Western United States forest wildfire activity is widely thought to have increased in recent decades, yet neither the extent of recent changes nor the degree to which climate may be driving regional changes in wildfire has been systematically documented. Much of the public and scientific discussion of changes in western United States wildfire has focused instead on the effects of 19th- and 20th-century land-use history. We compiled a comprehensive database of large wildfires in western United States forests since 1970 and compared it with hydroclimatic and land-surface data. Here, we show that large wildfire activity increased suddenly and markedly in the mid-1980s, with higher large-wildfire frequency, longer wildfire durations, and longer wildfire seasons. The greatest increases occurred in mid-elevation, Northern Rockies forests, where land-use histories have relatively little effect on fire risks and are strongly associated with increased spring and summer temperatures and an earlier spring snowmelt.

/pdf/warming-and-earlier-spring-increase-western-u-s-forest-33qvd39h8z.pdf

Warming and Earlier Spring Increase Western U.S. Forest Wildfire Activity

Summary Severe droughts have been associated with regional-scale forest mortality worldwide. Climate change is expected to exacerbate regional mortality events; however, pre- diction remains difficult because the physiological mechanisms underlying drought survival and mortality are poorly understood. We developed a hydraulically based theory considering carbon balance and insect resistance that allowed development and examination of hypotheses regarding survival and mortality. Multiple mechanisms may cause mortality during drought. A common mechanism for plants with isohydric

/pdf/mechanisms-of-plant-survival-and-mortality-during-drought-5rza45sn4g.pdf

Mechanisms of plant survival and mortality during drought: why do some plants survive while others succumb to drought?

Emerging recognition of two fundamental errors under-pinning past polices for natural resource issues heralds awareness of the need for a worldwide fundamental change in thinking and in practice of environmental management. The first error has been an implicit assumption that ecosystem responses to human use are linear, predictable and controllable. The second has been an assumption that human and natural systems can be treated independently. However, evidence that has been accumulating in diverse regions all over the world suggests that natural and social systems behave in nonlinear ways, exhibit marked thresholds in their dynamics, and that social-ecological systems act as strongly coupled, complex and evolving integrated systems. This article is a summary of a report prepared on behalf of the Environmental Advisory Council to the Swedish Government, as input to the process of the World Summit on Sustainable Development (WSSD) in Johannesburg, South Africa in 26 August 4 September 2002. We use the concept of resilience—the capacity to buffer change, learn and develop—as a framework for understanding how to sustain and enhance adaptive capacity in a complex world of rapid transformations. Two useful tools for resilience-building in social-ecological systems are structured scenarios and active adaptive management. These tools require and facilitate a social context with flexible and open institutions and multi-level governance systems that allow for learning and increase adaptive capacity without foreclosing future development options.

https://bioone.org/journals/AMBIO-A-Journal-of-the-Human-Environment/volume-31/issue-5/0044-7447-31.5.437/Resilience-and-Sustainable-Development--Building-Adaptive-Capacity-in-a/10.1579/0044-7447-31.5.437.pdf

Resilience and sustainable development: building adaptive capacity in a world of transformations

Riparian zones possess an unusually diverse array of species and environmental processes. The ecological diversity is related to variable flood regimes, geographically unique channel processes, altitudinal climate shifts, and upland influences on the fluvial corridor. The resulting dynamic environment supports a variety of life-history strategies, biogeochemical cycles and rates, and organisms adapted to disturbance regimes over broad spatial and temporal scales. Innovations in riparian zone management have been effective in ameliorating many ecological issues related to land use and environmental quality. Riparian zones play essential roles in water and landscape planning, in restoration of aquatic systems, and in catalyzing institutional and societal cooperation for these efforts.

The Ecology of Interfaces: Riparian Zones

Fire is a worldwide phenomenon that appears in the geological record soon after the appearance of terrestrial plants. Fire influences global ecosystem patterns and processes, including vegetation distribution and structure, the carbon cycle, and climate. Although humans and fire have always coexisted, our capacity to manage fire remains imperfect and may become more difficult in the future as climate change alters fire regimes. This risk is difficult to assess, however, because fires are still poorly represented in global models. Here, we discuss some of the most important issues involved in developing a better understanding of the role of fire in the Earth system.

