Coniferous Research Articles

Aggregation unveiled: A sequential modelling approach to bark beetle outbreaks

Tree-killing bark beetle infestations are a cause of massive coniferous forest mortality impacting forest ecosystems and the ecosystem services they provide. Models predicting bark beetle outbreaks are crucial for forest management and conservation, necessitating studies of the effect of epidemiological traits on the probability and severity of outbreaks. Due to the aggregation behaviour of beetles and host tree defence, this epidemiological interaction is highly non-linear and outbreak behaviour remains poorly understood, motivating questions about when an outbreak can occur, what determines outbreak severity, and how aggregation behaviour modulates these quantities. Here, we apply the principle of distributed delays to create a novel and mathematically tractable model for beetle aggregation in an epidemiological framework. We derive the critical outbreak threshold for the beetle emergence rate, which is a quantity analogous to the basic reproductive ratio, R0, for epidemics. Beetle aggregation qualitatively impacts outbreak potential from depending on the emergence rate alone in the absence of aggregation to depending on both emergence rate and initial beetle density when aggregation is required. Finally, we use a stochastic model to confirm that our deterministic model predictions are robust in finite populations.

Transcriptome and metabolome reveal the primary and secondary metabolism changes in Larix gmelinii seedlings under abiotic stress.

Larix gmelinii is an excellent stress resistant coniferous tree species with a wide distribution and important economic and ecological value. However, at seedling stage, L. gmelinii is extremely susceptible to abiotic stresses, and systematic research on the adaptation mechanisms of L. gmelinii seedlings to abiotic stress is still lacking. Phenotypic observation and physiological index detection showed that L. gmelinii seedlings wilted with needles withered and yellowish at later stages of drought and salt stress; Under low temperature, the seedlings grew slowly and turned red at later stage. Under all 3 abiotic stresses, the chlorophyll content in seedlings significantly decreased, while the MDA content significantly increased; The activity of SOD and CAT showed a trend of increasing first and then decreasing. Transcriptome analysis revealed that DEGs were mainly involved in carbohydrate and amino acid metabolism, phenylpropanoid biosynthesis, and flavonoid synthesis metabolism. Metabolomic analysis found unique DAMs under 3 stress treatments. The combined analysis of transcriptome and metabolome showed that the changing patterns of DEGs and DAMs in primary and secondary metabolism were consistent: carbohydrate were significantly accumulated under low temperature stress; amino acids showed the most significant changes under salt stress. The variation pattern of secondary metabolism was similar under both drought and salt stress, while anthocyanin accumulation was the most obvious only under low temperature stress. Our study provides insightful information about the different mechanisms that L. gmelinii seedlings employ in response to drought, low temperature or salt stress.

Comparative Analysis of Two Methods for Valuing Local Cooling Effect of Forests in Inner Mongolia Plateau

Studies have extensively examined the cooling effects of forests. Various methods exist for evaluating climate regulation at regional and global levels. Local-scale cooling effects and their valuing methods, however, remain poorly understood. In this study, the temperature difference and energy balance methods were compared to assess the value of cooling services of three forest types at a local scale. Using the window searching strategy, land surface temperature and sensible heat flux differences between forest and open land were compared. The average cooling temperature of broad-leaved forests was found to be 0.229 °C, significantly higher than that of coniferous forests, at 0.205 °C, while mixed coniferous–broad-leaved forests were not significantly different to the other two types. The average sensible heat flux differences in broad-leaved, coniferous, and coniferous–broad-leaved forests were found to be 0.23, 0.079, and 0.11 MJ/m2/day, respectively. According to the correlation analysis, the sensible heat flux was significantly correlated with the cooling degree (R = 0.33, p = 0.05), suggesting consistency between the two approaches. However, the total cooling value calculated with the energy balance method was CNY 0.51 billion, significantly higher than the temperature difference method at CNY 0.11 billion. The main reason for the differences between the two approaches is the uncertainty in cooling volume and cooling time for the temperature difference method and energy balance method, respectively. The impact of vegetation on the microclimate depends on the vegetation type, topography, local climate, and other factors. It is also important to note that cooling services are not required at all times of the day, and energy differences can hardly be calculated based on the hour. However, surface radiation and evapotranspiration generally occur during the daytime, which is also when the surface temperature is high. Therefore, there is a certain coincidence with the time when cooling is needed. The energy balance method presented herein provides a novel alternative approach to assessing the cooling services of local-scale forests, offering advantages over the commonly used temperature difference approach, which is associated with large uncertainty.

