Assessing the Effects of Climate Change and Fuel Treatments on Forest Dynamics and Wildfire in Dry Mixed-Conifer Forests of the Inland West: Linking Landscape and Social Perspectives

摘要

Over the past century in the western United States, warming has produced larger and more severe wildfires than previously recorded. General circulation models and their ensembles project continued increases in temperature and the proportion of precipitation falling as rain. Warmer and wetter conditions may change forest successional trajectories by modifying rates of vegetation establishment, competition, growth, reproduction, and mortality. Many questions remain regarding how these changes will occur across landscapes and how disturbances, such as wildfire, may interact with changes to climate and vegetation. Forest management is used to proactively modify forest structure and composition to improve fire resilience. Yet, research is needed to assess how to best utilize mechanical fuel reduction and prescribed fire at the landscape scale. Human communities also exist within these landscapes, and decisions regarding how to manage forests must carefully consider how management will affect such communities.;In this work, I analyzed three aspects of forest management at large spatiotemporal scales: (1) climate effects on forest composition and wildfire activity; (2) efficacy of fuel management strategies toward reducing wildfire spread and severity; and, (3) local resident perspectives on forest management. Using a forest landscape model, simulations of forest dynamics were used to investigate relationships among climate, wildfire, and topography with long-term changes in biomass for a fire-prone dry-conifer landscape in eastern Oregon, United States. I compared the effectiveness of fuel treatment strategies for reducing wildfire under both contemporary and extreme weather. Fuel treatment scenarios included "business as usual" and strategies that increased the area treated with harvest and prescribed fire, and all strategies were compared by distributing them across the landscape and by concentrating them in areas at the greatest risk for high-severity wildfire. To investigate local community preferences for forest management, I used focus groups, interviews, and questionnaires. Through open-ended questions and a public participation geographic information systems (PPGIS) mapping exercise, local residents expressed their views on fuels reduction treatments by commercial and non-commercial harvest and prescribed fire. Emergent themes were used to inform alternative management scenarios to explore the usefulness of using PPGIS to generate modeling inputs. Scenarios ranged from restoration-only treatments to short-rotation commercial harvest.;Under climate change, wildfire was more frequent, more expansive, and more severe, and ponderosa pine expanded its range into existing shrublands and high-elevation zones. There was a near-complete loss of native high-elevation tree species, such as Engelmann spruce and whitebark pine. Loss of these species were most strongly linked to burn frequency; this effect was greatest at high elevations and on steep slopes.;Fuel reduction was effective at reducing wildfire spread and severity compared to unmanaged landscapes. Spatially optimizing mechanical removal of trees in areas at risk for high-severity wildfire was equally effective as distributing tree removal across the landscape. Tripling the annual area of prescribed burns was needed to affect landscape-level wildfire spread and severity, and distributing prescribed burns across the study area was more effective than concentrating fires in high-risk areas.;Focus group participants generally approved of all types of forest management and agreed that all areas should be managed with the "appropriate" type of treatment for each forest stand, and that decisions about management should be made by "experts." However, there was disagreement related to who the "experts" are and how much public input should be included in the decision making process. Degree of trust in land management agencies contributed to polarized views about who the primary decision makers and what the focus of management should be. While most participants agreed that prescribed fire was a useful tool for preventing wildfire spread and severity, many expressed reservations about its use.;I conclude that forest management can be used to reduce wildfire activity in dry-mixed conifer forests and that spatially optimizing mechanical treatments in high-risk areas can be a useful tool for reducing the cost and ecological impact associated with harvest operations. While reducing the severity and spread of wildfire may slow some long-term species shifts, high sub-alpine tree mortality occurred under all climate and fuel treatment scenarios. Thus, while forest management may prolong the existence of sub-alpine forests, shifts in temperature, precipitation, and wildfire may overtake management within this century. The use of PPGIS was useful for delineating the range of forest management preferences within the local community, for identifying areas of agreement among residents who have otherwise polarized views, and for generating modeling inputs that reflect views that may not be obtained through extant official channels for public participation. Because the local community has concerns about the use of prescribed fire, more education and outreach is needed. This may increase public acceptance of the amounts of prescribed fire needed to modify wildfire trajectories under future climate conditions.