The Wildfire Pathogen

Author : Maia Moore Beh
Publisher :
ISBN 13 : 9781267238269
Total Pages : pages
Book Rating : 4.2/5 (382 download)

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Download or read book Consequences of Wildfire in the Sudden Oak Death-impacted Forests of the Big Sur Region, California written by Maia Moore Beh and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A novel disturbance interaction occurred in the Big Sur region of California's central coast during the summer of 2008 when wildfires occurred for the first time in forests severely impacted by Phytophthora ramorum, a non-native, invasive pathogen. This destructive oomycete pathogen causes sudden oak death, an emerging forest disease that is responsible for the mortality of millions of oaks (Quercus spp.) and tanoaks (Notholithocarpus densiflorus) in coastal forests of California. Ambrosia beetles, opportunistic scolytid beetles, often attack P. ramorum-infected trees and these secondary pests have been shown to hasten mortality. Data collected prior to the fires in a network of forest monitoring plots in Big Sur allowed for the rare opportunity to study the impacts of wildfire on P. ramorum-infested forests. In this thesis, I examined trends in the survival of P. ramorum following wildfires, as well as the landing rates of ambrosia beetles on tanoaks in forests disturbed both by P. ramorum and wildfire. The widespread wildfires of 2008 failed to eradicate P. ramorum from areas of the Big Sur landscape that were known to be already infested with the invasive forest pathogen. Phytophthora ramorum was successfully recovered from streams draining watersheds known to contain the pathogen prior to the fires and from a range of host tissues in burned, previously P. ramorum-infested plots. However, there was a much lower likelihood of recovering P. ramorum from burned plots than unburned plots, even two years following the fires, suggesting that fire did at least reduce the abundance of the pathogen. Recovery of P. ramorum in burned plots was positively correlated with the number of California bay laurels (Umbellularia californica) expressing symptoms of P. ramorum-infection prior to the fires, further highlighting the importance of this sporulating host of the establishment, spread, and persistence of the devastating pathogen. Surprisingly, two other Phytophthora spp., P. pseudosyringae and P. nemorosa, were frequently isolated from new vegetative growth in burned plots that were not known to contain these pathogens prior to the fires. One year following the fires, significantly more ambrosia beetles were trapped on tanoaks in forest plots disturbed both by P. ramorum and fire compared to undisturbed plots and plots with only P. ramorum disturbance in the Big Sur region. While the landing rates of ambrosia beetles are not necessarily equivalent to their actual rates of colonization, increased landing rates in the plots with multiple disturbances suggest that tanoaks in those areas were particularly attractive to ambrosia beetles. Specific host volatiles may have attracted ambrosia beetles to specific tanoaks, and greater quantities of moribund and recently-killed trees in forests affected by both disturbances likely led to greater population densities of ambrosia beetles in those areas. It is unlikely that large population of ambrosia beetles emerging from fire-injured trees will disperse to attack nearby green trees due to the opportunistic nature of ambrosia beetles and the ample supply of recently dead and dying trees in the area. However, given the imperiled state of tanoaks in coastal California due to P. ramorum-caused mortality, even the loss of fire-injured tanoaks to ambrosia beetle attack would have a major impact on the forests of the Big Sur region.