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When It's Hot, It's Hot... Or Maybe It's Not! (Surface Flaming May Not Portend Extensive Soil Heating)
Abstract
Fire effects on aplant community, soil, and air
are not apparent when judged only by surface fire intensity. The fire severity or fire impact can be described by
the temperatures reached within the forest floor and the
duration of heating experienced in the vegetation, forest
floor, and underlying mineral soil. Temporal distributions of temperatures illustrate heat flow in duff and
mineral soil in three instrumented plots: two with slash
fuel over moist duff and one with litter fuel over dry duff.
Fires in the two slash fuel plots produced substantial
flame lengths but minimal heating in the underlying
mineral soil. In contrast, smoldering combustion in the
dry duff plot produced long duration heating with nearly
complete duff consumption and lethal temperatures at the
mineral soil surface. Moisture content of duff and soil
were key variables for determining f i e impact on the
forest floor.
... However, collecting direct measurements for fire energy and soil heating is challenging. For one, soil heating through time cannot be measured from satellite imagery, (Morgan et al., 2014), and secondly, even though fire energy measurements provide a more direct approach than fire severity, they still do not consider soil properties that can influence belowground responses (Hartford & Frandsen, 1992). Therefore, to quantify soil heating during fires, we need groundbased, subsurface measurements of soil. ...
... Further, the frequency of severe wildland fires is increasing (Goss et al., 2020;Hanan et al., 2021;Schoennagel et al., 2017). However, soil heating is often perceived as minimal in most surface fires (Hartford & Frandsen, 1992), and as a result, has not been studied as extensively as fire effects aboveground. The SheFire modeling framework is a first step towards collecting, extrapolating, and applying soil temperature data more broadly. ...
... For the high temperature iButtons, that limit is 125 C. When soil temperatures exceed that limit, but are not high enough to damage the iButton, the sensor will record a timestamp at the appropriate data logging rate, but it will not record a temperature until it cools back to 125 C and below. Preliminary work indicates that the BFD fitting portion of the SheFire model can be used to accurately interpolate the missing data in the temperature peak when the maximum temperature is above 125 C. In cases where high temperatures are expected, such as under heavy fuel loads in pile burns (Massman et al., 2010) or below deep, smoldering duff (Hartford & Frandsen, 1992), the iButtons can be deployed deeper in the soil profile as peak soil temperatures decline rapidly with depth (Aznar et al., 2016;Badía-Villas et al., 2014;Giovannini & Lucchesi, 1997;Pereira et al., 2019). In our study, we had one thermocouple malfunction for unknown reasons and two iButtons malfunctioned: one lost to a possible software error and one lost to physical damage, not a result of heat damage or limited battery life. ...
Fire has transformative effects on soil biological, chemical, and physical properties in terrestrial ecosystems around the world. While methods for estimating fire characteristics and associated effects aboveground have progressed in recent decades, there remain major challenges in characterizing soil heating and associated effects belowground. Overcoming these challenges is crucial for understanding how fire influences soil carbon storage, biogeochemical cycling, and ecosystem recovery. In this paper, we present a novel framework for characterizing belowground heating and effects. The framework includes (1) an open‐source model to estimate fire‐driven soil heating, cooling, and the biotic effects of heating across depths and over time (Soil Heating in Fire model; SheFire) and (2) a simple field method for recording soil temperatures at multiple depths using self‐contained temperature sensor and data loggers (i.e., iButtons), installed along a wooden stake inserted into the soil (i.e., an iStake). The iStake overcomes many logistical challenges associated with obtaining temperature profiles using thermocouples. Heating measurements provide inputs to the SheFire model, and modeled soil heating can then be used to derive ecosystem response functions, such as heating effects on microorganisms and tissues. To validate SheFire estimates, we conducted a burn table experiment using iStakes to record temperatures that were in turn used to fit the SheFire model. We then compared SheFire predicted temperatures against measured temperatures at other soil depths. To benchmark iStake measurements against those recorded by thermocouples, we co‐located both types of sensors in the burn table experiment. We found that SheFire demonstrated skill in interpolating and extrapolating soil temperatures, with the largest errors occurring at the shallowest depths. We also found that iButton sensors are comparable to thermocouples for recording soil temperatures during fires. Finally, we present a case study using iStakes and SheFire to estimate in situ soil heating during a prescribed fire and demonstrate how observed heating regimes would influence seed and tree root vascular cambium survival at different soil depths. This measurement‐modeling framework provides a cutting‐edge approach for describing soil temperature regimes (i.e., soil heating) through a soil profile and predicting biological responses.
... In cooler needleleaf forests, where the SOM is combusted from the thick organic horizon 24,29 , C losses from wildfires can be especially large. Although direct heating during fire can be relatively shallow (for example, 4-7 cm in prescribed burns in coniferous forests 30 ), repeated burning can change the soil C stocks down to a depth of one metre in some cases 31 . Changes are more generally concentrated in the top 0-20 cm of soils [25][26][27][28] . ...
... Alternatively, aggregates can be destroyed during a fire 56 ; however, this can depend on soil moisture and heating, with faster heating in moister soils leading to greater aggregate disruption and C mineralization in temperate forest soils 57 . Direct heating effects are probably concentrated in the organic and upper mineral horizons 58 , with the heating depth depending on the fuel load and mineral content 30 . Thus, the degree and rate of heating are important for predicting how fire changes the aggregation and subsequent C turnover. ...
... Changes in stabilization potential shift the potential forms of biomass that are important for soil C pools; when matrix stabilization is high, leaf litter contributes relatively less to soil C than root biomass inputs and exudates 2 . Because fire tends to impact aboveground biomass and organic horizon stocks much more than it does belowground biomass, and the heating depths in soils decline with a greater mineral content because minerals dissipate heat 30 (Fig. 4 and references therein), we expect fire effects on SOM turnover to be lower in soils with a high stabilization potential. In soils with a low stabilization potential, particulate SOM is the dominant form and tends to be derived from leaf litter and is more prone to decomposition. ...
One paradigm in biogeochemistry is that frequent disturbance tends to deplete carbon (C) in soil organic matter (SOM) by reducing biomass inputs and promoting losses. However, disturbance by fire has challenged this paradigm because soil C responses to frequent and/or intense fires are highly variable, despite observed declines in biomass inputs. Here, we review recent advances to illustrate that fire-driven changes in decomposition, mediated by altered SOM stability, are an important compensatory process offsetting declines in aboveground biomass pools. Fire alters the stability of SOM by affecting both the physicochemical properties of the SOM and the environmental drivers of decomposition, potentially offsetting C lost via combustion, but the mechanisms affecting the SOM stability differ across ecosystems. Thus, shifting our focus from a top-down view of fire impacting C cycling via changes in plant biomass to a bottom-up view of changes in decomposition may help to elucidate counterintuitive trends in the response of SOM to burning. Given that 70% of global topsoil C is in fire-prone regions, using fire to promote SOM stability may be an important nature-based climate solution to increase C storage.
... Previous studies to delineate the main soil changes concerning temperatures during fires have shown distinguishable temperature variations in this system in similar environments (Santín and Doerr, 2016;Mataix-Solera et al., 2011). As regards slash-and-burn fire, the soil temperatures generally reached are between 150 and 700 °C (Thomaz, 2017a;Ketterings et al., 2000;Hartford and Frandsen, 1992;Chandler et al., 1983;Wells et al., 1979;Sertsu and Sanchez, 1978;Masson, 1948). Fire severity is critical to post-fire soil system response. ...
... The thickness and density characteristics of lowflammability litter can play a key role in protecting or insulating the temperature generated by above-ground burning (Ketterings et al., 2000;Hartford and Frandsen, 1992). According to Mondal and Sukumar (2014), this depends on factors such as the degree of flammability of the affected species, layer moisture, volume of living and dead material, wind severity during the fire, current solar radiation, and origin of the fire (spontaneous, induced, controlled, uncontrolled). ...
