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19 Pág., Microgeographical adaptation occurs when the effects of directional selection persist despite gene flow. Traits and genetic loci under selection can then show adaptive divergence, against the backdrop of little differentiation at other traits or loci. How common such events are and how strong the selection is that underlies them remain open questions. Here, we discovered and analysed microgeographical patterns of genomic divergence in four European and Mediterranean conifers with widely differing life-history traits and ecological requirements (Abies alba MIll., Cedrus atlantica [Endl.] Manetti, Pinus halepensis Mill. and Pinus pinaster Aiton) by screening pairs from geographically close forest stands sampled along steep ecological gradients. We inferred patterns of genomic divergence by applying a combination of divergence outlier detection methods, demographic modelling, Approximate Bayesian Computation inferences and genomic annotation to genomic data. Surprisingly for such small geographical scales, we showed that selection is strong in all species but generally affects different loci in each. A clear signature of selection was systematically detected on a fraction of the genome, of the order of 0.1%-1% of the loci depending on the species. The novel modelling method we designed for estimating selection coefficients showed that the microgeographical selection coefficient scaled by population size (Ns) was 2-30. Our results convincingly suggest that selection maintains within-population diversity at microgeographical scales in spatially heterogeneous environments. Such genetic diversity is likely to be a major reservoir of adaptive potential, helping populations to adapt under fluctuating environmental conditions., Agence Nationale de la Recherche, Grant/ Award Number: FLAG project (ANR-12- ADAP-0007-01); European Commission, Grant/Award Number: TOPWOOD project (MSCA-RISE-2014-645654- TOPWOOD) and grant agreement No. 676876 (GenTree); Ministère de l'Écologie, du Développement Durable et de l'Énergie, Grant/Award Number: GRAAL project (10-MCGOT-GICC-8-CVS-139)

National audience; Production de bois, espace de loisirs, puits de carbone…Les forêts offrent de multiples services essentiels aux humains et à la Terre. Face à des aléas météorologiques qui s’intensifient avec le réchauffement climatique et des changements globaux menaçants (commerce international, déforestation), certains massifs dépérissent à un rythme inquiétant et nous invite à revoir la façon de gérer les forêts.

Trees play a key role in the structure and function of many ecosystems worldwide. In the Mediterranean Basin, forests cover approximately 22% of the total land area hosting a large number of endemics (46 species). Despite its particularities and vulnerability, the biodiversity of Mediterranean trees is not well known at the taxonomic, spatial, functional, and genetic levels required for conservation applications. The WOODIV database fills this gap by providing reliable occurrences, four functional traits (plant height, seed mass, wood density, and specific leaf area), and sequences from three DNA-regions (rbcL, matK, and trnH-psbA), together with modelled occurrences and a phylogeny for all 210 Euro-Mediterranean tree species. We compiled, homogenized, and verified occurrence data from sparse datasets and collated them on an INSPIRE-compliant 10 × 10 km grid. We also gathered functional trait and genetic data, filling existing gaps where possible. The WOODIV database can benefit macroecological studies in the fields of conservation, biogeography, and community ecology.

International audience

International audience; One of the greatest challenges when addressing issues in complex social-ecological systems (SES), is the need for an efficient interdisciplinary framework when large-magnitude social and ecological disturbances occur. Teams comprising of scientists from different backgrounds and disciplines are frequently called upon to propose research methods and results that can be useful for policy and decision makers. However, most of the outcomes from these pluri-disciplinary teams appear extremely difficult to implement within a bigger picture because concepts, hypotheses, methods, and results are specific to each discipline. Here, we propose a reverse-engineering (RE) method to define the scientific needs that could help policy makers and citizens to assess the impacts of socioeconomic “disruptors” on social-ecological systems. We present this method using the example of an ongoing wood biomass energy plant (Gardanne) in the French Mediterranean region. In the Mediterranean region, species diversity is high, the forest cover is ample, but difficult access and low forest productivity make any biomass policy an ecological and social disruption. Our method is based on three complementary approaches to (1) describe the social-ecosystems, (2) draw up a map of interactions between actors and the impacts on the ecosystem, and (3) identify relevant questions needed for a global analysis of the impacts and potentialities of adaptation of actors and the ecosystems to the perturbation and the connections needed between the different disciplines. Our analysis showed that knowledge gaps have to be filled to assess forest resource vulnerability and better estimate how the different resource used (solid wood, biomass, landscape) competed together. Finally, we discuss how this method could be integrated into a broader transdisciplinary work allowing a coproduction of knowledge and solutions on a SES.

International audience; There is growing concern that the implementation of political agreements on climate change and biodiversity will not be enough to protect forests in the short run and up to the end of the 21st century. As mitigation efforts are lagging behind self-imposed, reasonable targets, genetic diversity will have a large and significant part to play in the process of adapting forests to climate change. Genetic diversity, the raw material of evolution, can be used for adaptation by natural selection and artificial breeding, in naturally regenerated and plantation forests alike. The two-day scientific conference: “#rescueforests: Genetics to the rescue - Managing forests sustainably in a changing world”, addressed the genetic diversity of forests. More specifically, the conference was about natural as well as assisted adaptive processes, their spatial scale, from fine grain to landscape and ecoregions, and how much of the genome it involves. It also dealt with phenotypes and how much of their variation is determined by underlying genetic diversity. And finally, and perhaps most importantly, the conference emphasized the importance of conservation and sustainable use of this genetic diversity as a nature-based solution to adapt under the fast pace of climate change. The conference demonstrated how improved knowledge on genomic diversity and evolutionary mechanisms can help to rescue forests, either naturally or by means of management.

Drought is one of the most important selection pressures for forest trees in the con-text of climate change. Yet, the different evolutionary mechanisms, and their envi-ronmental drivers, by which certain populations become more drought tolerant than others is still little understood. We studied adaptation to drought in 16 silver fir (Abies alba Mill.) populations from the French Mediterranean Alps by combining observa-tions on seedlings from a greenhouse experiment (N = 8,199) and on adult tress in situ (N = 315). In the greenhouse, we followed half-sib families for four growing seasons for growth and phenology traits, and tested their water stress response in a "drought until death" experiment. Adult trees in the field were assessed for δ13C, a proxy for water use efficiency, and genotyped at 357 SNP loci. SNP data was used to gen-erate a null expectation for seedling trait divergence between populations in order to detect the signature of selection, and 31 environmental variables were used to identify the selective environment. We found that seedlings originating from popula-tions with low soil water capacity grew more slowly, attained a smaller stature, and resisted water stress for a longer period of time in the greenhouse. Additionally, adult trees of these populations exhibited a higher water use efficiency as evidenced by their δ13C. These results suggest a correlated evolution of the growth-drought toler-ance trait complex. Population divergence in bud break phenology was adaptive only in the second growing season, and evolved independently from the growth-drought tolerance trait complex. Adaptive divergence in bud break phenology was principally driven by the inter- and intra-annual variation in temperature at the geographic origin of the population. Our results illustrate the different evolutionary strategies used by populations to cope with drought stress at the range limits across a highly heteroge-neous landscape, and can be used to inform assisted migration programs. ISSN:1752-4571 ISSN:1752-4563

