Biodiversity SF Central

Yellow-faced Bumble Bee

Yellow-faced Bumble Bee (Bombus vosnesenskii) on California poppy (Eschscholzia californica) in San Francisco

We hope that you benefit from these resources about the indigenous biodiversity of the Northern San Francisco Peninsula and why the California Native Plant Society believes it is worth learning about, experiencing, appreciating and saving.

In addition to some basic facts and images, we've linked to resources about biodiversity on a separate page. Our chapter members have been collecting this information during decades of exploration.

Contact us if you notice any discrepancies or inconsistencies in the information presented here.

What is Biodiversity and Why Does It Matter?

Biodiversity refers to the variety and variability of life on Earth and is typically a measure of variation at the genetic, species and ecosystem level.

Biodiversity matters because each species in an ecosystem has an important often vital role to play. This web of species supports and balances itself and helps ensure sustainability and resilience of the entire system. If certain species are removed or diminished, the entire system is affected. You can read about a real-life example of this in a recent study about the effect of neonicotinoids on an ecosystem.

The greater Bay Area biological systems have been co-evolving well, since the beginning of time. Usually at a glacial pace but also occasional punctuation marks from tectonic action, climate changes and sea level. Through a series of human actions beginning in the late 1700's, major disruptions have occurred here and our "biodiversity index" has realized significant losses.

Introductions of non-native species plus non-native mammals and birds peaked during the American Victorian era. Species introductions persist through present day, primarily through the landscape industry.

Join the Conversation on the

One of the ideas presented at the event was the creation of a Biodiversity forum for our community to share future ideas, agency and community meeting details, information related to biodiversity, best practices, educational opportunities, and restoration and habitat change events or happenings.

In that spirit, we have created the BiodiversitySF forum.

Join in the conversation by submitting your email address below. If you know of others who were not at the event but have interest in topics related to the biodiversity of the San Francisco Bay Area, please share this link:

What Makes San Francisco Bay Area Biodiversity So Special?

With a rare Mediterranean-style climate (wet winter, long, dry summers), a constantly shifting land mass and the incomparable San Francisco Bay, one of the most biologically productive oceanic regions in the world, the Bay Area is one of the most unique ecosystems in North America.

California Floristic Provence ranks in the top 35 Biodiversity Hotspots on Earth.

The California Floristic Province is consistently listed as one of the top Biodiversity Hotspots on Earth with more than 7,000 native plant species, one-third of which are endemic. An astounding number of micro-climates and biomes, including the largest and oldest trees in the world, are located within a short distance.

From our western shores on a clear day, we can see the Farallones Islands, one of the most productive seabird and marine mammal islands in the Pacific. It was part of the mainland only 12,000 years ago.

The Bay itself is noted for hosting more wintering shorebirds than any other estuary along the US Pacific Coast south of Alaska and is recognized as a site of Hemispheric Importance by the Western Hemisphere Shorebird Reserve Network.

Owing much to geographical position, the tiny county of San Francisco has documented an amazing 500+ species of birds, more than half of all of the birds in the U.S. and Canada combined.

Given a slightly different cultural history, the entire San Francisco Peninsula could have easily become an American National Park. We are fortunate that several former military bases have indeed been converted to that special designation due to their significant historical and natural resources.

Climate Change and Species Decline

Alarms about climate change disruption and species decline have been ringing louder and louder:

  • Dramatic warnings about insect apocalypses may be overblown but there is no doubt that the planet is experiencing major declines in insect numbers, which are one of the most critical element of the land-based biological food chain and its diversity.
  • National Audubon and Cornell Lab of Ornithology recently released a peer reviewed report, which reported that the number of individual birds has dropped by 30% in the last 50 years. Some species have dropped by more than 90%.
  • National Audubon has identified 389 bird species in North America that are on the brink of actual extinction.
  • Despite these worrisome trends some species such as ducks and geese are doing better due to sustained conservation efforts, indicating that it may not be too late to turn the declines around for other species.

For many people involved in conservation science this news of species loss is not surprising. The ever-increasing use of effective insecticides, pesticides and rodenticides in agriculture, commercial and residential properties, and even in our parks, are having the predicted effect. Poison kills. Sometimes in a targeted manner. Too often indiscriminately, as is the case with secondary poisoning by rodenticides.

Fortunately, San Francisco has a very strong Integrated Pest Management policy. However, this policy does not extend to private use.

There is zero regulation for Pest Control companies. The landscape industry prescribes tons of poisons, often routinely, at the first sign of insects eating plant leaves or as a prophylactic measure for rodents and other "pests."

