Large areas of African moist forests are being logged in the context of supposedly sustainable management plans. It remains however controversial whether harvesting a few trees per hectare can be ...maintained in the long term while preserving other forest services as well. We used a unique 24 year silvicultural experiment, encompassing 10 4 ha plots established in the Central African Republic, to assess the effect of disturbance linked to logging (two to nine trees ha−1 greater than or equal to 80 cm DBH) and thinning (11–41 trees ha−1 greater than or equal to 50 cm DBH) on the structure and dynamics of the forest. Before silvicultural treatments, above-ground biomass (AGB) and timber stock (i.e. the volume of commercial trees greater than or equal to 80 cm DBH) in the plots amounted 374.5 ± 58.2 Mg ha−1 and 79.7 ± 45.9 m3 ha−1, respectively. We found that (i) natural control forest was increasing in AGB (2.58 ± 1.73 Mg dry mass ha−1 yr−1) and decreasing in timber stock (−0.33 ± 1.57 m3 ha−1 yr−1); (ii) the AGB recovered very quickly after logging and thinning, at a rate proportional to the disturbance intensity (mean recovery after 24 years: 144%). Compared with controls, the gain almost doubled in the logged plots (4.82 ± 1.22 Mg ha−1 yr−1) and tripled in the logged + thinned plots (8.03 ± 1.41 Mg ha−1 yr−1); (iii) the timber stock recovered slowly (mean recovery after 24 years: 41%), at a rate of 0.75 ± 0.51 m3 ha−1 yr−1 in the logged plots, and 0.81 ± 0.74 m3 ha−1 yr−1 in the logged + thinned plots. Although thinning significantly increased the gain in biomass, it had no effect on the gain in timber stock. However, thinning did foster the growth and survival of small- and medium-sized timber trees and should have a positive effect over the next felling cycle.
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Africa is forecasted to experience large and rapid climate change
and population growth
during the twenty-first century, which threatens the world's second largest rainforest. Protecting and ...sustainably managing these African forests requires an increased understanding of their compositional heterogeneity, the environmental drivers of forest composition and their vulnerability to ongoing changes. Here, using a very large dataset of 6 million trees in more than 180,000 field plots, we jointly model the distribution in abundance of the most dominant tree taxa in central Africa, and produce continuous maps of the floristic and functional composition of central African forests. Our results show that the uncertainty in taxon-specific distributions averages out at the community level, and reveal highly deterministic assemblages. We uncover contrasting floristic and functional compositions across climates, soil types and anthropogenic gradients, with functional convergence among types of forest that are floristically dissimilar. Combining these spatial predictions with scenarios of climatic and anthropogenic global change suggests a high vulnerability of the northern and southern forest margins, the Atlantic forests and most forests in the Democratic Republic of the Congo, where both climate and anthropogenic threats are expected to increase sharply by 2085. These results constitute key quantitative benchmarks for scientists and policymakers to shape transnational conservation and management strategies that aim to provide a sustainable future for central African forests.
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GEOZS, IJS, IMTLJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK, ZAGLJ
•A survey of 5817 trees from 35 species in pure and mixed plantating in West Africa.•A high diversity of demographic performance with three highly-productive species.•A significantly positive effect ...(+0.7 mm.yr−1) of mixture on annual growth.•13 species retained for planting in the Sudanese zone of West Africa.
The rapidly growing human population in sudanian West Africa has generated increasing demand for agricultural land and forest products so that most of the original vegetation cover has disappeared and the remainder is highly degraded, meaning that it is urgent to draw up a long-term assessment of the potential of local species to be promoted in pure and mixed plantings as contribution to global forest restoration efforts. We inventoried the survival and growth of 5817 trees belonging to 35 species planted more than 25 years ago in pure and mixed plantings. For a subset of individuals, we estimated heights and volumes of standing timber. We found that (i) the long-term survival (from 50 to 99%.yr−1) and diameter growth (from 1 to 10 mm.yr−1) are highly diverse between species and not correlated to each other, (ii) the annual increase in biomass per tree averages 2.22 kg while the annual increase in stand biomass may be over 6 Mg. ha−1 for three highly-productive species (Khaya senegalensis, Pterocarpus erinaceus and Anogeissus leïocarpa) (iii) the effect of mixture on annual growth is significantly positive with an across-species gain of 0.7 mm.yr−1 while there is no effect on the survival probability. Considering a potential productivity of 10 m3 of timber wood per hectare at 30 years, 13 species have been retained in the list of woody species of interest for planting in the Sudanese zone of West Africa.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•African moist forests vary in structure, composition and functioning.•Forest types are determined by soil and disturbance history.•Forest types differ in population and ecosystem processes.•Forest ...types need adapted management and conservation strategies.
