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Open AccessArticle

Management Strategies for Conservation of Tanoak in California Forests Threatened by Sudden Oak Death: A Disease-Community Feedback Modelling Approach

1
Agriculture, School of Natural and Environmental Sciences, Newcastle University, Newcastle upon Tyne NE1 7RU, UK
2
Department of Plant Sciences, University of Cambridge, Cambridge CB2 3EA, UK
3
Department of Natural Resources and Environmental Science, California Polytechnic State University, San Luis Obispo, CA 93407, USA
4
Department of Plant Sciences, University of Cambridge, Cambridge CB2 3EA, UK
*
Author to whom correspondence should be addressed.
Forests 2019, 10(12), 1103; https://doi.org/10.3390/f10121103
Received: 18 September 2019 / Revised: 14 November 2019 / Accepted: 27 November 2019 / Published: 3 December 2019
We use a new modelling approach to predict the cumulative impact of Phytophthora ramorum on the dynamic distribution of tanoak (Notholithocarpus densiflorus) and other tree species in coastal-Californian forest-communities. We explore the effectiveness of disease-management strategies for the conservation of tanoak at stand level. Forest resources are increasingly threatened by emerging pathogens such as P. ramorum, a generalist that kills hosts and has altered ecosystems in the USA and Europe. In coastal California, P. ramorum has the greatest impact on tanoak through leaf sporulation and lethal bole infections, but also sporulates on the common overstory-tree bay laurel (Umbellularia californica) without significant health impact. Such epidemiological differences impede host-species coexistence and challenge pathogen management. For most disease-impacted natural systems, however, empirical evidence is still insufficient to identify effective and affordable pathogen-control measures for retaining at-risk host populations. Yet, landscape-scale tree mortality requires swift actions to mitigate ecological impacts and loss of biodiversity. We apply a mathematical model of the feedback between disease and forest-community dynamics to assess the impacts of P. ramorum invasion on tanoak under stand-scale disease-management strategies by landowners aiming to retain tanoak and slow disease progression: (1) removal of inoculum through reduction of bay laurel abundance; (2) prevention of tanoak infection through chemical protection (acting epidemiologically like a vaccine); and (3) a combination strategy. The model results indicate that: (1) both bay laurel removal and tanoak protection are required to help maintain tanoak populations; (2) treatment effectiveness depends on forest composition and on threshold criteria; (3) sustainable tanoak conservation would require long-term follow-up of preventive treatments; (4) arresting basal sprouting upon tree removal may help to reduce inoculum. These findings suggest potential treatments for specific forest conditions that could be tested and implemented to reduce P. ramorum inoculum and disease and to conserve tanoak at stand level. View Full-Text
Keywords: biodiversity conservation; disturbance; epidemic threshold; feedback; forest stand; invasive pathogens; integrated management; synergy; Phytophthora ramorum; mathematical model biodiversity conservation; disturbance; epidemic threshold; feedback; forest stand; invasive pathogens; integrated management; synergy; Phytophthora ramorum; mathematical model
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Filipe, J.A.N.; Cobb, R.C.; Salmon, M.; Gilligan, C.A. Management Strategies for Conservation of Tanoak in California Forests Threatened by Sudden Oak Death: A Disease-Community Feedback Modelling Approach. Forests 2019, 10, 1103.

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