High Burn Severity Research Articles

Wildfire severity alters soil microbial exoenzyme production and fungal abundances in the southern Appalachian Mountains

Climate change has increased drought frequency and duration that are exacerbated by increased temperatures globally. This effect has, and will continue, to increase fire occurrence across many regions of North America. In the southern Appalachian Mountains, wildfires with high burn severity occurred in 2016 due to increased drought and human activity. To investigate the effects of burn severity on soil physicochemical properties, microbial extracellular enzyme production, and microbial abundances in a temperate region, surface soils (0–15 cm) were collected from two sites (the Great Smoky Mountains National Park in Tennessee and the Nantahala National Forest in North Carolina, USA) spanning lightly, moderately, and severely burned areas, accompanied by adjacent unburned locations that act as controls. The soil samples were collected at three time points between 2017 and 2019 (i.e., 0.5, 1, and 2.5 years post-fire) among burn severity plots. Total hydrolytic enzyme production varied over time, with severe burn plots having significantly lower enzyme production at 2.5 years post-fire. Individual enzymes varied among burn severities and across time post-fire. Light burn plots showed greater carbon-specific (β-glucosidase and β-xylosidase) and phosphorus-specific (acid phosphatase) enzyme activities at 0.5 years post-fire, but this effect was transient. At 2.5 years post-fire, the β-xylosidase and acid phosphatase activities were lower in severe or moderate burn plots relative to the controls. In contrast, the activity of nitrogen-specific enzyme leucyl aminopeptidase was the lowest in severe burn plots at 0.5 years post-fire, but was the lowest in light burn plots at 2.5 years post-fire. The fungi:bacteria ratio declined with burn severity, indicating that fungi are sensitive or less resilient to high burn severity during recovery. These results suggest that wildfires alter trajectories for soil microbial structure and function within a 2.5-year timeframe, which potentially has long-term impacts on biogeochemical cycling.

Effects of nurse shrubs and biochar on planted conifer seedling survival and growth in a high-severity burn patch in New Mexico, USA

The synergistic effects of widespread high-severity wildfire and anthropogenic climate change are driving large-scale vegetation conversion. In the southwestern United States, areas that were once dominated by conifer forests are now shrub- or grasslands after high-severity wildfire, an ecosystem conversion that could be permanent without human intervention. Yet, the reforestation of these landscapes is rarely successful, with a mean planted seedling survival of just 25 %. Given these low rates, we carried out a planting experiment to quantify the impacts of biochar as a soil amendment and shrubs as nurse plants on planted conifer seedling survival and growth following high-severity wildfire. We planted 1200 seedlings of three species (Pinus ponderosa, P. strobiformis, and Pseudotsuga menziesii) in a 2-ha area within the footprint of the Las Conchas fire in New Mexico, USA. We used four treatments: under shrubs, or in the open and with or without biochar in a full-factorial design. We found that planting tree seedlings underneath shrubs increased tree seedling survival by 46 % after 3 years, with some marginal evidence that shrubs inhibited seedling diameter growth (mean R2 = 0.08). The addition of biochar increased seedling survival by 11 % but had no effect on seedling growth. Our study suggests that planted seedling survival in post-wildfire areas can be increased by planting under shrubs in soil amended with biochar. The widespread adoption of these methods may improve the success rates of post-wildfire reforestation efforts in semi-arid areas, regaining some of the ecosystem services lost to high-severity wildfire.

Declines in Peak Snow Water Equivalent and Elevated Snowmelt Rates Following the 2020 Cameron Peak Wildfire in Northern Colorado

AbstractWildfires are increasingly impacting high‐elevation forests in the western United States that accumulate seasonal snowpacks, presenting a major disturbance to a critical water reservoir for the region. In the first winter following the 2020 Cameron Peak wildfire in Colorado, the peak snow water equivalent in a high burn severity forest was 17%–25% less than nearby unburned sites. The loss of the forest canopy and a lower surface albedo led to an increasingly positive net shortwave radiation balance in the burned area, resulting in melt rates that were 82%–144% greater than unburned sites and snow disappearance occurred 11–13 days earlier. Late‐season snow storms temporarily buried soot, thus increasing the albedo and delaying melt‐out by an estimated 4 days per storm in our study area. While these storms temporarily reduce the higher melt rates imposed by wildfire impacts, SNOTEL measurements show that they occur non‐uniformly across the western U.S.

