References of "Doucet, Jean-Louis"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailTaking the pulse of Earth’s tropical forests using networks of highly distributed plots
ForestPlots.net; Blundo, Cecilia; Carilla, Julieta et al

in Biological Conservation (in press)

Tropical forests are the most diverse and productive ecosystems on Earth. While better understanding of these forests is critical for our collective future, until quite recently efforts to measure and ... [more ▼]

Tropical forests are the most diverse and productive ecosystems on Earth. While better understanding of these forests is critical for our collective future, until quite recently efforts to measure and monitor them have been largely disconnected. Networking is essential to discover the answers to questions that transcend borders and the horizons of funding agencies. Here we show how a global community is responding to the challenges of tropical ecosystem research with diverse teams measuring forests tree-by-tree in thousands of long-term plots. We review the major scientific discoveries of this work and show how this process is changing tropical forest science. Our core approach involves linking long-term grassroots initiatives with standardized protocols and data management to generate robust scaled-up results. By connecting tropical researchers and elevating their status, our Social Research Network model recognises the key role of the data originator in scientific discovery. Conceived in 1999 with RAINFOR (South America), our permanent plot networks have been adapted to Africa (AfriTRON) and Southeast Asia (T-FORCES) and widely emulated worldwide. Now these multiple initiatives are integrated via ForestPlots.net cyber-infrastructure, linking colleagues from 54 countries across 24 plot networks. Collectively these are transforming understanding of tropical forests and their biospheric role. Together we have discovered how, where and why forest carbon and biodiversity are responding to climate change, and how they feedback on it. This long-term pan-tropical collaboration has revealed a large long-term carbon sink and its trends, as well as making clear which drivers are most important, which forest processes are affected, where they are changing, what the lags are, and the likely future responses of tropical forests as the climate continues to change. By leveraging a remarkably old technology, plot networks are sparking a very modern revolution in tropical forest science. In the future, humanity can benefit greatly by nurturing the grassroots communities now collectively capable of generating unique, long-term understanding of Earth’s most precious forests. [less ▲]

Detailed reference viewed: 35 (7 ULiège)
Full Text
Peer Reviewed
See detailResistance of African tropical forests to an extreme climate anomaly
Bennett, Amy C.; Dargie, Greta C.; Cuni-Sanchez, Aida et al

in Proceedings of the National Academy of Sciences of the United States of America (2021), 118(21), 12

The responses of tropical forests to environmental change are critical uncertainties in predicting the future impacts of climate change. The positive phase of the 2015–2016 El Niño Southern Oscillation ... [more ▼]

The responses of tropical forests to environmental change are critical uncertainties in predicting the future impacts of climate change. The positive phase of the 2015–2016 El Niño Southern Oscillation resulted in unprecedented heat and low precipitation in the tropics with substantial impacts on the global carbon cycle. The role of African tropical forests is uncertain as their responses to short-term drought and temperature anomalies have yet to be determined using on-the-ground measurements. African tropical forests may be particularly sensitive because they exist in relatively dry conditions compared with Amazonian or Asian forests, or they may be more resistant because of an abundance of drought-adapted species. Here, we report responses of structurally intact old-growth lowland tropical forests inventoried within the African Tropical Rainforest Observatory Network (AfriTRON). We use 100 long-term inventory plots from six countries each measured at least twice prior to and once following the 2015–2016 El Niño event. These plots experienced the highest temperatures and driest conditions on record. The record temperature did not significantly reduce carbon gains from tree growth or significantly increase carbon losses from tree mortality, but the record drought did significantly decrease net carbon uptake. Overall, the long-term biomass increase of these forests was reduced due to the El Niño event, but these plots remained a live biomass carbon sink (0.51 ± 0.40 Mg C ha−1 y−1) despite extreme environmental conditions. Our analyses, while limited to African tropical forests, suggest they may be more resistant to climatic extremes than Amazonian and Asian forests. [less ▲]

Detailed reference viewed: 46 (9 ULiège)
Full Text
See detailGuide pratique des plantations d’arbres des forêts denses humides d’Afrique
Daïnou, Kasso ULiege; Tosso, Dji-ndé Félicien ULiege; Bracke, Charles et al

Book published by Les presses agronomiques de Gembloux (2021)