International audience; Adaptation is a major stake of forest management in the climate change context The genetic diversity of forest trees confers them a huge – yet not boundless – adaptive potential Taking evolutionary mechanisms into account in adaptive forest management practices will reinforce the capacity of managed forests to respond to climate-induced changes and hazards By laying the emphasis on forests under natural regeneration conditions,we propose a general conceptual framework that includes knowledge on these mechanisms in decision- making processes, in a silvicultural approach through and for evolution This general framework will encompass diverse and complex local situations by relying on knowledge of local contexts from forest managers. We developed a simple analysis grid based on a small number of parameters characterising evolutionary mechanisms to understand the impact of silvicultural practices on the genetic diversity dynamics and the maintenance of the evolutionary potential of forest tree populations After recalling the current state of knowledge on the evolutionary mechanisms of forest trees, we examined the expected effects of current or innovative silvicultural practices on these mechanisms To illustrate the complexity of these interacting mechanisms, we further studied the evolutionary consequences of biotic interactions and of interactions in a highly heterogeneous environment Silviculture through and for evolution can contribute to the adaptation of forests to climate change This will require combining short-term and long-term objectives We further propose lines ofresearch and experimentation to support this approach.; L’adaptation est un enjeu majeur de la gestion forestière dans le contexte du changement climatique La diversité génétique qui caractérise les arbres forestiers leur confère un potentiel adaptatif très important mais pas illimité Prendre en compte les mécanismes de l’évolution dans les pratiques de gestion forestière adaptative renforcera la capacité des forêts gérées à répondre aux changements et aux aléas induits par le climat. En mettant l’accent sur le cas des forêts en régénération naturelle, nous proposons un cadre conceptuel général permettant d’intégrer la connaissance de ces mécanismes dans la prise de décision, dans une démarche de sylviculture par et pour l’évolution Ce cadre général pourra être décliné dans des situations locales diverses et complexes en s’appuyant sur la connaissance du contexte qu’ont les gestionnaires forestiers Nous développonsune grille d’analyse simple, basée sur un petit nombre de paramètres caractérisant les mécanismes de l’évolution, pour comprendre l’impact des pratiques sylvicoles sur la dynamique de la diversité génétique et le maintien du potentiel d’évolution des populations d’arbres forestiers Après avoir rappelé l’état des connaissances sur les mécanismes de l’évolution chez les arbres forestiers, nous examinons les effets attendus de pratiques forestières actuelles ou innovantes sur ces mécanismes Pour illustrer la complexité des mécanismes en interaction, nous développons plus en détail les conséquences évolutives des interactions biotiques et celles d’un environnement fortement hétérogène La sylviculture par et pour l’évolution peut contribuer à l’adaptation des forêts au changement climatique Elle nécessite de combiner des objectifs à court et à long terme Nous proposons des pistes de recherche et d’expérimentation pour accompagner cette démarche.

International audience; We produced the first time-calibrated phylogeny of all 64 native tree genera occurring on the European side of the Mediterranean Basin. This phylogeny is based on 3 plastid DNA sequences (rbcL matK and trnH-psbA), 4 recognized fossil dates and 10 secondary calibrations. Based on the inferred topology, we then tested whether the investigated tree flora exhibits phylogenetic clustering in both life-history traits known to influence reproduction and species' vulnerability to extinction. Our topology and the estimated dates mostly conform to published partial phylogenies and are highly congruent with the Angiosperm Phylogeny Group classification except for some minor incongruences including the still debated phylogenetic position of Magnoliids. The four strictly endemic genera of the Mediterranean Basin (Chamaerops, Phillyrea, Spartium and Tetraclinis) all showed emergence dates (11-72 Ma) long before the onset of the Mediterranean climate. We did not find any imprints of phylogenetic sorting processes on the life-history traits we studied, except for the mode of seed dispersal, which showed a clustered distribution across our topology. The presence of species at risk of potential extinction within a given genus was randomly distributed along the phylogenetic tree. Species with deficient data were significantly nested within a few of the most recently evolved angiosperm genera. Our analysis closes knowledge gaps and provides a valuable basis for studying the biogeo-graphical and ecological processes that have generated the Mediterranean tree flora. It can also inform conservation planning strategies that aim at broadening traditional taxonomy-focused perspectives with components of evolutionary history and phylogenetic singularity.

The Mediterranean stone pine is currently on its way to domestication. Its genuine Mediterranean pine nuts are among the most expensive nuts in the world because they are mainly wild-collected from pine forests and woodlands. Despite the wide current distribution of stone pine over the whole Mediterranean biome, old-growth forests are scarce, often associated locally with dynamics on lose sands, coastal dunes or former estuary marshes. The species has been found to be genetically depauperate, putatively due to a population bottleneck in a local refugium during the Last Glacial Maximum confirmed in southern Iberia, and a possibly anthropic range expansion during Holocene. Only recently, cone harvesting and processing mechanisation have allowed for profitable pine nut production from orchard plantations. In Spain and Portugal, first elite clones have been registered for their use as grafted orchard crop.

International audience

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National audience

International audience; This study reinforces the argument that forest genetic resources for peripheral isolated plant populations (PIPP) need to come under rationalistic assessment, for developing and proposing conservation strategies of forest genetic resources. Cedrus brevifolia is a narrow endemic island tree occurring in a sole population. Using biparentally and paternally inherited microsatellites, the genetic contribution and genetic variation patterns within sites (subpopulations) and within plantations of this species were assessed. The C. brevifolia population recorded uneven partition of genetic diversity at the site and at local scales; mirroring the demography and genetic evolutionary factors that occurred in long-term at the intra-species level. Results from the plantations imply that screening and rejection of unsuitable seedlings before plantation establishment did not influence the genetic divergence of planted trees from the general genetic pool of natural population. Based on these outcomes, numerous conservation measures are proposed, towards maintaining the species’ genetic resources. These measures need to ensure the dynamic processes within stands. Thus, this study argues that for PIPP which recorded high genetic diversity and non-uniform distribution of genetic viability (complex genetic patterns), the several small conservation units seem to be the most rationalistic conservation units. In such case, forest genetic micro-reserves (GMR) can be enacted, where on-the-point dynamic in situ conservation activities can be adopted, while the GMR could be used for ex situ conservation purposes. In conclusion, in PIPP the maintenance of genetic diversity should be regarded as one of the main prerequisites for sustainable management and long-term survival of the species.

