Surface Fire Research Articles

The Transition and Spread of a Chaparral Crown Fire: Insights from Laboratory Scale Wind Tunnel Experiments

Fire occurring in the chaparral behaves as a crown fire, a dual-layer fire that typically ignites in a dead surface fuel layer and transitions to an elevated live crown layer where it continues to spread. In chaparral fuels including chamise, a dominant species in southern California, flame transition to live crown fuels is associated with higher spread rates and greater fire intensity. Despite the relative importance of surface-to-crown transition and crown fire spread, most fire models represent chaparral fire as surface fire, therefore omitting key behavior processes driving this fire system. The purpose of this study was to characterize transition and spread behavior in chaparral fires modeled experimentally as crown fires. We examined heat release rate in the surface and crown fuel layers, time to transition, flame height, and rate of spread in wind-driven and nonwind-driven fires at two crown base heights. Our results showed that wind increased heat release rate, rate of spread, and flame height. A marked increase in heat release rate was observed in wind-driven fires, where adding wind produced an increase from 328 kW to 526 for a crown base height of 0.6 m and from 243 kW to 503 kW for a crown base height of 0.7 m. Further, crown base height served to decrease heat release rate and rate of spread for wind-driven and nonwind-driven fires.

The North American tree‐ring fire‐scar network

AbstractFire regimes in North American forests are diverse and modern fire records are often too short to capture important patterns, trends, feedbacks, and drivers of variability. Tree‐ring fire scars provide valuable perspectives on fire regimes, including centuries‐long records of fire year, season, frequency, severity, and size. Here, we introduce the newly compiled North American tree‐ring fire‐scar network (NAFSN), which contains 2562 sites, >37,000 fire‐scarred trees, and covers large parts of North America. We investigate the NAFSN in terms of geography, sample depth, vegetation, topography, climate, and human land use. Fire scars are found in most ecoregions, from boreal forests in northern Alaska and Canada to subtropical forests in southern Florida and Mexico. The network includes 91 tree species, but is dominated by gymnosperms in the genus Pinus. Fire scars are found from sea level to >4000‐m elevation and across a range of topographic settings that vary by ecoregion. Multiple regions are densely sampled (e.g., >1000 fire‐scarred trees), enabling new spatial analyses such as reconstructions of area burned. To demonstrate the potential of the network, we compared the climate space of the NAFSN to those of modern fires and forests; the NAFSN spans a climate space largely representative of the forested areas in North America, with notable gaps in warmer tropical climates. Modern fires are burning in similar climate spaces as historical fires, but disproportionately in warmer regions compared to the historical record, possibly related to under‐sampling of warm subtropical forests or supporting observations of changing fire regimes. The historical influence of Indigenous and non‐Indigenous human land use on fire regimes varies in space and time. A 20th century fire deficit associated with human activities is evident in many regions, yet fire regimes characterized by frequent surface fires are still active in some areas (e.g., Mexico and the southeastern United States). These analyses provide a foundation and framework for future studies using the hundreds of thousands of annually‐ to sub‐annually‐resolved tree‐ring records of fire spanning centuries, which will further advance our understanding of the interactions among fire, climate, topography, vegetation, and humans across North America.

Investigating the turbulent dynamics of small-scale surface fires

High frequency (30 Hz) two-dimensional particle image velocimetry data recorded during a field experiment exploring fire spread from point ignition in hand-spread pine needles under calm ambient wind conditions are analysed in this study. In the initial stages, as the flame spreads approximately radially away from the ignition point in the absence of a preferred wind-forcing direction, it entrains cooler ambient air into the warmer fire core, thereby experiencing a dynamic pressure resistance. The fire-front, comprising a flame that is tilted inward, is surrounded by a region of downdraft. Coherent structures describe the initial shape of the fire-front and its response to local wind shifts while also revealing possible fire-spread mechanisms. Vortex tubes originating outside the fire spiral inward and get stretched thinner at the fire-front leading to higher vorticity there. These tubes comprise circulation structures that induce a radially outward velocity close to the fuel bed, which pushes hot gases outward, thereby causing the fire to spread. Moreover, these circulation structures confirm the presence of counter-rotating vortex pairs that are known to be a key mechanism for fire spread. The axis of the vortex tubes changes its orientation alternately towards and away from the surface of the fuel bed, causing the vortex tubes to be kinked. The strong updraft observed at the location of the fire-front could potentially advect and tilt the kinked vortex tube vertically upward leading to fire-whirl formation. As the fire evolves, its perimeter disintegrates in response to flow instabilities to form smaller fire “pockets”. These pockets are confined to certain points in the flow field that remain relatively fixed for a while and resemble the behavior of a chaotic system in the vicinity of an attractor. Increased magnitudes of the turbulent fluxes of horizontal momentum, computed at certain such fixed points along the fire-front, are symptomatic of irregular fire bursts and help contextualize the fire spread. Most importantly, the time-varying transport terms of the turbulent kinetic energy budget equation computed at adjacent fixed points indicate that local fires along the fire-front primarily interact via the horizontal turbulent transport term.

