Quercus Faginea Research Articles

Variation of Ring Width and Wood Density in Two Unmanaged Stands of the Mediterranean Oak Quercus faginea

Ring width and wood density variation were studied from pith-to-bark and along the stem in two naturally regenerated stands of Quercus faginea Lam. in Portugal. Ring width was significantly different between sites, in both heartwood and sapwood rings, ranging from 1.83 mm to 2.52 mm and from 0.77 mm to 2.11 mm, respectively. Wood density was significantly different between sites only in the heartwood, i.e., 914 kg m−3 and 1037 kg m−3. Site effects were the main source of variation for ring width and wood density within the heartwood as well as for sapwood ring width, while the between-tree effects explained more the density variation within the sapwood. Wood density showed within-tree uniformity that was not affected by site. The stand characteristics such as basal area and tree age may override the environmental growth conditions. There was also a weak correlation between wood density and ring width components therefore suggesting the possibility of forestry management for both fast tree growth and high wood density.

Suitability of multiple Mediterranean oak species as a food resource for Reticulitermes grassei Clément (Isoptera: Rhinotermitidae).

The subterranean termite Reticulitermes grassei Clément causes lesions in the trunk of Quercus suber L. by constructing feeding galleries, but no information is available regarding other Quercus species from the Mediterranean region. This work aimed to study the suitability of the other main oak species of Mediterranean forests as a food resource for R. grassei. Two experiments, choice and non-choice feeding, were conducted lasting for 15, 30, and 45 days each. In the non-choice experiment, termites were offered one of the following food types: Quercus suber, Quercus ilex L., Quercus faginea Lam, cork or Pinus pinea L., which was considered the control. The choice feeding experiment used all the same food types listed above, supplied simultaneously in the same container. Food selection was examined by analysing the relationships over time between surviving termites and food consumption. The results indicated that R. grassei could be considered a generalist species, as it consumed the cork and wood of all oak species, as well as displaying a clear preference for soft wood (pine). Correlation analysis indicated that consumption was not dependent on wood density. Survival of R. grassei was influenced by the time of exposure to different oak species, but a high survival rate was maintained over time in the pine treatment (upper 70% in the three experiments). Given these results, it can be concluded that all the oak species are a suitable food source for R. grassei.

Flammability of some companion species in cork oak (Quercus suber L.) forests

The high flammability of some companion species in Quercus suber forests, estimated in laboratory tests, could potentially generate an increase in fire vulnerability and in fire risk. Recurrent wildfire is one of the main causes of forest degradation, especially in the Mediterranean region. Increased fire frequency and severity due to global change could reduce the natural resilience of cork oak to wildfire in the future. Hence, it is important to evaluate the flammability of companion species in cork oak forests in the particularly dry bioclimatic conditions of North Africa. This study aimed to assess and compare flammability parameters at laboratory scale among ten companion frequent species in cork oak forests. Fuel samples were collected in a cork oak (Quercus suber L) forest in the southern part of the mountains of Tlemcen (Western Algeria). A series of flammability tests were carried out using a Mass Loss Calorimeter device (FTT ®). A cluster analysis to classify flammability of the selected species was conducted using the K-means algorithm. The results revealed differences in the four flammability parameters (ignitability, sustainability, combustibility and consumability), in both fresh and dried fine fuel samples from Quercus suber, Pinus halepensis, Quercus ilex, Quercus faginea, Erica arborea, Arbutus unedo, Pistacia lentiscus, Calicotome spinosa, Juniperus oxycedrus and Tetraclinis articulata. Application of the K-means clustering algorithm showed that C. spinosa, T. articulata, J. oxycedrus and P. halepensis are highly flammable because of their high combustibility and sustainability. The findings identify species that could potentially increase the vulnerability of cork oak forests to forest fires.

Acorn (Quercus spp.) as a novel source of oleic acid and tocopherols for livestock and humans: discrimination of selected species from Mediterranean forest.

