Surface Fire Research Articles

Pyros: a raster–vector spatial simulation model for predicting wildland surface fire spread and growth

Background Euro–Mediterranean regions are expected to undergo a climate-induced exacerbation of fire activity in the upcoming decades. Reliable predictions of fire behaviour represent an essential instrument for planning and optimising fire management actions and strategies. Aims The aim of this study was to describe and analyse the performance of an agent-based spatial simulation model for predicting wildland surface fire spread and growth. Methods The model integrates Rothermel’s equations to obtain fire spread metrics and uses a hybrid raster–vector implementation to predict patterns of fire growth. The model performance is evaluated in quantitative terms of spatiotemporal agreement between predicted patterns of fire growth and reference patterns, under both ideal and real-world environmental conditions, using case studies in Sardinia, Italy. Key results Predicted patterns of fire growth demonstrate negligible distortions under ideal conditions when compared with circular or elliptical reference patterns. In real-world heterogeneous conditions, a substantial agreement between observed and predicted patterns is achieved, resulting in a similarity coefficient of up to 0.76. Conclusions Outcomes suggest that the model exhibits promising performance with low computational requirements. Implications Assuming that parametric uncertainty is effectively managed and a rigorous validation encompassing additional case studies from Euro–Mediterranean regions is conducted, the model has the potential to provide a valuable contribution to operational fire management applications.

The impact of frequent wildfires during the Permian–Triassic transition: Floral change and terrestrial crisis in southwestern China

Wildfires are considered to have played an important role in the land plants crisis during the Permian–Triassic (P–T) transition. However, the nature and impact of wildfires in the P–T terrestrial crisis remains unclear. Organic petrology data from a terrestrial sequence from southwestern China show that the inertinite content ranges from 21.3% to 80.9% (mean 44.5%), suggesting that wildfires were a frequent phenomenon in low-latitude tropical rainforests during the P–T transition. Abundant inertinite and Hg/TOC peaks in earliest Triassic strata support the co-existence of wildfires and volcanism at that time. Volcanic emissions were potentially lethal for plants and adjacent arc volcanism represents a possible source of ignition. Inertinite reflectance values are used to estimate wildfire combustion temperatures, which themselves are a function of wildfire type. Inertinite with reflectances higher than 4.5% have concentrations between 47% and 65% in the P–T transitional strata. Crown fires with high combustion temperatures were prevalent in wetland settings in the latest Permian. However, surface fires with lower combustion temperatures became dominant during the major terrestrial extinction phase as a result of the sparse, scrubby vegetation that dominated at that time. The subsequent spread of gymnosperms in the earliest Triassic resulted in the re-establishment of high-temperature crown fires. Wildfires associated with the onset of volcanism in the late Permian likely contributed to ecological disturbance in terrestrial settings, which occurred notably earlier than that seen in marine environments. Thus, enhanced wildfire activity destabilised wetlands and increased ecological stress in the late Permian. Wildfire activity on land potentially had devastating consequences for late Permian marine environments via a complex cascade of terrestrial denudation, runoff, and nutrient flux.

Post-fire soil greenhouse gas fluxes in boreal Scots pine forests–Are they affected by surface fires with different severities?

Although forest fires are one of the main natural disturbance types in boreal forests, there is limited information regarding surface fires (dominant in Northern Europe), and how surface fires of different severities could affect post-fire soil greenhouse gas emissions. The results of our study show that fire severity, time since fire and post-fire changes in soil temperature were the main factors driving soil carbon dioxide (CO2) flux (forest floor ecosystem respiration) from burned boreal forest soils. Approximately two hours after the fire, soil CO2 emissions from burned areas were significantly higher compared to pre-fire conditions, and areas with high-severity fires had significantly higher soil CO2 emissions compared to those with low-severity fires. Later (days, months) after the fire, the unburned control areas always had higher soil CO2 emission values compared to burned areas. In the case of methane (CH4), time since fire and post-fire changes in soil temperatures were the main factors driving soil CH4 fluxes. Unburned study areas were sinks of CH4 through the entire measurement period, while immediately after the fire, the burned areas turned from CH4 sink to CH4 source. For nitrous oxide (N2O) measurements, time since fire was the only factor that significantly affected soil N2O fluxes. Shortly after the fire, N2O emissions increased significantly from both low- and high-intensity study plots. Two days after the fire, post-fire soil C and N content decreased in the O-horizon and increased within the first 5 cm of the soil mineral layer, and the trend was visible both in low- and high-severity fire plots. Samples collected four months after the fire, showed similar total soil C and N content as there was before the fire.

