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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.

Caractériser la dynamique d’une forêt est essentiel pour la gestion forestière. Les houppiers des arbres forment un élément clé de cette dynamique ; mais, en forêt tropicale, les mesurer n’est pas simple. Cette étude teste l’utilisation d’images aériennes à haute résolution pour estimer la croissance diamétrique des arbres, en intégrant des mesures fines des houppiers détectés. Des ortho-images de 10 cm/pixel de résolution ont été obtenues à l’aide d’un drone à aile fixe sur une parcelle de 9 ha, installée dans la forêt de Yoko en République démocratique du Congo. Les inventaires menés sur les arbres de DHP ≥ 10 cm en 2008 et en 2016 ont permis d’avoir accès à différentes caractéristiques dendrométriques individuelles, dont le diamètre des arbres et leur tempérament, et de calculer des accroissements diamétriques. Des modèles linéaires mixtes ont été calibrés pour prédire l’accroissement de 163 arbres identifiés à la fois sur le terrain et sur les ortho-images en utilisant les variables quantifiées uniquement sur le terrain et/ou à partir de variables mesurées sur les ortho-images. Les images aériennes ont permis de détecter 23,4 % des arbres de DHP ≥ 10 cm inventoriés au sol, et représentant 75,1 % de la biomasse aérienne du peuplement. La probabilité de détection des arbres a varié en fonction de leur DHP : de 0,09 pour les arbres de DHP < 30 cm à 0,97 pour les arbres de DHP ≥ 60 cm. Les variables quantifiées par télédétection ajoutées aux variables de terrain ont permis d’améliorer significativement la prédiction de l’accroissement diamétrique. Les meilleurs modèles d’estimation des accroissements diamétriques contiennent notamment un terme caractérisant la dimension du houppier des arbres qui n’a pu être mesuré que par télédétection. Parmi les variables déterminées par télédétection, la superficie convexe du houppier est apparue la plus performante dans les modèles, et s’avère ainsi être la mesure la plus intéressante pour décrire la compétition entre les houppiers. Ces résultats ouvrent des perspectives pour construire de nouveaux outils d’acquisition de données au service de l’aménagement forestier.

Tree growth and mortality are two central processes in mixed and structurally complex moist tropical forests, yet accurate estimates of the variables needed to model them remain sparse and scattered. It is thus still difficult to predict forest evolution at a local scale and build reliable management plans. To help fill this gap, for 1–7 years we annually monitored 21,180 trees belonging to 42 species exploited for timber production in Central Africa. We made new species-specific estimates of diameter increments and mortality rates, and investigated how tree growth varied with tree size and logging history. We compared our results with the legal values of diameter increments, mortality rates, and minimum cutting diameters used to build forest management plans in Cameroon. Diameter increment was found to vary with tree size for most of the species studied. The relationships between diameter increment and tree size were mostly humpback-shaped. The trees with diameters close to or lower than the reference minimum cutting diameter generally grew faster than the average. We also found that tree growth could slow for 1–2 years after timber exploitation and was then spurred for at least 5 years. The tree growth response to logging was nevertheless species-specific. This study provides new estimates of tree diameter increments and mortality rates that could help make more accurate forest projections and draw up sustainable management plans in Africa.

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.

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.

International audience; The transparency of trees is the most important indicator for a forest health assessment. This paper presents an efficient method for calculating the crown transparency coefficient from tree binary images. This coefficient is based on the automated quantification of the deep indentation, macro-hole and micro-hole densities. Circular structuring elements are introduced, among other things, to automatically find the significant biological size. The symmetric tree convex hull and the tree smoothed contour are defined to delineate the reference areas necessary to evaluate the above-mentioned densities. Statistical thresholds are proposed to eliminate human operator subjectivity, especially in the automated identification of anatomical elements such as soft and deep crown-indentations or macro and micro crown-holes. A point-wise transparency map is produced to better appreciate the origin of the visible skylight areas in the crown. The crown micro-hole density is calculated from the 0.1-to-0.5 transparency points, the crown macro-hole density from the 0.5-to-1 transparency points. We finally opt for weighting of the above three densities with regard to the importance of the symptoms they describe for a more relevant crown transparency coefficient. A comparative study on several trees from full-size and half-size binary images showed that our method is similar overall to the DSO and less sensitive to scale reduction.

Forest trees are an unparalleled group of organisms in their combined ecological, economic and societal importance. With widespread distributions, predominantly random mating systems and large population sizes, most tree species harbour extensive genetic variation both within and among populations. At the same time, demographic processes associated with Pleistocene climate oscillations and land-use change have affected contemporary range-wide diversity and may impinge on the potential for future adaptation. Understanding how these adaptive and neutral processes have shaped the genomes of trees species is therefore central to their management and conservation. As for many other taxa, the advent of high-throughput sequencing methods is expected to yield an understanding of the interplay between the genome and environment at a level of detail and depth not possible only a few years ago. An international conference entitled ‘Genomics and Forest Tree Genetics’ was held in May 2016, in Arcachon (France), and brought together forest geneticists with a wide range of research interests to disseminate recent efforts that leverage contemporary genomic tools to probe the population, quantitative and evolutionary genomics of trees. An important goal of the conference was to discuss how such data can be applied to both genome-enabled breeding and the conservation of forest genetic resources under land use and climate change. Here, we report discoveries presented at the meeting and discuss how the ecological genomic toolkit can be used to address both basic and applied questions in tree biology.

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).

