WETLANDS
Archaeological, historical, and natural sites of the marshes combine to provide a rich tapestry of experiences for anyone interested in exploration. The quest for a particular plant or animal species may be diverted by the remains of a brick factory, a Revolutionary War ship, or an arrowhead. The 1250 acre Hamilton / Trenton Marshes occupies an ancient meander of the Delaware River where one can find palustrine and riverine, as well natural and constructed wetlands. Half of the area is tidal.
This diversity of habitats supports many kinds of plants and animals. A plant list compiled in 1988 (Bartonia 47: 1-17) reported 426 species; since then additional species have been found so that by 1998 more than 780 had been recorded. About 230 species of birds have been observed with 100 species nesting there. Other groups of animals are less well known. The distribution of plants and animals, whether along a tidal stream or at the edge of a pond, is determined by the duration and depth of flooding. Organisms differ in their tolerances to water. (See Fig 1)
Wetlands:
Ponds -- Sturgeon Pond, Spring Lake, and Rowan Lake (tidal), as well as areas impounded by the highway construction of I195, I295, and NJ129 interchange and Tide Pool in the Duck Island constructed wetland, are to some degree, created by humans. They are of different ages and depths and have distinctive characteristics. Both Spring Lake and Sturgeon Pond show the effects of hydrological succession with obvious natural filling in along edges. With time and no human intervention they eventually would become marshes and then swamps. Additional impoundments have, since 1992, have been created by Beaver. The ponds have submerged and floating macrophytes that do not occur in other wetland types. These include White Water Lily, Creeping Water Primrose, which is rare in New Jersey, and Mermaid-weed. The ponds provide habitat for amphibians, such as Bullfrogs, Green Frogs, and Pickerel Frogs, and turtles including Red-bellied, Eastern Painted, Snapping, and Red-Eared. Great-blue Herons, Green Herons, Ring-necked Ducks, and Wood Ducks are frequently observed in ponded areas.
Marshes -- Examples of both tidal and nontidal marshes are found within the Abbott Farm National Landmark. Marshes may be found at the edges of ponds, along tidal channels, or other poorly drained areas. This wetland type, distinguished by non-woody vegetation, may be dominated by perennial species such as Cattails or Reed Grass, stands of which may grow 10 or more feet tall. Among tidal channels many annual species dominate the vegetation. These include Water Hemp , Water Smartweed, Giant Ragweed, and Wild Rice. The high marsh has Jewelweed, Halberd-leaved Tearthumb, and Dodder. Interspersed among the annuals are other perennials (e.g., Arrow Arum, Sweet flag, and River Bulrush). These marshes have high plant species diversity compared to salt marshes. The seasonal changes, from mud in January, to a carpet of tiny seedlings in March, to vegetation more than eight feet tall in August, are truly amazing. Because of such prodigious growth, tidal marshes are among the most productive ecosystems in the world. It should be noted that a number of plant species considered rare in parts of the Delaware River Estuary grow here. Some such Wild Rice are common; others like Subulate Arrowhead and Swamp Beggar’s Ticks appear to have more specific requirements and are less frequent.
Marshes provide habitat for Muskrats, Marsh Wrens, Least Bitterns, Yellowthroats, and Red-winged Blackbirds. An excellent place to look for Muskrat lodges, especially in winter, is the marsh on the north side of Spring Lake.
Shrub Forest -- As swamps, shrub forest wetlands are characterized by woody species. Shrub forests occur at the edges of marshes adjacent to upland areas; they also occur at the edges of marshes where they grade into swamps, with trees forming a distinct canopy, which in turn grade into wet forests and then to upland. The shrub thickets of Silky Dogwood, Buttonbush, Alder, Arrowwood, Red Maple, and Swamp Ash occur on hummocks surrounded by marsh. Some shrub forests, because of their openness and variety of microenvironments, support wildflowers such as Bitter Cress, Fringed Loosestrife, Purple-stemmed Aster and Turtlehead. In contrast, other areas are quite impenetrable. Among the animals observed have been Baltimore Butterflies, Woodchuck(!), Willow Flycatchers (nesting), Eastern Kingbirds, Cardinals and Brown Snake.
Wet Forests -- West of Spring Lake is a low-lying wooded area dominated by Red Maple and Sweet Gum. Nine species of ferns, including Rattlesnake Fern and Netted Chain-Fern can be seen in a leisurely one hour walk. Among the animals found in these wet woods are Grey Squirrels, Chipmunk, White-tailed Deer, Raccoons, and Red-tailed Hawks.
