Search Results (78)

Tropical forests continue to experience high levels of habitat loss and degradation, with wildfires becoming a frequent component of human-modified landscapes. Here we investigate the response of palm species to the conversion of old-growth forests to successional mosaics, including forest patches burned during wildfires. Palms (≥50 cm height) were recorded once in 2023–2024, across four habitat classes: terra firme old-growth stands, regenerating forest stands associated with slash-and-burn agriculture, old-growth stands burned once and twice, and active cassava fields, in the Tapajós-Arapiuns Extractive Reserve, in the eastern Brazilian Amazon. The flammability of palm leaf litter and forest litter were also examined to assess the potential connections between palm proliferation and wildfires. A total of 10 palm species were recorded in this social forest (including slash-and-burn agriculture and resulting successional mosaics), with positive, negative, and neutral responses to land use. Species richness did not differ among forest habitats, but absolute palm abundance was greatest in disturbed habitats. Only Attalea spectabilis Mart. (curuá) exhibited increased relative abundance across disturbed habitats, including active cassava field. Attalea spectabilis accounted for almost 43% of all stems in the old-growth forest, 89% in regenerating forests, 90% in burned forests, and 79% in crop fields. Disturbed habitats supported a five-to-ten-fold increment in curuá leaves as a measure of habitat flammability. Although curuá litter exhibited lower flame temperature and height, its lower carbon and higher volatile content is expected to be more sensitive to fire ignition and promote the spread of wildfires. The conversion of old-growth forests into social forests promotes the establishment of palm-dominated forests, increasing the potential for a forest transition further fueled by wildfires, with effects on forest resilience and social reproduction still to be understood. Full article

We evaluated the effects of different fire regimes on the ground-ant community from a savanna (Cerrado) reserve in southern Brazil, where a process of woody encroachment has been taking place. Ants are a dominant faunal group in tropical savannas. Over ~8 years, experimental plots were protected from fire or burned every one or two years. An additional treatment (adaptive) included annual fires and a reduction in woody biomass to increase fuel loads. Ants were collected prior to the first prescribed fire and again four times. We expected that fire would increase the diversity and overall abundance of open-savanna ant specialists, depending on the extent of changes in vegetation structure. Changes in litter depth, grass cover and bare ground in burned plots were most evident 88 months after the first fire and did not differ between fire regimes. Similarly, overall ant species richness and occurrence neither differed between fire treatments nor from the control. However, burned plots showed a significant increase in the richness and occurrence of open savanna specialists, and a decrease in species most typical of dense savanna or dry forests. As ant responses did not differ between the annual, biennial, and adaptive treatments, we suggest that a fire return interval of two years is enough for reverting the loss of open savanna ant specialists in areas that have been protected from fire for decades. Full article

Mapping potential fire intensity is a fundamental tool for fire management planning. Despite the wide use of Fire Radiative Power (FRP) as an indicator of expected fire intensity and fire emissions, very few studies have spatially analyzed the role of remotely sensed proxies of vegetation productivity to explain FRP. The current study aimed at modeling and mapping the relationships between aboveground biomass and Moderate Resolution Imaging Spectroradiometer (MODIS) maximum FRP, at 1 km pixel, in 2011–2020, for each of 46 fuel regions in the entirety of Mexico. Maximum FRP–biomass relationships supported a novel hypothesis of varying constraints of fire intensity. In lower-productivity areas, such as semiarid shrub- and grass-dominated ecosystems, fine fuel loads limited fire occurrence and FRP was positively related to biomass. In the more productive areas, such as temperate or tropical forests, a humped relationship of FRP against biomass was observed, suggesting an intermediate-productivity hypothesis of maximum fire intensity within those regions. In those areas, the highest fire intensity was observed in the intermediate biomass areas, where surface (timber understory) and crown fuel availability, together with higher wind penetration, can result in crown fires. On the contrary, within the most productive areas, the lowest intensity occurred, likely due to weather and fuel (timber litter) limitations. Full article

