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Forest protection and afforestation have been identified as a means to partially offset anthropogenic CO2 emissions. Yet, increasingly frequent observations of drought-induced tree mortality are reported. Here, we applied a risk analysis framework for global drought-induced forest mortality by examining extreme reductions in greenness and water content of forest canopies during past mortality events as well as growth recovery of surviving individual trees following stand-scale mortality events. We defined a drought-induced mortality risk index (DMR) that explains 80% of documented tree mortality. Rising CO2 alleviated the increase of DMR with short-term drought, however, the observed DMR increases with long-term drought no matter whether considering plant responses to CO2. DMR in sites where tree mortality has been observed significantly increased since the 1980s. More than that, drought exposure threatened 0.28 billion hectares of forested areas. Our framework highlights how climate change-induced drought, especially hotter-droughts, threatens the sustainability of global forests.

A warmer climate will increase aridity and threaten forest persistence in xeric areas. This is the case of some Atlas cedar (Cedrus atlantica) forests showing recent growth decline, dieback and high mortality rates in North Africa. A lower resistance to drought, manifested as stronger growth loss, could increase the drought-related mortality risk in these forests as has been found for gymnosperms worldwide. It could be also expected that changes in dryness are linked to large-scale atmospheric circulation patterns such as the North Atlantic Oscillation (NAO). We tested these hypotheses by analyzing growth resilience indices (resilience, recovery, resistance) derived from tree-ring data. We sampled nine Atlas cedar plots located in north-western Algeria, where climate shifted towards drier conditions in the 1980s. In these forests, drier winters, associated to positive NAO phases, constrained tree growth and resistance, two outputs of the drought impact. During dry years, the resilience index decreased as elevation increased. The association between cedar growth resistance and drought severity is strengthening: the drier the climate conditions, the lower the growth resistance. Resistance also showed a significant higher temporal variability in 8 out of 9 plots as drought intensified. These findings have allowed identifying the increase in the temporal variability of growth resistance as a new early-warning signal of drought stress.

Carbon accounting in the land sector requires a reference level from which to calculate past losses of carbon and potential for gains using a stock-based target. Carbon carrying capacity represented by the carbon stock in primary forests is an ecologically-based reference level that allows estimation of the mitigation potential derived from protecting and restoring forests to increase their carbon stocks. Here we measured and collated tree inventory data at primary forest sites including from research studies, literature and forest inventories (7982 sites, 288,262 trees, 27 countries) across boreal, temperate, and subtropical Global Ecological Zones within Europe. We calculated total biomass carbon stock per hectare (above- and below-ground, dead biomass) and found it was 1.6 times larger on average than modelled global maps for primary forests and 2.3 times for all forests. Large trees (diameter greater than 60 cm) accounted for 50% of biomass and are important carbon reservoirs. Carbon stock foregone by harvesting of 12–52% demonstrated the mitigation potential. Estimated carbon gain by protecting, restoring and ongoing growth of existing forests equated to 309 megatons carbon dioxide equivalents per year, additional to, and higher than, the current forest sink, and comparable to the Green Deal 2030 target for carbon dioxide removals.

Forests in tectonically active regions are disturbed by earthquakes. Besides direct injuries to trees, earthquakes also induce stand-wide changes in hydrological conditions, whose effects on long-term forest growth and resilience remain unknown. Here we establish spatio-temporal links between global tree-ring width series and earthquakes after 1900, disentangle seismic signals from climate-induced variations in ring width series, test growth changes using superposed epoch analysis and quantify post-earthquake resilience shifts along environmental gradients in seven regions around the world. We found sites with enhanced resilience locate in relatively dry areas of temperate regions, where the response of tree growth to growing-season precipitation also increased after earthquakes. Our results provide evidence that earthquake-induced soil cracks and fractures increased precipitation infiltration to deeper soil layers and enhanced the use of water and nutrients by trees. In contrast, reduced post-earthquake resilience in regions with abundant precipitation can be explained by increased soil erosion and nutrient leaching. We conclude that seismic disturbances cause decadal-scale shifts in forest resilience under specific environmental conditions, disentangling complex interactions between lithosphere, biosphere and atmosphere. These findings can contribute to a better understanding of how the Earth system functions.

The weakening Indian monsoon during recent warmer decades has caused greening and browning trends in water- and energy-limited terrestrial ecosystems of the Tibetan Plateau, respectively. Little is known, however, on the underlying mechanisms of such divergent responses of vegetation to the monsoon weakening. Herein, using the Indian monsoon index, high-resolution vegetation indices and multi-source climate data, we assessed the response of vegetation greenness to the Indian monsoon from 2000 to 2018 in two adjacent basins dominated by water- and energy-limited ecosystems and located in the southeastern Tibetan Plateau. The two basins showed opposite greenness trends due to direct and indirect effects of the weakening monsoon. The weakening monsoon increased vegetation greenness in the humid sites due to more heat exposure and solar radiation, but not in dry sites because of amplified drought stress. Thus, a weaker monsoon would not favor productivity in drought-prone ecosystems, whereas it would benefit energy-limited sites due to more radiation and warmer conditions associated to lower cloudiness. The effect of atmospheric circulation and its inter-decadal oscillation on basin-scale ecological processes should be therefore taken into account to refine earth system models and climate forecasts.

