Surface Fire Research Articles

Пірогенні зміни ґрунтів соснових насаджень

Унаслідок низових пожеж відбуваються зміни фізико-хімічних і біологічних властивостей ґрунтів. Досліджено пірогенні зміни властивостей ґрунтів у чистих соснових лісах, що ростуть у різних природних зонах України. У соснових насадженнях після низових пожеж у результаті як часткового, так і повного згорання підстилки утворюється попіл, що в подальшому впливає на хімізм верхнього шару ґрунту. Подібні особливості відзначали в різних природних зонах України. Надходження попелу в ґрунт призводило до зростання рН верхнього гумусового горизонту. Оскільки таке явище є одноразовим, то в подальшому після дощів значення рН водного витягу знижувалося до природнього рівня. Причиною пірогенних змін є високий уміст у попелі лужних металів. Інтенсивність змін реакції та вмісту лужних катіонів залежить від рівня згорання підстилки. Найбільш відчутними є зміни у разі повного згорання підстилки. Зазначені зміни мають поверхневий характер, тобто переважно притаманні лише верхньому шару ґрунту. На більшій глибині реакція не відрізняється від контролю.

Прогнозування постпірогенного відпаду в сосняках, пошкоджених літніми низовими пожежами, у Лівобережному Лісостепу України

Пожежі є одними із найнебезпечніших чинників дестабілізації лісів. У зв’язку зі зростанням посушливості клімату ризик збільшення частоти й масштабів лісових пожеж залишається високим, тому актуальним є розроблення науково обґрунтованих заходів із пом’якшення екологічних, економічних та соціальних наслідків лісових пожеж. Удосконалено та уточнено показники, що характеризують візуальні прояви пошкодження дерев після низових пожеж, та показники вогнестійкості середньовікових дерев сосни звичайної (Pinus sylvestris L.). Виявлено, що в міру збільшення середньої висоти нагару на стовбурах зростає частка відпаду в досліджуваних групах дерев (r = 0,87, tф = 5,80, t0,01 = 3,17). Встановлено, що вогнестійкість дерев збільшується зі збільшенням природного ступеня товщини дерева в насадженні (виявлено обернений достовірний кореляційний зв’язок між природним ступенем товщини (ПСТ) і категорією санітарного стану пошкоджених дерев: (r = -0,54; р = 0,05). Розроблено прогностичну модель для встановлення ймовірності відпаду дерев, пошкоджених низовими стійкими літніми пожежами, яка як предиктори включає середню висоту нагару на стовбурах та ПСТ (точність прогностичної моделі становить понад 78 %).

Основні показники вогнестійкості сосни звичайної в умовах Лівобережного Лісостепу

Метою дослідження є визначення основних морфометричних показників вогнестійкості дерев сосни звичайної в умовах свіжого субору Лівобережного Лісостепу та їхніх вікових змін. На відміну від пожежостійкості, вогнестійкість визначає ступінь потенційної спроможності дерева зберігати свою життєдіяльність на індивідуальному рівні після пірогенних пошкоджень. Виявлено, що верхня межа розташування грубої кори найбільше залежить від діаметра (r = 0,97) та віку дерев (Ff = 83,2, Fst = 1,8). Визначено, що товщина кори на всіх висотах заміру зазвичай є більшою в дерев із більшою висотою верхньої межі розташування грубої кори, в зоні переходу грубої кори в тонку вона становить 0,1–0,9 мм. Товщина кори в окоренковій частині дерев сосни звичайної в 10–15 разів перевищує товщину кори в тріщинах, де вона становить 1,5–5,8 мм, тому під час низових пожеж є ризик локального ураження камбію вздовж тріщин. Враховуючи отримані результати, було розроблено статистично-математичну модель, за якою можна оцінювати висоту верхньої межі розташування грубої кори дерев у сосняках.