The mechanism through which fine root biomass affects soil carbon accumulation after prescribed burning remains unclear. In this study, the biomass of fine roots in different life forms (larch, shrub, and grass) and the total soil carbon (STC) were determined after prescribed burning. Relative to a control, the total soil carbon increased one week after the fire (11.70 mg·g⁻¹; 28.1%) and decreased after 8 months (7.33 mg·g⁻¹; 16.7%), returning to control levels 10 months post-fire. There was a reduction in the larch fine root biomass (FRB) (0.20–0.48 t·ha⁻¹; 35.3%–46.1%; these ranges represent the significant variation interval of fine root biomass after the fire across different time periods, compared to the control) but an increase in the shrub FRB (0.06–0.14 t·ha⁻¹; 101.6%–158.4%) and herb FRB (0.06–0.13 t·ha⁻¹; 591%–3200%) during the vegetation recovery process after the fire. The complementary growth of different plant life forms contributed to the changes in FRB. This also caused changes in the different life forms of FRBs’ effects on STC. Prescribed burning increased the contribution of FRB to STC. The compensatory growth of fine roots from different life forms drives the stabilization of the soil carbon pool after prescribed burning. Prescribed burning reduced the litter fuel and changed the FRB of different life forms, but it did not affect the long-term accumulation of STC. Full article

Many eucalypt trees shed their bark annually. This bark becomes a component of the litter layer, which acts as fuel, especially during surface fires. The amount and quality of shed bark vary greatly among species, which might have important effects on forest surface fire behavior. In this study, we aimed to compare the bark fuel bed flammability of eight eucalypt tree species and tried to link their bark litter traits via the surface fuel bed structure to bark flammability. In controlled laboratory burns, three flammability parameters, the fire spread rate, total burning time, and maximum temperature, were measured. The bark litter traits included length, curliness, thickness, dry matter content, tissue density, carbon content, nitrogen content, and terpene content, while the litter bed packing ratio and packing density were also measured. We found significant differences in bark traits and flammability among species. Thicker bark fragments of the eucalypt tree species had higher packing densities in fuel beds, a slower fire spread, and a longer burning time. This relationship was strongly driven by the thick bark fragments of Eucalyptus punctata DC. Still, also within the other seven species, bark thickness was the strongest predictor of bark fuel bed flammability, with some additional explanatory power for bark length. For the first time, our study demonstrates that bark traits, particularly litter fragment thickness and length, drive bark litter flammability of eucalypt tree species through their effects on bark fuel bed structure. These findings contribute to our understanding and predictive power of wildfire behavior in forest stands dominated by different eucalypt species. Full article

Forest fuels are the core element of fire management; each fuel component plays an important role in fire behavior. Therefore, accurate determination of their characteristics and spatial distribution is crucial. This paper introduces a novel method for mapping the spatial distribution of litter and duff fuel loads using data collected by unmanned aerial vehicles. The approach leverages a very high-resolution multispectral data analysis within a machine learning framework to achieve precise and detailed results. A set of vegetation indices and texture metrics derived from the multispectral data, optimized by a “Variable Selection Using Random Forests” (VSURF) algorithm, were used to train random forest (RF) models, enabling the modeling of high-resolution maps of litter and duff fuel loads. A field campaign to measure fuel loads was conducted in the mixed forest of the natural protected area of “Sierra de Quila”, Jalisco, Mexico, to measure fuel loads and obtain field reference data for calibration and validation purposes. The results revealed moderate determination coefficients between observed and predicted fuel loads with R² = 0.32, RMSE = 0.53 Mg/ha for litter and R² = 0.38, RMSE = 13.14 Mg/ha for duff fuel loads, both with significant p-values of 0.018 and 0.015 for litter and duff fuel loads, respectively. Moreover, the relative root mean squared errors were 33.75% for litter and 27.71% for duff fuel loads, with a relative bias of less than 5% for litter and less than 20% for duff fuel loads. The spatial distribution of the litter and duff fuel loads was coherent with the structure of the vegetation, despite the high complexity of the study area. Our modeling approach allows us to estimate the continuous high-resolution spatial distribution of litter and duff fuel loads, aligned with their ecological context, which dictates their dynamics and spatial variability. The method achieved acceptable accuracy in monitoring litter and duff fuel loads, providing researchers and forest managers with timely data to expedite decision-making in fire and forest fuel management. Full article

