California is a magnificent state, with some of the most beautiful scenery in the world. It is also home to some of the most magnificent trees in the world, the giant Redwoods. These trees have survived for millennia, fending off attacks from diseases and fire. Now they face a new threat, the combined effects of sudden oak death and fire.

Usually resistant to the effects of wildfires, California's coast redwoods are now burning as fast as other trees. Why?

To find answers, plant pathologist David Rizzo of the University of California at Davis (UC Davis) and colleagues monitored more than 80,000 hectares of forests near Big Sur, Calif. In their plots, tanoaks, California bay laurels and coast redwoods grow.

The study began in 2006. "In 2008, almost half our plots were burned by wildfires that lasted the better part of a month," says Rizzo.

That was the beginning of the end for many coast redwoods, surprising researchers who expected the trees to be fire-proof.

The key to the redwood deaths, discovered Rizzo, Margaret Metz and Kerri Frangioso of UC Davis, along with Morgan Varner of Mississippi State University and Ross Meentemeyer of North Carolina State University, lies in the sudden oak death pathogen.

"If redwoods didn't live in forests affected by the disease," says Metz, "they could withstand fires just fine."

The biologists recently reported their results online in the journal Ecology, published by the Ecological Society of America.

After the fires were under control, the scientists returned to their study plots. Half had long been infested with the sudden oak death pathogen half had been spared. The redwoods' mortality risk, it turned out, was four times higher in the sudden oak death plots as in healthy plots.

"The disease likely created more fuel for wildfires as dead tanoak branches fell," says Rizzo. "The loss of the oaks also would have decreased the amount of shade, drying out the forest and turning it into a tinder box, one not even redwoods could survive."

Source: ENN