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See detailTowards improving the assessment of rainforest carbon: Complementary evidence from repeated diameter measurements and dated wood
Ilondea, Bhely Angoboy; De Mil, Tom ULiege; Hubau, Wannes et al

in Dendrochronologia (2020), 62

We explore whether a growth-ring analysis can produce additional information about carbon budgets in tropical forests. Such forests are characterized by a high number of species and by trees that rarely ... [more ▼]

We explore whether a growth-ring analysis can produce additional information about carbon budgets in tropical forests. Such forests are characterized by a high number of species and by trees that rarely have anatomically distinct annual growth rings, which hampers the application of dendrochronological tools in carbon balance assessments in the tropics. We use forest inventory data and archived annual diameter measurements from the Luki Biosphere Reserve in the southwestern margin of the Congo Basin forest massif. In addition, dated wood data are available from the same location thanks to tag nail traces that allow for the measurement of growth increments over a period of 66 years. We find that precise increment measurements based on dated wood are advisable for small subsets of many less abundant species and for functional species groups characterized by slow growth. The dated wood approach shows that many understory trees with non-periodical rings remain in a steady state for long periods of time. These results suggest a dated wood approach is advisable for studies of growth trajectories of individual trees that might be of importance for carbon assessments in degraded forests. [less ▲]

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See detailHow Can Remote Sensing Help Monitor Tropical Moist Forest Degradation?—A Systematic Review
Dupuis, Chloé ULiege; Lejeune, Philippe ULiege; Michez, Adrien ULiege et al

in Remote Sensing (2020), 12(7), 1087

In the context of the climate and biodiversity crisis facing our planet, tropical forests playing a key role in global carbon flux and containing over half of Earth’s species are important to preserve ... [more ▼]

In the context of the climate and biodiversity crisis facing our planet, tropical forests playing a key role in global carbon flux and containing over half of Earth’s species are important to preserve. They are today threatened by deforestation but also by forest degradation, which is more difficult to study. Here, we performed a systematic review of studies on moist tropical forest degradation using remote sensing and fitting indicators of forest resilience to perturbations. Geographical repartition, spatial extent and temporal evolution were analyzed. Indicators of compositional, structural and regeneration criteria were noted as well as remote sensing indices and metrics used. Tropical moist forest degradation is not extensively studied especially in the Congo basin and in southeast Asia. Forest structure (i.e., canopy gaps, fragmentation and biomass) is the most widely and easily measured criteria with remote sensing, while composition and regeneration are more difficult to characterize. Mixing LiDAR/Radar and optical data shows good potential as well as very high-resolution satellite data. The awaited GEDI and BIOMASS satellites data will fill the actual gap to a large extent and provide accurate structural information. LiDAR and unmanned aerial vehicles (UAVs) form a good bridge between field and satellite data. While the performance of the LiDAR is no longer to be demonstrated, particular attention should be brought to the UAV that shows great potential and could be more easily used by local communities and stakeholders. [less ▲]

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See detailQuantifying the Use of Forest Ecosystem Services by Local Populations in Southeastern Cameroon
Lhoest, Simon ULiege; Vermeulen, Cédric ULiege; Fayolle, Adeline ULiege et al

in Sustainability (2020), 12(6), 2505

In order to improve sustainability and design adequate management strategies in threatened tropical forests, integrated assessments of the use of ecosystem services are needed, combining biophysical ... [more ▼]

In order to improve sustainability and design adequate management strategies in threatened tropical forests, integrated assessments of the use of ecosystem services are needed, combining biophysical, social, and economic approaches. In particular, no integrated ecosystem services (ES) assessment has been conducted in Central Africa, where rural communities deeply depend on forests in a high-poverty context. Here, we aimed to quantify the use of ES provided by tropical forests to local populations in the Dja area (Cameroon), identify its determinants and evaluate its sustainability. We conducted various interviews and field surveys with 133 households in three villages, focusing on three provisioning services (bushmeat, firewood, and timber), and five cultural services (cultural heritage, inspiration, spiritual experience, recreation, and education). Local populations consumed a mean of 56 kg of bushmeat/person/year (hunting zones covering on average 213 km2), 1.17 m3 of firewood/person/year (collection zones covering on average 4 km2), and 0.03m3 of timber/person/year. Between 25% and 86% of respondents considered cultural services as important. The use of ES was mainly influenced by population size, deforestation rate, and forest allocations, whereas the influence of socio-demographic characteristics of households remained limited to slight di erences between Baka and Bantu people. We conclude that the consumption of firewood and timber is sustainable, whereas high hunting pressure has resulted in severe defaunation in the area due to the large decline in the abundance and biomass of forest mammals hunted for bushmeat by local populations. [less ▲]

