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In Switzerland, chestnut forests cover about 27,100 ha, plus some 6800 ha of mixed stands. Due to environmental and historical reasons, most of these still existing forests are located in the Swiss Southern Alps, whereas in the northern parts of the country the chestnut cultivation and the related knowledge strongly regressed since the Little Ice Age period. Nevertheless, Switzerland still hosts valuable genetic resources of the sweet chestnut tree. The present genetic study bases on a nationwide inventory, identification and precise localisation of old and/or grafted chestnut trees for conservation purposes. The main objectives were: (1) to evaluate the genetic diversity and the genetic structure of Castanea sativa in Switzerland, and (2) to define a program of conservation including the proposal of a defined core collection. We genetically analysed a pre-selection of 962 accessions (out of 14,165 inventoried trees throughout Switzerland), profiling them with 24 microsatellites. We identified 675 different genotypes out of 962 accessions with a 29.8% of repetitiveness due to clonality. A structural analysis based on a Bayesian method allowed to identify two main clusters, one mostly related to the genetic group from southern Europe (Reconstructed Panmictic Population RPP1) and a second one (RPP2) which revealed to be independent and genetically different from other European groups of chestnut cultivars. The Swiss RPP2 represents a new genetic group, and consequently a complement to genetic resources of chestnut tree in Europe. Genetic analysis allowed defining a core collection of 46 genotypes, which should be used in priority for the Swiss conservation program.

International audience; Despite recent developments in molecular markers, most forest tree breeding programmes do not use them routinely. One way to integrate markers would be to use them for pedigree reconstruction after a simplified mating design through polymix or open-pollinated breeding. Thanks to the latest developments in the POPSIM simulator, various breeding strategies, including some based on paternity recovery, were evaluated with specified constraints on the level of diversity over breeding cycles. These simulations were carried out in two case studies: the French Pinus pinaster (Ait.) and the New Zealand Eucalyptus nitens (H. Dean & Maiden) Maiden breeding programmes. The Pinus pinaster case study produced lower genetic gain for the polymix breeding strategy with paternity recovery compared with double-pair mating or optimal-contribution strategies. However, the polymix breeding strategy could be of interest if the mating design is faster to complete. In the Eucalyptus nitens case study, pedigree recovery was shown to be a mandatory step to controlling the erosion of diversity over breeding cycles. In both cases, the strategies based on pedigree reconstruction were applicable with a limited level of genotyping. Finally, these simulations allow some general recommendations to be drawn to help breeders when designing a strategy for forest tree breeding.; Dans la plupart des programmes d’amélioration forestiers, les marqueurs moléculaires ne sont pas utilisés en routine malgré les développements récents en génomique. Une des possibilités d’intégration des marqueurs serait de les utiliser pour reconstituer les pedigrees après des croisements simplifiés de type polycross ou pollinisation libre. Grâce aux derniers développements du simulateur POPSIM, différentes stratégies d’amélioration, dont certaines incluant une recherche de paternité, ont été évaluées avec des contraintes spécifiques relatives au niveau de diversité au cours des cycles de sélection. Ces simulations ont été menées pour deux cas d’étude : les programmes d’amélioration de Pinus pinaster (Ait.) en France et d’Eucalyptus nitens (H. Deane & Maiden) Maiden en Nouvelle-Zélande. Le cas d’étude Pinus pinaster révèle un gain génétique moindre pour la stratégie de croisements polycross avec recherche de paternité en comparaison aux stratégies de croisements double-paire ou de contributions optimales. Néanmoins, la stratégie de croisements polycross pourrait être intéressante si elle permet une réduction de la durée des cycles de sélection. Pour le cas d’étude Eucalyptus nitens, la reconstitution de pedigree est une étape obligatoire pour contrôler l’érosion de la diversité au cours des cycles de sélection. Dans les deux cas, les stratégies basées sur la reconstitution de pedigree peuvent être mises en œuvre en génotypant un nombre limité d’individus. Finalement, ces simulations ont permis de formuler des recommandations générales afin d’aider les sélectionneurs à élaborer des stratégies d’amélioration chez les arbres forestiers.

Cordia africana is a highly-valued timber tree species that is quite dominant in riparian habitat, native to several countries in Africa and the Arabian Peninsula. It is mainly propagated by pyrene, which is found to be attacked by an unidentified seed borer insect. The main objective of this study was to investigate the cause of pyrene deterioration of C. africana in Ethiopia. Drupes were collected from nine study locations. Paradecatoma bannensis has emerged from de-pulped drupes. The larval and adult stages of this wasp were also found inside crushed drupes. Of the pyrenes having no exit hole, 20.8% were noticed with the presence of dead and alive larvae and adults of the insect when examined after crushing. Percentages of infestation varied between the sites (nil to 17.5%). The float-and-sink test method that used to sort out infested against sound pyrenes were found not applicable in our trial for the reason that both pyrenes were found sunk. This wasp was reported for the first time on the pyrenes/drupes of C. africana in Ethiopia. Therefore, future studies need to address the biology and distribution of P. bannensis on C. africana in order to provide management options.

International audience; The rapid rate of deforestation in Côte d’Ivoire has led to loss of plant species diversity and also threatens some commercial tree species with extinction. Some reforestation and afforestation has been completed. However, for some species, the numbers of surviving transplants has declined. Hence, it is necessary to develop properly adapted and resilient genotypes that can effectively support the programs of forest restoration. In this context we evaluated the effects of the provenances of seeds and of various treatments on the germination rates and on plant growth of four commercial trees species (Pycnanthus angolensis, Terminalia superba, Mansonia altissima and Pterygota macrocarpa). We analyzed these parameters for seeds of three provenances (Daloa, Akoupé and Daoukro) of four species and for thirty plants aged 6 months per provenance. Time to begin germination and time to reach maximum germination were similar among species, and were not influenced by either treatment or provenance. Untreated seeds and those soaked for 24 and 48 h in water at room temperature yielded the highest germination rates, irrespective of species or provenance. The one exception was P. angolensis, for which no germination was recorded. Within species, some provenances produced higher germination percentages than did others. No clear relationship was computed between the germination rate and the morphometric characteristics of the seeds which varied significantly between provenances. Plant growth and morphological variability also depended greatly on provenance. Genetic factors might be implicated, therefore provenance trials should be undertaken and evaluated. Furthermore, molecular analysis should be undertaken to confirm the implications of genetic factors and allow for genetic selection.

In response to various stimuli, plants acquire resistance against pests and/or pathogens. Such acquired or induced resistance allows plants to rapidly adapt to their environment. Spraying the bark of mature Norway spruce (Picea abies) trees with the phytohormone methyl jasmonate (MeJA) enhances resistance to tree‐killing bark beetles and their associated phytopathogenic fungi. Analysis of spruce chemical defenses and beetle colonization success suggests that MeJA treatment both directly induces immune responses and primes inducible defenses for a faster and stronger response to subsequent beetle attack. We used metabolite and transcriptome profiling to explore the mechanisms underlying MeJA‐induced resistance in Norway spruce. We demonstrated that MeJA treatment caused substantial changes in the bark transcriptional response to a triggering stress (mechanical wounding). Profiling of mRNA expression showed a suite of spruce inducible defenses are primed following MeJA treatment. Although monoterpenes and diterpene resin acids increased more rapidly after wounding in MeJA‐treated than control bark, expression of their biosynthesis genes did not. We suggest that priming of inducible defenses is part of a complex mixture of defense responses that underpins the increased resistance against bark beetle colonization observed in Norway spruce. This study provides the most detailed insights yet into the mechanisms underlying induced resistance in a long‐lived gymnosperm.

Chestnut species have large ecological, cultural and economic importance. Developing genetic markers for these species is of interest for conservation, breeding or evolutionary studies. We designed 192 primer pairs targeting microsatellites detected in the Castanea mollissima reference genome and tested them on C. sativa and C. crenata. We PCR amplified 3 × 50 microsatellites in 106 chestnut trees. Microhaplotype calling accounting for all polymorphisms resulted in a total of 98 high confidence polymorphic markers. Mean number of haplotypes per marker was 9.05 with respectively 71%, 12% and 16% of the variation corresponding to microsatellite variation in repeats number, SNP within the repeat motif and SNP or INDEL in the flanking sequence. Overall, the simple protocol described here generated a powerful multilocus genetic dataset for chestnut genetic investigations.