The greater part of the semi-deciduous moist forests of the Congo basin has been given to logging companies for exploitation. In the next decades, very few of these forests will remain intact. In this paper, we aimed to identify large-scale variations in the structure, composition and functioning of African moist forests that could serve as a baseline for both management and conservation purposes. Commercial forest inventory data were assembled for 49,711 0.5-ha plots, covering an area of more than six million hectares, crossing the borders of Cameroon, Central African Republic and Republic of Congo. Floristic composition was analyzed for a subset of 176 genera reliably identified in the field. Three key functional traits of tropical trees: regeneration guild, leaf phenology, and wood specific gravity, were collected at the species level from various sources, and assigned at the genus level. We first investigated the main variations in forest structure and composition, and identified seven forest types based on these variations. Differences in the percentage of pioneer and deciduous stems, and mean wood specific gravity were tested between forest types. Most of the study area was composed of a mosaic of the structural variations of the forests characterized by the occurrence of Celtis (Ulmaceae) species, which are mostly composed of frequent and abundant genera that formed the common floristic pool of the region. Secondary Musanga (Moraceae) forest is located in repeatedly disturbed areas, along roads and around main cities; mixed Manilkara (Sapotaceae) forest covers a huge area in the southern Central African Republic and in the northern Republic of Congo; and monodominant Gilbertiodendron (Fabaceae) forest is sparsely distributed along rivers. The contrasted structure, composition, and functioning of the forest types imply pronounced differences in population and ecosystem processes, and call for adapted management and conservation strategies.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Selective logging can impact tree composition and the long-term sustainability of forests. Studying the ecological consequences of logging practices is crucial for guiding forest management ...strategies aiming at maintaining ecological integrity and supporting landscape-level conservation goals. We investigated the consequences of very low-intensity selective logging in multiple tree life stages across a logged forest chronosequence in Gabon. We found that species composition differed between logged and unlogged forests at all life stages (seedlings, saplings, and adults), which were most pronounced in the understory of older forests (logged 10 years prior) compared to unlogged areas. However, logging explained a small portion of the variation in species composition (<3% alone, <8% in combination with habitat). For functional composition, we observed higher wood density in the understory of older logged forests than in unlogged forests. Light-demanding saplings and saplings with animal-dispersed seeds were more prevalent in older logged forests than in unlogged forests. Timber species were less prevalent as seedlings and adults but more prevalent as saplings in logged forests compared to unlogged forests. Our results suggest that very low-intensity logging does not negatively impact key ecosystem services like carbon storage and food availability for frugivores. However, reduced prevalence of timber species may impact logging sustainability. Our study indicates that, when considering best-case scenarios, selectively logged forests have the potential to support conservation goals by offering refugia for biodiversity and maintaining essential ecosystem services. Thus, these forests have the potential to complement protected areas and serve as a sustainable alternative to more intensive land use.
