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See detailUnveiling African rainforest composition and vulnerability to global change
Réjou-Méchain, Maxime; Mortier, Frédéric; Bastin, Jean-François ULiege et al

in Nature (2021)

Africa is forecasted to experience large and rapid climate change1 and population growth2 during the twenty-first century, which threatens the world’s second largest rainforest. Protecting and sustainably ... [more ▼]

Africa is forecasted to experience large and rapid climate change1 and population growth2 during the twenty-first century, which threatens the world’s second largest rainforest. Protecting and sustainably managing these African forests requires an increased understanding of their compositional heterogeneity, the environmental drivers of forest composition and their vulnerability to ongoing changes. Here, using a very large dataset of 6 million trees in more than 180,000 field plots, we jointly model the distribution in abundance of the most dominant tree taxa in central Africa, and produce continuous maps of the floristic and functional composition of central African forests. Our results show that the uncertainty in taxon-specific distributions averages out at the community level, and reveal highly deterministic assemblages. We uncover contrasting floristic and functional compositions across climates, soil types and anthropogenic gradients, with functional convergence among types of forest that are floristically dissimilar. Combining these spatial predictions with scenarios of climatic and anthropogenic global change suggests a high vulnerability of the northern and southern forest margins, the Atlantic forests and most forests in the Democratic Republic of the Congo, where both climate and anthropogenic threats are expected to increase sharply by 2085. These results constitute key quantitative benchmarks for scientists and policymakers to shape transnational conservation and management strategies that aim to provide a sustainable future for central African forests. [less ▲]

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See detailArboreta reveal the invasive potential of several conifer species in the temperate forests of western Europe
Fanal, Aurore ULiege; Mahy, Grégory ULiege; Fayolle, Adeline ULiege et al

in NeoBiota (2021), 64

Identifying emerging invasive species is a priority to implement early preventive and control actions. In terms of the number of invasive tree species, forestry represents the second largest pathway of ... [more ▼]

Identifying emerging invasive species is a priority to implement early preventive and control actions. In terms of the number of invasive tree species, forestry represents the second largest pathway of introduction, with an invasive debt likely existing for alien conifers in Europe. In the early 1900s, a network of arboreta was established in southern Belgium to assess the wood production potential of prospective conifer and broadleaved species. Here, we use eight arboreta as natural experiments to identify alien conifers presenting invasive behavior. Through systematic sampling, we quantified the natural regeneration of alien conifers and recorded local environmental variables. For each species, regeneration density, dispersal distances, and age structure were analyzed. Generalized mixed effects models were fitted to test the effect of planted area and tree-stand type on regeneration. The environmental space occupied by regenerating alien conifers was evaluated using principal component analysis. Out of 31 planted alien species, 15 (48%) were identified in natural regeneration, of which eight (26%) exhibited important regeneration density and dispersal distances. The most invasive species were Tsuga heterophylla and Abies grandis, confirming earlier field observations. Both large planted areas and areas planted with alien conifer species increased the density of regeneration. Species that had the highest regeneration density tolerated a wide range of environmental conditions, including shaded understory, which could lead to the invasion of mature, undisturbed forests. This study showed that 17% of the studied alien conifers are potentially invasive because they show important regeneration, long-distance dispersal, and, of importance, have already produced offspring that have matured and are capable of creating new satellite populations. In conclusion, our results provide a guideline for future planting operations, recommending extreme caution when planting these species in the temperate forests of Western Europe. ---- Identifier les espèces invasives émergentes est prioritaire afin de pouvoir mettre des actions de contrôle en place. En termes de nombre d'espèces d'arbres invasifs, la sylviculture est la deuxième voie d'introduction la plus importante, et une dette d'invasion existe probablement pour les conifères en Europe. Au début des années 1900, un réseau d'arboreta forestier fut établi en Belgique afin d'étudier le potentiel de production de diverses espèces résineuses et feuillues. Dans cette étude, nous avons utilisé huit arboreta pour identifier les espèces de conifères exotiques présentant un caractère invasif. A travers un échantillonnage systématique, nous avons quantifié la régénération naturelle de conifères exotiques et mesuré des données environnementales locales. Pour chaque espèce, la densité de régénération, les distances de dispersion et la structure d'âge furent analysées. Des modèles généralisés à effets mixtes furent utilisés pour tester l'effet de la surface de plantation et du type de peuplement sur la densité de régénération. L'espace environnemental de chaque espèce fut également délimité à l'aide d'une PCA. Sur les 31 espèces de conifères fréquement plantées, 15 (48 %) ont été identifiées dans la régénération naturelle, et huit (26 %) se régénèrent et se dispersent abondamment. Les espèces les plus invasives sont Tsuga heterophylla et Abies grandis, confirmant des observations de terrain, suivis de Thuja plicata et Pseudotsuga menziesii. De larges plantations et des peuplements résineux augmentent tout deux la densité de régénération de conifères exotiques. Les espèces se régénérant le plus tolèrent des conditions environnementales assez larges, dont un sous-étage ombragé, ce qui pourrait permettre l'invasion de forêts matures. Cette étude montre que 17 % des conifères étudiés sont potentiellement invasifs car ils se régénèrent abondamment, se dispersent à longue distance et produisent des descendants matures, capables de créer des populations satellites. En conclusion, notre étude fournit des recommandations pour de futures plantations, et nous appelons à la prudence concernant la plantation de ces espèces. [less ▲]

