References of "Gourlet-Fleury, Sylvie"
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See detailTree growth and mortality of 42 timber species in central Africa
Ligot, Gauthier ULiege; Gourlet-Fleury, Sylvie; Daïnou, Kasso ULiege et al

in Forest Ecology and Management (2022), 505

Tree growth and mortality are two central processes in the functioning of mixed and structurally complex moist tropical forests. The outcome of these processes is usually predicted using estimates of tree ... [more ▼]

Tree growth and mortality are two central processes in the functioning of mixed and structurally complex moist tropical forests. The outcome of these processes is usually predicted using estimates of tree growth and mortality rates. Nevertheless, the accurate estimates of these parameters are still scarce which impedes our ability to predict forest evolution and build reliable management plans. To partly fill this gap, we carried out the permanent monitoring of 21,180 trees belonging to 42 species that are exploited for timber production in central Africa. Besides reporting new species-specific estimates of diameter increments and mortality rates, we aimed to evaluate how tree growth varies with tree size and logging history. Additionally, we discussed our results in regards to the reference values of diameter increments, mortality rates and minimum cutting diameters that are used to build forest management plans. Diameter increment was found to significantly depend on tree size for the majority of the studied species. The significant relationships between diameter increment and tree size were mostly hump-back shaped. The trees with a diameter close to or lower than the reference minimum cutting diameter were growing faster than the average. Moreover, we found that tree growth was reduced during 1-2 years after timber exploitation and then spurred during at least 5 years. Such tree growth response to logging was nevertheless species-specific. This study provided new estimates of tree growth and mortality rates that could help performing more accurate forest projections and establish sustainable management plans. [less ▲]

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See detailA 3D approach to model the taper of irregular tree stems: making plots biomass estimates comparable in tropical forests
Bauwens, Sébastien ULiege; Ploton, Pierre; Fayolle, Adeline ULiege et al

in Ecological Applications (2021)

In tropical forests, the high proportion of trees showing irregularities at the stem base complicates forest monitoring. For example, in the presence of buttresses, the height of the point of measurement ... [more ▼]

In tropical forests, the high proportion of trees showing irregularities at the stem base complicates forest monitoring. For example, in the presence of buttresses, the height of the point of measurement (HPOM) of the stem diameter (DPOM) is raised from 1.3 m, the standard breast height, up to a regular part of the stem. While DPOM is the most important predictor for tree aboveground biomass (AGB) estimates, the lack of harmonized HPOM for irregular trees in forest inventory increases the uncertainty in plot-level AGB stock and stock change estimates. In this study, we gathered an original non-destructive 3D dataset collected with terrestrial laser scanning and close range terrestrial photogrammetry tools in three sites in central Africa. For the 228 irregularly shaped stems sampled, we developed a set of taper models to harmonize HPOM by predicting the equivalent diameter at breast height (DBH’) from a DPOM measured at any height. We analyzed the effect of using DBH’ on tree-level and plot-level AGB estimates. To do so, we used destructive AGB data for 140 trees and forest inventory data from eight 1-ha-plots in the Republic of Congo. Our results showed that our best simple taper model predicts DBH’ with a relative mean absolute error of 3.7% (R²=0.98) over a wide DPOM range of 17 to 249 cm. Based on destructive AGB data, we found that the AGB allometric model calibrated with harmonized HPOM data was more accurate than the conventional local and pantropical models. At the plot level, the comparison of AGB stock estimates with and without HPOM harmonization showed an increasing divergence with the increasing share of irregular stems (up to -15%). The harmonization procedure developed in this study could be implemented as a standard practice for AGB monitoring in tropical forests as no additional forest inventory measurements is required. This would probably lead to important revisions of the AGB stock estimates in regions having a large number of irregular tree stems and increase their carbon sink estimates. The growing use of 3D data offers new opportunities to extend our approach and further develop general taper models in other tropical regions. [less ▲]

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See detailTaking the pulse of Earth’s tropical forests using networks of highly distributed plots
ForestPlots.net; Blundo, Cecilia; Carilla, Julieta et al

in Biological Conservation (2021), 260

Tropical forests are the most diverse and productive ecosystems on Earth. While better understanding of these forests is critical for our collective future, until quite recently efforts to measure and ... [more ▼]

