Construction of Texas coastal foredunes with sea oats (Uniola paniculata) and bitter panicum (Panicum amarum)

Abstract

Studies were conducted on Padre Island, Texas since 1968 to provide specifications for how to use vegetation to reconstruct destroyed portions of foredunes of Gulf Coast barrier islands. The area has a subtropical, semi-arid climate, moderated by maritime tropical air from the Gulf of Mexico. Annual precipitation averages 670 mm for the island. We established experimental foredunes in broad overwash areas, 1.5 m M.S.L. where foredunes were eroded by hurricanes or destroyed by blowouts and across hurricane overwash channels of lower elevation behind the berm and more susceptible to surges. Most successful establishment of a vegetated dune was by transplanting directly onto the level backbeach to reestablish the original duneline about 125 meters inland. Sea oats and bitter panicum proved best of all species tested. Bitter panicum was the more desirable because of higher transplant survival, a longer planting season, and ease of harvest. Transplant survival was influenced more by soil salinity, soil moisture, and plant vigor, than by planting season as successful plantings occurred during all seasons. December through February plantings were best for sea oats, but survival of bitter panicum transplants different little from November through May. Both species are capable of growth year round during periods of favorable climatic conditions, although little growth occurs from mid-December to mid-February. Transplants placed 0.6 m apart with total planting width of 15 m produced foredunes nearly 6 m high in 6 years. Such plantings trapped sand at the rate of 12.5 m³/m of beach. In hurricane overwash channels, we used 0.6 m high sand fence placed 3 m apart to produce a flat topped dune free of salt for a planting surface. Without this site preparation, no transplants survived due to high soil salinity. Dune width was effectively widened by planting a strip 15 m wide immediately beachward of a previously established 4-year old dune.