Slash-and-burn is a traditional agricultural system still widely used in Brazil. The variation in temperature during fires results in different levels of physical, chemical, and biological changes in the soil, which makes it necessarily better to understand the dynamics of fire severity in this system. The aim of this study was to make an analytical comparison of the variation in the temperature reached in the soil during fires in slash-and-burn agriculture. Temperature data were measured in burnt areas with similar fallow times at the following soil depths 0; 2.5 and 5 cm and compared with secondary data from other studies in the same slash-and-burn system in southern Brazil. The peak temperature showed more significant variations in the surface (0 cm) of different soils and different types of regeneration vegetation in each area. Overall, the peak temperatures ranged from 32 to 673 ºC across the three depths. The peak temperature reduction in the 5 cm layer was 88 % compared to the surface and 30 % compared to the 2.5 cm layer. The sandier soils showed greater thermal conductivity at depth. The surface litter seems to exert a more significant influence on the burning severity than the biomass load cut for burning, suggesting that the characteristics of the litter layer on the surface should be better characterized in future studies on fire severity.
soil heating; temperature; litter
... intensity), but also by the duration the heat is in contact with the soil, referred to as fire residence time (e.g. (Hartford and Frandsen 1992, DeBano et al. 1998, Parsons and Orlemann 2011. For this reason, the soil burn severity, vegetation burn severity, and fire intensity are not likely to be analogous (DeBano et al. 1998, Safford et al. 2008, Parsons et al. 2010, 2010, Morgan et al. 2014. ...
... Figure 1 presents a simple conceptual model of fire scenarios and the potential relationship between remotely sensed vegetation burn severity and soil burn severity. Although outside the scope of this paper, soil moisture is considered the most important factor governing heat transfer in soil (Hartford and Frandsen 1992) -thorough reviews are available from DeBano (1998) and Van Wagtendonk (2018) -which merits inclusion in the figure. ...
Medicine Lake Highlands/Fall River Springs Aquifer System, located in northeastern California, is home to some of the largest first‐order springs in the United States. This work assesses the likely effects of projected climate change on spring flow. Four anticipated climate futures (GFDL A2, GFDL B1, CCSM4 rcp 8.5, CNRM rcp 8.5) for California, which predict a range of conditions (generally warming and transitioning from snow to rain with variable amounts of total precipitation), are postulated to affect groundwater recharge primarily by changing evapotranspiration. The linkages between climate variables and spring flow are evaluated using a water balance model that represents the physics of evapotranspiration and recharge, the Basin Characterization Model. Three of the four climate scenarios (GFDL A2, GFDL B1, CCSM4 rcp 8.5) project that by the year 2100, groundwater recharge (and consequently decreased spring flow) will decrease by 27%, 21%, and 9%, respectively. The fourth scenario (CNRM rcp 8.5) showed an increase in recharge of 32% due to a significant increase in precipitation (27%). Evapotranspiration increases due to a shift in the type of precipitation and a longer growing season. While the likelihood of each scenario is outside the scope of this work, unless total precipitation increases dramatically in the future, increased temperatures and decreasing precipitation will likely result in reduced spring flows, along with warmer water temperatures in downstream habitats.
... In this context, it has to be kept in mind that controlled laboratory experiments on soil heating do not necessarily reflect or predict processes in the field. For example, Hartford and Frandsen (1992) examined the effects of prescribed fires on soil heating in three instrumented plots in western Montana (two plots with slash fuel over moist duff) and northern Idaho (one plot with litter fuel over dry duff), USA. They found temperatures at the mineral soil surface to reach maxima of 80 • C (slash fuel over moist duff) and 400 • C (litter fuel over dry duff). ...
... They found temperatures at the mineral soil surface to reach maxima of 80 • C (slash fuel over moist duff) and 400 • C (litter fuel over dry duff). From their results Hartford and Frandsen (1992) concluded moisture content of duff and soil to represent key variables for soil heating with moist duff acting as a 'protective shield' against mineral soil heating. Stoof et al. (2013) conducted a fire experiment in an instrumented catchment in Portugal to analyze relationships between fuel load (vegetation), fire behavior, and soil temperature. ...
Altered fire regimes as a response to climate change are significantly affecting terrestrial ecosystems and biogeochemical cycles. In this context, not only natural fires but also anthropogenic fires like rice straw burning have to be considered. While heat effects of fire on some nutrient cycles (e.g., carbon, nitrogen, phosphorus) have been well-studied, little is known about consequences of heat for the silicon (Si) cycle. There is some information that heat increases the release of Si from soil organic matter. However, nothing is known about the effect of heat on Si availability in mineral soils to the best of our knowledge. We analyzed the effect of heat on Si availability in six different mineral soils. Our data show that heat is increasing Si availability (Mehlich-3 extractable) of all tested soils. The same pattern was found for amorphous Si (alkaline extraction) for most of these soils. Consequently , heated soils might represent a strong and immediate source for plant available Si. Ecosystem characteristics (e.g., vegetation, soil type) that affect uptake-leaching balances determine the further fate of the released Si. In summary, heat might affect Si cycling not only by strongly increasing Si availability in soil organic matter but also in mineral soils.
... Note that this study focuses on a small, unreplicated burn. Because the properties and effects of prescribed burns vary substantially with factors such as fuel load, vegetation, moisture, or time of year (Hartford and Frandsen, 1992;Quigley et al., 2019), the implications of the results of this study should be limited to similar fires. ...
... The laboratory-burned soil was initially at 16% moisture and lost 27% of its dry mass. Only the O horizon was burned in the laboratory, since it has been noted that often only the top few centimeters of soils are heated during a fire (Neary et al., 2008;Certini, 2005), particularly under higher moisture conditions (Hartford and Frandsen, 1992). That said, in a fire as severe as the one mimicked in the muffle furnace, depending on moisture, fuel load, or other conditions, we might have expected to see meaningful temperature increases in the mineral soil, which we did not attempt to mimic here. ...
Core Ideas
Prescribed fire did not affect jack pine seed germination or seedling establishment.
Severely burned soil had 10‐fold the available P and significantly lower organic matter and higher pH.
Jack pine seedlings produced about twice as much biomass in severely burned soil.
Regional genetic differences in jack pine may alter seedling establishment.
Within the state of Wisconsin, there is a gradient of serotiny in Pinus banksiana Lamb. (jack pine). With prescribed burning becoming more common in Wisconsin, understanding the dynamic and variable effects of burning on soil properties and their interactions with post‐fire plant communities is critical. Our objective was to isolate and examine how fire effects on soil properties affect P. banksiana seed germination and seedling growth and establishment. We investigated these effects in two pot experiments and an intact paired core experiment, maintained in a greenhouse for 19 to 24 wk. Soils from the O and A horizons were collected from Coon Fork Barrens, Eau Claire County, WI, before and after a prescribed fire, and O horizon soil was burned in the laboratory to mimic a high‐severity wildfire. In the intact core experiment, seed germination and seedling aboveground mass were not affected by prescribed burning. In the pot experiments, jack pine seedlings produced more biomass in laboratory‐burned soils than prescribed‐burned soils, and seedlings from northwest seed lots consistently had a higher frequency of establishment compared to those from central seed lots. For the low‐severity prescribed fire considered in this study, effects on measured soil properties were minimal, and did not result in any improvement to seedling establishment. For soil properties to play an important role in promoting jack pine seedling growth, hotter fires may be required, while lower‐severity fires will require other effects‐ such as seed release, changes to moisture dynamics, or competition‐ to affect jack pine germination and establishment.
... Duff layers of 4 cm to 12 cm in depth can easily maintain smouldering combustion [41] and, here, at the top of the burned transects a greater reduction in duff was observed compared to figures recorded for the control zone. The bulk density in that areas is very low (e.g., D0), which means it is more porous and can burn more easily [3]. ...
... The most important factors for the ignition and consumption of the soil duff layer are the maximum temperatures reached and the duration of these temperatures during a forest fire [41]. The longer the time during which the duff is subject to high temperatures, the lower the heat energy needed for ignition [45]. ...
