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Sea Islands/Coastal Marsh

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About the Sea Islands/Coastal Marsh

The Sea Islands/Coastal Marsh region of the Southern Coastal Plain extends along the Atlantic coastline from near Jacksonville, FL, through Georgia, and most of South Carolina. This is the southernmost coastal region on the east coast of North America that was not originally covered in mangrove forests. It is also geographically separated from other barrier island regions to the north and south, by areas where the flatwoods on the mainland extend the whole way to the coast.

This region consists of barrier islands, dunes, beaches, and the tidal marshes and estuaries behind them. Soils in marshes have a finer-textured mix of deposits of silt, sand, peat, and clay, whereas barrier islands mostly have sandy soils originating from past beaches, dunes, and marine deposits. Elevations are low (to 30 feet) and landforms are dynamic, shifting with the influence of rivers, the ocean, and coastal storms.

The climate here is humid and subtropical, with wetter summers and drier winters, but some precipitation year-round. The ocean moderates the climate: high and low temperatures along the coast are 2-4°F milder than nearby inland regions, and rainfall averages a few inches lower but humidity is slightly higher. Although this area is subjected to coastal storms, the concave shape of the coastline here reduces the frequency and severity of hurricanes relative to areas farther north and south, leading this section of coast to be dubbed "The Protected Coast".

Evergreen maritime forests cover much of the sea islands, with live oak (Quercus virginiana) the dominant species, along with eastern redcedar (Juniperus virginiana), slash pine (Pinus elliottii), and cabbage palmetto (Sabal palmetto). This plant community is shaped by the combination of nutrient-poor, coarse, sandy soils, and the mild climate. Temperatures are mild enough that broadleaf evergreens are abundant. Many plant species reach their northern limit in this zone, and are also not found much farther inland. Coastal marshes feature various species of cordgrass (Spartina sp.), saltgrass (Distichlis spicata), and rushes (Juncus sp.)

Parts of this region have been severely altered by development, but other parts are relatively intact. The south of this region intersects the northern part of the Jacksonville, FL metro area, and the barrier islands and beach area here are heavily developed, but there are large areas of protected marshes. Farther north, through most of Georgia, the sea islands are less intensely developed, but there is some development around Brunswick, GA, and the Savannah, GA metro area stretches into this region, with some islands heavily developed. South Carolina has extensive, low-density suburban development on many of the islands, although some are also left intact. Besides the urbanization and suburbanization, this region is also utilized for recreation, fishing, and shellfish production.

There is significant protected land here, including numerous National Wildlife Refuges: Savannah, Wassaw, ACE Basin, and Blackbeard Island, other national protected land, including Sapelo Island National Estuarine Research Reserve and Cumberland Island National Seashore. There is also significant state protected land, including the Tom Yawkey Wildlife Center, the Santee Coastal Reserve, and the Altamaha Wildlife Management Area, and Timucuan Ecological and Historical Preserve, and numerous smaller preserves as well.

In the south of this region, it is bordered both inland and at its southern end by the Sea Island Flatwoods, except along major rivers where it borders the Floodplains and Low Terraces inland. In the northern part of this region, it is instead bordered inland, and to the north along the coast, by the Carolina Flatwoods, except along major rivers where it borders the Mid-Atlantic Floodplains and Low Terraces inland.

References

1. Griffith, G.E., Omernik, J.M., Comstock, J.A., Lawrence, S., Martin, G., Goddard, A., Hulcher, V.J., and Foster, T. "Ecoregions of Alabama and Georgia (color poster with map, descriptive text, summary tables, and photographs)", U.S. Geological Survey, Reston, VA (2001) Web.