Trees outside forests can play an important role in production and conservation and increase connectivity within agricultural landscapes. However, farmers' perceptions of the trees and the values they place on them will determine the extent to which they will do so in the future. In a case study in Costa Rica, Northwest of the Central Volcanic Talamanca Biological Corridor, we conducted 42 semi-structured interviews with farmers and other key informants. Results show that farmers maintain trees on their land and attribute to them diverse values (technical, economic, ecological, social, cultural, aesthetic, and heritage). Farmers reported limitations to the maintenance of trees (lack of financial capital, labour, land area, technical assistance, and adapted species). In addition to potentially unsustainable Payments for Environmental Services, there is scope for more collaborative approaches to conserving the trees built on existing farmer practices.

In Central Africa, most cacao is still cultivated in low-input agroforests where cacao associated trees are traditionally valued by farmers. These systems are sustainable on the long run, support biodiversity conservation and carbon storage. Yet, little knowledge exists on the contribution of tree community management to explain such results. In Central Cameroon, we investigated cacao agroforest associated tree community contributions to the long-term (i) maintenance of tree species encountering a conservation issue and (ii) carbon storage. We further simulated the simplification of these systems by checking for the effect of tree density decrease on community functional groups or traits. Finally, we linked farmers' use of associated trees to their functional features and conservation status. Cacao agroforestry systems were able to combine high levels of species richness with long-term conservation abilities and carbon storage. Simplification emphasized consistent shifts of functional traits/groups that will change the way they function and alter the existing balances between different associated tree uses. Since traditional agroforests are now foreseen as providers of timber/non-timber forest products, our study argues that this paradigm change in such low-input systems - if carried improperly - is likely to impair the provision of the services they currently provide as well as their sustainability.

In tropical forest, landscape fragmentation and the consequent degradation of disturbed forests increase the incidence of light and dry hot winds, causing a disturbance on natural regeneration. Under these conditions, lianas (woody vines) development is stimulated instead of other species, which are more suited to mature forest and under less influence of the edge effect. For this, lianas colonization is an important variable for assessing the disturbance level of a forest. In this context, it becomes important to understand the nature of the competitive relationships between hyper-abundant lianas and ring growth of the host trees. Here, we selected trees with occupation or absence of lianas from two tropical species – Pinus caribaea var. hondurensis (Caribbean pine) and Tectona grandis (teak) – localized in a semideciduous forest fragment in southeastern Brazil, aiming to compare growth, climatic response, anatomy (vessels and intra-annual density fluctuations), wood density and carbon, by tree-ring analysis. The results showed that the lianas caused a change in tree-ring anatomy of host trees in last 10 years, mainly. We observed that trees occupied by lianas had a decrease the radial growth and carbon in the two species, an increase of the vessels size in teak and a decrease of the IADF frequency in Caribbean pine. In teak, the climate-tree relationship indicated that trees with lianas had lower response to rainfall and higher response to temperature in the summer (rainy and hottest period); in Caribbean pine, we observed that trees with lianas had a 2-month delay in the radial growth response to rainfall in the dry season. In the teak group, we observed that host trees had higher wood density values than liana-free tree in the outer rings, and the opposite was showed for pine. These findings show that tree-ring growth of host trees are a strong bioindicator of forest disturbance caused by aggressive colonization of lianas. We believe that these methods are applicable to future studies relating to the effects of habitat fragmentation and forest degradation on biodiversity and ecosystem services, particularly in the context of global climate change. (Resume d'auteur)

High-throughput sequencing (HTS), combined with bioinformatics forde novodiscovery and assembly of plant virus or viroid genome reads, has promoted the discovery of abundant novel DNA and RNA viruses and viroids. However, the elucidation of a viral population in a single plant is rarely reported. In five birch trees of German and Finnish origin exhibiting symptoms of birch leaf-roll disease (BRLD), we identified in total five viruses, among which three are novel. The number of identified virus variants in each transcriptome ranged from one to five. The novel species are genetically - fully or partially - characterized, they belong to the generaCarlavirus, IdaeovirusandCapillovirusand they are tentatively namedbirch carlavirus,birch idaeovirus, andbirch capillovirus, respectively. The only virus systematically detected by HTS in symptomatic trees affected by the BRLD was the recently discovered birch leafroll-associated virus. The role of the new carlavirus in BLRD etiology seems at best weak, as it was detected only in one of three symptomatic trees. Continuing studies have to clarify the impact of the carlavirus to the BLRD. The role of theCapillovirusand theIdaeoviruswithin the BLRD complex and whether they influence plant vitality need to be investigated. Our study reveals the viral population in single birch trees and provides a comprehensive overview for the diversities of the viral communities they harbor.

Les espèces du genre Khaya procurent l’un des bois les plus prisés du continent africain. Elles sont commercialisées sous l’appellation « acajou d’Afrique » depuis environ deux siècles. En Afrique continentale, on reconnaît actuellement quatre espèces morphologiquement proches : Khaya anthotheca, K. grandifoliola, K. ivorensis et K. senegalensis. Le nombre de taxons du genre Khaya a varié au cours du temps et la délimitation de ces taxons n’est pas sans avoir des implications sur les stratégies de conservation et de gestion durable des espèces. L’objectif du travail présenté ici est de s’assurer de la délimitation de ces espèces sur la base d’un bilan des connaissances actuelles en taxonomie, génétique, écologie et chimiotaxonomie. Les données disponibles ne permettent pas toujours de séparer sans ambiguïté les quatre acajous d’Afrique continentale. Elles permettent toutefois d’avancer que K. ivorensis, K. grandifoliola et K. senegalensis seraient des espèces à part entière mais dont les limites taxonomiques doivent encore être précisées. Khaya nyasica serait également une espèce qui devrait être séparée de K. anthotheca. Au sein de cette dernière, plusieurs chémotypes ont été identifiés, ce qui suggère que ce taxon pourrait recouvrir un ensemble plus complexe d’au moins deux autres taxons dont le rang spécifique ou sous-spécifique reste à préciser. Des recherches morphométriques, génétiques et écologiques doivent être développées afin de clarifier le statut systématique et l’histoire évolutive de ces divers taxons, en vue de formuler des recommandations appropriées pour la gestion durable des acajous d’Afrique., Species of the genus Khaya produce some of Africa’s most valuable timber. For two centuries, these species have all been traded as “African mahogany”. On the African continent, four different but morphologically similar species are now recognised: Khaya anthotheca, K. grandifoliola, K. ivorensis and K. senegalensis. The number of taxa included in the genus Khaya has varied over time, and the way these taxa are distinguished has implications for the development of sustainable management strategies for the different species. The aim of the study described in this article was to make sure that these species are distinguished on the basis of up-to-date knowledge on taxonomy, genetics, ecology and chemotaxonomy. Although the data available do not always suffice to clearly distinguish between the four mahogany species on the African continent, they do indicate that K. ivorensis, K. grandifoliola and K. senegalensis are probably distinct species whose taxonomic limits are yet to be clearly defined. It also seems that Khaya nyasica should be distinguished from K. anthotheca. Several chemotypes have been identified in the latter, suggesting that it could in fact cover a more complex group including at least two other taxa whose rank as species or sub-species is yet to be determined. Morphometric, genetic and ecological studies need to be developed to clarify the systemic status and evolutionary history of these different taxa, in order to formulate appropriate recommendations for the sustainable management of African mahoganies.

Tall trees and vertical forest structure are associated with increased productivity, biomass and wildlife habitat quality. While climate has been widely hypothesized to control forest structure at broad scales, other variables could be key at fine scales, and are associated with forest management. In this study we identify the environmental conditions (climate, topography, soils) associated with increased tree height across spatial scales using airborne Light Detection and Ranging (LiDAR) data to measure canopy height. The study was conducted over a large elevational gradient from 200 to 3000 m in the Sierra Nevada Mountains (CA, USA) spanning sparse oak woodlands to closed canopy conifer forests. We developed Generalized Boosted Models (GBMs) of forest height, ranking predictor variable importance against Maximum Canopy Height (CHMax) at six spatial scales (25, 50, 100, 250, 500, 1000 m). In our study area, climate variables such as the climatic water deficit and mean annual precipitation were more strongly correlated with CHmax (18–52% relative importance) than soil and topographic variables, and models at intermediate (50–500 m) scales explained the most variance in CHMax (R2 0.77–0.83). Certain soil variables such as soil bulk density and pH, as well as topographic variables such as the topographic wetness index, slope curvature and potential solar radiation, showed consistent, strong associations with canopy structure across the gradient, but these relationships were scale dependent. Topography played a greater role in predicting forest structure at fine spatial scales, while climate variables dominated our models, particularly at coarse scales. Our results indicate that multiple abiotic factors are associated with increased maximum tree height; climatic water balance is most strongly associated with this component of forest structure but varies across all spatial scales examined (6.9–54.8% relative importance), while variables related to topography also explain variance in tree height across the elevational gradient, particularly at finer spatial scales (37.15%, 20.26% relative importance at 25, 50 m scales respectively).