L'impact de l'exploitation forestière sur le renouvellement du stock de bois d'œuvre reste largement méconnu en Afrique centrale du fait du manque de données sur la dynamique des populations d’arbres exploités. C’est en particulier le cas pour l’azobé, Lophira alata, un bois d’œuvre de grande valeur commerciale. L'objectif de cette étude était double : quantifier l'effet du type forestier et de l’exploitation sur la croissance de l’azobé et simuler l'évolution du stock exploitable et du taux de reconstitution après exploitation. Nous avons effectué pendant trois ans un suivi annuel de la croissance et de la mortalité dans trois types forestiers au Cameroun : en forêt sempervirente, en forêt mixte et en forêt semi-caducifoliée. Le recrutement a été étudié uniquement en forêt mixte, sous deux conditions : en milieu exploité et non exploité. Nous avons calibré, avec ces données, un modèle matriciel de Usher. Douze scénarios d’exploitation ont été simulés en faisant varier le diamètre minimum d’exploitation de 60, 70 et 80 cm, et l’intensité de prélèvement des arbres de 100, 80, 60 et 40 %. La croissance de l’azobé est influencée à la fois par le type forestier et l'exploitation. Les arbres de forêt sempervirente ont une croissance plus faible jusqu’à 50 cm de diamètre, alors que la croissance maximale prédite pour ce type forestier est la plus élevée. L'exploitation a par ailleurs stimulé la croissance. Enfin, l’exploitation de l'azobé ne respecte pas le principe du rendement soutenu : ses taux de croissance à long terme varient entre 0,54 et 0,83. Pour garantir la durabilité de son exploitation au Cameroun, une sylviculture dynamisant la croissance des futurs arbres exploitables, ainsi que leur régénération, s’avère indispensable.

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.

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.

International audience; Bien que les émergences de bioagresseurs ne soient pas des phénomènes récents, elles posent pour la santé des forêts de multiples questions et de nouveaux enjeux. Leur occurence est en effet en forte augmentation ces dernières décennies. Replacer ces phénomènes dans un cadre conceptuel commun à la santé végétale, animale et humaine, et dans le contexte des changements globaux, permet de mieux identifier les mécanismes et facteurs qui favorisent les maladies émergente, et ainsi les possibles leviers d'actions.

Le domaine de Namalok (4 500 ha), situé au nord-est de la Tanzanie, a été protégé par TPC Limited, une société sucrière privée, pour en faire une réserve privée de faune et de flore. La végétation locale est constituée de savanes arbustives à Salvadora persica, de fourrés de Suaeda monoica et de savanes arborées plus au moins denses à Acacia xanthophloea, Faidherbia albida et Acacia tortilis. Afin de répondre à un objectif de gestion suite à la réintroduction de grands herbivores, la composition floristique de ces formations ligneuses a été étudiée en association avec une approche cartographique du degré d’accessibilité des formations ligneuses par les herbivores, exprimé en classes de densité établies selon l’indice perpendiculaire de végétation (IPV). Les résultats révèlent tout d’abord une corrélation très élevée entre la densité calculée des ligneux et l’IPV (r2 = 0,96) et confirment l’intérêt de l’approche proposée d’analyse d’images satellitaires. Dans une perspective plus locale, ils montrent aussi que, sur le plan floristique, les niveaux successifs des densités cartographiées sont composés de 70 espèces végétales et relèvent d’un fond floristique d’espèces pantropicales. Ces savanes montrent également une distribution spécifique relativement équitable et très diverse, avec des fréquences spécifiques voisines les unes des autres. Les savanes arborées représentent 38 % de la surface du domaine. Par ordre croissant de densité, les savanes de moins de 100 arbres/ha couvrent 836 ha, celles comptant 100 à 200 arbres/ha occupent 654 ha et celles ayant des densités de 200 à 300 arbres/ha sont assez peu importantes et n’occupent que 206 ha. Les savanes de densité supérieure à 300 arbres/ha représentent des étendues beaucoup moins vastes, soit seulement 22 ha.

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; Les pépinières forestières jouent un rôle important dans la filière forestière : elles assurent par la production de plants la régénération artificielle des forêts. Les plants étant des vecteurs potentiels d’agents pathogènes, il est crucial d’éviter que des maladies infectieuses se propagent dans les écosystèmes forestiers et naturels. Les pépinières sont des systèmes complexes de par la diversité des intrants, du matériel utilisé et des méthodes de production, ce qui y rend difficile la gestion des maladies et ravageurs. Cependant, les contaminations des pépinières par des agents pathogènes, même si elles sont difficiles à détecter et à maîtriser, ne sont pas une fatalité. Les sources d’inoculum et les étapes clés de la chaîne de production, au cours desquelles les agents pathogènes se propagent au sein du site, doivent être bien identifiées pour gérer efficacement les maladies qu’ils causent. La mise en place de bonnes pratiques culturales, basées sur des principes élémentaires de prophylaxie et de prévention, permet de les limiter.

Dry forests play a significant role if the livelihoods strategies of millions of people, including many of the world's poorest. This paper reviews the role of dry forests in providing goods and services to the rural poor. The review shows that while dry forests are essential, rural communities are engaged in multiple activities that generate income and the economic importance of forests and trees is context specific. Although the majority of households benefit from forest resources, poorer households tend to generate more relative income from forest products than wealthier households. Community forestry, tourism and payment for environmental service (PES) are promising alternative sources of environmental income, but the outcomes for the poorest remain uncertain. Trade in non-timber forest products (NTFP) is often viewed as a last resort and provides the safety net to cope with both environmental and economic shocks, especially for women. Hence, beyond timber, there are few examples of dry forest products that have generated a sustainable source of significant wealth. As such, it seems likely that dry forests will continue to play a more supplementary role in direct poverty alleviation but an increasingly important role as a safety net that prevents the most vulnerable from slipping into increased poverty and food insecurity during times of crisis.

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.

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.