The aim of the present work was to characterization and compare acorns from selected Quercus spp. from the Mediterranean forest in Spain, namely, Portuguese oak (QF, Quercus faginea Lam.), Cork oak (QS, Quercus suber L.), Pyrenean oak (QP, Quercus pyrenaica Wild), Kermes oak (QC, Quercus coccifera L.), Holm oak (QB, Quercus ilex L. subsp. ballota [Desf.]). All physicochemical attributes varied significantly between species. Fat contents ranged from 1.30 to 4.70g 100g-1 fresh matter. The most abundant fatty acids were oleic (62.44, 56.25, 57.46, 48.02, 65.83%), followed by linoleic (16.42, 20.73, 21.30, 25.38, 14.17%) and palmitic (11.69, 14.27, 12.17, 16.22, 12.28) acids in QF, QS, QP, QC and QB species, respectively. The tocopherol content was high in the range of 31.83-45.25mgkg-1, and γ-tocopherol constituted 67-78% of total tocopherols. Only an effect of the location on γ-tocopherol content in QB was observed. The present results show the potential of different species of acorn to be used as agricultural and food resources and that geographical location plays a secondary role.

Ontogenetic changes in crown architecture and leaf arrangement: effects on light capture efficiency in three tree species differing in leaf longevity

AbstractPronounced strategy shifts along ontogeny have been observed in several tree species, mainly because of the trend to maximize growth during the seedling stage, which constitutes the most vulnerable part of the tree's life cycle. Our aim here was to analyze the ontogenetic changes in crown characteristics and light capture patterns in three Quercus species: the evergreens Quercus ilex and Quercus suber and the deciduous Quercus faginea co‐occurring in a Mediterranean open woodland. The seedlings were distributed in the large clearings among the adults and received full sunlight. We constructed three‐dimensional models of the aerial parts of seedlings and mature trees of the three species, using the YplantQMC program. Large differences between growth stages were observed for all variables. The seedlings exhibited smaller branch sizes and crown densities than those observed in the adult trees. Leaf angles to horizontal also tended to increase during ontogeny, whereas leaf dispersion and the observed distances between leaves tended to decrease. The amount of photosynthetic radiation absorbed per unit leaf area throughout the growing season was lower in adult specimens than in young specimens. Changes in absorption efficiency during ontogeny were more intense for the species with longer leaf life span at maturity. We conclude that more intense ontogenetic shifts in species with longer leaf life span reflect the priority change from the maximization of short‐term productivity at the seedling stage to maximizing leaf longevity during the adult stage.

Qual o significado de algumas marcas incisas no reverso dos suportes de madeira de pinturas antigas?

Algumas marcas incisas, de caracter tosco e caracterizadas por linhas a direito, entrecruzadas ou paralelas, incisas no reverso dos suportes de madeira de pinturas antigas de coleccoes portuguesas, de que se apresenta o respectivo levantamento bibliografico, tem sido relacionadas com o fabrico ou a qualidade dos paineis, mas o facto de essas marcas nao prosseguirem entre as tabuas de um mesmo suporte mostra que sao anteriores a construcao dos paineis. Como parece surgirem apenas sobre carvalho do Baltico e sobre superficies nao tratadas resultantes de debito por clivagem, deverao estar relacionadas com o abate das arvores e obtencao da madeira ou o seu comercio, como propoem J.-A. Glatigny e M. Rief, e nao sao marcas relacionadas com o fabrico dos paineis como tem sido consideradas.

Does the host tree exert any influence on the aromatic composition of the black truffle (Tuber melanosporum)?