This study analyses the smouldering combustion on soils that took place during the wildfires that occurred in Rocallaura (Northeastern Spain). The smouldering combustion after the first event, 23 June, was the potential source of flaming fire re-ignition of the second event, 19 July 2016. Re-ignitions are an important challenge for the firefighting system. Budget and efforts are spent on controlling these re-ignitions that can ultimately cause the collapse of the response system if the re-ignitions happen during periods of simultaneous fire events. Our objective is to contribute to better understand the dynamics of the smouldering combustion of organic soils associated with these wildfires and the impact on the Pinus halepensis Mill. forest ecosystem. Transects were established in adjacent control and post-fire zones. Laboratory analyses were conducted to determine some physical and chemical properties of both the duff and mineral soil. Using these variables, we estimate thresholds of duff ignition probability, percentage of duff consumption and smouldering combustion spread rates. Overall, we provide a set of tools for evaluating re-ignitions in forest ecosystems. We conclude that the concept of fire persistence should be a new variable for consideration in present and future analysis of fire regimes and demonstrates the significance of introducing smouldering combustion and re-ignition within the strategic framework of the wildfire hazard and integrating these phenomena into forest planning and management.
... Following slash-and-burn, peat MC decreased by ~10% but then returned to previous levels due to water migration over the subsequent 30 h. The small decrease of MC due to slash-and-burn is evidence of the shallow impact of flames on the soil that has been previously discussed in Hartford and Frandsen (1992); Rein et al. (2008) and Santoso et al. (2019). The drying front ahead of smouldering peat arrives at the sensor's location with a very swift decrease in peat MC to ~0% (very dry conditions). ...
O período entre 2018 e 2022 mostrou-nos que o problema dos incêndios à escala global não está a diminuir, antes pelo contrário. Parece que as consequências das alterações climáticas já estão a afectar a ocorrência de incêndios florestais em várias partes do Mundo, de uma forma que só esperaríamos que acontecesse vários anos mais tarde. Em muitos países do Sul da Europa, bem como em algumas regiões dos EUA, Canadá e Austrália, onde estamos habituados a enfrentar a presença de incêndios muito grandes e devastadores, continuamos a ter eventos que quebram recordes. Alguns países, como os da Europa Central e do Norte, que não estavam habituados a ter grandes incêndios, experimentaram-nos durante estes anos. Os anos anteriores foram muito exigentes para todo o Mundo, também noutros aspectos que nos afectaram a todos. Referimo-nos às restrições impostas pela pandemia que limitaram as nossas reuniões e viagens, afectando em muitos casos a saúde dos membros da Comunidade Científica Wildfire. Felizmente, conseguimos encontrar novas formas de comunicação, ultrapassar essas limitações e manter-nos em contacto uns com os outros. Durante semanas e meses, para muitos de nós, as reuniões pessoais e o trabalho de grupo foram substituídos por ligações em linha. Apesar da economia de dinheiro e tempo, e da facilidade de reunir uma grande variedade de pessoas que estas reuniões desde que nos apercebêssemos de que não substituem as reuniões presenciais, que trazem consigo outras dimensões inestimáveis, que fazem parte da comunicação pessoal e ajudam a construir uma comunidade científica.
... Following slash-and-burn, peat MC decreased by ~10% but then returned to previous levels due to water migration over the subsequent 30 h. The small decrease of MC due to slash-and-burn is evidence of the shallow impact of flames on the soil that has been previously discussed in Hartford and Frandsen (1992); Rein et al. (2008) and Santoso et al. (2019). The drying front ahead of smouldering peat arrives at the sensor's location with a very swift decrease in peat MC to ~0% (very dry conditions). ...
Peat wildfires can burn over large areas of peatland, releasing ancient carbon and toxic gases into the atmosphere over prolonged periods. These emissions cause haze episodes of pollution and accelerate climate change. Peat wildfires are characterised by smouldering – the flameless, most persistent type of combustion. Mitigation strategies are needed in arctic, boreal, and tropical areas but are hindered by incomplete scientific understanding of smouldering. Here, we present GAMBUT, the largest and longest to-date field experiment of peat wildfires, conducted in a degraded peatland of Sumatra. Temperature, emission and spread of peat fire were continuously measured over 4–10 days and nights, and three major rainfalls. Measurements of temperature in the soil provide field experimental evidence of lethal fire severity to the biological system of the peat up to 30 cm depth. We report that the temperature of the deep smouldering is ~13% hotter than shallow layer during daytime. During night-time, both deep and shallow smouldering had the same level of temperature. The experiment was terminated by suppression with water. Comparison of rainfall with suppression confirms the existence of a critical water column height below which extinction is not possible. GAMBUT provides a unique understanding of peat wildfires at field conditions that can contribute to mitigation strategies.
... Depending on climatic factors and future fire suppression and forest management practices, the trend in the occurrence of re-ignitions will vary, but an upwards trend could lead to a new fire regime. Smouldering combustion and reignitions will depend on fire intensity, which will determine combustion and spread characteristics (Hartford and Frandsen 1992). This would influence fire severity, as the more smouldering combustion there is, the greater the impact on the ecosystem (Certini et al. 2011). ...
This study was conducted following the fires that took place in Rocallaura (Spain) between 23/06/2016 and 19/07/2017. The aim is to analyse the importance of soil on forest planning and management mechanisms to mitigate the impacts of forest fire re-ignitions on risk and management framework. The main factors found to influence the occurrence of re-ignitions in a forest ecosystem dominated by Pinus halepensis were weather conditions, possible future climatic changes, soil and subsoil biomass amount and the physico-chemical properties of the organic layer. The re-ignition dynamics were included in the study as a new parameter-fire persistence-to be considered in fire regimes. It is proposed that fire persistence should be included in strategic framework for integrating wildfire risk in forest planning. This will entail identifying and including the potential for re-ignition in fire risk maps and fire suppression policies and implementing forest management actions in areas vulnerable to re-ignition.
... Thus, the intensity of a fire (i.e., the rate of energy release per meter of flaming front expressed in kW m −1 ), which is broadly related to the length of the flames, is not necessarily related to the impacts of a fire on soil. For example, a fast-moving intense fire with several meter-long flames rapidly consuming most of the aboveground vegetation may only lead to limited heating of the soil (Stoof et al., 2013), whereas a slow-moving low-intensity fire with small flames (i.e., a long residence time) consuming ground fuels (such as a thick litter layer) can lead to much greater soil heating (Hartford and Frandsen, 1992) (Fig. 1). ...
Fires affect many landscapes whether ignited by lightning or humans. They can affect soil physical, chemical and biological characteristics directly through heating and combustion, or indirectly through modified biological, pedological and hydrological processes after the fire. Direct effects include changes in organic matter, nutrients, biota, water repellency, aggregate stability, and an increased susceptibility to erosion. Indirect effects arise from incorporation of ash and from changes in vegetation cover, the water balance, organic matter inputs or protection from erosion. These effects can last from months to years and, in fire-adapted ecosystems, fire can be considered a key factor in soil formation.
... Compared with flaming combustion, smoldering can persist longer and under conditions that would extinguish flames. This characteristic of smoldering combustion allows it to penetrate deeper into the soil compared with flaming combustion, which generally causes shallower burns [4,5]. Thus, smoldering can actually cause greater destruction in affected ecosystems. ...
Smoldering combustion plays a key role in wildfires in forests, grasslands, and peatlands due to its common occurrence in porous fuels like peat and duff. As a consequence, understanding smoldering behavior in these fuels is crucial. Such fuels are generally composed of cellulose, hemicellulose, and lignin. Here we present an updated computational model for simulating smoldering combustion in cellulose and hemicellulose mixtures. We used this model to examine changes in smoldering propagation speed and peak temperatures with varying fuel composition and density. For a given fuel composition, increases in density decrease the propagation speed and increase mean peak temperature; for a given density, increases in hemicellulose content increase both propagation speed and peak temperature. We also examined the role of natural fuel expansion with the addition of water. Without expansion, addition of moisture content reduces the propagation speed primarily due to increasing (wet) fuel density. However, with fuel expansion similar to that observed in peat, the propagation speed increases due to the overall drop in fuel density. Finally, we studied the influence of fuel composition on critical moisture content of ignition and extinction: mixtures dominated by hemicellulose have 10% higher critical moisture content due to the increase in peak temperature.