Cross-Comparison of channel parameters between FY-3E/MERSI-LL and Himawari-8/AHI in China

ABSTRACT Fengyun-3E (FY-3E) is the world’s first operational meteorological satellite on dawn-dusk orbit. In order to realize the generality of algorithms for different satellites and provide a basis for subsequent inversion studies on remote sensing parameters, such as land surface temperature, fire, and atmospheric water vapour, we perform a cross-comparison of the brightness temperature (TB) of the six infrared (IR) channels between the Medium Resolution Spectral Imager Level L onboard the FY-3E satellite (FY-3E/MERSI-LL) and the Advanced Himawari Imager onboard the Himawari-8 satellite (Himawari-8/AHI). The statistical indicators, correlation coefficient, root mean square error (RMSE) and mean bias, are used to analyse the consistency and differences of the channel parameters between the MERSI-LL and AHI in terms of overall data, different regions and different TB. The results show that the TB data observed by the FY-3E/MERSI-LL and Himawari-8/AHI are generally consistent, with correlation coefficients of more than 0.99, mean biases of less than 1.60 K and RMSEs of less than 1.90 K. In terms of different channels, the TB in channel IR 038 has the best consistency between the two sensors, while the results from the MERSI-LL are higher than those of the AHI for channels IR038, IR086, IR108 and IR120, and lower than those of the AHI for channel IR041. Analysing the situation in different regions, we find that the MERSI-LL and AHI data are highly consistent and relatively stable in the Huang-Huai Region, with low RMSEs, low mean biases and high correlation coefficients (more than 0.95) at all channels. For the different TB ranges, the RMSEs and mean biases for the TB ranges of 270–280 K and 280–290 K between the MERSI-LL and AHI are small, and the data in the 290–300 K TB range has great differences and fluctuations between the two sensors.

Locating potential historical fire‐maintained grasslands of the eastern United States based on topography and wind speed

AbstractHistorically, grasslands with limited tree presence were embedded in a matrix of predominantly open oak and pine forests in the eastern United States. These open ecosystems mostly have been lost to other land uses, particularly agriculture, and also to closed forests under fire exclusion because frequent surface fire prevents tree encroachment. We located the potential extent of eastern fire‐maintained grasslands by applying the random forests and C5.0 classifiers to determine the relationship between mapped areas of historical grasslands and topography and wind speed, which are proxies for surface fire frequency. A generalized ruleset was that fire‐maintained grasslands occurred at roughness values of less than 95, or flatter sites, and wind speeds ≥3.4 m s−1, which created large fire compartments. Potential grasslands covered 27 million ha, or 14% of the 200 million ha of the eastern United States, although these fire‐maintained locations also may have been savannas or open woodlands historically. Currently, potential grassland locations are 40% crops, 25% pasture, 18% forests, and 13% developed land, with about 1.5% each of herbaceous upland vegetation, herbaceous wetlands, and shrublands. According to historical accounts, fire‐maintained grasslands generally transitioned to dense young tree growth within a 20‐year interval after fire exclusion; in Kentucky, the transition transpired during the periods 1790–1810 or 1810–1830, but dates vary with Euro‐American settlement time. Finding the forgotten grasslands of the eastern United States, with this mechanistic approach to estimate fire disturbance, is an important first step for recovering and managing eastern grassland biodiversity.

Transition from Surface Fire to Crown Fire and Effects of Crown Height, Moisture Content and Tree Flower

Transition from Surface Fire to Crown Fire and Effects of Crown Height, Moisture Content and Tree Flower

Effects of fire disturbance on species and functional compositions vary with tree sizes in a tropical dry forest.