International audience; Aim: Understanding the drivers of community diversity and composition is a major question in ecology, which is of particular significance for the conservation of narrowly distributed taxa facing habitat alteration. In this study, we examined three ecological processes (environmental and biotic filtering, and dispersal limitation) hypothesized to drive community assembly in the island biodiversity hotspot of New Caledonia, and whether the relative importance of these processes changes along environmental gradients. Methods: First, we assessed environmental filtering by stacking binary presence/absence species distribution models generated for 678 tree species from c. 40,000 occurrences. Second, we acknowledged the influence of dispersal limitation by applying a buffer around each occurrence. Third, we modelled a local hierarchy of performances by ranking species in decreasing order of their predicted habitat suitability, up to the predicted local species richness. Predictions of stacked species distribution models (S-SDMs) accounting for different combinations of the filtering processes were compared with the composition of 12 forest plots. Results The three filters appear to be important driving forces. Accounting for environmental filtering provided fairly accurate assemblage predictions but species richness was overestimated. Considering dispersal limitation increased assemblage specificity (the proportion of correctly predicted absences) while considering differences in local performances increased assemblage sensitivity (the proportion of correctly predicted presences). The predictive ability of all S-SDMs decreased with elevation, which suggests that unpredictable stochastic processes influenced biodiversity dynamics in more productive mountain habitats. Main conclusions: New Caledonian tree communities appear to be similar to those of other tropical regions in their structuring processes (important role of dispersal and biotic filtering, increasing role of neutral processes with productivity). Our findings stress the potential of using S-SDMs to understand and predict current and future biodiversity patterns.

This study highlighted the consistency of a functional scheme integrating leaf, stem and root traits, biomass allocation and stem anatomy for 15 tropical tree species at the seedling stage. This functional scheme was shaped by the trade-offs for resource use and the hydraulics of the plants and was found to determine seedling growth. Functional traits determine plant functioning, performance and response to the environment and define species functional strategy. The functional strategy of 15 African tree species was assessed by (1) highlighting the structure of traits covariance and the underlying functional trade-offs, (2) inferring a whole-plant functional scheme and (3) testing the correlation of the functional scheme with plant performance for two early developmental stages (seedlings and saplings). We selected 10 seedlings for each of the 15 species studied from a nursery in south-eastern Cameroon and measured 18 functional traits, including leaf, stem and root traits, biomass allocation and stem anatomy. We assessed the height and diameter growth of the seedlings and the DBH growth and survival for the saplings of nearby plantations. Multivariate analyses highlighted the covariations among the functional traits of the leaf/stem/root, biomass allocation ratios and stem anatomy. The major trait covariation axes were driven by two trade-offs, first between resource acquisition and conservation and second between hydraulic safety and efficiency. The axes were integrated into a Bayesian network inferring a functional scheme at the whole-plant scale, which was found to predict the growth of the seedlings but not the performance of the saplings. The functional strategies of the seedlings were determined by an integrated whole-plant scheme reflecting the trade-offs for resource use and plant hydraulics. The scheme predicted the growth of the seedlings through mechanistic pathways from the wood stem to all the plant traits, but it appeared to shift at the stage of the saplings.

Background and Aims Root anchorage function is crucial for tree survival as most trees are exposed to recurrent wind throughout their lifespan. Trees exhibit a large variability of root system architecture (RSA) due genetic and environmental factors. This study aims to understand the links between RSA and tree stability. Methods A 3D biomechanical model was used to simulate tree overturning. To capture the variability of sinker RSA, fourteen virtual root patterns were created from an ensemble average of measured Pinus pinaster root systems. Root virtual patterns and tree-pulling simulations were verified against experimental data. Results The model predicts realistic tree anchorage strength, root stress, and failure patterns. Only a few root components contribute significantly to anchorage strength. The taproot contributes the most to anchorage rigidity, representing 61 % of the anchorage strength. The windward roots failure drives ultimate anchorage failure, representing 25 % of the anchorage strength. Simulations show that root secondary thickening induces higher anchorage rigidity and increases anchorage strength by 58 %. Conclusions This innovative approach appears promising for describing tree stability and its acclimation to external constraints.

Key message This review highlights some of the discoveries and applications made possible by “omics” technologies over the last 10 years and provides perspectives for pioneering research to increase our understanding of tree biology. Context A decade after the first forest tree genome sequence was released into the public domain, the rapidly evolving genomics and bioinformatics toolbox has advanced our understanding of the structure, functioning, and evolution of forest tree genomes. Aims and methods This review highlights some of the discoveries and applications that “omics” technologies have made possible for forest trees over the past 10 years. Results In this review, we start by our current understanding of genome evolution and intricacies of gene regulation for reproduction, development, and responses to biotic and abiotic stresses. We then skim over advances in interactome analysis and epigenomics, the knowledge of the extent of genetic variation within and between species, revealing micro- and macro-evolutionary processes and species history, together with the complex architecture of quantitative traits. We finally end with applications in genetic resource conservation and breeding. Conclusion The knowledge gained through the use of these technologies has a huge potential impact for adapting forests to the main challenges they will have to face: changing demand from ecosystem services with potentially conflicting strategies in terms of conservation and use, as well as climate changes and associated threats. Genomics will undoubtedly play a major role over the next decade and beyond, not only to further understand the mechanisms underlying adaptation and evolution but also to develop and implement innovative management and policy actions to preserve the adaptability of natural forests and intensively managed plantations.

Key message : In tree communities, tree size inequality reduces productivity and interacts with tree shade tolerance to modulate stand productivity, with a higher productivity in stands where shade-intolerant species dominate shade-tolerant species in size.[br/] Context Positive diversity–productivity relationships have been reported in different plant communities, including tree communities. These effects may be strongly related to both structural diversity and functional diversity, but also to their interactions if there is a non-random distribution of species functional characteristics among canopy layers.[br/] Aims We explore the relative effects on forest productivity of tree species diversity, tree size inequality, and species shade tolerance diversity, as well as the effect of the distribution of tree shade tolerance in the canopy.[br/] Methods We used 11,054 mixed-species forest plots from the French Forest Inventory (IGN) distributed throughout France (2006–2011). We analyzed the effects of species richness, shade tolerance diversity, and height inequality on forest plot productivity, represented by basal area annual increment over a period of 5 years, while controlling for first-order structure characteristics (basal area and quadratic mean diameter) and environmental factors (soil water budget and sum of growing degree days). Using the covariance between tree height and shade tolerance in mixed species canopies, we also explored the effect of the distribution of species’ shade tolerance among canopy layers[br/] Results The results showed a positive effect of species richness (effect size, 0.02) and a negative effect of height inequality (− 0.05) on mixed-forest productivity. We also showed that a negative covariance between shade tolerance and height (e.g., higher proportion of shade-tolerant species in lower height classes) increased productivity (0.01). Shade tolerance diversity did not affect productivity.[br/] Conclusion In tree communities, as shown previously in monospecific forest stands, tree size inequality reduces productivity. This effect is modulated by the distribution of shade tolerance among canopy layers. Previous studies on species diversity effect have generally overlooked the importance of the size structure and the size hierarchy of functional characteristics. These effects are, however, crucial and deserve to be explored in greater detail.