Tropical forests are the most diverse and productive ecosystems on Earth. While better understanding of these forests is critical for our collective future, until quite recently efforts to measure and monitor them have been largely disconnected. Networking is essential to discover the answers to questions that transcend borders and the horizons of funding agencies. Here we show how a global community is responding to the challenges of tropical ecosystem research with diverse teams measuring forests tree-by-tree in thousands of long-term plots. We review the major scientific discoveries of this work and show how this process is changing tropical forest science. Our core approach involves linking long-term grassroots initiatives with standardized protocols and data management to generate robust scaled-up results. By connecting tropical researchers and elevating their status, our Social Research Network model recognises the key role of the data originator in scientific discovery. Conceived in 1999 with RAINFOR (South America), our permanent plot networks have been adapted to Africa (AfriTRON) and Southeast Asia (T-FORCES) and widely emulated worldwide. Now these multiple initiatives are integrated via ForestPlots.net cyber-infrastructure, linking colleagues from 54 countries across 24 plot networks. Collectively these are transforming understanding of tropical forests and their biospheric role. Together we have discovered how, where and why forest carbon and biodiversity are responding to climate change, and how they feedback on it. This long-term pan-tropical collaboration has revealed a large long-term carbon sink and its trends, as well as making clear which drivers are most important, which forest processes are affected, where they are changing, what the lags are, and the likely future responses of tropical forests as the climate continues to change. By leveraging a remarkably old technology, plot networks are sparking a very modern revolution in tropical forest science. In the future, humanity can benefit greatly by nurturing the grassroots communities now collectively capable of generating unique, long-term understanding of Earth’s most precious forests. [less ▲]

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See detailUnveiling African rainforest composition and vulnerability to global change
Réjou-Méchain, Maxime; Mortier, Frédéric; Bastin, Jean-François ULiege et al

in Nature (2021)

Africa is forecasted to experience large and rapid climate change1 and population growth2 during the twenty-first century, which threatens the world’s second largest rainforest. Protecting and sustainably ... [more ▼]

Africa is forecasted to experience large and rapid climate change1 and population growth2 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. [less ▲]

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See detailA map of African humid tropical forest aboveground biomass derived from management inventories
Ploton, Pierre; Mortier, Frédéric; Barbier, Nicolas et al

in Scientific Data (2020), 7(221),

Forest biomass is key in Earth carbon cycle and climate system, and thus under intense scrutiny in the context of international climate change mitigation initiatives (e.g. REDD+). In tropical forests, the ... [more ▼]

Forest biomass is key in Earth carbon cycle and climate system, and thus under intense scrutiny in the context of international climate change mitigation initiatives (e.g. REDD+). In tropical forests, the spatial distribution of aboveground biomass (AGB) remains, however, highly uncertain. There is increasing recognition that progress is strongly limited by the lack of field observations over large and remote areas. Here, we introduce the Congo basin Forests AGB (CoFor-AGB) dataset that contains AGB estimations and associated uncertainty for 59,857 1-km pixels aggregated from nearly 100,000 ha of in situ forest management inventories for the 2000 – early 2010s period in five central African countries. A comprehensive error propagation scheme suggests that the uncertainty on AGB estimations derived from c. 0.5-ha inventory plots (8.6–15.0%) is only moderately higher than the error obtained from scientific sampling plots (8.3%). CoFor-AGB provides the first large scale view of forest AGB spatial variation from field data in central Africa, the second largest continuous tropical forest domain of the world. [less ▲]

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See detailSentiers de suivi de la croissance, de la mortalité et de la phénologie des arbres tropicaux : Guide méthodologique
Tosso, Dji-ndé Félicien ULiege; Daïnou, Kasso ULiege; Sonké, Bonaventure et al

Book published by Presses Universitaires de Liège (2020)

La durabilité de l’aménagement des forêts naturelles d’Afrique centrale est tributaire d’une connaissance approfondie de la dynamique démographique des populations d’arbres commerciaux. Cette dynamique ... [more ▼]