Introduced rodents, especially Norway Rats and other wildlife with access to human food are a major health concern for humans, too, but exclusion and snap traps may be just as effective in rodent control with little or no risks to wildlife.

Our Green City?

Despite its reputation as a green city, San Francisco could have one of the most altered and degraded natural habitats of any city in the Americas.

The truth is few people who live in the San Francisco area today get to experience the flora and fauna that inhabited the peninsula 150 years ago. We have nearly lost our natural heritage and few recognize this loss.

Collectively, our backyards are nearly 0% native plants, our parks have only a tiny fraction of the wild indigenous species that evolved here over millions of years.

Many of the co-evolutionary and mutually beneficial relationships that developed between plants, insects, birds and mammals have been fractionalized through the relentless introductions of ornamentals and pathogens that arrived with them.

The commercial landscape-design industry offers only a tiny fraction of native plants on both a wholesale and retail level.

Plans for landscape architecture plants seldom call for our local natives. Retail garden shops sell the same ornamental plants in San Francisco as they do in New York, New Orleans, Chicago and Seattle.

Many of these plants are chosen for their resistance to insects. However, those plants do the same thing for biodiversity in the east, west, north and south: nothing.

Similarly, plantings in the current San Francisco building developments are typically ecological wastelands, sterile and devoid of butterflies, bees and birds. They seem to be literally starving our wildlife.

Advancing our Uniqueness

However, there is hope: Plans to bolster the biological uniqueness of the San Francisco Peninsula are beginning to take shape within our local governments.

San Francisco County: 

In addition to having a Department of the Environment, the San Francisco Board of Supervisors passed the San Francisco Biodiversity Resolution in 2018. While resolutions are simply aspirations and not binding (like ordinances and regulations), this is a very good first step.

National Parks in San Francisco (especially the Presidio and Land's End) have been actively engaged in biodiversity restoration and are crucibles for best practices.

Within the San Francisco Recreations and Parks Department a small but dedicated staff in the Natural Resource Division primarily fight non-native invasives and try to keep rare plants and native grasslands from going extinct.

Currently, there is a City Biodiversity Working Group made up of land management agency representatives meeting regularly.

What is lacking and what we hope the city achieves soon is the creation of a Biodiversity Strategy and meaningful policies to address biodiversity loss in SF.

San Mateo County: 

Being less densely populated and larger in geographic scope, San Mateo county has more land-steward opportunities and responsibilities.

San Mateo residents enjoy relatively abundant nature with San Bruno Mountain, significant National Parks parcels, much of the San Francisco watershed (Crystal Springs) and the beautifully restored coastal county park Devil's Slide Trail.

The County Park Service includes a science-based Natural Resource Management group, which employs biologists.

Resource Conservation District (RCD), established by state law, serves as a local hub for conservation, "connecting people with the technical, financial and educational assistance they need to conserve and manage natural resources."

Yerba Buenos have created an evolving Biodiversity resource page that we hope you will use and share.

Please email us information that you think should be added to our biodiversity pages:

Native vs. Non-Native Plants

  • Native plants host more caterpillars than non-native plants. When birds nest, almost all baby birds feed on the caterpillars of butterflies and moths.
  • Baby birds do not live on seeds, or berries, or sugar water. Caterpillars are not optional for baby birds. If we don’t have caterpillars, we won’t have baby birds.
  • It takes 6,000 to 9,000 caterpillars, collected by both the busy chickadee parents over the course of sixteen days, to raise a nest of chickadee babies. And chickadees are tiny birds; just a third of an ounce.
  • How many caterpillars does it take to raise a woodpecker, a bird about eight times heavier? Where do these caterpillars come from?
  • Butterflies and moths have specialized so that they lay their eggs on just one or two host plants.
  • If we don’t have those host plants for butterflies and moths to lay their eggs on, there will be no caterpillars, and thus no baby birds.
  • Native plants—and lots of them—are what’s required.
  • Here is a comparison of how many species of caterpillars are attracted to native and non-native plants:
  • Natives:
    Oak – 270
    California lilac – 117
    Currants - 120
  • Non-Natives:
    Gingko – 0
    Crepe myrtle – 0
    Eucalyptus – 5

Entomologist Doug Tallamy says, “With property ownership comes the responsibility to choose plants wisely. The days when we could choose a plant just because it’s pretty in the garden are over. When we make that choice, we choose ecological destruction. Native plants are bird feeders. If we plant natives, we’ll have birds, butterflies, and native bees in our gardens.”