In nature, sand dunes accrete (build up) or erode with little or no help from people. As they accrete, there are a number of plants which move in, then recede for the next group of plants as the conditions change. As ecosystems go, sand dunes can transform quickly from sand to something with some biomass over a number of years.
Understanding beach-dune ecosystems
Sand dunes will start with a mild accumulation of sand, with some simple grasses moving in, and eventually will become something more significant with a little organic material in it and some relatively significant biomass. Biomass basically means layers of plants and creatures that are dependent on them. The greater the biomass -- let's say a collection of dune grass, beach rose, and maybe some beach olive -- the more resistant the dunes are to being washed away when the ocean is stimulated by a storm.
Of course people have a different agenda. We want to build close to the water, walk out to the water, play in the dunes, and so on. Since this is a somewhat precarious ecosystem, it is easily disturbed (and usually is) by human activity. In order to protect our real estate investments, we have come up with sand fences, which in their most basic form are wooden slat fences with 50% spacing, usually wired together with galvanized wire. These are effective in stopping the movement of sand and accumulating sand in an area thus building a dune up, as well as restricting human intervention and movement through the dunes. The shortfall of sand fences is they do not hold the dune together -- they have no root systems. Basically, they don't prevent "scarping," which is the natural process where the sand in a dune is released into a beach and eventually out to help create sand bars that will limit the impact of storms on the beach later on. Though scarping is a natural process, it is NOT desirable if you are looking to prevent your beach house from becoming part of a future sand bar (or whatever). In addition to working with sand fences to build up your dunes, you will want to introduce some plants, keeping in mind that as the dune evolves it will need new species introduced if you want to help it along.
Installing sand fencing
Sand fencing is great for building up sand on a dune, or someplace where you want a dune to be. Effectively trapping sediment and mitigating wind damage can occur only when the fence is erected perpendicular to the prevailing wind. Perpendicular is best, however a slight angle won't hurt. Wind fences have been shown effective up to 22.5 degrees from perpendicular (Smolen et al., 1988). You can erect multiple fences to increase sediment trapping. Linear rows of fence, two to four feet high and spaced 20 to 40 feet apart will work well. Make sure to install them well away from the incoming tide to save your fences from going out to sea.
Since the purpose of sand fences is to trap sand that is being carried by the wind so that it accumulates on and around the fence, inevitably the fence will suffer one or both of the following fates: 1) the fence will be buried and will biodegrade into organic material for plants to feed on and/or 2) it will be washed out to sea. Plastic fences will not help the environment in either of these scenarios, since sand fencing is a very temporary measure relative even to human endeavors and plastic is forever. You can find helpful information on fences at the Kalinich Fence website.
Planting perennial grasses as a dune stabilizer
If you already have some dune, you may want to skip the fences or, at the very least, add some vegetation. Perennial grasses are the primary stabilizers of frontal dune systems along the Atlantic and Gulf coasts. The following are some grasses dominant in this corridor:
In the North: American beachgrass
In the South: sea oats
Bitter panicum or "running beachgrass" is also an important grass on frontal dunes in North Carolina.
Seashore elder grows well on frontal dunes and may be transplanted to add diversity to the dune system.
Saltmeadow cordgrass is not a true dune grass, but often traps sand to initiate dune growth.
Saltmeadow cordgrass grows well in low, moist areas such as sand flats and high salt marshes. It is more salt- and flood-tolerant than the dune grasses, and can be used in front of dunes.
Planting a combination of several of these species can enhance the beach-dune system's diversity and long term viability. After establishment, American beachgrass will grow through as much as four feet of sand accumulation during one growing season. However, it tends to die out behind the dune crest after only a few years. This die-out is caused by climatic effects, fungal disease, and insects. Dead patches of beachgrass should be replaced with sea oats, bitter panicum, or seashore elder.
Plant American beachgrass, which is a cool-season grass, from November through March. Plant small areas by hand and space the plants 18 to 24 inches apart at the crest of the dune. Increase the spacing to 2 to 3 feet on either side of the crest.
For more information on beach grasses and plant materials go to N.C. State University's Department of Soil Science website and Barwon Bluff Marine Sanctuary's "Plants of the Sand Dunes."