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The long-term implications of over-exploitation and degradation in the tropics are less well known than those of deforestation. Yet, robust information on the lasting impact of degradation on forest characteristics and tree species diversity as well as their recovery potential are essential. This case study focuses on the coastal rainforest of the Mondah peninsular (Gabon). The forest was frequently exploited for more than 200 years and put under conservation in 1971. Recovery of the forest was assessed by forest inventories performed in 1993 and 2011. Replicate analysis revealed that for trees with dbh≥10cm, the mean tree diameter, height, basal area as well as the above-ground biomass and carbon were significantly higher in 2011. On the stand level, 12 % less stems were counted in 2011 while the stand basal area, above-ground biomass and carbon were 31%, 41% and 40% higher. The thickening and heightening of the forest stand resulted in a shift in the stem diameter and height distribution, respectively: In 2014, less trees were found with a dbh<30cm while more trees were observed in the higher diameter classes up to 60cm dbh. In 1993, the vertical stratification of the forest comprised 66%, 28% and 6 % trees in the understory, medium, and canopy layer, respectively. In 2011, only 55% of the trees stuck in the understory, while 36% and 9% of the trees reach the medium and canopy layer, respectively. In 2011, 868 stems dbh≥10cm were represented by 94 tree species, while in 1993 the ratio was 85 species to 779 trees with dbh≥10cm. Abundance and dominance of the most important tree-species also changed between 1993 and 2011, e.g. the early pioneer tree Musanga cecropioides - most abundant in 1993 - was no longer found in the dense forest, while the long-lived pioneer Aucoumea klaineana became most abundant in 2011. Additional results referring to trees with a dbh< 10cm as well as a more detailed analysis of tree-species diversity will be provided in t

The Amazonian pioneer front region is a mosaic of different forests types and agricultural landscapes resulting from the colonization of the region through forest conversion into pasture and agricultural lands. Fearnside and Guimaraes (1996) showed that 47% of the deforested area is rapidly abandoned. It also appears that logged forests surface is equivalent to deforested areas (Asner et al., 2005). Consequently a degradation gradient exists from low-impacted logged forests (depending of the logging intensity) to young secondary (regrowth) forests. To obtain more accurate estimation of carbon stocks, it is important today to take into account the degraded forest gradient including all degraded forest stages between mature intact forests and non-forest areas. The first main challenge is to identify and to characterize the various stages. The identification of forest degradation is still a complex and expansive problem even if it has been focused until now only on logged tropical rainforest (Asner, 2009; Gond and Guitet, 2009; Desclées et al., 2006; Asner et al., 2005; Souza et al., 2003). In parallel estimation of biomass loss in the degraded forest is little-studied. Within temperate and boreal forests some estimation are made by Solberg et al., (2013). The combination of optical remotely sensed data (Landsat-8), radar (Terra-Sar-X) and Lidar (IceSat) have to be studied to analyze the potential of the multi-sensors techniques to characterize the tropical rainforest degradation (Betbeder et al., 2014). The study presents the first results obtained during the field work at Paragominas (Pará, Brazil) on different forest degradation intensities (Bérenguer et al., 2014). This field database is then compared with multi-sensors remote sensing to better understand multiple interactions and to establish a forest degradation typology. (Texte intégral)

Selective logging in tropical forests is restricted to a few species, the so-called commercial species. Among those commercial species, many produce fleshy fruits of large size. These tree species provide food to a large number of mammals and birds that often exclusively rely on these resources. These mammals and birds may also be vital for the demography of fleshy fruit trees because they act as dispersers towards more suitable place for seedling establishment (directed dispersal hypothesis or colonization hypothesis), or they increase seedling survival by avoiding conspecific high densities (escape hypothesis). Selective logging generally targets large trees, above the legal minimum cutting diameter, that also produce an important quantity of fruits to frugivores feeding in the canopy. Therefore, selective logging may impact frugivore populations in the long-term and in fine may disrupt the dispersal processes of logged species but not only. Indeed, selective logging of the largest - in terms of size and quantity -fleshy fruit producers may impact all fleshy fruit producers in decreasing the abundance of the resources hence creating local extinction of frugivores (the resource concentration hypothesis). Large frugivores feeding on the largest fruits may be more rapidly impacted. Until now studying the effect of logging is not an easy task because logging is generally correlated to hunting pressure. Based on a multispecies comparison using data from a replicated experimental logged forest with various intensities (and including control plots) at constant hunting pressure, we test the effect of selective logging on seed dispersal of tropical forest trees. Seed dispersal will be estimated as a cluster size using Ripley's K functions. In particular, we will test if dispersal distances of fleshy fruit species in logged plots decrease compared to control plots. We hypothesize that animal-dispersed species with larger seeds are dispersed less far away in treated vs contr

The seasonal climate drivers of the carbon cycle in tropical forests remain poorly known, although these forests account for more carbon assimilation and storage than any other terrestrial ecosystem. Based on a unique combination of seasonal pan-tropical data sets from 89 experimental sites (68 include aboveground wood productivity measurements and 35 litter productivity measurements), their associate canopy photosynthetic capacity (enhanced vegetation index, EVI) and climate, we ask how carbon assimilation and aboveground allocation are related to climate seasonality in tropical forests and how they interact in the seasonal carbon cycle. We found that canopy photosynthetic capacity seasonality responds positively to precipitation when rainfall is < 2000 mm per year (water-limited forests) and to radiation otherwise (light-limited forests); on the other hand, independent of climate limitations, wood productivity and litterfall are driven by seasonal variation in precipitation and evapotranspiration respectively. Consequently, lightlimited forests present an asynchronism between canopy photosynthetic capacity and wood productivity. Precipitation first-order control indicates an overall decrease in tropical forest productivity in a drier climate. (Texte intégral)

Tropical forests are both important carbon sinks and among the most biodiverse ecosystems on the earth. Patterns in aboveground biomass (AGB) and their relationship with species diversity of tropical forests over short altitudinal gradients are poorly known and the few previous studies on the subject have yielded variable results. Here, focusing on old-growth forests in Atlantic central Africa, we investigated how AGB varies with altitude, and how this variation is related to altitudinal changes in floristic composition and/or forest structure. We also investigate the relationship between AGB and species diversity along the altitudinal gradient. We inventoried all trees with a diameter (dbh) ≥ 10 cm in fifteen 1 ha permanent plots (100 m x 100 m) established along a transect from lowland (200 m) to submontane forests (900 m) in the Ngovayang Massif, southwestern Cameroon. Our data show a negative relationship between AGB and tree species richness, related to the elevation gradient. Forest AGB varied two-fold along this gradient, decreasing from 500-600 Mg ha-1 in lowland plots to less than 300 Mg ha-1 at the highest altitudes, while diversity increased, from 35.4 to 54.6 (Fisher's alpha index). The decreasing trend in AGB was mainly due to large trees (dbh ≥ 70 cm) whose contribution to AGB significantly decreased with altitude while the contribution from smaller trees was constant. Tree height and basal area also decreased significantly with increasing altitude, whereas stem density increased. While maximum potential tree height significantly decreased, wood specific gravity displayed no trend along the gradient. In particular, we showed that AGB variation was mainly determined by shift in species composition because large tree species were filtered out in the highest altitudes. Hence, our work further highlight the need for studying the drivers of large tree species distribution to better understand forest carbon stock variations in tropical forests. A