BackgroundDisturbances are crucial in determining forest biodiversity, dynamics, and ecosystem functions. Surface fire is a significant disturbance in tropical forests, but research on the effect of surface fire on structuring species and functional composition in a community through time remains scarce. Using a 20-year dataset of tree demography in a seasonal evergreen tropical forest in Thailand, we specifically addressed two essential questions: (1) What is the pattern of temporal turnover in species and functional composition in a community with frequent fire disturbance? (2) How did the temporal turnover vary with tree size?MethodsWe analyzed species compositional and functional temporal turnovers in four different tree size classes among five tree censuses. We quantified species turnover by calculating Bray-Curtis dissimilarity, and investigated its underlying mechanisms by comparing pairwise dissimilarity of functional traits with simulations from null models. If fire disturbances contribute more to a stochastic process, the functional composition would display a random pattern. However, if they contribute more towards a deterministic process, the functional composition should reveal a non-random pattern.ResultsOver 20 years (1994–2014), we observed changes in species composition, whereas functional composition remained relatively stable. The temporal turnover patterns of species and functional compositions varied with tree sizes. In particular, temporal functional turnover shifted very little for large trees, suggesting that changes in species composition of larger trees are contributed by species with similar functional traits through time. The temporal functional composition turnovers of smaller trees (DBH ≤ 5 cm) were mostly at random. We detected a higher functional turnover than expected by null models in some quadrats throughout the 50-ha study plot, and their observed turnover varied with diameter classes.ConclusionsSpecies compositional changes were caused by changes in the abundance of species with similar functional traits through time. Temporal functional turnover in small trees was random in most quadrats, suggesting that the recruits came from the equal proportions of surviving trees and new individuals of fast-growing species, which increased rapidly after fires. On the other hand, functional composition in big trees was more likely determined by surviving trees which maintained higher functional similarities than small trees through time. Fire disturbance is important for ecosystem functions, as changing forest fire frequency may alter forest turnover, particularly in functional composition in the new recruits of this forest.

Thermohydrological Impact of Forest Disturbances on Ecosystem‐Protected Permafrost

AbstractBoreal forests cover over half of the global permafrost area and protect underlying permafrost. Boreal forest development, therefore, has an impact on permafrost evolution, especially under a warming climate. Forest disturbances and changing climate conditions cause vegetation shifts and potentially destabilize the carbon stored within the vegetation and permafrost. Disturbed permafrost‐forest ecosystems can develop into a dry or swampy bush‐ or grasslands, shift toward broadleaf‐ or evergreen needleleaf‐dominated forests, or recover to the pre‐disturbance state. An increase in the number and intensity of fires, as well as intensified logging activities, could lead to a partial or complete ecosystem and permafrost degradation. We study the impact of forest disturbances (logging, surface, and canopy fires) on the thermal and hydrological permafrost conditions and ecosystem resilience. We use a dynamic multilayer canopy‐permafrost model to simulate different scenarios at a study site in eastern Siberia. We implement expected mortality, defoliation, and ground surface changes and analyze the interplay between forest recovery and permafrost. We find that forest loss induces soil drying of up to 44%, leading to lower active layer thicknesses and abrupt or steady decline of a larch forest, depending on disturbance intensity. Only after surface fires, the most common disturbances, inducing low mortality rates, forests can recover and overpass pre‐disturbance leaf area index values. We find that the trajectory of larch forests after surface fires is dependent on the precipitation conditions in the years after the disturbance. Dryer years can drastically change the direction of the larch forest development within the studied period.

The influence of land-use activities and regional drought on historical fire regimes of Buryatia, Siberia