AbstractThis work examines whether the host tree influences the aroma of Tuber melanosporum truffles. Samples were gathered in the same place (Teruel, Spain) and on the same day from four host trees: hazel, Portuguese oak, kermes oak and holm oak. The truffles were subjected to sensory and chemical analysis. The sensory analysis comprised two stages. The first was based on a sorting task while the second consisted of a descriptive analysis of the samples selected from the first test. The chemical analysis examined the volatile compounds having the greatest influence on the aroma of Tuber melanosporum by means of headspace‐solid phase microextraction followed by analysis by gas chromatography mass spectrometry (HS‐SPME‐GC‐MS). The sensory tests demonstrated that truffles gathered from the Portuguese oak had a more intense aroma than the rest of the samples, and significantly more than the holm oak truffles. The same pattern occurred for the animal descriptor which was considerably more intense in Portuguese oak truffles and significantly higher than that of holm oak truffles. Chemically, these differences can be explained by the levels of isoamyl alcohol and 3‐ethyl‐5‐methylphenol which were significantly greater in the Portuguese oak than the holm oak samples. Copyright © 2016 John Wiley & Sons, Ltd.

Distribución de plantas vasculares a escala local. Taxones con mayor ocupación geográfica en Ambite y Utande (La Alcarria Occidental)

The method for performing Floral Cover Indices (FCI), presented in a previous article, is applied to two 100 km 2 U.T.M. grid cells (30TVK86, Ambite and 30TWL02,Utande). They are located in different sectors of the natural region of Western “La Alcarria”. The goal is to know and compare distributions of presence and abundance of vascular plants at local scale. Geographical factors affecting cover of the flora is widely exposed. Analysis method and chorological maps drawing with four spatial levels (1, 4, 25 and 100 km 2 ) are presented. Results of the twelve taxa with the highest FCI in the set of two grid cells and phytogeographical interpretations are shown: Genista scorpius, Quercus ilex subsp. ballota, Thymus vulgaris, Helianthemum cinereum subsp. rotundifolium, Brachypodium retusum, Thymus zygis subsp. sylvestris, Lavandula latifolia, Dactylis hispanica, Rosmarinus officinalis, Koeleria vallesiana, Quercus faginea y Salvia lavandulifolia .

Age trends and within-site effects in wood density and radial growth in Quercus faginea mature trees

Aim of the study: This paper aims to valorize the wood of Quercus faginea Lam. for high quality end uses (e.g. furniture) by studying growth and quality properties using mature trees. Age trends in tree-ring width and wood density are shown and the main factors responsible for variations in tree-ring width and wood density within and between trees are investigated. Area of study: The study site is in the center of Portugal within the natural species distribution area.Material and methods: Radial samples from ten mature trees were collected at 6 heights (from base to 9.7 m) and prepared for X-ray microdensity.Main results: Wood density showed high values, ranging from 0.868 g/cm3 to 0.957 g/cm3. Wood density decreased from pith to bark and with stem height. Cambial age showed a linear relationship with wood density and most of the variation in wood is explained by age. Intra-ring and axial within-tree homogeneity was good.Research highlights: Mature trees of Q. faginea showed high wood density and a high potential for high quality end uses, comparable to other oaks. Wood density is influenced by cambial age and tree-ring width. Wood quality may be improved by tree growth rates adjustment e.g. through an adequate tree stand density (e.g. thinning operations).

Disentangling the effect of competition, CO2 and climate on intrinsic water‐use efficiency and tree growth

