References of "Ligot, Gauthier"
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See detailHow tree architecture varies across coexisting tropical tree species and relates to functional traits?
Loubota Panzou, Grâce Jopaul ULg; Ligot, Gauthier ULg; 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 detailHow tree architecture varies across coexisting tropical tree species and relate to ecological strategies?
Loubota Panzou, Grâce Jopaul ULg; Ligot, Gauthier ULg; Loumeto, Jean-Joël et al

Conference (2016, December 14)

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 ecological strategies. 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 were estimated at juvenile tree with diameter of 10 cm (H10, Cr10 and Cd10) and at adult stature with maximum diameter (Hmax, Crmax and Cdmax), life history traits (dispersal mode, phenology and regeneration guild) and functional traits (wood density and light requirement) were obtained. Our results showed a significant variation in tree allometry between coexisting species. The interspecific variation was related to light requirement (H-D allometry), dispersal mode (Cr-D allometry) and liana infestation (Cd-D allometry). Large-statured tree species were light demanding, deciduous and wind dispersed, while small-statured tree species were evergreen, dense wooded, and animal dispersed. Architectural traits strongly differed between regeneration guilds. [less ▲]

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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 ▲]

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See detailTree light capture and spatial variability of understory light increase with species mixing and tree size heterogeneity
Ligot, Gauthier ULg; Ameztegui, Aitor; Courbaud, Benoît et al

in Canadian Journal of Forest Research = Journal Canadien de la Recherche Forestière (2016)

Mixed and multi-layered forest ecosystems are sometimes more productive than monospecific and single-layered ones. It has been suggested that trees of different species and sizes occupy complementary ... [more ▼]

Mixed and multi-layered forest ecosystems are sometimes more productive than monospecific and single-layered ones. It has been suggested that trees of different species and sizes occupy complementary positions in space which would act as a mechanism to increase canopy light interception and wood production. However, greater canopy light interception reduces the average amount and variability of transmitted radiation offering fewer opportunities for all species to regenerate and to maintain forest heterogeneity in the long-run. We investigated whether increasing overstory heterogeneity indeed results in greater canopy light interception and lower variability in transmittance. We modeled the three-dimensional structure of forest stands with 3 typical forest structures, 10 mixtures of four tree species, and 3 different basal areas. We used the forest light interception model SAMSARALIGHT and performed three-way analyses of covariance to analyze the effects of the three varied components of forest heterogeneity. We found no evidence that increasing heterogeneity increases canopy light interception. In contrast, homogeneous stands intercept more light than heterogeneous stands. Variability in transmittance increased in some cases with compositional heterogeneity and, to a lesser extent, with tree size inequalities. The advantage of heterogeneous forests is in opportunities for natural regeneration rather than in opportunities to enhance canopy light interception. [less ▲]

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See detailTree light capture and spatial variability of understory light increase with species mixing and tree size heterogeneity
Ligot, Gauthier ULg; Ameztegui, Aitor; Courbaud, Benoît et al

Conference (2016)

Structurally heterogeneous forest ecosystems are generally considered to be more productive, resistant and resilient to future changes than simplified ones. The quantity of solar radiation available to ... [more ▼]