L'exploitation forestière sélective pourrait avoir un impact sur la composition des arbres et la durabilité à long terme de cette exploitation. L′étude des conséquences écologiques de l′exploitation forestière peut permettre d’améliorer la gestion des écosystèmes forestiers afin de garantir que les forêts exploitées sélectivement conservent leur intégrité écologique et puissent soutenir les objectifs de conservation à l′échelle du paysage. Au Gabon, nous avons étudié les conséquences de l′exploitation sélective à très faible intensité sur plusieurs stades de vie des arbres dans une chronoséquence de forêts exploitées. Nous avons constaté que la composition des espèces différait entre les forêts exploitées et non exploitées à tous les stades de la vie (plantules, jeunes arbres, et adultes). Ces différences se sont montrées plus prononcées dans le sous-étage des forêts exploitées depuis 10 ans par rapport aux sous-étage des forêts non exploitées. Cependant, l′exploitation forestière n′explique qu'une petite partie de la variation de la composition des espèces à tous les stades de la vie (<3% à l′exploitation forestière seule, <8% en combinaison avec l′habitat). En évaluant la composition fonctionnelle, nous avons constaté que les plantules et jeunes arbres des forêts anciennement exploitées avaient une densité de bois plus élevée que dans celui des forêts non exploitées. Les jeunes arbres héliophiles et les graines dispersées par les animaux avaient tendance à être plus prévalent dans le sous-étage des forêts exploitées que dans celui des forêts non exploitées. Les espèces commercialisées étaient moins prévalentes en tant que semis et d′adultes, mais plus prévalent en tant que jeunes arbres dans les forêts exploitées que dans les forêts non exploitées. Nos résultats suggèrent que l′exploitation forestière à très faible intensité na pas d′impact négatif sur les services écosystémiques tels que le stockage du carbone et la disponibilité en nourriture pour les frugivores. Cependant, la prévalence réduite de bois exploitable peut avoir des implications sur la durabilité de l′exploitation forestière. Notre étude indique que l’exploitation forestière modérée constitue une alternative viable face aux méthodes plus intensives. Ces espaces forestiers faiblement exploités peuvent contribuer à la conservation en reliant les zones protégées, en offrant des refuges pour la biodiversité et en maintenant des services écosystémiques essentiels.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Abstract
Identifying and quantifying factors that influence tree growth are crucial issues to ensure sustainable forest management, particularly in moist tropical forests. Tree growth depends on ...several factors comprising ontogenic stage, competition by neighbours and environmental conditions. Several studies have focused on one or two of them, but very few have considered all three, especially in Central Africa. We investigated the effects of diameter and competition on tree growth, in four Central African sites characterized by their soil physicochemical properties, at both tree community and population levels.
We calibrated growth models using diameter data collected on 29,741 trees between 2015 and 2018, on twelve 4 or 9‐ha plots spread over the four sites. These models included diameter, wood density, competition indices and site effect as explainable variables at the community level and excluded wood density at the population level.
At the community level, the best models explained 11% of growth variability with a decreasing effect of species wood density, diameter, site and competition. Our results show that even if low, site effect can result from different soil nutrients depending on both tree size and species wood density. We observed higher tree growth on sites with (i) high exchangeable K, organic C, total N and total P for low wood density species; (ii) high available P and C:N for small trees, high exchangeable Ca and Mg for medium to large trees, all belonging to medium and hard wood density species. At the population level, the best models explained between 0 to 43% of growth variability, with significant competition effect (resp. site effect) for 21 (resp. 9) of the 43 species studied. Site ranking varied greatly between the 9 species concerned, probably reflecting different sensitivities to the scarcity of particular soil nutrients.
Synthesis.
Our study provides original results on the factors influencing tree growth in Central Africa, showing that the potential effect of soil nutrients depends on tree size and species wood density. Remaining highly unpredictable at the population level, this effect makes it essential to increase the number of dynamics monitoring systems in logging concessions.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
In the past few years, functional genomics information has been rapidly accumulating on Rubiaceae species and especially on those belonging to the Coffea genus (coffee trees). An increasing number of ...expressed sequence tag (EST) data and EST- or genomic-derived microsatellite markers have been generated, together with Conserved Ortholog Set (COS) markers. This considerably facilitates comparative genomics or map-based genetic studies through the common use of orthologous loci across different species. Similar genomic information is available for e.g. tomato or potato, members of the Solanaceae family. Since both Rubiaceae and Solanaceae belong to the Euasterids I (lamiids) integration of information on genetic markers would be possible and lead to more efficient analyses and discovery of key loci involved in important traits such as fruit development, quality, and maturation, or adaptation. Our goal was to develop a comprehensive web data source for integrated information on validated orthologous markers in Rubiaceae.