Fire regimes and structural changes in oak-pine forests of the Mogollon Highlands ecoregion: Implications for ecological restoration

Ponderosa pine (Pinus ponderosa) forests occur at their warmer, drier environmental limits in the Mogollon Highlands ecoregion (MHE) of the Southwestern United States, and are commonly found in stringers or discrete stands that form ecotones with interior chaparral. These “rear edge” forests are likely to be highly vulnerable to rapid changes in structure and composition with climate warming, drought, and wildfire. There is increasing interest in understanding historical conditions, ecosystem changes, and restoration needs for MHE forests. However, comprehensive reconstruction analysis of fire regimes and stand structure has not been done for these systems, which differ from many montane ponderosa pine forests by having an abundance of understory shrubs. In this study we used demographic data from field plots, fire scar samples, and dendroecology to reconstruct historical fire regimes and landscape structure at ponderosa pine-dominated sites that spanned a range of environmental conditions on the Prescott and Tonto National Forests. We found strong evidence of historical surface fire regimes with mean fire intervals ranging 1.3–15.6 years across the five MHE sites during the period 1700–1879. We found very little evidence of historical high-severity fire at any study site. Historical forest structure was open with tree densities ranging 84.7–136.4 trees ha−1 and stand basal area (BA) ranging 4.5–8.4 m2 ha−1. Historical composition showed codominance of ponderosa pine, Arizona white oak (Quercus arizonica), Emory oak (Q. emoryi), and Gambel oak (Q. gambelii). Thus, oak species and likely other hardwoods were important historical components of these ecosystems. Contemporary forests are greater in stand density and BA by 359–703% and 285–502%, respectively, compared to historical estimates. In addition, we observed contemporary shifts in species composition. Changes related to disruption of historical fire regimes have increased susceptibility of ponderosa pine forests in the MHE to rapid shifts in structure and composition that may come about with climate change and high-intensity wildfire. Meeting fuels reduction and ecological restoration goals will be challenging for land managers due to vigorous regeneration responses of shrubs to tree thinning, prescribed burning, or other management activities. Managers will be required to balance attention to historical reference conditions, conservation of biological diversity, and needs for fuels management.

The Genetic Mechanism of Inertinite in the Middle Jurassic Inertinite-Rich Coal Seams of the Southern Ordos Basin

Inertinite is an important type of organic maceral in coal deposits, andalso an important geological information carrier of coal forming environments. In the southern section of the Ordos Basin, the No. 4 inertinite-richcoal seam of the Middle Jurassic Yan’an Formation in the Binchang Coalfield was selected as an example to study the genetic mechanism of theinertinite. In this study, the results obtained from experimental tests ofcoal rock, including principal and trace elements, stable carbon isotopes,scanning electron microscopy, inertinite reflectance, sporopollen andfree radical retorting methods, were analyzed. Then, the findings werecombined with the previous understanding of the oxygen content in theatmosphere and ground fire characteristics, in order to discuss the genesismechanism of inertinite in the No. 4 coal seam. The obtained researchresults were as follows: (1) During the coal forming period of the No. 4coal seam, the overall climate had been relatively dry. There were fourrelatively dry-wet climate cycles in the No.4 coal seam, which werecontrolled by the eccentricity astronomical period. The inertinite contentwere relatively high during the dry periods; (2) The temperature rangesuitable for microorganism activities during the oxidation processes wasbetween 0 and 80℃ . The simulation results of the free radical concentrations showed that the maximum temperature of fusain in the No. 4 coalseam during the process of coalification had not exceeded 300℃ , whichwas significantly higher than the temperature range of microorganismactivities. Therefore, these were not conducive to the activities of microorganism and formation of inertinite during the coal-forming period;(3) The genesis temperature of the inertinite in the No. 4 coal seam wascalculated according to the reflectance of the inertinite, which was lowerthan 400 ℃ . This result supported the cause of wildfire of the inertiniteand reflected that the type of wildfire was mainly ground fire, along withpartially surface fire. Moreover, the paleogeographic location, climaticconditions, atmospheric oxygen concentration, etc. of the study areashowed that the conditions for wildfire events were in fact available; (4)There were dense and scattered fusinite observed in the No. 4 coal seam,and the thickness of cell walls were found to differ. It was speculated thatthis was related to the type of wildfire, combustion temperatures, combustion timeframes, and different initial conditions of the burned objectsduring the coal forming periods.