International audience; The current distribution of forest genetic resources on Earth is the result of a combination of natural processes and human actions. Over time, tree populations have become adapted to their habitats including the local ecological disturbances they face. As the planet enters a phase of human-induced climate change of unprecedented speed and magnitude, however, previously locally-adapted populations are rendered less suitable for new conditions, and 'natural' biotic and abiotic disturbances are taken outside their historic distribution, frequency and intensity ranges. Tree populations rely on phenotypic plasticity to survive in extant locations, on genetic adaptation to modify their local phenotypic optimum or on migration to new suitable environmental conditions. The rate of required change, however, may outpace the ability to respond, and tree species and populations may become locally extinct after specific, but as yet unknown and unquantified, tipping points are reached. Here, we review the importance of forest genetic resources as a source of evolutionary potential for adaptation to changes in climate and other ecological factors. We particularly consider climate-related responses in the context of linkages to disturbances such as pests, diseases and fire, and associated feedback loops. The importance of management strategies to conserve evolutionary potential is emphasised and recommendations for policy-makers are provided.

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.

•Context[br/] The abundance and distribution of tree regeneration is driven by several processes acting at both the seedling establishment and survival stages. Plant– plant interactions highly contribute to regeneration dynamics through seed dispersal and competition or facilitation processes.[br/] [br/] •Aims[br/] The aim of the present study was to assess the relative importance of different functional groups of shrubs for the early establishment of oak seedlings in the coastal forest communities of south-western France.[br/] [br/] •Material and methods[br/] We applied spatial and non-spatial analysis methods in eleven 315-m2 regeneration plots. Within each plot, oak seedlings (height 50 cm and DBH

International audience; 1 Why focus on vulnerability?Forest research has been particularly efficient in detecting the impacts of variability and long-term trends of climate. It is indeed in these ecosystems gathering perennial plants with a long lifespan that the first visible impacts of climate change have been convincingly documented. At first, positive changes in productivity were detected (Becker 1989; Becker et al. 1994; Badeau et al. 1995; Badeau et al. 1996). Improved growth conditions linked to warming, to nitrogen deposition and to increased atmospheric CO2 were perceived fairly early and were also heterogeneous among biogeographical areas due to local limiting factors (trophic or climatic). The first thoughts about the Dryade project were initiated during 2006. In France, the first simulations of potential impacts of available climate scenarios generated awareness, criticism and concerns among managers and foresters (Carbofor, Loustau et al. 2005; Badeau et al. 2010). In addition to climate trends, extreme events had already been identified as a major cause of forest dieback. All major drought events were historically followed by cycles of dieback (Innes et al. 1989; Jones et al. 1993; Landmann 1994; Beniston and Innes 1998; Thomas et al. 2002; Liang et al. 2003; Jurskis 2005). In France, forest dysfunctions induced by the drought events of 2003–2006 were mostly reversible (growth decrease, temporary degradation of crown conditions) but sometimes also irreversible (tree mortality). Several indicators of forest health surveys pointed to a degradation of forest health in France and Europe: abnormal increases in tree mortality (Pauly and Belrose 2005), decline of crown conditions (Lloret et al. 2004; Pauly and Belrose 2005; Belrose et al. 2004, 2006; Carnicer et al. 2011) and upsurge in biotic hazards (Nageleisen 2004; Piou et al. 2006; Rouault et al. 2006).

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.

In northern Cameroon like in all Sudano-Sahelian regions, women have very few rights to trees, although they are key users of tree products. Surveys and feedback sessions were conducted in five villages, each being representative of an agroecological subregion, to understand the disparity between the importance of trees for women and their lack of involvement in tree management. Although women are aware of the pressure on available tree resources, they feel powerless to do anything about it. Tree management actions women have undertaken or intend to undertake are limited to the vicinity of the homestead. In other places, parkland fields and savannah bush, women are skeptical about and sometimes unaware of actions that could be undertaken. This is mainly due to the existing gender relations. Men have the power over rights of access to trees and make all decisions concerning management of trees in the parklands and savannahs. The gender division of labor is such that women are not involved in tree management. A change in gender relations and a complete reversal of opinion and behavior would be needed for a more balanced involvement of women and men in the management of trees.

Eremospatha macrocarpa and Laccosperma secundiflorum are two clonal rattan species: through vegetative reproduction each individual, i.e. each genet, may produce several stems that are linked to the same rhizome. To determine the impact of ramet harvest by local human populations in these species, we compared the demography of their ramets and studied the impact of the dynamics of their ramets on the demography of their genets. This also allowed a better analyze of their life-history and demography. Genets were classified in development stages. We counted for each genet the number of alive, new, dead and harvested ramets. We determined the impact of the number of ramets and changes in this number on the genet probability of survival, retrogression and recruitment. Ramet demography differed between the two rattan species. The average numbers of new, harvested and dead ramets are about two times higher in E. macrocarpa than in L. secundiflorum. Furthermore, ramet demography influenced genet demography in both species. The survival of adult genets in E. macrocarpa and juvenile genets in L. secundiflorum increased with the initial number of ramets (about 10% between the lower and higher ramet numbers). The genet probability of retrogression increased in L. secundiflorum and decreased in E. macrocarpa with the initial number of ramets. These results suggest the existence of some physiological integration between the ramets of the two rattan species which leads to some cooperation and competition between ramets, within a genet, and to the compensatory production of new ramets after harvest. Overall, for both species, the links between ramet and genet demography suggest that ramet harvest, at the present harvesting rate, is not detrimental to the studied rattan populations.