Structurally heterogeneous forest ecosystems are generally considered to be more productive, resistant and resilient to future changes than simplified ones. The quantity of solar radiation available to trees and the vegetation layer has been suggested to be a central driver among the possible mechanisms proposed to explain a greater productivity of heterogeneous stands. The idea that trees of different species and sizes can occupy complementary positions in space has led to the hypothesis that interception of radiation could increase in mixed and multi-layered forest stands, which should thus lead to an increase in production. In addition, the long-term sustainability of structurally heterogeneous forests with multiple coexisting species can only be ensured if the variability in light availability in the understory is sufficient for all species to be able to survive, grow and reproduce. However, better occupancy of canopy space should lead to reduced variability in understory light conditions. In this study, we investigate whether increasing overstory heterogeneity results in greater light capture by trees and greater variability in understory light. Greater light capture has been suggested as a possible explanation for the overyielding of complex stands and the greater variability in understory light as a mechanism for continuous recruitment of juvenile trees of various species. Based on allometric relationships developed in previous studies, we modeled the three-dimensional structure of forest stands (50 x 50 m) with 3 typical forest structures (single-layered, multi-layered and reverse j-shaped), 10 forest compositions combining beech, oak, fir and pine, 3 levels of basal area, and a fixed mean tree diameter (Figure 1). We predicted understory light conditions using the forest light interception model SAMSARALIGHT. The importance of each factor on understory light availability and variability was analyzed with three-way analyses of covariance. We found no evidence that increasing compositional or structural heterogeneity reduces understory light transmittance or increases tree light capture. Understory light transmittance in mixed stands was always intermediate between that is corresponding pure stands of the species involved in the mixture. Moreover, light transmittance slightly increased with increasing heterogeneity in forest structure. Stands composed of a single homogeneous tree layer transmitted less light than stands with two or more tree layers or stands composed of two or more species. Stand composition had the strongest influence on understory light in our simulations. Stand density was the second most important factor while heterogeneity in tree size had little effect. Compositional heterogeneity increased the variability in understory light conditions in some cases such as in fir-pine mixtures but adding beech to mixtures with oak generally limited variability in understory light, except in stands with very low basal area. Size inequality therefore increased understory light variability little and mainly in pure stands. The advantage of heterogeneous forest stands seems to lie in opportunities for the natural regeneration of various species to benefit from a diversity of light conditions in the understory rather than in opportunities to enhance light capture by the overstory although this effect depends on tree species composition. [less ▲]

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See detailMaintaining the coexistence of tree species of different shade tolerances with uneven-aged silviculture
Ligot, Gauthier ULg; Balandier, Philippe; Courbaud, Benoît et al

Conference (2016)

Maintaining the coexistence of multiple tree species is one of the greatest issues of uneven-aged silviculture as it is of great interest, for example, to maintain biodiversity or increase resilience to ... [more ▼]

Maintaining the coexistence of multiple tree species is one of the greatest issues of uneven-aged silviculture as it is of great interest, for example, to maintain biodiversity or increase resilience to global changes. In many places, while forest managers have successfully maintained complex stand structure with uneven-aged silviculture, they have often faced difficulties in maintaining some desired species mixtures. Naturally, the composition of uneven-aged forests evolves so that a few species successfully regenerate and suppress the others. Since a continuous canopy cover is usually maintained by uneven-aged silviculture, when nutrients and moisture are not limiting, the availability of light in the understory is the driving factor of natural regeneration dynamics. The amount of transmitted radiation determines, at least partly, the composition of the regeneration layer because of interspecific differences in growth and survival in shade. In theory, shade-tolerant species generally dominate the regeneration under closed canopies whereas less shade-tolerant species dominate the regeneration under partially open canopies. We hypothesize that, along a gradient of light availability, shade-tolerant species suppress less shade-tolerant species in understory with low availability of light whereas the opposite situation occurs in understory with high availability of light. In addition, we expect that forest managers can effectively control understory light with appropriate modifications of forest structure and density. We examined mixtures of sessile oak (Quercus petraea (Matt.) Liebl.) and European beech (Fagus sylvatica L.) in the Belgian Ardennes. We selected 23 sites with favorable water and nutrient supply. Regeneration areas (100-6500m²) were fenced off to protect them from browsing by deer. Saplings were sampled in 241 subplots and their height growth was annually monitored during two years. Understory light transmittance was measured in each subplot using hemispherical photography. The height growth of beech and oak saplings was modeled with mixed non-linear models. In order to simulate various silvicultural treatments, we used a model of light interception by heterogeneous canopies (SAMSARALIGHT). We simulated selective thinnings of 5 different types: harvesting preferentially small trees, large trees, or trees of shade-tolerant species or creating circular gaps. Understory light was found to be a key parameter in the dynamics of uneven-aged stands, as it affects regeneration growth and composition. There were interspecific differences in growth response to light availability. The optimum height growth of beech and oak regenerations were reached at 10% and 20% of transmittance, respectively. Our simulations highlighted that various silvicultural treatments can effectively be used to control understory light as long as harvest intensity is adapted to the chosen strategy (Figure 1). The results of this study also underscore the problem that even under good light conditions (transmittance > 20 %), regeneration of less shade-tolerant species might not overcome the regeneration of shade-tolerant species. Contrary to our hypothesis, we found no rank reversal of the height growth of the two study species along a wide light gradient. Consequently, maintaining less shade-tolerant species in stands with shade-tolerant species might require silvicultural interventions jointly in the overstory and regeneration layers. [less ▲]

