References of "Fayolle, Adeline"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailThe determinants of tropical forest deciduousness: disentangling the effects of rainfall and geology in central Africa
Ouedraogo, Dakis-Yaoba ULg; Fayolle, Adeline ULg; Gourlet-Fleury, Sylvie et al

in Journal of Ecology (2016)

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 ... [more ▼]

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 evapotranspiration depending on the geological substrate. [less ▲]

Detailed reference viewed: 29 (8 ULg)
Full Text
Peer Reviewed
See detailEnrichment of Central African logged forests with high-value tree species: testing a new approach to regenerating degraded forests
Doucet, Jean-Louis ULg; Daïnou, Kasso ULg; Ligot, Gauthier ULg et al

in International Journal of Biodiversity Science, Ecosystem Services and Management (2016)

In natural forests of Central Africa, several studies indicate a dramatic decrease in commercial trees, including species of concern for conservation. Enrichment planting with these species will favor ... [more ▼]

In natural forests of Central Africa, several studies indicate a dramatic decrease in commercial trees, including species of concern for conservation. Enrichment planting with these species will favor both the long-term recovery of their populations and biodiversity conservation in logged forests. In this study, we analyzed the survival and growth of 23 species in plantations. Fourteen 0.2–1.1 ha mixed species plantations consisting of single-species 15 × 15 m blocks were studied for 5 years in a logging concession of southeastern Cameroon. The plantation design considered both species light requirements and sensitivity to damage by pests. To identify the best species for enrichment planting, we assessed both species performance and plantation costs. We also tested for relationships between species traits and species performance. Mean annual diameter growth increments ranged from 1.67 to 42.9 mm. No significant relationship was found between growth and survival. Herbivory by wild Bovidae was the main cause of mortality and should be carefully considered in rehabilitation efforts. We found a significant negative relationship between wood density and maximum growth rate. The other traits tested were not good predictors of species performance in plantations. The two best-performing species, Triplochiton scleroxylon and Terminalia superba, could reach the minimum cutting diameter during a 30-year cutting cycle. Costs were high and mechanized site preparation is suggested to reduce them. Widespread adoption of such plantations will only occur if financial incentives or national regulations for assuring regeneration are implemented. [less ▲]

Detailed reference viewed: 35 (12 ULg)
Full Text
Peer Reviewed
See detailTaller trees, denser stands and greater biomass in semi-deciduous than in evergreen lowland central African forests
Fayolle, Adeline ULg; Loubota Panzou, Grâce Jopaul ULg; Drouet, Thomas et al

in Forest Ecology & Management (2016), 374

Accurate height-diameter allometry is crucial for the estimation of forest biomass and carbon stocks. Tree height measurements over a large range of diameters and species are urgently needed in the ... [more ▼]

Accurate height-diameter allometry is crucial for the estimation of forest biomass and carbon stocks. Tree height measurements over a large range of diameters and species are urgently needed in the tropics, specifically in central Africa, for the development of locally derived height-diameter allometric equations and the conversion of forest inventory data into biomass estimates, and for the validation of remotely sensed canopy height that mostly rely on a few specific field sites. In this study, we aimed to identify the variation in height-diameter allometry of tropical trees between forest types and among species in central Africa, and we examined the consequences for biomass estimation. Height and diameter were measured for a total of 521 trees over a large range of diameters in two forest types in southern Cameroon, 10–240 cm in the evergreen forest and 11–182 cm in the semi-deciduous forest. A total of ten allometric models including asymptotic and non-asymptotic models were fitted to the heightdiameter data. Measured tree diameters, grouped into 10 cm wide diameter classes up to 150, from commercial forest inventory data (0.5 ha plots, n = 2101 and n = 5152, respectively in the evergreen and in the semi-deciduous forests) were converted into biomass estimates using general allometric models with and without including our site-specific height-diameter allometry. Though debated in the literature, our results supported a saturation of tree height with tree diameter both at site and species level, with asymptotic models better depicting the height-diameter allometry. Height-diameter allometry significantly differed between forest types and these local height-diameter equations also differed from published equations. For a given diameter, trees tended to be taller in the semi-deciduous forest than in the evergreen forest, as already reported between moist and wet forests in pantropical studies. Similar trends were reported within species for the three species shared by both forest types, suggesting an environmental control of tree allometry. Because of the low performance of the bioclimatic stress variable to predict tree height and of the slight soil differences between the two forest types, the environmental determinants of height-diameter allometry remain to be explored. In addition to tree allometry variation, structural differences (basal area and density) were also identified between the two forest types using commercial forest inventory data at genus level, and both allometry and forest structure (taller trees and denser stands) contributed to the greater biomass per hectare of the semi-deciduous forest. [less ▲]

