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International audience; Aim: Examining tree species-environment association can offer insight into the drivers of vegetation patterns and key information of practical relevance to forest management. Here, we aim to quantify the contribution of climate and soil gradients to variation in Central African tree species composition (abundance and occurrence). Location: Tropical rainforests of southern and eastern Cameroon. Methods: We established 82 1-ha permanent plots across seven localities and censused all trees ≥ 10 cm in diameter, representing a total of 37,733 trees and 455 species. In 60 of those plots, we measured ten soil variables describing texture and nutrients levels and extracted ten bioclimatic variables from global-gridded climate databases. We synthesized the main environmental gradients by conducting principal component analyses on climate and soil data respectively. We performed unconstrained and constrained non-symmetric correspondence analyses to account for the individual and joint contributions of climate and soil on species abundance and occurrence. Results: Climate and soil contributed similarly to variances of species abundance and occurrence (12–15 % variance for climate vs. 11–12 % variance for soil). Climate influence mostly concerns some abundant species, while some of the less abundant species were mainly driven by soil. Fractions of species variances accounted for by climate and soil show strong correlation when assessed from species occurrence and abundance data. Conclusion: Variation in occurrence and abundance of tropical forest trees can be partly shaped by both climate and soil gradients in Cameroon, which emphasizes the importance to jointly consider soil and climate in species distribution modeling. Less abundant species may express environmental influence differently than abundant species and convey complementary information about community assemblage. Though showing congruent patterns here, species abundance and occurrence reflect different interacting community processes and both should be examined to better understand vegetation patterns.

The oceanic islands of the Gulf of Guinea display a large diversity of environmental conditions and biological communities, whose interactions have contributed to the development of a great variety of ecosystems, from mangroves to montane grasslands. Human activities have extensively and profoundly altered many of these natural ecosystems over the past five centuries. We review key studies to propose an updated classification map of terrestrial ecosystems, taking advantage of up-to-date spatial information on abiotic gradients and biological distributions. To guide future research and conservation programs, we highlight challenges and pending questions regarding our understanding of the structure, integrity, and dynamics of terrestrial ecosystems in these islands.

Aim: To delineate bioregions in tropical Africa and determine whether different plant growth forms (trees, terrestrial herbs, lianas and shrubs) display the same pattern of regionalization, diversity and endemism as the whole flora.Location: Tropical Africa (excl. Madagascar), from 20 degrees N to 25 degrees S.Taxon: Vascular plants.Methods: Analyses were based on occurrences of 24,719 vascular plant species distributed across tropical Africa extracted from the RAINBIO database. The majority of species (93%) were classified into four growth forms: terrestrial herbs, trees, shrubs and lianas. Biogeographical regions (bioregions) were delimited using a bipartite network clustering approach on the whole dataset and then separately for each growth form. Relationships among bioregions were investigated using non-metric multidimensional scaling ordination, flora nestedness and endemism patterns.Results: Analyses of the whole dataset identified 16 bioregions and 11 transition zones. These were congruent with most of the currently recognized phytogeographical classifications, and also highlighted previously under-recognized bioregions. Bioregion endemism rates were lower and species richness higher when compared to estimates from the White/Association pour l'Etude Taxonomique de la Flore d'Afrique Tropicale (AETFAT) classification. Analysed separately, plant growth forms showed contrasting geographical patterns. Bioregionalization was better resolved for closed forest types using trees and lianas and for open vegetation types using terrestrial herbs, while shrubs showed good discriminative power in all vegetation types.Main conclusions: We show that distribution patterns based on solely trees are not sufficient to define floristic bioregions in tropical Africa. Analyses of spatial patterns using different growth forms are complementary, likely reflecting different evolutionary processes and ecological relationships. The contribution of growth forms to delimit geographical floristic patterns across tropical Africa is of critical importance for land use planning and management, and for selecting priority conservation areas.

The fossil record in tropical Africa suggests that dry conditions during the Ice Ages caused expansion of savannahs and contraction of the rainforest. Forest refugia have been proposed to be located in areas of Central Africa that currently harbour high rates of endemic species. However, to what extent the forest was fragmented remains unknown. Nuclear microsatellites and plastid sequences of 732 trees of two species occurring in the same habitat—mature lowland evergreen rainforests—but with remarkably different dispersal capacities—animal versus gravity—were analysed. Geographical information system tools revealed intraspecific lineages partially congruent across the two species, suggesting common past barriers to gene flow in Central Africa. According to approximate Bayesian computation, the intraspecific genetic clusters diverged during the Pleistocene (less than 2 Ma), so that intraspecific differentiation is the appropriate scale to test the aridification effect of the Ice Ages on tree populations. Demographic tests revealed clear genetic signals of population expansion in both taxa, possibly following bottleneck events after forest fragmentation, with stronger evidence of expansion after the Penultimate rather than after the Last Glacial Maximum. The differential dispersal capacity may have modulated the particular response of each species to climate change, as revealed by the stronger evidence of expansion found in the animal-dispersed species than in the gravity-dispersed one.

