Freshwater Wetlands in New York City - Arden Heights Woods
New York City once contained 224,000 acres of freshwater wetland. This valuable ecosystem can slow erosion, prevent flooding by retaining storm waters, filter and decompose pollutants, and slow global warming by converting carbon dioxide into oxygen at a prodigious rate. In the past 200 years, the increasing demands of a growing metropolis have resulted in most of this land being filled for construction, or dredged for transport. Only 2,000 acres of freshwater wetland remain in the city today, and many species that once called the wetland home have been lost forever.
Most of Arden Heights Woods is a forested hardwood swamp. This site is the largest freshwater wetlands that the Department of Environmental Conservation has classified anywhere in the New York metropolitan area. It contains several ponds that are connected by an intricate network of streams and creeks, providing natural flood control for the area. This makes a more complicated and expensive man-made sewage system unnecessary.
The formation of wetlands can be traced back to the most recent ice age. A massive ice sheet called the Wisconsin Glacier advanced on New York City 75,000 years ago, pushing rock, soil, and boulders ahead. When the ice melted 17,000 years ago, water flowed to the sea, creating streams and rivers that carved through rock. Large glacial fragments broke off, melted, and left depressions called kettles. If layers of fine silt and clay were deposited on the bottom of the depressions, the kettles collected water and ponds formed. Where waters were shallow or flowed slowly, seeds and spores were able to take root and flourish. Generations of plants grew and decomposed, building peat-rich sediments. As wind and water eroded the soil, the steep slopes grew gentler, slowing the passage of water. Plant communities diversified under these favorable conditions, attracting animals that fed on the plants. The sophisticated food web that developed brought advanced predators to the wetlands: snapping turtles (Chelydra serpentina), wolves (Canis lupus), several species of hawks, and humans (Homo sapiens).
Water levels in wetlands are variable, influenced by the underlying rock and soil makeup, rainfall, season, and ground water inputs. Despite these variable conditions, freshwater wetlands teem with life. In the swamps of Arden Heights Woods, there are two particularly notable species of plant life. The first, Blue flags iris (Iris veriscolor) blooms from May through July, with its namesake violet blue flowers. These plants can be recognized by their sword-like leaves even when not in bloom. The second, common reed (Phragmites australis), is a member of the grass family, which thrives in both brackish and freshwater marshes, and can grow to be 12 feet tall. Phragmites often invade wetlands at the expense of other native marsh plants.
Many owls frequent this site, including the screech owl (Otus asio), saw whet owl (Aegolius acadicus), great horned owl (Bubo virginianus), and barn owl (Tyto alba). Occasionally, a barred owl (Strix varia) from the south will venture this far north. This bird is known as the “Southern Gentleman” because it makes a distinct sound that is suggestive of “who cooks for you, who cooks for you-all.” Bats come here because the swamp’s ample insect population helps satisfy their appetite. In addition to housing these native species, freshwater wetlands also provide resting, breeding, and feeding grounds for hundreds of thousands of migrating birds. Many of these birds arrive in New York City only twice a year as they travel along the Atlantic flyway, a major migratory route.