OBSERVATIONS ON THE COLEOPTERAN FAUNA IN THE FOREST ECOSYSTEM LOCATED IN THE NECHIT AREA, NEAMȚ COUNTY

In this study, the research material is represented by coleopteran species found in a mixed forest In this study, the research material is represented by beetle species found in a mixed forest composed of deciduous and coniferous tree species, covering an area of 8 hectares. The forest is located in an area with rich biodiversity, characterized by a natural succession of tree species and a varied pitfall, which is conducive to the development of diverse fauna.This paper focuses on analyzing the structure, dynamics, abundance, and ecological role of beetles within this forest ecosystem, emphasizing their interactions with other species and the abiotic environment. The collection of fauna was carried out using pitfall traps type Barber, which are ecological traps, during the year 2024, from July to September, over a period of three months. A total of 6 traps were installed at various marked locations in the forest, depending on vegetation density, to adequately cover habitat diversity. The material from the traps was collected at regular intervals of 10-14 days to monitor the activity of beetle species. Throughout the study, 6 collections of entomological material were conducted on the following dates: July 10, July 22, July 31, August 14, August 28, and September 11. Among the most frequently collected species are Poecilus cupreus, Necrophorus vespillo, Geotrupes vernalis, Aptinus bombarda, and Silpha carinata. These species have a significant ecological impact on the ecosystem, playing key roles in organic matter decomposition and nutrient recycling, pollination processes, and controlling populations of harmful insects. Additionally, some of these species may be classified as harmful fauna in certain contexts, having the potential to affect the natural balance of other insect species or even the vegetation. However, overall, the majority of the beetle species collected in this study have a beneficial role and are essential for maintaining the health of the analyzed forest ecosystem.

Shields against pollution: phytoremediation and impact of particulate matter on trees at Wigry National Park, Poland

This study examines the impact of airborne particulate matter (PM) and associated trace elements (TEs) on deciduous and coniferous trees at the edge of Wigry National Park in northeast Poland, focusing on pollution levels and the potential for phytoremediation. Researchers measured PM concentrations in the air and on the leaves of Picea abies, Quercus robur, and Corylus avellana, along with photosynthetic indicators (Fv/Fm ratio and performance index). The study found significant differences in pollution intensity across areas with varying levels of human activity. P. abies, an evergreen species, accumulated the highest PM levels (>200 μg/cm2), while Q. robur had the highest accumulation among deciduous trees (>50 μg/cm2). Trace elements such as Fe, Cu, Zn, Sr, and Cd were detected, with C. avellana being the most efficient in accumulating Cd (up to 7.5 mg/kg). The accumulation of pollutants correlated with reduced photosynthetic efficiency in trees closest to pollution sources. The findings suggest that strategically planting specific tree species can help mitigate air pollution in national parks and protect sensitive vegetation. Future research should explore the long-term effects of PM on forest health and the role of different species in phytoremediation.

