Potential Fire Behavior Research Articles

Stand composition and development stage affect fuel characteristics of quaking aspen forests in UT, USA

In western North America, quaking aspen stands (Populus tremuloides Michx.) have predominantly been described as low flammability, “fireproof” forests, but the specific relationship between aspen stand composition, fuel characteristics, and potential fire behavior is not fully understood. We investigated surface and canopy fuel characteristics in 80 aspen stands in Utah, U.S. that spanned gradients of tree species composition from aspen to conifer dominance and stand development from early to late stages. We quantified fuel type and load, measured fuel moisture content in representative stands across two summer seasons, and modeled flame lengths in each stand. Fuel type and load varied greatly across stands, though late development, conifer-dominated stands had significantly higher (~2-5 times) fine dead woody and litter load and significantly lower (~2-5 times) live understory herbaceous load compared to pure aspen stands. Fuel moisture content did not vary by stand type. Modeled flame lengths were lowest in pure aspen stands, and flame lengths increased linearly with decreasing aspen composition, suggesting that potential surface fire behavior increases as a seral aspen stand progresses through succession to conifer dominance.

Response of Fuel Characteristics, Potential Fire Behavior, and Understory Vegetation Diversity to Thinning in Platycladus orientalis Forest in Beijing, China

Objective: Active fuel management operations, such as thinning, can minimize extreme wildfire conditions while preserving ecosystem services, including maintaining understory vegetation diversity. However, the appropriate thinning intensity for balancing the above two objectives has not been sufficiently studied. Methods: This study was conducted to assess the impact of various thinning intensities (light thinning, LT, 15%; moderate thinning, MT, 35%; heavy thinning, HT, 50%; and control treatment, CK) on fuel characteristics, potential fire behavior, and understory vegetation biodiversity in Platycladus orientalis forest in Beijing using a combination of field measurements and fire behavior simulations (BehavePlus 6.0.0). Results: A significant reduction in surface and canopy fuel loads with increasing thinning intensity, notably reducing CBD to below 0.1 kg/m3 under moderate thinning, effectively prevented the occurrence of active crown fires, even under extreme weather conditions. Additionally, moderate thinning enhanced understory species diversity, yielding the highest species diversity index compared to other treatments. Conclusions: These findings suggest that moderate thinning (35%) offers an optimal balance, substantially reducing the occurrence of active crown fires while promoting biodiversity. Therefore, it is recommended to carry out moderate thinning in the study area. Forest managers can leverage this information to devise technical strategies that simultaneously meet fire prevention objectives and enhance understory vegetation species diversity in areas suitable for thinning-only treatments.

Transferability of Empirical Models Derived from Satellite Imagery for Live Fuel Moisture Content Estimation and Fire Risk Prediction

Estimating live fuel moisture content (LFMC) is critical for assessing vegetation flammability and predicting potential fire behaviour, thus providing relevant information for wildfire prevention and management. Previous research has demonstrated that empirical modelling based on spectral data derived from remote sensing is useful for retrieving LFMC. However, these types of models are often very site-specific and generally considered difficult to extrapolate. In the present study, we analysed the performance of empirical models based on Sentinel-2 spectral data for estimating LFMC in fire-prone shrubland dominated by Cistus ladanifer. We used LFMC data collected in the field between June 2021 and September 2022 in 27 plots in the region of Andalusia (southern Spain). The specific objectives of the study included (i) to test previous existing models fitted for the same shrubland species in a different study area in the region of Madrid (central Spain); (ii) to calibrate empirical models with the field data from the region of Andalusia, comparing the model performance with that of existing models; and (iii) to test the capacity of the best empirical models to predict decreases in LFMC to critical threshold values in historical wildfire events. The results showed that the empirical models derived from Sentinel-2 data provided accurate LFMC monitoring, with a mean absolute error (MAE) of 15% in the estimation of LFMC variability throughout the year and with the MAE decreasing to 10% for the critical lower LFMC values (<100%). They also showed that previous models could be easily recalibrated for extrapolation to different geographical areas, yielding similar errors to the specific empirical models fitted in the study area in an independent validation. Finally, the results showed that decreases in LFMC in historical wildfire events were accurately predicted by the empirical models, with LFMC <80% in this fire-prone shrubland species.

