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USGS2011

Estimated probabilities, volumes, and inundation area depths of potential postwildfire debris flows from Carbonate, Slate, Raspberry, and Milton Creeks, near Marble, Gunnison County, Colorado

During 2009, the U.S. Geological Survey, in cooperation with Gunnison County, initiated a study to estimate the potential for postwildfire debris flows to occur in the drainage basins occupied by Carbonate, Slate, Raspberry, and Milton Creeks near Marble, Colorado. Currently (2010), these drainage basins are unburned but could be burned by a future wildfire. Empirical models derived from statistical evaluation of data collected from recently burned basins throughout the intermountain western United States were used to estimate the probability of postwildfire debris-flow occurrence and debris-flow volumes for drainage basins occupied by Carbonate, Slate, Raspberry, and Milton Creeks near Marble. Data for the postwildfire debris-flow models included drainage basin area; area burned and burn severity; percentage of burned area; soil properties; rainfall total and intensity for the 5- and 25-year-recurrence, 1-hour-duration-rainfall; and topographic and soil property characteristics of the drainage basins occupied by the four creeks. A quasi-two-dimensional floodplain computer model (FLO-2D) was used to estimate the spatial distribution and the maximum instantaneous depth of the postwildfire debris-flow material during debris flow on the existing debris-flow fans that issue from the outlets of the four major drainage basins. The postwildfire debris-flow probabilities at the outlet of each drainage basin range from 1 to 19 percent for the 5-year-recurrence, 1-hour-duration rainfall, and from 3 to 35 percent for 25-year-recurrence, 1-hour-duration rainfall. The largest probabilities for postwildfire debris flow are estimated for Raspberry Creek (19 and 35 percent), whereas estimated debris-flow probabilities for the three other creeks range from 1 to 6 percent. The estimated postwildfire debris-flow volumes at the outlet of each creek range from 7,500 to 101,000 cubic meters for the 5-year-recurrence, 1-hour-duration rainfall, and from 9,400 to 126,000 cubic meters for the 25-year-recurrence, 1-hour-duration rainfall. The largest postwildfire debris-flow volumes were estimated for Carbonate Creek and Milton Creek drainage basins, for both the 5- and 25-year-recurrence, 1-hour-duration rainfalls. Results from FLO-2D modeling of the 5-year and 25-year recurrence, 1-hour rainfalls indicate that the debris flows from the four drainage basins would reach or nearly reach the Crystal River. The model estimates maximum instantaneous depths of debris-flow material during postwildfire debris flows that exceeded 5 meters in some areas, but the differences in model results between the 5-year and 25-year recurrence, 1-hour rainfalls are small. Existing stream channels or topographic flow paths likely control the distribution of debris-flow material, and the difference in estimated debris-flow volume (about 25 percent more volume for the 25-year-recurrence, 1-hour-duration rainfall compared to the 5-year-recurrence, 1-hour-duration rainfall) does not seem to substantially affect the estimated spatial distribution of debris-flow material. Historically, the Marble area has experienced periodic debris flows in the absence of wildfire. This report estimates the probability and volume of debris flow and maximum instantaneous inundation area depths after hypothetical wildfire and rainfall. This postwildfire debris-flow report does not address the current (2010) prewildfire debris-flow hazards that exist near Marble.

Colorado↗

USGS2012

Estimated probabilities and volumes of postwildfire debris flows—A prewildfire evaluation for the Pikes Peak area, El Paso and Teller Counties, Colorado

Debris flows are fast-moving, high-density slurries of water, sediment, and debris that can have enormous destructive power. Although debris flows, triggered by intense rainfall or rapid snowmelt on steep hillsides covered with erodible material, are a common geomorphic process in some unburned areas, a wildfire can transform conditions in a watershed with no recent history of debris flows into conditions that pose a substantial hazard to residents, communities, infrastructure, aquatic habitats, and water supply. The location, extent, and severity of wildfire and the subsequent rainfall intensity and duration cannot be known in advance; however, hypothetical scenarios based on empirical debris-flow models are useful planning tools for conceptualizing potential postwildfire debris flows. A prewildfire study to determine the potential for postwildfire debris flows in the Pikes Peak area in El Paso and Teller Counties, Colorado, was initiated in 2010 by the U.S. Geological Survey, in cooperation with the City of Colorado Springs, Colorado Springs Utilities. The study was conducted to provide a relative measure of which subwatersheds might constitute the most serious potential debris-flow hazards in the event of a large-scale wildfire and subsequent rainfall.

