The Mountain's Plants and Wildlife
Much of what was responsible for the incredible richness and abundance of life in California has been removed or suppressed. The incessant fire regimes of the Native Americans manipulated the fabric of the landscape to encourage grasses and berry bushes to flourish for nourishment and discouraged the establishment of shrubs and small trees for ease of movement.
In the Bay Area the presence of tule elk, black-tailed deer, and antelope ensured that shrubs and grasses would be browsed and grazed and 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. In order to establish an economy they needed to build dwellings and infrastructure, create 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 coup-de-grace was delivered around 1750 with the introduction of non-native plants by seeds which were lodged in farm animals’ fur and hooves or were brought for agricultural food production.
Because of their proximity to the ocean and bay, and geographic orientation the San Bruno Mountains host an impressive number of plant and animal communities. Due, in part, to this marine influence the northern or southern limit of distribution of several plants occurs here. Within this relatively small area one can find these numbers of different species: 662 plants, 42 butterflies, 195 birds, 5 bumblebees, 30 ants, 24 mammals, 13 reptiles, and 6 amphibians. These numbers are supported by 10 different floral communities, each unique from one another.
The mountains are 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 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, sand-mat, mock heather, dune knotweed and CA whitlow-wort. The last population of Xerxes blue butterflies was extirpated from the Presidio dunes in 1943 by the Army Corps of Engineers.
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. This happened in Owl Canyon on June 22, 2008 and needs to happen in upper Devil’s Arroyo where the blue blossom last burned in 1964.
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.
The mountains provide habitat for 13 rare and/or endangered plants - go to 13 Rare Plants for a list. One of them—San Bruno Mountain manzanita— occurs naturally only on San Bruno Mountain. Rock cress (Fairly Endangered) and San Francisco wallflower (Limited Distribution) have pretty healthy populations on the main ridge and provide awesome eye-candy in the spring.
With the amount of development surrounding the mountains natural corridors have disappeared. This tends to limit the movement of quadrupeds on and off the mountains. Nonetheless, over the years a few animals that formerly lived here have managed to find their way back. This says as much about the lure of the habitat here as to why they chose to leave where they were born. Are outside environmental pressures forcing movement back to the San Brunos? In addition to the Brush and Jack Rabbit, Pocket Gopher, CA Ground Squirrel, Meadow Vole, Deer-Harvest-House and Parasitic Mouse, Feral House Cat, Gray Fox, Long-tailed Weasel, Raccoon, Striped Skunk, Trowbridge’s Shrew and Opossum, there have been sightings or confirmed populations of the Mountain Lion, Red Fox, Coyote, Black-tailed Deer, Badger, Bobcat, Eastern Fox Squirrel and Western Gray Squirrel.
Birds continue to move freely over and around the mountains and because they offer a large natural respite many of them migrate through or over-winter here. Rare Eastern migrants to visit here include Indigo and Painted Bunting, Gray Catbird, Yellow-shafted Northern Flicker, Tropical Kingbird, Northern Parula, Rose-breasted Grosbeak, White-throated Sparrow, Scarlet Tanager, and nine warblers—Black and White, Black-throated Blue, Blue-winged, Chestnut-sided, Lucy’s, Magnolia, Palm, Prothonatory, and Tennessee. Because the mountains lie between the bay and the ocean many local transients pass over or briefly land as they commute.
Butterflies define the importance of the health of the mountains’ habitats. No where else in this country or possibly the world would you find three endangered butterflies within 3400 acres. The Mission Blue, San Bruno Elfin and Callippe Silverspot butterflies cling to existence here despite the pressures of development and shrinking native habitat, which is being lost to natural scrub succession and invasive non-native plants. And imagine this, a fourth endangered butterfly was extirpated from the mountain by a fire in 1982 and its host plant is still abundant here. That would be the Bay Checkerspot. The magnificent Pipevine Swallowtail is found only in Firth Canyon in southern Brisbane and a couple miles northwest in lower Colma Canyon. Monarchs visit in the winter and nothing overwhelms the senses more than to be standing on a ridge top during a full-blown migration of Painted Ladies.
Work is being done to restore habitat for two other endangered creatures, the San Francisco Garter Snake and California Red-legged Frog. Some enhancements need to done but it’s quite a do-able project. And last but not least; the lichens here are outrageous!