Opening the corridor

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San Francisco is a dangerous town for butterflies. Xerces blue, a species that once thrived in the city’s dunes, suffered a catastrophic demise in 1941, the first butterfly extinction in the United States caused by urban development.

In the years since, local butterflies haven’t fared much better. According to lepidopterist Liam O’Brien, 24 of 58 local species have been wiped out in regional extinctions caused mainly by habitat destruction. Another three or four, he said, will likely be gone within the next five years.

The green hairstreak is one of these on-the-brink butterflies. Boasting brilliantly verdant wings, the nickel-sized hairstreak lives only in the Inner Sunset’s Golden Gate Heights neighborhood and at Battery Crosby in the Presidio. Survival of the species depends on linking two populations on Rocky Outcrop (14th Ave. and Noriega) and Hawk Hill (14th Ave. and Rivera).

Separated by just five blocks — less than a mile but enough concrete to be the edge of the earth for smaller butterflies — the two hilltop populations are islands whose fluttery inhabitants have become genetically threatened by full sibling inbreeding.

Female hairstreaks rely on one of two native plants, coast buckwheat and deer weed — both of which once grew abundantly on natural dunes — as sites for their eggs. As O’Brien told the Guardian, "The females disperse, and they just disperse into oblivion if they don’t have the host plant to keep it going."

The Green Hairstreak Project is O’Brien’s plan to build a botanical bridge. "We could keep this butterfly alive in the city if we just totally bombard that area with these two plants," he said, adding that starters are being grown in preparation for October planting.

The project is a program of Nature in the City, an organization devoted to the ecological stewardship of San Francisco. Founding Director Peter Brastow said the city is full of "reservoirs of indigenous biodiversity," and believes that the whole urban landscape is a potential habitat. "The other piece of the puzzle," he said, "is connecting up wildlands via corridors."

O’Brien is considering various corridor-constructing strategies, from knocking on doors and giving buckwheat and deer weed plants to residents (he’s mapped potentially usable front yards) to professional dune restoration. During this past hairstreak season, between mid-March and the end of May, he led walks to introduce future stewards to the resident butterfly.

"Literally, can we please just put this plant in your front yard? It’s not complicated," O’Brien assured would-be-hosts, adding that he would like San Francisco to be celebrated for what it saved, not just for a species it destroyed. "Here’s a butterfly that flew at the same time Xerces did. Are we going to step up and do something?"

O’Brien’s hairstreak haven is not the only corridor being mapped out. A few neighborhoods east, artist Amber Hasselbring is building a series of native plant plots that zigzag along Mission District sidewalks. "Think about looking down from Dolores Park," she said, "and seeing this whole thing just unfolding in front of you so the park does not have a border anymore, [but] just flows into the next one."

At Mission Playground on 19th Street and Linda, Hasselbring explained her Mission Greenbelt Project, also a Nature in the City program. From her initial, mammoth vision to "daylight" the buried Mission Creek, she wondered instead about connecting the spaces, and people, that are already part of the community. "The Mission is such an incredible hotspot for culture," she said, "and then we have all these natural areas."

The urban wildlife corridor would meander from Dolores Park to Franklin Square at 17th Street and Bryant, a route based on both existing garden-able spaces — among them Alioto Mini Park (16th Street and Capp) and John O’Connell High School (18th Street and Harrison) — and potentially receptive businesses, such as Project Artaud Theater and KQED’s studios.

Hasselbring is eager to remove sections of unused sidewalk and transform them into sidewalk gardens. Mohammed Nuru, deputy director of operations for the Department of Public Works, told us that the city tries to make the permitting process as simple as possible to encourage citizen-built "green highways." He said it generally takes about six weeks, depending on the area’s status and the planting plan. In the two years it’s been available, more than 200 people have applied.

"We strongly support the greening of the city and the removal of asphalt," he said. "The city has a lot of vacant lots that at one time were planned to be streets, but because the city is so hilly, they never happened. Those are huge opportunities also for becoming green spaces."

In May, Hasselbring and 50 volunteers, organized by the Recreation and Park Department, established 200 individual plants in the three-foot-wide border around Mission Playground. Now, a habitat garden of 13 different species thrives where previously only Rugosa roses and ficus trees grew.

Dylan Hayes, a landscape ecologist and neighbor of this first site, selected the native plants for their ability to foster local fauna: creeping manzanita for wintering hummingbirds, pink flowering current for berry-loving thrushes, sticky monkey flower for bumblebees, and so on.

"It’s like the Field of Dreams: If you build it, they will come," Hayes said, mantra-like. "People are battling about what it means to be a ‘green city.’ But if you want a green city, you need to simply invite nature in."