Detailed reference viewed: 891 (35 ULiège)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 45 (9 ULiège)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 25 (2 ULiège)
Full Text
See detailElaboration et mise en oeuvre d'un plan de gestion de la faune. Guide Technique à destination des gestionnaires des forêts de production d'Afrique centrale
Haurez, Barbara ULiege; Fonteyn, Davy ULiege; Toint, Sarah et al

Book published by Presses Agronomiques de Gembloux (2020)

L’intensification des activités humaines, la demande croissante en protéines animales suite à l’explosion démographique et le braconnage organisé (ivoire, écailles de pangolins,...) entrainent une ... [more ▼]

L’intensification des activités humaines, la demande croissante en protéines animales suite à l’explosion démographique et le braconnage organisé (ivoire, écailles de pangolins,...) entrainent une pression croissante sur la faune sauvage des forêts d’Afrique centrale. Pour répondre à ces menaces, des stratégies sont mises en place aux échelles nationales et régionales. Une gestion efficace de la faune sauvage au sein des concessions certifiées concourt à l’objectif global d’une gestion raisonnée et durable du patrimoine forestier d’Afrique centrale. Le présent guide constitue un outil opérationnel à destination des exploitants forestiers d’Afrique centrale. Il présente de manière pragmatique et illustrée la démarche d’élaboration et de mise en oeuvre d’un plan de gestion de la faune, en partant des cadres législatifs et règlementaires à respecter jusqu’à l’évaluation de sa performance. Les principales mesures de gestion et de conservation de la faune à mettre en place sont décrites dans des fiches thématiques. Un canevas modèle de plan de gestion de la faune proposant une hiérarchisation dans la mise en oeuvre de ces différentes mesures est présenté. Cet ouvrage vise à améliorer les pratiques des exploitants forestiers en termes de gestion de la faune et à les accompagner dans une démarche de certification de légalité ou de durabilité. [less ▲]

Detailed reference viewed: 726 (40 ULiège)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 163 (27 ULiège)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 180 (51 ULiège)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 35 (7 ULiège)
Full Text
Peer Reviewed
See detailOld growth Afrotropical forests critical for maintaining forest carbon
Poulsen, J. R.; Medjibe, V. P.; White, L. J. T. et al

in Global Ecology and Biogeography (2020), 29

Aim: Large trees [≥ 70 cm diameter at breast height (DBH)] contribute disproportionately to aboveground carbon stock (AGC) across the tropics but may be vulnerable to changing climate and human activities ... [more ▼]

Aim: Large trees [≥ 70 cm diameter at breast height (DBH)] contribute disproportionately to aboveground carbon stock (AGC) across the tropics but may be vulnerable to changing climate and human activities. Here we determine the distribution, drivers and threats to large trees and high carbon forest. Location: Central Africa. Time period: Current. Major taxa studied: Trees. Methods: Using Gabon's new National Resource Inventory of 104 field sites, AGC was calculated from 67,466 trees from 578 species and 97 genera. Power and Michaelis–Menten models assessed the contribution of large trees to AGC. Environmental and anthropogenic drivers of AGC, large trees, and stand variables were modelled using Akaike’s information criterion (AIC) weights to calculate average regression coefficients for all p. ossible models. Results: Mean AGC for trees ≥ 10 cm DBH in Gabonese forestlands was 141.7 Mg C/ha, with averages of 166.6, 171.3 and 96.6 Mg C/ha in old growth, concession and secondary forest. High carbon forests occurred where large trees are most abundant: 31% of AGC was stored in large trees (2.3% of all stems). Human activities largely drove variation in AGC and large trees, but climate and edaphic conditions also determined stand variables (basal area, tree height, wood density, stem density). AGC and large trees increased with distance from human settlements; AGC was 40% lower in secondary than primary and concession forests and 33% higher in protected than non-managed areas. Main conclusions: AGC and large trees were negatively associated with human activities, highlighting the importance of forest management. Redefining large trees as ≥ 50 cm DBH (4.3% more stems) would account for 20% more AGC. This study demonstrates that protecting relatively undisturbed forests can be disproportionately effective in conserving carbon and suggests that including sustainable forestry in programs like reduced emissions for deforestation and forest degradation could maintain carbon dense forests in logging concessions that are a large proportion of remaining Central African forests. © 2020 John Wiley & Sons Ltd [less ▲]