Future fire events are likely to be worse than climate projections indicate – these are some of the reasons why

Background Climate projections signal longer fire seasons and an increase in the number of dangerous fire weather days for much of the world including Australia. Aims Here we argue that heatwaves, dynamic fire–atmosphere interactions and increased fuel availability caused by drought will amplify potential fire behaviour well beyond projections based on calculations of afternoon forest fire danger derived from climate models. Methods We review meteorological dynamics contributing to enhanced fire behaviour during heatwaves, drawing on examples of dynamical processes driving fire behaviour during the Australian Black Summer bushfires of 2019–20. Results Key dynamical processes identified include: nocturnal low-level jets, deep, unstable planetary boundary layers and fire–atmosphere coupling. Conclusions The future scenario we contend is long windows of multi-day fire events where overnight suppression is less effective and fire perimeters will expand continuously and aggressively over multiple days and nights. Implications Greater overnight fire activity and multi-day events present strategic and tactical challenges for fire management agencies including having to expand resourcing for overnight work, manage personnel fatigue and revise training to identify conditions conducive to unusually active fire behaviour overnight. Effective messaging will be critical to minimise accidental fire ignition during heatwaves and to alert the community to the changing fire environment

Spatial multi-criteria analysis for prioritising forest management zones to prevent large forest fires in Catalonia (NE Spain)

Large forest fires are one of the most common environmental issues in the Mediterranean region. In this study, we defined a set of indicators and criteria based on available spatial data to assess and prioritize management zones for preventing large forest fires in Catalonia (NE Spain). In total, 22 indicators were defined and grouped into 5 criteria. The process involved geospatial modelling using a Geographical Information System (GIS) and the Multi-Attribute Utility Theory (MAUT) analysis. The conducted MAUT analysis resulted in the development of rules for a more standardized assessment of priority management areas. This assessment is based on participatory evaluation and introduces a utility-function-based hierarchical spatial model. Within the model, each of the 5 criteria contains relevant information, including fuel hazard, potential fire behaviour, fire extinction accessibility, valuable resources at risk, and historical fire data, serving as the foundation for a comprehensive analysis of fire prevention measures. During the assessment, two distinct sets of weights were applied: one based on expert evaluation and another using equal weights. These weights describe the relative importance of the indicators within each criterion in the assessment of fire prevention measures. Our results reveal noticeable differences between the two applied approaches. In general terms, management priority levels showcase certain spatial aggregation patterns and spatial polarization characteristics. Our study underscores the importance of participatory planning for prioritizing forest management areas to reduce fire impacts and presents a methodological framework that facilitates such spatial assessments, utilizing tools that combine expert knowledge and scientific expertise. Therefore, the main focus of this study is not on the obtained results, but on the novel methodological framework used, which consists in combining geospatial modelling with MAUT and the participatory workshops for generating the utility rules. This framework allows participation of stakeholders which at the same time enlarges credibility and acceptance of the methodology and results.

Branching out: species-specific canopy architecture limits live crown fuel consumption in Intermountain West USA conifers

BackgroundAccurate estimates of available live crown fuel loads are critical for understanding potential wildland fire behavior. Existing crown fire behavior models assume that available crown fuels are limited to all tree foliage and half of the fine branches less than 6 mm in diameter (1 h fuel). They also assume that this relationship is independent of the branchwood moisture content. Despite their widespread use, these assumptions have never been tested, and our understanding of the physiochemical properties that govern live crown flammability and consumption remains limited. To test these assumptions, we sampled branches from 11 common Intermountain West USA conifers and determined the corrected available fuel estimates using physiochemical measurements, diameter subsize class distributions, and a bench-scale consumption experiment. Additional branches were air-dried to explore interaction between moisture content and consumption. Corrected available live crown fuel was compared to existing models across species and then used to determine potential differences in crown fire energy release.ResultsAcross the 11 common conifers, distinct patterns of sub 1 h fuel distributions were strong predictors of whether the existing available live crown fuel models overestimated, approximately correctly estimated, or underestimated available live fuel. Fine branchwood distributions generally fell into three archetypes: fine skewed, normally distributed, and coarse skewed. Based on our corrected estimates, existing models overestimated the potential canopy energy by 34% for an average-sized western larch and underestimated it by 18.8% for western hemlock. The critical fine branchwood consumption diameter varied with species and moisture content. Larger proportions of fine branches were consumed as the branchwood dried, and nearly all the 1 h fuel was consumed when the branches were completely dry.ConclusionsThese results suggest that available live canopy fuel load estimates should consider species and moisture content to accurately assess and map fuel loads across landscapes. This work has implications for forest and fire management in conifer-dominated forests throughout western North America, and in other similar forests worldwide.

