Bark Char Research Articles

The Interacting Influence of Fire and Tree Characteristics on Douglas-Fir Beetle Host-Tree Selection Five Years Post-Fire

Fire injury stresses Douglas-fir trees (Pseudotsuga menziesii) that survive a wildfire event, allowing subsequent Douglas-fir beetle (Dendroctonus pseudotsugae) infection to kill trees that may have otherwise survived. This study aimed to determine how fire injury, stand, and tree characteristics drive Douglas-fir beetle host tree selection five years post-fire. We paired 28 adjacent beetle-infected and uninfected stands (infected N = 14) and 140 Douglas-fir trees (infected N = 70) within the 416 Fire burn area in Southwest Colorado. We found no statistically significant differences between infected and uninfected stand characteristics. Individual tree height, DBH, and bark char severity index were significantly higher in infected versus uninfected trees. We created a regression decision tree model to determine the influence of fire injury and tree characteristics on the probability of infection. Trees with a height ≥ 27 m, bark char height < 2.3 m, and DBH < 80 cm had the greatest probability of attack (100%). Trees with a height < 27 m, bark char severity index < 5.5, and DBH < 49 cm had the lowest probability of attack (3.7%). Understanding the influence of fire on Douglas-fir beetle host selection allows land managers to model potential epidemic outbreaks and guide proactive management actions that may reduce beetle outbreak severity or preserve high-value trees not killed by fire.

Co-gasification of biomass and oil shale under CO2 atmosphere: Comparative analysis of fixed-bed reactor, gas chromatography and thermogravimetric analysis coupled with mass spectroscopy (TGA-MS)

Co-gasification of biomass with oil shale offers potential for integrating renewable and fossil energy sources, reducing reliance on fossil fuels. Biomass (pine and birch wood and bark) and oil shale blends (10–30 wt%) were gasified under CO2 conditions using thermogravimetric analysis coupled with mass spectrometry (TGA-MS), fixed-bed reactor, and gas chromatography. Results revealed an interaction between oil shale and biomass, enhancing CO and CH4 concentrations in the producer gas. Bark samples demonstrated higher CO concentrations compared to wood samples, particularly in pine, with 16.1 vol% and 5.4 vol%, respectively. While birch wood showed increased H2 evaporation in TGA-MS experiments, oil shale's impact on H2 concentration was inhibitive, as shown by quantitative analysis. Pine bark, with a threefold catalytic index compared to other biomass samples, demonstrated the highest total gas concentrations (19.2 vol%). Interestingly, pine bark char blends exhibited the lowest surface areas (up to 434 m2/g) among the tested samples.

Predictive accuracy of post-fire conifer death declines over time in models based on crown and bole injury.

A key uncertainty of empirical models of post-fire tree mortality is understanding the drivers of elevated post-fire mortality several years following fire, known as delayed mortality. Delayed mortality can represent a substantial fraction of mortality, particularly for large trees that are a conservation focus in western US coniferous forests. Current post-fire tree mortality models have undergone limited evaluation of how injury level and time since fire interact to influence model accuracy and predictor variable importance. Less severe injuries potentially serve as an indicator for vulnerability to additional stressors such as bark beetle attack or moisture stress. We used a collection of 164,293 individual tree records to examine post-fire tree mortality in eight western USA conifers: Abies concolor, Abies grandis, Calocedrus decurrens, Larix occidentalis, Pinus contorta, Pinus lambertiana, Pinus ponderosa, and Pseudotsuga menziesii. We evaluated the importance of fire injury predictors on discriminating between surviving trees versus immediate and delayed post-fire mortality. We fit balanced random forest models for each species using cumulative tree mortality from 1 to 5-years post-fire. We compared these results to multi-class random forest models using first-year mortality, 2-5-year mortality, and survival 5-years post-fire as a response variable. Crown volume scorched, diameter at breast height, and relative bark char height, were used as predictor variables. The cumulative mortality models all predicted trees that died within 1-year of fire with high accuracy but failed to predict 2-5-year mortality. The multi-class models were an improvement but had lower accuracy for predicting 2-5-year mortality. Multi-class model accuracies ranged from 85% to 95% across all species for predicting 1-year post-fire mortality, 42%-71% for predicting 2-5-year mortality, and 64%-85% for predicting trees that lived past 5-years. Our study highlights the differences in tree species tolerance to fire injury and suggests that including second-order predictors such as beetle attack or climatic water stress before and after fire will be critical to improve accuracy and better understand the mechanisms and patterns of fire-caused tree death. Random forest models have potential for management applications such as post-fire harvesting and simulating future stand dynamics.

