Fire Disturbance Research Articles

Long-term consequences of wildfire smoke exposure on the central nervous system of rats in experimental modeling

Introduction. The annual increase in air temperature is one of the reasons for the occurrence of large-scale destructive fires throughout the world. The consequences of the negative impact of air pollution during forest fires on the respiratory and cardiovascular systems have been widely and well studied. At the same time, insufficient attention is paid to the influence of forest fire smoke on the functioning of the central nervous system.
 The study aims to study the morphofunctional state of the central nervous system of white male rats under prolonged exposure to forest fire smoke.
 Materials and methods. The study was conducted on 60 outbred white mature male rats weighing 200–220 grams. Animals in the experimental group (n=30) were exposed to daily smoke inhalation for 4 weeks, 4 hours a day, 5 days a week. Rats in the control group (n=30) were supplied with clean air into the chamber. The examination of animals exposed to smoke was carried out in two stages. At the first stage, the morphofunctional state of experimental animals was assessed 24 hours after the end of exposure. At the second stage — 60 days after exposure (long-term period). The examination included an analysis of indicators of the central nervous system: histology and morphometry of the brain.
 Results. Analysis of the results of the studied indicators indicates a decrease in motor and exploratory activity in animals exposed to smoke, as well as impairment of the ability to navigate and spatial memory. In the tissue structure of the sensorimotor cerebral cortex, multiple foci of neuronophagia, an increase in the number of degeneratively changed neurons, the formation of glial nodules and expansion of perivascular spaces were found. At the same time, the results of the examination in the long-term period indicated the absence of complete restoration of the identified violations.
 Conclusions. The results of experimental modeling revealed cause-and-effect relationships between exposure to forest fire smoke and disturbances in the morphofunctional state of the central nervous system.
 Limitations. The study is limited to studying the effects of prolonged 4 weeks, 5 days a week, 4 hours a day, exposure to wildfire smoke on outbred male white rats.
 Ethics. The study was conducted in compliance with the rules of humane treatment of animals in accordance with the Helsinki Association of the World Medical Association for the Humane Treatment of Animals (edition – October 2008) in accordance with the requirements of applicability to the protection of vertebrate animals or in another scientific research (ETS). No. 123), Directive 2010/63/EC of the European Parliament and of the Council of the European Union of September 22, 2010, on the protection of animals used for scientific purposes. Permission was obtained from the Local Ethics Committee of the Federal State Budgetary Scientific Institution VSIMEI to conduct experiments (protocol No. 32/19 dated May 10, 2019).

Coleoptera Monitoring Following Prescribed Fire Disturbance Yields 43 New State Species Records for Kentucky, USA

Coleoptera Monitoring Following Prescribed Fire Disturbance Yields 43 New State Species Records for Kentucky, USA

Soil not fire: Field, glasshouse and dendrochronology studies show how edaphic factors control post-fire woody plant growth across a sedgeland – forest boundary in Tasmania

Western Tasmania contains large areas of treeless sedgeland interspersed with scrub and forest vegetation. Why these large treeless areas exist in a region wet enough to support rainforest remains unclear. Slower growth of woody plants in the sedgeland than the scrub and forest could be a factor, because smaller woody plants are more likely to be killed by frequent fire before they mature and set seed. However, there is little information regarding growth rates of woody plants in these communities. We characterised soils and compared growth rates of small woody plants in sedgeland, scrub and forest at two sites using diverse approaches: (i) field observational studies of seedlings from a broad range of species that established following a wildfire in 2019 at site 1; (ii) a dendrochronological study of mature myrtaceous shrubs that had established following a fire in 1983 and were killed by the 2019 fire at site 1 (iii) a field experiment in which fertiliser was applied to transplanted seedlings of the myrtaceous shrub Leptospermum scoparium at site 2. (iv) We also used a glasshouse experiment to test the effects of nutrients and waterlogging on L. scoparium seedlings.Sedgeland soils were organic and poorly drained, whereas forest soils were mineral and well drained; scrub soils were organic at the surface but well drained. Concentrations of most soil nutrients, including total P, K, Ca, Mg and Mn were highest in the forest, although N was highest in sedgeland. At both sites, woody plant species grew faster in scrub and forest than in sedgeland, by a factor of 1.7–3.4. When fertiliser was added to transplanted L. scoparium seedlings, there was no difference in growth between sedgeland and scrub. In the glasshouse experiment, growth was limited by both low soil nutrients and waterlogging. However, the waterlogging effect was not apparent in the field experiment because conditions were dry. Our study shows slow growth of woody plants in Tasmanian sedgelands associated with infertile and waterlogged organic soils. Fire disturbance sharpens the boundary but is not the cause of it.

