Thursday, May 18, 2017

Invasive Species: European Beachgrass

Visit a beach in California, particularly in the northern half of the state, and you are likely to come across stands of European Beachgrass (Arundo arenaria).  It looks so innocuous, picturesque even, waving in the Pacific breeze and blurring the line between land and sea.  But this grass, a plant you've probably never thought twice about, is much more than it seems.  Innocuous it is not.  European Beachgrass is one of California's most wanted offenders: an introduced, aggressive invasive species.

This picturesque photo of the California's Pacific Coast has a secret...  Most people won't notice that the grass seen
here is an imposter; it's not native to the area, but a species that doesn't belong in this ecosystem.

The main crime this grass is guilty of is being too good at its job.  In 1869, European Beachgrass was planted around Golden Gate Park in San Francisco, and since 1900, it has been introduced to other parts of California's coast in an effort to stabilize sand dunes.  But sand dunes are by nature fluid, ever-changing, ephemeral.  ("Shifting sands" is a saying for a reason.) 

Unfortunately, this unique quality of sand dunes and the distinct habitat that they create was recognized too late: the exotic grass had been introduced, and found California's climate more than suitable.  Where it has been introduced, European Beachgrass has spread vigorously, to the point that native vegetation is choked out and the dunes are cemented firmly in place by the tenacious clumps of grass.  Dunes are no longer able to shift, build and re-shape with the winds.  Dunes covered in European Beachgrass re-form to become parallel to the coast, rather than perpendicular, creating foredunes that are so high and steep, the sand supply to the rest of the dune system is effectually cut off.

European Beachgrass near Watsonville, California

European Beachgrass spreads by creeping rhizomes, underground stems that are capable of producing roots and shoots (just like the pesky Bermuda grass in your garden: every tiny piece will develop into a whole new plant).  Pieces of rhizomes that have been dislodged by crashing waves are easily carried to new sites, where they wash ashore and root.  The ability of rhizomes to sprout makes removal of European Beachgrass extremely difficult.

Threatened Western Snowy Plovers require the open spaces of beaches and dunes for breeding and for survival as a
species.

Beaches and dunes with extensive stands of European Beachgrass have lower biodiversity than those with native plant cover.  The thick growth of European Beachgrass excludes native plants, including dune wildflowers that provide a food source for native butterflies and other pollinators.  The lack of open spaces on dunes choked with the introduced grass severely reduces nesting habitat for threatened Western Snowy Plovers (Charadrius alexandrinus nivosus).  To make matters worse, thick beachgrass provides cover for plover predators, diminishing the success of breeding pairs nearby.  Our native perennial dune grass, American Dune Grass (Elymus mollis) grows with ample open space between clumps.  Other natives that are excluded by European Beachgrass include Yellow Sand Verbena (Abronia latifolia) and the endangered Menzie's Wallflowers (Erysimum menziesii).  Dune systems that have been extensively stabilized by European Beachgrass may then be colonized further by lupine and coyote bush, transforming the dune community entirely.

Endangered Menzie's Wallflower, one of many native species that is choked out by aggressive European Beachgrass

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