Mediterranean Tree Research Articles

Climate change and exotic pathogens shift carbon allocation in Mediterranean mixed forests

Abstract Forecasting the effects of global change drivers on ecosystems is one of the most pressing challenges for scientists worldwide. Particularly, climate change and exotic pathogens might have a large impact on plant community dynamics and ecosystem functioning through changes in carbon uptake and sinks. Nevertheless, we still have a poor understanding of the combined effects of these two drivers on plant communities. Here, we explored the impact of rainfall reduction and exotic pathogens on the carbon balance of Mediterranean tree species. For this, we performed a 3‐year field experiment taking advantage of rainfall exclusion infrastructures (30% exclusion) installed in the southernmost European oak forests invaded by the aggressive exotic pathogen Phytophthora cinnamomi. We measured a set of 10 variables representative of tree carbon sources (photosynthetic rates) and sinks (primary production, reproduction, defence, and reserves) in adult trees of three species in two forest types: closed forests of Quercus suber and Q. canariensis, and open woodlands of Q. suber and Olea europaea. We found a large variability in the sensitivity of the different carbon sources and sinks to the effects of drought and pathogens, from variables highly sensitive to both factors (carbon fixation and reproduction, root chemistry) to variables only responsive to drought (litter production) or totally unresponsive (tree trunk, leaf chemistry). Although negative effects predominated, positive effects of rainfall exclusion were also detected in wet years, likely due to a reduction of pathogen abundance in drier soil. Trade‐offs between carbon sinks appeared in all tree species, but rainfall exclusion only modified trade‐offs in Q. suber, the species most susceptible to P. cinnamomi. Synthesis. We provide evidence on the complexity of the combined effects of abiotic (drought) and biotic (pathogens) global change drivers on carbon source and sinks of adult trees, including both negative direct effects and positive indirect effects. Our results showed that these effects varied among co‐existing species, particularly for carbon sinks directly related to tree demography (reproduction). Therefore, long‐term changes in the structure of Mediterranean mixed forests might be expected towards the dominance of species highly resistant to both drought and pathogens.

Stem Growth and Dehydration Responses of Mediterranean Tree Species to Atmospheric and Soil Drought.

Stem growth responses to soil and atmospheric drought are critical to forecasting the tree carbon sink strength. Yet, responses of drought-prone forests remain uncertain despite global aridification trends. Stem diameter variations at an hourly resolution were monitored in five Mediterranean tree species from a mesic and a xeric site for 6 and 12 years. Stem growth and dehydration responses to soil (REW) and atmospheric (VPD) drought were explored at different timescales. Annually, growth was determined by the number of growing days and hours. Seasonally, growth was bimodal (autumn growth ≈ 8%-18% of annual growth), varying among species and sites across the hydrometeorological space, while dehydration consistently responded to REW. Sub-daily, substantial growth occurred during daytime, with nighttime-to-daytime ratios ranging between 1.2 and 3.5 (Arbutus unedo ≈ Quercus faginea < Quercus ilex < Pinus halepensis in the mesic site, and Juniperus thurifera < P. halepensis in the xeric site). Overall, time windows favourable for growth were limited by soil (rather than atmospheric) drought, modulating annual and seasonal growth in Mediterranean species, and stems maintained non-negligible growth during daytime. These patterns contrast with observations from wetter or cooler biomes, demonstrating the growth plasticity of drought-prone species to more arid climate conditions.