Detailed reference viewed: 29 (6 ULg)
Full Text
See detailL’aménagement forestier au Congo engendre-t-il plus de déforestation ?
Karsenty, Alain; Cerutti, P.; Doucet, Jean-Louis ULg et al

E-print/Working paper (2016)

Un article publié dans Land Use Policy début 2016 arrive à la conclusion a priori étonnante que la déforestation serait, au Congo, plus élevée dans les concessions forestières avec des plans d’aménagement ... [more ▼]

Un article publié dans Land Use Policy début 2016 arrive à la conclusion a priori étonnante que la déforestation serait, au Congo, plus élevée dans les concessions forestières avec des plans d’aménagement que dans celles qui n’en ont pas. L’analyse d’évaluation d’impact qui a conduit ces chercheurs à un tel résultat se base sur un appariement de parcelles sélectionnées aléatoirement dans des concessions avec et sans plans d’aménagement. Ces chercheurs indiquent que le réseau de routes forestières plus développé dans les concessions aménagées serait un des facteurs explicatifs. L’autre facteur serait le développement local lié aux cahiers des charges des plans d’aménagement, lequel conduirait à une augmentation de la population dans ces concessions et à une déforestation accrue. Notre groupe d’une vingtaine de chercheurs connaissant bien la problématique de l’aménagement forestier en Afrique centrale s’est penché à son tour sur cette question et a analysé la déforestation au niveau des concessions sur le même intervalle de temps. Nos résultats montrent, cette fois, que la déforestation est moins importante dans les concessions avec un plan d’aménagement que dans les autres. Et si l’on compare à production égale la déforestation dans des concessions avec et sans plan d’aménagement, il apparaît que les UFA aménagées sont environ deux fois plus « efficaces », c’est-à-dire qu’on observe deux fois moins de perte de couvert forestier par mètre-cube produit. Nous en concluons qu’il est nécessaire d’analyser précisément la dynamique des différents facteurs de déforestation, et éviter d’imputer mécaniquement à l’aménagement forestier un rôle excessif dans l’évolution dans un sens ou dans l’autre du taux de déboisement. Enfin, toute évaluation doit rappeler que les effets de l’aménagement forestier doivent être mesurés sur le long terme : l’objectif de l’aménagement est de permettre une mise en valeur forestière durable, en conservant l’essentiel du capital productif pour éviter, autant que possible, la conversion à d’autres usages après les cycles de coupe initiaux. [less ▲]

Detailed reference viewed: 74 (4 ULg)
Full Text
See detailBiomass and carbon stocks of tropical African forests: synthesis and perspectives
Loubota Panzou, Grâce Jopaul ULg; Doucet, Jean-Louis ULg; Loumeto, Jean-Joël et al

Poster (2015, November 26)

Quantifying the biomass and carbon stocks contained in tropical forests has become an international priority for the implementation of the REDD+ mechanism. Forest biomass is estimated through three ... [more ▼]

Quantifying the biomass and carbon stocks contained in tropical forests has become an international priority for the implementation of the REDD+ mechanism. Forest biomass is estimated through three successive levels: the tree, the stand and the region level. This study reviews the state of the art on the estimation of biomass and carbon stocks contained in tropical African forests. This review highlights that only few allometric equations, equations used for estimating biomass of the tree from non-destructive measurements (diameter, height), have been established for tropical African forests. At the stand level, this synthesis highlights the spatial and temporal variations in biomass between forests types in Central and Eastern Africa. While biomass recovery after disturbance (logging for instance) is rather quick, there is still a lot of uncertainity on the spatial variation in biomass, and there is no consensus on a regional biomass map. The quality of biomass mapping in tropical Africa stronly depends on the various sensors used (optical, RADAR or LIDAR), the allometric equation used to convert forest inventory data and sampling design. Based on the lack of precision of available allometric equations and forest inventory data a large spatial scale, many uncertainties persist on estimating the biomass and carbon stocks contained in the African tropical forests. It is important to develop reference sites (both allometry and forest inventory) to provide accurate biomass estimates for an effective implementation of the REDD+. [less ▲]

