Fire Patches Research Articles

Postfire reproduction of a serotinous conifer, the giant sequoia, in the Nelder Grove, California.

The giant sequoia, a serotinous conifer naturally occurring in mixed-conifer forests of the southern and central Sierra Nevada, California, USA, is the world's largest tree species. Giant sequoia reproduction has been severely lacking over the past century, due to fire exclusion, creating a significant conservation threat. Previous research on postfire sequoia reproduction in high-severity fire areas, relative to low- and moderate-severity areas, is limited. At 6 years postfire, we investigated giant sequoia reproduction in a high-severity fire area, and nearby low-/mixed-severity fire areas, in the Nelder Grove, which burned in 2017 in the Railroad fire. Postfire giant sequoia reproduction was positively correlated with fire severity in terms of density, height (growth), and proportion (relative to other conifer species), and sequoia seedling/sapling density was positively correlated with percent shrub cover. There was no correlation between distance to live sequoia seed source and density of sequoia reproduction. More research is needed in other mixed-severity fire areas, with larger high-severity fire patches, to determine whether a similar postfire response occurs elsewhere.

Spatio-temporal patterns of rangeland forage nutritive value and grazer selection with patch-burning in the US northern Great Plains

Understanding how management influences forage nutritive value and grazer selection within grazing seasons is an ongoing effort for researchers and land managers globally. We used six, 65 ha pastures managed with patch-burn grazing and stocked with either cow-calf pairs (0.45–0.5 ha • AUM−1) or gestating ewes (0.4–0.48 ha • AUM-1) to explore how patterns in rangeland forage drive grazer selection in semi-arid rangeland over four summer grazing seasons at monthly intervals. We used near-infrared spectroscopy to determine nutritive value parameters from monthly forage clippings. We evaluated livestock performance as the average daily weight gains of each animal. We used mixed-effect models and ordination to compare patch and grazer types across the time-since-fire gradient and found that time-since-fire was significant for all measured variables. Cattle and sheep consistently preferred recently burned patches throughout grazing seasons. These recently burned patches typically contained available forage with higher crude protein and moisture content, lower biomass, and lower acid detergent fiber, acid detergent lignin, and neutral detergent fiber compared to intermediate time since fire patches and patches burned three years ago. Differences between patch-burn grazing with cattle and sheep were observed as additional patch contrasts for available biomass and crude protein, but grazer type and ecological site were not statistically significant factors for the nutritive value ordination. Our study indicates that patch-burn grazing is capable of imposing and maintaining heterogeneous, grazer selection, forage biomass, and nutritive value patterns desirable for heterogeneity focused land management, regardless of grazer type. These findings are especially relevant to the northern Great Plains where introduced grasses are homogenizing the structural environment of remaining rangelands. With prescribed fire currently an uncommon practice throughout the region, these findings provide a baseline of expectations for practitioners and land managers implementing patch-burn grazing and illustrate how grazing livestock can benefit from the patch contrast in forage nutritive value and biomass.

Sediment Response after Wildfires in Mountain Streams and Their Effects on Cultural Heritage: The Case of the 2021 Navalacruz Wildfire (Avila, Spain)

The 2021 Navalacruz wildfire occurred in a mountainous area in the Sistema Central (Spain). Despite having an average low severity index (dNBR), the loss of vegetation cover associated with the fire was responsible for a high rate of sedimentation in the rivers and streams. Additionally, the burned area affected up to 60 cultural heritage sites, including archaeological and ethnological sites, and damage ranged from burnt pieces of wood to the burial of archaeological sites. In the present work, we document and analyze the post-fire evolution in several rivers and streams. This is based on a field survey of infiltration rates, hydrodynamic modeling, and the study of channel morphological changes. Our analysis revealed how the first post-fire rains caused the mobilization and transport of ashes. This created hydrophobicity in the soils, resulting in large amounts of materials being transported to rivers and streams by subsequent medium- and low-magnitude storms. A hydrological and hydraulic model of the study catchments under pre- and post-fire conditions suggests that these trends are a consequence of a post-fire increase in flow rates for similar rainfall scenarios. In this respect, our estimates point at a significant increase in sediment transport capacities associated with this post-fire increase in flow rates. The combination of locally steep slopes with high-severity fire patches, and a considerable regolith (derived from pre-fire weathering), resulted in a series of cascading responses, such as an exacerbated supply of sand to the drainage network and the triggering of debris flows, followed by erosion and entrenchment.