... Direct impacts.-Fires may kill fungi directly and can provide a strong selective pressure for fungal evolution. Some fungi can survive temperatures greater than 50 C and even up to 145 C (Kipfer et al. 2010;Seaver 1909;Suryanarayanan et al. 2011), albeit 60 C for 1 min has been commonly considered lethal for most soil organisms (Neary et al. 1999), with 100 C often discussed as an uppermost threshold (Hartford and Frandsen 1992). The food industry considers fungi heat-resistant if they can survive 75 C for 30 min (Samson et al. 2004). ...
Fires occur in most terrestrial ecosystems where they drive changes in the traits, composition, and diversity of fungal communities. Fires range from rare, stand-replacing wildfires to frequent, prescribed fires used to mimic natural fire regimes. Fire regime factors, including burn severity, fire intensity, and timing, vary widely and likely determine how fungi respond to fires. Despite the importance of fungi to post-fire plant communities and ecosystem functioning, attempts to identify common fungal responses and their major drivers are lacking. This synthesis addresses this knowledge gap and ranges from fire adaptations of specific fungi to succession and assembly fungal communities as they respond to spatially heterogenous burning within the landscape. Fires impact fungi directly and indirectly through their effects on fungal survival, substrate and habitat modifications , changes in environmental conditions, and/or physiological responses of the hosts with which fungi interact. Some specific pyrophilous, or "fire-loving," fungi often appear after fire. Our synthesis explores whether such taxa can be considered cosmopolitan, and whether they are truly fire-adapted or simply opportunists adapted to rapidly occupy substrates and habitats made available by fires. We also discuss the possible inoculum sources of post-fire fungi and explore existing conceptual models and ecological frameworks that may be useful in generalizing fungal fire responses. We conclude with identifying research gaps and areas that may best transform the current knowledge and understanding of fungal responses to fire.
... A thermocouple was used to measure the temperature at the supposed sample surface in the sample holder without fuel with the chosen heat flux. The corresponding temperature for 20 kW m −2 heat flux (without fuel) was measured to 346°C (±67°C, standard deviation, SD), which is within the range of previously observed temperatures in smoldering combustion (Hartford and Frandsen, 1992;Krause and Schmidt, 2000). ...
Radiocesium, ¹³⁷Cs, is one of the most common and dispersed human-made radionuclides. Substantial stocks of ¹³⁷Cs are stored in organic layers, like soils and peat, as a consequence of nuclear weapons fallout and accidental releases. As climate warming progresses these organic layers are subject to enhanced risks of wildfires, especially in the vast boreal biome of the northern hemisphere. Reemission of ¹³⁷Cs to the atmosphere is therefore presumed to increase. Here, we experimentally investigated the emissions and redistribution of ¹³⁷Cs in smoldering fires of boreal soil and peat by varying the oxygen concentration during combustion. For both soil and peat, significantly more ¹³⁷Cs was released through flaming combustion in 21% O2 (50% and 31%, respectively) compared to smoldering in reduced O2 environments (14% and 8%, respectively). The residual ashes were heavily enriched (>100%) in ¹³⁷Cs. Hence, after a wildfire induced volatilization of ¹³⁷Cs, there exists further pathways of ¹³⁷Cs enriched ash to proliferate in the environment. These results serve as a link between wildfire combustion conditions and the mobility of the ¹³⁷Cs inventory found in ground fuels of the boreal environment and can be valuable for radiological risk assessments in a warmer and a more nuclear energy reliant world.
... The kind of effect of fire depends on the features of fire, soil characteristics, and plant communities covering the soil (Neyişçi 1989). The intensity of fires does not reveal its direct impacts on soil, vegetation, and air instead, the fire temperatures reach the forest litter level, within the duration of fire following the trend as vegetation layer, forest litter layer, and mineral soil layer (Hartford and Frandsen 1992). Even there are conflicting thoughts on the definition of fire severity versus fire intensity. ...
... In general terms, flaming fires produced substantial flame heights but minimal heating to the soil [26]. In contrast, smouldering fires produce many times longer heating duration (more than 1 h) and reach lethal temperatures of most species [22,27]. The longer duration and the greater heat transferred to the forest floor by smouldering has been identified as an important factor in wildfire mortality [28]. ...
Wildfires can be divided in two types, flaming or smouldering, depending on the dominant combustion processes. Both types are present in most wildfires, and despite being fundamentally different in chemical and physical terms, one transitions to the other. Traditionally, science has focused on flames, while smouldering is often misinterpreted. But smouldering wildfires are emerging as a global concern because they cause extensive air pollution, emit very large amounts of carbon, are difficult to detect and suppress, and can accelerate climate change. Central to the topic are smouldering peat fires that lead of the largest fires on Earth. Smouldering also dominates the residual burning after flames have died out, and firebrand ignition. Finally, smouldering is an important part of Arctic wildfires which are increasing in frequency. Here we present a scientific overview of smouldering wildfires, the associated environmental and health issues, including climate change, and the challenges in prevention and mitigation.
... The kind of effect of fire depends on the features of fire, soil characteristics, and plant communities covering the soil (Neyişçi 1989). The intensity of fires does not reveal its direct impacts on soil, vegetation, and air instead, the fire temperatures reach the forest litter level, within the duration of fire following the trend as vegetation layer, forest litter layer, and mineral soil layer (Hartford and Frandsen 1992). Even there are conflicting thoughts on the definition of fire severity versus fire intensity. ...
Increased fire pressure on forests and recent increase in human needs have lead to diverse outputs in forest ecosystem management strategies for the sake of sustainability of forests. Increase in CO2 releases and substantial greenhouse gases have created unexpected climatic events which are highly determinant on forest fires. The plant community composition tends to change its current distribution map and the terrains previously dominated with fire-susceptible species are transforming into a more ignitable plant composition. Concurrent conversion of plant community compartments is affecting the soil chemistry, biology, and water budget. The most common problems arising following fires are loss of organic matter by ignition, susceptibility to erosion, and evaporation of forms of C and N compounds. We hypothesized that fire as an important dominating factor in the Mediterranean ecosystems has lead to several changes: (I) adaptation of plant communities and dynamics has been fostered; (II) consecutive fires convert soil conditions which become less tolerant; (III) water-dependent competitions are more severe than earlier periods. As conclusion, the reactions of the ecosystem in total have become more vulnerable, more susceptible, within the shortened adaptation time.
... The kind of effect of fire depends on the features of fire, soil characteristics, and plant communities covering the soil (Neyişçi 1989). The intensity of fires does not reveal its direct impacts on soil, vegetation, and air instead, the fire temperatures reach the forest litter level, within the duration of fire following the trend as vegetation layer, forest litter layer, and mineral soil layer (Hartford and Frandsen 1992). Even there are conflicting thoughts on the definition of fire severity versus fire intensity. ...
Northeast Anatolia is rich in a variety of ecosystems, habitats, and unique vascular plant diversity. A remarkable number of vascular plants have been used for several purposes such as food, medicine, etc. by the local people. This region is characterized by dune, riparian, wetland, pseudomacchie, forest (both deciduous and conifer) and subalpine-alpine vegetation types of which the last one is the richest zone in terms of both plant diversity and medicinal plants. This chapter provides scientific information about both native and non-native vascular medicinal plants and their uses, parts used and local names depending on literature and field observations available in this region of Turkey. A total of 510 medicinal vascular plants including 10 endemics are distributed in this region investigated by us
... Many plant species in pyrogenic communities have traits that make them fire tolerant (Lamont et al., 2011;Pellegrini et al., 2017) and soil can insulate seeds and buds from heat (Hartford & Frandsen, 1992). Below-ground, buds may contain thick sheaths that allow them to survive and resprout post-fire (Clarke et al., 2013). ...
