36 research outputs found
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Closing a gap in tropical forest biomass estimation: taking crown mass variation into account in pantropical allometries
Accurately monitoring tropical forest carbon stocks is a challenge that remains outstanding. 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 model in the coming years. However, this reference model shows a systematic bias towards 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 data set of 673 trees destructively sampled in five tropical countries (101 trees > 100 cm in diameter) and an original data set of 130 forest plots (1 ha) from central Africa to quantify the prediction error of biomass allometric models at the individual and plot levels when explicitly taking crown mass variations into account or not doing so. 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 1 Mg) and reduced the range of plot-level error (in %) 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 taking a crown mass proxy for the largest trees in a stand into account, thus suggesting that the accuracy of forest carbon estimates can be significantly improved at a minimal cost.This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by Copernicus Publications on behalf of the European Geosciences Union. The published article can be found at: http://www.biogeosciences.net
Consistent patterns of common species across tropical tree communities
Trees structure the Earth’s most biodiverse ecosystem, tropical forests. The vast number of tree species presents a formidable challenge to understanding these forests, including their response to environmental change, as very little is known about most tropical tree species. A focus on the common species may circumvent this challenge. Here we investigate abundance patterns of common tree species using inventory data on 1,003,805 trees with trunk diameters of at least 10 cm across 1,568 locations1,2,3,4,5,6 in closed-canopy, structurally intact old-growth tropical forests in Africa, Amazonia and Southeast Asia. We estimate that 2.2%, 2.2% and 2.3% of species comprise 50% of the tropical trees in these regions, respectively. Extrapolating across all closed-canopy tropical forests, we estimate that just 1,053 species comprise half of Earth’s 800 billion tropical trees with trunk diameters of at least 10 cm. Despite differing biogeographic, climatic and anthropogenic histories7, we find notably consistent patterns of common species and species abundance distributions across the continents. This suggests that fundamental mechanisms of tree community assembly may apply to all tropical forests. Resampling analyses show that the most common species are likely to belong to a manageable list of known species, enabling targeted efforts to understand their ecology. Although they do not detract from the importance of rare species, our results open new opportunities to understand the world’s most diverse forests, including modelling their response to environmental change, by focusing on the common species that constitute the majority of their trees.Publisher PDFPeer reviewe
Development and characterization of nuclear microsatellite markers for the African walnut Coula edulis Baill (Coulaceae)
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New taxonomic and conservation status of Ossiculum (Vandeae, Orchidaceae), a highly threatened and narrow-endemic angraecoid orchid from Central Africa
International audienceIn the context of producing a revised phylogenetic Linnean taxonomy of angraecoid orchids, the mono-typic and narrow-endemic genus Ossiculum is synonymised with Calyptrochilum. Accordingly, a new combination in Calyptrochilum is proposed for Ossiculum aurantiacum. The morphological and DNA-based evidence for this transfer is discussed. Moreover, Calyptrochilum aurantiacum is here firstly reported outside Cameroon, with a record from the Republic of the Congo. The Red List conservation status of this species is reassessed and it is to be downgraded from "Critically Endangered" (CR) to "Endangered" (EN), following the recent discovery of additional subpopulations in Cameroon. Résumé En vue de produire une classification taxonomique linnéenne des orchidées angraecoïdes, le genre mono-typique Ossiculum, longtemps considéré comme endémique du sud-ouest Cameroun, est placé en synon-ymie de Calyptrochilum. En conséquence, une nouvelle combinaison dans Calyptrochilum est proposée pour Ossiculum aurantiacum. Les données morphologiques et moléculaires qui justifient cette combinaison sont PhytoKeys 98: 85-97 (2018
Diversity, taxonomy, and history of the tropical fern genus Didymoglossum Desv. (Hymenophyllaceae, Polypodiidae) in Africa
International audienceThe fern genus Didymoglossum (Hymenophyllaceae) is not so diverse in Africa with seven species at most. However, its local taxonomy is surprisingly still strongly debated, in particular within the Didymoglossum erosum complex interpreted either as a single polymorphic species or as a group of at least three distinct but morphologically very close taxa (D. erosum, Didymoglossum chamaedrys, and Didymoglossum benlii). Investigating these taxonomic issues and more generally the diversity of the genus in Africa and its origin, we conducted a complete anatomo–morphological analysis coupled with a molecular phylogenetic work based on rbcL. Our results support the recognition of all seven species, including Didymoglossum robinsonii that is likely distinct from the Neotropical Didymoglossum reptans to which the African populations were traditionally attributed. We here propose new characters and a novel key to distinguish the seven African species which also include Didymoglossum ballardianum, Didymoglossum lenormandii, and Didymoglossum liberiense. Once the taxonomy is clarified with respect to the distinct evolutionary lineages evidenced, the biogeographic history of the genus in Africa is discussed based on a divergence time estimation and the reconstruction of the ancestral geographic areas. These analyses reveal a Mesozoic (Cretaceous) vicariance event within Didymoglossum which is the second one hypothesized for the family Hymenophyllaceae
Flora of Cameroon – Annonaceae Vol 45
Annonaceae is a major pantropical family with 113 genera and about 2550 species. Cameroon is one of the most biodiverse countries in Africa but its flora remains incompletely known. In this volume of the Flora of Cameroon, we describe 166 native taxa representing 163 species in 28 native genera within the family Annonaceae. A total of 22 species (about 13%) are endemic to the country. We provide keys to all native genera, species, and infraspecific taxa. For each species a detailed morphological description and a map of its distribution in Cameroon are provided. Distribution maps and diversity analyses are based on a taxonomically verified database of 2073 collections. Across Africa, Cameroon is a center of diversity for Annonaceae harboring one of the highest numbers of species and genera. For example, Cameroon harbors the highest number of African species for the only pantropical genus of Annonaceae, Xylopia. Annonaceae are found across all 10 administrative regions of Cameroon but diversity is concentrated within the tropical rain forest areas situated in the south and South-West. The areas around Bipindi and Mount Cameroon show the highest levels of diversity, but this is correlated with collection effort. Line drawings and/or photographs accompany most species. One species new to science Uvariopsis etugeana Dagallier & Couvreur sp. nov. is described. We also undertake a number of nomenclatural changes such as lectotypifications, six new synonymies and two new combinations (Uvaria anisotricha (Le Thomas) Couvreur, comb. nov.; Uvariodendron fuscum var. giganteum (Engl.) Dagallier & Couvreur, comb. nov.)
Additive influences of soil and climate gradients drive tree community composition of Central African rainforests
International audienceAim: 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
Pistes pour l'étude de la distribution des peuplements de Gilbertiodedron dewevrei comme signature des impacts climatiques ou anthropiques anciens
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