Search Results (340)

Against the background of global warming, forests across environmental gradients show distinct responses to climate change, necessitating research on tree growth patterns under specific conditions. Climate and competition are critical factors affecting tree growth, yet their combined effects across altitudinal gradients remain unclear, especially in arid regions such as Central Asia. This study investigated how climate and competition influence radial growth of Picea schrenkiana Fisch. et C.A.Mey. across altitudinal gradients (1500–2670 m) in the Middle Tianshan Mountains. Using dendroclimatology, competition indices, multivariate statistical analyses, and nonlinear models across 12 plots, we examined spatial variability in growth responses. Results revealed significant altitudinal differences in growth responses to climate and competition across altitudes. At low elevations, growth is primarily limited by water availability; drought indices and spring precipitation exert positive effects, while high temperatures inhibit growth. At mid-elevations, climate becomes the dominant driver, particularly spring temperature and precipitation playing key roles, while competition has no significant effect. At high elevations, temperature becomes the primary driver of growth; however, the overall sensitivity to climate is reduced compared to lower elevations. Multiple regression analyses confirm that water-related factors drive growth at lower and middle elevations, whereas temperature is the primary driver at higher elevations. Further model comparison indicates that while nonlinear models performed slightly better at mid-elevations, linear approaches similarly provided interpretable climate–growth relationships. This study demonstrates significant spatial variation in growth determinants, with water-driven controls dominating at lower elevations and competition effects ranging from significant to non-significant as altitude increases. Future warming may further intensify drought stress at lower elevations, and whether or not the weak positive responses currently observed at higher elevations will persist remains uncertain. These findings provide a scientific basis for sustainable management of arid mountain forests under climate change. Full article

The AT-hook motif nuclear localized (AHL) gene family encodes transcription factors pivotal in regulating plant growth, development, and responses to abiotic stimuli, including low temperature, salinity, darkness, and drought. In this study, we systematically identified 21 BpAHL genes in birch and characterized their sequence features, evolutionary relationships, and expression dynamics. Phylogenetic analysis classified BpAHLs into two clades (Clade-A and Clade-B) and three types (Type-I, -II, and -III), based on PPC domain and AT-hook motifs. Chromosomal mapping revealed an even distribution across nine chromosomes and one contig, with dispersed duplication events recognized as the major driver of BpAHL family expansion. Tissue-specific expression profiling uncovered striking divergence: Type-I BpAHLs displayed root-predominant expression, whereas Type-II/III BpAHLs were highly expressed in plant flowers and leaves. Notably, Type-II/III BpAHL genes in leaves showed distinct expression patterns in response to cold and heat stresses, while Type-I BpAHLs in roots were down-regulated under salt stress. This study provides a comprehensive phylogenomic and functional analysis of the AHLs in birch, providing insights into their roles in enhancing abiotic stress resilience in forest trees. Full article

Oak forests are an important part of temperate European ecosystems, where they are actively improving biodiversity, carbon storage, and ecological stability. However, current concerns such as climatic changes, and especially rising temperatures and changing precipitation patterns, are impacting their resilience. In this context, our study intends to evaluate the impact of climatic variability on temperate oak forests, focusing on the influence of temperature and precipitation. This covers different sites that have different environmental conditions. By using both a bibliometric approach and a systematic analysis of publications that have studied the influence of climate change on oak forests, our study has identified specific species and site responses to climate stressors. Furthermore, we have also evaluated trends in drought sensitivity. All these aspects have allowed us to understand and suggest improvements for the impact of climate change on the resilience and productivity of oak ecosystems. We have analyzed a total number of 346 publications that target the impact of climate change on oak forests. The articles were published between 1976 and 2024, with the majority originating from the USA, Spain, Germany, and France. These studies were published in leading journals from Forestry, Environmental Sciences, and Plant Sciences, among which the most cited journals were Forest Ecology and Management, the Journal of Biogeography, and Global Change Biology. As for the keywords, the most frequent ones were climate change, drought, growth, forest, and oak. However, we have observed a trend towards drought sensitivity, which indicates the intensification of climate changes on oak ecosystems. Moreover, this trend was more present in central and southern regions, which further highlights the impact of regional conditions. As such, certain local factors (soil properties, microclimate) were also taken into account in our study. Our literature review focused on the following aspects: Oak species affected by climate change; Impact of drought on oak forests; Influence of climate change on mixed forests containing oaks; Effects of climate change on other components of oak ecosystems; Radial growth of oaks in response to climate change; Decline of oak forests due to climate change. Our results indicate that oak forests decline in a process caused by multiple factors, with climate change being both a stressor and a catalyst. Across the globe, increasing temperatures and declining precipitation affect these ecosystems in their growth, functions, and resistance to pathogens. This can only lead to an increased forest decline. As such, our results indicate the need to implement forest management plans that take into account local conditions, species, and climate sensitivity. This approach is crucial in improving the adaptivity of oak forests and mitigating the impact of future climate extremes. Full article