Upland Sandpipers select for later time since fire and experience high nest survival in grasslands managed with patch-burn grazing

Abstract Upland Sandpipers (Bartramia longicauda) are a grassland obligate shorebird that nests in dense vegetation structure near recently disturbed areas and could benefit from management practices that promote heterogenous vegetation structure. Upland Sandpipers primary breeding range is generally managed for livestock production using traditional practices that lack patchy disturbances to facilitate higher levels of structural heterogeneity. Patch-burn grazing (PBG) could be an alternative management practice for Upland Sandpiper conservation for its use to create areas of dense vegetation structure near recently disturbed areas. However, limited information is available regarding nest production of Upland Sandpipers within a PBG framework. To assess the compatibility of PBG with Upland Sandpiper conservation, we estimated nest site selection and survival of Upland Sandpiper nests on private lands managed with PBG in the unglaciated plains region of North Dakota. We located 59 nests from 2017 to 2020. Upland Sandpipers avoided 1 year since fire (YSF) patches and selected for 2 and 3 YSF patches for nest sites. Additionally, nest site selection decreased with increased bare ground and at intermediate distances to the nearest Upland Sandpiper nest. Upland Sandpipers experienced high overall nest survival during the study with 51 of 59 nests successfully hatching, which limited our ability to make inferences between daily survival rates and variables of interest. Our findings suggest that PBG can provide suitable nesting cover for Upland Sandpipers in later YSF patches despite annual prescribed fire and livestock grazing during the nesting season. PBG seems a suitable grassland management strategy that should be included in conservation planning within Upland Sandpiper’s breeding distribution.

Madagascar's burned area from Sentinel-2 imagery (2016–2022): Four times higher than from lower resolution sensors

Madagascar is one of the most burned regions in the world, to the point that it has been called the ‘Isle of fire’ or the ‘Burning Island’. An accurate characterization of the burned area (BA) is crucial for understanding the true situation and impacts of fires on this island, where there is an active scientific debate on how fire affects multiple environmental and socioeconomic aspects, and how fire regimes should be in a complex context with differing interests. Despite this, recent advances have revealed that BA in Madagascar is poorly characterised by the currently available global BA products. In this work, we present, validate, and explore a BA database at 20 m spatial resolution for Madagascar covering the period 2016–2022. The database was built based on 75,010 Sentinel-2 images using a two-phase BA detection algorithm. The validation with independent long-term reference units showed Dice coefficients ≥79 %, omission errors ≤24 %, commission errors ≤18 %, and a relative bias ≥ − 8 %. An intercomparison with other available global BA products (GABAM, FireCCI51, C3SBA11, or MCD64) demonstrated that our product (i) exhibits temporal consistency, (ii) represents a significant accuracy improvement, as it reduces BA underestimations by about eightfold, (iii) yields BA estimates four times higher, and (iv) shows enhanced capability in detecting fires of all sizes. The observed BA spatial patterns were heterogeneous across the island, with 32 % of the grasslands burning annually, in contrast to other land cover types such as the dense tropical forest where <2 % burned every year. We conclude that the BA characterization in Madagascar must be addressed using imagery at spatial resolution higher than MODIS or Sentinel-3 (≥250 m), and temporal resolution higher than Landsat (16 days) to deal with cloudiness, the rapid attenuation of burn scars signals, and small fire patches.

Patterns and drivers of early conifer regeneration following stand-replacing wildfire in Pacific Northwest (USA) temperate maritime forests

