Delmarva bays are seasonally flooded freshwater wetlands that are among Maryland's rarest natural communities.
Jackson Lane Preserve Delmarva bays are seasonally flooded freshwater wetlands that are among Maryland's rarest natural communities. © Matt Kane / TNC

Places We Protect

Crescent Preserve

Maryland / DC

These seasonally flooded freshwater wetlands are among Maryland's rarest natural communities.

Overview

Crescent Preserve is a collection of five natural areas - three owned by the Conservancy (Baltimore Corner, Persimmon Pond, and Jackson Lane/Eaton’s Pond) and two that are state-owned Natural Heritage conservation areas (Bridgetown Pond and Hollingsworth Pond).  

Each features at least one coastal plain pond, also known as Delmarva bays. These seasonally flooded freshwater wetlands are among the state's rarest natural communities, hosting numerous rare plants and providing important habitat for amphibians.

As their name implies, these bays occur only on the Delmarva Peninsula, typically along the backbone of the peninsula where soils are poorly drained. The seasonal flooding and saturated soils discourage many tree species, creating a meadow-like opening in the forest dominated by grasses and sedges.

Although the surrounding forest is essential to the health of the bays, it is the openings that harbor nationally- and state-rare species. 

Crescent Preserve contains five globally rare and fifteen state-rare species of plants. Many of these species are at the northern limit of their range. The nationally rare Canby’s dropwort (Oxypolis canbyi) and pond spice (Litsea aestivalis) are known from only one site each in Maryland and then are not found again until North Carolina, and even there they are considered unusual.

Harper’s sedge (Fimbristylis perpusilla) and Torrey’s dropseed (Muhlenbergia torreyana) are two other nationally rare Delmarva bay plants. The bays harbor many state-rare plants as well, like the only Maryland occurrence of red-root (Lachnanthes caroliana) and the horned-rush (Rhynchospora inundata). Other state-rare species include the carpenter frog (Rana virgatipes). 

The Delmarva bays are puzzling in origin, dependent on unusual hydrology and diverse in flora. Scientists have carbon-dated the sediments of the bays and found them to be about 15,000 years old. This coincides with the retreat of the Pleistocene glaciers and the subsequent sea level rise, yet the origin of these shallow depressions still remains a mystery.

Locally, the bays are known as “whale wallows,” another mystery since scientists are certain that their origin has nothing to do with whales. 

Scientists do know that the bays have an unusual hydrology, but this too is only partially understood. It appears that the bays are fed entirely by rainwater and groundwater; in other words, there is no natural drainage into or out of the bays. This means that the bays’ entire ecosystem is dependent upon the natural fluctuation of the water table. Because of this, our conservation efforts include protecting the groundwater as well as the land.

Historically, thousands of bays occurred on the Eastern Shore of Maryland, but most have been drained, filled, or timbered. They are flooded in winter and early spring but usually dry up by late summer and fall, although this can vary in very wet or very dry years. 

The openings average 3 acres, with some being as large as 15 acres. The bays support three types of wetland plant communities: grassy openings, shrub swamps, and forested wetlands called flatwoods. The understory of all three is usually dominated by grasses and sedges: giant grass, Walter’s sedge, twig-rush, and maiden-cane included.

Most of the bays harbor sphagnum moss, a wetland indicator species. The shrub layers are dominated by buttonbush, mountain sweet pepperbush, and highbush blueberry. Trees that are water tolerant enough to grow in the bays are sweet gum, red maple, and willow oak. Persimmon is found in these wetlands, unusual for this dry-ground tree. Sometimes the bays attract nesting colonies of green herons, great blue herons, and various other species of waterfowl. 

1,236 acres have been protected by the Conservancy and the state of Maryland here since 1982. The former agricultural fields at Jackson Lane Preserve are the site of the largest and best-studied wetland restoration on the Delmarva Peninsula.

Management at these preserves includes:

  • Using manual removal and prescribed fire to reduce woody vegetation and enlarge open sunny habitat for rare plants
  • Invasive plant control
  • Annual monitoring of rare plants
  • Managing a permitted hunting program to reduce the impact of deer

This preserve is not open to the public due to the fragility of the ponds. Thank you for your understanding and help in protecting this important part of Maryland’s natural heritage.