The absence of disturbances promoted Late Holocene expansion of silver fir (Abies alba) in the Bohemian Forest

Temperate forests in the Northern Hemisphere are strongly affected by increasing annual temperatures and natural disturbances such as droughts, fires, and pest outbreaks. In many regions, alternatives are explored by the forestry industry for previously commercialized tree species which are rapidly declining in areas outside their optimal climatic niches. However, as the current ranges of tree species have been mainly constrained by human activity, their true climatic and ecological niches are likely different from our observations. For example, little is known about environmental niches and population dynamics of tree species with limited dispersal ability, such as silver fir (Abies alba). Long-term (paleo) records of past landscape composition, past climate, and past disturbances can help to reveal the natural environmental niches of tree species. This study focuses on the Bohemian Forest (Šumava) in Czechia, where the human alteration of forests in higher elevations (>1000 m asl) has only been demonstrated from Medieval times onward. We present an interdisciplinary approach of geochemistry, pollen, charcoal, botanical and insect macro remains from a high-elevation peat record for the last seven millennia. Our multi-proxy study aimed to identify episodes of increased fire and other disturbances such as insect outbreaks, which could have influenced forest dynamics and vegetation succession in this montane region. However, the charcoal and macro-fossil records do not indicate any large local fires, insect outbreaks, browsing, or other disturbances (e.g., anthropogenic) for a major part of the record, suggesting that changes in the vegetation after 6500 cal yr BP were mainly caused by climatic fluctuations. Silver fir (Abies alba) expanded from 4300 cal yr BP, and likely became the dominant tree species at this locality for the next 2000 years, with extremely high pollen values up to 60%. During the establishment of silver fir around the peat bog around 5600 cal yr BP and its expansion around 4300 cal yr BP, the geochemical record and low counts of the testate amoeba Archerella flavum indicate drier conditions on the peat bog. Comparison with climatic simulations on a 1 × 1-km scale from the CHELSA database suggests that the local expansion of silver fir possibly coincided with a decrease in precipitation during both the wettest and warmest quarter of the year, related to a decreasing trend in seasonality of annual precipitation; this might confirm the species' higher tolerance to drought. Although silver fir is currently extremely rare in the Bohemian Forest, it has the potential for local expansion if logging, fire, and game browsing are kept to a minimum.

Colonization–persistence trade-offs shape changes on vegetation island community assembly in campo rupestre under fire disturbance

We studied neglected island plant communities on rock outcrops (vegetation islands or patches) that harbor many endemic species. We assessed how the post-fire habitat conditions (factor related to habitat filtering), the patch area and substrate depth (factors related to resource availability and environmental filtering), and the patch distance (spatial factor related to dispersal limitation) shape the plant community attributes, life forms and persistence–reproduction trade-offs in a campo rupestre in the Chapada Diamantina, Brazil. Two years after a wildfire, we sampled 82 vegetation islands in two habitat conditions based on fire disturbance (burned and unburned). We verified high plant mortality caused by wildfire. All succulent and desiccation-tolerant chamaephytes died, but while the desiccation-tolerant chamaephyte recolonized burned vegetation islands by seedling recruitment, the succulent chamaephyte lack regeneration after disturbance, demonstrating their vulnerability to fire disturbances. The post-fire recovery was driven by obligate resprouters (hemicryptophytes and phanerophyte), post-fire colonizers (therophytes and phanerophytes), facultative seeders (phanerophytes), and desiccation-tolerant obligate seeders (chamaephytes). Despite the similar species richness between burned and unburned vegetation islands, the fire-habitat conditions determined changes in species composition and persistence–reproduction trade-offs. We demonstrated that random processes related to the colonization-survival and persistence–reproduction trade-offs can be a strong biotic factor shaping vegetation islands on rocky outcrops beyond environmental filtering and dispersal limitation. Our study is the first to investigate the fire effects on vegetation islands in rock outcrops and reveal the desiccation-tolerant obligate seeder as a novel post-fire regeneration strategy, that has a central role in the vegetation island community assembly.