Germination responses of carob (Ceratonia siliqua L.) seeds to salinity and water stresses: Implications for the restoration of Mediterranean marginal lands

The iconic Mediterranean tree, Ceratonia siliqua L., holds substantial potential for restoring arid and semi-arid marginal lands. However, there is limited knowledge about the interaction of various abiotic factors and environmental stressors on seed germination of C. siliqua. Therefore, we examined the influence of salinity levels (0, 75, 150, 225 mM) and water stress using PEG6000 (−0.4, −0.8, −1.2 MPa) on C. siliqua seed germination under varying thermoperiods (15/25 °C and 25/35 °C) and photoperiods (12 hours of light and complete darkness). Our findings indicate that higher temperatures (25/35 °C) significantly reduced germination of seeds compared to lower temperatures (15/25 °C). However, the photoperiods showed no significant impact, especially under minimal salinity stress and low osmotic potentials (75 mM NaCl and −0.4 MPa PEG). In general, C. siliqua seeds exhibited enhanced performance in darkness at higher osmotic potentials, while increased stress prolonged the germination period. The dry weight of seedlings decreased with higher osmotic potential, although 75 mM NaCl promoted seedling biomass production. Our results confirm C. siliqua resilience to high salinity and moderate drought, offering practical applications for its successful reintroduction and cultivation in challenging Mediterranean environmental conditions.

Exploring Juniperus phoenicea L extract through phytochemical analysis, anti-lipase effects, and comprehensive molecular studies

Lipase inhibitors are used in the treatment of candidiasis, obesity, and acne problems. Therefore, the investigation of new natural lipase inhibitors has generated great interest. Juniperus phoenicea is a small Mediterranean tree considered an important medicinal plant. Through this work, we investigated the composition and inhibition effect of J. phoenicea extract on Candida rugosa and human lipases; and we analyzed the interactions between detected compounds and lipases using molecular docking, ADME-T, and dynamic studies. We extracted the secondary metabolites from the plant aerial parts and tested their activities against lipase. We examined major components of J. phoenicea, using Autodock vina for molecular docking, Desmond from Schrodinger suite 2021–1 for dynamics, and evaluating its drug-likeness and toxicity properties using ADMET webserver. We found that the IC50 values of ethyl acetate and methanol extracts are 1.33±0.10 and 1.731 mg/mL. Using HPLC quantitative analysis we identified in ethyl acetate extract the following phenolic compounds gallic acid, rutin, apigenin-7-O-glucoside, cinnamic acid, and quercetin. The complex apigenin-7-O-glucoside-lipase is stabilized by four hydrogen bonds and hydrophobic interactions, and the binding energy equals -10 Kcal/mol, which is better than the interactions saved for orlistat. Dynamic Simulation demonstrated better stability in the ligand-protein complex apigenin-7-O-glucoside-1lpb within 100 ns than the orlistat-1lpb complex. This study is described in this work for the first time. The results indicated that apigenin-7-O-glucoside from J. phoenicea L could be a good choice to develop a new drug candidate against candidiasis, obesity, and other lipase-related diseases.

Hydraulic plasticity and water use regulation act to maintain the hydraulic safety margins of Mediterranean trees in rainfall exclusion experiments.

Hydraulic failure due to xylem embolism has been identified as one of the main mechanisms involved in drought-induced forest decline. Trees vulnerability to hydraulic failure depends on their hydraulic safety margin (HSM). While it has been shown that HSM globally converges between tree species and biomes, there is still limited knowledge regarding how HSM can adjust locally to varying drought conditions within species. In this study, we relied on three long-term partial rainfall exclusion experiments to investigate the plasticity of hydraulic traits and HSM for three Mediterranean tree species (Quercus ilex L., Quercus pubescens Willd., and Pinus halepensis Mill.). For all species, a homeostasis of HSM in response to rainfall reduction was found, achieved through different mechanisms. For Q. ilex, the convergence in HSM is attributed to the adjustment of both the turgor loss point (Ψtlp) and the water potential at which 50% of xylem conductivity is lost due to embolism (P50). In contrast, the maintenance of HSM for P. halepensis and Q. pubescens is related to its isohydric behavior for the first and leaf area adjustment for the latter. It remains to be seen whether this HSM homeostasis can be generalized and if it will be sufficient to withstand extreme droughts expected in the Mediterranean region.

