What Is Phragmites?

Phragmites australis, commonly known as the common reed, is a tall perennial grass that thrives in wetland environments. This species can reach heights of up to 18 to 20 feet, forming vast stands that dominate entire marsh systems. The reed is easy to spot because of its height and its distinctive fluffy seed heads, which appear late in the season. While there is a native North American subspecies, the non-native Eurasian form of Phragmites has become one of the most aggressive invasive plants in the United States. Scientists believe it was introduced to the East Coast during the late 1700s or early 1800s, most likely through shipping and ballast materials, and it has been spreading rapidly ever since (NY Invasive Species Information).

Why It Is a Problem

The invasive strain of Phragmites dramatically alters ecosystems. It outcompetes native marsh plants such as cattails and wild rice by growing taller and denser, blocking sunlight, and spreading with thick underground rhizomes. Over time, this creates an almost impenetrable monoculture that leaves little room for biodiversity. These stands reduce habitat quality for fish, amphibians, and waterfowl, and make it difficult for herons, egrets, and ducks to land, nest, or feed (Mass Audubon).

Phragmites also changes the physical and chemical makeup of wetlands. Its dense roots trap sediments, alter hydrology, and reduce salinity in brackish areas. This reshaping of marshes can increase flooding risks in some places while drying out others. In addition, its tall dry stalks become highly flammable, raising the risk of destructive fires (Great Lakes Phragmites Collaborative).

Wetlands are especially vulnerable to invasion when they have been disturbed by human activities such as road grading, ditch digging, or stormwater runoff. These disturbances create openings that allow Phragmites to establish and spread more easily.

Phragmites on Fishers Island

On Fishers Island, Phragmites has been steadily expanding for more than 45 years. The Fishers Island Conservancy has documented its spread across wetlands and shorelines, where it has displaced native vegetation and disrupted delicate ecosystems. In some locations, Phragmites has obliterated scenic views, such as at Hay Harbor, where it now forms solid walls along the sailing dock approach. What was once a diverse community of cattails, grasses, sedges, and flowering plants has been overtaken by reed monocultures, eliminating the food sources and open spaces that birds and other wildlife depend upon.

Despite more than a decade of management efforts that include mowing, controlled flooding, and targeted herbicide treatments, Phragmites remains a persistent challenge. However, there are encouraging signs. In some treated areas, native plants are re-establishing, root systems are recovering, and patches of marsh are beginning to regain their ecological balance.

The problem extends beyond just one species. A 2022 rare plant survey conducted by the Henry L. Ferguson Museum identified Phragmites as one of more than 45 non-native plants altering Fishers Island’s landscape, alongside species such as oriental bittersweet and Japanese knotweed. Among these, Phragmites is considered one of the most urgent to manage because of its ability to transform entire wetland systems.

The very name Phragmites comes from the Greek word pharma, meaning “fence” — an apt description of the tall, impenetrable barriers it creates in our wetlands.