Ongoing encroachment is driving recent alpine shrubline dynamics globally, but the role of shrub-shrub interactions in shaping shrublines and their relationships with stem density changes remain poorly understood. Here, the size and age of shrubs from 26 Salix shrubline populations along a 900-km latitudinal gradient (30°–38° N) were measured and mapped across the eastern Tibetan Plateau. Point pattern analyses were used to quantify the spatial distribution patterns of juveniles and adults, and to assess spatial associations between them. Mean intensity of univariate and bivariate spatial patterns was related to biotic and abiotic variables. Bivariate mark correlation functions with a quantitative mark (shrub height, basal stem diameter, crown width) were also employed to investigate the spatial relationships between shrub traits of juveniles and adults. Structural equation models were used to explore the relationships among conspecific interactions, patterns, shrub traits and recruitment dynamics under climate change. Most shrublines showed clustered patterns, suggesting the existence of conspecific facilitation. Clustered patterns of juveniles and conspecific interactions (potentially facilitation) tended to intensify with increasing soil moisture stress. Summer warming before 2010 triggered positive effects on population interactions and spatial patterns via increased shrub recruitment. However, summer warming after 2010 triggered negative effects on interactions through reduced shrub recruitment. Therefore, shrub recruitment shifts under rapid climate change could impact spatial patterns, alter conspecific interactions and modify the direction and degree of shrublines responses to climate. These changes would have profound implications for the stability of alpine woody ecosystems.

We lack understanding of how variable is radial growth of coexisting tree and shrub species, and how growth is constrained by drought depending on site aridity. Here, we compared the radial growth of two widespread and coexisting species, a winter deciduous shrub (Amelanchier ovalis Medik.) and an evergreen conifer tree (Pinus sylvestris L.). We sampled four sites in Northeastern Spain subjected to different aridity levels and used dendrochronological methods to quantify growth patterns and responses to climate variables. The growth of the two species varied between regions, being lower in the driest sites. The first-order autocorrelation (growth persistence) was higher in more mesic sites but without clear differences between species. Tree and shrub growth negatively responded to elevated summer temperatures and positively to spring-summer precipitation and wet conditions. However, negative growth responses of the shrub to drought were only observed in the two driest sites in contrast to widespread responses of the tree. Abrupt growth reductions were common in the drier sites, but resilience indices show that the two species rapidly recovered pre-drought growth levels. The lower growth synchrony of the shrub as compared to the tree can be due to the multistemmed architecture, fast growth and low stature of the shrub. Besides, the high dependency of the shrub growth on summer rainfall can explain why drought limitations were only apparent in the two driest sites. In any case, results point out to the dendrochronological potential of shrubs, which is particularly relevant giving its ability to inhabit woodlands and treeless regions under harsh climatic conditions. Nevertheless, further research is required to elucidate the capacity of shrub species to tolerate drought, as well as to understand how shrubs thrive in water- and cold-limited environments.

The olive tree is an iconic component of Mediterranean agricultural landscapes. Many monumental olive trees are regarded as millennial individuals, but their ages cannot be estimated through tree ring dating. Alternatively, 14C-dating of pith wood sample provides age estimates for these old trees. However, published age estimates indicate that most ages of old olive trees range between 200 and 700 years. Nevertheless, some rare individuals may be millennial or even older. Here we report the oldest dated olive tree, sampled in the so-called Noah olive grove in Bshaaleh (northern Lebanon), and having an age of 1161 ± 131 years according to 14C dating. By measuring tree diameter, ring counting, and 14C wood dating in old olive trees in Mediterranean countries an equation was obtained to estimate the 14C-estimated age of old olive trees: age = 37.56 + 1.835 diameter. We conclude that most monumental olive trees are centennial but not millennial, with very old trees probably restricted to harsh sites where trees show slow growth rates.

Cork is one of the main non-timber forest products in the world. Most of its production is concentrated in the Iberian Peninsula, a climate change hotspot. Climate warming may lead to increased aridification and reduce cork production in that region. However, we still lack assessments of climate-cork relationships across ample geographical and climatic gradients explicitly considering site aridity. We quantified cork growth by measuring cork ring width and related it to climate variables and a drought index using dendrochronology. Four cork oak (Quercus suber) forests located from north eastern Spain to south western Morocco (31.5–41.5° N) and subjected to different aridity levels were sampled. Warm conditions in spring to early summer, when cork is formed, reduced cork width, whereas high precipitation in winter and spring enhanced it. The response of cork to increased water availability in summer peaked (r = 0.89, p = 0.00002) in the most arid and continental site considering 14-month long droughts. A severe drought caused a disproportionate loss of cork production in this site, where for every five-fold decrease in the drought index, the cork-width index declined by a factor of thirteen. Therefore, site aridity determines the responses of cork growth to the soil water availability resulting from accumulated precipitation during winter and spring previous to cork growth and until summer. In general, this cumulative water balance, which is very dependent on temperature and evapotranspiration rate, is critical for cork production, especially in continental, dry sites. The precipitation during the hydrological year can be used as a proxy of cork production in similar sites. Assessments of climate-cork relationships in the western Mediterranean basin could be used as analogues to forecast the impacts of aridification on future cork production.

Contextualising anthropogenic warming and investigating linkages between past climate variability and human history require high-resolution temperature reconstructions that extend before the period of instrumental measurements. Here, we present maximum latewood density (MXD) measurements of 534 living and relict Pinus uncinata trees from undisturbed upper treeline ecotones in the Spanish central Pyrenees. Spanning the period 1119–2020 CE continuously, our new MXD composite chronology correlates significantly with gridded May–September mean temperatures over the western Mediterranean region (r = 0.76; p ≤ 0.001; 1950–2020 CE). Based on an integrative ensemble approach, our reconstruction reveals unprecedented summer warming since 2003 CE. The coldest and warmest reconstructed temperature anomalies are −3.4 (±1.4) °C in 1258 and 2.6 (±2.2) °C in 2017 (relative to 1961–90). Abrupt summer cooling of −1.5 (±1.0) °C was found after 20 large volcanic eruptions since medieval times. Comparison of our summer temperature reconstruction with newly compiled historical evidence from the Iberian Peninsula suggests a lack of military conflict during or following exceptionally hot or cold summers, as well as a general tendency towards less warfare and more stable wheat prices during warmer periods. Our study demonstrates the importance of updating and refining annually resolved and absolutely dated climate reconstructions to place recent trends and extremes of anthropogenic warming in a long-term context of natural temperature variability, and to better understand how past climate and environmental changes affected ecological and societal systems.