International audience; In forest tree genetic improvement, multi-trait genomic selection (GS) may have advantages in improving the accuracy of the genotype estimation and shortening selection cycles. For the breeding of Eucalyptus robusta, one of the most exotic planted species in Madagascar, volume at 49months (V49), total lignin (TL), and holo-cellulose (Holo) were considered. For GS, 2919 single nucleotide polymorphisms (SNP) were used with the genomic best linear unbiased predictor (GBLUP) method, which was as efficient as the reproducing kernel Hilbert space (RKHS) and elastic net methods (EN), but more adapted to multi-trait modeling. The efficiency of individual I model, including the genomic data, was much higher than the provenance effect P model. For example, with V49, mean goodness-of-fit was: r(I_Full)=0.79, r(P_Full)=0.37 for I and P, respectively. The prediction accuracies using the cross-validation procedure were lower for V49: r(I)=0.29 r(P)=0.28. The genetic gains resulting from the indexes associating (V49, TL) and (V49, Holo) were higher using I than for the P model; for V49, the relative genetic gain was 37 and 20%, respectively, with 5% of selection intensity. The single-trait approach was as efficient as the multi-trait approach given the weak correlations between V49 and TL or Holo. The I model also brings greater diversity: for V49 the number of provenances represented in a selected population was two and three with the P model, and 6 and 16 with the I model.

We present the first cross continental comparison of the flowering and fruiting phenology of tropical forests across Africa. Flowering events of 5,446 trees from 196 species across 12 sites, and fruiting events of 4,595 trees from 191 species, across 11 sites were monitored over periods of 6 to 29 years, and analysed to describe phenology at the continental level. To study phenology we used Fourier analysis to identify the dominant cycles of flowering and fruiting for each individual tree and we identified the time of year African trees bloom and bear fruit and their relationship to local seasonality. Reproductive strategies were diverse and no single regular cycle was found in >50% of individuals across all 12 sites. Additionally, we found annual flowering and fruiting cycles to be the most common. Sub-annual cycles were the next most common for flowering whereas supra-annual patterns were the next most common for fruiting. We also identify variation in different subsets of species, with species exhibiting mainly annual cycles most common in West and West-Central African tropical forests, while more species at sites in East-Central and Eastern African forests showed cycles ranging from sub-annual to supra-annual. Despite many trees showing strong seasonality, at most sites some flowering and fruiting occurred all year round. Environmental factors with annual cycles are likely to be important drivers of seasonal periodicity in trees across Africa, but proximate triggers are unlikely to be constant across the continent

Regional estimates of the effects of ozone pollution on forest growth depend on the availability of reliable injury functions that estimate a representative ecosystem response to ozone exposure. A number of such injury functions for forest tree species and forest functional types have recently been published and subsequently applied in terrestrial biosphere models to estimate regional or global effects of ozone on forest tree productivity and carbon storage in the living plant biomass. The resulting impacts estimated by these biosphere models show large uncertainty in the magnitude of ozone effects predicted. To understand the role that these injury functions play in determining the variability in estimated ozone impacts, we use the O-CN biosphere model to provide a standardised modelling framework. We test four published injury functions describing the leaf-level, photosynthetic response to ozone exposure (targeting the maximum carboxylation capacity of Rubisco (Vcmax) or net photosynthesis) in terms of their simulated whole-tree biomass responses against data from 23 ozone filtration/fumigation experiments conducted with young trees from European tree species at sites across Europe with a range of climatic conditions. Our results show that none of these previously published injury functions lead to simulated whole-tree biomass reductions in agreement with the observed dose–response relationships derived from these field experiments and instead lead to significant over- or underestimations of the ozone effect. By re-parameterising these photosynthetically based injury functions, we develop linear, plant-functional-type-specific dose–response relationships, which provide accurate simulations of the observed whole-tree biomass response across these 23 experiments.

Tree anchorage is a primary function for plant survival which may reach its limit under extreme conditions such as windstorms. To better understand the processes and influential factors underlying tree anchorage, we analyzed the mechanical effects of root morphology and the material properties of roots and soil on the tree-overturning process with the recently developed finite element model RootAnchor. The root system was represented by a simplified 3D root pattern derived from an ensemble average of seven measured root systems of 19-year-old Pinus pinaster grown in sandy spodosol. Soil properties were measured by direct shear tests. Taguchi orthogonal arrays were used to examine the sensitivity of the geometric and material factors of roots and soil to tree anchorage. Tree anchorage was characterized by anchorage strength TMc and anchorage stiffness K0. Using a small number of numerical experiments, the sensitivity analysis prioritized only two key factors contributing to tree anchorage among the 34 factors considered. The results showed root morphological traits that played a dominant role in the material properties of roots and soil in tree anchorage. Taproot depth, the dimensions of the Zone of Rapid Taper (ZRT) and basal diameter of the windward shallow roots were the key factors contributing to TMc (variations > 8%). The dimensions of the taproot, root and soil stiffness, and the basal diameter of the leeward shallow roots were the most active factors for K0 (variations > 10%). These results provide insight into simplified tree anchorage expressions for the prediction of wind-induced uprooting.

International audience; Methods to estimate xylem embolism resistance generally rely on hydraulic measurements, which can be far from straightforward. Recently, a pneumatic method based on air flow measurements of terminal branch ends was proposed to construct vulnerability curves by linking the amount of air extracted from a branch with the degree of embolism. We applied this novel technique for 10 temperate tree species, including six diffuse, two ring-porous and two gymnosperm species, and compared the pneumatic curves with hydraulic ones obtained from either the flow-centrifuge or the hydraulic-bench dehydration method. We found that the pneumatic method provides a good estimate of the degree of xylem embolism for all angiosperm species. The xylem pressure at 50% and 88% loss of hydraulic conductivity (i.e., Ψ50 and Ψ88) based on the methods applied showed a strongly significant correlation for all eight angiosperms. However, the pneumatic method showed significantly reduced Ψ50 values for the two conifers. Our findings suggest that the pneumatic method could provide a fast and accurate approach for angiosperms due to its convenience and feasibility, at least within the range of embolism resistances covered by our samples.

International audience; In forests, intraspecific genetic variation in trees can affect the entire ecosystem, which in turn depends on the different processes occurring through space and time in soil. We hypothesized that, in addition to the effect of the local site, tree genotype and season would have an effect on the properties and functions of the edaphic environment. We studied soils beneath different genotypes of Pinus pinaster Ait. (Atlantic, Mediterranean and African) in 45-year-old common gardens in spring and autumn. The pH, organic matter, nutrients and infrared spectroscopy, together with enzyme activities, were determined and used to evaluate the soil properties and biogeochemical functioning. In addition to strong site effects, tree genotype and seasonal effects were detected on soil properties and functions. Both were major controlling factors of microbially mediated functioning, especially processes related to the carbon (C) and nitrogen (N) cycles. In general, the soil environment beneath the Atlantic trees was different from that under the Mediterranean and African genotypes, with differences in raw infrared spectra and increased activities of enzymes involved in hemicellulose degradation and N mobilization. Regarding the season, the largest soil humidity (RH), electric conductivity (EC), and N and potassium (K) concentrations, coupled with the smallest phosphorus (P) concentration and C:N ratios, were detected in autumn. Degradation of C peaked in autumn, whereas P and N mobilization usually peaked in spring. Our results showed that, beyond local site effects, there were detectable effects of tree genotype and season in Mediterranean forest soils, which governed microbially mediated processes that might have relevant functional consequences at the ecosystem level.

International audience; Heartwood/sapwood profile and the tradeoff between trunk and crown increment in a natural forest: the case study of a tropical tree (Dicorynia guianensis Amsh., Fabaceae) Key message Sapwood area and the radial growth rate of the trunk follow the same pattern at breast height, with an initial increase and subsequent constant value, resulting from the increasing growth allocation toward the crown rather than tree decline. Heartwood area and heartwood volume in the trunk increase more rapidly after this shift occurs. Abstract Sapwood (SW) and heartwood (HW) are two functionally distinct classifications of wood in perennial stems for which quantities can vary greatly in tropical trees. Numerous positive correlations have been found between the radial growth rate (RGR) and SW quantity; however, variations in the SW/HW quantities have not been studied in light of the ontogenetic variation of RGR. Wood core sampling, intensive measurements of tree structure (number of branches, stem volumes), and radial growth monitoring were performed on an abundant and highly exploited tree species in French Guiana (Dicorynia guianensis) to investigate the relationship between RGR, SW/HW quantity, tree structure, and their variations on the course of a tree's ontogeny. SW area and RGR followed the same pattern of variation throughout tree development, both increasing first and reaching a steady state after 50 cm DBH (diameter at breast height). After this value, we observed a strong increase in both the HW area and HW volume increment, concomitant with a more rapid increase in crown volume. The stabilization of RGR for trees with DBH >50 cm was related not to a tree's decline but rather to an increasing wood allocation to the crown, confirming that RGR at breast height is a poor indicator of whole-tree growth for bigger individuals. We also confirmed that HW formation is an ontogenetic process managing SW quantity that is continuously and increasingly produced within the crown as the tree grows. This study highlights the effect of growth-mediated ontogenetic changes on the localization of water and carbohydrate storage within a tree, resulting from SW and HW dynamics throughout tree ontogeny.