Influence of canopy openness, ungulate exclosure, and low-intensity fire for improved oak regeneration in temperate Europe.

Failed oak regeneration is widely reported in temperate forests and has been linked in part to changed disturbance regimes and land‐use. We investigated if the North American fire–oak hypothesis could be applicable to temperate European oaks (Quercus robur, Quercus petraea) using a replicated field experiment with contrasting canopy openness, protection against ungulate browsing (fencing/no fencing), and low‐intensity surface fire (burn/no burn). Survival, relative height growth (RGRH), browsing damage on naturally regenerated oaks (≤300 cm tall), and changes in competing woody vegetation were monitored over three years. Greater light availability in canopy gaps increased oak RGRH (p = .034) and tended to increase survival (p = .092). There was also a trend that protection from browsing positively affected RGRH (p = .058) and survival (p = .059). Burning reduced survival (p < .001), nonetheless, survival rates were relatively high across treatment combinations at the end of the experiment (54%–92%). Most oaks receiving fire were top‐killed and survived by producing new sprouts; therefore, RGRH in burned plots became strongly negative the first year. Thereafter, RGRH was greater in burned plots (p = .002). Burning altered the patterns of ungulate browsing frequency on oaks. Overall, browsing frequency was greater during winter; however, in recently burned plots summer browsing was prominent. Burning did not change relative density of oaks, but it had a clear effect on competing woody vegetation as it reduced the number of individuals (p < .001) and their heights (p < .001). Our results suggest that young, temperate European oaks may respond similarly to fire as their North American congeners. However, disturbance from a single low‐intensity fire may not be sufficient to ensure a persistent competitive advantage—multiple fires and canopy thinning to increase light availability may be needed. Further research investigating long‐term fire effects on oaks of various ages, species‐specific response of competitors and implications for biodiversity conservation is needed.

Formation of stable aqueous foams on the ethanol layer: Synergistic stabilization of fluorosurfactant and polymers

The extreme instability of aqueous foams on the ethanol layer is an important issue to consider in the application of fire-fighting foams. We attempt making stable aqueous foams on the ethanol layer by using sodium dodecyl sulfate (SDS) as the foamer, with fluorosurfactant (FC1157) and xanthan gum polymers (XG) as the stabilizing agents. The surface properties, foam stability, and fire extinguishing performance of our studied systems were investigated respectively. The results show that ethanol destroys aqueous foams by dehydration and polar ethanol has a more significant defoaming effect than non-polar heptane. XG and FC1157 can inhibit the adverse effects of ethanol on foam stability. The addition of FC1157 improves the stability of the foam films and slows down the ethanol-induced dissolution of foams. XG polymers tend to form a gel-like membrane at the foam/ethanol interface, minimizing the mass transfer between foam and ethanol. The lifetime of foam stabilized by FC1157/ XG is much longer than that of foam stabilized by FC1157 or XG alone in the presence of ethanol. Foams can go from unstable foams to foams being stabilized by both XG membrane and FC1157 synergistically. As a result, the synergism of FC1157 and XG in stabilizing foams significantly enhances the fire extinguishing performance of foam.

Fluorescence procedures to assess the photosynthetic resilience in Scots pines after a surface fire

Forest fire represents one of the most serious abiotic stress factors that influence the function and productivity of ecosystems globally. Siberian pine forests are often exposed to forest fires but they are not always harmful to them. We have analyzed the effects of repeated heat stress on the photosynthetic apparatus of Scotch pines before and after surface fire exposure that occurred in the growing season in 2014. The survey area was the forest steppe zone of Krasnoyarsk region (South Siberia). First, we investigated the changes in the temperature-dependent responses of photosynthesis in the needles by means of fast and delayed chlorophyll fluorescence. Our results are indicative of some acclimation of Scotch pines after fire to the repeated high temperature stress. Also, this paper discusses the possibility of using chlorophyll fluorescence parameters for evaluating the presence of physiological changes after the fire affects. The time after fire effect and growth season were found to be important to assess the repair of photosynthesis and pigment content.

