Surface Fire Research Articles

Climatic controls of fire activity in the red pine forests of eastern North America

Large-scale modes of climate variability influence forest fire activity and may modulate the future patterns of natural disturbances. We studied the effects of long-term changes in climate upon the fire regime in the red pine forests of eastern North America using (a) a network of sites with dendrochronological reconstructions of fire histories over 1700–1900 A.D., (b) reconstructed chronologies of climate indices (1700–1900), and (c) 20th century observational records of climate indices, local surface climate and fire (1950s-2021). We hypothesized that (H1) there are states of atmospheric circulation that are consistently associated with increased fire activity, (H2) these states mark periods of increased climatological fire hazard, and (H3) the observed decline in fire activity in the 20th century is associated with a long-term decline in the frequency of fire-prone states.At the annual scale, years with significantly higher fire activity in the reconstructed and modern fire records were consistently associated with the positive phases of the Pacific North American pattern (PNA), either independently or in combination with the positive phase of the El Niño-Southern Oscillation index (ENSO). During years with both ENSO and PNA in their positive state, the region experienced positive mid-tropospheric heights and temperature anomalies resulting in drought conditions. The fire-prone climate states identified in the reconstructed records became less frequent in 1850 but re-emerged in the 20th century. While our study did not demonstrate a direct influence of climate on the observed decrease in fire activity in the 20th century, it does reveal a clear climate signal embedded within the fire history reconstruction of the region over the past centuries. This study underscores the importance of considering large-scale climatic patterns in understanding historical fire regimes and highlights their role for future fire dynamics in the region and shaping ecological effects of future fires.

Simulated fire injury: effects of trunk girdling and partial defoliation on reproductive development of apple trees (Malus domestica)

Fire damage can significantly impact fruit productivity in orchards. However, the effects of nonlethal fire injuries on the reproductive development of apple trees remain poorly understood. To investigate these effects, we implemented three treatments: trunk girdling to simulate fire injury to xylem, defoliation of a third of the canopy (simulated crown fire injury), and a combined treatment (simulated surface fire injury), alongside a control. The experiment was conducted during the 2021–22 growing season using a randomised block design with four biological replicate plots. Girdling was less effective than crown and surface fire treatments in influencing fruit composition during the current growing season, and flowering and fruiting in the following season. The crown and surface fire treatments induced localised detrimental effects on fruit sugar and titratable acidity while stimulating peel blush. Additionally, these treatments led to reduced starch reserves by harvest, which likely disrupted subsequent flowering and crop load near the previously defoliated sections of the canopy. When surface fires damage leaves near the base of the canopy in addition to the trunk, fruit production in the lower part of the canopy is more likely to be compromised in the following season. Crown fires, which cause leaf loss near the apex of the canopy, appear to be particularly detrimental to tree productivity, as the top defoliation treatment impaired carbohydrate reserves in shoot terminals and roots. In conclusion, fire-induced loss of leaf area during fruit growth alters fruit composition in the current growing season and may lead to lower yields in the subsequent season.

Differences in the intensity of past forest fire events inferred from stable oxygen isotope analysis of charred bark

Understanding past fire regimes requires reliable proxy data that record fire conditions and preserve them over time. The objective of this study was to determine if the oxygen isotope composition of charred bark samples (pyrogenic organic matter) could be used as proxy data to differentiate wildfires based on burn intensity. We collected charred and uncharred bark samples from three fire sites in northern Ontario, Canada that represented a gradient of fire intensity as depicted by Fire Weather Index (FWI) data. We hypothesized that the mean Δ18Obark-char (the difference between δ18O of uncharred bark and a charred sample) would be greater for fires with higher intensities. Analysis of variance of Δ18Obark-char indicated a significant effect of fire event ( F = 73.6, p < 0.001), which explained 57.0% of the variance. A prescribed surface fire treatment (mean FWI = 9.5) had significantly lower Δ18Obark-char than two natural crown fires (FWI = 21 and 27). These results demonstrate that Δ18Obark-char differentiated moderate from high intensity fires in a similar manner to the FWI data.

