I had traveled through Claremont Canyon several times before its plants caught my attention. Yellow leaves on bigleaf maples (Acer macrophyllum) many Novembers ago alerted me that Claremont Canyon contained more than a resort hotel and an avenue up to Grizzly Peak. Once I saw this unusual sprinkling of fall color in Oakland, then more native plants and people who care for them emerged. On return trips, I changed my perception of this changing mix of plant communities next to a dense urban footprint.
Between Grizzly Peak Boulevard and Ashby Avenue, Claremont Canyon stretches through a mosaic of coastal sage scrub, live oak–bay woodland, and riparian forest. Property boundaries divide the canyon’s open spaces into another mosaic, with the largest pieces held by the University of California, the East Bay Regional Park District (Claremont Canyon Regional Preserve), and the City of Oakland (Garber Park). In the upper part of the Claremont Canyon area, pandemic hikers explore trails leading up Telegraph Canyon from the UC Ecological Study Area between Claremont Avenue and Grizzly Peak Boulevard, but also through Gwin Canyon leading up and southward from a trailhead on the canyon’s opposite side.
In much of the UC Ecological Study Area, native plants persist as an understory beneath Tasmanian blue gum (Eucalyptus globulus), especially in the upper canyon areas. The East Bay Regional Park District removed some large eucalypts lower in the canyon near the Stonewall-Panoramic Trailhead, uncovering patches of naked-stem buckwheat (Eriogonum nudum), occasional blue elderberry bushes (Sambucus nigra ssp. caerulea), plus emerging coast live oak (Quercus agrifolia) and bay (Umbellularia californica) trees.
The steep trails on the south-facing slopes of Claremont Canyon resemble smooth cement in this drought year, nearly a polar opposite to the sticky morass of these same clay trails in a wet January. In November, only arroyo willows (Salix lasiolepis) and green tips on stinging nettles (Urtica dioica) reveal that moisture lies beneath these trails much of the year.
Poison oak (Toxicodendron diversilobum) sheds most of its leaves earlier in the fall, leaving only a few red remnants hanging onto its branch tips. If you do not see leaflets of three to let be, then look for—and avoid—shrubs with smooth, grayish-brown twigs joining larger stems at roughly 45-degree angles. As I scowl at the greenish-tan berries hanging from poison oak twigs, a song sparrow flies out to sing a proprietary song near its autumn food. Birds suffer no adverse reaction to poison oak.
In late October 1991, a dry year not so different from 2020, Claremont Canyon was scorched by the north end of one of the largest “wildland-urban interface” fires up to that time. That burn, often called the Oakland Hills Firestorm, devoured much of the south side of the canyon, but rebuilding and regrowth have concealed many traces of the fire.
The ferocity of the 1991 fire had a familiar contributor, Tasmanian blue gum. About a century ago, a property developer planted and then abandoned blue gum trees in an unsuccessful commercial forestry project. Since 1991 the three largest public landowners in Claremont Canyon have submitted and rewritten proposals for “fuel reduction” that center on competing ideas of how best to control the invasive tree overstory. You can read the most recent proposal by UC Berkeley, and the ensuing comments.
While the 1991 fire was the motivation for fire hazard vegetation management in Claremont Canyon and the East Bay Hills generally, it also spurred the creation of one of the area’s most dedicated stewardship organizations. In 2001, local citizens founded the nonprofit Claremont Canyon Conservancy, whose mission is to catalyze the long-term protection and restoration of the canyon’s natural environment and advocate for comprehensive fire safety along its wildland-urban interface. The conservancy’s website presents a map of the canyon’s open spaces, useful both for hiking and understanding fire management proposals.
In contrast to the canyon’s sunny south-facing side, on the north-facing side bigleaf maples hang over the roadside creek flowing below the slopes until it plunges into a culvert near the Claremont Hotel. As I cross Claremont Avenue uphill from Stonewall Road, I find myself in the denser shade of coast live oaks, maples, and bay trees next to the trailhead for Garber Park.
Garber Park occupies about 13 acres opposite the lower canyon of EBRPD’s Claremont Canyon Regional Preserve. Garber Park Stewards, a community group dedicated to safeguarding the park’s native wildland resources while reducing the risk of wildfire and improving the trail system, built and maintains the trails that start from the park’s Claremont Avenue entrance. A climb up the entrance trail leads past a slope of sword ferns (Polystichum munitum) and western wood ferns (Dryopteris arguta) underneath bay trees, oaks, and blackwood acacias (Acacia melanoxylon). Hand-built fascines (long bound bundles of sticks) shore up the trail past a steep arroyo, which leads to steps by the remnant outdoor fireplace, built before World War II. Garber Park Stewards’ website offers a brochure with a self-guided trail map, a list of events (in times when it is safe), and even an explanation of how fascines work in erosion control. More steps lead into the Garber Park loop trail, through a mixed woodland of coast live oaks, California buckeyes (Aesculus californica), and more bay trees.
Research into the pathogen that causes sudden oak death (Phytophthora ramorum) has raised concern about California bay trees as tolerant harbors of the disease. Several heritage oaks have died from this pathogen in Garber Park, with younger oaks, buckeyes, and blue elderberries filling in some of the void. Garber Park Stewards cleared some bay tree saplings to minimize pathogen spread, but they have also flagged some mature bay trees to monitor Phytophthora spread for the California Oak Mortality Task Force.
Exotic trees also die from pathogens, such as the recent deaths of large numbers of blackwood acacias from pistachio canker caused by the fungus Leptosillia pistaciae. The “fall colors” of blackwood acacias in Joaquin Miller Park and nearby in North Oakland reveal dead, not deciduous, trees. Again, microbial spread has outpaced public agency “fuel management” proposals.
In whatever way property managers address this canyon’s plant life and fire history, I value its public open spaces for their remaining biodiversity. Kay Loughman has photographed and cataloged photos of taxa from several kingdoms that live in Claremont Canyon. I enjoy her website for its collaborative nature and her diligent organization of web pages. There is much left to see in Claremont Canyon, but here is much to start with.
— Janet Gawthrop, Field Trips Chair, CNPS East Bay Chapter