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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 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 detailGrowth determinants of timber species Triplochiton scleroxylon and implications for forest management in central Africa
Ligot, Gauthier ULiege; Fayolle, Adeline ULiege; Gourlet-Fleury, Sylvie et al

in Forest Ecology and Management (2019), 437

The sustainability of the polycyclic logging system in tropical forests has been increasingly questioned for a variety of reasons, and particularly in central Africa as commercial species, mostly light ... [more ▼]

The sustainability of the polycyclic logging system in tropical forests has been increasingly questioned for a variety of reasons, and particularly in central Africa as commercial species, mostly light-demanding long-lived pioneer species, usually fail to recover a stable number of large trees after exploitation. Several factors are known to affect tropical tree demographic processes, like tree growth, survival and recruitment. Tree growth has particularly been showed to depend on ecological conditions, tree genetics, and competition with surrounding vegetation, as well as tree size or ontogeny. Yet, due to the paucity of available data, the importance of such factors is unclear and usually ignored when estimating future timber yields. To fill this gap, we chose to evaluate the variability in growth of one African long-lived pioneer and commercially very important species: Triplochiton scleroxylon K. Schum, gathering a broad dataset composed of tree ring data recorded in one site in Cameroon and periodic field inventory data recorded in seven sites across central Africa. In total, we analyzed 13,225 records of annual tree diameter increments recorded over 920 trees from seven sites in Cameroon, Republic of the Congo and Central African Republic. We evaluated (i) to what extent the average growth of trees that reach harvestable dimensions differs from population average and (ii) to what extent past perturbations influence the growth of remaining trees. We found the diameter growth of T. scleroxylon to be remarkably variable and this study provided an unprecedented quantification of the magnitude of some key growth determinants. In unlogged forests, the diameter increment of T. scleroxylon ranged between 0.40 cm year-1 in Southern Cameroon and 0.83 cm year-1 in South-Eastern Cameroon. The diameter increment was weakly related to tree size but increased twofold from unlogged to logged forests. Perturbation caused by logging stimulates growth of T. scleroxylon for at least 10-15 years. Finally, harvestable timber stock of large-sized T. scleroxylon was found to be constituted by trees that grew in average twice faster than trees of the entire extant population. As more and more inventory data become available, quantifying these effects could be replicated for other timber species and in other sites, to improve the accuracy of future timber resource estimates and improve forest management guidelines. [less ▲]

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See detailRéviser les tarifs de cubage pour prendre en compte l'évolution de la ressource au Cameroun
Ligot, Gauthier ULiege; Dubart, Nicolas; Tchowo Hapi, Mauriad et al

in Bois et Forêts des Tropiques (2018), 338

La connaissance du volume exploitable est une information essentielle tant pour la gestion que pour le contrôle de l’exploitation forestière. En Afrique centrale, l’estimation des volumes repose ... [more ▼]

La connaissance du volume exploitable est une information essentielle tant pour la gestion que pour le contrôle de l’exploitation forestière. En Afrique centrale, l’estimation des volumes repose essentiellement sur l’utilisation de tarifs de cubage à une entrée, spécifique à chaque essence, et prédisant le volume exploitable à partir du diamètre de l’arbre. Or, récemment, de nombreux acteurs de la gestion forestière au Cameroun reportent une inadéquation entre les volumes commerciaux estimés avec les tarifs de cubage imposés par l’administration et les volumes estimés à partir des mesures de la longueur et du diamètre des billes exploitées. Afin de vérifier la justesse des tarifs de cubage imposés par l’administration camerounaise, nous avons réalisé un échantillonnage destructif pour 12 essences jouant un rôle crucial dans le commerce du bois au Cameroun, et développé de nouveaux tarifs de cubage, qui ont été comparés avec les tarifs imposés par l’administration camerounaise et 52 autres tarifs de cubage disponibles dans la littérature. Dans quatre concessions forestières du Cameroun, représentatives des différentes conditions écologiques prévalant dans ce pays, 732 arbres ont été abattus et leur volume a été mesuré par la méthode des billons successifs. Des tarifs de cubage à une entrée, fonction uniquement du diamètre de référence, ont ensuite été ajustés par la méthode des moindres carrés généralisés. Notre étude confirme l’existence de biais entre les volumes mesurés et les volumes estimés en utilisant les tarifs de cubage imposés par l’administration camerounaise. En conséquence, de nouveaux tarifs de cubage et un abaque de correction sont proposés. Enfin, la majorité des tarifs de cubages testés présentaient un biais similaire qui résulte vraisemblablement d’une évolution de la ressource et des pratiques d’exploitation. [less ▲]

