Summer Wildfire Research Articles

Anatomy of a post-wildfire recovery: Responses of mammals to a Black Summer wildfire in a fox-free landscape

Wildfires are predicted to increase in frequency and severity with climate change. Devising effective strategies to ensure wildfires do not hasten a decline in wildlife populations hinges on developing a deeper understanding of how species are affected by recent wildfires. I investigated the response of eight species of medium-sized mammals over a 4-year period (2020–2023) following a wildfire in the Australian Black Summer fire season. Pre-wildfire population levels were not known. These species differed in their ability to survive the passage of fire; from being able to flee the fire front, to remaining in protective shelters, to favouring unburnt forest types, to none of these strategies. Camera trapping was conducted from 5 months to 4 years after the fire across 62 sites in wet and dry sclerophyll forest (burnt and unburnt) and rainforest (unburnt) to characterise both initial survival and subsequent reproduction-led post-fire occupancy. There was consistency in the response of species in year 1. Those assumed to be able to flee the fires showed medium-high post-fire occupancy regardless of whether a site was burnt. Those that use protective shelters and unburnt forest also showed high occupancy. One species without these options showed greatly reduced occupancy in year 1 relative to years 3 and 4. Most species showed evidence of increased detection across years, which is inferred to reflect increased abundance, and was expected given substantially above average rainfall for three years following the fire. The feral cat was the only predator sufficiently widespread to be of concern in species’ recovery but was rarely detected in years 1 and 2, relative to years 3 and 4. This study provides evidence that many species, including three threatened species, have the ability to survive the passage of fire, and show high post-fire occupancy. The study landscape contained abundant habitat elements (unburnt rainforest, boulder fields) that promote survival through a wildfire and post-fire recovery, providing insights to guide future conservation actions.

Wildfire Effects on the Soil Respiration and Bacterial Microbiota Composition in Mediterranean-Type Ecosystems

This work provides insights into the effect of fire on soil processes in Mediterranean-type ecosystems in Cyprus. Soil samples from mountainous sites that were subjected to a summer wildfire and adjacent control samples were collected. Incubations were used to estimate basal respiration and isolate soil CO2 release of heterotrophic microorganisms from autotrophic root respiration and heterotrophic respiration from litter decomposition. Physicochemical property changes, bacteria community changes using DNA extraction and 16S rRNA gene analysis, and the effects of ash and fresh litter addition were studied to reveal the microbial composition and the post-fire soil function. Laboratory incubation showed that burned soils constantly showed higher microbial respiration rates compared with control unburned areas, even six months after a fire. Adding ash to unburned samples increased microbial respiration, suggesting that increased nutrient availability positively corelates with the increased release of CO2 from fire-affected soil. Elevated temperatures due to the wildfire exerted significant effects on the composition of soil bacterial microbiota. Nevertheless, the wildfire did not affect the alpha-diversity of soil bacteria. New communities of microorganisms are still able to decompose fresh plant material after a fire, but at a slower rate than natural pre-fire populations.

Seasonal extreme temperatures and short-term fine particulate matter increases pediatric respiratory healthcare encounters in a sparsely populated region of the intermountain western United States

