35 results on '"Vieilledent G"'
Search Results
2. GlobAllomeTree: international platform for tree allometric equations to support volume, biomass and carbon assessment
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Henry M, Bombelli A, Trotta C, Alessandrini A, Birigazzi L, Sola G, Vieilledent G, Santenoise P, Longuetaud F, Valentini R, Picard N, and Saint-André L
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Forest Assessment ,LULUCF ,Trees Outside Forests ,Database ,Software ,Communication ,Forestry ,SD1-669.5 - Abstract
GlobAllomeTree is an international platform for tree allometric equations. It is the first worldwide web platform designed to facilitate the access of the tree allometric equation and to facilitate the assessment of the tree biometric characteristics for commercial volume, bio-energy or carbon cycling. The webplatform presents a database containing tree allometric equations, a software called Fantallomatrik, to facilitate the comparison and selection of the equations, and documentation to facilitate the development of new tree allometric models, improve the evaluation of tree and forest resources and improve knowledge on tree allometric equations. In the Fantallometrik software, equations can be selected by country, ecological zones, input parameters, tree species, statistic parameters and outputs. The continuously updated database currently contains over 5000 tree allometric equations classified according to 73 fields. The software Fantallometrik can be also used to compare equations, insert new data and estimate the selected output variables using field inventory. The GlobAllomeTree products are freely available at the URL: http://globallometree.org for a range of users including foresters, project developers, scientist, student and government staff.
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- 2013
- Full Text
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3. Estimating temporal changes in soil carbon stocks at ecoregional scale in Madagascar using remote-sensing
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Grinand, C., Maire, G. Le, Vieilledent, G., Razakamanarivo, H., Razafimbelo, T., and Bernoux, M.
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- 2017
- Full Text
- View/download PDF
4. A universal approach to estimate biomass and carbon stock in tropical forests using generic allometric models
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Vieilledent, G., Vaudry, R., Andriamanohisoa, S. F. D., Rakotonarivo, O. S., Randrianasolo, H. Z., Razafindrabe, H. N., Rakotoarivony, C. Bidaud, Ebeling, J., and Rasamoelina, M.
- Published
- 2012
5. Long-term (1990–2019) monitoring of forest cover changes in the humid tropics
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Vancutsem, C., primary, Achard, F., additional, Pekel, J.-F., additional, Vieilledent, G., additional, Carboni, S., additional, Simonetti, D., additional, Gallego, J., additional, Aragão, L. E. O. C., additional, and Nasi, R., additional
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- 2021
- Full Text
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6. Long-term (1990-2019) monitoring of tropical moist forests dynamics
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Vancutsem, C., primary, Achard, F., additional, Pekel, J.-F., additional, Vieilledent, G., additional, Carboni, S., additional, Simonetti, D., additional, Gallego, J., additional, Aragao, L., additional, and Nasi, R., additional
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- 2020
- Full Text
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7. Applying ecological model evaludation: Lessons learned with the forest dynamics model Samsara2
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Courbaud, B., primary, Lafond, V., additional, Lagarrigues, G., additional, Vieilledent, G., additional, Cordonnier, T., additional, Jabot, F., additional, and de Coligny, F., additional
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- 2015
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8. Estimating deforestation in tropical humid and dry forests in Madagascar from 2000 to 2010 using multi-date Land sat satellite images and the random farests classifier
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Grinand, C., Rakotomalala, F., Gond, V., Vaudry, R., Bernoux, Martial, and Vieilledent, G.
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Land cover ,REDD ,Landsat TM ,Machine learning ,Madagascar ,Change detection ,Deforestation ,Random forests ,Classification - Abstract
High resolution and low uncertainty deforestation maps covering large spatial areas in tropical countries are needed to plan efficient forest conservation and management programs such as REDD+ (Reducing Emissions from Deforestation and Forest Degradation). Using an open-source free software (R, GRASS and QGis) and an original statistical approach combining multi-date land cover observations based on Landsat satellite images and the random forests classifier, we obtained up-to-date deforestation maps for the periods 2000-2005 and 2005-2010 with a minimum mapping unit of 036 ha for 7.7 M hectares, i.e. 40.3% of the tropical humid forest and 20.6% of the tropical dry forest in Madagascar. Uncertainty in deforestation on the maps was calculated by comparing the results of the classification to more than 30,000 visual interpretation points on a regular grid. We assessed accuracy on a per-pixel basis (confusion matrix) and by measuring the relative surface difference between wall-to-wall approach and point sampling. At the pixel level, user accuracy was 84.7% for stable land cover and 60.7% for land cover change. On average for the whole study area, we obtained a relative difference of 2% for stable land cover categories and 21.1% land cover change categories respectively between the wall-to-wall and the point sampling approach. Depending on the study area, our conservative assessment of annual deforestation rates ranged from 0.93 to 233%.yr(-1) for the humid forest and from 0.46 to 1.17%.yr(-1) for the dry forest. Here we describe an approach to obtain deforestation maps with reliable uncertainty estimates that can be transposed to other regions in the tropical world.