Differentiating effects of salvage logging and recovery patterns on post-fire boreal forests in Northeast China using a modified forest disturbance index

ABSTRACT Forests are resilient to a range of disturbances, but combinations of severe natural and anthropogenic disturbances (e.g. wildfire and logging) may inhibit forest recovery and lead to forest degradation. Recent studies have explored long-term forest-disturbance detection and forest-recovery dynamics by using free and open-access remote-sensing images. However, mapping consecutive multiple disturbance agents is challenging using existing automated change-detection algorithms because the reduced canopy reflectance and the smoothing of consecutive disturbance signals mean that the initial disturbance cannot be spectrally separated from the second disturbance. Furthermore, uncertainty remains about post-disturbance vegetation dynamics and the effects of forest recovery under the interaction of burn severity, biological-legacy management, and active forest restoration (i.e. artificial regeneration and assisted natural regeneration). This contributes to biases in long-term forest-recovery monitoring, which are not conducive to the guidance of post-fire vegetation recovery. Here, we propose a modified disturbance index to separate the spectral characteristics of fire and forest logging using normalized tasseled-cap components (brightness and wetness) and detect the spatiotemporal distribution of post-fire logging by means of an index threshold and image differencing. On this basis, the recovery patterns of the post-fire forest are differentiated by considering the cumulative effect of fire, post-fire logging, and recovery approaches. The method is tested in the burn areas of the 5.6 Fire in the Greater Hinggan Mountain area (the largest forest fire in recorded history in China), giving an overall accuracy of 85% in post-fire forest logging mapping. Our results confirm that biological legacies (i.e. trees, logs, and snags) were removed across many areas in the fire, with activities peaking in the second year after the fire and located chiefly in areas of moderate and high burn severity. By identifying post-fire logging, the fluctuation and high disturbance index of the conventional temporal trajectory in the early stage of forest recovery are explained. The large-scale salvage logging slowed the recovery of the post-fire forest ecosystem and influenced the recovery process through the interaction of burn severity and active forest restoration. In areas of high burn severity, assisted natural regeneration (i.e. natural regeneration with artificial aids such as clearing the snags, weeding, digging pits, and supplemental planting) preserved biological legacies and achieved a higher proportion of forest recovery, second only to non-logged areas where natural regeneration (i.e. forestry recovering naturally without any artificial intervention) occurred. By contrast, salvage logging followed by artificial regeneration (i.e. clear-cutting all dead or damaged trees followed by tree planting or artificial seeding) hindered vegetation recovery in the early stage, but it improved the recovery rate in years 10–20 and approached the recovery proportion of non-logged areas where natural regeneration occurred as the recovery progressed and habitat conditions improved. The proposed method is shown to offer important advantages in detecting post-fire salvage logging, and it provides improved guidance for forest managers in developing strategies for forest recovery.

Estimation of the burned area with severity and its influencing factors for wildfire using Sentinel-2 satellite imagery

Wildfire is a natural disaster that harms human and animal habitats and the socio-economy. Remote sensing techniques are commonly used in the research of natural disasters, natural resources and monitoring. Timely and accurate estimation of the location of forest fires is particularly important for post-fire management and decision-making. Sentinel-2 satellite images of the European Space Agency ‘ESA’ were used to estimate the area affected by forest fires at Bayan-Uul and Bayandun soums in Dornod province, and classified the burn severity levels and comparison with other influencing factors in this study. The normalized burn ratio ‘NBR' and indices on pre-fire and post-fire were calculated. The total burned area was calculated as 58,131.6 ha, and low, moderate-low, moderate-high, and high burn severity levels cover 15,423.7 ha (26.3%), 29,529.4 ha (50.4%), 13,160.2 ha (22.5%), and 18.3 ha (0.03%), respectively. The 87.6% of the burned area is situated in Mongolian territory, while the remaining area (12.4%) belongs to the Russian Federation. Comparing 10 natural and geographical factors that can influence the burn severity and calculating the correlation coefficients by Pearson. Four of them related a positive lower, and six of them related negative lower. The weak relationships of Normalized Difference Vegetation Index ‘NDVI’, elevation were 0.4 and 0.23. However, the precipitation correlation was -0.22 (negative weak). The distribution of wildfire is strongly influenced by the wind, and the correlation coefficient demonstrates a negative correlation with no effect on combustion. The conditions of socio-economic and ecological disastrous consequences such as loss of plant species and resources, changes in plant structure, depletion of pasture resources, extinction of rare animals and plants, reduction of forest resources, and large-scale air pollution resulting in the loss of human and animal in post-fire. Therefore, this research is important to due for studying the burning, distribution and, coverage area of the fire, and create conditions for the prevention of future risks.

