A phylogenetic classification of the world’s tropical forests

Knowledge about the biogeographic affinities of the world’s tropical forests helps to better understand regional differences in forest structure, diversity, composition and dynamics. Such understanding will enable anticipation of region specific responses to global environmental change. Modern phylogenies, in combination with broad coverage of species inventory data, now allow for global biogeographic analyses that take species evolutionary distance into account. Here we present the first classification of the world’s tropical forests based on their phylogenetic similarity. We identify five principal floristic regions and their floristic relationships: (1) Indo-Pacific, (2) Subtropical, (3) African, (4) American, and (5) Dry forests. Our results do not support the traditional Neo- versus Palaeo-tropical forest division, but instead separate the combined American and African forests from their Indo-Pacific counterparts. We also find indications for the existence of a global dry forest region, with representatives in America, Africa, Madagascar and India. Additionally, a northern hemisphere Subtropical forest region was identified with representatives in Asia and America, providing support for a link between Asian and American northern hemisphere forests

An estimate of the number of tropical tree species

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

The global abundance of tree palms

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

Subsampling herbarium collections to assess geographic diversity gradients : a case study with endemic Orchidaceae and Rubiaceae in Cameroon

We compiled herbarium specimen data to provide an improved characterization of geographic patterns of diversity using indices of species diversity and floristic similarity based on rarefaction principles. A dataset of 3650 georeferenced plant specimens belonging to Orchidaceae and Rubiaceae endemic to Atlantic Central Africa was assembled to assess species composition per half-degree or one-degree grid cells. Local diversity was measured by the expected number of species (S(k)) per grid cell found in subsamples of increasing size and compared with raw species richness (S(R)). A nearly unbiased estimator of the effective number of species per grid cell was also used, allowing quantification of ratios of true diversity between grid cells. Species turnover was measured using a presence/absence-based similarity index (S phi rensen) and an abundance-based index that corrects for sampling bias (NNESS). Our results confirm that the coastal region of Cameroon is more diverse in endemic species than those more inland. The southern part of this coastal forest is, however, as diverse as the more intensively inventoried northern part, and should also be recognized as an important center of endemism. A strong congruence between S phi rensen and NNESS similarity matrices lead to similar delimitations of floristic units. Hence, heterogeneous sampling seems to confer more bias when measuring patterns of local diversity using raw species richness than species turnover using S phi rensen index. Overall, we argue that subsampling methods represent a useful way to assess diversity gradients using herbarium specimens while correcting for heterogeneous sampling effort

Annotated catalogue of the flowering plants of São Tomé and Príncipe

A catalogue of the flowering plants of the islands of São Tomé and Príncipe (Gulf of Guinea) is presented. Flowering plant diversity figures are updated to: 135 families (20 introduced), 624 genera (172 introduced), 1 104 species (301 introduced) plus 15 additional infraspecific taxa. At present 119 taxa (107 species and 12 infraspecific taxa) are known to be endemic to the two islands. The catalogue includes accepted names, synonyms used in recent literature, common names, voucher specimens and information on habit and habitat and on plant uses, particularly medicinally.http://www.sanbi.org/products/publications/bothalia.htmnf201

Taxonomy of Atlantic Central African orchids, 6 : three new species of Angraecum sect. Afrangraecum (Orchidaceae, Angraecinae) from Gabon and Sao Tomé

Three new species of Angraecum sect. Afrangraecum from Central Africa are here described and illustrated. They are morphologically similar to A. affine and A. cribbianum. Two of them, A. gereauanum and A. geerinckianum, are only known from Massif du Chaillu in Gabon and appear to be closely related based on morphological and preliminary molecular evidence. The third species, A. oliveirae, is endemic to Sao Tome. A dichotomous key to all fourteen species of A. sect. Afrangraecum and a table with the distinguishing characters of the three new species and closely allied taxa are provided. A preliminary assessment of the conservation status of the new species is also presented, using the IUCN Red List categories and criteria

Molecular phylogeny of the genus Bolusiella (Orchidaceae, Angraecinae)

Recent molecular studies have suggested the monophyly of Bolusiella, a small orchid genus comprising five species and one subspecies from Continental Africa, but sampling has been limited. Using the species delimitation presented in the recent taxonomic revision of the genus, this study aimed to confirm the monophyly of Bolusiella and assess the interspecific relationships using a comprehensive sampling and various analytical methods. DNA sequences of one nuclear spacer region (ITS-1) and five plastid regions (matK, rps16, trnL-trnF, trnC-petN, and ycf1) from 20 specimens representing all five species of the genus were analyzed using static homology, dynamic homology, and Bayesian methods. The monophyly of both the genus Bolusiella and each of its five species was confirmed, corroborating the previously published taxonomic revision. The use of dynamic homology methods was not conclusive for this particular group. The results of the total evidence analysis (combining all six sequence regions) using the dynamic homology approach yielded a slightly different hypothesis regarding interspecific relationships (namely the exchange of B. talbotii and Bolusiella iridifolia as the earliest diverging lineage), probably because the nodes in question are supported by a small subset of conflicting characters, compared to the hypotheses resulting from the static homology and Bayesian methods, which are congruent with the results of previous studies

Spatio-temporal patterns of orchids flowering in Cameroonian rainforests

We characterized the flowering patterns of 45 epiphytic orchid species occurring in Cameroonian rainforests to explore the environmental and evolutionary forces driving their phenology. We used a dataset of 3470 flowering events recorded over a period of 11 years in the Yaounde living collection (82% of the flowering events) and from in situ observations (18% of the flowering events) to (i) describe flowering frequency and timing and synchronization among taxa; (ii) test flowering patterns for phylogenetic relatedness at the generic level; and (iii) investigate the spatial patterns of phenology. An annual flowering pattern prevailed among the species selected for this study. The species-rich African genera Angraecum and Polystachya are characterized by subannual and annual frequency patterns, respectively. However, in terms of flowering time, no phylogenetic signal was detected for the four most diverse genera (Ancistrorhynchus, Angraecum, Bulbophyllum, and Polystachya). Results suggest also an important role of photoperiod and precipitation as climatic triggers of flowering patterns. Moreover, 16% of the taxa cultivated ex situ, mostly Polystachya, showed significant differences in flowering time between individuals originating from distinct climatic regions, pointing toward the existence of phenological ecotypes. Phenological plasticity, suggested by the lack of synchronized flowering in spatially disjunct populations of Polystachya, could explain the widespread radiation of this genus throughout tropical Africa. Our study highlights the need to take the spatial pattern of flowering time into account when interpreting phylogeographic patterns in central African rainforests