Prescribed burning is a cost-effective method for reducing hazardous fuels in pine- and oak-dominated forests, but smoke emissions contribute to atmospheric pollutant loads, and the potential exists for exceeding federal air quality standards designed to protect human health. Fire behavior during prescribed burns influences above-canopy sensible heat flux and turbulent kinetic energy (TKE) in buoyant plumes, affecting the lofting and dispersion of smoke. A more comprehensive understanding of how enhanced energy fluxes and turbulence are related during the passage of flame fronts could improve efforts to mitigate the impacts of smoke emissions. Pre- and post-fire fuel loading measurements taken during 48 operational prescribed burns were used to estimate the combustion completeness factors (CC) and emissions of fine particulates (PM_2.5), carbon dioxide (CO₂), and carbon monoxide (CO) in pine- and oak-dominated stands in the Pinelands National Reserve of southern New Jersey. During 11 of the prescribed burns, sensible heat flux and turbulence statistics were measured by tower networks above the forest canopy. Fire behavior when fire fronts passed the towers ranged from low-intensity backing fires to high-intensity head fires with some crown torching. Consumption of forest-floor and understory vegetation was a near-linear function of pre-burn loading, and combustion of fine litter on the forest floor was the predominant source of emissions, even during head fires with some crowning activity. Tower measurements indicated that above-canopy sensible heat flux and TKE calculated at 1 min intervals during the passage of fire fronts were strongly influenced by fire behavior. Low-intensity backing fires, regardless of forest type, had weaker enhancement of above-canopy air temperature, vertical and horizontal wind velocities, sensible heat fluxes, and TKE compared to higher-intensity head and flanking fires. Sensible heat flux and TKE in buoyant plumes were unrelated during low-intensity burns but more tightly coupled during higher-intensity burns. The weak coupling during low-intensity backing fires resulted in reduced rates of smoke transport and dispersion, and likely in more prolonged periods of elevated surface concentrations. This research facilitates more accurate estimates of PM_2.5, CO, and CO₂ emissions from prescribed burns in the Pinelands, and it provides a better understanding of the relationships among fire behavior, sensible heat fluxes and turbulence, and smoke dispersion in pine- and oak-dominated forests. Full article

The Canadian Fire Weather Index System (CFWIS), empirically developed for forests in Canada, estimates the fuel moisture content ($m_f$) at different depths and loads through meteorological parameters. While it is often suggested that adapting an existing fire danger rating system like CFWIS for a new environment requires developing new relationships or modifying existing ones, it is worth considering if such adaptations are always necessary. Based on a dataset of field measurements for surface litter (Pinus pinaster) carried out in the central region of Portugal (2014–2023), we propose a correction of $m_f$ based on the Fine Fuel Moisture Code (FFMC) of the CFWIS. This moisture correction was used to determine the Initial Spread Index (ISI) directly and, subsequently, the Fire Weather Index (FWI). Fire records from the study region were used to analyze the performance of the corrected indices. We found that the moisture correction led to higher values and potentially more accurate indices under dry conditions but did not provide a significant improvement in predicting the number of fires and burned areas compared to the original indices. The results suggest that, in relation to fire activity, the CFWIS is sufficiently robust to variations in the fuel moisture content in the study region. Full article

Headwater streams are reliant on riparian tree leaf litterfall to fuel brown food webs. Terrestrial agents like herbivores and contaminants can alter plant growth, litter production, litter quality, and the timing of litterfall into streams, influencing aspects of the brown food web. At Mount St. Helens (USA), early successional streams are developing willow (Salix sitchensis) riparian zones. The willows are attacked by stem-boring herbivores, altering litter quality and the timing of litterfall. Within a established experimental plots, willows (male and female plants) were protected from herbivores using insecticides and provided with experimental additions of nitrogen. This enabled us to test the interacting influences of herbivores, nitrogen deposition, and willow sex on leaf litter quality, aquatic litter decomposition, and microbial and invertebrate detritivores. We found weak litter quality effects (higher N and lower C:N) for the herbivore treatment, but no effect of nitrogen deposition. Although litter decomposition rates were not strongly affected by litter treatments, detritivore communities were altered by all treatments. Nitrogen deposition resulted in decreased bacterial richness and decreased fungal diversity in-stream. Aquatic macroinvertebrate communities were influenced by the interacting effects of herbivory and nitrogen addition, with abundances highest in herbivore litter with the greatest N addition. Shredders showed the highest abundance in male, herbivore-attacked litter. The establishment of riparian willows along early successional streams and their interacting effects with herbivores and nitrogen deposition may be influencing detritivore community assembly at Mount St. Helens. More broadly, global changes like increased wet and dry N deposition and expanded ranges of key herbivores might influence tree litter decomposition in many ecosystems. Full article