Evaluation of Mediterranean Tree Leaves as Valuable Biomass of Digestive Enzymes and Bacterial Inhibitors in the Concept of Circular Bioeconomy

This study aspires to evaluate the antibacterial and inhibitory effects of carbohydrate digestive enzymes in tree leaves that are widely distributed in the Mediterranean region. Leaves were sequentially extracted with solvents of increasing polarity. The results demonstrated a wide range of phenolic (3.5–770.7 mg gallic acid equivalent g−1) and flavonoid (0.2–321.3 mg catechin equivalent g−1) contents in leaf extracts. The minimum inhibitory and bactericidal concentration of leaf extracts was determined for six bacteria using the broth microdilution method. The polar extracts of carob, lentisk, and white mulberry leaves exerted strong antibacterial potency against Gram-positive bacteria, while the susceptibility of Escherichia coli on relative apolar extracts of carob, fig, and olive leaves was also observed. In parallel, the inhibitory effects of leaf extracts on carbohydrate digestive enzymes were evaluated. A robust inhibition of α-glucosidase was found for carob and lentisk leaf extracts, followed by extracts produced by white mulberry and olive leaves. Carob and lentisk leaves also act as a-amylase inhibitors at high concentrations. Overall, this study provides valuable data for the nutraceutical value of the “forgotten” treasure of Mediterranean tree leaves and assesses these plants as potential sources of antibacterial and carbohydrate digestive enzyme inhibitory agents for drug discovery.

Olive reproductive biology: implications for yield, compatibility conundrum, and environmental constraints.

Olive (Olea europaea L.) is an important Mediterranean tree species with a longstanding history of cultivation, boasting a diverse array of local cultivars. While traditional olive orchards are valued for their cultural and aesthetic significance, they often face economic sustainability challenges in the modern context. The success of both traditional and newly introduced cultivars (e.g. those obtained by cross-breeding) is hindered by self-incompatibility, a prevalent issue for this species that results in low fruit set when limited genetic diversity is present. Further, biological, environmental, and agronomic factors have been shown to interlink in shaping fertilization patterns, hence impacting on the final yield. Climatic conditions during pollination, such as excessive rainfall or high temperatures, can further exacerbate the problem. In this work, we provide an overview of the various factors that trigger the phenomenon of suboptimal fruit set in olive trees. This work provides a comprehensive understanding of the interplay among these factors, shedding light on potential mechanisms and pathways that contribute to the observed outcomes in the context of self-incompatibility in olive.

Soil mycobiome and forest endophytic fungi: Is there a relationship between them?

Fungi are important ecological agents in forests that contribute to increase the resilience of the whole ecosystem against environmental challenges. Mediterranean forests rank among the habitats most threatened by climate change and the spread of pests and diseases, which ultimately lead them into a spiral of decline. As such, changes in the composition of soil and trees’ mycobiota might correlate with health status of the forest and has been scarcely addressed in Mediterranean tree species. In this work, rhizosphere and bark-wood samples from declining Spanish forests of Castanea sativa Mill. (chestnut), Quercus ilex L. (holm oak), Q. suber L. (cork oak) and Q. pyrenaica Willd. (Pyrenean oak) were compared. Fungal communities were characterised by means of ITS metabarcoding. Higher diversity in terms of richness was found in soil, with 674 genera belonging to 15 phyla in soil vs 420 genera and 6 phyla in trees. Fungal genera exclusive to declining forests’ soils and trees didn’t include pathogenic organisms, thus preventing the association of certain genera with forest decline. Alpha diversity didn’t correlate with health status or sample type either, as it only increased in soils of asymptomatic chestnuts and not in any of the other analysed tree species. Some differentially abundant genera found in asymptomatic trees, such as Metarhizium, Aspergillus, Russula, Chaetomium, Mortierella or Cladophialophora, may be related to the biological control of decline-contributing pathogens. Finally, no relationship was found between health status and the primary lifestyles of fungi in soil and bark, which can be interpreted as a sign of resilience against adversities following cross-talk between soil and plant fungal communities.