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See detailTropical tree allometry and crown allocation, and their relationship with species traits in central Africa
Mankou, G. S.; Ligot, Gauthier ULiege; Loubota Panzou, G. J. et al

in Forest Ecology and Management (2021), 493(119262),

Common allometric patterns have been reported across the tropics and good performance on independent data was retrieved for the most recent pantropical model predicting tree aboveground biomass (AGB) from ... [more ▼]

Common allometric patterns have been reported across the tropics and good performance on independent data was retrieved for the most recent pantropical model predicting tree aboveground biomass (AGB) from stem diameter, wood density and total height. General models are undoubtedly useful for the estimation and monitoring of biomass and carbon stocks in tropical forests, however specific allometry, allocation, and traits, are at the core of many models of vegetation dynamics, and there is lack of such information for some regions and species. In this study, we specifically evaluated how size-dependent changes in above-ground biomass and biomass allocation to crown relate to other allometric and life-history traits for tropical tree species. We gathered destructive data available in eight terra firme forest sites across central Africa and the combined dataset consisted of 1,023 trees belonging to 54 tropical tree species phylogenetically dispersed, with only two congeneric species. A huge body of field and laboratory measurements was used for computing AGB and crown mass ratio (CMR) at the tree level, and to derive key allometric traits at the species level. For the latter, species-specific relationships between tree diameter and total height, crown exposure to light, wood density, and bark thickness were fitted for 50 species. Our results show interspecific variation in the relationships relating tree diameter to both AGB and CMR, and including species traits in a multi-specific AGB model confirmed that interspecific variation in biomass allometry is primarily determined by species wood density. We also showed that the allocation of biomass to crown increases linearly with tree diameter for most species, and that interspecific variation in the CMR model is associated with the species dispersal mode and maximum height. Trait covariations among our set of tropical tree species widespread and/or locally abundant in central Africa, revealed a continuum between large-statured species, which tended to be light-demanding, deciduous and wind-dispersed, and species with opposite attributes. Information on allometry, allocation, and traits provided here could further be used in comparative ecology and for parameterizing dynamic and succession models. Also importantly, the species-specific AGB models fitted for major tree species, including most timber species of central Africa, will help improve biomass estimates. [less ▲]

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See detailPantropical variability in tree crown allometry
Loubota Panzou, G. J.; Fayolle, Adeline ULiege; Jucker, T. et al

in Global Ecology and Biogeography (2020)

Aim: Tree crowns determine light interception, carbon and water exchange. Thus, understanding the factors causing tree crown allometry to vary at the tree and stand level matters greatly for the ... [more ▼]