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See detailAssessment of mammal biodiversity and bushmeat offtake in the tropical forests of southeastern Cameroon
Lhoest, Simon ULiege; Fonteyn, Davy ULiege; Hette, Samuel et al

Poster (2018, November 27)

Tropical forests of central Africa host an important part of the world’s terrestrial biodiversity and provide numerous provisioning, regulating, and cultural ecosystem services to human populations. Major ... [more ▼]

Tropical forests of central Africa host an important part of the world’s terrestrial biodiversity and provide numerous provisioning, regulating, and cultural ecosystem services to human populations. Major threats hang over those diverse ecosystems, namely land use changes and consumption of bushmeat. Our study aimed to assess mammal diversity and bushmeat consumption in three contrasted and largely represented forest land allocation types in southeastern Cameroon: (i) a protected area, (ii) a FSC-certified logging concession, and (iii) three community forests. Mammal inventories were conducted with 44 camera traps installed for 3 months. Bushmeat consumption was quantified using both tracking of volunteer hunters over 651 kilometers and the daily monitoring of the food bowl of 55 households for 3 months. Though a great part of the mammal diversity is retained inside the logging concession, the protected area holds the richest and most abundant mammal communities, whereas community forests were found to be defaunated and structurally disturbed. The size of the hunting territories is influenced by many factors such as human population density or the presence of alternative protein sources. Although poaching controls in the protected area and, to a lesser extent, in the certified logging concession appear to play a deterrent role, evidence of hunting activities were found in all land allocation types. Bushmeat represents on average 56% of the animal protein consumed by households, the remaining part being mainly fish. Our results demonstrated the ability of the certified logging concession and the protected area in the conservation of wildlife species and the provision of bushmeat for local populations. It remains essential to maintain and develop anti-poaching patrols in those areas, strategically based on geographic data of hunting pressure. Current levels of hunting activities also confirm the need for the development of alternatives to bushmeat. [less ▲]

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See detailSimulating last glacial and postglacial distributions of African tropical trees with a dynamic vegetation model.
Dury, Marie ULiege; Henrot, Alexandra-Jane ULiege; Lézine, Anne-Marie et al

Conference (2018, August 16)

Climate change and human pressure threaten species richness of African tropical forests. Understanding how the past climate changes have shaped the current distribution and composition of African ... [more ▼]

Climate change and human pressure threaten species richness of African tropical forests. Understanding how the past climate changes have shaped the current distribution and composition of African rainforests can certainly help to the ecosystem conservation in the future. This topic is addressed in the framework of the multi-disciplinary AFRIFORD project (Genetic and palaeoecological signatures of African rainforest dynamics: pre-adapted to change?, http://www.ulb.ac.be/facs/sciences/afriford/). In parallel to genetic and palynological analyses, the CARAIB dynamic vegetation model is applied at the level of African tropical plant species to simulate change in their distributions from the Last Glacial Maximum (21,000 years BP) to the present in sub-Saharan Africa. We prepared a set of about a hundred species, mostly composed of tropical tree species (evergreen/deciduous, cool/warm taxa) for which we compiled observed occurrence data (e.g.., RAINBIO database), determined climatic requirements and gathered some specific traits (e.g., TRY database). From LGM to present time, the vegetation model is forced with the 1-kyr snapshot outputs of the HadCM3 climate model. Statistically downscaled at a spatial resolution of 0.5°, we only kept modelled past anomalies that we added to the GSWP3 (20 CR) climate data chosen as the reference for the historical period. Sub-Saharan simulations are performed with CARAIB forced by these climatic projections to simulate the net primary productivity of the species over time and space. We analyse the modelled changes in tropical forest composition and extension as well as in the distribution of individual species whose glacial refugia and postglacial dynamics remain poorly known. [less ▲]

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See detailWhat controls local-scale aboveground biomass variation in central Africa? Testing structural, composition and architectural attributes
Loubota Panzou, Grâce Jopaul ULiege; Fayolle, Adeline ULiege; Feldpausch, Ted R. et al

in Forest Ecology and Management (2018), 429

Tropical forests play a key role in regulating the terrestrial carbon cycle and climate change by storing a large amount of carbon. Yet, there is considerable uncertainty about the amount and spatial ... [more ▼]