Metaheuristic algorithms for calibration of two-dimensional wildfire spread prediction model

Wildfires are complex phenomena with harmful consequences, ranging from environmental and property destruction to loss of human lives. In this sense, predicting wildfire behaviour is essential to mitigate its impacts and consequences. The Rothermel model is the most used fire rate of spread prediction model. However, input parameter uncertainty is a significant source of prediction error. In this paper, we propose the calibration of the input parameters of the fire propagation model by metaheuristic algorithms under a two-stage framework. The fire spread model consists on the Rothermel model in a two-dimensional approach for surface fires. The proposed calibration is performed in two stages iteratively repeated over time: (i) the calibration of the fire spread model’s input parameters and (ii) the wildfire spread prediction using the calibrated input parameters. The calibration was performed by the genetic algorithm, differential evolution, and simulated annealing, which calibrates the surface-area-to-volume ratio, fuel bed depth, live fuel moisture and dead fuel moisture. The symmetric difference between the real and predicted fire map shapes was defined as the fitness function of all three metaheuristic algorithms. For validation, simulations were done on two prescribed fires. The results for the real and estimated fire behaviour were then compared and revealed that all the tested metaheuristic algorithms produce a better fit to the real fire’s perimeter when compared to the uncalibrated Rothermel model. From the results, differential evolution provided the majority of best results when compared to genetic algorithm and simulated annealing algorithms in each scenario.

Predicting the rate of spread of mixed-fuel surface fires in northeastern China using the Rothermel wildfire behaviour model: a laboratory study

Predicting the rate of spread of mixed-fuel surface fires in northeastern China using the Rothermel wildfire behaviour model: a laboratory study

Угруповання мишовидих гризунів на ділянках з різним ступенем ураження пожежами: чорнобильські полігони

As a result of climate change, forest fires are becoming a common factor in the dynamics of ecosystems in the forest zone of Ukraine, but the assessment of the consequences of this shift in the ecological situation is in the process of pilot studies. In the spring of 2020, a number of large ecosystem fires occurred in the Central Polissia region, which affected forests the most. Among other things, a large fire occurred in ecosystems located in the Exclusion Zone and the Zone of Unconditional (Mandatory) Resettlement, which was formed as a result of the Chornobyl accident. The ecosystems of the Chornobyl Radiological and Ecological Biosphere Reserve located within its boundaries were also affected by the fire. The consequences of this fire were assessed a year later, using mouse-like rodents as a model group. The purpose of the study was to assess and compare the communities of mouse-like rodents in areas that were affected by two degrees of fire damage—where there was a surface fire and those that were most affected (highland fire). Four polygons were created in the control-impact scheme. Each of the pairs of plots was identical in terms of typical forest vegetation conditions. Sherman traps were used for trapping. A total of 560 trap-days were processed, and 101 animals were captured. The presence of four species of rodents from the genera Apodemus, Sylvaemus, and Myodes was recorded, namely the striped field mouse, the yellow-necked wood mouse, the European wood mouse, and the bank vole. The main indicators of species diversity were calculated using information indices—species richness, evenness, and similarity. The surveys revealed both negative and positive changes in areas affected by fires. Areas characterised by relatively higher values of species diversity indices compared to the control had a high intensity of vegetation recovery. They belonged to areas with wet, relatively fertile (sugrud) and infertile (subor) forest types. The plots with low intensity of vegetation recovery had a depleted community structure and belonged to fresh and dry boreal forest. Based on this, it is possible to create a forecast of ecosystem restoration by assessing the type of forest vegetation conditions.

Using AutoML and generative AI to predict the type of wildfire propagation in Canadian conifer forests

Accurate prediction of wildfire behaviour is critical for safe and effective fire management and suppression. This study focused on developing and evaluating machine learning (ML) models based on a dataset collected of outdoor experimental fires in Canadian conifer forests. Binary classification models (surface fire vs. crown fire) and multi-class fire type models (surface, passive crown, active crown) were created using ensemble tree methods (Random Forest, XGBoost) and automated ML (AutoGluon, TabPFN). Generative adversarial networks (GAN) were used to generate synthetic data to overcome imbalances in the type of fire distribution. The results show automated ML methods applied to the binary problem to perform best of all tested methods, with an overall accuracy of 91%. TabPFN had the highest accuracy for the multi-class problem, with the use of GAN improving model fit. Results show overfitting issues with some of the ML models, highlighting the need of independent evaluation when ML models are developed. The TabPFN models have potential for application in supporting fire management, namely in fuel management and identifying situations with high fire spread and intensity potential that can impact firefighter safety.

