From 2000 to 2005, a non-native plant and its hybrid rapidly changed the makeup of California’s San Francisco Bay.

The invasive species, Spartina alterniflora, created an even more adaptable hybrid with its relative, the bay’s native marsh plant, Spartina foliosa. The hybrid threatened to turn tidal mud flats into meadow, eliminate shorebird foraging habitat, and push the native S. foliosa toward extinction.

Peggy Olofson, director of the Berkeley-based San Francisco Estuary Invasive Spartina Project, says the non-native S. alterniflora, also known as smooth cordgrass, was introduced to San Francisco Bay’s eastern shoreline by contractors and workers for the U.S. Army Corps of Engineers during the 1970s, as part of a dredging restoration program.

S. alterniflora, and especially its hybrid, quickly took over large swaths of the bay.

“In San Francisco estuary, we have thousands of acres of open mud flat, and many of the plants, the hybrids, decided they loved it there,” Olofson says. “So they started filling in all of the mud flats. They decided that they also liked the high marsh area, where there are just a couple of species that live native in our state. So they started taking over those areas and displacing the natives from those areas also.”

The native cordgrass was just one species S. alterniflora and its hybrid threatened. The invasive species changed parts of the bay where the endangered California clapper rail, a salt marsh bird, forages, and shrank the habitat of the endangered salt marsh harvest mouse.

The plants not only became a problem for animal species. One unexpected consequence of the hybrid was its ability to thrive in pond water. The number of biting mosquitoes increased dramatically, inconveniencing the local community and discouraging public use of the area.

The plants also began to change natural drainages in the Bay Area.

“One of the things that is a concern for people who were responsible for flood control and protecting human houses is that the plant clogs the storm channels, the channels that are tidal right by the bay where all of the creeks and streams have to discharge in order to get the storm water off the hillsides. It clogs those up and causes them to back up and causes flooding in the adjacent areas and the upland areas.”

Established by the California State Coastal Conservancy in 2000, the San Francisco Estuary Invasive Spartina Project set about eliminating S. alterniflora and its hybrid from the estuary. The project is a partnership between government agencies, environmental organizations, and individuals.

In 2005, the organization began eradicating the invasive Spartina with the herbicide imazapyr.

“This is a very low-toxic substance, which just happens to work very, very well on this plant,” Olofson says.

Due largely to the organization’s efforts, the footprint of the invasive Spartina and its hybrid has been reduced from more than 800 acres in 2006 to fewer than 90 acres today. Still, Olofson says the work is not done.

“Now that we are getting close to being successful with eradicating the hybrid, the marsh is left without any [native] foliosa,” she says. “What we are doing now is we are starting a very large re-vegetation program and going back and introducing the native cordgrass into areas where it was completely removed or displaced by the hybrid.”