Gérer durablement les forêts tropicales de production nécessite de connaître leur diversité, leur dynamique et l’impact de l’exploitation sur ces caractéristiques. Cette connaissance peut s’obtenir avec de grands dispositifs de suivi permanents dont les arbres sont régulièrement mesurés. Un seul dispositif de ce type existe en Afrique centrale, M’Baïki, installé en 1982 en République centrafricaine. Il a fait référence pour établir les règles d’aménagement d’un grand nombre de concessions forestières de la région. Plusieurs projets ont permis l’installation de nouveaux dispositifs, en privilégiant des zones situées sur des substrats géologiques différents. Deux dispositifs ont ainsi été installés dans des concessions forestières aménagées au nord de la République du Congo, sur alluvions de l’ère cénozoïque (Loundoungou) et sur grès de Carnot de l’ère mésozoïque (Mokabi). Chaque dispositif est constitué de deux blocs de 400 ha, contenant chacun un sentier d’environ 4 000 arbres d’une vingtaine d’espèces commerciales et deux parcelles de 9 ha suivies en plein. Tous les arbres supérieurs à 10 cm de diamètre sont mesurés. Un bloc sera exploité après quelques années de suivi, l’autre restera en témoin. L’installation et le premier inventaire d’un dispositif ont nécessité en moyenne 34 mois de travail avec une équipe de huit personnes pour un coût total moyen de 94500 €. Les peuplements des deux dispositifs, Loundoungou et Mokabi respectivement, ont les caractéristiques suivantes : 240 et 230 espèces d’arbres, densité de 346,8 (± 5,8) et 426,8 (± 3,6) arbres par hectare, biomasse de 432,6 (± 13,8) et 457,3 (± 9,3) Mg/ha. Les difficultés rencontrées lors de l’installation des dispositifs (emplacement, localisation des parcelles, constitution des sentiers, application du protocole d’inventaire, logistique...) sont analysées. Plusieurs recommandations sont émises pour améliorer l’installation de tels dispositifs et leur protocole d’inventaire.

GlobAllomeTree is an international platform for tree allometric equations. It is the first worldwide web platform designed to facilitate the access of the tree allometric equation and to facilitate the assessment of the tree biometric characteristics for commercial volume, bio-energy or carbon cycling. The webplatform presents a database containing tree allometric equations, a software called Fantallomatrik, to facilitate the comparison and selection of the equations, and documentation to facilitate the development of new tree allometric models, improve the evaluation of tree and forest resources and improve knowledge on tree allometric equations. In the Fantallometrik software, equations can be selected by country, ecological zones, input parameters, tree species, statistic parameters and outputs. The continuously updated database currently contains over 5000 tree allometric equations classified according to 73 fields. The software Fantallometrik can be also used to compare equations, insert new data and estimate the selected output variables using field inventory. The GlobAllomeTree products are freely available at the URL: http://globallometree.org for a range of users including foresters, project developers, scientist, student and government staff.

In Central Cameroon cocoa is mainly produced by household farming systems based on complex associations between cocoa and companion trees. Setup either on native/remnant forest or savannah, these agroforestry systems (AFS) are managed according their geographical position and local pedoclimatic conditions. In this paper, we investigated the effects of local management strategies on carbon (C) storage of live trees in three different cocoa production zones of Central Cameroon. In the 58 fields studied, 8,996 cocoa trees and 1,258 companions were surveyed. Tree sampling was non-destructive and to estimate C storage we used allometric models for above- and belowground biomasses. We measured abundance, height, diameter at breast height and determined species of companion trees. We distinguished between four cocoa plantation age categories (immature, young, mature and senescent) and three preceding systems (forest, forest gallery and savannah). We surveyed farmers' use of each associated tree, allocated it to a functional category and asked if it had been introduced or conserved. Total C content of live trees was on average close to 70 t ha?1. We found that it mostly relied on associated trees-cocoa trees contribution being ac. 2-12 % of live trees total C. The level of contribution to C storage of companions from different use categories differed between sites-trees producing food had contributed most in Bokito and Obala while trees used for shading or fertility contributed most in Ngomedzap. Dynamics of C storage in live trees was found to be independent from cocoa trees growth and age. When aging, AFS continuously lost companion trees and especially conserved ones putatively because of farmers' selective logging. Yet, AFS apparently maintained equivalent C storage abilities with time. Hence, even if cocoa do not contribute significantly to C storage in our study, the systems into which they are included are able to significantly store C and may also contribute to other ecological services such as conservation.

Context: In the Mediterranean area, numerous decline and mortality processes have been reported during recent decades, affecting forest dynamics. They are likely due to increases in summer drought severity and therefore especially affect drought-sensitive species, such as silver fir (Abies alba Mill.). [br/] [br/] Aims and methods: To understand the relationships between tree growth, crown condition and mortality probability, radial growth trends of healthy, declining (showing crown damages) and dead trees were compared using tree-ring analysis. Factors involved in determining this mortality were also examined at the plot and tree level using altitudinal gradients on three contrasted sites in southeastern France. [br/][br/] Results: Individuals with higher inter-annual variability in growth were more prone to dieback. At two sites, dead trees displayed lower growth rates over their entire lifetime, while, on the last site, their juvenile growth rate was higher. Trees with crown damage had higher growth rates than healthy trees on one site, and their radial growth trends over time always differed from those of dead trees.Mortality and crown damage were little related to altitude, but strongly differed between sites and among plots underlining the importance of local edaphic and topographic conditions.[br/] [br/] Conclusion: These results suggest that the relationships among mortality probability, crown condition and growth can differ among sites, and highlight the impact of soil conditions and the need to assess them in tree mortality studies.

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.

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.