A convective–radiative propagation model for wildland fires

The ‘Balbi model’ is a simplified steady-state physical propagation model for surface fires that considers radiative heat transfer from the surface area of burning fuel particles as well as from the flame body. In this work, a completely new version of this propagation model for wildand fires is proposed. Even if, in the present work, this model is confined to laboratory experiments, its purpose is to be used at a larger scale in the field under operational conditions. This model was constructed from a radiative propagation model with the addition of a convective heat transfer term resulting from the impingement of packets of hot reacting gases on unburnt fuel elements located at the base of the flame. The flame inside the fuel bed is seen as the ‘fingers of fire’ described in the literature. The proposed model is physics-based, faster than real time and fully predictive, which means that model parameters do not change from one experiment to another. The predicted rate of spread is applied to a large set of laboratory experiments (through homogeneous pine needles and excelsior fuel beds) and is compared with the predictions of both a very simple empirical model (Catchpole) and a detailed physical model (FireStar2D).

Study of High-capacity Foam Discharging Systems for Full Surface Fire of Big Oil Tanks

Study of High-capacity Foam Discharging Systems for Full Surface Fire of Big Oil Tanks

3D modeling of coupled soil heat and moisture transport beneath a surface fire

Understanding the soil heat and moisture transport is significant for assessing the living condition of vegetation and microorganisms in soils. Numerous studies have been conducted to understand the coupled soil heat and moisture transport under “normal” environmental conditions; while this coupled transport under extremely high-temperature conditions caused by surface wildfires is little understood. Particularly, 3D modeling of such coupled transport is absent. Here, we develop a 3D model to understand more realistic characteristics of the soil heat and moisture transport beneath a surface fire. With the 3D model, we investigate the lateral transport of soil heat and moisture in a 3D space, the influence of a surface fire on soil moisture and temperature conditions in neighboring regions without fires, and the effect of initial water contents on the delay of soil heating. The modeling results showed that the lateral transport leads to an obvious difference in soil temperature and moisture between the inside and border area of the fire region. Such a difference cannot be considered with a 1D model widely used in existing studies. For the initial water content effect, we confirmed that a high initial water content delays the soil heating to cooler regions at deeper soil depths during the late stage of soil heating. Our results also showed that a surface fire significantly changes soil heat and moisture in the no-fire region neighboring to the simulated fire. At the location 50 m away from the fire region, the soil temperature and moisture in upper soil layers can increase to over 85 °C and decrease to 0.006 m3 m−3 within 5 h, respectively. This study provides important insights, which are useful for fire management but have not been reported before, for understanding more physically realistic characteristics of the 3D soil heat and moisture transport beneath a surface fire in both the fire and no-fire regions.

Study on quality characteristics of cassava flour and cassava flour short biscuits.

In this paper, the basic components, nutrient composition, and processing characteristics of cassava flour were determined. In addition, the effects of xanthan gum and inulin on the pasting properties, microstructure, and thermal properties of cassava flour were studied. Biscuits were prepared using cassava flour as the main raw material and the optimal technology and formula for the biscuits were determined by single‐factor and orthogonal tests. The effects of xanthan gum and inulin on the quality of cassava flour short biscuits were also investigated, and volatile components in the biscuits were determined using electronic nose technique. The addition of xanthan gum improved the pasting properties and microstructure of cassava flour, and improved the taste and increased hardness and brittleness of the biscuits, making their quality similar to that of commercially available short biscuits. The addition of inulin inhibited the setback of starch and improved starch gelatinization. However, inulin was not suitable for processing of cassava flour biscuits as it decreased their hardness, brittleness, and taste. The optimal formula and baking conditions of cassava flour short biscuits were as follows: cassava flour 100 g, water 24 g, shortening 25 g, sugar 30 g, baking powder 0.6 g, salt 1 g, and egg 25 g; the surface fire and primer fire temperatures were 180°C, and the baking time was 9 min. In addition, although the main aroma volatile components present in cassava flour and low gluten wheat flour short biscuits were similar, the proportions of each component were different.