Mapping the Future: Climate-Induced Changes in Aboveground Live-Biomass Carbon Density Across Mexico’s Coniferous Forests

Climate variations in temperature and precipitation significantly impact forest productivity. Precipitation influences the physiology and growth of species, while temperature regulates photosynthesis, respiration, and transpiration. This study developed bioclimatic models to assess how climate change will affect the carbon density of aboveground biomass (cdAGB) in Mexico’s coniferous forests for 2050 and 2070. We used cdAGB data from the National Forest and Soils Inventory (INFyS) of Mexico and 19 bioclimatic variables from WorldClim ver. 2.0. The best predictors of cdAGB were obtained using machine learning techniques with the “caret” library in R. The model was trained with 80% of the data and validated with the remaining 20% using Generalized Linear Models (GLMs). Current cdAGB prediction maps were generated using the best predictors. Future cdAGB was calculated with the average of three general circulation models (GCMs) of future climate projections from the Coupled Model Intercomparison Project Phase 5 (CMIP5), under four Representative Concentration Pathways (RCPs): 2.6, 4.5, 6.0, and 8.5 W/m2. The results indicate cdAGB losses in all climate scenarios, reaching up to 15 Mg C ha−1, and could occur under the RCP 8.5 scenario by 2070 in the central region of the country. Temperature-related variables are more important than precipitation variables. Bioclimatic variables can explain up to 20% of the total variance in cdAGB. The temperature in the study area is expected to increase by 2.66 °C by 2050 and 3.36 °C by 2070, while precipitation is expected to fluctuate by ±10% relative to the current values, which could geographically redistribute the cdAGB of the country’s coniferous forests. These findings underscore the need for forest management to focus not only on biodiversity conservation but also on the carbon storage capacity of these ecosystems.

The Driving Factors of the Tradeoff-Synergistic Relationship Among Forest Ecosystem Service Values in the Yangtze River Delta, China

The forest ecosystem is one of the planet’s critical ecosystems. Identifying the tradeoff-synergistic relationships among forest ecosystem service values and exploring their driving factors in the Yangtze River Delta are crucial for promoting the optimal overall benefits of regional ecosystem service values and realizing a mutually beneficial scenario that harmonizes regional socio-economic development with ecological and environmental conservation. The forest ecosystem service value in the Yangtze River Delta was evaluated through the improved equivalent factor method. Furthermore, an examination of the tradeoff-synergistic relationship among these ecosystem service values, along with their driving factors, was performed utilizing both the Pearson correlation coefficient method and the Geodetector model. The findings reveal that from 2000 to 2020, the forest ecosystem service values presented a general growth trend in the Yangtze River Delta, with higher values noted in the southern areas and lower values found in the northern regions. The average annual forest ecosystem service value was 279 billion RMB. The tradeoff-synergistic relationship among forest ecosystem service values mainly showed a synergistic relationship, while a significant tradeoff relationship was observed between the values of support and cultural services. The factors influencing the tradeoff-synergistic relationship among forest ecosystem service values included precipitation, normalized difference vegetation index, and temperature. Consequently, local governments should enhance forest coverage, particularly by expanding the regions of evergreen broadleaf, deciduous broadleaf, and coniferous forests. They should also proactively seek ways to realize the value of forest ecosystem services.

Higher Soil Mesofauna Abundance and Microbial Activities Drive Litter Decomposition in Subtropical Forests