Non‐native invasive grasses are driving intense fires across the globe but the impacts of native versus invader‐fuelled fires on community assemblages are poorly understood. By increasing fire intensity, grass invasions might increase below‐ground mortality of heat‐sensitive seeds and buds, thereby shifting community composition.
We compared fuel loads in native and non‐native invasive (cogongrass, Imperata cylindrica) plant‐dominated areas of pine savannas in Florida. Then, we conducted a field experiment to examine how fuel loads and native and invasive fuel types affected soil heating and seedling emergence or resprouting of native and invasive plant species.
Average fuel loads in invaded communities were 152% greater than that in native communities. Soil heating, including heating duration >60°C, maximum temperature and heat flux >60°C, increased, and seedling emergence and resprouting decreased with greater fuel loads; these relationships were similar across the overlapping range of native and invasive fuel loads. However, longer durations of soil heating at the higher average fuel loads of invaded communities resulted in 23% lower predicted probability of seedling emergence compared to average fuel loads of native communities.
Invasive cogongrass resprouting was not affected by fuel loads, indicating that cogongrass tolerates the intense fires it generates. In contrast, seedling emergence and resprouting of most other species was reduced by greater fuel loads.
Synthesis and applications. By increasing fuel loading and soil heating, grass invasions may alter post‐fire community assemblages and facilitate invasive grass dominance at the expense of native species via an invasion‐fire cycle. Fuel loads can be used to predict soil heating duration and depth, and these data, combined with information on species tolerances to heating, can be used to forecast the impacts of invasions on post‐fire community composition. To maintain fire regimes that promote native communities and resist invader dominance, it is critical to manage invasive species that increase fuel loads.
... This may explain our finding that moderate and high burn frequency sites (≥ 4 burns) had greater SHC than unburned control sites (Fig. 5). Moquah prescribed fires were conducted during late spring, when the duff layer remains cool and wet, and duff consumption is inversely related to duff moisture content (Garlough and Keyes, 2011;Hartford and Frandsen, 1992;Little et al., 1986). It is therefore likely that several growing season burns, or a burn period when the soil temperature is relatively warm and fuels are dry, would be required to achieve significant reductions in duff depth at brush and forested sites. ...
Prescribed fire is widely used for ecosystem restoration, yet the mechanisms that determine its effectiveness remain poorly characterized. Because soil hydrology influences ecosystem processes like erosion, runoff, and plant competition, it is important to understand how fire affects soil hydrology. A systematic approach to understanding relationships among vegetation, topography, and fire is needed to advance knowledge of how fire influences soil properties that in turn affect restoration success. Our objective was to characterize relationships among burn severity, vegetation, and soil hydrology in a heterogenous landscape under restoration management. Our study took place in a barrens-forest mosaic with recent prescribed fire history ranging from 0 to 10 burns since 1960, and additional variation in fuel loading, burn severity, vegetation cover, topography, and soils. We measured soil hydraulic conductivity (SHC) during two consecutive years, which represented control, prefire, postfire, and 1-year postfire conditions. Regression tree analysis identified an important threshold effect of antecedent soil moisture on SHC; soils with initial moisture < 13% had lower SHC than soils with initial moisture > 13%. Furthermore, above this threshold, sites with intermediate to high recent burn frequency (4–10 burns) had significantly greater SHC than unburned control sites. High fuel loads associated with brush cutting and piling increased SHC at barrens sites but not brush or pine sites, suggesting an interaction between vegetation cover and fire effects on SHC. At the local hillslope scale, toe-slopes had greater SHC than summits. Our results suggest that repeated prescribed fires of moderate to high frequency may enhance SHC, thereby reducing soil water retention and potentially restoring functional pine barren processes that limit woody plant growth. Prescribed fire may therefore be an important management tool for reversing mesophication and restoring a global array of open canopy ecosystems.
... Root necrosis from fire depends on root traits such as diameter and depth (McLean, 1969;Smirnova et al., 2008), soil characteristics such as depth of organic layer, moisture content, and texture (Busse et al., 2010), and fire characteristics such as temperature and duration. Smoldering combustion generally causes more severe root injury than flaming combustion because, although it has lower temperatures, it occurs for a much longer duration and thus conducts heat to greater depths (Hartford and Frandsen, 1992;Michaletz and Johnson, 2007). For example, longleaf pine ecosystems with deep organic soil experienced smoldering combustion that led to substantial root necrosis (Varner et al., 2005(Varner et al., , 2009O'Brien et al., 2010). ...
Wildland fires (including wildfire and prescribed burns) have many complex effects on vegetation and ecosystem function. These range from relatively minor injuries to tissues and organs (e.g., fire scars and crown scorch) to whole plant mortality and forest stand replacement. Fire effects are dependent upon fire behavior variables such as fire intensity and residence time, as well as plant traits such as bark thickness, stem diameter, tree height, and crown morphology. Despite an increasing need to understand and predict fire effects in a changing climate, we still have only a limited understanding of how fire behavior variables interact with plant traits to affect plant functioning across levels of biological organization.
In this chapter, we outline the physical processes linking fire behavior, plant traits, and plant physiology to tree injuries and mortality, from individuals to ecosystems. We begin by reviewing the history of fire modeling, followed by background on combustion processes that influence fire behavior and spread, and a brief description of current approaches to modeling fire. We then describe ways in which trees are heated by fires, and how this leads to plant root, stem, and crown injuries. Injuries to plant roots, stems and crowns can then be used to determine the effects of fire on whole-plant functioning via changes in carbon and water budgets. Lastly, we describe how size-dependent mortality of individuals “scale up” to determine stocks and fluxes of ecosystems (e.g., total stand biomass, primary productivity, and evapotranspiration).
... Thereby, the duration of a fire may range from minutes up to several hours [70]. Temperatures may vary from maximum surface temperatures of 400 • C in a ground fire (affecting litter and organic layer) [72] to ≥ 500 • C in shifting-cultivation fires [73]. In shifting-cultivation experiments conducted in Jambi Province, soil-surface temperatures during fire events varied widely, from 100 to 600 • C within the impacted area [67]. ...
The effects of land use and fire on ecosystem silicon (Si) cycling has been largely disregarded so far. We investigated the impacts of land use and fire on Si release from topsoils and litter of lowland rainforest and oil-palm plantations in Jambi Province, Indonesia. Lower concentrations of Si in amorphous silica (ASi) were found in oil-palm plantation topsoils (2.8 ± 0.7 mg g−1) compared to rainforest (3.6 ± 0.8 mg g−1). Higher total Si concentrations were detected in litter from oil-palm frond piles (22.8 ± 4.6 mg g−1) compared to rainforest litter (12.8 ± 2.2 mg g−1). To test the impact of fire, materials were burned at 300 °C and 500 °C and were shaken with untreated samples in simulated rainwater for 28 h. Untreated oil-palm topsoils showed a significantly lower Si release (p ≤ 0.05) compared to rainforest. The fire treatments resulted in an increased Si release into simulated rainwater. Si release from oil-palm topsoils and litter increased by a factor of 6 and 9 (500 °C), respectively, and Si release from rainforest topsoils and litter by a factor of 3 and 9 (500 °C). Differences between land use were related to initial ASi and litter Si concentrations, and to losses of soil organic matter during burning. We conclude that transformation of rainforest into oil palm plantations could be an important and immediate Si source after a fire event but may indirectly lead to a decrease in the long-term Si availability to plants.
... ''Initial position'' refers to where each thermocouple was at the beginning of the trial insulators: are extended above-ambient thermocouple readings a function of retained heat by these insulators, or a function of these insulators slowing the diffusion of heat away from the thermocouple? Furthermore, soil moisture plays an essential role in heat transfer rates (DeBano 2000;DeBano et al. 1979;Frandsen and Ryan 1986;Hartford and Frandsen 1992). Thus, unless soil moisture content is controlled-or at least measured and accounted for-very little about temperature changes over time in soil can be directly attributed to properties of the fire. ...