Spatial and temporal variation in functional traits allows trees to adjust to shifting environmental conditions such as water stress. However, the change of traits, both mean and variances, along water availability gradients and across growing seasons, as well as their covariation with tree performance, have been rarely assessed. We examined intraspecific trait variation in coexisting evergreen (Quercus ilex ssp. ilex and Q. ilex ssp. ballota) and deciduous (Quercus faginea and Quercus humilis) Mediterranean oaks along a wide water availability gradient in northeastern Spain during six years. We measured leaf area (LA), shoot twig mass (Sm), leaf mass per area (LMA) and the ratio of shoot twig to leaf biomass (Sm:Lm). We characterized tree performance through basal area increment (BAI) and drought resilience indices. Higher variation was found within individuals than between individuals across populations and years. Within species, we found trait adjustments toward more conservative water-use (low LA and Sm and high LMA) with increasing drier conditions. Intraspecific trait variation was constrained by water availability, particularly on the deciduous species. In Q. ilex, trait variance of LMA positively covaried with annual BAI, whereas variance of LA, Sm and Sm:Lm was positively related to resistance and resilience against the severe 2012 drought in deciduous oaks. Our results support a tradeoff between the ability to tolerate drought and the capacity to cope with unpredictable changes in the environment through increased intraspecific trait variation, which may have implications on tree performance in the face of increased extreme events.

Drought stress caused by global climate warming affects tree growth in both dry and wet areas. However, the differences in tree growth responses to drought in dry and wet areas are poorly understood. Here, we collected 93 tree cores to analyze the differences in the radial growth responses of larch (Larix gmelinii) under climate change and tree growth resilience under drought events in the Altai Mountains (dry area) and Changbai Mountains (wet area). The results showed that larch growth in the Altai Mountains was significantly positively correlated with the self-calibrating Palmer Drought Severity Index (sc-PDSI) in all months and precipitation in the previous growth season and May, whereas it was significantly (p < 0.05) negatively correlated with temperature in May and the previous June to August. In the Changbai Mountains, larch growth was significantly positively correlated with May maximum and mean temperature, and significantly positively and negatively correlated with precipitation in April and May，respectively (p < 0.05). The mean resistance (recovery) of larch growth to drought in wet areas were significantly stronger (weaker) than that in dry areas (p < 0.05). Moreover, strengthening the drought frequency led to a significant (p < 0.05) decline in larch resistance in dry areas. Therefore, warming-induced increases in drought stress will aggravate negative impacts on the radial growth of larch forests in temperate dry areas but not in wet areas in the future.

Thinning focused on achieving growth and diameter management objectives has typically led to stands with reduced climate sensitivity compared to unthinned stands. We integrated dendrochronological with Airborne Laser Scanner (LiDAR) data and growth models to assess the long-term impact of thinning intensity on Canary pine (Pinus canariensis) radial growth. In 1988, 18 permanent treatment units were established in 73-year-old Canary pine plantations and three thinning treatments were applied (C–control-unthinned; 0% basal area removal; MT–moderate thinning: 10% and 15% basal area removal, and HT–heavy thinning: 46% and 45% basal area removal on the windward and leeward slopes, respectively). Dendrochronological data were measured in 2022 and expressed as basal area increment (BAI). The impact of climate on growth was examined by fitting linear regression models considering two different Representative Concentration Pathway (RCP) climate scenarios, RCP 2.6 and RCP 4.5. Finally, LiDAR data were used for standing segmentation to evaluate changes in overall growth under different climatic scenarios. The LiDAR–stand attributes differed between aspects. The BAI of the most recent 20 years (BAI20) after thinning was significantly higher for the moderate and heavy treatments on the leeward plots (F = 47.31, p < 0.001). On the windward plots, BAI decreased after moderate thinning. Considerable thinning treatments resulted in stronger changes in growth when compared to RCP climatic scenarios. From a silviculture perspective, the mapping of canopy structure and growth response to thinning under different climatic scenarios provides managers with opportunities to conduct thinning strategies for forest adaptation. Combining dendrochronological and LiDAR data at a landscape scale substantially improves the value of the separate datasets as forecasted growth response maps allow improving thinning management plans.

The benefits of masting (volatile, quasi-synchronous seed production at lagged intervals) include satiation of seed predators, but these benefits come with a cost to mutualist pollen and seed dispersers. If the evolution of masting represents a balance between these benefits and costs, we expect mast avoidance in species that are heavily reliant on mutualist dispersers. These effects play out in the context of variable climate and site fertility among species that vary widely in nutrient demand. Meta-analyses of published data have focused on variation at the population scale, thus omitting periodicity within trees and synchronicity between trees. From raw data on 12 million tree-years worldwide, we quantified three components of masting that have not previously been analysed together: (i) volatility, defined as the frequency-weighted year-to-year variation; (ii) periodicity, representing the lag between high-seed years; and (iii) synchronicity, indicating the tree-to-tree correlation. Results show that mast avoidance (low volatility and low synchronicity) by species dependent on mutualist dispersers explains more variation than any other effect. Nutrient-demanding species have low volatility, and species that are most common on nutrient-rich and warm/wet sites exhibit short periods. The prevalence of masting in cold/dry sites coincides with climatic conditions where dependence on vertebrate dispersers is less common than in the wet tropics. Mutualist dispersers neutralize the benefits of masting for predator satiation, further balancing the effects of climate, site fertility and nutrient demands.

