The Living Bridge

The Santa Monica Mountains are home to around 450 species of mammals, birds, reptiles, and amphibians that roam a range packed with native plant varieties. But cut off by the US 101 freeway, the mountains have become something of a genetic island.

“It’s like old royalty,” jokes Beth Pratt, California regional executive director with the National Wildlife Federation, of the animals who live in the Santa Monica Mountains. “They’re mating with their relatives, and we know that does not result in a sustainable population.”

The answer? The Wallis Annenberg Wildlife Crossing, a transverse for both animal and plant species that will strengthen and sustain genetic diversity in the mountains. Following decades of planning and conceptualization toward a crossing, in 2014 the #SaveLACougars campaign was launched to raise the funding needed to make it a reality. The Annenberg Foundation—under the leadership of its late president and chairwoman Wallis Annenberg—donated a total of $26 million dollars toward the crossing’s realization.

The project found influential champions such as Leonardo DiCaprio and Gov. Gavin Newsom, and the State of California supported several stages of the crossing (including another $19 million in funding in February). The campaign’s “poster puma” was P-22, the famous mountain lion who was gravely injured in 2022 while attempting to cross one of the surrounding roadways and had to be compassionately euthanized. But while P-22’s celebrity status drove visibility and fundraising for the project, Pratt says that the crossing is intended to create a landscape hyper-authentic to its surroundings to benefit everything from mountain lions to monarch butterflies. The resulting creation is a literal ecological bridge between two long-divided parts of the mountains separated by
the freeway.

For this, the project partners (which include the National Wildlife Federation, National Park Service, Caltrans, and the Santa Monica Mountains Conservancy) turned to landscape architect Robert Rock of Chicago-based Rock Design Associates. Rock says he approached the project’s plant selections like any other project, considering his client’s tastes and preferences. Only this time, that client just happened to be hundreds of animals, big and small. “The aesthetic piece wasn’t what drove the design decisions,” he said. “We were viewing them through an entirely different lens.”

That animal’s-eye view led Rock and his team to an approach that was area-specific in the extreme. They sourced seeds directly from the surrounding landscapes and germinated them at an on-site nursery, which the team used both to keep costs down and also as a way of ensuring that the land bridge plantings accurately reflected the genetic adaptations of the areas immediately on either side of the bridge. Plantings include a wide variety of native sages (Salvia spp.), bush mallows (Malocothamnus spp.), toyon (Heteromeles arbutifolia), California buckwheat (Eriogonum fasciculatum), and others.

The Annenberg Wildlife Crossing is not a “garden” in the classic sense; it is not intended for humans and not open to the public. But the horticulture of the crossing reflects—and hopefully inspires—the intentionality of all great and lasting native plant gardens around California. The primary structure had its inaugural planting day last fall, and the emerging wildlife habitat shows the promise of greater genetic diversity for generations to come. Within months, Pratt says, butterflies, birds, and lizards have been spotted using the surrounding habitat within the Santa Monica Mountains. “Every time I’m up there, it’s wonderful to see the wildlife,” she says.

About the Project

Landscape plan credit: Rock Design Associates

Favorite native plants

Rock says his favorite native plant on the crossing is California buckwheat (Eriogonum fasciculatum). “It’s just spectacular,” he says. “You’ve got so many colors that define the landscape throughout the year”—from May’s beautiful white blooms to October’s crunchy, rusty-hued dried bulbs.   

Favorite element

It might not be the first thing that visitors—animal and non-animal alike—notice about the crossing, but Rock says he loves to “nerd out” about the site’s soil conditions. Rock and his team meticulously analyzed the soil in the areas surrounding the bridge, recreating everything from the presence of key soil microorganisms to changes in the soil structure caused by past wildfires.

Wildlife

Both Rock and Pratt are excited for the wildlife access the bridge will open for creatures of all types, from mountain lions to deer, foxes, and western fence lizards. But for Rock, there’s something special about hosting native hummingbirds, who will feast on the penstemons (Penstemon spp.), California fuchsia (Epilobium canum), and other species his team has planted. (Tiny and jewellike, hummingbirds also just happened to be Wallis Annenberg’s favorite animal.)

Irrigation

To help their recreated native landscape get a strong start, Rock and his team will use a drip irrigation system, with supplementary sprinklers mimicking a year with ideal rain conditions. Once everything is established, the sprinkler system will be used largely for fire suppression.

Maintenance   

“It’s not like the old Ronco Showtime Rotisserie infomercials,” Rock says of the crossing’s fledgling native plant habitat. “You can’t ‘set it and forget it.’ ” Since all the plants on the bridge are being grown from seed, active monitoring of their growth and the way they interact is an essential part of ensuring the project’s success. The Rock Design Associates team will observe the ongoing maintenance at the crossing, tracking plant succession and overall landscape health.

Advice

Rock and Pratt both stress the importance of thinking of your home garden as part of a larger ecosystem. Pratt says gardens can provide species of all kinds as welcome refuge from the surrounding urban environments. Rock urges thinking from the soil up
as part of a seasonal and annual cycle, always looking for new opportunities to protect your garden’s life and health.