Despite extensive research on how climate and environmental factors influence leaf stoichiometry at national and global scales, experimental evidence on their effects at the community level remains limited, particularly in extremely arid regions. Herein, we investigated the leaf stoichiometry including carbon (C), nitrogen (N), and phosphorus (P) along a fine-scale riparian gradient (50–1250 m from the riverbank) in an extremely arid Populus euphratica forest in northwest China. Our results show that the community-averaged leaf total carbon (TC), total nitrogen (TN), and total phosphorus (TP) contents were 442.58 mg/g, 21.69 mg/g, and 1.18 mg/g, respectively. The community-averaged C:N, C:P, and N:P ratios were 20.74, 379.97, and 18.43, respectively. Compared to findings from other studies, the P. euphratica community exhibited lower leaf TC and TP contents but higher TN content and N:P ratios. A high N:P ratio (mean = 18.43, N:P > 16) suggests that the P. euphratica community is more susceptible to phosphorus limitation. Along the riparian gradient, community-averaged leaf TC, C:N, and C:P increased significantly, reaching their maximum (479.49 mg/g, 27.12, and 478.06, respectively) at 1250 m from the riverbank. Conversely, leaf TN and TP contents, as well as N:P, decreased significantly with increasing distance from the river, reaching their minimum values (17.49 mg/g, 0.99 mg/g, and 17.17, respectively) at 1100–1250 m. Soil available phosphorus, soil water content, soil bulk density, and soil electrical conductivity significantly influenced the leaf stoichiometry of the P. euphratica community, collectively explaining 61.78% of the total variation. Among these factors, soil water content had the most pronounced effect, surpassing soil available phosphorus, bulk density, and electrical conductivity in shaping leaf stoichiometric characteristics. Our findings indicate that at fine spatial scales, the distribution of leaf nutrients and stoichiometry seem to be predominantly influenced by local-scale factors such as soil water content, soil nutrient levels, and salt stress; P. euphratica forests would be experiencing more negative impacts in leaf nutrients and stoichiometry due to increased droughts or salt stress. Full article

Cunninghamia lanceolata, contributing 25% to China’s commercial timber production, faces severe drought threats. However, provenance-specific photosynthetic adaptations remain poorly understood. Here, we compared gas exchange, prompt/delayed fluorescence (PF/DF), and modulated 820-nm reflection (MR) responses of two provenances (JXJJ and FJSM) under different drought treatment times. JXJJ maintained a higher net photosynthetic rate (Pn) and stomatal conductance (Gs) than FJSM under drought stress. The declining rates of F_V/F_M, φE_O, Ψ_O, δR_O, PI_ABS, TR_O/CS_M, and ET_O/CS_M were much more rapid in the FJSM than in the JXJJ. An MR kinetics analysis revealed significantly greater PSI impairment in FJSM, evidenced by a 60.2% reduction in P700⁺ re-reduction rate (V_red) compared to only 44.4% in JXJJ (p < 0.05) at 20 d drought treatment. Similarly, DF measurements demonstrated more pronounced PSII energy transfer disruption in FJSM, with the I₂/I₁ ratio increasing by 51.3% vs. 43.0% in JXJJ at 20 d drought treatment. These results demonstrate JXJJ’s superior drought resilience through coordinated stomatal and non-stomatal regulation. Our findings provide actionable criteria for selecting drought-tolerant C. lanceolata provenances, which is essential for sustainable forestry as the climate changes. This study underscores the significance of photosynthetic activity in how C. lanceolata responds to drought and gives insights into boosting drought tolerance in forest species through genetic improvements. Full article

