California Redwoods in Danger?

DAVIS, CALIFORNIA--A disease that has ravaged California's majestic oaks may be attacking a tree that is as much the symbol of the state as the Golden Gate Bridge and the Sierra Nevada Mountains: the coast redwood tree. But the announcement came before scientists were ready to confirm it, or make any predictions about its impact. Scientists say the resulting furor is unnecessary and the disease may yet turn out to pose little threat to redwoods.

Phytophthora ramorum, the fungus responsible for the disease "sudden oak death," has killed tens of thousands of coastal oak trees from Big Sur, California, to southern Oregon (ScienceNOW, 8 August 2000). It can infect more than a dozen other tree species, but certain oaks suffer a rapid irruption of blackening cankers that can kill in about a year. Plant pathologists have been struggling to learn where the disease came from, how it spreads, and what might be done about it.

Now, Ken Bovero, a tree-care specialist from Marin County, just north of San Francisco, has announced that he found cankers resembling sudden oak death on a 3-meter-tall coast redwood tree in Mill Valley. A private laboratory confirmed the tree contained Phytophthora, but could not identify the species. However, no other forest pathogen causes the symptoms that this tree has, Bovero says. "There's no question in my mind" that it is the same organism that causes sudden oak death, he says.

But forest pathologists insist more testing is needed: The pathogen in Bovero's tree may not be P. ramorum, and if it is, there is no reason to believe it will cause the epidemic seen in oak trees, says David Rizzo of the University of California (UC), Davis. In fact, it's not clear that the fungus in Bovero's tree is the cause of the tree's disease. Rizzo and Matteo Garbelotto of UC Berkeley have been testing redwoods for several months. "Obviously we were worried that it would get into redwood because we started testing it months ago."

Bovero's revelation was premature, Rizzo says. Everett Hansen, a forest pathologist at Oregon State University in Corvallis, agrees: "The evidence to date would be totally unacceptable in any scientific journal." Bovero says he told the press because scientists are moving too slowly on the question of whether the disease strikes redwoods.

Related sites
Garbelotto lab page
More about sudden oak death
Monitoring sudden oak death in California

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