Evaluating fireline effectiveness across large wildfire events in north-central Washington State

BackgroundWildfires are increasing in incidence, size, and severity in the USA along with associated firefighting costs. Evaluation of firefighting containment and mop-up activities are crucial to reduce costs and to inform safe and effective wildfire response. As geospatial technologies advance, fireline effectiveness metrics have continued to be updated and improved. However, to develop standard analysis protocols and performance evaluations, there is a need to understand how widely metrics vary within and across fire events and are dependent on the different sources and accuracy of geospatial datasets, including firelines, fire perimeters, and severity layers. To ascertain the usefulness and limitations of four fireline effectiveness metrics, we evaluated several metrics including ratios of fireline engaged, held, and burned over. We performed a sensitivity analysis across 13 recent wildfires in north-central Washington State.ResultsOur study found that fire perimeter source and fireline buffer width had the largest impact on quantified fireline effectiveness metrics. Misclassification of firelines produced dramatic erroneous results which artificially increased the effectiveness and decreased suppression effort. High-severity fires were shown to be less effective across all fireline types and required higher suppression than most low- and moderate-severity fires.ConclusionOur results suggest that the fireline effectiveness methodology we tested was robust but could benefit from further refinement with the additional step of visual inspection for fireline misclassifications and database errors. Users should also consider evaluating a range of buffer widths prior to calculating fireline metrics to allow for some minor discrepancies between firelines and fire perimeters. Importantly, our results showed that for high-severity burns firelines were less efficient, and the placement of firelines should be carefully considered to more efficiently allocate firefighting resources and new dozer lines within high-severity landscapes, such as dense mixed conifer forests.

Fuel connectivity, burn severity, and seed bank survivorship drive ecosystem transformation in a semiarid shrubland.

A key challenge in ecology is understanding how multiple drivers interact to precipitate persistent vegetation state changes. These state changes may be both precipitated and maintained by disturbances, but predicting whether the state change will be fleeting or persistent requires an understanding of the mechanisms by which disturbance affects the alternative communities. In the sagebrush shrublands of the western United States, widespread annual grass invasion has increased fuel connectivity, which increases the size and spatial contiguity of fires, leading to postfire monocultures of introduced annual grasses (IAG). The novel grassland state can be persistent and is more likely to promote large fires than the shrubland it replaced. But the mechanisms by which prefire invasion and fire occurrence are linked to higher postfire flammability are not fully understood. A natural experiment to explore these interactions presented itself when we arrived in northern Nevada immediately after a 50,000 ha wildfire was extinguished. We hypothesized that the novel grassland state is maintained via a reinforcing feedback where higher fuel connectivity increases burn severity, which subsequently increases postfire IAG dispersal, seed survivorship, and fuel connectivity. We used a Bayesian joint species distribution model and structural equation model framework to assess the strength of the support for each element in this feedback pathway. We found that prefire fuel connectivity increased burn severity and that higher burn severity had mostly positive effects on the occurrence of IAG and another nonnative species and mostly negative or neutral relationships with all other species. Finally, we found that the abundance of IAG seeds in the seed bank immediately after a fire had a positive effect on the fuel connectivity 3 years after the fire, completing a positive feedback promoting IAG. These results demonstrate that the strength of the positive feedback is controlled by measurable characteristics of ecosystem structure, composition, and disturbance. Further, each node in the loop is affected independently by multiple global change drivers. It is possible that these characteristics can be modeled to predict threshold behavior and inform management actions to mitigate or slow the establishment of the grass-fire cycle, perhaps via targeted restoration applications or prefire fuel treatments.