Colorado↗

USGS2015

Water resources during drought conditions and postfire water quality in the upper Rio Hondo Basin, Lincoln County, New Mexico, 2010-13

Stakeholders and water-resource managers in Lincoln County, New Mexico, have had long-standing concerns over the impact of population growth and groundwater withdrawals. These concerns have been exacerbated in recent years by extreme drought conditions and two major wildfires in the upper Rio Hondo Basin, located in south-central New Mexico. The U.S. Geological Survey (USGS), in cooperation with Lincoln County, initiated a study in 2006 to assess and characterize water resources in the upper Rio Hondo Basin. Data collected during water years 2010–13 are presented and interpreted in this report. All data presented in this report are described in water years unless stated otherwise. Annual mean streamflow at the Rio Ruidoso at Hollywood, N. Mex., streamflow-gaging station was less than 50 percent of the average streamflow during 2011–13 and was of similar magnitude to annual mean streamflow values measured during the drought of the 1950s. The first zero-streamflow values for the period of record (1954–2013) were recorded at the Rio Ruidoso at Hollywood, N. Mex., streamflow-gaging station on June 27–29, 2013. The lowest annual mean streamflow on record (1969–80; 1988–2013) occurred in 2011 at the Eagle Creek below South Fork near Alto, N. Mex., streamflow-gaging station, with the station recording zero streamflow for approximately 50 percent of the year. Discrete and continuous groundwater-level measurements indicated basinwide water-level declines during drought conditions in 2011–13. The average water-level change among 37 wells in which discrete groundwater-level measurements were collected was -7.6 ft from 2010 to 2013. The largest water-level declines were observed in the upper reaches of the Rio Bonito and Rio Ruidoso watersheds, and smaller declines were observed in the lower reaches of the watersheds. In general, water-level changes observed during 2010–13 were on the order of decadal-scale changes that previously have been observed in the upper Rio Hondo Basin. Stable-isotope data indicate that high-elevation winter precipitation generally contributes more to groundwater recharge than summer rains, except when there are large summer recharge events. This implies that little recharge is occurring at the lower elevations in the upper Rio Hondo Basin because these areas receive a smaller amount of total precipitation, receive a smaller proportion of the annual total falling as winter precipitation, and have higher average temperatures that result in more evaporative losses. Groundwater in the upper Rio Hondo Basin is a mix of younger and older water, and recharge likely is occurring primarily at higher elevations but there may be some areas where localized recharge is occurring at lower elevations. Surface-water- and groundwater-quality results from samples collected in 2012–13 were examined to characterize overall chemistry and were compared to historical waterquality data from streams in the upper Rio Hondo Basin collected during 1926–57. In general, specific conductance showed an increasing trend moving eastward (downstream) through the upper Rio Hondo Basin in surface-water and groundwater samples. Surface-water and groundwater samples appear to have similar overall major-ion chemical characteristics when compared to historical water-quality data. Geology was found to influence the chemical characteristics of surface-water and groundwater samples, with relatively higher concentrations of sulfate occurring in samples collected at lower elevations in the Permian regional aquifer system. Surface-water sample results also were analyzed to determine differences in unfiltered and filtered water-quality samples of streams in burned and unburned watersheds after the occurrence of the Little Bear Fire in June 2012. Samples were collected after postfire monsoon rain events and during periods of stable hydrologic conditions. The first postfire monsoon rain event in July 2012 generally produced the highest measured concentrations of selected fire-related constituents in unfiltered samples collected in the burned watersheds relative to later samples collected in burned watersheds and all samples collected in the unburned watershed. Monsoon rain events have impacted water quality by delivering larger sediment loads and fire-related constituents into streams in the upper Rio Hondo Basin. Changes in climate and increased groundwater and surface-water use are likely to affect the availability of water in the upper Rio Hondo Basin. Increased drought probably will increase the potential for wildfires, which can affect downstream water quality and increase flood potential. Climate-research predicted decreases in winter precipitation may have an adverse effect on the amount of groundwater recharge that occurs in the upper Rio Hondo Basin, given the predominance of winter precipitation recharge as indicated by the stable isotope results. Decreases in surface-water supplies because of persistent drought conditions and reductions in the quality of water because of the effects of wildfire may lead to a larger reliance on groundwater reserves in the upper Rio Hondo Basin. Decreasing water levels because of increasing groundwater withdrawal could reduce base flows in the Rio Bonito and Rio Ruidoso. Well organized and scientifically supported regional water-resources management will be necessary for dealing with the likely scenario of increases in demand coupled with decreases in supply in the upper Rio Hondo Basin.