Europe's "soft power" is based on norms, with a great emphasis on environmental ones. As the major commercial partner of more than 100 countries, norms adopted in Europe carry weight in non-European countries that seek to maintain or increase their market share. Europe's environmental norms are, therefore, considered well beyond Europe's boundaries. Sustainable land-use and forestry norms have been particularly promoted by Europe, such as forest certification adopted in some European countries for public purchasing of timber. The most prominent initiative is the association between the EUTR (European Union Timber Regulation) and the FLEGT (Forest Law Enforcement, Governance and Trade) initiative under which Voluntary Partnership Agreements (VPAs) have been proposed to timber-exporting tropical countries. VPAs call for ensuring the consistency of national laws, propose an independent auditing of the national system of legality verification and a bilateral commercial agreement allowing timber with FLEGT authorisation to be imported in the EU without need for proof of due diligence. The tandem EUTR-FLEGT/VPAs also impact bilateral commercial relationships between, say, China and Indonesia, as Chinese's furniture made with Indonesian timber might be exported to the EU. As a consequence, some Chinese exporters are endorsing certification for their supply chains, and contribute to the diffusion of such standards in non-EU-markets. EU Biodiversity Strategy 2020 states that "the EU will take measures to reduce the biodiversity impact of EU consumption patterns". This is why "zero-deforestation" commodity chains are the new issue involving Europe and some of its largest multinational corporations. Such commitments will have a worldwide impact and competitors are forced to endorse the same ones. But the main difficulty for Europe will be to go beyond the formal endorsement of norms. FLEGT/VPAs implementation has been delayed, and no FLEGT authorisation has yet been delivered.

With biodiversity being lost at unprecedented rates, mitigating the impacts of development projects is a growing concern. International best practice indicates that projects located in natural habitats must achieve no net loss of biodiversity, or preferably a net gain. To do so, when development projects generate impacts on biodiversity that could not be sufficiently avoided or reduced, offsets must be designed and implemented to effectively and fully compensate for the residual loss of biodiversity, by generating measurable conservation gains elsewhere. There are considerable technical and organizational challenges to designing and implementing biodiversity offsets, which must also respect the legal and customary rights of local populations. Offset frameworks have been put in place in several countries worldwide but, in many circumstances, it is financial institutions and multinational companies that require these approaches as part of their risk management strategies. As such, they represent an important external influence on the future of tropical forested landscapes. A further challenge, however, is that developing countries, eager to access their natural resources, don't all share this ambition. We illustrate this with mining development in the tropical forest landscape which straddles the borders of Cameroon, Gabon and the Republic of Congo. Conservationists fear that the infrastructure being built to service an emerging iron ore province will reduce a large intact forest landscape to a mosaic of isolated protected areas no longer fit to conserve its mega-fauna or maintain large scale ecosystem processes. We use companion modelling techniques to build a model of the socio-ecological system, and develop future scenarios. In doing so, we map the role of various actors in making these futures possible. A key conclusion is that managing the impacts of mining development requires a strategic and multi-sectorial landscape-level approach, rather than dealing with eac

Community's participation has been promoted as a way to empower local communities in REDD+ programs. A particular goal is that they would monitor forest change and measure carbon stocks, and thus reduce the costs of such assessments. More generically, the recent Paris Climate Agreement has further emphasized the need for transparency in reporting, the importance of the land use sector for both mitigation and adaptation, and the fact the targets can only be achieved through bottom-up engagement of multiple actors. So far, little empirical evidence shows that participatory measurement, reporting and verification (PMRV) is feasible. A series of multidisciplinary studies investigated the feasibility of local participation into MRV. The research was conducted in Indonesia, Vietnam, Ethiopia, Mexico, and China. We find that effective PMRV requires local communities' motivation. Motivation depends on people's knowledge, their interests, incentives, tenure, and the relevance of these monitoring activities to their other livelihood activities. Monitoring and reporting changes in forest cover, drivers of change, and carbon sequestration, are in general costly and require the capacity to monitor and report. Other sectors provide some relevant lessons and experiences on reporting from village to national levels. In Indonesia, for example, we learned that the health care system has simpler governance for monitoring and reporting compared to the forestry sector and has successfully been in place for more than 40 years. In contrast, the forestry sector failed in engaging local communities in the reporting of timber and non-timber forest products. Verification refers to assessing the accuracy, consistency and transparency of measurements to verify the attainment of emission reduction targets. We explain how verification can use a combination of remote sensing data, land use and land cover maps developed by/with villagers to identify gaps and points of disagreement, for which ground

Today, many European governments are setting up policies to promote wood energy as part of their plans to meet the EU ambitious target of 20% of energy consumption from renewable sources by 2020. In its various forms, from sticks to chips and pellets, wood accounts for about half of Europe's renewable-energy consumption. Analysts forecast that demand will increase at an annual rate near 5% until 2030. In 2014, Europe consumed 16m tonnes of wood pellets. On current trends, this demand will rise to 25m-30m a year by 2020. Europe does not produce enough timber to meet that extra demand. At the moment, EU is the largest wood energy market in developed countries and to supply its demand it is already importing huge quantities of fuelwood mainly from the USA, Canada and Russia. But the major exporters (Canada and USA) could soon be interested in using pellets for their own electricity needs replacing coal and the source could quickly dry up. Apart from the Republic of South Africa, Sub-Saharan Africa, still do not participate in this market. Yet the resources, particularly in Central Africa are significant. Central African countries have the potential to produce enough biomass that even after covering growing domestic energy demands, a net surplus of biofuel can be sustainably produced. Loggers and African processors begin studying the possibility of producing and exporting pellets and charcoal to Europe. This new market has the potential to completely revolutionize the current market of timber, its geography and its logging standards. First, the prices of wood energy are constantly increasing, and some economists expect the world price of fuelwood and industrial roundwood to converge in 2030. Then the wood energy market is not very demanding on the quality of wood; all wood is good to burn: sawmill residues, forest wastes, declassified logs, and secondary species. Then the woodfuel market is not very demanding on production standards, although voluntary standards are eme