Poultry litter was converted to biochar by torrefaction and to hydrochar by hydrothermal carbonisation. Many parameters were measured for the resulting chars, to investigate the effects of the production method and production temperature. SEM showed the presence of large quantities of crystalline material on the surface of the biochars. The elemental composition of some crystals was determined as 35% K and 31% Cl. This was confirmed as sylvite (KCl) crystals, which explains the high levels of water-extractable potassium in the biochar and may also be important in germination inhibition. Biochars almost totally inhibited germination, whilst hydrochars decreased germination. Although germination occurred on hydrochar, root growth was severely inhibited. Consequently, the germination index may be better to determine total phytotoxicity as it measures both effects and could be used as a bioassay for chars used as soil amendments. Washing removed germination inhibition in a low-temperature char (350 °C), possibly by removing KCl; however, root toxicity remained. There were very low levels of heavy metals, suggesting they are not the source of toxicity. In biochars, pore mean size decreased with temperature from 350 °C to 600 °C, due to changes in pore size distribution. The mean pore size was measured directly using SEM. The merits of this method are discussed. Low-temperature biochars seem best suited for fuel as they have a high calorific value, high hydrophobicity, a low ash content and a high yield. Higher temperatures are better for soil amendment and sequestration applications with a smaller mean pore size, higher surface area, and higher pH. Full article

In 2020, wildfires scarred over 4,000,000 hectares in the western United States, devastating urban populations and ecosystems alike. The significant impact that wildfires have on plants, animals, and human environments makes wildfire adaptation, management, and mitigation strategies a critical task. This study uses satellite imagery from Landsat to calculate burn severity and map the fire progression for the Dolan Fire of central Coastal California which occurred in August 2020. Several environmental factors, such as temperature, humidity, fuel type, topography, surface conditions, and wind velocity, are known to affect wildfire spread and burn severity. The aim of this study is the investigation of the relationship between these environmental factors, estimates of burn severity, and fire spread patterns. Burn severity is calculated and classified using the Difference in Normalized Burn Ratio (dNBR) before being displayed as a time series of maps. The Dolan Fire had a moderate severity burn with an average dNBR of 0.292. The ignition site location, when paired with the patterns of fire spread, is consistent with wind speed and direction data, suggesting fire movement to the southeast of the fire ignition site. Patterns of increased burn severity are compared with both topography (slope and aspect) and fuel type. Locations that were found to be more susceptible to high burn severity featured Long Needle Timber Litter and Mature Timber fuels, intermediate slope angles between 15 and 35°, and north- and east-facing slopes. This study has implications for the future predictive modeling of wildfires that may serve to develop wildfire mitigation strategies, manage climate change impacts, and protect human lives. Full article

The use of poultry litter (PL) as a sustainable fuel is gaining more attention due to its wide availability and carbon neutrality. However, this type of feedstock is rich in ash and typically contains a high concentration of chlorine (Cl) and alkali elements (Na, K). Therefore, it is likely to cause unwanted issues during combustion and co-combustion, such as chlorine-induced corrosion, ash deposition, and bed agglomeration. In this study, for the first time, the influence of aluminosilicate additives on the above problems of poultry litter was investigated. Three aluminosilicate minerals are under consideration: kaolin, halloysite, and bentonite. Their influence on the chemical composition and meting tendencies of two poultry litter ashes are determined. The investigated ashes, PL1 and PL2, are characterized by different chlorine contents of 6.38% and 0.42%, respectively. The results show that in the case of the chlorine-rich PL1 ash, the additives reduced the chlorine content by up to 45%, resulting in a 3.93% of chlorine in the case of halloysite, 3.48% in the case of kaolin, and 4.25% in the case of bentonite. The additives also positively influenced the shrinkage starting temperature and the deformation temperature of the PL1 ash. Full article