New Mexico↗

USGS2021

Hotter drought escalates tree cover declines in blue oak woodlands of California

California has, in recent years, become a hotspot of interannual climatic variability, recording devastating climate-related disturbances with severe effects on tree resources. Understanding the patterns of tree cover change associated with these events is vital for developing strategies to sustain critical habitats of endemic and threatened vegetation communities. We assessed patterns of tree cover change, especially the effects of the 2012–2016 drought within the distribution range of blue oak ( Quercus douglasii ), an endemic tree species to California with a narrow geographic extent. We utilized multiple, annual land-cover and land-surface change products from the U.S. Geological Survey (USGS) Land Change Monitoring, Assessment and Projection (LCMAP) project along with climate and wildfire datasets to monitor changes in tree cover state and condition and examine their relationships with interannual climate variability between 1985 and 2016. Here, we refer to a change in tree cover class without a land-cover change to another class as “conditional change.” The unusual drought of 2012–2016, accompanied by anomalously high temperatures and vapor pressure deficit, was associated with exceptional spikes in the amount of both fire and non-fire induced tree cover loss and tree cover conditional change, especially in 2015 and 2016. Approximately 1,266 km 2 of tree cover loss and 617 km 2 of tree cover conditional change were recorded during that drought. Tree cover loss through medium to high severity fires was especially large in exceptionally dry and hot years. Our study demonstrates the usefulness of the LCMAP products for monitoring the effects of climatic extremes and disturbance events on both thematic and conditional land-cover change over a multi-decadal period. Our results signify that blue oak woodlands may be vulnerable to extreme climate events and changing wildfire regimes. Here, we present early evidence that frequent droughts associated with climate warming may continue to affect tree cover in this region, while drought interaction with wildfires and the resulting feedbacks may have substantial influence as well. Consequently, efforts to conserve the blue oak woodlands, and potentially other vegetation communities in the Western United States, may benefit from consideration of climate risks as well as the potential for climate-fire and vegetation feedbacks.

California↗

USGS2018

Characterization and evaluation of controls on post-fire streamflow response across western U.S. watersheds

This research investigates the impact of wildfires on watershed flow regimes, specifically focusing on evaluation of fire events within specified hydroclimatic regions in the western United States, and evaluating the impact of climate and geophysical variables on response. Eighty-two watersheds were identified with at least 10 years of continuous pre-fire daily streamflow records and 5 years of continuous post-fire daily flow records. Percent change in annual runoff ratio, low flows, high flows, peak flows, number of zero flow days, baseflow index, and Richards–Baker flashiness index were calculated for each watershed using pre- and post-fire periods. Independent variables were identified for each watershed and fire event, including topographic, vegetation, climate, burn severity, percent area burned, and soils data. Results show that low flows, high flows, and peak flows increase in the first 2 years following a wildfire and decrease over time. Relative response was used to scale response variables with the respective percent area of watershed burned in order to compare regional differences in watershed response. To account for variability in precipitation events, runoff ratio was used to compare runoff directly to PRISM precipitation estimates. To account for regional differences in climate patterns, watersheds were divided into nine regions, or clusters, through k-means clustering using climate data, and regression models were produced for watersheds grouped by total area burned. Watersheds in Cluster 9 (eastern California, western Nevada, Oregon) demonstrate a small negative response to observed flow regimes after fire. Cluster 8 watersheds (coastal California) display the greatest flow responses, typically within the first year following wildfire. Most other watersheds show a positive mean relative response. In addition, simple regression models show low correlation between percent watershed burned and streamflow response, implying that other watershed factors strongly influence response. Spearman correlation identified NDVI, aridity index, percent of a watershed's precipitation that falls as rain, and slope as being positively correlated with post-fire streamflow response. This metric also suggested a negative correlation between response and the soil erodibility factor, watershed area, and percent low burn severity. Regression models identified only moderate burn severity and watershed area as being consistently positively/negatively correlated, respectively, with response. The random forest model identified only slope and percent area burned as significant watershed parameters controlling response. Results will help inform post-fire runoff management decisions by helping to identify expected changes to flow regimes, as well as facilitate parameterization for model application in burned watersheds.