BackgroundWestern Montana, USA, experiences complex air pollution patterns with predominant exposure sources from summer wildfire smoke and winter wood smoke. In addition, climate change related temperatures events are becoming more extreme and expected to contribute to increases in hospital admissions for a range of health outcomes. Evaluating while accounting for these exposures (air pollution and temperature) that often occur simultaneously and may act synergistically on health is becoming more important.MethodsWe explored short-term exposure to air pollution on children’s respiratory health outcomes and how extreme temperature or seasonal period modify the risk of air pollution-associated healthcare events. The main outcome measure included individual-based address located respiratory-related healthcare visits for three categories: asthma, lower respiratory tract infections (LRTI), and upper respiratory tract infections (URTI) across western Montana for ages 0–17 from 2017–2020. We used a time-stratified, case-crossover analysis with distributed lag models to identify sensitive exposure windows of fine particulate matter (PM2.5) lagged from 0 (same-day) to 14 prior-days modified by temperature or season.ResultsFor asthma, increases of 1 µg/m3 in PM2.5 exposure 7–13 days prior a healthcare visit date was associated with increased odds that were magnified during median to colder temperatures and winter periods. For LRTIs, 1 µg/m3 increases during 12 days of cumulative PM2.5 with peak exposure periods between 6–12 days before healthcare visit date was associated with elevated LRTI events, also heightened in median to colder temperatures but no seasonal effect was observed. For URTIs, 1 unit increases during 13 days of cumulative PM2.5 with peak exposure periods between 4–10 days prior event date was associated with greater risk for URTIs visits that were intensified during median to hotter temperatures and spring to summer periods.ConclusionsDelayed, short-term exposure increases of PM2.5 were associated with elevated odds of all three pediatric respiratory healthcare visit categories in a sparsely population area of the inter-Rocky Mountains, USA. PM2.5 in colder temperatures tended to increase instances of asthma and LRTIs, while PM2.5 during hotter periods increased URTIs.

Short-term effects of a high-severity summer wildfire on conifer forest moth (Lepidoptera) communities in New Mexico, USA.

Forest fires in North America are becoming larger in area and burning with higher severity as a result of climate change and land management practices. High-severity, stand-replacement fires can inflict major changes to forest insect communities, potentially extirpating many species through altered post-fire habitat resources. We assessed forest-dwelling macrolepidopteran moth communities in mixed conifer and ponderosa pine forests during the first year after the 2011 Las Conchas fire in New Mexico, USA. We deployed blacklight traps in replicated burned and unburned stands during June, July, and August in 2012. We collected 9,478 individuals, representing 211 species and 8 families. Noctuidae (124 species) and Geometridae (53) comprised the majority of the taxa, followed by Erebidae (21), Sphingidae (5), Notodontidae (3), Lasiocampidae (2), Saturniidae (2), and Drepanidae (1). Moth communities (species composition and abundances) in each forest type (mixed conifer vs. ponderosa pine) were statistically distinguishable, but shared 56.4% (119) of observed species. Overall, compared to unburned forests, post-fire moth communities in both forest types had significantly lower numbers of individuals, species richness and diversity, and lower evenness in ponderosa pine forests. As expected, categorizing moth taxa by larval host plant taxa revealed that reductions of moth populations following fire were associated with the elimination or reduction of available larval host plants (particularly conifers, oaks, and junipers). We predict that future moth community succession will likely parallel the overall transformation from a forested landscape to a montane meadow/grassland ecosystem, with continued reduction in tree-feeding species and increasing dominance by forb/grass-feeding species.

Space-based observation of early summer wildfire event and its environmental proxies during 2021 in Eastern Peninsular India

Space-based observation of early summer wildfire event and its environmental proxies during 2021 in Eastern Peninsular India

Climate Dynamics Preceding Summer Forest Fires in California and the Extreme Case of 2018

Abstract Recent record-breaking wildfire seasons in California prompt an investigation into the climate patterns that typically precede anomalous summer burned forest area. Using burned-area data from the U.S. Forest Service’s Monitoring Trends in Burn Severity (MTBS) product and climate data from the fifth major global reanalysis produced by the European Centre for Medium-Range Weather Forecasts (ERA5) over 1984–2018, relationships between the interannual variability of antecedent climate anomalies and July California burned area are spatially and temporally characterized. Lag correlations show that antecedent high vapor pressure deficit (VPD), high temperatures, frequent extreme high temperature days, low precipitation, high subsidence, high geopotential height, low soil moisture, and low snowpack and snowmelt anomalies all correlate significantly with July California burned area as far back as the January before the fire season. Seasonal regression maps indicate that a global midlatitude atmospheric wave train in late winter is associated with anomalous July California burned area. July 2018, a year with especially high burned area, was to some extent consistent with the general patterns revealed by the regressions: low winter precipitation and high spring VPD preceded the extreme burned area. However, geopotential height anomaly patterns were distinct from those in the regressions. Extreme July heat likely contributed to the extent of the fires ignited that month, even though extreme July temperatures do not historically significantly correlate with July burned area. While the 2018 antecedent climate conditions were typical of a high-burned-area year, they were not extreme, demonstrating the likely limits of statistical prediction of extreme fire seasons and the need for individual case studies of extreme years. Significance Statement The purpose of this study is to identify the local and global climate patterns in the preceding seasons that influence how the burned summer forest area in California varies year-to-year. We find that a dry atmosphere, high temperatures, dry soils, less snowpack, low precipitation, subsiding air, and high pressure centered west of California all correlate significantly with large summer burned area as far back as the preceding January. These climate anomalies occur as part of a hemispheric scale pattern with weak connections to the tropical Pacific Ocean. We also describe the climate anomalies preceding the extreme and record-breaking burned-area year of 2018, and how these compared with the more general patterns found. These results give important insight into how well and how early it might be possible to predict the severity of an upcoming summer wildfire season in California.