La durabilité de l’aménagement des forêts naturelles d’Afrique centrale est tributaire d’une connaissance approfondie de la dynamique démographique des populations d’arbres commerciaux. Cette dynamique est étudiée dans des dispositifs destinés à être suivis sur le long terme, dénommés parcelles et sentiers. Si la démarche méthodologique d’installation et de suivi des parcelles est assez bien documentée, celle des sentiers l’est moins. Le présent ouvrage vient combler ce vide en capitalisant l’expérience accumulée depuis plus de 20 ans par les membres du collectif DYNAFAC, un collectif créé à l’initiative de l’ATIBT, du CIRAD, de Nature+ et de Gembloux Agro-Bio Tech. Il s’agit d’un guide pratique et illustré explicitant la démarche nécessaire à l’installation et au suivi de ces sentiers. Outre les procédures techniques, le guide évalue également les coûts en tenant compte des spécificités économiques de différents pays de la sous-région. En s’adressant à l’ensemble des parties prenantes de l’aménagement et de la gestion des forêts d’Afrique, l’ouvrage a pour ambition de promouvoir la mise en œuvre de dispositifs robustes et efficients à la portée de tous. [less ▲]

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See detailAsynchronous carbon sink saturation in African and Amazonian tropical forests
Hubau, Wannes; Lewis, Simon L.; Phillips, Oliver L. et al

in Nature (2020), 579

Structurally intact tropical forests sequestered about half of the global terrestrial carbon uptake over the 1990s and early 2000s, removing about 15 per cent of anthropogenic carbon dioxide emissions1–3 ... [more ▼]

Structurally intact tropical forests sequestered about half of the global terrestrial carbon uptake over the 1990s and early 2000s, removing about 15 per cent of anthropogenic carbon dioxide emissions1–3. Climate-driven vegetation models typically predict that this tropical forest ‘carbon sink’ will continue for decades4,5. Here we assess trends in the carbon sink using 244 structurally intact African tropical forests spanning 11 countries, compare them with 321 published plots from Amazonia and investigate the underlying drivers of the trends. The carbon sink in live aboveground biomass in intact African tropical forests has been stable for the three decades to 2015, at 0.66 tonnes of carbon per hectare per year (95 per cent confidence interval 0.53–0.79), in contrast to the long-term decline in Amazonian forests6. Therefore the carbon sink responses of Earth’s two largest expanses of tropical forest have diverged. The difference is largely driven by carbon losses from tree mortality, with no detectable multi-decadal trend in Africa and a long-term increase in Amazonia. Both continents show increasing tree growth, consistent with the expected net effect of rising atmospheric carbon dioxide and air temperature7–9. Despite the past stability of the African carbon sink, our most intensively monitored plots suggest a post-2010 increase in carbon losses, delayed compared to Amazonia, indicating asynchronous carbon sink saturation on the two continents. A statistical model including carbon dioxide, temperature, drought and forest dynamics accounts for the observed trends and indicates a long-term future decline in the African sink, whereas the Amazonian sink continues to weaken rapidly. Overall, the uptake of carbon into Earth’s intact tropical forests peaked in the 1990s. Given that the global terrestrial carbon sink is increasing in size, independent observations indicating greater recent carbon uptake into the Northern Hemisphere landmass10 reinforce our conclusion that the intact tropical forest carbon sink has already peaked. This saturation and ongoing decline of the tropical forest carbon sink has consequences for policies intended to stabilize Earth’s climate. [less ▲]

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See detailQuantifier les dimensions des houppiers à l’aide d’images aériennes à haute résolution pour estimer l’accroissement diamétrique des arbres dans les forêts d’Afrique centrale
Ndamiyehe Ncutirakiza, Jean-Baptiste; Lejeune, Philippe ULiege; Gourlet-Fleury, Sylvie et al

in Bois et Forêts des Tropiques (2020), 343

Characterising forest dynamics of a forest is essential to its management. Tree crowns are a key factor in these dynamics, but measuring them in tropical forests is not an easy matter. This study tested ... [more ▼]