Detailed reference viewed: 78 (6 ULg)
Full Text
Peer Reviewed
See detailWood Specific Gravity Variations and Biomass of Central African Tree Species: The Simple Choice of the Outer Wood
Bastin, Jean-François ULg; Fayolle, Adeline ULg; Tarelkin, Yegor et al

in PLoS ONE (2015)

Context: Wood specific gravity is a key element in tropical forest ecology. It integrates many aspects of tree mechanical properties and functioning and is an important predictor of tree biomass. Wood ... [more ▼]

Context: Wood specific gravity is a key element in tropical forest ecology. It integrates many aspects of tree mechanical properties and functioning and is an important predictor of tree biomass. Wood specific gravity varies widely among and within species and also within individual trees. Notably, contrasted patterns of radial variation of wood specific gravity have been demonstrated and related to regeneration guilds (light demanding vs. shade-bearing). However, although being repeatedly invoked as a potential source of error when estimating the biomass of trees, both intraspecific and radial variations remain little studied. In this study we characterized detailed pith-to-bark wood specific gravity profiles among contrasted species prominently contributing to the biomass of the forest, i.e., the dominant species, and we quantified the consequences of such variations on the biomass. Methods: Radial profiles of wood density at 8% moisture content were compiled for 14 dominant species in the Democratic Republic of Congo, adapting a unique 3D X-ray scanning technique at very high spatial resolution on core samples. Mean wood density estimates were validated by water displacement measurements. Wood density profiles were converted to wood specific gravity and linear mixed models were used to decompose the radial variance. Potential errors in biomass estimation were assessed by comparing the biomass estimated from the wood specific gravity measured from pith-to-bark profiles, from global repositories, and from partial information (outer wood or inner wood). Results: Wood specific gravity profiles from pith-to-bark presented positive, neutral and negative trends. Positive trends mainly characterized light-demanding species, increasing up to 1.8 g.cm-3 per meter for Piptadeniastrum africanum, and negative trends characterized shade-bearing species, decreasing up to 1 g.cm-3 per meter for Strombosia pustulata. The linear mixed model showed the greater part of wood specific gravity variance was explained by species only (45%) followed by a redundant part between species and regeneration guilds (36%). Despite substantial variation in wood specific gravity profiles among species and regeneration guilds, we found that values from the outer wood were strongly correlated to values from the whole profile, without any significant bias. In addition, we found that wood specific gravity from the DRYAD global repository may strongly differ depending on the species (up to 40% for Dialium pachyphyllum). Main conclusion: Therefore, when estimating forest biomass in specific sites, we recommend the systematic collection of outer wood samples on dominant species. This should prevent the main errors in biomass estimations resulting from wood specific gravity and allow for the collection of new information to explore the intraspecific variation of mechanical properties of trees. [less ▲]

Detailed reference viewed: 43 (6 ULg)
Full Text
See detailThe last 1,000 years in the Northern Congo Basin
Morin, Julie ULg; Fayolle, Adeline ULg; Favier, Charly et al

Conference (2015, November)

Review of the events that happened in the northern Congo basin during the last 1,000 yr. Positive impact of human disturbances on the regeneration of light-demanding trees. Negative impact of the European ... [more ▼]

Review of the events that happened in the northern Congo basin during the last 1,000 yr. Positive impact of human disturbances on the regeneration of light-demanding trees. Negative impact of the European colonization and following events on human populations and tree regeneration. [less ▲]

Detailed reference viewed: 22 (4 ULg)
Full Text
Peer Reviewed
See detailSeeing Central African forests through their largest trees
Bastin, Jean-François ULg; Barbier, Nicolas; Réjou-Méchain, Maxime et al

in Scientific Reports (2015)

Large tropical trees and a few dominant species were recently identified as the main structuring elements of tropical forests. However, such result did not translate yet into quantitative approaches which ... [more ▼]

