Improving Native Plants to Protect and Preserve Louisiana’s Coastal Marshes

Stephen Harrison, Subudhi, Prasanta K., Schneider, Raymond W., Utomo, Herry S.  |  6/2/2005 11:47:02 PM

Stephen A. Harrison, Timothy P. Croughan, Michael D. Materne, Bradley C. Venuto, Gary A. Breitenbeck, Marc A. Cohn, Xiaobing Fang, Alicia Ryan, Raymond W. Schneider, R. Alan Shadow, Prasanta Subudhi and Herry Utomo

The improvement of native plant species for use in coastal protection and restoration activities is the focus of a multi-disciplinary, cooperative effort involving scientists from the LSU AgCenter and the U.S. Department of Agriculture’s Natural Resources Conservation Service (NRCS).

Although biotechnology and classical plant improvement methods are well established in agricultural crop production, their use in environmental remediation is still emerging. Scientists from the NRCS Plant Materials Center at Golden Meadow have collected, tested and released native plant materials with superior performance in coastal environments, including smooth cordgrass and black mangrove. The objective of the project is to develop a seed-based system of propagating smooth Spartina alterniflora, also known as smooth cordgrass or oystergrass, over large areas and to genetically improve the performance of native plant species for use in coastal restoration. This requires genetic improvement of seed production capability while maintaining vigor and disease resistance, and development of a system to produce, store and plant the seeds.

Louisiana’s coastal marshes are highly productive ecosystems. Smooth cordgrass is the predominant salt marsh species along the Gulf Coast, and it provides food and habitat for aquatic species. This plant and its decomposition products provide the foundation of the food chain for such species as small crustaceans, shrimp, crabs, shellfish and minnows. These in turn support larger fish, aquatic birds and other wildlife.

Louisiana loses more than two acres of coastal wetlands every hour, about 30 square miles each year, from natural processes and human activities. Levee systems protect low-lying regions from flooding but deprive the coastal marshes of the sediment deposition necessary for their formation. The marsh naturally subsides as organic matter decomposes and loose sediments compact. Channeling of the marshes to support petroleum and shipping activities has resulted in rapid and frequent mixing of salt and fresh water. Natural plant systems are unable to adapt to sudden changes from fresh to saline water that result from subsidence, saltwater infiltration through channels and other ecosystem disturbances brought about by human activities. As a result, large areas of productive marsh have been lost.

The Coastal Wetlands Planning, Protection and Restoration Act of 1990 (the Breaux Act) and other legislation have provided impetus and substantial funding for reclamation activities. These activities include sediment diversion and rebuilding barrier islands and eroded areas using dredge material and rocks. Revegetation of the eroded and newly created marshland must be an integral part of reclamation activities to preserve a natural ecosystem.

Spartina Ideal for Reclamation

Spartina alterniflora is the predominant marsh grass and tolerates a wide range of salinity from slightly brackish to seawater. It can readily be produced in freshwater ponds. It is an ideal species for coastal reclamation work because of its stress tolerance and rapid growth. A single Spartina alterniflora plant can grow to a clump of several feet in diameter within a year. It thrives in coastal marshes and intertidal regions along the Gulf Coast. It spreads underground and its dense canopy provides a significant buffer against wave energy. It controls erosion, traps suspended sediments and produces significant amounts of organic matter. It grows parallel to the shore in water up to 18 inches deep and in clumps on mud flats.

Smooth cordgrass is widely used for erosion control along shorelines and canal banks and for stabilization of loose soil on mud flats and dredge-fill sites. Its use is limited by the high cost for plant material, up to $6 per plant, and the amount of labor required to plant it. Aerial seeding would permit planting an acre in just a few seconds at a fraction of the cost of manual transplanting.

One of the primary objectives of this research is to develop a seed-based system of establishing vegetation in large reclaimed coastal areas. The need for a seed-based system became particularly apparent with the large brown marsh dieback that occurred in 2000 and affected up to 390,000 acres of salt marsh. An estimated 17,000 acres of densely vegetated marsh were converted to open mud flats in Louisiana.