Tree regeneration is a critical mechanism of forest resilience to stand-replacing wildfire (i.e., where fire results in >90 % tree mortality), and post-fire regeneration is a concern worldwide as the climate becomes warmer. Although post-fire tree regeneration has been relatively well-studied in fire-prone forests across western North America, it is less understood in fire regimes characterized by large patches of stand-replacing fire at long intervals, such as the nominally infrequent, high-severity fire regimes of the western Cascades of Washington and northern Oregon, USA (northwestern Cascadia) where some of world’s highest-biomass forests reside. Recent wildfire activity (2015–2020) in northwestern Cascadia provides a unique opportunity to build understanding of the mechanisms underpinning forest resilience to fire, with implications for forest management and the myriad socio-ecological values associated with these landscapes. Here, we asked: how is post-fire conifer regeneration across northwestern Cascadia affected by pre-fire stand age, burn-patch size, and topo-climatic conditions? We established 39 1-ha long-term monitoring plots across four recent wildfires in northwestern Cascadia to measure post-fire conifer abundance and species composition. We used generalized linear models to test how rates of conifer regeneration (seedlings ha−1 yr−1 of all heights) and establishment (seedlings ha−1 yr−1 with heights >10 cm) respond to differences in pre-fire stand age/seral stage (young, mid-seral, late-seral), distance to the nearest live seed source, and post-fire topo-climate setting. In general, initial post-fire seedling densities suggest tree regeneration is abundant following stand-replacing fire in most areas across the region. For example, at 3–5 years post-fire, established seedlings were present in 100 % of plots, and regeneration and establishment levels exceeded state forest practices minimum density thresholds (470 seedlings ha−1) in 82.1 % and 64.1 % of plots, respectively. Post-fire conifer regeneration and tree species richness were greater when pre-fire stand age was older, and was more dominated by shade tolerant species than when pre-fire stand age was younger. Regeneration decreased with farther distances to the nearest live seed source, though seedlings were still moderately abundant at distances as far as 400 m from edges of high-severity patches. Conifer establishment was greater in areas characterized by cooler and wetter macrosite (e.g., greater post-fire precipitation) and microsite (e.g., greater bryophyte ground cover) conditions. By providing information on the drivers and conditions in which land managers can expect natural regeneration to occur or not, our findings are directly relevant to pre- and post-fire forest management objectives under future climate and increased fire activity in systems structured in part by infrequent and severe wildfires.

High-resolution data reveal a surge of biomass loss from temperate and Atlantic pine forests, contextualizing the 2022 fire season distinctiveness in France

Abstract. The frequency and intensity of summer droughts and heat waves in Western Europe have been increasing, raising concerns about the emergence of fire hazard in less fire-prone areas. This exposure of old-growth forests hosting unadapted tree species may cause disproportionately large biomass losses compared to those observed in frequently burned Mediterranean ecosystems. Therefore, analyzing fire seasons from the perspective of exposed burned areas alone is insufficient; we must also consider impacts on biomass loss. In this study, we focus on the exceptional 2022 summer fire season in France and use very high-resolution (10 m) satellite data to calculate the burned area, tree height at the national level, and subsequent ecological impact based on biomass loss during fires. Our high-resolution semi-automated detection estimated 42 520 ha of burned area, compared to the 66 393 ha estimated by the European automated remote sensing detection system (EFFIS), including 48 330 ha actually occurring in forests. We show that Mediterranean forests had a lower biomass loss than in previous years, whereas there was a drastic increase in burned area and biomass loss over the Atlantic pine forests and temperate forests. High biomass losses in the Atlantic pine forests were driven by the large burned area (28 600 ha in 2022 vs. 494 ha yr−1 in 2006–2021 period) but mitigated by a low exposed tree biomass mostly located on intensive management areas. Conversely, biomass loss in temperate forests was abnormally high due to both a 15-fold increase in burned area compared to previous years (3300 ha in 2022 vs. 216 ha in the 2006–2021 period) and a high tree biomass of the forests which burned. Overall, the biomass loss (i.e., wood biomass dry weight) was 0.25 Mt in Mediterranean forests and shrublands, 1.74 Mt in the Atlantic pine forest, and 0.57 Mt in temperate forests, amounting to a total loss of 2.553 Mt, equivalent to a 17 % increase of the average natural mortality of all French forests, as reported by the national inventory. A comparison of biomass loss between our estimates and global biomass/burned areas data indicates that higher resolution improves the identification of small fire patches, reduces the commission errors with a more accurate delineation of the perimeter of each fire, and increases the biomass affected. This study paves the way for the development of low-latency, high-accuracy assessment of biomass losses and fire patch contours to deliver a more informative impact-based characterization of each fire year.