Background and aims – Diospyros (Ebenaceae), a large genus with a mostly tropical distribution, includes 736 species worldwide, 104 of which occur in continental Africa. During recent field work in west-central Gabon, two new species of Diospyros were collected. They are described and illustrated here, and compared with their most similar relatives. Preliminary conservation status assessments are also provided.Methods – Normal practices of herbarium taxonomy were applied to study all available herbarium material, mainly from BR, BRLU, LBV, MO, P and WAG. The conservation status of both species was evaluated following the IUCN Red List Categories and Criteria.Key results – Diospyros cleistantha O.Lachenaud & G.E.Schatz occurs in the Atlantic regions of Cameroon, Equatorial Guinea and Gabon; it belongs to D. sect. Calvitiella and closely resembles D. zenkeri and D. iturensis. Diospyros subargentea O.Lachenaud, Dauby & G.E.Schatz is endemic to west-central Gabon; it belongs to D. sect. Noltia and most closely resembles D. soyauxii. The conservation status of the two species is assessed as Endangered and Vulnerable, respectively.

AimIn this study we identified large-scale variation in tree species composition across tropical African forests and determined the underlying environmental and historical factors.LocationTropical forests from Senegal to Mozambique.MethodsDistribution data were gathered for 1175 tree species in 455 sample sites scattered across tropical Africa, including all types of tropical forests (wet, moist, dry, and lowland to moderate elevation montane forests). The value of elevation and 19 climatic variables extracted from the BIOCLIM data set were assigned to each sample site. We determined the variation in species composition using correspondence analysis and identified the environmental correlates. We defined floristic clusters according to species composition and identified the characteristic species using indicator analysis.ResultsWe identified a major floristic discontinuity located at the Albertine rift that separated the dry, moist and wet forests of West and Central Africa (the entire Guineo-Congolian Region) from the upland and coastal forests of East Africa. Except for the Albertine Rift, we found no evidence to support the other proposed floristic discontinuities (Dahomey Gap etc.). We detected two main environmental gradients across tropical African forests. The rainfall gradient was strongly correlated with the variation in tree species composition in West and Central Africa. The elevation/temperature gradient highlighted the major floristic differences within East Africa and between East Africa and the Guineo-Congolian Region, the latter being most probably due to the geological disruption and associated climatic history of the East African uplift.Main conclusionsWe found floristic evidence for three main biogeographical regions across the tropical African forests, and described six floristic clusters with particular environmental conditions within these regions: Coastal and Upland for East Africa, Dry and Wet-Moist for West Africa, and Moist and Wet for Central Africa.

Aim Large trees (d.b.h. 70 cm) store large amounts of biomass. Several studies suggest that large trees may be vulnerable to changing climate, poten- tially leading to declining forest biomass storage. Here we determine the importance of large trees for tropical forest biomass storage and explore which intrinsic (species trait) and extrinsic (environment) variables are associated with the density of large trees and forest biomass at continental and pan-tropical scales. Location Pan-tropical.

International audience; The biogeographic history of the African rain forests has been contentious. Phylogeography, the study of the geographic distribution of genetic lineages within species, can highlight the signatures of historical events affecting the demography and distribution of species (i.e. population fragmentation or size changes, range expansion/contraction) and, thereby, the ecosystems they belong to. The accumulation of recent data for African rain forests now enables a first biogeographic synthesis for the region. In this review, we explain which phylogeographic patterns are expected under different scenarios of past demographic change, and we give an overview of the patterns detected in African rain forest trees to discuss whether they support alternative hypotheses regarding the history of the African rain forest cover. The major genetic discontinuities in the region support the role of refugia during climatic oscillations, though not necessarily following the classically proposed scenarios. We identify in particular a genetic split between the North and the South of the Lower Guinean region. Finally we provide some perspectives for future study.; L’histoire biogéographique des forêts tropicales africaines reste controversée. La phylogéographie, l’étude de la répartition géographique des lignées génétiques au sein des espèces, peut révéler la signature d’événements historiques qui ont affecté la démographie et la répartition des espèces (fragmentation ou changement de taille de population, extension/contraction de leur distribution) et de leurs écosystèmes constitutifs. La récente accumulation de données pour les forêts pluviales africaines permet une première synthèse biogéographique. Dans cette revue, nous expliquons quels patrons phylogéographiques sont attendus selon différents scénarios de changement démographique passé, puis nous donnons un aperçu des patrons détectés chez les arbres des forêts pluviales africaines, afin de discuter s’ils appuient des hypothèses alternatives concernant l’histoire de la couverture forestière. Les discontinuités génétiques majeures dans la région tendent à soutenir le rôle des refuges lors des oscillations climatiques, mais pas forcément selon les scénarios classiquement proposés. Elles mettent notamment en évidence une discontinuité génétique entre le Nord et le Sud de la basse Guinée. Nous terminons par quelques perspectives pour des études futures.