Differential Post-Fire Recovery of Tree and Shrub Growth and Water-Use Efficiency in a Mediterranean Coastal Dune System

Assessing post-fire recovery is essential to forecast how ecosystems will respond to future warmer conditions and higher fire severity. Such assessments must consider site conditions and the post-fire recovery of trees and shrubs. We used tree-ring data and intrinsic water-use efficiency (WUEi) to quantify the post-fire responses of a tree (Pinus pinea) and a shrub (Juniperus phoenicea) in Mediterranean coastal dunes located in the Doñana protected area, SW Spain. We compared pines and junipers growing in an inter-dune slack with those growing in a nearby dune ridge. We quantified crown damage and bark char in pines impacted by a wildfire. Pines with lower crown damage after the fire showed a higher growth rate one year later. Growth decreased afterwards in the case of fast-growing pines from the slack site, whereas slow-growing dune pines showed increasing growth rates one to three years after the fire. The fire did not change the pines’ WUEi, whereas the junipers located in dunes presented the highest WUEi values. Severe crown damage (damage > 60%) impairs long-term growth recovery in P. pinea. Open and heterogeneous landscapes can reduce the wildfire risk in the study Mediterranean area, where slack vs. dune and tree vs. shrub differences should be considered in post-fire management plans.

Improving Coastal Plain Hardwoods for Deer and Turkeys with Canopy Reduction and Fire

ABSTRACTPrescribed fire and canopy reduction are accepted forest management practices used to increase forage and cover for white‐tailed deer (Odocoileus virginianus) and wild turkeys (Meleagris gallopavo) in pine systems throughout the southeastern United States. However, use of prescribed fire to improve conditions for deer and turkeys has not been evaluated in upland hardwood forests of the Coastal Plain, and some land managers remain skeptical of the utility of fire in this ecoregion. We designed a manipulative experiment to measure deer and turkey habitat components following canopy reduction and prescribed fire in 4 upland hardwood stands in the Coastal Plain of Alabama, USA, during 2018 and 2019. Specifically, we used herbicide to kill trees with low value to deer and turkeys and retained oaks (Quercus spp.) and other species considered important as part of a forest stand improvement (FSI) operation to reduce canopy coverage. We then applied low‐intensity prescribed fire to half of each treatment unit. One unit in each replicate served as a control. We measured total understory plant coverage, biomass of deer forage, and turkey brooding cover for 2 years following canopy reduction and one year after fire. Coverage of herbaceous plants increased by 134% in FSI/Burn, and coverage of woody and semiwoody plants increased by 33% and 97%, respectively, following FSI only. Deer forage biomass was greater in both FSI and FSI/Burn compared to control, but there was no difference in deer forage biomass between FSI and FSI/Burn. FSI/Burn provided better turkey brooding cover than FSI or control. No overstory trees were killed by fire. We detected minor cambium damage to 13% of water oaks (Quercus nigra) in the FSI/Burn units; other species only showed light bark charring or no sign of burning. We recommend FSI and low‐intensity prescribed fire in Coastal Plain hardwoods to improve brooding cover for turkeys and understory forage for deer while retaining acorn production. © 2020 The Wildlife Society.

Spatial patterns of nineteenth century fire severity persist after fire exclusion and a twenty-first century wildfire in a mixed conifer forest landscape, Southern Cascades, USA

Spatial patterns of fire severity are influenced by fire-vegetation patch dynamics and topography. Since the late nineteenth century, fire exclusion has increased fuels and recent fire severity patterns may diverge from historical patterns. We used data from a 2008 wildfire burning in a landscape with known nineteenth century fire severity patterns to answer the following questions: (1) Were the spatial patterns of fire severity and fire effects after the 2008 fire similar to those in the late nineteenth century? (2) What factors were most important in controlling spatial patterns of fire severity in 2008? Fire severity patterns in the late nineteenth century were identified by Beaty and Taylor (J Veg Sci 18:879, 2001) using dendroecology. Plots were remeasured after the 2008 fire and geospatial layers of vegetation type, topography, fire weather, daily fire extent and fire severity were used to identify controls on 2008 fire severity. Fire severity in 2008 varied in ways similar to the nineteenth century. Tree mortality and bark char in plots were lowest on lower slopes and southwest facing slopes, intermediate on middle slopes, and highest on upper slopes and northeast slopes. At the landscape scale, vegetation type, elevation, slope aspect, slope position and weather were the variables controlling fire severity. Spatial patterns of fire severity persisted, despite more than a century of fire exclusion. Our findings suggest that wildfires burning under moderate conditions even with a warming climate can help reduce the fire deficit and promote forest resilience in fire prone landscapes.

