References of "Ligot, Gauthier"
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See detailTransforming even-aged coniferous stands to uneven-aged stands: an opportunity to increase tree species diversity?
Ligot, Gauthier ULiege; Balandier, Philippe; Schmitz, Sophie et al

Conference (2019, March)

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See detailConservation value of protected and logged tropical forests in Cameroon
Lhoest, Simon ULiege; Fonteyn, Davy ULiege; Daïnou, Kasso ULiege et al

Scientific conference (2019, January 25)

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See detailUn réseau d'expérimentations de sylviculture suivi à long terme
Ligot, Gauthier ULiege; Mackels, Benoit ULiege; Delinte, Thibault ULiege et al

in Forêt.Nature (2019)

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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 detailNeuf peuplements résineux gérés sans coupe rase sous la louppe
Ligot, Gauthier ULiege

Conference (2019)

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See detailNeuf peuplements résineux gérés sans coupe rase sous la louppe
Ligot, Gauthier ULiege

in Forêt.Nature (2019)

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See detailRéviser les tarifs de cubage pour prendre en compte l'évolution de la ressource au Cameroun
Ligot, Gauthier ULiege; Dubart, Nicolas; Tchowo Hapi, Mauriad et al

in Bois et Forêts des Tropiques (2018), 338

La connaissance du volume exploitable est une information essentielle tant pour la gestion que pour le contrôle de l’exploitation forestière. En Afrique centrale, l’estimation des volumes repose ... [more ▼]

La connaissance du volume exploitable est une information essentielle tant pour la gestion que pour le contrôle de l’exploitation forestière. En Afrique centrale, l’estimation des volumes repose essentiellement sur l’utilisation de tarifs de cubage à une entrée, spécifique à chaque essence, et prédisant le volume exploitable à partir du diamètre de l’arbre. Or, récemment, de nombreux acteurs de la gestion forestière au Cameroun reportent une inadéquation entre les volumes commerciaux estimés avec les tarifs de cubage imposés par l’administration et les volumes estimés à partir des mesures de la longueur et du diamètre des billes exploitées. Afin de vérifier la justesse des tarifs de cubage imposés par l’administration camerounaise, nous avons réalisé un échantillonnage destructif pour 12 essences jouant un rôle crucial dans le commerce du bois au Cameroun, et développé de nouveaux tarifs de cubage, qui ont été comparés avec les tarifs imposés par l’administration camerounaise et 52 autres tarifs de cubage disponibles dans la littérature. Dans quatre concessions forestières du Cameroun, représentatives des différentes conditions écologiques prévalant dans ce pays, 732 arbres ont été abattus et leur volume a été mesuré par la méthode des billons successifs. Des tarifs de cubage à une entrée, fonction uniquement du diamètre de référence, ont ensuite été ajustés par la méthode des moindres carrés généralisés. Notre étude confirme l’existence de biais entre les volumes mesurés et les volumes estimés en utilisant les tarifs de cubage imposés par l’administration camerounaise. En conséquence, de nouveaux tarifs de cubage et un abaque de correction sont proposés. Enfin, la majorité des tarifs de cubages testés présentaient un biais similaire qui résulte vraisemblablement d’une évolution de la ressource et des pratiques d’exploitation. [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 detailPan-tropical prediction of forest structure from the largest trees
Bastin, Jean-François; Rutishauser, Ervan; Kellner, James R. et al

in Global Ecology and Biogeography (2018)

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See detailTransforming even-aged coniferous stands to uneven-aged stands: an opportunity to increase tree species diversity?
Ligot, Gauthier ULiege; Rozet, Sevan; Claessens, Hugues ULiege

Conference (2018)

In the hope of increasing forest adaptability, there is a growing interest in converting coniferous even-aged stands to uneven-aged stands. While the former silviculture has a long tradition, the latter ... [more ▼]

In the hope of increasing forest adaptability, there is a growing interest in converting coniferous even-aged stands to uneven-aged stands. While the former silviculture has a long tradition, the latter as well as the conversion between the two systems remain complex and far less documented. Depending on the proximity of seed bearers of different species, the seedling diversity can be important, offering good opportunities to increase future tree diversity. Nevertheless, with continuous cover forestry that limits forest perturbations, there is a fear that only a few late-successional vigorous species and eventually limit future stand diversity. Nine 1-ha permanent plots have been established in even-aged coniferous stands managed to progressively convert them to uneven-aged stands. The stands were chosen to span contrasted forest composition and a gradient of stand ages at the beginning of the conversion from even-aged to uneven-aged. Twelve subplots were installed in each plot to monitor the natural regeneration and light conditions using hemispherical photography. In contrast to the regeneration density and diversity, the height growth rate of dominant saplings was well related to light conditions. In similar light conditions, saplings of Norway spruce, Douglas fir and European silver fir showed relatively similar height increments, while, in some plots, saplings of Western hemlock and larch had higher height growth rate and might threaten future stand diversity. [less ▲]

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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 detailThe role of large trees in the biomass production of heterogeneous forest
Ligot, Gauthier ULiege; Ouedraogo; Bauwens, Sébastien ULiege et al

Poster (2017, September)

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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 detailHow tree architecture varies across coexisting tropical tree species and relates to functional traits?
Loubota Panzou, Grâce Jopaul ULiege; Ligot, Gauthier ULiege; Loumeto, Jean-Joël et al

Conference (2017, February 06)

Architecture refers to the overall shape of a tree and the spatial position of its components. Tree height determines the position in the forest canopy and access to light, while the amount and spatial ... [more ▼]

Architecture refers to the overall shape of a tree and the spatial position of its components. Tree height determines the position in the forest canopy and access to light, while the amount and spatial distribution of the foliage depend on the depth and the width of the crown. The aim of this study is to understand how tree architecture varies across coexisting tropical tree species and relates to functional traits. Forty five coexisting tree species were sampled in the semi-deciduous forests of Northern Congo. Species were classified according to ecological strategies, specifically regeneration guilds: shade bearers (27 species), non-pioneers light demanding (14 species) and pioneers (4 species). For each species, 14–72 trees (968 trees in total) were measured over a large range of diameter (10–162 cm). At the tree level, we measured the diameter (D in cm), height (H in m), crown radius (Cr in m) and crown depth (Cd in m) and crown exposure index (CEI) was visually estimated. At species level, architectural traits (Dmax, Hmax, Crmax and Cdmax), life history traits (dispersal mode, phenology and guild) and functional traits (wood density and light requirement) were obtained. We investigates the H-D, Cr-D and Cd-D allometric relationships at the tree level using linear mixed models on log-transformed data with species as a random effect on both slope and intercept. We used the multivariate analysis to quantify the relationship between architectural, functional traits and life history traits. Based on AIC, we found that the best linear mixed model was the one with two species random parameters (intercept and slope) for H-D and Cr-D allometries, while the best model for Cd-D allometry was the one with only a random intercept. Thus, our results showed a significant variation in tree allometry between coexisting species. The interspecific variation in H-D allometry was related to light requirement while Cr-D and Cd-D allometries were more related to dispersal mode and wood density, respectively. The confirmed the existence of three ecological strategies (shade bearers, non-pioneers light demanding and pioneers) in tropical forests, specifically in Central Africa. Architectural traits were the main traits that differentiate between ecological strategies. Architectural traits are therefore strong predictors of ecological strategies of coexisting tropical tree species. [less ▲]

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See detailWhat is the importance of large trees to biomass productivity in heterogeneous forests?
Ligot, Gauthier ULiege; Ouedraogo, Dakis-Yaoba ULiege; Gourlet, Sylvie et al

Conference (2017)

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