Detailed reference viewed: 68 (13 ULiège)
Full Text
Peer Reviewed
See detailA map of African humid tropical forest aboveground biomass derived from management inventories
Ploton, Pierre; Mortier, Frédéric; Barbier, Nicolas et al

in Scientific Data (2020), 7(221),

Forest biomass is key in Earth carbon cycle and climate system, and thus under intense scrutiny in the context of international climate change mitigation initiatives (e.g. REDD+). In tropical forests, the ... [more ▼]

Forest biomass is key in Earth carbon cycle and climate system, and thus under intense scrutiny in the context of international climate change mitigation initiatives (e.g. REDD+). In tropical forests, the spatial distribution of aboveground biomass (AGB) remains, however, highly uncertain. There is increasing recognition that progress is strongly limited by the lack of field observations over large and remote areas. Here, we introduce the Congo basin Forests AGB (CoFor-AGB) dataset that contains AGB estimations and associated uncertainty for 59,857 1-km pixels aggregated from nearly 100,000 ha of in situ forest management inventories for the 2000 – early 2010s period in five central African countries. A comprehensive error propagation scheme suggests that the uncertainty on AGB estimations derived from c. 0.5-ha inventory plots (8.6–15.0%) is only moderately higher than the error obtained from scientific sampling plots (8.3%). CoFor-AGB provides the first large scale view of forest AGB spatial variation from field data in central Africa, the second largest continuous tropical forest domain of the world. [less ▲]

Detailed reference viewed: 56 (7 ULiège)
Full Text
Peer Reviewed
See detailPalabres autour des arbres : des discours sur leur intelligence aux dérives de l’anthropomorphisme
Doucet, Jean-Louis ULiege

in Biotechnologie, Agronomie, Société et Environnement (2020), 24(3), 203-206

The intelligence of trees is an issue that fascinates people in urban areas. It is the subject of passionate debate between forest sector stakeholders. This article aims to objectify this debate by ... [more ▼]

The intelligence of trees is an issue that fascinates people in urban areas. It is the subject of passionate debate between forest sector stakeholders. This article aims to objectify this debate by synthesizing recent knowledge on the subject. It shows that trees can communicate with each other, either via volatile molecules or via underground exchanges, in particular through a mycorrhizal network. Trees can also perceive light and sound. They can therefore adapt to a changing environment, which reflects a certain form of intelligence. Nevertheless, abandoning timber logging for this reason is not acceptable. This would result in environmental impacts that are often overlooked by the opponents of logging. [less ▲]

Detailed reference viewed: 128 (17 ULiège)
Full Text
Peer Reviewed
See detailThe global abundance of tree palms
Muscarella, Robert; Emilio, Thaise; Phillips, Oliver L. et al

in Global Ecology and Biogeography (2020), 00

Aim: Palms are an iconic, diverse and often abundant component of tropical ecosystems that provide many ecosystem services. Being monocots, tree palms are evolutionarily, morphologically and ... [more ▼]

Aim: Palms are an iconic, diverse and often abundant component of tropical ecosystems that provide many ecosystem services. Being monocots, tree palms are evolutionarily, morphologically and physiologically distinct from other trees, and these differences have important consequences for ecosystem services (e.g., carbon sequestration and storage) and in terms of responses to climate change. We quantified global patterns of tree palm relative abundance to help improve understanding of tropical forests and reduce uncertainty about these ecosystems under climate change. Location: Tropical and subtropical moist forests. Time period: Current. Major taxa studied: Palms (Arecaceae). Methods: We assembled a pantropical dataset of 2,548 forest plots (covering 1,191 ha) and quantified tree palm (i.e., ≥10 cm diameter at breast height) abundance relative to co-occurring non-palm trees. We compared the relative abundance of tree palms across biogeographical realms and tested for associations with palaeoclimate stability, current climate, edaphic conditions and metrics of forest structure. Results: On average, the relative abundance of tree palms was more than five times larger between Neotropical locations and other biogeographical realms. Tree palms were absent in most locations outside the Neotropics but present in >80% of Neotropical locations. The relative abundance of tree palms was more strongly associated with local conditions (e.g., higher mean annual precipitation, lower soil fertility, shallower water table and lower plot mean wood density) than metrics of long-term climate stability. Life-form diversity also influenced the patterns; palm assemblages outside the Neotropics comprise many non-tree (e.g., climbing) palms. Finally, we show that tree palms can influence estimates of above-ground biomass, but the magnitude and direction of the effect require additional work. Conclusions: Tree palms are not only quintessentially tropical, but they are also overwhelmingly Neotropical. Future work to understand the contributions of tree palms to biomass estimates and carbon cycling will be particularly crucial in Neotropical forests. [less ▲]