Characterising forest dynamics of a forest is essential to its management. Tree crowns are a key factor in these dynamics, but measuring them in tropical forests is not an easy matter. This study tested the use of highresolution aerial imagery to estimate the tree diameter growth by incorporating detailed measurements of the detected tree crowns. Ortho-images at a resolution of 10 cm/pixel were captured by a fixed-wing drone over a 9 ha plot in the Yoko forest in the Democratic Republic of Congo. Inventories conducted on trees ≥ 10 cm diameter at breast height (DBH) in 2008 and 2016 provided access to a variety of tree dendrometric characteristics, including DBH and species temperament, and allowed the calculation of diameter increments. Mixed linear models were calibrated to predict diameter increment of 163 trees identified both on the ground and on the ortho-images, using variables quantified on the ground only and/or from variables measured from the orthoimages. From the aerial images, we were able to detect 23.4% of the trees with DBH ≥ 10 cm listed in the ground inventories, representing 75.1% of the stand’s aerial biomass. The probability of detecting the trees varied with their DBH, from 0.09 for trees with DBH < 30 cm to 0.97 for trees with DBH ≥ 60 cm. Predictions of diametric growth improved significantly when the variables quantified by remote sensing were added to the ground variables. The best models for estimating diameter increment include, in particular, a term characterising the size of tree crowns, which can only be measured by remote sensing. Of the variables determined by remote sensing, convex crown area was the most successfull in the models and therefore appears to be the most accurate variable to describe competition between tree crowns. These results open up possibilities to build new tools of data acquisition to support forest planning. [less ▲]

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See detailDynamique des populations d’azobé, Lophira alata Banks ex C. F. Gaertn., et implications pour sa gestion durable au Cameroun
Biwolé, Achille ULiege; Ouédraogo, Dakis-Yaoba; Betti, Jean Lagarde et al

in Bois et Forêts des Tropiques (2019), 342(novembre 2019), 55-68

L’impact de l’exploitation forestière sur le renouvellement du stock de bois d’oeuvre reste largement méconnu en Afrique centrale du fait du manque de données sur la dynamique des populations d’arbres ... [more ▼]

L’impact de l’exploitation forestière sur le renouvellement du stock de bois d’oeuvre reste largement méconnu en Afrique centrale du fait du manque de données sur la dynamique des populations d’arbres exploités. C’est en particulier le cas pour l’azobé, Lophira alata, un bois d’oeuvre de grande valeur commerciale. L’objectif de cette étude est double : quantifier l’effet du type forestier et de l’exploitation sur la croissance de l’azobé et simuler l’évolution du stock exploitable et du taux de reconstitution après exploitation. Nous avons effectué pendant trois ans un suivi annuel de la croissance et de la mortalité dans trois types forestiers au Cameroun : en forêt sempervirente, en forêt mixte et en forêt semi-caducifoliée. Le recrutement a été étudié uniquement en forêt mixte, sous deux conditions : en milieu exploité et non exploité. Nous avons calibré, avec ces données, un modèle matriciel de Usher. Douze scénarios d’exploitation ont été simulés en faisant varier le diamètre minimum d’exploitation de 60, 70 et 80 cm, et l’intensité de prélèvement des arbres de 100 à 40 %. La croissance de l’azobé est influencée à la fois par le type forestier et l’exploitation. Les arbres de forêt sempervirente ont une croissance plus faible jusqu’à 50 cm de diamètre, alors que la croissance maximale prédite pour ce type forestier est la plus élevée. L’exploitation a par ailleurs stimulé la croissance. Enfin, l’exploitation de l’azobé ne respecte pas le principe du rendement soutenu : ses taux de croissance à long terme varient entre 0,54 et 0,83 %. Pour garantir la durabilité de son exploitation au Cameroun, une sylviculture dynamisant la croissance des futurs arbres exploitables, ainsi que leur régénération, s’avère indispensable. [less ▲]

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See detailGrowth determinants of timber species Triplochiton scleroxylon and implications for forest management in central Africa
Ligot, Gauthier ULiege; Fayolle, Adeline ULiege; Gourlet-Fleury, Sylvie et al

in Forest Ecology and Management (2019), 437

The sustainability of the polycyclic logging system in tropical forests has been increasingly questioned for a variety of reasons, and particularly in central Africa as commercial species, mostly light ... [more ▼]