Predicting forest fire danger using fuel characteristics in Berbak Sembilang National Park

Analyzing the fuel characteristics of a forest is essential when creating fire danger rating system (FDRS) and understanding how forest fires behave. In this study, the researchers predicted the intensity of forest fires by examining the amount of fuel present Berbak and Sembilang Natinal Park between November 2020 and December 2021. The fuel load measurement was carried out on surface fuel in the burned peatland area by modifying the line-intersect method (triangular plot - Van Wanger 1982) and the method developed during the Kalimantan Forest Climate Project (KFCP). We assessed the possibility of forest fires occurring, based on the fuel conditions. Variations were found in the fuel quantity and composition on the forest’s surface layer across different regions. Consequently, the intensity and type of forest fires changed accordingly. The Berbak Sembilang National Park area proved more intense surface fires. These results underscore the importance of understanding regional fuel characteristics and analyzing the predicted intensity and type of forest fires to take timely preventive measures against early fire occurrences.

Impacts of rainfall on peat fire during the dry season and wet dry season on degraded tropical peatland in South Sumatra, Indonesia

Peat fires on cleared and drained tropical peatlands continue to cause tremendous damage to their ecological functions, contribute to global warming, and reduce in health of local communities, where the fire incidents in 2019 and 2020 correlated with weather conditions. The research aims to determine and clarify the correlation between rainfall dynamics and the occurrence and severity of peat fires in degraded tropical peatlands in South Sumatra, Indonesia. The research was conducted by recording rainfall Indonesian Agency for Meteorology, Climatology, and Geophysics (BMKG) data, surface and peat fuel, and peat fire area primer data from 2019 to 2020. The results show that two types of weather correlate with the size of the burned area in the Ogan Komering Ilir (OKI) regency. Temporal rainfall distribution, quantity, and duration a determining factor for the transition of surface fires to peat fires, especially in the role they play in the hydrology and moisture conditions of peat and surface fuels. This study will present the effect of rainfall in the dry and wet dry seasons on peatland fires and the extent of peat fires that occurred in two years.

Applicability analysis of flame height estimation based on Byram’s fireline intensity model under flat and windless conditions

Forest fire have a serious impact on forest ecosystems, the safety of people’s lives and property, and social stability. The height of surface flames, as the main indicator of forest fire behavior, which is an important parameter for forest fire management. The relationship between fireline intensity and flame height proposed by Byram has been widely used in estimating flame height; however, its applicability to the surface fuel of typical forest stands in the Yunnan–Guizhou Plateau of China has not yet been analyzed. In this study, the surface fuel in the area was taken as the research object, and the flame height of different fuel bed characteristics was measured through an indoor burning experiment. The applicability of three methods—the directly used Byram’s model, corrected model, and re-established prediction model—was analyzed to estimate the flame height in the Yunnan–Guizhou Plateau. We found that the flame height of the typical forest stands in the Yunnan–Guizhou Plateau ranged from 0.05 to 1.2 m and was significantly affected by the moisture content, load, and height of the fuel bed. Although the fireline intensity exhibited a significant linear relationship with the flame height, directly using Byram’s method to predict the flame height of surface fires was impractical, as its mean prediction error exceeded 150%. The mean relative errors of the prediction model obtained by modifying Byram’s method and that based on the characteristics of the fuel bed were both within 15%, which is significantly lower than that of the original Byram’s method. Based on the results of this study, we propose two methods that are suitable for predicting the flame height of surface fires in the typical forests of the Yunnan–Guizhou Plateau in China, which is of great significance for further understanding the relationship between flame height, fireline intensity, and scientific forest fire management.