Aim: Tree crowns determine light interception, carbon and water exchange. Thus, understanding the factors causing tree crown allometry to vary at the tree and stand level matters greatly for the development of future vegetation modelling and for the calibration of remote sensing products. Nevertheless, we know little about large-scale variation and determinants in tropical tree crown allometry. In this study, we explored the continental variation in scaling exponents of site-specific crown allometry and assessed their relationships with environmental and stand-level variables in the tropics. Location: Global tropics Major taxa studied: Woody plants. Main conclusions: Our results provide new insight into geographical variability, with large continental differences in tropical tree crown allometry that were driven by stand-level and environmental variables. They have implications for the assessment of ecosystem function and for the monitoring of woody biomass by remote sensing techniques in the global tropics. Methods: Using a dataset of 87,737 trees distributed among 245 forest and savanna sites across the tropics, we fitted site-specific allometric relationships between crown dimensions (crown depth, diameter and volume) and stem diameter using power-law models. Stand-level and environmental drivers of crown allometric relationships were assessed at pantropical and continental scales. Results: The scaling exponents of allometric relationships between stem diameter and crown dimensions were higher in savannas than in forests. We identified that continental crown models were better than pantropical crown models and that continental differences in crown allometric relationships were driven by both stand-level (wood density) and environmental (precipitation, cation exchange capacity and soil texture) variables for both tropical biomes. For a given diameter, forest trees from Asia and savanna trees from Australia had smaller crown dimensions than trees in Africa and America, with crown volumes for some Asian forest trees being smaller than those of trees in African forests. Main conclusions: Our results provide new insight into geographical variability, with large continental differences in tropical tree crown allometry that were driven by stand-level and environmental variables. They have implications for the assessment of ecosystem function and for the monitoring of woody biomass by remote sensing techniques in the global tropics. [less ▲]

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See detailWildlife trail or systematic? Camera trap placement has little effect on estimates of mammal diversity in a tropical forest in Gabon
Fonteyn, Davy ULiege; Vermeulen, Cédric ULiege; Deflandre, Nicolas et al

in Remote Sensing in Ecology and Conservation (2020)

Camera traps (CTs) have been increasingly used for wildlife monitoring worldwide. In the tropics, most CT inventories target wildlife‐friendly sites, and CTs are commonly placed towards wildlife trails ... [more ▼]

Camera traps (CTs) have been increasingly used for wildlife monitoring worldwide. In the tropics, most CT inventories target wildlife‐friendly sites, and CTs are commonly placed towards wildlife trails. However, it has been argued that this placement strategy potentially provides biased results in comparison to more systematic or randomized approaches. Here, we investigated the impact of CT placement on the remotely sensed mammal diversity in a tropical forest in Gabon by comparing pairs of systematically placed and wildlife‐trail‐oriented CTs. Our survey protocol consisted of 15–17 sampling points arranged on a 2 km2 grid and left for one month in the field. This protocol was replicated sequentially in four areas. Each sampling point comprised a CT pair: the ‘systematic CT’, installed at the theoretical point and systematically oriented towards the most uncluttered view; and the ‘trail CT’, placed within a 20‐m radius and facing a wildlife trail. For the vast majority of species, the detection probabilities were comparable between placements. Species average capture rates were slightly higher for trail‐based CTs, though this trend was not significant for any species. Therefore, the species richness and composition of the overall community, such as the spatial distribution patterns (from evenly spread to site‐restricted) of individual species, were similarly depicted by both placements. Opting for a systematic orientation ensures that pathways used preferentially by some species—and avoided by others—will be sampled proportionally to their density in the forest undergrowth. However, trail‐based placement is routinely used, already producing standardised data within large‐scale monitoring programmes. Here, both placements provided a comparable picture of the mammal community, though it might not be necessarily true in depauperate areas. Both types of CT data can nevertheless be combined in multi‐site analyses, since methods now allow accounting for differences in study design and detection bias in original CT data. [less ▲]

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See detailDaily Activity Patterns and Co-Occurrence of Duikers Revealed by an Intensive Camera Trap Survey across Central African Rainforests
Houngbegnon, Fructueux ULiege; Cornelis, Daniel; Vermeulen, Cédric ULiege et al

in Animals (2020)

The duiker community in Central African rainforests includes a diversity of species that can coexist in the same area. The study of their activity patterns is needed to better understand habitat use or ... [more ▼]

