Forest fires are key ecosystem modifiers affecting the biological, chemical, and physical attributes of forest soils. The extent of soil disturbance by fire is largely dependent on fire intensity, duration and recurrence, fuel load, and soil characteristics. The impact on soil properties is intricate, yielding different results based on these factors. This paper reviews research investigating the effects of wildfire and prescribed fire on the biological and physico-chemical attributes of forest soils and provides a summary of current knowledge associated with the benefits and disadvantages of such fires. Low-intensity fires with ash deposition on soil surfaces cause changes in soil chemistry, including increase in available nutrients and pH. High intensity fires are noted for the complete combustion of organic matter and result in severe negative impacts on forest soils. High intensity fires result in nutrient volatilization, the break down in soil aggregate stability, an increase soil bulk density, an increase in the hydrophobicity of soil particles leading to decreased water infiltration with increased erosion and destroy soil biota. High soil heating (> 120 °C) from high-intensity forest fires is detrimental to the soil ecosystem, especially its physical and biological properties. In this regard, the use of prescribed burning as a management tool to reduce the fuel load is highly recommended due to its low intensity and limited soil heating. Furthermore, the use of prescribed fires to manage fuel loads is critically needed in the light of current global warming as it will help prevent increased wildfire incidences. This review provides information on the impact of forest fires on soil properties, a key feature in the maintenance of healthy ecosystems. In addition, the review should prompt comprehensive soil and forest management regimes to limit soil disturbance and restore fire-disturbed soil ecosystems.

Any-aged forest management (AAF) is a means to reduce clear-felling without compromising profitability or timber production. The concept of AAF is to choose between clear-felling or thinning one harvest at a time based on what is better at that time in terms of the management objectives for the forest. No permanent choice is made between rotation forest management (RFM) and continuous cover forestry (CCF). Optimized AAF is never less profitable than RFM or CCF because all cutting types of both RMF and CCF are also allowed in AAF. This study developed a new set of guidelines for managing boreal forest stands under AAF when the forest landowner maximizes economic profitability. The first part of the guidelines indicates whether the stand should be cut or left to grow. This advice is based on stand basal area, mean tree diameter, minimum allowable post-thinning basal area, site productivity, and discount rate. If the optimal decision is harvesting, the second instruction determines whether the harvest should be clear-felling or thinning. In the case of thinning, the remaining two steps determine the optimal harvest rate in different diameter classes. The guidelines were developed using two different modeling approaches, regression analysis, and optimization, and applied to two Finnish forest holdings, one representing the southern boreal zone and the other the northern parts of the boreal zone. The results show that AAF improves profitability compared to current Finnish management instructions for RFM. The use of clear-felling also decreased the lower the minimum acceptable post-thinning basal area of the stand.

Overstory basal area, ericaceous shrub cover (Kalmia latifolia L. and Rhododendron maximum L.), and fuels (i.e., woody fuel loads and depths and O Horizon thickness) were assessed within Great Smoky Mountains National Park, USA, in 2003 − 2004. Due to recent wildfire activity within the southern Appalachian Mountain region (including Great Smoky Mountains National Park), the potential spread and expansion of ericaceous shrubs, and the impacts of the hemlock woolly adelgid (Adelges tsugae Annand) on eastern hemlock (Tsuga canadensis (L.) Carrière), these same ecosystem components were again assessed in 2019. Elevation and moisture regime (xeric, intermediate, and mesic) were included in this assessment as potential influential factors. An evaluation of repeated measurements from 40 plots suggested that O Horizon thickness did not change significantly over the 16-year period, but increased as elevation increased, and moisture regime (xeric O Horizon thickness > mesic O Horizon thickness) was a significant, related factor. The sum of 1-, 10-, and 100-h fuel loads (fuels less < 7.6 cm diameter) increased, whereas woody fuel depth decreased over the 16-year period. No significant changes in 1000-h fuel loads (> 7.6 cm diameter), total woody fuel loads, ericaceous shrub cover, total basal area, or live T. canadensis basal area were observed. Live T. canadensis basal area decreased with increasing elevation. Dead, standing T. canadensis basal area increased from 2003–2019, and that increase was most pronounced as elevation increased on xeric and intermediate sites. Overall, we found that: 1. hypothesized increases in total woody fuel loads and ericaceous shrub cover were not present; and 2. elevation and moisture regime were most related to observed changes in vegetation and fuel condition.