Summary Climate change scenarios forecast rising temperatures for the Mediterranean region, which could enhance the vulnerability to drought stress in forest ecosystems. The long‐term effects of climate forcing on tree performance can be, however, modulated by other environmental factors, such as competition and rising atmospheric CO2 concentrations. We assessed the concomitant effect of competition, climate and CO2 concentrations on the tree‐ring δ13C‐derived intrinsic water‐use efficiency (iWUE) and basal area increments (BAI) of species with different drought tolerance: two Mediterranean deciduous species (Quercus faginea Lam. and Quercus pyrenaica Willd.) and one conifer (Pinus sylvestris L.). Additionally, given that competition may be managed to mitigate the effect of increasing drought stress, we further examined the influence of this variable on iWUE and growth using data compiled from the literature, providing the first review on the response of iWUE to competition. Competition had no significant effect on iWUE in any of the three species studied, whereas, as expected, growth rates were significantly higher under low‐competition levels. This was consistent with the literature review, which showed that shifts in iWUE with competition changes are rare; supporting the hypothesis that leaf‐level gas exchange tends to be a homeostatic trait. In the long term, the three species exhibited a significant increasing trend in iWUE due to the combined effect of increased CO2 concentration, climate and age. Growth, however, was mostly affected by competition and climate and in most cases was not enhanced as a result of the increase in iWUE. Synthesis. Regardless of their functional response to drought, trees respond to reduced competition through the structural shifts such as increased radial growth rather than leaf‐level gas exchange adjustments. CO2 and climate are, therefore, the main drivers of iWUE variability, rather than competition. Thus, if temperature‐induced drought becomes limiting, reducing competition for resources may not offset the detrimental effect of increasing drought stress on tree physiology and growth decline may occur without a CO2 fertilization effect.

Simulating the stabilization effect of soil bioengineering interventions in Mediterranean environments using limit equilibrium stability models and combinations of plant species

One of the critical problems in projecting soil bioengineering interventions is the difficulty in developing precise calculations of the evolution of the structures and the type and combination of vegetation plantations that are planned for the particular site and problem. This is mainly due to the uncertainties in the plant development in each type of soil, the long and short term weather patterns and other edapho-climatic factors that determine limited calculation possibilities causing considerable degrees of uncertainty. This leads to a reduced level of reliability of bioengineering projects in terms of pre-determined factors of safety. In Mediterranean conditions this problem is even stronger due to the high seasonal and year-to-year climatic variability, and high degree of uncertainty in the vegetation installment and growth patterns.To evaluate the comparative short and long term (up to 20 years) efficacy of the most used slope stabilization techniques, common calculation models were used to assess the factor of safety of those techniques. SLIP4EX was used to evaluate the factor of safety, while the normal Coulomb model was used to assess the resistance to sliding and overturning. Considering the average Mediterranean climatic conditions, the considered environmental conditions were the least favorable, in order to assess the reliability of the “worst case scenario”. Two common tree species in the western Mediterranean region (Pinus halepensis and Quercus faginea) were selected for the simulation and three common soil types were considered (stony clay, loose sandstone and sandy marl).The results of the simulations for different types of substrates, plant combinations and designs, show that, according to the modeling approaches, the use of soil bioengineering techniques, present a reliable effectiveness, confirmed by the experience gathered in interventions in Mediterranean sites with similar edapho-climatic conditions.Additionally, because bioengineering is about the factor of safety of the target vegetation after the decay of the combined structure, the efficiency as a slope support structure of a vegetated log cribwall was compared with the expected developed vegetation. It was concluded that an adequate development of the vegetation ensures all safety requirements even in the worst considered scenarios.Our results also illustrate that there is a generalized lack of data on the geotechnical characteristics of the Mediterranean vegetation, which is particularly critical in a geo-ecological context where bioengineering techniques face important limitations (very few species able of vegetative development of roots and shoots from live cuttings).

Earlywood vessel features in Quercus faginea: relationship between ring width and wood density at two sites in Portugal

Abstract: Wood anatomy holds relevant information for tree development and timber quality (e.g., wood density), which is important for the sustainability of the species. Quercus faginea Lam. (Portuguese or Lusitanian oak) is an autochthonous Mediterranean oak species characterized by a shrinking natural distribution area and use abandonment. We studied the variation of several wood properties and their relationships with the aim of determining and possibly increasing the wood economic value of this species. The anatomical features of earlywood vessels (area, number, frequency and proportion) were investigated in twenty Q. faginea trees sampled at two locations within the natural distribution of the species in Portugal. Moreover, we analyzed the variation of vessel features from pith to bark, the radial growth and the wood density to search for patterns and relationships among the analyzed parameters. Mean earlywood vessel area increased with cambial age up to 60-70 years and then leveled off. An inverse pattern was found for the number of vessels per ring beyond that age. Similar radial patterns of all vessel features were found at both sites, and no significant differences in earlywood vessel area were found between sites. The within-tree development of earlywood vessels was age-related, though not influenced by growth. Earlywood vessel features explained the variation of wood density, i.e., wood density of Q. faginea was strongly negatively correlated with both mean vessel area and proportion.