Hydrology and Earth System Sciences↗

USGS2012

Genetic variation reveals influence of landscape connectivity on population dynamics and resiliency of western trout in disturbance-prone habitats

Salmonid fishes have evolved and persisted in dynamic ecosystems where disturbance events vary in frequency, magnitude, timing, and duration, as well as the specific nature of associated effects (e.g., changes in thermal or flow regimes, geomorphology, or water chemistry). In the western United States, one of the major drivers of disturbance in stream ecosystems is fire. Although there is a growing consensus that fish populations can ultimately benefit from the productive and heterogeneous habitats created by fire, to persist they obviously have to withstand the immediate and shorter-term effects of fire, which can reduce or even extirpate local populations. Movement among interconnected stream habitats is thought to be an important strategy enabling persistence during and following fire, and there is mounting concern that the extensive isolation of salmonid populations in fragmented habitats is reducing their resiliency to fire. In spite of this concern, there are few direct observations of salmonid responses to fire. In fact, guidance is based largely on a broader understanding of the influences of landscape structure and disturbance in general on salmonid fishes, and there is considerable uncertainty about how best to manage for salmonid resilience to wildfire. Studies are limited by the difficult logistics of following fish responses in the face of unpredictable events such as wildfires. Therefore, BACI (Before-After-Control-Impact) study designs are nearly impossible, and replication is similarly challenging because fires are often low-frequency events. Furthermore, conventional ecological study approaches (e.g., studies of fish distribution, abundance, life histories, and movement) are logistically difficult to implement. Overall, a major challenge to understanding resilience of salmonid populations in fire-prone environments is related to moving beyond localized case studies to those with broader applicability in wildfire management . Genetic data can be useful for overcoming many of the limitations inherent in ecological studies. Here we review several case studies of western trout where population genetic data have provided insight about fish responses to fragmentation and disturbance more generally, and specifically in relation to fire. Results of these studies confirm the importance of movement and landscape connectivity for ensuring fish persistence in fire-prone landscapes, and highlight the usefulness of genetic approaches for broad-scale evaluation and monitoring of population responses to fire and related management actions.

Technical Report↗

USGS2016

Chaparral

One of the most dynamic California ecosystems is chaparral. Dominated by evergreen, sclerophyllous shrubs and small trees, chaparral is the most extensive vegetation type in the state (Figure 1). The nearly impenetrable tangle of stiff branches of this unusual vegetation inhibits exploration, and as a consequence the public know little about its natural history and unique characteristics. This under-valued ecosystem is recognized instead by the threat of its extensive, high-intensity canopy-burning wildfires that characterize the dry summer and fall seasons of the state. Because urban areas frequently share borders or intermix with chaparral, societal interests often conflict with conservation of this ecosystem, and understanding its history and dynamics are a key to appreciating its importance. In this chapter we emphasize the principal structure and dynamics of this important ecosystem. The long summer rainless period has strong impacts on all organisms and, importantly, the droughts influence the fire regime that characterizes chaparral. An ecosystem currently characterized by a specific drought and wildfire regime can expect significant impacts from climate change. Because of its dominance at lower elevations, chaparral also is frequently found at or near the boundaries of urban developments and metropolitan centers. Attempts to suppress fire also affect chaparral dynamics in the long absence of fire. The conflicts between the impacts of chaparral wildfire and human life and structures has been an aspect of California’s history since the beginning, but as development encroaches ever more into chaparral regions, the conflicts have increased. Consequently, understanding this vegetation is important not only because of its significance in understanding ecological evolution and the ecological services provided by chaparral, but also because of its direct impacts on human settlements.

Book chapter↗

USGS2019

Soil microbial communities and global change

Soils and soil microbial communities mediate the biogeochemical processes that underly ecosystem-level changes. This chapter examines why soils and soil microbial communities are important for understanding impacts and feedbacks to global change. It discusses the technological approaches and challenges that are at the frontiers of this research area. Global change impacts on microbial communities can be categorized as press or pulse disturbances. Global increases in atmospheric temperature are among the most profound and concerning long-term changes affecting human society. The chapter focuses on the examples from Western North America, where issues such as land cover change, wildfire, and permafrost thaw are some of the most observable global change impacts. Wildfire is a natural phenomenon that lies at the basis of the process of plant succession. Recovery and regrowth of vegetation after wildfire regenerates carbon and nutrient pools, such that long-term impacts on the ecosystems may be small.

