Search

Tree seedling dynamics underpin subsequent forest structure and diversity as different species/guilds respond variously to abiotic and biotic stresses. Thus, understanding differential seedling responses to stresses helps us to predict forest trajectories. Because forests vary in both environment and species composition, generalisations across tropical forests are difficult. Afromontane forests are important carbon stores, harbour high diversity and provide critical ecosystem services, yet they are vulnerable to climate change. Here, we investigate the importance of key abiotic and biotic factors on survival of seedling guilds along spatial and temporal scales in a montane forest in south-eastern Nigeria. We use data from 318 seedling plots censused every 3 months from 2017 to 2020 to identify seven key abiotic and four biotic factors influencing seedling survival. We used the Kaplan–Meier method to estimate the persistence time of 1,145 seedlings at community and guild levels. At the community level, newly recruited seedlings had a median survival time of 15 months and about 37% of the seedlings sampled where still alive after 24 months. Understory tree species survived significantly longer than the other growth form guilds and seedling survival did not differ across shade tolerance guilds. Conspecific adult density and steeper, more north facing slopes had a negative effect on tree seedlings survival. In addition, tree seedlings that recruited in October (end of wet season/beginning of dry) had lower survival probabilities compared to those that recruited in the other months. Except for initial height, seedling survival in lianas was not impacted by any of the abiotic and biotic variables tested. Our results suggest that under the current environment forest structure and diversity is changing, most noticeably lianas are increasing in abundance relative to trees.

The relationship of mycorrhizal associations with latitudinal gradients in tree beta-diversity is unexplored. Using a global dataset approach, this study examines how trees with arbuscular mycorrhizal and ectomycorrhizal associations contribute to latitudinal beta-diversity patterns and the environmental controls of these patterns.

Abstract The need to address wildlife conservation outside of protected areas has become more urgent than ever before to meet environmental and socio‐economic goals. However, there is limited knowledge about how woody plants respond to herbivory within landscapes shared by wildlife and domestic herbivores in African savanna, thus management decisions might be based on inaccurate information and ultimately be ineffective. We compared woody vegetation dynamics between two adjacent ranches with different management objectives and subjected to varying levels of herbivory by both wildlife and domesticated mammals using 421 square plots of 400 m2 nested on three transects, each 3 km long and purposively selected to minimize bio‐physical differences. Both species and structural diversity were significantly higher (p

Rhaptopetalum rabiense Kenfack & Nguema, sp. nov. from the Rabi forest in south-western Gabon is described, illustrated and assigned a provisional conservation status of “Critically Endangered”. An identification key to the five Gabonese species of Rhaptopetalum is also provided.

When Darwin visited the Galapagos archipelago, he observed that, in spite of the islands' physical similarity, members of species that had dispersed to them recently were beginning to diverge from each other. He postulated that these divergences must have resulted primarily from interactions with sets of other species that had also diverged across these otherwise similar islands. By extrapolation, if Darwin is correct, such complex interactions must be driving species divergences across all ecosystems. However, many current general ecological theories that predict observed distributions of species in ecosystems do not take the details of between-species interactions into account. Here we quantify, in sixteen forest diversity plots (FDPs) worldwide, highly significant negative density-dependent (NDD) components of both conspecific and heterospecific between-tree interactions that affect the trees' distributions, growth, recruitment, and mortality. These interactions decline smoothly in significance with increasing physical distance between trees. They also tend to decline in significance with increasing phylogenetic distance between the trees, but each FDP exhibits its own unique pattern of exceptions to this overall decline. Unique patterns of between-species interactions in ecosystems, of the general type that Darwin postulated, are likely to have contributed to the exceptions. We test the power of our null-model method by using a deliberately modified data set, and show that the method easily identifies the modifications. We examine how some of the exceptions, at the Wind River (USA) FDP, reveal new details of a known allelopathic effect of one of the Wind River gymnosperm species. Finally, we explore how similar analyses can be used to investigate details of many types of interactions in these complex ecosystems, and can provide clues to the evolution of these interactions.

Do hotspots of plant biodiversity translate into hotspots in the abundance and diversity of large mammalian herbivores? A common expectation in community ecology is that the diversity of plants and animals should be positively correlated in space, as with the latitudinal diversity gradient and the geographic mosaic of biodiversity. Whether this pattern ‘scales down’ to landscape-level linkages between the diversity of plants or the activities of highly mobile megafauna has received less attention. We investigated spatial associations between plants and large herbivores by integrating data from a plant-DNA-barcode phylogeny, camera traps, and a comprehensive map of woody plants across the 1.2-km2 Mpala Forest Global Earth Observatory (ForestGEO) plot, Kenya. Plant and large herbivore communities were strongly associated with an underlying soil gradient, but the richness of large herbivore species was negatively correlated with the richness of woody plants. Results suggest thickets and steep terrain create associational refuges for plants by deterring megaherbivores from browsing on otherwise palatable species. Recent work using dietary DNA metabarcoding has demonstrated that large herbivores often directly control populations of the plant species they prefer to eat, and our results reinforce the important role of megaherbivores in shaping vegetation across landscapes.