Understanding the forces that drive decision-making by stakeholders is a crucial aspect in developing successful strategies for natural resource management. Empirical knowledge is only one of these drivers, as practices are also decided by individuals' beliefs, perceptions and interests, by the assets available and the institutions and norms dictating what is acceptable. Uncovering the underlying reasons for individual management decisions thus requires integrated approaches, and is particularly relevant to ensure the engagement of local communities and the effective implementation of community-based initiatives. Throughout the Colombian Amazon communities carry out subsistence as well as small-scale commercial bushmeat hunting. Overharvesting, together with habitat loss, poses a dual threat to biodiversity and to the people who depend on it for food and income: the hunters and their families. Having empirical knowledge and being aware of the high stakes if the resource crashes, hunters might have developed effective strategies for game management. Given this, we wanted to explore how hunters perceive and handle the well-known trade-off between biodiversity conservation and socio-economic development, particularly in the context of the Ticoya indigenous reserve in the Colombian Amazon. To this end, we used ReHab, a role-playing game that revolves around the management of a renewable resource. Players are either Harvesters that need to feed their families using the resource, or Park Managers seeking to protect a migratory bird sensitive to resource level and human disturbance. ReHab allows players to explore the concepts of natural resource management and sustainability when dealing with conflicting agendas and partial knowledge. The game has been played in multiple occasions in different contexts, creating a benchmark against which to compare sessions played within the culturally homogeneous group of the Ticoya hunters. We found a positive effect of communication an

Background: Ectomycorrhizal (ECM) fungi play key roles in ecosystems functioning, such as in plant community dynamic. However, very few studies have been undertaken in the tropics. New Caledonia is an archipelago located in the South West Pacific and is wellrecognized for its exceptional biodiversity, especially due to its geographical isolation and the presence of ultramafic soils. In this study, we present the first large molecular study on ECM fungal communities in New Caledonian rainforests from ultramafic soils. Method: We collected ECM root tips and fruit bodies from three sites located in the South of the main island. In each site, sampling was performed in two monodominant rainforests, with an upper canopy dominated by Nothofagus aequilateralis (Nothofagaceae) or Arillastrum gummiferum (Myrtaceae). Adjacent mixed rainforests were also studied. These formations might represent different successional stages of forest dynamic. Fungi were identified by sequencing the internal transcribed spacer (ITS) of the nuclear ribosomal genes, and host plant were identified as well using the same genomic region. Results: Out of the 587 ECM root tips and 2372 fruit bodies, 312 OTUs, belonging to at least 29 lineages, were delineated. The community was largely dominated by the /cortinarius lineage in the above- and below-ground communities. Furthermore, community structure analyses strongly suggested host preferences. Discussion - conclusion: This work increases our knowledge of ECM fungal biodiversity in the tropics, particularly in terms of diversity and dynamic. Indeed, the species diversity seems to be similar to the diversity observed in other tropical and temperate forests and most of the molecular species delineated might be unique to New Caledonia. We could also hypothesise that some fungal groups play major roles in the community dynamic as inoculums sources. Additionally, in the context of land disturbance, the results obtained will permit to develop biological indi

Background: Large-scale ecosystem services (ES) mapping is a challenge for environmental management. A possible and low-cost method is the up-scaling approach, which we tested on Pará State, Brazil. Method: We mapped four ES indicators (vegetation carbon stocks, rates of water infiltration into soil and a biodiversity and a chemical quality index) at the regional scale, from field and remote sensing data. To do so, we first classified the land cover from MODIS images. Then, we averaged the ES indicators (field data) per MODIS land cover class. Finally, we evaluated regional maps' accuracy through three different procedures: first, we mapped the variability of the ES indicators per land cover type. Secondly, we compared, statistically and visually, the regional ES indicators maps with local scale maps made from statistical models that linked remote sensing (Landsat and DEM Aster) and field (ES indicators) data. Finally, we calculated the correlations between our predicted values and independent datasets. Results: Our results showed the spatial distribution of some ES indicators for Pará Sate. ES indicators providing is the highest in the forest, except the soil chemical quality index. Yet, Pará State, still mainly covered by forests, has known a large movement of deforestation from the east to the west, despite the creation of protected areas. The western part, marginally affected by deforestation, is thus characterized by high ES providing. On the contrary, the eastern part, severely damaged by deforestation, is associated with poor ES providing. Our results also showed the unequal capacity to get reliable ES maps at the regional scale. In other words, our results show the additional complexity of modeling ES whose variations are very partially based on land cover changes, such as the biodiversity index. Discussion: Up-scaling approaches should bridge the gap between the spatial scales. These approaches complete large-scale maps by local knowledge and enable the est

Deadwood is an important stock of carbon in logged-over Dipterocarp forests but still remains poorly studied. Here we present the study of deadwood in logged-over Dipterocarp forests using two common approaches: plot-based approach and line-intersect-based approach. We conducted our research in three sites which are forest logged in 2003, 2007, and 2010 within Hutansanggam Labanan Lestari (HLL) forest, a certified forest concessionaire in Indonesia. We established 1,500 m of transect line (broken down in 50 m section) for each site. As a reference, we established 47 10 m x 10 m subplot for three sites. All fallen deadwood with diameter > 10 cm were recorded. Our results shows that the mass of fallen deadwood resulted by line-intersect-based method was much higher in compare to plotbased method. The mass of fallen deadwood in plot-based study (44.563 ± 9.155 Mg/ha) was significantly different with the mass of fallen deadwood in line-intersect-based study (69.587 ± 8.079 Mg/ha). Furthermore, for the variability of deadwood, both methods show consistence results which is the variability in 2003 was lower than that in 2007 and 2010. Based on our data, in order to get coefficient of variation of 10%, we recommend the use of minimum 40 plots of 20 m x 20 m to estimate deadwood in logged-over Dipterocarp forests. (Texte intégral)

Southern African models of wildlife management are based on the devolution of wildlife management rights and benefits to private owners and communities. The guiding assumption behind these models is that wildlife management becomes more effective once local users are able to manage it and benefit from it. In recent decades, Namibia, South Africa, Zambia and Zimbabwe have decentralized state decision-making to local stakeholders, thus enabling them to benefit from numerous opportunities offered by the wildlife tourism industry, especially trophy hunting (a high-value-added activity). This approach has been particularly successful on commercial farmlands, where substantial areas have been converted to game ranches that generate profits mainly through trophy hunting but also through live animal sales, ecotourism and game meat production, among others. Although making good profits while conserving wildlife and providing social and economic benefits in rural areas, commercial wildlife ranches have been often perceived as “While only” elite businesses, resulting in some cases in serious political and land tenure tensions. The decentralization approach has been less straightforward on communal lands because communal property regimes (in which defined groups may collectively exploit common resources within a defined jurisdiction) need to be established. Community-based wildlife management approaches were initiated successfully in Zimbabwe in the early 1990s under the CAMPFIRE programme, although these were later hampered by political developments. Other countries have also adopted community-based wildlife management approaches. In Namibia, for example, communal area conservancies are proving to be highly successful in a context of low human population density. There is a need however, to develop community commercial conservancy as a wildlife-based land use option in the more general context of Southern African populated communal lands. In this communication, we promote the