Book chapter↗

USGS2019

User guide to the FireCLIME Vulnerability Assessment (VA) Tool: A rapid and flexible system for assessing ecosystem vulnerability to climate-fire interactions

Decisionmakers need better methods for identifying critical ecosystem vulnerabilities to changing climate and fire regimes. Climate-wildfire-vegetation interactions are complex and hinder classification and projection necessary for development of management strategies. One such vulnerability assessment (VA) is FireCLIME VA, which allows users to compare management strategies under various climate scenarios and gauge the potential effectiveness of those strategies for reducing undesirable impacts of climate on wildfire regimes and resulting impacts of wildfire on natural ecosystems. Developed as part of the SW FireCLIME science-management partnership, FireCLIME is meant to be quick, flexible, and amendable to a range of data inputs (literature review, expert, and modeling or monitoring activities), allowing users to easily compare various fire-climate outcomes for one or more ecosystems of interest. Users can use literature, hypothetical scenarios, or quantitative data to implement the FireCLIME VA tool. This tool, unlike other vulnerability assessment, is best used iteratively to explore a range of possible scenarios and management strategies.

Report↗

USGS2020

Why are so many structures burning in California?

California has earned a reputation for wildfires that inflict serious damage on human infrastructure, dating back to images of Richard Nixon hosing down the roof of his house in the 1961 Bel-Air fire, and of the famous “fireproof” home of grocery store entrepreneur Fred Roberts burning to the ground in 1982. In recent years, this notoriety has been transformed into public alarm, reflected in the apocalyptic headlines of recent newspaper articles suggesting the “end of California” (New York Times, 30 October 2019) and that “California is becoming unlivable” (The Atlantic, 30 October 2019). Now the phrase “the new normal” has worked its way into the lexicon, sustained by record-breaking struc- ture loss numbers in 2017 and 2018 despite significantly lower structure losses in 2019. It remains to be seen whether or not those two recent years were back-to-back one-in-a-hundred-year events, or if the trend has crossed some kind of tipping point, but data do show a longterm trend of significant increase in structures lost to wildfires since the beginning of the 20th century (Fig. 1). What was an average of ~500 homes lost per year in Southern California from about 1950–2000 (CalFire 2000) has recently climbed to ~2700 structures per year statewide from 2000–2018 (Syphard and Keeley 2019). California is not alone in the U.S., or in the world, in suffering increasing impacts from wildfires (e.g., Blanchi et al. 2012, Haynes 2015, Viegas 2018). Impacts so far in the current Australian bushfire season have been recordbreaking, with several thousand structures lost, more than 25 fatalities, and unthinkable losses to wildlife. The question that follows, then, is why?

California↗

USGS2006

Dissemination of LANDFIRE Prototype Project data

The transfer of LANDFIRE data to users is the most important aspect of the Landscape Fire and Resource Management Planning Tools Project (LANDFIRE Prototype Project). The creation of an accurate, consistent, nationwide data set provides the foundation for a successful project. The final step is to make the data readily available to the user community. User capabilities and needs vary widely. Many users require LANDFIRE data to solve day-to-day wildfire management problems such as planning fuel treatments or managing active wildfires. Others use LANDFIRE data to gather information over large geographic areas for strategic planning and analyses. The diversity of users and the variety of applications of LANDFIRE data present an interesting challenge: to develop a data dissemination system that is comprehensive, user-friendly, and flexible. The system must be functional across many levels of technology, ranging from powerful computing capability to support national-scale strategic planning to field-level tactical wildfire operations support. The system must be sustainable, dependable, affordable, and adaptable to various levels of and changes in technology.