Is a Forest Fire a Natural Disaster? Investigating the Fire Tolerance of Various Tree Species-An Educational Module.

Wildfires are unplanned conflagrations perceived as a threat by humans. However, fires are essential for the survival of fire-adapted plants. On the one hand, wildfires cause major damage worldwide, burning large areas of forests and landscapes, threatening towns and villages, and generating high levels of air pollution. On the other hand, fire-adapted plants (pyrophytes) in the fire landscapes of the Earth are able to survive exposure to heat (e.g., because of their thick bark, which protects their living tissue) and benefit from fire directly (e.g., fire initiates cone opening and seed release) or indirectly (e.g., fewer competing plants of fire-sensitive species remain, seeds germinate in the ash-fertilized soil). We present the experimental set-up and results of a fire experiment on bark samples used as a basis to assess the fire tolerance of various trees. Fire tolerance is defined as the ability of a tree to survive a surface fire (up to 200 °C and 5 min duration). The measure of the fire tolerance for a tree species is the time taken for the vascular cambium under the insulating bark to reach the critical temperature of 60 °C. Within an educational module, we provide worksheets for teachers and students enabling them to analyze the fire tolerance of various tree barks.

Sustaining eastern oak forests: Synergistic effects of fire and topography on vegetation and fuels.

Across much of the eastern United States, oak forests are undergoing mesophication as shade-tolerant competitors become more abundant and suppress oak regeneration. Given the historical role of anthropogenic surface fires in promoting oak dominance, prescribed fire has become important in efforts to reverse mesophication and sustain oaks. In 2000 we established the Ohio Hills Fire and Fire Surrogate (FFS) study to examine whether repeated prescribed fire (Fire), mechanical partial harvest (Mech), and their combined application (Mech + Fire) reduced the dominance of subcanopy mesophytic competitors, increased the abundance of large oak-hickory advance regeneration, created a more diverse and productive ground-layer flora, and produced fuel beds more conducive to prescribed fire, reducing the risk of high-severity wildfire. Here we report on the ~20-year effects of treatments on vegetation and fuels and examine the support for interactive effects across a topographic-moisture and energy gradient. In general, we found that Fire and Mech + Fire treatments tended to reverse mesophication while the Mech-only treatment did not. The moderate and occasionally high-intensity fires resulted in effects that were ultimately very similar between the two fire treatments but were modulated by topography with increasing fire severity on drier sites. In particular, we found support for an interaction effect between treatment and topography on forest structure and tree regeneration responses. Fire generally reduced mesophytic tree density in the midstory and sapling strata across all site conditions, while leading to substantial gains in the abundance of large oak-hickory advance regeneration on dry and intermediate landscape positions. Fire also promoted ground-layer diversity and created compositionally distinct communities across all site conditions, primarily through the increased richness of native perennial herbs. However, the fire had limited effects on fine surface fuel loading and increased the loading of large woody fuels, potentially increasing the risk of high-severity wildfire during drought conditions. We conclude that two decades of repeated fires, with and without mechanical density reduction, significantly shifted the trajectory of mesophication across most of the landscape, particularly on dry and intermediate sites, highlighting the capacity of a periodic fire regime to sustain eastern oak forests and promote plant diversity but modulated by topography.

Atmospheric turbulence observed during a fuel-bed-scale low-intensity surface fire