Severe droughts limit tree growth and forest productivity worldwide, a phenomenon which is expected to aggravate over the next decades. However, how drought intensity and climatic conditions before and after drought events modulate tree growth resilience remains unclear, especially when considering the range-wide phenotypic variability of a tree species. We gathered 4632 Aleppo pine (Pinus halepensis Mill.) tree-ring width series from 281 sites located in 11 countries across the Mediterranean basin, representing the entire geographic and bioclimatic range of the species. For each site and year of the period 1950–2020, we quantified tree-growth resilience and its two components, resistance and recovery, to account for the impact of drought and the capacity to recover from it. Relative drought intensity of each year was assessed using SPEI (Standardized Precipitation Evapotranspiration Index), a climatic water deficit index. Generalized additive mixed models were used to explore the non-linear relationships between resilience and its two components and drought intensity, preceding and following years climatic conditions. We found that P. halepensis radial growth was highly dependent on the SPEI from September of the previous year to June of the current year. Trees growing under more arid bioclimates showed higher inter-annual growth variability and were more sensitive to drought, resulting in an increased response magnitude to pre-, during and post-drought conditions. In contrast to our expectations, drought intensity only slightly affected resilience, which was rather negatively affected by favorable preceding conditions and improved by favorable following conditions. Resilience and its components are highly dependent on preceding and following years climatic conditions, which should always be taken into account when studying growth response to drought. With the observed and predicted increase in drought frequency, duration and intensity, favorable conditions followi

Understanding the chemical composition of our planet's crust was one of the biggest questions of the 20th century. More than 100 years later, we are still far from understanding the global patterns in the bioavailability and spatial coupling of elements in topsoils worldwide, despite their importance for the productivity and functioning of terrestrial ecosystems. Here, we measured the bioavailability and coupling of thirteen macro- and micronutrients and phytotoxic elements in topsoils (3–8 cm) from a range of terrestrial ecosystems across all continents (∼10,000 observations) and in response to global change manipulations (∼5,000 observations). For this, we incubated between 1 and 4 pairs of anionic and cationic exchange membranes per site for a mean period of 53 days. The most bioavailable elements (Ca, Mg, and K) were also amongst the most abundant in the crust. Patterns of bioavailability were biome-dependent and controlled by soil properties such as pH, organic matter content and texture, plant cover, and climate. However, global change simulations resulted in important alterations in the bioavailability of elements. Elements were highly coupled, and coupling was predictable by the atomic properties of elements, particularly mass, mass to charge ratio, and second ionization energy. Deviations from the predictable coupling-atomic mass relationship were attributed to global change and agriculture. Our work illustrates the tight links between the bioavailability and coupling of topsoil elements and environmental context, human activities, and atomic properties of elements, thus deeply enhancing our integrated understanding of the biogeochemical connections that underlie the productivity and functioning of terrestrial ecosystems in a changing world.

Key message: Abies alba Mill.–Pinus uncinata Ramond. ecotone dynamics are examined along both altitudinal and protection level gradients by combining field inventories and Landsat data. An upward expansion of A. alba to the subalpine belt is observed in the last decades as a result of stand maturation after logging cessation. Context: High-mountain forests constitute sensitive locations to monitor the impacts of global change on tree-species composition and ecotone dynamics. In this study, we focus on the Spanish Pyrenees where silver fir (Abies alba Mill.) coexists with mountain pine (Pinus uncinata Ramond.) forming montane-subalpine ecotones. Aims: The main goal of this study is to assess the spatiotemporal dynamics of the silver fir–mountain pine ecotone and its underlying driving factors. Methods: We reconstructed the spatial distribution and dynamics of the species by combining remote sensing imagery and field plot data from 1989 to 2015, employing support vector machine techniques for image classification. Using variance analysis and mixed effects models, we then analyzed the evolution of basal area and replacement index, a measure of relative change in species composition, over time and altitude range. Additionally, we explored their relationship with site factors and protection level (National Park vs. protection buffer zone). Results: Silver fir has expanded its distribution in both the National Park and the protection buffer zone, whereas mountain pine has remained stable. Both species exhibit increased basal area associated with stand maturation and a higher level of protection. The replacement index indicates a rise in silver fir in the understory on North-facing slopes, attributed to stand densification. These findings are particularly noticeable in the area with the highest level of protection. Conclusion: The cessation of traditional land uses has led to ongoing stand densification, promoting succession and favoring the increased abundance of silver f

Recent drought-induced dieback alters forest dynamics, which are also shaped by past management. In western Pyrenean silver fir (Abies alba) stands, dieback concurs in space and time with the legacies of past management, but the impacts on forest growth, structure and composition are unknown. We aim to disentangle how dieback interacts with the legacies of past human use and modulates the recent dynamics of silver fir forests. To this end, we sampled eleven silver fir forests across wide climatic gradients and included declining and non-declining sites. We measured radial growth, structure, composition, understory cover and type and amount of deadwood. Silver fir growth declines in response to late-summer drought. In declining sites, most defoliated stands showed the lowest silver fir density and were those where growth depended more on water availability. Tree death enhanced the cover of dominant understory plants such as Buxus sempervirens. Past management activities leave an imprint in the growth of silver fir, such as releases due to past logging, but also affect the number of stumps and snags and the current tree density. A more extensive monitoring will be required to fully disentangle the multiple influences of past management legacies and current climate change on forest dynamics.