Every year, millions of hectares burn across Siberia, driven by a combination of warming temperatures, regional drought and human-caused ignitions. Dendrochronology provides a long-term context to evaluate recent trends in fire activity and interpret the relative influence of humans and climate drivers on fire regimes. We developed a 400 year record of fire-scarred trees from 17 sites in pine-dominated forests located southeast of Lake Baikal. Site-level mean fire return intervals (MFIs) ranged from 4 to 27 years for all fires and 8 to 35 years for widespread fires within sites. Sites with the lowest MFI values were located within 1 km of agricultural fields in grassland valleys, suggesting that agricultural burning influenced MFIs at nearby sites. Fire frequency varied over the record, with significantly high values around 1790, from 1865 to 1880, 1948 to 1955 and 1995 to 2005. The increased fire activity corresponded with migration waves to the region and major socio-economic change connected with the establishment and breakdown of the Soviet Union. At broader scales, superposed epoch analysis showed that synchronous fire years were associated with regional drought and precipitation deficits. Wet conditions for 2–3 years prior to the event year were also significant, suggesting that increased moisture promoted growth of understory fine fuels to support more extensive fires across the study area. Although fire frequencies increased during the 20th century, fire–climate relationships weakened, suggesting increased human-caused ignitions may override regional climate drivers. Our dataset presents a continuous record of frequent surface fires over the past 400 years, providing a valuable opportunity to compare dendrochronology-based reconstructions with satellite and documentary records.

A Field Study of Tropical Peat Fire Behaviour and Associated Carbon Emissions

Tropical peatlands store vast volumes of carbon belowground. Human land uses have led to their degradation, reducing their carbon storage services. Clearing and drainage make peatlands susceptible to surface and belowground fires. Satellites do not readily detect smouldering peat fires, which release globally significant quantities of aerosols and climate-influencing gases. Despite national and international desire to improve management of these fires, few published results exist for in situ tropical peat fire behaviour and associated carbon emissions. We present new field methodology for calculating rates of fire spread within degraded peat (average spread rates, vertical 0.8 cm h−1, horizontal 2.7 cm h−1) and associated peat volume losses (102 m3 ha−1 in August, 754 m3 ha−1 in September) measured at six peat fire sites in Kalimantan, Indonesia, in 2015. Utilizing locally collected bulk density and emission factors, total August and September gas emissions of 27.2 t ha−1 (8.1 tC ha−1) and 200.7 t ha−1 (60.2 tC ha−1) were estimated. We provide much needed, but currently lacking, IPCC Tier 3-level data to improve GHG estimates from tropical peat fires. We demonstrate how calculations of total emission estimates can vary greatly in magnitude (+798% to −26%) depending on environmental conditions, season, peat burn depth methodology, bulk density and emission factors data sources, and assumed versus observed combustion factors. This illustrates the importance of in situ measurements and the need for more refined methods to improve accuracies of GHG estimates from tropical peat fires.

PYROLOGICAL CHARACTERISTICS OF FOREST EDGES UNDER INTENSIVE RECREATIONAL LOADS

-The increase in fires in urban landscapes causes adverse and sometimes irreversible changes in forest ecosystems. The modern solution is to find the places of primary fires and the most dangerous areas. The purpose of this study was to find dependences between the forest typological features of forest stands and their fire danger. To fulfil this purpose, a systematic analysis of forest fire danger and phytoindication were performed. The composition of the flora of edge biotopes was figured out using the route geobotanical method. The article analyses forest fires that occurred in urban forests of Kyiv during 2014-2021. Primary ignition locations have been identified. It was proved that fires often occurred on the forest edges, as well as along highways and railways. Among the standard indicators of fire danger (number and area of forest fires), the method makes provision for establishing the fire frequencies in the same forest area. This indicator allows figuring out the most dangerous areas from the pyrogenic standpoint. It was found that the simple edge is characterised by a minimal taxonomic composition in the ground vegetation and its projective cover of up to 20%. The grass tier stabilises the environment and mitigates the effects of extreme natural phenomena. The vegetation cover of an elementary and multicomponent edge is one of the barriers that can stop surface fires. Taxonomic diversity, especially of deciduous species, determines the pyrological features of forest edges. Analysis of the flora of marginal biotopes showed that oligotrophs, xerophytes, and xeromesophytes predominate among the species of simple edges. The share of ruderal elements in the ground vegetation was 36%, which indicates a significant anthropogenic impact and synanthropisation of the flora of the edges. These processes adversely impact the conservation of typical species but have a fire-retaining effect. Analysis of forest fires dynamics under intensive recreational loads allows substantiating the vectors for fire safety improvement, choosing a strategy for ensuring fire safety, and increasing the economic and social efficiency of fire prevention measures. It is proved that the forest edge is one of the decisive factors in the fire behaviour arising from a nonwooded area. The formation of multicomponent edges will help minimise the risks of fires

Escaping the fire trap: Does frequent, landscape-scale burning inhibit tree recruitment in a temperate broadleaf ecosystem?