Wet woods may also be found on the flood plain of Crosswicks Creek up stream of the Route 206 bridge. Tree species there include Willows, Box Elder, and White Ash. Vines of grape, Virginia Creeper, and Poison Ivy festoon the trees along the stream banks. Skunk Cabbage may be locally common.
Disturbed Wetland Edges -- Highway construction, which began in 1984, caused considerable disturbance in some areas. Such open places provide a transitory habitat for a variety of species. For example, during a Torrey / Philadelphia Botanical Clubs trip in September 1990, 12 Smartweed species were observed. Birds commonly found along disturbed edges are: Goldfinches, White-throated Sparrows, and Indigo Bunting.
Constructed Wetland -- The Duck Island constructed wetland is the largest Department of Transportation wetland mitigation project in New Jersey. The 94 acre site has approximately 70 acres of wetlands, of which about 70% are tidal; this replaces 57 acres lost during highway construction. Prior to mitigation, Duck Island had no existing wetland except for a small poorly drained area that covered less than one quarter acre. Now there are a series of tidal channels and eight islands of varying sizes and elevations above mean high tide. Wetland construction was completed in stages beginning in fall 1993 and extending to November 1994. By October 1995, more than 300 plant species, not including landscaping plants, had been found. Many were weedy species associated with upland areas. Some were transitory, observed on only one occasion (e.g., Riverbank Quillwort and Pearlwort. Since 1995, many more were added. Several rare species such as Swamp Beggar’s Ticks, American Waterwort , Subulate Arrowhead, Torrey’s Rush, Narrow-panicled Rush, Water Willow, and a Hop Tree, found on the wooded fringe adjacent to the Delaware River, have made botanizing exciting.
The constructed wetland, because of its proximity to the Delaware River, openness, and sand / gravel soil that is different from the fine silty soils found elsewhere, has been a place where unusual species have turned up. These include Perennial Wall Rocket, Elsholtzia, and some of the rare species mentioned above.
This constructed wetland provides a unique outdoor laboratory for monitoring the progress of vegetation change (succession) in a tidal riverine setting. Colonization patterns by plants and animals should provide valuable insights regarding natural community dynamics.
Uplands:
Upland Forests -- There are two types of upland forests, second growth in places that were once agricultural fields or otherwise altered by human activities and the oak woods along the bluffs north of Bordentown. The second growth forests, which may be found along the bluffs near Spring Lake and on the islands near Spring Lake and the Hamilton Water Treatment Plant, are dominated by Oaks, Tuliptrees, and other hardwood trees. These woods support a variety of wild flowers, such as the spring-blooming Mayapple, Dutchman’s Breeches, and Celandine. In open sandy areas on Duck Island and near Spring Lake in summer can be found Blue Curls, Wild Sensitive Plant , and Bush Clovers, as well as native grasses, such as Little Bluestem and Indian Grass. Such second growth woods can also be observed around the perimeter and just north of the constructed wetland on Duck Island. There the dominant tree species is Black Locust.
The oak woods on the bluffs overlooking Crosswicks Creek near Bonaparte’s Landing contain Tuliptrees, Black Gums, a few Eastern Hemlocks and Pitch Pines, as well as White, Chestnut, and Black Oaks. There is even an American Chestnut sprout. Unique for this part of New Jersey are dense thickets of Mountain Laurel and Great Rhododendron that dominate the shrub layer. In spring morels may be found. Except for destruction caused by a tornado during late June 1996, this appears to be the least disturbed of the wooded ares within the Abbott Farm National Landmark.
During the course of the year, a great variety of birds may be found in upland forests especially during spring and fall migrations. Nesting Brown Thrashers, Song Sparrows, and Carolina Chickadees are common in second growth forests; Titmice and Chickadees are common in the Mountain Laurel-Rhododendron thickets; Blue Jays are wide ranging.
Disturbed Areas -- Construction and maintenance activities along roadways, the railroad, sewage treatment plants, and other buildings, as well as places where tidal debris is deposited offer obviously altered and disturbed environments. They occur on a variety of soil types and are places to look for weeds and other plants whose lifestyle is suitable for these open, often ephemeral habitats. Among the more interesting species found in such places have been Camphor-Weed, Slender Vetch, and Lance-leaved Coreopsis. In the spring Princess Tree. with its bare branches and large blue flowers, is conspicuous. Perhaps one of the most notable finds was Pale Indian Plantain, an endangered species; this was found in an area which had been burned in the 1950’s(?).
Another element of human activity are the numerous bridges that cross waterways. These are prime nesting sites for the endangered Cliff Swallow.
Scientific names of plant species referred to in this section:
Alder (Alnus rugosa) |