Effect of Sea Oats (Uniola paniculata) Plant Size on Survival and Performance at Beaches with Low Dune Profiles

In the United States, northern Gulf of Mexico sand dunes are important for reducing the effects of tropical storms and hurricanes on coastal communities and infrastructure (Claudino-Sales et al. 2008). Dunes accumulate more quickly when vegetation is present because vegetation traps windblown sediments (Snyder and Boss 2002, Claudino-Sales et al. 2008, Houser et al. 2008). Most dune restoration projects along the northern Gulf of Mexico coast utilize sea oats (Uniola paniculata), a perennial dune grass native to the southern Atlantic and northern Gulf of Mexico coasts in the United States (Wagner 1964, Judd et al. 1977). The primary habitat of sea oats is coastal dunes that are subject to high winds, salt spray, tropical storms and hurricanes, sand burial, low soil nutrients, xeric conditions, and extremely high soil temperatures (Lonard et al. 2011).

The size of sea oats planted for beach restoration projects along northern Gulf of Mexico beaches varies widely. In Louisiana, most sea oats are large, established container plants that are vegetatively reproduced for at least 1 year. Every plant is genetically identical, which eliminates genetic diversity necessary for plants to adapt to environmental changes (Huenneke 1991, Ledig 1996). In Mississippi and Florida, most sea oats plants used for beach restoration are produced from seeds and can vary significantly in plant age and size. This preserves genetic diversity; however, most seeds are harvested from natural beach environments, a practice that disrupts natural ecosystems.

Investigations to determine whether large, vegetative sea oats plants survive and perform better than seedlings have not been documented to our knowledge. This is critical information needed to plan and implement successful beach restoration projects. The objective of this study was to determine if survival and performance differed for large vegetative sea oats plants and small sea oats seedlings at beach environments with low dune profiles.

Sea oats seeds collected from eight states (TX, LA, MS, AL, FL, SC, NC, VA) were germinated, transplanted to natural beaches, and evaluated for plant performance at beaches with low dune profiles (Bertrand-Garcia et al. 2012). In 2005, rhizomes were harvested from plants selected for superior performance in low dune profile beaches (Bertrand-Garcia er al. 2012), planted into 1-gallon containers and maintained in controlled greenhouses. We divided rhizomes of greenhouse propagated material, replanted them into 1-gallon containers, and allowed plants to grow in controlled greenhouses for one year to provide vegetative plants for the study; each plant had at least five stems. In 2009 we harvested sea oats seeds from beach field trials described above. We germinated seeds in controlled greenhouses. Large seedlings were eight months old and more than 30 cm tall. Small seedlings were three months old and 10 to 15 cm tall.

We established a preliminary study in May 2008 at Biloxi, MS, to evaluate sea oats seedling performance; 384 vegetative plants, 25 large seedlings, and 25 small seedlings were included. Larger trials established in March 2009 and June 2010 at Long Beach, MS, included 365 vegetative plants, 664 small seedlings, and 64 large seedlings and 140 vegetative plants, 720 large seedlings, and 113 small seedlings, respectively.

In 2008, plant survival and vigor were measured for each plant in August, September, and October (3, 4, and 5 months after transplant). We considered plants with any green color as alive while plants without any green color were considered dead. Plant vigor was measured with a 0-10 scale: 0 was a dead plant and 10 was a plant with numerous dark green leaves and stems, densely distributed stems, and aggressive vegetative spread. Heavy machinery unintentionally destroyed seedlings after month 5 evaluations. In 2009, plant survival at a second site was measured for each plant in May and June (2 and 3 months after transplant) at Long Beach. Heavy equipment also destroyed these seedlings prior to the 3 month assessments. In 2010, another field site was established at Long Beach; sea oats seedling locations were communicated to equipment operators to avoid plant destruction. Plant survival was measured for each plant in August, September, October...