Frequent prescribed burning is commonly used to restore and maintain open forest ecosystems in temperate broadleaf regions of the eastern United States. Repeated surface fires reduce the abundance of small woody stems through top-kill or mortality, with implications for age structure and ecosystem development. In this study, we quantified tree recruitment patterns over two decades across two landscape-scale studies in Missouri: the Missouri Ozark Forest Ecosystem Project (a control, with no burning) and the Chilton Creek Management Area (burned on 2–3 year fire return interval). Through time, frequent burning reduced the rate of ingrowth (i.e., new trees entering the overstory size class, defined as ≥11.4 cm diameter at breast height (DBH)), and the effect of burning on the ingrowth rate was consistent across site types (summits, exposed backslopes, protected backslopes, or upland waterways). Two decades of frequent burning reduced the abundance of scarlet oak (Quercus coccinea) in the ingrowth population. In the unburned control, the proportional abundance of mesic species such as red maple (Acer rubrum) and blackgum (Nyssa sylvatica) increased during the study period; frequent fire controlled the population of red maple but resulted in a similar increase in blackgum abundance in the ingrowth population of the burned area. Our results indicate that frequent burning affects the tree recruitment process in multiple ways: 1) reducing the source population for recruitment by reducing midstory abundance; 2) increasing probability of mortality or top-kill during the recruitment period. Fire-free periods may be necessary to allow eventual replacement of canopy trees in temperate broadleaf open forest ecosystems.

Historical links between climate and fire on species dispersion and trait evolution

The interaction effects between climate and fire regime in controlling the type of vegetation and species composition is well established among the Earth’s biomes. Climate and the associated fire regime are never stable for long, and annual temperatures, atmospheric carbon dioxide and oxygen levels, and burn probability have varied radically over the last 350 million years. At the scale of thousands of years, floras have oscillated between spreading and retracting as climate and the dependent fire regime have fluctuated. At the scale of millions of years, distinct traits have evolved along three lines: fire resistance, fire-stimulated dormancy release, and rapid postfire growth, all limited by the type of fire (as controlled by climate) and postfire weather. Eight pairings of fire- and postfire-related traits resulting from the interplay between fire and climate are noted here. Smoke-released seed dormancy is beneficial on two counts: it increases the chance of recruitment under the present fireprone climate and increases the chances of survival should the wet season shift to another time of year where temperatures are higher or lower. Four pathways can be recognized with respect to the fire regimes induced by climate changes: (1) from non-fireprone to fireprone habitats (gains fire-adapted trait, 13 studies covering the last 115 million years (My) described here); (2) from a surface fire to a crown fire-type habitat (gains a different fire-adapted trait, 13 studies); (3) from a crown fire-type to surface fire-type habitat (loss of fire-adapted trait, 12 studies); and (4) from moderately burnt (crown fire) to non-fireprone habitat, such as desert, rainforest, or alpine habitats (loss of fire-adapted trait, 6 studies). Four case studies, at decreasing taxonomic rank, are used to illustrate the intimate relationship between climate change with its associated vegetation and fire regime change as they promote adaptive trait evolution: gain then loss of heat-released seed dormancy in Dipterocarpaceae–Cistaceae–Bixaceae over 90 My, gain then loss of serotiny in Callitroid Cupressaceae over the last 65 My, gain then loss of smoke-released seed dormancy in Proteoid Proteaceae over the last 120 My, and gain then loss of resprouting and serotiny among Hakea species (Grevilleoid Proteaceae) over the last 20 My. Examples of within-species rates of migration and trait change, including a model describing increasing degree of serotiny with intensifying drought, are given. The relevance of this historical approach to current (anthropogenic) climate change and associated fire regime alteration is discussed. Despite major threats expected to species conservation status at both the macro-(biome) and micro-(population) scales, I conclude that insufficient time or opportunities remain for effective migration to less-stressed areas or suitable adaptive responses to climate/fire regime change to evolve.

