North Atlantic Coast Ecoregion

Description & Physiography

The North Atlantic Coast Ecoregion (NAC) consists of parts of nine states (DE, PA, NJ, NY, CT, RI, MA, NH, ME) and their near shore marine waters.  The land and freshwater component of the ecoregion encompasses 12.7 million acres in a narrow band from the southwestern shore of Delaware Bay north to Pemaquid Point in Maine.  The widest portion of the ecoregion is eastern Massachusetts (78 miles from the coast to the eastern border of the Lower New England Ecoregion) and the narrowest is 6 miles at the mouth of the Hudson River.  The ecoregion is approximately 465 miles long from north to south.

The mainland and offshore islands are typified by generally flat topography, scattered morainal features, outwash plains, and glacial ice contact features (Figure 2).  Elevations reach only 600 feet at Mt. Agamenticus in southern Maine.  The Laurentide Ice Cap, which reached its maximum advance 23,000 years ago, deposited sediment along its southern boundary which today form the barrier islands of Long Island, Martha’s Vineyard, Nantucket, Block Island and other smaller islands.  By 15,000 years ago, the ice shield had retreated from the Gulf of Maine, leaving behind moraines that acted as dams, creating three significant glacial lakes in northern New Jersey and southeastern New York: Lake Passaic, Lake Hackensack, and Lake Flushing. Glacial deposits on Cape Cod are estimated to be 200 to 600 feet deep.  Sediment deposition from flooding south of the extent of glaciation formed much of Delaware and New Jersey.  Kettle holes formed by ice blocks buried by glacial sediments resulted in present day coastal plain and outwash ponds.

The influence of marine waters both on the climate and the natural processes that shape the freshwater and terrestrial systems creates a unique assemblage of ecosystems in NAC. Coastal plain ponds, sea level fens, tidal marshes, beach and dune complexes, and pitch pine barrens are characteristic systems found within the ecoregion.  Small streams that drain directly to the ocean are numerous within NAC.  These streams are typically low gradient meandering streams occurring on coastal flats with both a freshwater component and a lower tidal brackish creek and/or salt marsh system.


The temperate climate of NAC is characterized by mild humid weather.  Climate tends to be tempered by coastal waters resulting in cooler summer temperatures and warmer winter temperatures than those found farther inland.  Normal precipitation averages between 40 and 45" per year.  Daily mean temperature averages 45o at the northern portion of NAC and 54° at the southern boundary of the ecoregion.  Average July temperature for Portland, ME is 78° compared to 86° for Wilmington, DE and average January temperature for Portland, ME is 30° compared to 39° for Wilmington, DE. Average annual relative humidity for Portland, ME is 70% compared to 85% for Wilmington, DE.

Plants & Animals

The North Atlantic Coast Ecoregion harbors a remarkable array of biodiversity, with over 100 imperiled species, 13 of which are endemic to the ecoregion.  The ecoregion’s biodiversity is sustained by glacial history, sandy coastal plain soils, coastal processes, fire, and mild humid climate.  The interface of land and sea along this long stretch of coastline gives rise to significant concentrations of biodiversity in the Delaware Bay and bayshores, the South Shore Estuaries and Peconic Estuary of Long Island, Buzzard’s Bay, the Merrimack and Parker River Estuaries in Massachusetts, Great Bay in New Hampshire, and the Lower Kennebec River and Merrymeeting Bay in Maine.

The rarest species in the ecoregion are generally habitat specialists restricted to the rarest or most threatened ecosystems.  Examples of such species concentrations include:

Beaches & Dunes:  piping plover, seabeach amaranth, sea-blight, Northeastern beach tiger beetle, seabeach knotweed, and Papaipema duovata (a stem borer moth).

Maritime Grasslands/Heathlands:  sandplain gerardia, Nantucket shadbush, bushy rockrose, regal fritillary (now believed extirpated in ecoregion).

Brackish & Freshwater Tidal Rivers:  short nose sturgeon, Atlantic sturgeon, Eaton’s beggars ticks, Maryland bur-marigold, sensitive joint vetch, Parker’s pipewort, Long’s bittercress.

Coastal Plain Ponds:  lateral bluet and pine barrens bluet damselflies, Hirsts’ panic grass, creeping St. Johnswort, Boykin’s lobelia, Plymouth gentian, slender arrowhead, awned meadowbeauty.

Pine Barrens: Knieskern’s beaked rush, New Jersey rush, Bog asphodel, resinous boneset, Pine Barrens gentian, swamp pink, Torrey’s dropseed, curly grass fern, and coastal barrens buckmoth.

Flanking the coast are vast stretches of salt marsh with brackish and freshwater tidal marshes developing at the upper reaches of tidal rivers and creeks.  The extent of tidal marshes becomes smaller to the north as a rocky coastline begins to develop.  Dunes and beaches, the most threatened ecosystem in the ecoregion, trace a thin band along much of the ecoregion’s coast, decreasing in length to the north.

Humans & History

The ecoregion is heavily settled with 26% of its area developed, 14% in some form of agriculture and the remaining 60% in natural or semi-natural cover (Figure 3). Land ownership is mostly private although one million acres (14%) is permanently secured against conversion to development.  Most of the secured land (88%) is publicly owned state land that is intended for multiple uses. A smaller percentage (3%) is secured expressly for nature conservation.


Historically, the North Atlantic Coast was covered by a nearly continuous forest which graded from a mesic, mixed oak coastal plain forest -- to drier oak-heath forests -- to a white pine/oak/hemlock forest at the northern end of the ecoregion.  Patch communities, including wetlands, grasslands, heathlands and pine barrens, were imbedded in the matrix forest.  Today, following 300 years of land clearing, agriculture, and widespread urban, suburban, and rural development, NAC’s large swaths of forest are gone.  Although there are several large unfragmented forested blocks remaining in NAC (the largest remaining unfragmented habitat block in NAC is within the New Jersey pine barrens (75,872 acres) these are limited compared to adjacent ecoregions. The highly fragmented nature of this ecoregion precludes significant restoration opportunities for most forest types.

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