetland-level) factors and regional landscape settings potentially influence vegetation composition and dynamics. Wetland sites were stratified across three Upper Coastal Plain landscape settings that differ in soils, surface geology, topography, and land use. We sampled plant composition, measured relevant local variables, and analyzed historical transitions in vegetative cover types. Cluster analysis identified six vegetation types, ranging from open-water ponds and emergent marshes to closed forests. Significant vegetation-environment relationships suggested environmental “templates” for plant community development. Of all local factors examined, wetland hydrologic regime was most strongly correlated with vegetation type, but depression size, soil textural type, and disturbance history were also significant. Because hydrogeologic settings influence wetland features, local factors important to vegetation were partly predictable from landscape setting, and thus wetland types were distributed non-randomly across landscape settings. Analysis of long-term vegetation change indicated relative stability in some wetlands and succession in others. We developed a landscape-contingent model for vegetation dynamics, with hydroperiod and fire as major driving variables. The wetland classification, environmental templates, and dynamics model provide a reference framework to guide conservation priorities and suggest possible outcomes of restoration or management.

Agricultural conservation practices and wetland ecosystem services in the wetland-rich Piedmont-Coastal Plain region

In the eastern U.S. Coastal Plain and Piedmont region, diverse inland wetlands (riverine, depressional, wet flats) have been impacted by or converted to agriculture. Farm Bill conservation practices that restore or enhance wetlands can return their ecological functions and services to the agricultural landscape. We review the extent of regional knowledge regarding the effectiveness of these conservation practices. Riparian buffers and wetland habitat management have been the most commonly applied wetland-related practices across the region. Riparian Forest Buffers (RFB) have been most studied as a practice. Water quality functions including pollutant removal, provision of aquatic habitat, and enhanced instream chemical processing have been documented from either installed RFBs or natural riparian forests; forest buffers also serve wildlife habitat functions that depend in part on buffer width and connectivity. Wetland restoration/creation and habitat management practices have been less studied on regional agricultural lands; however, research on mitigation wetlands suggests that functional hydrology, vegetation, and faunal communities can be restored in depressional wetlands, and the wetland habitat management practices represent techniques adapted from those used successfully on wildlife refuges. Other conservation practices can also support wetland services. Drainage management on converted wetland flats restores some water storage functions, and viable wetlands can persist within grazed flats if livestock access and grazing are managed appropriately. Because wetland hydrogeomorphic type influences functions, ecosystem services from conservation wetlands will depend on the specifics of how practices are implemented. In a region of diverse wetlands, evaluation of ecological benefits could be improved with more information on the wetland types restored, created, and managed.

Effects of dominant species on vegetation change in Carolina bay wetlands following a multi-year drought

Abstract Mulhouse, J. M. (University of Georgia, Savannah River Ecology Laboratory, Drawer E, Aiken, SC 29802), D. De Steven (USDA Forest Service, Southern Research Station, Center for Bottomland Hardwoods Research, P.O. Box 227, Stoneville, MS 38776), R. F. Lide (Northwest Florida Water Management District, 81 Water Management Dr., Havana, FL, 32333), and R. R. Sharitz (University of Georgia, Savannah River Ecology Laboratory, Drawer E, Aiken, SC 29802). Effects of dominant species on vegetation change in Carolina bay wetlands following a multi-year drought. J. Torrey Bot. Soc. 132: 411–420. 2005.—Wetland vegetation is strongly dependent upon climate-influenced hydrologic conditions, and plant composition responds in generally consistent ways to droughts. However, the extent of species composition change during drought may be influenced by the pre-existing structure of wetland vegetation. We characterized the vegetation of ten herbaceous Carolina bay wetlands on the South Carolina Upper Coastal Plain during a period of average rainfall and again near the end of a four-year drought. We hypothesized that, as a group, bays dominated by less robust plant species (characteristic of open-water pond and depression meadow vegetation types) would show greater compositional change than bays dominated by dense, robust-form clonal graminoids (characteristic of grass and sedge marsh vegetation types). Aquatic species decreased during the drought in all wetlands, regardless of vegetation group. Compared to grass/sedge marshes, pond/meadow wetlands acquired more species, particularly non-wetland species, during the drought. Pond/meadow wetlands also had greater increases in the abundances of species that require unflooded conditions to establish. Prior to the drought, all wetlands were ponded almost continuously, but during drought the pond/meadow wetlands had shorter and more variable hydroperiods than the grass/sedge marshes. Thus, vegetation change may be partly confounded with hydrologic conditions that provide greater opportunities for species recruitment in pond/meadow bays. The results suggest that Carolina bay vegetation dynamics may differ as a function of dominant vegetation and climate-driven variation in wetland hydrologic condition.