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- 2013
9. Is the strength of competition among tree species influenced by phylogenetic or functional relatedness?
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Kunstler, Georges, Albert, C.H., Coomes, D.A., Courbaud, Benoît, Lavergne, S., Thuiller, W., Viard-Cretat, F., Vieilledent, G., Zimmermann, N.E., Irstea Publications, Migration, Ecosystèmes montagnards (UR EMGR), Centre national du machinisme agricole, du génie rural, des eaux et forêts (CEMAGREF), Centre National de la Recherche Scientifique (CNRS), UNIVERSITY OF CAMBRIDGE GBR, Partenaires IRSTEA, Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA), Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad), and Swiss Federal Research Institute
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[SDE] Environmental Sciences ,[SDE]Environmental Sciences - Abstract
International audience; Understanding the nature of competitive interactions among trees is critical to understand forest community structure and dynamics, and to predict their responses to global change. However, predicting the outcome of competitive interaction between numerous pairs of tree species and across large gradients of abiotic conditions remains challenging. A classical hypothesis -the competition-relatedness hypothesis- assumes that because of niche and trait conservatism, closely related species tend to be ecologically more similar and thus compete more severely than distantly related species. However, this hypothesis has remained largely untested with direct measurements of competition. Rather, it was only evaluated from simple patterns of species co-occurrence in the past. Recent publications have challenged this hypothesis on the ground that coexistence requires more complex explanations than simply niche differentiation. Coexistence is also driven by differences in species' competitive ability, and this could have effects opposed to the competition- relatedness hypothesis. For instance, pairs of species sharing similar values of trait responsible for a high competitive ability should compete less strongly than species with more distinct trait values. Using data on individual tree radial growth from more than 17000 forest plots in the French Alps, we explore the relative role of these two contrasting views of competitive interactions for 130 pairs of species. We developed a Bayesian neighbourhood growth competition model to estimate the intensity of competition between pairs of species. We then tested the relation between strength of competition between pairs of species and i)their phylogenetic distance or ii)their functional similarity for several key functional traits.
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- 2011
10. Effet des perturbations sur la dynamique des forêts résineuse de montagne : de l'arbre au peuplement
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Courbaud, Benoît, De Coligny, F., Vieilledent, G., Cordonnier, Thomas, Seignobosc, M., Lafond, Valentine, Mermin, E., Ecosystèmes montagnards (UR EMGR), Centre national du machinisme agricole, du génie rural, des eaux et forêts (CEMAGREF), and Irstea Publications, Migration
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[SDE] Environmental Sciences ,[SDE]Environmental Sciences - Abstract
National audience; Les perturbations naturelles jouent un rôle fondamental dans la dynamique forestière en provoquant des ouvertures qui permettent l'arrivée de lumière au sol, le développement de la régénération et la structuration du peuplement. Par son action de prélèvement, le forestier influence le peuplement d'une manière qui peut être comparée à une perturbation. L'objectif du travail présenté est de quantifier l'effet des perturbations naturelles en forêt de montagne à Epicéa et Sapin, d'analyser comment les processus démographiques à l'échelle de l'individu génèrent la dynamique du peuplement et d'évaluer les possibilités d'action du forestier sur cette dynamique. Nous utilisons le modèle individu-centré spatialement explicite Samsara qui simule la compétition pour la lumière entre arbres, la croissance de chaque individu, le recrutement, la mortalité de base et le régime de perturbations naturelles. Le modèle a été calibré à partir de données de placettes permanentes et de séries temporelles longues de peuplements Savoyards. Les simulations montrent que les perturbations naturelles jouent un rôle central dans ces forêts en réduisant la densité et la surface terrière dans des proportions qui peuvent atteindre jusque 50%, en augmentant l'éclairement au sol jusqu'à 20%, en réduisant la proportion de bois moyens et gros bois au profit des recrus. Les perturbations réduisent également le risque d'extinction de l'épicéa, plus fécond mais moins tolérant à l'ombre que le sapin. Le forestier peut également jouer sur la structure du peuplement, la production et sur des fonctions telles que la protection contre les risques naturels ou la biodiversité. Les simulations montrent qu'un prélèvement en trouées favorise le maintien durable d'une structure irrégulière, la permanence de la fonction de protection et la coexistence du sapin et de l'épicéa.
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- 2010
11. Mortality of silver fir and norway spruce in the Western Alps: a semi-parametric bayesian approach combining size-dependent and growth-dependent mortality
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Vieilledent, G., Courbaud, B., Kunstler, G., Dhôte, J.F., Ecosystèmes montagnards (UR EMGR), Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA), Laboratoire d'Etudes des Ressources Forêt-Bois (LERFoB), AgroParisTech-Institut National de la Recherche Agronomique (INRA), and Institut National de la Recherche Agronomique (INRA)-AgroParisTech
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Sciences de l'environnement ,ABIES ALBA ,MORTALITE ,NON PARAMETRIC MODEL ,STATISTIQUES BAYESIENNE ,MODELE DE CROISSANCE ,PICEA ABIES ,MODELE DYNAMIQUE ,GROWTH RELATED MORTALITY ,[SDE]Environmental Sciences ,Environmental Sciences - Abstract