Identification of peat-fire-burnt areas among other wildfires using the peat fire index

Fires in peat soils are distinguished from other wildfires by their duration, the release of combustion pollutants dangerous to human health, carbon loss, and other environmental impacts. Peat fires can be detected by superimposing fire data extracted on the basis of the thermal anomalies of the MODIS Terra/Aqua Moderate Resolution Imaging spectroradiometer on previously developed peatland maps. It is necessary to take into account, not all forest fires in peatlands turn into underground (peat) fires. In the example of the extensive fires that occurred in Central European Russia in 2010, the potential of using fire activity indicators (fire radiative power (FRP), temperature, duration, etc., obtained according to MODIS data) to identify soil (peat) fires and separate them from surface fires was investigated. A special peat fire index (consisting of maximum values of FRP, average temperature, duration of burning, and area of ignition) was proposed and tested. A model of the peat fire index is a value that shows the degree of confidence that this fire is a peat fire. This index takes values from 0 to 1: 0 – surface fire, 1 – peat soil fire; values in the interval mean that a fire can affect both the surface and soil of the peatland. After analyzing the proportions of identified fires, we found out that the devised peat fire index is the most effective indicator compared with others. This indicator makes it possible to identify with high probability not only peat fires, but also to identify surface fires, and this reduces the area of uncertainty. Although the obtained results require verification at other sites, they provide convincing evidence that remote data can be used to detect peat fires.

Geochemical implications of uranium-bearing thucholite aggregates in the Upper Permian Kupferschiefer shale, Lubin district, Poland

New inorganic and organic geochemical data from thucholite in the Upper Permian (Wuchiapingian) Kupferschiefer (T1) shale collected at the Polkowice-Sieroszowice Cu-Ag mine in Poland are presented. Thucholite, which forms spherical or granular clusters, appears scattered in the T1 dolomitic shale at the oxic-anoxic boundary occurring within the same shale member. The composition of thucholite concretions and the T1 shale differs by a higher content of U- and REE-enriched mineral phases within the thucholite concretions compared to the T1 shale, suggesting a different mineralising history. The differences also comprise higher Ntot, Ctot, Htot, Stot contents and higher C/N, C/S ratios in thucholite than in the T1 shale. The hydrocarbon composition of the thucholite and the surrounding T1 shale also varies. Both are dominated by polycyclic aromatic compounds and their phenyl derivatives. However, higher abundances of unsubstituted polycyclic aromatic hydrocarbons in the thucholite are indicative of its pyrogenic origin. Pyrolytic compounds such as benz[a]anthracene or benzo[a]pyrene are more typical of the thucholite than the T1 shale. Microscopic observations of the thucholite and its molecular composition suggest that it represents well-rounded small charcoal fragments. These charcoals were formed during low-temperature combustion, as confirmed by semifusinite reflectance values, indicating surface fire temperatures of about 400 °C, and the absence of the high-temperature pyrogenic polycyclic aromatic hydrocarbons. Charred detrital particles, likely the main source of insoluble organic matter in the thucholite, migrated to the sedimentary basin in the form of spherical carbonaceous particulates, which adsorbed uranium and REE in particular, which would further explain their different contents and sorption properties in the depositional environment. Finally, the difference in mineral content between thucholite and the T1 shale could also have been caused by microbes, which might have formed biofilms on mineral particles, and caused a change in the original mineral composition.

