Assateague Island National Seashore

Assateague Island National Seashore

Plants

Trees and Shrubs

On barrier islands such as Assateague that are subjected to strong, salt-laden winds, tree and shrub growth is restricted both in size and location. Sheltered areas behind dunes allow tree and shrub communities to grow, but where the island is narrow or lacks protective dunes few or no species may exist. Shrub communities on Assateague establish themselves on or behind dunes, in protected depressions, and along the edges of marshes, with characteristic species growing in each location depending on the levels of salinity and moisture present. One of the most distinctive shrubs of Assateague is beach heath (Hudsonia tomentosa), a dense, low shrub common to dunes and sandy areas along the eastern seaboard. It sometimes acts as a pioneer plant, providing cover that allows other species to become established. Beach heath blooms in May and June, producing numerous small, yellow flowers.

Shrub communities on Assateague establish themselves on or behind dunes, in protected depressions, and along the edges of marshes, with characteristic species growing in each location depending on the levels of salinity and moisture present. One of the most distinctive shrubs of Assateague is beach heath (Hudsonia tomentosa), a dense, low shrub common to dunes and sandy areas along the eastern seaboard. It sometimes acts as a pioneer plant, providing cover that allows other species to become established. Beach heath blooms in May and June, producing numerous small, yellow flowers.

Taller shrub communities behind dunes are limited in height by salt winds blowing above the plants, which exert a natural pruning force. Wax-myrtle (Myrica cerifera), an evergreen whose berries are eaten by tree swallows and myrtle warblers, is the most common shrub in these protected areas. Marsh elder (Iva frutescens), which is capable of tolerating brackish or saltwater areas, dominates the shrub thickets surrounding salt marshes on the bay side of the island and marks the transition between upland and marsh.

In central portions of the island where shelter from overwash and salt winds allow, tree communities occur. The majority of large trees in these forests are evergreen, with loblolly pine (Pinus taeda) being the dominant. Interspersed among the pines are deciduous species such as red maple (Acer rubrum), sweetgum (Liquidambar styraciflua), persimmon (Diospyros virginiana), sassafras (Sassafras albidum), and several species of oak (Quercus sp.). Other evergreen species present in the forests include American holly (Ilex opaca) and red cedar (Juniperus virginiana).

Assateague's Plant Life

From sandy beaches along the island's seaward side to salt marshes on the western bay, Assateague hosts a wide variety of vegetative communities. A diverse array of environmental conditions - elevation, the availability of fresh water, distance from the ocean, the movement of sand, storm-driven winds and seas - all work to shape these communities, as each species has developed adaptations to the unique challenges of the zone in which it lives.

Plants living on the beach and dunes must withstand some of the harshest conditions. Continuous exposure to strong, salt-laden winds, constantly shifting sands, low substrate moisture, and intense summer heat all contribute to a landscape that is less than 1% vegetated. Plants like sea rocket (Cakile edentula) have fleshy, thick-skinned leaves to store water and withstand the salty environment of the beach and lower dunes. Higher up the dunes, American beachgrass (Ammophila breviligulata) adapts to shifting sands by growing additional stems when buried, thus helping to bind the substrate and reduce erosion.

In the sheltered zone beyond the dunes where fresh water is more plentiful, vegetative cover jumps to 80% and is predominantly characterized by less salt-tolerant shrubs and thickets. Here, taller plants undergo a natural pruning process, as salt winds blowing over the dunes limit their height. Common species in these areas include wax myrtle (Myrica cerifera) and northern bayberry (Myrica pensylvanica), which provide food and cover for songbirds, small rodents, and rabbits. Other species commonly found among the shrub thickets include blackberry (Rubus argutus) and poison ivy (Toxicodendron radicans).

Where the island is wide enough to allow sufficient protection from the ocean's salt spray and overwash, trees are able to establish a foothold. The forests of Assateague are predominantly pine woodlands, with loblolly pine (Pinus taeda) being the most prevalent tree species. Scrub pine (Pinus virginiana), greenbrier (Smilax rotundifolia), and muscadine grape (Vitis rotunifolia) are also common in the forest understory.

