In riparian forests, litter decay provides essential energy and nutrients for both terrestrial and fluvial ecosystems. Litter mixing effects (LMEs) are crucial in regulating litter decay and nutrient dynamics, yet how LMEs change over time is unclear in riparian forests. In this study, leaf litter of three common species (Alnus sibirica Fisch. ex Turcz, Betula platyphylla Sukaczev, and Betula fruticosa Pall.) were mixed in an equal mass ratio and LMEs were measured for mass and nitrogen (N) remaining in whole litter mixtures over a 3-year period in a boreal riparian forest, northeastern China. LMEs were also assessed for component litter mass and N remaining by separating litter mixtures by species. During the decay of litter mixtures, antagonistic effects on mass and N remaining were dominant after one and two years of decay, whereas only additive effects were observed after three years. LMEs correlated negatively with functional diversity after the first and two years of decay but disappeared after three years. When sorting litter mixtures by species, non-additive LMEs on mass and N remaining decreased over incubation time. Moreover, non-additive LMEs were more frequent for litter of both B. platyphylla and B. fruticosa with lower N concentration than for A. sibirica litter with higher N concentration. These results indicate that incubation time is a key determinant of litter mixing effects during decay and highlight that late-stage litter mixture decay may be predicted from single litter decay dynamics in boreal riparian forests.

Methanotrophs, organisms that obtain oxygen by oxidizing methane, are recognized as the only known biological sink for atmospheric CH₄, and forest soil methanotrophs play crucial roles in mitigating global warming. The succession patterns of methanotrophic communities and functions in Wudalianchi volcano forest soils could provide a basis for the study of evolutionary mechanisms between soil microorganisms, the environment, and carbon cycling of temperate forest ecosystems under climate change. In this study, the characteristics and drivers of methanotrophic community structure and function of two volcanic soils at different stages of development are analyzed, including an old volcano and a new volcano, which most recently erupted 300 years and 17 − 19 × 10⁵ years ago, respectively, and a non-volcano hills as control, based on space for time substitution and Miseq sequencing and bioinformation technology. The results showed that CH₄ fluxes were significantly higher in old-stage volcano forest soils than new-stage forest soils and non-volcano forest soils. There were significant differences in the community composition and diversity of soil methanotrophs from different volcano forest soils. Methylococcus was the dominant genus in all soil samples. Additionally, the relative abundance of Methylococcus, along with Clonothrix, Methyloglobulus, Methylomagum, Methylomonas and Methylosarcina, were the important genera responsible for the differences in methanotrophic community structure in different volcano forest soils. The relative abundance of methanotroph belonging to γ-proteobacteria was significantly higher than that belonging to α-proteobacteria (P < 0.05). Chao1, Shannon and Simpson indices of soil methanotrophic community were significantly lower in new-stage volcanos and were significantly affected by bulk density, total porosity, pH, nitrate, dissolved organic carbon and dissolved organic nitrogen. There were significant differences in community structure between new-stage and old-stage volcanoes. Bulk density and pH are important soil properties contributing to the divergence of methanotrophs community structure, and changes in soil properties due to soil development time are important factors driving differences in methanotrophs communities in Wudalianchi volcanic soils.

Afforestation has an important role in biodiversity conservation and ecosystem function improvement. A meta-analysis was carried out in China, which has the largest plantation area globally, to quantify the effects of plantings on soil microbial diversity. The results showed that the overall effect of afforestation on soil microbial diversity was positive across the country. Random forest algorithm suggested that soil carbon was the most important factor regulating microbial diversity and the positive response was only found with new plantings on low-carbon bare lands but not on high-carbon farmlands and grasslands. In addition, afforestation with broadleaved species increased microbial diversity, whereas planting with conifers had no effect on microbial diversity. This study clarified the effects of plantings on soil microbial diversity, which has an important implication for establishing appropriate policies and practices to improve the multiple functionalities (e.g., biodiversity conservation and climate change mitigation) during plantation establishment.

Effective development and utilization of wood resources is critical. Wood modification research has become an integral dimension of wood science research, however, the similarities between modified wood and original wood render it challenging for accurate identification and classification using conventional image classification techniques. So, the development of efficient and accurate wood classification techniques is inevitable. This paper presents a one-dimensional, convolutional neural network (i.e., BACNN) that combines near-infrared spectroscopy and deep learning techniques to classify poplar, tung, and balsa woods, and PVA, nano-silica-sol and PVA-nano silica sol modified woods of poplar. The results show that BACNN achieves an accuracy of 99.3% on the test set, higher than the 52.9% of the BP neural network and 98.7% of Support Vector Machine compared with traditional machine learning methods and deep learning based methods; it is also higher than the 97.6% of LeNet, 98.7% of AlexNet and 99.1% of VGGNet-11. Therefore, the classification method proposed offers potential applications in wood classification, especially with homogeneous modified wood, and it also provides a basis for subsequent wood properties studies.

Tree interactions are essential for the structure, dynamics, and function of forest ecosystems, but variations in the architecture of life-stage interaction networks (LSINs) across forests is unclear. Here, we constructed 16 LSINs in the mountainous forests of northwest Hebei, China based on crown overlap from four mixed forests with two dominant tree species. Our results show that LSINs decrease the complexity of stand densities and basal areas due to the interaction cluster differentiation. In addition, we found that mature trees and saplings play different roles, the first acting as “hub” life stages with high connectivity and the second, as “bridges” controlling information flow with high centrality. Across the forests, life stages with higher importance showed better parameter stability within LSINs. These results reveal that the structure of tree interactions among life stages is highly related to stand variables. Our efforts contribute to the understanding of LSIN complexity and provide a basis for further research on tree interactions in complex forest communities.

Light levels determine regeneration in stands and a key concern is how to regulate the light environment of different stand types to the requirements of the understory. In this study, we selected three stands typical in south China (a Cryptomeria japonica plantation, a Quercus acutissima plantation, and a mixed stand of both) and three thinning intensities to determine the best understory light environment for 3-year-old Phoebe bournei seedlings. The canopy structure, understory light environment, and photosynthesis and growth indicators were assessed following thinning. Thinning improved canopy structure and understory light availability of each stand; species composition was the reason for differences in the understory light environment. Under the same thinning intensity, the mixed stand had the greatest light radiation and most balanced spectral composition. P. bournei photosynthesis and growth were closely related to the light environment; all three stands required heavy thinning to create an effective and sustained understory light environment. In a suitable understory light environment, the efficiency of light interception, absorption, and use by seedlings was enhanced, resulting in a higher carbon assimilation the main limiting factor was stomatal conductance. As a shade-avoidance signal, red/far-red radiation is a critical factor driving changes in photosynthesis and growth of P. bournei seedlings, and a reduction increased light absorption and use capacity and height: diameter ratios. The growth advantage transformed from diameter to height, enabling seedlings to access more light. Our findings suggest that the regeneration of shade-tolerant species such as P. bournei could be enhanced if a targeted approach to thinning based on stand type was adopted.

Parameterization is a critical step in modelling ecosystem dynamics. However, assigning parameter values can be a technical challenge for structurally complex natural plant communities; uncertainties in model simulations often arise from inappropriate model parameterization. Here we compared five methods for defining community-level specific leaf area (SLA) and leaf C:N across nine contrasting forest sites along the North–South Transect of Eastern China, including biomass-weighted average for the entire plant community (AP_BW) and four simplified selective sampling (biomass-weighted average over five dominant tree species [5DT_BW], basal area weighted average over five dominant tree species [5DT_AW], biomass-weighted average over all tree species [AT_BW] and basal area weighted average over all tree species [AT_AW]). We found that the default values for SLA and leaf C:N embedded in the Biome-BGC v4.2 were higher than the five computational methods produced across the nine sites, with deviations ranging from 28.0 to 73.3%. In addition, there were only slight deviations (< 10%) between the whole plant community sampling (AP_BW) predicted NPP and the four simplified selective sampling methods, and no significant difference between the predictions of AT_BW and AP_BW except the Shennongjia site. The findings in this study highlights the critical importance of computational strategies for community-level parameterization in ecosystem process modelling, and will support the choice of parameterization methods.

Among the impacts of climate change, there is the intensification of phenomena such as the El Niño Southern Oscillation (ENSO) responsible for El Niño and La Niña. However, understanding their effects on the functional processes of forests is limited. Therefore, this study evaluated the effects of ENSO on litter stock and water holding capacity (WHC) in a successional forest in eastern Amazonia. Evaluations occurred in periods with the most rainfall in El Niño (2019) and least in La Niña (2021) years. Twelve permanent plots were used to sample litter. ENSO effects were evident for WHC, higher during El Niño. However, this influence was not clear for litter, as only in the rainy season effects were found. There was a positive correlation of WHC with precipitation and humidity, while litter stocks were negatively correlated with temperature and wind speed. Although the subject of this study requires long-term assessments, preliminary results suggests that, depending on the intensity of ENSO, forest functional processes can be strongly impacted and altered. The conclusion reinforces warnings by the scientific community about the impacts of climate change on the maintenance of litter stocks, decomposition and, consequently, the biogeochemical cycle and essential ecosystem services for the maintenance of Amazonia biodiversity. The need to develop long-term research to understand the effects of climatic change on litter stocks and water holding capacity is highlighted, especially in Amazonia.

As an important material for manufacturing resonant components of musical instruments, Paulownia has an important influence on the sound quality of Ruan. In this paper, a model for evaluating the sound quality of Ruan based on the vibration characteristics of wood is developed using machine learning methods. Generally, the selection of materials for Ruan manufacturing relies primarily on manually weighing, observing, striking, and listening by the instrument technician. Deficiencies in scientific theory have hindered the quality of the finished Ruan. In this study, nine Ruans were manufactured, and a prediction model of Ruan sound quality was proposed based on the raw material information of Ruans. Out of a total of 180 data sets, 145 and 45 sets were chosen for training and validation, respectively. In this paper, typical correlation analysis was used to determine the correlation between two single indicators in two adjacent pairwise combinations of the measured objects in each stage of the production process in Ruan. The vibration characteristics of the wood were tested, and a model for predicting the evaluation of Ruan’s acoustic qualities was developed by measuring the vibration characteristics of the resonating plate material. The acoustic quality of the Ruan sound board wood was evaluated and predicted using machine learning model generalized regression neural network. The results show that the prediction of Ruan sound quality can be achieved using Matlab simulation based on the vibration characteristics of the soundboard wood. When the model-predicted values were compared with the traditional predicted results, it was found that the generalized regression neural network had good performance, achieving an accuracy of 93.8% which was highly consistent with the experimental results. It was concluded that the model can accurately predict the acoustic quality of the Ruan based on the vibration performance of the soundboards.

There is considerable interest devoted to old-growth forests and their capacity to store carbon (C) in biomass and soil. Inventories of C stocks in old-growth forests are carried out worldwide, although there is a lack of information on their actual potential for C sequestration. To further understand this, soil organic carbon (SOC) was measured in one of Italy’s best-preserved old-growth forests, the Sasso Fratino Integral Nature Reserve. This reserve is on the World Heritage List along with other ancient beech forests of Europe, and it is virtually untouched due to the steepness of the terrain, even before legal constraints were imposed. Although the sandstone-derived soils are often shallow, they are rich in organic matter. However, no quantification had been carried out. By systematically sampling the topsoil across the forest, we accurately determined the average amount of SOC (62.0 ± 16.9 Mg ha^–1) and nitrogen (4.0 ± 1.2 Mg ha^–1) in the top 20 cm. Using the CENTURY model, future dynamics of SOC stocks were predicted to 2050 according to two climate scenarios, A1F1 and B2, the first of high concern and the second more optimistic. The model projected an increase of 0.2 and 0.3 Mg ha^–1 a^–1 by 2030 under the A1F1 and B2 scenarios, respectively, suggesting that the topsoil in old-growth forests does not reach equilibrium but continues accumulating SOC. However, from 2030 to 2050, a decline in SOC accumulation is predicted, indicating SOC net loss at high altitudes under the worst-case scenario. This study confirms that soils in old-growth forests play a significant role in carbon sequestration. It also suggests that climate change may affect the potential of these forests to store SOC not only in the long term but also in the coming years.

Heat shock transcription factors (Hsfs) have important roles during plant growth and development and responses to abiotic stresses. The identification and function of Hsf genes have been thoroughly studied in various herbaceous plant species, but not woody species, especially Phoebe bournei, an endangered, unique species in China. In this study, 17 members of the Hsf gene family were identified from P. bournei using bioinformatic methods. Phylogenetic analysis indicated that PbHsf genes were grouped into three subfamilies: A, B, and C. Conserved motifs, three-dimensional structure, and physicochemical properties of the PbHsf proteins were also analyzed. The structure of the PbHsf genes varied in the number of exons and introns. Prediction of cis-acting elements in the promoter region indicated that PbHsf genes are likely involved in responses to plant hormones and stresses. A collinearity analysis demonstrated that expansions of the PbHsf gene family mainly take place via segmental duplication. The expression levels of PbHsf genes varied across different plant tissues. On the basis of the expression profiles of five representative PbHsf genes during heat, cold, salt, and drought stress, PbHsf proteins seem to have multiple functions depending on the type of abiotic stress. This systematic, genome-wide investigation of PbHsf genes in P. bournei and their expression patterns provides valuable insights and information for further functional dissection of Hsf proteins in this endangered, unique species.

To study non-structural carbohydrate characteristics and nutrient utilization strategies of Pinus yunnanensis under continuous drought conditions, 2-year-old seedlings were planted in pots with appropriate water, light and moderate and severe drought treatments [(80 ± 5), (65 ± 5), (50 ± 5), and (35 ± 5)% of field water-holding capacity]. Non-structural carbohydrates, carbon (C), nitrogen (N), and phosphorus (P) concentrations were measured in each plant component. The results show that: (1) With increasing drought, non-structural carbohydrates gradually increased in leaves, stems, and coarse roots, while gradually decreased in fine roots; (2) C concentrations of all were relatively stable under different stress levels. Phosphorous utilization of each component increased under light and moderate drought conditions, while N and P utilization efficiency of each plant component decreased under severe drought. Growth was mainly restricted by N, first decreasing and then increasing with increased drought; (3) There was a correlation between the levels of non-structural carbohydrates and C, N, and P in each component. Changes in N concentration affected the interconversion between soluble sugar and starch, which play a regulatory role in the fluctuation of the concentration of non-structural carbohydrates; and, (4) Plasticity analysis showed that P. yunnanensis seedlings responded to drought mainly by altering starch concentration, the ratio of soluble sugar to starch in leaves and stems, and further by altering N and P utilization efficiencies. Overall, these results suggest that the physiological activities of all organs of P. yunnanensis seedlings are restricted under drought and that trade-offs exist between different physiological indicators and organs. Our findings are helpful in understanding non-structural carbohydrate and nutrient adaptation mechanisms under drought in P. yunnanensis seedlings.

