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La procédure officielle d'inventaire des ressources ligneuses pour les forêts communautaires camerounaises constitue un obstacle technique et financier majeur. Plusieurs études ont testé des démarches simplifiées mais sans jamais pouvoir proposer une alternative satisfaisante à la méthode standard d'inventaire, à savoir plus abordable financièrement et techniquement pour les populations locales, tout en étant statistiquement robuste. L'article récapitule la démarche et les résultats d'un inventaire forestier à dire d'acteurs, qui a été expérimenté dans une forêt communautaire de 4 800 ha, au couvert forestier dégradé. Cet inventaire repose sur cinq simplifications (1) les seules espèces inventoriées sont celles vendues sur le marché domestique ; (2) les arbres inventoriés sont ceux situés à une distance inférieure à deux kilomètres d'une piste ou d'une rivière d'évacuation ; (3) seuls les arbres ayant un diamètre supérieur ou égal au diamètre minimum d'exploitabilité sont relevés ; (4) l'inventaire n'est réalisé qu'avec les propriétaires coutumiers volontaires ; (5) leur droit de possession coutumière sur les arbres est reconnu. Cet inventaire à dire d'acteurs a permis de recenser 3 885 arbres pour un volume de 19 297 m3 dans la forêt communautaire. La quasi-totalité (93 %) de ces arbres sont situés en cacaoyères. La démarche est techniquement robuste puisque le taux de sondage est estimé au minimum à 35 %, et est donc largement supérieur à celui de l'inventaire forestier standard de 2 %. Cet inventaire est également économique puisque son coût revient à moins de 0,5 €/ha, c'est-à-dire moins de la moitié du coût d'un inventaire classique. Il est enfin socialement acceptable puisqu'il valorise les savoirs traditionnels et permet d'élaborer un mode d'exploitation des arbres favorable aux propriétaires coutumiers. Il incite ces derniers à la durabilité en leur permettant de devenir les principaux bénéficiaires de cette activité. Cette méthode paraît adaptée au contexte

Understanding what controls global leaf type variation in trees is crucial for comprehending their role in terrestrial ecosystems, including carbon, water and nutrient dynamics. Yet our understanding of the factors influencing forest leaf types remains incomplete, leaving us uncertain about the global proportions of needle-leaved, broadleaved, evergreen and deciduous trees. To address these gaps, we conducted a global, ground-sourced assessment of forest leaf-type variation by integrating forest inventory data with comprehensive leaf form (broadleaf vs needle-leaf) and habit (evergreen vs deciduous) records. We found that global variation in leaf habit is primarily driven by isothermality and soil characteristics, while leaf form is predominantly driven by temperature. Given these relationships, we estimate that 38% of global tree individuals are needle-leaved evergreen, 29% are broadleaved evergreen, 27% are broadleaved deciduous and 5% are needle-leaved deciduous. The aboveground biomass distribution among these tree types is approximately 21% (126.4 Gt), 54% (335.7 Gt), 22% (136.2 Gt) and 3% (18.7 Gt), respectively. We further project that, depending on future emissions pathways, 17–34% of forested areas will experience climate conditions by the end of the century that currently support a different forest type, highlighting the intensification of climatic stress on existing forests. By quantifying the distribution of tree leaf types and their corresponding biomass, and identifying regions where climate change will exert greatest pressure on current leaf types, our results can help improve predictions of future terrestrial ecosystem functioning and carbon cycling.

Tree growth is key to species performance. However, individual growth variability within species remains underexplored for a whole community, and the role of species evolutionary legacy and local environments remains unquantified. Based on 36 years of diameter records for 7961 trees from 138 species, we assessed individual growth across an Amazonian forest. We related individual growth to taxonomy, topography and neighbourhood, before exploring species growth link to functional traits and distribution along the phylogeny. We found most variation in growth among individuals within species, even though taxonomy explained a third of the variation. Species growth was phylogenetically conserved up to the genus. Traits of roots, wood and leaves were good predictors of growth, suggesting their joint selection during convergent evolutions. Neighbourhood crowding significantly decreased individual growth, although much of inter-individual variation remains unexplained. The high intraspecific variation observed could allow individuals to respond to the heterogeneous environments of Amazonian forests.