Interannual variability in competitive effects in mixed and monospecific forests of Mediterranean stone pine

The management of species composition and competition are two of the main adaptive options that forest managers propose to cope with the expected negative impacts of climate change on forest growth in the Mediterranean basin. Species mixture can improve the resistance and resilience of forest ecosystems to face up global change. However, it seems likely that global change will modify mixed stands dynamics. Thus, studying inter-tree relationships on an annual basis is key to understanding ecosystem dynamics in the region. The aim of this paper was to evaluate the effects of tree species composition and competition on Pinus pinea annual secondary growth in mixed vs. monospecific stands over a period of 15years with contrasting climatic conditions. We obtained basal area growth data from tree ring measurement on cores and cross section slices from 372 trees of P. pinea L., Juniperus thurifera L., Quercus ilex subsp. ballota (Desf.)) Samp. and Quercus faginea Lam., in the Spanish Northern plateau, approximately half of which were in monospecific stands and half in mixed stands. We analysed the effect of intra and interspecific competition on P. pinea secondary growth comparing the performance of several distance dependent competition indexes through linear mixed models. These competition indices were calculated for all trees within each plot for each year of study. The results showed competitive reduction and tree growth amelioration in mixed vs. monospecific stands of P. pinea indicating a spatial and temporal niche separation between species and size-symmetric effects for interspecific competition. Size-asymmetric results obtained for competition within pines indicated that the largest individuals obtain the majority of the contested resources suppressing the growth of their smaller pine neighbours. Intraspecific interactions were more negative than interspecific interactions. And we finally provide evidence of a growth enhancement in mixed vs. monospecific stands in water stressed years indicating that the promotion of mixtures in P. pinea stands is a powerful management tool to buffer the effects of climate change in the region.

Prior height, growth, and wood anatomy differently predispose to drought-induced dieback in two Mediterranean oak speciesk

Coexisting Mediterranean oaks are differently predisposed to heat- and drought-induced dieback as a function of height, prior growth, wood anatomy, and growth responsiveness to temperatures. To forecast post-dieback damage, the variability of species and individual traits must be considered. Forests are susceptible to drought-induced dieback. However, considerable variability in how drought translates into tree damage exists in coexisting species. This study aimed to assess if tree size, radial growth, and wood anatomy predisposed trees to drought damage, measured as defoliation and changes in non-structural carbohydrate (NSC) concentrations. We measured radial growth, wood anatomy, and post-drought NSC concentrations in highly defoliated and less defoliated holm oak (Quercus ilex) and Portuguese oak (Quercus faginea) trees co-occurring in a coppice stand. Highly defoliated trees showed a lower height than less defoliated individuals. In holm oak, a reduced previous growth and the formation of vessels with smaller lumen areas predisposed to drought damage, which suggests hydraulic deterioration. In Portuguese oak, most defoliated trees grew less in response to elevated growing season temperatures. Sapwood starch and NSC concentrations decrease in defoliated holm oaks. A height-dependent predisposition modulates the responses to drought-induced dieback in Mediterranean oak coppices. Coexisting oak species presented different predisposing factors to drought-induced dieback related to growth (holm oak) and its sensitivity to temperature (Portuguese oak). To forecast post-dieback damage, we should consider the variability of traits between and within species.