Пожежостійкість і постпірогенний відпад соснових лісів лівобережної частини Харківської області за різних рівнів пожежної небезпеки за умовами погоди

Пожежі є одними з найнебезпечніших чинників дестабілізації лісів. Визначення особливостей постпірогенного розвитку сосняків дає змогу пом’якшити негативні наслідки, спричинені лісовими пожежами, та допомогти в прийнятті рішень стосовно ведення господарства в таких лісах. Виявлено, що санітарний стан насаджень залежав від значення комплексного показника пожежної небезпеки (КППН) на момент пожежі та погіршувався у міру його збільшення (r = 0,71; p = 0,05). За вищих значень КППН підвищуються інтенсивність тепловиділення під час пожежі та ступінь вигорання лісової підстилки. Встановлено, що за КППН від 1 500 до 3 000 балів індекс санітарного стану насаджень варіює від II,0 до III,9; частка відпаду сягає 20 %. За подальшого збільшення значень КППН понад 5 000 балів індекс стану насадження через рік після пожежі становить III,5–V,0. З’ясовано, що висота полум’я та висота нагару на стовбурах достовірно не залежать від рівня пожежної небезпеки за умовами погоди. Вдосконалено підходи до прогнозування постпірогенного відпаду на рівні насадження з урахуванням характеристик пожежонебезпечного сезону, ступеня пошкодження дерев у насадженні та його таксаційних характеристик.

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 %).

Reduction Study of Iron Ore Pellets with Wooden Bark Char

In the process of iron making reduction of iron ores to metallic iron is done by coke which acts as a reluctant. As, both the reduction process, conventional blast furnace and DRI technologies are driven by the Boudouard reaction, so there is a probability for substituting of coal/coke with biochars, which could provide a good source of carbon and energy for the reduction. Hence, the utilization of bio char can become an emerging technology and better option for replacing coking coal for metallurgical purposes. This study includes characterization and comparative study of reduction of Iron ore pellets and fines using Wooden Bark Char (WBC) as one of the biomass waste. From the results, reduction of iron-ore fines with comparable ratios with WBC gives the maximum degree of reduction than reduction of iron-ore pellets. Thus, WBC can play an important role in behind the premium quality of coking coal reserves.

The influence of surface fire on radial and height growth of Pinus sylvestris L. in forest-steppe in Ukraine

Abstract The article presents the results of the research on the peculiarity of response of Pinus sylvestris L. growth in height and diameter in young pine forest stand of the Left-Bank forest-steppe of Ukraine under the influence of surface fire that happened in May 2011. Forestry taxation, comparative ecology, standard dendrochronological methods were used. Response of trees was different for the height growth and the radial increment in the year of fire (2011). The radial growth got depressed in the year of fire; at the same time, the height of trees showed positive trend of growth against the background of favourable weather conditions. The growth in height was more ductile and completed its recovery to a particular level in 2014, unlike the radial growth, which recovered only in 2016. The relationships between radial growth on one side and stand sanitary state and height of bark char on the other were approximated by quadratic and cubic regression equations. Dynamics of pine growth depends on climatic factors also. Percentage of the late wood should be used to assess the condition of stands after fire. Research of post-pyrogenic development of forest ecosystems will allow more effective planning of forest management measures, and also allow the adjustment of the monitoring duration for pine forest stands damaged by fires.

An all-gluten biocomposite: Comparisons with carbon black and pine char composites

Three different charcoals (gluten char, pine bark char and carbon black) were used to rectify certain property disadvantages of wheat gluten plastic. Pyrolysis process of gluten was investigated by analysing the compounds released at different stages. Nanoindentation tests revealed that the gluten char had the highest hardness (ca. 0.5 GPa) and modulus (7.8 GPa) followed by pine bark char and carbon black. The addition of chars to gluten enhanced the indenter-modulus significantly. Among all the charcoals, gluten char was found to impart the best mechanical and water resistant properties. The addition of only 6 wt% gluten char to the protein caused a substantial reduction in water uptake (by 38%) and increase of indenter-modulus (by 1525%). It was shown that it is possible to obtain protein biocomposites where both the filler and the matrix are naturally sourced from the same material, in this case, yielding an all-gluten derived biocomposite.