Soil fauna play an important role in litter decomposition and affect the “home-field advantage” (HFA) of litter decomposition. However, how this effect is modulated by the microenvironment needs further investigation. We conducted a reciprocal transplant experiment of litter decomposition using different mesh-size litterbags across litter and soil layers in subtropical coniferous (Pinus massoniana) and broad-leaved (Quercus variabilis) forests. Our results revealed a pronounced HFA in P. massoniana. P. massoniana litter decomposed faster in its home habitat by 40.6% in the litter layer and 10.2% in the soil layer in coarse mesh bags and by 21.8% in the litter layer and 21.4% in the soil layer in fine mesh bags. However, Q. variabilis litter showed faster decomposition in its home soil layer by 10.8% and 4.3% for coarse and fine mesh bags, whereas in the litter layer it decomposed faster in the away habitat by 16.7% and 20.6% for coarse and fine mesh bags, respectively. Higher soil mesofauna abundance and microbial activities in the coniferous forest compared to the broad-leaved forest drive the observed HFA of litter decomposition. Especially in the litter layer, the abundance of mesofauna was 89.8% higher in the coniferous forest. Coarse mesh bags generally facilitated a higher decomposition rate across litter and soil layers, likely due to a better interaction between soil mesofauna and extracellular enzyme activity. The HFA index exhibited distinct seasonal fluctuations, peaking in October for coarse mesh bags and in April for fine mesh bags within the litter layer, while soil layer peaks occurred in August and April. Notably, an increase in Acarina abundance strongly correlated with enhanced decomposition and HFA effects in the litter layer during October. This study revealed the sensitivity of HFA to the soil layer and soil fauna and underscores the complex role of the microclimate in shaping interactions among soil microorganisms, litter quality, and mesofauna, thereby enriching our understanding of litter decomposition dynamics in forest ecosystems.

Comparative Assessment of Different Architectures of Convolutional Neural Network for Semantic Segmentation of Forest Disturbances from Multi-Temporal Satellite Images

Algorithms based on convolutional neural networks are the most efficient for semantic segmentation of images, including segmentation of forest cover disturbances from satellite images. In this study, we consider the applicability of various modifications of the U-net architecture of convolutional neural network for recognizing logged, burnt and windthrow areas in forests from multi-temporal and multi-seasonal Sentinel-2 satellite images. The assessment was carried out on three test sites that differ significantly in the characteristics of forest stands and forest management. The highest accuracy (average F-measure of 0.59) was obtained from the U-net model, while the models that showed the best results during training (Attention U-Net and MobilNetv2 U-Net) did not improve segmentation of independent data. The resulting accuracy estimates are close to those previously published for forests with a substantial proportion of selective logged areas. Characteristics of logged areas and windthrows, namely their area and type are the main factor determining the accuracy of semantic segmentation. Substantial differences were also revealed between the images taken in different seasons of the year, with the maximum segmentation accuracy based on winter pairs of images. According to summertime and different-season pairs of images, the area of forest disturbances is substantially underestimated. Forest species composition has a less significant effect, although for two of the three test sites, the maximum accuracy was observed in dark coniferous forests, and the minimum in deciduous forests. There was no statistically significant effect of slope lighting factor calculated from digital elevation model on segmentation accuracy based for winter pairs of images. The accuracy of segmentation of burnt areas, which was assessed using the example of 14 large forest fires in 2021-2022, is unsatisfactory, which is probably due to the varying degrees of damage to the forest cover in the burnt areas.

Influence of Soil Texture on Carbon Stocks in Deciduous and Coniferous Forest Biomass in the Forest-Steppe Zone of Oka–Don Plain

Forests play a crucial role in climate change mitigation by acting as a carbon sink. Understanding the influence of soil properties on carbon stocks in forests is essential for developing effective forest management strategies. The aim of the study was to assess the impact of soil texture on carbon stocks in the biomass of deciduous and coniferous tree stands of a forest-steppe ecotone. Soil samples were collected from 55 soil pits, and forest inventory data were obtained from eight permanent sample plots. The results showed that the distribution of mechanical particles in soils, particularly the stocks of silt and clay, significantly influenced the accumulation of carbon in tree stands. The stock of silt and clay was shown to increase with an increase in the diversity of tree species in forests and carbon stocks in forest stands. While soil organic carbon stocks did not exhibit a clear relationship with tree stand carbon stocks, a strong positive correlation (r = 0.802, p < 0.05) was found between the stocks of fine particles in the 2 m root-inhabited soil layer and the carbon stocks in tree biomass. The study provides a classification of forest types based on soil texture, which can facilitate differentiated forest management strategies for enhancing the carbon sequestration potential of forest ecosystems in the forest-steppe zone.

