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Water Science and Restoration

Native and Invasive Plants: Supporting Healthy Ecosystems

The healthiest Nashua River watershed ecosystems consist of native plants and native animals that have evolved together into a sustainable web of life, balanced to adapt to our watershed’s geography and weather. Over the decades, non-native species that evolved elsewhere have been purposely or accidentally relocated by humans or environmental alterations, such as climate change. Not all introduced species become invasive. Some appear to be relatively benign, but others are strong competitors or voracious predators with devastating effects. The Massachusetts Invasive Plant Advisory Group defines “invasive” as “non-native species that have, or are likely to, spread into native or minimally-managed plant systems and cause economic or environmental harm by developing self-sustaining populations and becoming dominant or disruptive to those systems.”1 Invasives crowd out native species, alter natural food webs, and destroy wildlife habitat.
Nashua River at Pepperell Pond by Will Stevenson

NRWA has focused its efforts on addressing the extensive growth of invasive water chestnut in the mainstem Nashua River. The exotic water chestnut (trapa natans) was first discovered in the Pepperell Pond impoundment on the Nashua River (on the Pepperell/Groton line) in the late 1990’s. At roughly the same time, the plants were found in the Nashua River upstream of Mine Falls Dam in Nashua, New Hampshire. Invasive water chestnut plants create an impenetrable mat of growth that makes the river inaccessible to boating and fishing. Their growth replaces ecologically critical native plant species. When the dense mats die off in the fall, they sink and decay, which depletes oxygen levels vital to fish, destroying native fish habitat with resulting negative impact on fish populations.

In early years of the infestation, NRWA helped to organize hand-pulling efforts from canoes and kayaks in Pepperell Pond. However, water chestnut grows in an exponential way (each seed can produce up to 120 new plants). The Town of Pepperell and the MA Department of Conservation and Recreation (DCR) have worked to address the largest infestation area in the Pond (at one point as large as 80 acres), through mechanical harvesting and treatment. The City of Nashua also used mechanical harvesting to tackle its much smaller 14 acre area of water chestnut.

NRWA continues to address this invasive in the mainstem Nashua River by organizing and managing both staff and volunteer scouting and hand pulling groups to deal with water chestnut plants along river reaches from the Oxbow National Wildlife Refuge in Devens downstream to Nashua, NH where is coordinates efforts with the City of Nashua. Funding for this project is provided by the Nashua, Squannacook, and Nissitissit Rivers Wild & Scenic Stewardship Council and the Nashua River Regional Aquatic Invasives Alliance.

NRWA also works to remove invasive plants and replant native species along streambanks which you can read about on our Riparian Restoration page.

1Massachusetts Invasive Plant Advisory Group. (2005). The Evaluation of Non-Native Plant Species for Invasiveness in Massachusetts. Page 5.

River cleanup effort