The increasing frequency, intensity, and duration of heatwaves and droughts pose significant societal and environmental challenges across Europe. This study analyzes land surface temperature (LST) observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) between 2003 and 2023 to identify thermal anomalies associated with heatwaves. Additionally, this study examines the role of different land cover types in modulating heatwave impacts, employing turbulent flux observations from micrometeorological towers. The interaction between heatwaves and droughts is further explored using the Standardized Precipitation Evapotranspiration Index (SPEI) and soil moisture data, highlighting the amplifying role of water stress through land–atmosphere feedbacks. The results reveal a statistically significant upward trend in LST-derived thermal anomalies, with the 2022 heatwave identified as the most extreme event, when approximately 75% of Europe experienced strong positive anomalies. On average, 91% of heatwave episodes identified in reanalysis-based air temperature records coincided with LST-defined anomaly events, confirming LST as a robust proxy for heatwave detection. Flux tower observations show that, during heatwaves, evergreen coniferous and mixed forests predominantly enhance sensible heat fluxes (mean anomalies during midday of 74 W/m² and 62 W/m², respectively), while grasslands exhibit increased latent heat flux (89 W/m²). Notably, under extreme compound heat–drought conditions, this pattern reverses for grassed sites due to rapid soil moisture depletion. Overall, the findings underscore the combined influence of surface temperature and drought in driving extreme heat events and introduce a novel, multi-source approach that integrates satellite, reanalysis, and ground-based data to assess heatwave dynamics across scales. Full article

Seasonal droughts induced by climate change pose a significant threat to the normal growth patterns of forests in the subtropical regions of southern China. Therefore, it is crucial to explore the response of tree water use patterns to seasonal drought to maintain tree physiological activities. However, it remains unknown whether changes in dry and wet seasons have an impact on the water use patterns of trees of different ages. In this study, a two-year experiment was conducted in Eucalyptus urophylla × Eucalyptus grandis (hereinafter referred to as Eucalyptus) plantations at three ages (4, 7, and 17 years). Specifically, the water use patterns of Eucalyptus in dry and wet seasons were calculated using hydrogen stable isotopes (including the isotopes in xylem water and 0–150 cm soil layers) coupled with MixSIAR. The results showed that there were notable variations in the proportions of water absorption from different soil layers by Eucalyptus during dry and wet seasons. During the dry season (April 2024), 4-year-old and 7-year-old Eucalyptus primarily utilized water from the 40–90 cm soil layer, while 17-year-old Eucalyptus mainly relied on deep soil water at depths of 60–150 cm, with a utilization ratio of 50.9%. During the wet season (August 2023), the depth of water uptake by Eucalyptus of different ages significantly shifted towards shallow layers, and the trees primarily utilized surface soil water from the 0–60 cm layer, with utilization ratios of 59.9%, 64.8%, and 61.6% for 4-year-old, 7-year-old, and 17-year-old Eucalyptus, respectively. The water sources of Eucalyptus during dry and wet seasons were variable, which allowed Eucalyptus to cope with seasonal drought stress. The differences in the water uptake strategies of Eucalyptus between dry and wet seasons can be attributed to their long-term adaptation to the environment. Our research revealed the differences in the water utilization of Eucalyptus with various ages between dry and wet seasons in subtropical China, providing new insights for a better understanding of the adaptive mechanisms of subtropical forests in response to alterations in water conditions caused by climate change. Full article