Rhizosphere as a hotspot for microbial necromass deposition into the soil carbon pool

Abstract Microbial leftovers, known as necromass, are key players in storing carbon in the soil around plant roots (i.e. rhizosphere), a zone characterized by high‐efficiency microbial anabolism. Yet, the extent and mechanisms through which the rhizosphere contributes to soil organic carbon (SOC) via microbial necromass, especially under changing environments remain unclear. We aimed to evaluate the contributions of microbial necromass to SOC and influencing factors from the rhizosphere perspective. We collected the rhizosphere and bulk soil from 39 alpine coniferous forest sites on the eastern Tibetan Plateau to assess the extent of microbial necromass contribution to SOC in the rhizosphere from a dynamic perspective by calculating the ratio of increased amino sugars (AS) to increased SOC in the rhizosphere relative to that in bulk soil (RAS/SOC). We also collected climate data and determined nutrient concentrations and microbial physiological traits in rhizosphere soil to elucidate the factors affecting RAS/SOC. The results showed that across all sampling sites, the average concentrations of SOC‐normalized AS in the rhizosphere were significantly higher than those in the bulk soil. Furthermore, the average RAS/SOC was greater than 1, indicating a faster microbial necromass accumulation than SOC accumulation in the rhizosphere. These results implied that the rhizosphere sustains a greater capacity for microbial necromass contribution to the SOC pool than the bulk soil does. Soil nutrient availability was the primary factor affecting RAS/SOC, and precipitation indirectly affected microbial anabolism and RAS/SOC by changing soil nutrient status. Additionally, with increasing rhizosphere soil nutrient availability, microbial carbon‐use efficiency and growth rate increased but the biomass‐specific enzyme activity declined, indicating that microorganisms tended to exhibit high‐yield strategies with increasing soil nutrient availability. Synthesis. Our findings underpin the vital effect of microbial necromass in SOC accumulation from the rhizosphere perspective and offer valuable insights into mechanisms underlying microbial C metabolic processes in rhizosphere SOC accumulation under changing environments.

Correlation between Woody Species and Environmental Variables in a Tropical Forest in Central Laos

The tropical forest biome serves as a significant focal point for conservation endeavors. However, understanding the variations in woody plant composition and the underlying driving factors remains limited. The vegetation gradient within Phou Khao Khouay (PKK) National Park in central Laos presents an intriguing environmental model for investigating these patterns. This study, conducted within PKK National Park, aims to classify woody plant communities of three different forest types: mixed deciduous forest (MDF), dry evergreen forest (DEF), and mixed coniferous forest (MCF), utilizing both the phytosociology approach and multivariate analysis. Data from 32 permanent plots (each measuring 50 m × 50 m) were analyzed, revealing 5,477 tree individuals with a diameter at breast height (DBH) ≥ 5 cm, representing 194 woody species from 64 families and 133 genera. The results indicate significant diversity at the family and genus levels, identifying four distinct plant communities and 44 indicator species based on Tichy and Chytry's phi coefficient method. Stability characterizes the MCF forest type, while the stands of DEF and MDF exhibit differentiation into three communities each. Notably, high heterogeneity in species composition and environmental conditions is evident, with elevation and soil nutrient levels (specifically total phosphorus and total potassium) emerging as primary influencers on species coexistence. The study also highlights correlations between woody plant species composition and topographic and soil variables. These findings underscore the importance of identifying microhabitats conducive to growing and conserving woody plant species within PKK National Park for future research and conservation efforts.