Fuel types misrepresent forest structure and composition in interior British Columbia: a way forward

BackgroundA clear understanding of the connectivity, structure, and composition of wildland fuels is essential for effective wildfire management. However, fuel typing and mapping are challenging owing to a broad diversity of fuel conditions and their spatial and temporal heterogeneity. In Canada, fuel types and potential fire behavior are characterized using the Fire Behavior Prediction (FBP) System, which uses an association approach to categorize vegetation into 16 fuel types based on stand structure and composition. In British Columbia (BC), provincial and national FBP System fuel type maps are derived from remotely sensed forest inventory data and are widely used for wildfire operations, fuel management, and scientific research. Despite their widespread usage, the accuracy and applicability of these fuel type maps have not been formally assessed. To address this knowledge gap, we quantified the agreement between on-site assessments and provincial and national fuel type maps in interior BC.ResultsWe consistently found poor correspondence between field assessment data and both provincial and national fuel types. Mismatches were particularly frequent for (i) dry interior ecosystems, (ii) mixedwood and deciduous fuel types, and (iii) post-harvesting conditions. For 58% of field plots, there was no suitable match to the extant fuel structure and composition. Mismatches were driven by the accuracy and availability of forest inventory data and low applicability of the Canadian FBP System to interior BC fuels.ConclusionsThe fuel typing mismatches we identified can limit scientific research, but also challenge wildfire operations and fuel management decisions. Improving fuel typing accuracy will require a significant effort in fuel inventory data and system upgrades to adequately represent the diversity of extant fuels. To more effectively link conditions to expected fire behavior outcomes, we recommend a fuel classification approach and emphasis on observed fuels and measured fire behavior data for the systems we seek to represent.

Developing customized fuel models for shrub and bracken communities in Galicia (NW Spain)

Geospatial fire behaviour and fire hazard simulators, fire effects models and smoke emission software commonly use standard fuel models in order to simplify data collection and the inclusion of complex fuel scenarios. These fuel models are often mapped using remotely sensed data. However, given the great complexity of fuelbeds, with properties that vary widely in both time and space, the use of these standard fuel models can greatly limit accurate fuel mapping. This affects fuel hazard assessment, fuel reduction treatment plans, fire management decision-making and evaluation of the environmental impact of wildfire. In this study, we developed unique customized fire behaviour fuel models for shrub and bracken communities, by using k-medoids clustering analysis based on both fuel structural characteristics and potential fire behaviour. We used an original database of 722 destructive sample plots in nine different shrub and bracken communities covering the entire distribution area in Galicia (NW Spain), one of the regions in Europe most affected by forest fires. Measurements of cover, height and fuel fractions loads differentiated by size and vegetative state (live or dead) were used to estimate the potential rate of fire spread with five different models including fireline intensity, heat per unit area and the flame length for each sampling site and considering extreme environmental conditions. The optimal number of clusters was established by combining practical knowledge about the shrubland communities under study and their associated fire behaviour, with maximization of the mean value of the silhouette variable and minimization of the within-cluster sum of squares. The structural characteristics of the medoids derived from the analysis were associated with each of the proposed customized fuel models. Finally, a simple dichotomous classification based only on shrub height was developed to enable construction of spatially explicit fuel model maps based on remotely sensed data. Thus, the methodology applied allows generation of a more realistic representation of fuel distribution in the landscape, based on fuel structure measurements of natural regional ecosystems rather than on the use of standard models. We believe that the proposed methodology is generally applicable to communities composed of other shrub and fern species in different biogeographical regions.

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.