Large tropical trees and a few dominant species were recently identified as the main structuring elements of tropical forests. However, such result did not translate yet into quantitative approaches which are essential to understand, predict and monitor forest functions and composition over large, often poorly accessible territories. Here we show that the above-ground biomass (AGB) of the whole forest can be predicted from a few large trees and that the relationship is proved strikingly stable in 175 1-ha plots investigated across 8 sites spanning Central Africa. We designed a generic model predicting AGB with an error of 14% when based on only 5% of the stems, which points to universality in forest structural properties. For the first time in Africa, we identified some dominant species that disproportionally contribute to forest AGB with 1.5% of recorded species accounting for over 50% of the stock of AGB. Consequently, focusing on large trees and dominant species provides precise information on the whole forest stand. This offers new perspectives for understanding the functioning of tropical forests and opens new doors for the development of innovative monitoring strategies. [less ▲]

Detailed reference viewed: 132 (21 ULg)
Full Text
See detailLate-Holocene tropical moist-forests of southeastern Cameroon: some insight from soil charcoal analysis
Morin, Julie ULg; Biwolé, Achille; Bourland, Nils et al

Conference (2015, August)

Tropical forests of Central Africa constitute the second most important block of moist forest of the world. Little is known, however, about past vegetation in this region that remains underexplored ... [more ▼]

Tropical forests of Central Africa constitute the second most important block of moist forest of the world. Little is known, however, about past vegetation in this region that remains underexplored (Vleminckx et al. 2014; Morin-Rivat et al. 2014). Determining the past specific composition of these forests could allow bringing insights into their evolution over time and providing data about their resilience capacity facing global change. We performed a pedoanthracological analysis in the semi-deciduous forests of southeastern Cameroon. We excavated 53 test pits of 53 50 × 50 × 60 cm in plots of botanical inventory along a NS 80-km long mega-transect that followed a vegetation gradient. We sorted and quantified charred macrobotanical remains by layers of 10 cm, then identified species from wood charcoals. We used the InsideWood database, implemented with 163 new anatomical descriptions of woods present in the study area by using the reference collection of African woods of the Royal Museum for Central Africa (Belgium). Finally, we obtained 25 radiocarbon dates on charcoals and oil palm endocarps. Results showed that repeated fire events occurred across the study area during the last 2500 years, soon after the well-documented “rainforest crisis” (e.g. Lézine et al. 2013). The analyzed charcoals are likely human-induced regarding evidence of associated human settlements (e.g. potsherds). Aged were distributed into two time periods: the Early Iron Age (2300-1300 BP) and the Late Iron Age (700-100 BP) with an intermediate hiatus in human occupation (see e.g. Wotzka 2006; Morin-Rivat et al. 2014). Specific composition during both periods did not strongly differ from current composition, which is now dominated by light-demanding canopy trees belonging to old-growth semi-deciduous Celtis forests (Gond et al. 2013; Fayolle et al. 2014). This argues in favor of the maintenance of light-demanding tree species by anthropogenic activities, such as slash-and-burn shifting cultivation. We conclude that moist forests have a good resilience capacity regarding moderate and scattered disturbances. These forests can nonetheless be deeply impacted by land-use intensification (e.g. degraded forests along roads and close to cities; Gond et al. 2013). [less ▲]

Detailed reference viewed: 25 (3 ULg)
Full Text
See detailContributing to wood anatomical databases to improve species identification, phylogeny and functional trait research in Central Africa
Morin, Julie ULg; Fayolle, Adeline ULg; De Ridder, Maaike et al

Poster (2015, May 26)

Central African rainforests shelter a high number of woody species that are anatomically very different. Knowledge of taxon-specific wood anatomical features has proven indispensable for scientific and ... [more ▼]