Effect of climate fluctuations on long-term vegetation dynamics in Carolina Bay wetlands

Carolina bays and similar depression wetlands of the U.S. Southeastern Coastal Plain have hydrologic regimes that are driven primarily by rainfall. Therefore, climate fluctuations such as drought cycles have the potential to shape long-term vegetation dynamics. Models suggest two potential long-term responses to hydrologic fluctuations, either cyclic change maintaining open emergent vegetation, or directional succession toward forest vegetation. In seven Carolina bay wetlands on the Savannah River Site, South Carolina, we assessed hydrologic variation and vegetation response over a 15-year period spanning two drought and reinundation cycles. Changes in pond stage (water depth) were monitored bi-weekly to monthly each year from 1989–2003. Vegetation composition was sampled in three years (1989, 1993, and 2003) and analyzed in relation to changes in hydrologic conditions. Multi-year droughts occurred prior to the 1989 and 2003 sampling years, whereas 1993 coincided with a wet period. Wetland plant species generally maintained dominance after both wet and dry conditions, but the abundances of different plant growth forms and species indicator categories shifted over the 15-year period. Decreased hydroperiods and water depths during droughts led to increased cover of grass, upland, and woody species, particularly at the shallower wetland margins. Conversely, reinundation and longer hydroperiods resulted in expansion of aquatic and emergent species and reduced the cover of flood-intolerant woody and upland species. These semi-permanent Upper Coastal Plain bays generally exhibited cyclic vegetation dynamics in response to climate fluctuation, with wet periods favoring dominance by herbaceous species. Large basin morphology and deep ponding, paired with surrounding upland forest dominated by flood-intolerant pines, were features contributing to persistence of herbaceous vegetation. Drought cycles may promote directional succession to forest in bays that are smaller, shallower, or colonized by flood-tolerant hardwoods.

Ecological outcomes and evaluation of success in passively restored Southeastern depressional wetlands

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.

Old Forests and Endangered Woodpeckers: Old-Growth in the Southern Coastal Plain

ABSTRACT: Southern old-growth forests are small and rare, but critical in their support of biodiversity. While the remnant old-growth forests contain diversity that is significant regionally and globally, they most likely represent only a portion of the variety that old forests once sustained. High within-habitat diversity and rarity in the landscape magnify the conservation value of these systems. Old-growth stands of two particular communities—longleaf pine (Pinus palustris) forests and floodplain (bottomland/swamp) forests—have emblematic links to two notable bird species of concern, the Red-cockaded (Picoides borealis) and Ivory-billed (Campephilus principalis) Woodpeckers. In addition to conservation importance, southern old forests have social and economic values that are in danger of further impoverishment if these systems are lost to future generations. Summarizing the findings from a recenatus and values, identify current threats, and describe potential strategies to promote greater long-term conservation of old forests across the South.

