Fire Regimes

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Contrasting the role of human- and lightning-caused wildfires on future fire regimes on a Central Oregon landscape

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No significant change was projected for the number of human-caused fire ignitions, but we projected a 14% reduction in lightning-caused ignitions under future conditions. Mean fire sizes were 31% and 22% larger under future conditions (2031–2060) for human and lightning-caused ignitions, respectively. All but one climate model projected increased frequency of record-breaking events relative to the contemporary period, with the largest future fires being about twice the size of those of the contemporary period. This work contributes to understanding the role of lightning- and human-caused fires on future fire regimes and can help inform successful adaptation strategies in this landscape.

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Recent fire regimes of the bi-national Madrean Sky Islands: Implications for collaborative, transboundary fire management

Webinar recording.

Overview: This webinar shares results of a recent study of contemporary fire regimes over a 32-year period (1985-2017) in the Madrean Sky Islands of the U.S. and México. During the study period 335 fires burned approximately 28% of the study area, with re-burns occurring on over 25% of the burned areas. The greatest variation in fire regimes, including fire size, frequency, and severity was observed in places with the most diverse human activities and land uses – particularly in the mountain ranges adjacent to the U.S.- México border. Average severity of recent fires was low despite some extreme outliers in cooler, wetter environments. Fire frequency was also higher than historical expectations in these cool and wet environments that support forest types such as Spruce-Fir, indicating threats to these systems possibly attributable to drought and other factors. In cooler and wetter environments in more remote areas of México, pine-oak forests burned with fire frequencies close to historical. In contrast, fires were absent or infrequent across large expanses of lower elevation Woodlands and Grasslands due possibly to overgrazing, which reduces abundance and continuity of fine fuels needed to carry fire. Our findings provide a new depiction of fire regimes in the Sky Islands that can help inform fire management, restoration, and regional conservation planning, fostered by local and traditional knowledge and collaboration among landowners and managers.

Presenter: Dr. Miguel Villarreal
Co-authors: José M. Iniguez, Aaron D. Flesch, Jamie S. Sanderlin, Citlali Cortés Montaño, Caroline R. Conrad, Sandra L. Haire


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Quantifying pyrodiversity and its drivers

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This study presents a generalizable functional diversity approach for measuring pyrodiversity, which incorporates multiple fire regime traits and can be applied across scales. Further, we tested the socioecological drivers of pyrodiversity among forests of the western United States. Largely mediated by burn activity, pyrodiversity was positively associated with actual evapotranspiration, climate water deficit, wilderness designation, elevation and topographic roughness but negatively with human population density. These results indicate pyrodiversity is highest in productive areas with pronounced annual dry periods and minimal fire suppression. This work can facilitate future pyrodiversity studies including whether and how it begets biodiversity among taxa, regions and fire regimes.

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Fire science and management in an uncertain future: Tools and approaches for managing fire in future climates in the SW

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Workshop purpose: Identify fire science and management needs and discuss tools and approaches to natural resource assessments and adaptation strategies for fire dynamics in future climates in Southwest (DOI Regions 8 & 10 [CA, NV, AZ]) bioregions.

Provide awareness of tools needed for decision-making in an uncertain future
Generate a list of new science actions to meet fire needs for practitioners/planners in future, non-analog landscapes and communities
Suggest how we might address and accomplish these identified needs going forward
Exchange Information
Make connections

This four-hour, virtual Summit was an abbreviated, rescheduled version of ‘Building Bridges and Solutions: Partners in Facing Fire-Science Challenges’ that was cancelled in April due to COVID-19. We assembled scientists and fire practitioners/leaders in an interagency effort to identify fire science and management needs and to discuss decision-making tools and approaches that address resource assessments and adaptation strategies for fire dynamics in future climates in the Southwest (Department of Interior [DOI] Regions 8 and 10 [CA, NV, AZ]). This overriding goal threaded together the Summit’s talks, Q&A, and break-out sessions. Speakers from various agencies, institutes, and academia focused on fire management and planning in future non-analog landscapes and climate-fire-ecosystem impact relationships in western forest (e.g., mixed-conifer, subalpine), desert (hot and cold, grassland, pinyon-juniper, sage-steppe), and Mediterranean/chaparral bioregions. Syntheses from talks, Mentimeter-conducted discussions, and break-out groups on management and actionable-science needs will be summarized in a white paper and posted on the Southwest, Great Basin, and California Fire Science Exchange websites. Let’s work together to address fire science and management in an uncertain future!

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Weather impacts on fire thresholds: Recipe for big fire

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Because three key thresholds must be crossed all at once for a wildfire to start, avoiding just one of these thresholds─ ignitions, drought, or continuous fuels (Fig.1)─ could significantly reduce the likelihood of wildfire. As climate change makes fire weather more common everywhere, managing ignitions where wind is problematic and managing fuels where drought is problematic will help to keep stochastic, out-of-regime fires contained. Where fire management tools won’t help, a fire danger zone should be designated to reduce human activity and development, much like volcano or flooding zone designations.