Climate influences on future fire severity: a synthesis of climate-fire interactions and impacts on fire regimes, high-severity fire, and forests in the western United States

Abstract Background Increases in fire activity and changes in fire regimes have been documented in recent decades across the western United States. Climate change is expected to continue to exacerbate impacts to forested ecosystems by increasing the frequency, size, and severity of wildfires across the western United States (US). Warming temperatures and shifting precipitation patterns are altering western landscapes and making them more susceptible to high-severity fire. Increases in large patches of high-severity fire can result in significant impacts to landscape processes and ecosystem function and changes to vegetation structure and composition. In this synthesis, we examine the predicted climatic influence on fire regimes and discuss the impacts on fire severity, vegetation dynamics, and the interactions between fire, vegetation, and climate. We describe predicted changes, impacts, and risks related to fire with climate change and discuss how management options may mitigate some impacts of predicted fire severity, and moderate some impacts to forests, carbon, and vegetation changes post fire. Results Climate change is increasing fire size, fire severity, and driving larger patches of high-severity fire. Many regions are predicted to experience an increase in fire severity where conditions are hotter and drier and changes in fire regimes are evident. Increased temperatures, drought conditions, fuels, and weather are important drivers of fire severity. Recent increases in fire severity are attributed to changes in climatic water deficit (CMD), vapor pressure deficit (VPD), evapotranspiration (ET), and fuels. Fire weather and vegetation species composition also influence fire severity. Future increases in fire severity are likely to impact forest resilience and increase the probability of forest type conversions in many ecosystems. Conclusions Increasing warming and drying trends are likely to cause more frequent and severe disturbances in many forested ecosystems in the near future. Large patches of high-severity fire have lasting legacies on vegetation composition and structure, and impacts on tree regeneration. In some ecosystems and under certain fire-weather conditions, restoration and fuel treatments may reduce the area burned at high severity and reduce conversions from forest to non-forest conditions, increasing forest resistance and resilience to wildland fire. Thinning and prescribed fire treatments can be effective at reducing the potential for crown fire, reducing fuels, and promoting forest resilience.

Landscape fires disproportionally affect high conservation value temperate peatlands, meadows, and deciduous forests, but only under low moisture conditions

Landscape fires are a natural component of the Earth System. However, they are of growing global concern due to climate change exacerbating their multiple impacts on biodiversity, ecosystems, carbon storage, human health, economies, and wider society. Temperate regions are predicted to be at greatest risk of increasing fire activity due to climate change, where fires can seriously impact important ecosystems for biodiversity and carbon storage, such as peatlands and forests. There is insufficient literature on the background prevalence, distribution, and drivers of fires in these regions, especially within Europe, to assess and mitigate their risks. Using a global database of fire patches based on the MODIS FireCCI51 product, we address this knowledge gap by quantifying the current prevalence and size of fires in Polesia, a 150,000 km2 area comprising a mosaic of peatland, forest, and agricultural habitats in northern Ukraine and southern Belarus. Between 2001 and 2019, fires burned 31,062 km2 of land, and were most frequent in spring and autumn. Although most fires started in agricultural land, fires disproportionately affected natural and semi-natural land cover types, particularly in protected areas. Over one fifth of protected land burned. Coniferous forests were the most common land cover type in protected areas, but fires mostly occurred in meadows, open peatlands (especially fen and transition mires), and native deciduous forests. These land cover types were highly susceptible to fires under low soil moisture conditions, but the risk of fire was low under average or higher soil moisture conditions. Restoring and maintaining natural hydrological regimes could be an effective nature-based solution to increase the resilience of fire-vulnerable ecosystems and support global biodiversity and carbon storage commitments under the United Nations Framework Conventions on Climate Change and Convention on Biological Diversity.

An improved spatio-temporal clustering method for extracting fire footprints based on MCD64A1 in the Daxing’anling Area of north-eastern China

Background Understanding the spatio-temporal dynamics associated with a wildfire event is essential for projecting a clear profile of its potential ecological influences. Aims To develop a reliable framework to extract fire footprints from MODIS-based burn products to facilitate the understanding of fire event evolution. Methods This study integrated the Jenks natural breaks classification method and the density-based spatial clustering of applications with noise (DBSCAN) algorithm to extract the fire footprints in Daxing’anling region of China between 2001 and 2006 from MCD64A1 burned area data. Key results The results showed that the fire footprints extracted by the model gained an overall accuracy of 80% in spatial and temporal domains after an intensive validation by using the historical fire records provided by the local agency. The agreement of burned area between the extracted fire patches and the historical fire records for those matched fire points was characterised by an overall determination coefficient R2 at 0.91. Conclusions The proposed framework serves as an efficient and convenient wildfire management tool for areas requiring large-scale and long-term wildfire monitoring. Implications The current framework can be used to create a reliable large-scale fire event database by providing an important alternative for the improvement of field investigation.