Most studies on tropical plant phenology have focused on patterns of flowering, fruiting and leaf-shedding. They are based on time consuming continuous surveys over seasons or years and the basic considered scale is the tree integrated within a population or a community. So, the functioning of the different axis categories inside the crown of one individual have been poorly considered and studied. Here, we want to demonstrate the efficacy of a retrospective analysis based on morpho-anatomical growth markers coupled with a field survey to study phenology and growth at different scales from within-individual to populations. In French Guiana, we collected dominant branches from 5 Moronobea coccinea adults, a hemi-tolerant tree of Neotropical rain forests. We identified growth markers delimiting longitudinal and radial increments. We coupled this retrospective analysis with a 30-month survey of (i) leaf-shedding and primary growth on twenty-two trees every month and (ii) for the repeated collecting of microcores from five trees every fifteen days to determine intra-annual cambial activity (i.e. formation of secondary xylem). Successive growth units and growth rings were identifiable based on morpho-anatomical markers. These structural regularities traduce the phenological cycle defined by leaves shedding, growth-unit elongation and growth-ring formation. The retrospective analysis was few time consuming and in comparison we reconstructed the tree growth history of individual trees in only two weeks. Our study shows that retrospective analysis and field survey are two complementary approaches to understand plant phenology and to interpret morpho-anatomical structure. Dating a branch by counting the number of growth units or growth rings is possible in many years with a reasonable error. Nevertheless, estimating their precise month of formation in order to study climatic influences remains difficult if a growth monitoring isn't coupled in the same time. The cycle of M. co

In Africa, participatory mapping of land use by local people is a quite old field practice in conservation or development projects. More recently, massive on line mapping of customary rights were born under the impulse of activist NGO. These include The Mapping for Right Initiative which notably proposed to communities to prove by themselves their presence inside the forest. The announced purpose is to help the decision-makers and the private sector to recognize this presence and help international community to recognize rights linked with this presence. Promoted as a decision making-tool, this initiative try in fact to make recognize customary rights at large scale in order to put them against land management and planning (logging concession, protected areas…).The important things is that conservation world take it into consideration not as an constraint but as an opportunity. We propose as line of conduct three possibilities i) for existing protected areas, mapping of rights should promote more participation of local population in decision structure and access to benefits-sharing, but exclude rights of hunting ii) for new protected areas, mapping of rights will help the free prior and informed consent process and should lead to land sharing based on overlapping rights officially acknowledged through contracts (participation in decision structure, sharing benefits), with village hunting areas outside and around this new protected area and iii) about non protected areas where wildlife is still abundant, mapping of rights should promote community-based management and hunting rights on non-protected species. (Texte intégral)

A major challenge in conservation biology is to identify areas to be protected in priority. With the hypotheses in mind that areas presenting unique environmental features when compared to their surroundings are more likely 1) to be vulnerable to changes and 2) hosting relatively more specialized species, we performed a global analysis to identify singular forested areas and further explored the relationship of those areas with forest bird richness and endemism. Using a moving window of 50 x 50 km, we computed, across the earth's surface, on a grid of 5 x 5 km resolution the probabilities for each cell to find similar biophysical features elsewhere in the window. The input variables were, NDVI and NDWI, slope, and the percentages of grassland and tree covers. This systematic screening allowed us to map areas presenting unique features and to further correlate this information with the level of the correlation between bird endemism and species richness. At the global scale, we found the forested biomes of the Congo Basin, namely the Tropical & Subtropical Moist Broadleaf Forests and the Tropical & Subtropical Grasslands, Savannas & Shrublands among the most homogeneous ones for what concern our environmental variables. While it is well-known that the Tropical Moist Forest is the biome holding the biggest diversity in terms of bird-species richness, the relationship between biomes and endemism levels is less documented. If we found that more than half of our variables explained bird endemism for the moist forests, such characterization of the level of endemism was not straightforward for other biomes. More relevant to the identification of potential new areas to focus on for biodiversity conservation, we found that the Tropical and Subtropical Moist Broadleaf Forests shown little ecological heterogeneity and consequently present only a few unique areas. Interestingly, while we found that the relationship between endemism and areas presenting unique environmental featu

Accurate expertise on plant development in space and time is fundamental to underpin conservation and management practices. Considering that trees are long-life organisms with a complex structure, understanding the rules of tree development, from seedlings to adult trees and for a given environment, is a steep task. Compared to field monitoring, retrospective analysis of plant incremental development (RAPID), based on the observation of morpho-anatomical markers allows accessing the past dynamics of plant architecture on many varied plants. However, it is clear that besides this very general approach, works based on axis thickening (mainly trunk) and growth rings structure (GR) remain a broad majority and they are recognized as a full-fledged discipline called dendrochronology. Etymologically, dendrochronology is the science (-logia) of reading the time (khronos) in trees (dendron). Nevertheless, it is clear that this definition applies equally to the crown expansion and to the understanding of the primary growth, branching or flowering processes through the study of morphological or macro-anatomical markers. Moreover, it is important to note that theses approaches can be applied not only in trees, but also in perennial herbaceous herbs or mosses that conduce some authors to propose the term herbchronology. Without trying to change the term of dendrochronology, etymologically limited, but widely used and deeply rooted in the scientific landscape, we support the idea that it should be extended to all approaches concerning the RAPID. In this presentation, we'll depict a summary of methods that allow accessing the past development of plants considering four major processes, growth I and II, branching, and flowering whatever the biological life-form. We'll discuss the close connection amongst the nature of theses processes, their phenology and the resulting morpho-anatomical structure. Considering that plant form integrates multiple environmental factors but, also, inte

In Central Africa, oil palm is a major food-crop used in everyday cooking. All the countries of the region are importing palm oil, often from south-east Asia, to cover their domestic demand. Palm oil production is dominated by small scale agriculture, with a diversity going from the small backyard garden to the monospecific plantation of several hundred hectares. Most of the industrial plantations date from colonial periods. New industrial plantations have been expanding in the last decade, with successes and failures, with the help of southeast Asian and European multinationals and domestic investors. The States want to increase their national palm oil production and industrial investments. They hope for socioeconomic benefits and food security. Such plans for agricultural development also present threats such as deforestation, loss of biodiversity and land use conflicts, and caution and planning are needed to avoid negative social and environmental impacts. In order to provide decision-makers with accurate information and useful decision-making tools to plan the development of the palm oil sector at national and subregional scales, the WWF asked CIRAD to map lands potentially favourable to the production of sustainable (P&C RSPO) palm oil in 5 countries of the Congo basin: Cameroon, Gabon, Republic of Congo, Democratic Republic of Congo and Republic of Central Africa. We use a step by step method to 1/ measure and locate territories which are suitable for oil palm culture, 2/ prevent threats over biodiversity and land use by respecting the social and environmental constraints edited by the principles and criteria of the Roundtable on Sustainable Palm Oil (P&C RSPO), 3/ plan development strategies for palm oil production which are coherent with the national context and specificities (through an evaluation of the adequacy of various production models). The maps resulting from this study are useful decision-making tools that allow analysing trade-offs between opportu