The identification of flowering plants using DNA barcoding proposed in last decades has slowly gained ground in Africa, where it has been successfully used to elucidate the systematics and ecology of several plant groups, and to understand their evolutionary history. Existing inferences on the effectiveness of DNA barcoding to identify African trees are mostly based on lowland forests, whereas adjacent montane forests significantly differ from the latter floristically and structurally. Here, we tested the efficiency of chloroplast DNA barcodes (rbcLa, matK, and trnH-psbA) to identify Afromontane Forest tree species in a 20.28 ha permanent plot in Ngel Nyaki, Taraba state, Nigeria. We collected, identified, and vouchered 274 individuals with diameter at breast height ≥ 1 cm belonging to 101 morphospecies, 92 genera, and 48 families. rbcLa and matK used alone or in combination performed better than in lowland forests, with the best species discrimination obtained with the two-locus combination of matK + rbcLa. The intragenic spacer trnH-psbA was too variable to align and could not be tested using the genetic distance method employed. Classic DNA barcode can be a powerful tool to identify Afromontane tree species, mainly due to the non-prevalence in these communities of species—rich genera (low species-to-genus ratio) that constitute the biggest challenge of DNA barcoding of flowering plants.

Background and aims – Cola, the second largest genus of the Malvaceae-Sterculioideae comprises 100–135 small to large tree species confined in nature to African forests, though cultivated elsewhere. Current species distribution ranges show that the genus is highly diverse in the seasonally wet forests along the Nigeria-Cameroon border, including the Korup National Park (KNP). In this paper we examine the diversity and abundance of Cola in KNP compared to other forests for which comparable data are available. We also describe two novelties in the genus.Methods – We used inventory data from a 50-ha permanent plot in southern KNP where all Cola trees and saplings down to 1 cm in diameter were tagged, mapped and identified. Additional collections of the genus came from the 11 km trail leading to the plot. Classic herbarium techniques and field observations were used for the morphological identification and description of specimens at MO and YA and from our personal collections. Cola species richness and abundance was estimated from the plot data and compared to other African forest sites for which comparable data are available. The evaluation of the conservation status of the two new species described in this paper followed the IUCN Red List Categories and Criteria. Key results – Twenty-five species of Cola were identified in the southern part of the KNP, including four undescribed species, raising the total number of Cola species in Cameroon to 46. The abundance of the genus in KNP was three orders of magnitude higher than in the Rabi forest in southwestern Gabon or in the Ituri forest in eastern D.R. Congo. This high species richness and abundance suggests that KNP is part of the center of diversity of the genus. Two new species, Cola zemagoana Kenfack & D.W.Thomas and C. mamboana Kenfack & Sainge are described and illustrated. Both species are only known from the lowland rainforest of southwestern Cameroon. Cola zemagoana is narrow endemic of southern KNP and its conservation status is assessed as Endangered. Cola mamboana is confined to the lowland forests of southwestern Cameroon, is locally very abundant in protected areas and is also assigned the conservation status Endangered.

Background: The Rumpi Hills Forest Reserve (RHFR) is a montane forest area in south-western Cameroon. Although RHFR is presumed to be rich in biodiversity and vegetation types, little information exists regarding its floristic composition and vegetation patterns. Objectives: Our goal was to characterise vegetation patterns in the reserve and to understand how elevation influences distributions and diversity of species. We aimed to provide a first detailed plant species inventory for this important forest area, as well as basic information on forest structure. Method: We characterised floristic composition and vegetation patterns of the reserve in 25 1-ha plots along an elevational gradient from 50 m to 1778 m. In each plot, trees and lianas of diameter at breast height (dbh) ≥ 10 cm were measured; shrubs 10 cm were measured in nested plots of 0.01 ha. Results: In all, 16 761 trees, shrubs and lianas with dbh ≥ 1 cm were censused, representing 71 families, 279 genera and 617 morphospecies. Floristic composition ranged from 94 to 132 species, with a mean of 117.5 species per hectare in lowland forest (50 m – 200 m) and 36–41 species, with a mean of 38.5 species per hectare in montane cloud forest (1600 m – 1778 m) near the summit of Mount Rata. Two-way indicator species analysis classified the 25 plots into six vegetation types corresponding to lowland evergreen rainforest, lowland evergreen rainforest on basalt rocks, middle-elevation evergreen forest, submontane forest, transitional submontane forest and montane cloud forest. In all, 0.006% of the reserve was included in our sample plots. Detrended correspondence analysis highlighted the importance of elevation in shaping vegetation patterns. Conclusion: The RHFR is composed of different vegetation types, which show impressive variation in terms of structure, species composition and diversity. The detailed, fine-scale inventory data obtained in this study could be useful in planning efficient management of this and other montane tropical forests.