Detailed reference viewed: 135 (11 ULiège)
Full Text
See detailSentiers de suivi de la croissance, de la mortalité et de la phénologie des arbres tropicaux : Guide méthodologique
Tosso, Dji-ndé Félicien ULiege; Daïnou, Kasso ULiege; Sonké, Bonaventure et al

Book published by Presses Universitaires de Liège (2020)

La durabilité de l’aménagement des forêts naturelles d’Afrique centrale est tributaire d’une connaissance approfondie de la dynamique démographique des populations d’arbres commerciaux. Cette dynamique ... [more ▼]

La durabilité de l’aménagement des forêts naturelles d’Afrique centrale est tributaire d’une connaissance approfondie de la dynamique démographique des populations d’arbres commerciaux. Cette dynamique est étudiée dans des dispositifs destinés à être suivis sur le long terme, dénommés parcelles et sentiers. Si la démarche méthodologique d’installation et de suivi des parcelles est assez bien documentée, celle des sentiers l’est moins. Le présent ouvrage vient combler ce vide en capitalisant l’expérience accumulée depuis plus de 20 ans par les membres du collectif DYNAFAC, un collectif créé à l’initiative de l’ATIBT, du CIRAD, de Nature+ et de Gembloux Agro-Bio Tech. Il s’agit d’un guide pratique et illustré explicitant la démarche nécessaire à l’installation et au suivi de ces sentiers. Outre les procédures techniques, le guide évalue également les coûts en tenant compte des spécificités économiques de différents pays de la sous-région. En s’adressant à l’ensemble des parties prenantes de l’aménagement et de la gestion des forêts d’Afrique, l’ouvrage a pour ambition de promouvoir la mise en œuvre de dispositifs robustes et efficients à la portée de tous. [less ▲]

Detailed reference viewed: 799 (94 ULiège)
Full Text
Peer Reviewed
See detailMiocene Diversification in the Savannahs Precedes Tetraploid Rainforest Radiation in the African Tree Genus Afzelia (Detarioideae, Fabaceae)
Donkpegan, Armel S. L. ULiege; Doucet, Jean-Louis ULiege; Hardy, Olivier J. et al

in Frontiers in Plant Science (2020), 11(798),

The dating of diversification events, including transitions between biomes, is key to elucidate the processes that underlie the assembly and evolution of tropical biodiversity. Afzelia is a widespread ... [more ▼]

The dating of diversification events, including transitions between biomes, is key to elucidate the processes that underlie the assembly and evolution of tropical biodiversity. Afzelia is a widespread genus of tropical trees, threatened by exploitation for its valuable timber, that presents an interesting system to investigate diversification events in Africa. Africa hosts diploid Afzelia species in the savannahs north and south of the Guineo-Congolian rainforest and autotetraploid species confined to the rainforest. Species delimitation and phylogenetic relationships among the diploid and tetraploid species remained unresolved in previous studies using small amounts of DNA sequence data. We used genotyping-by-sequencing in the five widespread Afzelia species in Africa, the savannah species A. africana and A. quanzensis and the rainforest species A. bipindensis, A. pachyloba, and A. bella. Maximum likelihood and coalescent approaches resolved all species as monophyletic and placed the savannah and rainforest taxa into two separate clades corresponding to contrasted ploidy levels. Our data are thus compatible with a single biome shift in Afzelia in Africa, although we were unable to conclude on its direction. SNAPP calibrated species trees show that the savannah diploids started to diversify early, at 12 (9.09–14.89) Ma, which contrasts with a recent and rapid diversification of the rainforest tetraploid clade, starting at 4.22 (3.12 – 5.36) Ma. This finding of older diversification in a tropical savannah clade vs. its sister rainforest clade is exceptional; it stands in opposition to the predominant observation of young ages for savannahs lineages in tropical regions during the relatively recent expansion of the savannah biome. [less ▲]