Everyday Agency in Precarious Times

I live in a region of northwest Oregon that, over the past half decade, has experienced an accelerated accumulation of climate-related disasters. From September 2020 to July 2021, fire, ice, and heat killed people, plants, birds, and animals in and around the Willamette Valley. Other climate events are more routine: severe drought is widespread, while summer wildfire smoke regularly smothers the atmosphere. These events overlapped with a global pandemic that continues to ravage everything. Distressed over our overwhelming and overwhelmed planet, I often wonder what can I—can we—do?Four years ago, I gained a backyard and started gardening; now, my husband and I grow food year-round. It’s a challenging, messy, fulfilling pastime that unfailingly reveals the limits of my intentions. When I’m working with the earth, I reflect on theories of agency that shaped my dissertation. In “Toward a Posthuman Perspective,” Sarah Hallenbeck invites scholars to examine how everyday rhetorics of “seemingly nondeliberate and arhetorical embodied activities” (12) shape cultural notions of gender. Her vocabulary of “nondeliberate” and “arhetorical” led me to Marilyn Cooper’s “Rhetorical Agency as Emergent and Enacted,” then Stephanie Kerschbaum’s “On Rhetorical Agency and Disclosing Disability in Academic Writing.” Cooper identifies rhetorical agency as a property that manifests during dynamic “dance[s] of perturbation and response” (421) among agents. Moving beyond causal logics, Cooper untethers agents from consciously creating change and advances rhetorical agency as acting in the world while remaining open to the potential for (unpromised) difference. Kerschbaum sees agency as “a kind of kinetic energy” (63) that inhabits the interplay within rhetorical encounters. That interplay is meaningful independent of results, which broadens notions of rhetorical success.These texts animate key associations within rhetorical studies: individuals and systems, intentions and outcomes, evidence and assessment. They help me recognize an agency that arises as I interact with the environment and attempt to create something new. Valuing the commonplace activities that texture my days—seeding, watering, inspecting—means that agency emerges as I try. Difficult weather and pests may disrupt plants and plans, yet the authors expanded my sense of what agency can be when released from assumptions about human control. Indeed, learning to separate intentions from results and to locate meaning in efforts has enriched my outlook beyond my backyard. Hallenbeck reminds me that posthuman agency doesn’t disregard human action but “redeems [the] agent as a participant” (19) in networks and a contributor to larger, unknowable transformations. I feel this acutely, for my individual actions situate me in a broader collective whose members work toward food, environmental, and racial justices from where we can. Climate change has arrived, and I will continue to garden at home and at community gardens with others as we learn about and revise enactments of resilience in these precarious times. Hallenbeck, Cooper, and Kerschbaum have offered more than a critical orientation—they’ve revealed a sustainable ethic for living in this world.