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

We examined how fire hazard was affected by prescribed burning and fuel recovery over the first six years following treatment. Eight common Mediterranean fuel complexes managed by means of prescribed burning in limestone Provence (South-Eastern France) were studied, illustrating forest and woodland, garrigue and grassland situations. The coupled atmosphere-wildfire behaviour model FIRETEC was used to simulate fire behaviour (ROS, intensity) in these complex vegetations. The temporal threshold related to the effectiveness of prescribed burning in reducing the fire hazard was assessed from derivated fuel dynamics after treatment. The study showed that prescribed burning treatment was effective for the first two years in most of the Mediterranean plant communities analysed. Thereafter, all forests and shrublands were highly combustible with a fire line intensity of more than 5000 kW/m except for pine stands with or without oak (medium intensity of 2000 kW m −1 3 years after treatment). Low fire line intensity (900 kW m −1 ) was obtained for grassland which was entirely treatment-independent since the resprouter hemicryptophyte, Brachypodium retusum , is highly resilient to fire. Fire behaviour was greatly affected by fuel load accumulation of Quercus ilex in woodland, and by standing necromass of Rosmarinus officinalis in treated garrigue. Pure pine stands with shrub strata similar to garrigue showed a lower fire intensity due to wind speed decrease at ground level under tree canopy, underlining the advantage of maintaining a proportion of canopy cover in strategic fuel-break zones.

Allometric models are necessary for estimating biomass in terrestrial ecosystems. Generalized allometric relationship exists for many tropical trees, but species- and region-specific models are often lacking. We developed species-specific allometric models to predict aboveground biomass for 11 native tree species of the Sudanian savannawoodlands. Diameters at the base and at breast height, with species means ranging respectively from 11 to 28 cm and 9 to 19 cm, and the height of the trees were used as predictor variables. Sampled trees spanned a wide range of sizes including the largest sizes these species can reach. As a response variable, the biomass of the trees was obtained through destructive sampling of 4 754 trees during wood harvesting. We used a stepwise multiple regression analysis with backward elimination procedure to develop models separately predicting, total biomass of the trees, stem biomass, and biomass of branches and twigs. All speciesspecific regression models relating biomass with measured tree dimensions were highly significant (p < 0.001). The biomass of branches and twigs was less predictable compared to stem biomass and total biomass, although their models required fewer predictors and predictor interactions. The best-fit equations for total above-ground biomass and stem biomass had R2 > 0.70, except for the Acacia species; for branches including twig biomass, R2-values varied from 0.749 for Anogeissus leiocarpa to 0.183 for Acacia macrostachya. The use of these equations in estimating available biomass will avoid destructive sampling, and aid in planning for sustainable use of these species.

Forking is a frequent flaw in beech which can adversely affect the formation of high quality logs. Even though the hypothesis that late frosts increase forking is widely accepted by forest managers, it remains to be proved and quantified experimentally. Damage caused by a late frost on 15 May 1995 to young beech trees in an experimental site at Lyons-La-Forêt (France) and the consequences on the development of forking were analysed. The beech trees were 17 years old with heights between 1.5 and 9 m. Of all the plantation densities tested only the lowest density (625/ha) showed various and severe frost damage. Three levels of immediate damage to the growing terminal shoot were observed, with increasing intensity from: (1) no trace of frost damage, (2) reddened leaves and (3) frost-nipped shoots. The intensity of visible damage to the terminal shoot appeared to be very dependent on the height of the plant which justified our original experimental approach, based on an evaluation of the damage for each individual. Almost all of the beech trees less than 4 m high suffered frost damage and all those taller than 7 m were unaffected. Three-year-old forks due to frost which occurred in May 1995 were recorded at the end of 1997 using an objective definition based on dendrometric and age criteria. The worst frost damage resulted in a significant increase in the risk of fork emergence (71.7% of the plants were forked). With a risk related to forking in the presence of frost-nipped shoots equal to 2.15 and a fraction of the attributed risk of 0.36 it was concluded that the late frost observed played a significant role in the degradation of the shape of the beech affected by frost and the overall quality of the stand, Les dégâts de gel tardif sur la pousse terminale : un facteur de risque d’apparition de fourches chez le hêtre (Fagus sylvatica L.). La fourchaison est un défaut fréquent du hêtre qui peut nuire à la formation d’une grume de qualité. L’hypothèse d’un effet des gelées tardives contribuant à aggraver la fourchaison, bien que largement admise par les gestionnaires forestiers, restait pourtant à démontrer et à quantifier dans un cadre expérimental. Les dégâts occasionnés par la gelée tardive du 15 mai 1995 sur de jeunes plants de hêtre du dispositif expérimental de Lyons-La-Forêt (France) et leurs conséquences sur la mise en place de fourches ont été analysés. Les hêtres étaient alors âgés de 17 ans et de hauteur comprise entre 1,5 et 9 m. Parmi toutes les densités de plantation testées seule la plus faible (625/ha) présentait un impact fort et diversifié du gel. Trois niveaux d’intensité croissante de dégâts immédiats sur la pousse terminale en élongation ont pu être distingués : (1) aucune trace de gel, (2) feuilles roussies (3) pousse gelée. L’intensité des dégâts visibles sur la pousse terminale est apparue très dépendante de la hauteur du plant justifiant notre approche expérimentale originale centrée sur l’évaluation individuelle des dégâts. La quasi totalité des hêtres de hauteur inférieure à 4 m avaient gelé et tous ceux de hauteur supérieure à 7 m étaient indemnes. Les fourches imputables au gel ont été inventoriées fin 1997 selon une définition objective basée sur des critères dendrométriques et sur un critère d’âge. Le dégât de gel le plus intense a eu pour conséquence une augmentation significative du risque de fourchaison (71,7 % de plants fourchus). Avec un risque relatif de fourchaison en présence de pousse gelée égale à 2,15 et une fraction du risque attribuable de 0,36 on peut conclure que le gel tardif observé contribue notablement à la dégradation de la forme du hêtre touché par le gel et à la qualité globale du peuplement