This study was conducted in Juniperus excelsa stands on the southern slopes of Iran's Alborz Mountains, to determine the effects of fire and seasonal variations on soil physicochemical properties and enzyme activities. A total of 64 composite soil samples were randomly collected in the spring and fall from two burned and unburned sites at depths of 0−10 and 10−20 cm. The results of a two-way ANOVA analysis indicate that fire increased the organic carbon (OC), total nitrogen (TN), and available phosphorus (P_ava) contents of the soil by 16%, 59%, and 53%, respectively. Similarly, when burned sites were compared to unburned sites, the activities of acid phosphatase (ACP) and urease enzymes increased by 73% and 12%, respectively. Nevertheless, fire did not affect soil texture, bulk density (BD), pH, electric conductivity (EC), exchangeable potassium (K_exc), or the activities of alkaline phosphatase (ALP) and dehydrogenase. According to two-way ANOVA results, OC, TN, P_ava, K_exc, and EC values were significantly higher in the fall, whereas pH and ALP values were significantly higher in the spring. Additionally, phosphorous and dehydrogenase activity were significantly different in selected soil factors at 0−10 and 10–20 cm depths. The interaction of fire, season, and soil depth were significant for phosphorous and urease. Moreover, the activity of ALP correlated well with pH (r = 0.68), P (r =  − 0.74), OC (r =  − 0.53), and TN (r =  − 0.37), whereas the activity of ACP correlated significantly with OC (r = 0.64) and TN (r = 0.71). Two years after the fire, soil properties in J. excelsa stands had either improved or remained unaffected, returning to pre-fire levels. Additionally, soil chemical properties varied significantly across sampling seasons, which should be considered when comparing and interpreting soil data in future research.

Tropical regions are biodiversity hotspots and are well-suited to explore the potential influence of global climate change on forest ecosystems. Bryophytes have essential ecological functions in tropical forest ecosystems, but knowledge of the potential impact of global warming and possible changes in water availability patterns on terrestrial bryophytes is limited. We transplanted eight terrestrial moss species from two elevations (900 and 500 m) to warmer and drier elevations (500 and 100 m) during a half-year observation period on Tai Mo Shan, southern China. The simulated climate change resulted in severely declined health status and marked decrease in growth of the transplanted species when compared with their performance at the original elevations. Five of the eight selected species survived for six months after being transplanted to the warmer and drier lowlands, though their health status deteriorated severely. Sematophyllum subhumile, Pseudotaxiphyllum pohliaecarpum and Brachythecium buchananii were highly susceptible to changes in temperature and rainfall patterns and might be used as suitable bioindicators. As the tropics are expected to become hotter and drier, terrestrial mosses might be negatively affected or even be at risk of extinction. Bryophytes in the tropics could represent one of the best biological communities to reflect the direct adverse impact of climate change and provide early warning of the biological outcomes induced by ongoing climate crisis.

Existing almost deep learning methods rely on a large amount of annotated data, so they are inappropriate for forest fire smoke detection with limited data. In this paper, a novel hybrid attention-based few-shot learning method, named Attention-Based Prototypical Network, is proposed for forest fire smoke detection. Specifically, feature extraction network, which consists of convolutional block attention module, could extract high-level and discriminative features and further decrease the false alarm rate resulting from suspected smoke areas. Moreover, we design a meta-learning module to alleviate the overfitting issue caused by limited smoke images, and the meta-learning network enables achieving effective detection via comparing the distance between the class prototype of support images and the features of query images. A series of experiments on forest fire smoke datasets and miniImageNet dataset testify that the proposed method is superior to state-of-the-art few-shot learning approaches.

