Tariq Stevart

Seeing Central African forests through their largest trees

Large tropical trees and a few dominant species were recently identified as the main structuring elements of tropical forests. However, such result did not translate yet into quantitative approaches which are essential to understand, predict and monitor forest functions and composition over large, often poorly accessible territories. Here we show that the above-ground biomass (AGB) of the whole forest can be predicted from a few large trees and that the relationship is proved strikingly stable in 175 1-ha plots investigated across 8 sites spanning Central Africa. We designed a generic model predicting AGB with an error of 14% when based on only 5% of the stems, which points to universality in forest structural properties. For the first time in Africa, we identified some dominant species that disproportionally contribute to forest AGB with 1.5% of recorded species accounting for over 50% of the stock of AGB. Consequently, focusing on large trees and dominant species provides precise information on the whole forest stand. This offers new perspectives for understanding the functioning of tropical forests and opens new doors for the development of innovative monitoring strategies.

Congruent phylogeographical patterns of eight tree species in Atlantic Central Africa provide insights into the past dynamics of forest cover

Cycles of Quaternary climatic change are assumed to be major drivers of African rainforest dynamics and evolution. However, most hypotheses on past vegetation dynamics relied on palaeobotanical records, an approach lacking spatial resolution, and on current patterns of species diversity and endemism, an approach confounding history and environmental determinism. In this context, a comparative phylogeographical study of rainforest species represents a complementary approach because Pleistocene climatic fluctuations may have left interpretable signatures in the patterns of genetic diversity within species. Using 1274 plastid DNA sequences from eight tree species (Afrostyrax kamerunensis, A. lepidophyllus, Erythrophleum suaveolens, Greenwayodendron suaveolens, Milicia excelsa, Santiria trimera, Scorodophloeus zenkeri and Symphonia globulifera) sampled in 50 populations of Atlantic Central Africa (ACA), we averaged divergence across species to produce the first map of the region synthesizing genetic distinctiveness and standardized divergence within and among localities. Significant congruence in divergence was detected mostly among five of the eight species and was stronger in the northern ACA. This pattern is compatible with a scenario of past forest fragmentation and recolonization whereby forests from eastern Cameroon and northeastern Gabon would have been more affected by past climatic change than those of western Cameroon (where one or more refugia would have occurred). By contrast, southern ACA (Gabon) displayed low congruence among species that may reflect less drastic past forest fragmentation or a more complex history of vegetation changes. Finally, we also highlight the potential impact of current environmental barriers on spatial genetic structures.

Exploring the floristic diversity of tropical Africa

BackgroundUnderstanding the patterns of biodiversity distribution and what influences them is a fundamental pre-requisite for effective conservation and sustainable utilisation of biodiversity. Such knowledge is increasingly urgent as biodiversity responds to the ongoing effects of global climate change. Nowhere is this more acute than in species-rich tropical Africa, where so little is known about plant diversity and its distribution. In this paper, we use RAINBIO – one of the largest mega-databases of tropical African vascular plant species distributions ever compiled – to address questions about plant and growth form diversity across tropical Africa.ResultsThe filtered RAINBIO dataset contains 609,776 georeferenced records representing 22,577 species. Growth form data are recorded for 97% of all species. Records are well distributed, but heterogeneous across the continent. Overall, tropical Africa remains poorly sampled. When using sampling units (SU) of 0.5°, just 21 reach appropriate collection density and sampling completeness, and the average number of records per species per SU is only 1.84. Species richness (observed and estimated) and endemism figures per country are provided. Benin, Cameroon, Gabon, Ivory Coast and Liberia appear as the botanically best-explored countries, but none are optimally explored. Forests in the region contain 15,387 vascular plant species, of which 3013 are trees, representing 5–7% of the estimated world’s tropical tree flora. The central African forests have the highest endemism rate across Africa, with approximately 30% of species being endemic.ConclusionsThe botanical exploration of tropical Africa is far from complete, underlining the need for intensified inventories and digitization. We propose priority target areas for future sampling efforts, mainly focused on Tanzania, Atlantic Central Africa and West Africa. The observed number of tree species for African forests is smaller than those estimated from global tree data, suggesting that a significant number of species are yet to be discovered. Our data provide a solid basis for a more sustainable management and improved conservation of tropical Africa’s unique flora, and is important for achieving Objective 1 of the Global Strategy for Plant Conservation 2011–2020.

RAINBIO: a mega-database of tropical African vascular plants distributions

Abstract The tropical vegetation of Africa is characterized by high levels of species diversity but is undergoing important shifts in response to ongoing climate change and increasing anthropogenic pressures. Although our knowledge of plant species distribution patterns in the African tropics has been improving over the years, it remains limited. Here we present RAINBIO, a unique comprehensive mega-database of georeferenced records for vascular plants in continental tropical Africa. The geographic focus of the database is the region south of the Sahel and north of Southern Africa, and the majority of data originate from tropical forest regions. RAINBIO is a compilation of 13 datasets either publicly available or personal ones. Numerous in depth data quality checks, automatic and manual via several African flora experts, were undertaken for georeferencing, standardization of taxonomic names and identification and merging of duplicated records. The resulting RAINBIO data allows exploration and extraction of distribution data for 25,356 native tropical African vascular plant species, which represents ca. 89% of all known plant species in the area of interest. Habit information is also provided for 91% of these species.