Model analysis of post-fire management and potential reburn fire behavior

Recent trends in wildfire area burned have been characterized by large patches with high densities of standing dead trees, well outside of historical range of variability in many areas and presenting forest managers with difficult decisions regarding post-fire management. Post-fire tree harvesting, commonly called salvage logging, is a controversial management tactic that is often undertaken to recoup economic loss and, more recently, also to reduce future fuel hazard, especially when coupled with surface fuel reduction. It is unclear, however, whether the reductions in future fuels translate to meaningful changes to reburn fire behavior, particularly in the context of potentially detrimental effects of harvest on other ecosystem services. We used observed post-fire snag structure in four high severity burn scars located in the Western United States that had variable post-fire snag basal area (13.3–63.9 mg ha−2) to initialize a simulation study of future coarse and fine woody fuel hazard and associated reburn fire behavior and effects. We compared untreated controls to intensive and intermediate intensity harvest treatments, both simulated and actual. All treatments showed some number of years of extreme fire behavior during which flame lengths exceeded thresholds associated with wildfire resistance to control, implying that future fuel reductions achieved by the treatments did not translate to conditions conducive for effective reburn fire management. Harvested stands had less severe soil fire effects (soil heating and smoldering duration) than untreated controls, explained by lower predicted peak coarse woody fuels (CWD) in the harvested stands. At higher pre-treatment snag basal area, harvested stands better maintained CWD within the range desired to maintain ecosystem functions such as nutrient cycling and wildlife habitat. These simulation results indicate that, even with reduced fuel hazard, salvage treatments may still be associated with severe fire behavior for some time after wildfire, but achieved reductions in coarse woody fuels may also reduce some soil fire effects. Tradeoffs in the effects of post-fire harvest must be considered carefully in the context of forest regeneration, local conditions that govern salvage methods, snag fall and decomposition, and associated potential reburn fire effects.

A forest fire hazard model and map for a wildland urban interface not meteorologically prone to forest fires

Fire Hazard (FH) modelling is a relevant fire prevention/assessment tool. This work proposes a FH model and generates a FH map for a wildland urban interface area in Germany that is not prone to extreme fires. The main input data include weather, topography, fuel, and anthropic-related potential ignition points. The main steps include (1) identification/description of weather scenarios, and for each scenario (2) analysis of potential fire ignition through simulation of Fire Probability (FP), (3) modelling the potential fire behaviour through simulation of Fireline Intensity (FLI), (4) generation of a FH map by combining FP and FLI maps, and (5) integration of all maps into a final FH map. Extreme ignition and propagation conditions were considered: (1) a fuel model that describes the fire performance in an extreme drought scenario, (2) the human influence through mechanistic ignitions, and (3) the worst case of all scenarios. As results, four weather scenarios were identified and described. FP maps, FLI maps, and FH maps were created for each of them, and finally an integrated FH map (IFHM) was derived.

Effects of Prescribed Burning on Surface Dead Fuel and Potential Fire Behavior in Pinus yunnanensis in Central Yunnan Province, China

Prescribed burning is a widely used fuel management employed technique to mitigate the risk of forest fires. The Pinus yunnanensis Franch. forest, which is frequently prone to forest fires in southwestern China, serves as a prime example for investigating the effects of prescribed burning on the flammability of surface dead fuel. This research aims to establish a scientific foundation for managing dead fuel in forests, as well as fire prevention and control strategies. Field data was collected from P. yunnanensis forests located in central Yunnan Province in 2021 and 2022. The study implemented a randomized complete block design with two blocks and three treatments: an unburned control (UB), one year after the prescribed burning (PB1a), and three years after the prescribed burning (PB3a). These treatments were evaluated based on three indices: surface dead-bed structure, physicochemical properties, and potential fire behavior parameters. To analyze the stand characteristics of the sample plots, a paired t-test was conducted. The results indicated no significant differences in the stand characteristics of P. yunnanensis following prescribed burning (p > 0.05). Prescribed burning led to a significant decrease in the average surface dead fuel load from 10.24 t/ha to 3.70 t/ha, representing a reduction of 63.87%. Additionally, the average fire−line intensity decreased from 454 kw/m to 190 kw/m, indicating a decrease of 58.15%. Despite prescribed burning, there were no significant changes observed in the physical and chemical properties of dead fuels (p > 0.05). However, the bed structure of dead fuels and fire behavior parameters exhibited a significant reduction compared with the control sample site. The findings of this study provide essential theoretical support for the scientific implementation of prescribed burning programs and the accurate evaluation of ecological and environmental effects post burning.