Grazing and defoliation timing effects in Great Plains ponderosa pine woodland following a large summer wildfire

There remains a high level of ambiguity around post-fire grazing management. The Lodgepole Complex fire burned 109,346 ha in east-central Montana in July 2017, including areas previously burned in 2003 by the Bureau of Land Management for fuels mitigation. We hypothesized that herbaceous productivity and species composition in ponderosa pine woodlands are resistant to moderate grazing and timing of defoliation the first growing season after fire. Eight exclosures (25 × 15 m) were built, 4 on reburned area and 4 on wildfire area. To determine grazing effects, a 15 × 10 m sampling area in each exclosure was paired with a grazed section outside the exclosure. Additionally, four 5x10-m plots were established within each exclosure and were mowed to 10 cm in June, July, August, or not mowed to determine seasonal defoliation effects. Differences between grazed and nongrazed sites in 2019 were limited. There was a trend for less old dead biomass in grazed than nongrazed treatments. Species richness was greater on grazed sites than nongrazed or reburn sites. Native species richness was greater on grazed sites than nongrazed sites and reburn sites had an intermediate level of native species richness. Standing crop was reduced by defoliation, with current year and perennial grass biomass being unaffected. The reduction in standing crop was driven by less old dead biomass on defoliated plots. June defoliation reduced C3 grasses and increased C4 grasses, and June and July defoliation each reduced annual grasses. Simpson’s and native Simpson’s diversity were greater on defoliated plots. Results indicate ponderosa pine woodland is resilient to moderate post-fire grazing.

Operational Evaluation of a Wildfire Air Quality Model from a Forecaster Point of View

Abstract An evaluation of an operational wildfire air quality model (WFAQM) has been performed. Evaluation metrics were chosen through an analysis of interviews and a survey of professionals who use WFAQM forecasts as part of their daily responsibilities. The survey revealed that professional users generally focus on whether forecast air quality will exceed thresholds that trigger local air quality advisories (e.g., an event), their analysis scale is their region of responsibility, they are interested in short-term (≈24 h) guidance, missing an event is worse than issuing a false alarm, and there are two types of users—one that takes the forecast at face value, and the other that uses it as one of several information sources. Guided by these findings, model performance of Environment and Climate Change Canada’s current operational WFAQM (FireWork) was assessed over western Canada during three (2016–18) summer (May–September) wildfire seasons. Evaluation was performed at the geographic scale at which individual forecasts are issued (the forecast region) using gridded particulate matter 2.5 (PM2.5) fields developed from a machine learning–based downscaling of satellite and meteorological data. For the “at face value” user group, model performance was measured using the Peirce skill score. For the “as information source” user group, model performance was measured using the divergence skill score. For this metric, forecasts were first converted to event probabilities using binomial regression. We find when forecasts are taken at face value, FireWork cannot outperform a nearest-neighbor-based persistence model. However, when forecasts are considered as an information source, FireWork is superior to the persistence-based model.

Impact of fine particulate matter (PM2.5) smoke during the 2019 / 2020 Australian bushfire disaster on emergency department patient presentations

The aim of this paper was to describe the patient characteristics and outcomes from a metropolitan emergency department (ED) during the 2019/2020 ‘Black Summer Bushfires’ disaster in Australia and compare the patient characteristics and outcomes to a matched period from the same ED one year earlier. Years of drought, low relative humidity, high temperatures, and high forest fuel loads led to catastrophic fire conditions across Australia during 2019 and 2020. As a result; 33 people died, 3 billion animals and 24 to 40 million hectares were lost, and 3,000 homes were destroyed. The impact of wildfire smoke is emerging in the literature regarding an exacerbation of respiratory, cardiac and cardiovascular disease. However, the impact on Australian EDs is minimally reported in the literature. This retrospective cross-sectional cohort study used routinely collected data from the ED patient information system from one metropolitan Australian ED. Data were obtained for patient presentations during the 2019/2020 Black Summer Bushfire period and a matched period, 2018/2019, one year earlier. Daily mean air quality indicators (PM 2.5 , PM 10 ) were obtained from the nearest air quality monitoring station. Data analysis included descriptive statistics, correlation coefficient and inferential statistics. Statistical significance was set at p ≤ 0.05. The 2019/2020 study period had a statistically significantly higher airborne particulate matter (PM 2.5 ) when compared to the matched period (p=<0.001), with comparable presentations between the study periods. However, an increase in respiratory related presentations (p<0.001; χ 2 = 34.31) was noted in the 2019/2020 period, with a positive correlation between daily increasing mean air quality (PM 2.5 , PM 10 ) and increasing patient presentations with respiratory related illness (p<0.001). Proportionately, patient demographics; mode of arrival, triage category, length of stay and admissions did not differ between periods. However, there was an increase in the raw number of patients being admitted to hospital with respiratory related illnesses, with a statistically significantly longer stay in the ED when compared to those discharged home (p<0.001). Wildfires produce smoke and subsequently poor air quality. The 2019/2020 Black Summer wildfire disaster in Australia resulted in an increase in respiratory-related patient presentations to the ED. Targeted public warning systems could be implemented in an attempt to limit an individual's exposure to wildfire smoke. Further, health services should monitor air quality as a predictor of patient presentations and subsequent health service demand, in support of ED preparedness.