Analyses of stable isotopes (C, O, H) in tree rings are increasingly important cross-disciplinary programs. The rapid development in this field documented in an increasing number of publications requires a comprehensive review. This study includes a bibliometric analysis-based review to better understand research trends in tree ring stable isotope research. Overall, 1475 publications were selected from the Web of Science Core Collection for 1974–2023. The findings are that: (1) numbers of annual publications and citations increased since 1974. From 1974 to 1980, there were around two relevant publications per year. However, from 2020 to 2022, this rose sharply to 109 publications per year. Likewise, average article citations were less than four per year before 1990, but were around four per article per year after 2000; (2) the major subjects using tree ring stable isotopes include forestry, geosciences, and environmental sciences, contributing to 42.5% of the total during 1974–2023; (3) the top three most productive institutions are the Chinese Academy of Sciences (423), the Swiss Federal Institute for Forest, Snow and Landscape Research (227), and the University of Arizona (204). These achievements result from strong collaborations; (4) review papers, for example, (Dawson et al., Annu Rev Ecol Syst 33:507–559, 2002) and (McCarroll and Loader, Quat Sci Rev 23:771–801, 2004), are among the most cited, with more than 1000 citations; (5) tree ring stable isotope studies mainly focus on climatology and ecology, with atmospheric CO₂ one of the most popular topics. Since 2010, precipitation and drought have received increasing attention. Based on this analysis, the research stages, key findings, debated issues, limitations and directions for future research are summarized. This study serves as an important attempt to understand the progress on the use of stable isotopes in tree rings, providing scientific guidance for young researchers in this field.

Birch has long suffered from a lack of active forest management, leading many researchers to use material without a detailed management history. Data collected from three birch (Betula pendula Roth, B. pubescens Ehrh.) sites in southern Sweden were analyzed using regression analysis to detect any trends or differences in wood properties that could be explained by stand history, tree age and stem form. All sites were genetics trials established in the same way. Estimates of acoustic velocity (AV) from non-destructive testing (NDT) and predicted AV had a higher correlation if data was pooled across sites and other stem form factors were considered. A subsample of stems had radial profiles of X-ray wood density and ring width by year created, and wood density was related to ring number from the pith and ring width. It seemed likely that wood density was negatively related to ring width for both birch species. Linear models had slight improvements if site and species were included, but only the youngest site with trees at age 15 had both birch species. This paper indicated that NDT values need to be considered separately, and any predictive models will likely be improved if they are specific to the site and birch species measured.

This study assessed the effect of patch scarification and mounding on the physical properties of the root layer and the success of tree planting in various types of forests. This study was conducted on 12 forest sites in taiga forests of the European part of Russia. A total of 54 plots were set up to assess seedling survival; root collar diameter, height, and heigh increment were measured for 240 seedlings to assess growth. In the rooting layer, 240 soil samples were taken to determine physical properties. The study showed that soil treatment methods had no effect on bulk density and total porosity in Cladina sites. However, reduced soil moisture was noted, particularly in mounds, resulting in increased aeration. In Myrtillus sites, there were increased bulk density, reduced soil moisture, and total porosity in the mounds. Mounding treatment in Polytrichum sites resulted in reduced soil moisture and increased aeration porosity. In the Myrtillus and Polytrichum sites, patch scarification had no effects on physical properties. In Polytrichum sites, survival rates, heights, and heigh increments of bareroot Norway spruce seedlings in mounds were higher than in patches; however, the same did not apply to diameter. In Cladina and Myrtillus sites, there was no difference in growth for bareroot and containerised seedlings with different soil treatments. Growing conditions and soil types should be considered when applying different soil treatment methods to ensure high survival rates and successful seedling growth.

Forest tree species reproduction is a key factor in maintaining the genetic diversity of future generations and the stability of forest ecosystems. The ongoing ash dieback disease could affect the reproductive ecology of Fraxinus excelsior L. and have a major impact on the quantity and quality of pollen and seeds. In this study, we investigated pollen production and viability of pollen and seeds of ash trees with different health status from 2018 to 2022. Inflorescences were collected from 105 trees (pollen production), pollen from 125 trees (pollen viability), and seeds from 53 trees (seed quality) in two seed orchards and in one floodplain forest in southern Germany. Not all parameters were examined at every site every year. The average pollen production per tree was estimated at 471.2 ± 647.9 billion pollen grains. In addition, we found that a high number of inflorescences did not equate to high pollen production per inflorescence. Pollen production of healthy and diseased trees did not differ significantly, although only 47% of severely diseased male trees (vs. 72% for healthy trees) produced flowers. With regards to pollen viability, the TTC test showed an average viability of 73% ± 17%. Overall, there was a slight tendency for diseased trees to have less viable pollen. However, a significant difference could only be calculated for trees in the floodplain forest. The percentage of germinable seeds in 2018 was 38% in the floodplain forest and 57% in one of the seed orchards. The percentage of viable seeds (TTC test) ranged from 17 to 22% in the orchards in 2020. Non-viable seeds were usually heavily infested by insects. In general, seed quality was not significantly different between healthy and diseased trees. Our results indicate that ash dieback affects flower formation and pollen viability but not pollen production or seed quality. Nevertheless, the fact that hardly any flowering was observed, especially for trees that were seriously affected, suggests a negative effect of ash dieback on reproductive performance. Thus, severely diseased trees will transfer their genes to a smaller extent to the next generation.

Atmospheric nitrogen (N) deposition is predicted to increase, especially in the subtropics. However, the responses of soil microorganisms to long-term N addition at the molecular level in N-rich subtropical forests have not been clarified. A long-term nutrient addition experiment was conducted in a subtropical evergreen old-growth forest in China. The four treatments were: control, low N (50 kg N ha⁻¹ a⁻¹), high N (100 kg N ha⁻¹ a⁻¹), and combined N and phosphorus (P) (100 kg N ha⁻¹ a⁻¹ + 50 kg P ha⁻¹ a⁻¹). Metagenomic sequencing characterized diversity and composition of soil microbial communities and used to construct bacterial/fungal co-occurrence networks. Nutrient-treated soils were more acidic and had higher levels of dissolved organic carbon than controls. There were no significant differences in microbial diversity and community composition across treatments. The addition of nutrients increased the abundance of copiotrophic bacteria and potentially beneficial microorganisms (e.g., Gemmatimonadetes, Chaetomium, and Aureobasidium). Low N addition increased microbiome network connectivity. Three rare fungi were identified as module hubs under nutrient addition, indicating that low abundance fungi were more sensitive to increased nutrients. The results indicate that the overall composition of microbial communities was stable but not static to long-term N addition. Our findings provide new insights that can aid predictions of the response of soil microbial communities to long-term N addition.

Thinning is an effective management step for sustainable forest development, yet less attention is paid to the restoration of soil microbiota after thinning. In this study, both abundant and rare soil microbial communities (i.e., bacterial, fungal), were evaluated under various thinning treatments in a mixed stand of Cunninghamia lanceolata and Sassafras tzumu using MiSeq sequencing. Thinning did not significantly change either abundant or rare bacterial and fungal community composition, but affected their alpha diversity. The Shannon– Wiener indexes of rare fungal taxa under medium thinning were significantly lower than in the light thinning (P < 0.05 level). Xanthobacteraceae dominated the abundant bacterial taxa, and Saitozyma and Mortierlla the abundant fungal taxa. The most common rare bacterial taxa varied; there was no prevalent rare fungal taxa under different thinnings. In addition, soil available nitrogen, total phosphorus, and pH had significant effects on rare bacterial taxa. Nutrients, especially available phosphorus, but not nitrogen, affected abundant and rare soil fungi. The results indicate that soil properties rather than plant factors affect abundant and rare microbial communities in soils of mixed stands. Thinning, through mediating soil properties, influences both abundant and rare bacterial and fungal communities in the mixed C. lanceolata and S. tzumu stand.

Due to the lack of a uniform and accurate definition of ‘drought’, several indicators have been introduced based on different variables and methods, and the efficiency of each of these is determined according to their relationship with drought. The relationship between two drought indices, SPI (standardized precipitation index) and SPEI (standardized precipitation-evapotranspiration index) in different seasons was investigated using annual rings of 15 tree samples to determine the effect of drought on the growth of oriental beech (Fagus orientalis Lipsky) in the Hyrcanian forests of northern Iran. The different evapotranspiration calculation methods were evaluated on SPEI efficiency based on Hargreaves-Samani, Thornthwaite, and Penman–Monteith methods using the step-by-step M5 decision tree regression method. The results show that SPEI based on the Penman–Monteith in a three-month time scale (spring) had similar temporal changes and a better relationship with annual tree rings (R ² = 0.81) at a 0.05 significant level. Abrupt change and a decreasing trend in the time series of annual tree rings are similar to the variation in the SPEI based on the Penman–Monteith method. Factors affecting evapotranspiration, temperature, wind speed, and sunshine hours (used in the Penman–Monteith method), increased but precipitation decreased. Using non-linear modeling methods, SPEI based on Penman–Monteith best illustrated climate changes affecting tree growth.

Tree-ring chronologies were developed for Sabina saltuaria and Abies faxoniana in mixed forests in the Qionglai Mountains of the eastern Tibetan Plateau. Climate-growth relationship analysis indicated that the two co-existing species reponded similarly to climate factors, although S. saltuaria was more sensitive than A. faxoniana. The strongest correlation was between S. saltuaria chronology and regional mean temperatures from June to November. Based on this relationship, a regional mean temperature from June to November for the period 1605–2016 was constructed. Reconstruction explained 37.3% of the temperature variance during th period 1961–2016. Six major warm periods and five major cold periods were identified. Spectral analysis detected significant interannual and multi-decadal cycles. Reconstruction also revealed the influence of the Atlantic Multi-decadal Oscillation, confirming its importance on climate change on the eastern Tibetan Plateau.

Forest fires are natural disasters that can occur suddenly and can be very damaging, burning thousands of square kilometers. Prevention is better than suppression and prediction models of forest fire occurrence have developed from the logistic regression model, the geographical weighted logistic regression model, the Lasso regression model, the random forest model, and the support vector machine model based on historical forest fire data from 2000 to 2019 in Jilin Province. The models, along with a distribution map are presented in this paper to provide a theoretical basis for forest fire management in this area. Existing studies show that the prediction accuracies of the two machine learning models are higher than those of the three generalized linear regression models. The accuracies of the random forest model, the support vector machine model, geographical weighted logistic regression model, the Lasso regression model, and logistic model were 88.7%, 87.7%, 86.0%, 85.0% and 84.6%, respectively. Weather is the main factor affecting forest fires, while the impacts of topography factors, human and social-economic factors on fire occurrence were similar.

On an agrosilvopastoral farm in central Italy where Maremmana cattle graze in Turkey oak forests, we evaluated the impact of different livestock densities on stand structure, tree diversity and natural regeneration in four types of grazed areas based on the grazing regime adopted: calf-grazed, high-intensity-grazed, low-intensity-grazed, ungrazed control. For each area, we set up three permanent circular plots (radius of 15 m) to survey the structural and dasometric characteristics of the overstorey, understorey, and regeneration layer. The results showed that grazing negatively affected the complexity of the forest structure and its potential to regenerate and maintain a high level of biodiversity. The differences in stand structure observed between the grazing areas were closely related to livestock density. The most sensitive components of the system were the understorey and the regeneration layers. Contrarily, the current grazing management did not affect the dominant tree structure or its composition. Our findings identified medium-term monitoring and regeneration management as the two significant aspects to consider when assessing sustainable livestock. New forests can be established by excluding grazing for about 20–25 years.

Quercus arkansana (Arkansas oak) is at risk of becoming endangered, as the total known population size is represented by a few isolated populations. The potential impact of climate change on this species in the near future is high, yet knowledge of its predicted effects is limited. Our study utilized the biomod2 R package to develop habitat suitability ensemble models based on bioclimatic and topographic environmental variables and the known locations of current distribution of Q. arkansana. We predicted suitable habitats across three climate change scenarios (SSP1-2.6, SSP2-4.5, and SSP5-8.5) for 2050, 2070, and 2090. Our findings reveal that the current suitable habitat for Q. arkansana is approximately 127,881 km² across seven states (Texas, Arkansas, Alabama, Louisiana, Mississippi, Georgia, and Florida); approximately 9.5% is encompassed within state and federally managed protected areas. Our models predict that all current suitable habitats will disappear by 2050 due to climate change, resulting in a northward shift into new regions such as Tennessee and Kentucky. The large extent of suitable habitat outside protected areas suggests that a species-specific action plan incorporating protected areas and other areas may be crucial for its conservation. Moreover, protection of Q. arkansana habitat against climate change may require locally and regionally focused conservation policies, adaptive management strategies, and educational outreach among local people.

Needle chlorosis (NC) in Pinus taeda L. systems in Brazil becomes more frequent after second and third harvest rotation cycles. In a study to identify factors contributing to yellowing needle chorosis (YNC), trees were grown in soils originating from contrasting parent materials, and soils and needles (whole, green and chlorotic portions) from 1- and 2-year-old branches and the first and second needle flush release at four sites with YNC on P. taeda were analyzed for various elements and properties. All soils had very low base levels (Ca²⁺, Mg²⁺ and K⁺) and P, suggesting a possible lack of multiple elements. YNC symptoms started at needle tips, then extended toward the needle base with time. First flush needles had longer portions with YNC than second flush needles did. Needles from the lower crown also had more symptoms along their length than those higher in the canopy. Symptoms were similar to those reported for Mg. In chlorotic portions, Mg and Ca concentrations were well below critical values; in particular, Mg levels were only one third of the critical value of 0.3 g kg⁻¹. Collectively, results suggest that Mg deficiency is the primary reason for NC of P. taeda in various parent soils in Brazil.

In overlapping distribution areas of Sorbus pohuashanensis and S. discolor in North China (Mount Tuoliang, Mount Xiling and Mount Baihua), Sorbus individuals were found with pink fruit, which have never been recorded for the flora of China. Fourteen morphological characters combined with four chloroplast DNA markers and internal transcribed spacer (ITS) were used to analyze the origin of the Sorbus individuals with pink fruits and their relationship to S. pohuashanensis and S. discolor. PCA, SDA and one-way (taxon) ANOVA of morphological characters provided convincing evidence of the hybrid origin of Sorbus individuals with pink fruits based on a novel morphological character and many intermediate characters. Haplotype analysis based on four cpDNA markers showed that either S. pohuashanensis or S. discolor were maternal parents of Sorbus individuals with pink fruits. Incongruence of the position of Sorbus individuals with pink fruits between cpDNA and ITS in cluster trees supported by DNA sequence comparative analysis, implying former hybridization events between S. pohuashanensis and S. discolor. Multiple hybridization events between S. pohuashanensis and S. discolor might have contributed to the generation of Sorbus individuals with pink fruits. This study has provided insights into hybridization between species of the same genus in sympatric areas, which is of great significance for the study of interspecific hybridization.

