Hybrid beachgrass could mean trouble for Northwest coast

A new potential threat has emerged to coastal dunes in the Pacific Northwest. Scientists at Oregon State University have confirmed that two widespread, invasive beachgrasses are now genetically mixing, which could present additional challenges to communities and dune restoration.

Before the introduction of European and American beachgrass, there was far more open sand on the Oregon and Washington coasts. Where it as present, native vegetation promoted lower dunes that tended to shift and morph.

“The non-native grasses out-compete some of the native non-grass – like the herbs and the forbs (flowering herbaceous plants) that were part of our system 150 years ago. There are efforts to try to restore dunes back to that native state,” said OSU coastal ecologist Sally Hacker.

On the other hand, it’s often better for communities and infrastructure if those dunes don’t move and instead provide a steady buffer against winter storms and surges.

That’s why European beachgrass was brought in at the turn of the 20th century. A few decades later, American beachgrass was introduced in Washington, and eventually became the dominant beachgrass in that state.

Now, where the ranges of the European and American beachgrasses overlap in northern Oregon and southern Washington, scientists have found clusters of beachgrass that don’t look like either.

“We found this other kind of strange grass that had intermediate characteristics of the two species. We didn’t know, really, what was going on,” Hacker said.

The researchers thought the new grass just might be a slightly different version, or variant, of one of the grasses. But they quickly realized that the physical characteristics were too distinct.

OSU Ph.D. student Rebecca Mostow began studying the new grass, documenting the physical traits and conducting a genetic analysis that confirmed the new grass is a hybridized cross between European and American beachgrass.

The results were published in the journal Ecosphere.

“We look at these small morphological character[istics] that grass people care about… and we found that the hybrid was intermediate in some of those traits, but then we also found that the hybrid was taller than either parent’s species,” Mostow said.

This is a phenomenon called hybrid vigor.

“A cross between a donkey and a horse is a mule. The one thing that people know about mules is that they’re bigger and stronger than donkeys and horses. That’s hybrid vigor, and that’s part of the story of hybrids that we study,” she said.

The height of beachgrass matters because taller grass creates taller dunes. Different dune formations offer differing levels of protection for coastal communities.

“And so now we have this new type of grass growing on the dunes and we don’t totally know what kind of dune it will build. But because it grows taller than the parent species, we have this guess that maybe it’ll change the dune shape,” Mostow said.

Hacker says early results from research still underway shows that, unlike mules, the new hybrid grass can go on to reproduce. It produces viable seed, although not very many.

And there’s concern that the hybrid beachgrass will crossbreeds back with one of the original grasses – basically allowing genes to flow back and forth between European and American beachgrass.

“It has some real important consequences if it’s happening on the coast,” Mostow said. “Gene flow between invasive species - and increasing genetic variation in invasive species - has been shown to increase their invasive potential.”

It’s also unknown how the hybrid will impact dune ecosystems and efforts underway to protect them from invading grasses. This is a significant focus of the conservation and restoration work underway at the Oregon Dunes National Recreation Area on the central Oregon coast.

“We’re expecting some differences in sand capture… and so that may affect the speed with which the grasses move,” said Siuslaw National Forest restoration botanist Armand Rebischke, who works at the Oregon Dunes to remove encroaching vegetation. “But… it’s not an immediate concern.”

So far the hybrid beachgrass hasn’t been found south of Pacific City.

“We’re keeping one eye on our ground here on the Siuslaw and another eye up north to see how things pan out up there,” he said.

The hybrid grass has been found at 12 sites along the Oregon and Washington coast. And Mostow says she is recruiting citizen scientists to help look for the hybrid grass at other locations on the coast.