Plant ecologists have long been interested in the effects of fire on vegetation. Thermocouples have been in their proverbial toolbox for decades, despite temperature not being a direct product or measure of wildland fire behaviour or fire effects. To better represent the cumulative impact of high-temperature exposure on organisms, ecologists often use temperature–time curves from thermocouples to calculate residence time—the duration of heat exposure above a threshold temperature—which can be used to calculate another popular metric, degree ·seconds. A systematic literature review of 105 published papers shows that residence time, especially, and degree · seconds are common metrics derived from raw temperature–time data. While several errors in thermocouple readings have been previously identified and addressed—responsiveness to heating, discrepancy between thermocouple temperature and actual temperature of the medium surrounding the thermocouple—this paper highlights a previously unconsidered source of error that must be reconciled for metrics like residence time to be biologically valid: the disproportionately long time it takes for thermocouples to cool once heat input is complete. Using an array of thermocouples in a fume hood over a Bunsen burner before and after the flame is extinguished, this paper shows that after being exposed to flame, 30-gauge K-type thermocouples require 80–100 s to register ambient temperatures despite taking only about 5 s to respond to heating. The review indicates ecologists give no consideration for this disproportionately slow cooling response. These findings indicate that residence time (and therefore degree · seconds) have been over-estimated in the fire ecology literature. The proposed solution is to simply truncate temperature–time curves at the point temperature begins to decline, which indicates a shift from the biologically relevant effect of heat input to the biologically irrelevant, physical properties (heat diffusivity) of the thermocouple itself. Conceptual models present these biologically relevant portions of the temperature–time curve and identify parts of the biologically relevant curve that might be useful in quantifying components of flammability.
... Este estudio representa el inicio de una línea de investigación de gran interés para la restauración de áreas quemadas, como es el empleo de técnicas de teledetección para el análisis de la severidad de incendios forestales La severidad del fuego Cuando se habla de los efectos del fuego es importante diferenciar entre intensidad y severidad de los incendios, porque con frecuencia no son lo mismo(6) . El término intensidad se utiliza para describir la velocidad a la que un fuego libera energía térmica(7) . ...
P oder estimar con precisión los cambios ocurridos en los suelos tras un incendio forestal es esen-cial para programar las tareas de restau-ración de manera eficaz. La gestión post-incendio y los tratamientos paliativos a realizar tras un incendio (repoblaciones, extracciones madereras, protección con-tra la erosión, mapas de intervención prioritaria, etc.) no son siempre los mis-mos, sino que dependen en gran medi-da de la severidad del incendio y de los efectos ocurridos sobre los suelos afec-tados. Además, la severidad del fuego no es homogénea para toda la superficie del incendio. Dentro de un mismo incendio suele haber áreas afectadas en mayor o menos medida por el fuego. Por este mo-tivo, también es importante conocer la distribución espacial de la severidad del fuego sobre el área afectada. Pese a la importancia de poder evaluar los efectos del fuego sobre el suelo, los mé-todos usados hoy en día para estimar su severidad suelen resultar costosos, subje-tivos y poco precisos (1). Motivados por esa SEGURIDAD Y MEDIO AMBIENTE Nº 128 Cuarto trimestre 2012 10 Medio ambiente EFECTOS y su comportamiento espectral Estudio sobre el potencial de la radiometría para estimar la severidad del fuego DEL FUEGO sobre las propiedades de los suelos Conocer los efectos del fuego sobre el suelo es fundamental de cara a la aplicación de medidas paliativas. Sin embargo, los métodos usados hoy en día para estimar la severidad del fuego suelen resultar costosos, subjetivos y poco precisos. En el Centro de Investigación del Fuego (CIFU) se ha evaluado el potencial de la radiometría VNIR (visible e infrarrojo cercano) para caracterizar de manera rápida y eficaz el efecto de incendios de diferente duración e intensidad sobre las propiedades de los suelos.
... Other indicators of fire intensity include residence time, and peak temperature. Fire intensity can be useful for evaluating potential fire effects above the surface, although no direct correlation has been found between fire intensity and soil heating (Hungerford, 1989;Hartford and Frandsen, 1992). ...
First order fire effects in mixed grass and tallgrass prairies may differ between current and historic fire regimes. To determine potential differences, the thermal dynamics of nine prescribed grassland fires and six experimental fires were evaluated.
Fires were instrumented with dataloggers and arrays of up to twelve thermocouples set at heights ranging from -5 cm to 300 cm. Soil moisture and texture were documented, along with fuel characteristics. A series of experimental fires allowed soil moisture to be manipulated while minimizing other variables.
Maximum temperature for the prescribed fires was 875°C at 75 cm, and for the experimental fires 920°C at 10 cm. In experimental fires, the greatest temperature difference was at the surface with the dry substrate averaging 130°C higher than saturated. Average temperatures at -1 cm differed by 33°C. At 60°C, residence times in dry substrate averaged almost four minutes, while the average for saturated treatment was only 1 second. Surface residence times on dry substrate averaged over 7 minutes, almost
3 times longer than saturated.
Soil moisture was shown to influence relative humidity and fine fuel moisture near the ground surface. An increased evaporation of soil water at the surface is suggested by a slight drop in subsurface temperatures as the flaming front moves over the surface. These data suggest that soil moisture affects fire intensity, decreasing temperatures at all levels of a fire.
Temperatures and residence times were compared with data from studies documenting temperatures significantly affecting seed germination and edaphic effects at and below the surface. Temperatures increasing the germination of some seeds were found at all heights. Temperatures documented can be expected to decrease organic matter content and aggregate stability at the surface, slightly increasing erodibility.
Thermal dynamics from the fires in this study represent a broad range of 2 grassland fires under conditions common for prescribed fire. Soil moisture appears to significantly affect temperatures and residence times below, at, and above the soil surface.
Data were compared with output from FOFEM 5.2 to access the applicability of FOFEM for use in mixed grass and tallgrass prairie. FOFEM consistently underestimated soil heating by up to 419°C.
... Fire alters multiple physical, chemical and biological properties of soil, such as texture, aggregation, pH, nutrient content and microbial community composition. The magnitude of fire effects on soils depends on above-ground fire behaviour (Massman, 2012), organic horizon depth and moisture content (Hartford & Frandsen, 1992) and the physical properties of mineral soil (Giovannini, Lucchesi, & Giachetti, 1988). Fire directly impacts the upper organic horizons via pyrolysis and combustion reactions, including physical loss of the organic horizon, and the underlying mineral soil by conductive and advective heating during a fire (Araya, Fogel, & Berhe, 2017;Certini, 2005;Neary, Ryan, & DeBano, 2008). ...
Fire is a powerful ecological and evolutionary force that regulates organismal traits, population sizes, species interactions, community composition, carbon and nutrient cycling and ecosystem function. It also presents a rapidly growing societal challenge, due to both increasingly destructive wildfires and fire exclusion in fire‐dependent ecosystems. As an ecological process, fire integrates complex feedbacks among biological, social and geophysical processes, requiring coordination across several fields and scales of study.
Here, we describe the diversity of ways in which fire operates as a fundamental ecological and evolutionary process on Earth. We explore research priorities in six categories of fire ecology: (a) characteristics of fire regimes, (b) changing fire regimes, (c) fire effects on above‐ground ecology, (d) fire effects on below‐ground ecology, (e) fire behaviour and (f) fire ecology modelling.
We identify three emergent themes: the need to study fire across temporal scales, to assess the mechanisms underlying a variety of ecological feedbacks involving fire and to improve representation of fire in a range of modelling contexts.
Synthesis: As fire regimes and our relationships with fire continue to change, prioritizing these research areas will facilitate understanding of the ecological causes and consequences of future fires and rethinking fire management alternatives.