The sustainability of the polycyclic logging system in tropical forests has been increasingly questioned for a variety of reasons, and particularly in central Africa as commercial species, mostly light-demanding long-lived pioneer species, usually fail to recover a stable number of large trees after exploitation. Several factors are known to affect tropical tree demographic processes, like tree growth, survival and recruitment. Tree growth has particularly been showed to depend on ecological conditions, tree genetics, and competition with surrounding vegetation, as well as tree size or ontogeny. Yet, due to the paucity of available data, the importance of such factors is unclear and usually ignored when estimating future timber yields. To fill this gap, we chose to evaluate the variability in growth of one African long-lived pioneer and commercially very important species: Triplochiton scleroxylon K. Schum, gathering a broad dataset composed of tree ring data recorded in one site in Cameroon and periodic field inventory data recorded in seven sites across central Africa. In total, we analyzed 13,225 records of annual tree diameter increments recorded over 920 trees from seven sites in Cameroon, Republic of the Congo and Central African Republic. We evaluated (i) to what extent the average growth of trees that reach harvestable dimensions differs from population average and (ii) to what extent past perturbations influence the growth of remaining trees. We found the diameter growth of T. scleroxylon to be remarkably variable and this study provided an unprecedented quantification of the magnitude of some key growth determinants. In unlogged forests, the diameter increment of T. scleroxylon ranged between 0.40 cm year-1 in Southern Cameroon and 0.83 cm year-1 in South-Eastern Cameroon. The diameter increment was weakly related to tree size but increased twofold from unlogged to logged forests. Perturbation caused by logging stimulates growth of T. scleroxylon for at least 10-15 years. Finally, harvestable timber stock of large-sized T. scleroxylon was found to be constituted by trees that grew in average twice faster than trees of the entire extant population. As more and more inventory data become available, quantifying these effects could be replicated for other timber species and in other sites, to improve the accuracy of future timber resource estimates and improve forest management guidelines. [less ▲]

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See detailBanque de graines du sol et déterminants de la germination du tali, Erythrophleum suaveolens (Guill. & Perr.) Brenan
Douh, Chauvelin ULiege; Gorel, Anaïs ULiege; Daïnou, Kasso ULiege et al

in Bois et Forêts des Tropiques (2018), 338

Cette étude évalue l’abondance des graines d’Erythrophleum suaveolens dans la banque du sol des forêts denses humides d’Afrique centrale. Les travaux ont été menés au Nord-Congo dans deux types forestiers ... [more ▼]

Cette étude évalue l’abondance des graines d’Erythrophleum suaveolens dans la banque du sol des forêts denses humides d’Afrique centrale. Les travaux ont été menés au Nord-Congo dans deux types forestiers : la forêt à Celtis sur des sols argilo-sableux à sablo-argileux et la forêt à Manilkara sur des sols sableux. Les tiges d’E. suaveolens (dhp ≥ 10 cm) ont été inventoriées dans deux parcelles de 400 ha, et les structures diamétriques de leurs populations ont été comparées. En outre, 80 fosses (2 x 40 fosses par type de forêt) ont été creusées aux pieds de 20 arbres (10 par forêt), sur trois couches contiguës de 10 cm chacune, soit à une profondeur totale de 30 cm, et l’abondance des graines dans la banque du sol a été évaluée. La dormance des graines récoltées a été testée par des essais de germination après traitement au H2SO4 et cinq graines prélevées jusqu’à une profondeur de 20 cm dans la forêt à Celtis ont été utilisées pour estimer leur âge par Spectroscopie de Masse par Accélérateur (SMA). La comparaison des structures diamétriques indique une plus grande proportion de tiges de faible diamètre dans la forêt à Celtis. Alors que les densités de tiges (dhp ≥ 10 cm) sont proches, avec 0,85 et 1,05 tige/ha respectivement, dans la forêt à Celtis et la forêt à Manilkara, les densités de graines sont significativement plus élevées dans la forêt à Celtis (8,55 graines/m2) que dans la forêt à Manilkara (0,15 graine/m2). Le pourcentage maximum de germination obtenu était de 19,1 % pour des graines n’ayant subi aucun traitement. Les lots traités à l’acide ont présenté de moindres taux de germination. Ces graines pourraient se conserver une dizaine d’années dans la banque du sol. Les facteurs pouvant influencer les variations de densité des graines sont discutés et des recommandations sylvicoles sont formulées. [less ▲]

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See detailWhat controls local-scale aboveground biomass variation in central Africa? Testing structural, composition and architectural attributes
Loubota Panzou, Grâce Jopaul ULiege; Fayolle, Adeline ULiege; Feldpausch, Ted R. et al

in Forest Ecology and Management (2018), 429

Tropical forests play a key role in regulating the terrestrial carbon cycle and climate change by storing a large amount of carbon. Yet, there is considerable uncertainty about the amount and spatial ... [more ▼]

