Decimating Tree Disease Spreads to Redwoods -- and Beyond?
The organism responsible for killing tens of thousands of oaks in California has been found among redwood trees. If confirmed, the presence of Phytophthora ramorum, the fungus associated with Sudden Oak Death, has dire implications for both California and the rest of the nation.
The disease already threatens to forever alter the California landscape by eliminating most oaks. But the destruction of redwoods would be an ecological and economic catastrophe. And no one is sure what will prevent the spread of this dreaded tree disease across the continent and even the globe.
Arborist Ken Bovero found the disease when he was called to a Mill Valley, California home to look at a dying redwood, which he removed to prevent it from falling on the home. Suspecting Sudden Oak Death, he ordered a series of tests at a private lab. After receiving preliminary confirmation that the virus was Phytophthora ramorum, Bovero contacted the University of California at Berkeley to request additional tests.
Shortly thereafter, researchers at Berkeley decided to release their preliminary findings that Sudden Oak Death symptoms had been observed in redwoods in September, and that genetic tests confirmed the presence of the virus.
Bovero had been one of the first to spot that something was wrong with California oaks a decade ago.
"I first identified what turned out to be Sudden Oak Death in a few trees in 1991. It didn't really take off until El Nino, when torrential rains and terrific winds might have moved the spores around."
Sudden Oak Death was not labeled until 1995, and the Phytophthora ramorum fungus was pinpointed about a year ago. Scientist are unsure exactly how the fungus spreads. Dispersal could be through the air, water, or human transporting infected wood products or plants.
The finding of Sudden Oak Death among the redwoods is part of a catastrophe that has been unfolding across the nation, according to Charles Little, contacted at his home in New Mexico. Little is author of The Dying of the Trees (1997), which describes trees stressed from pollution and other factors dying across the American landscape.
"This oak fungus is a serious as anything in my book. It is especially bad since oaks are emblematic of the California landscape, and redwoods are the other tree that is emblematic of California. If true, this will drastically change a wonderful landscape."
The fungus associated with Sudden Oak Death was finally identified until June of 2000. It typically attacks tanoak, coast live oak, black oak and Shreve's oak. But recently Phytophthora ramorum has turned up in surprising places. It is moving into oaks in drier, non-coastal areas where the climate was thought to be a limiting factor. It has infected oaks in southwestern Oregon, and was found on ornamental rhododendron shrubs in Germany and in the Netherlands.
Sudden Oak Death has also infected several new species besides redwoods. The fungus has been identified in ornamental rhododendron, huckleberry, bay laurel, madrone, "dawn" viburnum, California buckeye, manzanita, bigleaf maple, western azalea -- and California rhododendron, possibly the source of the infected European shrubs. Not all of these hosts are killed by Sudden Oak Death.
There is more: pathologist Dr. David Rizzo of UC-Berkeley conducted a study which showed that red and pin oaks -- very common in the Midwest and the East -- seem even more susceptible to Sudden Oak Death than western trees. It is possible the problem could spread to these regions, according to Rizzo.
Other regions have already to taken steps to keep out potentially infected California products. Oregon enacted a 90-day quarantine of oak products from California. In March of 2001 the Canadian Food Inspection Agency took action to restrict the import of California nursery products.
The finding of the fungus responsible for Sudden Oak Death among California redwoods has profound implications for increased risk in spreading the disease widely, since California redwood forest products are shipped all over the world. It also means that non-hardwoods species may be vulnerable to Sudden Oak Death.
But Ralph Zinagro, an arborist who like Bovero works with diseased redwoods and oaks, thinks there is more to the story than a fungus.
"These trees have survived thousands of years of horrific rain, and heat in the summer," said Zinagro. So why are they dying now? Trees weakened from stress are succumbing to pests, he said.
"While air pollution has gotten better for humans, it's not good enough for trees. In California it's mostly nitrate deposition that's robbing them of nutrition. They're starving."
Zinagro said he has good results with some treating trees with nutrients.
"Unless we wake up this is going to get worse. Worse and worse."
Jeff Gibbs is a freelance writer living in Cedar, Michigan. He is working on a documentary about tree health.