September 4, 2008

Sudden Oak Death Takes Toll on Crystal Springs Trees

By Julia Scott

CRYSTAL SPRINGS -- David Moore is used to dealing with trees suffering the ravages of Sudden Oak Death. He knows the telling details: desiccated leaves and brown cankerous lesions oozing from the bark.

But even Moore, San Mateo County's parks superintendent, got a little depressed recently when his crew had to cut down more than 40 trees afflicted with the disease along some trails at Crystal Springs. He feared the trees were about to fall over and hit someone.

"We've had tree branches that fall off when you cut them. When they hit the ground they disintegrate into powder," he said.

For reasons nobody quite understands, the disease known as Sudden Oak Death has colonized the forests surrounding Crystal Springs Reservoir with greater brutality than other areas of the county that also contain trees susceptible to the disease, such as Woodside, Portola Valley, or the county parks in the hills above Pescadero. Biologists have detected only a handful of affected trees in those areas, whereas hundreds of trees are visibly affected throughout the Crystal Springs watershed -- and absent a cure, the number continues to increase.

Experts have noticed the problem gaining momentum in San Mateo County this year in particular, Moore said. The results are there for all to see.

"When you're in there on the trail and you see a dead tree, that's one thing. But if you're on Highway 280 and you're looking at the watershed, you see pockets, patches of dead trees. It's summer - - it's not like they're supposed to be dropping their leaves," he said.

One of the most insidious aspects of Sudden Oak Death, which is thought to have spread from imported European nursery plants in Marin and Santa Cruz counties in 1994, is that its symptoms do not always manifest themselves until the very end, which makes it hard to stop it from spreading to other trees. And once a tree has contracted the disease, it cannot be cured.

Sudden Oak Death affects tanoaks, coast live oaks, and bay laurel trees. No one has been able to prove how it spreads from tree to tree, but tainted water (in the form of blowing fog or raindrops) and transported soil are possible factors.

"It just all of a sudden strikes a tree. The foliage will wilt and it will brown out, and it's quite rapid from there," said Joe Naras, watershed resources manager for the San Francisco Public Utilities Commission, which owns Crystal Springs.

Short of clear-cutting whole sections of forest, there is not a whole lot that officials can do other than monitor the problem, Naras said. Right now he is particularly worried about dead branches raining on the heads of trail users and the fact that the dead trees provide excellent tinder for a forest fire. The Crystal Springs watershed has not had a large-scale burn in 50 years, and Naras says it is due.

Forest officials have one tool available to them in the fight against Sudden Oak Death: a product called Agri-Fos developed in the laboratory of Matteo Garbelotto, a forest pathologist at UC Berkeley. The product, applied either to the bark or the roots of a tree, is designed to boost that tree's natural immune system in the event it comes into contact with the disease.

The San Francisco Public Utilities Commission singled out a small grove of healthy tanoaks in a remote southwestern corner of the Crystal Springs watershed and applied the product this spring. It is too expensive to spray on an entire forest but can be used to protect choice species and heritage trees.

"It's probably the only intact tanoak grove we have left in the Bay Area," Garbelotto said. "It's a pity because it's a keystone, ecologically speaking. It provides large crops of acorns that sustain many species of wildlife."

Those losses may be irreversible, but Garbelotto thinks forests will redesign themselves to accommodate the changes over time.

"The oaks aren't going to disappear, but they're going to be rearranged. These forests are going to progress more toward Douglas fir or they're going to go back into grasslands, which is the way the Bay Area was 150 years ago," he said.

Reach staff writer Julia Scott at 650-348-4340 or julia.scott

Originally published by Julia Scott, San Mateo County Times.

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