Fragmentation acting over geological times confers wide, biogeographical scale, genetic diversity patterns to species, through demographic and natural selection processes. To test the effects of historical fragmentation on the genetic diversity and differentiation of a major European forest tree and to resolve its demographic history, we describe and model its spatial genetic structure and gene genealogy. We then test which Pleistocene event, whether recent or ancient, could explain its widespread but patchy geographic distribution using population genetic data, environmental data and realistic demographic timed scenarios.The taxon of interest is a conifer forest tree,Pinus nigra(Arnold), the European black pine, whose populations are located in the mountains of southern Europe and North Africa, most frequently at mid-elevation. We used a set of different genetic markers, both neutral and potentially adaptive, and either bi-parentally or paternally inherited, and we sampled natural populations across the entire range of the species. We analysed the data using frequentist population genetic methods as well as Bayesian inference methods to calibrate realistic, demographic timed scenarios.Species with geographically fragmented distribution areas are expected to display strong among-population genetic differentiation and low within-population genetic diversity. Contrary to these expectations, we show that the current diversity ofPinus nigraand its weak genetic spatial structure are best explained as resulting from late Pleistocene or early Holocene fragmentation of one ancestral population into seven genetic lineages, which we found to be the main biogeographical contributors of the natural black pine forests of today. Gene flow among the different lineages is strong across forests and many current populations are admixed between lineages. We propose to modify the currently accepted international nomenclature made of five subspecies and name these seven lineages using regionally accepted subspecies-level names.HighlightsThe European black pine,Pinus nigra(Arnold), has a weak spatial genetic structure.Gene flow among populations is frequent and populations are often of admixed origin.Current genealogies result from recent, late Pleistocene or Holocene events.Seven modern genetic lineages emerged from divergence and demographic contractions.These seven lineages warrant a revision of subspecies taxonomic nomenclature.

Rapport final du projet Dolar publié en octobre 2019; La maladie des bandes rouges, d’envergure internationale et causée en France par les deux agents pathogènes du genre Dothistroma, provoque des dégâts sévères dans les houppiers des pins laricio. Le projet Dolar visait à identifier les facteurs pédoclimatiques favorisant l’expression de la maladie des bandes rouges, à étudier la sensibilité à la maladie de matériels d’origines génétiques différentes, et à quantifier l’impact de la maladie des bandes rouges sur la croissance et la production des peuplements en lien avec les scénarios de sylviculture appliqués. Ce travail a été mené principalement dans les régions Centre-Val de Loire et Pays de la Loire. Il s’est appuyé sur des réseaux existants de placettes d’observation et de dispositifs d’expérimentation sylvicole ou génétique, créés et gérés par les différents organismes intervenant dans le projet (CNPF, IGN, INRA, Irstea et ONF).Les principaux résultats obtenus sont les suivants : (1) Les facteurs climatiques, en particulier les variables liées au régime pluviométrique, sont les principaux déterminants de l’expression des dégâts de la maladie des bandes rouges. Au niveau pédologique, seul un léger effet de la richesse trophique a pu être mis en évidence. Ainsi, les précipitations et la fréquence des épisodes pluvieux au printemps augmentent les dégâts, la fréquence des épisodes secs en été les réduit, et les dégâts sont plus sévères dans les stations de faible niveau trophique.(2) Les conjonctions de facteurs stressants ou contraignants pour le pin laricio sont plus favorables à la maladie des bandes rouges.(3) La variabilité de l’intensité des dégâts se trouve essentiellement au niveau de l’individu, quel que soit le domaine étudié : contexte pédoclimatique, gestion sylvicole ou origine génétique.(4) L’intensité des symptômes de la maladie des bandes rouges au niveau de l’arbre est négativement corrélée au statut social de l’arbre au sein du peuplement : les arbres les plus gros sont en moyenne moins affectés.(5) La mortalité causée par la maladie des bandes rouges reste négligeable mais la sévérité des dégâts augmente la probabilité de mortalité des arbres dominés au sein des peuplements de densité élevée.(6) L’accroissement radial des arbres est très lourdement impacté par la maladie, l’intensité des dégâts s’imposant comme le facteur expliquant la plus grande part de variabilité de l’accroissement. En moyenne, l’accroissement individuel est réduit de 50 % pour une intensité de dégâts de 50%. Une sylviculture avec des densités plus faibles permet de maintenir un niveau d’accroissement plus satisfaisant.(7) A l’échelle du peuplement, la maladie des bandes rouges provoquent des pertes de production en surface terrière proportionnelles et équivalentes à la proportion des dégâts, mais la croissance des peuplements reste positive dans la plupart des cas. L’application d’une sylviculture avec des densités plus faibles permet de réduire les pertes d’accroissement, et ce d’autant plus que le niveau de sévérité de la maladie est important.(8) A l’échelle du peuplement, l’intensité des dégâts de la maladie est d’autant plus importante que la densité du peuplement est élevée : une sylviculture en peuplement plus clair permet donc de réduire les dégâts. L’application d’une sylviculture dynamique présente donc le double avantage de réduire et l’intensité de la maladie et les pertes de production (à niveau de maladie constant).(9) Malgré la diversité des matériels génétiques évalués (variété, massif d’origine dans l’aire naturelle, provenance, descendance, clone), l’unité génétique explique peu la variabilité des dégâts observés. Des différences significatives sont mises en évidence, mais également dans certains cas, des interactions entre les effets site et les effets unité génétique. Les différentes analyses menées conduisent parfois à des résultats contradictoires.(10) C’est notamment le cas concernant la variété. Dans les dispositifs génétiques, les deux variétés, Corse et Calabre, se distinguent peu, alors que l’analyse de 17 dispositifs d’expérimentation sylvicole montre que le pin laricio de Calabre est moins atteint par la maladie des bandes rouges que le pin laricio de Corse. L’origine génétique précise des 17 peuplements en question n’est pas connue. Ce résultat est l’illustration de l’importante variabilité existant au sein de chacune des deux variétés de pin laricio.(11) Néanmoins, les Matériels Forestiers de Reproduction (MFR) issus du verger de Pin laricio de Calabre de Sivens sont classés moins sensibles à la maladie des bandes rouges que les MFR produits dans les deux vergers à graines de pin laricio de Corse. L’hybridation des clones composant le verger de Sivens a été génétiquement établie, les clones appartenant à quatre provenances distinctes, une Corse, une Calabre et deux provenances non référencées génétiquement. Les analyses conduites dans le cadre du projet révèlent également que 25% des clones sont des hybrides entre le pin laricio et trois autres sous-espèces de pins noirs.Bien que des analyses complémentaires soient encore envisagées, des recommandations peuvent être formulées à partir des résultats acquis et des enseignements tirés de la littérature internationale. Dans le contexte actuel d’aggravation des épisodes de sécheresse et de risques sanitaires liés à Diplodia pinea, le 2e pathogène foliaire d’importance concernant le pin laricio, et malgré leur sensibilité avérée à la maladie des bandes rouges, nous conseillons de conserver les deux variétés de pin laricio dans le panel des essences de boisement et reboisement utilisables en France. Nous formulons des propositions de gestion sylvicole visant en particulier à réduire l’impact de la maladie sur les peuplements. Les recommandations concernant la gestion des vergers à graines ou plus généralement l’utilisation des Matériels Forestiers de Reproduction visent également à lutter contre l’extension de la maladie ou de son potentiel d’évolution génétique.