Key message The position of trees in the canopy impacts xylem structure and its inter-annual variation. After canopy release, the increase in the hydraulic conductivity of growth rings was driven by an increase in radial growth in large trees, and by both an increase in radial growth and changes in xylem structure in saplings. Context Forest canopies are frequently subjected to disturbances that allow understory trees to access the upper canopy. The effect of canopy release on xylem anatomy has been assessed in juvenile trees and saplings, while the potential acclimation of larger trees remains poorly documented. Aims We estimated the potential hydraulic conductivity of growth rings in large understory trees compared to overstory trees, and evaluated the responses to canopy release in large trees and in saplings. Methods We recorded radial growth, wood density, and vessel structure in beech trees according to their position within the canopy and their size. Xylem traits were followed during 6 years after canopy release for large trees, and during 2 years for saplings. Vessel diameter and frequency as well as ring area were used to compute the potential annual ring hydraulic conductivity. Results Large understory trees displayed lower radial growth increments and lower potential annual ring hydraulic conductivity than overstory trees. After canopy release, potential annual ring hydraulic conductivity increased in large trees, due exclusively to increased radial growth without any change in specific hydraulic conductivity. It increased in saplings due to both increased radial growth and increased specific conductivity. Conclusion Tree size impacted xylem structure and resulted in plasticity of the potential hydraulic conductivity of the annual tree ring following canopy release.

Most temperate forest tree species will suffer important environmental changes as result of the climate change. Adaptiveness to local conditions could change at different sites in the future. In this context, the study of intra-specific variability is important to clarify the singularity of different local populations. Phenotypic differentiation between three beech provenances covering a wide latitudinal range (Spain/ES, Germany/DE and Sweden/SE), was studied in a greenhouse experiment. Non-target leaf metabolite profiles and ecophysiological response was analyzed in well-watered and water stressed seedlings. There was a provenance-specific pattern in the relative concentrations of some leaf metabolites regardless watering treatment. The DE and SE from the center and north of the distribution area of the species showed a clear differentiation from the ES provenance in the relative concentration of some metabolites. Thus the ES provenance from the south maintained larger relative concentration of some organic and amino acids (e.g. fumaric and succinic acids or valine and isoleucine), and in some secondary metabolites (e.g. kaempferol, caffeic and ferulic acids). The ecophysiological response to mild water stress was similar among the three provenances as a consequence of the moderate water stress applied to seedlings, although leaf N isotope composition (δ15N) and leaf CN ratio were higher and lower respectively in DE than in the other two provenances. This would suggest potential differences in the capacity to uptake and post-process nitrogen according to provenance. An important focus of the study was to address for the first time inter-provenance leaf metabolic diversity in beech from a non-targeted metabolic profiling approach that allowed differentiation of the three studied provenances. © 2017 Elsevier Masson SAS

1. Hybridization is a key evolutionary process with major consequences for conservation and speciation. However, sexual barriers interact with the local context to determine hybridization rates in a way that is still poorly explored. For instance, in the context of an expanding or introduced plant population, where a few individuals are isolated in populations dominated by heterospecific individuals, what is the hybridization potential? 2. To obtain baseline predictions on hybridization rate between two species differing in abundance and to evaluate the effect of pollen limitation, we first used a mean-field model. We then explored a spatially explicit individual-based mating model relying on pollen dispersal kernels to predict hybridization rates in a mixed-species stand, under different scenarios for (i) the strength of sexual barriers; (ii) the spatial distribution of individuals within the site; (iii) the variation in individual fecundity; and (iv) the magnitude, shape and asymmetry of pollen dispersal kernels. 3. Pollen limitation was shown to have the potential to greatly increase hybridization rates. Similarly, fine-scale variation in species composition can result in elevated hybridization rates compared to mean-field predictions, especially with strong sexual barriers. However, species clustering in combination with reduced pollen dispersal has the opposite effect, protecting from hybridization. 4. Synthesis. Our simulation results show that variation of the pollen pool composition at the scale of individuals or stigmas due to spatial configurations or pollen limitation can substantially modify hybridization rates. We explain this by the disproportionate effect of some pollen environments on average hybridization rates. This suggests thoroughly evaluating individual behaviour in terms of hybridization, especially for rare or patchy species.

Aim Mediterranean refugial areas are generally underrepresented in large-scale genetic surveys of forest trees. In the case of silver fir (Abies alba Mill.), this has led to divergent hypotheses about the exact location of glacial refugia and the trajectory of recolonization routes. Based on the comprehensive sampling of Apennine populations, we aimed to reconcile discrepancies about the number and location of refugia for silver fir in the Apennines and test alternative demographic scenarios developed from palaeobotanical and genetic data. Location Mediterranean Basin; the Apennines and surrounding areas. Methods 1167 individuals from 16 Apennine populations, extensively covering the species’ distribution along the Italian Peninsula, and eight populations from the Alps and Eastern Europe were genotyped at 16 nuclear and three chloroplast microsatellite markers. The geographical distribution of genetic variation was explored using Bayesian clustering and multivariate methods. Based on the inferred genetic structure, the demographic history of A. alba was assessed by the approximate Bayesian computation (ABC) analysis. Results Two unexpected characteristics of genetic structure emerged: a sharp genetic boundary in the central Apennines and a tight genetic connection between southern Apennine and Eastern European gene pools. Two Apennine areas, corresponding precisely with refugial areas hypothesized in most recent palaeobotanical syntheses, have high genetic diversity on a par with Eastern European populations. ABC analysis showed an ancient separation between Apennine and Eastern European gene pools followed by an admixture event that, mainly through directional gene flow via pollen, might have established the genetic similarity between southern Apennine and Eastern European populations. In addition, there was evidence that the central Apennines acted as a small-scale, isolated refugium during the Last Glacial Maximum. Main conclusions Silver fir rear edge populations have experienced a complex demographic history across several glacial-interglacial cycles, leading to unexpected genetic structure. Our study provides new insights into forest tree dynamics in the Mediterranean, showing the putative presence of multiple refugia for silver fir in the Apennines and a trans-Adriatic connection between silver fir populations in the southern Italy and the Balkans.

Tree height-diameter allometry, the link between tree height and trunk diameter, reflects the evolutionary response of a particular species’ allocation patterns to above and belowground resources. As a result, it differs among and within species due to both local adaptation and phenotypic plasticity. These phenotypic variations in tree height-diameter allometry determine tree productivity, resistance and resilience to climate variation and, ultimately, the success of plant material used in restoration projects. We tested the effect of climate change and population origin on the phenotypic variation of tree allometry in four pine species at an early stage of development (ca. 11 years old) based upon data originated from multi-site provenance tests and planted along a wide climatic range in south-western Europe. For a representative sample of populations from each species, we used already-developed species-specific height-diameter allometric models to assess changes in allometry between present and future climatic conditions. We found that Pinus halepensis and Pinus pinaster were the most plastic species, while Pinus sylvestris and Pinus nigra showed negligible plastic responses. In addition, our models stressed that pine tree height-diameter allometry will change and phenotypic variation could increase, except in P. sylvestris, under future environmental conditions. For some of the species, this might allow the selection of phenotypes better suited to novel climatic conditions. These foreseeable changes in tree height-diameter allometry (among and within-species) could entail eco-evolutionary effects on the early forest plantation dynamics. Therefore, restoration and reforestation plans should consider these effects, as they may interfere with production and/or environmental goals. © 2016, Springer Science+Business Media Dordrecht.