Restoration and fuel hazard reduction result in equivalent reductions in crown fire behavior in dry conifer forests.

Over the past several decades, the management of historically frequent-fire forests in the western United States has received significant attention due to the linked ecological and social risks posed by the increased occurrence of large, contiguous patches of high-severity fire. As a result, efforts are underway to simultaneously reduce potential fire and fuel hazards and restore characteristics indicative of historical forest structures and ecological processes that enhance the diversity and quality of wildlife habitat across landscapes. Despite widespread agreement on the need for action, there is a perceived tension among scientists concerning silvicultural treatments that modify stands to optimally reduce potential fire behavior (fuel hazard reduction) versus those that aim to emulate historical forest structures and create structurally complex stands (restoration). In this work, we evaluated thinning treatments in the Black Hills National Forest that exemplify the extremes of a treatment continuum that ranges from fuel hazard reduction to restoration. The goal of this work was to understand how the differing three-dimensional stand structures created by these treatment approaches altered potential fire behavior. Our results indicate that restoration treatments created higher levels of vertical and horizontal structural complexity than the fuel hazard reduction treatments but resulted in similar reductions to potential crown fire behavior. There were some trade-offs identified as the restoration treatments created larger openings, which generated faster mean rates of fire spread; however, these increased spread rates did not translate to higher levels of canopy consumption. Overall, our results suggest that treatments can create vertical and horizontal complexity desired for restoration and wildlife habitat management while reducing fire hazard and that they can be used in concert with traditional fuel hazard reduction treatments to reduce landscape scale fire risk. We also provide some suggestions to land managers seeking to design and implement prescriptions that emulate historical structures and enhance forest complexity.

Building a small fire database for Sub-Saharan Africa from Sentinel-2 high-resolution images

Coarse resolution sensors are not very sensitive at detecting small fire patches, making current estimations of global burned areas (BA) very conservative. Using medium or high-resolution sensors to generate BA products becomes then a priority, particularly in areas where fires tend to be small and frequent.Building on previous work that developed a small fire dataset (SFD) for Sub-Saharan Africa for 2016, this paper presents a new version of the dataset for 2019 using the two Sentinel-2 satellites (A and B) and VIIRS active fires. Total estimated BA was 4.8 Mkm2. This value was much higher than estimations from two global, coarser-spatial resolution BA products based on MODIS data for the same area and period: 80 % greater than estimates from FireCCI51 (based on MODIS 250 m bands) and 120 % larger than MCD64A1 (based on MODIS 500 m bands). The main differences were observed in those months with higher fire occurrence (November to January for the Northern Hemisphere regions and June to September for the Southern Hemisphere ones).Accuracy assessment of the SFD product was based on a novel sampling strategy designed to obtain independent fire reference perimeters. Validation results showed remarkable high accuracy values comparing to existing global BA products. Overall omission errors (OE) were estimated as 8.5 %, commission errors (CE) as 15.0 %, with a Dice Coefficient of 87.7 %. All of these estimations implied significant improvements over the global, coarser spatial resolution BA products (OE > 50 % and CE > 20 % for the same area and period), as well as over the previous SFD product for 2016 of the same area, generated from a single Sentinel-2 satellite and MODIS active fires (OE = 26.5 % and CE = 19.3 %). Temporal accuracies greatly increased as well with the new product, with 92.5 % of fires detected within the first 10 days of occurrence.