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See detailPredicting forest site characteristics from floristics ; an automated approach for forest management in the Walloon Region.
Lisein, Jonathan ULiege; Fayolle, Adeline ULiege; Claessens, Hugues ULiege

Poster (2020, January 31)

Forest tree and plant species prosper in the specific ecological conditions of their ecological niche. Together, the proper knowledge of the ecological niche of tree species and the proper description of ... [more ▼]

Forest tree and plant species prosper in the specific ecological conditions of their ecological niche. Together, the proper knowledge of the ecological niche of tree species and the proper description of a Forest site form a keystone that ensures a good match between forest trees and their environment. In Wallonia, an original toolbox is in use since 1991, made up of an extensive documentation about tree species ecological requirements and a comprehensive methodology of forest site characterization. Gathered under the denomination of "forest tree autecology tool", this toolbox has been recently reviewed and updated by a scientific consortium and is now available online (https://www.fichierecologique.be/). The objective of this toolbox is to determine which tree species fits the best a particular forest site. It is based on the location of the site and of the ecological niche of the tree species into a 3 axis matrix “ecogram” (climatic zone, nutrient and moisture level) summarizing soil and topographic information, issued from direct observations or cartographic data, thanks to dichotomic keys. Along with the abiotic approach that helps to position the forest site in the ecogram, a floristic approach has also been used independently for years. Thange (1969) has settled the foundations of the socio-ecological groups, which are defined as a set of forest plant species who share the same ecological niche. These socio-ecological groups are commonly used in southern Belgium to describe forest sites. But still, the determination of the nutrient and moisture levels of a forest site based on its species composition is a complex task which requires a high level of expertise. Here, we present an automated approach which aims at determining nutrient and moisture levels of any sites from the plant species sampled. We believe that an increased level of automatization will promote the use of these methodology of forest site identification, tested for long but requiring detailed expertise. Numerous floristic samples were compiled over years and resulted in a comprehensive collection of 2074 forest site observations, which grasp all the nutrient and moisture gradients of Wallonia. Determination of the nutrient and moisture levels for each site has been achieved by the use of the abiotic dichotomic keys from the "forest tree autecology tool". An automated classifier algorithm (random forest) was trained with these data in order to predict the nutrient and moisture levels of any new sites in Wallonia from the presence or absence of every indicator plant species of the Wallonian ecological groups [n=260 species tested]. Results suit well our expectations and this classifier has been integrated into a web application dedicated to forest managers ; http://phytospy.gembloux.ulg.ac.be/ Tanghe, M., 1969. Groupes écologiques , Associations stationnelles et Associations régionales des Forêt du sud-est de la Belgique. PhD thesis, ULB, Bruxelles. Internet site of the "tree species ecological file" : https://www.fichierecologique.be/ [less ▲]

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See detailQuantifier les dimensions des houppiers à l’aide d’images aériennes à haute résolution pour estimer l’accroissement diamétrique des arbres dans les forêts d’Afrique centrale
Ndamiyehe Ncutirakiza, Jean-Baptiste; Lejeune, Philippe ULiege; Gourlet-Fleury, Sylvie et al

in Bois et Forêts des Tropiques (2020), 343

Characterising forest dynamics of a forest is essential to its management. Tree crowns are a key factor in these dynamics, but measuring them in tropical forests is not an easy matter. This study tested ... [more ▼]

