After a few seasons of prime conditions and exponential growth, the pathogen which causes sudden oak death has exploded in the California oak tree population.
A recent study by the U.S. Forest Service — aided by UC Berkeley and the California Oak Mortality Task Force — found nearly 376,000 dead oak trees in areas struck by the pathogen.
Last year, 38,000 dead trees were found, albeit in an area much smaller than that surveyed this year.
The culprit is thought to be sudden oak death, borne from a pathogen that resides in neighboring vegetation.
The pathogen was introduced to California about 25 years ago. While researchers are still unsure of how it got here, but it is known to get under tree bark and destroy the tree’s living outer layer which carries nutrients.
Despite the sudden drop in trees, it’s not be the worst in recent years, Katie Palmieri of the California Oak Mortality Task Force told KTVU:
“It’s huge. It’s really huge, but it’s not the largest die-off we’ve had.”
That title is left to 2007, when a rainy spring fostered growth of the pathogen. 830,000 trees died that year.
The pathogen is quick and efficient and is present in 14 counties in California. It also develops in Oregon.
Only the Sierras have been safe from this tiny-but-deadly bug’s wrath. It is thought the pathogen and sunlight do not work well together, making it more difficult for the bug to spread.
That’s no hindrance to the tree-killer, which is spreading its reach more and more each year. Scientists fear that if it continues its expansion, it could wipe out a more expansive area of trees.
The largest number of dead trees have been found in rural places like the Carmel Valley, but sick and dead trees have also been found in urban settings, Golden Gate Park being one of them.
A surge of dead trees could also mean fire hazards for surrounding residents, said Tom Smith, a forest pathologist at CalFire:
“When individual trees die it’s sad, but when groups of trees die it becomes a huge concern for fire hazard, particularly in the Bay Area, where it’s so developed and we have a wildland-urban interface.”
Trees can be protected by injecting a solution of phosphites, but cannot be revived once they are dead.
Treatment must also be used as a preventative measure. That means all the trees showing signs of spotty leaves, a symptom of the pathogen, will be immune to the treatment.