Glancing around the dunes west of Abbotts Lagoon in California's Point Reyes National Seashore, you might not see much but sand. In fact, those dunes are home to several endangered plant species that require something a bit counterintuitive: instability. Indeed, decades of conservation efforts aimed at stabilizing dunes likely harmed several endangered plants while actually exacerbating erosion, according to a recent study.
As far back as 1870 and continuing into the 1970s, land managers introduced European beachgrass to the West Coast to stabilize ever-changing sand dunes in hopes of protecting ocean beaches (not to mention roads and property). Now regarded as an invasive species, European beachgrass spread rapidly up and down the West Coast, where it did its job too well. By stabilizing some parts of the dunes and not others, beachgrass combined with ocean tides to create the steep, erosion-damaged walls now common along beaches from San Diego to Neah Bay, at the tip of Washington's Olympic Peninsula.
Along the way, beachgrass also had a substantial impact on plants, including two endangered species—beach layia and Tidestrom's lupine—native to California's fragile coast. Still, how, and to what degree, beachgrass made trouble for those species remained largely unknown.
By stabilizing some parts of the dunes and not others, beachgrass combined with ocean tides to create the steep, erosion-damaged walls now common along beaches.
Now, Washington University in St. Louis researchers Eleanor Pardini, Kyle Vickstrom, and Tiffany Knight report that the lifecycle of plant species like beach layia and Tidestrom's lupine depend largely on unstable, ever-changing dunes. Tidestrom's lupine seeds, for example, need to be buried in sand, roughed up a bit, and then uncovered by wind to germinate. (It's worth noting that researchers weren't sure just how big an impact invasive beachgrass could have on that process.)
So as part of a broader project on endangered species, the trio of biologists traveled to Point Reyes and sampled vegetation at 36 sites around Abbotts Lagoon, including spots where beachgrass both had and had not invaded. Beach layia and Tidestrom's lupine were much more common in sandier areas, they found. In addition, Tidestrom's lupine seedlings were present in 86 percent of the plots, while they were nearly absent in less sandy, beachgrass-covered areas. Most likely that's because beachgrass' stabilizing influence prevents seeds opening up and becoming new plants, the researchers explain.
Removing beachgrass from Point Reyes National Seashore and other beaches along the California coast would have "clear benefits" to both plants and animals—western snowy plovers, for instance, nest on open sand. The removal process, though, is likely to be a major headache, the researchers write in PLoS One. Beachgrass roots grow deep, and getting rid of them often requires heavy digging machinery or a combination of fire and herbicides. Still, restoration efforts at Abbotts Lagoon have been successful, and removing invasive beachgrass "with the purpose of restoring disturbance dynamics ... should be a conservation priority," the team writes.
Quick Studies is an award-winning series that sheds light on new research and discoveries that change the way we look at the world.