Missing Climate Feedbacks in Fire Models: Limitations and Uncertainties in Fuel Loadings and the Role of Decomposition in Fine Fuel Accumulation

AbstractClimate change has lengthened wildfire seasons and transformed fire regimes throughout the world. Thus, capturing fuel and fire dynamics is critical for projecting Earth system processes in warmer and drier future. Recent advances in fire regime modeling have linked land surface models with fire behavior models. Such models often rely on fine surface fuels to drive fire behavior and effects, and while many models can simulate processes that control how these fuels change through time (i.e., fine fuel accumulation), fuel loading estimates remain highly uncertain, largely due to uncertainties in the algorithms controlling decomposition. Uncertainties are often amplified in climate change forecasts when initial conditions and feedbacks are not well represented. The goal of this review is to highlight fine fuel decomposition as a key uncertainty in model systems. We review the current understanding of mechanisms controlling decomposition, describe how they are incorporated into models, and evaluate the uncertainties associated with different approaches. We also use three state‐of‐the‐art land surface fire regime models to demonstrate the sensitivity of decomposition and subsequent wildfire projections to both parameter and model structure uncertainty and show that sensitivity can increase substantially under future climate warming. Given that many of the governing decomposition equations are based on individual case studies from a single location, and because key parameters are often hard coded, critical uncertainties are currently ignored. It is essential to be transparent about these uncertainties as the domain of land surface models is expanded to include the evaluation of future wildfire regimes.

Experimental study on the foam performance and fire extinguishing performance of aqueous foam stabilized by alkyl polyglucoside and urea

Foam extinguishing agents are the most effective extinguishing agents for liquid fires. The search of relevant domestic and foreign commercial foam fire extinguishing agent patents found that most commercial foam fire extinguishing agent formulations contain urea. In order to understand the mechanism of urea’s influence and clarify the application parameters of urea-added aqueous foam in the fire extinguishing process, this research investigated the surface tension, foaming ability, foam stability, and fire extinguishing performance for alkyl polyglucoside and alkyl polyglucoside/urea foams. It is found that the addition of urea promotes the formation of surfactant micelles, resulting in a decrease in critical micelle concentration, while the surface tension and foaming ability of the alkyl polyglucoside solution are only moderately affected by the urea. Besides, urea significantly improves the fire extinguishing performance of alkyl polyglucoside foam and the influence of urea concentration on fire extinguishing time is remarkable. On the one hand, the enhanced extinguishing performance can be explained by the increase of foam stability. On the other hand, urea produces incombustible gases such as NH3 and CO2 under the action of the high temperature of the fire, which may improve the fire extinguishing performance by cooling effect and asphyxiation effect. The increase in expansion ratio and the foam flow rate are beneficial to shorten the extinguishing time. The research results can guide the design of foam extinguishing agents.

Numerical Simulation of the Effect of Fire Intensity on Wind Driven Surface Fire and Its Impact on an Idealized Building

This paper presents an investigation on the effect of fire intensity of a wind driven surface fire, similar to a large wildfire, on an idealized structure located downstream from the fire source. A numerical simulation was conducted using an open source CFD code called FireFOAM, which is a transient solver for fire simulation and turbulent diffusion flames, supported by a large eddy simulation (LES) solver for incompressible flow. The numerical data were verified using the aerodynamic experimental data of a full-scale building model with no fire effects. An idealized cubic obstacle representing a simplified building with the dimension of 6 × 6 × 6 m; is considered downstream from the fire source. Different fire intensity values of the fire line representing different grassland fuels were simulated to analyse the impact of wind-fire interaction on a built area. To solve the problem, a coupled velocity and pressure method was applied through a PIMPLE scheme in FireFoam solver of OpenFoam platform. There is a good agreement between simulated results and experimental measurements with a maximum error of 18%, which confirms the validity and accuracy of the model. The results showed that by increasing the fire intensity; the velocity of the crosswind stream increases, which causes low-density air and generates an extra stream behind the fire plume. It was also found that increasing fire intensity from 10 MW/m to 18 MW/m raises the integrated temperature on the ground near the building and on the surface of the building by 26%, and 69%, respectively.

