All About Marshes: Plants of the Marsh

Of all the environments in the eastern United States, the tidal salt marsh might be the most unassumingly abundant with life. These vast, low-lying green landscapes sustain a rich diversity of life, and the food web relies largely on the foundation of the seemingly monocultural vegetation found within them. Inland habitats of the Coastal Plain are separated into multiple natural communities, for example, forests, river systems, and bogs/swamps, each having particular defining criteria based on soil type, hydrology, and elevation that give rise to very different plant communities. Each of these plant communities may be characterized by a species or assemblage of species such as an “oak/hickory forest”, but each has scores, if not hundreds, of species that fill the habitat from the treetop canopy to the forest floor. This is not the case in tidal marshes where each individual marsh zone is usually dominated by one or just a few plant species.  The plants that are adapted to this zone experience changeable, but historically predictable, environmental conditions including continuous tidal fluctuations, so it is not surprising that fewer species of plants are suited to growing in these areas. In addition to having to adapt to a wide range of wet and dry conditions, these plants also had to adapt to salty waters. As a result, the different zones of marsh are readily identifiable even from aerial or satellite imagery based on the type and abundance of the plant species.

Aerial photo illustrating the transition from low marsh (dark brown vegetation) to high marsh (light green vegetation) to upland forest (darker green vegetation). Photo credit: Larisa Prezioso, Eastern Shore Land Conservancy

In the lower marsh, smooth cordgrass (Spartina alterniflora) is the dominant vegetation due to its ability to tolerate large changes in inundation and salinity. Smooth cordgrass has two forms, tall and short, that appear at slightly different depths of tidal inundation. These low spartina marshes are typically less prominent in the Mid-Atlantic, though they can cover substantial tidal areas along the coast to the north and south.

Snails perched on Spartina alterniflora in the “low marsh” zone. Photo credit: Sophia Seufert, USFWS

Salt pannes are areas within the marsh that typically have low vegetation cover due to high salt content and pools of water. Saltwort (Salicornia spp.), a well-known plant that is adapted to salt pannes, is edible and can be steamed, blanched, sauteed, or added fresh to a salad.

Salt panne with pooled water. Photo credit: Sophia Seufert, USFWS

Hummocks are elevated bumps in the marsh that protrude above the surrounding marsh and may contain a much higher diversity of plants, due to the more stable environmental conditions and less exposure to salt.  Hummocks include species such as hightide bush (Baccharis halimifolia), marsh elder (Iva frutescens), and even trees such as eastern red cedar (Juniperus virginiana). These more densely vegetated hummocks can form along the edge of a creek or ditch alluding to the historic manipulation of these landscapes where hand dug sediment was left.

Iva frutescens growing on hummocks flanking a ditch. Photo credit: Sophia Seufert, USFWS

Of particular concern in the mid-Atlantic is the health and long-term viability of the upper or high marsh, which has been declining due to pressures from sea level rise, saltwater intrusion, ditching, and land development. This high marsh is where the main species of concern of the Marshes for Tomorrow project, the saltmarsh sparrow, lives and raises its young. The birds that nest in this zone depend on large expanses of salt hay (Spartina patens) that remain inundation-free for the breeding season. Due to the ecological importance of the high marsh and unique wildlife that depends on it, the Marshes for Tomorrow initiative will focus on maintaining the health of the plants and animals within the highmarsh zone.

Meadow of Spartina patens, the nesting plant for the Saltmarsh Sparrow. Photo credit: Sophia Seufert, USFWS

Explore this saltmarsh plant identification guide to learn more! https://www.saltmarshguide.org/guide/identification-guide/terrestrial-plants/

Marshes for Tomorrow (MfT) is an ambitious project led by Audubon mid-Atlantic and regional partners of the Delmarva Restoration and Conservation Network (DRCN) to identify, protect, and restore at least 25,000 acres of the most important tidal salt marsh habitat on Maryland’s Eastern Shore for saltmarsh sparrows. MfT is utilizing the most recent scientific analysis coupled with community input to select the areas to concentrate our efforts. If you would like to learn more about MfT or join one of our upcoming public meetings, please visit the MfT website at https://www.delmarvarcn.org/marshesfortomorrow.

All About Marshes: Salt Marsh Structure

By Jared Parks, Director of Land Programs, Lower Shore Land Trust

To fully appreciate the challenges that our Atlantic and Chesapeake Bay salt marshes are facing, it is essential to understand how factors such as flooding and elevation create the unique zones found within a typical salt marsh. Though small, these differences lead to very distinct differences in what plant and animal communities each zone can support. Marshes are described by separate zones based on the small elevation rise from the edge of the water to the edge of dry land; “low marsh,” “high marsh,” “pannes” (high salt, low vegetation areas), “hummocks” (taller bumps that rise above the overall marsh platform), and marsh/land border. 

Aerial photo illustrating the transition from low marsh (dark brown vegetation) to high marsh (light green vegetation) to upland forest (darker green vegetation). Photo credit: Larisa Prezioso, Eastern Shore Land Conservancy

Low Marsh Zone

The “low marsh” is flooded twice a day by the normal tidal cycle. As such, the low marsh is a haven for many species of aquatic life such as blue crabs, small fish, and shellfish. The main vegetation is Spartina alterniflora, or cordgrass, which is a vigorous plant that helps make the low marsh one of the most productive ecosystems in the world. Due to the regular flooding, this zone is not suitable for species like the saltmarsh sparrow that nest very low to the ground.

Blue crab in low marsh zone. Photo credit: Brian Henderson.

High Marsh Zone

The focal zone of  “Marshes for Tomorrow”  is the “high marsh” and its unique assemblage of organisms, particularly the saltmarsh sparrow (Ammospiza caudacuta). Unlike the low marsh, the high marsh is not flooded by daily tides during the summer months making it an ideal location for the saltmarsh sparrow to nest. The high marsh zone is particularly susceptible to storm surges and sea level rise because it falls only a few inches in elevation above the low marsh. Based on statistical computer models, Maryland is predicted to lose a larger proportion of this high marsh zone than the low marsh. With increased flooding and high marsh loss, we see a corresponding decrease in successful breeding attempts by Saltmarsh Sparrow. This loss is a key driver of our restoration planning effort for the lower Eastern Shore’s salt marshes. 

Saltmarsh Sparrow chicks in a nest in the high marsh zone. Photo credit: Lauren Owens Lambert, USFWS

Here on the Delmarva, the tidal range is very narrow (only a couple of feet), and the marsh is very flat, with only a small change in elevation from the shoreline to the upland. The topography and tidal regime in our region has created these large expanses of marsh, but it also makes it more difficult for the marsh to adapt with sea level rise. 

Marsh migration is the process through which marsh can begin to move inland if unobstructed, as sea level rises and flooding frequency increases. As the water rises, the low marsh will begin to displace the high marsh, but, in most cases, the high marsh will not be able to migrate inland due to obstacles such as roads and buildings. This is playing out right now in mid-Atlantic marshes, and it is creating serious problems for the saltmarsh sparrow, which has lost nearly 90% of its total population since the late 1990’s.

Marshes for Tomorrow (MfT) is an ambitious project led by Audubon mid-Atlantic and regional partners of the Delmarva Restoration and Conservation Network (DRCN) to identify, protect, and restore at least 25,000 acres of the most important tidal salt marsh habitat on Maryland’s Eastern Shore for Saltmarsh Sparrows. MfT is utilizing the most recent scientific analysis coupled with community input to select the areas to concentrate our efforts. If you would like to learn more about MfT or join one of our upcoming public meetings, please visit the MfT website at https://www.delmarvarcn.org/marshesfortomorrow.