Prediction of air pollutant concentrations based on the long short-term memory neural network

In recent years, environmental problems caused by air pollutants have received increasing attention. Effective prediction of air pollutant concentrations is an important way to protect the public from harm. Recently, due to extreme climate and social development, the forest fire frequency has increased. During the biomass combustion process caused by forest fires, the content of particulate matter (PM) in the atmosphere increases significantly. However, most existing air pollutant concentration prediction methods do not consider the considerable impact of forest fires, and effective long-term prediction models have not been established to provide early warnings for harmful gases. Therefore, in this paper, we collected a daily air quality data set (aerodynamic diameter smaller than 2.5 µm, PM2.5) for Heilongjiang Province, China, from 2017 to 2023 and A novel Long Short-Term Memory (LSTM) model was proposed to effectively predict the situation of air pollutants. The model could automatically extract information of the effective time step from the historical data set and combine forest fire disturbance and climate data as auxiliary data to improve the model prediction ability. Moreover, we created artificial neural network (ANN) and permissive regression (support vector machine, SVR) models for comparative experiments. The results showed that the precision accuracy of the developed LSTM model is higher. Unlike the other models, the LSTM neural network model could effectively predict the concentration of air pollutants in long-term series. Regarding long-term observation missions (7 days), the proposed model performed well and stably, with R2 reaching over 88%.

Enhancing individual tree mortality mapping: The impact of models, data modalities, and classification taxonomy

Tree mortality is rapidly increasing as a result of more frequent and extensive droughts and forest fires across the globe. The increasing pace and scale of disturbance and resulting mortality necessitates the study of tree mortality at the scale at which it occurs (individual trees) to develop effective management strategies. Achieving this objective requires high-resolution aerial or satellite remote sensing data supported by field validation and efficient modeling. However, the optimal remote sensing data modalities and models for mapping overstory tree mortality remain uncertain and there is a lack of benchmark datasets for reproducible research, comparison, and model improvement. In this research, we propose a framework to generate tree mortality maps at the scale of individual trees and a labeled benchmark dataset using open-source high-resolution remote sensing data. Our benchmark dataset consists of over 15,000 image crops that have been manually labeled via multi-annotator majority for live, dead, mixed, and other classes in National Ecological Observatory Network (NEON) RGB, NEON hyperspectral, and National Agriculture Imagery Program (NAIP) RGBNIR imagery. Specifically, we present a multi-class classification framework that categorizes lidar-derived tree segments as live, dead, mixed, or other. We compared the performance of different machine learning models, remote sensing data modalities and their associated spatial resolution, spectral depth, and orthorectification using our benchmark dataset. Among various models, we found Convolutional Neural Network (CNN) models outperformed all other models with the highest accuracies and F1 scores across all data modalities. Similarly, among remote sensing data modalities, NEON RGB data at 0.1 m resolution performed best due to its high spatial resolution and high quality orthorectification. The overall accuracy of 87.27% with a macro F1 score of 0.76 was achieved using the RGB data with the CNN model. Our framework can be applied to any forest ecosystem in which lidar and raster imagery are available. We applied the framework using the best performing model and data modality to produce an individual tree mortality map over the Teakettle Experimental Forest in the southern Sierra Nevada. The framework and high-resolution mortality map can be valuable resources for forest managers and provide an invaluable basis for studying potential mortality drivers of dominant trees, forest inventory, selective logging, fire disturbance, and succession modeling.

