Graduate Thesis Or Dissertation
 

Scaling the Issue of Changing Disturbance Regimes: Implications of Novel Landscape Conditions for Black Stain Root Disease

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  • Changes to disturbance regimes resulting from shifts in forest management practices have created novel landscape conditions in the Pacific Northwest (PNW). I analyzed the implications of changes to landscape conditions caused by forest management for the spread of a native root disease: black stain root disease (BSRD) of Douglas-fir. BSRD spreads via root and insect vectors and causes rapid decline and mortality in young Douglas-fir (below age 30-40). Management practices including thinnings, clear-cut harvests, soil compaction, and roadside disturbance, e.g., tree damage from traffic and machinery, are associated with increased BSRD infection. In western Oregon and Washington, decreases in rotation lengths are altering Douglas-fir age class distributions, and the associated increased prominence of younger stands and harvest frequency have created concern about BSRD leading to increased Douglas-fir mortality. Management changes are influencing patterns of disturbance and Douglas-fir age distribution at both the stand and landscape scale. Therefore, for my research efforts, the probability of BSRD infection for each stand was hypothesized to be influenced by drivers at multiple scales, within and beyond stand boundaries. I used a spatially explicit model to simulate BSRD transmission in forest landscapes to evaluate whether forest management and the resulting stand and landscape conditions influence BSRD spread. Factors affecting the probability of infection, including their variability and uncertainty, were determined and quantified from literature, verified by expert opinion, and used to develop and parameterize the model. By comparing BSRD spread in different landscape scenarios, I analyzed the influence of management disturbances and stand age class distributions on BSRD infection, mortality, and spatial distribution at the stand and landscape scale. Critical knowledge gaps were identified regarding BSRD spread and impacts and highlighted as priorities for future research. In the simulations, infection spread was found to be highest in landscapes dominated by extensively managed stands, driven in part by higher tree densities and longer rotations. In contrast, infections were lowest in a landscape with all stands managed intensively. In landscapes with 50% intensively managed and 50% extensively managed stands, infection increased in intensively managed stands and decreased in extensively managed stands relative to the 100% intensive and extensive management scenarios, respectively, suggesting drivers of infection spread operate at the stand and landscape scales. Simulation results also suggested the hypothesis that the insects Pissodes fasciatus and Hylastes nigrinus account for the highest proportion of infections. This model was intended as a first step to connect management scenarios with disease outcomes and generate hypotheses to be examined in future research. The model also aims to serve as a tool to inform forest management practices regarding the impact of BSRD and stimulate future research on this disease.
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  • Bouché, Adam J. (2020). Scaling the Issue of Changing Disturbance Regimes: Implications of Novel Landscape Conditions for Black Stain Root Disease. [Master's thesis, Oregon State University]. ScholarsArchive at Oregon State University.
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  • GitHub repository for this model
  • GitHub repository for the "spread-infection" program needed for this model
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  • This research was funded in part by the Richardson Family Fellowship in the College of Forestry and the Edmund Hayes Professorship in Silviculture Alternatives at Oregon State University.
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