Accurately monitoring tropical forest carbon stocks is an outstanding challenge. Allometric models that consider tree diameter, height and wood density as predictors are currently used in most tropical forest carbon studies. In particular, a pantropical biomass model has been widely used for approximately a decade, and its most recent version will certainly constitute a reference in the coming years. However, this reference model shows a systematic bias for the largest trees. Because large trees are key drivers of forest carbon stocks and dynamics, understanding the origin and the consequences of this bias is of utmost concern. In this study, we compiled a unique tree mass dataset on 673 trees measured in five tropical countries (101 trees > 100 cm in diameter) and an original dataset of 130 forest plots (1 ha) from central Africa to quantify the error of biomass allometric models at the individual and plot levels when explicitly accounting or not accounting for crown mass variations. We first showed that the proportion of crown to total tree aboveground biomass is highly variable among trees, ranging from 3 to 88 %. This proportion was constant on average for trees < 10 Mg (mean of 34 %) but, above this threshold, increased sharply with tree mass and exceeded 50 % on average for trees ≥ 45 Mg. This increase coincided with a progressive deviation between the pantropical biomass model estimations and actual tree mass. Accounting for a crown mass proxy in a newly developed model consistently removed the bias observed for large trees (> 1 Mg) and reduced the range of plot-level error from −23–16 to 0–10 %. The disproportionally higher allocation of large trees to crown mass may thus explain the bias observed recently in the reference pantropical model. This bias leads to far-from-negligible, but often overlooked, systematic errors at the plot level and may be easily corrected by accounting for a crown mass proxy for the largest trees in a stand, thus suggesting that the accuracy of forest carbon estimates can be significantly improved at a minimal cost.

A theoretical framework based on Hill numbers has recently been advocated to measure and partition diversity sensu stricto. Hill numbers can be interpreted intuitively as eff ective number of species (ENS). Th ey conform to the so-called replication principle allowing a mathematically coherent multiplicative partitioning of diversity. Th ey form a family of ENS defi ned by the parameter q which controls the weight attributed to rare species. Despite its advantages, this framework was developed without considering its robustness when treating community samples. In this study, we fi rst show that Hurlbert diversity indices (expected number of species among k individuals) can be transformed into ENS that conform asymptotically to the replication principle while controlling the weight given to rare species through parameter k . We investigate the statistical properties of Hill and Hurlbert ENS using simulated communities with contrasted diversity. Th e properties of multiplicative beta diversity estimators based on ENS are also characterized by simulating communities with diff erent levels of diff erentiation. We show that Hurlbert ENS provides a better statistical performance than Hill numbers when dealing with small sample sizes. By contrast, Hill numbers and their estimators suff er from substantial bias except when rare species have a low weight ( q 2). An estimator of ENS estimating both Hill numbers for q 2 and Hurlbert ENS for k 2 is shown to give the best performance and is recommended for processing real datasets when rare species receive low weight. In order to better take account of rare species, current estimators of Hill numbers are not recommended when sample size is too low while Hurlbert’s ENS performs reliably. In conclusion, while Hill numbers possess some interesting mathematical properties that are not shared by Hurlbert’s ENS, the latter outperforms Hill numbers in terms of statistical properties and is well suited to processing community samples, as illustrated on a real dataset.

Since the publication of the Gabon Checklist in 2006, intensive fieldwork activity has led to the discovery of many novelties. We document here 61 new records for the flora of Gabon, including nine new generic records. Five taxa are also removed from the Gabon flora. © 2011 Trustees of the Royal Botanic Garden Edinburgh.

Our aim was to evaluate the extent to which we can predict and map tree alpha diversity across broad spatial scales either by using climate and remote sensing data or by exploiting spatial autocorrelation patterns in tropical rain forest, West Africa and Atlantic Central Africa.