Characterising forest dynamics of a forest is essential to its management. Tree crowns are a key factor in these dynamics, but measuring them in tropical forests is not an easy matter. This study tested the use of highresolution aerial imagery to estimate the tree diameter growth by incorporating detailed measurements of the detected tree crowns. Ortho-images at a resolution of 10 cm/pixel were captured by a fixed-wing drone over a 9 ha plot in the Yoko forest in the Democratic Republic of Congo. Inventories conducted on trees ≥ 10 cm diameter at breast height (DBH) in 2008 and 2016 provided access to a variety of tree dendrometric characteristics, including DBH and species temperament, and allowed the calculation of diameter increments. Mixed linear models were calibrated to predict diameter increment of 163 trees identified both on the ground and on the ortho-images, using variables quantified on the ground only and/or from variables measured from the orthoimages. From the aerial images, we were able to detect 23.4% of the trees with DBH ≥ 10 cm listed in the ground inventories, representing 75.1% of the stand’s aerial biomass. The probability of detecting the trees varied with their DBH, from 0.09 for trees with DBH < 30 cm to 0.97 for trees with DBH ≥ 60 cm. Predictions of diametric growth improved significantly when the variables quantified by remote sensing were added to the ground variables. The best models for estimating diameter increment include, in particular, a term characterising the size of tree crowns, which can only be measured by remote sensing. Of the variables determined by remote sensing, convex crown area was the most successfull in the models and therefore appears to be the most accurate variable to describe competition between tree crowns. These results open up possibilities to build new tools of data acquisition to support forest planning. [less ▲]

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See detailConservation value of tropical forests: Distance to human settlements matters more than management in Central Africa
Lhoest, Simon ULiege; Fonteyn, Davy ULiege; Daïnou, Kasso ULiege et al

in Biological Conservation (2020), 241(108351),

Tropical forests in Central Africa host unique biodiversity threatened by human degradation of habitats and defaunation. Forests allocated to conservation, production and community management are expected ... [more ▼]

Tropical forests in Central Africa host unique biodiversity threatened by human degradation of habitats and defaunation. Forests allocated to conservation, production and community management are expected to have different conservation values. Here, we aimed to identify the determinants of the conservation value of tropical forests in southeastern Cameroon, by disentangling the effects of forest allocations, proximity to human settlements, and local habitat. We inventoried two taxonomical groups: mammal species with camera traps (3464 independent detection events) and dung beetle species with pitfall traps (4475 individuals). We used an integrated analytical approach, examining both species richness and composition. For both mammals and dung beetles, species richness decreased from the protected area to the community forests, and the logging concession showed intermediate richness. Species richness of both groups was negatively correlated to the proximity to human settlements and disturbance, with a decreasing gradient of body mass and the loss of the most threatened species. The replacement (i.e., spatial turnover) of both mammal and dung beetle species among forest allocations suggest an integration of conservation initiatives to a large number of different sites, with a priority on protected and remote areas of high biodiversity. These results confirm the high conservation value of protected areas and their essential role in conservation strategies, ecologically connected with well-managed production forests with variable conservation value mainly depending on accessibility. Community forests located close to villages are much more degraded but not totally defaunated and still provide bushmeat to local populations. © 2019 Elsevier Ltd [less ▲]

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See detailCarte blanche : "Quels arbres pour la forêt de demain?"
Fanal, Aurore ULiege; Monty, Arnaud ULiege; Claessens, Hugues ULiege et al

Article for general public (2019)

17 scientifiques et académiques de la Fédération Wallonie – Bruxelles cosignent cette carte blanche pour alerter sur les risques de destruction de l’écosystème des forêts wallonnes par l’introduction ... [more ▼]

17 scientifiques et académiques de la Fédération Wallonie – Bruxelles cosignent cette carte blanche pour alerter sur les risques de destruction de l’écosystème des forêts wallonnes par l’introduction massive d’espèces végétales exotiques. [less ▲]

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See detailA sharp floristic discontinuity revealed by the biogeographic regionalization of African savannas [presence data]
Fayolle, Adeline ULiege

Textual, factual or bibliographical database (2019)

Aim. In tropical Africa, savannas cover huge areas, have high plant species richness, and are considered as a major natural resource for most countries. There is, however, little information available on ... [more ▼]

Aim. In tropical Africa, savannas cover huge areas, have high plant species richness, and are considered as a major natural resource for most countries. There is, however, little information available on their floristics and biogeography at the continental scale, despite the importance of such information for our understanding of the drivers of species diversity at various scales and for effective conservation and management. Here, we collated and analysed floristic data from across the continent in order to propose a biogeographic regionalization for African savannas. Location. We collated floristic information (specifically woody species lists) for 298 samples of savanna vegetation across Africa, extending from 18°N to 33°S and from 17°W to 48°E. Taxon. We focused on native woody species. Methods. We used ordination and clustering to identify the floristic discontinuities and gradual transitions across African savannas. Floristic relationships, specificity and turnover, within and between floristic clusters, were analysed using a (dis-)similarity-based approach. Results. We identified eight floristic clusters across African savannas which in turn were grouped into two larger macro-units. Ordinations at species and genus levels showed a clear differentiation in woody species composition between the North/West macro-unit and the South/East macro-unit. This floristic discontinuity matches to the High (i.e., N&W) and Low (S&E) division of Africa previously proposed by White (1983) and which tracks climatic and topographic variation. In the N&W savannas, the floristic gradient determined by rainfall was partitioned into the Sudanian (drier) and Guinean (wetter) clusters. Within the highly heterogeneous S&E savannas and woodlands, six clusters were identified: Ugandan, Ethiopian, Mozambican, Zambezian, Namibian and South-African. Main conclusions. The proposed pan-African classification of savannas and woodlands might assist the development of coordinated management and conservation policies. [less ▲]