Mapping burn severity and uncovering spread patterns of the 2021 Varibopi wildfire

This work unveils how the wildfire of August 3rd, 2021 that initiated at the northeastern part of Attica (Varibopi), spread and burned during the four days of its active propagation. This fire is a characteristic large-scale event that affected the wildland-urban interface of Athens, revealing weaknesses of both pillars of fire management: prevention and suppression. Initially, we provide a short description of how and under which conditions (vegetation and weather) the fire initiated and propagated after debriefing reports, news articles and satellite data. Then, we applied the difference Normalized Burn Ratio on a pair of Sentinel 2A satellite images (one right before and another taken one year later) to map the extended burn severity and delineate the fire perimeter. Finally, using the Minimum Travel Time Algorithm, we simulated major spread vectors and rate of spread to answer how the fire would have been evolved in the absence of active fire suppression. We found that from the 8,445-ha included in the final delineated perimeter, 1,000 ha were unburned, 4,715 ha experienced low or moderate-low burn severity, and 2,730 moderate-high or high burn severity. Without suppression, the fire could have escaped from three directions to the west with high spread rate, potentially affecting the Parnitha National Park. The most imminent post-fire issue is not whether the conifer vegetation will recover, but if during the next decade vegetation management measures are not applied in selected locations, then a new ignition can spread faster and burn a more extended area compared to the 2021 fire.

Drivers of wildfire burn severity in the montane rainforests of northern Vietnam

Background Fire impacts and drivers of wildfire burn severity remain poorly understood for tropical forests. Aims To assess variation and environmental drivers of burn severity for nine forest fires in northern Vietnam. Methods Burn severity was estimated from satellite image analyses, and associations with a remotely sensed index of annual fuel production, topographic factors (elevation, slope, aspect) and weather variables (temperature, rainfall, relative humidity, wind speed) were evaluated. Key results High severity burn areas were found to be fairly uncommon and were associated with steeper, south-west facing slopes, higher elevations and lower fuel abundance. There was a weak tendency for higher burn severity on days with lower relative humidity. Conclusions Conditions that increase fire intensity and the dryness and flammability of fuels are important contributors to high severity fires in wet tropical systems. However, the pattern of higher burn severity at high elevation, where forests tend to be denser and more humid, is counter to this interpretation and may be due to species compositional changes and greater vulnerability of high-elevation forests to fire impacts. Implications Better understanding of fire risk and where in the montane forests of northern Vietnam fires are most likely to burn at high severity will assist forest fire management and recovery strategies.

Wildfire Burn Severity Affects Postfire Shifts in Evapotranspiration in Subalpine Forests

Highlights After wildfire, actual evapotranspiration (ETa) in four subalpine areas decreased proportionally to burn severity. High-severity burn areas maintained the highest ETa before fire and the lowest ETa after fire. After fire, ETa decreased more in areas that had higher prefire ETa. ETa was a useful system-level measure of susceptibility to fire and impact after fire. Abstract. The ecohydrologic response to fire is complex, with devastating consequences for source-water hydrology. Postfire canopy structure, leaf area, infiltration, and soil-water storage all may act to reduce evapotranspiration (ET), a key hydrologic variable and indicator of ecohydrologic function. This study explored the use of 30-m resolution Landsat-based SSEBop-model estimates of actual ET (ETa) to assess the effects of fire in the Upper Rio Grande Basin (2002 Million Fire, CO; 1996 Hondo Fire, NM; 2002 Montoya Fire, NM; 2000 Cerro Grande Fire, NM). SSEBop ETa data from 1985-2019 were analyzed to better understand postfire response and recovery in several sub-alpine burned areas. Results show step reductions in ETa after fire across all burn severities in all four fire areas. Prior to the fire, ETa was generally higher in high-severity burn areas, indicative of higher fuel loads, although high variability indicated the influence of additional factors. All areas had a greater response (decreased ETa) to fire in high-severity areas and a lesser response as burn severity decreased. The decrease in ETa after high-severity fire ranged from 42% to 63%, compared to the decrease after low-severity fire, which ranged from 24% to 44%. None of the four burn areas demonstrated postfire ETa recovery after 17 to 23 years. This study demonstrates the clear utility for remote-sensing ETa estimates as a system-level measure of susceptibility to fire, impact of fire, and, potentially, recovery after fire. However, additional research is needed to account for the covariate effects of other fuel, topographic, weather, and climate factors. Keywords: Ecohydrology, Postfire recovery, Remote sensing, Upper Rio Grande Basin.