Typhoons have caused considerable damage to individual tree and forest ecosystems. To reduce wind-induced tree damage and better predict the risk of damage, improving our understanding of wind-tree interactions during strong wind conditions is important. To this purpose, wind characteristics and movements of an individual Betula platyphylla Suk. in a forest stand were monitored during three typhoons (Bavi, Maysak and Haishen). Results revealed that the average wind twists with increasing height, with a large twist gradient within the canopy and a small twist gradient outside the canopy. The maximum wind twist angle was approximately 110°. The disturbance of trees increases the turbulence intensity of the wind field in the canopy. The maximum power of the wind spectra and the turbulence anisotropy of the three turbulence components decrease with increasing height. B. platyphylla did not resonate with the wind in any of the typhoons but responded strongly to gusts near its free vibration peak frequencies. The peak frequency of the mechanical transfer function of B. platyphylla is essentially the same as the peak frequency of the response power spectra. The mechanical transfer function of the wind-induced response of the tree is almost the same as the transfer function of the damped harmonic oscillator which has similar characteristics to coniferous trees.

Forest gaps restrict the restoration of temperate secondary forest to broad-leaved Korean pine forest in zonal climax vegetation by affecting the growth of Korean pine (Pinus koraiensis). However, the photosynthetic adaptability of Korean pine to gap size and position within the gap is unclear. In order to explore the adaptability of young Korean pine (35 years) to different gap sizes in Xiaoxing’anling, photosynthetic capacity and microenvironmental factors (leaf temperature, light transmittance) of Korean pine needles in three positions in the gap (central, transition, and edge areas) were investigated. Three gaps were identified in the secondary Populus davidiana forest: a large 201 m² gap, a middle 112 m² gap, and a small 50 m² gap; 12 m² of the understory was sampled as a control. The results show that: (1) maximum net photosynthetic rate (P _max) in needles of Korean pine growing in the large gap was higher than in the small gap, and P_max in the centre in the same gap was higher than in the transition and edge areas; (2) light saturation point (LSP) and photosynthetic quantum yield (AQY) of needles in the large gap were higher than in the small gap, while the light compensation point (LCP) and chlorophyll contents of needles were lower in the small gap; and, (3) P _max had a significant positive correlation with temperature and light transmittance. It is suggested that the larger the gap in secondary Populus davidiana forests, the greater the change in light intensity and temperatures, the stronger the light adaption of Korean pine needles and the higher the photosynthetic capacity. Therefore, in the recovery of broad-leaved/Korean pine forests, suitable gaps should be created and gap microhabitats fully utilized to accelerate the restoration process.

The regulation of plant transpiration is a key factor affecting transpiration efficiency, growth and adaptation of Eucalyptus species to limited water availability in tropical and subtropical environments. However, few studies have related this trait to the performance of Eucalyptus seedlings and none have investigated the influence of vapor pressure deficit (VPD) on transpiration rates and growth. In this study, the transpiration and growth responses of seedlings of Eucalyptus urophylla (S.T. Blake) and Eucalyptus cloeziana (F. Muell.) to progressive soil water deficits were evaluated under semi-controlled conditions using the fraction of transpirable soil water (FTSW) method. In addition, the influence of VPD on seedling transpiration, development and growth was also investigated. The FTSW threshold ranged from 0.40 to 0.99 for the transpiration rate and from 0.32 to 0.97 for the development and growth variables. Little or no changes in the FTSW threshold were detected in response to changes in atmospheric VPD. Both Eucalyptus species presented a conservation strategy under drought stress. In addition, water-conserving mechanisms during the seedling phase were related to rapid stomatal closure, reduced leaf area, and number of leaves.

Voxel-based canopy profiling is commonly used to determine small-scale leaf area. Layer thickness and voxel size impact accuracy when using this method. Here, we determined the optimal combination of layer thickness and voxel size to estimate leaf area density accurately. Terrestrial LiDAR Stonex X300 was used to generate point cloud data for Masson pines (Pinus massoniana). The canopy layer was stratified into 0.10–1.00-m-thick layers, while voxel size was 0.01–0.10 m. The leaf area density of individual trees was estimated using leaf area indices for the upper, middle, and lower canopy and the overall canopy. The true leaf area index, obtained by layered harvesting, was used to verify the inversion results. Leaf area density was inverted by nine combinations of layer thickness and voxel size. The average relative accuracy and mean estimated accuracy of these combined inversion results exceeded 80%. When layer thickness was 1.00 m and voxel size 0.05 m, inversion was closest to the true value. The average relative accuracy was 92.58%, mean estimated accuracy 98.00%, and root mean square error 0.17. The combination of leaf area density and index was accurately retrieved. In conclusion, nondestructive voxel-based canopy profiling proved suitable for inverting the leaf area density of Masson pine in Hetian Town, Fujian Province.