Interactions Between Fire Refugia and Climate-Environment Conditions Determine Mesic Subalpine Forest Recovery After Large and Severe Wildfires

Infrequent stand-replacing wildfires are characteristic of mesic and/or cool conifer forests in western North America, where forest recovery within high-severity burn patch interiors can be slow, yet successful over long temporal periods (decades to centuries). Increasing fire frequency and high-severity burn patch size, under a warming climate, however, may challenge post-fire forest recovery, promoting landscape-level shifts in forest structure, composition, and distribution of non-forest patches. Crucial to a delay and/or impediment to this shift, fire refugia (i.e., remnant seed sources) may determine forest recovery trajectories and potential forest state-transitions. To examine how fire refugia attributes (i.e. extent, composition, and structure) interact with local climate and environmental conditions to determine post-fire forest recovery responses, we developed fine-grain maps of fire refugia via remote sensing and conducted field-based assessment of post-fire conifer tree establishment largely originating (i.e., dispersed) from fire refugium in the Central Cascade Range of the Pacific Northwest United States. We found that limitations on seed availability, represented by the distance2-weighted density (D2WD) of fine-grain refugia extent, largely explained post-fire tree establishment responses within our relatively mesic and cool subalpine study sites. Interactions between seed availability, climate, and environmental conditions indicated that the structural attributes of refugia (e.g., tree height) and site abiotic/biotic environmental controls (e.g., climate water deficit, canopy cover, and coarse woody debris cover) interplayed to constrain or enhance species-specific tree establishment responses. Importantly, these interactions illustrate that when seed availability is critically low for a given area, climate-environment conditions may strongly determine whether forests recover following fire(s). Toward modelling and predicting tree establishment responses and potential forest state-transitions after large stand-replacing fires(s), our study demonstrates the importance of accurately quantifying seed availability via the fine-grain extent, configuration, and attributes of remnant seed source legacies.

Mass fire behavior created by extensive tree mortality and high tree density not predicted by operational fire behavior models in the southern Sierra Nevada

Large, severe wildfires continue to burn in frequent-fire adapted forests but the mechanisms that contribute to them and their predictability are important questions. Using a combination of ground based and remotely sensed data we analyzed the behavior and patterns of the 2020 Creek Fire where drought and bark beetles had previously created substantial levels of tree mortality in the southern Sierra Nevada. We found that dead biomass and live tree densities were the most important variables predicting fire severity; high severity fire encompassed 41% of the area and the largest high severity patch (19,592 ha) comprised 13% of total area burned. Areas with the highest amounts of dead biomass and live tree densities were also positively related to high severity fire patch size indicating that larger, more homogenous conditions of this forest characteristic resulted in adverse, landscape-scale fire effects. The first two days of the Creek Fire were abnormally hot and dry but weather during the days of the greatest fire growth was largely within the normal range of variation for that time of year with one day with lower windspeeds. From September 5 to 8th the fire burned almost 50% of its entire area and fire intensity patterns inferred from remotely sensed brightness-temperature data were typical except on September 6th when heat increased towards the interior of the fire. Not only was the greatest heat concentrated away from the fire perimeter, but a significant amount of heat was still being generated within the fire perimeter from the previous day. This is a classic pattern for a mass fire and the high amount of dead biomass created from the drought and bark beetles along with high live tree densities were critical factors in developing mass fire behavior. Operational fire behavior models were not able to predict this behavior largely because they do not include post-frontal combustion and fire-atmosphere interactions. An important question regarding this mass fire is if the tree mortality event that preceded it could have been avoided or reduced or was it within the natural range of variation for these forests? We found that the mortality episode was outside of historical analogs and was exacerbated by past management decisions. The Creek Fire shows us how vulnerable of our current frequent-fire forest conditions are to suffering high tree mortality and offering fuel conditions capable of generating mass fires from which future forest recovery is questionable because of type conversion and probable reoccurring high severity fire.

Characterizing Global Fire Regimes from Satellite-Derived Products

We identified four global fire regimes based on a k-means algorithm using five variables covering the spatial, temporal and magnitude dimensions of fires, derived from 19-year long satellite burned area and active fire products. Additionally, we assessed the relation of fire regimes to forest fuels distribution. The most extensive fire regime (35% of cells having fire activity) was characterized by a long fire season, medium size fire events, small burned area, high intensity and medium variability. The next most extensive fire regime (25.6%) presented a long fire season, large fire events and the highest mean burned area, yet it showed the lowest intensity and the least variability. The third group (22.07%) presented a short fire season, the lowest burned area, with medium-low intensity, the smallest fire patches and large variability. The fourth group (17.3%) showed the largest burned area with large fire patches of moderate intensity and low variability. Fire regimes and fuel types showed a statistically significant relation (CC = 0.58 and CC’ = 0.67, p &lt; 0.001), with most fuel types sustaining all fire regimes, although a clear prevalence was observed in some fuel types. Further efforts should be directed towards the standardization of the variables in order to facilitate comparison, analysis and monitoring of fire regimes and evaluate whether fire regimes are effectively changing and the possible drivers.