Cambio postincendio en la estructura y composición del estrato arbóreo y carga de combustibles en un bosque de Pinus douglasiana de México

En los bosques de pino con un régimen histórico de incendios superficiales frecuentes de baja severidad, bajo condiciones extremas del estado del tiempo o a consecuencia de la supresión del fuego, la severidad de los incendios puede incrementar. La respuesta de la vegetación a eventos de incendios severos se estudió en una cronosecuencia postincendio de 8 años, 28 años y 60 años en un bosque dominado por Pinus douglasiana en México. La densidad de árboles con diámetro &gt; 2.5 cm y su área basal alcanzaron valores de 1095 árboles ha-1 ± 609 árboles ha-1 y 10.0 m2 ha-1 ± 2.2 m2 ha-1 a los 8 años; a los 28 años el área basal (44.6 m2 ha-1 ± 3.0 m2 ha-1) fue cercana a la de los rodales de 60 años (49.0 m2 ha-1 ± 6.4 m2 ha-1). Los pinos mantuvieron el mayor valor de importancia con el tiempo postincendio, se observó la formación de un subdosel de latifoliadas tolerantes a la sombra y un aumento en la riqueza y diversidad de especies; también se documentó que periodos largos sin incendios incrementan la carga de combustibles superficiales ligeros (66.0 Mg ha-1 ± 5.5 Mg ha-1 en los sitios de 28 años y 61.5 Mg ha-1 ± 4.6 Mg ha-1 en los sitios de 60 años) y modifican el comportamiento del fuego (velocidad de propagación de 1.3 m s-1 a 4.1 m s-1 y la longitud de la llama de 0.7 m a 1.7 m entre los rodales de 8 años y los de 28 años y 60 años combinados). El manejo de los bosques de pino debe considerar el balance entre objetivos de conservación biológica y mitigación del peligro de incendios de alta severidad.

Integrating fire effects on vegetation carbon cycling within an ecohydrologic model

Wildfire affects landscape ecohydrologic processes through feedbacks between fire effects, vegetation growth and water availability. Despite the links between these processes, fire is rarely incorporated dynamically into ecohydrologic models, which couple vegetation growth with water and nutrient fluxes. This omission has the potential to produce inaccurate estimates of long-term changes to carbon and water cycling in response to climate change and management. In this study, we describe a fire-effects model that is coupled to a distributed ecohydrologic model, RHESSys, and a fire-spread model, WMFire. The fire-effects model has intermediate structural complexity so as to be commensurate with the ecohydrologic model. The fire-effects model includes processes for litter and coarse woody debris consumption, processes for fire-associated vegetation mortality and consumption, and takes into account canopy structure (i.e. ladder fuels) for propagation of fire effects into a forest canopy. We evaluated the model in four Western U.S. sites representing different vegetation, climate, and fire regimes. The fire-effects model was able to replicate patterns of expected fire effects across different ecosystems and stand ages without being tuned to produce them; an emergent property of the model. Fire effects of shrubland and understory vegetation varied with surface fire intensity, by design, and fire effects in forest canopies were sensitive to parameters associated with the buildup of litter and understory ladder fuels. These findings demonstrate that the fire-effects model provides an effective tool for evaluating the post-fire changes to physical and ecological processes. Future work will project future fire regimes and improve understanding of watershed dynamics under climate change and land management via the simulation of the fire-effects model with fire spread and ecohydrology.

Can wildland fire management alter 21st‐century subalpine fire and forests in Grand Teton National Park, Wyoming, USA?