Key message [br/] We developed precise, consistent, generic, and robust biomass equations for seven aboveground tree components of sessile and pedunculate oaks. These equations can be used to accurately estimate carbon stocks and fluxes in and out of the forest. [br/] Context[br/] Large uncertainties still persist when using existing biomass equations for larger scale applications. [br/] Aims [br/] The objective of this study was to test two contrasting modeling approaches to obtain biomass estimates of various components (stem, stem wood, stem bark, crown, and three branch categories) for Quercus petraea and Quercus robur and to compare them in terms of predictive capacity, genericity, consistency, and robustness. [br/] Methods [br/] All models were calibrated on a total of 117 oak trees sampled over a wide range of sites and stands and further tested on an independent data set of 33 trees. The “empirical” approach consisted in declining a common allometric equation based on two variables (diameter at breast height and total height) into all its possible forms and selecting the final model on purely statistical performances; the “structural” method was based on the fitting of a priori dedicated model forms for each component to allow a clear interpretation of the model parameters. [br/] Results [br/] For the stem components, both approaches resulted in similar statistical performances despite difference in model forms and number of parameters. Although equally performant on the validation data set for the total crown, only the structural model gave satisfactory results when applied to the independent data set. Both approaches failed to accurately predict the branch fractions on the validation data set. [br/] Conclusion [br/] Using physically based model forms increased the robustness of the biomass equations.

Agroforestry systems in humid tropical areas are complex multispecies cropping systems whose value for farmers is often hard to assess. We present the findings of a participatory assessment that we applied to cocoa agroforestry systems. This assessment, adapted from the pebble distribution method, was used to quantify the value given by farmers to each species of their cocoa agroforestry system according to the attributed uses. A tree inventory in 50 cocoa agroforests was carried out in central Cameroon. Overall, 122 non-cocoa tree species were inventoried. The mean species richness was 23 species per plot and the mean Shannon index was 2.42, for a mean density of 180 non-cocoa trees ha−1 and 1,511 cocoa trees ha−1. Cocoa farmers defined seven different uses for tree species, including Theobroma cacao. 81 % of the species (including cocoa trees) had one to seven uses whereas the highest use value was given to T. cacao, with a mean score of 23.6 %. Then, in descending order, the 10 non-cocoa species with the highest use values were Dacryodes edulis, Persea americana, Elaeis guineensis, Citrus sinensis, Mangifera indica, Milicia excelsa, Cola nitida, Citrus sp., Ricinodendron heudelotii, and Terminalia superba. The frequency of non-cocoa species was significantly and positively correlated with their use value (R2 = 0.914). Our results showed that technical innovations designed to improve cocoa agroforestry systems should take into account farmers’ knowledge to propose them systems so as to be able to more effectively address their expectations.

International audience; This paper provides a review of theoretical and practical aspects related to genetic management of forest trees. The implementation of international commitments on forest genetic diversity has been slow and partly neglected. Conservation of forest genetic diversity is still riddled with problems, and complexities of national legal and administrative structures. Europe is an example of a complex region where the dis- tribution ranges of tree species extend across large geographical areas with profound environmental dif- ferences, and include many countries. Conservation of forest genetic diversity in Europe has been hampered by a lack of common understanding on the management requirements for genetic conserva- tion units of forest trees. The challenge resides in integrating scientific knowledge on conservation genet- ics into management of tree populations so that recommendations are feasible to implement across different countries. Here, we present pan-European minimum requirements for dynamic conservation units of forest genetic diversity. The units are natural or man-made tree populations which are managed for maintaining evolutionary processes and adaptive potential across generations. Each unit should have a designated status and a management plan, and one or more tree species recognized as target species for genetic conservation. The minimum sizes of the units are set at 500, 50 or 15 reproducing individuals depending on tree species and conservation objectives. Furthermore, silvicultural interventions should be allowed to enhance genetic processes, as needed, and field inventories carried out to monitor regen- eration and the population size. These minimum requirements are now used by 36 countries to improve management of forest genetic diversity.

The forest-savanna ecotone may be very sharp in fire-prone areas. Fire and competition for light play key roles in its maintenance, as forest and savanna tree seedlings are quickly excluded from the other ecosystem. We hypothesized a tradeoff between seedling traits linked to fire resistance and to competition for light to explain these exclusions. We compared growth- and survival-related traits of two savanna and two forest species in response to shading and fire in a field experiment. To interpret the results, we decomposed our broad hypothesis into elementary tradeoffs linked to three constraints, biomass allocation, plant architecture, and shade tolerance, that characterize both savanna and adjacent forest ecosystems. All seedlings reached similar biomasses, but forest seedlings grew taller. Savanna seedlings better survived fire after topkill and required ten times less biomass than forest seedlings to survive. Finally, only savanna seedlings responded to shading. Although results were consistent with the classification of our species as mostly adapted to shade tolerance, competition for light in the open, and fire tolerance, they raised new questions: how could savanna seedlings survive better with a 10-times lower biomass than forest seedlings? Is their shade intolerance sufficient to exclude them from forest understory?

Drought frequency and intensity are predicted to increase in many parts of the Northern Hemisphere and the effects of such changes on forest growth and tree mortality are already evident in many regions around the world. Mixed-species forests and increasing tree species diversity have been put forward as important risk reduction and adaptation strategies in the face of climate change. However, little is known about whether the species interactions that occur in diverse forests will reduce drought susceptibility or water stress. In this study, we focused on the effect of drought on individual tree species (n=16) within six regions of Europe and assessed whether this response was related to tree species diversity and stand density, and whether community-level responses resulted from many similar or contrasting species-level responses. For each species in each plot, we calculated the increase in carbon isotope composition of latewood from a wet to a dry year (C-13) as an estimate of its drought stress level. When significant community-level relationships occurred (three of six regions), there was only one species within the given community that showed a significant relationship (three of 25 species-region combinations), showing that information about a single species can be a poor indicator of the response of other species or the whole community. There were many two-species mixtures in which both species were less water-stressed compared with their monocultures, but also many mixtures where both species were more stressed compared with their monocultures. Furthermore, a given species combination responded differently in different regions.Synthesis and applications. Our study shows that drought stress may sometimes be reduced in mixed-species forests, but this is not a general pattern, and even varies between sites for a given combination. The management or prediction of drought stress requires consideration of the physiological characteristics of the mixed species, and how this complements the water-related climatic and edaphic features of the site, rather than species richness. Our study shows that drought stress may sometimes be reduced in mixed-species forests, but this is not a general pattern, and even varies between sites for a given combination. The management or prediction of drought stress requires consideration of the physiological characteristics of the mixed species, and how this complements the water-related climatic and edaphic features of the site, rather than species richness.

Highlights:• Many forests have an heterogeneous structure not accounted for in models.• We developed NOTG, a 3D, individual-based model of carbon and water budgets.• The model was parameterized for a mixed Mediterranean forest.• 3D simulation was more consistent with observations than 1D simulation.• Results show the importance of above- and below-ground spatial structures.Abstract:Many natural terrestrial ecosystems, agroforestry systems, and, increasingly, forest plantations, are made of a mixture of species and display significant structural heterogeneity. Yet most carbon-based biophysical models are limited to homogeneous, monospecific canopies. We explored whether the spatial structure at the Font-Blanche experimental site, located in a mixed Mediterranean forest of Aleppo pine and holm oak in south-east France, could affect the components of the carbon and water cycles. We used NOTG, a new 3D, process-based, and individual-based model specifically developed to study the importance of the spatial structure on the carbon and water cycles of complex ecosystems. It incorporates processes involved in the energy, carbon, and water cycles at the tree (radiation interception, photosynthesis, phenology, allocation, senescence, transpiration), and soil (soil moisture, soil organic matter decomposition) levels. It is designed to handle various plant phenological types (deciduous, non opportunistic evergreen, and opportunistic evergreen), and a comprehensive description of plant C pools. The model is designed to study water and carbon fluxes at the stand scale over one to a few years. In this study, NOTG was parameterized for the Font-Blanche forest and two five-year simulations were made using either the full 3D representation, or a simplified 1D representation. Comparison of model outputs against observations at the tree, soil, and ecosystem scales, showed a much better accuracy when using the 3D representation. This illustrates the dependence of plant and ecosystem function to the above- and below-ground spatial structures, and the usefulness of such detailed models when dealing with structurally complex ecosystems.