International audience; How populations of long-living species respond to climate change depends on phenotypic plasticity and local adaptation processes. Marginal populations are expected to have lags in adaptation (i.e. differences between the climatic optimum that maximizes population fitness and the local climate) because they receive pre-adapted alleles from core populations preventing them from reaching a local optimum in their climatically marginal habitat. Yet, whether adaptation lags in marginal populations are a common feature across phylogenetically and ecologically different species and how lags can change with climate change remain unexplored. To test for range-wide patterns of phenotypic variation and adaptation lags of populations to climate, we (a) built model ensembles of tree height accounting for the climate of population origin and the climate of the site for 706 populations monitored in 97 common garden experiments covering the range of six European forest tree species; (b) estimated populations' adaptation lags as the differences between the climatic optimum that maximizes tree height and the climate of the origin of each population; (c) identified adaptation lag patterns for populations coming from the warm/dry and cold/wet margins and from the distribution core of each species range. We found that (a) phenotypic variation is driven by either temperature or precipitation; (b) adaptation lags are consistently higher in climatic margin populations (cold/warm, dry/wet) than in core populations; (c) predictions for future warmer climates suggest adaptation lags would decrease in cold margin populations, slightly increasing tree height, while adaptation lags would increase in core and warm margin populations, sharply decreasing tree height. Our results suggest that warm margin populations are the most vulnerable to climate change, but understanding how these populations can cope with future climates depend on whether other fitness-related traits could show similar adaptation lag patterns.

International audience; Cedar is an emblematic Mediterranean forest tree. Genetic research activities on Mediterranean Cedrus species are progressively developed in relation to conservation, restoration, and exploitation plans of these forest tree species. However, currently available molecular biology tools supporting genetic research in these fields are still scarce and have a limited genetic resolution potential. We developed a new set of 12 nuclear microsatellite markers (nSSRs) on Cedrus atlantica that we combined with four previously developed ones in three multiplexes. We checked their monogenic inheritance in controlled crosses. We used a collection of 131 samples from six populations of C. atlantica to estimate null allele frequencies and probability of identity and to characterize the structure of genetic diversity in the fragmented distribution range of this species. We also tested the transferability of the markers to another set of 36 samples from the other Mediterranean Cedrus species and performed a phylogenetic analysis. The three multiplexes reached a high level of resolution potential that we used to evaluate sampling quality. Null allele frequency estimates showed no specific pattern across populations or across species and did not affect the results of biogeographic and phylogenic analyses. Our results reveal a very clear geographical genetic structure within C. atlantica, and the phylogenic tree matched previous analyses based on other markers. Our results confirm the potential interest of these nSSR multiplexes for genotyping in Cedrus.

Demographic and evolutionary history of the European black pine (Pinus nigra Arn). Réunion du groupe AFORGEN

International audience

International audience; The adaptation of social-ecological systems such as managed forests depends largely on decisions taken by forest managers who must choose among a wide range of possible futures to spread risks. We used robust decision theory to guide management decisions on the translocation of tree populations to compensate for climate change.We calibrated machine learning correlational models using tree height data collected from five common garden tests in France where Abies alba provenances from 11 European countries are planted. Resulting models were used to simulate tree height in the planting sites under current and 2050 climates (regional concentration pathway scenarios (RCPs) 2.6, 4.5, 6.0 and 8.5). Our results suggest an overall increase in tree height by 2050, but with large variation among the predictions depending on the provenance and the RCPs. We applied maximin, maximax and minimax decision rules to address outcomes under five uncertain states of the world represented by the four RCPs and the present climate (baseline). The maximin rule indicated that for 2050, the best translocation option for maximising tree height would be the use of provenances from Northwest France into all target zones. The maximax and minimax regret rules pointed out the same result for all target zones except for the ‘Les Chauvets’ trial, where the East provenance was selected. Our results show that decision theory can help management by reducing the number of options if most decision rules converge. Interestingly, the commonly suggested recommendation of using multiple provenances to mitigate long-term maladaptation risks or from ‘pre-adapted’ populations from the south was not supported by our approach.

Author Keywords:Pinus nigra Arn.; Tree-ring; Climate change; Dendroecology; Growth-climate response; Intraspecific variation; Provenances; International audience; In the Mediterranean region, the effects of climate change on tree growth have been more and more noticeable in recent decades. Pinus nigra is one of the most common mid-elevation pine in this region and one of the species most affected by increasing dryness. In Tunisia, in order to guide species selection for future reforestation of the Khroumirie Mountains, research studies are under way to improve knowledge of black pine ecology. The effects of interannual climate variations on radial growth were compared for 19 provenances of black pine in a 51-year-old common garden experiment in Souiniet (NW Tunisia, 492m) in a humid Mediterranean bioclimate. A significant positive correlation with April precipitation and a significant negative correlation with spring temperature were noted. A cool wet spring is beneficial to growth as it affects tree water balance at the onset of the growing season; in contrast, spring drought is responsible for low annual growth. Mild January–February temperatures have a positive influence on ring width as mild winters may foster photosynthesis and promote early resumption of cambial activity. Analysis of the pointer years showed that winter snow and hail are major factors limiting growth of black pine in the studied area. Despite overall similarities in ring width to climate relationships among provenances, differences observed attest to the interaction of the environment and genetic control of black pine diameter growth.

International audience; Cedrus brevifolia is a narrowly distributed conifer species, currently limited to a single mountain in Cyprus, growing in restricted habitats on sites of different densities and sizes. This study assessed the influence of seed and pollen dispersal, as well as the effect of demographic and genetic features on the magnitude of fine-scale spatial genetic structure (SGS). Sampling was performed in 11 plots where 50 neighboring adult trees were sampled from each plot, while biparentally and paternally inherited genomes were used for analysis with microsatellites. Fine-scale SGS was significant but showed contrasting patterns among plots. Although the magnitude of SGS in C. brevifolia mainly results from restricted seed dispersal, short-distance pollen dispersal could also explain fine-scale SGS in some plots, which is rather uncommon in wind-pollinated conifer species. The lack of a general and consistent trend of SGS among plots and between genomes indicates that pollen and seed dispersal varies at plot level. The complex SGS patterns in C. brevifolia may result from the unequal ratio of male and female strobilies of trees within the same plots, at different reproductive periods. Demographic features such as habitat fragmentation did not influence the magnitude of SGS in C. brevifolia, whereas low tree aggregation reduced it. Further, the significant correlation observed between linkage disequilibrium (LD) and plots with significant SGS supports the assumption that under specific conditions, LD is likely to be caused by the magnitude of SGS.

Le pin de Salzmann : une espèce à protéger

Species distribution maps are often lacking for scientific investigation and strategic management planning at international level. Here, we present the range-wide, natural distribution maps of twenty-four Mediterranean and European forest-tree species of key ecological and economic importance in the Mediterranean. Dataset access: https://doi.org/10.5281/zenodo.1308577. Associated metadata access: http://www.fao.org/geonetwork/srv/en/metadata.show?id=56996.