... The soil temperatures experienced by seeds during a fire are dependent on fuel consumption, with the depth of heating significantly affected by the amount of fuel consumed at ground level (Hartford and Frandsen 1992;Bradstock and Auld 1995;Neary et al. 1999;Busse et al. 2005Busse et al. , 2013Kreye et al. 2013). Fine fuel consumption during a fire determines temperature penetration profiles and whether this is sufficient to break dormancy in species with physical seed dormancy and influences the depths from which seedlings emerge. ...
Potential impacts of soil temperatures in a post-fire environment were examined for seeds of legume species with a physical seed dormancy typically found in the eucalypt communities in eastern Australia. Soil temperatures in a post-fire environment may be elevated owing to increased solar radiation and this may influence germination of species with soil-stored seed banks. Seeds were heated at 50, 60 or 70°C, with one unheated control, for 3h per day for 5 days to simulate soil temperatures where canopy gaps existed. More germination of small-seeded species (<12.6mg) occurred owing to changes in simulated soil temperatures than large-seeded species (>14.0mg). Temperatures up to 70°C significantly increased the germination of species with relatively small-sized seeds than large-seeded species (>70°C). This study demonstrated that small-seeded species are able to germinate across a range of temperatures (50–70°C) and can have dormancy broken either during the passage of a fire, or after fire from increased solar radiation, potentially resulting in the decline of the post-fire residual soil seed bank. In contrast, post-fire germination of large-seeded species may be dependent solely on the degree of soil heating during the passage of fire and the species may have a relatively stable residual soil seed bank thereafter.
... Soil heating during fires is a function of the fuels being burned and the characteristics of the soils in which heat is being transferred (Aston and Gill 1976, Hartford and Frandsen 1992, Campbell 1994, 1995, Midttomme and Roaldset 1998, Abu-Hemdeh and Reeder 2000. Smoldering is a low intensity combustion process given its slow burning rate, i.e., on the order of cm h -1 , but can release substantial energy over a given area where significant forest floor fuels are consumed over protracted periods (Miyanishi 2001, Rein et al. 2008. ...
Prescribed fire is commonly used in southeastern US forests and is being more widely applied in fire-prone ecosystems elsewhere. Research on direct effects of burning has focused on aboveground impacts to plants with less attention to belowground effects. We measured soil heating during experimental burns in longleaf pine sandhill and flatwoods ecosystems in the southeastern US. Soil heating was minimal in frequently burned sites. Where fire had been excluded for several decades, however, we detected substantial soil heating sustained for considerable durations. Long-duration heating was most prominent where accumulated forest floor duff (Oe and Oa organic horizons) was deepest, particularly at the base of mature pines in long-unburned sites. Temperatures potentially lethal to plant tissues (≥60°C) were sustained for several hours as deep as 10 cm near pines in flatwoods sites. Sustained temperatures ≥300°C, when impacts to soil nutrients can occur, were observed for up to 35 min at mineral soil surfaces. Patterns of heating were similar in long-unburned sandhill sites; however, temperatures were generally lower and durations more brief. Heat transfer resulting from smoldering in forest floor duff deserves further attention to predict mineral soil heating, forecast fire effects, and inform restoration efforts in fire-prone ecosystems.
... In a recent review on biological responses to soil heating associated with wildland fire, it was asserted that the mechanism driving direct biological impacts of fire on soil depends upon its intensity and duration (Pingree and Kobziar, 2019). During wildland fires, temperatures range from less than 100°C to well above 400°C depending upon the loads and type of fuel, fire behavior, and soil conditions (Busse et al., 2013;DeBano et al., 1979;Hartford and Frandsen, 1992;Massman and Frank, 2004a,b;Raison et al., 1986). In particular, soil abiotic components (e.g. ...
... This impact decreases water transport and nutrient acquisition in the short-term and results in nonstructural carbohydrate drains to rebuild lost roots over longer periods (O'Brien et al. 2010;Taudière et al. 2017;Varner et al. 2009). Fire-caused tree mortality from root death alone is uncommon, as mineral soil is a poor conductor of heat and forest floor organic soils insulate underlying mineral soil and roots from flames (Hartford and Frandsen 1992). Long-term heating required to kill roots often also impacts the tree stem, making resulting tree death a combination of injuries to the roots and stem. ...
This chapter provides a overview of direct and indirect causes of tree mortality from fire, describes resprouting vs. top-kill responses, and applications that predict post-fire tree mortality.
... Burn severity is defined as the degree to which an ecosystem has changed as a result of the fire. Vegetation rehabilitation may specifically vary based on burn severity after a fire [17][18][19][20][21][22]. Previous studies classified burn severity into four or five classes, such as extreme, high, moderate, low, and unburned, using remote sensing data based on the composite burn index (CBI) suggested by the United States Forest Service [23][24][25]. ...
Unmanned aerial vehicle (UAV)-based remote sensing has limitations in acquiring images before a forest fire, although burn severity can be analyzed by comparing images before and after a fire. Determining the burned surface area is a challenging class in the analysis of burn area severity because it looks unburned in images from aircraft or satellites. This study analyzes the availability of multispectral UAV images that can be used to classify burn severity, including the burned surface class. RedEdge multispectral UAV image was acquired after a forest fire, which was then processed into a mosaic reflectance image. Hundreds of samples were collected for each burn severity class, and they were used as training and validation samples for classification. Maximum likelihood (MLH), spectral angle mapper (SAM), and thresholding of a normalized difference vegetation index (NDVI) were used as classifiers. In the results, all classifiers showed high overall accuracy. The classifiers also showed high accuracy for classification of the burned surface, even though there was some confusion among spectrally similar classes, unburned pine, and unburned deciduous. Therefore, multispectral UAV images can be used to analyze burn severity after a forest fire. Additionally, NDVI thresholding can also be an easy and accurate method, although thresholds should be generalized in the future.
Addressing post-fire impacts largely depends on burn “severity.” A singular severity classification that encompasses the holistic effects of fire on all ecosystem processes does not currently exist. Lumping vegetation burn severity and soil burn severity into one metric, or using them interchangeably, can induce large inaccuracies and uncertainties in the intended ecosystem response to forcing. Often, burn “severity” reflects fire impacts on vegetation, which can be measured through remote sensing. Vegetation burn severity is likely more apropos for ecological research, whereas soil burn severity is more relevant for hydrological analyses. This paper reviews different remotely sensed vegetation severity products currently (mis)used for hydrological modeling, provides examples of when vegetation burn severity may (not) match soil burn severity, and summarizes the potential synergistic future of remote sensing with in situ severity metrics. While the focus in this paper is on the western United States, the lessons and principles apply universally.
En el presente trabajo se documenta la presencia de un fenómeno de combustión latente residual (CLR) reportado el 30 de abril del 2022 en el volcán Quinceo, Morelia. Para identificar los gases difusos emanados, el 14 de mayo se realizaron mediciones de los flujos y concentraciones de metano (CH4), dióxido de carbono (CO2) y sulfuro de hidrógeno (H2S) en 25 sitios con la cámara de acumulación de gases. Adicionalmente se determinó la concentración de monóxido de carbono (CO) amoniaco (NH3) y oxígeno (O2) en ésos mismos sitios con un detector de gases múltiples ALTAIR 5X y se midió la temperatura del subsuelo (15 cm de profundidad) mediante un termopar. Los resultados mostraron que las temperaturas más altas registradas en el subsuelo fueron de hasta 341 °C, donde no fue posible determinar los flujos por la inestabilidad del equipo debido a la temperatura elevada. El cálculo del coeficiente de correlación mostró una relación positiva entre la temperatura y la concentración de H2S, CH4 y NH3. El bajo flujo de metano y el límite inferior de explosividad (LIE) no detectado en la mayoría de los sitios medidos, indican bajo riesgo de explosividad. Sin embargo, hay una zona donde confluyen condiciones tales como las altas temperaturas en el subsuelo, altos flujos de gases, elevadas concentraciones de CH4 y O2 y un LIE entre 7 a 10 %, que indican un riesgo de explosividad muy focalizado. La evaluación del riesgo de una explosión en la zona por la falla en el ducto de la tubería de gas natural localizado a unos metros de la zona de CLR, estimó que podría causar daño hasta una distancia de 250 m. Adicionalmente, los altos niveles de metano en esta zona, representan una fuente importante de producción de gases de efecto invernadero. Es posible que este fenómeno (CLR) haya sido provocado por un incendio forestal reportado el 30 de abril, cuyas condiciones de desertificación del lugar como el tipo de suelo (Feozem, rico en materia orgánica) y condiciones ambientales (temperaturas máximas para el mes de mayo de 31 °C), aumentan los riesgos de una explosión del gasoducto.