Detailed reference viewed: 99 (10 ULiège)
Full Text
Peer Reviewed
See detailLong-term thermal sensitivity of Earth’s tropical forests
Sullivan, Martin J.P.; Lewis, Simon L.; Affum-Baffoe, Kofi et al

in Science (2020), 368

The sensitivity of tropical forest carbon to climate is a key uncertainty in predicting global climate change. Although short-term drying and warming are known to affect forests, it is unknown if such ... [more ▼]

The sensitivity of tropical forest carbon to climate is a key uncertainty in predicting global climate change. Although short-term drying and warming are known to affect forests, it is unknown if such effects translate into long-term responses. Here, we analyze 590 permanent plots measured across the tropics to derive the equilibrium climate controls on forest carbon. Maximum temperature is the most important predictor of aboveground biomass (−9.1 megagrams of carbon per hectare per degree Celsius), primarily by reducing woody productivity, and has a greater impact per °C in the hottest forests (>32.2°C). Our results nevertheless reveal greater thermal resilience than observations of short-term variation imply. To realize the long-term climate adaptation potential of tropical forests requires both protecting them and stabilizing Earth’s climate. [less ▲]

Detailed reference viewed: 61 (13 ULiège)
Full Text
Peer Reviewed
See detailAsynchronous carbon sink saturation in African and Amazonian tropical forests
Hubau, Wannes; Lewis, Simon L.; Phillips, Oliver L. et al

in Nature (2020), 579

Structurally intact tropical forests sequestered about half of the global terrestrial carbon uptake over the 1990s and early 2000s, removing about 15 per cent of anthropogenic carbon dioxide emissions1–3 ... [more ▼]

Structurally intact tropical forests sequestered about half of the global terrestrial carbon uptake over the 1990s and early 2000s, removing about 15 per cent of anthropogenic carbon dioxide emissions1–3. Climate-driven vegetation models typically predict that this tropical forest ‘carbon sink’ will continue for decades4,5. Here we assess trends in the carbon sink using 244 structurally intact African tropical forests spanning 11 countries, compare them with 321 published plots from Amazonia and investigate the underlying drivers of the trends. The carbon sink in live aboveground biomass in intact African tropical forests has been stable for the three decades to 2015, at 0.66 tonnes of carbon per hectare per year (95 per cent confidence interval 0.53–0.79), in contrast to the long-term decline in Amazonian forests6. Therefore the carbon sink responses of Earth’s two largest expanses of tropical forest have diverged. The difference is largely driven by carbon losses from tree mortality, with no detectable multi-decadal trend in Africa and a long-term increase in Amazonia. Both continents show increasing tree growth, consistent with the expected net effect of rising atmospheric carbon dioxide and air temperature7–9. Despite the past stability of the African carbon sink, our most intensively monitored plots suggest a post-2010 increase in carbon losses, delayed compared to Amazonia, indicating asynchronous carbon sink saturation on the two continents. A statistical model including carbon dioxide, temperature, drought and forest dynamics accounts for the observed trends and indicates a long-term future decline in the African sink, whereas the Amazonian sink continues to weaken rapidly. Overall, the uptake of carbon into Earth’s intact tropical forests peaked in the 1990s. Given that the global terrestrial carbon sink is increasing in size, independent observations indicating greater recent carbon uptake into the Northern Hemisphere landmass10 reinforce our conclusion that the intact tropical forest carbon sink has already peaked. This saturation and ongoing decline of the tropical forest carbon sink has consequences for policies intended to stabilize Earth’s climate. [less ▲]

Detailed reference viewed: 75 (15 ULiège)
Full Text
Peer Reviewed
See detailPast human disturbances and soil fertility both influence the distribution of light-demanding tree species in a Central African tropical forest
Vleminckx, Jason; Bauman, David; Demanet, Marine et al

in Journal of Vegetation Science (2020), 31

Questions: In vast areas of Central African forests, the upper canopy is presently dominated by light-demanding tree species. Here, we confront three hypotheses to explain this dominance: (a) these ... [more ▼]