The Tongbai Mountains is an ecologically sensitive region and the northern boundary of Pinus massoniana Lamb. To analyze the effect of different microenvironments on tree growth response to climate factors, we developed standard chronologies for earlywood width (EWW), latewood width (LWW), and total ring width (TRW) of P. massoniana at two sampling sites on slopes with different orientations, then analyzed characteristics of the chronologies and their correlations with climate variables from five stations in the region and with a regional normalized difference vegetation index (NDVI). Statistical results showed that the TRW/EWW/LWW chronology consistency and characteristics (mean sensitivity, signal to noise ratio, expressed population signal) for trees growing on the southeastern slope were much higher than for trees on the northeastern slope. Correlations indicated that temperature in current March and August has a significant positive effect on TRW/EWW/LWW formation, and the effect on the northeastern slope was weaker than on the southeastern slope. Compared to temperature, precipitation has more complicated effects on tree growth, but the effect on the northeastern slope was also generally weaker than on the southeastern slope. Stepwise linear regression analyses showed that temperature in August was the main limiting factor at the two sampling sites. Similarly, the response of tree growth on the southeastern slope as determined by the NDVI is better than on the northeastern slope, and the TRW/EWW/LWW chronologies for the southeastern slope explained over 50% of the total NDVI variances in June. Overall, the results indicate that the difference in the climate response of P. massoniana at two sampling sites is clearly caused by differences in the microenvironment, and such differences should be properly considered in future studies of forest dynamics and climate reconstructions.

Despite its enormous benefits, mining is responsible for intense changes to vegetation and soil properties. Thus, after extraction, it is necessary to rehabilitate the mined areas, creating better conditions for the establishment of plant species which is challenging. This study evaluated mineral and organic fertilization on the growth, and carbon and nitrogen (N) metabolism of two Crotalaria species [Crotalaria spectabilis (exotic species) and Crotalaria maypurensis (native species from Carajás Mineral Province (CMP)] established on a waste pile from an iron mine in CMP. A control (without fertilizer application) and six fertilization mixtures were tested (i = NPK; ii = NPK + micronutrients; iii = NPK + micronutrients + organic compost; iv = PK; v = PK + micronutrients; vi = PK + micronutrients + organic compost). Fertilization contributed to increased growth of both species, and treatments with NPK and micronutrients had the best results (up to 257% cf. controls), while organic fertilization did not show differences. Exotic Crotalaria had a greater number of nodules, higher nodule dry mass, chlorophyll a and b contents and showed free ammonium as the predominant N form, reflecting greater increments in biomass compared to native species. Although having lower growth, the use of this native species in the rehabilitation of mining areas should be considered, mainly because it has good development and meets current government legislation as an opportunity to restore local biodiversity.

A set of standard chronologies for tree-ring width (TRW), earlywood width (EWW) and latewood width (LWW) in Pinus tabuliformis Carr. along an altitudinal gradient (1450, 1400, and 1350 m a.s.l.) on Baiyunshan Mountain, Central China to analyze the effect of varying temperature and precipitation on growth along the gradient. Correlation analyses showed that at all three altitudes and the TRW and EWW chronologies generally had significant negative correlations with mean and maximum temperatures in the current April and May and with minimum temperatures in the prior July and August, but significant positive correlations with precipitation in the current May. Correlations were generally significantly negative between LWW chronologies and all temperatures in the prior July and August, indicating that the prior summer temperature had a strong lag effect on the growth of P. tabuliformis that increased with altitude. The correlation with the standardized precipitation evapotranspiration index (SPEI) confirmed that wet conditions in the current May promoted growth of TR and EW at all altitudes. Significant altitudinal differences were also found; at 1400 m, there were significant positive correlations between EWW chronologies and SPEI in the current April and significant negative correlations between LWW chronologies and SPEI in the current September, but these correlations were not significant at 1450 m. At 1350 m, there were also significant negative correlations between the TRW and the EWW chronologies and SPEI in the prior October and the current July and between LWW chronology and SPEI in the current August, but these correlations were not significant at 1400 m. Moving correlation results showed a stable response of EWW in relation to the SPEI in the current May at all three altitudes and of LWW to maximum temperature in the prior July–August at 1400 m from 2002 to 2018. The EWW chronology at 1400 m and the LWW chronology at 1450 m were identified as more suitable for climate reconstruction. These results provide a strong scientific basis for forest management decisions and climate reconstructions in Central China.

Tropical peat comprises decomposed dead plant material and acts like a sponge to absorb water, making it fully saturated. However, drought periods dry it readily and increases its vulnerability to fire. Peat fires emit greenhouse gases and particles contributing to haze, and prevention by constructing fire-break canals to reduce fire spread into forest reserves is crucial. This paper aims to determine peat physical and chemical properties near a fire-break canal at different fire frequency areas. Peat sampling was conducted at two forest reserves in Malaysia which represent low fire frequency and high fire frequency areas. The results show that peat properties were not affected by the construction of a fire-break canal, however lignin and cellulose content increased significantly from the distance of the canal in both areas. The study concluded that fire frequency did not significantly influence peat properties except for porosity. The higher fibre content in the high frequency area did not influence moisture content nor the ability to regain moisture. Thus, fire frequency might contribute differently to changes in physical and chemical properties, hence management efforts to construct fire- break canals and restoration efforts should protect peatlands from further degradation. These findings will benefit future management and planning for forest reserves.

In this study, we investigated how tree species affect N mineralization in connection to some soil properties and seconder metabolite levels of litter, in the soil of the oldest native forest communities. In the oldest pure communities of Pinus nigra (PN), Fagus orientalis (FO), and Abies bornmuelleriana (AB) in the mountain range of Mount Uludağ, Bursa, Turkey, annual net yield and N mineralization in the 0–5- and 5–20-cm soil layers were determined in a field incubation study over 1 year. Sampling locations were chosen from 1300 to 1600 m a.s.l., and moisture content (%), pH, water-holding capacity (%), organic C, total N, and C/N ratio, and annual net mineral N yield of the soil and hydrolyzed tannic acid and total phenolic compounds in litter were compared for these forest communities. F. orientalis had the highest annual net Nmin yield (43.9 ± 4.8 kg ha^–1 a^–1), P. nigra the lowest (30.5 ± 4.2 kg ha^–1 a^–1). Our findings show that in the oldest forest ecosystems, the seasonal soil moisture content and tree species play an essential role in N cycling and that hydrolyzed tannic acids and total phenolic compounds effectively control N turnover. Tannic acid and total phenolics in the litter were found to inhibit nitrification, but total phenolics were found to stimulate ammonification.

The number and composition of species in a community can be quantified with α-diversity indices, including species richness (R), Simpson’s index (D), and the Shannon–Wiener index ($H^\prime$). In forest communities, there are large variations in tree size among species and individuals of the same species, which result in differences in ecological processes and ecosystem functions. However, tree size inequality (TSI) has been largely neglected in studies using the available diversity indices. The TSI in the diameter at breast height (DBH) data for each of 999 20 m × 20 m forest census quadrats was quantified using the Gini index (GI), a measure of the inequality of size distribution. The generalized performance equation was used to describe the rotated and right-shifted Lorenz curve of the cumulative proportion of DBH and the cumulative proportion of number of trees per quadrat. We also examined the relationships of α-diversity indices with the GI using correlation tests. The generalized performance equation effectively described the rotated and right-shifted Lorenz curve of DBH distributions, with most root-mean-square errors (990 out of 999 quadrats) being < 0.0030. There were significant positive correlations between each of three α-diversity indices (i.e., R, D, and $H^\prime$) and the GI. Nevertheless, the total abundance of trees in each quadrat did not significantly influence the GI. This means that the TSI increased with increasing species diversity. Thus, two new indices are proposed that can balance α-diversity against the extent of TSI in the community: (1 − GI) ×  D, and (1 − GI) × $H^\prime$. These new indices were significantly correlated with the original D and $H^\prime$, and did not increase the extent of variation within each group of indices. This study presents a useful tool for quantifying both species diversity and the variation in tree sizes in forest communities, especially in the face of cumulative species loss under global climate change.

As a crucial component of terrestrial ecosystems, urban forests play a pivotal role in protecting urban biodiversity by providing suitable habitats for acoustic spaces. Previous studies note that vegetation structure is a key factor influencing bird sounds in urban forests; hence, adjusting the frequency composition may be a strategy for birds to avoid anthropogenic noise to mask their songs. However, it is unknown whether the response mechanisms of bird vocalizations to vegetation structure remain consistent despite being impacted by anthropogenic noise. It was hypothesized that anthropogenic noise in urban forests occupies the low-frequency space of bird songs, leading to a possible reshaping of the acoustic niches of forests, and the vegetation structure of urban forests is the critical factor that shapes the acoustic space for bird vocalization. Passive acoustic monitoring in various urban forests was used to monitor natural and anthropogenic noises, and sounds were classified into three acoustic scenes (bird sounds, human sounds, and bird-human sounds) to determine interconnections between bird sounds, anthropogenic noise, and vegetation structure. Anthropogenic noise altered the acoustic niche of urban forests by intruding into the low-frequency space used by birds, and vegetation structures related to volume (trunk volume and branch volume) and density (number of branches and leaf area index) significantly impact the diversity of bird sounds. Our findings indicate that the response to low and high frequency signals to vegetation structure is distinct. By clarifying this relationship, our results contribute to understanding of how vegetation structure influences bird sounds in urban forests impacted by anthropogenic noise.

Forest degradation induced by intensive forest management and temperature increase by climate change are resulting in biodiversity decline in boreal forests. Intensive forest management and high-end climate emission scenarios can further reduce the amount and diversity of deadwood, the limiting factor for habitats for saproxylic species in European boreal forests. The magnitude of their combined effects and how changes in forest management can affect deadwood diversity under a range of climate change scenarios are poorly understood. We used forest growth simulations to evaluate how forest management and climate change will individually and jointly affect habitats of red-listed saproxylic species in Finland. We simulated seven forest management regimes and three climate scenarios (reference, RCP4.5 and RCP8.5) over 100 years. Management regimes included set aside, continuous cover forestry, business-as-usual (BAU) and four modifications of BAU. Habitat suitability was assessed using a species-specific habitat suitability index, including 21 fungal and invertebrate species groups. “Winner” and “loser” species were identified based on the modelled impacts of forest management and climate change on their habitat suitability. We found that forest management had a major impact on habitat suitability of saproxylic species compared to climate change. Habitat suitability index varied by over 250% among management regimes, while overall change in habitat suitability index caused by climate change was on average only 2%. More species groups were identified as winners than losers from impacts of climate change (52%–95% were winners, depending on the climate change scenario and management regime). The largest increase in habitat suitability index was achieved under set aside (254%) and the climate scenario RCP8.5 (> 2%), while continuous cover forestry was the most suitable regime to increase habitat suitability of saproxylic species (up to + 11%) across all climate change scenarios. Our results show that close-to-nature management regimes (e.g., continuous cover forestry and set aside) can increase the habitat suitability of many saproxylic boreal species more than the basic business-as-usual regime. This suggests that biodiversity loss of many saproxylic species in boreal forests can be mitigated through improved forest management practices, even as climate change progresses.

Budding is an important grafting technique to asexually propagate pecan (Carya illinoinensis (Wangenh.) K. Koch). To determine factors that might hamper successful budding of the species, a representative easy-to-survive cultivar ‘Pawnee’ and a typical difficult-to-survive cultivar ‘Jinhua’ were used for comprehensive analysis. Morphological observation showed that cells surrounding the secretory cells or sieve tube had collapsed in ‘Jinhua’ but not in ‘Pawnee’ during grafting. ‘Jinhua’ might suffer more hypoxia stress than ‘Pawnee’ as ‘Jinhua’ had higher catalase, superoxide dismutase, polyphenol oxidase, pyruvate decarboxylase (PDC), alcohol dehydrogenase (ADH) activities during grafting and contained greater levels of hydrogen peroxide 12 days after grafting (DAG). Transcriptions of PDC and ADH were also up-regulated significantly in ‘Jinhua’ whereas they were not significantly affected in ‘Pawnee’. Phenylalanine ammonia-lyase activities of ‘Jinhua’ were consistently lower than that of ‘Pawnee’. Initial phenol contents were similar between the two cultivars. Graft-promoting substances, including soluble sugar, soluble protein, and gibberellin (GA) were incompletely recovered in ‘Jinhua’ 12 DAG while fully restored in ‘Pawnee’. Increased levels of trans-zeatin riboside in ‘Jinhua’ were much smaller than in ‘Pawnee’ 3 DAG. The contents of indole-3-acetic acid were similar, and the dynamics of abscisic acid were the same between the two genotypes. Results suggest that hypoxia stress and shortages of sugar, protein, GA, and cytokinin during the healing process might be key factors limiting successful budding of pecan. The degree of scion-rootstock compatibility and the content of phenols might be excluded as constraints for successful budding.

Differences in forest attributes and carbon sequestration of each organ and layer between broadleaved and conifer forests of central and outer urban areas are not well-defined, hindering the precise management of urban forests and improvement of function. To clarify the effect of two forest types with different urbanization intensities, we determined differences in vegetation composition and diversity, structural traits, and carbon stocks of 152 plots (20 m × 20 m) in urban park forests in Changchun, which had the largest green quantity and carbon density effectiveness. We found that 1.1-fold thicker and healthier trees, and 1.6- to 2.0-fold higher, healthier, denser, and more various shrubs but with sparser trees and herbs occurred in the central urban forests (p < 0.05) than in the outer forests. The conifer forests exhibited 30–70% obviously higher tree aboveground carbon sequestration (including stem and leaf) and 20% bigger trees, especially in the outer forests (p < 0.05). In contrast, 1.1- to 1.5-fold higher branch stocks, healthier and more diverse trees were found in broadleaved forests of both the inner and outer forests (p < 0.05). Plant size and dominant species had similarly important roles in carbon stock improvement, especially big-sized woody plants and Pinus tabuliformis. In addition, a higher number of deciduous or needle species positively affected the broadleaved forest of the central urban area and conifer forest of the outer urban area, respectively. These findings can be used to guide precise management and accelerate the improvement of urban carbon function in Northeast China in the future.

Minimum temperatures have remarkable impacts on tree growth at high-elevation sites on the Tibetan Plateau, but the shortage of long-term and high-resolution paleoclimate records inhibits understanding of recent minimum temperature anomalies. In this study, a warm season (April–September) reconstruction is presented for the past 467 years (1550–2016) based on Sabina tibetica ring-width chronology on the Lianbaoyeze Mountain of the central eastern Tibetan Plateau. Eight warm periods and eight cold periods were identified. Long-term minimum temperature variations revealed a high degree of coherence with nearby reconstructions. Spatial correlations between our reconstruction and global sea surface temperatures suggest that warm season minimum temperature anomalies in the central eastern Tibetan Plateau were strongly influenced by large-scale ocean atmospheric circulations, such as the El Niño-Southern Oscillation and the Atlantic Multidecadal Oscillation.

Discerning vulnerability differences among different aged trees to drought-driven growth decline or to mortality is critical to implement age-specific countermeasures for forest management in water-limited areas. An important species for afforestation in dry environments of northern China, Mongolian pine (Pinus sylvestris var. mongolica Litv.) has recently exhibited growth decline and dieback on many sites, particularly pronounced in old-growth plantations. However, changes in response to drought stress by this species with age as well as the underlying mechanisms are poorly understood. In this study, tree-ring data and remotely sensed vegetation data were combined to investigate variations in growth at individual tree and stand scales for young (9 − 13 years) and aging (35 − 52 years) plantations of Mongolian pine in a water-limited area of northern China. A recent decline in tree-ring width in the older plantation also had lower values in satellited-derived normalized difference vegetation indices and normalized difference water indices relative to the younger plantations. In addition, all measured growth-related metrics were strongly correlated with the self-calibrating Palmer drought severity index during the growing season in the older plantation. Sensitivity of growth to drought of the older plantation might be attributed to more severe hydraulic limitations, as reflected by their lower sapwood- and leaf-specific hydraulic conductivities. Our study presents a comprehensive view on changes of growth with age by integrating multiple methods and provides an explanation from the perspective of plant hydraulics for growth decline with age. The results indicate that old-growth Mongolian pine plantations in water-limited environments may face increased growth declines under the context of climate warming and drying.