Influence of H2O on NO formation during char oxidation of biomass

The present study investigates conversion of char-N to NO in mixtures of O2/N2 and in O2/H2O/N2. Biomass particles of spruce bark were combusted in an electrically heated single particle reactor at 900 °C at various O2/H2O/N2 concentrations. NO concentrations of the product gases were measured during the char combustion stage. The conversion of char-N to NO was significantly higher with H2O as compared to without H2O in the gas. Additional fixed bed experiments were conducted to investigate the products of the reaction between H2O and spruce bark char. The results showed that NH3 is the primary product in the reaction between char-N and steam. These results explain the observation that more NO is formed during char combustion in the presence of steam: the char-N reacts partly with H2O to form NH3, which reacts further to NO.

Ethanol and primary attraction of red turpentine beetle in fire stressed ponderosa pine

Trees injured and weakened by wild or prescribed fires are susceptible to bark beetle attacks. Nonaggressive Dendroctonus valens in North American forests is often the first bark beetle to colonize fire injured pine. Although not an important contributor to post-fire mortality it does vector pathogens, and surviving diseased trees may serve as pathogen redistribution centers. Traps baited with both ethanol and monoterpene lures are known to attract D. valens, and fire injured pine are known to accumulate ethanol in tissues containing monoterpenes. The primary objective of this study was to quantify ethanol concentrations in fire injured ponderosa pine tissue near pioneering D. valens gallery entrances and compare them with levels from the unattacked side of the same tree, or their unattacked neighbors. The secondary objective was to quantify α-pinene in the same samples. Two separate but related studies were conducted, one in a June wildfire, the other in an October prescribed fire, near Bend, Oregon, USA where phloem and sapwood cores were collected for analysis by headspace gas chromatography. Wildfire damaged trees attacked by D. valens were sampled above beetle gallery entrance holes and on the opposite bole side without an entrance hole. An adjacent unattacked tree of similar size and injury was sampled at the same aspect and height. Prescribed fire damaged trees were sampled in groups of three characterized by: (1) one or more D. valens attacks with 100% crown scorch; (2) unattacked with 100% crown scorch; and (3) unattacked with ≤95% crown scorch. They were sampled above a beetle gallery entrance or equivalent positions on unattacked trees. Ethanol and α-pinene concentrations at both fires were higher in tissues above beetle entrance holes than in corresponding tissues from unattacked sides of the same tree, or adjacent trees. Ethanol concentrations in wildfire damaged trees were three or more orders of magnitude greater than in prescribed fire trees, likely a consequence of wildfire trees experiencing higher temperatures and greater heat stress indicated by injury measurements. Ethanol concentrations in stem bark char, analyzed only in the prescribed fire were two to four orders of magnitude greater than in the underlying phloem, a result of it being adsorbed and concentrated during outward diffusion. Ethanol synthesis, accumulation, and atmospheric release in combination with host monoterpenes, is proposed as the critical physiological process contributing to initial D. valens host tree and bole position selection of fire stressed ponderosa pine.

Fire effects in Pinus uncinata Ram plantations

Aim of study: Understanding fire ecology of main forest species is essential for a sound, scientifically based on managing of wildlands and also to assess likely implications due to changes in fire regime under a global change scenario. Few references can be found about fire ecology of Pinus uncinata Ram. (PU). PU species grows in the Central Pyrenees where large, severe wildland fires did not occur frequently in the past. However, several fires with extreme fire behavior have affected PU stands in last years and they might disturb other PU forest in the future.Area of study: Cabdella fire (February 2012), in Lleida province, is one of the several wildland fires occurred in 2012 (winter season) in the Central Pyrenees. Fire affected a large PU plantation (102 ha) located at 1.800-2,100 meters above the sea.Material and methods: We have analyzed first order fire effects in three fireline intensity thresholds along three years in terms of mortality ratio, scorched height, percentage of scorched crown volume and bark char height.Main results: PU seems to be a very tolerant species to low and medium fire line intensity but fire effects were very significant when fire line intensity was high. In medium fireline intensity sites, probability of mortality ranged from 15 to 30% and the dead trees had the highest values on scorched height and percentage of scorched crown volume.Research highlights: Results from this work supports that prescribed burning might be used to efficiently decrease fuel load and fuel vertical continuity while avoiding considerable PU mortality. It also displayed that when fuel management has been implemented, PU mortality might be limited even under extreme fire behavior.Abbreviations used: PU: Pinus uncinata Ram.