National audience

The European black pine (Pinus nigra Arn.) is an ecologically and economically important conifer discontinuously and often patchily distributed across different ecological environments and climatic conditions around the Mediterranean Basin. Many studies aiming at understanding the evolutionary history of the species have been carried out, particularly in the hope of resolving the taxonomy of this collective species where many subspecies have been described. So far, neither morphology, enzyme, and metabolite polymorphism nor DNA marker studies have been able to converge on a single taxonomy, and the evolutionary history of the European black pine remains unclear. To date, nuclear microsatellites (nSSRs) are not available for P. nigra. In this work we designed two multiplexes of eight and six nSSRs each, both characterized by high amplification quality and polymorphism. Nine nSSRs were specifically developed for the European black pine starting from six transcriptomes sequenced using Next Generation Sequencing (NGS) techniques following the Illumina method, while five previously developed for other pines were successfully transferred to P. nigra. The mean number of alleles per locus was 5.9, and the observed heterozygosity ranged between 0.341 and 0.875. F ST was statistically significant for all loci, and Bayesian clustering approaches revealed a geographically meaningful population structure. We thus show this set of 14 nSSRs to be highly informative for population genetic studies and of significant interest to resolve the taxonomy of the European black pine.

Synthesis centers offer a unique amalgam of culture, infrastructure, leadership, and support that facilitates creative discovery on issues crucial to science and society. The combination of logistical support, postdoctoral or senior fellowships, complex data management, informatics and computing capability or expertise, and most of all, opportunity for group discussion and reflection lowers the “activation energy” necessary to promote creativity and the cross-fertilization of ideas. Synthesis centers are explicitly created and operated as community-oriented infrastructure, with scholarly directions driven by the ever-changing interests and needs of an open and inclusive scientific community. The last decade has seen a rise in the number of synthesis centers globally but also the end of core federal funding for several, challenging the sustainability of the infrastructure for this key research strategy. Here, we present the history and rationale for supporting synthesis centers, integrate insights arising from two decades of experience, and explore the challenges and opportunities for long-term sustainability. Postprint

Seed production is a strong indicator of plant fitness and plays a major role in population dynamics. However, the environmental and Seed production is a strong indicator of plant fitness and plays a major role in population dynamics. However, the environmental and endogenous factors driving seed production are still poorly described and are often hard to disentangle. Consequently, we combined principal components analysis and mixed-effects linear models that can consider the multicollinearity of the explanatory variables and quantify their respective influence on the spatio-temporal variability in reproduction. We applied this method to analyze the relationships between cone production in Abies alba Mill. trees (6829 individual reports of cone production). We estimated the relationships between cone production and climate, elevation, tree size (diameter and height), age, crown defoliation rate, and past radial growth. We found that the distribution of annual cone production was highly skewed; 21% of the trees did not produce any cones, whereas 3.7% produced more than 100 cones in a single year. Among the endogenous factors, tree size explained 57% of the variation in cone production with large trees being the most productive. Low radial growth rates in previous years were mostly associated with higher cone production (14% of the variation), while elevation and crown defoliation had non-monotonic effects on reproduction. Finally, years of high cone production were strongly correlated with the difference between the April temperatures of the two previous years and were also associated with a dry spring 2 yr prior to cone production followed by a humid spring the previous year. These results highlight the complexity of the abiotic and biotic factors involved in reproduction and their respective and interactive influence on the interannual and interindividual variability in cone production.endogenous factors driving seed production are still poorly described and are often hard to disentangle. Consequently, we combined principal components analysis and mixed-effects linear models that can consider the multicollinearity of the explanatory variables and quantify their respective influence on the spatio-temporal variability in reproduction. We applied this method to analyze the relationships between cone production in Abies alba Mill. trees (6829 individual reports of cone production). We estimated the relationships between cone production and climate, elevation, tree size (diameter and height), age, crown defoliation rate, and past radial growth. We found that the distribution of annual cone production was highly skewed; 21% of the trees did not produce any cones, whereas 3.7% produced more than 100 cones in a single year. Among the endogenous factors, tree size explained 57% of the variation in cone production with large trees being the most productive. Low radial growth rates in previous years were mostly associated with higher cone production (14% of the variation), while elevation and crown defoliation had non-monotonic effects on reproduction. Finally, years of high cone production were strongly correlated with the difference between the April temperatures of the two previous years and were also associated with a dry spring 2 yr prior to cone production followed by a humid spring the previous year. These results highlight the complexity of the abiotic and biotic factors involved in reproduction and their respective and interactive influence on the interannual and interindividual variability in cone production.

International audience

The fate of peripheral forest tree populations is of particular interest in the context of climate change. These populations may concurrently be those where the most significant evolutionary changes will occur; those most facing increasing extinction risk; the source of migrants for the colonization of new areas at leading edges; or the source of genetic novelty for reinforcing standing genetic variation in various parts of the range. Deciding which strategy to implement for conserving and sustainably using the genetic resources of peripheral forest tree populations is a challenge. Here, we review the genetic and ecological processes acting on different types of peripheral populations and indicate why these processes may be of general interest for adapting forests and forest management to climate change. We particularly focus on peripheral populations at the rear edge of species distributions where environmental challenges are or will become most acute. We argue that peripheral forest tree populations are “natural laboratories” for resolving priority research questions such as how the complex interaction between demographic processes and natural selection shape local adaptation; and whether genetic adaptation will be sufficient to allow the long-term persistence of species within their current distribution. Peripheral populations are key assets for adaptive forestry which need specific measures for their preservation. The traditionally opposing views which may exist between conservation planning and sustainable forestry need to be reconciled and harmonized for managing peripheral populations. Based on existing knowledge, we suggest approaches and principles which may be used for the management and conservation of these distinctive and valuable populations, to maintain active genetic and ecological processes that have sustained them over time.

Chapitre 2; All around the Mediterranean, forest systems have been shaped by long-term anthropogenic impacts. Today, they provide multiple goods and services. We show how the social-ecological system approach offers a good framework to understand their biodiversity, functioning and dynamics. Mediterranean forests have a huge biodiversity, not only in terms of the number of species but also in terms of within-species genetic diversity (at least tree species). We present a tentative typology of Mediterranean forests regarding this biodiversity. Then, we explain how the dynamics of Mediterranean forests is driven in particular by a combination of three characteristics: specific environmental constraints (mainly summer water deficit), a marked spatial heterogeneity of the environment at all scales, disturbance regime (e.g. fire, droughts, pest attacks, human pressure) of variable intensity and frequency. The future challenges for the Mediterranean forests will be to respond simultaneously to: (i) increased threats related to climate change and human pressure, (ii) new demand for multiple ecosystem services locally, (iii) emerging interest for Mediterranean resources to support adaptive strategies in other regions.