Questions: In vast areas of Central African forests, the upper canopy is presently dominated by light-demanding tree species. Here, we confront three hypotheses to explain this dominance: (a) these species have expanded their distribution because of widespread past slash-and-burn activities, as suggested by important charcoal amounts recorded in the soils of the region; (b) their abundance is rather explained by soil properties, as this guild establishes preferentially on favourable physico-chemical conditions for rapid growth; (c) soil properties have been substantially influenced by past human disturbances and those two effects cannot be disentangled. Location: Pallisco-CIFM logging concession, southeastern Cameroon (300,000 ha). Methods: We quantified soil charcoal abundance and measured ten soil variables at the basis of 60 target trees that belonged to a list of three long-living pioneer lightdemanding (LLP) and four shade-bearer (SB) species. We identified all stems with a diameter at breast height (DBH) ≥ 20 cm within a distance of 15 m around each target tree. Species were characterised by their wood-specific gravity (WSG), which reflected their light requirement. Multiple regression models were used to quantify and test the relative effects of charcoal abundance and soil variables on the mean WSG of the 60 tree communities, as well as the abundance of three guilds: LLP, SB, and non-pioneer light demanders (NPLD). Results: The mean WSG was the only response variable significantly explained by soil variables and charcoal abundance combined. It was significantly negatively associated with soil calcium and Mg content and with charcoal abundance, with soil and charcoal influencing the mean WSG independently. Conclusion: Our study provides evidence that past human disturbances and soil fertility have independently promoted the establishment of light-demanding species in western Central African forests, thereby shedding light on tree community assembly rules in these ecosystems which remain considerably understudied compared to the tropical forests of other continents. [less ▲]

Detailed reference viewed: 38 (7 ULiège)
Full Text
Peer Reviewed
See detailPopulation genomics of the widespread African savannah trees Afzelia africana and Afzelia quanzensis reveals no significant past fragmentation of their distribution ranges
Donkpegan, Armel S. L. ULiege; Piñeiro, Rosalía; Heuertz, Myriam et al

in American Journal of Botany (2020), 107(3), 498-509

PREMISE: Few studies have addressed the evolutionary history of tree species from African savannahs. Afzelia contains economically important timber species, including two species widely distributed in ... [more ▼]

PREMISE: Few studies have addressed the evolutionary history of tree species from African savannahs. Afzelia contains economically important timber species, including two species widely distributed in African savannahs: A. africana in the Sudanian region and A. quanzensis in the Zambezian region. We aimed to infer whether these species underwent range fragmentation and/or demographic changes, possibly reflecting how savannahs responded to Quaternary climate changes. METHODS: We characterized the genetic diversity and structure of these species across their distribution ranges using nuclear microsatellites (SSRs) and genotyping-by-sequencing (GBS) markers. Six SSR loci were genotyped in 241 A. africana and 113 A. quanzensis individuals, while 2800 high-quality single nucleotide polymorphisms (SNPs) were identified in 30 A. africana individuals. RESULTS: Both species appeared to be mainly outcrossing. The kinship between individuals decayed with the logarithm of the distance at similar rates across species and markers, leading to relatively small Sp statistics (0.0056 for SSR and 0.0054 for SNP in A. africana, 0.0075 for SSR in A. quanzensis). The patterns were consistent with isolation by distance expectations in the absence of large-scale geographic gradients. Bayesian clustering of SSR genotypes did not detect genetic clusters within species. In contrast, SNP data resolved intraspecific genetic clusters in A. africana, illustrating the higher resolving power of GBS. However, these clusters revealed low levels of differentiation and no clear geographical entities, so that they were interpreted as resulting from the isolation by distance pattern rather than from past population fragmentation. CONCLUSIONS: These results suggest that populations have remained connected throughout the large, continuous savannah landscapes. The absence of clear phylogeographic discontinuities, also found in a few other African savannah trees, indicates that their distribution ranges have not been significantly fragmented during the climatic oscillations of the Pleistocene, in contrast to patterns commonly found in African rainforest trees. [less ▲]

Detailed reference viewed: 38 (3 ULiège)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 263 (64 ULiège)