Invasive Spartina Eradication

woman scientist with binoculars looks out over a marsh with Spartina plants

Pacific cordgrass (Spartina foliosa) is a major component of tidal marsh vegetation in San Francisco Bay, which historically covered thousands of acres across the region. In the 1970s, the Army Corps of Engineers introduced Atlantic cordgrass (Spartina alterniflora) to the Bay, which hybridized with its native cousin. The hybrids expanded aggressively across lower tidal mudflats and tidal marshes, displacing Pacific cordgrass, altering vegetation communities and “engineering” the ecosystem through sediment accretion. Tidal marshes are important habitat for the federally-listed Ridgway’s rail, salt marsh harvest mouse, and migratory waterfowl. It became apparent that cordgrass across the entire bay would be replaced by hybrid cordgrass and mudflat habitat would be lost if the situation was not addressed.

In the year 2000, the state-led Coastal Conservancy and Federal-led US Fish and Wildlife Service initiated the Invasive Spartina Project (ISP) to head up a multi-agency response effort with the goal of eradicating invasive Spartina from the Bay. After four years of planning and environmental documentation, treatment started in 2005. To date, the overall population of invasive Spartina in the bay has been reduced 95%, from 805 acres to less than 38 acres across a 70,000-acre project area (see the 2019-2020 Monitoring and Treatment Report and the latest treatment schedule). More than 450,000 native plants have also been planted, restoring many acres of Ridgway’s rail habitat (see the 2020 Ridgway’s rail survey report).

Since 2019, Cal-IPC has partnered with the ISP to continue to lead this highly successful effort toward completion. The regional collaboration comprises more than 150 partner groups, including private, local, state, and federal landowners, resource agencies, and community stakeholders in all 9 counties. This extensive partnership and the innovative project structure and tracking methodology that have evolved through this program presents a model for landscape-scale invasive species response.

ISP received a Cal-IPC Outstanding Project Award in 2012 and an Outstanding Implementation Project Award from the San Francisco Estuary Project in 2015. It has also been featured in several publications, including Bay Nature Magazine, Alameda Magazine, ESRI ArcNews, and the San Jose Mercury News.

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Plants being managed

Start date



San Francisco Bay Estuary Project map in Calflora Bay Area region

Resources protected

Tidal marsh habitat supporting endangered wildlife (Ridgway’s rail, salt marsh harvest mouse) and other marsh-dependent species, and tidal mudflats supporting migratory waterfowl and shorebirds.

Project goal

Eradication of hybrid Spartina from the San Francisco Bay. This is a long-term goal and is considered feasible due to the isolated nature of this hybrid swarm, the lack of new introductions, and the success of the program to date.

Project photos

An ISP biologist mapping a detection of hybrid Spartina alterniflora emerging from the native Spartina in a channel along Corte Madera Creek, Marin County. Inventory surveys are conducted throughout 70,000 acres of tidal marsh and mudflat.
Inventory mapping and subsequent treatment of hybrid Spartina requires using airboats to access mudflats and marshes at the appropriate tide both to detect plants and effectively treat them. Treatment at Bair Island, shown in this photo, will protect nearby restoration projects including ponds within the Ravenswood Complex of the South Bay Salt Ponds (projects that are part of a future funding proposal).
A man in gaiters aims a careful stream of herbicide onto mature Spartina plants.
Invasive Spartina treatment often requires locating isolated occurrences to ensure complete elimination of mature plants and new seed. The imazapyr herbicide used to treat invasive Spartina is a very low-toxicity product, approved by the U.S. Environmental Protection Agency, the State Water Quality Control Board, and the Department of Pesticide Regulation for use in the sensitive estuarine environment. To minimize herbicide use, a blue non-toxic dye is added to the mixture to help applicators see what has already been treated.
Six smiling people lean over a muddy garden plot, setting small native Spartina plants in neat rows
The Watershed Nursery in Richmond, CA has propagated most of the species used by the ISP Restoration Program. This photo shows native Pacific cordgrass (Spartina foliosa), which is grown in propagation beds from plant material originally harvested from various marshes throughout the bay. Source populations were selected using multiple criteria and verified as native Pacific cordgrass using genetic testing.