Thermal Comfort and Green Spaces: The Role of Temperature-Regulating Elements in Neighborhood Parks

According to current studies, the thermal effects of global warming will affect urban areas more intensely. In the face of this situation, strategies for the improvement and management of urban green spaces are becoming increasingly important in sustainable landscape design. These strategies promote social sustainability by positively affecting individuals’ physical and psychological well-being, taking into consideration ecological sustainability. Projections regarding global warming emphasize that the density of hardscapes and green spaces, the selection of plant species, and the distribution of plants considered within the scope of this study should be taken into account. This research was conducted in the Görükle neighborhood of Bursa, focusing on the role of temperature-regulating elements in 14 neighborhood parks. Systematic temperature measurements were carried out in the research area on the 10th, 20th, and 30th of July and August, specifically between 12:00 and 13:00, during peak temperature hours. The presence of parks that are close to each other and relatively far away from each other in the study area was seen as advantageous to filter the effects of plant differences in similar conditions. Furthermore, evaluating these various factors together highlights the multifaceted nature of thermal comfort. Designated temperature measurement points included three points (hard surfaces and hard surfaces surrounded by vegetation and planted green spaces) in each park. An analysis utilizing SPSS and the RayMan program revealed that parks with a softscape to hardscape ratio of approximately two to one experienced temperature reductions of 2.5 to 3 °C. Furthermore, the findings indicate that coniferous trees have a more significant impact on thermal comfort compared to deciduous trees. The significant differences identified in this study underscore essential considerations for urban design processes aimed at achieving sustainability.

Plants and microorganisms both contribute to soil organic matter formation through mineral interactions: Evidence from a subtropical forest succession

Understanding the formation and stabilization of soil organic carbon (SOC) is essential for predicting SOC dynamics. Traditionally, it was believed that SOC accumulates primarily through the selective retention of recalcitrant plant lignin components. However, an emerging hypothesis suggests that microbial necromass adsorbed onto mineral-associated soil fractions play a more significant role in promoting SOC formation. In this study, we tested the above hypothesis by investigating SOC content, particulate fraction (LF + POC) vs. mineral-associated fraction (MAOC), along with microbial necromass (amino sugars as biomarker) and plant lignin component (lignin phenols as biomarker) in the topsoil (0–20 cm) and subsoil (20–40 cm) across three successional stages: early coniferous forest, middle mixed forest and climax broadleaved forest in southern China. Results showed that SOC content increased with forest succession, accompanied by increasing contributions of MAOC in both soil layers. Interestingly, the contribution of microbial necromass to SOC increased throughout the succession only in the subsoil, whereas in the topsoil, it increased from the early to the middle stage, then slightly decreased at the climax stage. Additionally, the contributions of lignin phenols or LF + POC to SOC decreased in both soil layers with forest succession. A partial least squares path model further revealed that MAOC played a dominate role in governing SOC accumulation, driven by active mineral content combined with plant-derived dissolved organic matter in the topsoil and microbial necromass in the subsoil. Collectively, our findings suggest that plants and microorganisms contribute to SOC formation through interactions with minerals, unveiling an intricate interactive mechanism of plant–microbe-mineral continuum in SOC stabilization.

Using Earth observation to support the predictive accuracy of species distribution models in ecological restoration: a case study of Poland beavers (Castor fiber)

Abstract. The ability of Earth observation and remote sensing to identify the potential of species to restore ecosystems is a critical element in combating habitat degradation and biodiversity loss. Historical climate data and current species occurrence, coupled with geospatial modelling methods, can significantly aid in decision-making to support ecosystem restoration. We chose Eurasian beavers (spp. Castor fiber) as our case species, which are known ecosystem engineers that create wetland habitats and significantly alter/reinforce the morphology, dynamics, and hydraulics of riverine landscapes. To investigate their ecosystem restoration potential, we applied species distribution modelling (SDM) to determine their current and future distribution scenarios. Our SDMs used current and simulated future environmental data along with different classes of rasters such as elevation, inland swamps, water bodies, natural seasonally or permanently wet grasslands, open mires, riparian mixed forests, riparian swamp broadleaved forests, riparian swamp coniferous forests, watercourses, protected areas, and urban and built-up areas derived from Google Earth Engine to predict areas suitable for beaver habitats. Further, by using the zonation method, we were able to develop a stepping stone model to prioritize habitat conservation efforts. We provide habitat projections according to time periods of "2041–2060", "2061–2080" and "2081–2100", and to different climate change scenarios (SSP126, SSP245, SSP370, and SSP585). Thus, using a potential nature-based solution, we have employed remote sensing data and tools to develop a holistic framework for not only quantifying the ecosystem restoration potential of beavers but will also provide a new direction for understanding species-specific importance in climate change mitigation.

