• Fort Matanzas

    Fort Matanzas

    National Monument Florida

Grasses

Sea oats crest a dune which protects inland areas from the open ocean seen in the distance.

Sea oats crest the dunes which act as a bulwark against the energy of the open ocean

NPS Photo

One of the most common plants growing within the sand dune system at Fort Matanzas is sea oats (Uniola paniculata). It can be argued that sea oats is one of the most important species comprising the dune ecosystem, particularly the foredune. It is a hardy and salt tolerant plant that can survive in the harsh seashore environment. (It can even survive being inundated by sea water for short periods.) It and other pioneer plants help trap wind-blown sand, which is the first step in dune formation. Once the dune becomes established, sea oat's extensive root system acts to anchor the dune in place. Besides its vital role in contributing to sand dune stabilization, the seeds of sea oats are a crucial food source for one of the rarest animals at Fort Matanzas, the Anastasia Island beach mouse. In addition to beach mice, red-winged blackbirds, sparrows, and marsh rabbits also readily consume sea oats seeds.

Let's look at sea oats in more detail. It is a plant belonging to the grass family (Poaceae). It is a semitropical perennial, meaning that it produces seeds from year to year, and inhabits the zone between the temperate climate to the north, and the tropical climate to the south. Its leaves are thin (about a quarter inch in width) and vary from eight to twenty-four inches in length, coming to a point at their tips. The plant itself is erect and can grow up to six feet tall.

One of the most conspicuous features of sea oats is its large seed heads. They look a little bit like flattened oats, and turn a straw color in late summer. The plant reproduces itself by these seeds (their flat shape helps them disperse in the wind), but its primary method of reproduction is through the action of rhizomes (underground stems), which the parent plant shoots out in a radial pattern. Roots emerge at nodes along the rhizome where new clonal plants emerge into the daylight. This growth pattern contributes importantly to sea oats' ability to stabilize shifting sand dunes. In fact, being buried by sand actually stimulates growth in this species. The hot climate of Florida allows for a long growing season for sea oats, which lasts from spring through the fall.

One of the most interesting aspects of sea oats biology takes place beneath the surface. The plant benefits from existing in a symbiotic relationship with mycorrhizal fungi. This fungus uses the roots of sea oats as a substrate upon which to live. By doing so they in effect increase the surface area of the roots, by which the plant absorbs nutrients from the soil. This contributes to overall plant community health.

Sea oats is considered such an important plant in terms of its integral role in sand dune formation and stabilization, that it has been given special protected status by the state of Florida. (It is illegal to destroy or remove sea oats without a permit.) To understand why this is so, think of the protective nature of sand dunes. They drastically reduce the impact of the wind (and the associated salt spray) coming in off the ocean. This allows other plants to grow in the leeward side of the foredunes, protected from the direct onslaught of the ocean. Where a greater variety of plants survive, organic matter (humus) is eventually laid down as leaves fall and plants die, forming a moist soil into which even more plants can grow (particularly woody species like trees). Eventually over hundreds of years a mature maritime forest forms where once was open seashore. Forests grow vertically as well as horizontally, supporting a greater variety of ecological niches that are filled with a multitude of animal species, leading to overall increased biodiversity. Without the initial formation of sand dunes, catalyzed by the presence of plants like sea oats, a mature forest would never have the chance to form.

Of course, sand dunes also perform a much more utilitarian purpose besides ensuring biodiversity. They are nature's first line of defense against hurricanes and other large storms. By breaking up the wind and surf energy of a storm, and acting as a bulwark against tidal surge, sand dunes spare inland areas from the full fury of a storm's pounding. It follows that whenever sand dunes are compromised by putting roads and trails across them, or by constructing buildings upon them, they are no longer able to mitigate a storm's negative effects, thus increasing the likelihood that inshore areas will be subjected to greater damage. All this may be something to keep in mind the next time you see sea oats waving nonchalantly in the ocean breeze as you walk along the seashore!

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