Grazing and Defoliation Timing Effects in Great Plains Ponderosa Pine Woodland Following a Large Summer Wildfire

Grazing and Defoliation Timing Effects in Great Plains Ponderosa Pine Woodland Following a Large Summer Wildfire

The Summer 2019-2020 Wildfires in East Coast Australia and Their Impacts on Air Quality and Health in New South Wales, Australia.

The 2019–2020 summer wildfire event on the east coast of Australia was a series of major wildfires occurring from November 2019 to end of January 2020 across the states of Queensland, New South Wales (NSW), Victoria and South Australia. The wildfires were unprecedent in scope and the extensive character of the wildfires caused smoke pollutants to be transported not only to New Zealand, but also across the Pacific Ocean to South America. At the peak of the wildfires, smoke plumes were injected into the stratosphere at a height of up to 25 km and hence transported across the globe. The meteorological and air quality Weather Research and Forecasting with Chemistry (WRF-Chem) model is used together with the air quality monitoring data collected during the bushfire period and remote sensing data from the Moderate Resolution Imaging Spectroradiometer (MODIS) and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellites to determine the extent of the wildfires, the pollutant transport and their impacts on air quality and health of the exposed population in NSW. The results showed that the WRF-Chem model using Fire Emission Inventory (FINN) from National Center for Atmospheric Research (NCAR) to simulate the dispersion and transport of pollutants from wildfires predicted the daily concentration of PM2.5 having the correlation (R2) and index of agreement (IOA) from 0.6 to 0.75 and 0.61 to 0.86, respectively, when compared with the ground-based data. The impact on health endpoints such as mortality and respiratory and cardiovascular diseases hospitalizations across the modelling domain was then estimated. The estimated health impact on each of the Australian Bureau of Statistics (ABS) census districts (SA4) of New South Wales was calculated based on epidemiological assumptions of the impact function and incidence rate data from the 2016 ABS and NSW Department of Health statistical health records. Summing up all SA4 census district results over NSW, we estimated that there were 247 (CI: 89, 409) premature deaths, 437 (CI: 81, 984) cardiovascular diseases hospitalizations and 1535 (CI: 493, 2087) respiratory diseases hospitalizations in NSW over the period from 1 November 2019 to 8 January 2020. The results are comparable with a previous study based only on observation data, but the results in this study provide much more spatially and temporally detailed data with regard to the health impact from the summer 2019–2020 wildfires.

Predicting burnt areas during the summer season in Portugal by combining wildfire susceptibility and spring meteorological conditions

Wildfire susceptibility maps are a well-known tool for optimizing available means to plan for prevention, early detection, and wildfire suppression in Portugal, especially regarding the critical fire season (1 July − 30 September). These susceptibility maps typically disregard seasonal weather conditions on each given year, being based on predisposing variables that remain constant on the long-term, such as elevation. We employ logistic regression for combining wildfire susceptibility with a meteorological index representing spring conditions (the Seasonal Severity Rating), with the purpose of predicting, for any given year and ahead of the critical fire season, which areas will burn. Results show that the combination of the index with wildfire susceptibility slightly increases the capability to predict which areas will burn, when compared with susceptibility alone. Spring meteorological context was found better suited for predicting if the following summer wildfire season will be more severe, rather than predicting where wildfires will effectively occur. The model can be updated yearly after the critical wildfire season and can be applied to optimize the allocation of human and material resources regarding the prevention, early detection and suppression activities, required to reduce the severity of wildfires in the country.