/pdf/fire-in-the-earth-system-481yvwaoo1.pdf

Fire in the Earth System

It was once widely believed that landscapes become increasingly stable over time until eventually reaching a "climax state" of complete stability. In recent years, however, that idea has been challenged by a new understanding of the importance and inevitability of forces such as storms and fires that keep ecosystems in a state of constant change. The dynamics of fire ecology has emerged as a central feature of the new understanding as scientists and land managers redefine traditional assumptions about the growth and development of ecosystems. Fire Ecology of Pacific Northwest Forests is a historical, analytical, and ecological approach to the effects and use of fire in Pacific Northwest wildlands. James K. Agee, a leading expert in the emerging field of fire ecology, analyzes the ecological role of fire in the creation and maintenance of the natural forests common to most of the western United States. 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 and control of fire in the United States. In addition to serving as a sourcebook for natural area managers interested in restoring or maintaining fire regimes in Pacific Northwest wildlands, this volume provides an essential base of knowledge for all others interested in wildland management who wish to understand the ecological effects of fire. Although the chapters on the ecology of specific forest zones focus on the Pacific Northwest, much of the book addresses issues not unique to that region.

/pdf/fire-ecology-of-pacific-northwest-forests-pu0p65ynhm.pdf

Fire Ecology of Pacific Northwest Forests

https://www.fs.fed.us/psw/publications/skinner/psw_2005_skinner(agee)001.pdf

Basic principles of forest fuel reduction treatments

Our objective was to infer the controls of spatial variation in historical fire regimes. We reconstructed a multicentury history of fire frequency, size, season, and severity from fire scars and establishment dates of 1426 trees sampled on grids in four watersheds (-64 plots, over -1620 ha each) representative of the Blue Mountains, Oregon and Wash- ington, USA. The influence of regional climate, a top-down control, was inferred from among-watershed variation in fire regimes, while the influence of local topography, a bot- tom-up control, was inferred from within-watershed variation. Before about 1900, fire regimes varied among and within watersheds, suggesting that both top-down and bottom- up controls were important. At the regional scale, dry forests (dominated by ponderosa pine), burned twice as frequently and earlier in the growing season in southern watersheds than in northern watersheds, consistent with longer and drier fire seasons to the south. Mesic forests (dominated by subalpine fir or grand fir) probably also burned more frequently to the south. At the local scale, fire frequency varied with different parameters of topography in watersheds with steep terrain, but not in the watershed with gentle terrain. Frequency varied with aspect in watersheds where topographic facets are separated by significant barriers to fire spread, but not in watersheds where such facets interfinger without fire barriers. Frequency varied with elevation where elevation and aspect interact to create gradients in snow-cover duration and also where steep talus interrupts fuel continuity. Frequency did not vary with slope within any watershed. The presence of both regional- scale and local-scale variation in the Blue Mountains suggests that top-down and bottom- up controls were both important and acted simultaneously to influence fire regimes in the past. However, an abrupt decline in fire frequency around 1900 was much greater than any regional or local variation in the previous several centuries and indicates that 20th-century fire regimes in these watersheds were dramatically affected by additional controls such as livestock grazing and fire suppression. Our results demonstrate the usefulness of examining spatial variation in historical fire regimes across scales as a means for inferring their controls.

Spatial controls of historical fire regimes: a multiscale example from the interior west, usa

https://www.fs.fed.us/pnw/pubs/journals/pnw_2005_hessburg002.pdf

Dry forests and wildland fires of the inland Northwest USA: Contrasting the landscape ecology of the pre-settlement and modern eras

With projected climate change, we expect to face much more forest fire in the coming decades. Policy-makers are challenged not to categorize all fires as destructive to ecosystems simply because they have long flame lengths and kill most of the trees within the fire boundary. Ecological context matters: In some ecosystems, high-severity regimes are appropriate, but climate change may modify these fire regimes and ecosystems as well. Some undesirable impacts may be avoided or reduced through global strategies, as well as distinct strategies based on a forest's historical fire regime.

https://science.sciencemag.org/content/sci/342/6154/41.full.pdf

James K. Agee

Papers

Fire Ecology of Pacific Northwest Forests

Basic principles of forest fuel reduction treatments

Spatial controls of historical fire regimes: a multiscale example from the interior west, usa

Dry forests and wildland fires of the inland Northwest USA: Contrasting the landscape ecology of the pre-settlement and modern eras

Managing Forests and Fire in Changing Climates