Life in the Dunes
When you spend time at the shore, you have an interesting relationship with coastal sand dunes. This is because they play many different roles, and how we view those roles defines our relationship to them.
I’m talking about the narrow ribbon of sand that is nestled between the high-tide line of the beach and the landscaping of beachfront homes. The dunes have become an engineered barrier that we are banking on to be the first line of defense from the attack of angry storm waves. The dunes of Seven Mile Beach typically rise to 14 feet, though a few are higher, and in most places they form a single ridge. In the middle of the Island, and especially in the 40th to 50th street blocks, the dunes are much higher and wider and consist of a series of dune ridges. This is more typical of natural dune systems and is reminiscent of how the beach front was before the island was developed. If you talk to some of the folks who have made this island their place for decades, they will tell you all about the impressive coastal sand dunes that defined this island in the past.
Beaches are very dynamic features, which I think is why so many of us are drawn to them. They automatically know the level of the sea and, in undeveloped situations, they move. As sea levels change, the beach moves – landward when its rising, and yes – seaward when the relative level is falling. I say relative level because in areas where there is an excess of sand, the island can build out into the sea even if the seas are rising. As the island became developed, that development and our use of the island is trying to impose a fixed position on the beach. Collectively, the Army Corp of Engineers, the New Jersey Department of Environmental Management and both boroughs spend millions of dollars annually on Seven Mile Beach alone, to try to hold this position. The success of holding this position – which includes a healthy dune line and wide beach, is dependent on the whims of Mother Nature. The time the “success” lasts is entirely dependent on the time between storms. For us, that is most frequently winter storms and nor’easters. Less frequently, it is tropical storms and hurricanes.
The dunes are the first line of defense in these storms; their role is to sacrifice themselves to absorb the incoming wave attack. Thus, it is expected that following the high water and waves of storms, the dune is cut back, leaving a steep cliff face to a beach that is also eroded down. The dune did its job, though.
Dunes are remarkably fragile yet resilient. The plants that live on them serve many purposes. American beachgrass (Ammophila breviligulata) is the native grass of our dunes and is adapted to life in the harsh dune conditions. Beach grass thrives under conditions of shifting sand, sand burial, and high winds. Their roots help hold the sand in place and strengthen the dune. The grasses that grow on them also trap blowing sand to help build the dunes. The sandy dune habitat is very dry and limited in nutrients. The plants actually need the occasional overwash of the ocean that deposits seaweed, which brings an injection of nutrients to feed the grasses. They also need the stress of burial and wind to keep them growing. While they benefit from wind stress, they are intolerant of crushing. Even a few steps can kill dune grass. This is why dune access is limited and any pathway through the dunes is devoid of vegetation, so do your part and remain on formal dune pathways.
There are a number of other plant species that occur in the primary dune/American beachgrass community and even between the beach and first dune. They are all tolerant of harsh winds, salt spray, and dry, nutrient poor conditions. The most well-known of these species is seaside goldenrod (Solidago sempervirens), which can be identified year-round by its clump of broad, almost succulent leaves. In the late summer and fall, their yellow flowers are a magnet for monarch butterflies that are moving through our area on the way to their wintering grounds in Mexico. These goldenrods flower well into October and are one of the few plants still flowering, and provide much-needed fuel for these remarkable fliers. Dune restoration throughout coastal New Jersey has provided a crucial interstate for migratory butterflies.
While the life of the grasses in the primary dunes is harsh and difficult, the dunes are home to myriad types of wildlife. Birds, both resident and migratory, use the dunes for food, shelter and nesting. Small mammals can be abundant in the larger dune fields. On the beach-face dunes, Ghost crab burrows can be abundant.
The dunes also provide nesting habitat to several species of seabirds and shorebirds including piping plovers (Charadrius melodus), American oystercatchers (Haematopus palliatus), common terns (Sterna hirundo), least terns (Sternula antillarum), and black skimmers (Rynchops niger). They favor the sparsely vegetated and shifting sand habitats, but they are primarily only found on Stone Harbor Point, where there is suitable habitat for them. All of these species are struggling to find space among the heavy beach use on the island.
As fall comes, a common but amazing sight is the mass groupings of tree swallows (Tachycineta bicolor) that feed and congregate in the coastal dunes. They are the same birds that land on wires in large numbers each fall. Every year, I get a lot of questions about these birds. They are dapper little birds that look to me to be wearing mini-tuxedos, with their clean white breast and shimmering blue-black backs. They hunt insects on the wing and consume 2,000 insects each day, surely putting a dent in the insect population of the island. During migration, they also feed on berries found on trees that grow in the dunes including bayberry (Myrica carolinensis) and wax myrtle (Myrica cerifera). They leave our area for South America in October. During the winter, the dunes are graced with the visits of snowy owls that move south from their northern homes. The number that visit each year, and whether they visit at all, is highly variable and related to weather patterns in the North, among other things.
Next time you visit the beach, spend a moment thinking about the coastal dunes and the various roles they play. Whether they are our line of defense in storms, the home of resilient grasses, nesting areas for shorebirds, or habitat for migratory species, they are majestic and largely untamed. In mid-September, The Wetlands Institute holds its Fall Migration Festival in which you can join guided beach and dune walks, see monarch butterflies up close, and learn more about the world-class migration in our area.
Our coastal dunes are resilient, fragile and simply beautiful. It’s worth thinking about them in new ways.