Liquidambar formosana Hance is an attractive landscape tree species because its leaves gradually change from green to red, purple or orange in autumn. In this study, the red variety of L. formosana was used to establish a quantitative model of leaf color. Physiological changes in leaf color, pigment levels, enzyme activity, photosynthetic fluorescence characteristics and chloroplast ultrastructure were monitored. The relationship between leaf color and physiological structure indices was quantitatively analyzed to systematically explore the mechanisms behind leaf color. Our data showed that with a decrease in external temperatures, chloroplast numbers and sizes gradually decreased, thylakoid membranes became distorted, and chlorophyll synthesis was blocked and gradually decreased. As a result, chloroplast membranes could not be biosynthesized normally; net photosynthesis, maximum and actual photochemical efficiency, and rate of electron transfer decreased rapidly. Excess light energy caused leaf photoinhibition. With intensification of photoinhibition, leaves protected themselves using two mechanisms. In the first, anthocyanin synthesis was promoted by increasing chalcone isomerase and flavonoid glycosyltransferase activities and soluble sugar content so as to increase anthocyanin to filter light and eliminate reactive oxygen species to reduce photoinhibition. In the second, excessive light energy was consumed in the form of heat energy by increasing the non-photochemical quenching coefficient. These processes tuned the leaves red.

Shoot organogenesis is critical for the shortening of long breeding cycles and circumvent the barrier of cloning mature Eucalyptus cloeziana trees. It enables large-scale production of plants from transformed tissues. This study evaluates the effect of α-naphthaleneacetic acid (NAA), thidiazuron (TDZ) and benzylaminopurine (BAP) on the organogenesis of E. cloeziana from hypocotyls and cotyledonary leaves. In the induction stage, hypocotyls and cotyledonary leaves were established in a Murashige and Skoog (MS) culture medium supplemented with NAA or TDZ. Callus tissues were cultivated in a MS culture medium containing only BAP or different concentrations of BAP/NAA in the differentiation stage. Adventitious buds were multiplied in vitro and elongated in a WPM culture medium supplemented with 0.89 µM BAP and 0.05 µM NAA. Cotyledonary leaves exhibited the best in vitro regeneration. The induction of adventitious buds occurred only in calluses induced from TDZ. In the differentiation stage, 4.4 µM BAP treatment promoted an increase of adventitious bud regeneration. Micro-cuttings from regenerated shoots were acclimatized and rooted ex vitro in mini-incubators. The results confirm the establishment of an efficient protocol for the in vitro regeneration of E. cloeziana by indirect organogenesis, providing new insights regarding cloning of this species.

This article examines the physiological relationships between fine roots and foliage, and how their biomass ratio correlates with changes in stand quality class. The biomass of fine roots ≤ 3 mm in diameter of spruce stands in the Republic of Karelia (Northwest Russia) was determined by the soil monolith method. Foliage biomass was calculated using a previously designed technique from the standing stock, average height and quality class of the stand. A relation between fine-root: foliage biomass ratio and stand quality class (representing soil fertility) has been established. The closest correlation between fine-root: foliage biomass ratio and stand quality based on soil fertility was for the 1–2 mm root fraction. Analysis of the water flux balance in the trees revealed a correlation between fine-root: foliage ratio and the ratio of the specific volume of transpiration by the stand to the specific volume of water uptake from the soil by roots. Theoretical explanations for the decrease in fine-root: foliage biomass ratios with increasing stand quality class are offered.

