Fire History
In the Western U.S., the 2020 fire season is setting new records in terms of geographic scale, fire intensity, and rates of spread. Tens of millions of people are currently being forced to breathe beneath a dense layer of smoke, as others have lost their lives and property.
With each new record-setting fire, the same question comes up again and again: is this due to climate change, or is this due to forest mismanagement? After dueling appearances on Monday, this question now appears to be a matter of debate in the Presidential campaign.
The climate change vs. management question ignores nuance that is crucial for finding scientific answers and policy solutions. The factors influencing wildfire behavior are complex, and the dominant drivers vary between different locations and events. Below are five key things to know about the causes of the current wildfire problem. Understanding them can help us navigate the question of what is driving increased fire activity and what can be done to reduce such large fires in the future.
Disturbance refugia – locations that experience less severe or frequent disturbances than the surrounding landscape – provide a framework to highlight not only where and why these biological legacies persist as adjacent areas change but also the value of those legacies in sustaining biodiversity. Recent studies of disturbance refugia in forest ecosystems have focused primarily on fire, with a growing recognition of important applications to land management. Given the wide range of disturbance processes in forests, developing a broader understanding of disturbance refugia is important for scientists and land managers, particularly in the con-text of anthropogenic climate change. We illustrate the framework of disturbance refugia through the individual and interactive effects of three prominent forest disturbance agents: fire, drought, and insect outbreaks. We provide examples of disturbance ref-ugia and related applications to natural resource management in western North America, demonstrate methods for characterizing refugia, identify research priorities, and discuss why a more comprehensive definition of disturbance refugia is relevant to conser-vation globally
Webinar recording.
Description: Range of Variability (ROV) concepts – including Natural (NRV), Historic (HRV), Current (CRV), and Future (FRV) – are frequently used by the US Forest Service to help define land management goals. This webinar provides an introduction to ROV terminology and examples of how the Malheur, Umatilla, and Wallowa-Whitman National Forests in the Blue Mountains have applied ROV concepts during project planning when addressing key requirements of the Eastside Screens. The discussion includes overviews of tools commonly used to conduct ROV analyses.
Presenter: Nathan Poage, Forest Service Ecologist,
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The structure and composition of sagebrush‐dominated ecosystems have been altered by changes in fire regimes, land use, invasive species, and climate change. This often decreases resilience to disturbance and degrades critical habitat for species of conservation concern. Basin big sagebrush (Artemisia tridentata ssp. tridentata) ecosystems, in particular, are greatly reduced in distribution as land has been converted to agriculture and other land uses. The fire regime, relative proportions of shrub and grassland patches, and the effects of repeated burns in this ecosystem are poorly understood. We quantified postfire patterns of vegetation accumulation and modeled potential fire behavior on sites that were burned and first measured in the late 1980s at John Day Fossil Beds National Monument, Oregon, USA. The area partially reburned 11 yr after the initial fire, allowing a comparison of one vs. two fires. Repeated burns shifted composition from shrub‐dominated to prolonged native herbaceous dominance. Fifteen years following one fire, the native‐dominated herbaceous component was 44% and live shrubs were 39% of total aboveground biomass. Aboveground biomass of twice‐burned sites (2xB; burned 26 and 15 yr prior) was 71% herbaceous and 12% shrub. Twenty‐six years after fire, total aboveground biomass was 113–209% of preburn levels, suggesting a fire‐return interval of 15–25 yr. Frequency and density of Pseudoroegneria spicata and Festuca idahoensis were not modified by fire history, but Poa secunda was reduced by repeated fire, occurring in 84% of plots burned 26 yr prior, 72% of plots burned 15 yr prior, and 49% in 2xB plots. Nonnative annual Bromus tectorum occurred at a frequency of 74%, but at low density with no differences due to fire history. Altered vegetation structure modified fire behavior, with modeled rates of fire spread in 2xB sites double that of once‐burned sites. This suggests that these systems likely were historically composed of a mosaic of shrub and grassland. However, contemporary increases in fire frequency will likely create positive feedbacks of more intense fire behavior and prolonged periods of early‐successional vegetation in basin big sagebrush communities.
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Historically, the ecotone was a matrix of prairie with extensive savanna and some forest. More than half of the ecotone area was prairie, which is now dominated by agriculture, with some residential development. The 16% of the landscape that was pine savanna is now forest or shrubs, agriculture, perennial vegetation under the Conservation Reserve Program, or developed; no savanna now exists. Forests covered 12% of the ecotone and these are still mostly forest. Fires were historically frequent, occurring on average every 5 to 8 years at most sites. Lightning was not frequent but could likely have been sufficient to ignite fires that could spread readily given the rolling terrain and long fire season. Fire was far more frequent historically than currently. Conservation, restoration, and other ongoing land-use changes will likely result in more continuous vegetation and hence fuel for fires. Lightning and people may ignite fires that therefore spread readily in the future. Understanding the past and potential future of fire in the Palouse Prairie bioregion may help us live with fire while conserving ecological values here and in similar prairie–forest ecotones.
Rick Miller, Professor Emeritus, OSU, discusses the intent and goals of his latest publication, The Ecology, History, Ecohydrology, and Management of Pinyon and Juniper Woodlands in the Great Basin and Northern Colorado Plateau in the Western United States. This includes 1) Describing the the woodlands and the vast variation across the GB and CP, 2) Telling the story of their history and variables influencing woodland expansion and contraction, and 3) Interpretation of the wide variation in responses and the variables influencing ecosystem response to restoration.
Humanity’s fire practices are creating the fire equivalent of an ice age. Our shift from burning living landscapes to burning lithic ones is affecting all aspects of Earth. Presenter is Stephen Pyne.
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For this study, we used big sagebrush (Artemisia tridentata) as a model species to explore whether including human‐induced factors improves the fit of the species distribution models (SDM). Models including fire attributes and restoration treatments performed better than those including only climate and topographic variables. Number of fires and fire occurrence had the strongest relative effects on big sagebrush occurrence and cover, respectively. The models predicted that the probability of big sagebrush occurrence decreases by 1.2% (95% CI: −6.9%, 0.6%) when one fire occurs and cover decreases by 44.7% (95% CI: −47.9%, −41.3%) if at least one fire occurred over the 36 year period of record. Restoration practices increased the probability of big sagebrush occurrence but had minimal effect on cover. Our results demonstrate the potential value of including disturbance and land management along with climate in models to predict species distributions.
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There is wide agreement that prescribed fire is essential and under-utilized for restoring and maintaining natural ecosystem function, sustaining native wildlife populations, and mitigating wildfire hazard. There is less agreement on the history of fire, specifically the degree to which historic fire regimes and the natural communities that depend on them are essentially anthropogenic as opposed lightning-initiated as a function of climate and topography. This presentation provides an over-simplified summary of the two positions and present examples of more comprehensive research approaches that embrace data over dogma.
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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.