Tropical forests play a key role in regulating the terrestrial carbon cycle and climate change by storing a large amount of carbon. Yet, there is considerable uncertainty about the amount and spatial variation of aboveground biomass (AGB), especially in the relatively less studied African tropical forests. In this study, we explore the local-scale variation and determinants of plot-level AGB, between and within two types of forests, the Celtis and Manilkara forests, growing under the same climate but on different geological substrates in the northern Republic of Congo. In each forest site, all trees ≥10 cm diameter were censured in 36 × 1-ha plots and we measured tree height and crown size using a subsample of 18 × 1-ha of these plots. We developed height-diameter and crown-diameter allometric relationships and tested whether they differed between the two sites. For each 1-ha plot, we further estimated the AGB and calculated structural attributes (stem density and basal area), composition attributes (wood density) and architectural attributes (tree height and crown size), the latter being derived from site-specific allometric relationships. We found strong between-site differences in height-diameter and crown-diameter allometries. For a given diameter, trees were taller in the Celtis forest while they had larger crown in the Manilkara forest. Similar trends were found for the sixteen species present in both forest sites, suggesting an environmental control of tree allometry. Although there were some between-site differences in forest structure, composition and architecture, we did not detect any significant difference in mean AGB between the Celtis and the Manilkara forests. The AGB variation was related to the heterogeneous distribution of large trees, and influenced by basal area, height and crown dimensions, and to a lesser extent wood density. These forest attributes have strong practical implications on emerging remote-sensing technologies for carbon monitoring in tropical forests. [less ▲]

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See detailThe importance of stand structure and tree allometry for local-scale variation in aboveground biomass
Loubota Panzou, Grâce Jopaul ULiege; Feldpausch, Ted; Ligot, Gauthier ULiege et al

Poster (2018, March 26)

Aboveground biomass (AGB) plays a critical role in determining the long-term dynamics of carbon in tropical forests. Consequently, understanding what factors are important in controlling AGB in tropical ... [more ▼]

Aboveground biomass (AGB) plays a critical role in determining the long-term dynamics of carbon in tropical forests. Consequently, understanding what factors are important in controlling AGB in tropical forests has major implications for projecting the terrestrial carbon stocks, in the context of an increasingly uncertain future. In this study, we aimed to explore the local-scale AGB variation in two forest sites in northern Congo, representative of two contrasted forest types under the same climate but growing on vastly different soils and parent material (quartzite substrate for CIB and sandstone substrate for Mokabi). Tree diameter was measured in 36 permanent forest plots of 1-ha in each site, and tree allometry (total tree height, height of the first branch and crown dimensions) was measured on a subsample of 18 plots of 1-ha in each site. Allometric data were available for a total of 2202 trees (1040 for CIB and 1162 for Mokabi) covering a large range of diameters (10 – 200 cm). We first developed site-specific allometric models that were then used to estimate AGB at plot level. We then explore the determinants of AGB variation at plot level using multiple regressions and mixed linear models. For a given diameter, trees tended to be taller and to have deeper crown in the Celtis forest of the CIB (rich soil) while they tended to have larger crown in the Manilkara forest of the Mokabi (sandy soil). Similar trends were reported within species for the sixteen species shared by both forest types, suggesting an environmental control of tree allometry. We found that AGB strongly varied between the two forest sites, with greater AGB per hectare in the Celtis forest of the CIB. Within sites AGB variation was positively related to basal area, though between-site allometric attributes (total height and crown radius) were important determinants of AGB variation. These results have strong implications for forest biomass and carbon monitoring. [less ▲]

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See detailHow do tropical trees cope with drought: the case of Erythrophleum species
Gorel, Anaïs ULiege; Fayolle, Adeline ULiege

Poster (2018)

Understanding the mechanisms used by tropical tree species to cope with drought will be central in predicting forest responses to climate change. The study of plant traits, as wood anatomy and hydraulics ... [more ▼]