Quantifying surface fuels for fire modelling in temperate forests using airborne lidar and Sentinel-2: potential and limitations

Surface fuel information is an essential input for models of fire behaviour and fire effects. However, spatially explicit, continuous information on surface fuel loads and fuelbed depth is scarce because the collection of field data is laborious, while suitable methods for deriving estimates from remote sensing data are still at an early stage of development. Fine-scale surface fuel mapping using both passive and active remote sensing has not yet been carried out in Central European forest types, and it remains unexplored how prediction uncertainties of different fuel components affect modelled fire behaviour. This study combines very detailed airborne lidar and multispectral satellite data to extract metrics describing forest structure and composition in two forested areas in southwestern Germany. These metrics were used to predict field-sampled surface fuel components using random forest regression. Accuracies of continuous fuel load predictions were compared to accuracies that could be achieved if only forest type-specific average fuels were assigned. Results revealed that models based on remotely sensed metrics explain part of the variance in litter and fine dead woody fuels (R2=0.27-0.41), but not in coarser dead woody fuels. Estimates for herb and shrub fuels were fairly accurate (R2=0.55-0.64) but limited for the more fire-relevant fine fraction of shrub fuels (R2=0.39). Fuelbed depth was moderately well predicted based on remote sensing data (R2=0.44). Lidar-derived metrics were particularly useful for predicting understory fuels and fuelbed depth. Litter and fine woody fuel predictions were linked to canopy characteristics captured with both lidar and multispectral data and similarly accurate estimates could be obtained using average values based on forest type. We used the fine-scale surface fuel maps derived from remote sensing to predict potential surface fire behaviour in the study area and analysed the sensitivity of modelled fire behaviour to errors in the predicted loads of different surface fuel components: fire behaviour was most sensitive to errors in litter and especially shrub fuel loads, hence estimates of these components need to be improved. Overall, this study showed that statistical relationships between remotely sensed metrics describing forest composition and structure and surface fuels have some potential for estimating fuel loads in Central European forest types and should be further developed to provide starting points for realistic fire behaviour models.

Mechanical treatments and prescribed burning can reintroduce low-severity fire in southern Australian temperate sclerophyll forests

The establishment of sustainable, low-intensity fire regimes is a pressing global challenge given escalating risk of wildfire driven by climate change. Globally, colonialism and industrialisation have disrupted traditional fire management, such as Indigenous patch burning and silvo-pastoral practices, leading to substantial build-up of fuel and increased fire risk. The disruption of fire regimes in southeastern Tasmania has led to dense even-aged regrowth in wet forests that are prone to crown fires, and dense Allocasuarina-dominated understoreys in dry forests that burn at high intensities.Here, we investigated the effectiveness of several fire management interventions at reducing fire risk. These interventions involved prescribed burning or mechanical understorey removal techniques. We focused on wet and dry Eucalyptus-dominated sclerophyll forests on the slopes of kunanyi/Mt. Wellington in Hobart, Tasmania, Australia. We modelled potential fire behaviour in these treated wet and dry forests using fire behaviour equations based on measurements of fuel load, vegetation structure, understorey microclimate and regional meteorological data.We found that (a) fuel treatments were effective in wet and dry forests in reducing fuel load, though each targeted different layers, (b) both mechanical treatments and prescribed burning resulted in slightly drier, and hence more fire prone understorey microclimate, and (c) all treatments reduced predicted subsequent fire severity by roughly 2–4 fold. Our results highlight the importance of reducing fuel loads, even though fuel treatments make forest microclimates drier, and hence fuel more flammable.Our finding of the effectiveness of mechanical treatments in lowering fire risk enables managers to reduce fuels without the risk of uncontrolled fires and smoke pollution that is associated with prescribed burning. Understanding the economic and ecological costs and benefits of mechanic treatment compared to prescribed burning requires further research.