Question: Tree mortality can be modeled using two complementary covariates, tree size and tree growth. Tree growth is an integrative measure of tree vitality while tree diameter is a good index of sensitivity to disturbances and can be consider as a proxy for tree age which determines senescence. Few mortality models integrate both covariates as classical model calibration need large permanent plots data-sets which are rare. How then to obtain a multivariate mortality model including size and growth when permanent plots data are not available? Location: To answer this question, we studied A. alba and P. abies mortality in the French and Swiss Alps. Method: Our study proposes an alternative semi-parametric Bayesian method which includes a random sample of living and dead trees with diameter and growth measurements. Results: We were able to obtain a mortality model combining both size-dependent and growth-dependent mortality. We demonstrated that A. alba had a lower mortality rate (10%) than P. abies (18%) for low growth (
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- 2010
12. (trad auto)Structuring uncertainty and variability in forest dynamics models. Application to the coexistence of fir and spruce in mountain forests
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Vieilledent, G., AgroParisTech, Ecole, AgroParisTech, Jean-François Dhôte, Ecosystèmes montagnards (UR EMGR), Centre national du machinisme agricole, du génie rural, des eaux et forêts (CEMAGREF), and Docteur AgroPariTech ENGREF
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Recrutement ,F40 - Écologie végétale ,F60 - Physiologie et biochimie végétale ,Lumière ,Trade-off ,Growth ,[MATH] Mathematics [math] ,Variabilité ,Mortalité ,Forest dynamics ,[SDU] Sciences of the Universe [physics] ,Allométrie ,Démographie ,K01 - Foresterie - Considérations générales ,Dynamique des populations ,Variability ,[MATH]Mathematics [math] ,thèse ,Demography ,Dynamique forestière ,Picea abies ,thesis ,Montagne ,Abies alba ,[SDU]Sciences of the Universe [physics] ,[SDE]Environmental Sciences ,Forêt ,Incertitude ,Coexistence - Abstract
Practitioners and decision-makers need information on how to conserve mixed Fir and Spruce forests in mountains. To answer this question, we modelled demographic (growth, mortality, recruitment) and allometric functions from field data for the two species. These functions have been implemented in a forest dynamics model to improve the knowledge on natural dynamics of the two species and to test for silvicultural practices. Parameter estimation was performed within a hierarchical Bayesian framework. Estimation permitted to quantify and underline species differences : Fir, the relatively shade-tolerant species compared to Spruce, was less sensitive to self-thinning, had a higher growth and a higher probability of recruitment at low light than Spruce. Models took into account observation errors and spatio-temporal process variability. Individual variability (or so-called intra-specific variability) and temporal variability (interannual and intraindividual variability) were significant and tended to equalize species fitness, inverting species hierarchy locally in space or sporadically in time. First simulations with simulator Samsara2 showed a better behavior of the model when including process variability. Variability led to patterns for stand structuration (tree heights and diameters) and to patterns for basal-area evolution with time which were much more realistic than without variability. Running simulations on a mixed Fir and Spruce stand, we observed a competitive exclusion of Spruce by Fir. Equalizing mechanisms associated to variability were not able to blur the competitive advantage of Fir on Spruce. Nevertheless, transient dynamics of the system was slow and apparent coexistence of the two species lasted for several hundred years., Les gestionnaires forestiers sont demandeurs d'une aide à la décision pour la conservation du mélange Sapin et Epicéa en forêt de montagne. Pour répondre à leur attente, nous avons modélisé, pour les deux espèces, les fonctions démographiques (croissance, mortalité et recrutement) et les fonctions d'allométries à partir de données de terrain. Ces fonctions ont été implémentées dans un modèle de dynamique forestière afin d'améliorer les connaissances sur la dynamique naturelle des deux espèces et d'envisager des tests de scénarios sylvicoles. L'estimation statistique des paramètres des modèles a été effectuée dans un cadre bayésien hiérarchique. Elle a permis de mettre en évidence et de quantifier les différences entre espèces : le Sapin, espèce tolérante à l'ombre comparativement à l'Epicéa, est moins sensible à l'autoéclaircie, a une croissance plus forte et un taux de recrutement plus important à faibles niveaux de lumière que l'Epicéa. Les modèles développés ont pris en compte l'incertitude sur les observations et la variabilité spatio-temporelle des processus. La variabilité individuelle (ou intraspécifique) et temporelle (interannuelle et intra-individuelle) est forte et tend à égaliser la fitness des deux espèces en inversant la hiérarchie des espèces localement dans l'espace ou sporadiquement dans le temps. Les premières simulations à l'aide du simulateur Samsara2 indiquent un meilleur comportement du modèle lorsque la variabilité spatio-temporelle est inclue dans les processus. La variabilité assure une structuration en hauteur et en diamètre ainsi qu'une évolution de la surface terrière qui correspondent à des patterns plus réalistes que lorsque la variabilité n'est pas prise en compte. A l'issue des premières simulations sur un peuplement test en mélange, on observe une exclusion compétititve systématique de l'Epicéa par le Sapin. Les mécanismes égaliseurs associés à la variabilité ne parviennent pas à contrebalancer l'avantage compétitif du Sapin sur l'Epicéa. Toutefois, la dynamique transitoire du système est lente et la coexistence apparente des deux espèces peut s'étaler sur plusieurs centaines d'années.
