The removal of invasive beach grasses on the Oregon coast to improve nesting habitat for the western snowy plover, a threatened shorebird, can harm non-target, native plant species and dune ecosystems, a study shows.
The findings, published by researchers from Oregon State University in Ecosphere, a professional journal, suggest that restoration projects to aid a threatened species should also consider the broader ecosystem in which it lives.
“By just targeting one species, you’re not reestablishing the ecosystem function and allowing the other native species that are also in decline to recover,” said Sally Hacker, an OSU associate professor of zoology. “We looked at the whole process to see if there were ways to help restore things to benefit the plover as well as other species.”
The western snowy plover, a small, open-ground nesting shorebird that prefers bare or sparsely-vegetated, low, sandy dunes, was listed as a threatened species in the early 1990s after populations in Oregon declined to only about 28 surviving individuals.
The listing triggered protection and monitoring, including restoration sites on public land along the Pacific coast. Bulldozers and other mechanical and hand methods were used to remove two invasive beach grass species, Ammophila arenaria and Ammophila breviligulata. These grasses make it difficult for the plover to nest, see predators, and access the open beaches to feed.
The non-native grasses had been introduced in Oregon in the late 1800s and early 1900s to stabilize beach sand that was inundating coastal roadways and homes, and create foredunes to protect properties from winter storm surges.
But the introduced grasses transformed vast stretches of what was once dynamic beach dunes populated by low-growing native plants into dense, static monocultures of the bristly beach grass. The invasive grasses shade out low-growing native plants and have caused continuous foredunes to form at heights of as much as 45 feet.
With support from Oregon Sea Grant, Hacker and Eric Seabloom, a former OSU professor, and doctoral candidate Phoebe Zarnetske, studied 10 of the plover restoration sites.
They found that use of intensive mechanical methods like bulldozers to remove the invasive grasses has helped the shorebird population begin to recover, but the process flattens the foredune and interrupts the natural formation of dynamic dunes where native plant species can succeed.
“Lower-intensity treatments such as hand pulling and targeted herbicide application appear to allow the coastal dune system to regain more of its endemic vegetation and natural topography,” said Zarnetske. “This helps restore the functional attributes of the dune as well as native species, including the plover.”
Because plovers appear to respond similarly to any of the restoration methods, the study proposes a shift away from repetitive bulldozing.
“We’re not suggesting that hand-pulling as a management strategy is ideal, because it’s labor intensive and potentially more expensive,” said Hacker. “But we’re asking if there are better ways to manage the system, such as less frequent bulldozing combined with hand-pulling and targeted herbicide applications, which will benefit the ecosystem as a whole.”
Aside from the ecological issues, some property owners welcome how the beach grass has stabilized the sand and formed a foredune as a defense against rising wave heights and sea levels. In some locations, however, the high foredune obstructs ocean views. The research is trying to consider the broader ecosystem, which includes humans.
Researchers say it is also important for people not to disturb the signed restoration sites along the coast by driving vehicles or allowing dogs to run loose.