Global plant responses to intensified fire regimes

AbstractAimGlobal change factors, such as warming, heatwaves, droughts and land‐use changes, are intensifying fire regimes (defined here as increasing frequency or severity of fires) in many ecosystems worldwide. A large body of local‐scale research has shown that such intensified fire regimes can greatly impact on ecosystem structure and function through altering plant communities. Here, we aim to find general patterns of plant responses to intensified fire regimes across climates, habitats and fire regimes at the global scale.LocationWorldwide.Time periodStudies published 1962–2023.Major taxa studiedWoody plants, herbs and bryophytes.MethodsWe carried out a global systematic review and meta‐analysis of the response of plant abundance, diversity and fitness to increased fire frequency or severity. To assess the context dependency of those responses, we tested the effect of the following variables: fire regime component (fire frequency or severity), time since the last fire, fire type (wildfire or prescribed fire), historical fire regime type (surface or crown fire), plant life form (woody plant, herb or bryophyte), habitat type and climate.ResultsIntensified fire regimes reduced overall plant abundance (Hedges' d = −0.24), diversity (d = −0.27), and fitness (d = −0.69). Generally, adverse effects of intensified fire regimes on plants were stronger due to increased severity than frequency, in wildfires compared to prescribed fires, and at shorter times since fire. Adverse effects were also stronger for woody plants than for herbs, and in conifer and mixed forests than in open ecosystems (e.g. grasslands and shrublands).Main conclusionsIntensified fire regimes can substantially alter plant communities in many ecosystems worldwide. Plant responses are influenced by the specific fire regime component that is changing and by the biotic and abiotic conditions.

Environmentally friendly fluorine-free fire extinguishing agent based on the synergistic effect of silicone, hydrocarbon surfactants and foam stabilizers

The environmentally friendly fluorine-free fire extinguishing agent based on the silicone surfactant was developed in order to solve the environmental hazards and bio-accumulative of traditional aqueous film-forming foam (AFFF). The carboxyl modified polyether polysiloxane surfactant (CMPS) was an efficient alternative to fluorocarbon surfactant, which was firstly synthesized via the esterification reaction using hydroxyl-containing polyether modified polysiloxane (HPMS) and maleic anhydride (MA) as raw materials. Then the surface activity, foam properties, micellar morphology of the CMPS and four hydrocarbon surfactants, as well as their mixture are evaluated by surface tension, Ross-Miles and cryo-transmission electron microscopy (Cryo-TEM). And the suitable key amount of CMPS and hydrocarbon surfactants added to the extinguishing agent were optimized by orthogonal tests. Moreover, the effect of foam stabilizer on the surface activity, foam property and fire extinguishing performance of fire extinguishing agent are also analyzed. Consequently, a new environmentally friendly fluorine-free fire extinguishing agent was prepared and the surface tension, the interfacial tension, foam properties, bubble morphology, spreading behavior and fire extinguishing mechanism were systematically characterized. The Cryo-TEM results illustrate that the intense interaction among silicone and hydrocarbon molecules exists in the the mixture of CMPS and hydrocarbon surfactants, which is produced through the change of micellar morphology, i.e. microscopic larger spheroidal micelles of CMPS transited to smaller spheroidal micelles and wormlike micelles in the mixed system. The surface tension of synthesized foam extinguishing agent is 22.3 mN/m and the spread coefficient is 0.9 mN/m, which has excellent surface activity and spreading property. The prepared foam extinguishing agent exhibits superior fire-fighting property, which can be attributed to the high surface activity, good foam property and superior foam stability. The research results of this paper lay a theoretical foundation for the research and development of efficient environmentally friendly foam extinguishing agent.

The influence of multidecadal climate variability and abrupt landscape change on terrestrial ecosystem composition and fire regime in the upper Columbia River basin - A high-resolution Holocene perspective

High-resolution paleoclimatic and paleoecologic datasets from a small lake in eastern Washington (USA) help elucidate Holocene environmental dynamics in the interior Pacific Northwest. Round Lake lies near the ecotone between sagebrush steppe and dry pine forest, making it highly sensitive to changes in precipitation-evaporation (P-E) balance. We present isotopic, sedimentological, and paleoecological data from a single sedimentary sequence analyzed at sufficient resolution to detect sub-decadal climatic variability. During the early Holocene (11,000–8500 cal yr BP), when summer insolation was higher than present, Round Lake experienced persistent aridity that led to reduced forest cover and small, probably frequent surface fires. Sub-centennial hydroclimate fluctuations during this period were muted, as indicated by low multi-decadal variability in δ18Ocarbonate records from the region. Oxygen isotopes indicate increased cool-season moisture during the middle Holocene (8500-5300 BP), but stratigraphic evidence suggests intermediate and variable lake levels. The deposition of the Mazama tephra (ca. 7600 cal yr BP) immediately preceded to a protracted expansion of steppe at the expense of forest. Increased hydroclimate variability and fire activity following ash deposition likely restricted conifer taxa even when elevated cool-season moisture would have facilitated their growth. The late Holocene was marked by persistently high lake levels, as indicated by the lithostratigraphic and pollen records. Comparatively large multidecadal variations in precipitation, which peaked during the last millennium, were also prominent features of late-Holocene hydroclimate, and may have been related to the strengthening of the El Niño Southern Oscillation and Pacific Decadal Oscillation. Pinus and Pseudotsuga show a 60–100 year lag in their response to hydroclimatic variations inferred from the oxygen isotope records. These results highlight how millennial-to-decadal scale hydroclimate conditions, along with abrupt landscape change, influence ecology in a water-stressed region of western North America.