Central African rainforests shelter a high number of woody species that are anatomically very different. Knowledge of taxon-specific wood anatomical features has proven indispensable for scientific and non-scientific applications. The field of wood anatomy and identification has been drastically revolutionized by the development of internationally recognized lists of precisely illustrated microscopic features (e.g. IAWA Committee 1989), together with the launch of InsideWood, an online search database using these features to narrow down identification results (e.g. Wheeler 2011). However, despite these massive efforts, the anatomy of many species or even genera remains in the dark, especially in species-rich regions. Wood anatomy has been formally described for less than 25% of the Central African woody species (Hubau et al. 2012), the focus has been mainly on timber species and variations in wood anatomical structure remain to be explored. Therefore, we are assembling a wood anatomical database of about 800 species covering the Guineo-Congolian region using material from InsideWood and the Tervuren xylarium (new descriptions). As such, we present how large anatomical databases hold interesting perspectives for (i) wood and charcoal identification, (ii) exploring the phylogenetic signal of wood anatomy, and (iii) the relationship between wood anatomical features and functional traits. [less ▲]

Detailed reference viewed: 29 (3 ULg)
Full Text
See detailFiches techniques de mesure de la biomasse
Bauwens, Sébastien ULg; Fayolle, Adeline ULg; Dubiez, Emilien et al

Report (2015)

Detailed reference viewed: 46 (7 ULg)
Full Text
See detailHigh spatial resolution of late-Holocene human activities in the moist forests of Central Africa using soil charcoal and charred botanical remains
Morin, Julie ULg; Biwolé, Achille; Gorel, Anaïs ULg et al

Conference (2015, April 27)

Palaeoecological and archaeological studies have demonstrated that human populations have long inhabited the moist forests of central Africa. However, spatial and temporal patterns of human activities ... [more ▼]

Palaeoecological and archaeological studies have demonstrated that human populations have long inhabited the moist forests of central Africa. However, spatial and temporal patterns of human activities have hardly been investigated with satisfactory accuracy. In this study, we propose to characterize past human activities at local scale by using a systematic quantitative and qualitative methodology based on soil charcoal and charred botanical remains. A total of 88 equidistant test-pits were excavated along six transects in two contrasting forest types in southern Cameroon. Charred botanical remains were collected by water-sieving and sorted by type (wood charcoals, oil palm endocarps, and unidentified seeds). A total of 50 Accelerator Mass Spectrometry 14C dates were also obtained. Results showed that charred macroremains were found at multiple places in the forest, suggesting scattered human activities, which were distributed into two main periods (Phase A: 2300-1300 BP – Phase B: 580 BP to the present). Charred botanical remains indicated two types of land use: (i) domestic, with oil palm endocarps most often associated with potsherds (villages) and (ii) agricultural, with charcoal as probable remnant of slash-and-burn cultivation (fields). Oil palm endocarp abundance decreased with distance from the identified human settlements. Our methodology allowed documenting, at high resolution, the spatial and temporal patterns of human activities in central African moist forests and could be applied to other tropical contexts. [less ▲]

Detailed reference viewed: 18 (4 ULg)
Full Text
See detailNineteenth century human history explains the dominance of light-demanding tree species in Central African moist forests
Morin, Julie ULg; Fayolle, Adeline ULg; Favier, Charly et al

Poster (2015, March 21)

The canopy of central African moist forests is dominated by light-demanding trees. Most of these species show a distribution of diameters that indicates a regeneration shortage. Here we show through the ... [more ▼]

The canopy of central African moist forests is dominated by light-demanding trees. Most of these species show a distribution of diameters that indicates a regeneration shortage. Here we show through the combined analysis of botanical, palaeoecological, archaeological and historical data that most of these trees are not older than ca. 180 years. This age corresponds to the early 19th century (around 1830) when the slave-raiding, the interethnic wars and the colonization of the inlands by the Europeans disturbed the human spatial occupancy. After 1885, the spatial clumping of people and villages along the main communication axes induced less itinerancy in the forest. We believe that former activities such as shifting cultivation created scattered openings in the canopy, large enough to allow light-demanding trees to establish. Nowadays, common logging operations do not create openings sufficiently large for the regeneration of these high value timber species. Our findings emphasize the need to include considerations about the history of human spatial occupancy and activities to understand forest dynamics. We need silvicultural guidelines adapted to the autecology of the species. Population enforcements (e.g. enrichment) will be needed to ensure the sustainability of timber yields in forests dominated by long-lived light-demanding trees. [less ▲]

