Published 5/1/2025
Sprawling branches, spiny leaves and plentiful acorns fill the oak woodlands that lay across the Santa Cruz Mountains and support one of the richest and most biologically diverse habitats in the state. However, spread of Sudden Oak Death (SOD) is threatening the health of these ecosystems.
First detected in the Bay Area in the 1980s, SOD has spread dramatically since its discovery. SOD is caused by Phytophthora ramorum, a pathogen that thrives in cool, wet climates and spreads through moist winds, stream water and soil moisture. In the past decade, it is estimated that the disease has killed millions of oak and tanoak trees throughout coastal California and Oregon.
Since detecting SOD in Long Ridge Open Space Preserve in 2000, Midpen has committed to finding ways to track and prevent the disease. Every year, Midpen partners with the University of California, Berkeley’s Forest Pathology and Mycology Lab, and volunteer community scientists, to monitor Midpen preserves for the presence of SOD as part of the larger SOD Blitz Survey Project.
The data generated by the annual SOD Blitz helps inform researchers, land managers, and the public, so we can all collectively manage the spread and impact of this disease to the greatest extent possible.
The results of last year’s SOD Blitz revealed the spread of a new lineage of the disease throughout the region and in Midpen preserves. This new lineage is active in warmer and drier conditions, allowing it to spread more effectively outside of the rainy season and potentially into new areas.
“While the detection of this new SOD lineage is unfortunate news, it is a testament to the power of volunteers and community science,” Midpen Ecologist Arianna Camponuri said.
This month, the annual SOD Blitz is looking for volunteers in the Bay Area to help identify SOD symptoms in California bay laurel trees, record data and collect and submit symptomatic leaf samples for testing to determine whether or not the trees have been infected by the disease.
Those who would like to participate in surveying Midpen preserves will need to attend a mandatory one-hour training on the morning of Saturday, May 31 at Midpen’s administrative office in Los Altos. Trained volunteers will then have the weekend to visit select Midpen preserves and collect valuable data and leaves in support of the project.