Increased burned area in the Pantanal over the past two decades

Wildfires are behaving differently now compared to other time in history in relation to frequency, intensity and affected ecosystems. In Brazil, unprecedented fires are being experienced in the last decade. Thus, to prevent and minimize similar disasters, we must better understand the natural and human drivers of such extreme events. The Brazilian Pantanal is the largest contiguous wetland in the world and a complex environmental system. In 2020, Pantanal experienced catastrophic wildfires due to the synergy between climate, inadequate fire management strategies and weak environmental regulations. In this study, we analyzed recent patterns and changes in fire behavior across the Pantanal based on land use and cover (LULC) classes. The inter-annual variability of the fire and land cover changes between 2000 and 2021 was assessed using BA from MCD64A1 V.6 product and LULC data from Landsat satellite. Our work reveals that fires in the Pantanal over the last two decades tended to occur more frequently in grassland than in others land cover types, but the 2020 fires have preferentially burned forest regions. Large fire patches are more frequent in forest and grasslands; in contrast, croplands exhibit small patches. The results highlight that a broad scale analysis does not reflect distinct localized patterns, thus stratified and refined studies are required. Our work contributes as a first step to disentangling the role of anthropogenic-related drivers, namely LULC changes, in shaping the fire regime in the Pantanal biome. This is crucial not only to predict future fire activity but also to guide appropriated fire management in the region.

Combustion of Aboveground Wood from Live Trees in Megafires, CA, USA

Biomass combustion is a major biogeochemical process, but uncertain in magnitude. We examined multiple levels of organization (twigs, branches, trees, stands, and landscapes) in large, severe forest fires to see how combustion rates for live aboveground woody parts varied with tree species, size, and fire severity in Ponderosa pine (Pinus ponderosa Dougl. ex Laws.) and mixed conifer-dominated forests of the Sierra Nevada, California, USA. In high severity fire patches, most combustion loss was from branches &lt; 2 cm diameter; in low to moderate severity patches, most was from bole charring. Combustion rates decreased as fire severity declined and with increasing tree size. Pinus species had little branch combustion, leading them to have ≈50% the combustion rate of other taxa. Combustion rates could be 100% for small branch segments and up to 57% for small tree aboveground woody biomass in high severity fire patches. However, combustion rates are very low overall at the stand (0.1%–3.2%) and landscape level (0.6%–1.8%), because large trees with low combustion rates comprise the majority of biomass, and high severity fire patches are less than half of the area burned. Our findings of low live wood combustion rates have important implications for policies related to wildfire emissions and forest management.

Fire severity and its local extent are key to assessing impacts of Australian mega‐fires on koala (Phascolarctos cinereus) density

AbstractAimMega‐fires are predicted to increase with climate change. Australia experienced the largest ever documented forest fires in 2019–2020, but the response of most taxa remains poorly known. We used acoustic arrays to estimate impact of the mega‐fires on the density of an iconic marsupial.LocationNorth‐east New South Wales, Australia.Time periodPre‐fire density estimated in 2018–2019 and post‐fire density in 2019–2020.Major taxa studiedKoala, Phascolarctos cinereus.MethodsWe estimated male density before and after fires using large acoustic arrays and spatial count models. Acoustic arrays sampled three timber production forests with a gradient in fire severity and three unburnt controls in national parks.ResultsKoalas were temporarily extirpated where high fire severity dominated the landscape, but some localized recovery was evident after 1 year. Where moderate severity fire dominated, density was reduced by about 50% within 1 year, but koalas were widespread throughout the burnt area. In our third area dominated by low severity fire, no impact was detected as pre‐ and post‐fire uncertainty intervals overlapped. Control sites surveyed at similar times showed little change in density between years. There was no relationship between pyrodiversity and koala density. Within arrays broadly dominated by moderate or high severity fire, density 1 year after fire was lower in burnt patches of both low and high severity fire. Regionally, 9.8% of landscape samples (2 km × 2 km) in koala habitat were dominated by high fire severity, while a further 6.1% were dominated by moderate fire severity, suggesting c. 13% decline in koala density.Main conclusionsA substantial impact of high severity fire was confirmed. Severe impacts were localized across the landscape, recovery had begun within a year and resilience was evident where low severity fire dominated. However, more frequent fires in the future will compound koala losses.