Abstract. The ambient atmospheric environment affects the growth and spread of wildland fires, whereas heat and moisture released from the fires and the reduction of the surface drag in the burned areas can significantly alter local atmospheric conditions. Observational studies on fire–atmosphere interactions have used instrumented towers to collect data during prescribed fires, but a few towers in an operational-scale burn plot (usually > 103 m2) have made it extremely challenging to capture the myriad of factors controlling fire–atmosphere interactions, many of which exhibit strong spatial variability. Here, we present analyses of atmospheric turbulence data collected using a 4 × 4 array of fast-response sonic anemometers during a fire experiment on a 10 m × 10 m burn plot. In addition to confirming some of the previous findings on atmospheric turbulence associated with low-intensity surface fires, our results revealed substantial heterogeneity in turbulent intensity and heat and momentum fluxes just above the combustion zone. Despite the small plot (100 m2), fire-induced atmospheric turbulence exhibited strong dependence on the downwind distance from the initial line fire and the relative position specific to the fire front as the surface fire spread through the burn plot. This result highlights the necessity for coupled atmosphere–fire behavior models to have 1–2 m grid spacing to resolve heterogeneities in fire–atmosphere interactions that operate on spatiotemporal scales relevant to atmospheric turbulence. The findings here have important implications for modeling smoke dispersion, as atmospheric dispersion characteristics in the vicinity of a wildland fire are directly affected by fire-induced turbulence.

Early Cretaceous wildfires and their palaeoenvironmental significance in the Jiuxi Basin, Gansu Province, Northwestern China

The occurrence of palaeowildfires in terrestrial ecosystems coincides with the colonization of plants, rendering it one of the most significant geological events and holding paramount importance for comprehending paleoclimate and paleoenvironmental changes. This study provides strong evidence of persistent palaeowildfire occurrences in the Jiuxi Basin, Northwestern China, during the Aptian to Albian period, considering the abundant, continuous, sedimentary charcoal fossils from the uppermost Chijinbao, Xiagou, and Zhonggou Formations of the Hanxia Section. Micromorphological studies based on the scanning electron microscopy indicate that substantial portion of the charcoal fossils originated from conifers. The fusinite reflectance values of the charcoal fossils range from 1.32% to 4.32%, indicating that the palaeowildfire temperatures may have been 330 °C to 700 °C, and can be divided into three stages, evolving from ground fires to surface fires and crown fires, and finally developing to ground fires. Furthermore, high atmospheric oxygen and seasonally dry climate promoted the frequent palaeowildfire environment in the Jiuxi Basin during the late Early Cretaceous. However, the persistent and repeated wildfires may have effected the palaeoecosystem of the Jiuxi Basin during the late Early Cretaceous, which is evidenced by the decline of coniferous trees and the increase of the early herbaceous angiosperms.

Variation and Driving Mechanisms of Bark Thickness in Larix gmelinii under Surface Fire Regimes

Bark is vital for woody plants, providing protection, transporting nutrients and water, and storing essential resources. For fire-prone ecosystems, bark thickness is a key adaptive trait conferring fire resistance. Few studies have been conducted on the drivers of variation in bark thickness of the widely distributed Larix gmelinii (Rupr.) Kuzen in the Great Xing’an Mountains region, on the southern edge of East Siberia, where surface fire disturbances are frequent. To elucidate the relationships between variation in bark thickness (inner vs. outer bark) of L. gmelinii and plant size, environmental factors, and co-variation with other fire-tolerance traits, we selected 26 sites to set up plots and carried out a survey and bark sampling. Results showed that stem diameter primarily determines variation in bark thickness, especially outer bark. The proportion of outer bark to total bark increased accordingly as the tree increased in size. We also observed stronger correlated variation in outer bark thickness, tree height, and self-pruning capacity, implying that larger trees have thicker protective outer bark and taller heights with greater self-pruning, mitigating crown fire risks. Environmental factors appear to have a relatively limited effect on changes in bark thickness in L. gmelinii. Mean air temperature, annual precipitation, and total soil nitrogen content had some effect on outer bark thickness, and mean air temperature had some effect on inner bark thickness.

Impacts of wildfire on soil characteristics in subtropical Chir Pine forests of Murree, Pakistan

Wildfires are a natural component of forest ecosystem. These fires are a major cause of significant perturbations in the forest habitat due to temperature extremes and drought conditions particularly in summer. Wildfires occur frequently during summer in the subtropical Chir pine forests of Murree, Pakistan. These fires influence soil characteristics as well as tree-species growth and survival. The present study was thus conducted to investigate soil characteristics of wildfire-affected and non-affected areas. Four sites were selected based on wildfire incidents in the study area. Soil samples were collected from the fire-affected and adjacent non-affected areas. The collected soil samples were analyzed for physical and chemical characteristics using appropriate methods. The study showed that bulk density, moisture content, electrical conductivity, and soil nitrogen and soil carbon content declined in the burnt soil. However, soil pH, and phosphorus and potassium contents were higher in the burnt soils than those in the non-burnt soils. Generally, low intensity forest fire (surface fire) is an important component of forest ecosystem and it enhances natural regeneration as well as soil fertility. It is suggested that government forest departments should take into account burn severity while developing hazard reduction and restoration strategies of wildfire affected areas.