Drought stress substantially impacts the development and viability of Populus spp., which are essential for forestry and bioenergy production. This review summarizes and describes the functions of phytohormones, such as abscisic acid, auxins, and ethylene, in modulating physiological and molecular responses to water scarcity. Drought-induced ABA-mediated stomatal closure and root extension are essential adaptation processes. Furthermore, auxin–ABA (abscisic acid) interactions augment root flexibility, whereas ethylene regulates antioxidant defenses to alleviate oxidative stress. The advantageous function of endophytic bacteria, specifically plant growth-promoting rhizobacteria (PGPR), can augment drought resistance in spruce trees by enhancing nutrient absorption and stimulating root development. Structural adaptations encompass modifications in root architecture, including enhanced root length and density, which augment water uptake efficiency. Similarly, Arbuscular Mycorrhizal Fungi (AMF) significantly enhance stress resilience in forest trees. AMF establishes symbiotic relationships with plant roots, improving water and nutrient uptake, particularly phosphorus, during drought conditions. Furthermore, morphological alterations at the root–soil interface enhance interaction with soil moisture reserves. This review examines the complex mechanisms by which these hormones influence plant responses to water shortage, aiming to offer insights into prospective techniques for improving drought tolerance in common tree species and highlights the importance of hormone control in influencing the adaptive responses of prominent trees to drought stress, providing significant implications for research and practical applications in sustainable forestry and agriculture. These findings lay the groundwork for improving drought tolerance in Populus spp. by biotechnological means and by illuminating the complex hormonal networks that confer drought resistance. Full article

Drought threatens the stability of artificial black locust forests on the Loess Plateau, yet there is limited research on the physiological and metabolic responses of mature black locust to drought stress. This study employed a throughfall exclusion system—i.e., moderate drought (40% throughfall reduction), extreme drought (80% throughfall reduction), and 0% throughfall reduction for control—to analyze leaf microstructure, relative water content (RWC), osmotic adjustment substances, hormone levels, and flavonoid metabolites in black locust under controlled drought stress. The results demonstrated that as drought stress intensified, stomatal aperture and density decreased, while trichome density and length exhibited significant increases. MDA, proline, IAA, and osmotic adjustment substances (soluble protein, reducing sugar, and total sugar) first increased and then decreased as drought stress intensified. A total of 245 flavonoid compounds were identified through metabolomic analysis, among which 91 exhibited differential expression under drought treatments. Notably, 37 flavonoids, including flavonols and glycosylated derivatives, were consistently upregulated. These findings suggest that drought stress can lead to the accumulation of flavonoids. This study explored the physiological and metabolic responses of mature black locust trees to drought stress, offering insights for selecting drought-resistant species in vegetation restoration and informing ecological management practices in arid regions. Full article

The leaf economic spectrum framework explains how plants optimize leaf traits for productivity, distribution, and stress tolerance. Orchids in Southwestern China’s karst forests, especially lithophytic species, are challenged by prolonged drought and limited light availability. This study investigated different leaf strategies between lithophytic and terrestrial orchids under the harsh karst environment. We measured key leaf traits, including photosynthesis, structure, biomechanics, nitrogen allocation, and water relations, in twenty-two lithophytic and six terrestrial orchids in a subtropical karst forest. After accounting for phylogenetic influences, we found that lithophytic orchids had a higher leaf mass per area, cuticle thickness, and biomechanical resistance (F_p) but a lower maximum photosynthetic rate (A_max-mass), nitrogen allocation to photosynthesis (N_T), and saturated water content (SWC) than terrestrial orchids. These results suggest that lithophytic orchids prioritize structural investment and stress tolerance over photosynthetic efficiency. Across species, N_T correlated positively with A_max-mass and negatively with F_p, highlighting nitrogen allocation as a key mechanism in leaf cost–benefit strategies. Additionally, SWC emerged as a critical driver of variation in multiple traits, supporting its integration into the leaf economic spectrum for orchids in karst ecosystems. This study offers new insights into orchid adaptation in subtropical karst environments, with implications for plant resilience under changing climates. Full article