Fire regimes have shaped extant vegetation communities, and subsequently fuel arrays, in fire-prone landscapes. Understanding how resilient fuel arrays are to fire regime attributes will be key for future fire management actions, given global fire regime shifts. We use a network of 63-field sites across the Sydney Basin Bioregion (Australia) to quantify how fire interval (short: last three fires <10 years apart, long: last two fires >10 years apart) and severity (low: understorey canopy scorched, high: understorey and overstorey canopy scorched), impacted fuel attribute values 2.5 years after Australia’s 2019–2020 Black Summer fires. Tree bark fuel hazard, herbaceous (near-surface fuels; grasses, sedges <50 cm height) fuel hazard, and ground litter (surface fuels) fuel cover and load were higher in areas burned by low- rather than high-severity fire. Conversely, midstorey (elevated fuels: shrubs, trees 50 cm–200 m in height) fuel cover and hazard were higher in areas burned by high- rather than low-severity fire. Elevated fuel cover, vertical connectivity, height and fuel hazard were also higher at long rather than short fire intervals. Our results provide strong evidence that fire regimes rearrange fuel arrays in the years following fire, which suggests that future fire regime shifts may alter fuel states, with important implications for fuel and fire management. Full article

Tropical coastal freshwater forested wetlands in coastal regions are rapidly disappearing as a result of various disturbance agents, mainly wildfires caused by high accumulations of forest fuels. The objective of this study was to characterize the structure and composition of fuel beds in tropical coastal freshwater forested wetlands with three levels of disturbance at El Castaño, La Encrucijada Biosphere Reserve. Seventeen sampling units were used to describe the structure of the forest’s fuel beds (canopy, sub-canopy, and understory). Fallen woody material and litter (surface and fermented) were characterized using the planar intersection technique. Diversity comprised eight species of trees, two shrubs, five lianas, and two herbaceous species. The vertical strata were dominated by trees between 2 and 22 m in height. The horizontal structure had a higher percentage of trees with normal diameter between 2.5 and 7.5 cm (61.4%) of the total. Sites with low disturbance had the highest arboreal density (2686 ind. ha⁻¹). Diversity of species showed that the Fisher, Margalef, Shannon, and Simpson α indices were higher in the low disturbance sites. The Berger–Parker index exhibited greater dominance in the sites with high disturbance. Pachira aquatica Aubl. Showed the highest importance value index and was the largest contributor to fuel beds. Sites with the highest disturbance had the highest dead fuel load (222.18 ± 33.62 Mg ha⁻¹), with woody fuels of classes 1, 10, and 1000 h (rotten) being the most representative. This study contributes to defining areas prone to fire in these ecosystems and designing prevention strategies. Full article

In recent decades, the versatility of fossil-based polymers has led them to become one of the most used materials for the production of several consumer goods. The destiny of post-consumer plastics is crucial for environmental sustainability. Two are the alternatives to landfilling: (i) energy recovery, i.e., replacement of traditional fuel with plastic litter, and (ii) recycling, i.e., processing of plastic wastes to produce secondary raw materials that may substitute primary raw materials. This work presents the investigation of a device for the hydraulic separation of heterogeneous plastic wastes, which, when properly upscaled, may be efficiently used within recycling plants. This apparatus is suitable for the separation of granules or flakes of plastics with a density higher than 1000 Kg/m³ and may replace existing technologies for mechanical recycling. The purpose of the device is to separate the useful fraction from a mixture of plastics and water introduced inside. The separation procedure efficacy relies on the difference in density, dimension, and shape of the processed plastic particles and on the flow features within the device. Experiments were carried out to test the efficacy of the device as a function of those factors. To increase the range of variation in the key parameters influencing the apparatus’s working principles, Computational Fluid Dynamics was employed to build a numerical model of the device. The validated numerical model suitable to fully characterize the apparatus performance features a hybrid grid with an inner mesh of 3·10⁻³ m size, a careful modeling of the near-wall region, and the k-ω SST turbulent model. Full article