International audience; The main aim of this paper is to illustrate, using a large set of indicators, the consequences of management choices imposed under five socio-economic forward-looking scenarios within a given case study area during the next 60 years. This 101,000 ha case study area is centred around the village of Pontenx-les-Forges in south west France. This paper details this INTEGRAL project case study area and some forest management schemes implemented by forest owners under various scenarios. Using a landscape simulator handling two forest growth models, the evolution of all forest stands in the landscape is simulated using 9 indicators over a 60-year period: growing stock, harvested volume, carbon sequestered in trees, mean tree volume, commercial value of growing stock, susceptibility to wind and fire and biodiversity indexes. One of the main results of this study was to show up the magnitude of effects on growing stock and harvested volumes: according to the scenarios, annual harvesting could vary by 50% as from 2030. As a consequence, other indicators are impacted, such as biodiversity, wind and fire susceptibility. All these changes are observed despite the fact that the dominant species remain the same and that forest owners are considered not very prone to changing their behaviour. In conclusion, options for future improvement are discussed and the opportunities offered by high definition data acquisition from remote sensing are considered.; L'objectif de cette étude est d'illustrer à l'aide d'indicateurs les conséquences de choix de gestion imposés par cinq scénarios socioéconomiques prospectifs appliqués à une large zone forestière pour les 60 prochaines années. Le cas d'étude choisi est la zone centrée sur la commune de Pontenx-les-Forges dans le sud-ouest de la France et couvrant 101000 hectares. Cet article présente une description de la zone d'étude et des itinéraires sylvicoles mis en ½uvre par les propriétaires forestiers selon des scénarios. À l'aide d'un simulateur pilotant deux modèles de croissance, l'évolution de la zone d'étude à l'échelle de chaque parcelle est synthétisée par 9 indicateurs sur une période de 60 ans : le volume sur pied, le carbone sur pied, le volume total exploité, la valeur commerciale sur pied, le volume de l'arbre moyen, la vulnérabilité au vent et au feu, et des indices de biodiversité. Un des principaux résultats de cette étude est de montrer l'amplitude des changements pour la production et le volume sur pied : selon les scénarios les récoltes annuelles peuvent varier de 50 % dès 2030. Par conséquent, d'autres indicateurs sont impactés comme la biodiversité, la vulnérabilité au vent ou au feu. Pourtant, l'espèce dominante est maintenue et le comportement partiellement conservateur des types de propriétaires est pris en compte. En conclusion, des améliorations pour de futures simulations sont envisagées ; dans ce but, des synergies avec la télédétection sont nécessaires pour la collecte des données d'initialisation sur de larges territoires, ce qui permettra d'améliorer la précision des résultats.

Negative correlation caused by competition among individuals and positive spatial correlation due to environmental heterogeneity may lead to biases in estimating genetic parameters and predicting breeding values (BVs) from forest genetic trials. Former models dealing with competition and environmental heterogeneity did not account for the additive relationships among trees or for the full spatial covariance. This paper extends an individual-tree mixed model with direct additive genetic, genetic, and environmental competition effects, by incorporating a two-dimensional smoothing surface to account for complex patterns of environmental heterogeneity (competition + spatial model (CSM)). We illustrate the proposed model using simulated and real data from a loblolly pine progeny trial. The CSM was compared with three reduced individual-tree mixed models using a real dataset, while simulations comprised only CSM versus true-parameters comparisons. Dispersion parameters were estimated using Bayesian techniques via Gibbs sampling. Simulation results showed that the CSM yielded posterior mean estimates of variance components with slight or negligible biases in the studied scenarios, except for the permanent environment variance. The worst performance of the simulated CSM was under a scenario with weak competition effects and small-scale environmental heterogeneity. When analyzing real data, the CSM yielded a lower value of the deviance information criterion than the reduced models. Moreover, although correlations between predicted BVs calculated from CSM and from a standard model with block effects and direct genetic effects only were high, the ranking among the top 5 % ranked individuals showed differences which indicated that the two models will have quite different genotype selections for the next cycle of breeding. Fil: Cappa, Eduardo Pablo. Instituto Nacional de Tecnología Agropecuaria; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Muñoz, Facundo. Institut National de la Recherche Agronomique; Francia Fil: Sanchez, Leopoldo. Institut National de la Recherche Agronomique; Francia Fil: Cantet, Rodolfo Juan Carlos. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Vegetal; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Erratum paru dans Agroforestry Systems = ISSN 0167-4366. - (2015)vol.89:n°1 p. 95-96. In Sudano-Sahelian agriculture, organic amendments are often limited by resource availability. Small branches (ramial wood, RW) represent an organic resource found in many landscapes but little is known about their effects. This field trial (2007-2009) studied the effects of RW or straw at low application rate (0.69 Mg C ha?1 year?1) on topsoil carbon (C), nitrogen (N) and available phosphorus (P, Pav), termite cast abundance, and sorghum yield. Straw and RW were chopped and either buried (StBu, WoBu) or mulched (StMu, WoMu). Mineral fertilizers were added to straw so that RW- and straw-amended plots received similar applications of C, N, P, and potassium. Another treatment had RW buried with additional N (WoBuN), and there was a control (Ctrl). Branches came from Piliostigma reticulatum, very common in the area. The treatments had little significant effect on topsoil and crop, owing to the low application rate and spatial variability. However, Pav was significantly lower with buried than mulched amendments in 2009, and decreased significantly over time in Ctrl and with buried amendments. Topsoil C also decreased significantly with time in WoMu. Significantly more termite casts were observed with RW. The sorghum yield averaged 0.87 Mg DM ha?1 in 2007 and then decreased. The treatments affected yield significantly in 2008 only: it was higher in WoBuN and StBu than in Ctrl. In 2009, the yield was mainly affected by initial topsoil Pav. These results suggest that RW stimulated biological activity, leading to P immobilization and C mineralization, but had little effect on yields.