Cortinarius and Tomentella Fungi Become Dominant Taxa in Taiga Soil after Fire Disturbance.

Fungi have important ecological functions in the soil of forests, where they decompose organic matter, provide plants with nutrients, increase plant water uptake, and improve plant resistance to adversity, disease, and disturbance. A forest fire presents a serious disturbance of the local ecosystem and can be considered an important component affecting the function of ecosystem biomes; however, the response of soil fungi to fire disturbance is largely unknown. To investigate the effects of fire disturbance on the community composition and diversity of soil fungi in a taiga forest, we collected soil from plots that had undergone a light, moderate, and heavy fire 10 years previously, with the inclusion of a fire-free control. The present soil fungi were characterized using Illumina MiSeq technology, and the sequences were analyzed to identify differences in the community composition and diversity in response to the changed soil physicochemical properties. The results showed that the Chao1 index, which characterizes the alpha diversity of the fungi, did not change significantly. In contrast, the Shannon index increased significantly (p < 0.05) and the Simpson index decreased significantly (p < 0.05) following a light or heavy fire disturbance compared to the control. The relative abundance of Basidiomycota was significantly higher in the soil of the fire sites than that in the control (p < 0.01), and the relative abundance of Ascomycota was significantly lower (p < 0.01). The results of principal coordinates analyses (PCoAs) showed that fire disturbance highly significantly affected the beta diversity of soil fungi (p < 0.001), while the results of canonical correlation analysis (CCA) indicated that the available nitrogen (AN), moisture content (MC), pH, available potassium (AK), and total nitrogen (TN) contents of the soil significantly affected the compositional structure and diversity of the soil fungal communities. The results of functional prediction showed that the majority of the detected soil fungi were symbiotrophs, followed by saprotrophs and saprotroph-symbiotrophs, with ectomycorrhiza being the dominant functional taxon. Fire disturbance significantly reduced the relative abundance of ectomycorrhiza (p < 0.05). This study illustrates that fire disturbance alters the structural composition, diversity, dominance, and relative abundance of the guilds of soil fungal communities in taiga forest, and strongly affected the beta diversity of soil fungi, with AN, MC, pH, AK, and TN being the most important factors affecting their community structure. The results may provide a useful reference for the restoration and rehabilitation of taiga forests after fire disturbance.

A novel, post-Soviet fire disturbance regime drives bird diversity and abundance on the Eurasian steppe.

Many grassland ecosystems and their associated biodiversity depend on the interactions between fire and land-use, both of which are shaped by socioeconomic conditions. The Eurasian steppe biome, much of it situated in Kazakhstan, contains 10% of the world's remaining grasslands. The break-up of the Soviet Union in 1991, widespread land abandonment and massive declines in wild and domestic ungulates led to biomass accumulation over millions of hectares. This rapid fuel increase made the steppes a global fire hotspot, with major changes in vegetation structure. Yet, the response of steppe biodiversity to these changes remains unexplored. We utilized a unique bird abundance dataset covering the entire Kazakh steppe and semi-desert regions together with the MODIS burned area product. We modeled the response of bird species richness and abundance as a function of fire disturbance variables-fire extent, cumulative burned area, fire frequency-at varying grazing intensity. Bird species richness was impacted negatively by large fire extent, cumulative burned area, and high fire frequency in moderately grazed and ungrazed steppe. Similarly, overall bird abundance was impacted negatively by large fire extent, cumulative burned area and higher fire frequency in the moderately grazed steppe, ungrazed steppe, and ungrazed semi-deserts. At the species level, the effect of high fire disturbance was negative for more species than positive. There were considerable fire legacy effects, detectable for at least 8 years. We conclude that the increase in fire disturbance across the post-Soviet Eurasian steppe has led to strong declines in bird abundance and pronounced changes in community assembly. To gain back control over wildfires and prevent further biodiversity loss, restoration of wild herbivore populations and traditional domestic ungulate grazing systems seems much needed.