Breeding bird abundance and species diversity greatest in high-severity wildfire patches in central hardwood forests

In 2016, mixed-severity wildfires in the southern Appalachians created a gradient of forest structures not typical following prescribed burns, providing a unique opportunity to study temporally dynamic conditions and breeding bird response. We measured forest structure and breeding bird communities across a fire-severity gradient in 3 burned and 3 unburned watersheds for 5 years (Y1-Y5). We categorized plots as unburned (NB), low- (L), moderate- (M), or high-severity (H) using a composite fire-severity index. Tree mortality increased with fire-severity category (FSC) and over time; by Y5, 7 % of trees in NB, 11 % in L, 38 % in M, and 71 % in H had died. Shrub recovery was rapid and most pronounced in H, exceeding other FSCs (70 % vs 21 %–44 %) by Y5. Total bird abundance, species richness, and diversity increased over time in H (by Y3) and M (by Y4); by Y5, these metrics were highest in H and twice as high in H as in NB. Low-severity wildfires had no detectable effects on birds. Abundance of 7 species was greatest in higher-severity FSCs; 11 species did not differ among FSC, although ovenbirds (Seiurus aurocapilla) indicated a trend of lower abundance in H. No species was limited to NB, L, or M, whereas disturbance-dependent indigo bunting (Passerina cyanea), chestnut-sided warbler (Setophaga pensylvanica), and eastern towhee (Pipilo erythrophthalmus) were primarily associated with H. Increased richness and diversity were associated with heavy tree mortality and subsequent shrub recovery in H, accompanied by an influx of disturbance-dependent species and positive or neutral responses by most other species. Results highlight the interrelated roles of fire severity and time in driving forest structure and breeding bird response. Breeding birds responded to high-severity burns similarly to silvicultural treatments with heavy canopy reduction documented in other studies, offering possible alternatives when managing for breeding bird diversity in hardwood forests.

Fire severity and the legacy of mountain pine beetle outbreak: high-severity fire peaks with mixed live and dead vegetation

Bark beetle outbreaks and wildfires are two of the most prevalent disturbances that influence tree mortality, regeneration, and successional trajectories in western North American forests. Subboreal forests have experienced broad overlaps in these disturbances, and recent wildfires have burned through landscapes with substantial tree mortality from prior outbreaks. This study investigated how fuel conditions associated with mountain pine beetle outbreaks influence the probability of high burn severity (i.e. stand-replacing fire) across a range of fire weather conditions in subboreal forests of central interior British Columbia, Canada. We focused on three large fires that occurred in 2012, 2013, and 2014. We characterized outbreak severity, outbreak-influenced prefire vegetation, and subsequent burn severity using Landsat spectral vegetation indices, high-resolution imagery, and field observations. Substantial portions of the prefire landscape contained mixtures of live and dead vegetation created by variable beetle damage and vegetation response—spatial patterns that are related to, but distinct from, peak outbreak severity. We evaluated drivers—fuels, weather, and topography—of high-severity fire under ‘extreme,’ ‘moderate,’ and ‘benign’ fire weather conditions (i.e. burning conditions) using Boosted Regression Trees. While fire weather was a primary driver in most cases, prefire vegetation was an influential predictor variable across all burning conditions, and the probability of high-severity fire was highest when prefire vegetation was a mixture of tree mortality from bark beetles and live vegetation. Thus, while weather and drought are important drivers of wildfires in subboreal forests, bottom-up drivers of elevation and vegetation, including the fuel legacies of bark beetle outbreaks, are crucial factors influencing high-severity burning. The legacy of recent bark beetle outbreaks will continue for decades on these landscapes, affecting fuel structures, future wildfires, forest dynamics, and the broader social-ecological systems of the region.