Lightning is one of the essential causes of wildfires. However, the ignition criteria for lightning-caused wildfires have significant limitations due to a lack of understanding of the ignition mechanism. This work aims to reveal the mechanism of lightning-induced smoldering ignition of wildland fuels and explore a more reasonable ignition criterion by experimental means. The solidified peat cake samples were ignited by the electric arcs with different discharge currents (from 100 to 220 A with a step of 30 A) and durations (from 40 to 480 ms with an interval of 40 ms). The observations show that the ignition process follows a unique flaming-to-smoldering mode consisting of three stages: discharge heating (Stage I), thermal feedback (Stage II), and sustaining smoldering (Stage III) stages. The flame column that appears in Stage I is attributed to intense gasification and burnup of the peat, and seems to have little contribution to the ignition outcome. The carbonized region formed in Stage I, not the sample gasified in the discharge channel, is the main energy deposition to drive the successful smoldering ignition. It is found that the discharge duration required for smoldering ignition decreases with increasing discharge current ( I arc ) when I arc < 160 A, but weakly depends on the discharge current when I arc ≥160 A. Critical discharge energy is also required when I arc < 160 A. A segmented ignition criterion is proposed based on the critical discharge duration and energy. For the peat cake sample, a minimum size, initial temperature, and absorbed energy of the carbonized zone are required for a sustaining smoldering ignition.
Smouldering combustion plays a key role in wildfires in forests, grasslands, and peatlands due to its common occurrence in porous fuels like peat and duff. As a consequence, understanding smouldering behaviour in these fuels is crucial. Such fuels are generally composed of cellulose, hemicellulose, and lignin. Here we present an updated computational model for simulating smouldering combustion in cellulose and hemicellulose mixtures. We used this model to examine changes in smouldering propagation speed and peak temperatures with varying fuel composition and density. For a given fuel composition, increases in density decrease the propagation speed and increase mean peak temperature; for a given density, increases in hemicellulose content increase both propagation speed and peak temperature. We also examined the role of natural fuel expansion with the addition of water. Without expansion, addition of moisture content reduces the propagation speed primarily due to increasing (wet) fuel density. However, with fuel expansion similar to that observed in peat, the propagation speed increases due to the overall drop in fuel density. Finally, we studied the influence of fuel composition on critical moisture content of ignition and extinction: mixtures dominated by hemicellulose have 10% higher critical moisture content due to the increase in peak temperature.
Underground fires are slow spreading, long-lasting and low temperature smoldering combustion without flames, mainly occurring in peatlands and wetlands with rich organic matter. The spread of the smoldering is maintained by heat released during combustion and monitoring this is an important approach to detect underground fires. The Daxing’an Mountains region is a hotspot for underground fires in northeast China. This study examined a Larix gmelinii plantation in the Tatou wetlands of the Daxing’an Mountains and determined the maximum temperature variation of humus of varying particle sizes, and the temperature rising process based on non-linear mixed effects models by an indoor combustion experiment. Maximum combustion temperatures up to 897.5 °C, increased with humus depth; among the three models tested, Richard’s equations were best for characterizing temperature variations; a non-linear equation with three parameters had the highest accuracy in fitting the combustion temperature variations with varying humus particle sizes. These results are informative for predicting temperature variations and provide technical support for underground fire monitoring.
Vegetation often fuels fires. We describe both vegetation fuels and how fires burn with specific terms central to understanding fire science and management. Fuel type, amount (load), and structure mediate both the effects of fire on ecosystems and human impacts on fires. Independent of its biological nature, characterizing how readily vegetation could burn as fuels is required to describe and model fire behavior and fire effects for multiple fire science and management applications. Fire behavior terms apply to either flaming and smoldering combustion, except when preceded by a qualifier. Our book, Fire Science: From Chemistry to Landscape Management, offers a logical progression of combustion to vegetation dynamics. In this and other chapters, visually compelling examples bring key concepts to life. This chapter builds on the previous chapters focused on the chemistry of ignition and combustion, and sets up the following chapters on fire effects on people and ecosystems, then managing fuels and fires in a dynamic and changing world.
Underground fires are a smoldering combustion with a slow spread rate, low temperatures and no flame. They can last from days to several months, and can even become overwintering fires. They are difficult to find, leading to considerable damage to the forests. The moisture content of combustible fuels is an important factor in the occurrence and persistence of underground forest fires. The Daxing’an Mountains are a hot spot for underground fires in China. This paper looks at the influence of different moisture contents on underground fire characteristics using simulation combustion experiments in the laboratory. The study showed that peak temperature and spread rate fluctuation of humus at different moisture levels increased with humus depth. Peak temperature and spread rate fluctuation of humus at different depths decreased with increased moisture; moisture content and depth of humus had a significant effect on peak temperature and spread rate fluctuation; peak temperature at different depths decreased with increased moisture; the spread rate in upper layers increased with moisture content, while the spread rate in the lower layers decreased with increased moisture content.
The application of water, or water mixed with suppressants, to combat wildfires is one of the most common firefighting methods but is rarely studied for smouldering peat wildfire, which is the largest type of fire worldwide in term of fuel consumption. We performed experiments by spraying suppressant to the top of a burning peat sample inside a reactor. A plant-based wetting agent suppressant was mixed with water at three concentrations: 0% (pure water), 1% (low concentration), and 5% (high concentration), and delivered with varying flowrates. The results showed that suppression time decreased non-linearly with flow rate. The average suppression time for the low-concentration solution was 39% lower than with just water, while the high-concentration solution reduced suppression time by 26%. The volume of fluid that contributes to the suppression of peat in our experiments is fairly constant at 5.7±2.1L kg−1 peat despite changes in flow rate and suppressant concentration. This constant volume suggests that suppression time is the duration needed to flood the peat layer and that the suppressant acts thermally and not chemically. The results provide a better understanding of the suppression mechanism of peat fires and can improve firefighting and mitigation strategies.
A Natural England evidence review on the occurrence, causes, prevention and management of wildfires on open, semi-natural habitats in the UK, with a particular focus on heathlands and peatlands in England. This reflects Natural England’s role and interest in relation to maintaining and restoring the structure and function of semi-natural habitats, including supporting ecosystem services and related government environment objectives and policies. Supporting information and summary data are given in 12 appendices.
Prescribed fire – the intentional use of fire to help achieve a land management goal – is becoming increasingly common as a land management practice. Soil physical, chemical, and biological properties can be affected by prescribed fires, but depend on the fire, soil type, residence time and frequency, and may not be changed substantially in low-severity burns. Here, we examined soil bacterial community composition immediately post-fire (15 days) in a sandy jack pine barrens soil in Wisconsin, USA. Soil bacterial communities clustered significantly by sample site (p < 0.001) and by soil horizon (p = 0.048), but not by whether or not soil samples were visibly burned. There were also no significant differences in total relative abundance at the phylum level in visibly burned vs. not visibly burned soils, and only two significant differences in abundance or variability of individual taxa. Soil properties remained unchanged post-fire and the fire was visibly patchy, suggesting that the low severity prescribed fire most likely had a minimal soil heating effect. Therefore, we suggest the minimal bacterial community composition shifts seen in this study were likely mediated more by plants than by direct heat-killing or changes to soil properties.
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