There has been a significant increase in fire activity in the western United States over the past two decades, attributed to climate change, but much of the data that support this attribution are from fires in frequent, low-severity fire regimes. Recent increases in fires with mixed- and high-severity fire regimes of the Pacific Northwest have highlighted the importance of collecting baseline data and understanding fire-climate interactions in forests with less frequent fire to inform research and guide management. My dissertation focuses on these objectives in three chapters. In the first chapter, I characterized historical fire frequency and severity over 400 years in a dry, mixed conifer forest in Stehekin, Lake Chelan National Recreation Area in Washington state, and used ANOVA and GLM to identify the bottom-up controls on fire in this mountainous terrain. I found that fire frequency was high before the fire suppression era (31-year mean fire-interval), increased significantly during the non-Indigenous settlement period, and was impacted by fire suppression (51-year mean fire interval following suppression). Both fire frequency and severity are controlled by a complex interaction among topography, site, and environmental variables, which could increase resilience to climate change. In the second chapter, I classified and mapped fuel characteristics (fuelbeds) and fire potentials across a low-frequency, high-severity fire regime (Mount Rainier National Park, (the Park)) using a combination of field data, LiDAR, and climate data. Using this examination at high-resolution, I identified higher fuel loadings and fire potentials on the west side of the Park that could eventually indicate greater impacts and changes there, although the effects of climate change are more certain and will come sooner on the east side. In the last chapter, I reviewed bottom-up controls (topography and fuels) on fire frequency across the continuum of moist, high-severity fire regimes to dry, low-severity fire regimes from the west side of the Olympic Mountains to the east side of the north and central Cascades. Using this examination, I identify and describe a corresponding “fuel management continuum” to inform wildfire and forest management strategies.

A leading expert in the emerging field of fire ecology, James Agee analyzes the ecological role of fire in the creation and maintenance of the natural forests common to most of the western U.S. In addition to examining fire from an ecological perspective, he provides insight into its historical and cultural aspects, and also touches on some of the political issues that influence the use of fire. Although the focus of chapters on the ecology of specific forest zones is on the Pacific Northwest, much of the book addresses issues that are applicable to other regions. Illustrations, tables, index.

This synthesis provides an ecological foundation for management of the diverse ecosystems and fire regimes of North America, based on scientific principles of fire interactions with vegetation, fuels, and biophysical processes. Although a large amount of scientific data on fire exists, most of those data have been collected at small spatial and temporal scales. Thus, it is challenging to develop consistent science-based plans for large spatial and temporal scales where most fire management and planning occur. Understanding the regional geographic context of fire regimes is critical for developing appropriate and sustainable management strategies and policy. The degree to which human intervention has modified fire frequency, intensity, and severity varies greatly among different ecosystems, and must be considered when planning to alter fuel loads or implement restorative treatments. Detailed discussion of six ecosystems--ponderosa pine forest (western North America), chaparral (California), boreal forest (Alaska and Canada), Great Basin sagebrush (intermountain West), pine and pine-hardwood forests (Southern Appalachian Mountains), and longleaf pine (Southeastern United States)-- illustrates the complexity of fire regimes and that fire management requires a clear regional focus that recognizes where conflicts might exist between fire hazard reduction and resource needs. In some systems, such as ponderosa pine, treatments are usually compatible with both fuel reduction and resource needs, whereas in others, such as chaparral, the potential exists for conflicts that need to be closely evaluated. Managing fire regimes in a changing climate and social environment requires a strong scientific basis for developing fire management and policy.