Extreme climate has increasingly led to negative impacts on forest ecosystems globally, especially in semiarid areas where forest ecosystems are more vulnerable. However, it is poorly understood how tree growth is affected by different drought events. In 2006–2009, the larch plantations in the semiarid areas of Northwest China were negatively affected by four consecutive dry years, which was a very rare phenomenon that may occur frequently under future climate warming. In this study, we analyzed the effect of these consecutive dry years on tree growth based on the data of the tree rings in the dominant layer of the forest canopy on a larch plantation. We found that the tree-ring width index (RWI) in dry years was lower than that in normal years, and it experienced a rapidly decreasing trend from 2006 to 2009 (slope =  − 0.139 year⁻¹, r =  − 0.94) due to water supply deficits in those dry years. Drought induced legacy effects of tree growth reduction, and consecutive dry years corresponded with greater growth reductions and legacy effects. Growth reductions and legacy effects were significantly stronger in the third and fourth consecutive dry years than that of single dry year (p < 0.05), which might have been due to the cumulative stress caused by consecutive dry years. Our results showed that larch trees experienced greater tree growth reduction due to consecutive dry years and their legacy effect, and the trees had lower recovery rates after consecutive dry years. Our results highlight that consecutive dry years pose a new threat to plantations under climate warming, and thus, the effect of climate extremes on tree growth should be considered in growth models in semiarid areas.

Betula platyphylla and Betula costata are important species in mixed broadleaved-Korean pine (Pinus koraiensis) forests. However, the specific ways in which their growth is affected by warm temperatures and drought remain unclear. To address this issue, 60 and 62 tree-ring cores of B. platyphylla and B. costata were collected in Yichun, China. Using dendrochronological methods, the response and adaptation of these species to climate change were examined. A “hysteresis effect” was found in the rings of both species, linked to May–September moisture conditions of the previous year. Radial growth of B. costata was positively correlated with the standardized precipitation-evapotranspiration index (SPEI), the precipitation from September to October of the previous year, and the relative humidity in October of the previous year. Growth of B. costata is primarily restricted by moisture conditions from September to October. In contrast, B. platyphylla growth is mainly limited by minimum temperatures in May–June of both the previous and current years. After droughts, B. platyphylla had a faster recovery rate compared to B. costata. In the context of rising temperatures since 1980, the correlation between B. platyphylla growth and monthly SPEI became positive and strengthened over time, while the growth of B. costata showed no conspicuous change. Our findings suggest that the growth of B. platyphylla is already affected by warming temperatures, whereas B. costata may become limited if warming continues or intensifies. Climate change could disrupt the succession of these species, possibly accelerating the succession of pioneer species. The results of this research  are of great significance for understanding how the growth changes of birch species under warming and drying conditions, and contribute to understanding the structural adaptation of mixed broadleaved-Korean pine (Pinus koraiensis) forests under climate change.

Understanding the relationship between forest management and water use efficiency (WUE) is important for evaluating forest adaptability to climate change. However, the effects of thinning and understory removal on WUE and its key controlling processes are not well understood, which limits our comprehension of the physiological mechanisms of various management practices. In this study, four forest management measures (no thinning: NT; understory removal: UR; light thinning: LT; and heavy thinning: HT) were carried out in Pinus massoniana plantations in a subtropical region of China. Photosynthetic capacity and needle stable carbon isotope composition (δ ¹³C) were measured to assess instantaneous water use efficiency (WUE_inst) and long-term water use efficiency (WUE_i). Multiple regression models and structural equation modelling (SEM) identified the effects of soil properties and physiological performances on WUE_inst and WUE_i. The results show that WUE_inst values among the four treatments were insignificant. However, compared with the NT stand (35.8 μmol·mol⁻¹), WUE_i values significantly increased to 41.7 μmol·mol⁻¹ in the UR, 50.1 μmol·mol⁻¹ in the LT and 46.6 μmol·mol⁻¹ in HT treatments, largely explained by photosynthetic capacity and soil water content. Understory removal did not change physiological performance (needle water potential and photosynthetic capacity). Thinning increased the net photosynthetic rate (A _n) but not stomatal conductance (g _s) or predawn needle water potential (ψ _pd), implying that the improvement in water use efficiency for thinned stands was largely driven by radiation interception than by soil water availability. In general, thinning may be an appropriate management measure to promote P. massoniana WUE to cope with seasonal droughts under future extreme climates.

Soil pedestals have long been used as qualitative indicators of soil splash erosion. In rangelands, plant-capped pedestals, generally grass tussocks, have also been used to quantitatively estimate soil loss since the first half of the twentieth century. In agricultural lands, forests, and badlands, stone-capped pedestals have been used as qualitative and semi-quantitative indicators of active, ‘extreme’ erosion. Little work has been reported on using capstone pedestal data for quantifying soil loss. We postulate that three distinct capstone pedestal types may be present in any given location and that a detailed analysis of a pedestal height histogram may be used to recognize their populations. This analysis can subsequently inform if soil loss can be reliably estimated and if so, which of the existing methods using pedestal height data will provide more accurate results. The three proposed capstone pedestal types are: (1) neo-pedestals formed underneath surface stones exposed by (partial) removal of the soil surface cover; (2) endo-pedestals formed underneath stones that were buried in the soil but have been exposed by erosion; and (3) phoenix-pedestals formed underneath stones from collapsed pedestals. In the pedestal height histogram of any given location, a skew to smaller heights may indicate the existence of endo- and/or phoenix-pedestals, which may be revealed as a bi-(or tri) modal distribution when using a smaller bin size. This concept was applied to a case study where soil loss had been monitored for control plots and mulched plots during a 5-year period following wildfire in a eucalypt plantation. We measured pedestal heights and used methods to quantitatively assess soil loss from soil pedestal data in the available literature. Soil pedestal data at the end of the 5-year period under or overestimated soil loss in the control treatment, with results ranging from 60 to 115% of measured soil loss, depending on the method. It is postulated that phoenix- and endo-pedestals may be a driving factor behind the observed discrepancies. We discuss how future research may provide more insight into dominant processes, and how frequency distributions may be used to select the best methods for estimating soil loss from pedestals.

In our previous screening of the transcriptome of the causal agent of the devastating pine wilt disease, pine wood nematode (PWN, Bursaphelenchus xylophilus), after treatment with the nematicide fomepizole, Surfeit locus gene sft-4, which encodes a regulatory factor, was found to be downregulated. In situ hybridization results showed that the sft-4 was continuously expressed from egg to adult and was especially high in the reproductive system. Here in a study of the effect of RNA interference (RNAi) of sft-4 and recombinant SFT-4 on PWN activity, treatment with sft-4 dsRNA inhibited feeding, reproduction, oviposition and egg hatching of PWN with the greatest inhibition on reproduction and oviposition, whereas recombinant SFT-4 had the opposite effect. In addition, RNAi of sft-4 changed the female–male ratio and lifespan of PWN. In bioassays of PWNs, with RNAi of sft-4 on seedlings and 2-year-old Pinus thunbergii trees, none of the treated plants developed symptoms during the monitoring period, indicating that virulence of PWNs was either significantly weakened. These results indicate that the influence of sft-4 on PWN pathogenicity may be mainly through regulating reproductive function of PWN and its lifespan.

Global warming will affect growth strategies and how trees will adapt. To compare the response of tree radial growth to climate warming in different slope directions, samples of Pinus armandii Franch were collected and tree-ring chronologies developed on northern and western slopes from the Lubanling in the Funiu Mountains. Correlation analyses showed that two chronologies were mainly limited by temperatures in the previous June–August and the combination of temperatures and moisture in the current May–July. The difference of the climate response to slopes was small but not negligible. Radial growth of the LBL01 site on the northern slope was affected by the combined maximum and minimum temperatures, while that of the LBL02 site was affected by maximum temperatures. With regards to moisture, radial growth of the trees on the north slope was influenced by the relative humidity in the current May–July, while on the western slope, it was affected by the relative humidity in the previous June–August, the current May–July and the precipitation in the current May–July. With the change in climate, the effects of the main limiting factors on growth on different slopes were visible to a certain extent, but the differences in response of trees on different slopes gradually decreased, which might be caused by factors such as different slope directions and the change in diurnal temperature range. These results may provide information for forest protection and ecological construction in this region, and a scientific reference for future climate reconstruction.

Recent methodological advances in quantitative wood anatomy have provided new insights into the climatic responses of radial growth at the scale of cell structure of tree rings. This study considered long-term chronologies of tracheid measurements, indexed by a novel approach to separate their specific climatic responses from signal recorded in cell production (closely reflected in tree-ring width). To fill gaps in understanding the impact of climate on conifer xylem structure, Scots pine (Pinus sylvestris L.) trees > 200 years old were selected within the forest-steppe zone in southern Siberia. Such habitats undergo mild moisture deficits and the resulting climatic regulation of growth processes. Mean and maximum values of cell radial diameter and cell wall thickness were recorded for each tree ring. Despite a low level of climatogenic stress, components of cell chronologies independent of cambial activity were separated to obtain significant climatic signals revealing the timing of the specific stages of tracheid differentiation. Cell expansion lasted from mid-April to July and was impacted similarly to tree-ring width (stimulated by precipitation and stressed by heat), maximum cell size formed late June. A switch in the climatic responses of mean anatomical traits indicated transition to latewood in mid-July. Secondary wall deposition lasted until mid-September, suppressed by end of season temperatures. Generally, anatomical climatic responses were modulated by a less dry May and September compared with summer months.

The regeneration of Tetracentron sinense Oliv. is poor in the understory and in open areas due to the characteristics of natural regeneration of the species on forest edges and in gaps. It is unclear whether different light intensities in various habitats affect eco-physiological characteristics of saplings and their natural regeneration. In this study, the light intensity in T. sinense habitats was simulated by artificial shading (L1: 100% NS (natural sunlight) in the open; L2: 50% NS in a forest gap or edge; L3: 10% NS in understory) to investigate differences in morphology, leaf structure, physiology, and photosynthesis of 2-year-old saplings, and to analyze the mechanism of light intensity on sapling establishment. Significant differences were observed in morphology (including leaf area, and specific leaf area) under different light intensities. Compared to L1 and L3, chloroplast structure in L2 was intact. With increasing time, superoxide dismutase (SOD) and catalase (CAT) activities in L2 became gradually higher than under the other light intensities, while malondialdehyde (MDA) content was opposite. Shading decreased osmoregulation substance contents of leaves but increased chlorophyll. The results suggest that light intensities significantly affect the eco-physiological characteristics of T. sinense saplings and they would respond most favorably at intermediate levels of light by optimizing eco-physiological characteristics. Therefore, 50% natural sunlight should be created to promote saplings establishment and population recovery of T. sinense during in situ conservation, including sowing mature seeds in forest edges or gaps and providing appropriate shade protection for seedlings and saplings in the open.

Changes in annual radial growth is an important indication of climate change. Dendroclimatology studies in northern China have focused on linear statistical analysis, but lacking studies based on the process of ring formation to clarify the radial growth of trees. Tree-ring width standard chronology (STD) was established using samples of Larix principis-rupprechtii collected at 2303 m altitude on Luya Mountain. Using the Vaganov-Shashkin (VS) model to simulate growth and development, the internal physiological mechanism of radial growth is identified. It was concluded that: (1) the growing season of L. principis-rupprechtii was May to September; (2) soil moisture was a significant factor in the early and late growing seasons, and temperature was the dominant factor in its main growth period; and (3) formation of narrow ring widths was closely related to drought stress, the development of wide ring widths will be restricted by increasing future temperatures. The VS model is applicable for radial growth simulation of subalpine coniferous forests and for guiding the cultivation of local tree species in the future.

Biodiversity loss is a significant problem at a global scale and may be amplified by climate change. In recent years, coniferous forests have had substantial dieback across Europe due to drought and subsequent bark-beetle outbreaks. As many studies on the consequences of disturbance and subsequent management have focused on natural stands, management implications for managed spruce stands are not well understood, even though such stands are widespread throughout Europe. In this study, beetle taxonomy, conservation value, and community composition are compared among spruce plantations and four post-disturbance management approaches: standing deadwood, lying deadwood, clear cuts, and long-term succession. Diversity and community composition differed significantly among management categories, while different beetle families responded similarly. Intact spruce stands harbored the lowest beetle diversity while the highest taxonomic diversity and conservation value was on clear cuts and stands with lying or standing deadwood. The proportion of forest specialists was highest in successional forests. In summary, different forest management categories harbored distinct beetle communities at the family-, species-, and ecological guild levels. Therefore, post-disturbance management should consider the landscape scale and include different management types. This enhances landscape heterogeneity and thus overall biodiversity but could also mitigate negative impacts of natural disturbances on ecosystem services.

Global warming and frequent extreme drought events lead to tree death and extensive forest decline, but the underlying mechanism is not clear. In drought years, cambial development is more sensitive to climate change, but in different phenological stages, the response relationship is nonlinear. Therefore, the dynamic relationship between tree radial growth and climatic/environmental factors needs to be studied. We thus continuously monitored radial growth of Qinghai spruce (Picea crassifolia Kom.) and environmental factors from January 2021 to November 2022 using point dendrometers and portable meteorological weather stations in the central area of the Qilian Mountains. The relationship and stability between the radial growth of Qinghai spruce and environmental factors were compared for different levels of drought in 2021 and 2022. The year 2022 had higher temperatures and less precipitation and was drier than 2021. Compared with 2021, the growing period in 2022 for Qinghai spruce was 10 days shorter, maximum growth rate (Grmax) was 4.5 μm·d⁻¹ slower, and the initiation of growth was 6 days later. Growth of Qinghai spruce was always restricted by drought, and the stem radial increment (SRI) was more sensitive to precipitation and air relative humidity. Seasonal changes in cumulative radial growth were divided into four phenological stages according to the time of growth onset, cessation, and maximum growth rate (Grmax) of Qinghai spruce. Stability responses of SRI to climate change were stronger in Stage 3 and Stage 4 of 2021 and stronger in Stage 1 (initiation growth stage) and Stage 3 of 2022. The results provide important information on the growth of the trees in response to drought and for specific managing forests as the climate warms.