In French Guiana, forest accounts for almost 96% of the territory, with the habitat maintaining a good state of conservation. Nonetheless, forest management in this region faces new challenging issues given the emerging and increasing demands for wood products. The present-day challenge is to develop sustainable and efficient wood production solutions, whilst preventing deforestation and reducing the current dependence on importation. Plantations of native fast-growing species here represent a real potential. Cordia alliodora is a long-lived pioneer species known only in French Guiana in the vicinity of the town of Saül. This species appears to match the requirements for plantation growth, in relation to its very high growth rate and good wood properties. Nevertheless, to our knowledge, no growth monitoring has been conducted in French Guiana, with little information on the performance of local populations under natural conditions. Here, we present a retrospective analysis of C. alliodora development (primary and secondary growth) based on anatomical and morphological markers. To achieve this work, we also describe the past development of adjacent trees belonging to the pioneer species C. obtusa. This last species was considered here as "standard" to (i) estimate the age of secondary forest within which both species belong, (ii) demonstrate the annual nature of growth rings in C. alliodora and (iii) compare the growth trajectories of the two species. We sampled 13 and 15 individuals of C. alliodora and C. obtusa trees respectively in three contrasted sites in the region of Saül. Above 10 meters in height, which is the flowering stage of C. obtusa, our results show that C. obtusa and C. alliodora have a competitive growth in height despite two contrasted growth strategies (continuous growth vs. polycyclic rhythmic growth). Beyond this point, C. alliodora becomes dominant in the stand. Strong differences were observed in C. alliodora growth trajectory depending on the

Managed forests are a major component of tropical landscapes and almost half of standing primary tropical forests, up to 400 million ha, are designated by national forest services for timber production. However, so far, most of our understanding of the tropical forest carbon cycle yields is from plot networks located in old-growth undisturbed forests while the carbon balance of managed forests at the regional and continental scale remains poorly studied. Here we propose a methodological framework in order to quantify the carbon footprint of selective logging at a regional scale. The yearly balance of a logged forest unit is modeled by aggregating 3 submodels dealing with (i) emissions from extracted wood, (ii) emissions from logging damages and (iii) storage from biomass recovery after logging. Models are parameterized and uncertainties are propagated through a MCMC algorithm. We used the 30-years statistics from the National Forest Service to estimate the carbon balance of managed forests in French Guiana. Over this period, selective logging emitted 0.76 Tg C in the atmosphere. Our results highlight the key role of the local carbon cycle in managed forests for climate regulation at the global scale. (Texte intégral)

We will present recent findings arising from the Tropical managed Forests Observatory. Results from the first regional analysis of above-ground carbon stocks dynamics post-logging in Amazon managed forests will be presented. We found that the percentage of initial carbon lost during logging was the main driver of post-logging dynamic, enabling on his own to accurately predict time of recovery wherever in the Amazon Basin.Moving from forest stand to tree responses, we show how logging, by releasing competition for light, may affect trees morphology. We found a significant reduction of both total and bole heights proportional to logging intensity in a tropical logged forest in French Guiana. This resulted in a 10-13% reduction of tree biomass and timber volume. These results will be discussed in terms of future management and provision of ecosystem services in tropical production forests. (Texte intégral)

Background: Tree above ground biomass (AGB) is currently estimated by tree-level allometrical models that take into account, tree volume estimated from proxy variables of tree size (DBH) and species average wood specific gravity (WSG). These methods are common and realistic from a practical point of view. However, they do not take into account deviance from fixed allometrical trajectories and spe-cies or tree level WSG variations. Here, we present Xtrawood software that allows computation of tree AGB according to structure and WSG variations. Method: Xtrawood reconstructs tree structure and integrates WSG variations by merging tree structure and WSG data measured at different position in trees, leading to the computation of global AGB and visualization of WSG variation along tree structure. Tree structure is measured according to stem dimensions (length, diameter) and positions within tree, and encoded in Multiscale Tree Graph format (MTG). WSG data is made of radial WSG profiles (1 measure each 0,5 cm from pith to bark) sampled at different heights within whole tree. Xtrawood output are illustrated using a dataset collected on an Amazonian forest "biomass dominant species", Dicorynia guianensis Amsh., also known to exhibit substantial WSG gradients along both radial and vertical axis. 9 trees ranging from 15 to 60 cm DBH were measured by climbers. Each tree was felled and samples were collected at different positions (3 in trunk, 1 to 5 in crown) to record WSG radial profiles. Results: Xtrawood allows computation of tree volume, but also visualization of WSG variations in tree as well as inference of WSG radial profiles at different heights. Output variables are decomposed according to different tree scale and locations (axis, trunk/crown) and easy to extract. Xtrawood results will be compared to those of standard estimation method and can be used to identify positions in trees where WSG value leads to the better estimate of tree AGB. Conclusion: Xtrawood produces

Background: Pleistocene climatic oscillations led to range fluctuations in African rain forest organisms. Isolation of populations during the driest climatic phases resulted in genetic differentiation through mutation and drift. Recent re-expansion of the forest brought differentiated groups into secondary contact. We investigated whether past climate changes may have led to sufficient differentiation to trigger speciation in a central African rainforest tree, Barteria fistulosa (Passifloraceae). Method: We genotyped 765 individuals of B. fistulosa at 12 microsatellite loci and characterized the spatial genetic structure by using Bayesian clustering algorithms, isolation-by-distance analyses and clines of synthetic alleles. We used species niche modelling (environmental and soil variables) to investigate ecological variables associated with genetic discontinuities. Results: Trees showed a very steep genetic discontinuity between groups north and south of latitude 1°N. There was no evidence for effective gene flow between the two tree lineages in contact at the transition zone, despite the presence of a few hybrids. Niche modelling did not predict the occurrence of northern trees south of this genetic transition, and vice versa. The variable that contributed the most to niche differentiation was precipitation during the driest quarter of the year. Discussion: The genetic discontinuity near latitude 1°N is inferred to be a tension zone resulting from reproductive incompatibilities between previously allopatric tree lineages. This tension zone may have stabilized at a climatic transition (between boreal and austral seasonal regimes), and matches patterns of genetic structure previously observed in other forest plant species of the region, suggesting that a tension zone may separate distinct lineages of several central African forest plants near the thermal equator. Our results suggest that northern and southern lineages could be locally adapted to climatic parameters

Understanding the response of communities to spatially heterogeneous environmental conditions is an important challenge for ecologists. Whereas broad-scale Amazonian forest types have been shown to influence the structure of the communities of mediumto large-sized vertebrates, their natural heterogeneity within the terra firme rainforests remains poorly investigated. Here we question the drivers of the diversity and composition of medium and large fauna assemblages from a species-neutral, functional and phylogenetic perspective. In this study, we disentangled the effects of various physical, biological and spatial covariates on the composition and diversity of 21 communities of 19 medium- and large-sized vertebrates in neotropical terra firme rainforests, French Guiana (~84,000 km²). We sampled each local vertebrates community using standardized line transects (sampling effort of ~5,000 km). We estimated species densities using distance sampling method taking into account temporary emigration and imperfect detection. Raw population density data were used to analyse species-neutral assemblages. Functional compositions and diversities were estimated from 9 morphological and behavioral traits while phylogenetic ones were measured from discrepancies between taxonomic levels (from species to classes). Physical environmental conditions were extracted from remote sensing data (e.g. mean landforms slope, mean elevation). Biological environmental conditions were estimated in the field (e.g. biomass, dominant tree families). Finally, geographic distances between sites were calculated to assess spatial effects on the structure of communities. We implemented variation partitioning to determine the relative importance of each covariate in shaping fauna assemblages. At this spatial extent, we can hypothesize that biological conditions explain better composition and diversities than physical conditions because of their potentially direct influences on fauna. In addition, these res