International audience; In order to determine the mechanical resistance of several forest tree species to rockfall, an inventory of the type of damage sustained in an active rockfall corridor was carried out in the French Alps. The diameter, spatial position and type of damage incurred were measured in 423 trees. Only 5% of trees had sustained damage above a height of 1.3 m and in damaged trees, 66% of broken or uprooted trees were conifers. Larger trees were more likely to be wounded or dead than smaller trees, although the size of the wounds was relatively smaller in larger trees. The species with the least proportion of damage through stem breakage, uprooting or wounding was European beech (Fagus sylvatica L.). Winching tests were carried out on two conifer species, Norway spruce (Picea abies L.) and Silver .r (Abies alba Mill.), as well as European beech, in order to verify the hypothesis that beech was highly resistant to rockfall and that conifers were more susceptible to uprooting or stem breakage. Nineteen trees were winched downhill and the force necessary to cause failure was measured. The energy (Efail) required to break or uproot a tree was then calculated. Most .r trees failed in the stem and spruce usually failed through uprooting. Beech was either uprooted or broke in the stem and was twice as resistant to failure as .r, and three times more resistant than spruce. Efail was strongly related to stem diameter in European beech only, and was signi.cantly higher in this species compared to Norway spruce. Results suggest that beech would be a better species to plant with regards to protection against rockfall. Nevertheless, all types of di.erent abiotic stresses on any particular alpine site should be considered by the forest manager, as planting only broadleaf species may compromise the protecting capacity of the forest e.g. in the case of snow avalanches. In order to determine the mechanical resistance of several forest tree species to rockfall, an inventory of the type of damage sustained in an active rockfall corridor was carried out in the French Alps. The diameter, spatial position and type of damage incurred were measured in 423 trees. Only 5% of trees had sustained damage above a height of 1.3 m and in damaged trees, 66% of broken or uprooted trees were conifers. Larger trees were more likely to be wounded or dead than smaller trees, although the size of the wounds was relatively smaller in larger trees. The species with the least proportion of damage through stem breakage, uprooting or wounding was European beech (Fagus sylvatica L.). Winching tests were carried out on two conifer species, Norway spruce (Picea abies L.) and Silver .r (Abies alba Mill.), as well as European beech, in order to verify the hypothesis that beech was highly resistant to rockfall and that conifers were more susceptible to uprooting or stem breakage. Nineteen trees were winched downhill and the force necessary to cause failure was measured. The energy (Efail) required to break or uproot a tree was then calculated. Most .r trees failed in the stem and spruce usually failed through uprooting. Beech was either uprooted or broke in the stem and was twice as resistant to failure as .r, and three times more resistant than spruce. Efail was strongly related to stem diameter in European beech only, and was signi.cantly higher in this species compared to Norway spruce. Results suggest that beech would be a better species to plant with regards to protection against rockfall. Nevertheless, all types of di.erent abiotic stresses on any particular alpine site should be considered by the forest manager, as planting only broadleaf species may compromise the protecting capacity of the forest e.g. in the case of snow avalanches.

Introduction. Ricinodendron heudelotii Baill. est une essence forestiere en voie de domestication au Cameroun ou la plante est appreciee pour ses vertus alimentaires, ecologiques et medicinales. Les degâts causes par le psylle Diclidophlebia xuani Messi et al. aux jeunes plants, en pepiniere ou apres leur plantation, constituent l'une des principales contraintes a la domestication de l'espece. La biologie de ce ravageur a donc ete etudiee afin d'envisager son controle. Materiel et methodes. Differents aspects de la biologie de D. xuani ont ete abordes: processus d'accouplement, choix du site de ponte par la femelle, maturation sexuelle des imagos, fecondite des femelles, longevite des imagos, developpement embryonnaire et larvaire, sex-ratio a l'emergence et specificite alimentaire. Les experimentations ont eu lieu dans la region de Yaounde soit en champ, soit en milieu controle durant les annees 2001 et 2002. Resultats et discussion. Les mâles de D. xuani ont emerge avant les femelles et le rapprochement des sexes a eu lieu 15 min environ apres la mue imaginale. La longevite des femelles a ete de 29 jours en moyenne, celle des mâles, de 7 jours. La ponte a commence 3 jours apres l'emergence et s'est poursuivie jusqu'a la fin de la vie de la femelle. En periode chaude (28°C environ), une femelle a pondu en moyenne 532 oeufs pendant toute sa vie; en periode de basses temperatures (24°C a 26°C environ), la fecondite moyenne a ete de 758 oeufs. Les oeufs sont essentiellement deposes sur les etages foliaires les plus jeunes de R. heudelotii. Les developpements embryonnaire et larvaire ont dure respectivement 7 jours et 22 jours environ. Le cycle de developpement, d'oeuf a oeuf, a necessite 32 jours en moyenne. Le sex-ratio a ete proche de 1. Conclusion. D. xuani se developpe entierement et sans interruption sur R. heudelotii; il n'a jamais ete rencontre sur d'autres especes de plantes. Il serait donc etroitement associe a cette plante. (Resume d'auteur)

Trees can pull tons of water up to 100 m above ground, whereas even the best engineered suction pumps can manage only 10 m at most. Beyond this height, the pull of gravity exceeds atmospheric pressure. The pressure at the top of the water column then becomes negative, and pumps drain by a process of vaporization called cavitation. So how do plants, particularly tall trees, cope with cavitation? Do they have an astonishingly high resistance to this process or are they routinely exposed to cavitation events and possess remarkable repair capacities? These questions were first asked when the mechanism of sap ascent in trees was discovered in the late nineteenth century (Brown 2013), but were not answered until reliable methods for measuring cavitation were introduced a century later. Early studies of plant hydraulics suggested that cavitation occurred only in conditions of severe drought (Fig. 1a). However, many studies carried out in the last decade have called this understanding of tree physiology and ecology into question. Diurnal cycles of cavitation and repair have been reported, even in well watered plants, suggesting that plants routinely face cavitation and recover easily from it. Writing in Plant Cell and Environment, Wheeler et al. (2013) provided compelling new experimental evidence that trees are much more resistant to cavitation than previously thought, demonstrating that this change of paradigm should now be reconsidered.