Repeated fall prescribed fire in previously thinned Pinus ponderosa increases growth and resistance to other disturbances

In western North America beginning in the late 19th century, fire suppression and other factors resulted in dense ponderosa pine (Pinus ponderosa) forests that are now prone to high severity wildfire, insect attack, and root diseases. Thinning and prescribed fire are commonly used to remove small trees, fire-intolerant tree species, and shrubs, and to reduce surface and aerial fuels. These treatments can be effective at lowering future fire severity, but prescribed burns must be periodically repeated to maintain favorable conditions and are feasible only outside the historical summer wildfire season. This study examines tree growth and mortality associated with spring and fall burning repeated at five (5 yr) and fifteen-year (15 yr) intervals in six previously thinned ponderosa pine stands in the southern Blue Mountain Ecoregion near Burns, Oregon, USA. Each stand consisted of an unburned control, and four season-by-burn interval treatments: spring 5 yr, spring 15 yr, fall 5 yr, and fall 15 yr. Burning was initiated in fall 1997 and spring 1998. Pine height and diameter growth was evaluated in 2013, 15 years following initial treatment. Mortality was assessed annually from 2002 to 2017, when these stands experienced severe defoliation from pine butterfly (PB, Neophasia menapia), followed by a moderate outbreak of western pine beetle (WPB, Dendroctonus brevicomis), allowing us to examine resistance to these disturbances. Pine in the 5 yr fall treatments added more diameter than spring 15 yr and marginally more than spring 5 yr, while fall 15 yr added marginally more diameter than spring 15 yr. In addition, the fall 5 yr treatments had lower mortality associated with prescribed fire, PB, WPB, Ips spp., red turpentine beetle (RTB, D. valens), and mountain pine beetle (MPB, D. ponderosae), but the effect was not always significant. Annosus root disease (ARD, caused by Heterobasidion irregulare) and black stain root disease (BSRD, caused by Leptographium wagneri var. ponderosum) appear to be unaffected by burning. However, BSRD occurrence dramatically declined in all treatments, probably a result of thinning prior to study initiation. Results from this study demonstrate that repeated fall burning, especially at 5-year intervals, improves ponderosa pine diameter growth and may provide resistance to future biotic and abiotic disturbances while spring burning, regardless of frequency, does not.

The botanical biofiltration of elevated air pollution concentrations associated the Black Summer wildfire natural disaster

The ‘Black Summer’ wildfires that affected Australia over the 2019–2020 summer have led to concern over the health effects of exposure to wildfire emissions, and generated a need for means to reduce exposure. Recently, active green infrastructure has been implemented in cities to assist in the removal of urban air pollution, however the filtration of wildfire emissions has not been previously tested. Here, we field trial botanical biofiltration for the reduction of elevated air pollutant concentrations associated with Black Summer. Two active green walls were installed in outdoor environments in Sydney over Black Summer, with the concentrations of NO2, O3 and PM2.5 in ambient and filtered air streams monitored over 14 days with elevated air pollution concentrations due to wildfire emissions. Average pollutant single pass removal efficiencies of 63.17%, 38.79% and 24.84% for NO2, O3 and PM2.5 respectively were recorded, with clean air delivery rates of 558.90 m3/h, 343.19 m3/h and 219.77 m3/h for NO2, O3 and PM2.5 respectively for each 5 m2 biofilter wall. Weak negative associations were observed between the removal efficiency of NO2 and PM2.5 and their corresponding ambient concentrations. Strategic employment of botanical biofiltration may thus be of value in reducing wildfire emissions in sensitive populations.

