Bay Researchers Fight Uphill Battle with Invasive Cordgrass
by Rachel Diaz-Bastin on November 21, 2013
Three years ago, managers at the Invasive Spartina Project thought they’d be almost out of a job by now. Their remarkable success up to that point in treating one of the most ominous invasive species in the Bay Area had left the once widespread invader, Spartina alterniflora, clinging to just a few dozen acres of scattered marsh. But the ruthlessly fast-spreading cordgrass has never made things easy. It hasn’t spread anymore, but it hasn’t been eradicated either, and after hopeful projections of near complete elimination by 2013, project managers now say it’ll be at least another three years. Despite their achievements, that last push has been the hardest of all.
“The last couple percent of hybrids are really the most difficult to get,” says Invasive Spartina Project treatment manager Drew Kerr. “They are the needle in the haystack.”
Spartina alterniflora, or Atlantic cordgrass, is a Bay invader with an unusual past. While most invasive species arrive in the Bay accidentally, hitchhikers in the ballast waters of ships from all over the world, Atlantic cordgrass was brought here intentionally.
In the 1970s the Army Corps of Engineers planted Spartina alternifolia, a resident of the Atlantic and Gulf Coasts, in an effort to stabilize levees around the South Bay salt ponds. It worked for that purpose – but then the Atlantic cordgrass cross-pollinated with our native species of California cordgrass, Spartina foliosa, creating a race of super-hybrids that were much more gregarious than their predecessors, a common phenomenon known as “hybrid vigor.”
Not only did the hybrids produce more pollen, they had the ability to self-pollinate, hybridizing among themselves and California cordgrass to create a highly fertile “hybrid swarm.”
By the 1980s, the hybrid swarm had suffocated tidal marshes and displaced California cordgrass throughout the Central and South Bay. The unintended consequences of that original planting have bedeviled efforts at Bay restoration since.
“Hindsight is 20-20,” says Marilyn Latta, who manages the Invasive Spartina Project through the California State Coastal Conservancy. “Not only were the hybrids more fertile, they grew taller, and were able to grow both lower in the tidal frame and higher up in the marsh.”
The hybrids, in other words, grew where the natives could not. And once they got cozy, they started making changes. Hybrid spartina plants are “ecological engineers” says Kerr, in that they “profoundly alter the habitat in which they live.”
Close to the tide-line, the hybrid swarm clogs channels and makes meadows out of mudflats, eliminating critical habitat for shorebirds and marsh birds, like the endangered California clapper rail, that forage in the mud at low tide. Higher up in the marsh the swarm out-competes native pickleweed, a plant that the endangered salt marsh harvest mouse requires for shelter and salty sustenance. Native California cordgrass was also threatened with local extinction as a result of cross-pollination with the hybrid swarm.
So in 2000, the California Coastal Conservancy partnered with the Don Edwards San Francisco Bay Wildlife Refuge to create the ISP. By the time the new partners had conducted four years of research about how best to counter the hybrid, the invasive cordgrass had spread into 800 net acres and spread widely over most of the Bay’s wetlands, with highest concentrations near the original introduction sites in Alameda and San Mateo counties.
Beginning in 2005, ISP staffers counterattacked with Imazapyr, an herbicide that works by disrupting synthesis of the proteins the plants require for growth. And by 2010, the hybrid swarm had been reduced by 90 percent to less than 100 net acres. That’s when ISP managers projected that, with continued control, up to 90 percent of the remaining 175 sites would have no detectable hybrids by 2013.
But success came with a caveat as biologists in and outside the project worried about the California clapper rail, which had switched from nesting in scarce native grasses to sleeping with the enemy, nesting among the hybrid cordgrass. It became the ultimate damned-if-you-do damned-if-you-don’t problem: the rails were relying on an invasive cordgrass that for now provided excellent habitat but in the long term would choke off the marshes and drive the birds out. So: treat the marsh, kill the Spartina, and leave the rails without cover? Or back off and wait for potential long-term calamity?
“This presented quite a management conflict,” Latta says.
In 2011, the U.S. Fish and Wildlife Service (USFWS) began regulating areas that could be treated with herbicide, restricting ISP access to 26 sites around the Bay. By 2012, this was reduced to 11 sites containing the last remaining 20 acres of hybrids. But with the future treatment authorizations unknown, the project timeline for total eradication has been extended by at least three years.
The ISP, in turn, has come up with a potential solution. For the first decade, the project relied mainly on passive dispersal of native seeds on the winds and tides to re-vegetate treated marshland. But to increase clapper rail habitat quickly, the ISP has begun planting native species. They chose 35 sites, mostly in the South Bay, where California cordgrass was at the lowest risk for cross-pollination, areas where the hybrid cordgrass was only found in tiny amounts.
In the last two winters they have planted more than 165,000 California cordgrass and gumplant seedlings.
Kerr and Latta say they hope the restoration efforts will boost clapper rail populations and encourage the USFWS to open up the remaining 20 acres of hybrid-infested land to treatment.
So while it might be frustrating to be so close and – still – so far away, most still consider the project with satisfaction. There have even been some unanticipated bonuses, like observing that native pickleweed happens to be highly resistant to the herbicide. Not just resistant, project managers say, but flourishing in the aftermath: in marshes left to their own devices following treatment, native plants have crept back and reclaimed their lost turf.
“It has been an incredible success story,” Latta says.
Perhaps the best measure of success is that in those limited areas the project has been able to restore native cordgrass to areas where it had been all but wiped out.
“It has come full circle,” Kerr says. “We are back to planting native California cordgrass in sites where original introduction of Atlantic cordgrass took place, which is very gratifying.”
Rachel Diaz-Bastin is a Bay Nature editorial intern.