Landels-Hill Big Creek Reserve

25 Mar, 08 AM - 27 Mar, 08 AM

The ecology of native forest pathogens in California?s coastal mixed evergreen forests Introduction The purpose of this study is to gain a better understanding of the ecology of native plant pathogens in California?s coastal mixed evergreen forests. In the past few years, a great deal of attention has been focused on the exotic forest pathogen, Phytophthora ramorum, causal agent of Sudden Oak Death. Since its appearance around 1995, P. ramorum has led to the death of hundreds of thousands of trees along coastal California and in Southern Oregon (Rizzo et. al 2002). The massive survey effort and research surrounding P. ramorum in California and Oregon, has led to the discovery of two previously unknown Phytophthora species in California?s forests and woodlands. One of which, P. nemorosa, is newly described and only found in California and Oregon forests (Davidson et. al 2002, Hansen et. al 2003). The other Phytophthora species discovered in California forests was found to be the same as the recently described pathogen from European oak woodlands P. pseudosyringae (Jung et. al 2003). Both new Phytophthora species cause symptoms that are indistinguishable in the field from P. ramorum, including lethal cankers on tanoaks (Lithocarpus densiflorus) and coast live oaks (Quercus agrifolia) as well as the tip dieback seen on species such as California bay (Umbellularia californica). However, the two new pathogens typically appear to be less virulent than P. ramorum as they are often associated with patchy or single tree mortality, which contrasts to the extensive patches of mortality due to the exotic and invasive P. ramorum. The behavior of both P. nemorosa and P. pseudosyringae is suggestive of an endemic pathogen (Hansen et. al 2003). Genetic research, which will help to determine this, is currently underway. Although the last few years of research have produced a great deal of knowledge on the invasive pathogen, P. ramorum, little is known about the distribution and ecology of P. nemorosa and P. pseudosyringae. Objectives My research will focus on the distribution and ecology of these two newly discovered pathogens within coastal mixed evergreen forests. P. nemorosa and P. pseudosyringae have been found throughout areas where P. ramorum is active, but I will focus on the distribution of these pathogens in areas that have so far escaped infection by P. ramorum. This will provide baseline information on the role of these pathogens in forests without any interaction affects due to P. ramorum. The field component of my research will involve surveying areas in California for the presence of these pathogens, as well as establishing plots to gain a further understanding of the pathogens ecology. The research questions I will focus on are as follows: 1. What is the distribution of these two pathogens? 2. What is the level of mortality due to P. nemorosa and P. pseudosyringae in California mixed evergreen forests? 3. What site variables and environmental factors correlate with disease incidence and/or intensity? 4. Do the two ?native? pathogens P. nemorosa and P. psuedosyringae occupy the same niche or is there some level of site, host, ecological or seasonal differentiation? Site and Plot Selection Various study sites throughout California will be chosen for the establishment of plots. Sites will be located at parks and reserves that contain a mixed evergreen forest type, with some Umbellularia californica and Quercus spp. component. Plots will be placed in forests that are thought to be absent of the pathogen, P. ramorum. As always, all equipment and shoes that have been in Sudden Oak Death infested areas will be cleaned thoroughly before going to a new site, especially a non-infested area. At each site, plots will be randomly distributed and greater than 100 m apart, and attempts will be made to locate plots at various elevations and aspects. Each plot will be a 1/20th hectare circular plot with a tagged center tree and four tagged witness trees (if the tagging of trees is undesired, another method of identification can be used). GPS coordinates will be taken at each plot center. Plot Measurements Within each 1/20th hectare plot diameter at breast height (dbh) of all tree species with measurements greater than 1 cm at breast height will be recorded. From the plot center, the azimuth and distance to each tree (dbh >1 cm) or shrub (height > 1m) will be recorded. All other shrubs and saplings and seedlings will be counted. Percent cover of all woody species will be recorded. Tree and shrub species will be examined for potential cankers and leaf spots caused by Phytophthora species, although focus will be on Quercus species. and U. californica. The extent of the visual canker on boles of trees will be measured as well as notation made of any bleeding or the presence of bark beetles. Bark from cankers will be collected in a manner, which provides enough material for identification of disease, but limits harm done to the tree. Representative symptomatic leaves and stems will be collected. All plant material will be determined infected through direct isolation techniques and/or PCR-based molecular techniques (Rizzo et al. 2002). A rating of healthy, fair, poor, or dead will be given to all tree and shrub species. The presence of other diseases will be noted. Dead host trees and shrubs will be examined to determine apparent mortality agents. Crown position of all tree species will be recorded with the five crown classes being emergent, dominant, codominant, intermediate and understory. Soil will be collected from three different spots in each plot (total being no more than 500 grams from each plot). The slope, aspect, elevation, percent light and litter depth for each plot will be recorded along with notes of other topographical features. Distance from the nearest road or trail and creek or river to each plot will be estimated. Significance of Research Phytophthora species are known worldwide as extremely destructive invasive pathogens of crops and forests. Examples include jarrah (eucalyptus forest) decline in Australia, death of Port Orford cedar in the Pacific Northwest and now Sudden Oak Death in California and Oregon. However, what has not been well documented is the presence of Phytophthoras as native agents of disease in a forest (Hansen et al. 2003). The discovery of these likely native pathogens provides a great opportunity to understand what the natural levels of disease are in the coastal forests, something that was unknown before the occurrence of Sudden Oak Death. This is important to understand as single tree mortality due to a native pathogen is an important process in the ecology of a forest; effecting such things as succession, nutrient cycling and wildlife habitat. My research will also provide information on two pathogens that appear to be genetically and ecologically similar. This research will help to tease out what ecological differences there may be between P. nemorosa and P. pseudosyringae. Because both these pathogens inhabit forests that are being invaded by P. ramorum, all of this information will aid in the understanding of any current and future interactions between native and exotic species in the natural environment. Any reports that are developed as a result of this research will be provided to interested parks and reserves. Literature Cited Davidson, J.M., M. Garbellotto, E.M. Hansen, P. Reeser and D.M. Rizzo. 2002. Another canker causing Phytophthora from California and Oregon forests. Phytopathology 92: S17. Hansen, E.M., P. Reeser, J.M. Davidson, M. Garbelotto, K. Ivors, L. Douhan, and D.M. Rizzo. 2003. Phytophthora nemorosa, a new species causing cankers and leaf blight of forest trees in California and Oregon, U.S.A. Mycotaxon 88:129-138 Jung, T., J. Nechwatal,, D.E.L. Cooke, G. Hartmann, M. Blaschke, W.F. Obwald, J.M. Duncan and C. Delatour. 2003. Phytophthora pseudosyringae sp. nov,. a new species causing root collar rot of deciduous tree species in Europe. Mycological Research 107:772-789. Rizzo, D.M., M. Garbelotto, J..M. Davidson, G.W. Slaughter and S.T. Koike. 2002. Phytophthora ramorum as the cause of extensive mortality of Quercus spp. and Lithocarpus densiflorus in California. Plant Disease 86: 205-214.

Visit #4969 @Landels-Hill Big Creek Reserve

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Under Project # 1326 | Research

University of California Davis - Plant Pathology

research_scientist - University of California, Davis

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Group of 2 Graduate Student Mar 25 - 27, 2004 (3 days)

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Whale Point Researcher Cabin 2 Mar 25 - 27, 2004