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- 2009
13. Impact of climate constrains and individual level variability on tree-tree interactions in mountain mixed-forests
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Kunstler, Georges, Vieilledent, G., Courbaud, Benoît, Irstea Publications, Migration, Ecosystèmes montagnards (UR EMGR), and Centre national du machinisme agricole, du génie rural, des eaux et forêts (CEMAGREF)
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[SDE] Environmental Sciences ,[SDE]Environmental Sciences - Abstract
International audience; Mountain forests have complex and multiple pathway dynamics which are difficult to predict because stands are often mixed-age and mixed-species, and encompass a large range of climatic conditions. A key point in these dynamics is the way trees interact locally and how these interactions scale up to the community level. The output of local tree-tree interactions is primary driven by differences in ecological strategies between species. However when differences in species strategies are taken into account, tree-tree interactions remain extremely variable. Abiotic factors such as climatic constraints can change species competitive hierarchy and tree-tree interaction intensity. It has been proposed that increasing climate harshness can lead to a decrease of competition intensity or even a shift to positive interaction (facilitation), modifying the importance of tree-tree interactions as a driver of forest dynamics. In addition, intra-specific variability in tree growth, survival and regeneration is high. Intra-specific variability results from genetic variability, past biotic interaction legacy and small environmental effects not measurable by the ecologist and is usually discarded as noise. It can blur species strategies and competitive hierarchy, making the output of tree-tree interactions less clear than based on species average performances. We are currently developing Hierarchical Bayesian models to improve our understanding of local tree-tree interactions in mountain forests. We focus on climate and intra-specific variability effects on these interactions. We will illustrate our research with two examples. A first example analyses the effect of competition on tree growth with a large scale data base. We specifically quantify change of tree-tree interactions (in intensity and in type) with climate. We found limited evidence of a strong effect of climate on tree-tree interaction intensity (competition's absolute impact). There was however large change of the importance (competition's relative impact) of tree -tree interaction with climate, meaning that tree-tree interactions were less important drivers of forest dynamics in harsh climate. A second example analyses tree competition for light, and illustrates how individual variability can change light interception. Light on forest floor appears more heterogeneous when intra-specific variability in crown size and shape is taken into account. This leads to an increase of the number of patches with high light levels, providing more opportunities for the regeneration of light demanding species.
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- 2009
14. Structurer l'incertitude et la variabilité dans les modèles de dynamique forestière. Application à la coexistence du Sapin et de l'Epicéa en forêt de montagne
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Vieilledent, G., Ecosystèmes montagnards (UR EMGR), Centre national du machinisme agricole, du génie rural, des eaux et forêts (CEMAGREF), and Docteur AgroPariTech ENGREF
- Subjects
[SDE]Environmental Sciences ,thesis ,thèse - Abstract
Practitioners and decision-makers need information on how to conserve mixed Fir and Spruce forests in mountains. To answer this question, we modelled demographic (growth, mortality, recruitment) and allometric functions from field data for the two species. These functions have been implemented in a forest dynamics model to improve the knowledge on natural dynamics of the two species and to test for silvicultural practices.; Les gestionnaires forestiers sont demandeurs d'une aide à la décision pour la conservation du mélange Sapin et Epicéa en forêt de montagne. Pour répondre à leur attente, nous avons modélisé, pour les deux espèces, les fonctions démographiques (croissance, mortalité et recrutement) et les fonctions d'allométries à partir de données de terrain. Ces fonctions ont été implémentées dans un modèle de dynamique forestière afin d'améliorer les connaissances sur la dynamique naturelle des deux espèces et d'envisager des tests de scénarios sylvicoles.
- Published
- 2009
15. Sylviculture et modélisation de la dynamique des sapinières-pessières de montagne : validation et ajustement du modèle
- Author
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Vieilledent, G., Courbaud, Benoît, Ecosystèmes montagnards (UR EMGR), Centre national du machinisme agricole, du génie rural, des eaux et forêts (CEMAGREF), irstea, Ministère de l'Agriculture et de la Pêche - DGFAR, and Irstea Publications, Migration
- Subjects
[SDE] Environmental Sciences ,[SDE]Environmental Sciences - Abstract
Les forestiers sont demandeurs d'outils d'aide à la décision pour la gestion des peuplements mélangés Sapin-Epicéa en montagne. Les modèles de dynamiques forestières peuvent répondre à leurs attentes. Le modèle Samsara modélise la dynamique des peuplements en mélange Sapin-Epicéa en zone de montagne. Toutefois, les fonctions d'allométrie (hauteur-diamètre, houppier-diamètre) et de démographie (recrutement, croissance et mortalité) associées au modèle de dynamique doivent d'une part être calibrées sur des données de terrain et d'autre part prendre en compte la variabilité rencontrée dans les observations. Ce rapport présente la calibration des fonctions d'allométrie, de croissance et de mortalité à l'aide des statistiques bayésiennes hiérarchiques. Il comprend la récolte des données, la méthodologie statistiques utilisée et les premières conclusions écologiques en termes de dynamique.
- Published
- 2007
16. Sylviculture et modélisation de la dynamique des sapinières-pessières de montagne : validation et ajustement du modèle
- Author
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Vieilledent, G., Courbaud, Benoît, Irstea Publications, Migration, Ecosystèmes montagnards (UR EMGR), Centre national du machinisme agricole, du génie rural, des eaux et forêts (CEMAGREF), irstea, and Ministère de l'Agriculture et de la Pêche - DGFAR
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[SDE] Environmental Sciences ,[SDE]Environmental Sciences - Abstract
This report is linked to the Cemagref-DGFAR contract which deals with "Sylviculture and modelisation of mountain Fir and Spruce stands: model calibration and validation". It presents the first results after one year of study. The presentation is divided in 4 chapters : A first chapter summarizes the socio-economical context of the study : 1- Necessity of help-decision in the management of uneavened mixed mountain stands. 2- Possibility to use a forest dynamic model such as Samsara. 3- Ecological problematics studied along the calibration of the model. Three other chapters deal with data accumulated and first results concerning function calibration for growth, mortality and recruitment., Ce rapport fait suite à la convention CEMAGREF-DGFAR portant sur le thème « Sylviculture et modélisation de la dynamique des sapinières-pessières de montagne : validation et ajustement du modèle ». Il présente les résultats préliminaires des travaux de recherche à l'issue de la première année. La présentation se divise en 4 chapitres : Un premier chapitre récapitule le contexte socio-économique en résumant : 1- La nécessité de fournir une aide à la décision concernant la gestion de peuplements mélangés en forêt irrégulière de montagne. 2- La possibilité pour cela de s'appuyer sur l'utilisation de modèles de dynamique forestière appropriés tel Samsara. 3- Les problématiques écologiques que l'on pourra étudier plus précisément au cours de la calibration et de l'utilisation du modèle. Les trois autres chapitres présentent les jeux de données accumulées et les premiers résultats concernant la calibration des fonctions de croissance, de mortalité et de recrutement que l'on souhaitera implémenter dans Samsara.