Rural communities have long been using ecosystems to sustain their livelihoods, especially in times of disasters when forests act as safety nets and natural buffers. However, it is less clear how climate variability influences changes in land uses, and their implications for human well-being. We examined how forests and trees can reduce human vulnerability by affecting the three components of vulnerability: exposure, sensitivity, and adaptive capacity. A total of 24 focus group discussions and 256 household surveys were conducted in two smallholder-dominated rural landscapes in Indonesia, which were affected by floods, drought and disease outbreaks. Our results suggest that forests and trees are important in supporting community resilience and decreasing their vulnerabilities to climate-related stresses in different ways. The role of trees varied according to the type of ecosystem service, whether provisioning or regulating, in relation to the phase of the climatic hazard, either in the pre-disaster phase or in the post-disaster recovery phase. It is therefore important to distinguish between these elements when analyzing people's responses to climatic variability in order to fully capture the contribution of forests and trees to reducing people's vulnerability. Landscape spatial characteristics, environmental degradation and community awareness of climate variability are crucial because if their linkages are recognized, local people can actively manage natural resources to increase their resilience. Interventions related to forests and trees should take into consideration these aspects to make ecosystem services a valuable option for an integrated strategy to reduce disaster risks and climate-related vulnerabilities.

Aim Knowledge about suitable ecological conditions for tree species remains largely incomplete. We aim to quantify and compare suitable environmental conditions for some of the most common tree species in Europe using a modelling approach and a large array of predictors that describe the different dimensions of the environmental niche. Location France. Methods Using a large database of 46 768 plots distributed across France (550 000 km2), we compared the performance of 61 physiologically relevant predictors that describe temperature, soil nutrient supply, soil water availability and aeration at fine spatial resolution to model the distribution of 32 tree species. To allow some comparisons between species along the same gradients, the most efficient predictors were determined and used to characterize the species requirements. Results Mean annual temperature, soil water deficit, soil pH, C/N and temporary and permanent waterlogging gave the best performances. The efficiency of species distribution models based on these six variables was comparable to models calibrated with 61 variables. For the first time, those models provide a unique quantitative framework of homogeneous information concerning the requirements for a large number of tree species. Conclusions Our results highlight the importance of soil descriptors to shape plant distribution and allow each species to delineate areas inside the climate envelope with favourable nutritional and moisture conditions. These results emphasize a gap between existing studies on species distribution, mainly based on large-scale climatic predictors, and empirical knowledge or existing practices where soil is recognized as a main driver.

Key message Variability of embolism resistance within individual trees was assessed in four Pinaceae species by using a single method of measurement: the Cavitron. Contrary to what has been previously observed, our findings show a small variability in embolism resistance within and between organs. Indeed, we found (i) a lack of variability between branches within the crown, and (ii) that roots and trunks are either equally resistant or slightly more vulnerable to embolism than branches. This contradicts the vulnerability segmentation hypothesis proposed in the early 1990s. This paper also demonstrates that only few branches are necessary to determine the embolism resistance of a given tree.[br/] Context Embolism formation in xylem has an important impact on plant growth and survival. Since most studies on xylem embolism resistance focus on branches, it remains questionable how the entire plant deals with embolism across organs.[br/] Aims In this study, we aimed to evaluate the variability of embolism resistance within a given organ and between different organs within a single tree.[br/] Methods Based on the Cavitron method, we estimated the intra-organ and the intra-plant variability of embolism resistance for four Pinaceae species. In addition, we compared pit anatomical characters for wood of all organs and species.[br/] Results We found no variability of embolism resistance for a given organ within a tree. At the tree level, trunks and roots were either equally or more vulnerable to embolism than branches. For all species, organs that showed a similar range of embolism resistance presented similar torus-aperture overlap values. However, the least negative P 50 value for roots of Pinus pinaster was associated with the lowest torus-aperture overlap value.[br/] Conclusion Our findings suggest that P 50 values are constrained within a particular organ and that intra-tree variation in embolism resistance is less substantial than previously reported. Moreover, our data do not support the vulnerability segmentation hypothesis which suggests that distal organs are more vulnerable to xylem embolism.

Key message Increasing human impacts on forests, including unintentional movement of pathogens, climate change, and large-scale intensive plantations, are associated with an unprecedented rate of new diseases. An evolutionary ecology perspective can help address these challenges and provide direction for sustainable forest management. Context Forest pathology has historically relied on an ecological approach to understand and address the practical management of forest diseases. A widening of this perspective to include evolutionary considerations has been increasingly developed in response to the rising rates of genetic change in both pathogen populations and tree populations due to human activities. Aims Here, five topics for which the evolutionary perspective is especially relevant are highlighted. Results The first relates to the evolutionary diversity of fungi and fungal-like organisms, with issues linked to the identification of species and their ecological niches. The second theme deals with the evolutionary processes that allow forest pathogens to adapt to new hosts after introductions or to become more virulent in homogeneous plantations. The third theme presents issues linked to disease resistance in tree breeding programs (e.g., growth-defense trade-offs) and proposes new criteria and methods for more durable resistance. The last two themes are dedicated to the biotic environment of the tree–pathogen system, namely, hyperparasites and tree microbiota, as possible solutions for health management. Conclusion We conclude by highlighting three major conceptual advances brought by evolutionary biology, i.e., that (i) “not everything is everywhere”, (ii) evolution of pathogen populations can occur on short time scales, and (iii) the tree is a multitrophic community. We further translate these into a framework for immediate policy recommendations and future directions for research.

International audience; Future patterns of biodiversity have been extensively explored to design conservation strategies in large continental hotspots. However, little research has focused on island hotspots, although limited opportunities to migrate and the inherent characteristics of island species are likely to cause sensitivity to rapid environmental changes. This study addresses the question of how climate change could affect species richness in New Caledonia, the world’s smallest biodiversity hotspot. An individual species distribution model was built for 469 native tree species and projected according to nine climate change scenarios. Results indicated that the range size of 87–96% of species will have declined by 2070, 52–84% will lose at least half of their current range, and 0–15% will become extinct. Surprisingly, these predictions did not significantly exceed those for larger biodiversity hotspots. Underlying reasons may include an oceanic buffering effect that attenuates increases in air temperature, and the complex topography that generates micro-refugia. Major losses in local species richness were predicted to occur on ultramafic substrates and at mid-elevation. Loss on ultramafic substrates may stem from the number of ultramafic-specialist species that will lack a suitable climate on this specific substrate, while substrate-ubiquitous species are more likely to find refugia. Loss at mid-elevation could mirror a shift in optimum temperature-precipitation value, whose role in shaping the current pattern of diversity may have been overestimated by the models. Hopefully, these results will encourage further research to define the right mitigation and adaptation strategies on oceanic islands, where extinctions would contribute disproportionally to global biodiversity decline.

The tropical rainforest of Amazonia is one of the most species-rich ecosystems on earth, with an estimated 16000 tree species. Due to this high diversity, botanical identification of trees in the Amazon is difficult, even to genus, often requiring the assistance of parataxonomists or taxonomic specialists. Advances in informatics tools offer a promising opportunity to develop user-friendly electronic keys to improve Amazonian tree identification. Here, we introduce an original multi-access electronic key for the identification of 389 tree genera occurring in French Guiana terra-firme forests, based on a set of 79 morphological characters related to vegetative, floral and fruit characters. Its purpose is to help Amazonian tree identification and to support the dissemination of botanical knowledge to non-specialists, including forest workers, students and researchers from other scientific disciplines. The electronic key is accessible with the free access software Xper², and the database is publicly available on figshare: https://figshare.com/articles/GuiaTreeKey/2682550 (doi: 10.6084/m9.figshare.2682550).

Background: Local adaptation is a key driver of phenotypic and genetic divergence at loci responsible for adaptive traits variations in forest tree populations. Its experimental assessment requires rigorous sampling strategies such as those involving population pairs replicated across broad spatial scales. Methods: A hierarchical Bayesian model of selection (HBM) that explicitly considers both the replication of the environmental contrast and the hierarchical genetic structure among replicated study sites is introduced. Its power was assessed through simulations and compared to classical 'within-site' approaches (FDIST, BAYESCAN) and a simplified, within-site, version of the model introduced here (SBM). Results: HBM demonstrates that hierarchical approaches are very powerful to detect replicated patterns of adaptive divergence with low false-discovery (FDR) and false-non-discovery (FNR) rates compared to the analysis of different sites separately through within-site approaches. The hypothesis of local adaptation to altitude was further addressed by analyzing replicated Abies alba population pairs (low and high elevations) across the species' southern distribution range, where the effects of climatic selection are expected to be the strongest. For comparison, a single population pair from the closely related species A. cephalonica was also analyzed. The hierarchical model did not detect any pattern of adaptive divergence to altitude replicated in the different study sites. Instead, idiosyncratic patterns of local adaptation among sites were detected by within-site approaches. Conclusion: Hierarchical approaches may miss idiosyncratic patterns of adaptation among sites, and we strongly recommend the use of both hierarchical (multi-site) and classical (within-site) approaches when addressing the question of adaptation across broad spatial scales.

