Climate & Fire & Adaptation
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Despite late twentieth‐century increases in area burned, we show that Pacific Northwest forests have experienced an order of magnitude less fire over 32 yr than expected under historic fire regimes. Within fires that have burned, severity distributions are disconnected from historical references. From 1984 to 2015, 1.6 M ha burned; this is 13.3–18.9 M ha less than expected. Deficits were greatest in dry forest ecosystems adapted to frequent, low‐severity fire, where 7.2–10.3 M ha of low‐severity fire was missing, compared to a 0.2–1.1 M ha deficit of high‐severity fire. When these dry forests do burn, we observed that 36% burned with high‐severity compared to 6–9% historically. We found smaller fire deficits, 0.3–0.6 M ha, within forest ecosystems adapted to infrequent, high‐severity fire. However, we also acknowledge inherent limitations in evaluating contemporary fire regimes in ecosystems which historically burned infrequently and for which fires were highly episodic. The magnitude of contemporary fire deficits and disconnect in burn severity compared to historic fire regimes have important implications for climate change adaptation. Within forests characterized by low‐ and mixed‐severity historic fire regimes, simply increasing wildfire extent while maintaining current trends in burn severity threatens ecosystem resilience and will potentially drive undesirable ecosystem transformations. Restoring natural fire regimes requires management that facilitates much more low‐ and moderate‐severity fire.
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Over the last 30 years, in woodland and forested ecosystems across the southwestern US, there has been an increasing trend in fire activity. Altered land use practices and more recent changes in precipitation patterns and warmer temperatures are widely thought to contribute to departures in fire regimes toward more frequent and larger fires with more extreme fire behavior that threatens the persistence of the various forested ecosystems. We examined climate-fire relationships in these vegetation types in Arizona and New Mexico using an expanded satellite-derived burn severity dataset that incorporates over one million additional burned hectares analyzed as extended assessments to the MTBS project’s data and five climate variables from PRISM. Climate-fire relationships were identified by comparing annual total area burned, area burned at high/low severity, and percent high severity regionally with fire season (May-August) and water year (October-September) temperature, precipitation, and vapor pressure deficit (VPD) variables. The high severity indicators were also derived for each fire individually to see if climate-fire relationships persist at the scale of the individual fire. Increasing trends toward more arid conditions were observed in all but two of the climate variables. Furthermore, VPD-fire correlations were consistently as strong or more correlated compared to temperature or precipitation indicators alone, both regionally and at the scale of the individual fire. Thus, our results support the use of VPD as a more comprehensive climate metric than temperature or other water-balance measures to predict future fire activity. Managers will have to face the implications of increasing high severity fire as trends in climate toward warmer and drier conditions become an increasingly dominant factor in driving fire regimes towards longer and more intense fire seasons across the Southwest.
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This study used pollen and high-resolution charcoal analysis of lake sediment to reconstruct a 7600 yr vegetation and fire history from Anthony Lake, located in the Blue Mountains of northeastern Oregon. From 7300 to 6300 cal yr BP, the forest was composed primarily of Populus , and fire was common, indicating warm, dry conditions. From 6300 to 3000 cal yr BP, Populus declined as Pinus and Picea increased in abundance and fire became less frequent, suggesting a shift to cooler, wetter conditions. From 3000 cal yr BP to present, modern-day forests composed of Pinus and Abies developed, and from 1650 cal yr BP to present, fires increased. We utilized the modern climate-analogue approach to explain the potential synoptic climatological processes associated with regional fire. The results indicate that years with high fire occurrence experience positive 500 mb height anomalies centered over the Great Basin, with anomalous southerly component of flow delivering dry air into the region and with associated sinking motions to further suppress precipitation. It is possible that such conditions became more common over the last 1650 cal yr BP, supporting an increase in fire despite the shift to more mesic conditions.
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Comparisons of observed and simulated historical area burned indicate simulated future fire vulnerability could be underestimated by 3% in the Sierra Nevada and overestimated by 3% in the Rocky Mountains. Projections show that water‐limited forests in the Rocky Mountains, Southwest, and Great Basin regions will be the most vulnerable to future drought‐related mortality, and vulnerability to future fire will be highest in the Sierra Nevada and portions of the Rocky Mountains. High carbon‐density forests in the Pacific coast and western Cascades regions are projected to be the least vulnerable to either drought or fire. Importantly, differences in climate projections lead to only 1% of the domain with conflicting low and high vulnerability to fire and no area with conflicting drought vulnerability. Our drought vulnerability metrics could be incorporated as probabilistic mortality rates in earth system models, enabling more robust estimates of the feedbacks between the land and atmosphere over the 21st century.
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Find research briefs, tools, and more on specific topics in natural resource sciences and management related to climate change
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This study quantified relationships between annual climate conditions and regeneration of ponderosa pine and Douglas-fir, two ecologically and economically important conifer species in low-elevation forests of western North America. We found that regeneration exhibited a threshold response to annual climate conditions and the forests we sampled crossed these climate thresholds in the past 20 years, resulting in fewer recruitment opportunities through time. In areas that have crossed climatic thresholds for regeneration, stand-replacing fires may result in abrupt ecosystem transitions to nonforest states.
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Bristlecone pine has weathered many climate changes. They’ve been getting punched in the face their entire species history and even, in some ways, thrive in the face of adversity. But whether they can make those adjustments in their range fast enough to keep up with climate change, that’s the question.
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New fire management paradigms are emerging that recognize fire is inevitable, and in many cases desirable. During this webinar you will be introduced to a new process for spatial fire planning using tools such as Potential Control Line atlases (PCLs), Quantitative wildfire Risk Assessments (QRAs), and Suppression Difficulty Index (SDI). Chris Dunn, Oregon State Univ, will demonstrate how these tools can align wildfire management decisions and actions, from the development of strategic wildfire response zones to in situ wildfire response decisions that balance operational success, firefighter safety and values at risk.
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In increasingly arid regions such as the western U.S., water managers are learning that careful management and restoration of watershed ecosystems, including thinning trees and conducting prescribed burns, are important tools in coping with a hotter, drier climate.
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This publication identifies areas where big sagebrush populations are most and least vulnerable to climate change and demonstrates where continued investment in sagebrush conservation and restoration could have the most impact.