- Published
- 2006
17. Planning and decision-making aids - Feedback from workshop 2a,Aménagement et aide à la décision restitution de l'atelier 2a
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Christine Deleuze, Courbaud, B., Dhôte, J. -F, Arnal, D., Barbier, S., Dumas, S., Fournier, M., Heuret, P., Kunstler, G., Goff, N. L., Montpied, P., Bieng, M. -A N., Vallet, P., Couwenberghe, L., Vieilledent, G., and Zalamea, A.
18. Human and environmental controls over aboveground carbon storage in Madagascar
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Asner Gregory P, Clark John K, Mascaro Joseph, Vaudry Romuald, Chadwick K Dana, Vieilledent Ghislain, Rasamoelina Maminiaina, Balaji Aravindh, Kennedy-Bowdoin Ty, Maatoug Léna, Colgan Matthew S, and Knapp David E
- Subjects
aboveground carbon density ,biomass ,carbon stocks ,Carnegie Airborne Observatory ,CLASlite ,LiDAR ,REDD ,tropical forest ,Environmental sciences ,GE1-350 - Abstract
Abstract Background Accurate, high-resolution mapping of aboveground carbon density (ACD, Mg C ha-1) could provide insight into human and environmental controls over ecosystem state and functioning, and could support conservation and climate policy development. However, mapping ACD has proven challenging, particularly in spatially complex regions harboring a mosaic of land use activities, or in remote montane areas that are difficult to access and poorly understood ecologically. Using a combination of field measurements, airborne Light Detection and Ranging (LiDAR) and satellite data, we present the first large-scale, high-resolution estimates of aboveground carbon stocks in Madagascar. Results We found that elevation and the fraction of photosynthetic vegetation (PV) cover, analyzed throughout forests of widely varying structure and condition, account for 27-67% of the spatial variation in ACD. This finding facilitated spatial extrapolation of LiDAR-based carbon estimates to a total of 2,372,680 ha using satellite data. Remote, humid sub-montane forests harbored the highest carbon densities, while ACD was suppressed in dry spiny forests and in montane humid ecosystems, as well as in most lowland areas with heightened human activity. Independent of human activity, aboveground carbon stocks were subject to strong physiographic controls expressed through variation in tropical forest canopy structure measured using airborne LiDAR. Conclusions High-resolution mapping of carbon stocks is possible in remote regions, with or without human activity, and thus carbon monitoring can be brought to highly endangered Malagasy forests as a climate-change mitigation and biological conservation strategy.
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- 2012
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19. The effect of a political crisis on performance of community forests and protected areas in Madagascar.
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Neugarten RA, Rasolofoson RA, Barrett CB, Vieilledent G, and Rodewald AD
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- Madagascar, Biodiversity, Conservation of Natural Resources, Forests
- Abstract
Understanding the effectiveness of conservation interventions during times of political instability is important given how much of the world's biodiversity is concentrated in politically fragile nations. Here, we investigate the effect of a political crisis on the relative performance of community managed forests versus protected areas in terms of reducing deforestation in Madagascar, a biodiversity hotspot. We use remotely sensed data and statistical matching within an event study design to isolate the effect of the crisis and post-crisis period on performance. Annual rates of deforestation accelerated at the end of the crisis and were higher in community forests than in protected areas. After controlling for differences in location and other confounding variables, we find no difference in performance during the crisis, but community-managed forests performed worse in post-crisis years. These findings suggest that, as a political crisis subsides and deforestation pressures intensify, community-based conservation may be less resilient than state protection., (© 2024. The Author(s).)
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- 2024
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20. Global patterns of tree wood density.
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Yang H, Wang S, Son R, Lee H, Benson V, Zhang W, Zhang Y, Zhang Y, Kattge J, Boenisch G, Schepaschenko D, Karaszewski Z, Stereńczak K, Moreno-Martínez Á, Nabais C, Birnbaum P, Vieilledent G, Weber U, and Carvalhais N
- Subjects
- Canada, Forests, Plant Leaves, Carbon, Wood, Ecosystem
- Abstract
Wood density is a fundamental property related to tree biomechanics and hydraulic function while playing a crucial role in assessing vegetation carbon stocks by linking volumetric retrieval and a mass estimate. This study provides a high-resolution map of the global distribution of tree wood density at the 0.01° (~1 km) spatial resolution, derived from four decision trees machine learning models using a global database of 28,822 tree-level wood density measurements. An ensemble of four top-performing models combined with eight cross-validation strategies shows great consistency, providing wood density patterns with pronounced spatial heterogeneity. The global pattern shows lower wood density values in northern and northwestern Europe, Canadian forest regions and slightly higher values in Siberia forests, western United States, and southern China. In contrast, tropical regions, especially wet tropical areas, exhibit high wood density. Climatic predictors explain 49%-63% of spatial variations, followed by vegetation characteristics (25%-31%) and edaphic properties (11%-16%). Notably, leaf type (evergreen vs. deciduous) and leaf habit type (broadleaved vs. needleleaved) are the most dominant individual features among all selected predictive covariates. Wood density tends to be higher for angiosperm broadleaf trees compared to gymnosperm needleleaf trees, particularly for evergreen species. The distributions of wood density categorized by leaf types and leaf habit types have good agreement with the features observed in wood density measurements. This global map quantifying wood density distribution can help improve accurate predictions of forest carbon stocks, providing deeper insights into ecosystem functioning and carbon cycling such as forest vulnerability to hydraulic and thermal stresses in the context of future climate change., (© 2024 The Authors. Global Change Biology published by John Wiley & Sons Ltd.)