General Technical Report↗

USGS2002

Strategic plan for the Coordinated Intermountain Restoration Project

In 1982, the Bureau of Land Management’s (BLM) Idaho State Office began the Intermountain Greenstripping and Rehabilitation Research Project (IGRRP), or the “Greenstripping Program,” to investigate plant materials and technologies that can reduce wildfire incidence and improve rehabilitation practices. Rehabilitation is normally applied as a reactive process to wildfires, yet land managers in the Great Basin wish to become proactive by replacing fire-prone invasive annual grasses with native plants. The Coordinated Intermountain Restoration Project (CIRP) evolved from the Greenstripping Program to conduct research studies and provide technical assistance on restoration of native ecosystems on rangelands that are infested with invasive annual grasses or other invasive or noxious weeds. To accomplish this objective, the CIRP will promote the understanding of ecosystem disturbance dynamics as well as evaluate plant materials, site preparation techniques, weed control methods, seeding equipment, management methods, and monitoring techniques for restoration projects. The CIRP will not address the restoration of forested or woodland (juniper [Juniperus]) ecosystems. It will include a component on fuel management to reduce the impacts of wildfires on semiarid rangeland ecosystems where exotic annual grasses provide the fuel. The people who will benefit directly from this research include land managers and users of public and private lands in the northern Great Basin, the Columbia Plateau, and the Snake River Plain. The CIRP will provide an integration framework for a multidisciplinary approach to research with numerous opportunities for input and collaboration. The U.S. Geological Survey will initially dedicate approximately \$1 million over 5 years (about \$200,000 per year) to jump-start this effort. U.S. Geological Survey funds will establish a science advisory board to oversee the project. This board will contain members of Federal research and management agencies within the region. U.S. Geological Survey funds will support (1) continued development of VegSpec, a computer program that is a restoration expert system, (2) research to examine changes in ecosystem processes when native plant-dominated communities shift to communities dominated by exotic annual grasses, and (3) research to address mechanisms for establishing native plants in locations dominated by exotic annual grasses. Through these initial funds, USGS hopes to leverage additional research with other agencies (e.g., BLM’s Great Basin Restoration Initiative or the Native Plant Materials Development Project, which is an interagency program to supply and manage native plant materials for restoration and rehabilitation on Federal lands) or funding organizations (e.g., the U.S. Department of Agriculture’s [USDA] National Research Initiative Competitive Grants Program, or the USDA’s and U.S. Department of the Interior’s [USDOI] Joint Fire Science Program), and to obtain additional research partners (e.g., university or Federal scientists) willing to expand this effort to address all aspects of this strategic plan.

Information and Technology Report↗

USGS2021

Summary of wetland carbon and environmental management: Path forward

Wetlands around the world are under pressure from both anthropogenic sources such as land-use change and accelerating climate change (Erwin, 2009; Moomaw et al., 2018). Storage of carbon resources is a key ecosystem service of wetlands and offer natural solutions to climate change mitigation; policies and management actions could determine the fate of these resources and their contributions to climate mitigation and society needs. Inland and tidal wetlands store and sequester more carbon in soil and biomass than any other ecosystems on a per unit area basis, but also are responsible for the majority of ecosystem methane emissions (NASEM, 2019; Knox et al., 2019). Most of wetland carbon is stored deep in soils, thus providing long-term preservation of the resource (Nahlik and Fennessy, 2016). In addition to productive carbon sequestration in situ, wetlands also play a major role in lateral fluxes of carbon and other greenhouse gases along the continuum of different landscape features, including lakes, rivers, and coastal waters (Aufdenkampe et al., 2011; Ciais et al., 2008; Troxler et al., 2013). The ability of wetlands to regulate key processes of the carbon cycle is related to characteristics of the ecosystem, particularly hydrologic functions (Zhou et al., 2018). Disturbances to wetland hydrology, from land use change to natural disturbances such as wildfire, could lead to major disruptions to the wetland carbon cycle (Moomaw et al., 2018). This book is organized to first introduce fundamentals of wetland biogeochemistry (Neubauer and Megonigal, 2020) and carbon stock distribution and management in broad geographic and temporal domains, then provide a more in-depth treatment of case studies of different wetland types across the world (Fig. 1). A range of wetland management actions are described in the context of carbon sequestration and greenhouse gas emissions, including hydrology, sediment, avoided loss, restoration, wildfire, and co-habitation of multiple uses. Different wetland types or land uses considered in this book include freshwater herbaceous wetlands, peatlands of temperate as well as tropical climate, coastal tidal marshes and mangroves, drained croplands, and rice paddies.

Book chapter↗

USGS2016

Climate change and the eco-hydrology of fire: Will area burned increase in a warming western USA?