Detailed reference viewed: 15 (2 ULg)
See detailThe need for site-specific height-diameter allometry of Central African moist forests
Loubota Panzou, Grâce Jopaul ULg; Doucet, Jean-Louis ULg; Fayolle, Adeline ULg

Conference (2015, March 21)

L’utilisation de l’allométrie hauteur-diamètre globale ou régionale en milieu tropical pourrait avoir des conséquences importantes dans les estimations de biomasse et des stocks de carbone. L’objectif de ... [more ▼]

L’utilisation de l’allométrie hauteur-diamètre globale ou régionale en milieu tropical pourrait avoir des conséquences importantes dans les estimations de biomasse et des stocks de carbone. L’objectif de ce travail est d’identifier les variations de l’allométrie hauteur-diamètre au sein de deux types de forêts (forêt sempervirente et forêt semi-décidue) au sud du Cameroun et d’examiner leurs conséquences sur les estimations de biomasse. Le diamètre et la hauteur ont été mesurés sur un total de 521 arbres appartenant à 15 espèces et couvrant une gamme de diamètre de 10 à 240 cm. Une calibration des mesures non destructives et destructives de la hauteur a été réalisée sur 60 arbres. Dix modèles allométriques ont été ajustés sur ces données. Le meilleur modèle a été sélectionné avec Akaike Information Criterion (AIC). L’allométrie hauteur-diamètre au niveau des sites et entre les espèces a montré une tendance asymptotique (Modèle de Michaelis-Menten). Pour un même diamètre, les arbres étaient plus hauts dans les forêts semi-décidues que dans les forêts sempervirentes. Les différences de biomasse entre les deux types de forêts sont dues par les variations de l’allométrie hauteur-diamètre. Les variations de l’allométrie hauteur-diamètre sont donc d’une extrême importance dans les estimations de biomasse et des stocks de carbone des forêts denses humides tropicales d’Afrique centrale. [less ▲]

Detailed reference viewed: 96 (17 ULg)
Full Text
See detailSite-specific height-diameter allometry of Central African moist forests
Loubota Panzou, Grâce Jopaul ULg; Doucet, Jean-Louis ULg; Fayolle, Adeline ULg

Poster (2015, February 04)

In this study we aimed to identify the variation in height-diameter allometry between forest types and among species in Central African moist forests. We also examined the consequences on biomass ... [more ▼]

In this study we aimed to identify the variation in height-diameter allometry between forest types and among species in Central African moist forests. We also examined the consequences on biomass estimation. Two forest sites in southern Cameroon with contrasting levels of deciduousness. Height and diameter were measured for a total of 521 trees belonging to 12 timber species over a large range of diameter, 10-240 cm for the Ma’an site and 11-182 cm for the Mindourou site. Non-destructive height measurements were calibrated with destructive measurements for a total of 60 trees, 30 in each site. Commercial forest inventory data (n=7253 0.5ha plots) were gathered for the Ma’an (n=34 samples and 2101 plots) and Mindourou (n=117 samples and 5152 plots) sites. A total of ten allometric models (including asymptotic and non-asymptotic models) were fitted to the height-diameter data at species (n=12) and site (n=2) level. Biomass estimates were computed based on forest inventory data and general allometric models using both site-specific and published height-diameter equations. Given the strong correlation between the non-destructive and destructive height measurements we had confidence in using the non-destructive height measurements to establish site- and species-specific height-diameter allometric equations. The height measurements performed over a wide range of diameters, 10-240 cm, tended to support an asymptotic shape (and most often the Michaelis Menten model) for the height-diameter allometry either at species and site level. We identified a significant difference in height-diameter allometry between the two study sites. For a given diameter, trees tended to be taller in the more semi-deciduous Mindourou site than in the more evergreen Ma’an site, with a maximum height of 39.5 and 46.5 m, respectively. The two sites significantly differed in stand structure and biomass. This difference is due to the variation in height-diameter allometry. Height-diameter allometry strongly varies between sites and site-specific height-diameter allometric equations should be developed to further improve the estimation of biomass and carbon stock contained in tropical forests. [less ▲]