Understanding local adaptation in forest trees is currently a key research and societal priority. Geographically and ecologically marginal populations provide ideal case studies, because environmental stress along with reduced gene flow can facilitate the establishment of locally adapted populations. We sampled European silver fir (Abies alba Mill.) trees in the French Mediterranean Alps, along the margin of its distribution range, from pairs of high- and low-elevation plots on four different mountains situated along a 170-km east-west transect. The analysis of 267 SNP loci from 175 candidate genes suggested a neutral pattern of east-west isolation by distance among mountain sites. F(ST) outlier tests revealed 16 SNPs that showed patterns of divergent selection. Plot climate was characterized using both in situ measurements and gridded data that revealed marked differences between and within mountains with different trends depending on the season. Association between allelic frequencies and bioclimatic variables revealed eight genes that contained candidate SNPs, of which two were also detected using F(ST) outlier methods. All SNPs were associated with winter drought, and one of them showed strong evidence of selection with respect to elevation. Q(ST)-F(ST) tests for fitness-related traits measured in a common garden suggested adaptive divergence for the date of bud flush and for growth rate. Overall, our results suggest a complex adaptive picture for A. alba in the southern French Alps where, during the east-to-west Holocene recolonization, locally advantageous genetic variants established at both the landscape and local scales.

During the last decade, large data sets have been increasingly used to address key questions in the field of forest science, including: (1) the impact of climate change on productivity and species distribution; (2) the long-term course of carbon, water, and nutrient cycles; (3) the spread and virulence of pathogens; (4) the genetic basis of local adaptation; and (5) sustainable socio-economic strategies (Rehfeldt et al. 2001, 2002; Diaz-Balteiro and Romero 2008; Cappa et al. 2012; Benito-Garzon et al. 2013; Porth et al. 2013; Stephenson et al. 2014). Sound data are difficult to produce in forest science because trees are long lived, are elements of complex ecosystems, and are not easily amenable to simple experiments. Yet, foresters have observed, monitored, and measured trees and forest ecosystems for a very long time, producing impressive data sets. International provenance tests are carefully monitored since the early twentieth centrury (Rehfeldt et al. 2001, 2002); they compare in common gardens trees from seeds collected in different localities (provenances) in order to record the genetic diversity of traits of importance for forestry and adaptation. Similarly, long-term records are now available for the carbon budget, water use, and nutrient cycling of a large number of forest ecosystems in temperate, boreal, as well as tropical forests (Luyssaert et al. 2007). However, like in other fields of research, the fate of these data remains, in many cases, uncertain, which has certainly detrimental effects for the advancement of forest science and for the improvement of forest ecosystem management. In the best of cases, they were published (usually not in the form of raw data) along with companion articles discussing the results. In most cases, they are stored under heterogeneous formats in the personal files of researchers and risk disappearing when these researchers change interests or retire. Recent European and international projects have taken this concern very seriously and have initiated the construction of large metadata and databases (e.g., TreeBreedex and Evoltree for genetic data, European Fluxes Database Cluster like ICOS, CarboExtreme, GHG-Europe, InGOS, for long-term ecological monitoring). International networks that monitor functional and morphological changes in forests are pushing in this direction. Institutes and research departments simultaneously consolidate available data into standardized and interconnected databases. Such a wealth of data requires very specific database management and data sharing procedures (Michener and Jones 2012). In addition to producing increasingly large data sets from monitoring and automated machine collections, forest science also relies on a large number of short-term experiments whose main results are published in scientific journals, usually without providing the corresponding data that are sometimes lost after publication. There is a general feeling that such data are often under-analyzed by their authors and that they should be made available for re-use through synthesis and analysis to generate novel ideas and test theories at unprecedented scales. Handling Editor: Erwin Dreyer B. Fady : C. Pichot INRA, UR 629, Ecologie des Forets Mediterraneennes, Domaine St Paul, Site Agroparc, 84914 Avignon, France

International audience; The availability of high-resolution, cost-effective polymorphic genetic markers displaying Mendelian inheritance is a prerequisite for fine-scale population genetic analyses as well as informed conservation and sustainable management. Silver fir (Abies alba Mill.) is a widespread European species of economic and ecological importance for which genetic markers are needed but difficult to develop, as in most conifer species. In this work, we introduce two sets of new multiplexed transcriptome-derived expressed sequence tag microsatellites (EST-simple sequence repeats (SSRs)) which we compare to a set of multiplexed genomic microsatellites (gSSRs). For both marker types, transferability was tested in 17 congeneric taxa. A total of 16 new EST-SSRs and two new gSSRs were developed. The EST-SSR multiplexes produced easily scorable amplification patterns that allow rapid and cost-effective genotyping at low-error rates, and include loci that display very low null allele frequencies. Generally, EST-SSRs displayed lower polymorphism and frequency of null alleles, but higher genetic differentiation among populations than gSSRs. Preliminary tests revealed that the EST-SSR markers are highly transferable and polymorphic across Abies species. This study also confirmed that SSRs can be successfully developed using next-generation sequencing technology also in large genome species such as conifers.

International audience; The Salzmann pine (Pinus nigra ssp. salzmannii) is an endemic subspecies of black pine native to the Western Mediterranean basin. In Spain, Salzmann pine covers extensive areas (approx. 350 000 ha), while in France where few scattered populations subsist, its distribution area is estimated at approx. 3 000 ha. We used a dendroecological approach to understand the impact of climate fluctuations on Salzmann pine from France. Spatial and temporal variability of radial growth response was compared in three ecologically different populations (Conflent, Gorges du Tarn, Saint-Guilhem-le-D,sert). The Conflent population showed a strong sensitivity to spring precipitation deficits (March to June), while at Gorges du Tarn and Saint-Guilhem sites, autumn (October) of the previous year and winter (February) temperatures explained more variance than precipitations and were, respectively, negatively and positively correlated to radial growth. Although covering a limited distribution range in France, Salzmann pine demonstrated large differences in radial growth response to climate and soil variations.

International audience; Mediterranean pines share many common life-history traits. They are found at almost all altitudinal levels around the Mediterranean Basin, from sea level to high-elevation mountains, and from hot and dry to wet and cold bioclimates. Their distribution ranges from widespread to regional and narrow, and from dense extensive populations to small populations of scattered individuals. They have been extensively used by human civilizations for millennia. I show which are the main phylogenetic, ecological, and climatic factors explaining the patterns of within and among-population genetic diversity in Mediterranean pines. I use a narrative synthesis approach and multiple examples from the literature on pine species from the Mediterranean Basin and California. While Mediterranean pines have the highest levels of differentiation worldwide, their genetic diversity increases from west to east and is significantly reduced in low-elevation species. Factors such as ancestral adaptation to wildfire, reduction of effective population size during the Last Glacial Maximum, long distance dispersal during the Holocene, and more recent adaptation to patchy environmental conditions could explain these patterns. Because of contrasted ecological, demographic, historical, and geographical processes, and despite their common biological attributes, pines of the Mediterranean Basin display complex biogeographic patterns at neutral gene level that can help retrace their evolutionary history. Although individual species often represent unique case studies that make generalizations risky, locating habitats of significantly high and low genetic diversity is key for detecting and understanding the major factors affecting gene diversity and may prove useful for profiling areas of high conservation value in the Mediterranean.

