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A six-year pilot study on Santa Monica Beach shows how seeding of native flora can restore habitats for threatened species and protect against climate change-driven sea level rise.

by Emily Ortega, PhD Student at the University of Alaska, Fairbanks, and the NGA LTER.

Credit: Kyle Emery, CC BY-SA 4.0.

Dune restoration site on Santa Monica Beach with grooming tracks in the foreground over the control site.

Coasts Under Threat

Picture a beach at dawn. The golden sand is cool, not yet baked by the sun, and it’s spread across a wide, flat expanse as far as the eye can see. Now take a closer look. What are those tracks? They weren’t left there by bird, turtle, or even human feet. No, those are tire treads and rake marks. This beach has been groomed. 

Beach grooming is the process of clearing beaches of manmade and natural debris by mechanically raking the sand. This practice was deemed necessary on many coastal recreation beaches worldwide, including California’s Santa Monica Beach, which has been routinely groomed for several decades. Grooming creates the manicured landscape some beach-goers expect, but the alteration of natural beach geomorphology may leave groomed beaches susceptible to flooding and coastal erosion and impact the long-term connectivity and nutrient cycling between beach and coastal ocean habitats. 

With this in mind, PhD student Karina Johnston and other researchers in collaboration with the Santa Barbara Coastal LTER, of which a key component is habitat connectivity along California’s beach ecosystems, established a six-year experiment to study the ecological impacts of passive dune management. Throughout the study period, they assessed the effectiveness of a passive, nature-based, approach at recovering geomorphological structures and ecosystem services in comparison to a continually groomed control site. 

Setting Restoration in Motion

Credit: Karina Johnston, CC BY-SA 4.0.

Red sand verbena (Abronia maritima) growing in the dune restoration area.

In December 2016, the restoration team embarked to allow sand dunes to rebuild themselves naturally from the ground up. They installed fences around three sides of a 1.2-hectare plot, leaving the seaward side open. They also seeded the area with four species of native dune vegetation, including red sand verbena (Abronia maritima) and beach bur (Ambrosia chamissonis). These specially adapted ecosystem engineering plants would form the scaffolding for dune morphology that hadn’t been seen on the beach in decades. 

Just two months later, seeds had begun germinating. Six months after seeding, dune vegetation had already covered about 1% of the restoration plot, and after six years of growth, plant cover had increased to 7% of the area, providing enough cover for a well-functioning foredune ecosystem. While 7% cover may not seem like much, all of that growth was accomplished passively: no irrigation and only occasional removal of a non-native plant, sea rocket. Meanwhile, the nearby control area continued to be groomed as usual and remained completely uncovered by dune vegetation and morphology. In addition to the seeded species, two unexpected native plants also appeared in the restoration area, one of which, the rare woolly head (Nemacaulis denudata), was particularly surprising. “We’re not sure where it came from, because it isn’t anywhere along the groomed beach or surrounding areas,” Johnston says, showing just how beneficial restored dunes can be to local plantlife. 

Dunes and associated plant species are mutually beneficial. Just as the cessation of grooming practices allows for plant growth, that regrowth also traps sand and allows it to accumulate. This starts the formation of dune structures called vegetation hummocks, and as they develop, specialized dune plants continue to grow upward on top of them allowing for more and more dune growth. In fact, Johnston explains that the dunes were growing faster than the rate of sea level rise in the region, thus providing a buffer zone for the coastal region. 

Credit: Karina Johnston, CC BY-SA 4.0.

Plants weren’t the only ones who returned to the shore. These burgeoning dunes also provide habitat and cover for all kinds of beach wildlife from dune beetles to threatened shorebirds like the western snowy plover, who were seen nesting within the restoration site during the first year of the project. The return of coastal wildlife is a huge step in validating this low-maintenance, nature-based approach to dune habitat restoration.

While there is no one-size-fits-all approach to urban, coastal restoration, the holistic, process-focused approach exemplified by this project provides a case study for larger scale, long-term coastal restoration. This approach can inform future restoration efforts and allow some degree of predictability in expected long-term restoration outcomes across a variety of coastal habitats.

Dunes Restore Ecosystem Services

In January 2023, a strong storm with large swell and high tides hit California beaches. Yet following the January storm, no significant erosion was seen to affect the restored dune site, and the newly formed foredune on the seaward side provided a barrier to waves. Over the nearby control area, meanwhile, waves extended an additional 20-30 meters up the beach. The resilience of the restoration area to this disturbance provides evidence that the restoration of dunes along this and similar sites in California and beyond may increase resilience of urban coastlines to flooding and coastal erosion in the face of climate change-driven sea level rise. 

“The dunes want to form. Grooming is the main barrier,” says Johnston. Cutting out grooming provides a solution to crucial climate-based challenges and aligns with typical beach use, incurs low financial and management cost, and provides crucial habitat for threatened species. In other words, when looking at dune restoration from a passive, nature-based perspective, everyone is a winner.