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See detailPerceptions of ecosystem services provided by tropical forests to local populations in Cameroon
Lhoest, Simon ULiege; Dufrêne, Marc ULiege; Vermeulen, Cédric ULiege et al

in Ecosystem Services (2019), 38

In Central Africa, local populations are deeply dependent on tropical forests, which provide numerous ecosystem services (ES). For the first time in Central Africa, we assessed the perceptions of ES ... [more ▼]

In Central Africa, local populations are deeply dependent on tropical forests, which provide numerous ecosystem services (ES). For the first time in Central Africa, we assessed the perceptions of ES provided by tropical forests to local populations, considering three land allocation types: a protected area, a Forest Stewardship Council (FSC)-certified logging concession, and three community forests. We conducted a questionnaire survey with 225 forest stakeholders in southeastern Cameroon, combining an open-ended question and 16 directed questions to evaluate the perceptions of ES significance and abundance, respectively. The ES most frequently reported as significant were provisioning (93% of respondents) and cultural & amenity services (68%), whereas regulating services were less mentioned (16%). Bushmeat provision was the only ES perceived as highly significant but not very abundant. There were slight variations of perceptions among forest land allocation types and respondents, suggesting a relative homogeneity in ES abundance. For further integrative ES assessment, we suggest quantifying ES with complementary ecological and economic approaches, such as meat provision, recreation, tourism, timber provision, spiritual experience, firewood provision, water quality regulation, and inspiration for culture. We also give three concrete recommendations for forest management, the most urgent being to provide sources of protein alternative to bushmeat. [less ▲]

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See detailAn assessment of the terrestrial mammal diversity in a sustainably logged forest in east Gabon: Impact of camera trap placement strategy on the detected species
Fonteyn, Davy ULiege; Cornélis, Daniel; Deflandre, Nicolas et al

Conference (2019, August)

Camera traps are widely used for assessing terrestrial vertebrate diversity across tropical forests. Non-random placement strategy is traditionally adopted, with camera traps oriented towards specific ... [more ▼]

Camera traps are widely used for assessing terrestrial vertebrate diversity across tropical forests. Non-random placement strategy is traditionally adopted, with camera traps oriented towards specific features such as game trails. However, this could artificially bias the capture rates of certain species. Here, we first assessed the terrestrial mammal diversity of sustainably logged forests in east Gabon. Then, we investigated the impact of placement strategy on the detected diversity by comparing game-trail based and systematically oriented camera traps. We followed a grid design replicated consecutively in four areas, composed of 15-17 sampling points placed every 2 km², and left for one month on the field. Each sampling point was composed of two cameras: the ‘systematic camera’ was placed close to the theoretical point and oriented towards a naturally cleared area, while the ‘game-trail oriented camera’ was located within a 20 m radius of the random camera. A total of 31 mammal species were identified, including gorillas, chimps, elephants, and leopards. Game-trail placement provided greater relative abundance for most species and the deviation to this pattern only concerned extremely infrequent species (sitatunga, golden cat). Multivariate analyses did not distinguish different species composition between the two strategies at the site scale (grid), although local differences did appear between pairs at the camera scale. When examining species occupancy, game-trail strategy does not seem to bias inventories compared to the random placement, and data from both strategies can be used in multi-site analyses, but this does not hold true for relative abundance. However, it is almost impossible to set up a strict random sampling and both strategies need a subjective decision when installing camera traps. We recommend maintaining game-trail orientation for large-scale camera trapping inventories conducted at species or community level. [less ▲]

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See detailAn assessment of the terrestrial mammal diversity in a sustainably logged forest in east Gabon: Impact of camera trap placement strategy on the detected species
Fonteyn, Davy ULiege; Cornélis, Daniel; Deflandre, Nicolas et al