L'émergence de l'agroforesterie en Côte d'Ivoire est devenue une priorité nationale. Le secteur agricole du pays génère 70 % des recettes d'exportation, emploie les deux tiers de la population active et contribue à un tiers du PIB. Cependant, ces performances économiques remarquables reposent sur une agriculture de rente qui se développe au détriment des forêts naturelles, entraînant l'un des taux de déforestation les plus alarmants au monde. Pour faire face à cette situation, l'État ivoirien promeut l'agroforesterie comme solution, en particulier dans le secteur du cacao. Cependant, une analyse fine de l'origine des arbres présents dans les champs suggère que l'agroforesterie en Côte d'Ivoire peut être divisée en deux catégories : l'agroforesterie de reforestation, qui permet de reconstituer le couvert forestier en associant progressivement des arbres aux cacaoyers, et l'agroforesterie de déforestation, qui dégrade et appauvrit la couverture forestière en convertissant les forêts naturelles en systèmes agroforestiers. Il est crucial de distinguer ces deux formes d'agroforesterie afin de développer des politiques qui encouragent la reforestation plutôt que la déforestation. Il est également nécessaire de mettre en place des indicateurs dynamiques qui permettent d'évaluer les trajectoires agroforestières des champs dans le temps et, ainsi, de favoriser un engagement à long terme des agriculteurs dans l'augmentation de la couverture forestière.

Soil nutrient availability and functional traits interact in complex ways during the assembly of tree communities hindering our understanding of the implications that this may have for their phylogenetic and functional diversity. We combined abundance, taxonomic, phylogenetic and functional trait data of 222 tree species distributed along nutrient concentration gradients at 24 plots in two tropical forest study sites. We analysed micro and macronutrient concentration in organic and topsoil horizons and tested for the following: (1) nutrient-based species sorting due to contrasting trait–environment relationships, (2) whether nutrient filtering has consequences for phylogenetic and functional diversity, and functional space size and occupancy and (3) we mapped trait distributions across the phylogeny of tree species to track the evolutionary signature of nutrient availability. We found that total nitrogen (N), available phosphorus and total potassium in soil accounted for 68% of the variation in tropical tree species community composition, with strong associations with nutrient concentration for 89% of the tree species included in the analysis. This nutrient-based species selection was mediated by interactions between the three soil nutrient concentrations with leaf nitrogen, leaf thickness and wood density. Soil N concentration was positively associated with the functional space at site level. At plot level, soil N concentration positively correlated with functional evenness and it was negatively associated with the functional space not occupied by any species in the tree community. Despite the phylogenetic conservatism of leaf N across tree lineages even when not considering legumes, many sister-species pairs show contrasting values which match with their habitat preferences thus indicating the evolutionary lability of this trait, particularly within recently diversified clades. Synthesis. Our results demonstrate that soil nutrient-based species selection is a prev

Dry and warm conditions have exacerbated the occurrence of large and severe wildfires over the past decade in Canada's Northwest Territories (NT). Although temperatures are expected to increase during the 21st century, we lack understanding of how the climate-vegetation-fire nexus might respond. We used a dynamic global vegetation model to project annual burn rates, as well as tree species composition and biomass in the NT during the 21st century using the IPCC's climate scenarios. Burn rates will decrease in most of the NT by the mid-21st century, concomitant with biomass loss of fire-prone evergreen needleleaf tree species, and biomass increase of broadleaf tree species. The southeastern NT is projected to experience enhanced fire activity by the late 21st century according to scenario RCP4.5, supported by a higher production of flammable evergreen needleleaf biomass. The results underlie the potential for major impacts of climate change on the NT's terrestrial ecosystems.