Small-scale water deficits after wildfires create long-lasting ecological impacts

Ecological droughts are deficits in soil–water availability that induce threshold-like ecosystem responses, such as causing altered or degraded plant-community conditions, which can be exceedingly difficult to reverse. However, ‘ecological drought’ can be difficult to define, let alone to quantify, especially at spatial and temporal scales relevant to land managers. This is despite a growing need to integrate drought-related factors into management decisions as climate changes result in precipitation instability in many semi-arid ecosystems. We asked whether success in restoration seedings of the foundational species big sagebrush (Artemisia tridentata) was related to estimated water deficit, using the SoilWat2 model and data from >600 plots located in previously burned areas in the western United States. Water deficit was characterized by: (1) the standardized precipitation-evapotranspiration index (SPEI), a coarse-scale drought index, and (2) the number of days with wet and warm conditions in the near-surface soil, where seeds and seedlings germinate and emerge (i.e. days with 0–5 cm deep soil water potential >−2.5 MPa and temperature above 0 °C). SPEI, a widely used drought index, was not predictive of whether sagebrush had reestablished. In contrast, wet-warm days elicited a critical drought threshold response, with successfully reestablished sites having experienced seven more wet-warm days than unsuccessful sites during the first March following summer wildfire and restoration. Thus, seemingly small-scale and short-term changes in water availability and temperature can contribute to major ecosystem shifts, as many of these sites remained shrubless two decades later. These findings help clarify the definition of ecological drought for a foundational species and its imperiled semi-arid ecosystem. Drought is well known to affect the occurrence of wildfires, but drought in the year(s) after fire can determine whether fire causes long-lasting, negative impacts on ecosystems.

Exploring the effect of hydrological connectivity and soil burn severity on sediment yield after wildfire and mulching

AbstractSoil erosion can potentially threaten different resources inside and outside of burned areas, and the risk of water becoming contaminated with sediment may be particularly severe. Various postfire actions, such as applying straw mulch, have been carried out in northwestern Spain in recent years with the aim of mitigating the risk of soil erosion. Nonetheless, because of the short interval between summer wildfire and autumn rains, careful selection and prioritization of the areas to be treated is crucial. Changes in hydrological connectivity could be measured and used as a criterion for selecting such areas. However, studies addressing changes in hydrological connectivity as a consequence of forest fires are scarce. In the present study, we assessed the effects of fire and postfire helimulching on the hydrological connectivity and sediment loads in a forest catchment burned by a wildfire in August 2016. Sediment yields were recorded in 20 plots (180 m2). Hydrological connectivity was computed with a version of the Borselli index and two alternative weighting factors: the C factor from the Revised Universal Soil Loss Equation and a factor based on field surveys of soil burn severity. The effect of mulching was also considered. The results indicate that the version of the Borselli index based on field measurements of soil burn severity best reflects the susceptibility to postfire sediment delivery. Moreover, this method was also suitable for evaluating the effect of mulching on soil erosion. The study findings may help forest managers to plan postfire actions.

Use of low-cost PM monitors and a multi-wavelength aethalometer to characterize PM2.5 in the Yakama Nation reservation

