The Beach Dune community is where you can see special plant relationships. The stronger plants that are able to withstand the alkaline soil, wide temperature range, salt spray, and strong winds inhabit the front of the dune. The most common plant found here are the sea oats. They are able to survive both partial burials by sand and exposure of their root system when sand is blown away. Sea oats are the "glue- that holds the sandy island in place. They help form and stabilize dunes, which block the sea salt spray which allow for less salt tolerant plants to grow in habitats behind the fore dune. .
The Interdunal Community has an assortment of species depending upon elevation and soil moisture. In the higher areas, the vegetation is composed of grasses and broad-leaved plants. In the lower, areas where the water table is close to the surface, there is more of a variety of plants. These moist interdunal areas are occupied by the Juncus Scirpoides, with panic grass found in the wetter areas. .
The next community on the Gulf Islands National Seashore Barrier Islands is the Upland Woody Community. Here on this wider part of the Islands, you will find some interior dunes and the dune ridges. This area is far away enough from the wind and salt spray to offer adequate protection for the vegetation. These higher and more stable inland dune ridges are occupied by vegetation. The dune ridges are occupied mostly by scrub live oak rosemary and turtle grass. .
All of the barrier islands have saltwater marsh areas. These marshes are usually divided into three types: high marsh, brackish marsh, and tidal marsh. The high marsh occurs on level ground at about one meter above sea level. Dense mats of salt-marsh grass keep the soil moist constantly by shading it and lowering the rate of evaporation. Plants in this area are less salt-resistant than those found in the tidal marsh.
The lowest marsh zone, the tidal marsh, is flooded by the tides two times a day, and it is the most productive of the marsh zones.
