Posted by: Stan Russell | April 12, 2013

Big Sur Sudden Oak Death Update 2013 University of California, Davis

Hello Big Sur!

Kerry Frangioso of the Big Sur, Sudden Oak Death Project from the University of California Davis has sent us an research update on Sudden Oak Death.

Here it is in text and in PDF format (attached)



Big Sur Sudden Oak Death Update 2013 University of California, Davis

The Big Sur Sudden Oak Death (SOD) network of forest monitoring plots remains a major research priority of the Rizzo Lab (UC Davis, Plant Pathology Department), and we thank you for your continued collaboration in this project. We did not collect field data in Big Sur in 2012 while we studied SOD spread in other parts of northern California. The break from field collections in Big Sur allowed us an opportunity to analyze data already collected and work on publishing papers. With this year’s update we would like to give you a summary of recent findings that have come out of this project.

One publication titled, “An emergent disease causes directional changes in forest species composition in coastal California” examined forest composition across the entire network of 280 plots, which was established in 2006 & 2007. We found differences in infested and uninfested plots due to both historical differences and disease impacts. Forests containing more and larger stems of tanoak and bay trees were significantly more likely to become infested with the pathogen responsible for SOD1. Both tanoak and bay are the pre-dominant spreaders of the pathogen, so canopies dominated by these trees made it easier for pathogen spores dispersed across the landscape in large rainstorms to be intercepted and establish infection sites. Infested locations show large changes in species composition over just a short time period, most notably due to the loss of dominant, overstory tanoak1.

A second publication tracked what happened to the pathogen during and following the fires of 2008. Data collected post fire during the summers of 2009 & 2010 showed that the fires suppressed the pathogen but did not eradicate it. In 2009, we recovered the pathogen in ~20% of the plots that had previously been infested, and this percentage increased over time (40% in 2010). Recovery success was linked with both pre- and post-fire bay density, the predominant driving mechanism in the spread of SOD3. An interesting aspect of this project was that we found other species of Phytophthora (P. nemorosa and P. pseudosyringae) in burned plots where we had never found them before (although they were known to exist in the Big Sur area). These other species are also thought to be non-native introduced pathogens; however they do not seem to cause as much damage as P.ramorum. A new PhD candidate in our lab intends to start exploring this phenomenon in the summer of 2013 by looking at how these pathogens might be able to survive fires or spread to post-disturbance landscapes, and how these various species of Phytophthora interact and are affected by climate change.

A third paper that is undergoing review for publication examines how the potential interactions between SOD and fire affect the composition of redwood forests. Intermediate-sized redwood trees experienced significantly higher mortality when fire burned through diseased stands, even though redwood is typically fire resistant and not susceptible to SOD. This was not due to direct effects of the disease on redwoods, but rather the ways SOD changes fuel structure as the disease progresses, which affects flame heights and fire behavior in a way that increased redwood mortality relative to burned areas that are not infested with the disease. For some size classes, mortality increased four-fold.

There are on-going analyses looking at litter and soil nutrient composition and cycling. Interestingly, we have found that a large proportion of the carbon and nitrogen were burned off during the 2008 fires which is different than better-studied but low intensity fires. Changes in soil properties by fire in the Santa Lucia Mountains is not very well studied and our further analysis aims to understand if these changes are typical of how fire in Big Sur affects soil nutrients. Our future surveys aim to measure the rate that litter and soil recover over time.

The Big Sur plot network is not only valuable for SOD research at UC Davis but is also helping the USFS map vegetation types across the county, and is the basis for a UC Berkeley project to study fungi that exist on the central coast. The fungi project is specifically looking at mushrooms associated with the roots of tanoak trees that facilitate nutrient uptake for all species in the forest.

As we continue to expand the breadth of knowledge about the forests in Big Sur we look to the 2013 field season to develop our understanding on how SOD and fire interact to shape forest community composition and function as it relates to the spread of the pathogen. We turn our attention to looking at the seedlings and the re-sprouts of all species within the burned area as regeneration in general and post fire, has never been documented in these forests before. All citations are available through Kerri Frangioso (, on our website at, or at the Big Sur library.

2Meentemeyer, R.K., N.E. Rank, B.L. Anacker, D.M. Rizzo, and J.H. Cushman. 2008. Influence of landcover change on the spread of an invasive forest pathogen. Ecological Applications 18:159-171

3Maia M. Beh, Margaret R. Metz, Kerri M. Frangioso and David M. Rizzo. 2012. The key host for an invasive forest pathogen also facilitates the pathogen’s survival of wildfire in California forests. New Phytologist (2012) doi: 10.1111/j.1469-8137.2012.04352.x

4Metz, Margaret R., J. Morgan Varner, Kerri M. Frangioso, Ross K. Meentemeyer, and David M. Rizzo. 2013. Unexpected mortality in California’s coast redwood from synergies between wildfire and an emerging infectious disease. (in press).

Big Sur_SOD Update 2013.pdf


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