Wildfire area is predicted to increase with global warming. Empirical statistical models and process-based simulations agree almost universally. The key relationship for this unanimity, observed at multiple spatial and temporal scales, is between drought and fire. Predictive models often focus on ecosystems in which this relationship appears to be particularly strong, such as mesic and arid forests and shrublands with substantial biomass such as chaparral. We examine the drought–fire relationship, specifically the correlations between water-balance deficit and annual area burned, across the full gradient of deficit in the western USA, from temperate rainforest to desert. In the middle of this gradient, conditional on vegetation (fuels), correlations are strong, but outside this range the equivalence hotter and drier equals more fire either breaks down or is contingent on other factors such as previous-year climate. This suggests that the regional drought–fire dynamic will not be stationary in future climate, nor will other more complex contingencies associated with the variation in fire extent. Predictions of future wildfire area therefore need to consider not only vegetation changes, as some dynamic vegetation models now do, but also potential changes in the drought–fire dynamic that will ensue in a warming climate.

Western United States↗

USGS2017

Fuel-reduction management alters plant composition, carbon and nitrogen pools, and soil thaw in Alaskan boreal forest

Increasing wildfire activity in Alaska's boreal forests has led to greater fuel-reduction management. Management has been implemented to reduce wildfire spread, but the ecological impacts of these practices are poorly known. We quantified the effects of hand-thinning and shearblading on above- and belowground stand characteristics, plant species composition, carbon (C) and nitrogen (N) pools, and soil thaw across 19 black spruce ( Picea mariana ) dominated sites in interior Alaska treated 2-12 years prior to sampling. The density of deciduous tree seedlings was significantly higher in shearbladed areas compared to unmanaged forest (6.4 vs. 0.1 stems m −2 ), and unmanaged stands exhibited the highest mean density of conifer seedlings and layers (1.4 stems m −2 ). Understory plant community composition was most similar between unmanaged and thinned stands. Shearblading resulted in a near complete loss of aboveground tree biomass C pools while thinning approximately halved the C pool size (1.2 kg C m −2 compared to 3.1 kg C m −2 in unmanaged forest). Significantly smaller soil organic layer (SOL) C and N pools were observed in shearbladed stands (3.2 kg C m −2 and 116.8 g N m −2 ) relative to thinned (6.0 kg C m −2 and 192.2 g N m −2 ) and unmanaged (5.9 kg C m −2 and 178.7 g N m −2 ) stands. No difference in C and N pool sizes in the uppermost 10 cm of mineral soil was observed among stand types. Total C stocks for measured pools was 2.6 kg C m −2 smaller in thinned stands and 5.8 kg C m −2 smaller in shearbladed stands when compared to unmanaged forest. Soil thaw depth averaged 13 cm deeper in thinned areas and 46 cm deeper in shearbladed areas relative to adjacent unmanaged stands, although variability was high across sites. Deeper soil thaw was linked to shallower SOL depth for unmanaged stands and both management types, however for any given SOL depth, thaw tended to be deeper in shearbladed areas compared to unmanaged forest. These findings indicate that fuel-reduction management alters plant community composition, C and N pools, and soil thaw depth, with consequences for ecosystem structure and function beyond those intended for fire management.

Alaska↗

USGS2019

Fire legacies in eastern ponderosa pine forests

Disturbance legacies structure communities and ecological memory, but due to increasing changes in disturbance regimes, it is becoming more difficult to characterize disturbance legacies or determine how long they persist. We sought to quantify the characteristics and persistence of material legacies (e.g., biotic residuals of disturbance) that arise from variation in fire severity in an eastern ponderosa pine forest in North America. We compared forest stand structure and understory woody plant and bird community composition and species richness across unburned, low‐, moderate‐, and high‐severity burn patches in a 27‐year‐old mixed‐severity wildfire that had received minimal post‐fire management. We identified distinct tree densities (high: 14.3 ± 7.4 trees per ha, moderate: 22.3 ± 12.6, low: 135.3 ± 57.1, unburned: 907.9 ± 246.2) and coarse woody debris cover (high: 8.5 ± 1.6% cover per 30 m transect, moderate: 4.3 ± 0.7, low: 2.3 ± 0.6, unburned: 1.0 ± 0.4) among burn severities. Understory woody plant communities differed between high‐severity patches, moderate‐ and low‐severity patches, and unburned patches (all p < 0.05). Bird communities differed between high‐ and moderate‐severity patches, low‐severity patches, and unburned patches (all p < 0.05). Bird species richness varied across burn severities: low‐severity patches had the highest (5.29 ± 1.44) and high‐severity patches had the lowest (2.87 ± 0.72). Understory woody plant richness was highest in unburned (5.93 ± 1.10) and high‐severity (5.07 ± 1.17) patches, and it was lower in moderate‐ (3.43 ± 1.17) and low‐severity (3.43 ± 1.06) patches. We show material fire legacies persisted decades after the mixed‐severity wildfire in eastern ponderosa forest, fostering distinct structures, communities, and species in burned versus unburned patches and across fire severities. At a patch scale, eastern and western ponderosa system responses to mixed‐severity fires were consistent.