Detailed reference viewed: 151 (45 ULg)
Full Text
Peer Reviewed
See detailDifferential Performance between Two Timber Species in Forest Logging Gaps and in Plantations in Central Africa
Fayolle, Adeline ULg; Ouedraogo, Dakis-Yaoba ULg; Ligot, Gauthier ULg et al

in Forests (2015), 6(2), 380-394

To develop silvicultural guidelines for high-value timber species of Central African moist forests, we assessed the performance of the pioneer Milicia excelsa (iroko, Moraceae), and of the non-pioneer ... [more ▼]

To develop silvicultural guidelines for high-value timber species of Central African moist forests, we assessed the performance of the pioneer Milicia excelsa (iroko, Moraceae), and of the non-pioneer light demander Pericopsis elata (assamela, Fabaceae) in logging gaps and in plantations in highly degraded areas in south-eastern Cameroon. The survival and size of each seedling was regularly monitored in the silvicultural experiments. Differences in performance and allometry were tested between species in logging gaps and in plantations. The two species performance in logging gaps was significantly different from plantations and concurred with the expectations of the performance trade-off hypothesis but not with the expectations of species light requirements. The pioneer M. excelsa survived significantly better in logging gaps while the non-pioneer P. elata grew significantly faster in plantations. The high mortality and slow growth of M. excelsa in plantations is surprising for a pioneer species but could be explained by herbivory (attacks from a gall-making psyllid). Identifying high-value native timber species (i) with good performance in plantations such as P. elata is of importance to restore degraded areas; and (ii) with good performance in logging gaps such as M. excelsa is of importance to maintain timber resources and biodiversity in production forests. [less ▲]

Detailed reference viewed: 28 (5 ULg)
Full Text
See detailIdentification of charred botanical remains provides more accurate information on past history in Central Africa
Morin, Julie ULg; Biwolé, Achille; Bourland, Nils et al

Poster (2015, January 30)

In palaeoenvironmental studies, charred botanical remains have rarely been identified to the species level before being sent to radiocarbon dating. Moreover, the age of most tropical spp. and thereby the ... [more ▼]

In palaeoenvironmental studies, charred botanical remains have rarely been identified to the species level before being sent to radiocarbon dating. Moreover, the age of most tropical spp. and thereby the age of the carbon sequestered during plant growth is not known. Dating unidentified charred wood in the tropics should be thus treated with caution because the accuracy of the dates is not guaranteed. Here we present 71 dates obtained on charred endocarps and wood charcoals sampled in soil pits in Cameroon and in the Rep. of the Congo. We taxonomically identified 43 samples then selected both identified and unidentified individual fragments for radiocarbon dating. We performed summed probability distributions of the dates calibrated in BP for the 43 identified and the 28 unidentified samples separately then for the whole dates. Results showed that the dates obtained on unidentified samples better fit the established chronology for Central Africa but that they also presented less precise standard deviations than the dates obtained on identified short-lived material, and that the dates on identified samples provide more detailed trends about the phases of human occupation in Central Africa after 2,500 BP. We can assume that dating unidentified material may introduce some blur into chronologies and that the selection of identified charred botanical remains should be systematically applied for palaeoenvironmental reconstructions in tropical contexts to refine the chronologies. [less ▲]

Detailed reference viewed: 13 (2 ULg)
Full Text
Peer Reviewed
See detailHow Tightly Linked Are Pericopsis elata (Fabaceae) Patches to Anthropogenic Disturbances in Southeastern Cameroon?
Bourland, Nils; Cerisier, François; Daïnou, Kasso ULg et al

in Forests (2015), 6(2), 293-310

While most past studies have emphasized the relationships between specific forest stands and edaphic factors, recent observations in Central African moist forests suggested that an increase of slash-and ... [more ▼]

While most past studies have emphasized the relationships between specific forest stands and edaphic factors, recent observations in Central African moist forests suggested that an increase of slash-and-burn agriculture since 3000–2000 BP (Before Present) could be the main driver of the persistence of light-demanding tree species. In order to examine anthropogenic factors in the persistence of such populations, our study focused on Pericopsis elata, an endangered clustered timber species. We used a multidisciplinary approach comprised of botanical, anthracological and archaeobotanical investigations to compare P. elata patches with surrounding stands of mixed forest vegetation (“out-zones”). Charcoal samples were found in both zones, but were significantly more abundant in the soils of patches. Eleven groups of taxa were identified from the charcoals, most of them also present in the current vegetation. Potsherds were detected only inside P. elata patches and at different soil depths, suggesting a long human presence from at least 2150 to 195 BP, as revealed by our charcoal radiocarbon dating. We conclude that current P. elata patches most likely result from shifting cultivation that occurred ca. two centuries ago. The implications of our findings for the dynamics and management of light-demanding tree species are discussed. [less ▲]

