California’s Oak Trees at Risk: New Sudden Oak Death Strains Discovered

The rainy season in California brings much-needed water to the state, but it also often results in floods, mudslides, and falling trees. In addition to these hazards, a new and growing threat has emerged in the form of sudden oak death disease, a devastating plant pathogen that has been killing millions of trees for over two decades.

Since its detection 20 years ago, sudden oak death has claimed the lives of up to 50 million oak and tan oak trees, with more than 150 million trees affected by the disease. The pathogen, which starves the trees to death, has spread across 16 coastal and near-coastal counties, from the Oregon border down to Monterey County in the south.

UC Berkeley Professor Matteo Garbelotto, one of the researchers who discovered the original pathogen strains, notes that the Bay Area now faces a more dangerous situation with two new strains of the disease. “The NA2 lineage is more infectious than the original strains and thrives in warmer climates,” he explained, which makes it particularly concerning for California, where the climate is increasingly prone to higher temperatures.

These new strains of the disease have already been detected in the East Bay and the Peninsula. Professor Garbelotto is particularly concerned because of the potential for more severe damage in consecutive rainy seasons. “Every time we have a rainy year, the situation becomes more serious. And this year, we’ve already had two years of heavy rain, which increases the likelihood of widespread infection,” he said.

Weather plays a key role in spreading the pathogen. According to Environmental Horticulturist Steven Swain from the UC Cooperative Extension in Marin, “The pathogen blows around in wind-driven rain, which is how it moves through the area.” The new strains appear to be more dangerous, with the ability to penetrate oak tree trunks—a rare and concerning ability for pathogens.

The spread of this pathogen is unpredictable. “The numbers are ever-changing because the disease is always on the move,” Garbelotto added. Infected trees pose an increased fire danger, as well as risks from falling branches or complete collapse. The loss of these oaks also affects local wildlife, as many species, including squirrels, jays, bears, and deer, rely on acorns for food. The loss of these trees disrupts the ecosystem, threatening the survival of various species.

If the disease continues to spread unchecked, the face of California’s landscape could change permanently, with dire consequences for both the environment and the wildlife that depend on these trees.

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Alton Walker

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