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- 2024
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21. Rethinking the nature of intraspecific variability and its consequences on species coexistence.
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Girard-Tercieux C, Maréchaux I, Clark AT, Clark JS, Courbaud B, Fortunel C, Guillemot J, Künstler G, le Maire G, Pélissier R, Rüger N, and Vieilledent G
- Abstract
Intraspecific variability (IV) has been proposed to explain species coexistence in diverse communities. Assuming, sometimes implicitly, that conspecific individuals can perform differently in the same environment and that IV increases niche overlap, previous studies have found contrasting results regarding the effect of IV on species coexistence. We aim at showing that the large IV observed in data does not mean that conspecific individuals are necessarily different in their response to the environment and that the role of high-dimensional environmental variation in determining IV has largely remained unexplored in forest plant communities. We first used a simulation experiment where an individual attribute is derived from a high-dimensional model, representing "perfect knowledge" of individual response to the environment, to illustrate how large observed IV can result from "imperfect knowledge" of the environment. Second, using growth data from clonal Eucalyptus plantations in Brazil, we estimated a major contribution of the environment in determining individual growth. Third, using tree growth data from long-term tropical forest inventories in French Guiana, Panama and India, we showed that tree growth in tropical forests is structured spatially and that despite a large observed IV at the population level, conspecific individuals perform more similarly locally than compared with heterospecific individuals. As the number of environmental dimensions that are well quantified at fine scale is generally lower than the actual number of dimensions influencing individual attributes, a great part of observed IV might be represented as random variation across individuals when in fact it is environmentally driven. This mis-representation has important consequences for inference about community dynamics. We emphasize that observed IV does not necessarily impact species coexistence per se but can reveal species response to high-dimensional environment, which is consistent with niche theory and the observation of the many differences between species in nature., Competing Interests: All authors declare that they have no conflict of interest., (© 2023 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd.)
- Published
- 2023
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22. Altered cyclone-fire interactions are changing ecosystems.
- Author
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Ibanez T, Platt WJ, Bellingham PJ, Vieilledent G, Franklin J, Martin PH, Menkes C, Pérez-Salicrup DR, Russell-Smith J, and Keppel G
- Subjects
- Ecosystem, Trees, Forests, Cyclonic Storms, Fires
- Abstract
Global change is altering interactions between ecological disturbances. We review interactions between tropical cyclones and fires that affect woody biomes in many islands and coastal areas. Cyclone-induced damage to trees can increase fuel loads on the ground and dryness in the understory, which increases the likelihood, intensity, and area of subsequent fires. In forest biomes, cyclone-fire interactions may initiate a grass-fire cycle and establish stable open-canopy biomes. In cyclone-prone regions, frequent cyclone-enhanced fires may generate and maintain stable open-canopy biomes (e.g., savannas and woodlands). We discuss how global change is transforming fire and cyclone regimes, extensively altering cyclone-fire interactions. These altered cyclone-fire interactions are shifting biomes away from historical states and causing loss of biodiversity., Competing Interests: Declaration of interests No interests are declared., (Copyright © 2022 Elsevier Ltd. All rights reserved.)
- Published
- 2022
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23. Not all species will migrate poleward as the climate warms: The case of the seven baobab species in Madagascar.
- Author
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Tagliari MM, Danthu P, Leong Pock Tsy JM, Cornu C, Lenoir J, Carvalho-Rocha V, and Vieilledent G
- Subjects
- Climate Change, Ecosystem, Geography, Madagascar, Temperature, Adansonia
- Abstract
It is commonly accepted that species should move toward higher elevations and latitudes to track shifting isotherms as climate warms. However, temperature might not be the only limiting factor determining species distribution. Species might move to opposite directions to track changes in other climatic variables. Here, we used an extensive occurrence data set and an ensemble modelling approach to model the climatic niche and to predict the distribution of the seven baobab species (genus Adansonia) present in Madagascar. Using climatic projections from three global circulation models, we predicted species' future distribution and extinction risk for 2055 and 2085 under two representative concentration pathways (RCPs) and two dispersal scenarios. We disentangled the role of each climatic variable in explaining species range shift looking at relative variable importance and future climatic anomalies. Four baobab species (Adansonia rubrostipa, Adansonia madagascariensis, Adansonia perrieri¸ and Adansonia suarezensis) could experience a severe range contraction in the future (>70% for year 2085 under RCP 8.5, assuming a zero-dispersal hypothesis). For three out of the four threatened species, range contraction was mainly explained by an increase in temperature seasonality, especially in the North of Madagascar, where they are currently distributed. In tropical regions, where species are commonly adapted to low seasonality, we found that temperature seasonality will generally increase. It is, thus, very likely that many species in the tropics will be forced to move equatorward to avoid an increase in temperature seasonality. Yet, several ecological (e.g., equatorial limit, or unsuitable deforested habitat) or geographical barriers (absence of lands) could prevent species to move equatorward, thus increasing the extinction risk of many tropical species, like endemic baobab species in Madagascar., (© 2021 John Wiley & Sons Ltd.)
