Relation between Plant Community Structure and Function and the Effectiveness of Wetland Restoration Efforts

Science Center Objects

High rates of wetland loss continue to occur along the northern Gulf of Mexico coast, and this remains an issue of concern to resource managers.

A freshwater pond at Lacassine National Wildlife Refuge

A freshwater pond at Lacassine National Wildlife Refuge, Lake Arthur, Louisiana. The plant with floating leaves is American waterlily (Nymphaea odorata).

The Science Issue and Relevance: High rates of wetland loss continue to occur along the northern Gulf of Mexico coast, and this remains an issue of concern to resource managers. Although suitable hydrology and soils are critical components of wetland restoration projects, the ability of plant communities to establish and thrive in restored wetlands will often determine if a project's goals are met. In regions characterized by high soil subsidence, such as coastal Louisiana, plants growing at restoration sites must produce enough organic matter to supplement outside sources of mineral material so that sediment accretion exceeds subsidence, resulting in soil surface elevations that support continued plant growth. Growth differences between plant species (interspecific variation) and within a species (intraspecific, or clonal, variation) in response to environmental factors and other stressors must be considered to ensure the resiliency of restored wetlands. Plant communities that include multiple species or clones within a species have the flexibility to adapt under stress and persist over time, even if a few species or clones are eliminated. By identifying specific growth characteristics and stress tolerances of wetland plants, these studies identify species and individual clones that will grow well under a range of expected environmental conditions. This research provides information to assist resource managers in designing restoration projects with a high likelihood of success, and resulting products address important information needs identified by DOI partner agencies (i.e., U.S. Fish and Wildlife Service, National Park Service).

Estimating vegetation cover in a brackish marsh

Estimating vegetation cover in a brackish marsh at Ten Thousand Islands National Wildlife Refuge, Naples, Florida.

Methodologies for Addressing the Issue: Greenhouse and field experiments centered on emergent and woody plants of fresh and saline wetlands are designed to develop an understanding of how biotic and abiotic factors affect plant community structure, function and composition; to determine how wetland plants respond to human-induced and physical and chemical stressors and disturbances; and to describe mechanisms responsible for spatial and temporal variation in plant communities. Field study components include the use of permanent transects for recording vegetation changes, analyses of soil physical and chemical characteristics, and the installation of surface elevation tables and marker horizons to describe soil surface elevation and vertical accretion. Greenhouse experiments employ a mesocosm approach to investigate plant response to environmental stressors, including elevated atmospheric carbon dioxide concentration, increased salinity, drought, and flooding.

Future Steps: Baseline data collected at an area affected by a large hydrologic restoration project in south Florida (Picayune Strand Restoration Project) will be used to identify restoration impacts to marsh and mangrove habitats over time. Future studies will examine the effects of additional physical and chemical stressors on the interactions between wetland plant species and the effects on vegetation regime shifts.