Integrating climate change criteria in reforestation projects using a hybrid decision-support system

The selection of appropriate species in a reforestation project has always been a complex decision-making problem in which, due mostly to government policies and other stakeholders, not only economic criteria but also other environmental issues interact. Climate change has not usually been taken into account in traditional reforestation decision-making strategies and management procedures. Moreover, there is a lack of agreement on the percentage of each one of the species in reforestation planning, which is usually calculated in a discretionary way. In this context, an effective multicriteria technique has been developed in order to improve the process of selecting species for reforestation in the Mediterranean region of Spain. A hybrid Delphi-AHP methodology is proposed, which includes a consistency analysis in order to reduce random choices. As a result, this technique provides an optimal percentage distribution of the appropriate species to be used in reforestation planning. The highest values of the weight given for each subcriteria corresponded to FR (fire forest response) and PR (pests and diseases risk), because of the increasing importance of the impact of climate change in the forest. However, CB (conservation of biodiversitiy) was in the third position in line with the aim of reforestation. Therefore, the most suitable species were Quercus faginea (19.75%) and Quercus ilex (19.35%), which offer a good balance between all the factors affecting the success and viability of reforestation.

Potential of oak tree-ring chronologies from Southern Portugal for climate reconstructions

The present work reports a first attempt to assemble long tree-ring chronologies from Portugal potentially useful for climate reconstructions. Three oak species (Quercus pyrenaica, Quercus faginea, and Quercus ilex) were sampled at three sites in southern Portugal to obtain tree-ring chronologies. The longest tree ring series covers 173 years extending back to 1840. Our tree-ring records show, depending on the site, moderate-to-high correlations with precipitation in different seasons (from r=0.40, p<0.01, to 0.81, p<0.001) and temporal stability in the growth/climate relationship for two sites. Calibration-verification trials confirm the reliability of climate/growth models for climatic reconstructions back to periods represented by tree-ring records from these two sites. Regional precipitation for Alentejo can be estimated for the following seasons: April through August (calibration r2=0.24); September, from previous year, to July (calibration r2=0.65). The results are a promising kick-off for Portuguese dendroclimatology, since they represent a significant breakthrough in the Mediterranean region, especially for Iberian Peninsula, where there is a considerable lack of dendroclimatic reconstructions. Further efforts to extend the tree-ring records back in time using subfossil material should be undertaken.

Epiphytic bryophytes of Quercus forests in Central and North inland Iberian Peninsula

Diversity patterns are governed by a complex network of interacting factors. Studies directed to disentangle the most important factors affecting diversity have frequently shown divergent results, which has encouraged a rewarding debate about the relative importance of each factor. Scale dependency has been identified as a direct cause of at least part of such divergences. However, studies with spatially-explicit measurements at different scales are costly and therefore they are relatively scarce despite their importance. Here, we present a database to disentangle the cross-scale variation in the importance of factors affecting the diversity of epiphytic bryophyte communities in Quercus dominated forests (Quercus ilex L., Quercus pyrenaica Willd. and Quercus faginea Lam.) in the North-western region of the Iberian Peninsula. We provide species-per-site abundance information with more than 9000 entries and an environmental table containing 20 in situ measured variables at three different scales (forest, stand, and sample). The database will help to advance the research of cross-scale effects of diversity patterns while at the same time providing valuable information on the distribution of a poorly known group of organisms.&nbsp

Stand competition determines how different tree species will cope with a warming climate.