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See detailDosage de la lumière pour maintenir la coexistence d’espèces d’ombre et de demi-ombre dans la régénération de la futaie irrégulière
Ligot, Gauthier ULg; Balandier, Philippe; Courbaud, Benoît et al

in Revue Forestière Française (2015), 3

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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 ▲]

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See detailSamsara Light Loader
Ligot, Gauthier ULg; Courbaud, Benoît; de Coligny, François

Software (2015)

see http://capsis.cirad.fr/capsis/help_en/samsaralightloader

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See detailMaintaining the coexistence of forest species of different shade tolerances with close-to-nature forestry
Ligot, Gauthier ULg; Philippe, Balandier

Conference (2014, December 12)

Continuous-cover forestry has the goal of relying on natural regeneration, and maintaining irregular stand structure and tree species mixture. However, maintaining mixture of species with different shade ... [more ▼]

Continuous-cover forestry has the goal of relying on natural regeneration, and maintaining irregular stand structure and tree species mixture. However, maintaining mixture of species with different shade tolerances appears arduous with such a silvicultural system. Successfully managing irregular and mixed forests, relying on natural processes, requires a strong knowledge of the ecology of natural regeneration. In theory, regeneration dynamics depends upon the amount of transmitted radiation: shade-tolerant species dominate the regeneration under closed canopies whereas less shade-tolerant species dominate the regeneration under partially open canopies. Nevertheless, it explains hardly the difficulties faced by forest managers to maintain the coexistence of species of different shade tolerances. The purpose of this research is to define light requirements of two species with contrasting shade tolerances (Fagus sylvatica L. and Quercus petraea (Matt.) Liebl.) and, next, determining how understory light can be controlled by forest managers. We find that, contrary to our expectations, the shade-tolerant species outgrow the less shade-tolerant species in all light conditions. We next examine the effects of canopy structure and composition on understory light availability with a model of light interception by heterogeneous canopies. Various silvicultural treatments are tested in order to provide favorable understory light conditions for natural regeneration. The results underline that creating favorable understory light conditions for natural regeneration can be achieved with various regeneration treatments. However, the adequate reduction of stand density depends upon the chosen silvicultural strategies. The outcomes of this study highlight that the control of understory light can be insufficient to maintain the coexistence of species of contrasting shade tolerance, and provide guidelines for the management of understory light in heterogeneous forests. [less ▲]

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See detailManaging understory light to maintain the coexistence of forest tree species with different shade tolerances
Ligot, Gauthier ULg

Doctoral thesis (2014)

Similar to the management of the other environmental resources, forest management has been questioned and more sustainable practices of forest management are being sought. New close-to-nature practices ... [more ▼]