Spartina Produces Few Seeds

Spartina flowers in the late summer and produces seed each year, but the seed quality and quantity are generally low. Spartina seed must be stored under cool, wet conditions that mimic falling into the marsh in the fall and remaining in a dormant state until spring. Seed does not germinate at the time of shattering, and seed that dries out rapidly loses viability. This major obstacle to commercial seeding must be overcome.

An initial collection of native smooth cordgrass was made in 1998. Approximately 100 seed heads were harvested from each of 126 sites across south Louisiana. Seed varied significantly in weight and germination. Seedlings from 101 accessions were planted at the NRCS Plant Materials Center and under marsh conditions in Lafourche and Cameron parishes to evaluate vegetative vigor, spread, pest resistance, adaptation and seed production. Forty selected accessions were planted in replicated trials at the LSU AgCenter Ben Hur Research Farm.

In the fall of 2000, 40 genetically distinct plants, representing eight of these accessions, were chosen based on performance across two locations. These were transplanted to a pond at Ben Hur and at Grand Terre, a barrier island near Grand Isle, for additional evaluation and use as parents in the breeding program. The five best accessions from an earlier LSU AgCenter Rice Research Station collection, along with surviving plants collected from brown marsh sites in 2000, were added to this gene pool for use in development of genetically broad-based synthetic populations with superior performance.

The original Rice Research Station accessions have been evaluated extensively for vigor, adaptation and seed production. Five of these accessions are being vegetatively increased and one of these will probably be released in 2002 to enhance genetic diversity of available plant material. Vermilion, which was released in 1989, is the only commercially available cultivar and is used extensively in coastal wetland restoration projects.

Other Research Projects

Vermilion fingerprinting. Commercial contracts for coastal revegetation projects sometimes specify Vermilion smooth cordgrass because of its vigor, wide adaptation and proven performance; however, there is no easy way to determine if plants used to fulfill such contracts really are Vermilion. Two studies have been undertaken to address this dilemma. The first study is to develop genetic fingerprinting technology for rapid determination of the genetic identity of plants supplied for reclamation efforts. The second study will compare the performance of vegetative clones of Vermilion to seed-propagated plants.

Smooth cordgrass diseases. Rapid and vigorous stand establishment is essential if large areas are to be revegetated. Numerous pathogens may affect plants at different growth stages, although most can be controlled with seed-applied fungicides. Other diseases of mature plants may affect rate of colonization, biomass accumulation and seed production. These diseases will be assessed and varieties screened for resistance to the most damaging diseases.

Producing seed volume. A seed-based production system requires a method of handling seed in large volume and management practices for optimum seed production. A study was initiated at Galliano in the spring of 2001 to evaluate the effects of fertilizer, insecticide and fungicide application on seed production and quality in a freshwater pond environment. In Spartina, the traditional seed treatment of chilling seeds stimulates the loss of dormancy and maintenance of seed viability. The critical moisture content and rate of drying necessary to maintain viability and break dormancy will be defined. Alternative dormancy-breaking treatments of short duration that are amenable to commercial application will be evaluated as replacements for moist-chilling and seed storage methods.

Other plants with promise. Although smooth cordgrass is the main focus of the coastal plant project, research is ongoing with several other species to identify and improve the ones that work well in the many different niches within the coastal ecosystem. Black mangrove provides nesting sites for pelicans and is an important barrier island species. Native Louisiana accessions of black mangrove collected by the NRCS are being evaluated.

Sea oats have extensive root systems and are excellent dune stabilizers. In Florida, a thriving commercial sea oat industry produces plants from seed for use in dune stabilization. However, the Florida accessions do not grow well in Louisiana, and the native Louisiana sea oat is a poor seed producer. The native sea oat will be hybridized with sea oats from the Atlantic Coast to increase seed production. Cultural practices for increased seed production will be evaluated beginning in 2001. Research on bitter Panicum, marsh-hay cordgrass and other species will be added as the coastal plants project develops.

Plants provide a self-sustaining, environmentally sound and aesthetically pleasing approach to controlling coastal erosion that can persist indefinitely. Commercial enterprises to supply marsh plant material will expand as coastal reclamation activities increase over the next decade. The coastal plants project will play an important role in developing genetically superior varieties and improved technology to protect our valuable coastal ecosystem.

(This article appeared in the summer 2001 issue of Louisiana Agriculture.)

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