Aim: Tropical forest succession and associated changes in community composition are driven by species demographic rates, but how demographic strategies shift during succession remains unclear. Our goal was to identify generalities in demographic trade-offs and successional shifts in demographic strategies across Neotropical forests that cover a large rainfall gradient and to test whether the current conceptual model of tropical forest succession applies to wet and dry forests. Location: Mexico and Central America. Time period: 1985–2018. Major taxa studied: Trees. Methods: We used repeated forest inventory data from two wet and two dry forests to quantify demographic rates of 781 tree species. For each forest, we explored the main demographic trade-offs and assigned tree species to five demographic groups by performing a weighted principal components analysis to account for differences in sample size. We aggregated the basal area and abundance across demographic groups to identify successional shifts in demographic strategies over the entire successional gradient from very young (<5 years) to old-growth forests. Results: Across all forests, we found two demographic trade-offs, namely the growth–survival trade-off and the stature–recruitment trade-off, enabling the data-driven assignment of species to five demographic strategies. Fast species dominated early in succession and were then replaced by long-lived pioneers in three forests. Intermediate and slow species increased in basal area over succession in all forests, but, in contrast to the current conceptual model, long-lived pioneers continued to dominate until the old-growth stage in all forests. The basal area of short-lived breeders was low across all successional stages. Main conclusions: The current conceptual model of Neotropical forest succession should be revised to incorporate the dominance of long-lived pioneers in late-successional and old-growth forests. Moreover, the definition of consistent demograp

Using 2.046 botanically-inventoried tree plots across the largest tropical forest on Earth, we mapped tree species-diversity and tree species-richness at 0.1-degree resolution, and investigated drivers for diversity and richness. Using only location, stratified by forest type, as predictor, our spatial model, to the best of our knowledge, provides the most accurate map of tree diversity in Amazonia to date, explaining approximately 70% of the tree diversity and species-richness. Large soil-forest combinations determine a significant percentage of the variation in tree species-richness and tree alpha-diversity in Amazonian forest-plots. We suggest that the size and fragmentation of these systems drive their large-scale diversity patterns and hence local diversity. A model not using location but cumulative water deficit, tree density, and temperature seasonality explains 47% of the tree species-richness in the terra-firme forest in Amazonia. Over large areas across Amazonia, residuals of this relationship are small and poorly spatially structured, suggesting that much of the residual variation may be local. The Guyana Shield area has consistently negative residuals, showing that this area has lower tree species-richness than expected by our models. We provide extensive plot meta-data, including tree density, tree alpha-diversity and tree species-richness results and gridded maps at 0.1-degree resolution.

In a time of rapid global change, the question of what determines patterns in species abundance distribution remains a priority for understanding the complex dynamics of ecosystems. The constrained maximization of information entropy provides a framework for the understanding of such complex systems dynamics by a quantitative analysis of important constraints via predictions using least biased probability distributions. We apply it to over two thousand hectares of Amazonian tree inventories across seven forest types and thirteen functional traits, representing major global axes of plant strategies. Results show that constraints formed by regional relative abundances of genera explain eight times more of local relative abundances than constraints based on directional selection for specific functional traits, although the latter does show clear signals of environmental dependency. These results provide a quantitative insight by inference from large-scale data using cross-disciplinary methods, furthering our understanding of ecological dynamics.