Short- to medium-term effects of crown and surface fires on soil respiration in a Canadian boreal forest

Fires are an important perturbation for the carbon (C) dynamics of boreal forests, especially when they are stand-replacing. In North American boreal forests, crown fires are predominant and, therefore, the most studied. However, surface fires can also lead to major tree mortality with substantial implications for the C balance. Here, we assess the short- (hours to days) to medium-term (1–3 years) effects of the different fire types (surface vs. crown) on the postfire soil C effluxes in jack pine (Pinus banksiana Lamb.) and black spruce (Picea mariana (Mill.) BSP) forest stands in the Northwest Territories, Canada. We found that while trees were instantly killed by the four crown fires studied, trees also died within 1 year after two of three surface fires studied. Associated with this tree mortality, soil autotrophic respiration decreased after both fire types, although at different timings. The soil heterotrophic respiration was either lower or unchanged when measured 1–3 years after either fire type but was increased when measured immediately after a surface fire, possibly due to the interaction between ash generation and wetting performed to suppress the fire. Our results suggest that both fire types can thus substantially alter C fluxes in the short to medium term, both through changes in vegetation and the soil environment.

Evidence for the repeated occurrence of wildfires in an upper Pliocene lignite deposit from Yunnan, SW China

Charcoal remains and bulk lignites collected from the late Pliocene Jinsuo Basin in Yunnan, southwestern China, have been studied to reveal changes in the wildfire regime related to changes of the palaeoenvironment, palaeoclimate, and paleobotany. Different types of wildfire occurred in this paleomire with a predominance of low-temperature surface fires, as indicated by mean inertinite reflectance (Ro) values ranging from 1% to 2% in most samples. High-temperature fires are less recorded and occurred more frequently in dark layers compared with pale layers and charcoal layers, as deduced from the elevated proportion of high Ro values (>3%) produced by crown fires or high-temperature surface fires. Wildfire distribution in pale and dark layers was probably influenced by, changes of both plant community and of the depositional environment during their formation. Charcoal layers represent in situ surface and ground fires, whereas pale and dark layers probably record both in situ and remote fire events inside and/or around the basin. PAH were detected in all samples throughout the whole lignite seam, indicating that burning temperatures were low (<400 °C) in most cases in the peatland. Evidence of pre-charring decay observed in some macro-charcoal fragments and pyrogenic inertinite, along with the relatively high content of perylene, shows that decaying wood materials could be a part of the source fuel for the combustion during ground or surface fires. The occurrence and spread of wildfires in the basin during the formation of pale layers probably owe to the drought conditions driven by climate, whereas seasonality of precipitation and temperature was probably the major factor for the occurrence of wildfires recorded from dark layers. The distribution of wildfires within the profile may be relate to climate changes during the mid-Piacenzian.

Variation in eucalypt bark allometry across Australia

Positive bark allometry (hyperallometry), characterised by rapid early bark growth, is expected where fire selects for thicker bark to resist cambial damage and topkill. We examine this prediction for 52 Australian eucalypt species. An effective bark allometric coefficient (α) was estimated from the first segment of breakpoint regression, which included fire-affected young trees. Eucalypts presented a negative–positive bark allometry continuum. Contrary to expectation, 73% of species (n = 38) displayed negative effective bark allometry. Early rapid bark growth was observed (α = 0.92 ± 0.04, x ± s.e., n = 168 sites), but was slower than isometry and bark was thinner overall than expected. Fire type (crown-fire propensity) and net primary productivity (resource availability) most influenced bark allometry. Productive ecosystems experienced crown-fire and bark was thicker at standardised diameter (x ± s.e. = 2.04 ± 0.20 cm) than in less productive ecosystems under surface fire (x ± s.e. = 1.68 ± 0.18 cm). Bark morphology types did not differ in their stem diameter (x ± s.e. = 21.47 ± 1.06 cm) or bark thickness (x ± s.e. = 1.88 ± 0.08 cm) thresholds, representing putative stable alternative evolutionary solutions. Fundamentally, many eucalypts possess negative bark allometry with a relatively thin bark compared to non-eucalypts, because unique bark bud traces sustain post-fire resilience through epicormic resprouting. The resource allocation trade-off to thin bark v. height growth, selected by fire and resource limitation, accounts for eucalypt persistence and domination of Australia’s flammable ecosystems.

Composition of Inorganic Elements in Fine Particulate Matter Emitted During Surface Fire in Relation to Moisture Content of Forest Floor Combustibles

Composition of Inorganic Elements in Fine Particulate Matter Emitted During Surface Fire in Relation to Moisture Content of Forest Floor Combustibles