Field-based generic empirical flame length–fireline intensity relationships for wildland surface fires

Background Fireline intensity (If) quantifies the power of the fireline and is used for various purposes. If and flame length (Lf) are relatable to each other using an empirical power function, which has been considered fuel-specific. Aims The aim of this study was to develop generic Lf − If relationships based on a robust set of field head fires from the literature (n = 797) conducted worldwide in forest, shrubland and grassland. Methods Lf was determined from the base of the fuel bed for comparability across fires in different fuel heights, and the effect of vegetation type was examined. Key results Although If could be approximately described using the same function in forest and shrubland, fires in grassland required different fitted coefficients; we speculate that fuel particles’ surface area-to-mass ratio is the main fuel metric influencing flame structure. Conclusions Fuel-generic relationships for If are reasonably accurate and encompass the high end of surface fire If. Previous studies suggested their unviability, most likely because of limitations in the number of observations and data ranges, difficulty in objectively measuring Lf and variation in Lf definition. Implications The generic relationships presented in this work will be of interest for research and management purposes when specific models for If are non-existent.

Modification of the Rothermel model parameters – the rate of surface fire spread of Pinus koraiensis needles under no-wind and various slope conditions

Background The prediction accuracy for the rate of surface fire spread varies in different regions; thus, increasing the prediction accuracy for local fuel types to reduce the destructive consequences of fire is critically needed. Aims The objective of this study is to improve the Rothermel model’s accuracy in predicting the ROS for surface fuel burning in planted forests of Pinus koraiensis in the eastern mountains of north-east China. Methods Fuel beds with various fuel loads and moisture content was constructed on a laboratory burning bed, 276 combustion experiments were performed under multiple slope conditions, and the ROS data from the combustion experiments were used to modify the related parameters in the Rothermel model. Results The surface fire spread rate in Pinus koraiensis plantations was directly predicted using the Rothermel model but had significant errors. The Rothermel model after modification predicted the following: MRE = 25.09%, MAE = 0.46 m min−1, and R2 = 0.80. Conclusion The prediction accuracy of the Rothermel model was greatly enhanced through parameter tuning based on in-lab combustion experiments Implications This study provides a method for the local application of the Rothermel model in China and helps with forest fire fighting and management in China.

Heat input determines the response and rapid recovery of post-fire soil microbial biomass

Background The post-fire recovery of soil microbes is critical for ecological conservation, yet the mechanisms behind it are not well understood. Aim In this study, we examined the recovery patterns of culturable soil microbes following a fire. Methods A field experiment was conducted in which a forest soil was subjected to surface fire, and the culturable microbial biomass and soil physicochemical characteristics were evaluated 1 day after the fire, and subsequently every 10 days for 90 days. Key results Microbial biomass significantly reduced post-fire, with varying effects across microbial taxa and soil layers. The recovery patterns of microbial biomass at topsoil (0–10 cm) and subsoil (10–20 cm), and among different microbial taxa were also different and were determined by the residual microbiomes. Heat released during a fire (the combination of heat duration and temperature reached during treatment) was significantly related to the decrease and recovery of microbial biomass, whereas there was no relationship between soil physicochemical properties and microbial biomass recovery. Conclusions Soil microbial biomass recovered quickly post-fire, which can be mainly due to the rapid attenuation of heat along the soil profile. Heat released during fire was the key factor determining the residual biomass, and the residual microbiomes determined the recovery patterns of the various taxa that comprise the culturable microbial biomass. Implications Due to the complexity of natural fire, simulated fire experiment and systematic sampling based on space (soil profile) and time are crucial to investigate the dynamics of soil microbes post-fire.