A Quarter-Century of Change Without Fire: The High-Elevation Pitch Pine Community on Panther Knob, Pendleton County, West Virginia

The Panther Knob Preserve is important in the Central Appalachians because it is the region's largest high-elevation pitch pine (Pinus rigida) community, containing numerous rare and threatened plants and animals. Plant community structure and evidence of fire in 2008 were quantified to (a) document successional changes since 1985, and (b) test the hypothesis of pitch pine regeneration failure without recent fire. Diameter at breast height (dbh) of trees and percent cover of plants within 19 plots, each 20 × 20 m, were measured. Increment borings were used to estimate stand age, and evidence of fire, such as bark charring and soil charcoal, was recorded. Mineral soil from the top 10 cm was collected to evaluate the connection between soil characteristics and plant composition. Cluster analysis of percent cover values identified four plant community types. Diameter distributions, age structure, and the presence of only seven seedlings indicated little recent pine regeneration on the plateau. Comparisons with Fleming's (1985) observations showed that pines are taller but declined in percent cover, that ericaceous shrubs are denser, and that the threatened variable sedge, Carex polymorpha, has declined. Charred woody debris, fire scars, or soil charcoal occurred at 16 of 19 sites. Plant community structure, represented by nonmetric multidimensional scaling (NMS) ordination axes, was not correlated directly with the presence of fire evidence or soil mineral nutrients (principal components analysis [PCA] axes). A new conceptual model of pine dynamics on Panther Knob is introduced. Successional pathways with and without fire are discussed in the context of management.

Improved lignin pyrolysis for phenolics production in a bubbling bed reactor – Effect of bed materials

Lignin pyrolysis was studied in a bubbling fluidized bed reactor equipped with a fractional condensation train, using nitrogen as the fluidization gas. The effect of different bed materials (silica sand, lignin char, activated lignin char, birch bark char, and foamed glass beads) on bio-oil yield and quality was investigated for a pyrolysis temperature of 550°C.Results how that a bed of activated lignin char is preferable to the commonly used silica sand: pyrolysis of Kraft lignin with a bed of activated lignin char not only provides a pure char product, but also a higher dry bio-oil yield (with a relative increase of 43%), lower pyrolytic water production, and better bio-oil quality. The bio-oil obtained from Kraft lignin pyrolysis with a bed of activated lignin char has a lower average molecular weight, less tar, more phenolics, and less acidity than when sand is used as bed material.

Diversity of chemical composition and combustion reactivity of various biomass fuels

A simple and fast method for measuring simultaneously the chemical compositions and combustion reactivities of biomasses and evaluating their heterogeneity was developed using a commercial thermogravimetric analyzer. Wood, straw, and bark pellets were selected as the biomass fuels. Compared to the variations observed for volatiles and char contents, the variations of moisture and ash contents for the three types of biomass were large in an individual pellet. The straw char was more reactive than the bark char and wood char, probably due to the high ash content of the straw, which is especially rich in potassium. Furthermore, the variations of the characteristic temperatures and kinetics in an individual pellet increased from the wood char to bark char to straw char. The experimental results for char combustion can be described by the two simple reaction models: the volumetric model and the shrinking particle model. For each type of biomass, the differences in predictions between the two reaction models were much smaller than the differences in the accuracy of the measured kinetics for the different particles. For the kinetic parameters, the activation energy E and the natural logarithm of apparent pre-exponential factor A∗ (lnA∗) showed a linear correlation in the two applied models (A∗=e(0.2140E-8.713)), while the measured activation energies of the two applied reaction models were also linear (Eshrinkingparticle=0.8136Evolumetric). The performed analyses revealed that 10 biomass samples could ably characterize the conversion of a batch of biomass char particles and the average kinetics of the reactions. In addition, the distribution of conversion rates of the different chars in a batch at a specific time or temperature could be estimated from the standard deviation of the average value for the kinetics.