Purpose of Review: Increasing the diversity of commercial tree plantations is a promising approach to adapt forests to climate change, but it may complicate management. Here, we evaluate stakeholders' perspectives about tree-species diversity in plantations and explore policy alternatives to make mixed plantations a viable strategy for climate change mitigation and adaptation. Recent Findings: Current evidence shows that improving the diversity of tree species in plantations can be a viable, scalable, and economically accessible strategy for sustainable wood production and reconciling economic and environmental benefits. Tree diversity is particularly important in the context of global environmental changes and associated increases in abiotic and biotic stresses, such as severe droughts and pest outbreaks. Even though there is substantial scientific evidence supporting mixed-tree plantations, most forest plantations globally are still conventional monocultures. Summary: Our findings (i) describe the geographical distribution of publications investigating human perspectives about forest plantation diversity; (ii) build understanding of how political engagement and governance systems can support forest initiatives on forest conservation, management, and restoration; and (iii) demonstrate how these perspectives can create possibilities and opportunities for sustainable development in forestry. We conclude that new strategies will only be widely applied if there is political and institutional interest, particularly in strengthening land-governance systems.

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.

Allometric equations for calculation of tree above-ground biomass (AGB) form the basis for estimates of forest carbon storage and exchange with the atmosphere. While standard models exist to calculate forest biomass across the tropics, we lack a standardized tool for computing AGB across boreal and temperate regions that comprise the global extratropics. Here we present an integrated R package, allodb, containing systematically selected published allometric equations and proposed functions to compute AGB. The data component of the package is based on 701 woody species identified at 24 large Forest Global Earth Observatory (ForestGEO) forest dynamics plots representing a wide diversity of extratropical forests. A total of 570 parsed allometric equations to estimate individual tree biomass were retrieved, checked and combined using a weighting function designed to ensure optimal equation selection over the full tree size range with smooth transitions across equations. The equation dataset can be customized with built-in functions that subset the original dataset and add new equations. Although equations were curated based on a limited set of forest communities and number of species, this resource is appropriate for large portions of the global extratropics and can easily be expanded to cover novel forest types.

Tree rings provide an invaluable long-term record for understanding how climate and other drivers shape tree growth and forest productivity. However, conventional tree-ring analysis methods were not designed to simultaneously test effects of climate, tree size, and other drivers on individual growth. This has limited the potential to test ecologically relevant hypotheses on tree growth sensitivity to environmental drivers and their interactions with tree size. Here, we develop and apply a new method to simultaneously model nonlinear effects of primary climate drivers, reconstructed tree diameter at breast height (DBH), and calendar year in generalized least squares models that account for the temporal autocorrelation inherent to each individual tree's growth. We analyze data from 3811 trees representing 40 species at 10 globally distributed sites, showing that precipitation, temperature, DBH, and calendar year have additively, and often interactively, influenced annual growth over the past 120 years. Growth responses were predominantly positive to precipitation (usually over ≥3-month seasonal windows) and negative to temperature (usually maximum temperature, over ≤3-month seasonal windows), with concave-down responses in 63% of relationships. Climate sensitivity commonly varied with DBH (45% of cases tested), with larger trees usually more sensitive. Trends in ring width at small DBH were linked to the light environment under which trees established, but basal area or biomass increments consistently reached maxima at intermediate DBH. Accounting for climate and DBH, growth rate declined over time for 92% of species in secondary or disturbed stands, whereas growth trends were mixed in older forests. These trends were largely attributable to stand dynamics as cohorts and stands age, which remain challenging to disentangle from global change drivers. By providing a parsimonious approach for characterizing multiple interacting drivers of tree growth, our method reveals

Tree size shapes forest carbon dynamics and determines how trees interact with their environment, including a changing climate. Here, we conduct the first global analysis of among-site differences in how aboveground biomass stocks and fluxes are distributed with tree size. We analyzed repeat tree censuses from 25 large-scale (4–52 ha) forest plots spanning a broad climatic range over five continents to characterize how aboveground biomass, woody productivity, and woody mortality vary with tree diameter. We examined how the median, dispersion, and skewness of these size-related distributions vary with mean annual temperature and precipitation. In warmer forests, aboveground biomass, woody productivity, and woody mortality were more broadly distributed with respect to tree size. In warmer and wetter forests, aboveground biomass and woody productivity were more right skewed, with a long tail towards large trees. Small trees (1–10 cm diameter) contributed more to productivity and mortality than to biomass, highlighting the importance of including these trees in analyses of forest dynamics. Our findings provide an improved characterization of climate-driven forest differences in the size structure of aboveground biomass and dynamics of that biomass, as well as refined benchmarks for capturing climate influences in vegetation demographic models.