Impacts of burn severity on short-term postfire vegetation recovery, surface albedo, and land surface temperature in California ecoregions.

Wildfire burn severity has important implications for postfire vegetation recovery and boundary-layer climate. We used a collection of Moderate Resolution Imaging Spectroradiometer (MODIS) datasets to investigate the impact of burn severity (relative differenced Normalized Burn Ratio, RdNBR) on vegetation recovery (Enhanced Vegetation Index, EVI), albedo change, and land surface temperature in seven California ecoregions, including: Southern California Mountains (SCM), Southern California Coast (SCC), Central California Foothills (CCF), Klamath (K), Cascades (C), Eastern Cascades (EC), and Sierra Nevada (SN). A statewide MODIS-derived RdNBR dataset was used to analyze the impact of burn severity on the five-year postfire early-summer averages of each biophysical variable between the years 2003-2020. We found that prefire EVI values were largest, and prefire albedo and temperature were lowest in the K, C, EC, and SN ecoregions. Furthermore, the largest changes between prefire and first-year postfire biophysical response tended to occur in the moderate and high burn severity classes across all ecoregions. First-year postfire albedo decreased in the K, C, EC, and SN but increased in the SCM, SCC, and CCF ecoregions. The greatest decreases, but most rapid recovery, of EVI occurred after high severity fires in all ecoregions. After five-years post-fire, EVI and land surface temperature did not return to prefire levels in any burn severity class in any ecoregion.

Comparison of Physical-Based Models to Measure Forest Resilience to Fire as a Function of Burn Severity

We aimed to compare the potential of physical-based models (radiative transfer and pixel unmixing models) for evaluating the short-term resilience to fire of several shrubland communities as a function of their regenerative strategy and burn severity. The study site was located within the perimeter of a wildfire that occurred in summer 2017 in the northwestern Iberian Peninsula. A pre- and post-fire time series of Sentinel-2 satellite imagery was acquired to estimate fractional vegetation cover (FVC) from the (i) PROSAIL-D radiative transfer model inversion using the random forest algorithm, and (ii) multiple endmember spectral mixture analysis (MESMA). The FVC retrieval was validated throughout the time series by means of field data stratified by plant community type (i.e., regenerative strategy). The inversion of PROSAIL-D featured the highest overall fit for the entire time series (R2 > 0.75), followed by MESMA (R2 > 0.64). We estimated the resilience of shrubland communities in terms of FVC recovery using an impact-normalized resilience index and a linear model. High burn severity negatively influenced the short-term resilience of shrublands dominated by facultative seeder species. In contrast, shrublands dominated by resprouters reached pre-fire FVC values regardless of burn severity.

Role of burn severity and posttraumatic stress symptoms in the co-occurrence of itch and neuropathic pain after burns: A longitudinal study.

Itch and pain are common after burns. Neuropathic mechanisms may underlie both modalities but remain not well-understood. This study aims to prospectively document neuropathic pain symptoms and to identify potential itch symptom profiles that differ regarding duration and co-occurrence with neuropathic pain which may inform underlying pathophysiological mechanisms and respond to different treatments. Adult burn survivors (n = 192) self-reported itch and neuropathic pain at 2 weeks post-discharge, 3, 6, 12, and 18 months post-burn. Based on the presence of itch and pain symptoms over time, participants were allocated to one itch profile: transient itch/pain, chronic itch, or chronic itch & pain. Profiles were compared on itch intensity over time using General Linear Modeling. Age, gender, burn severity, posttraumatic stress (PTS) symptoms and baseline itch intensity were examined as potential predictors of the profiles in a Multi-nominal regression analysis. Neuropathic pain occurred in 54% after discharge which decreased to 24% 18 months later. Itch intensity was highest in the chronic itch & pain profile. Compared to the transient itch profile, the chronic itch & pain profile was associated with higher burn severity and more PTS symptoms. Compared to the chronic itch profile, the chronic itch & pain profile was associated with more PTS symptoms. Findings suggest that biological and psycho-dermatological processes underlie both chronic neuropathic pain and itch processes in burn scars. Further research should elucidate the mechanisms underlying the different itch profiles, with specific focus on skin innervation and psychological factors.