Fossil charcoal from the Upper Triassic Karamay Formation in the Junggar Basin, NW China, and its geological implications

Fossil charcoal can provide important evidence for understanding the ancient forest fires and predicting changes in vegetation, paleoclimate and paleoenvironment throughout geological history. In this research, a systematic study was conducted on fossil charcoal from the Upper Triassic Karamay Formation in the Junggar Basin, NW China. The charred wood is secondary xylem, pycnoxylic and homoxyleous, composed of tracheids and parenchymatous rays. Based on their anatomical features, the charcoal fossils are identified as Protophyllocladoxylon sp. The presence of well-preserved macroscopic charcoal fossils, along with carbonized leaves, suggests that these fossils were formed as a result of local surface fires. Based on the analysis of the mean random reflectance (Romean) values of charcoal from the Karamay Formation, the estimated temperature range for the production of the charcoal is between 407.49 °C and 369.17 °C. This temperature range aligns with the typical temperatures associated with surface fires, indicating that the fires in this region during the Late Triassic were of low intensity and occurred under relatively low temperatures. The presence of fossil charcoal in Junggar Basin suggests that the paleoatmospheric oxygen level in northwest China during Late Triassic was above 13% or 15%, which is the minimum required for sustained burning of natural wildfires. This finding is in accordance with the paleoatmospheric oxygen concentration models on the basis of variations in inertinite content and Phanerozoic wildfire history combined with the phosphorus cycle. The abundant presence of fossil charcoal herein suggests a humid and warm climate with intermittent droughts in the Late Triassic Junggar Basin.

Methyltriethoxysilane modified nano-alumina sol to fabricate organic/inorganic hybrid refractory coating

The development of refractory coating with dense surface and excellent fire resistance is an urgent need in practical application. Herein, an organic/inorganic hybrid refractory coating containing methyltriethoxysilane modified nano-alumina sol was fabricated. The film-forming ability of the coating materials was significantly improved via the hybridization reaction between methyltriethoxysilane and nano-alumina sol. The effect of the ratio of methyltriethoxysilane to nano-alumina sol on the performance of the coatings was thoroughly explored. The results showed that the mechanical property of the coating increased while the flame retardancy slightly decreased with the increase of the molar ratio of methyltriethoxysilane and aluminum sol. The comprehensive performance of the hybrid coating was best when the molar ratio of aluminum sol and methyltriethoxysilane was about 1:3 (R1-M3). The coating that sprayed on the clean aluminum alloy panels demonstated high rigidity (4 H), excellent adhesion (5B) and good impact resistance (50 cm). Furthermore, the organic/inorganic hybrid coating of R1-M3 shown smooth and dense surface and exhibited excellent fire resistance. It was observed that the residual weight at 900 °C was as high as 82.18%.

Experimental Analysis on the Behaviors of a Laboratory Surface Fire Spreading across a Firebreak with Different Winds

In this work, a series of laboratory surface fire experiments were performed over a pine needle fuel bed to investigate the effectiveness of a firebreak and the behaviors of a surface fire across a firebreak. Seven wind velocities of 0~3.0 m/s and six firebreak widths of 10~35 cm are varied. The behaviors of a surface fire across the firebreak, the heat flux received by fuel surface and fuel temperature before and after the firebreak are analyzed and compared simultaneously. The main conclusions are as follows: the behaviors of a surface fire spreading across a firebreak under different wind velocities are classified into three categories—no ignition, ignition by flame contact and ignition by spot fires. When the wind velocity is not more than 1.0 m/s, the surface fire cannot successfully cross the firebreak; as wind velocity changes from 1.5 m/s to 2.5 m/s, the fuel after the firebreak can be ignited by flame contact for relatively narrow firebreak conditions; when the wind velocity increases to 3.0 m/s, the burning fuel can be blown away along the fuel bed, and the fuel behind the firebreak will be ignited by spot fire. A linear relationship between the threshold of firebreak width and the fireline intensity is obtained, and the linear fitting coefficient in this paper is larger than the results reported by Wilson (0.36). For no ignition conditions, the fuel temperature and the heat flux received by the fuel after firebreak are significantly lower than those before the firebreak, whereas their variations over time are similar to those before the firebreak for ignition conditions. Moreover, for no ignition conditions, the maximum fuel temperature and the heat flux after the firebreak increase with wind velocity, but decrease with firebreak width. Additionally, when the fuel temperature (253 °C) and the heat flux received by the fuel considering the radiation and convection (43 kW/m2) after firebreak exceed a threshold value, the surface fire can successfully cross the firebreak.