Influence of fire regime on the taxonomic and phylogenetic diversity of frog communities in a fire-prone Brazilian ecosystem

Fire is a natural disturbance that has shaped Earth's biodiversity for millions of years. In a fire-prone ecosystems, fire acts as an important environmental filter, selecting species presenting tolerant traits to fire events and post-fire environmental conditions. It is expected that intense fire activity selects for closely-related species, thus promoting a phylogenetic and functional clustering of communities. In view of the severe changes in natural fire regimes observed in different regions of the planet, an increasing body of research has been dedicated to exploring their impact on frogs, a particularly susceptible group in the context of wildfires. However, it is notable that most of the research focuses on the traditional dimension of diversity, the taxonomic diversity, leaving a significant gap in our understanding of how fire disturbances affect the phylogenetic diversity of these communities. Here, we tested the effects of three fire regime parameters (i.e., total burned area, time since the last fire and fire count at the landscape scale) on the taxonomic and phylogenetic diversity of frog communities in 26 sites within a fire-prone Brazilian protected area. We used Hill numbers to characterize the taxonomic (Species richness, Shannon and Simpson's diversity) and phylogenetic diversity (Phylogenetic richness, Mean phylogenetic diversity of common lineages and Mean phylogenetic diversity of dominant lineages). We found that the fire regime did not explain patterns of the taxonomic diversity. Nonetheless, there was a positive correlation between phylogenetic richness and the frequency of fire occurrences, while a slight negative correlation was observed with the percentage of burned area. In addition, moderate fire activity seems to be an important driver of phylogenetic diversity. Therefore, management practices toward a mosaic of areas with different fire histories are fundamental in this protected area. We finally emphasize that all diversity facets of anurans should be assessed and considered in management decisions to guaranteeing anuran conservation in this region.

Quantitative Characteristics and Environmental Interpretation of Vegetation Restoration in Burned Areas of the Dry Valleys of Southwest China

Fire is a common natural disturbance in forest ecosystems and plays an important role in subsequent vegetation patterns. Based on the spatial sequence method, adopted as an alternative to the time successional sequence method, we selected burned areas in different locations in the Anning River Basin, which encompasses typical dry valleys. Quadrat surveys and quantitative classification were used to identify and classify the vegetation and distribution pattern and to carry out environmental interpretation during the natural restoration process after a forest fire. The results showed the following: (1) in the early stage of natural recovery after a forest fire disturbance, the vegetation community could be divided into seven community types, and Quercus guyavaefolia H. Leveille (Qg) was the dominant species in the community; (2) the vegetation samples could be divided into five ecological types, and the classification and distribution pattern of community types in this region changed most notably with altitude; and (3) a detrended correspondence analysis could be used to accurately classify vegetation community types, while a detrended canonical correspondence analysis could reveal the relationships between species and environmental factors. This study provides a scientific basis for guiding the restoration of ecosystem structural stability and biodiversity in burned areas.

Climate, fire disturbance regime, and vegetation response of the past 2500 years for central Nova Scotia

AbstractThe interaction between climate change and disturbances affects forest composition and dynamics, but most of our empirical knowledge comes from short‐term studies of the past century. Pollen and charcoal analyses of lake sediment cores retrieved from three sites in Nova Scotia were used to produce a landscape‐level analysis of long‐term forest cover dynamics and fire disturbances of the past ~2500 years. The present‐day forests had been established by that time, although a long‐term increase in Picea at the expense of northern hardwoods was seen at all sites, consistent with other pollen records found across New England and Eastern Canada. The driving influences of forest change prior to European settlement were a combination of climate and disturbance, acting on site characteristics of each region. Fires were relatively infrequent in this region and did not have a major impact on the evolution of the forests of central Nova Scotia. Changes in the relative abundances of the tree taxa occurred in response to long‐term cooling during the past 3000 years and century‐scale climate variability such as the Little Ice Age (ce 1450–1850) and Medieval Warm Period (ce 800–1300). The impact of climate variability on the fire regime depends on the landscape and vegetation type. “Borealization” of the Acadian Forest, noted during the period of European colonization, has been occurring for millennia.