Tropical forests play a key role in regulating the terrestrial carbon cycle and climate change by storing a large amount of carbon. Yet, there is considerable uncertainty about the amount and spatial variation of aboveground biomass (AGB), especially in the relatively less studied African tropical forests. In this study, we explore the local-scale variation and determinants of plot-level AGB, between and within two types of forests, the Celtis and Manilkara forests, growing under the same climate but on different geological substrates in the northern Republic of Congo. In each forest site, all trees ≥10 cm diameter were censured in 36 × 1-ha plots and we measured tree height and crown size using a subsample of 18 × 1-ha of these plots. We developed height-diameter and crown-diameter allometric relationships and tested whether they differed between the two sites. For each 1-ha plot, we further estimated the AGB and calculated structural attributes (stem density and basal area), composition attributes (wood density) and architectural attributes (tree height and crown size), the latter being derived from site-specific allometric relationships. We found strong between-site differences in height-diameter and crown-diameter allometries. For a given diameter, trees were taller in the Celtis forest while they had larger crown in the Manilkara forest. Similar trends were found for the sixteen species present in both forest sites, suggesting an environmental control of tree allometry. Although there were some between-site differences in forest structure, composition and architecture, we did not detect any significant difference in mean AGB between the Celtis and the Manilkara forests. The AGB variation was related to the heterogeneous distribution of large trees, and influenced by basal area, height and crown dimensions, and to a lesser extent wood density. These forest attributes have strong practical implications on emerging remote-sensing technologies for carbon monitoring in tropical forests. [less ▲]

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See detailThe importance of stand structure and tree allometry for local-scale variation in aboveground biomass
Loubota Panzou, Grâce Jopaul ULiege; Feldpausch, Ted; Ligot, Gauthier ULiege et al

Poster (2018, March 26)

Aboveground biomass (AGB) plays a critical role in determining the long-term dynamics of carbon in tropical forests. Consequently, understanding what factors are important in controlling AGB in tropical ... [more ▼]

Aboveground biomass (AGB) plays a critical role in determining the long-term dynamics of carbon in tropical forests. Consequently, understanding what factors are important in controlling AGB in tropical forests has major implications for projecting the terrestrial carbon stocks, in the context of an increasingly uncertain future. In this study, we aimed to explore the local-scale AGB variation in two forest sites in northern Congo, representative of two contrasted forest types under the same climate but growing on vastly different soils and parent material (quartzite substrate for CIB and sandstone substrate for Mokabi). Tree diameter was measured in 36 permanent forest plots of 1-ha in each site, and tree allometry (total tree height, height of the first branch and crown dimensions) was measured on a subsample of 18 plots of 1-ha in each site. Allometric data were available for a total of 2202 trees (1040 for CIB and 1162 for Mokabi) covering a large range of diameters (10 – 200 cm). We first developed site-specific allometric models that were then used to estimate AGB at plot level. We then explore the determinants of AGB variation at plot level using multiple regressions and mixed linear models. For a given diameter, trees tended to be taller and to have deeper crown in the Celtis forest of the CIB (rich soil) while they tended to have larger crown in the Manilkara forest of the Mokabi (sandy soil). Similar trends were reported within species for the sixteen species shared by both forest types, suggesting an environmental control of tree allometry. We found that AGB strongly varied between the two forest sites, with greater AGB per hectare in the Celtis forest of the CIB. Within sites AGB variation was positively related to basal area, though between-site allometric attributes (total height and crown radius) were important determinants of AGB variation. These results have strong implications for forest biomass and carbon monitoring. [less ▲]

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See detailThe limited contribution of large trees to annual biomass production in an old-growth tropical forest
Ligot, Gauthier ULiege; Gourlet-Fleury, Sylvie; Ouédraogo, Dakis-Yaoba et al

in Ecological Applications (2018)

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See detailArchitectural differences associated to functional traits among 45 coexisting tree species in central Africa
Loubota Panzou, Grâce Jopaul ULiege; Ligot, Gauthier ULiege; Gourlet-Fleury, Sylvie et al

in Functional Ecology (2018)