Large areas (2 million hectares per year) of Amazonian forests are selectively logged in a polycyclic harvest system. Modeling the post-logging dynamics of these production forests is thus of primary importance to assess their future carbon storage capacity as well as the structural and dynamic features of the forest that will be found in the next logging cycle. In this study, we used a network of 100 permanent sample plots in 10 sites spread across the Amazon basin to model three post-logging biomass fluxes (recruitment, growth and mortality). The temporal evolution of these biomass fluxes (recruitment, growth and mortality) for surviving trees and recruits and their relative importance in explaining biomass recovery through the Amazonian basin were modeled taking into account spatial as well as temporal autocorrelation in a mixed model framework. Incorporating both the environmental variability and the logging characteristics in the developed model indicate that the two key drivers of post-logging biomass fluxes are the relative biomass loss due to logging and the initial aboveground biomass. Overall, environmental factors had little additional weight in explaining the Amazon-wide variations of post-logging biomass fluxes. Our results stress the importance of developing specific modelling frameworks to account for the peculiar carbon cycle in managed tropical forests in order to better recognize their key role for climate regulation at the global scale. (Texte intégral)

Microclimates have long been recognized in controlling the physiology and ecology of species. However, in the context of global warming and increasing climatic variability, a major uncertainty that hampers effective pest management is related to the thermal characteristics of agricultural landscapes, which are known to have profound effects on insect pest dynamics. Here, we addressed the issue of considering microclimates experienced by crop pests in their environments to infer their distribution and develop innovative pest control strategies based on processes of thermal agro-ecology. We assessed the heterogeneity of microclimates experienced by pests and natural enemies in complex agricultural landscapes of Ecuador (from 2800 to 3600 m.a.s.l.), made of various crop types and natural habitats. The assessment of microclimates was performed at the agrosystem, crop field, and plant scales using a combination of UAVs, thermal cameras and temperature micro-loggers. Then, we determined the relationship between microclimates heterogeneity (characterized using spatial metrics) and pest occurrences (measured in the field with pheromone traps and local plant samplings). Results revealed that microclimates heterogeneity must be taken into consideration when estimating ectotherm occurrences. Indeed, at the landscape scale, microclimates of crops and natural habitats substantially affect pest dynamics. At the field scale, the spatial metrics shaping microclimatic conditions are significantly related to pest occurrences. And at the plant scale, we found that pests can access in their close vicinity (<1.2 m) most of the thermal micro-environments recorded at the field level. In complex agro-ecological landscapes, there is likely a wide range of microclimatic conditions resulting in the presence of locallysuitable and unfavourable conditions for ectotherms (crop pests but also natural enemies), the existence of which might not be apparent at a coarser resolution. Consequently, thi

Africa's cocoa producing countries are challenged to identify sustainable cropping models to replace the currently prevailing monoculture systems. In this context, cocoa-based agroforestry systems (c-AFS) from Central Cameroon could represent an initial model from which to work on as they are able to support many ecosystem services and maintain a sound cocoa production on the long-term. In Talba, an old pioneer front, various cocoa systems cohabit for about 40 years. Some are very simple, close to the conventional model, while others are rather complex and contain many associated tree species. Such circumstances represent an opportunity to check for differences in their functioning and management in very similar pedoclimatic and ecological conditions. In this study, we focused on functional features of associated trees community (AT) within a set of 3 types of c-AFS. We studied 54 plots of 800m² and setup 3 groups according to their AT density (ind.ha-1): low (< 50), medium (50 to 99), high (≥ 100). The systems studied ranged from 5 to 64 years old. We used 5 forest plots as controls. We characterized AT' species diversity, leaf-life span strategy, succession guild, N-fixation and wood specific gravity (WSG). We measured cocoa and AT basal area (BA) and height. In total, 695 associated trees and 64 species were assessed. Diversity indices and mean WSG increased with AT density. Mean height canopy was found higher at low AT density than in forest. Basal area of non-pioneer light demander, shade tolerant and evergreen species increased with AT density. Basal area of N-fixers was poorly affected by AT density. Cocoa BA steadily increased while AT density decreased. Ageing significantly affected cocoa and AT densities but did not change the relative BA shares between functional features for the groups tested. The study of AT functional “profiles” shows that farmers' c-AFS management differs according to AT density and affects c-AFS structures and functioning whist

The date palm, Phoenix dactylifera L. (Arecaceae), is a subtropical palm widely cultivated for numerous uses and ecosystematic services. The date palm is a dioecious species, which shows a marked dimorphism in inflorescence structure. To describe this dimorphism, architecture and geometry of male and female inflorescences were studied through kinetics of inflorescencial development and architectural and geometrical characterization of mature inflorescences. Two methodological approaches were used: a visual approach consisting of direct observations of inflorescence architecture of trees in situ and a technical approach through the valuation of different structural and geometric parameters of inflorescence. On every plant, inflorescence development is acrotone. Every palm leaf axils an inflorescencial bud. Inflorescence and female spikelets are longer than male ones. For female inflorescence, spikelets lengths are linked to their relative position on the rachis, the number of spikelets is on average 62, every spikelet carries 55 flowers on average. For male inflorescence, the length of spikelets seems independent of their relative position on the rachis. Number of spikes and flowers is higher with on average 236 spikes per rachis and 81 flowers per spike. In conclusion, architecture of male spikelets is more complex than female one. (Texte intégral)

Background: Differences in the distribution of biota across Africa have been described for well over 100 years. There is however little information on the forest types at a regional scale. In this study we aimed to identify large-scale variation in tree species composition across tropical Africa, and within central Africa, to detail the structure and functioning of moist forests. Methods: Distribution data were gathered for 1175 tree species in 455 samples from the literature scattered across tropical Africa, from Senegal to Mozambique, and including all types of tropical forests. The value of elevation and 19 climatic variables (BIOCLIM) were assigned to each sample. Management forest inventory data were assembled for 49,711 0.5-ha plots across central Africa, covering an area of more than six million hectares. Using ordinations, we determined the variations in species composition across tropical African forests and for central African moist forests we used both genus composition and forest structure. We defined floristic clusters and identified the characteristic species/genera at both levels of resolution. Results: We found floristic evidence for three main biogeographic regions across the tropical African forests, and described six floristic clusters with particular environmental conditions within these regions: Coastal and Upland for East Africa, Dry and Wet-Moist for West Africa, and Moist and Wet for Central Africa. Within the central African moist forests, we identified 7 forest types based on genus composition and forest structure. Most of these forests were composed of a mosaic of the structural derivatives of the Celtis (Ulmaceae) forest. Secondary Musanga (Moraceae) forest was located along roads and around main cities; mixed Manilkara (Sapotaceae) forest covers a huge area in the Sangha River Interval; and monodominant Gilbertiodendron (Fabaceae) forest was sparsely distributed along rivers. Conclusions: The forest types identified across tropical Afric