During drought, a major abiotic stressor for European forests, excessive reactive oxygen species (ROS) are produced, causing oxidative damage that affects structural and metabolic tree functions. This research examines the effects of drought, phosphorus (P) fertilization, and provenance on photosynthetic pigments, malondialdehyde (MDA) concentrations, and antioxidant enzyme activities in common beech (Fagus sylvatica L.) and sessile oak (Quercus petraea (Matt.) Liebl.) saplings from two provenances. In a common garden experiment, four treatments were applied: regular watering with (+PW) and without P fertilization (−PW), and drought with (+PD) and without (−PD) P fertilization. Results showed that drought increased both MDA concentrations and antioxidant enzyme activity, particularly superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX), which are responsible for ROS scavenging. Additionally, chlorophyll a + b concentrations were lower in drought-exposed plants. Phosphorus fertilization minimally affected MDA levels but enhanced antioxidant responses, particularly APX and CAT activities in oak during drought. Provenance differences were notable, with oak and beech from the drier provenance showing better adaptation, reflected in lower MDA levels and higher enzyme activities. This study underscores the importance of antioxidant defenses in coping with drought stress, with phosphorus fertilization and provenance shaping the species’ adaptive capacity. Full article

The introduction of novel plant species to new habitats may have consequences for native herbivores. We examined the impact of Alliaria petiolata, a Eurasian invader of forest understories and edges in North America, on adult oviposition behavior and on larval preference and the performance of Anthocharis midea, a univoltine butterfly that specializes on plants in the Brassicaceae. We compared the usage of A. petiolata by this butterfly to that of one of its common native hosts, Cardamine concatenata, and additionally explored the impact of drought and larval age on the larval success of these hosts. In the field, adults oviposited on the native host preferentially earlier in the season, but they strongly preferred A. petiolata later in the season and laid more eggs overall and in multiples more often on this plant. Larvae strongly preferred to feed on leaves of C. concatenata over A. petiolata in the laboratory and survived to pupation at a high rate on it. Conversely, larvae fed little and died when offered A. petiolata. Larvae preferentially chose tissues of droughted C. concatenata over well-watered plants, but drought stress had no impact on larval mass and survival to pupation. Larvae showed no preference for droughted or non-droughted A. petiolata and while drought stress tended to extend survival on this plant, all larvae still died on it. Older larvae were no better at feeding and surviving on A. petiolata than young larvae. Our results indicate that A. petiolata currently serves as an ecological trap for A. midea, being both highly attractive to ovipositing adults yet lethal to larvae. This effect could cause both local declines in the abundance of this butterfly and drive selection for the altered behavior of adults and larvae to either avoid or better tolerate this plant. Full article