Consistent geographical gradient of water use efficiency evidences local adaptations to drought across the complete latitudinal distribution of Quercus suber

RationaleIncreased aridity has led to drought-induced mortality or loss of health for many tree species. Of particular interest is to explore the response of the Mediterranean tree species cork oak (Quercus suber) to this declining phenomenon due to its severity and its large implications for the local economy and the provision of highly relevant ecosystem services. ApproachTo assess geographical variations in the response to water stress, we analyzed under controlled conditions the effects of four watering levels and the resistance to a terminal drought on seedlings collected from nine populations covering the complete latitudinal distribution of the species. We explored the response of a number of physiological traits and markers of oxidative stress potentially related with drought-resistance. FindingsWe found a highly plastic phenotypic response of most variables to water availability and a large influence of seedlings provenance in the drought-resistance strategies. Although the oxidative stress enzymes ruled out differential water stress throughout the distribution range, we found that seedlings from the southern limit are less vulnerable to drought than other populations. Southern seedlings adapted to xeric conditions displayed a larger sensitivity of stomata to changes in soil humidity and a higher water use efficiency. These physiological local adaptations coupled with larger acorn size in the southern populations, resulted in larger aboveground biomass and higher drought resistance at the southern distribution edge. ConclusionsOur data suggest that this evergreen tree species relies on its physiological plasticity to develop adaptative features that allows it to overcome water shortage and that southern populations hold genetic diversity that could improve the specie´s adaptation in the forecasted drought context with relevant implications for conservation programs.

THE VEGETATION HISTORY OF THE SHEPHELAH, SOUTHERN LEVANT: MIDDLE BRONZE AGE–HELLENISTIC PERIOD (c.2000–100 BC)

SummaryAlthough the Shephelah region (Israel) is of a great archaeological significance and has been intensively excavated, very little is known about its landscape history. This study presents two large‐scale charred wood assemblages (&gt;2300 items) that were recovered from Tel Azekah and Tel Lachish in order to reconstruct the ancient vegetation of the Shephelah. The two assemblages cover a temporal range from the Middle Bronze Age through the Hellenistic period (c.2000–100 BC). This new diachronic environmental investigation demonstrates that the natural arboreal vegetation in the Shephelah was dominated by oak and pistachio. From the perspective of the regional fruit tree horticulture, olive was the dominant component, indicating that the region included extensive olive orchards. Other documented fruit trees are grapevine, fig, sycamore fig, carob, date palm and almond. The high frequencies of olive remains throughout all investigated periods point to climatic conditions in the region being close to what we are facing today, with at least 400–450 mm of annual precipitation, which is required for a profitable grove. During the Iron Age II, the proportion of olive remains reached its zenith, most probably as a result of Assyrian agroeconomic management that assigned the Shephelah to olive oil production. At the same time, a reduction in natural Mediterranean trees was identified, representing intense human pressure on the natural environment. The discovery of charred cedar of Lebanon remains only at Lachish points to the high status of the site within the region.

Is olive crop modelling ready to assess the impacts of global change?

Olive trees, alongside grapevines, dominate the Mediterranean tree crop landscape. However, as climate change intensifies, the Mediterranean region, which encompasses 95% of the global olive cultivation area, faces significant challenges. Rising carbon dioxide (CO2) levels, increasing temperatures, and declining precipitation pose substantial threats to olive tree performance. Photosynthesis, respiration, phenology, water use and ultimately yield are possibly the main factors affected. To address this future scenario, it is crucial to develop adaptation and mitigation strategies. Nevertheless, breeding programs and field management practice testing for tree crops are time-consuming endeavors. Fortunately, models can accelerate the evaluation of tailored solutions. In this review, we critically examine the current state of olive tree modeling and highlight key areas requiring improvement. Given the expected impact of climate change, prioritizing research on phenology, particularly regarding bloom and pollination, is essential. Simulations of biomass should incorporate approaches that account for the interactive effects of CO2 and temperature on photosynthesis and respiration. Furthermore, accurately simulating the influence of water stress on yield necessitates the development of models that integrate canopy behavior with root performance under conditions of water scarcity. By addressing these critical aspects, olive tree models can enhance our understanding of climate change impacts and inform sustainable agricultural practices.