International audience; Geographic patterns of genetic variation at chloroplast markers have been successfully used to address the phylogeography and the demographic history of many plant species. Very few studies have however been conducted in important tropical centers of plant biodiversity like the African rainforests. The phylogeography of a tree species widespread in Central African mature forests, Greenwayodendron suaveolens subsp. suaveolens (Annonaceae), was investigated in the Lower Guinea phytogeographic domain (essentially Gabon and Cameroon) by sequencing an intergenic spacer of the chloroplast genome (trnC-petN1R). A total of 11 polymorphic sites, including nine single nucleotide polymorphisms (SNPs), two insertions/deletions and two inversions, defined 12 haplotypes. The taxon is represented by two sympatric varieties (var. suaveolens and var. gabonica) that carried distinct and relatively divergent haplotypes. These varieties, also well distinguishable morphologically, might therefore represent true biological species. The variety suaveolens, more common and more widespread than the variety gabonica, was represented by ten haplotypes. This taxon showed a weak but statistically significant phylogeographic structure, indicating that two sets of related haplotypes essentially occurred respectively in the northern and the southern hemispheres. These results suggest that the distribution of Greenwayodendron suaveolens subsp. suaveolens, which is currently continuous in the Lower Guinea domain, might have been more fragmented in the past, possibly in relation with Pleistocene forest fragmentation.

The high species richness of tropical forests has long been recognized, yet there remains substantial uncertainty regarding the actual number of tropical tree species. Using a pantropical tree inventory database from closed canopy forests, consisting of 657,630 trees belonging to 11,371 species, we use a fitted value of Fisher's alpha and an approximate pantropical stem total to estimate the minimum number of tropical forest tree species to fall between ∼40,000 and ∼53,000, i.e. at the high end of previous estimates. Contrary to common assumption, the Indo-Pacific region was found to be as species-rich as the Neotropics, with both regions having a minimum of ∼19,000-25,000 tree species. Continental Africa is relatively depauperate with a minimum of ∼4,500-6,000 tree species. Very few species are shared among the African, American, and the Indo-Pacific regions. We provide a methodological framework for estimating species richness in trees that may help refine species richness estimates of tree-dependent taxa., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

Scorodophloeus zenkeri is a tropical tree from mature rainforests of Central Africa, locally threatened by overexploitation. Ten nuclear microsatellite markers, amplifiable in two multiplexed reactions, were developed and characterized in one population. The levels of polymorphism observed (3–15 alleles per locus, expected heterozygosity ranging from 0.198 to 0.905) point at the promising application of the markers for conservation purposes regarding the location of past forest refugia, assessment of mating system and evaluation of genetic diversity in isolated and threatened populations.

Taxonomic classification based on morphology alone can prove difficult. This is the case of the polymorphic forest tree species Santiria trimera in Africa, whose classification has remained controversial for over a century. Studies combining chloroplast and nuclear DNA sequences show the existence of several phylogenetic clades in this taxon, with some occurring in sympatry in western Central Africa suggesting the existence of at least two species. By combining genetic and morphological markers, we aim to assess the species delimitation in the Santiria species complex. Morphological trait (trunk, leaflet, flower and fruit characteristics) analysis using 223 standing individuals and 103 herbarium samples were combined with genetic analyses using 479 individuals genotyped at eight microsatellite markers. Genetic clusters were identified using Bayesian assignment in order to delimit species following the Biological Species Concept and to identify distinctive characters from morphometric analyses in retrospect. Three genetic clusters were identified and found to occur in sympatry. The type of inflorescence and the colour of unripe fruit were the most discriminant morphological traits among those genetic clusters, while many quantitative traits showed overlapping distributions between genetic clusters and explain the difficulty encountered by previous botanists to resolve the taxonomy of Santiria. The combination of genetic and morphological data suggests the presence of three species within the taxon Santiria trimera from western Central Africa. This work should guide a taxonomic revision within the genus Santiria in Africa., SCOPUS: ar.j, info:eu-repo/semantics/published

PREMISE OF THE STUDY Microsatellite loci were developed in the endangered Pericopsis elata using a combination of low-cost procedures. METHODS AND RESULTS Microsatellite isolation was performed simultaneously on three distinct species through a newly available procedure that associates multiplex microsatellite enrichment and next-generation sequencing, allowing the rapid and low-cost development of microsatellite-enriched libraries through the use of a 1/32nd GS-FLX plate. Genotyping using M13-like labeling in multiplexed reactions allowed additional cost savings. From 72 primers selected for initial screening, 21 positively amplified P. elata, and 11 showed polymorphism with two to 11 alleles per locus and a mean value of 5.4 alleles per locus. CONCLUSIONS These microsatellite loci will be useful to further investigate the level of genetic variation within and between natural populations of P. elata in Africa.

A new species Afrothismia gabonensis Dauby & Stevart (Burmanniaceae) is described from the Pongara National Park (Gabon). It is the second Afrothismia species recorded from this country and the twelfth of the genus. The new species mainly differs from Afrothismia winkleri by its dorsal tepals which are much longer. Information on the species’ ecology, phenology and distribution is provided.