1. Architectural traits that determine the light captured in a given environment are an important aspect of the life-history strategies of tropical tree species. In this study, we examined how ... [more ▼]

1. Architectural traits that determine the light captured in a given environment are an important aspect of the life-history strategies of tropical tree species. In this study, we examined how interspecific variation in architectural traits is related to the functional traits of 45 coexisting tree species in central Africa. 2. At the tree level, we measured tree diameter, total height and crown dimensions for an average of 30 trees per species (range 14–72, total 968 trees) distributed over a large range of diameters (up to 162 cm). Using log-log models, we fitted species-specific allometric relationships between tree diameter, height and crown dimensions. At the species level, we derived architectural traits (height and crown dimensions) at 15 cm and maximum diameters from species-specific allometries. The architectural traits were then related to functional traits, including light requirements, wood density, leaf habit, and dispersal mode. 3. Among the 45 coexisting tree species, we identified strong variations in height and crown allometries, along with architectural traits derived from these species-specific allometries. There was a positive correlation among architectural traits, suggesting that large-statured canopy species were taller and had larger and deeper crowns than small-statured understory species at all ontogenic stages. The relationships between architectural and functional traits highlighted a continuum of species between the large-statured canopy species and the smallstatured understory species. In this moist and seasonal forest, large-statured canopy species tended to be light-demanding, wind-dispersed, deciduous and large contributors to forest biomass (high basal area), while small-statured understory species tended to be shadetolerant, animal-dispersed, evergreen and most abundant in terms of stem density. 4. Our results highlighted strong architectural differences among coexisting tropical tree species in central Africa. The relationships between architectural and functional traits provided insights into the life-history strategy of tropical tree species. [less ▲]

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See detailAnnual cycles are the most common reproductive strategy in African tropical tree communities
Adamescu, Gabriela S.; Plumptre, Andrew J.; Abernethy, Katharine A. et al

in Biotropica (2018), 50(3), 418-430

We present the first cross-continental comparison of the flowering and fruiting phenology of tropical forests across Africa. Flowering events of 5446 trees from 196 species across 12 sites and fruiting ... [more ▼]

We present the first cross-continental comparison of the flowering and fruiting phenology of tropical forests across Africa. Flowering events of 5446 trees from 196 species across 12 sites and fruiting events of 4595 trees from 191 species across 11 sites were monitored over periods of 6 to 29 years and analyzed to describe phenology at the continental level. To study phenology, we used Fourier analysis to identify the dominant cycles of flowering and fruiting for each individual tree and we identified the time of year African trees bloom and bear fruit and their relationship to local seasonality. Reproductive strategies were diverse, and no single regular cycle was found in >50% of individuals across all 12 sites. Additionally, we found annual flowering and fruiting cycles to be the most common. Sub-annual cycles were the next most common for flowering, whereas supra-annual patterns were the next most common for fruiting. We also identify variation in different subsets of species, with species exhibiting mainly annual cycles most common in West and West Central African tropical forests, while more species at sites in East Central and East African forests showed cycles ranging from sub-annual to supra-annual. Despite many trees showing strong seasonality, at most sites some flowering and fruiting occurred all year round. Environmental factors with annual cycles are likely to be important drivers of seasonal periodicity in trees across Africa, but proximate triggers are unlikely to be constant across the continent. [less ▲]

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See detailVariation of tree allometry and aboveground biomass in central African forests
Loubota Panzou, Grâce Jopaul ULiege; Ligot, Gauthier ULiege; Bastin, Jean-François et al

Conference (2017, August 23)

Quantifying the biomass and carbon stocks contained in tropical forests has become an international priority for the implementation of the REDD+ initiative. Many techniques exist to estimate forest ... [more ▼]

