Biodiversity on San Bruno Mountain is robust with 662 plant species, 42 butterflies, 195 birds, 5 bumblebees, 30 ant species, 24 mammals, 13 reptiles, and 6 amphibians all living together on the mountain. These numbers are supported by 10 different floral communities, each unique from one another. Some indigenous plants to the mountain are shown below.
The Native Americans who lived on San Bruno Mountain before the Europeans came had a very close relationship to the environment that surrounded them and that they depended on for survival. They often manipulated the landscape with controlled fires that encouraged grasses and berry bushes to flourish. This provided Native Americans with nourishment and discouraged the establishment of shrubs and small trees for ease of movement and hunting. Many native plants thrive once burned, with seeds that are sometimes many years old opening only once burned.
In the Bay Area the presence of tule elk, black-tailed deer, and antelope ensured that shrubs and grasses would be browsed and grazed. They in turn attracted predators such as mountain lions, bobcats, coyotes and wolves. The state’s largest population of grizzly bears was happy to consume a vast array of immobile provisions, be they berries, oysters or clams. With a small investment of energy they could dine on fish, animals or dig for grubs.
When Europeans were introduced into this rich ecosystem everything changed. They built dwellings, infrastructure, and created farms for agriculture and animal husbandry. Those activities devastated an extremely diverse and complex landscape that miraculously still exists although to a much lesser degree. The introduction of non-native plants by seeds which were lodged in farm animals’ fur and hooves or were brought for agricultural food production has had a particularly pernicious effect. Many of these plants have no natural predators outside of their native ecosystems and can overtake native plants that have co-evolved over thousands of years.
San Bruno Mountain Manzanita
The mountain is home to the largest remaining remnant of Northern (Franciscan) Coastal Scrub that once covered most of the peninsula and San Francisco. It’s a unique collection of plant characters that includes coyote brush, CA sagebrush, bush monkey flower, poison oak, lizard tail, snowberry, and coffee berry.
The mountain's seasonal streams and seeps support plants and trees that make up the Central Coast Riparian Scrub community. It’s dominated by arroyo and Sitka willows and their hybrids with quite a bit of wax myrtle, coast red elderberry, self-heal, and ferns and horsetails.
As recently as 1940, the western portion of the northern peninsula was predominantly sand dunes. This wind-blown habitat, Central Dune Scrub, supported yellow and blue beach lupine, spine-flower, lessingia (endangered), sand-mat, mock heather, dune knotweed and CA whitlow-wort.
Blue Blossom Chaparral is a fairly closed community until it begins to senesce after 35-40 years allowing other scrub species to replace it. Due to its high moisture content, it takes a very hot fire to burn it and its seeds are protected by a hard cover that requires fire to germinate. After a fire, the community rejuvenates and begins a new cycle.
California Fescue Valley Needlegrass Grassland occurs on drier south and southwest-facing slopes in thinner soils. Although purple needlegrass is the dominant species other grass species include California melic, June grass, blue wild rye and San Francisco blue grass along with a vast array of wildflowers. Grasslands are the most productive habitats. They contain the greatest plant diversity, which attracts insects, birds and animals. On the other hand, Coastal Terrace Prairie exists as grassland with a more northerly exposure and subject to marine influences. Fog and wind are companions to Pacific reed grass, California oat and hair grass, and California, Idaho and red fescue. Both habitats provide the host plants to the mountains’ endangered butterflies.
Valley Wild Rye Grassland is very rare and due to the thick rhizomatous roots of wild rye grass. It has few associated grasses. Also scattered in distribution is Freshwater Marsh habitat. The most accessible marsh is part of the saddle along the Bog Trail where it is fed by Colma Creek, a few seeps and springs, and winter rains. With many species of rushes and sedges, willows, creek dogwood and ever-increasing stands of scrub this relatively small area contains about a fifth of the plant species on the mountains.
Freshwater Seep: The San Bruno Mountains have an astounding number of seeps. Most seeps flow year round and the rest require very little winter rainfall to erupt from the ground. Willows, rushes, sedges, horsetails, creek monkey flower, self-heal, and lady and chain ferns are common around seeps.
Coast Live Oak Woodland is prevalent in and around Brisbane but is mostly limited to Buckeye and Owl canyons. The most common species are coast live oak, buckeye, California bay, holly-leaved cherry, hazelnut and toyon.
ENDANGERED AND RARE PLANTS
The following plants found on San Bruno Mountain are all endemic to California (found only in California) and are considered to be rare. Many are listed as endangered by the California Native Plant Society (CNPS). More information about how plants are listed can be found at the CNPS Rare Plant Program site.
The CNPS has created 5 lists which attempt to categorize plants based on degrees of concern. The rare plants below fall into 2 categories:
List 1B: Plants that are Rare, Threatened, or Endangered in California and Elsewhere
List 4: Plants of Limited Distribution - A Watch List