Numerous growth and physiological variables of 3-week-old Populus simonii ×  P. nigra seedlings were assessed after treatment with either nitrate nitrogen (NO₃ ⁻–N) (0.1, 0.5, 1, 5, or 10 mmol·L⁻¹) or ammonium nitrogen (NH₄ ⁺–N) (0.1, 0.5, 1, 5, or 10 mmol·L⁻¹) to determine the best nitrogen form and concentration to optimize growth, biomass allocation, pigment content, and photosynthetic capacity. The results of combining membership function and an evaluation index suggested that, 5 mmol·L⁻¹ nitrogen, regardless of the form, yielded the highest comprehensive evaluation index and good growth. In addition, a Pearson correlation analysis and network visualization revealed that the total mass, shoot mass, root mass, leaf dry mass, plant height, leaf area, chlorophyll a and total chlorophyll had a physiological index connectivity degree ≥ 15 for both nitrogen forms. Net photosynthetic rate, stomatal conductance, transpiration rate, maximum photochemical efficiency of PSII, total nitrogen content, ground diameter, chlorophyll b, and carotenoid were unique indices for evaluating NH₄ ⁺–N-based nutrition, which could provide a theoretical basis for evaluating the effects of nitrogen fertilizer on seedlings, cultivation periods, and stress tolerance in P. simonii ×  P. nigra.

Ultrafine bubbles and low doses of gamma irradiation had a positive effect on seed germination. This research tested the effectiveness of ultrafine bubbles (UFB) water and gamma irradiation for improving the viability and vigor of Albizia chinensis (Osbeck) Merr. seeds that had been stored for four years. A completely randomized two-factor experiment, i.e., UFB water and gamma irradiation treatments, were used to determine the best seed treatment. The UFB water treatment had a significant effect on all seed germination parameters; the gamma irradiation treatment did not have a significant effect on improving the viability and vigor of the seeds, with a very low initial germination (11.7%). Soaking the seeds in UFB water for 30 min gave the best germination (51.3%). These improvements also occurred in other germination parameters such as germination rate, germination value, radicle length and vigor index. The UFB water treatment has the potential to improve the germination of seeds with low physiological qualities.

Basic Leu zipper (bZIP) genes play pivotal, versatile roles in abiotic or biotic stress responses and in other biological processes. Knowledge on the evolutionary relationships and patterns of gene expression of bZIP family members in woody plants, however, has been limited. Here we identified and characterized 47 BpbZIP genes across the silver birch (Betula pendula Roth.) genome. With reference to bZIP classifications for Arabidopsis thaliana, all BpbZIP proteins clustered among 10 groups in phylogeny. The bZIP domains were divided into five patterns based on intron positions and splicing phases. A total of 24 conserved motifs were detected in BpbZIPs with high group specificity. We also analyzed the protein structure of the BpAREB/ABF/ABI5 subfamily, the most important subfamily in the bZIP family. Expression analyses demonstrated that BpbZIP genes were widely involved in abscisic acid, salt, drought, and heat stress responses, with BpbZIP07/ABF4 and BpbZIP21/ABF2 most highly expressed. Our results on genome-wide identification, evolutionary relationships, gene structure, and motif and promoter element identification for BpbZIP family members in silver birch provide a comprehensive understanding of bZIP transcription factors in birch and will lead to a deeper understanding of their evolution and potential biological functions.

This study aimed to explore and improve the different economic values of Pinus koraiensis (Siebold and Zucc.) by examining the variations in 6 growth traits and 9 physicochemical wood properties among 53 P. koraiensis half-sib families. Growth traits assessed included height, diameter at breast height, volume, degree of stem straightness, stem form, and branch number per node, while wood properties assessed included density, fiber length and width, fiber length to width ratio, and cellulose, hemicellulose, holocellulose, lignin, and ash contents. Except for degree of stem straightness and branch number per node, all other traits exhibited highly significant variations (P < 0.01) among families. The coefficients of variation ranged from 5.3 (stem form) to 66.7% (ash content), whereas, the heritability ranged from 0.136 (degree of stem straightness) to 0.962 (ash content). Significant correlations were observed among growth traits and wood physicochemical properties. Principal component analysis identified four distinct groups representing growth traits, wood chemical and physical properties, and stem form traits. Multi-trait comprehensive evaluation identified three groups of elite families based on breeding objectives, including rapid growth, improved timber production for building and furniture materials, and pulpwood production. These specific families should be used to establish new plantations.