Genomicus is a database and web-server dedicated to comparative genomics in eukaryotes. Its main functionality is to graphically represent the conservation of genomic blocks between multiple genomes, locally around a specific gene of interest or genome-wide through karyotype comparisons. Since 2010 and its first release, Genomicus has synchronized with 60 Ensembl releases and seen the addition of functions that have expanded the type of analyses that users can perform. Today, five public instances of Genomicus are supporting a total number of 1029 extant genomes and 621 ancestral reconstructions from all eukaryotes kingdoms available in Ensembl and Ensembl Genomes databases complemented with four additional instances specific to taxonomic groups of interest.

Lianas can create dense foliage that reduces the light available for the host trees on which they grow and can directly damage the host trees during their development. A better estimation of liana load and understanding of the determinants and impacts of liana load in tropical forests are both important in community ecology and ecosystem science. This has, however, never been studied to date in central Africa. Here, we evaluated the intensity, determinants, and impacts of liana load in three forest sites in central Africa. We determined the liana load categories for all trees belonging to 78 of the most dominant tree species (2683 trees in total), with tree diameters ranging from 10 to 250 cm. The liana load was visually estimated as the liana cover on host tree using simple scale indices, and the proportion of trees covered by lianas defined as the liana prevalence was estimated for each species. Overall, 42% of the 2683 trees were liana-loaded and the number of liana-loaded trees was higher for smaller diameter classes in the three forest sites. Within each forest site, there was a significant difference in liana prevalence among coexisting species. Taller trees with shallow crowns were less covered by liana at the tree level, whereas trees belonging to light-demanding and wind-dispersed species showed a lower liana prevalence rate at the species level. In each forest site, the liana load significantly affected tree height–diameter allometry, with liana-loaded trees being shorter for the same diameter. Lianas promote the structural complexity and influence tree diversity and ecosystem functioning of tropical forests.

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 houppi

Amazonian forests are extraordinarily diverse, but the estimated species richness is very much debated. Here, we apply an ensemble of parametric estimators and a novel technique that includes conspecific spatial aggregation to an extended database of forest plots with up-to-date taxonomy. We show that the species abundance distribution of Amazonia is best approximated by a logseries with aggregated individuals, where aggregation increases with rarity. By averaging several methods to estimate total richness, we confirm that over 15,000 tree species are expected to occur in Amazonia. We also show that using ten times the number of plots would result in an increase to just ~50% of those 15,000 estimated species. To get a more complete sample of all tree species, rigorous field campaigns may be needed but the number of trees in Amazonia will remain an estimate for years to come.

Les systèmes agroforestiers à base de cacaoyers du Centre-Cameroun présentent des niveaux de stockage de carbone (C), de conservation d'espèces d'arbres et de production de cacao intéressants. Les services de conservation et de stockage de carbone peuvent s'y révéler synergiques, mais ils semblent tous les deux antagonistes des niveaux de production supérieurs à une tonne/ha de fèves de cacao marchand. Le stockage de carbone peut néanmoins être découplé de la conservation car dans ces systèmes, il est principalement réalisé par de très grands arbres. Ainsi, un nombre réduit d'individus peut suffire à atteindre des stocks de 100 t C/ha. La conservation des espèces ligneuses apparaît, quant à elle, dépendante du niveau de multifonctionnalité que les agriculteurs attendent de leurs systèmes agroforestiers à base de cacaoyers. Par ailleurs, les systèmes ayant des niveaux de stockage de carbone élevés ou moyens semblent être en mesure de soutenir une production cacaoyère intéressante au-delà de 40 ans (0,75 à 1 t/ha cacao marchand). Les travaux présentés permettent de distinguer trois groupes de systèmes agroforestiers à base de cacaoyers : simples, peu durables et peu multifonctionnels, mais avec de bonnes capacités de production de cacao ; complexes, plus durables avec des niveaux de stockage de carbone et de production de cacao intéressants, mais peu de capacité de conservation ; très complexes avec de bons niveaux de stockage de C et de conservation, mais limités en production de cacao. Ces trois groupes, correspondant à des situations réelles, ils permettent de mieux cibler les intervalles dans lesquels des compromis entre services écosystémiques sont acceptables.