Simulating burn severity maps at 30 meters in two forested regions in California

Climate change is altering wildfire and vegetation regimes in California’s forested ecosystems. Present day fires are seeing an increase in high burn severity area and high severity patch size. The ability to predict future burn severity patterns could better support policy and land management decisions. Here we demonstrate a methodology to first, statistically estimate individual burn severity classes at 30 meters and second, cluster and smooth high severity patches onto a known landscape. Our goal here was not to exactly replicate observed burn severity maps, but rather to utilize observed maps as one realization of a random process dependent on climate, topography, fire weather, and fuels, to inform creation of additional realizations through our simulation technique. We developed two sets of empirical models with two different vegetation datasets to test if coarse vegetation could accurately model for burn severity. While visual acuity can be used to assess the performance of our simulation process, we also employ the Ripley’s K function to compare spatial point processes at different scales to test if the simulation is capturing an appropriate amount of clustering. We utilize FRAGSTATS to obtain high severity patch metrics to test the contiguity of our high severity simulation. Ripley’s K function helped identify the number of clustering iterations and FRAGSTATS showed how different focal window sizes affected our ability to cluster high severity patches. Improving our ability to simulate burn severity may help advance our understanding of the potential influence of land and fuels management on ecosystem-level response variables that are important for decision-makers. Simulated burn severity maps could support managing habitat and estimating risks of habitat loss, protecting infrastructure and homes, improving future wildfire emissions projections, and better mapping and planning for fuels treatment scenarios.

Event Scale Analysis of Streamflow Response to Wildfire in Oregon, 2020

Wildfire increases the magnitude of runoff in catchments, leading to the degradation of ecosystems, risk to infrastructure, and loss of life. The Labor Day Fires of 2020 provided an opportunity to compare multiple large and severe wildfires with the objective of determining potential changes to hydrologic processes in Oregon Cascades watersheds. Geographic information systems (GIS) were implemented to determine the total percentage burned and percentage of high burn severity class of six watersheds on the west slope of the Oregon Cascade Range. In addition, two control watersheds were included to contrast the influence of climatic effects. Spatial arrangements of burned patches were investigated for correlation to streamflow response by utilizing landscape metrics algorithms, including Largest Patch Index (LPI), mean gyration (GYRATE), Contiguity Index (CONTIG), Patch Cohesion Index (COHESION), and Clumpiness Index (CLUMPY). Results of the first-year post-fire response were consistent with other studies of fire effects in the Pacific Northwest (PNW) and indicated changes to runoff dynamics were difficult to detect with inferential statistics, but the largest changes in runoff coefficients occurred in watersheds having the greatest percentage burned. Correlation analysis indicated relationships between event runoff coefficients and percentage burned during the 2020 fire season. Control watersheds show confounding runoff coefficients, point to the influence of ongoing drought, and complicate conclusions about the role of spatial burn severity patterns. These results could guide future post-fire studies of spatial patterns of burn severity and could assist watershed managers to prioritize at-risk PNW catchments to minimize harm to ecological and societal values.

Fire severity and post‐fire mulching effects on N transformation rates of temperate soils during the first critical winter–spring period