In subalpine forests of the western United States that historically experienced infrequent, high-severity fire, whether fire management can shape 21st-century fire regimes and forest dynamics to meet natural resource objectives is not known. Managed wildfire use (i.e., allowing lightning-ignited fires to burn when risk is low instead of suppressing them) is one approach for maintaining natural fire regimes and fostering mosaics of forest structure, stand age, and tree-species composition, while protecting people and property. However, little guidance exists for where and when this strategy may be effective with climate change. We simulated most of the contiguous forest in Grand Teton National Park, Wyoming, USA to ask: (1) how would subalpine fires and forest structure be different if fires had not been suppressed during the last three decades? And (2) what is the relative influence of climate change vs. fire management strategy on future fire and forests? We contrasted fire and forests from 1989 to 2098 under two fire management scenarios (managed wildfire use and fire suppression), two general circulation models (CNRM-CM5 and GFDL-ESM2M), and two representative concentration pathways (8.5 and 4.5). We found little difference between management scenarios in the number, size, or severity of fires during the last three decades. With 21st-century warming, fire activity increased rapidly, particularly after 2050, and followed nearly identical trajectories in both management scenarios. Area burned per year between 2018 and 2099 was 1,700% greater than in the last three decades (1989-2017). Large areas of forest were abruptly lost; only 65% of the original 40,178ha of forest remained by 2098. However, forests stayed connected and fuels were abundant enough to support profound increases in burning through this century. Our results indicate that strategies emphasizing managed wildfire use, rather than suppression, will not alter climate-induced changes to fire and forests in subalpine landscapes of western North America. This suggests that managers may continue to have flexibility to strategically suppress subalpine fires without concern for long-term consequences, in distinct contrast with dry conifer forests of the Rocky Mountains and mixed conifer forest of California where maintaining low fuel loads is essential for sustaining frequent, low-severity surface fire regimes.

Spatial model of peatland fire control strategies through peat maturity level approach: Case Study of the Kepulauan Meranti District

Tropical peatland in Indonesia is the largest in the world. Approximately 30% of the area potentially can be converted into agriculture and plantations. However, it is very susceptible to forest fires due to agricultural land preparation. The practice of burning forests is done because of some reasons namely fast, inexpensive, and produced ash that will fertilize the soil. The impact of land and forest fires is very large both in terms of economic, social, and environmental. Fires on peat lands consist of crown fire, surface fire, and ground fire which have a severe impact on environmental, social and economic impacts. In terms of management, it is also more difficult and longer time compares to fires on mineral land. The main objective of this paper is to use spatial modeling to provide an early warning system for forest fires on peat lands based on peat maturity level approaches. Physical data, which include the level of maturity, peat thickness, land unit, and land cover will be considered as an independent variable. Meranti Islands District, Riau Province is selected as a case area. The spatial analysis was carried out on physical aspects and the distribution of hotspots that had a level of confidence greater than 80%. The results showed that identification of potential fires through peat maturity levels, cannot be used optimally because peat areas that have different levels of maturity are not separate polygons or still in atribut form., The land cover of shrubs should be a major concern in the identification of potential fires.

Increase of fire protection and strength of wooden structures by modification in a thin surface layer by nanodispersion composites

Currently, the industrial construction of multi-storey houses of wooden structures (DK) is increasing. In world practice, multi-storey buildings from a recreation center are being built in Austria, Great Britain, Norway, and Canada. In Russia, 9-13 storey buildings are being designed using a recreation center. High-rise construction using a recreation center for earthquake-prone areas is especially relevant. For modern multi-story building from a recreation center, effective surface fire protection should not increase the weight of structures. At the same time, their strength should increase. The solution of complex issues of DC fire protection in thin layers with a simultaneous increase in its strength is an unresolved problem.