The duiker community in Central African rainforests includes a diversity of species that can coexist in the same area. The study of their activity patterns is needed to better understand habitat use or association between the species. Using camera traps, we studied the temporal activity patterns, and quantified for the first time the temporal overlap and spatial co-occurrence between species. Our results show that: (i) Two species are strongly diurnal: Cephalophus leucogaster and Philantomba congica, (ii) two species are mostly diurnal: C. callipygus and C. nigrifrons, (iii) one species is strongly nocturnal: C. castaneus, (iv) and one species is mostly nocturnal: C. silvicultor. Analyses of temporal activities (for five species) identified four species pairs that highly overlapped (Δ ≥ 0.80), and six pairs that weakly overlapped (Δ between 0.06 and 0.35). Finally, co-occurrence tests reveal a truly random co-occurrence (plt > 0.05 and pgt > 0.05) for six species pairs, and a positive co-occurrence (pgt < 0.05) for four pairs. Positive co-occurrences are particularly noted for pairs formed by C. callipygus with the other species (except C. nigrifrons). These results are essential for a better understanding of the coexistence of duikers and the ecology of poorly known species (C. leucogaster and C. nigrifrons), and provide clarification on the activity patterns of C. silvicultor which was subject to controversy. Camera traps proved then to be a powerful tool for studying the activity patterns of free-ranging duiker populations. [less ▲]

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See detailFloristic evidence for alternative biome states in tropical Africa
Aleman, J. C.; Fayolle, Adeline ULiege; Favier, C. et al

in Proceedings of the National Academy of Sciences of the United States of America (2020), 117(45), 28183-28190

The idea that tropical forest and savanna are alternative states is crucial to how we manage these biomes and predict their future under global change. Large-scale empirical evidence for alternative ... [more ▼]

The idea that tropical forest and savanna are alternative states is crucial to how we manage these biomes and predict their future under global change. Large-scale empirical evidence for alternative stable states is limited, however, and comes mostly from the multimodal distribution of structural aspects of vegetation. These approaches have been criticized, as structure alone cannot separate out wetter savannas from drier forests for example, and there are also technical challenges to mapping vegetation structure in unbiased ways. Here, we develop an alternative approach to delimit the climatic envelope of the two biomes in Africa using tree species lists gathered for a large number of forest and savanna sites distributed across the continent. Our analyses confirm extensive climatic overlap of forest and savanna, supporting the alternative stable states hypothesis for Africa, and this result is corroborated by paleoecological evidence. Further, we find the two biomes to have highly divergent tree species compositions and to represent alternative compositional states. This allowed us to classify tree species as forest vs. savanna specialists, with some generalist species that span both biomes. In conjunction with georeferenced herbarium records, we mapped the forest and savanna distributions across Africa and quantified their environmental limits, which are primarily related to precipitation and seasonality, with a secondary contribution of fire. These results are important for the ongoing efforts to restore African ecosystems, which depend on accurate biome maps to set appropriate targets for the restored states but also provide empirical evidence for broad-scale bistability. [less ▲]

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See detailLong-Term Vegetation Change in Central Africa: The Need for an Integrated Management Framework for Forests and Savannas
Aleman, Julie ULiege; Fayolle, Adeline ULiege

in Gasparatos, A.; Abubakari, A.; Naidoo, M. (Eds.) et al Sustainability Challenges in Sub-Saharan Africa I (2020)

Tropical forests and savannas are the main biomes in sub-Saharan Africa, covering most of the continent. Collectively they offer important habitat for biodiversity and provide multiple ecosystem services ... [more ▼]

Tropical forests and savannas are the main biomes in sub-Saharan Africa, covering most of the continent. Collectively they offer important habitat for biodiversity and provide multiple ecosystem services. Considering their global importance and the multiple sustainability challenges they face in the era of the Anthropocene, this chapter undertakes a comprehensive analysis of the past, present, and future vegetation patterns in central African forests and savannas. Past changes in climate, vegetation, land use, and human activity have affected the distribution of forests and savannas across central Africa. Currently, forests form a continuous block across the wet and moist areas of central Africa, and are characterized by high tree cover (>90% tree cover). Savannas and woodlands have lower tree cover (<40% tree cover), are found in drier sites in the north and south of the region, and are maintained by frequent fires. Recent tree cover loss (2000–2015) has been more important for forests than for savannas, which, however, reportedly experienced woody encroachment. Future cropland expansion is expected to have a strong impact on savannas, while the extent of climatic impacts depends on the actual scenario. We finally identify some of the policy implications for restoring ecosystems, expanding protected areas, and designing sustainable ecosystem management approaches in the region. [less ▲]

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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 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 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 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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