Nonlinear mixed-effects-models are applied successfully to estimate the cambial age of juvenile-mature wood transition in Scots pine sample trees from slow-grown stands. Till now segmented regression models are applied separately for each pith-to-bark-profile of wood density. The nonlinear mixed-effects-model overcomes this limitation while consistently and efficiently estimating the transition point for the whole sample. Furthermore standard errors can be calculated and impacts of stand and tree variables on the shape of pith-to-bark-curves can be tested. Mean ring density, earlywood, and latewood density profiles from 99 trees were determined by X-ray densitometric analysis of disks taken at 4-m stem height. The cambial age of transition from juvenile to mature wood is described according to nonlinear mixed-effects-models based on latewood density profiles. The time-series nature of the data are taken into account. The segmented quadratic-linear model shows the transition at cambial age of 21.77, which vary with the probability of 0.95 within the interval of [18.31; 26.85]. Impacts of tree variables or stands on the location of the transition point were not found, but impacts of stands on the shape of pith-to-bark-curves., Des modèles mixtes non linéaires ont été utilisés avec succès afin d'estimer l'âge (compté depuis la moelle) du passage bois juvénile-bois adulte pour des pins sylvestres provenant de peuplements à croissance lente. Jusqu'à présent, des modèles de régression segmentés étaient ajustés individuellement à chaque profil de densité du bois de la moelle à l'écorce. Le modèle mixte non linéaire permet de dépasser cette limitation en estimant de manière efficace et cohérente l'âge du point de passage pour l'ensemble de la population échantillonnée. En outre, des variances peuvent être estimées et les impacts des peuplements et des caractéristiques des arbres sur la forme des profils de densité du bois de la moelle à l'écorce peuvent être testés. À cette fin, les profils de densité moyenne de cerne, de densité du bois initial et de densité du bois final de 99 arbres ont été mesurés par exploration microdensitométrique de clichés radiographiques obtenus à partir d'échantillons prélevés dans des disques découpés à 4 mètres de hauteur. L'âge compté depuis la moelle du passage bois juvénile-bois adulte a été identifié à partir de modèles mixtes non linéaires appliqués aux profils de densité du bois final. La nature longitudinale des données a été prise en compte. Le modèle segmenté linéaire quadratique retenu permet d'identifier un âge moyen de passage du bois juvénile au bois adulte de 21,77 ans assorti d'un intervalle de confiance à 5 % de 18,31 à 26,85 ans. Si les impacts des variables "caractéristiques des arbres" et "peuplement" sur l'âge de passage bois juvénile-bois adulte n'ont pas été identifiés comme significatifs, le peuplement est apparu avoir un effet sur la forme des courbes d'évolution de la moelle à l'écorce du caractère considéré.

International audience; Allozyme diversity of natural and introduced cypress stands in Morocco: consequences for management of genetic resources. For the purpose of managing Cupressus atlantica natural genetic resources in Morocco, diversity among 9 provenances from 3 cypress species (Cupressus atlantica and 2 introduced species: C. sempervirens and C. arizonica) was studied using seven enzymatic systems. Mean allele number per locus (A) ranged from 2.0 in C. atlantica and C. arizonica to 1.7 in C. sempervirens. Genetic diversity was high (He = 0.29 in C. atlantica; 0.27 in C. sempervirens and 0.33 in C. arizonica) but heterozygote deficiencies were observed. C. atlantica provenances exhibited a low differentiation (GST = 0.013). The high interspecific differentiation (GST = 0.279) was due to the distance between the 2 Mediterranean cypresses (C. atlantica and C. sempervirens) and the Arizonica cypress. Two enzymatic systems (GOT et SOD) strictly differentiated these 2 origins and could be used for introgression monitoring. Advice for preserving and using C. atlantica genetic resources and for reducing the degradation of these natural stands are proposed.; Dans une perspective de gestion des ressources génétiques naturelles du cyprès de l'Atlas au Maroc, la diversité de 9 provenances appartenant à trois espèces (Cupressus atlantica endémique et 2 espèces introduites : C. sempervirens et C. arizonica) a été évaluée à l'aide de sept systèmes enzymatiques. Le nombre moyen d'allèles par locus (A) varie de 2,0 chez C. atlantica et C. arizonica à 1,7 chez C. sempervirens. La diversité génétique est importante (He = 0,29 pour C. atlantica ; 0,27 pour C. sempervirens et 0,33 pour C. arizonica) mais un déficit généralisé d'hétérozygotie a été constaté. Les provenances de C. atlantica s'avèrent peu différenciées (GST = 0,013). Au niveau inter-spécifique, la forte divergence entre les espèces (GST = 0,279) est due à l'éloignement entre les deux cyprès méditerranéens (C. atlantica et C. sempervirens) et le cyprès de l'Arizona. Deux systèmes enzymatiques (GOT et SOD) différencient strictement les espèces méditerranéennes de l'espèce américaine et permettront de suivre d'éventuelles introgressions. Des recommandations sont formulées afin de préserver et valoriser la diversité génétique des populations de cyprès de l'Atlas et de limiter la dégradation de ces peuplements naturels.