Diversité botanique dans le sud du parc national de Taï, Côte d’Ivoirean

Botanical diversity of the South of Taï National Park, Côte d’IvoireThe Tai National Park (TNP) is one of the last vestiges of ≪ primary ≫ forest remained in West Africa. The northern part is almost well known but the southern one is not. To mitigate this lack, we conducted a study in the South of the TNP. To achieve the inventory, two methods were used: “walk set up” and the “plot set up”. Nine hundred height plants species were recorded. They belonged to 550 genera and 116 families. The richest families were Rubiaceae, Euphorbiaceae and Caesalpiniaceae. Among all the species, 175 were endemic of West African forests, 11 endemic to Ivorian forests and 61 “sassandrian”. The study showed that for tree species with dbh ≥10 cm Hymenostegia afzelii, Strombosia pustulata,  Diospyros sanza-minika, Funtumia africana, Calpocalyx brevibracteatus and representatives of Caesalpiniaceae, Euphorbiaceae and Ebenaceae families were the richest and had the highest values of IVI and FIV. Endemic, “sassandrian”, rare and threatened species constitute the major characteristic of the TNP and confirm that it includes in the Guinean Forests of West Africa Hotspot

Climatic controls of decomposition drive the global biogeography of forest-tree symbioses

The identity of the dominant root-associated microbial symbionts in a forest determines the ability of trees to access limiting nutrients from atmospheric or soil pools1,2, sequester carbon3,4 and withstand the effects of climate change5,6. Characterizing the global distribution of these symbioses and identifying the factors that control this distribution are thus integral to understanding the present and future functioning of forest ecosystems. Here we generate a spatially explicit global map of the symbiotic status of forests, using a database of over 1.1 million forest inventory plots that collectively contain over 28,000 tree species. Our analyses indicate that climate variables—in particular, climatically controlled variation in the rate of decomposition—are the primary drivers of the global distribution of major symbioses. We estimate that ectomycorrhizal trees, which represent only 2% of all plant species7, constitute approximately 60% of tree stems on Earth. Ectomycorrhizal symbiosis dominates forests in which seasonally cold and dry climates inhibit decomposition, and is the predominant form of symbiosis at high latitudes and elevation. By contrast, arbuscular mycorrhizal trees dominate in aseasonal, warm tropical forests, and occur with ectomycorrhizal trees in temperate biomes in which seasonally warm-and-wet climates enhance decomposition. Continental transitions between forests dominated by ectomycorrhizal or arbuscular mycorrhizal trees occur relatively abruptly along climate-driven decomposition gradients; these transitions are probably caused by positive feedback effects between plants and microorganisms. Symbiotic nitrogen fixers—which are insensitive to climatic controls on decomposition (compared with mycorrhizal fungi)—are most abundant in arid biomes with alkaline soils and high maximum temperatures. The climatically driven global symbiosis gradient that we document provides a spatially explicit quantitative understanding of microbial symbioses at the global scale, and demonstrates the critical role of microbial mutualisms in shaping the distribution of plant species

Le rôle de l’éléphant dans la germination des graines de Irvingia gabonensis (Irvingiaceae), Balanites wilsoniana (Balanitaceae), Parinari excelsa (Chrysobalanaceae) et Sacoglottis gabonensis (Humiriaceae) en forêt tropicale : cas du Parc National d’Azagn

Les éléphants sont d’importants consommateurs de fruits des forêts tropicales africaines. Après défécation, leurs graines gardent leur pouvoir germinatif. Dans le Parc National d’Azagny, parmi les 94 espèces de plante dont les fruits sont consommés, Irvingia gabonensis, Balanites wilsoniana, Parinari excelsa et Sacoglottis gabonensis sont les plus appétées. L’effet de l’ingestion suivie de défécation sur la germination des graines a été analysé dans trois types de formations végétales. Le taux de germination des grainesdéféquées a été supérieur à celui des graines non ingérées placées dans les mêmes conditions. Irvingia gabonensis et Balanites wilsoniana ont montré un taux de germination plus élevé que les autres espèces dans les trois milieux considérés. Nous avons conclu qu’en favorisant la germination de certaines espèces, les éléphants jouent un rôle écologique important dans la régénération de ces espèces. Ce rôle est irremplaçable et important pour la conservation des espèces et des forêts qui les abritent