Design of fluorine-free foam extinguishing agent with high surface activity, foam stability and pool fire suppression by optimization of surfactant composition and foam system

To meet the environmental requirement of foam extinguishing agent, a novel fluorine-free surfactant named amino-terminated polyether modified silicone (ATPMS) was successfully synthesized, and then in combination with hydrocarbon surfactant prepared fluorine-free foam extinguishing agent. The study carefully investigated surface tension, foamability, foam stability and fire extinguishing performance of fluorine-free foam extinguishing agent. The results indicate that ATPMS has a low surface tension of 21.17 mN/m, which combined with hydrocarbon surfactant at the mass concentration ratio of 1:1 imparts high surface activity. The sodium lauryl ether sulfate (AES)/ATPMS system owes the optimal comprehensive performance with an initial foam height value of 85.8 mm, a surface tension value of 24.76 mN/m and a foam stability value (the ratio of foam height between initial foam and five-minute foam) of 64.0 % at critical micelle concentration (CMC), respectively. Fire suppression test shows that the obtained fluorine-free foam extinguishing agent is effective in fighting diesel pool fires. The firefighting efficiency of foam agent links to the mixing chamber structure of compressed air foam fire extinguishing system (CAFS). When the mixing chamber of CAFS has a recurrent segment length of 50 mm and the filled particle size of 10 mm, the firefighting efficiency of fluorine-free foam extinguishing agent is optimal with a fire extinguishing time of 33 s and a temperature drop rate of 6.49 °C/s.

Thermal Characteristics of Surface Fire Spreading Front Under Ambient Wind

Surface fire is the most common form of forest fire, primarily spreading along the forest land's surface and causing damage to nearby low-lying seedlings, shrubs, and the root systems of vegetation at its base. In actual forest fire scenarios, the occurrence of fires is often accompanied by environmental winds due to the typically complex terrain in forested areas. Forest vegetation is densely distributed, and when surface fires encounter obstacles such as tree trunks, the advancing fire front may interact with the tree trunks under the influence of environmental winds. This study focuses on understanding the thermal characteristics of the interaction between the advancing fire front and tree trunks in the presence of environmental winds. To investigate this interaction, temperature measurements are conducted on both sides of the obstacles and in the downstream region of the flame. Additionally, measurements of radiant heat flux are taken in the upper space above the experimental setup. By analyzing flame morphology parameters and experimental measurements, trends in thermal characteristic parameters with spatial position are identified. Regression formulas are developed to describe the temperature difference between the windward and leeward sides of the obstacles and the height above the experimental platform. Furthermore, the influence of flame climbing on radiant heat transfer in the upper space is discussed.

Investigating Fire–Atmosphere Interaction in a Forest Canopy Using Wavelets

Wildland fire–atmosphere interaction generates complex turbulence patterns, organized across multiple scales, which inform fire-spread behaviour, firebrand transport, and smoke dispersion. Here, we utilize wavelet-based techniques to explore the characteristic temporal scales associated with coherent patterns in the measured temperature and the turbulent fluxes during a prescribed wind-driven (heading) surface fire beneath a forest canopy. We use temperature and velocity measurements from tower-mounted sonic anemometers at multiple heights. Patterns in the wavelet-based energy density of the measured temperature plotted on a time–frequency plane indicate the presence of fire-modulated ramp–cliff structures in the low-to-mid-frequency band (0.01–0.33 Hz), with mean ramp durations approximately 20% shorter and ramp slopes that are an order of magnitude higher compared to no-fire conditions. We then investigate heat- and momentum-flux events near the canopy top through a cross-wavelet coherence analysis. Briefly before the fire-front arrives at the tower base, momentum-flux events are relatively suppressed and turbulent fluxes are chiefly thermally-driven near the canopy top, owing to the tilting of the flame in the direction of the wind. Fire-induced heat-flux events comprising warm updrafts and cool downdrafts are coherent down to periods of a second, whereas ambient heat-flux events operate mainly at higher periods (above 17 s). Later, when the strongest temperature fluctuations are recorded near the surface, fire-induced heat-flux events occur intermittently at shorter scales and cool sweeps start being seen for periods ranging from 8 to 35 s near the canopy top, suggesting a diminishing influence of the flame and increasing background atmospheric variability thereat. The improved understanding of the characteristic time scales associated with fire-induced turbulence features, as the fire-front evolves, will help develop more reliable fire behaviour and scalar transport models.