A new species of Diacheopsis (Myxomycetes) and a new habitat for myxomycetes

ABSTRACT We describe a new species, Diacheopsis resinae (Myxomycetes), collected from a microhabitat new for myxomycetes: stem wounds of coniferous trees (Norway spruce) where the resin is overgrown with a community of resinicolous fungi. The 80 known collections come from the Vosges (France), the Black Forest (Germany), Swabian Alp (Germany), and several localities in Denmark and Norway. Observations, but as well as metabarcoding of substrate samples with fungal (ITS [internal transcribed spacer]), bacterial (16S rDNA), and myxomycete (18S nuc rDNA) primers from eight trunks, revealed the new myxomycete to co-occur with resin-degrading ascomycetes (Infundichalara microchona, Lophium arboricola, Zythia resinae). The gram-negative bacterial genera Endobacter and Sphingomonas were found to be abundant in the substrate and may be a food source for the myxomycete. Fruit bodies were found mostly during the more humid winter season, with a peak in January/February. Partial sequences of two independent molecular markers (18S nuc rDNA, EF1α [elongation factor 1-alpha] gene) were obtained for 41 accessions, which form a monophyletic cluster in a two-gene phylogeny of Stemonititidales but do not group with other species of Diacheopsis, thus rendering this genus paraphyletic. The new species, although exclusively developing sessile sporocarps and morphologically undoubtedly falling into the genus Diacheopsis, is most closely related to species of Lamproderma, especially L. album, L. zonatum, and L. zonatopulchellum. Within D. resinae, three groups can be differentiated, which show nearly complete reproductive isolation, as judged from a recombination analysis of the two unlinked markers and the allelic combinations of the EF1α gene.

Experimental study on fire extinguishing efficiency of polymer hydrogel fire extinguishing agent in pine-fir mixed coniferous forest fires

Pine and fir wood is commonly used in furniture, gardening and construction industries, and has high economic value. It is in great demand in the timber industry. Therefore, pine and fir trees are now widely planted in China. However, pine and fir trees belong to flammable species, with a high content of oil and grease, and the ignition point of pine and fir leaf litter is extremely low. Once burning occurs, it spreads rapidly and can easily turn into a major forest fire. Therefore, the use of extinguishing agents to mitigate and prevent the spread of forest fires is of great importance. In this paper, fire and extinguishing tests were investigated using mixed wood stack burning of pine and fir and mixed fuel from leaf litter. The suppression effects of three different extinguishing agents, AFFF, CAF and hydrogel, on wood fires and leaf litter combustion were compared. And the suppression supply strength of different extinguishing agents to suppress pine and fir trees was determined. The results show that both hydrogel and CAF can effectively extinguish wood stack fires, and AFFF shows re-ignition phenomenon after extinguishing wood stack fires; Comparison of extinguishing time, cooling rate and heat dissipation capacity revealed that hydrogel was superior to CAF; Hydrogel has a highly efficient fire extinguishing properties. It is calculated that the amount of hydrogel used to extinguish pine and cedar fires is only 54 % of the water required, about 87 % of the amount of Class A foam required under the same circumstances, and about 79 % of the amount of aqueous film-forming foam required; Compared with the foam extinguishing agent, the hydrogel extinguishing agent showed better cooling effect, less extinguishing agent dosage, and shorter extinguishing time of 11 s when extinguishing fires in leaf litter; For the rapid spread of leaf litter combustion and easy to re-ignite characteristics, hydrogel has a significant anti-reignition effect.