MoccaDB is an online MySQL-PHP driven relational database that houses annotated and/or mapped microsatellite markers in Rubiaceae. In its current release, the database stores 638 markers that have been defined on 259 ESTs and 379 genomic sequences. Marker information was retrieved from 11 published works, and completed with original data on 132 microsatellite markers validated in our laboratory. DNA sequences were derived from three Coffea species/hybrids. Microsatellite markers were checked for similarity, in vitro tested for cross-amplification and diversity/polymorphism status in up to 38 Rubiaceae species belonging to the Cinchonoideae and Rubioideae subfamilies. Functional annotation was provided and some markers associated with described metabolic pathways were also integrated. Users can search the database for marker, sequence, map or diversity information through multi-option query forms. The retrieved data can be browsed and downloaded, along with protocols used, using a standard web browser. MoccaDB also integrates bioinformatics tools (CMap viewer and local BLAST) and hyperlinks to related external data sources (NCBI GenBank and PubMed, SOL Genomic Network database).
We believe that MoccaDB will be extremely useful for all researchers working in the areas of comparative and functional genomics and molecular evolution, in general, and population analysis and association mapping of Rubiaceae and Solanaceae species, in particular.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract A vast silvicultural experiment was set up in 1982 nearby the town of M’Baïki in the Central African Republic to monitor the recovery of tropical forests after disturbance. The M’Baïki ...experiment consists of ten 4-ha Permanent Sample Plots (PSPs) that were assigned to three silvicultural treatments in 1986 according to a random block design. In each plot, all trees with a girth at breast height greater than 30 cm were spatially located, numbered, measured, and determined botanically. Girth, mortality and newly recruited trees, were monitored almost annually over the 1982–2022 period with inventory campaigns for 35 years. The data were earlier used to fit growth and population models, to study the species composition dynamics, and the effect of silvicultural treatments on tree diversity and aboveground biomass. Here, we present new information on the forest stand structure dynamics and tree demography. The data released from this paper cover the three control plots and constitute a major contribution for further studies about the biodiversity of intact tropical forests.
1. Understanding the environmental determinants of forests deciduousness i.e. proportion of deciduous trees in a forest stand, is of great importance when predicting the impact of ongoing global ...climate change on forests. In this study, we examine (i) how forest deciduousness varies in relation to rainfall and geology, and (ii) whether the influence of geology on deciduousness could be related to differences in soil fertility and water content between geological substrates. 2. The study was conducted in mixed moist semi-deciduous forests in the northern part of the Congo basin. We modelled the response of forest deciduousness to the severity of the dry season across four contrasting geological substrates (sandstone, alluvium, metamorphic and basic rocks). For this, we combined information on forest composition at genus level based on commercial forest inventories (62 624 0.5 ha plots scattered over 6 million of ha), leaf habit, and rainfall and geological maps. We further examined whether substrates differ in soil fertility and water-holding capacity using soil data from 37 pits in an area that was, at the time, relatively unexplored. 3. Forest deciduousness increased with the severity of the dry season, and this increase strongly varied with the geological substrate. Geology was found to be three times more important than the rainfall regime in explaining the total variation in deciduousness. The four substrates differed in soil properties, with higher fertility and water-holding capacity on metamorphic and basic rocks than on sandstone and alluvium. The increase in forest deciduousness was stronger on the substrates that formed resource-rich clay soils (metamorphic and basic rocks) than on substrates that formed resource-poor sandy soils (sandstone and alluvium). 4. Synthesis. We found evidence that tropical forest deciduousness is the result of both the competitive advantage of deciduous species in climates with high rainfall seasonality, and the persistence of evergreen species on resource-poor soils. Our findings offer a clear illustration of wellknown theoretical leaf carbon economy models, explaining the patterns in the dominance of evergreen versus deciduous species. And, this large-scale assessment of the interaction between climate and geology in determining forest deciduousness may help to improve future predictions of vegetation distribution under climate change scenarios. In central Africa, forest is likely to respond differently to variation in rainfall and/or évapotranspiration depending on the geological substrate.
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