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Effect of seeding treatments and climate on fire regimes in Wyoming sagebrush

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Sites drill seeded before the most recent fire had fewer, less frequent fires with longer fire return intervals (15–20 years) than aerially seeded sites (intervals of 5–8 years). The response of fire regime variables at unseeded sites fell between those of aerial and drill seeding. Increased moisture availability resulted in decreased fire frequency between 1994 and 2014 and the total number of fires since 1955 on sites with unseeded and aerially pre-fire seeding, but fire regimes did not change when drill seeded. Greater annual grass biomass likely contributed to frequent fires in the arid region. In Wyoming big sagebrush steppe, drill seeding treatments reduced wildfire risk relative to aerial seeded or unseeded sites.

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Disturbance and sustainability in forests of the western US

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This report assesses recent forest disturbance in the Western United States and discusses implications for sustainability. Individual chapters focus on fire, drought, insects, disease, invasive plants, and socioeconomic impacts. Disturbance data came from a variety of sources, including the Forest Inventory and Analysis program, Forest Health Protection, and the National Interagency Fire Center. Disturbance trends with the potential to affect forest sustainability include alterations in fire regimes, periods of drought in some parts of the region, and increases in invasive plants, insects, and disease. Climate affects most disturbance processes, particularly drought, fire, and biotic disturbances, and climate change is expected to continue to affect disturbance processes in various ways and degrees.

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Great Basin pinyon and juniper: Ecology, history, and restoration website

Visit the PJ website, authored by Rick Miller

Pinyon (Pinus spp.) and juniper (Juniperus spp.) woodlands occupy over 78,000 square miles of the Great Basin and northern Colorado Plateau. These woodlands have persisted for tens of thousands of years and provide important biodiversity and habitat for many species across the region. Yet, relatively recent infill of new trees into old-growth woodlands and expansion of trees into adjacent sagebrush-steppe, riparian, and aspen communities have created a considerable mix of concerns around wildfire, drought-mortality, invasive species, watershed function, tree removal, and loss of habitat, biodiversity, and resilience.

This website provides background information on the ecology and management of PJ woodlands useful to the interested public and emerging information important to resource managers.
1) PJ 101 provides a brief introduction to and description of PJ woodlands with links to more in-depth information.
2) FAQ (Frequently Asked Questions) briefly addresses questions related to the ecology and management of PJ woodlands.
3) Tools provides information and concepts for evaluating landscapes, which are specifically useful for predicting disturbance or vegetation management responses in PJ woodlands.
4) Literature provides brief summaries and links to recently published PJ woodlands studies. Study findings are highlighted and discussed in terms of our current understanding.

This website will be continually updated with new articles, questions, and tools.

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How climate change and fire exclusion drive wildfire regimes at actionable scales

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Extreme wildfires are increasing in frequency globally, prompting new efforts to mitigate risk. The ecological appropriateness of risk mitigation strategies, however, depends on what factors are driving these increases. While regional syntheses attribute increases in fire activity to both climate change and fuel accumulation through fire exclusion, they have not disaggregated causal drivers at scales where land management is implemented. Recent advances in fire regime modeling can help us understand which drivers dominate at management-relevant scales. We conducted fire regime simulations using historical climate and fire exclusion scenarios across two watersheds in the Inland Northwestern U.S., which occur at different positions along an aridity continuum. In one watershed, climate change was the key driver increasing burn probability and the frequency of large fires; in the other, fire exclusion dominated in some locations. We also demonstrate that some areas become more fuel-limited as fire-season aridity increases due to climate change. Thus, even within watersheds, fuel management must be spatially and temporally explicit to optimize effectiveness. To guide management, we show that spatial estimates of soil aridity (or temporally averaged soil moisture) can provide a relatively simple, first-order indicator of where in a watershed fire regime is climate vs. fuel-limited and where fire regimes are most vulnerable to change.

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The effects of prescribed fire on wildfire regimes and impacts

Webinar recording.

Prescribed fire can result in significant benefits to ecosystems and society. Examples include improved wildlife habitat, enhanced biodiversity, reduced threat of destructive wildfire, and enhanced ecosystem resilience. Prescribed fire can also come with costs, such as reduced air quality and impacts to fire sensitive species. To plan for appropriate use of prescribed fire, managers need information on the tradeoffs between prescribed fire and wildfire regimes. In this study, we argue that information on tradeoffs should be presented at spatial and temporal scales commensurate with the scales at which these processes occur and that simulation modeling exercises should include some realistic measure of wildfire probability. To that end, we synthesized available scientific literature on relationships between prescribed fire and wildfire regimes, and their associated ecological and societal effects, focusing specifically on simulation modeling studies that consider wildfire probability and empirical and modeling studies that consider prescribed fire and wildfire regimes at spatial and temporal scales beyond individual events.

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