Establishing an optimum range of inter-species spacing that reduces competition among trees and mitigates the effects of drought is a critical yet complex challenge in forest management. Stand density plays a crucial role in forest functioning by regulating resource allocation within individual trees. Higher stand densities have been shown to reduce sap velocities, indicating intensified competition for water and other resources. However, determining the precise spacing that minimizes competition while maintaining ecosystem balance remains unclear. In this study, conducted in temperate Norway spruce forests at an altitude range of 400–500 m in the Czech Republic, we propose a novel technique to define tree spacing that reduces competitive interactions. We used xylem sap flow residuals of an ordinary least square (OLS) regression model to filter out the effects of elevation and diameter at breast height (DBH) on field-measured sap flow for 101 planted Norway spruce trees with a DBH range of 40 ± 5 cm (≈90–100 years old). The model residuals allowed us to account for the most important driver of sap flow variability: tree density and its underlying effects on individual tree traits. To minimize the confounding effects of temporal and spatial variability, we used twelve consecutive daily measurements of sap flow (6 a.m. to 6 p.m.) taken at the start of the growing season. By constructing an experimental variogram, we quantified sap flow variability as a function of tree spacing. The results showed a steady sap flow pattern at tree densities of 12, 11, and 10 trees per 314 m² (equivalent to 350 ± 32 trees per hectare), corresponding to inter-tree spacing measurements of 5.12 m, 5.34 m, and 5.60 m, respectively. These findings suggest that when the N number of trees (median) per unit area (A) is in equilibrium with resource availability, increasing or decreasing the n number of trees may not significantly change competition levels (A; f(A) = N ± n). The size or deviation of n depends on the area to define the minimum and maximum thresholds or tolerance capacity for the number of trees allowed to be in the area. This technique—using a variogram of sap flow residuals to determine tree spacing—can be periodically applied, such as every 10–15 years, and adapted for different elevation gradients (e.g., within 100 m intervals). It offers a practical tool for forest managers and policymakers, guiding thinning and planting strategies to enhance forest resilience in the face of water-stress conditions. Full article

Droughts present a significant global challenge, particularly to forest ecosystems in regions such as eastern New South Wales, Australia, which is known for its dry climate and frequent, intense droughts. Recent studies have indicated a notable increase in tree mortality and canopy browning across this area, especially during the recent extreme drought period culminating in the Black Summer of 2019–2020. Our study investigates the impacts of drought on eucalypt forests by leveraging remote sensing and field observation data to detect and analyse vegetation health and stress indicators. Utilising data from Sentinel-2, alongside historical Landsat observations, we applied multiple spectral vegetation indices, namely the Normalized Difference Vegetation Index (NDVI), Normalized Difference Moisture Index (NDMI), Normalized Burn Ratio (NBR), and Tasseled Cap Transformation, to assess the extent of drought impacts. We found NBR to show the most consistent agreement with ground-based observations of drought-related tree mortality. Additionally, by integrating ground-based data from the “Dead Tree Detective” citizen science project, we were able to validate the remote sensing outcomes with a 90.22% consistency, providing confirmation of the extensive spatial distribution and severity of the inferred impacts. Our findings reveal that 13.16% of eucalypt forests and woodlands across eastern New South Wales experienced severe stress associated with drought during the 2019–2020 Black Summer drought. This study demonstrates the utility of satellite-derived drought indicators in monitoring forest health and highlights the necessity for continuous monitoring and research to understand the factors that trigger tree vitality loss. Full article

Chlorophyll fluorescence is a useful indicator of a plant’s physiological status, particularly under stress conditions. Remote sensing is an increasingly adopted technology in modern agriculture, allowing the acquisition of crop information (e.g., chlorophyll fluorescence) without direct contact, reducing fieldwork. The objective of this study is to improve the monitoring of olive tree fluorescence (Fv′/Fm′) via remote sensing in a Mediterranean environment, where the frequency of stress factors, such as drought, is increasing. An advanced approach combining explainable artificial intelligence and multispectral Sentinel-2 satellite data was developed to predict olive tree fluorescence. Field measurements were conducted in southeastern Italy on two olive groves: one irrigated and the other one under rainfed conditions. Sentinel-2 reflectance bands and vegetation indices were used as predictors and different machine learning algorithms were tested and compared. Random Forest showed the highest predictive accuracy, particularly when Sentinel-2 reflectance bands were used as predictors. Using spectral bands preserves more information per observation, enabling models to detect variations that VIs might miss. Additionally, raw reflectance data minimizes potential bias that could arise from selecting specific indices. SHapley Additive exPlanations (SHAP) analysis was performed to explain the model. Random Forest showed the highest predictive accuracy, particularly when using Sentinel-2 reflectance bands as predictors. Key spectral regions associated with Fv′/Fm′, such as red-edge and NIR, were identified. The results highlight the potential of integrating remote sensing and machine learning to improve olive grove management, providing a useful tool for early stress detection and targeted interventions. Full article