Quantifying the biomass and carbon stocks contained in tropical forests has become an international priority for the implementation of the REDD+ initiative. Many techniques exist to estimate forest biomass at different spatial scales, but all ultimately rely on allometric equations calibrated on destructive measurements of individual tree biomass, in order to convert forest inventory data into biomass estimates. For many tropical forest ecosystems, that are structurally complex and species rich, these allometric equations have not yet been developed and general allometric equations are being used instead, with possibly local adjustment of tree allometry with non-destructive data. Variation in height-diameter allometry and in crown-diameter allometry across forest types and environmental conditions have been demonstrated to be of extreme importance for the estimation of biomass and carbon stocks in tropical forests, but yet poorly explored in central Africa. In this study we aimed to determine the variation in tree height-diameter and crown-diameter allometries across central African forests and the consequences for biomass and carbon stocks. Tree allometry data were collected in two of semi-deciduous forest sites in northern Republic of Congo that have vastly different substrate and soils (clay soils on quartzite and sandy soils on sandstone plateau), and forest communities, but similar rainfall regimes. These data will be analyzed to test two hypotheses: (i) tree allometry strongly varies across forest types with contrasted environmental conditions (and specifically soils), and (ii) both allometry and forest structure contributed to the greater biomass of the site on rich soil (quartzite substrate). Our newly collected data for two sites in northern Congo will be confronted to existing allometry and inventory data available elsewhere in the Congo basin to get a broader picture of allometric variations and its consequences for the estimation of biomass and carbon stocks. [less ▲]

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See detailProjet « Synthèse sur les Intact Forest Landscapes adaptée aux pays d’Afrique centrale » Rapport final du projet
Haurez, Barbara ULiege; Gourlet-Fleury, Sylvie; Mortier, Frédéric et al

Report (2017)

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See detailA look at Intact Forest Landscapes and their relevance to Central African forest policy
Haurez, Barbara ULiege; Daïnou, Kasso ULiege; Vermeulen, Cédric ULiege et al

Conference (2017, February)

Tropical forests are important providers of natural resources and ecosystem services but their ecological functions are facing increasing human pressure, linked to economic development. The preservation ... [more ▼]

Tropical forests are important providers of natural resources and ecosystem services but their ecological functions are facing increasing human pressure, linked to economic development. The preservation of tropical forest ecosystems is interrelated with effective land use planning and identification of priority areas for conservation. Initially defined by Greenpeace and the World Resources Institute (WRI) in 2000, Intact Forest Landscapes (IFLs) are large areas of forest minimally impacted by human activities. IFLs were identified by mapping industrial activities, road networks and infrastructure using remote sensing. Since 2014, when IFLs were recognized and adopted by the certification scheme Forest Stewardship Council (FSC), the IFLs have become integrated into forest management policies. In order to trace the history and evaluate the applicability of IFLs for forest management policy in the Central African context, we searched for documents related to the IFL method, and previous similar concepts. The IFL method is simple and cost-effective and enables the monitoring of forest degradation at a global scale. However, the approach mainly considers forest cover and is imprecise at the local scale. For example, hunting, one of the main threats faced by Central African ecosystems, cannot be detected by satellite imagery and is therefore disregarded in IFL identification processes. In contrast, there are other considered anthropogenic activities, such as reduced-impact selective logging, which may be compatible with forest ecosystem conservation. To better tailor the IFL approach to Central African forests, we recommend (i) the consideration of wildlife communities distribution in the analysis of disturbance, (ii) a thorough evaluation of the impacts of different human activities on forest ecosystems, and (iii) the integration of local stakeholders and governments in the design of land management strategies devised to address social, economic and environmental needs. [less ▲]

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See detailPresent-day central African forest is a legacy of the 19th century human history
Morin, Julie ULiege; Fayolle, Adeline ULiege; Favier, Charly et al

in eLife (2017)

The populations of light-demanding trees that dominate the canopy of central African forests are now aging. Here, we show that the lack of regeneration of these populations began ca. 165 ya (around 1850 ... [more ▼]

The populations of light-demanding trees that dominate the canopy of central African forests are now aging. Here, we show that the lack of regeneration of these populations began ca. 165 ya (around 1850) after major anthropogenic disturbances ceased. Since 1885, less itinerancy and disturbance in the forest has occurred because the colonial administrations concentrated people and villages along the primary communication axes. Local populations formerly gardened the forest by creating scattered openings, which were sufficiently large for the establishment of light-demanding trees. Currently, common logging operations do not create suitable openings for the regeneration of these species, whereas deforestation degrades landscapes. Using an interdisciplinary approach, which included paleoecological, archaeological, historical, and dendrological data, we highlight the long-term history of human activities across central African forests and assess the contribution of these activities to present-day forest structure and composition. The conclusions of this sobering analysis present challenges to current silvicultural practices and to those of the future. [less ▲]

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