Modeling Juvenile Stand Development and Fire Risk of Post-Fire Planted Forests under Variations in Thinning and Fuel Treatments Using FVS–FFE

In the past, the dry mixed conifer forests of California’s Sierra Nevada mountains experienced frequent low to mixed severity fires. However, due to fire suppression and past management, forest structure has changed, and the new fire regimes are characterized by large, high severity fires which kill a majority of the overstory trees. These new disturbance patterns require novel approaches to regenerate the forest as they are not adapted to large, high severity fires. We forecasted growth and fire behavior of young plantations for 100 years into the future using the Forest Vegetation Simulator (FVS) and its Fire and Fuels Extension (FFE). In these simulations, we tested combinations of different fuel treatments (mastication only, mastication with prescribed burning, and no fuels treatments) with different overstory thinning intensities (residual densities of 370 SDI (stand density index), 495 SDI, 618 SDI (TPH), and no overstory thinning) on stand growth and potential fire behavior using analysis of variance. We compared growth and crowning index at the end of the simulation and the simulation age when the flame length, basal area mortality, and fire type reached low severity between fuel treatment, thinning intensity, and original management of stands (plantation with PCT [precommercial thinning], plantation without PCT, and natural regenerating stands). These comparisons are essential to identify which fuel treatment categories reduce fire risk. We found an overall pattern of decreasing crown fire occurrence and fire induced mortality across all simulations due to increasing canopy base height and decreasing canopy bulk density. In particular, stands with mastication and prescribed burning transitioned from crown fire types to surface fires 10 years earlier compared to mastication only or no fuel treatment. Furthermore, pre-commercially thinned stands transitioned from crown fire states to surface fires 10 years earlier in the simulations compared to un-thinned and naturally regenerating stands. Stands with mastication and burning went below 25% reference threshold of basal area mortality 11 and 17 years earlier before the mastication only and no fuel treatment, respectively. In addition, pre-commercially thinned stands went below 25% basal area mortality 9 and 5 years earlier in the simulation compared to un-thinned or naturally regenerated stands, respectively. Mastication with prescribed burning (MB) was the most effective treatment for quickly reducing fire behavior by consuming surface fuels, thus drastically lowing flame length (e.g., surface flame length of MB was 0.6 m compared to mastication only [1.3 m] and no treatment [1.4 m]). Furthermore, intensive thinning reduced risk of active crown fires spreading through the stand. Prioritizing prescribed burning, when possible, and thinning (both pre-commercially and from below) are the most effective ways to quickly improve fire resistance in mixed conifer plantations. Our results highlight the different stressors that post-fire planted forests experience and how different silvicultural treatments interact over time to reduce fire risk, which demonstrates the importance of treating stands early and the effectiveness of surface fuel treatments.

Improvements of Fire Fuels Attributes Maps by Integrating Field Inventories, Low Density ALS, and Satellite Data in Complex Mediterranean Forests

One of the most determining factors in forest fire behaviour is to characterize forest fuel attributes. We investigated a complex Mediterranean forest type—mountainous Abies pinsapo–Pinus–Quercus–Juniperus with distinct structures, such as broadleaf and needleleaf forests—to integrate field data, low density Airborne Laser Scanning (ALS), and multispectral satellite data for estimating forest fuel attributes. The three-step procedure consisted of: (i) estimating three key forest fuel attributes (biomass, structural complexity and hygroscopicity), (ii) proposing a synthetic index that encompasses the three attributes to quantify the potential capacity for fire propagation, and (iii) generating a cartograph of potential propagation capacity. Our main findings showed that Biomass–ALS calibration models performed well for Abies pinsapo (R2 = 0.69), Juniperus spp. (R2 = 0.70), Pinus halepensis (R2 = 0.59), Pinus spp. mixed (R2 = 0.80), and Pinus spp.–Juniperus spp. (R2 = 0.59) forests. The highest values of biomass were obtained for Pinus halepensis forests (190.43 Mg ha−1). The structural complexity of forest fuels was assessed by calculating the LiDAR Height Diversity Index (LHDI) with regard to the distribution and vertical diversity of the vegetation with the highest values of LHDI, which corresponded to Pinus spp.–evergreen (2.56), Quercus suber (2.54), and Pinus mixed (2.49) forests, with the minimum being obtained for Juniperus (1.37) and shrubs (1.11). High values of the Fuel Desiccation Index (IDM) were obtained for those areas dominated by shrubs (−396.71). Potential Behaviour Biomass Index (ICB) values were high or very high for 11.86% of the area and low or very low for 77.07%. The Potential Behaviour Structural Complexity Index (ICE) was high or very high for 37.23% of the area, and low or very low for 46.35%, and the Potential Behaviour Fuel Desiccation Index (ICD) was opposite to the ICB and ICE, with high or very high values for areas with low biomass and low structural complexity. Potential Fire Behaviour Index (ICP) values were high or very high for 38.25% of the area, and low or very low values for 45.96%. High or very high values of ICP were related to Pinus halepensis and Pinus pinaster forests. Remote sensing has been applied to improve fuel attribute characterisation and cartography, highlighting the utility of integrating multispectral and ALS data to estimate those attributes that are more closely related to the spatial organisation of vegetation.