Understanding the mechanisms used by tropical tree species to cope with drought will be central in predicting forest responses to climate change. The study of plant traits, as wood anatomy and hydraulics, holds promise for capturing response to drought with the major aim of informing projections of climate impacts. However, the links between wood anatomy, plant hydraulics and species fitness in a given environment are still barely understood for the majority of tropical trees. We proposed to use hydraulics and wood traits to examine adaptation to water availability among congeneric tropical tree species in Africa. We hypothesized that wood anatomy determines tree hydraulics and drought responses which, in turn, influence individual tree performance and fitness. We specifically focused on two congeneric species, Erythrophleum ivorense and Erythrophleum suaveolens, with known phylogeny and occupying contrasting habitats. In the natural habitat of each species, we quantified vulnerability to cavitation, volumetric water content and capacitance and the underlying wood traits in branch and stem. Growth was also examined. A common garden in the natural habitat of E. suaveolens was specifically used to confirm that the observed differences in wood traits and growth are largely genotypic in origin rather than environmentally plastic. While the two species broadly share the same general wood anatomical features (Inside Wood 2004) and are hard to distinguish in the field, we identified some but slight differences in wood traits, particularly in vessel-associated traits, that resulted in strong differences in tree hydraulics, performance and overall distribution. Specifically, the wet forest species, E. ivorense, had wider vessels, lower vessel cell-wall reinforcement and wider intervessel pits than E. suaveolens. These traits allow a high hydraulic conductivity and the fast growth of E. ivorense, but confer high vulnerability to cavitation. [less ▲]

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See detailThe limited contribution of large trees to annual biomass production in an old-growth tropical forest
Ligot, Gauthier ULiege; Gourlet-Fleury, Sylvie; Ouédraogo, Dakis-Yaoba et al

in Ecological Applications (2018)

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See detailPan-tropical prediction of forest structure from the largest trees
Bastin, Jean-François; Rutishauser, Ervan; Kellner, James R. et al

in Global Ecology and Biogeography (2018)

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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 (2018)

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 detailArchitectural differences associated to functional traits among 45 coexisting tree species in central Africa
Loubota Panzou, Grâce Jopaul ULiege; Ligot, Gauthier ULiege; Gourlet-Fleury, Sylvie et al

in Functional Ecology (2018)

1. Architectural traits that determine the light captured in a given environment are an important aspect of the life-history strategies of tropical tree species. In this study, we examined how ... [more ▼]

1. Architectural traits that determine the light captured in a given environment are an important aspect of the life-history strategies of tropical tree species. In this study, we examined how interspecific variation in architectural traits is related to the functional traits of 45 coexisting tree species in central Africa. 2. At the tree level, we measured tree diameter, total height and crown dimensions for an average of 30 trees per species (range 14–72, total 968 trees) distributed over a large range of diameters (up to 162 cm). Using log-log models, we fitted species-specific allometric relationships between tree diameter, height and crown dimensions. At the species level, we derived architectural traits (height and crown dimensions) at 15 cm and maximum diameters from species-specific allometries. The architectural traits were then related to functional traits, including light requirements, wood density, leaf habit, and dispersal mode. 3. Among the 45 coexisting tree species, we identified strong variations in height and crown allometries, along with architectural traits derived from these species-specific allometries. There was a positive correlation among architectural traits, suggesting that large-statured canopy species were taller and had larger and deeper crowns than small-statured understory species at all ontogenic stages. The relationships between architectural and functional traits highlighted a continuum of species between the large-statured canopy species and the smallstatured understory species. In this moist and seasonal forest, large-statured canopy species tended to be light-demanding, wind-dispersed, deciduous and large contributors to forest biomass (high basal area), while small-statured understory species tended to be shadetolerant, animal-dispersed, evergreen and most abundant in terms of stem density. 4. Our results highlighted strong architectural differences among coexisting tropical tree species in central Africa. The relationships between architectural and functional traits provided insights into the life-history strategy of tropical tree species. [less ▲]

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See detailAnnual cycles are the most common reproductive strategy in African tropical tree communities
Adamescu, Gabriela S.; Plumptre, Andrew J.; Abernethy, Katharine A. et al

in Biotropica (2018), 50(3), 418-430

We present the first cross-continental comparison of the flowering and fruiting phenology of tropical forests across Africa. Flowering events of 5446 trees from 196 species across 12 sites and fruiting ... [more ▼]

We present the first cross-continental comparison of the flowering and fruiting phenology of tropical forests across Africa. Flowering events of 5446 trees from 196 species across 12 sites and fruiting events of 4595 trees from 191 species across 11 sites were monitored over periods of 6 to 29 years and analyzed to describe phenology at the continental level. To study phenology, we used Fourier analysis to identify the dominant cycles of flowering and fruiting for each individual tree and we identified the time of year African trees bloom and bear fruit and their relationship to local seasonality. Reproductive strategies were diverse, and no single regular cycle was found in >50% of individuals across all 12 sites. Additionally, we found annual flowering and fruiting cycles to be the most common. Sub-annual cycles were the next most common for flowering, whereas supra-annual patterns were the next most common for fruiting. We also identify variation in different subsets of species, with species exhibiting mainly annual cycles most common in West and West Central African tropical forests, while more species at sites in East Central and East African forests showed cycles ranging from sub-annual to supra-annual. Despite many trees showing strong seasonality, at most sites some flowering and fruiting occurred all year round. Environmental factors with annual cycles are likely to be important drivers of seasonal periodicity in trees across Africa, but proximate triggers are unlikely to be constant across the continent. [less ▲]

