Chesapeake Bay Lowlands Ecoregion
Description & Physiography
Fed from as far away as southern New York by the Susquehanna River, the Chesapeake Bay Lowlands ecoregion is centered on one of the largest estuaries in the world, spanning three states from Maryland and Delaware in the north southward 195 miles to its mouth in eastern Virginia. The Bay proper separates two distinct landforms – the Delmarva Peninsula to the east and the mainland to the west. Throughout, a complex and dynamic patchwork of islands, saltmarshes, tidal flats and open water, the coastal systems make up an area about one-tenth the size of the open waters of the Bay itself.
From the west, the five major rivers that empty into the Bay – the Patuxent, the Potomac, the Rappahannock, the York, and the James – form a series of large, parallel upland peninsulas running northwest to southeast. These “necks” generally feature low slopes and gentle drainage divides, except where steep slopes have developed due to stream erosion.
To the east, the Delmarva Peninsula features low, very flat, sandy plains cut by wide, slow-flowing rivers with extensive tidal reaches and broad expanses of tidal marsh.
Climate
Temperatures are moderated by the Bay and the ocean, producing an annual climate pattern more typical of southern locations, with cool, wet winters and warm, humid summers. Annual precipitation averages 40-50 inches, with average monthly temperatures above freezing in winter months, and in the upper 70’s in summer months. Hurricanes and nor’easters (winter storms) affect the region but are infrequent.
Plants & Animals
The distinct east-west landforms feature different environmental diversity, as well.
On the western shore of the Bay, the typical upland forest is dominated by American beech, white oak, tulip poplar and hickory, with red maple increasingly abundant. Drier upland forests are feature oaks, and sometimes hickory, with dogwood, arrowood, and laurel common in the sub-canopy layer, and huckleberries and blueberries ubiquitous throughout. Early successional stands on dry uplands are often dominated by Virginia pine. The extensive floodplain and slope-bottom habitats on the western shore also support sweet gum, red maple, and tulip poplar, with sycamore, birch and ironwood common along riparian edges.
To the east, in uplands on the Delmarva Peninsula, loblolly pine forests - both natural and planted - predominate, with oaks (esp. southern red, white, and willow), hickory, red maple, and American holly common. Again, Virginia pine typically dominates dry upland habitats recovering from disturbance. In lower, wetter areas, red maple and sweet gum are more abundant, along with black gum, but loblolly pine and American holly remain common where flooding is seasonal. Highbush blueberries and sweet pepperbush predominate in the shrub layer, while sweetbay magnolia reaches into the sub-canopy. Black gum and green ash become common in tidally influenced swamps on Delmarva, and some areas contain sizable stands of Atlantic white cedar.
As for animals, the Bay supports populations of all of the common vertebrate species typical of low elevation habitats in the Mid-Atlantic. In Maryland, vertebrate diversity includes 62 species of mammals, 292 birds, 42 reptiles, 38 amphibians and many species of freshwater fish. All of the vertebrates found in Delaware probably also occur in Maryland, while a few more typically southern species are found in the Virginia portion of the ecoregion.
Given the predominance of the Chesapeake Bay and numerous major tidal rivers, animal species characteristic of the ecoregion include muskrat, bald eagles, osprey, Canada geese, great blue herons, many species of diving and dabbling ducks, gulls and other shorebirds. Aquatic species representative of the ecoregion include rockfish, spot, yellow perch, several shad and herring species, blue crab, oyster, diamondback terrapin and horseshoe crab. Many of the aquatic reptiles (turtles, snakes) and amphibians common in the Mid-Atlantic are likely more abundant in the Bay than in adjacent Piedmont areas, simply because of the greater abundance of aquatic, river, and wetland habitats.
Humans & History
The terrestrial landscape that existed around the Chesapeake Bay prior to the arrival of European settlers in the mid-1600’s is poorly documented. Presumably, the region was primarily mature, mixed deciduous forest, with small areas of cleared land and disturbed forest around Native American settlements. Population densities of Native Americans were relatively low, and concentrated near river and Bay shorelines and other water sources Native Americans certainly used fire to clear settlement areas and garden plots, and to manage habitat for game species, but such impacts were mostly confined to areas of only a few tens of acres. The most significant alteration of natural processes on a small - but widespread - scale that took place following European colonization may have been the virtual elimination of beaver during the 18th and 19th centuries. On the other hand, the pre-colonial population density of beaver may have been held in check by Native Americans and the large predators now absent from the ecoregion.
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