Detailed reference viewed: 43 (7 ULg)
Full Text
Peer Reviewed
See detailLight Response of Seedlings of a Central African Timber Tree Species, Lophira alata (Ochnaceae), and the Definition of Light Requirements
Biwolé, Achille Bernard; Daïnou, Kasso ULg; Fayolle, Adeline ULg et al

in Biotropica (2015), 47(6), 681-688

Light is of primary importance in structuring tropical tree communities. Light exposure at seedling and adult stages has been used to characterize the ecological profile of tropical trees, with many ... [more ▼]

Light is of primary importance in structuring tropical tree communities. Light exposure at seedling and adult stages has been used to characterize the ecological profile of tropical trees, with many implications in forest management and restoration ecology. Most shadetolerance classification systems have been proposed based on empirical observations in a specific area and thus result in contradictions among categories assigned to a given species. In this study, we aimed to quantify the light requirements for seedling growth of a Central African timber tree, Lophira alata (Ochnaceae), taking into account effects of population origin. In two controlled experiments: a light response experiment and a comparative population experiment, conducted in southwestern Cameroon, using seeds collected from four populations (three from Cameroon and one from Gabon), we examined the quantitative responses to irradiance of seedlings. After 2 years, mortality was very low (<3%), even in extremely low irradiance. Growth and biomass allocation patterns varied in response to light, with intermediate irradiance (24–43%) providing optimal conditions. Light response differed between populations. The Boumba population in the northeastern edge of the species’ distribution exhibited the highest light requirements, suggesting a local adaptation. As a result of positive growth at low irradiance and maximum growth at intermediate irradiance, we concluded that L. alata exhibits characteristics of both non-pioneer and pioneer species. Implications of our results to propose an objective way to assign the light requirement for tropical tree species are discussed. [less ▲]

Detailed reference viewed: 22 (5 ULg)
Full Text
Peer Reviewed
See detailNew data on the recent history of the littoral forests of southern Cameroon: an insight into the role of historical human disturbances on the current forest composition
Biwolé, Achille ULg; Morin-Rivat, Julie ULg; Fayolle, Adeline ULg et al

in Plant Ecology and Evolution (2015), 148(1), 19-28

Background and aims – Prior to European colonisation of Central Africa, human populations were dispersed through the forests, where they practiced slash-and-burn cultivation. From the 19th century they ... [more ▼]

Background and aims – Prior to European colonisation of Central Africa, human populations were dispersed through the forests, where they practiced slash-and-burn cultivation. From the 19th century they were progressively concentrated in villages along roads, leaving large areas of forest derelict. In south-western Cameroon, and elsewhere in Central Africa, forest canopy is dominated by long-lived lightdemanding tree species, suggesting a possible role of human disturbance. The aim of this study was to bring new insights into the possible effect of historical human disturbances in terms of timing and spatial extent on the current forest composition. Location – Wet evergreen littoral forest in south-western Cameroon. Methods and key results – A combined vegetation sampling and archaeobotanical survey were conducted. Potsherds, oil-palm endocarps, and charcoal were found throughout the study area, suggesting generalised human occupation and anthropogenic fire. Human occupancy occurred in two periods: between 2200 and 1500 BP, and, more recently, beginning three centuries ago. High frequency of fire and the presence of Elaeis guineensis both dated recently (between 260 and 145 BP) suggest slash-and-burn shifting cultivation practices. These human-induced disturbances may coincide with the age of the current emergent lightdemanding species, the age of which can be estimated around 200 years, or with the phases of drying climate recorded in the Central African forest in the early 18th century. Conclusions – These results support the idea that historical human disturbances are one of the major factors that shaped the current forest composition in Central Africa. [less ▲]

Detailed reference viewed: 114 (39 ULg)