In seasonally dry forests, wildfires can reduce competition for soil water among trees and improve forest resilience to drought. We tested this idea by comparing tree-ring growth patterns of Pinus pinea stands subjected to two prescribed burning intensities (H, high; L, low) and compared them with unburned (U) control stands in southwestern Spain. Then, we assessed post-growth resilience to two droughts that occurred before (2005) and after (2012) the prescribed burning (2007). Resilience was quantified as changes in radial growth using resilience indices and as changes in cover and greenness using the NDVI. The NDVI sharply dropped after the fire, and minor drops were also observed after the 2005 and 2012 droughts. We found that post-drought growth and resilience were improved in the H stands, where growth also showed the lowest coherence among individual trees and the lowest correlation with water year precipitation. In contrast, trees from the L site showed the highest correlations with precipitation and the drought index. These findings suggest that tree growth recovered better after drought and responded less to water shortage in the H trees. Therefore, high-intensity fires are linked to reduced drought stress in Mediterranean pine forests.

Editorial on the Research Topic: Forests under pressure: The need for interdisciplinary approaches to address forest vulnerability to tree mortality in response to drought

This document provides supporting analysis and figures for the main article., Identifying Korean pine tree species from carbonized trees. In this study, the tree species of carbonized trees was identified by analyzing the microscopic anatomical features of wood on three planes (cross-, radial-, and tangential-section). For the identified Korean pine (Pinus koraiensis Siebold & Zucc.) in this study, the microscopic anatomical features were showed below, Cross-section features. The boundary of growth ring is slightly obvious, and the early wood gradually changes to late wood within the ring. The growth of early wood is uniform, and the early wood accounts for most of the ring width. The axial parenchyma tissue is absent. The resin channels are divided into axial and radial types. The axial channels are mostly single and usually distributed in the late wood or located at 2/3 of the ring width. The lipid cells are thin-walled and often contain quasi-invasion bodies. There are 3~6 lipid cells around the maximum axial resin channel. The transverse section of early wood tracheid is square, rectangular and polygon, and the axial parenchyma tissue is absent., Radial-section features. Radiative tracheids are located in 1~2 columns of the upper and lower edges, and are occasionally seen in the middle of the rays. The xylem low rays are sometimes made up entirely of radial tracheids. The inner wall is smooth and the outer edge is wavy. The cross field pattern between ray parenchyma cells and early wood tracheids was pane-like, or pine type was occasionally seen in late wood, with number of 1~4, 1 (rare 2) in horizontal line. Axial parenchyma cell horizontal wall perforation and end wall nodular thickening are usually absent or few, not obvious, no indentation., Tangential-section features. There are 4-8 wood rays per mm, including two types: single column and spindle-shaped. The single column of rays is 2~13 cells or more in height, most of them are 3~8 cells; the spindle rays have radial resin canals, 2~3 columns of ray cells above and below the approach; The upper and lower ends gradually sharpen into a single column, the height of which is 3-10 cells or more. The ray cells are usually oval in shape. The radial resin tract is much smaller, with 3-5 adipocytes around the tract., Conclusions. According to the microscopic anatomical characteristics of the above three planes, the carbonized logs, No. CBSXA-01, CBSXA-12, CBSXA-21, CBSXA-24, CBSXA-27, CBSXB-01, CBSXB-02, CBSXB-03, CBSXB-05, CBSXB-07, CBSXB-08, CBSXB-10, CBSXB-11, CBSXB-14, CBSXB-15, CBSXB-17, CBSXB-21, and CBSXB-26, were identified as Korean pine (Pinus koraiensis) of the family Pinaceae and the genus Pinus. The anatomical features of the tree planes of the 18 samples were separately showed below in the large Figure S1.

[Purpose of Review] The capacity of woody plants to cope with climate change depends on their adjustments to changing environmental conditions by phenotypic plasticity or by genotypic changes (i.e., local adaptation). To determine whether intraspecific trait variation (ITV) translates into resistance or tolerance to drought and eventually how it relates to performance when facing drought, we reviewed the recent literature on the intraspecific variation in woody plant functional traits along aridity gradients., [Recent Findings] At the intraspecific level, functional traits vary along aridity gradients, but this variation depends on the considered trait and species. While ITV is ubiquitous and of relevant magnitude, its relationship with tree performance in the case of growth or survival is unclear and very idiosyncratic., [Summary] ITV varies along aridity gradients and, for several traits, is of comparable magnitude as interspecific trait variation. However, the relationship between ITV and tree performance is not consistent among species. This makes the use of ITV challenging when quantifying its contribution to drought tolerance.