How are long-term stand structure, fuel profiles, and potential fire behavior affected by fuel treatment type and intensity in Interior Pacific Northwest forests?

Fuel treatments are commonly applied to increase resilience to wildfire in dry and historically frequent-fire forests of western North America. The long-term effects of fuel treatments on forest structure, fuel profiles (amount and configuration of fuels), and potential wildfire behavior are not well known relative to short-term effects. Additionally, long-term treatment effects on the development of stand structure and fuel profiles have rarely been compared to the long-term effects of pre-treatment conditions, treatment intensity, and site productivity. In this study, we addressed these knowledge gaps by resurveying 204 permanent plots at the Northeastern Cascades site of the Fire and Fire Surrogates study 13–18 years (‘long-term’) after burn-only, thin-only, and thin plus burn treatments, and comparing results to pre-treatment conditions and un-treated controls. Methods included ordinations, generalized linear mixed models, and fire models. All treatments shifted long-term average stand structure toward lower tree density, basal area, and crown fire potential, with thin plus burn treatments showing the highest magnitude of effects for most variables. However, the direction and magnitude of trajectories among plots within treatment types were highly variable. Long-term responses of stand structure, fuel profiles, and modelled fire behavior were positively correlated with their pre-treatment values. Treatment intensity strongly affected long-term stand structure and canopy fuel loads. By ∼15 years post-treatment and under 80th percentile fire weather conditions, most plots in all treatments and un-treated controls failed to meet target thresholds for surface flame length, basal area mortality, and torching index, while most plots met thresholds for crowning index. However, live stand structure following wildfire simulated under 80th percentile fire weather conditions was characterized by lower stand density and a shift toward dominance by large-diameter and fire-resistant trees, suggesting that treated stands may be resilient to wildfires occurring under moderate weather. Our study suggests that understanding fuel treatment efficacy and longevity may be improved in future studies by incorporating fine-scale (i.e., plot-level) drivers of variability in stand structure, fuel profiles, and modelled fire behavior, and by using multiple methods of evaluating treatment effectiveness. Thin plus burn treatments and intensely applied burn-only and thin-only treatments can reduce basal area and potential for crown-fire for more than a decade. However, additional maintenance treatments may be needed by 15 years after initial treatment, to further reduce potential for severe surface fire and high tree mortality in subsequent wildfire.

Validating MCD64A1 and FireCCI51 burned area mapping in the Qinghai-Tibetan Plateau

As an alpine area, surface fires significantly affect the fragile ecosystems of the Qinghai-Tibetan Plateau (QTP). However, no studies on the accuracy of any remote sensing burned area (BA) products on the QTP has not been evaluated, resulting in higher uncertainties in BA mapping. To address this, we used 56-view medium-resolution Landsat images of the QTP from 2001 to 2020 to verify the MCD64A1 and FireCCI51 products by stratified sampling. The results showed that MCD64A1 was more accurate than FireCCI51 for identifying small-scale (<2 km2) BAs within the QTP, whereas FireCCI51 was more accurate for identifying medium-scale (2–5 km2) and large-scale (>5 km2) BAs. Additionally, MCD64A1 was more accurate than FireCCI51 for identifying BAs in forests, FireCCI51 was more accurate than MCD64A1 for identifying BAs in grasslands, shrublands, and wetlands. These results can aid fire risk assessment in the region to improve ecosystem stewardship and inform further improvements in BA products.