- Published
- 2021
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24. New formula and conversion factor to compute basic wood density of tree species using a global wood technology database.
- Author
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Vieilledent G, Fischer FJ, Chave J, Guibal D, Langbour P, and Gérard J
- Subjects
- Forests, Models, Biological, Biomass, Trees physiology, Wood physiology
- Abstract
Premise of the Study: Basic wood density is an important ecological trait for woody plants. It is used to characterize species performance and fitness in community ecology and to compute tree and forest biomass in carbon cycle studies. While wood density has been historically measured at 12% moisture, it is convenient for ecological purposes to convert this measure to basic wood density, i.e., the ratio of dry mass over green volume. Basic wood density can then be used to compute tree dry biomass from living tree volume., Methods: Here, we derive a new exact formula to compute the basic wood density D
b from the density at moisture content w denoted Dw , the fiber saturation point S, and the volumetric shrinkage coefficient R. We estimated a new conversion factor using a global wood technology database where values to use this formula are available for 4022 trees collected in 64 countries (mostly tropical) and representing 872 species., Key Results: We show that previous conversion factors used to convert densities at 12% moisture into basic wood densities are inconsistent. Based on theory and data, we found that basic wood density could be inferred from the density at 12% moisture using the following formula: Db = 0.828D12 . This value of 0.828 provides basic wood density estimates 4-5% smaller than values inferred from previous conversion factors., Conclusions: This new conversion factor should be used to derive basic wood densities in global wood density databases. Its use would prevent overestimating global forest carbon stocks and allow predicting better tree species community dynamics from wood density., (© 2018 The Authors. American Journal of Botany is published by Wiley Periodicals, Inc. on behalf of the Botanical Society of America.)- Published
- 2018
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25. Small room for compromise between oil palm cultivation and primate conservation in Africa.
- Author
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Strona G, Stringer SD, Vieilledent G, Szantoi Z, Garcia-Ulloa J, and A Wich S
- Subjects
- Africa, Animals, Arecaceae growth & development, Biodiversity, Conservation of Natural Resources, Crops, Agricultural growth & development, Primates physiology
- Abstract
Despite growing awareness about its detrimental effects on tropical biodiversity, land conversion to oil palm continues to increase rapidly as a consequence of global demand, profitability, and the income opportunity it offers to producing countries. Although most industrial oil palm plantations are located in Southeast Asia, it is argued that much of their future expansion will occur in Africa. We assessed how this could affect the continent's primates by combining information on oil palm suitability and current land use with primate distribution, diversity, and vulnerability. We also quantified the potential impact of large-scale oil palm cultivation on primates in terms of range loss under different expansion scenarios taking into account future demand, oil palm suitability, human accessibility, carbon stock, and primate vulnerability. We found a high overlap between areas of high oil palm suitability and areas of high conservation priority for primates. Overall, we found only a few small areas where oil palm could be cultivated in Africa with a low impact on primates (3.3 Mha, including all areas suitable for oil palm). These results warn that, consistent with the dramatic effects of palm oil cultivation on biodiversity in Southeast Asia, reconciling a large-scale development of oil palm in Africa with primate conservation will be a great challenge., Competing Interests: The authors declare no conflict of interest., (Copyright © 2018 the Author(s). Published by PNAS.)
- Published
- 2018
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26. Moving forward socio-economically focused models of deforestation.
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Dezécache C, Salles JM, Vieilledent G, and Hérault B
- Subjects
- Agriculture, Commerce, Environmental Monitoring, Forestry economics, Social Conditions, Conservation of Natural Resources, Forests
- Abstract
Whilst high-resolution spatial variables contribute to a good fit of spatially explicit deforestation models, socio-economic processes are often beyond the scope of these models. Such a low level of interest in the socio-economic dimension of deforestation limits the relevancy of these models for decision-making and may be the cause of their failure to accurately predict observed deforestation trends in the medium term. This study aims to propose a flexible methodology for taking into account multiple drivers of deforestation in tropical forested areas, where the intensity of deforestation is explicitly predicted based on socio-economic variables. By coupling a model of deforestation location based on spatial environmental variables with several sub-models of deforestation intensity based on socio-economic variables, we were able to create a map of predicted deforestation over the period 2001-2014 in French Guiana. This map was compared to a reference map for accuracy assessment, not only at the pixel scale but also over cells ranging from 1 to approximately 600 sq. km. Highly significant relationships were explicitly established between deforestation intensity and several socio-economic variables: population growth, the amount of agricultural subsidies, gold and wood production. Such a precise characterization of socio-economic processes allows to avoid overestimation biases in high deforestation areas, suggesting a better integration of socio-economic processes in the models. Whilst considering deforestation as a purely geographical process contributes to the creation of conservative models unable to effectively assess changes in the socio-economic and political contexts influencing deforestation trends, this explicit characterization of the socio-economic dimension of deforestation is critical for the creation of deforestation scenarios in REDD+ projects., (© 2017 John Wiley & Sons Ltd.)
- Published
- 2017
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27. Catastrophic Decline of World's Largest Primate: 80% Loss of Grauer's Gorilla (Gorilla beringei graueri) Population Justifies Critically Endangered Status.