Background: The tropical forests in general, and those of Central Africa in particular, stand at the cross-road. The combined and interacting effects of land-use change, resource extraction, defaunation, fire, fragmentation and climate change are pushing these ecosystems towards critical points where transitions to altered states will happen. The future of these forests depends on our capacity to understand and anticipate these transitions, and to identify these states the forest ecosystems are likely to take. Yet, to date, there was not a unified model that presented the best available knowledge on the forest dynamics of the regions. The field is highly fragmented and we lack a general overview. Method: We propose here a general unified model of forest dynamics in Central Africa. This model represents the best available knowledge on the topic and is the result of a collaborative effort based on expert knowledge and an analysis of the literature. We built it using methods issued from the fields of facilitation, participatory modelling and team science. Result: Our model identifies the main forest types present in the area, the dynamic links and possible transitions between them and the potential impacts of environmental factors - climate, soil, large mammals - and human factors - logging, fire, clearings. It provides a description of these forest types and allows the layman to grasp the general dynamics at play in the region. For those willing to deepen their understanding, we provide all the necessary literature leads to guide them in their discovery of the topic. Conclusion: Our aim is to propose as an easy to access gateway for those needing to take decisions on how to manage the forests of Central Africa in the coming decades. It sums up our current understanding of the system, helps chart knowledge gaps and highlight avenues for future research, serving as basis for discussions. An accepted common understanding of the dynamics of these forests will be solid fou

Changes in land use and management affect the capacity of ecosystems to deliver services that contribute to the well-being of societies and their resilience to climate variations. For example, forest ecosystems help regulating water flows during extreme rains depending on species characteristics (roots and leaves) and people's inputs and decisions (planting trees in specific areas) determined by governance and economic settings (land ownership and labour). The linkages between ecosystems services and people's resilience to climate variations are mostly studied indirectly and findings are scattered in the literature. In particular, the social-ecological systems interactions for resilience have often been described generically (as ecosystem services and land management), considered as unidirectional (flows of services from ecosystems to people), and neglected multiple aspects (ecosystems own sensitivity or role in livelihoods diversification). The study aimed to identify mechanisms or mediating factors that enable or constrain the supply of ecosystem services to build people's resilience to climate variations. We reviewed the literature on forest ecosystems' contributions to increase rural people's resilience and proposed a framework that was applied to case studies in Indonesian communities affected by drought and floods. Forest ecosystem services and their benefits to local people were assessed through forest inventories, satellite images, focus group discussions, and household surveys. People's response strategies to climate-related events partially relied on the benefits provided by forest ecosystems but surprisingly in less forested places there were more strategies based on trees. This difference between potential and actual use suggested that human inputs and other favourable conditions determine whether ecosystems service can effectively contribute to increase people's resilience. In fact, the provision of benefits was mediated by ecological and anthropogenic

Background. Predicting the current and future natural distributions of species is challenging, especially in the tropics where large remote areas remain poorly known. Such challenge can only be met with an in-depth understanding of the drivers of species distribution, a well-designed and extensive survey and appropriate statistical models. Method. In this study, we use a large dataset of forest inventories from logging companies, which provides information on the abundance of 123 tree genera, in 140,000 plots spread over four Central African countries. In order to predict the current and future distribution of these tree genera, we use a set of bioclimatic, geological and anthropogenic variables. We rely on a recently published methodology, called Supervised Component Generalized Linear Regression (SCGLR), which identifies the most predictive dimensions among a large set of predictors. Result. Using a calibration and validation scheme, we show that the distribution of most tree genera can be well predicted over the whole study area at the present time. At the community level, the floristic and functional composition of tree genera is also inferred with a good accuracy. Finally, using spatially explicit null models, we show that species-climate association are in most cases not better than chance, thus challenging our ability to predict how forest composition will be affected by climatic changes. Conclusion. Overall, our study shows that tropical tree distributions can be predicted with good accuracy at the present time, offering new perspectives to manage tropical forests at large spatial scales, but that predicting shifts in species distribution under climate change scenarios is challenging. (Texte intégral)

If wildlife is considered as a renewable natural resource, for many rural Africans the occurrence of human wildlife conflict (HWC) overshadows expected outcomes from conservation and co-management initiatives. To reduce the magnitude of HWC, modern approaches deal with problem animals that cause conflicts while increasing the level of tolerance in the affected human populations. Assessing the local impact of HWC is part of this mitigation package, the objective been to provide timely information to adapt strategies and actions as data indicates what works and why. Lack of communication and trust between wildlife authorities and people concerned by HWC makes the effectiveness of the reporting poor, which raises the question of selecting the most appropriate technology for a real-time monitoring scheme with the capacity to inform decision-makers and improve the understanding of conflicts. To explore the feasibility of HWC monitoring, a series of tests was conducted in central Africa with KoBoCollect, an application from the KoBoToolbox an open source of tools for data collection and analysis based on OpenDataKit. With this application, data were collected using Smartphone on and off-line then synchronized into a database. Involving a regional HWC working group the 5W&H method was chosen to develop data trees of the key information needed to understand HWC problems. The 30+ variables were selected to develop an electronic form and responses to questions been facilitated by multiple choice responses with checkbox options. After a 9 month field test from April to December 2015, more than 300 electronic submissions were collected from Congo (42%), DRC (28%), Gabon (19%) and Cameroun (7%). Not surprisingly the elephant is the species most often involved in HWC (51%) followed by the hippo (11%) and rodents (11%), the other 11 species involved in HWC playing a minor role. If human casualties were rare (2%), the most predominant impact was crop raiding (82%). Mitigation measu

During the past 25 years, forest laws in Central African countries have undergone major changes. Management plans were made mandatory: nearly 19 million hectares of timber concessions (38% of total granted concessions) were subject to a management plan in 2013 and the dynamics is currently underway. The management plan is based on a set of technical and scientific studies, including statistical surveys (management inventories) covering the whole concession and taking into account all timber species, large mammals and the main non timber forest products. These inventories allow, at concession level, to characterize ecosystems and to assess the forest conservation values, through floristic and faunal biodiversity indicators and by taking into account threats to the forest ecosystems, especially anthropogenic ones. Such management inventories are used especially for planning and forecasting harvests, while minimising environmental impacts on the forest structure and functioning, and retaining regeneration capacities of the timber species and the forest ecosystems. The knowledge gained on specific and ecosystemic biodiversity helps to define management rules to ensure the sustainability of different timber species' populations, noticeably the exploited ones. It is also used to design areas within the concessions were exploitation will not take place due to conservation interest (most biodiversity-rich areas, protection of rare or endangered species...). Such so-called “conservation series” therefore complement the protected areas network. Well-managed forest concessions can help conserve the regional forest ecosystems and maintain essential functions that they provide. However, management plans were up to now designed at the concession scale. Data acquired in forest concessions also significantly contribute to improve knowledge of the forest ecosystems and their functioning at the regional level. Using this data, the CoForChange Project (http://www.coforchange.eu) issue

The livelihood of almost all indigenous peoples of the Congo basin depends on their free access to the forest natural resources. At present, some technical and legal means exist to improve the forest rights of indigenous peoples but the main question is what indigenous peoples themselves would request to truly fit their needs while conserving biodiversity. Based on the case of the Democratic Republic of Congo, this paper will explore the possible legal solutions such as protected areas and their various forms of governance and discuss the most/less suitable options and their conditions. Indeed, Indigenous peoples' and community conserved territories and areas (ICCAs) have been highly debated over the past few years, along with participatory management. If those models could support both IP livelihoods and biodiversity conservation in some protected areas, their implementation could be the first step towards the creation of a new form of "protected area" created and managed by indigenous peoples. This paper will therefore discuss this option further and put it in the broader context of the Congo basin.