Fuels change quickly after California drought and bark beetle outbreaks with implications for potential fire behavior and emissions

BackgroundAn extreme drought from 2012–2016 and concurrent bark beetle outbreaks in California, USA resulted in widespread tree mortality. We followed changes in tree mortality, stand structure, and surface and canopy fuels over four years after the peak of mortality in Sierra mixed conifer and pinyon pine (Pinus monophylla) forests to examine patterns of mortality, needle retention after death, and snag fall across tree species. We then investigated how the tree mortality event affected surface and canopy fuel loading and potential impacts on fire hazard and emissions.ResultsDrought and beetle-related tree mortality shifted mortality patterns to be more evenly distributed across size classes and concentrated in pines. Substantial changes to surface fuel loading, stand density, canopy fuel loads, and potential wildfire emissions occurred within four years following peak levels of tree mortality, with the largest changes related to increases in coarse woody debris. Nearly complete needle fall occurred within four years of mortality for all species except red fir (Abies magnifica). Pine species and incense cedar (Calocedrus decurrens) snags fell more quickly than fir species. Potential fire behavior modelling suggested that crowning and torching hazard decreased as trees dropped dead needles and fell, but as canopy fuels were transferred to surface fuels, potential for smoldering combustion increased, causing greater emissions.ConclusionsOur study increases understanding of how extreme tree mortality events caused by concurrent disturbances alter canopy and surface fuel loading and have the potential to affect fire behavior and emissions in two compositionally different seasonally dry forest types. After a major tree mortality event, high canopy fuel flammability may only last a few years, but surface fuels can increase considerably over the same time period in these forest types. The accumulation of coarse woody surface fuels resulting from multi-year drought and concurrent bark beetle outbreaks combined with the increasing frequency of drought in the western U.S. have the potential to lead to heavy and dry fuel loads that under certain weather conditions may result in more extreme fire behavior and severe effects, particularly in forest types where decades of successful fire suppression has caused forest densification.

Wildfire Threat to Inpatient Health Care Facilities in California, 2022.

Objectives. To assess wildfire risks to California inpatient health care facilities in 2022. Methods. Locations of inpatient facilities and associated inpatient bed capacities were mapped in relation to California Department of Forestry and Fire Protection fire threat zones (FTZs), which combine expected fire frequency with potential fire behavior. We computed the distances of each facility to the nearest high, very high, and extreme FTZs. Results. Half (107 290 beds) of California's total inpatient capacity is within 0.87 miles of a high FTZ and 95% (203 665 beds) is within 3.7 miles of a high FTZ. Half of the total inpatient capacity is within 3.3 miles of a very high FTZ and 15.5 miles of an extreme FTZ. Conclusions. Wildfires threaten a large number of inpatient health care facilities in California. In many counties, all health care facilities may be at risk. Public Health Implications. Wildfires in California are rapid-onset disasters with short preimpact phases. Policies should address facility-level preparedness including smoke mitigation, sheltering measures, evacuation procedures, and resource allocation. Regional evacuation needs, including access to emergency medical services and patient transportation, must also be considered. (Am J Public Health. 2023;113(5):555-558. https://doi.org/10.2105/AJPH.2023.307236).

