October 19th, 2012 by

The clock is ticking for oaks in northern California. The 2012 U.S. Forest Service aerial survey reveals that cases of sudden oak death (SOD) — caused by the pathogen p. ramorum — have increased tenfold in the last year. The disease is fatal for tanoaks and a number of oak species and also is damaging to other trees, including coastal redwoods.

Sudden Oak Death mortality of tanoak in Marin County, California

Sudden Oak Death mortality of tanoak in Marin County, California. Credit: USFS Region 5/Flickr

The first known incidents were in the 1990s in European nurseries, from which the disease spread into wild areas in the Netherlands and England. The first documented case on this side of the pond was in 2001. How exactly it got here is still unclear, but the aggressive rate at which it’s spreading is hard to miss. Last year, there were 38,000 new cases across 8,000 acres. This year? Nearly 376,000 cases across a whopping 54,000 acres. The pathogen thrives in the wet coastal tanoak and redwood rainforest and so far is confined mostly in northern California, with some pockets in Oregon, Washington and British Columbia. However, the disease tends to crop up in nurseries, where the ideal conditions can be mimicked, creating potential for it to spread outside its current range.

So, what are the consequences if these oak die? A major change in species composition will affect ecosystem functioning in many ways. According to the California Oak Mortality Task Force, food sources for wildlife will be lost, water quality could decrease and wildfires could become more frequent and more intense. In addition, another alarming finding of the most recent survey is that SOD is becoming more common in urban areas as well, including a few confirmed cases in San Francisco’s Golden Gate Park. If the disease becomes common in the urban forest, it could affect neighborhoods’ air quality, water quality, housing prices and more.

As with many things, it seems the solution to preventing the spread of this horrible disease lies in communities coming together. The University of California-Berkley is spearheading community-based “SOD Blitzes” to educate citizens about SOD and get people involved in detecting and tracking the disease. These “citizen-scientist surveys” have helped to create a detailed map of the pathogen’s distribution, mainly by looking at the leaves of California bay laurels, p. ramorum‘s preferred host. If the pathogen can be detected before it spreads to oak trees, successful management may be possible. It’s a race against the clock.