Fire Survival of Longleaf Pine (Pinus palustris) Grass Stage Seedlings: The Role of Seedling Size, Root Collar Position, and Resprouting

Longleaf pine (Pinus palustris Mill.) forest is a well-known fire-dependent ecosystem. The historical dominance of longleaf pine in the southeast United States has been attributed to its adaptation known as the grass stage, which allows longleaf pine seedlings to survive under a frequent surface fire regime. However, factors affecting post-fire survival of grass stage seedlings are not well understood. In this study, we measured live and dead longleaf pine grass stage seedlings to quantify the role of seedling size, root collar position, and sprouting in seedling survival following a wildfire in the sandhills of South Carolina. We found that fire resulted in almost 50% mortality for longleaf pine grass stage seedlings. Fire survival rate increased with seedling size, but a size threshold for fire tolerance was not supported. Fire survival depended on the position of root collar relative to the mineral soil. Seedlings with protected root collars (i.e., buried in or at the level of mineral soil) experienced &lt;21%, while seedlings with exposed root collars (i.e., elevated above mineral soil) suffered &gt;90% post-fire mortality. Ability to resprout contributed to 45.6% of the total fire survival, with the small seedlings (root collar diameter (RCD) &lt; 7.6 mm) almost exclusively depending on resprouting. Our findings had significant implications for fire management in longleaf pine ecosystems, and the current frequency of prescribed fire in sandhills might need to be lengthened to facilitate longleaf pine natural regeneration.

Wildfire Detection Using Sound Spectrum Analysis Based on the Internet of Things.

Wildfire is a sudden and hazardous natural disaster. Currently, many schemes based on optical spectrum analysis have been proposed to detect wildfire, but obstacles in forest areas can decrease the efficiency of spectral monitoring, resulting in a wildfire detection system not being able to monitor the occurrence of wildfire promptly. In this paper, we propose a novel wildfire detection system using sound spectrum analysis based on the Internet of Things (IoT), which utilizes a wireless acoustic detection system to probe wildfire and distinguish the difference in the sound between the crown and the surface fire. We also designed a new power supply unit: tree-energy device, which utilizes the biological energy of the living trees to generate electricity. We implemented sound spectrum analysis on the data collected by sound sensors and then combined our classification algorithms. The results describe that the sound frequency of the crown fire is about 0–400 Hz, while the sound frequency of the surface fire ranges from 0 to 15,000 Hz. However, the accuracy of the classification method is affected by some factors, such as the distribution of sensors, the loss of energy in sound transmission, and the delay of data transmission. In the simulation experiments, the recognition rate of the method can reach about 70%.

Lacustrine charcoal peaks provide an accurate record of surface wildfires in a North European boreal forest

We evaluated the skills of different palaeofire reconstruction techniques to reconstruct the fire history of a boreal landscape (Russian Karelia) affected by surface fires. The analysis of dated lacustrine sediments from two nearby lakes was compared with independent dendrochronological dating of fire scars, methods which have rarely been used in context of surface fires. We used two sediment sub-sampling volumes (1 and 3.5 cm3, wet volumes) and three methods of calculating the Charcoal Accumulation Rate to reconstruct fire histories: CHAR number, charcoal surface area and estimated charcoal volume. The results show that palaeofire reconstructions obtained with fossil charcoal data from lake sediments and dendrochronology are similar and complementary. Dendrochronological reconstruction of fire scars established 12 fire dates over the past 500 years, and paleo-data from lake sediments identified between 7 and 13 fire events. Several ‘false fire events’ were also recorded in the charcoal chronologies, likely because of errors associated with the estimation of the sediment accumulation rate in the unconsolidated part of the sediment. The number of replicates, that is, number of sub-samples and lakes analyzed, had an effect on the number of identified fire events, whereas no effect was seen in the variation in the analyzed sediment volume or the choice of the charcoal-based metric. Whenever possible, we suggest the use of the dendrochronological data as an independent control for the calibration of charcoal peak series, which helps provide more realistic millennia-long reconstruction of past fire activity. We also argue for the use of 1 cm3sample volume, a sampling protocol involving sampling of more than one lake, and sufficient number of intra-sample replicates to achieve skilful reconstructions of past fire activity.