New species and records of Orchidaceae from São Tomé and Príncipe

Four new orchid species, Angraecopsis thomensis, Dinklageella scandens, Polystachya principia, and Stolzia thomensis from the islands of Sao Tome and Principe are described and illustrated.

Taxonomy of Atlantic Central African Orchids 1. A New Species of Angraecum sect. Pectinaria (Orchidaceae) from Gabon and Equatorial Guinea

Abstract During a recent survey of Atlantic central African orchids, we collected four orchid specimens in Rio Muni (Equatorial Guinea) that share the general morphology at Angraecum gabonense, the most frequent member of Angraecum section Pectinaria in Central Africa, but differ in leaf shape and flower size. Further inspection of specimens deposited at the Wageningen herbarium and cultivated in their greenhouse led to the discovery of additional specimens from the Monts Doudou area in Gabon. Comparison with other Angraecum specimens indicate that these collections represent a new species, which we describe here as Angraecum atlanticum, the fifth species of Angraecum section Pectinaria recorded in central Africa. The new species is restricted to submontane forests covering the mountain chain situated along the coasts of Gabon and Equatorial Guinea. The distinguishing features of the species include its leaves, which are more widely spaced than A. gabonese, and are 2.2 mm wide; its petals and sepals, which are slightly longer than the lip; its spur, which is somewhat inflated in the middle; and its larger ovary. Information on the ecology, phenology and distribution of Angraecum atlanticum is presented, along with a preliminary conservation assessment using the IUCN Red List Categories and Criteria.

Liste des Orchidaceae de Sao-Tomé et Principe

Abstract A list of the orchids of Sao-Tomé and Principe is provided. 129 taxa are listed including 44 taxa supplementary to the previous studies. Furthermore, some observations on the morphological variation are given for Bulbophyllum mediocre Summerh., B. intertextum Lindl, and B. sandersonii (Hook, f.) Rchb. f., Chamaeangis vagans (Lindl.) Schltr., Liparis deistelii Schltr., Tridactyle armeniaca (Lindl.) Schltr. and T. tridactylites (Rolfe) Schltr. Two names become new synonyms: Cyrtorchis acuminata (Rolfe) Schltr. as synonymous of C. arcuata (Lindl.) Schltr. subsp. variabilis Summerh. and Diaphananthe subclavata (Rolfe) Schltr. as synonymous of D. acuta (Ridi.) Schltr.

Synopsis of the Genus Chamaeangis (Orchidaceae), Including Two New Taxa

Abstract A synopsis of Chamaeangis (Orchidaceae) with a taxonomic key to the genus is provided. Twelve taxa are recognized. Detailed examination of the specimens revealed two novelties: Chamaeangis spiralis from Nigeria and Cameroon, and Chamaeangis lecomtei var. tenuicalcar, a new variety from Ivory Coast, Ghana, and Gabon. Chamaeangis auciflora is shown to be synonymous with Chamaeangis letouzeyi, which is here redescribed in detail. Chamaeangis thomensis is neotypified, and Chamaeangis lecomtei var. lecomtei is lectotypified. Chamaeangis gracilis is treated as an excluded species. Several new country records of Chamaeangis are provided.

New orchid records from atlantic central Africa

Several papers dealing with Orchidaceae from Atlantic Central Africa have recently been published. However, orchid distributions in this area remain poorly known. Over the last decade, we have conducted an intensive fieldwork programme in Cameroon and Equatorial Guinea. This has enabled us to collect 22 taxa that are new national records. Ten taxa are new records for Cameroon, eight for Equatorial Guinea and four for both countries. One of these taxa is also a new record from Nigeria. Fifteen taxa are endemic to the Lower Guinea area and six were previously known only from the type locality.

Le genre Stolzia (Orchidaceae) en Afrique centrale avec deux nouveaux taxons

Droissart V., Simo M., Sonké B., Cawoy V. & Stévart T. 2009. — Le genre Stolzia (Orchidaceae) en Afrique centrale avec deux nouveaux taxons. Adansonia, sér. 3, 31 (1): 25-40. ABSTRACT The genus Stolzia (Orchidaceae) in central Africa with two new taxa. A taxonomic revision of genus Stolzia (Orchidaceae) occurring in central Africa is given. Nine taxa are recognized. Two new taxa from Cameroon and Equatorial Guinea (Rio Muni) are described and illustrated. Stolzia repens (Rolfe) Summerh. var. cleistogama Stévart, Droissart & Simo differs from the two other varieties of S. repens by its dorsal sepal, which is jointed to lateral sepal on one third of his total length, and by its smaller and non-reflected sepals and petals. Stolzia grandiflora P.J.Cribb subsp. lejolyana Stévart, Droissart & Simo is morphologically close to the type subspecies, endemic to Ethiopia, but differs from it by a longer inflorescence with two flowers that are smaller. The morphological affinity of S. grandiflora subsp. lejolyana appears to lie with the varieties of S. repens (Rolfe) Summerh. However, the new species differs by having inflorescences with two flowers and a longer and thinner peduncle. Stolzia cupuligera (Kraenzl.) Summerh. and S. peperomioides (Kraenzl.) Summerh. are neotypified. The position of S. thomensis Stévart & P.J.Cribb is reconsidered and proposed as S. peperomioides (Kraenzl.) Summerh. subsp. thomensis (Stévart & P.J.Cribb) Stévart, Droissart & Simo. Many new records of Stolzia are given. Key to identification of species and synopsis table of all taxa occurring in central Africa are given.