International audience; Dispersal and recruitment play a critical role in determining the abundance and the spatial structure of regeneration. In this study, we estimated landscape scale seed dispersal using the inverse modeling method by fitting seedling counts to seed tree location and fertility in the European silver fir Abies alba Miller. Seed trees and seedlings from three age cohorts were counted in 30 plots on Mont Ventoux (southeastern France) at elevations from 995 to 1,605 m, where the following ecological variables were measured: elevation, slope, aspect, light availability, and tree density. We developed and fitted a dispersal model, including a new parameter, recruitment rate, which depended both on the ecological characteristics of the plots and on seed production. Elevation was the factor that affected seedling recruitment the most, with an optimum value at around 1,200 m. Estimated A. alba seed dispersal distances were short (median values for the three cohorts, respectively, 16.4-13.2-19.6 m). We demonstrated that including the ecological characteristics of plots and post-dispersal recruitment processes realistically reduced estimates of seed dispersal distances which are otherwise grossly over-estimated using inverse modeling procedures.

International audience; Inbreeding depression is a key factor affecting the persistence of natural populations, particularly when they are fragmented. In species with mixed mating systems, inbreeding depression can be estimated at the population level by regressing the average progeny fitness by the selfing rate of their mothers. We applied this method using simulated populations to investigate how population genetic parameters can affect the detection power of inbreeding depression. We simulated individual selfing rates and genetic loads from which we computed fitness values. The regression method yielded high statistical power, inbreeding depression being detected as significant (5 % level) in 92 % of the simulations. High individual variation in selfing rate and high mean genetic load led to better detection of inbreeding depression while high among-individual variation in genetic load made it more difficult to detect inbreeding depression. For a constant sampling effort, increasing the number of progenies while decreasing the number of individuals per progeny enhanced the detection power of inbreeding depression. We discuss the implication of among-mother variability of genetic load and selfing rate on inbreeding depression studies.

Leaf unfolding is a key ecosystem parameter controlling carbon and water fluxes and affecting forest dynamics. This parameter is highly sensitive to temperature and, consequently, often used as an indicator of global change. In this paper, we analyzed weekly leaf unfolding dynamics for seven temperate species ( Fagus sylvatica L., Acer opalus Mill., Sorbus aria L., Quercus pubescens Willd. Abies alba Mill., Pinus sylvestris L., Pinus nigra Arnold). The effects of temperature on leaf unfolding were studied in situ using several methods and proxies. First, in a spatial approach, leaf unfolding dates were measured along two altitudinal gradients situated on the north and south face of the Mont Ventoux to test altitudinal and slope effects. Second, in a temporal approach, the year effect was analyzed on the north face by comparing two contrasted years (2006 and 2007). Finally, the role of temperature was investigated directly by linking leaf unfolding patterns and temperatures recorded during the leaf unfolding process itself. Two major conclusions were obtained. First, three distinct leaf unfolding patterns were revealed: a rapid sigmoid pattern for the deciduous species group, a slow kinetic pattern for the pines and an intermediate pattern for A. alba . Second, we found an unexpected pattern of variation in the response to spatial or temporal variation of temperature. The more sensitive a species was to temperature variations between years, the less sensitive it was to temperature variations due to altitude. Finally, we discuss that these results can be correlated to two major life history traits: evergreen vs. deciduous and shade tolerant vs. shade intolerant.

International audience; Diffusion is one of the most frequently used assumptions to explain dispersal. Diffusion models and in particular reaction–diffusion equations usually lead to solutions moving at constant speeds, too slow compared to observations. As early as 1899, Reid had found that the rate of spread of tree species migrating to northern environments at the beginning of the Holocene was too fast to be explained by diffusive dispersal. Rapid spreading is generally explained using long distance dispersal events, modelled through integro-differential equations (IDEs) with exponentially unbounded (EU) kernels, i.e. decaying slower than any exponential. We show here that classical reaction–diffusion models of the Fisher–Kolmogorov–Petrovsky–Piskunov type can produce patterns of colonisation very similar to those of IDEs, if the initial population is EU at the beginning of the considered colonisation event. Many similarities between reaction–diffusion models with EU initial data and IDEs with EU kernels are found; in particular comparable accelerating rates of spread and flattening of the solutions. There was previously no systematic mathematical theory for such reaction–diffusion models with EU initial data. Yet, EU initial data can easily be understood as consequences of colonisation–retraction events and lead to fast spreading and accelerating rates of spread without the long distance hypothesis.

International audience; Our study is part of a multi-disciplinary research project aimed at stimulating debate among researchers and local managers. The central question of this multi-disciplinary research project was to better understand and manage high biodiversity value open habitats threatened with shrub encroachment and landscape closure, a common problem throughout Europe. Here, we study shrub encroachment and its impact on biodiversity conservation in Mount Ventoux, a MAB Biosphere Reserve located at the southernmost tip of the French Alps. We show how using a multi-agent modelling approach provide a valuable framework to confront two potentially conflicting conservation efforts in this mountain Mediterranean landscape, that of the within-species diversity of a tree (Abies alba, the European silver fir) and that of an endangered species (Vipera ursinii ursinii, the Orsini viper). A companion modelling approach – approach which aims at transmitting and sharing knowledge, methods and tools that help understand and strengthen the collective decision making process of stakeholders sharing a common resource – was used in order to collectively represent the main activities underway on the mountain and to have a tool to address both open landscapes rehabilitation and restoration of forest environments. The co-construction of the model allowed us to build a shared representation of the territory under study and to develop and compare alternative management scenarios with local stakeholders, both to evaluate their impact on biodiversity and to provide information for forest and grazing management practice

International audience; Oleaginous seeds are among the functional foods most recognized for their tocopherols and triacylglycerols because of their role in lipid metabolism. In this paper, the tocopherol and triacylglycerol contents in seeds of several Pinus pinea L. populations around the Mediterranean Basin were investigated. Lipids were extracted from fully ripen seeds with petroleum ether. The tocopherol (a-tocopherol, g-tocopherol, and d-tocopherol) contents were, respectively, 15.349 3.75 ppm, 1,681.759404.03 ppm and 41.8799.79 ppm. Lipids (mainly triacylglycerols) in P. pinea seeds averaged 48% on a dry weight basis. Triacylglycerols with an equivalent carbon number of 44 (32.27%) and of 46 (30.91%) were dominant. The major triacylglycerol was LLO (24.06%). Tocopherols and triacylglycerols were present at remarkably high levels, thus making P. pinea oil a valuable source of antioxidants and unsaturated fatty acids with varying levels across the geographical range of P. pinea

Nuclear SSRs are notorious for having relatively high frequencies of null alleles, i.e. alleles that fail to amplify and are thus recessive and undetected in heterozygotes. In this paper, we compare two kinds of approaches for estimating null allele frequencies at seven nuclear microsatellite markers in three French Fagus sylvatica populations: (1) maximum likelihood methods that compare observed and expected homozygote frequencies in the population under the assumption of Hardy-Weinberg equilibrium and (2) direct null allele frequency estimates from progeny where parent genotypes are known. We show that null allele frequencies are high in F. sylvatica (7.0% on average with the population method, 5.1% with the progeny method), and that estimates are consistent between the two approaches, especially when the number of sampled maternal half-sib progeny arrays is large. With null allele frequencies ranging between 5% and 8% on average across loci, population genetic parameters such as genetic differentiation (F ST) may be mostly unbiased. However, using markers with such average prevalence of null alleles (up to 15% for some loci) can be seriously misleading in fine scale population studies and parentage analysis.

