Abstract
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.
Highlights
Emerging tree pathogens and insect pests are an increasing threat to forest resources worldwide [1,2,3,4]
We address the problem for P. ramorum; how to mitigate the sheer loss of tanoak in coastal California and Oregon forests caused by sudden oak death
We develop a spatial model of the dynamics of competing hosts and redwood under a P. ramorum epidemic parameterized from extensive field data [45] from longitudinal observations of individual trees located in plots across the range of the P. ramorum hosts
Summary
Emerging tree pathogens and insect pests are an increasing threat to forest resources worldwide [1,2,3,4]. The introduction of these invasive organisms has been facilitated by expanding international trade, while their establishment and ecological impacts have been influenced by climate. (b) removal of bay What laurel are to reduce pathogen spread, with andimpacts without herbicide strategies: the short and long-term disease with:. (a) no application to prevent stump resprouting, and with and without follow-up removals; preventive management; (b) removal of bay laurel to reduce pathogen spread, with and without herbicide chemical protection of tanoak; and (d) a combination of treatments b and c. (a) no application to prevent stump resprouting, and with and without follow-up removals; preventive management; (b) removal of bay laurel to reduce pathogen spread, with and without herbicide chemical protection of tanoak; and (d) a combination of treatments b and c. removals; (c) preventive application to prevent stump resprouting, and with and without follow-up
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