Respectueux de l'environnement et garantissant une sécurité alimentaire soutenue par la diversification des productions et des revenus qu'ils procurent, les systèmes agroforestiers apparaissent comme un modèle prometteur d'agriculture durable dans les pays du Sud les plus vulnérables aux changements globaux. Cependant, ces systèmes agroforestiers ne peuvent être optimisés qu'à condition de mieux comprendre et de mieux maîtriser les facteurs de leurs productions. L'ouvrage présente un ensemble de connaissances récentes sur les mécanismes biophysiques et socio-économiques qui sous-tendent le fonctionnement et la dynamique des systèmes agroforestiers. Il concerne, d'une part les systèmes agroforestiers à base de cultures pérennes, telles que cacaoyers et caféiers, de régions tropicales humides en Amérique du Sud, en Afrique de l'Est et du Centre, d'autre part les parcs arborés et arbustifs à base de cultures vivrières, principalement de céréales, de la région semi-aride subsaharienne d'Afrique de l'Ouest. Il synthétise les dernières avancées acquises grâce à plusieurs projets associant le Cirad, l'IRD et leurs partenaires du Sud qui ont été conduits entre 2012 et 2016 dans ces régions. L'ensemble de ces projets s'articulent autour des dynamiques des systèmes agroforestiers et des compromis entre les services de production et les autres services socio-écosystémiques que ces systèmes fournissent.

In Central Nicaragua, in a rural landscape where trees grow everywhere, we studied the relations between land uses and the perception of ecosystem services (ES) provision by farmers. We worked in 3 municipalities and interviewed more than 100 households distributed among 10 communities, from 2016 to 2018. During gender specific focus groups we produced participatory maps of land uses (following Braslow et al. 2016), localized ES with the Pebble Distribution Method (described by Sheil et al. 2002), and analyzed land tenure issues using the analysis grid for land tenure proposed by Le Roy et al. (1996). Participatory observation (as detailed by Jankowski y Sabourin 2012) and semi-structured interviews (Newing 2010; Sibelet et al. 2013) were used to analyze livelihoods conditions, households' economies (data later analyzed with the support of Olympe software), and determining factors regarding land uses and tree planting. Results prove no relation between land tenure security and the plantation of trees. Land occupation by any farming system with or without trees, such as food crop or pasture, is informally recognized as proof of ownership. Farmers plant trees around their house, in pastures or on the borders of paths, for the high value they attached to them. Trees provide goods (timber, fuel wood, fruits, medicine…) and services (preservation of soils and water resources, regulation of pests and diseases, action on the local climate), and are also recognized for their social value. With the same logic, both women and men recognized forest as the main land use regarding ES provision. By contrast, they consider it of less interest than agricultural land uses regarding household's income and livelihoods. Logging is not a well-remunerated activity, and the forestry law imposes strong restrictions to timber sale. Women and men farmers perceived that forests are important for soil, water and biodiversity preservation. They may provide fuel wood and timber for family needs