Linking crown fire likelihood with post-fire spectral variability in Mediterranean fire-prone ecosystems

Background Fire behaviour assessments of past wildfire events have major implications for anticipating post-fire ecosystem responses and fuel treatments to mitigate extreme fire behaviour of subsequent wildfires. Aims This study evaluates for the first time the potential of remote sensing techniques to provide explicit estimates of fire type (surface fire, intermittent crown fire, and continuous crown fire) in Mediterranean ecosystems. Methods Random Forest classification was used to assess the capability of spectral indices and multiple endmember spectral mixture analysis (MESMA) image fractions (char, photosynthetic vegetation, non-photosynthetic vegetation) retrieved from Sentinel-2 data to predict fire type across four large wildfires Key results MESMA fraction images procured more accurate fire type estimates in broadleaf and conifer forests than spectral indices, without remarkable confusion among fire types. High crown fire likelihood in conifer and broadleaf forests was linked to a post-fire MESMA char fractional cover of about 0.8, providing a direct physical interpretation. Conclusions Intrinsic biophysical characteristics such as the fractional cover of char retrieved from sub-pixel techniques with physical basis are accurate to assess fire type given the direct physical interpretation. Implications MESMA may be leveraged by land managers to determine fire type across large areas, but further validation with field data is advised.

Low-severity fires in the boreal region: reproductive implications for black spruce stands in between stand-replacing fire events.

Stand-replacing crown fires are the most prevalent type of fire regime in boreal forests in North America. However, a substantial proportion of low-severity fires are found within fire perimeters. Here we aimed to investigate the effects of low-severity fires on the reproductive potential and seedling recruitment in boreal forests stands in between stand-replacing fire events. We recorded site and tree characteristics from 149 trees within twelve sites dominated by mature black spruce [Picea mariana (Mill.) B.S.P.] trees in the Northwest Territories, Canada. The presence of fire-scarred trees supported classification of sites as unburned or affected by low-severity fires in recent history. We used non-parametric tests to evaluate differences in site conditions between unburned and low-severity sites, and mixed effect models to evaluate differences in tree age, size, and reproductive traits among unburned trees and trees from low-severity sites. Results showed significantly higher density of dead black spruce trees in low-severity sites, and marginally significant higher presence of permafrost. Trees from low-severity fire sites were significantly older, exhibited significantly lower tree growth, and showed a tendency towards a higher probability of cone presence and percentage of open cones compared to trees from unburned sites. Surviving fire-scarred trees affected by more recent low-severity fires showed a tendency towards higher probability of cone presence and cone production. Density of black spruce seedlings significantly increased with recent low-severity fires. Trees in low-severity sites appeared to have escaped mortality from up to three fires, as indicated by fire scar records and their older ages. Shallow permafrost at low-severity sites may cause lower flammability, allowing areas to act as fire refugia. Low-severity surface fires temporarily enhanced the reproductive capacity of surviving trees and the density of seedlings, likely as a stress response to the fire event.

A Fireline Displacement Model to Predict Fire Spread

Most current surface fire simulators rely upon Rothermel’s model, which considers the local properties of fuel, topography, and meteorology to estimate the rate of spread, and utilises the concept of elliptical growth to predict the evolution of the fire perimeter throughout time. However, the effects of convective processes near the fireline, which modify fire spread conditions along the fire perimeter, are not considered in this model. An innovative fire prediction simulator based on the concept of fireline element displacement, which is composed of translation, rotation, and extension, rather than a point-by-point displacement, is proposed in this article. Based on the laws of convective heat fluxes across and along the fireline and on laboratory experiments, models to estimate the angular rotation velocity and the extension of the fireline during its displacement are proposed. These models are applied to a set of laboratory experiments of point ignition fires on slopes of 30° and 40° and, given the fact that the rate of spread of the head, back, and flank fire are known, the evolution of the fire perimeter can be predicted. The fire spread model can be applied to other situations of varying boundary conditions provided that the parameters required by the model are known.

