San Bruno Mountain Fire, June 2008

This was a generational event, a pyrotechnic three-ring circus of enormous importance and magnitude. On Sunday evening, June 22, a wildfire that eventually reached five alarms erupted just northwest of the town of Brisbane in Buckeye and Owl Canyons. It will take a few years for this portion of San Bruno Mountain to sort out the effects of the fire and the process will be very educational and probably frustrating as well.

The two adjacent canyons offer different habitats and the fire affected each in a different way. Buckeye Canyon, aptly named for the dense riparian forest that inhabits the ravine, suffered little damage except for the two ridges that define it. The heavily-brushed Owl Canyon, on the other hand, was literally vaporized except for a lightly forested area on its north ridge. California Department of Fire reported 100-foot flame lengths as mature coastal scrub heartily burned. Both canyons burned from bottom to top and the fire jumped the road along the main ridge and headed down the western flank toward South San Francisco. The wildfire consumed about 300 acres.

Grassland fires burn cooler because the leading flame edges move faster and the fuel loads are lighter, so deep-rooted native bunchgrasses generally survive wildfires. It is areas where hot-burning scrub drove flames into the grasslands that are cause for concern. If the grasses were root-killed due to prolonged exposure, they are not coming back.

Even with intensive management we will probably lose those patches to weeds.

This fire was the third wildfire on the mountain since late April. One was extremely small and the other managed to threaten a home in an area prone to near-annual fires in southern Brisbane near the South City border along Old Bayshore Road. Although fire of any magnitude is significant in the mountain’s wildlands, the Buckeye-Owl fire is the largest event in many decades. Two hundred residents were evacuated but no personal property was damaged.

Fire is an adaptive management tool that, along with natural grazing and browsing, has been missing in promoting healthy grasslands that once covered much of the lower elevations in California. Grasslands are the most productive habitats, providing the greatest range of food and plant diversity. Two of the three species of endangered butterflies, the mission blue and callippe silverspot, use plants that thrive in healthy grasslands. The threats to native grasslands are invasions of non-native grasses and forbs, and succession by native and invasive shrubs. Succession has been claiming almost fourteen acres of grassland per year on the mountain.

Fortunately the fire scrubbed the canyons pretty clean of just about everything. This gives the land a shot of nutrients to recharge the soil and awaken seedbanks that have long been lying dormant. Unfortunately, invasive grasses like wild oats (Avena spp.) and quaking grass (Briza maxima) will come back along with a host of pioneer invasive forbs like Italian thistle (Carduus pycnocephalus) and Australian fireweed (Erichtites spp.).

The real opportunity lies with the removal of large stands of coastal scrub. These shrubs are adapted to fire and those not outright killed by the fire will begin stump sprouting new growth within a month after the fire. If designated plots of scrub were removed by hand, it might be possible to encourage grasslands to return. The fire scorched two callippe silverspot monitoring transects and burned several acres of callippe silverspot and mission blue host plants, California golden violet or johnny-jump-up (Viola pedunculata) and silver lupine (Lupinus albifrons), at the height of callippe flight season. Many callippe were observed flying and mating immediately after the fire. Life went on.

Jake Sigg and Doug Allshouse are planning a series of field trips to Buckeye and Owl Canyons to observe and discuss the progress of habitat recovery.

Posted in Local Ecology.

Doug Allshouse

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