Conference (2019, August)

Camera traps are widely used for assessing terrestrial vertebrate diversity across tropical forests. Non-random placement strategy is traditionally adopted, with camera traps oriented towards specific ... [more ▼]

Camera traps are widely used for assessing terrestrial vertebrate diversity across tropical forests. Non-random placement strategy is traditionally adopted, with camera traps oriented towards specific features such as game trails. However, this could artificially bias the capture rates of certain species. Here, we first assessed the terrestrial mammal diversity of sustainably logged forests in east Gabon. Then, we investigated the impact of placement strategy on the detected diversity by comparing game-trail based and systematically oriented camera traps. We followed a grid design replicated consecutively in four areas, composed of 15-17 sampling points placed every 2 km², and left for one month on the field. Each sampling point was composed of two cameras: the ‘systematic camera’ was placed close to the theoretical point and oriented towards a naturally cleared area, while the ‘game-trail oriented camera’ was located within a 20 m radius of the random camera. A total of 31 mammal species were identified, including gorillas, chimps, elephants, and leopards. Game-trail placement provided greater relative abundance for most species and the deviation to this pattern only concerned extremely infrequent species (sitatunga, golden cat). Multivariate analyses did not distinguish different species composition between the two strategies at the site scale (grid), although local differences did appear between pairs at the camera scale. When examining species occupancy, game-trail strategy does not seem to bias inventories compared to the random placement, and data from both strategies can be used in multi-site analyses, but this does not hold true for relative abundance. However, it is almost impossible to set up a strict random sampling and both strategies need a subjective decision when installing camera traps. We recommend maintaining game-trail orientation for large-scale camera trapping inventories conducted at species or community level. [less ▲]

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See detailUne forte saisonnalité du climat et de la phénologie reproductive dans la forêt du Mayombe : l’apport des données historiques de la Réserve de Luki en République démocratique du Congo
Ilondea, B. A.; Beeckman, H.; Ouédraogo, D.-Y. et al

in Bois et Forêts des Tropiques (2019), (341), 39-53

En Afrique, la phénologie reproductive des arbres tropicaux, majoritairement annuelle, semble présenter une certaine régularité. Cette étude documente les variations intra- et interannuelles de la ... [more ▼]

En Afrique, la phénologie reproductive des arbres tropicaux, majoritairement annuelle, semble présenter une certaine régularité. Cette étude documente les variations intra- et interannuelles de la phénologie reproductive des arbres de la forêt du Mayombe à partir des données historiques de la Réserve de Luki (République démocratique du Congo). Le diamètre de reproduction des espèces exploitées pour le bois, encore largement méconnu, a été également examiné pour les espèces suffisamment représentées dans les données. Le suivi phénologique de 3 642 arbres appartenant à 158 espèces et 39 familles a été réalisé tous les 10 jours de 1948 à 1957. Les statistiques circulaires ont été utilisées pour tester le synchronisme de la phénologie entre arbres, à l’échelle de la communauté, pour la forêt dans son ensemble, et individuellement pour 87 espèces, dont 35 espèces bien représentées (n ≥ 20 arbres), 16 espèces commerciales et 36 autres espèces. Des régressions logistiques ont permis de déterminer le diamètre de fructification (minimum et régulier) de ces espèces. Pour la majorité des espèces, la floraison était régulière, annuelle et largement saisonnière (81,6 %, 71 espèces). Les pics étaient plus marqués pour la floraison que pour la fructification, plus étalée dans le temps, bien que significativement agrégée temporellement. La majorité des arbres et des espèces fleurissaient entre décembre et février, pendant la petite saison sèche, bien que des fleurs et des fruits étaient observables toute l’année à l’échelle de la communauté. Seules 13 espèces ont montré une relation significative entre le diamètre et la reproduction, parmi lesquelles sept espèces de canopée, cinq de sous-bois et une héliophile. Pour ces espèces, la moyenne du diamètre minimum de reproduction était de 17,3 cm. [less ▲]

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See detailModeling tree growth, harvesting and regeneration from national forest inventory data: A case study of Southern Belgium forest resources evolution
Perin, Jérôme ULiege; Bauwens, Sébastien ULiege; Hebert, Jacques ULiege et al

Poster (2019, May)

We developed an easily replicable methodology to develop harmonized growth and management models from national forest inventory data. These models are compatible with a wide range of forest composition ... [more ▼]