Defaunation is linked to the decline of tree species that depend on large animals for seed dispersal, but it is unclear if this affects carbon storage. Here the authors show that defaunation effects on carbon storage vary across continents, driven by relationships between seed dispersal strategies and adult tree size.

Local factors can play an important role in defining tree species distributions in species rich tropical forests. To what extent the same applies to relatively small, species poor West African montane forests is unknown. Here, forests survive in a grassland matrix and fire has played a key role in their spatial and temporal dynamics since the Miocene. To what extent these dynamics influence local species distributions, as compared with other environmental variables such as altitude and moisture remain unknown. Here, we use data from the 20.28 ha montane forest plot in Ngel Nyaki Forest Reserve, South-East Nigeria to explore these questions. The plot features a gradient from grassland to core forest, with significant edges. Within the plot, we determined tree stand structure and species diversity and identified all trees ≥1 cm in diameter. We recorded species guild (pioneer vs. shade tolerant), seed size, and dispersal mode. We analyzed and identified to what extent species showed a preference for forest edges/grasslands or core forest. Similarly, we looked for associations with elevation, distance to streams and forest versus grassland. We recorded 41,031 individuals belonging to 105 morphospecies in 87 genera and 47 families. Around 40% of all tree species, and 50% of the abundant species, showed a clear preference for either the edge/grassland habitat or the forest core. However, we found no obvious association between species guild, seed size or dispersal mode, and distance to edge, so what leads to this sorting remains unclear. Few species distributions were influenced by distance to streams or altitude.

Mapping tree species diversity is increasingly important in the face of environmental change and biodiversity conservation. We explore a potential way of mapping this diversity by relating forest structure to tree species diversity in Gabon. First, we test the relation between canopy height, as a proxy for niche volume, and tree species diversity. Then, we test the relation between vertical canopy structure, as a proxy for vertical niche occupation, and tree species diversity. We use large footprint full-waveform airborne lidar data collected across four study sites in Gabon (Lopé, Mabounié, Mondah, and Rabi) in combination with in situ estimates of species richness (S) and Shannon diversity (H′). Linear models using canopy height explained 44% and 43% of the variation in S and H′ at the 0.25 ha resolution. Linear models using canopy height and the plant area volume density profile explained 71% of this variation. We demonstrate applications of these models by mapping S and H′ in Mondah using a simulated GEDI-TanDEM-X fusion height product, across the four sites using wall-to-wall airborne lidar data products, and across and between the study sites using ICESat lidar waveforms. The modeling results are encouraging in the context of developing pan-tropical structure-diversity models applicable to data from current and upcoming spaceborne remote sensing missions.

Tropical forests have long been recognized for their biodiversity and ecosystem services. Despite their importance, tropical forests, and particularly those of central Africa, remain understudied. Until recently, most forest inventories in Central Africa have focused on trees ≥10 cm in diameter, even though several studies have shown that small-diameter tree population may be important to demographic rates and nutrient cycling. To determine the ecological importance of small-diameter trees in central African forests, we used data from a 25-ha permanent plot that we established in the rainforest of Gabon to study the diversity and dynamics of these forests. Within the plot, we censused 175,830 trees ≥1 cm dbh from 54 families, 192 genera, and 345 species. Average tree density was 7,026 trees/ha, basal area 31.64 m2/ha, and above-ground biomass 369.40 Mg/ha. Fabaceae, Ebenaceae and Euphorbiaceae were the most important families by basal area, density and above-ground biomass. Small-diameter trees (1 cm ≥ dbh

Background Many tree species in tropical forests have distributions tracking local ridge-slope-valley topography. Previous work in a 50-ha plot in Korup National Park, Cameroon, demonstrated that 272 species, or 63% of those tested, were significantly associated with topography. Methods We used two censuses of 329,000 trees ≥1 cm dbh to examine demographic variation at this site that would account for those observed habitat preferences. We tested two predictions. First, within a given topographic habitat, species specializing on that habitat (‘residents’) should outperform species that are specialists of other habitats (‘foreigners’). Second, across different topographic habitats, species should perform best in the habitat on which they specialize (‘home’) compared to other habitats (‘away’). Species’ performance was estimated using growth and mortality rates. Results In hierarchical models with species identity as a random effect, we found no evidence of a demographic advantage to resident species. Indeed, growth rates were most often higher for foreign species. Similarly, comparisons of species on their home vs. away habitats revealed no sign of a performance advantage on the home habitat. Conclusions We reject the hypothesis that species distributions along a ridge-valley catena at Korup are caused by species differences in trees ≥1 cm dbh. Since there must be a demographic cause for habitat specialization, we offer three alternatives. First, the demographic advantage specialists have at home occurs at the reproductive or seedling stage, in sizes smaller than we census in the forest plot. Second, species may have higher performance on their preferred habitat when density is low, but when population builds up, there are negative density-dependent feedbacks that reduce performance. Third, demographic filtering may be produced by extreme environmental conditions that we did not observe during the census interval.