Global intercomparison of functional pyrodiversity from two satellite sensors

ABSTRACT Fires create substantial ecosystem disturbances, which affect biodiversity and climate processes. Previously, satellite-derived burned areas were assessed, and fire patches and morphological traits related to fire spread functions identified. The cut-off value in days is a critical parameter for the algorithms used to identify fire patches, as it identifies when two contiguous burned pixels should be grouped together as one patch. Our understanding of how fire patches and their morphologies change with the cut-off values between satellite sensors is currently insufficient for model development and pyrogeographic studies. We have addressed this using the FRY v1.0 global database of fire patch functional traits, with cut-off values of 3, 5, 9, and 14 days, derived from two burned area products, the MERIS Fire_cci version 4.1 and MODIS MCD64A1 collection 6, from two satellite sensors with different spatial and temporal resolutions. We intercompared the FRY products with functional diversity trait methods that assess their morphological pyrodiversity structures and dissimilarities. We have assessed the functional pyrodiversity of the FRY products with four cut-off values, for fire patches ≥ 300 ha, on 1° resolution tiles for the world and Global Fire Emissions Database (GFED) region scales, from 2005–2011. The functional structures and dissimilarities between the FRY products varied with the regions, while cut-off value sensitivity varied with the regions and between the satellite sensor products. These variations in functional structures and dissimilarities mirrored the regional fire spread processes and satellite sensor resolutions. The functional pyrodiversity that varied with the regions and similar cut-off values did not lead to the best agreement between the satellite sensor products. These variations reinforce the need to combine high temporal resolution optical sensors with radar in tropical regions, to consistently meet the monitoring requirements and for international organizations, to enable improved assessments of climate and biodiversity.

Post-fire landscape evaluations in Eastern Washington, USA: Assessing the work of contemporary wildfires

In the western US, wildfires are modifying the structure, composition, and patterns of forested landscapes at rates that far exceed mechanical thinning and prescribed fire treatments. There are conflicting narratives as to whether these wildfires are restoring landscape resilience to future climate and wildfires. To evaluate the landscape-level work of wildfires, we assessed four subwatersheds in eastern Washington, USA that experienced large wildfires in 2014, 2015, or 2017 after more than a century of fire exclusion and extensive timber harvest. We compared pre- and post-fire landscape conditions to an ecoregion-specific historical (HRV) and future range of variation (FRV) based on empirically established reference conditions derived from a large dataset of historical aerial photo imagery. These four wildfires proved to be a blunt restoration tool, moving some attributes towards more climate-adapted conditions and setting others back. Fires reduced canopy cover and decreased overall tree size and canopy complexity, which moved them into, or slightly outside, the FRV ranges. Moderate- and low-severity fire generally shifted closed-canopy forest structure to open-canopy classes. Patches of high-severity fire shifted patterns of forest, woodland, grassland, and shrubland towards or beyond the HRV ranges and within the FRV ranges by increasing the total area and size of non-forest patches. However, large patches of high-severity fire in dry and moist mixed-conifer forests homogenized landscape patterns beyond FRV ranges towards simplified conditions dominated by non-forest vegetation types. Fires realigned and reconnected landscape patterns with the topo-edaphic template in some cases, but pre-existing fragmentation and spatial mismatches were compounded in many others. Patches of large-tree, closed-canopy forest were reduced by high-severity fire, and the potential to restore more climate-adapted large-tree, open-canopy forest was lost. Re-establishing landscape patterns with desired patch sizes of forest, in particular patches with large trees, will take many decades to centuries and may not occur in drier locations or where seed trees are no longer present. While large wildfires burning during extreme fire weather conditions can move some attributes towards HRV and FRV ranges, intentionally planned mechanical and prescribed-fire treatments that are integrated with strategic wildfire response will better prepare and adapt landscapes for future wildfires and climate.