Influence of management and stand composition on ecosystem multifunctionality of Mediterranean tree forests

Influence of management and stand composition on ecosystem multifunctionality of Mediterranean tree forests

Rhizosphere mycobiome diversity in four declining Mediterranean tree species

IntroductionForests in the Mediterranean basin are currently in decline. Their resilience has been eroded as a result of climate change and anthropogenic impacts, making them vulnerable to increasingly frequent episodes of drought, fire and the spread of pests and diseases. The impact of these natural and anthropogenic events on soil biodiversity is of particular concern, as the soil fungal community plays a key role in ecosystem homeostasis.Objectives and methodsIn order to analyse the relationship between soil health status and fungal diversity, soil samples were collected from declining Mediterranean forests of Castanea sativa (chestnut), Quercus ilex (holm oak), Quercus suber (cork oak) and Quercus pyrenaica (Pyrenean oak). A metabarcoding study was carried out by sequencing the ITS genomic region.ResultsA total of 674 fungal genera were found. It has not been possible to explain the differences in health status from the fungal genera found exclusively on declining forest soils, as none of them have been described as pathogenic. Healthy chestnut soils were characterized by a high alpha diversity and a higher abundance of the genus Metarhizium. No differentially abundant genera were found in any of the other forest species tested. Declining chestnut soils harbored more abundance of ectomycorrhizae and soil saprotrophs than healthy samples. Ectomycorrhizae were the dominant lifestyle in all oak species regardless of health status, whereas arbuscular mycorrhizae were preferentially found in declining cork oak soils.DiscussionThis work highlights the resilience of fungal communities of soil against decline and highlights the need to further investigate its relationship with the forest’s ability to cope with the challenges of climate change.

QUERCUS CERRIS L.: ANTIBACTERIAL AND ANTIBIOFILM POTENTIAL

Invasion of pathogenic infections, antibiotic resistance, and formation of biofilms represent serious contemporary issues that threaten human health. Quercus cerris L. is a deciduous Mediterranean tree that has been used in folk medicine since the ancient times but without knowing its phytochemical profile. The aim of this study was to evaluate the antibacterial potential of aqueous and ethanolic leaf extracts against two Gram-positive bacteria (Streptococcus intermedius and Enterococcus faecium) and two Gram-negative bacteria (Escherichia coli and Stenotrophomonas maltophilia) using agar well diffusion and broth microdilution methods. The antibiofilm properties of Quercus cerris L. extracts were also tested against the listed bacteria. The results of this study showed that both extracts displayed antibacterial capacity. However, the test cultures were found to be more susceptible to the ethanolic extract than the aqueous one. The lowest minimum inhibitory concentration (MIC) (12 mg/ml) and minimum bactericidal concentration (MBC) (25 mg/ml) values of the ethanolic extract were registered against Escherichia coli, while the highest values were noted against Streptococcus intermedius. As for the aqueous extract, it showed only a bacteriostatic activity against all the tested bacteria with a MIC of 100 mg/ml. The results of the antibiofilm assays also showed that the ethanolic extract exhibited significant antibiofilm effects against the investigated microorganisms. In the light of the findings of this research study, the aqueous and ethanolic extracts of Quercus cerris L. may be very useful in the development of new plant-based antimicrobial agents.