Rural lower Yakima Valley, Washington is home to the reservation of the Confederated Tribes and Bands of the Yakama Nation, and is a major agricultural region. Episodic poor air quality impacts this area, reflecting sources of particulate matter with a diameter of less than 2.5 μm (PM2.5) that include residential wood smoke, agricultural biomass burning and other emissions, truck traffic, backyard burning, and wildfire smoke. University of Washington partnered with the Yakama Nation Environmental Management Program to investigate characteristics of PM2.5 using 9 months of data from a combination of low-cost optical particle counters and a 5-wavelength aethalometer (MA200 Aethlabs) over 4 seasons and an episode of summer wildfire smoke. The greatest percentage of hours sampled with PM2.5 >12 μg/m3 occurred during the wildfire smoke episode (59%), followed by fall (23%) and then winter (21%). Mean (SD) values of Delta-C (μg/m3), which has been posited as an indicator of wood smoke, and determined as the mass absorbance difference at 375–880 nm, were: summer – wildfire smoke 0.34 (0.52), winter 0.27 (0.32), fall 0.10 (0.22), spring 0.05 (0.11), and summer – no wildfire smoke 0.04 (0.14). Mean (95% confidence interval) values of the absorption Ångström exponent, an indicator of the wavelength dependence of the aerosol, were: winter 1.5 (1.2–1.8), summer – wildfire smoke 1.4 (1.0–1.8), fall 1.3 (1.1–1.4), spring 1.2 (1.1–1.4), and summer – no wildfire smoke 1.2 (1.0–1.3). The trends in Delta-C and absorption Ångström exponents are consistent with expectations that a higher value reflects more biomass burning. These results suggest that biomass burning is an important contributor to PM2.5 in the wintertime, and emissions associated with diesel and soot are important contributors in the fall; however, the variety of emissions sources and combustion conditions present in this region may limit the utility of traditional interpretations of aethalometer data. Further research on the interpretation of aethalometer data in regions with complex emissions would contribute to much-needed understanding in communities impacted by air pollution from agricultural as well as residential sources of combustion.

Observed Impacts of Anthropogenic Climate Change on Wildfire in California

AbstractRecent fire seasons have fueled intense speculation regarding the effect of anthropogenic climate change on wildfire in western North America and especially in California. During 1972–2018, California experienced a fivefold increase in annual burned area, mainly due to more than an eightfold increase in summer forest‐fire extent. Increased summer forest‐fire area very likely occurred due to increased atmospheric aridity caused by warming. Since the early 1970s, warm‐season days warmed by approximately 1.4 °C as part of a centennial warming trend, significantly increasing the atmospheric vapor pressure deficit (VPD). These trends are consistent with anthropogenic trends simulated by climate models. The response of summer forest‐fire area to VPD is exponential, meaning that warming has grown increasingly impactful. Robust interannual relationships between VPD and summer forest‐fire area strongly suggest that nearly all of the increase in summer forest‐fire area during 1972–2018 was driven by increased VPD. Climate change effects on summer wildfire were less evident in nonforested lands. In fall, wind events and delayed onset of winter precipitation are the dominant promoters of wildfire. While these variables did not change much over the past century, background warming and consequent fuel drying is increasingly enhancing the potential for large fall wildfires. Among the many processes important to California's diverse fire regimes, warming‐driven fuel drying is the clearest link between anthropogenic climate change and increased California wildfire activity to date.

Montane valley grasslands are highly resistant to summer wildfire

AbstractAimsUnderstanding the ecological role of fire in shaping plant communities in fire‐prone ecosystems is needed for ecosystem restoration, preservation and management. We investigated the effects of wildfire on plant community structure and the biotic and abiotic factors that are most influential in stabilizing and/or driving change before and after burning in high‐elevation montane grasslands dominated by C3 species receiving a mean annual precipitation of 545 mm.LocationValles Caldera National Preserve, Jemez Mountains, New Mexico, USA.MethodsLong‐term data (10 year pre‐fire; 5 year post‐fire) on plant community composition of nine burned and seven unburned grassland sites were used to determine the response of montane grasslands to a summer wildfire. We used multivariate and univariate analyses to determine changes in plant community composition and structure, pre‐ and post‐wildfire on burned and unburned grasslands.ResultsThe montane grassland community consisted of 155 plant taxa, including 44 perennial grasses, one annual grass, 92 perennial forbs and nine annual forbs. We found that these fire‐adapted plant communities were highly resilient to fire; fire had no significant effects on composition or structure beyond the normal range of inter‐annual variability. Instead, seasonal precipitation had the largest influence on plant community dynamics over time, with lower average plant canopy height and diversity during drought periods.ConclusionOur results show that fire has very limited effects on the composition and structure of these C3‐dominated montane grasslands. Our results support efforts by land managers to reintroduce fire on these historically burned landscapes.