Key message We review the recent findings on the influence of drought on tree mortality, growth or ecosystem functioning in tropical rainforests. Drought plays a major role in shaping tropical rainforests and the response mechanisms are highly diverse and complex. The numerous gaps identified here require the international scientific community to combine efforts in order to conduct comprehensive studies in tropical rainforests on the three continents. These results are essential to simulate the future of these ecosystems under diverse climate scenarios and to predict the future of the global earth carbon balance. Context Tropical rainforest ecosystems are characterized by high annual rainfall. Nevertheless, rainfall regularly fluctuates during the year and seasonal soil droughts do occur. Over the past decades, a number of extreme droughts have hit tropical rainforests, not only in Amazonia but also in Asia and Africa. The influence of drought events on tree mortality and growth or on ecosystem functioning (carbon and water fluxes) in tropical rainforest ecosystems has been studied intensively, but the response mechanisms are complex. Aims Herein, we review the recent findings related to the response of tropical forest ecosystems to seasonal and extreme droughts and the current knowledge about the future of these ecosystems. Results This review emphasizes the progress made over recent years and the importance of the studies conducted under extreme drought conditions or in through-fall exclusion experiments in understanding the response of these ecosystems. It also points to the great diversity and complexity of the response of tropical rainforest ecosystems to drought. Conclusion The numerous gaps identified here require the international scientific community to combine efforts in order to conduct comprehensive studies in tropical forest regions. These results are essential to simulate the future of these ecosystems under diverse climate scenarios and to predict the future of the global earth carbon balance.

Climate change is predicted to increase the occurrence of extreme droughts, which are associated with elevated mortality rates in tropical trees. Drought-induced mortality is thought to occur by two main mechanisms: hydraulic failure or carbon starvation . This chapter focuses on the strategies that plants use to survive these two drought-induced mortality mechanisms and how these mechanisms are distributed among the immense diversity of tropical tree species. The traits that tropical trees may use to survive drought include (1) xylem that is resistant to drought-induced cavitation , (2) high sapwood capacitance that protects xylem from critically low water potentials , (3) drought deciduousness, (4) photosynthetic stems that have the potential to assimilate carbon at greater water-use efficiency than leaves, (5) deep roots, (6) regulation of gas exchange to reduce leaf water loss or to maintain photosynthesis at low leaf water potential and (7) when all else fails, low cuticular conductance from exposed tissues during extended drought. To date, most research has focused on deciduousness, resistant xylem, soil water, gas exchange behavior and sapwood capacitance, whereas little is known about the role of photosynthetic stems or cuticular conductance during extreme extended drought, making these processes a high priority for a complete understanding of tropical tree physiology during drought.

International audience; No abstract available

International audience; Effects of recent climate change have already been detected in many species, and, in particular, in insects. The present paper reviews the key impacts of global warming on insect development and dispersal. The effects of climate change appear to be much more complex than a simple linear response to an average increase in temperature. They can differ between seasons and bioclimatic regions. Earlier flight periods, enhanced winter survival and acceleration of development rates are the major insect responses. Differential response of insects and hosts to warming up might also lead to disruption of their phenological synchrony, but adaptive genetic processes are likely to quickly restore this synchrony. In a number of cases, warming results in removing or relocating the barriers that limit present species’ ranges. It is also likely to facilitate the establishment and spread of invasive alien species. Finally, knowledge gaps are identified and future research interests are suggested.

International audience; There is an increasing recognition that long distance dispersal (LDD) plays a key role in establishing spatial genetic structure during colonization. Recent works, focused on short distance dispersal, demonstrated that a neutral mutation arising at the colonization front can either 'surf' with the wave front and reach high frequencies or stay near its place of origin at low frequencies. Here, we examine how LDD, and more generally the shape of the dispersal kernel, modifies this phenomenon and how the width of the colonization corridor affects the fate of the mutation. We demonstrate that when LDD events are more frequent, the 'surfing phenomenon' is less frequent, probably because any alleles can get far ahead from the colonization front and preclude the invasion by others alleles, thus leading to an attenuation of the diversity loss. We also demonstrate that the width of the colonization corridor influences the fate of the mutation, wide spaces decreasing the probability of invasion. Overall, the genetic structure of diversity resulted not only from LDD but also particularly from the shape of the dispersal kernel

International audience; Wide variation and overlap inmorphological characters have led to confusion in species identification within the fungal rust genus Melampsora. The Melampsora species with uredinial– telial stages on white poplar and aspens are especially prone to misidentification. This group includes the Melampsora populnea species complex and the highly destructive pine twisting rust, Melampsora pinitorqua, which alternates between hosts in Populus section Populus and Pinus. Our objective was to compare morphologically based identification to genetic material extracted fromMelampsora species pathogenic to aspen and white poplar.Wecomparedmorphometric traits and DNA barcodes obtained frominternal transcribed spacer (ITS), large ribosomal RNA subunit (28S), and mitochondrial cytochromeoxidase 1 (CO1) sequences to delimit within this taxonomically difficult group. Eight different Melampsora species were initially defined based on host specificity and morphometric data. DNA barcodes were then overlaid on these initial species definitions. The DNA barcodes, specifically those defined on ITS and 28S sequences, provided a highly accurate means of identifying and resolving Melampsora taxa. We highlighted species misidentification in specimens from Canadian herbaria related to either Melampsora medusae f. sp. tremuloidae or Melampsora aecidioides. Finally, we evidenced that the north-American species found on Populus alba, M. aecidioides is closely related but distinct from the four species of the M. populnea complex (Melampsora larici-tremulae, Melampsora magnusiana, Melampsora pinitorqua, and Melampsora rostrupii) found in Eurasia.

Interindividual variance of male reproductive success (MRS) contributes to genetic drift, which in turn interacts with selection and migration to determine the short-term response of populations to rapid changes in their environment. Individual relative MRS can be estimated through paternity analysis and can be further dissected into fecundity and spatial components. Existing methods to achieve this decomposition either rely on the strong assumption of a random distribution of pollen donors (TwoGener) or estimate only the part of the variance of male fecundity that is explained by few covariates. We developed here a method to estimate jointly the whole variance of male fecundity and the pollen dispersal curve from the genotypic information of sampled seeds and their putative fathers and geographical information of all individuals in the study area. We modelled the relative individual fecundities as a log-normally distributed random effect. We used a Bayesian approach, well suited to the hierarchical nature of the model, to estimate these fecundities. When applied to Sorbus torminalis, the estimated variance of male fecundity corresponded to an effective density of trees 13 times lower than the observed density (d(obs)/d(ep ) approximately 13). This value is between the value (approximately 2) estimated with a classical mating model including three covariates (neighbourhood density, diameter, flowering intensity) that affect fecundity and the value (approximately 30) estimated with TwoGener. The estimated dispersal kernel was close to previous results. This approach allows fine monitoring of ongoing genetic drift in natural populations, and quantitative dissection of the processes contributing to drift, including human actions.

A large quantity of high quality RNA is often required in the analysis of gene expression. However, RNA extraction from samples taken from woody plants is generally complex, and represents the main limitation to study gene expression, particularly in refractory species like conifers. Standard RNA extraction protocols are available but they are highly time consuming, and not adapted to large scale extraction. Here we present a high-throughput RNA extraction protocol. This protocol was adapted to a micro-scale by modifying the classical cetyltrimethylammonium (CTAB) protocol developed for pine: (i) quantity of material used (100-200 mg of sample), (ii) disruption of samples in microtube using a mechanical tissue disrupter, and (iii) the use of SSTE buffer. One hundred samples of woody plant tissues/organs can be easily treated in two working days. An average of 15 \ig of high quality RNA per sample was obtained. The RNA extracted is suitable for applications such as real time reverse transcription polymerase chain reaction, cDNA library construction or synthesis of complex targets for microarray analysis.