Ecologists have historically used species-area relationships (SARs) as a tool to understand the spatial distribution of species. Recent work has extended SARs to focus on individual-level distributions to generate individual species area relationships (ISARs). The ISAR approach quantifies whether individuals of a species tend have more or less species richness surrounding them than expected by chance. By identifying richness 'accumulators' and 'repellers', respectively, the ISAR approach has been used to infer the relative importance of abiotic and biotic interactions and neutrality. A clear limitation of the SAR and ISAR approaches is that all species are treated as evolutionarily independent and that a large amount of work has now shown that local tree neighborhoods exhibit non-random phylogenetic structure given the species richness. Here, we use nine tropical and temperate forest dynamics plots to ask: (i) do ISARs change predictably across latitude?; (ii) is the phylogenetic diversity in the neighborhood of species accumulators and repellers higher or lower than that expected given the observed species richness?; and (iii) do species accumulators, repellers distributed non-randomly on the community phylogenetic tree? The results indicate no clear trend in ISARs from the temperate zone to the tropics and that the phylogenetic diversity surrounding the individuals of species is generally only non-random on very local scales. Interestingly the distribution of species accumulators and repellers was non-random on the community phylogenies suggesting the presence of phylogenetic signal in the ISAR across latitude.

BACKGROUND: DNA barcoding of rain forest trees could potentially help biologists identify species and discover new ones. However, DNA barcodes cannot always distinguish between closely related species, and the size and completeness of barcode databases are key parameters for their successful application. We test the ability of rbcL, matK and trnH-psbA plastid DNA markers to identify rain forest trees at two sites in Atlantic central Africa under the assumption that a database is exhaustive in terms of species content, but not necessarily in terms of haplotype diversity within species. METHODOLOGY/PRINCIPAL FINDINGS: We assess the accuracy of identification to species or genus using a genetic distance matrix between samples either based on a global multiple sequence alignment (GD) or on a basic local alignment search tool (BLAST). Where a local database is available (within a 50 ha plot), barcoding was generally reliable for genus identification (95-100% success), but less for species identification (71-88%). Using a single marker, best results for species identification were obtained with trnH-psbA. There was a significant decrease of barcoding success in species-rich clades. When the local database was used to identify the genus of trees from another region and did include all genera from the query individuals but not all species, genus identification success decreased to 84-90%. The GD method performed best but a global multiple sequence alignment is not applicable on trnH-psbA. CONCLUSIONS/SIGNIFICANCE: Barcoding is a useful tool to assign unidentified African rain forest trees to a genus, but identification to a species is less reliable, especially in species-rich clades, even using an exhaustive local database. Combining two markers improves the accuracy of species identification but it would only marginally improve genus identification. Finally, we highlight some limitations of the BLAST algorithm as currently implemented and suggest possible improvements for barcoding applications.

L’arbre. Les arbres du genre Carapa (Meliaceae) sont présents dans toutes les forêts d’Afrique tropicale au niveau de l’équateur, du rift d’Albertine jusqu’au Sénégal et au Mali pour sa distribution la plus septentrionale. En Afrique comme en Amérique tropicale, le carapa est une source importante de Produits Forestiers ligneux (bois) et Non-Ligneux (PFNL). Le fruit et les graines. Le fruit typique de carapa est une capsule à quatre ou cinq valves qui renferment chacune deux à cinq graines, soit un total de huit à vingt graines par fruit. L’extraction de l’huile. Les villageois ramassent les graines tombées au sol avant qu’elles ne soient parasitées ou germées, ce qui est défavorable à la production d’une huile de qualité. L’extraction de l’huile se fait par ébouillantage des graines. L’huile extraite, polyvalente, est la substance issue de la plante qui est la plus utilisée devant les extraits de feuilles, d’écorce et de racines. Le marché. En Afrique, le commerce de l’huile de carapa est essentiellement local et reste une activité très marginale. Une demande accrue émane toutefois de l’utilisation de cette huile comme insecticide naturel dans la culture du coton biologique. Discussion. Compte tenu du potentiel économique de l’huile de carapa, sa commercialisation devrait respecter une rétribution équitable des paysannes afin de mieux rentabiliser la production. Des mesures de protection des arbres de carapa et de leur habitat doivent également être prises pour permettre une gestion de la production d’huile à long terme. La plantation semble être une option durable en vue de la conservation des peuplements naturels de carapa. [ABSTRACT FROM AUTHOR]