AbstractWildfires are increasing worldwide and, therefore, the extents of their on‐ and off‐site impacts are particularly important on soil erosion and nutrient cycles. To mitigate post‐fire erosion, mulching is increasingly being used, but its effects on the nitrogen (N) cycle are poorly known. To fill this gap of knowledge, gross N fluxes were modelled with Ntrace to compare with unburnt soils (US) the effects of intermediate (BI) and high severity (BH) burning, and post‐fire straw mulching (BIM and BHM). Two wildfires, two‐time points after the fire and 20 soil‐treatment combinations were studied. The mineralization of soil organic N to NH4+ (MSON) increased in BI (1.9–6.9×) with respect to US, with no clear trends observed in BH and mulched treatments. In most soils, NH4+ immobilisation in labile () and recalcitrant soil organic matter (SOM) () was more important than abiotic NH4+ fixation () and together were larger (3.5–11×) in BI than in US, while contrasting results were found depending on time after a fire (BH, BHM, BIM) and wildfire characteristics (BHM, BIM). Autotrophic nitrification () was included in the best model for all soils, whereas heterotrophic nitrification (OSON) was undetectable in most BH soils. Total nitrification ( + OSON) decreased with time after the fire in BH, increased in US and BI, and was differently affected by mulching depending on fire severity and time from the fire. While NO3− immobilisation () was frequently modelled only for BI soils, the dissimilatory NO3− reduction to NH4+ (DNRA) was retained in the best models for all soils and it was reduced by soil burning, whereas a short‐lived increase was induced by mulching. Denitrification (), modelled for most soils, was negatively affected by burning and positively by mulching. In summary, wildfires tended to increase MSON and , decrease DNRA and and had no clear influence on and nitrification. These effects are usually mitigated by mulching which, however, tended to enhance nitrification.Highlights Direction and magnitude of changes in soil gross N fluxes depend on fire severity. Usually, wildfires increased MSON and , and decreased DNRA and . No clear post‐fire trend was found for and nitrification. Fire effects on gross N fluxes are (partially) counterbalanced by mulching.

Use of geostatistical models to evaluate landscape and stream network controls on post‐fire stream nitrate concentrations

AbstractForested watersheds provide many ecosystem services, such as the filtration of sediment, pollutants, and nutrients, which are increasingly threatened by wildfire. For example, stream nutrient concentrations often increase following wildfire and can remain elevated for decades, making downstream waters susceptible to eutrophication. We investigated the drivers of persistent elevated stream nutrients, specifically nitrate (NO3−), in nine watersheds that were burned 16 years prior by the Hayman fire, Colorado, USA. We evaluated the ability of multiple linear regression and spatial stream network modeling approaches to predict observed concentrations of the biologically active solute NO3− and the conservative solute sodium (Na+) which serves as a partial control. Specifically, we quantified the degree to which landscape and stream network characteristics predict stream solute concentrations. Stream Na+ exhibited strong spatial autocorrelation that was primarily controlled by topography and hydrology. In contrast, stream NO3− had higher spatial variability and was inversely correlated to vegetation cover, measured as mean normalized differenced moisture index (NDMI). Spatially heterogeneous wildfire behaviour left intact forest patches interspersed with high burn severity patches dominated by shrubs and grasses which contributes to the spatial variability in stream NO3− concentrations. Post‐fire vegetation also interacts with watershed structure to influence stream NO3− patterns. For example, severely burned convergent hillslopes in headwaters positions were associated with the highest stream NO3− concentrations due to the high proportional influence of hillslope water in these locations. Our findings suggest that targeted reforestation in severely burned convergent hillslopes in headwater positions may enhance the recovery of stream NO3− concentrations to pre‐fire levels.

Wildfire impacts on western United States snowpacks

Mountain snowpacks provide 53–78% of water used for irrigation, municipalities, and industrial consumption in the western United States. Snowpacks serve as natural reservoirs during the winter months and play an essential role in water storage for human consumption and ecosystem functions. However, wildfires across the West are increasing in severity, size, and frequency, progressively putting snowpacks at risk as they burn further into the seasonal snow zone. Following a fire, snow disappears 4–23 days earlier and melt rates increase by up to 57%. In a high burn severity fire in the Oregon Cascades, the black carbon and charred woody debris shed from burned trees onto the snowpack decreased the snow albedo by 40%. Canopy cover loss causes a 60% increase in solar radiation reaching the snow surface. Together, these effects produce a 200% increase in net shortwave radiation absorbed by the snowpack. This mini-review synthesizes the implications of wildfire for snow hydrology in mountainous watersheds with the primary aim to characterize wildfires' varied influences on the volume and timing of water resources across time scales (daily to decadal), space (plot to watershed) and burn severity (low to high). The increase in the geographical overlap between fire and snow poses unique challenges for managing snow-dominated watersheds and highlights deficiencies in research and operational snow hydrologic modeling, emphasizing the need for additional field and remote-sensing observations and model experiments.