San Francisco is part of the California Floristic Province, which stretches from Baja into Oregon and is one of just 36 global hot spots for biodiversity. A hot spot is an area of extraordinarily rich flora and fauna, where there are high numbers of endemic species, which means they are found nowhere else on Earth. In this coastal region, there are some 7,000-8,000 native plants and more than 2,000 endemic ones.
According to the Critical Ecosystems Partnership Fund, the California Floristic Province also has an amazing diversity of ecosystems, including: the sagebrush steppe; prickly pear shrubland; coastal sage scrub; chaparral; juniper-pine woodland; upper montane-subalpine, alpine, riparian, cypress, mixed evergreen, Douglas fir, sequoia, and redwood forests; coastal dunes and salt marshes.
In addition to the temperate climate, it’s this wondrous abundance of biodiversity that perhaps lures so many people to California. But over-development has put remaining wild places at risk — just a quarter of original ecosystems are in pristine condition.
And in San Francisco, the amount of space for these ecosystems is far less — only 5 percent of the city, which makes them even more precious. On a tour at American Planning Association conference, we learned about the ambitious efforts of the San Francisco city government to both protect and restore remnant ecosystems.
Peter Brastow is the city’s biodiversity czar. As our tour bus wheezed its way up precipitous hills, he explained how the city recently formulated a biodiversity policy, formalized through a Board of Supervisors’ resolution, which gives extra support to his department’s efforts to coordinate biodiversity programs across the government and non-profits in the city.
The resolution bolstered the new urban forest plan, approved by city voters in 2016, which transferred ownership of the city’s 124,000 street trees from private property owners to the city’s public works department. San Franciscans saw this as important because the city falls way behind others in its total tree coverage at just 13.7 percent, far less than the nearly 30 percent found in Washington, D.C. The goal is to add another 50,000 trees by 2035, many of which will be native and support native insect and bird species.
The resolution also supports the city’s green connections program, which aims to get more San Franciscans into parks and educated about local biodiversity though a set of ecological guides, explained Scott Edmonston, San Francisco’s strategic sustainability planner, who co-organized the tour.
At our first stop, powerful blasts of cold wind greet us. This means it’s early summer at the Twin Peaks Natural Area, some 900 feet above sea level and near the center of the peninsula. The photogenic pair of hills are a remnant of the coastal shrubland ecosystem and home to the endangered Mission Blue butterfly, which relies solely on lupine plants. Brastow explained that the U.S. Fish and Wildlife Service re-introduced the butterfly on the peak with specimens from the San Bruno Mountain. The San Francisco parks and recreation department has been restoring the native shrubland and removing invasive plants.
Twin Peaks shows why the city has so much biodiversity, even in tiny pockets. Because of the city’s unique topography, the fog that rolls in from the Pacific Ocean covers some areas in moisture more than others. This results in micro-climates that in turn lead to unique micro-assemblages of plants. Hill tops, ridges, river bed landscapes introduce more complexity.
Edmonston said the problem for those restoring assemblages is that climate change may cause fog patterns to change. So the city and its partners can’t just restore ecosystems to what they were previously; they must instead plant what can survive a changing climate. “There is a lot of uncertainty now. The plant palletes we use now are much drier-loving. We really just need to restore more of nature, so she can be more resilient.”
For Brastow, the city needs to better identify the value of ecosystem services provided by remaining habitats and use those to push for reincorporating nature into more of the city. “That’s the frontier that can guide restoration ecology, landscape architecture, and urban design.”
The bus struggled mightily trying to reach the Sutro native plant nursery found at the top of a sheer slope at the University of California at San Francisco (UCSF) Medical Center. There, volunteers have grown more than 6,000 plants from 150 native species, which are being planted in 30 restoration sites in the 61-acre Mount Sutro area that includes UCSF’s campus. “The goal is to improve native plant diversity,” Brastow said.
For many in San Francisco, truly restoring native plant diversity on a broader scale means removing the groves of towering non-native Eucalyptus trees. But others are very protective of the Tasmanian trees and efforts to remove them have led to major protests. “For generations, Californians grew up smelling the trees — and they love it.” (A recent article in The Atlantic provides more context: “The Bay Area’s Great Eucalyptus Debate.”) There is one important reason to support their removal: “they are highly flammable.” And as the city gets drier with climate change, “some day we will have a big fire here.”
Amid the hills of the Sunset neighborhood that rest on ancient sand dunes, we come across a derelict hilltop right-of-way alongside staircases that was transformed into a native plant park and habitat for the Green Hairstreak Butterfly. In neighborhood rights-of-way, parks, and other green spaces, the city finds local site stewards, small non-profits, to manage upkeep.
Last stop was the Presidio, the only U.S. national park that gets 30 percent of its budget from renting out its restored U.S. Army military housing. There, we saw the results of the U.S. department of defense’s base realignment and closure (BRAC) environmental restoration program. A deep ravine that was once a garbage dump was transformed back into a native shrub habitat, thanks to a multi-million-dollar restoration effort and countless National Park Service volunteer hours.
As we drove back to the Moscone Convention Center, Brastow pointed out the ubiquitous London Planetrees that line Market Street. While not native to San Francisco, they are a cultivar related to the Sycamore tree.
Canyons are the natural home of the Tiger Swallowtail Butterfly. Market Street appears to them like a canyon formed by tall buildings on either side. London planetrees are close to their host Sycamores, and there is water in fountains along the street, so these insects have made a home there. “This is an example of how nature is also adapting to the city.”