Latewood width (LWW) indices of trees are considered a reliable proxy of summer precipitation in the Northern Hemisphere. However, the strong coupling and high correlation between earlywood width (EWW) and LWW indices often prevent registration of climate signals of the LWW index. In this study, 328-year-long earlywood width and latewood width chronologies were developed from Chinese pine at two sites in the Hasi Mountains, north central China. The climate responses of these chronologies were analyzed and the LWW index used to derive summer precipitation signals. Correlation analyses showed that LWW was particularly influenced by earlywood growth and recorded stronger climate signals of the previous year as EWW, rather than those of the current year with infrequent summer climate signals. However, after removing the effect of earlywood growth using a simple regression model, the adjusted LWW chronology (LWW_adj) showed a strong relationship with July precipitation in dry years. This suggests that the LWW_adj chronology has the potential to be used to investigate long-term variability in summer precipitation in drought-limited regions.

In the Mediterranean region, despite bamboo being an alien species that can seriously alter plant and animal biocoenosis, the area occupied by bamboo plantations continues to increase, especially for the purpose to sequester carbon (C). However, the C dynamics in the soil–plant system when bamboo is grown outside its native area are poorly understood. Here we investigated the C mitigation potential of the fast-growing Moso bamboo (Phyllostachys edulis) introduced in Italy for climate-change mitigation. We analyzed aboveground (AGB) and belowground (as root/shoot ratio) biomass, litter and soil organic C (SOC) at 0–15- and 15–30-cm depths in a 4-year-old bamboo plantation in comparison with the former annual cropland on which the bamboo was established. To have an idea of the maximum C stored at an ecosystem level, a natural forest adjacent the two sites was also considered. In the plantation, C accumulation as AGB was stimulated, with 14.8 ± 3.1 Mg C ha^–1 stored in 3 years; because thinning was done to remove culms from the first year, the mean sequestration rate was 4.9 Mg C ha^–1 a^–1. The sequestration rates were high but comparable to other fast-growing tree species in Italy (e.g., Pinus nigra). SOC was significantly higher in the bamboo plantation than in the cropland only at the 0–15 cm depth, but SOC stock did not differ. Possibly 4 years were not enough time for a clear increase in SOC, or the high nutrient uptake by bamboos might have depleted the soil nutrients, thus inhibiting the soil organic matter formation by bacteria. In comparison, the natural forest had significantly higher C levels in all the pools. For C dynamics at an ecosystem level, the bamboo plantation on the former annual cropland led to substantial C removal from the atmosphere (about 12 Mg C ha^–1 a^–1). However, despite the promising C sequestration rates by bamboo, its introduction should be carefully considered due to potential ecological problems caused by this species in overexploited environments such as the Mediterranean area.

Carbon (C), nitrogen (N), and phosphorus (P) are of fundamental importance for growth and nutrient dynamics within plant organs and deserve more attention at regional to global scales. However, our knowledge of how these nutrients vary with tree size, organ age, or root order at the individual level remains limited. We determined C, N, and P contents and their stoichiometric ratios (i.e., nutrient traits) in needles, branches, and fine roots at different organ ages (0–3-year-old needles and branches) and root orders (1st–4th order roots) from 64 Pinus koraiensis of varying size (Diameter at breast height ranged from 0.3 to 100 cm) in northeast China. Soil factors were also measured. The results show that nutrient traits were regulated by tree size, organ age, or root order rather than soil factors. At a whole-plant level, nutrient traits decreased in needles and fine roots but increased in branches with tree size. At the organ level, age or root order had a negative effect on C, N, and P and a positive effect on stoichiometric ratios. Our results demonstrate that nutrient variations are closely related to organ-specific functions and ecophysiological processes at an individual level. It is suggested that the nutrient acquisition strategy by younger trees and organ fractions with higher nutrient content is for survival. Conversely, nutrient storage strategy in older trees and organ fractions are mainly for steady growth. Our results clarified the nutrient utilization strategies during tree and organ ontogeny and suggest that tree size and organ age or root order should be simultaneously considered to understand the complexities of nutrient variations.

Evapotranspiration is an important parameter used to characterize the water cycle of ecosystems. To understand the properties of the evapotranspiration and energy balance of a subalpine forest in the southeastern Qinghai–Tibet Plateau, an open-path eddy covariance system was set up to monitor the forest from November 2020 to October 2021 in a core area of the Three Parallel Rivers in the Qinghai–Tibet Plateau. The results show that the evapotranspiration peaked daily, the maximum occurring between 11:00 and 15:00. Environmental factors had significant effects on evapotranspiration, among them, net radiation the greatest (R ² = 0.487), and relative humidity the least (R ² = 0.001). The energy flux varied considerably in different seasons and sensible heat flux accounted for the main part of turbulent energy. The energy balance ratio in the dormant season was less than that in the growing season, and there is an energy imbalance at the site on an annual time scale.

Litterfall is the largest source of nutrients to forest soils of tropical rainforests. However, variability in litterfall production, nutrient remobilization, and changes in leaf nutrient concentration with climate seasonality remain largely unknown for the central Amazon. This study measured litterfall production, leaf nutrient remobilization, and leaf area index on a forest plateau in the central Amazon. Litterfall was measured at monthly intervals during 2014, while nitrogen, phosphorus, potassium, calcium and magnesium concentrations of leaf litter and canopy leaves were measured in the dry and rainy seasons, and remobilization rates determined. Leaf area index was also recorded in the dry and rainy seasons. Monthly litterfall varied from 33.2 (in the rainy season) to 87.6 g m^‒2 in the dry season, while leaf area index increased slightly in the rainy season. Climatic seasonality had no effect on concentrations of nitrogen, calcium, and magnesium, whereas phosphorous and potassium responded to rainfall seasonality oppositely. While phosphorous increased, potassium decreased during the dry season. Over seasons, nitrogen, potassium, and phosphorous decreased in leaf litter; calcium increased in leaf litter, while magnesium remained unaffected with leaf aging. Regardless, the five nutrients had similar remobilization rates over the year. The absence of climate seasonality on nutrient remobilization suggests that the current length of the dry season does not alter nutrient remobilization rates but this may change as dry periods become more prolonged in the future due to climate change.

Urbanization has profound impacts on ecological environments. Green spaces are a vital component of urban ecosystems and play a crucial role in maintaining ecological balance and enhancing sustainability. This study aimed to investigate the community composition characteristics of butterflies in urban green spaces within the context of rapid urbanization. Simultaneously, it explored the status and differences in butterfly taxonomic diversity, functional diversity, and functional traits among different types of urban green spaces, regions, and urban gradients to provide relevant insights for further improving urban green space quality and promoting biodiversity conservation. We conducted a year-long survey of 80 green spaces across different urban regions and ring roads within Hefei City, Anhui Province, with monthly sampling intervals over 187 transects. A total of 4822 butterflies, belonging to 5 families, 17 subfamilies, 40 genera, and 55 species were identified. The species richness, Shannon, Simpson, functional richness, and Rao's quadratic entropy indices of butterflies in urban park green spaces were all significantly higher than those in residential and street green spaces (P < 0.05). Differences in butterfly diversity and functional traits among different urban regions and ring roads were relatively minor, and small-sized, multivoltine, and long flying duration butterflies dominated urban green spaces. Overall, these spaces offer more favorable habitats for butterflies. However, some residential green spaces and street green spaces demonstrate potential for butterfly conservation.

Tree-ring width (RW), density, elemental composition, and stable carbon and oxygen isotope (δ¹³C, δ¹⁸O) are widely used as proxies to assess climate change, ecology, and environmental pollution; however, a specific pretreatment has been needed for each proxy. Here, we developed a method by which each proxy can be measured in the same sample. First, the sample is polished for ring width measurement. After obtaining the ring width data, the sample is cut to form a 1-mm-thick wood plate. The sample is then mounted in a vertical sample holder, and gradually scanned by an X-ray beam. Simultaneously, the count rates of the fluorescent photons of elements (for chemical characterization) and a radiographic grayscale image (for wood density) are obtained, i.e. the density and the element content are obtained. Then, cellulose is isolated from the 1-mm wood plate by removal of lignin, and hemicellulose. After producing this cellulose plate, cellulose subsamples are separated by knife under the microscope for inter-annual and intra-annual stable carbon and oxygen isotope (δ¹³C, δ¹⁸O) analysis. Based on this method, RW, density, elemental composition, δ¹³C, and δ¹⁸O can be measured from the same sample, which reduces sample amount and treatment time, and is helpful for multi-proxy comparison and combination research.

Interest in the dynamics of soil respiration (R _s) in subalpine forest ecosystems is increasing due to their high soil carbon density and potential sensitivity to environmental changes. However, as a principal silvicultural practice, the long-term impacts of thinning on R _s and its heterotrophic and autotrophic respiration components (R _h and R _a, respectively) in subalpine plantations are poorly understood, especially in winter. A 3-year field observation was carried out with consideration of winter CO₂ efflux in middle-aged subalpine spruce plantations in northwestern China. A trenching method was used to explore the long-term impacts of thinning on R _s, R _h and R _a. Seventeen years after thinning, mean annual R _s, R _h and R _a increased, while the contribution of R _h to R _s decreased with thinning intensity. Thinning significantly decreased winter R _s because of the reduction in R _h but had no significant effect on R _a. The temperature sensitivity (Q ₁₀) of R _h and R _a also increased with thinning intensity, with lower Q ₁₀ values for R _h (2.1–2.6) than for R _a (2.4–2.8). The results revealed the explanatory variables and pathways related to R _h and R _a dynamics. Thinning increased soil moisture and nitrate nitrogen (${\text{NO}}_{3}^{ - }$-N), and the enhanced nitrogen and water availability promoted R _h and R _a by improving fine root biomass and microbial activity. Our results highlight the positive roles of ${\text{NO}}_{3}^{ - }$-N in stimulating R _s components following long-term thinning. Therefore, applications of nitrogen fertilizer are not recommended while thinning subalpine spruce plantations from the perspective of reducing soil CO₂ emissions. The increased Q ₁₀ values of R _s components indicate that a large increase in soil CO₂ emissions would be expected following thinning because of more pronounced climate warming in alpine regions.

Tree radial growth can have significantly different responses to climate change depending on the environment. To elucidate the effects of climate on radial growth and stable carbon isotope (δ¹³C) fractionation of Qinghai spruce (Picea crassifolia), a widely distributed native conifer in northwestern China in different environments, we developed chronologies for tree-ring widths and δ¹³C in trees on the southern and northern slopes of the Qilian Mountains, and analysed the relationship between these tree-ring variables and major climatic factors. Tree-ring widths were strongly influenced by climatic factors early in the growing season, and the radial growth in trees on the northern slopes was more sensitive to climate than in trees on the southern. Tree-ring δ¹³C was more sensitive to climate than radial growth. δ¹³C fractionation was mainly influenced by summer temperature and precipitation early in the growing season. Stomatal conductance more strongly limited stable carbon isotope fractionation in tree rings than photosynthetic rate did. The response between tree rings and climate in mountains gradually weakened as climate warmed. Changes in radial growth and stable carbon isotope fractionation of P. crassifolia in response to climate in the Qilian Mountains may be further complicated by continued climate change.

Existing streamflow reconstructions based on tree-ring analysis mostly rely on species from upland, mainly montane areas, while lowland species (generally plain) areas are rarely used. This limits the understanding of streamflow change history in the lowlands, which is an important basis for water resource management. This study focused on Populus euphratica stands located along the main stream, eastern and western tributaries in the lower reaches of the Heihe River basin (HRb), in arid northwestern China. We investigated how streamflow regulation interferes with riparian trees in lowlands when they used for streamflow reconstruction. Tree-ring width chronologies were developed and analyzed in conjunction with meteorological and hydrologic observation data. The results show streamflow regulation leads in sharp fluctuations in the streamflow allocation between the eastern tributaries and western tributaries. This resulted in instability of the correlation between streamflow at the two tributaries and at the Zhengyixia hydrologic station, with corresponding fluctuations in radial growth of poplar trees on the banks of the two tributaries and at the station. Streamflow regulation altered the natural patterns of seasonal streamflow below the station, changing the time window of poplar response. This study provides useful insight into tree-ring width based streamflow reconstruction in the lowlands.

Since the launch of the Google Earth Engine (GEE) cloud platform in 2010, it has been widely used, leading to a wealth of valuable information. However, the potential of GEE for forest resource management has not been fully exploited. To extract dominant woody plant species, GEE combined Sentinel-1 (S1) and Sentinel-2 (S2) data with the addition of the National Forest Resources Inventory (NFRI) and topographic data, resulting in a 10 m resolution multimodal geospatial dataset for subtropical forests in southeast China. Spectral and texture features, red-edge bands, and vegetation indices of S1 and S2 data were computed. A hierarchical model obtained information on forest distribution and area and the dominant woody plant species. The results suggest that combining data sources from the S1 winter and S2 yearly ranges enhances accuracy in forest distribution and area extraction compared to using either data source independently. Similarly, for dominant woody species recognition, using S1 winter and S2 data across all four seasons was accurate. Including terrain factors and removing spatial correlation from NFRI sample points further improved the recognition accuracy. The optimal forest extraction achieved an overall accuracy (OA) of 97.4% and a map-level image classification efficacy (MICE) of 96.7%. OA and MICE were 83.6% and 80.7% for dominant species extraction, respectively. The high accuracy and efficacy values indicate that the hierarchical recognition model based on multimodal remote sensing data performed extremely well for extracting information about dominant woody plant species. Visualizing the results using the GEE application allows for an intuitive display of forest and species distribution, offering significant convenience for forest resource monitoring.

Native grasslands in the Pampas of South America are increasingly being replaced by Eucalyptus and Pinus stands. The short rotation regimes used for the stands require high nutrient levels, with litterfall being a major source of nutrient return. To model the litterfall production using climatic variables and assess the nutrient return in 14-year-old Eucalyptus grandis and Pinus taeda stands, we measured litter production over 2 years, using conical litter traps, and monitored climatic variables. Mean temperature, accumulated precipitation, and mean maximum vapor pressure deficit at the seasonal level influenced litterfall production by E. grandis; seasonal accumulated precipitation and mean maximum temperature affected litterfall by P. taeda. The regression tree modeling based on these climatic variables had great accuracy and predictive power for E. grandis (N = 33; MAE (mean absolute error) = 0.65; RMSE (root mean square error) = 0.91; R ² = 0.71) and P. taeda (N = 108; MAE = 1.50; RMSE = 1.59; R ² = 0.72). The nutrient return followed a similar pattern to litterfall deposition, as well as the order of importance of macronutrients (E. grandis: Ca > N > K > Mg > P; P. taeda: N > Ca > K > Mg > P) and micronutrients (E. grandis and P. taeda: Mn > Fe > Zn > Cu) in both species. This study constitutes a first approximation of factors that affect litterfall and nutrient return in these systems.

