Iona Marsh Habitat Restoration

Jul 19, 2020Conservation

Iona Marsh Restoration at Bear Mountain State Park

By 2000, the biodiverse brackish tidal marshes of Iona Island were overrun by the invasive, non-native common reed, Phragmites australis. Restoration began in 2008 with the removal of Phragmites from a 10-acre test plot to allow native marsh flora and fauna to recolonize. With success and development of improved technologies, restoration and management efforts are expanded annually. In effect, Iona’s marshlands have become increasingly more biodiverse and beautiful.


Iona Island is located on an elbow of the Hudson River in Bear Mountain State Park. The archipelago of three islands is connected by 153 acres of marshlands. As tides rise and fall, the marsh’s salt concentrations fluctuate.

Before New York State purchased Iona in the 1960s, the marshland had a long human history. Indigenous Lenape families harvested shellfish for millennia. With the onset of European colonization, Lenape were displaced. Iona was developed for varied purposes that undermined the natural landscape—an unsuccessful vineyard, a hotel and weekend destination, a U.S. Navy arsenal, and finally a partially built recreation area.

Since the mid-1970s, Trailside Museums and Zoo and Bear Mountain State Park have focused on Iona’s ecological significance. In 1974, Iona was designated as a National Natural Landmark and subsequently a New York State Bird Conservation Area and Audubon Important Bird Area. The eastern side of Iona, beyond the railroad tracks, was closed to the public in the 1980s. The majority of the island has been reverting to a more natural state. As vegetation has colonized the shoreline, upland, terrestrial, and avian wildlife have found habitat. In winter, bald eagles find sanctuary.


Iona’s tidal marshes once teemed with life including a variety of fish, waterfowl, waterbirds, crustaceans, and plants including some state-listed rare species. The complex web of marsh dependent flora and fauna is threatened by the non-native plant, Phragmites australis, known as common reed. Early in the 1960s, the first colony of Phragmites appeared near a pipe draining into the marsh. Tall with dark blue-green leaves, Phragmites formed dense stands crowding out native cattails, rushes, asters, amongst other marsh plants. Over the next 40 years, nearly 80% of the marsh was invaded.


Researchers noted a concurrent decline in marsh specialist birds and specialized brackish marsh plants. To reverse these trends, the Palisades Interstate Park Commission partnered with the Hudson River National Estuarine Research Reserve and the Highlands Environmental Research Institute with funding from the NYS Department of Environmental Conservation (NYSDEC). The trial project was implemented on a 10-acre plot (1/15th of the marsh) in 2008. The goal was to reduce Phragmites to enable native plants to reestablish and thereby create habitat for marsh dependent wildlife. The test project was successful.

Wetlands present a unique variety of obstacles to overcome when managing the land. Specialized vehicles including DR mowers and the larger and more efficient, Marsh Master, were used to navigate the difficult terrain. These machines were imperative to the cutting and leveling of Phragmites to make space for native species to reestablish.

Since 2013, researchers and managers have implemented a multi-faceted control and monitoring program. The results have been dramatic. One year after removing Phragmites from 10 acres, more than 90% of the area was free of the invasive plant. In the next two years, Phragmites was reduced by nearly 97%.

Without seeding or planting, the newly exposed seed bank germinated huge meadows of annual native marsh plants, including perennial cattail stands and some state-threatened species such as salt marsh aster and New England bulrush. Marsh specialist birds such as Virginia Rail, Least Bittern (state-threatened), and Marsh Wren followed soon thereafter. In 2013, the project was expanded to a 32-acre area called Ring Meadow. By 2018, both areas had less than 5% Phragmites cover.

The research team continues to expand on Phragmites removal efforts. In 2019, approximately 20 acres of land were added to the management area. This journey demands hard work and commitment; its rewards are the renewed health of an extraordinary national landmark.

Long-term Goals

While complete eradication of Phragmites is improbable, continued monitoring and spot treating can control it. Management is informed by annual bird and vegetation surveys. Measurements of sediment build-up on the marsh surface are recorded each year to assess sea level rise. This data helps consider other impacts that may be working synergistically with Phragmites to inhibit native plants from establishing. A healthy marsh, brimming with native species, will increase habitat for fish, birds, herps, and mammals far into the future. The long-term outlook is positive for this Hudson River jewel, one of only four large brackish marshes on the Hudson.


Though the majority of Iona Island is protected and not accessible by the public, there are two parking areas that provide visitors an opportunity to view the unique ecosystem (Google Maps, Google Maps links to parking areas). There is plenty of wildlife to view from these provided overlooks. Whether it be watching Bald Eagles and Kestrels soar through the sky or sneaking a peek at a Great Blue Heron wading through the shallows in search of a tasty meal, there is never a dull moment in the fleeting wildlife encounters you will have.

Public canoeing and kayaking are not permitted in Iona; however, every summer the DEC offers an opportunity to safely do so. Public canoe programs are held to connect visitors more closely with the plants and wildlife of the marsh. To spend your day paddling through Iona or one of the three other tidal marshes on the Hudson River, you simply need to register and follow the instructions listed on the following webpage;

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