Nebraska↗

USGS2022

Demographic effects of a megafire on a declining prairie grouse in the mixed-grass prairie

Recent studies have documented benefits of small, prescribed fire and wildfire for grassland-dependent wildlife, such as lesser prairie-chickens ( Tympanuchus pallidicintus ), but wildlife demographic response to the scale and intensity of megafire (wildfire >40,000 ha) in modern, fragmented grasslands remains unknown. Limited available grassland habitat makes it imperative to understand if increasing frequency of megafires could further reduce already declining lesser prairie-chicken populations, or if historical evolutionary interactions with fire make lesser prairie-chickens resilient. To evaluate lesser prairie-chicken demographic response to megafires, we compared lek counts, nest density, and survival rates of adults, nests, and chicks before (2014–2016) and after (2018–2020) a 2017 megafire in the mixed-grass prairie of Kansas, USA (Starbuck fire ~254,000 ha). There was a 67% decline in attending males on leks post-fire and a 57% decline in occupied leks post-fire. Despite population declines as indicated by lek counts, adult female breeding season survival ( Ŝ ) was similar pre- ( Ŝ = 0.65 ± 0.08 [SE]) and post-fire (0.61 ± 0.08), as was chick survival (pre-fire: 0.23 ± 0.07; post-fire: 0.27 ± 0.11). Nest survival appeared lower post-fire (pre-fire: 0.38 ± 0.06; post-fire: 0.20 ± 0.06), but did not differ at the 95% confidence interval. Nest density of marked females declined 73% in areas burned by megafire. Although lesser prairie-chickens persisted in the study area and we documented minimal effects on most demographic rates, reduced lesser prairie-chicken abundance and reproductive output suggests full recovery may take >3 years. Increased propensity for megafire resulting from suppression of smaller fires, compounded by climate change and woody encroachment, may impose a short-term (3–5 year) threat to already declining lesser prairie-chicken populations.

Kansas, Oklahoma↗

USGS2016

Mid-21st-century climate changes increase predicted fire occurrence and fire season length, Northern Rocky Mountains, United States

Climate changes are expected to increase fire frequency, fire season length, and cumulative area burned in the western United States. We focus on the potential impact of mid-21st-century climate changes on annual burn probability, fire season length, and large fire characteristics including number and size for a study area in the Northern Rocky Mountains. Although large fires are rare they account for most of the area burned in western North America, burn under extreme weather conditions, and exhibit behaviors that preclude methods of direct control. Allocation of resources, development of management plans, and assessment of fire effects on ecosystems all require an understanding of when and where fires are likely to burn, particularly under altered climate regimes that may increase large fire occurrence. We used the large fire simulation model FSim to model ignition, growth, and containment of wildfires under two climate scenarios: contemporary (based on instrumental weather) and mid-century (based on an ensemble average of global climate models driven by the A1B SRES emissions scenario). Modeled changes in fire patterns include increased annual burn probability, particularly in areas of the study region with relatively short contemporary fire return intervals; increased individual fire size and annual area burned; and fewer years without large fires. High fire danger days, represented by threshold values of Energy Release Component (ERC), are projected to increase in number, especially in spring and fall, lengthening the climatic fire season. For fire managers, ERC is an indicator of fire intensity potential and fire economics, with higher ERC thresholds often associated with larger, more expensive fires. Longer periods of elevated ERC may significantly increase the cost and complexity of fire management activities, requiring new strategies to maintain desired ecological conditions and limit fire risk. Increased fire activity (within the historical range of frequency and severity, and depending on the extent to which ecosystems are adapted) may maintain or restore ecosystem functionality; however, in areas that are highly departed from historical fire regimes or where there is disequilibrium between climate and vegetation, ecosystems may be rapidly and persistently altered by wildfires, especially those that burn under extreme conditions.

Idaho↗