Similar to the management of the other environmental resources, forest management has been questioned and more sustainable practices of forest management are being sought. New close-to-nature practices aim to favor natural processes over human interventions. Particularly, continuous-cover forestry has the goal of relying on natural regeneration, and maintaining irregular stand structure and tree species mixture. However, maintaining mixture of species with different shade tolerances appears arduous with such a silvicultural system. Successfully managing irregular and mixed forests, relying on natural processes, requires a strong knowledge of the ecology of natural regeneration. In particular, strong knowledge is required to predict the result of the interspecific competition in the understory depending upon light availability. The amount of radiation transmitted to the understory is indeed a critical factor determining regeneration dynamics. It determines, at least in part, regeneration composition because of interspecific differences of growth and survival under shade. Moreover, our quantitative understanding of understory light in uneven-aged and mixed stands remains incomplete. A better quantitative understanding of understory light is needed to provide quantitative guidelines for the management of understory light in uneven-aged and mixed stands and, hence, for the management of natural regeneration. The purpose of this thesis is to determine how close-to-nature forest management can maintain mixtures of species with contrasting shade tolerances. I consider ecological conditions with good water and nutrient supplies. In these conditions, partially closed canopy limits the amount of light that reaches the understory, and light is the major factor driving regeneration composition. Consequently, I study the dynamics of natural regeneration with regards to light availability as well as the interception of light by the canopy of heterogeneous stands. Studying the regeneration ecology of two species with contrasting shade tolerances (Fagus sylvatica L. and Quercus petraea (Matt.) Liebl.), I find that the shade-tolerant species outgrow the less shade-tolerant species in all light conditions. Even though the control of understory light with continuous-cover silviculture is required to sustain the growth of less shade-tolerant regenerations, it might not be sufficient to maintain the coexistence of species with contrasting shade tolerances. In order to examine the effects of canopy structure and composition on understory light availability, I use a model of light interception by heterogeneous canopies after synthesizing and discussing the approaches reported in the literature. The model predicts satisfactorily measures of transmitted light even though it is a relatively simple radiative transfer model. I next explore how various silvicultural treatments can be manipulated to provide favorable understory light conditions for natural regeneration. These silvicultural strategies correspond to selective thinnings of five different types, e.g., harvesting preferentially small trees, large trees, or trees of shade-tolerant species or creating circular gaps. The results underline that creating favorable understory light conditions for natural regeneration can be achieved with various regeneration treatments. However, the adequate reduction of stand density depends upon the chosen silvicultural strategies. In particular, creating gaps of about 500 m2 provides adequate light for small regeneration clumps. Harvesting preferentially small and trees of shade-tolerant species are also appropriate but required higher harvest intensity. Harvesting preferentially large trees slightly increases understory light and promotes more shade-tolerant species than less shade-tolerant species. In order to maintain the coexistence of species with contrasting shade tolerances, forest manager must control understory light and manually suppress the regeneration of the shade-tolerant species. The outcome of this study provides foresters with the necessary tools to evaluate how silvicultural treatments can be manipulated to create or maintain favorable light conditions for the regeneration of species of different shade tolerances. Guidelines are additionally proposed for forest managers wanting to maintain the coexistence of species with contrasting shade tolerances. [less ▲]

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See detailForest radiative transfer models: which approach for which application?
Ligot, Gauthier ULg; Balandier, Philippe; Courbaud, Benoît et al

in Canadian Journal of Forest Research = Journal Canadien de la Recherche Forestière (2014), 44(5), 385-397

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See detailDynamique des forêts irrégulières et mélangées: de la modélisation aux recommandations sylvicoles
Ligot, Gauthier ULg

Conference (2014, April 29)

Close-to-nature management of forests has been increasingly advocated and practiced. However forest managers often face difficulties in maintaining the mixture of species with different shade tolerance ... [more ▼]

Close-to-nature management of forests has been increasingly advocated and practiced. However forest managers often face difficulties in maintaining the mixture of species with different shade tolerance. We studied this issue in uneven-aged acidophile medio-European beech forests. In these forests, while forest management has achieved regular timber production, it has rarely succeeded in promoting a diversified natural regeneration. In view of this, our objective is to refine our knowledge about the dynamic of uneven-aged mixed forests using a modelling approach. A set of consistent models were carried out to describe stand dynamic with, in particular, models of regeneration growth and light interception. The models were then implemented in a simulator in order to perform prospective analysis. In contrast to expectations, we found that saplings of beech, the shade-tolerant species, had the highest height growth rate at all light levels. Beech saplings reached an optimum growth at transmittance of 10%, whereas oak saplings needed more than 20%. These results indicate that oak saplings are systematically outcompeted by beech saplings across the light gradient. Thus, the control of canopy opening is not sufficient to promote the natural regeneration of oak beneath a stand also containing beech. Taking into account these latter results, we compared cutting strategies varying in type and intensity. Creating gaps of about 500 m² provided adequate light for small regeneration clumps. Cutting from below, species-specific cutting and uniform cutting were also appropriate but uniform cutting required higher harvest intensity. Cutting from above weakly increased understory light and promoted rather shade tolerant species. Finally we provided indications on different strategies that promote the regeneration of less-shade tolerant species, depending on the spatial aggregation of saplings, and the desired post-harvest stand structure and composition. [less ▲]

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See detailLa régénération naturelle des hêtraies-chênaies en lumière : approche expérimentale en forêt ardennaise
Ligot, Gauthier ULg; Claessens, Hugues ULg; Baudry, Olivier et al

in Forêt Wallonne (2014), (129), 19-21

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See detailModélisation de la dynamique des peuplements irréguliers
Ligot, Gauthier ULg

Scientific conference (2014, February 18)

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