We developed an easily replicable methodology to develop harmonized growth and management models from national forest inventory data. These models are compatible with a wide range of forest composition and structure and can be directly applied on forest inventory data or integrated in a forest simulation software. [less ▲]

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See detailEcosystem services assessment in Southeast Cameroon tropical forests
Lhoest, Simon ULiege; Dufrêne, Marc ULiege; Jamar, Pierre et al

Scientific conference (2019, March 11)

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See detailEcological niche divergence associated with species and populations differentiation in Erythrophleum (Fabaceae, Caesalpinioideae)
Gorel, Anaïs ULiege; Duminil, Jérôme; Doucet, Jean-Louis ULiege et al

in Plant Ecology and Evolution (2019)

Background and aims – The isolation of populations inside forest refugia during past climate changes has widely been hypothesized as a major driver of tropical plant diversity. Environmental conditions ... [more ▼]

Background and aims – The isolation of populations inside forest refugia during past climate changes has widely been hypothesized as a major driver of tropical plant diversity. Environmental conditions can also influence patterns of diversity by driving divergent selection leading to local adaptation and, potentially, ecological speciation. Genetic and phylogenetic approaches are frequently used to study the diversification of African tree clades. However, the environmental space occupied by closely related species or intra-specific gene pools is barely quantified, though needed to properly test hypotheses on diversification processes. Methods – Using species distribution models, we determined the bioclimatic constraints on the distribution of closely related species and intra-specific gene pools. Our study model, Erythrophleum (Fabaceae - Caesalpinioideae), is a tropical tree genus widespread across Africa, and vastly investigated for genetics. Here, we combined the available phylogenetic data with information on niche divergence to explore the role of ecology into diversification at the species and gene pool levels. Key results – Ecological speciation through climate has probably played a key role in the evolution of the Erythrophleum species. The differential climatic niche of the species indicated adaptive divergence along rainfall gradients, that have probably been boosted by past climate fluctuations. At the gene pool level, past climate changes during the Pleistocene have shaped genetic diversity, though within Erythrophleum suaveolens, adaptive divergence also occurred. Conclusions – We believe that ecological speciation is a key mechanism of diversification for tropical African tree species, since such climatic niche partition exist among many other genera. Modeling the environmental niche of closely related taxa, and testing for niche differentiation, combined with divergence dates offered new insights on the process of diversification. [less ▲]

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See detailConservation value of protected and logged tropical forests in Cameroon
Lhoest, Simon ULiege; Fonteyn, Davy ULiege; Daïnou, Kasso ULiege et al

Scientific conference (2019, January 25)

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See detail11C-autoradiographs to image phloem loading
Hubeau, Michiel; Mincke, Jens; Vanhove, Christian et al

in Frontiers in Forests and Global Change (2019), 2:20

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See detailHighlighting convergent evolution in morphological traits in response to climatic gradient in African tropical tree species: The case of genus Guibourtia Benn.
Tosso, Dji-ndé Félicien ULiege; Doucet, Jean-Louis ULiege; Daïnou, Kasso ULiege et al

in Ecology and Evolution (2019)

Adaptive evolution is a major driver of organism diversification, but the links between phenotypic traits and environmental niche remain little documented in tropical trees. Moreover, trait-niche ... [more ▼]

Adaptive evolution is a major driver of organism diversification, but the links between phenotypic traits and environmental niche remain little documented in tropical trees. Moreover, trait-niche relationships are complex because a correlation between the traits and environmental niches displayed by a sample of species may result from (a) convergent evolution if different environmental conditions have selected different sets of traits, and/or (b) phylogenetic inertia if niche and morphological differences between species are simply function of their phylogenetic divergence, in which case the trait-niche correlation does not imply any direct causal link. Here, we aim to assess the respective roles of phylogenetic inertia and convergent evolution in shaping the differences of botanical traits and environmental niches among congeneric African tree species that evolved in different biomes. This issue was addressed with the tree genus Guibourtia Benn. (Leguminosae and Detarioideae), which contains 13 African species occupying various forest habitat types, from rain forest to dry woodlands, with different climate and soil conditions. To this end, we combined morphological data with ecological niche modelling and used a highly resolved plastid phylogeny of the 13 African Guibourtia species. First, we demonstrated phylogenetic signals in both morphological traits (Mantel test between phylogenetic and morphological distances between species: r =.24, p =.031) and environmental niches (Mantel test between phylogenetic and niche distances between species: r =.23, p =.025). Second, we found a significant correlation between morphology and niche, at least between some of their respective dimensions (Mantel's r =.32, p =.013), even after accounting for phylogenetic inertia (Phylogenetic Independent Contrast: r =.69, p =.018). This correlation occurred between some leaflet and flower traits and solar radiation, relative humidity, precipitations, and temperature range. Our results demonstrate the convergent evolution of some morphological traits in response to climatic factors in congeneric tree species and highlight the action of selective forces, along with neutral ones, in shaping the divergence between congeneric tropical plants. © 2019 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd. [less ▲]