Plant-plant interactions influence how forests cope with climate and contribute to modulate species response to future climate scenarios. We analysed the functional relationships between growth, climate and competition for Pinus sylvestris, Quercus pyrenaica and Quercus faginea to investigate how stand competition modifies forest sensitivity to climate and simulated how annual growth rates of these species with different drought tolerance would change throughout the 21st century. Dendroecological data from stands subjected to thinning were modelled using a novel multiplicative nonlinear approach to overcome biases related to the general assumption of a linear relationship between covariates and to better mimic the biological relationships involved. Growth always decreased exponentially with increasing competition, which explained more growth variability than climate in Q. faginea and P. sylvestris. The effect of precipitation was asymptotic in all cases, while the relationship between growth and temperature reached an optimum after which growth declined with warmer temperatures. Our growth projections indicate that the less drought-tolerant P. sylvestris would be more negatively affected by climate change than the studied sub-Mediterranean oaks. Q. faginea and P. sylvestris mean growth would decrease under all the climate change scenarios assessed. However, P. sylvestris growth would decline regardless of the competition level, whereas this decrease would be offset by reduced competition in Q. faginea. Conversely, Q. pyrenaica growth would remain similar to current rates, except for the warmest scenario. Our models shed light on the nature of the species-specific interaction between climate and competition and yield important implications for management. Assuming that individual growth is directly related to tree performance, trees under low competition would better withstand the warmer conditions predicted under climate change scenarios but in a variable manner depending on the species. Thinning following an exponential rule may be desirable to ensure long-term conservation of high-density Mediterranean woodlands, particularly in drought-limited sites.

A linkage disequilibrium perspective on the genetic mosaic of speciation in two hybridizing Mediterranean white oaks.

We analyzed the genetic mosaic of speciation in two hybridizing Mediterranean white oaks from the Iberian Peninsula (Quercus faginea Lamb. and Quercus pyrenaica Willd.). The two species show ecological divergence in flowering phenology, leaf morphology and composition, and in their basic or acidic soil preferences. Ninety expressed sequence tag-simple sequence repeats (EST-SSRs) and eight nuclear SSRs were genotyped in 96 trees from each species. Genotyping was designed in two steps. First, we used 69 markers evenly distributed over the 12 linkage groups (LGs) of the oak linkage map to confirm the species genetic identity of the sampled genotypes, and searched for differentiation outliers. Then, we genotyped 29 additional markers from the chromosome bins containing the outliers and repeated the multilocus scans. We found one or two additional outliers within four saturated bins, thus confirming that outliers are organized into clusters. Linkage disequilibrium (LD) was extensive; even for loosely linked and for independent markers. Consequently, score tests for association between two-marker haplotypes and the 'species trait' showed a broad genomic divergence, although substantial variation across the genome and within LGs was also observed. We discuss the influence of several confounding effects on neutrality tests and review the evolutionary processes leading to extensive LD. Finally, we examine how LD analyses within regions that contain outlier clusters and quantitative trait loci can help to identify regions of divergence and/or genomic hitchhiking in the light of predictions from ecological speciation theory.

Influence of species interactions on transpiration of Mediterranean tree species during a summer drought

Recent research has shown that interactions between species with different functional traits can promote forest ecosystem processes. In the context of climate change, understanding whether species interactions in mixed-species ecosystems can improve the adaptation of these ecosystems to extreme climatic events is crucial to developing new management strategies. In this study, we investigated the impact of species interactions on the sap flux density of three Mediterranean tree species (Quercus faginea, Pinus nigra and Pinus sylvestris) during a summer drought. Measurements of foliar carbon isotopic composition (δ 13C) were also conducted on the same trees. The decline in transpiration during drought was the greatest for P. sylvestris and the least pronounced for Q. faginea. For P. nigra and Q. faginea, the decrease in transpiration as the drought progressed was lower when these species where interacting with another tree species, particularly with P. sylvestris. In contrast, the decrease for P. sylvestris was higher when this species was interacting with another species. Differing drought effects were consistent with the δ 13C values. We showed that the identity of the species present in the direct neighbourhood of a given tree can differentially influence water availability and water-use of these three co-existing Mediterranean tree species during a summer drought. Our findings suggest that species interactions play an important role in modulating the response of tree species to drought. Favouring tree species diversity in this region does not seem to be systematically beneficial in terms of soil water availability and water-use for all the interacting species.