Increasing human activity is altering the structure of forests, which affects the composition of communities, including birds. However, little is known about the key forest structure variables that determine the richness of bird communities in European temperate oak forests. We, therefore, aimed to identify key variables in these habitats that could contribute to the design of management strategies for forest conservation by surveying 11 oak-dominated forest sites throughout the mid-mountain range of Hungary at 86 survey points to reveal the role of different compositional and structural variables for forest stands that influence the breeding bird assemblages in the forests at the functional group and individual species levels. Based on decision tree modelling, our results showed that the density of trees larger than 30 cm DBH was an overall important variable, indicating that large-diameter trees were essential to provide diverse bird communities. The total abundance of birds, the foliage-gleaners, primary and secondary cavity nesters, residents, and five specific bird species were related to the density of high trunk diameter trees. The abundance of shrub nesters was negatively influenced by a high density of trees over 10 cm DBH. The density of the shrub layer positively affected total bird abundance and the abundance of foliage gleaners, secondary cavity nesters and residents. Analysis of the co-dominant tree species showed that the presence of linden, beech, and hornbeam was important in influencing the abundance of various bird species, e.g., Eurasian Treecreeper (Certhia familiaris), Marsh Tit (Poecile palustris) and Wood Warbler (Phylloscopus sibilatrix). Our results indicated that large trees, high tree diversity, and dense shrub layer were essential for forest bird communities and are critical targets for protection to maintain diverse and abundant bird communities in oak-dominated forest habitats.

As one of the regions most affected by global climate warming, the Tianshan mountains has experienced several ecological crises, including retreating glaciers and water deficits. Climate warming in these mountains is considered mainly to be caused by increases in minimum temperatures and winter temperatures, while the influence of maximum temperatures is unclear. In this study, a 300-year tree-ring chronology developed from the Western Tianshan Mountains was used to reconstruct the summer (June–August) maximum temperature (T _max6–8) variations from 1718 to 2017. The reconstruction explained 53.1% of the variance in the observed T _max6–8. Over the past 300 years, the T _max6–8 reconstruction showed clear interannual and decadal variabilities. There was a significant warming trend (0.18 °C/decade) after the 1950s, which was close to the increasing rates of the minimum and mean temperatures. The increase in maximum temperature was also present over the whole Tianshan mountains and its impact on climate warming has increased. The T _max6-8 variations in the Western Tianshan mountains were influenced by frequent volcanic eruptions combined with the influence of solar activity and the summer North Atlantic Oscillation. This study reveals that climate warming is significantly influenced by the increase in maximum temperatures and clarifies possible driving mechanisms of temperature variations in the Western Tianshan mountains which should aid climate predictions.

Research has indicated that simple forest ecosystem composition, structure and diversity have uncomplicated community relationships and insufficient pest control capabilities. To investigate changing characteristics of plant and insect communities in under pest outbreaks in Larix principis-rupprechtii plantations, the research areas were defined as mature (48–50 years) and young (24–29 years) infested stands along with healthy stands. The results show a reduction in the complexity and diversity of plant communities and herbaceous plant guilds (polycultures of beneficial plants) and the complexity and dominance of insect communities, especially natural insect enemies. The results also show the relative simplicity of the main factors of community change and development that represent the characteristics of pest outbreaks in L. principis-rupprechtii plantations. The complexity and diversity of plant communities, particularly herbaceous plant guilds play a fundamental role in the regulation and development in forest ecosystems.

Disturbances such as forest fires, intense winds, and insect damage exert strong impacts on forest ecosystems by shaping their structure and growth dynamics, with contributions from climate change. Consequently, there is a need for reliable and operational methods to monitor and map these disturbances for the development of suitable management strategies. While susceptibility assessment using machine learning methods has increased, most studies have focused on a single disturbance. Moreover, there has been limited exploration of the use of “Automated Machine Learning (AutoML)” in the literature. In this study, susceptibility assessment for multiple forest disturbances (fires, insect damage, and wind damage) was conducted using the PyCaret AutoML framework in the Izmir Regional Forest Directorate (RFD) in Turkey. The AutoML framework compared 14 machine learning algorithms and ranked the best models based on AUC (area under the curve) values. The extra tree classifier (ET) algorithm was selected for modeling the susceptibility of each disturbance due to its good performance (AUC values > 0.98). The study evaluated susceptibilities for both individual and multiple disturbances, creating a total of four susceptibility maps using fifteen driving factors in the assessment. According to the results, 82.5% of forested areas in the Izmir RFD are susceptible to multiple disturbances at high and very high levels. Additionally, a potential forest disturbances map was created, revealing that 15.6% of forested areas in the Izmir RFD may experience no damage from the disturbances considered, while 54.2% could face damage from all three disturbances. The SHAP (Shapley Additive exPlanations) methodology was applied to evaluate the importance of features on prediction and the nonlinear relationship between explanatory features and susceptibility to disturbance.

Episodes of drought-induced decline in tree growth and mortality are becoming more frequent as a result of climate warming and enhanced water stress in semi-arid areas. However, the ecophysiological mechanisms underlying the impact of drought on tree growth remains unresolved. In this study, earlywood and latewood tree-ring growth, δ¹³C, and δ¹⁸O chronologies of Picea mongolica from 1900 to 2013 were developed to clarify the intra- and inter-annual tree-ring growth responses to increasingly frequent droughts. The results indicate that annual basal area increment residuals (BAI_res), which removed tree age and size effects, have significantly decreased since 1960. However, the decreasing trend of earlywood BAI_res was higher than that of latewood. Climate response analysis suggests that the dominant parameters for earlywood and latewood proxies (BAI_res, δ¹³C and δ¹⁸O) were drought-related climate variables (Palmer drought severity index, temperature, relative humidity, and vapor pressure deficit). The most significant period of earlywood and latewood proxies’ responses to climate variables were focused on June–July and July–August, respectively. BAI_res, and δ¹³C were significantly affected by temperature and moisture conditions, whereas δ¹⁸O was slightly affected. Decreasing stomatal conductance due to drought outweighed the influence of increasing CO₂ on intrinsic water use efficiency (iWUE), and ultimately led to a decline in BAI_res. Compared to latewood, the faster decreasing BAI_res and smaller increasing iWUE of earlywood suggested trees were more vulnerable to water stress in the early growing season. Our study provides insights into the inter- and intra-annual mechanisms of tree-ring growth in semi-arid regions under rising CO₂ and climate change.

Prediction, prevention, and control of forest fires are crucial on at all scales. Developing effective fire detection systems can aid in their control. This study proposes a novel CNN (convolutional neural network) using an attention blocks module which combines an attention module with numerous input layers to enhance the performance of neural networks. The suggested model focuses on predicting the damage affected/burned areas due to possible wildfires and evaluating the multilateral interactions between the pertinent factors. The results show the impacts of CNN using attention blocks for feature extraction and to better understand how ecosystems are affected by meteorological factors. For selected meteorological data, RMSE 12.08 and MAE 7.45 values provide higher predictive power for selecting relevant and necessary features to provide optimal performance with less operational and computational costs. These findings show that the suggested strategy is reliable and effective for planning and managing fire-prone regions as well as for predicting forest fire damage.

Populus alba ‘Berolinensis’ is a fast-growing, high-yielding species with strong biotic and abiotic stress resistance, and widely planted for timber, shelter belts and aesthetic purposes. In this study, molecular development is explored and the important genes regulating xylem formation in P. alba ‘Berolinensis’ under artificial bending treatments was identified. Anatomical investigation indicated that tension wood (TW) was characterized by eccentric growth of xylem and was enriched in cellulose; the degree of lignification was lower than for normal wood (NW) and opposite wood (OW). RNA-Seq-based transcriptome analysis was performed using developing xylem from three wood types (TW, OW and NW). A large number of differentially expressed genes (DEGs) were screened and 4889 counted. In GO and KEGG enrichment results, genes involved in plant hormone signal transduction, phenylpropanoid biosynthesis, and cell wall and secondary cell wall biogenesis play major roles in xylem development under artificial bending. Eight expansin (PalEXP) genes were identified from the RNA-seq data; four were differentially expressed during tension wood formation. Phylogenetic analysis indicated that PalEXLB1 belongs to the EXPB subfamily and that the other PalEXPs are members of the EXPA subfamily. A transcriptional regulatory network construction showed 10 transcription factors located in the first and second layers upstream of EXP, including WRKY, ERF and bHLH. RT‒qPCR analysis in leaves, stems and roots combined with transcriptome analysis suggests that PalEXPA2, PalEXPA4 and PalEXPA15 play significant regulatory roles in cell wall formation during tension wood development. The candidate genes involved in xylem cell wall development during tension wood formation marks an important step toward identifying the molecular regulatory mechanism of xylem development and wood property improvement in P. alba ‘Berolinensis’.

Quantifying the biomass of saplings in the regeneration component is critical for understanding biogeochemical processes of forest ecosystems. However, accurate allometric equations have yet to be developed in sufficient detail. To develop species-specific and generalized allometric equations, 154 saplings of eight Fagaceae tree species in subtropical China’s evergreen broadleaved forests were collected. Three dendrometric variables, root collar diameter (d), height (h), and crown area (ca) were applied in the model by the weighted nonlinear seemingly unrelated regression method. Using only d as an input variable, the species-specific and generalized allometric equations estimated the aboveground biomass reasonably, with ${R}_{adj}^{2}$ values generally > 0.85. Adding h and/or ca improved the fitting of some biomass components to a certain extent. Generalized equations showed a relatively large coefficient of variation but comparable bias to species-specific equations. Only in the absence of species-specific equations at a given location are generalized equations for mixed species recommended. The developed regression equations can be used to accurately calculate the aboveground biomass of understory Fagaceae regeneration trees in China’s subtropical evergreen broadleaved forests.

The role of the temperate mixed broadleaf-Korean pine forest (BKF) in global biogeochemical cycles will depend on how the tree species community responds to climate; however, species-specific responses and vulnerabilities of common trees in BKF to extreme climates are poorly understood. Here we used dendrochronological methods to assess radial growth of seven main tree species (Pinus koraiensis, Picea jezoensis, Abies nephrolepis, Fraxinus mandshurica, Phellodendron amurense, Quercus mongolica, and Ulmus davidiana) in an old-growth BKF in response to climate changes in the Xiaoxing’an Mountains and to improve predictions of changes in the tree species composition. Temperature in most months and winter precipitation significantly negatively affected growth of P. jezoensis and A. nephrolepis, but positively impacted growth of P. koraiensis and the broadleaf species, especially F. mandshurica and U. davidiana. Precipitation and relative humidity in June significantly positively impacted the growth of most tree species. The positive effect of the temperature during the previous non-growing season (PNG) on growth of F. mandshurica and Q. mongolica strengthened significantly with rapid warming around 1981, while the impact of PNG temperature on the growth of P. jezoensis and A. nephrolepis changed from significantly negative to weakly negative or positive at this time. The negative response of radial growth of P. jezoensis and A. nephrolepis to precipitation during the growing season gradually weakened, and the negative response to PNG precipitation was enhanced. Among the studied species, P. koraiensis was the most resistant to drought, and U. davidiana recovered the best after extreme drought. Ulmus davidiana, P. jezoensis and A. nephrolepis were more resistant to extreme cold than the other species. Climate warming generally exacerbated the opposite growth patterns of conifer (decline) and broadleaf (increase) species. Deciduous broadleaf tree species in the old-growth BKF probably will gradually become dominant as warming continues. Species-specific growth-climate relationships should be considered in future models of biogeochemical cycles and in forestry management practices.

Research on fires at the wildland-urban interface (WUI) has generated significant insights and advancements across various fields of study. Environmental, agriculture, and social sciences have played prominent roles in understanding the impacts of fires in the environment, in protecting communities, and addressing management challenges. This study aimed to create a database using a text mining technique for global researchers interested in WUI-projects and highlighting the interest of countries in this field. Author’s-Keywords analysis emphasized the dominance of fire science-related terms, especially related to WUI, and identified keyword clusters related to the WUI fire-risk-assessment-system—“exposure”, “danger”, and “vulnerability” within wildfire research. Trends over the past decade showcase shifting research interests with a growing focus on WUI fires, while regional variations highlighted that the “exposure” keyword cluster received greater attention in the southern Europe and South America. However, vulnerability keywords have relatively a lower representation across all regions. The analysis underscores the interdisciplinary nature of WUI research and emphasizes the need for targeted approaches to address the unique challenges of the wildland-urban interface. Overall, this study provides valuable insights for researchers and serves as a foundation for further collaboration in this field through the understanding of the trends over recent years and in different regions.

Forest productivity is closely linked to seasonal variations and vertical differentiation in leaf traits. However, leaf structural and chemical traits variation among co-existing species, and plant functional types within the canopy are poorly quantified. In this study, the seasonality of leaf chlorophyll, nitrogen (N), and phosphorus (P) were quantified vertically along the canopy of four major tree species and two types of herbs in a temperate deciduous forest. The role of shade tolerance in shaping the seasonal variation and vertical differentiation was examined. During the entire season, chlorophyll content showed a distinct asymmetric unimodal pattern for all species, with greater chlorophyll levels in autumn than in spring, and the timing of peak chlorophyll per leaf area gradually decreased as shade tolerance increased. Chlorophyll a:b ratios gradually decreased with increasing shade tolerance. Leaf N and P contents sharply declined during leaf expansion, remained steady in the mature stage and decreased again during leaf senescence. Over the seasons, the lower canopy layer had significantly higher chlorophyll per leaf mass but not chlorophyll per leaf area than the upper canopy layer regardless of degree of shade tolerance. However, N and P per leaf area of intermediate shade-tolerant and fully shade-tolerant tree species were significantly higher in the upper canopy than in the lower. Seasonal variations in N:P ratios suggest changes in N or P limitation. These findings indicate that shade tolerance is a key feature shaping inter-specific differences in leaf chlorophyll, N, and P contents as well as their seasonality in temperate deciduous forests, which have significant implications for modeling leaf photosynthesis and ecosystem production.

Acorn production in oak (Quercus spp.) shows considerable inter-annual variation, known as masting, which provides a natural defence against seed predators but a highly-variable supply of acorns for uses such as in commercial tree planting each year. Anthropogenic emissions of greenhouse gases have been very widely reported to influence plant growth and seed or fruit size and quantity via the ‘fertilisation effect’ that leads to enhanced photosynthesis. To examine if acorn production in mature woodland communities will be affected by further increase in CO₂, the contents of litter traps from a Free Air Carbon Enrichment (FACE) experiment in deciduous woodland in central England were analysed for numbers of flowers and acorns of pedunculate oak (Quercus robur L.) at different stages of development and their predation levels under ambient and elevated CO₂ concentrations. Inter-annual variation in acorn numbers was considerable and cyclical between 2015 and 2021, with the greatest numbers of mature acorns in 2015, 2017 and 2020 but almost none in 2018. The numbers of flowers, enlarged cups, immature acorns, empty acorn cups, and galls in the litter traps also varied amongst years; comparatively high numbers of enlarged cups were recorded in 2018, suggesting Q. robur at this site is a fruit maturation masting species (i.e., the extent of abortion of pollinated flowers during acorn development affects mature acorn numbers greatly). Raising the atmospheric CO₂ concentration by 150 μL L⁻¹, from early 2017, increased the numbers of immature acorns, and all acorn evidence (empty cups + immature acorns + mature acorns) detected in the litter traps compared to ambient controls by 2021, but did not consistently affect the numbers of flowers, enlarged cups, empty cups, or mature acorns. The number of flowers in the elevated CO₂ plots’ litter traps was greater in 2018 than 2017, one year after CO₂ enrichment began, whereas numbers declined in ambient plots. Enrichment with CO₂ also increased the number of oak knopper galls (Andricus quercuscalicis Burgsdorf). We conclude that elevated CO₂ increased the occurrence of acorns developing from flowers, but the putative benefit to mature acorn numbers may have been hidden by excessive pre- and/or post-dispersal predation. There was no evidence that elevated CO₂ altered masting behaviour.