不同烈度林火对油松林潜在地表火行为的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 不同烈度林火对油松林潜在地表火行为的影响 DOI: 10.5846/stxb202111223283 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重点研发计划项目（2020YFC1511601） Effects of wildfire of different severities on potential surface fire behavior of Pinus tabuliformis forest Author: Affiliation: Fund Project: the Key Project of National Key Research and Development Plan 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:油松是我国华北地区代表性树种之一，含有丰富油脂，容易引发大面积高烈度森林火灾。阐明不同烈度林火对油松林地表可燃物负荷量和潜在地表火行为的影响，对于油松林林火管理具有重要意义。以辽河源自然保护区2014年不同烈度林火干扰后油松林分为研究对象，根据不同烈度（重度、中度、轻度）和对照（未过火）分别设置3块20 m×20 m样地，共12块样地，调查地表可燃物和林分结构指标，结合室内实验，利用BehavePlus 5.0软件进行潜在火行为模拟，探讨不同烈度林火5年后油松林地表可燃物负荷量和潜在地表火行为特点，并分析影响潜在地表火行为的主要因素。研究结果表明：（1）不同烈度林火之间，细小可燃物负荷量和地表可燃物总负荷量均不存在显著性差异（P>0.05）。（2）不同烈度林火后，在不同风速和可燃物含水率条件下，油松林潜在地表火蔓延速度、火线强度不存在显著性差异（P>0.05），单位面积发热量、火焰高度、反应强度存在显著性差异（P<0.05）。（3）不同烈度林火后油松林潜在地表火行为主要受油松更新幼苗基径、灌木负荷量、油松平均冠幅、上层枯叶负荷量、油松更新幼苗密度的影响。研究结果表明不同烈度林火均可以降低再次燃烧的火烈度和风险。 Abstract:Pinus tabuliformis is one of the representative tree species in North China, which is rich in oil and easy to cause large area and high severity wildfire. It is of great significance for wildfire management of Pinus tabuliformis forest to elucidate the influence of wildfire of different severities on the surface fuel load and potential surface fire behavior of Pinus tabuliformis forest. In this study, Pinus tabuliformis forests with different severities of wildfire disturbance in Liaoheyuan Nature Reserve in 2014 were taken as the research object. According to different severities (high, moderate, low) and control (unburned), three 20 m×20 m sample plots were set, and a total of 12 plots were set. Based on the investigation of surface fuel and stand structure index, combined with indoor experiments, the potential fire behavior was simulated by BehavePlus 5.0 software. The characteristics of surface fuel load and potential surface fire behavior of Pinus tabuliformis forest after 5 years of fire with different severities were discussed, and the main factors affecting the potential surface fire behavior were analyzed. The results indicated that (1) there was no significant difference in the fine fuel load and the total surface fuel load between different severities wildfire disturbance (P>0.05). (2) Under the conditions of different wind speeds and fuel moisture content, there were no significant differences in the potential surface fire spread rate and fireline intensity (P>0.05), but there were significant differences in the calorific value per unit area, flame height and reaction intensity (P<0.05) after forest fire disturbance with different severities. (3) The potential surface fire behavior of Pinus tabuliformis forest with different severities was mainly affected by the regeneration seedling base diameter of Pinus tabuliformis, shrub load, average canopy width of Pinus tabuliformis, load of upper dead leaves, and the regeneration seedling density of Pinus tabuliformis. The results showed that forest fires with different severities could reduce the severity and risk of reburning. 参考文献 相似文献 引证文献

Exploring the impact of airtanker drops on in-stand temperature and relative humidity

Background There has been little quantification of the extent and duration of micrometeorological changes within a forest after airtanker drops of water-based suppressant. It has been speculated that a period of prolonged relative humidity – referred to as a ‘relative humidity (RH) bubble’ – temporarily exists in the canopy understorey post-drop. Aims We quantify the RH bubble from the drops of five airtankers commonly used by wildland fire management organisations in Canada. Methods We measured airtankers dropping water, foam concentrates, and gel enhancers in a mature jack pine stand. We examined the duration of change in RH and temperature using Generalised Additive Models, and the consequence of these changes on fine fuel moisture. Key results The average maximum RH increased and temperature decreased, indicating that the effects of the ‘RH bubble’ in-stand lasted from 25 to 76 min, depending upon the airtanker type and load configuration. Conclusion Airtanker drops cause an in-stand increase in RH and decrease in temperature, but this ambient change has a limited effect on potential fire behaviour. Implications The direct effect of water wetting the fuel is the most impactful effect of an airtanker drop. The ‘RH bubble’ created, though observable, does not change fine fuel moisture enough to impact fire behaviour.