Transplanting native dominant plants to facilitate community development in restored Coastal Plain wetlands

Drained depressional wetlands are typically restored by plugging ditches or breaking drainage tiles to allow recovery of natural ponding regimes, while relying on passive recolonization from seed banks and dispersal to establish emergent vegetation. However, in restored depressions of the southeastern United States Coastal Plain, certain characteristic rhizomatous graminoid species may not recolonize because they are dispersal-limited and uncommon or absent in the seed banks of disturbed sites. We tested whether selectively planting such wetland dominants could facilitate restoration by accelerating vegetative cover development and suppressing non-wetland species. In an operational-scale project in a South Carolina forested landscape, drained depressional wetlands were restored in early 2001 by completely removing woody vegetation and plugging surface ditches. After forest removal, tillers of two rhizomatous wetland grasses (Panicum hemitomon, Leersia hexandra) were transplanted into singlespecies blocks in 12 restored depressions that otherwise were revegetating passively. Presence and cover of all plant species appearing in planted plots and unplanted control plots were recorded annually. We analyzed vegetation composition after two and four years, during a severe drought (2002) and after hydrologic recovery (2004). Most grass plantings established successfully, attaining 15%–85% cover in two years. Planted plots had fewer total species and fewer wetland species compared to control plots, but differences were small. Planted plots achieved greater total vegetative cover during the drought and greater combined cover of wetland species in both years. By 2004, planted grasses appeared to reduce cover of non-wetland species in some cases, but wetter hydrologic conditions contributed more strongly to suppression of non-wetland species. Because these two grasses typically form a dominant cover matrix in herbaceous depressions, our results indicated that planting selected species could supplement passive restoration by promoting a vegetative structure closer to that of natural wetlands.

Diverse characteristics of wetlands restored under the Wetlands Reserve Program in the Southeastern United States

The Wetlands Reserve Program (WRP) restores converted or degraded wetlands on private working lands; however, the nature and outcomes of such efforts are undocumented in the Southeastern U.S. Identification of wetland types is needed to assess the program’s conservation benefits, because ecological functions differ with hydrogeomorphic (HGM) type. We reviewed >100 WRP projects across the Southeast Piedmont–Coastal Plain to characterize their wetland types and to evaluate whether restoration practices favored original or modified functions. The projects encompassed four HGM types and diverse pre-restoration conditions. Nearly half were converted wetlands retired from active agriculture; the remainder were either drained vegetated wetlands or forested bottomlands degraded by timber harvest. Hydrology-repair practices varied by wetland type and prior condition, with differing functional implications. Depressions and flats typically were restored, whereas low-order riparian sites and prior-agriculture floodplains were often modified to enhance water retention. Timber-harvested floodplains were restored by removing barriers to water flow and biotic connectivity. Vegetation restoration was generally passive, but tree planting was frequent on prior-agriculture sites. Field surveys suggested that most projects had positive indicators of wetland hydrology, vegetation, and faunal use. The variety of Southeastern WRP wetlands has implications for ecosystem services at local and landscape scales.

Multiple factors influence the vegetation composition of Southeast U.S. wetlands restored in the Wetlands Reserve Program

Abstract Degradation of wetlands on agricultural lands contributes to the loss of local or regional vegetation diversity. The U.S. Department of Agricultures Wetlands Reserve Program (WRP) funds the restoration of degraded wetlands on private ‘working lands’, but these WRP projects have not been studied in the Southeast United States. Wetland hydrogeomorphic type influences hydrodynamics and thus the vegetation of restored sites, but species composition may also be affected by prior land-condition and restoration methods. We examined the variation in restored wetland vegetation of 61 WRP sites (representing 52 projects) across the Southeast region. Field surveys identified the common plant species at each site, and species composition was analyzed in relation to hydrogeomorphic type and specific restoration methods that were linked to pre-restoration habitat status. At least 380 plant species were recorded across all sites. Site floristic composition generally reflected variation in wetness conditions and vegetation structure. Wetlands restored by ‘non-intensive’ methods overlapped in species composition irrespective of hydrogeomorphic type, as a consequence of successional dynamics related to natural hydrologic variation. More distinctive species composition occurred in wetlands restored by ‘intensive’ methods designed to compensate for intense agricultural land-use before restoration. In the Southeast U.S., WRP wetlands are supporting a variety of plant assemblages influenced by hydrogeomorphic settings, site land-use history, and differing restoration approaches.