Vegetation productivity on the southern edge of the Inner Mongolian Plateau, which plays a vital role in the ecological environment and in the arable and pastoral production in this region, can be characterized by the NDVI (normalized difference vegetation index). However, the observed NDVI data span only the last ~ 40 years. The growth of Pinus tabulaeformis Carr. is strongly correlated with the NDVI, making it a valuable proxy for extending the length of observed NDVI datasets. In this study, we reconstructed an NDVI series for 1776–2021 for the Daqing Mountains, based on a tree-ring width chronology. The reconstructed data accounted for 55% of the variance in the observed data, and its statistical characteristics and validation indicate that the reconstruction is dependable. Spatial correlation analysis demonstrated the consistency of climate signals in central Inner Mongolia in both the arable and pastoral zones. The results of superposed epoch analysis revealed a good temporal consistency between drought and flood events and the reconstructed NDVI sequence in this region.

Tree canopies influence atmospheric pollutant depositions depending on type, ecosystem characteristics, and local climatic conditions. This study investigated the impact of Pinus sylvestris L. and Picea abies (L.) H. Karst., and a mixture of both, on the chemical composition of precipitation. Three permanent plots within the ICP forest level II monitoring network in Lithuania were selected to illustrate typical hemiboreal coniferous forests. The study analysed (1) the concentrations of NO₂, NH₃ and SO₂ in the ambient air; (2) the concentrations of SO₄ ²⁻, NO₃ ⁻, NH₄ ⁺, Na⁺, K⁺, Ca²⁺ and Cl^– in throughfall beneath canopies and in precipitation collected in an adjacent field, and (3) S and total N, Na⁺, K⁺, Ca²⁺ and Cl⁻ depositions in throughfall and precipitation over 2006–2022. Results show a significant decrease in SO₂ emissions in the ambient air; NO₂ and NH₃ emissions also decreased. The canopies reduced the acidity of throughfall, although they led to notably higher concentrations of SO₄ ²⁻, NO₃ ⁻, Na⁺, and particularly K⁺. During the study, low variability in NO₃ ^– deposition and a decrease in NH₄ ⁺ deposition occurred. Deposition loads increased by 20–30% when precipitation passed through the canopy. The cumulative deposition of S, Cl, Na, K, Ca, and N was greater under P. abies than under P. sylvestris. However, K deposition in throughfall was considerably lower under P. sylvestris compared to the P. abies or mixed stand. Throughfall S depositions declined across all three coniferous plots. Overall, there was no specific effect of tree species on throughfall chemistry.

Temporal changes in the relationship between tree growth and climate have been observed in numerous forests across the world. The patterns and the possible regulators (e.g., forest community structure) of such changes are, however, not well understood. A vegetation survey and analyses of growth-climate relationships for Abies georgei var. Smithii (Smith fir) forests were carried along an altitudinal gradient from 3600 to 4200 m on Meili Snow Mountain, southeastern Tibetan Plateau. The results showed that the associations between growth and temperature have declined since the 1970s over the whole transect, while response to standardized precipitation-evapotranspiration indices (SPEI) strengthened in the mid- and lower-transect. Comparison between growth and vegetation data showed that tree growth was more sensitive to drought in stands with higher species richness and greater shrub cover. Drought stress on growth may be increased by heavy competition from shrub and herb layers. These results show the non-stationary nature of tree growth-climate associations and the linkage to forest community structures. Vegetation components should be considered in future modeling and forecasting of forest dynamics in relation to climate changes.

Urbanization has resulted in a significant degradation of soil quality, subjecting plants to persistent abiotic stressors such as heavy metal pollution, salinization, and drought. UDP-glycosyltransferases (UGTs) participate in protein glycosylation, secondary metabolite synthesis, and detoxification of exogenous toxic substances. Iris sanguinea Donn ex Hornem exhibits a high degree of resistance to various abiotic stressors. To enhance the plant’s response to adversity, a novel glycosyltransferase belonging to the UGT78 family, encoding flavonoid 3-O-glucosyltransferase (UF3GT), was cloned from the monocot species I. sanguinea. Compared with the control group, overexpression of IsUGT78 enhanced sensitivity to cadmium stress, while showing no significant impact under NaCl and d-sorbitol treatments. Under cadmium treatment, arabidopsis exogenously transformed with the IsUGT78 gene possessed lower germination, fresh weight, root length, and chlorophyll content and increased malondialdehyde content than the wild type arabidopsis. In addition, metabolomics in leaves led to the identification of 299 flavonoid metabolites, eight and 127 which were significantly up- and down-regulated, respectively, in the transgenic plants. Of note, all eight upregulated flavonoid compounds were glycosylated. Given that arabidopsis, which exogenously expresses the IsUGT78 gene, has reduced resistance to cadmium, IsUGT78 may lead to a reduced ability to cope with cadmium stress.

Evaluating long-term changes in precipitation resources is important for accurate hydrological evaluation and forecasting, water security and rational allocation of water resources. For this purpose in the Xinjiang Habahe area, tree-ring specimens were collected from Picea obovata, Larix sibirica, and Betula platyphylla to establish a tree-ring width chronology, which was used to analyse a correlation with the average temperature and precipitation per month for 1958–2016. Based on correlation coefficients for monthly temperature and precipitation with the chronology of tree-ring widths, radial tree growth was mainly restricted by precipitation, and tree-ring width chronology was significantly correlated with overall precipitation from the previous July to the next June (r = 0.641, P < 0.01). The above results were used to establish a transformation equation, and the overall precipitation from the previous July to the following June from 1800 to 2016 in Habahe was reconstructed after adjusted degrees of freedom, and obtain an explanatory rate of the variation up to 41.1% (40.0%). In addition to the reliability of the reconstructed values, the stability of the conversion function was determined via the “leave-one-out” method, which is commonly used in research on tree rings, and by cross-checking the conversion function with the reduced error value (RE), product mean test (t), with a sign test (ST). During the last 217 years, there were nine dry periods: 1803–1829, 1861–1865, 1872–1885, 1892–1905, 1916–1923, 1943–1954, 1961–1966, 1973–1981, and 2005–2011; and 12 wet periods: 1830–1834, 1836–1860, 1866–1871, 1886–1891, 1906–1915, 1925–1930, 1934–1942, 1955–1960, 1967–1972, 1982–1996, 2000–2004, and 2012–2016. Comparisons of the reconstructions for neighboring regions and a spatial correlation analysis showed that the reconstructed sequence of the present precipitation data better represented the changes in precipitation in Habahe. Additionally, a power spectrum analysis revealed that precipitation over the past 217 years in Habahe Province exhibited 2–5 years of quasiperiodic variation. A power spectrum analysis and wavelet analysis indicated that El Niño-Southern Oscillation influenced the precipitation cycles. This reconstruction provides more information on high-frequency precipitation, which is an important supplement to the existing tree-ring reconstruction of precipitation in the study area. The reconstruction of regional high-resolution precipitation changes over the last several hundred years provides unique, important data for understanding regional differences in climate at the decadal-centennial scale.

This paper introduces a new method of calculating crown projection area (CPA), the area of level ground covered by a vertical projection of a tree crown from measured crown radii through numerical interpolation and integration. This novel method and other four existing methods of calculating CPA were compared using detailed crown radius measurements from 30 tall trees of Eucalyptus pilularis variable in crown size, shape, and asymmetry. The four existing methods included the polygonal approach and three ways of calculating CPA as the area of a circle using the arithmetic, geometric and quadratic mean radius. Comparisons were made across a sequence of eight non-consecutive numbers (from 2 to 16) of measured crown radii for each tree over the range of crown asymmetry of the 30 trees through generalized linear models and multiple comparisons of means. The sequence covered the range of the number of crown radii measured for calculating the CPA of a tree in the literature. A crown asymmetry index within the unit interval was calculated for each tree to serve as a normative measure. With a slight overestimation of 2.2% on average and an overall mean error size of 7.9% across the numbers of crown radii that were compared, our new method was the least biased and most accurate. Calculating CPA as a circle using the quadratic mean crown radius was the second best, which had an average overestimation of 4.5% and overall mean error size of 8.8%. These two methods remained by and large unbiased as crown asymmetry increased, while the other three methods showed larger bias of underestimation. For the conventional method of using the arithmetic mean crown radius to calculate CPA as a circle, bias correction factors were developed as a function of crown asymmetry index to delineate the increasing magnitude of bias associated with greater degrees of crown asymmetry. This study reveals and demonstrates such relationships between the accuracy of CPA calculations and crown asymmetry and will help increase awareness among researchers and practitioners on the existence of bias in their CPA calculations and for the need to use an unbiased method in the future. Our new method is recommended for calculating CPA where at least four crown radius measurements per tree are available because that is the minimum number required for its use.

The combined use of LiDAR (Light Detection And Ranging) scanning and field inventories can provide spatially continuous wall-to-wall information on forest characteristics. This information can be used in many ways in forest mapping, scenario analyses, and forest management planning. This study aimed to find the optimal way to obtain continuous forest data for Catalonia when using kNN imputation (kNN stands for “k nearest neighbors”). In this method, data are imputed to a certain location from k field-measured sample plots, which are the most similar to the location in terms of LiDAR metrics and topographic variables. Weighted multidimensional Euclidean distance was used as the similarity measure. The study tested two different methods to optimize the distance measure. The first method optimized, in the first step, the set of LiDAR and topographic variables used in the measure, as well as the transformations of these variables. The weights of the selected variables were optimized in the second step. The other method optimized the variable set as well as their transformations and weights in one single step. The two-step method that first finds the variables and their transformations and subsequently optimizes their weights resulted in the best imputation results. In the study area, the use of three to five nearest neighbors was recommended. Altitude and latitude turned out to be the most important variables when assessing the similarity of two locations of Catalan forests in the context of kNN data imputation. The optimal distance measure always included both LiDAR metrics and topographic variables. The study showed that the optimal similarity measure may be different for different regions. Therefore, it was suggested that kNN data imputation should always be started with the optimization of the measure that is used to select the k nearest neighbors.

COVID-19 posed challenges for global tourism management. Changes in visitor temporal and spatial patterns and their associated determinants pre- and peri-pandemic in Canadian Rocky Mountain National Parks are analyzed. Data was collected through social media programming and analyzed using spatiotemporal analysis and a geographically weighted regression (GWR) model. Results highlight that COVID-19 significantly changed park visitation patterns. Visitors tended to explore more remote areas peri-pandemic. The GWR model also indicated distance to nearby trails was a significant influence on visitor density. Our results indicate that the pandemic influenced tourism temporal and spatial imbalance. This research presents a novel approach using combined social media big data which can be extended to the field of tourism management, and has important implications to manage visitor patterns and to allocate resources efficiently to satisfy multiple objectives of park management.

This study comprehensively assessed long-term vegetation changes and forest fragmentation dynamics in the Himalayan temperate region of Pakistan from 1989 to 2019. Four satellite images, including Landsat-5 TM and Landsat-8 Operational Land Imager (OLI), were chosen for subsequent assessments in October 1989, 2001, 2011 and 2019. The classified maps of 1989, 2001, 2011 and 2019 were created using the maximum likelihood classifier. Post-classification comparison showed an overall accuracy of 82.5% and a Kappa coefficient of 0.79 for the 2019 map. Results revealed a drastic decrease in closed-canopy and open-canopy forests by 117.4 and 271.6 km², respectively, and an increase in agriculture/farm cultivation by 1512.8 km². The two-way ANOVA test showed statistically significant differences in the area of various cover classes. Forest fragmentation was evaluated using the Landscape Fragmentation Tool (LFT v2.0) between 1989 and 2019. The large forest core (> 2.00 km²) decreased from 149.4 to 296.7 km², and a similar pattern was observed in medium forest core (1.00–2.00 km²) forests. On the contrary, the small core (< 1.00 km²) forest increased from 124.8 to 145.3 km² in 2019. The perforation area increased by 296.9 km², and the edge effect decreased from 458.9 to 431.7 km². The frequency of patches also increased by 119.1 km². The closed and open canopy classes showed a decreasing trend with an annual rate of 0.58% and 1.35%, respectively. The broad implications of these findings can be seen in the studied region as well as other global ecological areas. They serve as an imperative baseline for afforestation and reforestation operations, highlighting the urgent need for efficient management, conservation, and restoration efforts. Based on these findings, sustainable land-use policies may be put into place that support local livelihoods, protect ecosystem services, and conserve biodiversity.

Deciduous oaks (Quercus spp.) are distributed from subalpine to tropical regions in the northern hemisphere and have important roles as carbon sinks and in climate change mitigation. Determining variations in plant functional traits at multiple biological levels and linking them to environmental variables across geographical ranges is important for forecasting range-shifts of broadly-distributed species under climate change. We sampled leaves of five deciduous Quercus spp. covering approximately 20° of latitude (~ 21° N − 41° N) and 20 longitude (~ 99° E − 119° E) across China and measured 12 plant functional traits at different biological levels. The traits varied distinctively, either within each biological level or among different levels driven by climatic and edaphic variables. Traits at the organ level were significantly correlated with those at the cellular and tissue levels, while traits at the whole-plant level only correlated with those at the tissue level. The Quercus species responded to changing environments by regulating stomatal size, leaf thickness and the palisade mesophyll thickness to leaf thickness ratios with contrasting degree of effect to adjust the whole-plant functioning, i.e., intrinsic water use efficiency (iWUE), carbon supply and nitrogen availability. The results suggest that these deciduous Quercus spp. will maintain vigour by increasing iWUE when subjected to large temperature changes and insufficient moisture, and by accumulating leaf non-structural carbohydrates under drought conditions. The findings provide new insights into the inherent variation and trait coordination of widely distributed tree species in the context of climate change.

Long-term temperature variations inferred from high-resolution proxies provide an important context to evaluate the intensity of current warming. However, temperature reconstructions in humid southeastern China are scarce and particularly lack long-term data, limiting us to obtain a complete picture of regional temperature evolution. In this study, we present a well-verified reconstruction of winter-spring (January–April) minimum temperatures over southeastern China based on stable carbon isotopic (δ¹³C) records of tree rings from Taxus wallichiana var. mairei from 1860 to 2014. This reconstruction accounted for 56.4% of the total observed variance. Cold periods occurred during the 1860s–1910s and 1960s–1970s. Although temperatures have had an upward trend since the 1920s, most of the cold extremes were in recent decades. The El Niño-Southern Oscillation (ENSO) variance acted as a key modulator of regional winter-spring minimum temperature variability. However, teleconnections between them were a nonlinear process, i.e., a reduced or enhanced ENSO variance may result in a weakened or intensified temperature-ENSO relationship.