The effects of drought on tree mortality at forest stands are not completely understood. For assessing their water supply, knowledge of the small-scale distribution of soil moisture as well as its temporal changes is a key issue in an era of climate change. However, traditional methods like taking soil samples or installing data loggers solely collect parameters of a single point or of a small soil volume. Electrical resistivity tomography (ERT) is a suitable method for monitoring soil moisture changes and has rarely been used in forests. This method was applied at two forest sites in Bavaria, Germany to obtain high-resolution data of temporal soil moisture variations. Geoelectrical measurements (2D and 3D) were conducted at both sites over several years (2015–2018/2020) and compared with soil moisture data (matric potential or volumetric water content) for the monitoring plots. The greatest variations in resistivity values that highly correlate with soil moisture data were found in the main rooting zone. Using the ERT data, temporal trends could be tracked in several dimensions, such as the interannual increase in the depth of influence from drought events and their duration, as well as rising resistivity values going along with decreasing soil moisture. The results reveal that resistivity changes are a good proxy for seasonal and interannual soil moisture variations. Therefore, 2D- and 3D-ERT are recommended as comparatively non-laborious methods for small-spatial scale monitoring of soil moisture changes in the main rooting zone and the underlying subsurface of forested sites. Higher spatial and temporal resolution allows a better understanding of the water supply for trees, especially in times of drought.

The effect of reforestation on carbon sequestration has been extensively studied but there is less understanding of the changes that stand age and vegetation types have on changes in biomass carbon and soil organic carbon (SOC) after reforestation. In this study, 150 reforested plots were sampled across six provinces and one municipality in the Yangtze River Basin (YRB) during 2017 and 2018 to estimate carbon storage in biomass and soil. The results illustrate that site-averaged SOC was greater than site-averaged biomass carbon. There was more carbon sequestered in the biomass than in the soil. Biomass carbon accumulated rapidly in the initial 20 years after planting. In contrast, SOC sequestration increased rapidly after 20 years. In addition, evergreen species had higher carbon density in both biomass and soil than deciduous species and economic species (fruit trees). Carbon sequestration in evergreen and deciduous species is greater than in economic species. Our findings provide new evidence on the divergent responses of biomass and soil to carbon sequestration after reforestation with respect to stand ages and vegetation types. This study provides relevant information for ecosystem management as well as for carbon sequestration and global climate change policies.

The poplar and willow weevil, Cryptorhynchus lapathi L., a major universally destructive wood-boring insect has become one of the important quarantine pests that is extremely destructive to forestry development and needs to be controlled. Entomopathogenic fungi (EPF) are considered safe and friendly for humans and the environment and play important roles in controlling insect pest populations. In this study, the screening of entomopathogenic fungi for control of C. lapathi is reported through the evaluation of virulence of four fungal Beauveria bassiana (CFCC81428, CFCC83116, CFCC83486, CFCC87297) strains, one B. brongniartii (CFCC83487) strain and one Metarhizium anisopliae (CFCC88953) strain. The virulence of the different strains was appraised by correct mortality rate, cumulative mortality rate, median lethal concentration (LC₅₀) and median lethal time (LT₅₀). B. bassiana strains CFCC81428 and CFCC83116 were the most virulent among the six strains with a mortality up to 100%, and the LT₅₀ were 2.7 and 3.1 days. Five conidia concentrations of three strains (CFCC81428, CFCC83116 and CFCC87298) that caused high virulence was screened for dose-relationship. Their effect on controlling C. lapathi larvae were also determined under field condition by brushing conidia suspensions on C. lapathi larvae infested in a poplar trunk. The cumulative rate in the field was lower than those obtained from the laboratory, but the order of the virulence of different strains did not change. Mortality in all three strains occurred at their highest concentration (1.0 × 10⁸ conidia mL⁻¹). Under field conditions, the CFCC81428 strain was the most effective, causing mortalities of 80.3% and 75.2% in two plots in Beipiao and Lindian counties, respectively, followed by CFCC83116 (69.1%, 66.6%) and CFCC87298 (60.7%, 59.3%). Based on our results, the B. bassiana strain CFCC81428 has the potential as a biological insecticide to control C. lapathi larvae.