Geoscience Reference
In-Depth Information
Beach plum and heather “holds” brighten and anchor a Cape Cod dune.
The thicket also provides protection for the growth of the larger trees that form the maritime forest, a dense,
junglelike environment. This rare forest type is restricted to barrier islands and other exposed coastal sites. The
trees that grow here cannot grow in saline waters but are tolerant of salt spray and include pitch pine, Atlantic
white cedar, red maple, American holly, southern red oak, sweet bay magnolia, and willow oak. Freshwater
wetlands develop in depressions among these patches of forest and provide habitat for muskrat, frogs, turtles,
and aquatic insects. Dragonflies often congregate on the islands in massive swarms during their fall migra-
tions, using the straight lines of the barrier islands as navigational markers. In addition, migratory songbirds
depend on coastal maritime forests for food and cover during their fall migration, when huge flocks, or “torna-
dos,” of swallows descend on bayberry bushes, bending them to the ground with their weight.
The maritime forest is also where most terrestrial vertebrates are to be found. Toads, frogs, and snakes can
easily reach the islands, as do skinks and salamanders, though with greater difficulty. One amphibian that com-
monly occurs in beach habitat from New England to the Gulf Coast is Fowler's toad, which is slightly smaller
than the more familiar American toad found inland. The isolation of the islands favors genetic drift—as Dar-
win in the Galápagos Islands and Wallace in the Malay Archipelago first deduced. This phenomenon, which
can result in the loss of a particular gene variant in small populations, has produced separate species or subspe-
cies of amphibians, reptiles, and even mammals on some islands. The mammals, in fact, have adapted best to
the island habitat and include herbivores such as squirrels, mice, rabbits, and deer, along with predators such as
foxes, mink, and otters.