Simulation of Soil Organic Carbon Dynamics in Postfire Boreal Forests of China by Incorporating High-Resolution Remote Sensing Data and Field Measurement

Soil organic carbon (SOC) is an important component of the ecosystem carbon pool, and fire is one of the important disturbances in forest ecosystems. With global warming, there has been a gradual increase in boreal forest fires, which has a nonnegligible impact on the SOC dynamics in forests. The CENTURY model was employed in our study to simulate the changes in SOC stocks in boreal forests of the Great Xing’an Mountains, China under different fire severity conditions. Fire severity was represented by the metric of difference normalized burn ratio (dNBR) derived from 30-m Landsat-8 imageries. Changes in forest SOC stocks following fire disturbance were predicted under four future Representative Concentration Pathway (RCP) scenarios (RCP2.6, RCP4.5, RCP6.0, and RCP8.5). We found that the CENTURY model had good results in simulating the SOC stocks in the postfire of China’s boreal forests. Forest SOC dynamics responded differently to fire severities and the larger SOC loss was associated with increasing fire severity. Importantly, a feedback mechanism was found between climate change and SOC stocks, which reduces SOC stocks with increasing temperatures. High-severity forest fires tended to cause serious damage to the SOC pool and delay forest SOC recovery time; after such events, forest SOC stocks cannot be fully recovered to the prefire levels (6.74% loss). In addition, higher CO2 emissions and warmer temperatures significantly affected the recovery of SOC stocks after fire disturbance, resulting in larger SOC losses. Overall, we projected losses of 10.14%, 12.06%, 12.41%, and 15.70% of SOC stocks after high-severity fires in four RCP scenarios, respectively. Our findings emphasize the importance of fire disturbance and climate change on future dynamics of SOC stocks in China’s boreal forests, providing a scientific basis for future boreal forest management and fire management.

Forest composition change and biophysical climate feedbacks across boreal North America

Deciduous tree cover is expected to increase in North American boreal forests with climate warming and wildfire. This shift in composition has the potential to generate biophysical cooling via increased land surface albedo. Here we use Landsat-derived maps of continuous tree canopy cover and deciduous fractional composition to assess albedo change over recent decades. We find, on average, a small net decrease in deciduous fraction from 2000 to 2015 across boreal North America and from 1992 to 2015 across Canada, despite extensive fire disturbance that locally increased deciduous vegetation. We further find near-neutral net biophysical change in radiative forcing associated with albedo when aggregated across the domain. Thus, while there have been widespread changes in forest composition over the past several decades, the net changes in composition and associated post-fire radiative forcing have not induced systematic negative feedbacks to climate warming over the spatial and temporal scope of our study.

Estimating annual GHG and particulate matter emissions from rural and forest fires based on an integrated modelling approach

Rural and forest fires represent one of the most significant sources of emissions in the atmosphere of trace gases and aerosol particles, which significantly impact carbon budget, air quality, and human health. This paper aims to illustrate an integrated modelling approach combining spatial and non-spatial inputs to provide and enhance the estimation of GHG and particulate matter emissions from surface fires using Italy as a case study over the period 2007–2017. Three main improvements characterize the approach proposed in this work: (i) the collection and development of comprehensive and accurate data inputs related to burned area; (ii) the use of the most recent data on fuel type and load; and (iii) the modelling application to estimate fuel moisture, burning efficiency, and fuel consumption considering meteorological factors and combustion phases. On average, Italy's GHG and particulate matter emissions were 2621 Gg yr−1, ranging from a minimum of 772 Gg yr−1 in 2013 to a maximum of 7020 Gg yr−1 in 2007. Emissions from fire disturbances in broadleaf forests, shrublands, and agricultural fuel types account for about 76 % of the total. Results were compared with global and national inventories and showed good agreement, especially considering CO2 and particulate matter. The approach of this study added confidence in emission estimates, and the results can be utilized in decision support systems to address air quality management and fire impact mitigation policies.