Riparian alder forests are threatened by Phytophthora across Europe. Comparative studies of the pathogenicity of Phytophthora species are crucial for developing effective management strategies. Although only a limited number of species, particularly P. × alni, lead to tree decline in natural environments, many species demonstrate pathogenicity in inoculation trials. Phytophthora species vary in their ability to infect different tissues, such as phloem and xylem, and trigger defence responses in the host through the formation of tyloses and callose. By comparing the histological responses of alder to various Phytophthora species, we can gain insights into the success of P. × alni and the potential damage that could be caused by other species. To investigate the defence strategies of black alder (Alnus glutinosa) against attack by Phytophthora and Halophytophthora species present in Catalonia (NE Spain), we conducted inoculation trials on saplings using nine potentially pathogenic species and compared the histological responses. Phytophthora × alni and P. plurivora were the most aggressive species followed by other exotic species such as P. × cambivora and P. cactorum. Phytophthora × alni and P. plurivora were equally damaging despite the higher prevalence of P. × alni in declining alders in natural settings. Although P. × alni mainly invaded the phloem, P. plurivora also invaded the xylem and triggered the production of tyloses. Histological analyses revealed a diverse range of plant responses to infection by Phytophthora species, providing a better understanding of their adaptability in natural environments compared with solely observing lesions. The low level of callose production in saplings inoculated with P. × alni compared with callose production in saplings inoculated with less pathogenic species suggests that P. × alni can evade recognition by the host and, hence, could partially explain its success.

Tree phenology is sensitive to climate warming and changes in seasonal precipitation. Long xylogenesis records are scarce, thus limiting our ability to analyse how radial growth responds to climate variability. Alternatively, process-based growth models can be used to simulate intra-annual growth dynamics and to better understand why growth bimodality varies along temperature and precipitation gradients. We used the Vaganov-Shashkin (VS) growth model to analyse the main climatic drivers of growth bimodality in eight trees and shrubs conifers (four pines and four junipers) across Spain. We selected eleven sites with different continentality degree and spring/autumn precipitation ratios since we expected to find pronounced bimodal growth in less continental sites with spring and autumn precipitation peaks. The VS model successfully simulated annual growth rates at all sites as a function of daily temperature and soil moisture data. Bimodal growth patterns clustered into less continental sites showing low spring/autumn precipitation ratios. This finding agrees with observed climate-growth associations showing that growth was enhanced by wet-cool winter-to-spring conditions, but also by wet autumn conditions in the most bimodal sites. We observed a stronger growth bimodality in pines compared to junipers. We discuss the spatial variability of climate drivers in bimodality growth pattern and how increasing continentality and shifts in seasonal precipitation could affect growth patterns. Bimodality could be an advantageous response to overcome summer drought in Mediterranean forests. The ability of some species to reactivate growth during autumn might determine their capacity to withstand increasing summer aridity.

The growth responses to climate variability are still unknown in locally threatened conifers from dry regions, but this information is necessary for improving the conservation of relict populations under increasing aridification. We characterized the radial growth patterns and responses to climate of Tetraclinis articulata, a Cupressaceae tree endemic to the western Mediterranean Basin, in a relict population located in southwestern Spain (Doñana) and two populations from the northern Morocco where the species core habitat is found (Tétouan, Ifarten). We assessed climate-growth relationships by using tree-ring width, climate data, drought and North Atlantic Oscillation (NAO) indices. Climate-growth analyses were refined using the climwin R package to select the most informative statistical models. The main climatic constraints of growth were inferred by using the process-based Vaganov-Shashkin (VS) model explicitly considering non-linear climate-growth relationships. Tetraclinis articulata growth was favored by wet conditions from the prior autumn to the spring of the growth year. In Doñana, warmer May conditions led to growth decline but this negative effect could be reversed by wet-warm conditions in the prior late autumn. Growth in the two Moroccan sites was constrained by 6- to 18-month long droughts peaking in summer, which account for cumulative water deficit since the previous autumn. Winter and early spring precipitation were the main climate drivers of growth in the Moroccan T. articulata populations, and their year-to-year variability was linked to the NAO. The VS model simulations showed that T. articulata growth is enhanced by wet soil conditions in late winter and early spring, probably recharging shallow soil water pools. The VS model also confirmed that warmer spring-summer conditions could amplify drought stress and threaten the long-term persistence of the relict Doñana population.

During the past years, growth and productivity of different oak species have been constrained by water shortage in seasonally dry regions such as the Mediterranean Basin. Thinning could improve oak radial growth in these drought-prone regions through the reduction of tree competition for soil water in summer. However, we still lack adequate, long-term assessments on how lasting are thinning treatments effects and to what extent they contribute to oak growth recovery after drought. Here we aim: (i) to study the radial growth sensitivity to drought of Quercus subpyrenaica in the Spanish Pre-Pyrenees, and (ii) to verify if thinning represents a suitable option to enhance growth resistance to drought and post-drought growth recovery. We analysed basal area increment (BAI) trends in the period 1960–2020 of formerly coppiced oak stands thinned in 1984 and compared them with unthinned plots and also with coexisting Scots pine (Pinus sylvestris) growing in thinned plots. We used the Standardized Precipitation Evapotranspiration Index (SPEI) to estimate the severity of droughts and we also assessed climate-growth relationships. Oaks in thinned plots showed higher BAI (369 mm2) than those in unthinned plots (221 mm2). Growth rates remained higher in thinned than in unthinned plots also under severe drought stress. A severe summer drought in 1986 caused abrupt BAI reductions in both oaks (- 40.5%) and pines (- 40.1%). The positive effect of thinning on growth lasted for over 20 years and slightly declined as canopies closed. In the thinned plots, trees with smaller diameter showed the greatest growth release. Oaks in unthinned plots and Scots pine were more sensitive to short-term droughts in terms of growth reduction than oaks in thinned plots, while long term droughts have similar effects on oaks from both thinned and unthinned plots. Oaks were resilient to drought, showing recovery periods lasting from 1 to 2 years in both thinned and unthinned plots. However, intense and p