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See detailA regional allometry for the Congo basin forests based on the largest ever destructive sampling
Fayolle, Adeline ULiege; Ngomanda, Alfred; Mbasi, Michel et al

in Forest Ecology and Management (2018), 430

The estimation and monitoring of the huge amount of carbon contained in tropical forests, and specifically in the above-ground biomass (AGB) of trees, is needed for the successful implementation of ... [more ▼]

The estimation and monitoring of the huge amount of carbon contained in tropical forests, and specifically in the above-ground biomass (AGB) of trees, is needed for the successful implementation of climate change mitigation strategies. Its accuracy depends on the availability of reliable allometric equations to convert forest inventory data into AGB estimates. In this study, we tested whether central African forests are really different from other tropical forests with respect to biomass allometry, and further examined the regional variation in tropical tree allometry across the Congo basin forests. Following the same standardized protocol, trees were destructively sampled for AGB in six sites representative of terra firme forests. We fitted regional and local allometric models, including tree diameter, wood specific gravity, tree height, and crown radius in the AGB predictors. We also evaluated the AGB predictions at the tree level across the six sites of our new models and of existing allometric models, including the pantropical equations developed by Chave et al. (2014, 2005) and the local equations developed by Ngomanda et al. (2014) in Gabon. With a total of 845 tropical trees belonging to 55 African species and covering a large range of diameters (up to 200 cm), the original data presented here can be considered as the largest ever destructive sampling for a tropical region. Regional allometric models were established and including tree height and crown radius had a small but significant effect on AGB predictions. In contrast to our expectations, tree height and crown radius did not explain much between-site variation. Examining the performance of general models (pantropical or regional) versus local models (site-specific), we found little advantage of using local equations. Earlier pantropical equations developed for moist forests were found to provide reasonable predictions of tree AGB in most sites, though the wettest sites, i.e., evergreen forests in Equatorial Guinea and, to a lesser extent in Gabon, tended to show a wet forest allometry. For the Congo basin forests, except in Equatorial Guinea where local models might be preferred, we recommend using our regional models, and otherwise the most recent pantropical models, that were validated here. These results constitute a critical step for the estimation and monitoring of biomass/carbon stocks contained in the second largest contiguous block of tropical forests worldwide, and the successful implementation of climate change mitigation strategies, such as REDD+. [less ▲]

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See detailThe size at reproduction of canopy tree species in central Africa
Ouedraogo, Dakis-Yaoba ULiege; Doucet, Jean-Louis ULiege; Daïnou, Kasso ULiege et al

in Biotropica (2018), 50(3), 465-476

Size at reproduction is a key aspect of species life history that is relatively understudied for long-lived tropical trees. Here, we quantified reproductive diameter for 31 major timber species across 11 ... [more ▼]

Size at reproduction is a key aspect of species life history that is relatively understudied for long-lived tropical trees. Here, we quantified reproductive diameter for 31 major timber species across 11 sites in Cameroon, Congo, and Central African Republic. Specifically, we examined whether (1) between-species variability is correlated with other species traits; (2) reproductive diameter varies within-species among sites; (3) reproductive status varies with crown exposure; and (4) the minimum cutting diameter limits (MCDL) imposed by national forest regulations enable seed trees to persist after logging operations. Consistent with studies conducted elsewhere in the tropics, we found great variability in diameter at reproduction among species, which correlated with adult stature (maximum diameter and height). For some species, reproductive diameter thresholds substantially varied between sites, and crown exposure had a significant positive effect on reproductive status. Most MCDLs were found to be suitable, with trees having a high probability of being seed trees at MCDL. Our findings have implications for the sustainable management of production forests, and they highlight questionable MCDLs for some species and between-site variation in reproductive diameter. The study also highlights the need for long-term phenological monitoring of tree species spanning a large range of ecological strategies to address both theoretical (species life history, allocation tradeoffs) and practical questions (MCDL). [less ▲]

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