New insights into a sensitive life stage: hydraulics of tree seedlings in their first growing season.

The first year in a tree's life is characterized by distinct morphological changes, requiring constant adjustments of the hydraulic system. Despite their importance for the natural regeneration of forests and future vegetation composition, little has been known about the hydraulics of tree seedlings. At different times across the first growing season, we analysed xylem area-specific (Kshoot_Axyl) and leaf area-specific (Kshoot_L) shoot hydraulic conductance, as well as embolism resistance of three temperate conifer trees, two angiosperm trees and one angiosperm shrub, and related findings to cell osmotic parameters and xylem anatomical traits. Over the first 10 wk after germination, Kshoot_Axyl and Kshoot_L sharply decreased, then remained stable until the end of the growing season. Embolism resistance was remarkably low in the youngest stages but, coupled with an increase in cell wall reinforcement, significantly increased towards autumn. Contemporaneously, water potential at turgor loss and osmotic potential at saturation decreased. Independent of lineage, species and growth form, the transition from primary to secondary xylem resulted in a less efficient but increasingly more embolism-resistant hydraulic system, enabling stable water supply under increasing risk for low water potentials.

Fire-associated microbial shifts in soils of western conifer forests with Armillaria root disease.

With its influence on ecosystem processes and functions, the soil microbiome can interact with soilborne pathogens to facilitate or suppress plant disease development. These forest ecosystems are experiencing increased wildfire frequency and burn severity that could influence the fungal root pathogen, Armillaria solidipes, and interactions with the soil microbiome. We examined changes to the soil microbiome following three levels of burn severity, and examined how these changes correspond with A. solidipes, and a putatively beneficial species, A. altimontana. Following severe burn, there was a decreased relative abundance of ectomycorrhizal fungi associated A. altimontana. A. solidipes and associated microbial taxa dominated following high-severity burns, suggesting that severe fires provide suitable environmental conditions for these species. Our results suggest that shifts in the soil microbiome and an associated increase in the activity of A. solidipes following high-severity burns in conifer forests may result in priority areas for monitoring and proactive management of Armillaria root disease.

Combined Analysis of Metabolomics and Transcriptome Revealed the Effect of Bacillus thuringiensis on the 5th Instar Larvae of Dendrolimus kikuchii Matsumura.

Dendrolimus kikuchii Matsumura (D. kikuchii) is a serious pest of coniferous trees. Bacillus thuringiensis (Bt) has been widely studied and applied as a biological control agent for a variety of pests. Here, we found that the mortality rate of D. kikuchii larvae after being fed Bt reached 95.33% at 24 h; the midgut membrane tissue was ulcerated and liquefied, the MDA content in the midgut tissue decreased and the SOD, CAT and GPx enzyme activities increased, indicating that Bt has toxic effects on D. kikuchii larvae. In addition, transmission electron microscopy showed that Bt infection caused severe deformation of the nucleus of the midgut tissue of D. kikuchii larvae, vacuoles in the nucleolus, swelling and shedding of microvilli, severe degradation of mitochondria and endoplasmic reticulum and decreased number. Surprisingly, metabolomics and transcriptome association analysis revealed that four metabolic-related signaling pathways, Nicotinate and nicotinamide metabolism, Longevity regulating pathway-worm, Vitamin digestion and absorption and Lysine degradation, were co-annotated in larvae. More surprisingly, Niacinamide was a common differential metabolite in the first three signaling pathways, and both Niacinamide and L-2-Aminoadipic acid were reduced. The differentially expressed genes involved in the four signaling pathways, including NNT, ALDH, PNLIP, SETMAR, GST and RNASEK, were significantly down-regulated, but only SLC23A1 gene expression was up-regulated. Our results illustrate the effects of Bt on the 5th instar larvae of D. kikuchii at the tissue, cell and molecular levels, and provide theoretical support for the study of Bt as a new biological control agent for D. kikuchii.