In French Guiana, the forest sector (including private and public actors) will face strategic choices to respond to the increasing demand in wood supply for the coming decades. Indeed population in French Guiana is currently growing at a rate of around 2.5% per year and should exceed 500 000 inhabitants by 2050 leading to an increased consumption of material, energy and space. Tropical humid forests that cover 90% of the territory will be at the center of production and conservation concerns. Strategic choices, based on strong political decisions, include the volume of wood to be produced locally, the type of production (timber vs fuelwood) and the origin (plantation vs natural forest). We conducted a work to analyze the opportunities of the forestry sector to meet these challenges. All wood supply is currently provided through the management of natural forests. An alternative issue would be to produce wood from forest plantation. Experimental tree plantations have been developed since the 70's in French Guiana. More than 30 local species and 26 exotic species have been tested to evaluate their potential in tree plantation. Up to now no plantation were established at lager scale in French Guiana. We identified various scenarios to reach the wood supply by 2050. The scenarios were elaborated in two phases. First, we interviewed key actors of the forestry sector who gave their view on that perspective. It appeared that tree plantation is considered as a real opportunity for most of the actors. Second, species performance in tree plantation trials was carefully analyzed through mortality rates and tree productivity. Six species (four locals and two exotics) were identified with a high potential for sustainable forest plantation. Sustainability of natural forest management was also assessed based on the results provided by the Paracou experimental plot. Four main scenarios were identified. Wood production is calculated for both managed forests and forest plantation and

In wet tropical conditions, the improved pastures are usually implanted after deforestation and most times with a single forage grass (mainly C4 and exotic grasses) and more rarely with legumes. These artificial grasslands ecosystems are more unstable than native pastures. Grasslands can be degraded by the colonization of "undesirable" plants. These species are unpalatable and so reduce the production of the grasslands ("agronomical impact"). Some of these species are also invasive and colonize also the natural forests ("ecological impacts"). Understand the dynamics of undesirable species regarding the climate, soil, management and the vegetation is the key to propose sustainable management of tropical grasslands. The studies of undesirable plants are generally using species approaches within one region. Considering the diversity of tropical area, the undesirable species may differ from one region to another. These species approaches limit the generality of the results of these studies. The objective of this work is to test the use of functional trait approach for the understanding of the dynamics of undesirables' species. We used datasets from three different tropical regions: the Reunion Island in Indian Ocean New Caledonia Island in the Pacific Ocean and the French Guyana in the Amazonian region. The islands are biodiversity hotspots threaten by biological invasion. The grassland ecosystems studied are a major element of plants invasion process. In the French Guyana the grassland are implanted after deforestation of Amazonian forest. In each region, the grassland botanical composition and the dynamic of undesirable species were monitored during several years: 1994,1995,1996,2001 and 2004 for the Reunion, from 1999 to 2005 for New Caledonia and from1997 to 2000 and from 2010 to 2013 for the Guyana. The trait values of 84 functional traits were extracted from the TRY database (www.try-db.org) from the 367 species presented in the surveys. We imputed some of the mis

In most mycorrhizal symbioses, including most adult green orchids, fungi provide soil minerals to the plant, in exchange for photosynthetic sugar. Yet, during orchid germination, the fungi, which belong to the polyphyletic rhizoctonias, provide carbon to germinating seedlings that have no reserve. Moreover, in some orchid species, adult plants also recover carbon from their fungi: some are achlorophyllous and non-photosynthetic (mycoheterotrophic species) while others are green but mix photosynthesis and exploitation of fungal carbon (mixotrophic species). Mixotrophic and mycoheterotrophic orchids have lost association to rhizoctonias, but connect (often with high specificity) to ectomycorrhizal fungi, so that their carbon issues from surrounding trees. But this scenario is mostly based on temperate studies – how is it challenged in tropical regions, where additionally most orchids are epiphytic? Our recent researches provide clues on this question. First, and although this was sometimes questioned, epiphytic orchids are always mycorrhizal. We characterized the orchid fungi across the natural habitats of Reunion Island (Pacific) and investigated the architecture of bipartite plant-fungal networks for 73 orchid species and 95 taxonomic units of mycorrhizal fungi. Unlike some recent evidence for nestedness in mycorrhizal symbioses, we found a highly modular architecture that largely reflected an ecological barrier between epiphytic and terrestrial sub-networks. By testing for phylogenetic signal in this network, it was stronger for both partners in the epiphytic subnetwork. Moreover, in the sub-network of epiphytic angraecoid orchids, the signal in orchid phylogeny was stronger than the signal in fungal phylogeny. Epiphytic associations are therefore more conservative and may coevolve more than terrestrial ones. Second, our study of tropical mycoheterotrophic and mixotrophic orchids in the paleo- and neotropics revealed that specificity is not the rule and that, if rh

Background: Understanding the reaction of ecosystems to climate change and anthropogenic pressure is a central question in ecology and environmental sciences. In the terrestrial tropics, theoretical and empirical works suggest that once external disturbances have reached a given threshold, forest-savanna systems can switch from one state to another. Considering the multiplicity of the tropical forest systems, we make the assumption that numerous shifts may actually occur within the forest itself, without changes in forest cover but with risks of critical modifications in forest functioning. Methods: To test this hypothesis, we used a finite mixture of regression models aiming at simultaneously predicting and grouping forest functional profiles at the stand level with respect to anthropogenic pressure, climate and soil. The model is built on a dataset of more than 140 000 plots of 0.5-ha each gathered from Central African forest companies. Forest stand functions are analyzed through two key functional traits: the successional status - pioneer vs. non-pioneer trees- and the leaf phenology - evergreen vs. deciduous trees. Results: Our model captured a significant part of variation in the functional composition over the study area and revealed how anthropogenic pressure, climate change, soils or their combination lead to profound modifications within the forests. In particular, we showed that shifts from evergreen to deciduous stands can be mediated both by anthropogenic pressure or climate change. Discussion: This work shows for the first time how external forcing may jointly lead to multiple shifts in the functional composition of tropical forests. Our model allowed to predict directional changes in forest functioning according to anthropogenic pressure and climate thus opening new perspectives in theoretical ecology, global vegetation modelling and in the understanding of the vulnerability of tropical forests to global changes. (Texte intégral)