Variations in the Diversity and Biomass of Soil Bacteria and Fungi under Different Fire Disturbances in the Taiga Forests of Northeastern China

Fire is a crucial disturbance factor for the structure and function of forest ecosystems, as it directly or indirectly affects plant growth, animal life and soil biogeochemical properties. Here, the effects of different fire severities and key driving environmental factors on soil microbial diversity and biomass were investigated in taiga forests that had undergone light, moderate or heavy fires, more recently or in the past, with unburned taiga forest included as a control (CK). The sample sites were located in the Greater Khingan mountains in the northeast of China. Critical soil parameters were determined, and bacterial and fungal content was inferred from determined phospholipid fatty acids (TPLFAs). The results showed that (1) all three fire severities significantly increased the concentrations of soil microbial carbon (MBC), moisture content (MC) and total nitrogen content (TN), but they significantly decreased soil available potassium (AK) content compared with the CK. (2) Recent light and moderate fires significantly decreased the Simpson and Shannon indices of soil microbial communities compared to CK; moderate fire did not change the Menhinick and Margalef indices. (3) Following moderate fire disturbance, there were no significant differences (p &gt; 0.05) in relative abundance of total soil bacteria (Ba), Gram-positive bacteria (G+), Gram-negative bacteria (G−) and content of TPLFAs compared to the control, either as a result of more recent fires or earlier fires. (4) Redundancy analysis revealed that soil MC, TN, soil organic carbon (SOC), available P (AP) and alkaline N (AN) all strongly significantly affected the composition of the microbial communities, with a total explanation of 85.16% of the data. The species diversity and biomass of Ba, G+, G− and TPLFAs were in accordance with the intermediate disturbance hypothesis. The change pattern of soil fungi was in accordance with their own characteristics of reproduction and growth, which was in line with k-selection and ecological countermeasures.

Persistence of a pine tree with mixed fire-adapted life history strategy in subtropical spring fire-prone habitats

Whether pines can cope with fire depends on either species persistence or individual survival. Pinus yunnanensis is the most widely distributed endemic species in Southwest China, and is well adapted to fire with a mixed fire-adapted strategy of post-fire regeneration and fire resistance. However, whether its regeneration depends on fire disturbances is unclear. We reconstructed the fire history of a P. yunnanensis forest in Yunlong Tianchi National Nature Reserve over the past 100 years using fire scars and forest age structures to determine relationships between historical fires and recruitments. Additionally, post-fire regeneration processes of three burned patches were examined to explore P. yunnanensis dynamics after fires. The P. yunnanensis population in the Reserve had a “discontinuous multi-cohort” structure. There was a 6–16 year gap between cohorts, and each cohort comprised individuals that differed by 1–7 years. The study area experienced seven fires in the past 100 years, with an average interval of about 12 years, with surviving individuals in every fire. These historical fires align with P. yunnanensis cohorts emergence. Post-fire P. yunnanensis regeneration in the burned patches mainly occurred in the first two rainy seasons after the fire, then the number of new individuals significantly dropped and remained very low from the fourth year onward. P. yunnanensis population structure has undergone a shift following the enforcement of a fire suppression policy. Some P. yunnanensis adults appear able to survive low to moderate severity fires, and the population could achieve post fire functional recruitment, thus maintaining a “discontinuous multi-cohort” structure in fire-prone habitats as a result of a mixed fire-adapted strategy. Recurrent fire is the key driving factor in maintaining the long-term persistence of pure P. yunnanensis forests.

