Marine Plants / Algae

The once-plentiful eelgrass is the only type of seagrass now present in Boston Harbor; it is now confined to only four isolated areas, the largest of which is near the south coast of Bumpkin Island. Seagrass beds are critical wetlands components of shallow coastal ecosystems where they hold sediment, providing food and cover for a great variety of animals. Salt marshes, the most highly productive ecosystems in the world, are dominated by saltwater cordgrass and provide habitat for many marine organisms. More than 50 percent of the state's salt marshes have been filled. The largest remaining salt marshes on the islands are found on Thompson and Snake islands. Smaller brackish marshes have been identified on Calf, Grape, Lovells, and Peddocks.

Plants

The flora of the islands reflects a long history of human alteration, including introduction of a large number of invasive exotic species. The islands' drumlins are thought to have been covered with mature forests of hemlock, maple, oak, pine, and hickory, which were cleared to support agriculture and pasturage, and to supply firewood for fuel. In addition, the construction of the islands' massive fortifications severely disrupted much of the native flora.

Thorough documentation of the characteristics of the terrestrial environment is just beginning, but successional species including aspen, pine, birch, and white poplar are clearly evident on most of the islands. Farming is known to have been carried out by Native Americans as well as later colonial settlers. Most of the fertile sites found on the islands have been converted to agriculture. The remnants of attempts at subsistence farming are evident in the appearance of apples, pears, grapes, chives, garlic, asparagus, and horseradish. Today, patches of undisturbed native flora are rare on the islands, and vegetation on most of the islands is dominated by grasses and sumac. The owners of Worlds End and Thompson Island have continued to manage expansive grasslands that are part of the cultural landscape. Worlds End and Thompson Island have communities of mixed oak forest; on Thompson they cover approximately one-tenth of the island.

Lichens

A survey of the Boston Harbor Islands national park area yielded 175 lichen species in 67 genera, and 70 bryophyte species in 44 genera. Ten percent of the lichens represent a maritime floristic element, and 4% represent a coastal plain element. Caloplaca verruculifera, an orange lichen of rocky shores, is reported new for Massachusetts. Human disturbance and air pollution seem to be the major factors limiting the colonization of lichens and bryophytes on the islands, and specific recommendations for protecting sensitive lichen and bryophyte communities are presented. (Lagreca S, Lay E, Greene D, Kneiper E, Lincoln M (2005) The Lichens and Bryophytes of the Boston Harbor Islands. Northeastern Naturalist: Vol. 12, No. sp3 pp. 77-98)