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See detailA sharp floristic discontinuity revealed by the biogeographic regionalization of African savannas
Fayolle, Adeline ULiege; Swaine, Michael D.; Aleman, Julie et al

in Journal of Biogeography (2019)

Aim: In tropical Africa, savannas cover huge areas, have high plant species richness and are considered as a major natural resource for most countries. There is, however, little information available on ... [more ▼]

Aim: In tropical Africa, savannas cover huge areas, have high plant species richness and are considered as a major natural resource for most countries. There is, however, little information available on their floristics and biogeography at the continental scale, despite the importance of such information for our understanding of the drivers of species diversity at various scales and for effective conservation and management. Here, we collated and analysed floristic data from across the continent in order to propose a biogeographical regionalization for African savannas. Location: We collated floristic information (specifically woody species lists) for 298 samples of savanna vegetation across Africa, extending from 18° N to 33° S and from 17° W to 48° E. Taxa: We focused on native woody species. Methods: We used ordination and clustering to identify the floristic discontinuities and gradual transitions across African savannas. Floristic relationships, specificity and turnover, within and between floristic clusters, were analysed using a (dis‐)similarity‐ based approach. Results: We identified eight floristic clusters across African savannas which in turn were grouped into two larger macro‐units. Ordinations at species and genus levels showed a clear differentiation in woody species composition between the North/ West macro‐unit and the South/East macro‐unit. This floristic discontinuity matches to the High (i.e. N&W) and Low (S&E) division of Africa previously proposed by White (1983) and which tracks climatic and topographical variation. In the N&W savannas, the floristic gradient determined by rainfall was partitioned into the Sudanian (drier) and Guinean (wetter) clusters. Within the highly heterogeneous S&E savannas and woodlands, six clusters were identified: Ugandan, Ethiopian, Mozambican, Zambezian, Namibian and South African. Main conclusions: The proposed pan‐African classification of savannas and woodlands might assist the development of coordinated management and conservation policies. [less ▲]

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See detailTesting the divergent adaptation of two congeneric tree species on a rainfall gradient using eco-physio-morphological traits
Gorel, Anaïs ULiege; Steppe, Kathy; Beeckman, Hans et al

in Biotropica (2019)

In tropical Africa, evidence of widely distributed genera transcending biomes or habitat boundaries has been reported. The evolutionary processes that allowed these lineages to disperse and adapt into new ... [more ▼]

In tropical Africa, evidence of widely distributed genera transcending biomes or habitat boundaries has been reported. The evolutionary processes that allowed these lineages to disperse and adapt into new environments are far from being resolved. To better understand these processes, we propose an integrated approach, based on the eco-physio-morphological traits of two sister species with adjacent distributions along a rainfall gradient. We used wood anatomical traits, plant hydraulics (vulnerability to cavitation, wood volumetric water content and hydraulic capacitance) and growth data from the natural habitat, in a common garden, to compare species with known phylogeny, very similar morphologically, but occupying contrasting habitats: Erythrophleum ivorense (wet forest) and Erythrophleum suaveolens (moist forest and forest gallery). We identified some slight differences in wood anatomical traits between the two species associated with strong differences in hydraulics, growth, and overall species distribution. The moist forest species, E. suaveolens had narrower vessels and intervessel pits, and higher vessel cell-wall reinforcement than E. ivorense. These traits allow a high resistance to cavitation and a continuous internal water supply of the xylem during water shortage, allowing a higher fitness during drought periods, but limiting growth. Our results confirm a trade-off between drought tolerance and growth, controlled by subtle adaptations in wood traits, as a key mechanism leading to the niche partitioning between the two Erythrophleum species. The generality of this trade-off and its importance in the diversification of the African tree flora remains to be tested. Our integrated eco-physio-morpho approach could be the way forward. [less ▲]

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