Discrimination of Leaves in a Multi-Layered Mediterranean Forest through Machine Learning Algorithms

Terrestrial laser scanning (TLS) technology characterizes standing trees with millimetric precision. An important step to accurately quantify tree volume and above-ground biomass using TLS point clouds is the discrimination between timber and leaf components. This study evaluates the performance of machine learning (ML)-derived models aimed at discriminating timber and leaf TLS point clouds, focusing on eight Mediterranean tree species datasets. The results show the best accuracies for random forests, gradient boosting machine, stacked ensemble model, and deep learning models with an average F1 score equal to 0.92. The top-performing ML-derived models showed well-balanced average precision and recall rates, ranging from 0.86 to 0.91 and 0.92 to 0.96 for precision and recall, respectively. Our findings show that Italian maple, European beech, hazel, and small-leaf lime tree species have more accurate F1 scores, with the best average F1 score of 0.96. The factors influencing the timber–leaf discrimination include phenotypic factors, such as bark surface (i.e., roughness and smoothness), technical issues (i.e., noise points and misclassification of points), and secondary factors (i.e., bark defects, lianas, and microhabitats). The top-performing ML-derived models report a time computation ranging from 8 to 37 s for processing 2 million points. Future studies are encouraged to calibrate, configure, and validate the potential of top-performing ML-derived models on other tree species and at the plot level.

Species-specific growth responses to local and regional climate variability indicate the presence of a diversity portfolio effect in mediterranean tree assemblages

Understanding the role of tree biodiversity in stabilizing ecosystem processes is of paramount importance in forest ecology, especially because of increasing temperatures and droughts. The portfolio effect is one of the main hypotheses explaining the biodiversity-stability relationship that has been defined as a variance reduction effect of biodiversity in an ecosystem process, so that fluctuations over time in highly diverse communities become significantly smaller in low-diversity communities. In this work, two main objectives were established: to analyze a potential portfolio effect in a tree assemblage through functional mechanisms of compensation, and to identify the local climatic factors and teleconnections responsible for the interannual variations in the growth of tree species. The study was carried out in a region of the Iberian Peninsula with transitional climatic characteristics that allow the coexistence of needleleaf and broadleaf tree species with a wide variety of strategies and functional traits allowing them to respond differentially to climatic conditions. A dendrochronological approach was followed to analyze tree growth in relation to climate factors. We found that the magnitude and sensitivity of the response to both local climatic elements and teleconnections were species-dependent and that during climatically extreme years, the species exhibited marked differences in tree growth and compensatory responses that contributed to an increase in temporal stability. These results point to the existence of a portfolio effect in Mediterranean woodlands that supports tree diversity as an effective driver of ecosystem stability. Although the combination of dry and hot years always has a negative effect on tree growth, the association of coniferous and broadleaved (evergreen and marcescent) species at our study site could have a significantly positive influence by increasing temporal stability at landscape level through complementary functional responses.

Wood anatomy and dendrochronological potentiality of some woody shrubs from the southern Mediterranean coast in Egypt.

In tropical and subtropical regions, much research is still required to explore the dendrochronological potential of their trees. This study aims to evaluate the anatomical structure and dendrochronological potential of three Mediterranean desert shrubs in Egypt (Lycium schweinfurthii var. schweinfurthii, L. europaeum, and Calligonum polygonoides subsp. comosum) supported by X-ray density. The results showed that the target species had distinct growth rings at macroscopic and microscopic levels. The vessel traits reflected the adaptability of each species with the prevailing arid climate conditions. After the exclusion of the non-correlated series, we obtained three site chronologies that cover the years 2013-2022 for L. schweinfurthii, 2012-2022 for L. europaeum, and 2011-2022 for C. comosum. The mean series intercorrelation was 0.746, 0.564, and 0.683 for L. schweinfurthii, L. europaeum, and C. comosum, respectively. The EPS (expressed population signal) values ranged from 0.72 to 0.80, while the SNR (species-to-noise ratio) ranged from 9.1 to 21.5. Compiling all series of L. schweinfurthii raised the EPS value to 0.86. The chronologies developed for the studied species were relatively short since we dealt with multi-stemmed shrubs. The average percentage difference between latewood density (LWD) and earlywood density (EWD) in C. comosum, L. europaeum, and L. schweinfurthii were 11.8% ± 5.5, 5.2%± 1.87, and 3.6% ± 1.86, respectively. X-ray densitometry helped in the precise determination of the ring borders of the studied species. The relationships between the radial growth of the studied species and the climate variables were weak to moderate but mostly not significant (i.e., r < 0.7). Generally, the radial growth of the target species had a weak to moderate positive correlation with temperature and precipitation during the wet season (winter), while negatively correlated with temperature for the rest of the year, particularly in summer. Our data agrees with earlier findings that ring formation starts at the beginning of the long vegetative stage, then the rest of the assimilated carbohydrates are directed to the flowering and fruiting at the end of the vegetative stages. For more efficient dendrochronological studies on subtropical and Mediterranean trees, we recommend carrying out xylogenesis studies, collection of phenological data, sampling 45-80 trees per species, using new techniques, and choosing homogeneous and close sites for wood sampling.

