Sudden Oak Death Update, California Aerial Survey

Oaks ‘n’ Folks – Volume 20, Issue 1 – January 2004

The USDA Forest Service and California Polytechnic University, San Luis Obispo are currently cooperating on a broad-scale aerial survey to locate new areas with infestations of Sudden Oak Death (SOD). The objectives of the aerial survey were to identify from the air and accurately map host tree mortality in areas at risk to Phytophthora ramorum, the fungus responsible for causing SOD.


The area to survey was determined based on three factors: 1) whether or not a given county was currently under quarantine, 2) the proximity to existing confirmations, and 3) the level of predicted risk. The survey focused on areas at risk to the disease generally outside those counties with confirmed infestations. However, counties under quarantine and with a limited distribution of confirmed disease centers were also required to be surveyed. The methodology to model risk was developed at Sonoma State University (Ross Meentemeyer) and combined variables such as climate, proximity to existing confirmations, and the abundance of host plant species as determined by CALVEG statewide vegetation data, USDA Forest Service Pacific Southwest Region Remote Sensing Lab. Those areas that were determined to be at risk in the moderate to very high categories were prioritized for survey.

Aerial observers were to map tree mortality, photograph, and identify species as surveyed from the airplane. Immediately following the survey, mapped areas were prioritized for ground visits with the goal to visit as many as economically feasible. Approximately 400 distinct sites were mapped during the aerial survey. Initially, 25 percent of those areas have been prioritized for field visits. The first priority for field visits was given to sites occurring within uninfested counties and immediately adjacent to infested counties. Within infested counties, the second priority was given to sites at the greatest distance away from an existing confirmation – the reason being that a new find would be more significant the further away it is from a known infestation. Field visits to every site had to be coordinated with individual landowners, each county Agricultural Commissioner’s Office, and other public agencies in order to obtain access.

In addition to initial visits to sites mapped during the 2003 survey, revisits were planned for specific sites mapped during a similar 2002 survey. These revisits were necessary in areas observed to be symptomatic by last year’s field crew, but where samples had yielded inconclusive results in laboratory tests. Visits to areas not checked in 2002 and to lower priority areas mapped in 2003 will also occur, but the exact number and location is funding dependent. Beyond the current prioritization scheme, additional visits will likely be conducted by a combination of California Department of Food and Agriculture, University of California Davis, County Agricultural Commissioners, USDA Forest Service, and Cal Poly San Luis Obispo.


The aerial survey portion of the project was initiated May 29, 2003 and continued into July. Approximately 10,000 miles were flown using a fixed-wing aircraft covering 13,000,000 acres of host habitat. Counties flown in northern California include: Del Norte, Humboldt, Mendocino, and portions of Siskiyou, Trinity, Tehema, Glenn, and Lake. Counties flown in southern California include: Monterey, San Benito, San Luis Obispo, Santa Barbara, and portions of Ventura and Los Angeles. Additionally, a band of hardwood along the foothills of the Sierra Nevada was also flown over portions of Kern, Tulare, Fresno, Madera, Mariposa, Tuolumne, Calaveras, Amador, El Dorado, Placer, Nevada, Yuba, Sierra, and Butte counties. Approximately 400 sites were mapped using state-of-the-art digital mapping equipment developed by the USDA Forest Service Forest Health and Technology Enterprise Team.

In addition to the fixed-wing flights, helicopter flights were conducted into August to acquire even more accurate geographic coordinates. These helicopter flights were limited to five days over portions of Mendocino, Del Norte, Humboldt, Santa Barbara, San Luis Obispo, and Kern counties. A global positioning system (GPS) was used to navigate to approximately 25 percent of the sites mapped. Once there, the GPS was used to pinpoint the precise coordinate where often only a few trees were mapped. Many of the areas mapped are in very remote, rugged terrain with dense vegetation and difficult to access on the ground. These improved GPS coordinates aided navigation on the ground and proved to be a real time saver for field crews.

Preliminary Results

Field visits have been completed for portions of Humboldt, Mendocino, Trinity, and San Benito, and all sites mapped in Del Norte and Siskiyou counties. Lab results are negative for the first 16 sites sampled in Mendocino County and pending for all other counties. Over the course of the next few months, results will trickle in for the other counties where samples have been collected. These results will be provided to county agricultural commissioners and to the statewide database maintained at UC Berkeley. General information on Sudden Oak Death, past surveys, maps and existing confirmations, and the results of this survey (to be posted soon) can be found at

Primary folks directly involved in planning and implementing the 2003 Aerial Survey and field visits are Lisa Levien, Jeff Mai, and Bill Woodruff, USDA Forest Service; Dr. Wally Mark and Amy Jirka, Cal Poly San Luis Obispo; credit for lab diagnostics for our samples can be given to the Rizzo Lab at UC Davis and the California Department of Food and Agriculture.

Lisa Fisher
USDA Forest Service,
in cooperation with State and Private Forestry and California State Polytechnic San Luis Obispo