On the mainland side of the island adjacent to the bay, one can find large areas of salt marsh dominated by salt marsh cordgrass (Spartina alterniflora), a plant that has adapted to periodic flooding by seawater by releasing salt through its leaves. Within the waters of the bay itself, beds of eel grass (Zostera marina)and other submerged aquatic vegetation provide shelter and spawning areas for aquatic animals, while microscopic phytoplankton produces vast amounts of oxygen.

The plant life of Assateague and its surrounding waters mirrors the rich diversity of its habitats, playing a variety of vital roles in the island ecosystem.

Grasses

The more than two dozen species of grasses found on Assateague are vital members of the island's plant communities, acting as sediment stabilizers in both dunes and marshes. Some species are conspicuous, such as sugarcane plumegrass (Erianthus giganteus), which can grow in moist fields to a height of 12 feet. The invasive common reed (Phragmites australis), which can also reach heights of 12 feet, is an easily recognizable inhabitant of fresh water and brackish habitats, where it can out-compete many other native species. Sandburs (Cenchrus tribuloides) disperse seeds by sticking onto animal fur or clothing, and occasionally attack campers' inflatable sleeping pads. Other, less obtrusive grasses include ticklegrasses (Agrostis sp.) - short, tufted grasses which live in woods, fields, bogs, and marshes.

One of the most important grasses on the island is American beachgrass (Ammophila breviligulata), which stabilizes sand dunes and reduces erosion from wind. It continues to grow as sands blow over its stems, sometimes creating up to 40 feet of buried plant above the roots. Because of this trait, it is often planted during beach restoration projects.

Specific habitats on the island where grasses are the dominant plants include: brackish tidal marshes characterized by cattail (Typha angustifolia); marshes dominated by common reed or needlerush (Juncus roemerianus); saltwater cordgrass (Spartina alterniflora) marshes; interdunal sand bogs characterized by pathrush (Juncus dichotomus) and sundew (Drosera intermedia); and other dune, interdune, and bayside plant communities.

Wildflowers

Wildflowers play an important role in the coastal ecosystem of Assateague Island. They serve as food sources for many animals, and their roots aid in the stabilization of sand, securing substrates that might otherwise be eroded by wind. Wildflowers flourish in every habitat on Assateague. Because of continuously changing habitat conditions, plants that can rapidly adjust tend to survive well on the island.

Beach habitats tend to be sparsely vegetated, with a scattering of the few species that are specialized for survival on exposed sands. Beach-dwelling wildflowers tend to grow low to the ground and have tough, fleshy leaves to avoid water loss and withstand salt and sand blown by strong winds. One such species is the federally threatened seabeach amaranth (Amaranthus pumilus), which grows in mats of over 1 foot in diameter on the beaches of Atlantic coast barrier islands. Assateague Island is the only place in Maryland where seabeach amaranth is found, and an active monitoring and management program for the species is currently underway at the park.

Other rare plants, including two species of orchids, can be found in Assateague's damp forests and wetlands. The crested fringed orchid (Platanthera cristata) lives in damp pine forests and has bright orange flowers that appear in late summer. Rose pogonia (Pogonia ophioglossoides) plants display a single pink flower in late spring and can be found in a variety of moist areas, including sphagnum bogs, swamps, meadows, and forests.

Many of Assateague's wildflowers species flourish in disturbed areas such as roadsides. In summer, hundreds of rose mallow (Hibiscus moscheutos) line the entrance road with large white blooms. These are joined by collections of yellow, white, purple, or pink flowers produced by various members of the aster family (Asteraceae).

Assateague's wildflowers are as varied as the changing conditions of the island. They constitute important components of the island's natural systems, while also providing beauty and enjoyment to the Seashore's many visitors.