International audience; We present a range-wide synthesis of our own research and related work on the complex postglacial history of Abies alba Mill. It is based on macroremains, fossil pollen records as well as on different genetic markers. The geographic distribution of genetic lineages and allele frequencies together with the fossil records confirm multiple refugia with at least three of them being sources for the Holocene range expansion into Central Europe, representing so-called effective refugia. One is located in the northern Apennines. A long-term refugium in the southern Balkans contributes to northward expansion with a branch along the Carpathians in the East and the Dinaric Alps in the West. Furthermore, new allozyme data indicate a third effective refugium in the northern or western Balkans, respectively. Using different genetic marker categories the differentiation of A. alba populations could be attributed to different time scales. A separation of maternal lineages took place in previous glacial cycles of the Quaternary, while a second pattern of genetic differentiation is the result of isolation processes during the last glaciation and subsequent gene flow after range expansion. Suture and introgression zones of refugial gene pools were clearly recognised. The patterns of genetic variation and genetic diversity spanning between rear and leading edges of the present range are discussed for evolutionary implications and conservation strategies.

International audience; Aim To investigate the impact of past environmental changes on Cedrus atlantica and its current genetic diversity, and to predict its future distribution. Location Morocco, Algeria and Tunisia. Methods Eleven fossil pollen records from these three countries were used to locate putative glacial refugia and to reconstruct past climate changes. A mechanistic vegetation distribution model was used to simulate the distribution of C. atlantica in the year 2100. In addition, a genetic survey was carried out on modern Moroccan C. atlantica. Results Pollen records indicate that Cedrus was present during the last glacial period, probably in scattered refugia, in Tunisia, Algeria and Morocco. In the Tunisian and Algerian sites, cedar expanded during the late glacial and the early Holocene, then disappeared after c. 8000 yr bp. Reconstructed mean annual precipitation and January temperature show that the last glacial period in Morocco was cooler by 10–15C and drier by c. 300–400 mm year)1 than the climate today. Modern chloroplast microsatellites of 15 C. atlantica populations in Morocco confirm the presence of multiple refugia and indicate that cedar recolonized the Moroccan mountains fairly recently. Model simulation indicates that by the year 2100 the potential distribution of C. atlantica will be much restricted with a potential survival area located in the High Atlas. Main conclusions Environmental changes in northern Africa since the last glacial period have had an impact on the geographical distribution of C. atlantica and on its modern genetic diversity. It is possible that by the end of this century C. atlantica may be unable to survive in its present-day locations. To preserve the species, we suggest that seedlings from modern C. atlantica populations located in the High Atlas mountains, where a high genetic diversity is found, be transplanted into the western High Atlas.

International audience; We used paternally inherited chloroplast microsatellites (cpSSR) to study population genetic structure in the endemic and highly restricted Serbian spruce Picea omorika. Fragment size polymorphism at the five cpSSR regions that could be amplified out of the nine tested combined into only four different haplotypes in the seven populations studied. Mean total haplotypic diversity was H T = 0.395, and mean within-population diversity was H s = 0.279. Haplotypic variation was lower than in most conifers described so far and partitioned into two geographical groups. All northern P. omorika populations were fixed or nearly fixed for the common haplotype, while southern populations exhibited two to three haplotypes. We suggest that current P. omorika populations are shaped by extreme demographic bottleneck and random genetic drift linked to Quaternary glacial cycles. P. omorika thus belongs to the small group of genetically depauperate tree species

Genetic variation is generally considered a prerequisite for adaptation to new environmental conditions. Thus the discovery of genetically depauperate but geographically widespread species is unexpected. We used 12 paternally inherited chloroplast microsatellites to estimate population genetic variation across the full range of an emblematic circum-Mediterranean conifer, stone pine (Pinus pinea L.). The same chloroplast DNA haplotype is fixed in nearly all of the 34 investigated populations. Such a low level of variation is consistent with a previous report of very low levels of diversity at nuclear loci in this species. Stone pine appears to have passed through a severe and prolonged demographic bottleneck, followed by subsequent natural- and human-mediated dispersal across the Mediterranean Basin. No other abundant and widespread plant species has as little genetic diversity as P. pinea at both chloroplast and nuclear markers. However, the species harbors a nonnegligible amount of variation at adaptive traits. Thus a causal relationship between genetic diversity, as measured by marker loci, and the evolutionary precariousness of a species, cannot be taken for granted. © 2007 The Author(s).

Mixed mating, where a single tree progeny results from a mixture of selfing and outcrossing, is widespread in conifers and could be an evolutionary advantage at ecological margins when mating partners become scarce. This study analyzes how the mating system responds to bioclimate and density variations. We surveyed published data on the mating system of Abies, Picea and Pinus species when information on bioclimate and stand density was available. Our survey revealed that Mediterranean species demonstrate a lower selfing rate than other species and that the proportion of selfed versus outcrossed progeny is not fixed within species. The highest variability in mating types within populations was found when stand density was the most variable. To show how density affects the proportion of selfed versus outcrossed progeny, we used isozymes to genotype single tree seeds from a marginal Abies alba forest in Mediterranean France (Mont Ventoux) where low-to high-density stands are found. We then tested the adaptive potential of the different high and low density progenies by sowing them under controlled nursery conditions and measuring germination rate and seedling survival after 4 yr under 3 different water regimes. Although the mean value of outcrossing rate was typical for mixed mating conifers (tm = 0.85), individual outcrossing rates varied from 0.05 to 0.99 and were strongly correlated with stand type and density (tm from 0.87 in high-density to 0.43 in low-density marginal stands). Significantly fewer seeds from the low density marginal stand germinated (32% vs. 53% in the high density mature stand), although seedlings from the marginal stand had a better 4-yr survival (81%) than seedlings from the high-density mature stand (63%) when the three water regimes (from least to most stressful) were averaged. Trees from low density stands may be at a selective disadvantage because they produce more selfed progeny than trees from high-density stands. However, selfed seeds may be purged early on (at the embryo stage) and the remaining seeds tend to produce seedlings with better fitness. Variability of the selfing rate might thus be an adaptive strategy for species in highly contrasted environments where selection of both reproductive assurance and avoidance of inbreeding depression may be density dependent.