Response of hardwood tree regeneration to surface fires, western Chaco region, Argentina

We assessed the response of seedlings and pole-sized individuals of Aspidosperma quebracho-blanco Schlecht., Schinopsis lorentzii (Griseb.) Engler and Ziziphus mistol Griseb. to surface fires. We assessed traits of fire resistance (bark thickness and bark density) and fire tolerance (mortality and sprouting type, basal or epicormic) in each species. Burns were carried out using two fine fuel loads (high, 8000kgha−1; and low 4000kgha−1, respectively) and two dates of fire application (early and late fire season). Field work was performed during 2008 and 2009. Using a randomized design, 120 2m×2m plots were burnt each year. Using ANOVA, we tested the effect of species, fuel load and date of fire on the bark char height of the bole. The resprouting pattern (basal or epicormic) and post-fire mortality (complete or top-kill) were analysed using a logistic regression approach. There were a significant effect of species (p<0.0001), fuel load (p<0.0001) and of the interaction year of burning *date of fire (p<0.0001) on the mean char height. A. quebracho-blanco had greater char height than S. lorentzii and Z. mistol (p<0.05), but differences between the latter two species were no significant. Diameter to breast height (DBH) was significant and positively correlated to char height for A. quebracho-blanco and Z. mistol. High fuel load produced higher char height than the low fuel load fires. A. quebracho-blanco had the greatest total, inner and outer bark thickness, and the lowest bark density among the studied species. It was followed by S. lorentzii, while Z. mistol had the lowest total bark thickness, the highest inner bark proportion and the highest bark density (p<0.05). The likelihood of complete mortality was significantly larger in Z. mistol than in A. quebracho-blanco and S. lorentzii. Mortality and top-kill were lower in the late season burns (p<0.05). Sprouting type was significantly affected by species (p<0.05), DBH, date of fire and by the interactions species×DBH and season of fire×DBH (p<0.0001). A. quebracho-blanco presented only basal resprouts, while the other two species showed both epicormic and basal resprouts. The two species with greater bark thickness had lower mortality than Z. mistol. Epicormic resprouts were not observed at the more severe late burns. The three species studied showed high resistance and tolerance to medium to high severity fires.

FireStem2D – A Two-Dimensional Heat Transfer Model for Simulating Tree Stem Injury in Fires

FireStem2D, a software tool for predicting tree stem heating and injury in forest fires, is a physically-based, two-dimensional model of stem thermodynamics that results from heating at the bark surface. It builds on an earlier one-dimensional model (FireStem) and provides improved capabilities for predicting fire-induced mortality and injury before a fire occurs by resolving stem moisture loss, temperatures through the stem, degree of bark charring, and necrotic depth around the stem. We present the results of numerical parameterization and model evaluation experiments for FireStem2D that simulate laboratory stem-heating experiments of 52 tree sections from 25 trees. We also conducted a set of virtual sensitivity analysis experiments to test the effects of unevenness of heating around the stem and with aboveground height using data from two studies: a low-intensity surface fire and a more intense crown fire. The model allows for improved understanding and prediction of the effects of wildland fire on injury and mortality of trees of different species and sizes.

Fire‐induced tree mortality in a neotropical forest: the roles of bark traits, tree size, wood density and fire behavior

AbstractLarge‐scale wildfires are expected to accelerate forest dieback in Amazônia, but the fire vulnerability of tree species remains uncertain, in part due to the lack of studies relating fire‐induced mortality to both fire behavior and plant traits. To address this gap, we established two sets of experiments in southern Amazonia. First, we tested which bark traits best predict heat transfer rates (R) through bark during experimental bole heating. Second, using data from a large‐scale fire experiment, we tested the effects of tree wood density (WD), size, and estimated R (inverse of cambium insulation) on tree mortality after one to five fires. In the first experiment, bark thickness explained 82% of the variance in R, while the presence of water in the bark reduced the difference in temperature between the heat source and the vascular cambium, perhaps because of high latent heat of vaporization. This novel finding provides an important insight for improving mechanistic models of fire‐induced cambium damage from tropical to temperate regions. In the second experiment, tree mortality increased with increasing fire intensity (i.e. as indicated by bark char height on tree boles), which was higher along the forest edge, during the 2007 drought, and when the fire return interval was 3 years instead of one. Contrary to other tropical studies, the relationship between mortality and fire intensity was strongest in the year following the fires, but continued for 3 years afterwards. Tree mortality was low (≤20%) for thick‐barked individuals (≥18 mm) subjected to medium‐intensity fires, and significantly decreased as a function of increasing tree diameter, height and wood density. Hence, fire‐induced tree mortality was influenced not only by cambium insulation but also by other traits that reduce the indirect effects of fire. These results can be used to improve assessments of fire vulnerability of tropical forests.