Evaluation of the Spatial Distribution of Predictors of Fire Regimes in China from 2003 to 2016

Wildfire has extensive and profound impacts on forest structure and function. Therefore, it is important to study the spatial and temporal patterns of forest fire regimes and their drivers in order to better understand the feedbacks between climate change, fire disturbance, and forest ecosystems. Based on the Global Fire Atlas dataset, three forest fire regime components (fire occurrence density, burned rate, and median fire size) were extracted for China from 2003 to 2016. Three statistical models (Boosted Regression Tree, Random Forest, and Support Vector Machine) were used to systematically analyze the relationships between patterns of forest fire disturbance and climate, human activities, vegetation, and topography in China, as well as their spatial heterogeneity in different climatic regions. The results indicate that the spatial distribution of forest fires is heterogeneous, and different forest fire regime components are predicted by different factors. At the national level, the distribution of forest fire regimes mainly corresponds to climatic factors, although the relationship between median fire size and predictors is obscure. At the scale of each ecoregion, the main climate predictors of forest fire occurrence density and burned rate change from temperature in the north to temperature and precipitation in the south. Median fire size varies with elevation and temperature in the south. These results demonstrate that the spatial heterogeneity of predictors and scaling effects must be fully considered in the study of forest fire disturbance.

Biome- and timescale-dependence of Holocene vegetation variability in the Northern Hemisphere.

Global climatic changes expected in the next centuries are likely to cause unparalleled vegetation disturbances, which in turn impact ecosystem services. To assess the significance of disturbances, it is necessary to characterize and understand typical natural vegetation variability on multi-decadal timescales and longer. We investigate this in the Holocene vegetation by examining a taxonomically harmonized and temporally standardized global fossil pollen dataset. Using principal component analysis, we characterize the variability in pollen assemblages, which are a proxy for vegetation composition, and derive timescale-dependent estimates of variability using the first-order Haar structure function. We find, on average, increasing fluctuations in vegetation composition from centennial to millennial timescales, as well as spatially coherent patterns of variability. We further relate these variations to pairwise comparisons between biome classes based on vegetation composition. As such, higher variability is identified for open-land vegetation compared to forests. This is consistent with the more active fire regimes of open-land biomes fostering variability. Needleleaf forests are more variable than broadleaf forests on shorter (centennial) timescales, but the inverse is true on longer (millennial) timescales. This inversion could also be explained by the fire characteristics of the biomes as fire disturbances would increase vegetation variability on shorter timescales, but stabilize vegetation composition on longer timecales by preventing the migration of less fire-adapted species.

Forest resilience and regeneration dynamics following wildfire disturbance

AbstractSpecies that are adapted to specific disturbance regimes may be sensitive to changes such as severity, frequency, and extent of ecosystem perturbation. Along range margins, these sensitivities may be exacerbated by concurrent changes in climate resulting in loss of resilience and shifts to alternative ecosystem states. Pinus banksiana (jack pine) is a serotinous species dependent on fire disturbance to open cones, release seed, reduce understory competition, and expose mineral soil. The Altona Flat Rock in northern New York is a globally rare sandstone pine barrens, at the southern edge of jack pine's range. In the summer of 2018, a wildfire burned approximately 200 ha of the Flat Rock barrens, providing the opportunity to study post‐disturbance jack pine and understory resilience. We aimed to establish if jack pine regeneration would occur, and if so, would it be influenced by fire severity, pre‐fire stand characteristics, and competition. We predicted that higher seedling densities would be associated with higher burn severity, higher pre‐fire jack pine stand density, and lesser understory competition. We collected seedling density and understory composition data annually from 2019 to 2022 across 45 plots spanning the disturbed and adjacent undisturbed barrens. In 2021 and 2022, seedling heights were also collected. Seedling densities following the disturbance ranged from 275,385 to 390,513 ha−1; = 357,821 ha−1. Jack pine seedling density was positively associated with fire severity and moss abundance for all years. Pre‐fire stand density along with ericaceous shrub, grass, and duff abundance were also positively associated with seedling density in some years. Seedling height was positively associated with fire severity along with grass and blueberry abundance. These factors, for both establishment/survival and growth, point to the importance of seed supply, microsite conditions, and facilitation in jack pine regeneration success. At this point, it does not appear that the interaction of disturbance with changing climate has shifted enough to prevent the recovery of this ecosystem to its pre‐disturbance jack pine‐dominated state. However, ongoing climate change may still have an impact on seedlings/saplings as this forest continues to mature.