Forest growth is driven by climate variability at continental to regional scales, but other factors play major roles at local scales (0.1–1 ha). Topography impacts on tree growth responses to climate stressors, including drought, by modifying radiation, evapotranspiration rates and the access to soil moisture. However, there is a lack of studies investigating how topographical factors (elevation, aspect, slope) affect climate-growth relationships considering both continuous (tree-ring width) and discrete wood-anatomical features (e.g., intra-annual density fluctuations–IADFs). Here, we investigated how topography modulated the influences of climate and drought on semi-arid Juniperus thurifera forests from north-eastern Spain. We compared two stands located in valley bottoms and two stands located in steep slopes. Radial growth was measured using dendrochronology which also allowed quantifying latewood IADFs. A proxy of topographic influence (incident radiation) was calculated. In addition, the Vaganov-Shashkin (VS) model was used to infer the main climatic constraints of growth at intra-annual scales. We found that junipers growing in valley bottoms were taller and produced more IADFs than junipers growing in steep slopes, but responded less to precipitation variability. This was confirmed by the VS model which showed that low soil moisture in June limited growth, particularly in steep-slope sites and during dry periods. Wet-cool late-summer conditions induced the formation of IADFs. The topoclimatic modulation of growth was explained by the interaction between incident radiation and tree age. Furthermore, climate-growth associations are changing as temperatures rise. Drought impacts on growth are strengthening, but less responsive junipers growing in valley bottoms may be buffered against intensified aridification.

Floodplain forests are sensitive to climate warming and increased drought, as showed by recent oak (Quercus robur) dieback and mortality episodes. However, a comprehensive comparison of coexisting tree species under different climate settings or biomes are lacking. Herein, we compared growth rates, growth responses to climate and drought severity, and modeled climate mediated growth of oak and three coexisting tree species (ash, Fraxinus angustifolia; alder, Alnus glutinosa; elm, Ulmus minor). Two floodplain forests subjected to cooler (temperate climate, Ticino) and warmer (Mediterranean climate, Bosco Pantano) conditions in northern and southern Italy, respectively, were analyzed. Ash seemed to be the most sensitive to drought, particularly at the Mediterranean site where oak and elm growth were also negatively affected by water shortages. Alder appeared to be the least sensitive species in terms of growth variability to drought under both temperate and Mediterranean climate conditions. Furthermore, the growth model revealed the influence of soil moisture in spring and summer on the constrained growth of ash and oak and illustrated how oak growth could be severely reduced during drastic hotter droughts. Alder seemed to be the most drought-resistant species under both environmental conditions. These results could represent the first attempts in documenting the ecological consequences of drought in terms of projected climate trends in less investigated Mediterranean floodplain forests. Furthermore, these results highlight how climate and tree-ring data combined with growth models could be useful tools to detect early warning signals of growth decline and impending dieback in floodplain forests in response to dry spells.

Extreme climate events such as late spring frosts (LSFs) negatively affect productivity and tree growth in temperate beech forests. However, detailed information on how these forests recover after such events are still missing. We investigated how LSFs affected forest cover and radial growth in European beech (Fagus sylvatica L.) populations located at different elevations at four sites in the Italian Apennines, where LSFs have been recorded. We combined tree-ring and remote-sensing data to analyse the sensitivity and recovery capacity of beech populations to LSFs. Using daily temperature records, we reconstructed LSF events and assessed legacy effects on growth. We also evaluated the role played by elevation and stand structure as modulators of LSFs impacts. Finally, using satellite images we computed Normalized Difference Vegetation Index (NDVI), Enhanced Vegetation Index (EVI) and LAI (Leaf Area Index) to evaluate the post-LSF canopy recovery. The growth reduction in LSF-affected trees ranged from 36 % to 84 %. We detected a negative impact of LSF on growth only during the LSF year, with growth recovery occurring within 1–2 years after the event. LSF-affected stands featured low vegetation indices until late June, i.e. on average 75 days after the frost events. We did not find a clear relationship between beech forest elevation and occurrence of LSFs defoliations. Our results indicate a high recovery capacity of common beech and no legacy effects of LSFs.

Drought reduces canopy cover, productivity and tree growth in forests. However, there is still little knowledge on how drought affects coupling between canopy greenness assessed by remote sensing and hydraulic conductivity detected by wood anatomy. This combination could improve the understanding of forest response to climate change. Thus, we investigated the impacts of a hot drought, which occurred in summer 2017, on radial growth, earlywood hydraulic diameter (Dh), a proxy of conductivity, and several remote-sensing indices in mixed Mediterranean hardwood forests (Quercus pubescens Willd. – Fraxinus ornus L.). In general, growth showed a higher coherence among trees and a higher responsiveness to climate. Growth decreased during the drought year, particularly for Q. pubescens, which showed high defoliation and dieback intensity. Both species showed a decline of Dh in 2018 after the drought and subsequent warm winter conditions. We found positive relationships between Dh and remote-sensing data for Q. pubescens in some of these vulnerable sites, where (i) growth was constrained by dry spring-summer conditions and (ii) Dh and growth covaried. These findings indicate a high variability among sites and tree species in their responses to drought considering earlywood anatomy, growth canopy cover and water content. However, some common patterns emerge such as links between potential hydraulic conductivity (Dh), tree cover and Dh-growth covariation in the most impacted sites. Further, F. ornus seem to perform better in terms of growth under drought conditions, showing less mortality and dieback than Q. pubescens. Future studies could explore how water transport and changes in canopy cover respond to dry and warm conditions and if that covariation indicates vulnerability to drought.