Ungulates mitigate the effects of drought and shrub encroachment on the fire hazard of Mediterranean oak woodlands.

Climate change is increasing the frequency of droughts and the risk of severe wildfires, which can interact with shrub encroachment and browsing by wild ungulates. Wild ungulate populations are expanding due, among other factors, to favorable habitat changes resulting from land abandonment or land-use changes. Understanding how ungulate browsing interacts with drought to affect woody plant mortality, plant flammability, and fire hazard is especially relevant in the context of climate change and increasing frequency of wildfires. The aim of this study is to explore the combined effects of cumulative drought, shrub encroachment, and ungulate browsing on the fire hazard of Mediterranean oak woodlands in Portugal. In a long-term (18 years) ungulate fencing exclusion experiment that simulated land abandonment and management neglect, we investigated the population dynamics of the native shrub Cistus ladanifer, which naturally dominates the understory of woodlands and is browsed by ungulates, comparing areas with (no fencing) and without (fencing) wild ungulate browsing. We also modeled fire behavior in browsed and unbrowsed plots considering drought and nondrought scenarios. Specifically, we estimated C. ladanifer population density, biomass, and fuel load characteristics, which were used to model fire behavior in drought and nondrought scenarios. Overall, drought increased the proportion of dead C. ladanifer shrub individuals, which was higher in the browsed plots. Drought decreased the ratio of live to dead shrub plant material, increased total fuel loading, shrub stand flammability, and the modeled fire parameters, that is, rate of surface fire spread, fireline intensity, and flame length. However, total fuel load and fire hazard were lower in browsed than unbrowsed plots, both in drought and nondrought scenarios. Browsing also decreased the population density of living shrubs, halting shrub encroachment. Our study provides long-term experimental evidence showing the role of wild ungulates in mitigating drought effects on fire hazard in shrub-encroached Mediterranean oak woodlands. Our results also emphasize that the long-term effects of land abandonment can interact with climate change drivers, affecting wildfire hazard. This is particularly relevant given the increasing incidence of land abandonment.

Depositional conditions, wildfires, maturity, and hydrocarbon potential evaluation of Central Carpathian Paleogene Basin based on integrative approach from Orava Basin

Central Carpathian Paleogene Basin (CCPB, Central Western Carpathians) comprises mainly Oligocene clastic autochthonous age-equivalents of the widely known Menilite shale formation from the Outer Carpathians. However, little is known about the paleoenvironment and its subsequent changes during the basin's evolution. Furthermore, the available hydrocarbon potential data are based on anachronous methods and are not investigated on the sub-basin level. Gas chromatography-mass spectrometry (GC–MS) analyses supported by Rock-Eval data along with petrographic measurements enabled us to identify and document the paleoenvironmental evolution of the Orava sub-basin (NW remnant of CCPB). Thermal maturity based on vitrinite reflectance, 22S/(22S + 22R) homohopane ratio and 20S/(20S + 20R) sterane ratio increases from N to S and from Upper to Lower Oligocene. In the least mature samples ββ-hopanes, hopenes, and oleanenes are present, whereas in the most mature deposits less thermally stable compounds dissapeared. This maturation trend is shown also by the Rock-Eval data. Terrestrial organic matter input is documented by the predominance of III- and II/III-type of kerogen and the occurrence of several biomarkers, such as 3,3,7-trimethyl-1,2,3,4-tetrahydrochrysene, cadalene, retene, and perylene. The significant contribution of polycyclic aromatic hydrocarbons (PAHs) may be linked with wildfire-related land degradation and following runoff to the basin. Based on the measured fusinite reflectance values the wildfire types could range from hotter crown fires to colder surface fires. Depositional conditions in Lower Oligocene units are characterized by intermittent euxinia, as derived from small (<5 μm) pyrite framboid diameters and the presence of isorenieratane. Subsequently, a change of conditions to oxic/dysoxic in younger units is observed, and the input of terrestrial organic matter increased.