From giant Sequoias in the east to wind-swept Monterey cypresses in the west, California is defined by its trees, so a surge this year in oak deaths is cause for consternation across the Bay Area.
A recently completed survey shows 376,000 dead oak trees across the coastal regions impacted by sudden oak death, a pathogen that develops on host plants ranging from the bay laurel to ornamental rhododendrons.
Last year’s survey, like this one aided by volunteers led by scientists at UC Berkeley and the California Oak Mortality Task Force, found 38,000 dead trees across a much smaller area.
“It’s huge. It’s really huge, but it’s not the largest die-off we’ve had,” said Katie Palmieri of the task force.
That came in 2007 after extremely wet springs the previous two years left 830,000 trees dead. The fewest number of dead trees were counted in 2010, when 2,700 trees died after a dry spring in 2009.
In the current survey, the highest rates of new infection in oaks and the beech-family member tanoak were discovered in the Carmel Valley south of Monterey and in the areas around Saratoga west of San Jose. But infected trees also were found inside San Francisco’s Golden Gate Park, and in Santa Cruz and the East Bay.
“When individual trees die it’s sad, but when groups of trees die it becomes a huge concern for fire hazard, particularly in the Bay Area, where it’s so developed and we have a wildland-urban interface,” said Tom Smith, a forest pathologist with Cal Fire.