Tree-ring studies are still lacking in tropical African forests. This is the case in the seasonally dry miombo forests located in Southern Africa. In the Angolan miombo, subject to intense charcoal exploitation, tree-ring data is urgently needed to estimate the age at which the minimum permitted cutting diameter is reached. Further, climate-growth relationships must be also investigated to understand how major miombo tree species respond to climate constraints and teleconnections such as the El Niño Southern Oscillation (ENSO). To achieve both aims, we studied radial growth data of two miombo tree legume species (Brachystegia spiciformis, Julbernardia paniculata) in wet (Bailundo) and dry (Caála) Angolan sites using dendrochronological methods. Both species have diffuse porous wood and conspicuous ring boundaries delimited by terminal parenchyma in latewood. Sampled individuals had ages (at 1.3 m) between 28 and 34 years with ring widths ranging 3.8–4.3 and 5.5–6.0 mm in dry and wet sites, respectively. In the wet (dry) site, Brachystegia and Julbernardia reached maximum diameter increment rates of 1.05–1.32 (0.74–0.91) cm yr−1 at an age of 12 (14−20) years. Both species took 12–15 years to reach a minimum cutting diameter of 15 cm. The growth variability among conspecific individuals was lower in the dry (mean standard error, 1.4 cm) than in the wet site (mean standard error, 2.7 cm). We also found that wet conditions from November to February, often linked to El Niño events, enhanced growth for both species, with greater growth consistency among individuals and higher sensitivity to climate found in the dry site. This information may help to estimate the optimal age for minimum cutting diameter that guarantees the sustainable use of charcoal and fuelwood.

Despite the importance of species interaction in modulating the range shifts of plants, little is known about the responses of coexisting life forms to a warmer climate. Here, we combine long-term monitoring of cambial phenology in sympatric trees and shrubs at two treelines of the Tibetan Plateau, with a meta-analysis of ring-width series from 344 shrubs and 575 trees paired across 11 alpine treelines in the Northern Hemisphere. Under a spring warming of +1°C, xylem resumption advances by 2–4 days in trees, but delays by 3–8 days in shrubs. The divergent phenological response to warming was due to shrubs being 3.2 times more sensitive than trees to chilling accumulation. Warmer winters increased the thermal requirement for cambial reactivation in shrubs, leading to a delayed response to warmer springs. Our meta-analysis confirmed such a mechanism across continental scales. The warming-induced phenological mismatch may give a competitive advantage to trees over shrubs, which would provide a new explanation for increasing alpine treeline shifts under the context of climate change.

Local differentiation at distribution limits may influence species' adaptive capacity to environmental changes. However, drivers, such gene flow and local selection, are still poorly understood. We focus on the role played by range limits in mountain forests to test the hypothesis that relict tree populations are subjected to genetic differentiation and local adaptation. Two alpine treelines of mountain pine (Pinus uncinata Ram. ex DC) were investigated in the Spanish Pyrenees. Further, an isolated relict population forming the species' southernmost distribution limit in north-eastern Spain was also investigated. Using genotyping by sequencing, a genetic matrix conformed by single nucleotide polymorphisms (SNPs) was obtained. This matrix was used to perform genotype-environment and genotype-phenotype associations, as well as to model risk of non-adaptedness. Increasing climate seasonality appears as an essential element in the interpretation of SNPs subjected to selective pressures. Genetic differentiations were overall weak. The differences in leaf mass area and radial growth rate, as well as the identification of several SNPs subjected to selective pressures, exceeded neutral predictions of differentiation among populations. Despite genetic drift might prevail in the isolated population, the Fst values (0.060 and 0.066) showed a moderate genetic drift and Nm values (3.939 and 3.555) indicate the presence of gene flow between the relict population and both treelines. Nonetheless, the SNPs subjected to selection pressures provide evidences of possible selection in treeline ecotones. Persistence in range boundaries seems to involve several selective pressures in species' traits, which were significantly related to enhanced drought seasonality at the limit of P. uncinata distribution range. We conclude that gene flow is unlikely to constrain adaptation in the P. uncinata rear edge, although this species shows vulnerability to future climate change scenarios involving

[Aims] Shifts in xylem phenology directly determine the forest capacity for carbon sequestration. However, a systematic understanding of the spatial patterns and the underpinning drivers in determining the cessation of wood formation (Ccw) is lacking at a pan-continental scale. Here, we addressed this knowledge gap by compiling a new dataset of multiple xylem phenology timings for northern conifers., [Locations] Sixty-two study sites, Northern Hemisphere (25–55° N)., [Time period] 2003–2018 (16 years)., [Taxa] Thirty-three conifer species., [Methods] A generalized additive model was fitted to characterize the latitudinal pattern in Ccw. Structural equation modelling and a linear mixed-effects model were applied to determine the main drivers underlying the latitudinal pattern in Ccw., [Results] The Ccw followed a flat S-shaped pattern with increasing latitude. Photoperiod was the dominant determinant of the latitudinal pattern of Ccw, and a longer photoperiod was associated with an earlier Ccw. Both mean growing-season temperature and total growing-season precipitation exhibited significantly positive relationships to the cessation of cell elongation and thus the Ccw across all study sites. In arid regions, the pre-growing-season temperature had a significantly negative effect on Ccw. In humid regions, Ccw was positively affected by the mean growing-season temperature. The onset of wood formation showed significantly positive coupling with Ccw at arid sites but not at humid sites. Early successional species were sensitive to hydrothermal variations during the pre-growing season., [Main conclusions] We reveal the dominant role of photoperiod in determining the cessation of wood formation for northern conifers and highlight differentiated interactive effects between photoperiod and seasonal climatic factors and the preceding xylem phenophases in determining Ccw among ecoregions and tree species. These insights provide evidence to reduce uncertainty in prediction of the forest carbon uptake potential and the consequent biophysical feedbacks of northern forests.