Water use, soil water balance and soil salinization risks of Mediterranean tree orchards in southern Portugal under current climate variability: Issues for salinity control and irrigation management

Water use, soil water balance and soil salinization risks of Mediterranean tree orchards in southern Portugal under current climate variability: Issues for salinity control and irrigation management

Role Of Hydraulic Traits On Stomatal Regulation Of Transpiration Under Different Vapor Pressure Deficits Across Five Mediterranean Tree Crops.

The differential stomatal regulation of transpiration among plant species in response to water deficit is not fully understood, although several hydraulic traits have been reported to influence it. This knowledge gap is partly due to a lack of direct and concomitant experimental data of transpiration, stomatal conductance and hydraulic traits. We measured sap flux density (Js), stomatal conductance (gs) and different hydraulic traits in five crop species. We aim to contribute to establish the causal relationship between water consumption and its regulation using a hydraulic trait-based approach. The results showed that the species-specific regulation of Js by gs was overall coordinated with the functional hydraulic traits analyzed. Especially relevant was the negative and significant relationship found between the Huber value (Hv) and its functional analogue ratio between maximum Js and gs (Jsmax/gsmax) which can be understood as a compensation to maintain the hydraulic supply to the leaves. Hv was also significantly related to the slope of the relationship between gs and Js response to vapor pressure deficit and explained most of its variability, adding up to evidence recognizing Hv as a major trait in plant water relations. Thus, hydraulic basis for the regulation of tree water use should be considered.

Effect of environmental and spatial factors on the phylogenetic and functional diversity of the Mediterranean tree communities of Europe.

The tree flora of the Mediterranean Basin contains an outstanding taxonomic richness and a high proportion of endemic taxa. Contrary to other regions of the Mediterranean biome, a comprehensive phylogenetic analysis of the relationship between phylogenetic diversity, trait diversity and environmental factors in a spatial ecological context is lacking. We inferred the first calibrated phylogeny of 203 native tree species occurring in the European Mediterranean Basin based on 12 DNA regions. Using a set of four functional traits, we computed phylogenetic diversity for all 10,042 grid cells of 10 × 10 km spatial resolution to completely cover Mediterranean Europe. Then, we tested the spatial influence of environmental factors on tree diversity. Our results suggest that the nature of the relationship between traits and phylogeny varies among the different studied traits and according to the evolutionary distance considered. Phylogenetic diversity and functional diversity of European Mediterranean trees correlated strongly with species richness. High values of these diversity indices were located in the north of the study area, at high altitude, and minimum temperature of the coldest month. In contrast, the two phylogenetic indices that were not correlated with species richness (Mean Phylogenetic Distance, Phylogenetic Species Variability) were located in the south of the study area and were positively correlated with high altitude, soil organic carbon stock and sand soil texture. Our study provides support for the use of phylogenies in conservation biology to assess ecosystem functioning, and provides insights for the implementation of sustainable forest ecosystem management.