Anthropogenic disturbances are widespread in tropical forests and influence the species composition in the overstory. However, the impacts of historical disturbance on tropical forest overstory recovery are unclear due to a lack of disturbance data, and previous studies have focused on understory species. In this study, the purpose was to determine the influence of historical disturbance on the diversity, composition and regeneration of overstory species in present forests. In the 20-ha Xishuangbanna tropical seasonal rainforest dynamics plot in southwestern China, the historical disturbance boundaries were delineated based on panchromatic photographs from 1965. Factors that drove species clustering in the overstory layer (DBH ≥ 40 cm) were analyzed and the abundance, richness and composition of these species were compared among different tree groups based on multiple regression tree analysis. The coefficient of variation of the brightness value in historical panchromatic photographs from 1965 was the primary driver of species clustering in the overstory layer. The abundance and richness of overstory species throughout the regeneration process were similar, but species composition was always different. Although the proportion of large-seeded and vigorous-sprouting species showed no significant difference between disturbed and undisturbed forests in the treelet layer (DBH < 20 cm), the difference became significant when DBH increased. The findings highlight that historical disturbances have strong legacy effects on functional group composition in the overstory and the recovery of overstory species was multidimensional. Functional group composition can better indicate the dynamics of overstory species replacement during secondary succession.

Bushfires are devastating to forest managers, owners, residents, and the natural environment. Recent technological advances indicate a potential for faster response times in terms of detecting and suppressing fires. However, to date, all these technologies have been applied in isolation. This paper introduces the latest fire detection and suppression technologies from ground to space. An operations research method was used to assemble these technologies into a theoretical framework for fire detection and suppression. The framework harnesses the advantages of satellite-based, drone, sensor, and human reporting technologies as well as image processing and artificial intelligence machine learning. The study concludes that, if a system is designed to maximise the use of available technologies and carefully adopts them through complementary arrangements, a fire detection and resource suppression system can achieve the ultimate aim: to reduce the risk of fire hazards and the damage they may cause.

Global forests are increasingly crucial for achieving net-zero carbon emissions, with a quarter of the mitigation efforts under the Paris Climate Agreement directed towards forests. In China, forests currently contribute to 13% of the global land's carbon sink, but their stability and persistence remain uncertain. We examined and identified that published studies suffered from oversimplifications of ecosystem succession and tree demographic dynamics, as well as poor constraints on land quality. Consequently, substantial estimations might have been suffered from underrepresented or ignored crucial factors, including tree demographic dynamics, and disturbances and habitat shifts caused by global climate change. We argue that these essential factors should be considered to enhance the reliability and accuracy of assessments of the potential for forest carbon sinks.

Trees progress through various growth stages, each marked by specific responses and adaptation strategies to environmental conditions. Despite the importance of age-related growth responses on overall forest health and management policies, limited knowledge exists regarding age-related effects on dendroclimatic relationships in key subtropical tree species. In this study, we employed a dendrochronological method to examine the impact of rapid warming on growth dynamics and climatic sensitivity of young (40–60 years) and old (100–180 years) Pinus massoniana forests across six sites in central-southern China. The normalized log basal area increment of trees in both age groups increased significantly following rapid warming in 1984. Trees in young forests further showed a distinct growth decline during a prolonged severe drought (2004–2013), whereas those in old forests maintained growth increases. Tree growth was more strongly influenced by temperature than by moisture, particularly in old forests. Spring temperatures strongly and positively impacted the growth of old trees but had a weaker effect on young ones. Old forests had a significantly lower resistance to extreme drought but faster recovery compared to young forests. The “divergence problem” was more pronounced in younger forests due to their heightened sensitivity to warming-induced drought and heat stress. With ongoing warming, young forests also may initially experience a growth decline due to their heightened sensitivity to winter drought. Our findings underscore the importance of considering age-dependent changes in forest/tree growth response to warming in subtropical forest management, particularly in the context of achieving “Carbon Peak & Carbon Neutrality” goals in China.

Different chemical compositions of soil organic carbon (SOC) affect its persistence and whether it significantly differs between natural forests and plantations remains unclear. By synthesizing 234 observations of SOC chemical compositions, we evaluated global patterns of concentration, individual chemical composition (alkyl C, O-alkyl C, aromatic C, and carbonyl C), and their distribution evenness. Our results indicate a notably higher SOC, a markedly larger proportion of recalcitrant alkyl C, and lower easily decomposed carbonyl C proportion in natural forests. However, SOC chemical compositions were appreciably more evenly distributed in plantations. Based on the assumed conceptual index of SOC chemical composition evenness, we deduced that, compared to natural forests, plantations may have higher possible resistance to SOC decomposition under disturbances. In tropical regions, SOC levels, recalcitrant SOC chemical composition, and their distributed evenness were significantly higher in natural forests, indicating that SOC has higher chemical stability and possible resistance to decomposition. Climate factors had minor effects on alkyl C in forests globally, while they notably affected SOC chemical composition in tropical forests. This could contribute to the differences in chemical compositions and their distributed evenness between plantations and natural stands.

Forest disturbances at gap levels are one of the most important events for the regeneration and establishment of intermediate tree species. Abrupt canopy openings expose plants to high light intensity and high evaporative demands that stress shade-acclimated plants. Later, the slow closure of gaps reduces light availability to plants established when the incident irradiation was higher. This work evaluated the morphological and physiological acclimation of Cabralea canjerana (Vell) Mart. regeneration to sudden and to gradual changes in canopy cover. A pot experiment was carried out with plants exposed to a sudden opening. A few days after the light shock, plants rapidly increased photosynthetic rates and decreased leaf water potential. After two months, plants activated physiological responses at leaf and whole plant levels to high light and water stresses, e.g., increased stomatal conductance, stomatal index and reduction of leaf: fine roots ratio and chlorophyll. After seven months, hydraulic conductivity of petioles and the whole leaf increased, and growth was much higher than plants that remained under the canopy. In a field experiment in gaps in the rainforest, plants acclimated to all canopy covers. Seven years after planting, growth was maximum in open environments within the gaps, even if the canopy closed during the first 20 months after planting. In conclusion, if this species is planted to enrich the rainforest, positions within gaps with lower canopy cover should be chosen and gap closure will not affect growth. To manage C. canjerana natural regeneration, the opening of gaps and removal of understory will increase survival and growth without the risk that the stress caused by these sudden openings could lead to the death of seedlings. Combining pot and field experiments helps to understand the autecology of trees with particular ecological interest, and to build sound restoration practices.

Unstable environments intensify the frequency of extreme disasters. Long-term climate changes can lead to agricultural and ecological degradation that threatens population sustainability. To better understand past climatic events and consequences, here we present a reconstruction of the self-calibrating Palmer drought severity index (scPDSI) from September to August for the desert margins of northern China, dating back to 1742. The reconstruction accounts for 42.9% of the variation of meteorological data between 1951 and 2020. Our spatial correlation analyses showed significant correlations between scPDSI, runoff, and precipitation. Over the past 279 years, the study area has undergone nine dry and eight wet periods, with the most severe climate extremes between the 1850s and 1890s. This period of prolonged drought in northeastern China coincided with the combined impacts of climatic factors and human influences, contributing to the fall of the Qing Dynasty. Analysis of periodicity and anomalies in sea surface temperatures indicate a strong association between wet and dry cycles and El Niño-Southern Oscillations. Our findings offer insights into long-term dry and wet fluctuations at the desert margins in northern China and elucidate the relationship between drought and the dynamics of civilizations. They also highlight the potential impact of extremes in climate on modern society, especially under the four projected shared socioeconomic pathways climatic scenarios, which predict worsening droughts in northern China.

The use of mobile laser scanning to survey forest ecosystems is a promising, scalable technology to describe forest 3D structures at high resolution. To confirm the consistency in the retrieval of forest structural parameters using hand-held laser scanning (HLS), before operationalizing the method, confirming the data is crucial. We analyzed the performance of tree-level mapping based on HLS under different phenology conditions on a mixed forest in western Spain comprising Pinus pinaster and two deciduous species, Alnus glutinosa and Quercus pyrenaica. The area was surveyed twice during the growing season (July 2022) and once in the deciduous season (February 2022) using several scanning paths. Ground reference data (418 trees, 15 snags) was used to calibrate the HLS data and to assess the influence of phenology when converting 3D data into tree-level attributes (DBH, height and volume). The HLS-based workflow was robust at isolating tree positions and recognizing stems despite changes in phenology. Ninety-six percent of all pairs matched below 65 cm. For DBH, phenology barely altered estimates. We observed a strong agreement when comparing HLS-based tree height distributions. The values exceeded 2 m when comparing height measurements, confirming height data should be carefully used as reference in remote sensing-based inventories, especially for deciduous species. Tree volume was more precise for pines (r = 0.95, and relative RMSE = 21.3 –23.8%) compared to deciduous species (r = 0.91 –0.96, and relative RMSE = 27.3–30.5%). HLS data and the forest structural complexity tool performed remarkably, especially in tree positioning considering mixed forests and mixed phenology conditions.

Rapid increase in desertification is an environmental concern, especially for the health and sustainability of ecosystems in changing climates. How ecosystems respond to such changes may be partially understood by studying interactions and performance of critically important groups such as soil fungi functional groups. This study investigated variations in diversities of three soil fungi functional guilds (saprotrophic, symbiotic, pathogenic) and influencing abiotic factors in a Pinus densata forest on the southeast Tibetan Plateau where desertification is intense. The results indicate desertification significantly decreased the proportion of dominant fungal guild-symbiotic fungi (mean relative abundance decreasing from 97.0% to 68.3%), in contrast to saprotrophic fungi (increasing from 2.7% to 25.7%) and pathogenic (from 0.3% to 5.9%). Soil pH had the most significant impact on fungal community structure and negatively correlated with symbiotic fungal richness, which was significantly lower in arid soils, and positively correlated with saprotrophic and pathogenic fungal alpha-diversity, which were abundant. Different community structures and regulators of the three fungi communities were observed, with pH, total phosphorus and ammonium (NH₄ ⁺) as the main determinants. This study links the biotic and abiotic components during desertification and the interactions between them, and may be used as indicators of ecosystem health and for amendments to mitigate the effects of a changing climate.

Forest ecosystems within national parks are threatened by various biotic and abiotic factors. To determine the causes of the desiccation and death of trees in mixed coniferous and deciduous forests of Tara National Park (TNP), Serbia, we monitored defoliation and mortality of individual trees in permanent experimental plots. Data on the desiccation of a large number of trees were gathered by determining the total volume of dry trees and areas of forests under drying stress. The two sets of data were combined to determine the impact of climatic events, primarily drought periods, on the desiccation of forests. Combining data from the International Co-operative Program on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) with TNP data helped relate forest desiccation to climate events. Key climate signals were identified by monitoring tree defoliation changes in two permanent experimental plots, and then assessed for their influence on tree desiccation in the entire national park. The standardized precipitation evapotranspiration index (SPEI) was used for a more detailed analysis of the drought period. Despite the lack of climate data for a certain period, the SPEI index revealed a link between climate variables and the defoliation and desiccation of forests. Furthermore, the desiccation of trees was preceded by a long drought period. Although mixed coniferous-deciduous forests are often considered less vulnerable to natural influences, this study suggests that forest ecosystems can become vulnerable regardless of tree species composition due to multi-year droughts. These findings contribute to a better understanding of important clues for predicting possible future desiccation of forests. Continuous monitoring of the state of forests and of more permanent experimental plots in national parks could provide better quality data and timely responses to stressful situations.

In recent decades, the rapid climate warming in polar and alpine regions has been accompanied by an expansion of shrub vegetation. However, little is known about how changes in shrub distribution will change as the distribution of tree species and snow cover changes as temperatures rise. In this work, we analyzed the main environmental factors influencing the distribution and structure of Juniperus sibirica, the most common shrub species in the Southern Ural Mountains. Using mapping and digital elevation models, we demonstrated that J. sibirica forms a well-defined vegetation belt mainly between 1100 and 1400 m a.s.l. Within this zone, the abundance and cover of J. sibirica are influenced by factors such as rockiness, slope steepness, water regime and tree (Picea obovata) cover. An analysis of data spanning the past 9 years revealed an upward shift in the distribution of J. sibirica with a decrease in its area. The primary limiting factors for the distribution of J. sibirica were the removal of snow cover by strong winter winds and competition with trees. As a consequence of climatic changes, the tree line and forest limit have shifted upward, further restricting the distribution of J. sibirica to higher elevations where competition for light with trees is reduced and snow cover is sufficiently deep.

Investing in projects that support environmental benefits, such as tree harvesting, has the potential to reduce air pollution levels in the atmosphere in the future. However, this kind of investment may increase the current level of emissions. Therefore, it is necessary to estimate how much the policy affects the current level of CO₂ emissions. This makes sure the policy doesn’t increase the level of CO₂ emissions. This study aims to analyze the effect of the One Billion Trees program on CO₂ emissions in New Zealand by employing the 2020 input–output table analysis. This investigation examines the direct and indirect effects of policy on both the demand and supply sides across six regions of New Zealand. The results of this study for the first year of plantation suggest that the policy increases the level of CO₂ emissions in all regions, especially in the Waikato region. The direct and indirect impact of the policy leads to 64 kt of CO₂ emissions on the demand side and 270 kt of CO₂ emissions on the supply side. These lead to 0.19 and 0.74% of total CO₂ emissions being attributed to investment shocks. Continuing the policy is recommended, as it has a low effect on CO₂ emissions. However, it is crucial to prioritize the use of low-carbon machinery that uses fossil fuels during the plantation process.

In the context of ongoing climate change, relationships between tree growth and climate present uncertainties, which limits the predictions of future forest dynamics. Northwest China is a region undergoing notable warming and increased precipitation; how forests in this region will respond to climate change has not been fully understood. We used dendrochronological methods to examine the relationship between climate and the radial growth of four tree species in a riparian forest habitat in Altai region: European aspen (Populus tremula), bitter poplar (Populus laurifolia), Swedish birch (Betula pendula), and Siberian spruce (Picea obovata). The results reveal that European aspen was insensitive to climate changes. In contrast, bitter poplar showed a positive response to elevated temperatures and negative to increased moisture during the growing season. Swedish birch and Siberian spruce were adversely affected by higher temperatures but benefited from increased precipitation. A moving correlation analysis suggested that, against a backdrop of continuous warming, growth patterns of these species will diverge: European aspen will require close monitoring, bitter poplar may likely to show accelerated growth, and the growth of Swedish birch and Siberian spruce may be inhibited, leading to a decline. These findings offer insight into the future dynamics of riparian forests under changing climate.

In recent years, the situation of the Hyphantria cunea (Drury) (Lepidoptera: Erebidae), infestation in China has been serious and has a tendency to continue to spread. A comprehensive analysis was carried out to examine the spatial distribution trends and influencing factors of H. cunea. This analysis involved integrating administrative division and boundary data, distribution data of H. cunea, and environmental variables for 2021. GeoDetector and gravity analysis techniques were employed for data processing and interpretation. The results show that H. cunea exhibited high aggregation patterns in 2021 and 2022 concentrated mainly in eastern China. During these years, the focal point of the infestation was in Shandong Province with a spread towards the northeast. Conditions such as high vegetation density in eastern China provided favorable situations for growth and development of H. cunea. In China, the spatial distribution of the moth is primarily influenced by two critical factors: precipitation during the driest month and elevation. These play a pivotal role in determining the spread of the species. Based on these results, suggestions are provided for a multifaceted approach to prevention and control of H. cunea infestation.