Dans ce travail, nous montrons que la structure spatiale des individus (arbres et cacaoyers) au sein d'agroforêts à cacaoyers influence l'intensité d'attaque de bioagresseurs des cacaoyers. À l'échelle de la parcelle, des organisations spatiales régulières ou aléatoires d'arbres forestiers réduisent les intensités d'attaques de la moniliose au Costa Rica et des mirides au Cameroun. À l'échelle de l'individu, le nombre de voisins cacaoyers (à 3,7 m) et fruitiers (à 4,3 m) influence négativement l'intensité d'attaque de la moniliose au Costa Rica. Nos résultats révèlent l'importance de la structure spatiale dans la description des agroforêts tropicaux et la compréhension des mécanismes influençant la régulation agroécologique des bioagresseurs au sein de ces systèmes complexes. La gestion de la structure spatiale des individus dans les systèmes agroforestiers pourrait ainsi constituer un levier intéressant pour le contrôle agroécologique des bioagresseurs.

Global measurements of forest height, biomass are urgently needed as essential climate and ecosystem variables, but can benefit from greater co-operation between remote sensing (RS) and forest ecological communities. The Forest Observation System - FOS (https://forest-observation-system.net/ [https://forest-observation- system.net/]) is an international cooperation to establish a global in-situ forest biomass database to support earth observation and to encourage investment in relevant field-based observations and science. FOS aims to link the RS community with ecologists who measure forest biomass and estimating biodiversity in the field. The FOS aims to overcome data sharing issues and introduce a standard biomass data flow from tree-level measurement to the plot-level aggregation served in the most suitable form for the RS. Ecologists benefit from the FOS with improved access to global biomass information, data standards, gap identification and potentially improved funding opportunities to address the known gaps and deficiencies in the data. FOS closely collaborate with the CTFS-ForestGEO, the ForestPlots.net (incl. RAfNFOR, AfriTRON and T-FORCES), AusCover, TmFO and the llASA network. FOS is an open initiative with other networks and teams most welcome to join. The online database provides open access for forest plot location, canopy height and above-ground biomass. Plot size is 0.25ha or larger. Comparison of plot biomass data with available global and regional maps (incl. Kindermann et al., 2013; Thurner et al., 2013; Saatchi et al., 2011; Baccini et al., 2012; Avitabile et al., 2016; Hu et al., 2016; Santoro et al., 2018) shows wide range of uncertainties associated with biomass estimation.

L'impact de l'exploitation forestière sur le renouvellement du stock de bois d'oeuvre 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'oeuvre de grande valeur commerciale. L'objectif de cette étude est 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 recrute-ment 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 à 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 dia-mètre, 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 régé-nération, s'avère indispensable.

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.

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.

Wind damage is an important driver of forest structure and dynamics, but it is poorly understood in natural broadleaf forests. This paper presents a new approach in the study of wind damage: combining terrestrial laser scanning (TLS) data and finite element analysis. Recent advances in tree reconstruction from TLS data allowed us to accurately represent the 3D geometry of a tree in a mechanical simulation, without the need for arduous manual mapping or simplifying assumptions about tree shape. We used this simulation to predict the mechanical strains produced on the trunks of 21 trees in Wytham Woods, UK, and validated it using strain data measured on these same trees. For a subset of five trees near the anemometer, the model predicted a five-minute time-series of strain with a mean cross-correlation coefficient of 0.71, when forced by the locally measured wind speed data. Additionally, the maximum strain associated with a 5 ms−1 or 15 ms-1 wind speed was well predicted by the model (N = 17, R2 = 0.81 and R2 = 0.79, respectively). We also predicted the critical wind speed at which the trees will break from both the field data and models and find a good overall agreement (N = 17, R2 = 0.40). Finally, the model predicted the correct trend in the fundamental frequencies of the trees (N = 20, R2 = 0.38) although there was a systematic underprediction, possibly due to the simplified treatment of material properties in the model. The current approach relies on local wind data, so must be combined with wind flow modelling to be applicable at the landscape-scale or over complex terrain. This approach is applicable at the plot level and could also be applied to open-grown trees, such as in cities or parks.