- Author
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Plumptre AJ, Nixon S, Kujirakwinja DK, Vieilledent G, Critchlow R, Williamson EA, Nishuli R, Kirkby AE, and Hall JS
- Subjects
- Animals, Body Size, Population Density, Endangered Species statistics & numerical data, Gorilla gorilla anatomy & histology
- Abstract
Grauer's gorilla (Gorilla beringei graueri), the World's largest primate, is confined to eastern Democratic Republic of Congo (DRC) and is threatened by civil war and insecurity. During the war, armed groups in mining camps relied on hunting bushmeat, including gorillas. Insecurity and the presence of several militia groups across Grauer's gorilla's range made it very difficult to assess their population size. Here we use a novel method that enables rigorous assessment of local community and ranger-collected data on gorilla occupancy to evaluate the impacts of civil war on Grauer's gorilla, which prior to the war was estimated to number 16,900 individuals. We show that gorilla numbers in their stronghold of Kahuzi-Biega National Park have declined by 87%. Encounter rate data of gorilla nests at 10 sites across its range indicate declines of 82-100% at six of these sites. Spatial occupancy analysis identifies three key areas as the most critical sites for the remaining populations of this ape and that the range of this taxon is around 19,700 km2. We estimate that only 3,800 Grauer's gorillas remain in the wild, a 77% decline in one generation, justifying its elevation to Critically Endangered status on the IUCN Red List of Threatened Species., Competing Interests: The analysis presented in this paper was funded by the ARCUS Foundation using data collected by Wildlife Conservation Society (WCS), Fauna and Flora International and Institut Congolais pour la Conservation de la Nature and funded by a variety of donors listed in the financial disclosure section. Two of these funders, KfW and World Bank are a commercial source of funds but this does not alter our adherence to PLOS ONE policies on sharing data and materials.” (as detailed online in our guide for authors http://journals.plos.org/plosone/s/competing-interests) as the IP and data sharing rights are owned by WCS.
- Published
- 2016
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28. Plant functional traits have globally consistent effects on competition.
- Author
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Kunstler G, Falster D, Coomes DA, Hui F, Kooyman RM, Laughlin DC, Poorter L, Vanderwel M, Vieilledent G, Wright SJ, Aiba M, Baraloto C, Caspersen J, Cornelissen JH, Gourlet-Fleury S, Hanewinkel M, Herault B, Kattge J, Kurokawa H, Onoda Y, Peñuelas J, Poorter H, Uriarte M, Richardson S, Ruiz-Benito P, Sun IF, Ståhl G, Swenson NG, Thompson J, Westerlund B, Wirth C, Zavala MA, Zeng H, Zimmerman JK, Zimmermann NE, and Westoby M
- Subjects
- Forests, Internationality, Models, Biological, Plant Leaves physiology, Trees growth & development, Wood analysis, Phenotype, Trees anatomy & histology, Trees physiology
- Abstract
Phenotypic traits and their associated trade-offs have been shown to have globally consistent effects on individual plant physiological functions, but how these effects scale up to influence competition, a key driver of community assembly in terrestrial vegetation, has remained unclear. Here we use growth data from more than 3 million trees in over 140,000 plots across the world to show how three key functional traits--wood density, specific leaf area and maximum height--consistently influence competitive interactions. Fast maximum growth of a species was correlated negatively with its wood density in all biomes, and positively with its specific leaf area in most biomes. Low wood density was also correlated with a low ability to tolerate competition and a low competitive effect on neighbours, while high specific leaf area was correlated with a low competitive effect. Thus, traits generate trade-offs between performance with competition versus performance without competition, a fundamental ingredient in the classical hypothesis that the coexistence of plant species is enabled via differentiation in their successional strategies. Competition within species was stronger than between species, but an increase in trait dissimilarity between species had little influence in weakening competition. No benefit of dissimilarity was detected for specific leaf area or wood density, and only a weak benefit for maximum height. Our trait-based approach to modelling competition makes generalization possible across the forest ecosystems of the world and their highly diverse species composition.
- Published
- 2016
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29. Ecosystem Services and Biodiversity in a Rapidly Transforming Landscape in Northern Borneo.
- Author
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Labrière N, Laumonier Y, Locatelli B, Vieilledent G, and Comptour M
- Subjects
- Agriculture, Borneo, Soil, Biodiversity, Conservation of Natural Resources economics, Crops, Agricultural growth & development, Forests
- Abstract
Because industrial agriculture keeps expanding in Southeast Asia at the expense of natural forests and traditional swidden systems, comparing biodiversity and ecosystem services in the traditional forest-swidden agriculture system vs. monocultures is needed to guide decision making on land-use planning. Focusing on tree diversity, soil erosion control, and climate change mitigation through carbon storage, we surveyed vegetation and monitored soil loss in various land-use areas in a northern Bornean agricultural landscape shaped by swidden agriculture, rubber tapping, and logging, where various levels and types of disturbance have created a fine mosaic of vegetation from food crop fields to natural forest. Tree species diversity and ecosystem service production were highest in natural forests. Logged-over forests produced services similar to those of natural forests. Land uses related to the swidden agriculture system largely outperformed oil palm or rubber monocultures in terms of tree species diversity and service production. Natural and logged-over forests should be maintained or managed as integral parts of the swidden system, and landscape multifunctionality should be sustained. Because natural forests host a unique diversity of trees and produce high levels of ecosystem services, targeting carbon stock protection, e.g. through financial mechanisms such as Reducing Emissions from Deforestation and Forest Degradation (REDD+), will synergistically provide benefits for biodiversity and a wide range of other services. However, the way such mechanisms could benefit communities must be carefully evaluated to counter the high opportunity cost of conversion to monocultures that might generate greater income, but would be detrimental to the production of multiple ecosystem services.
- Published
- 2015
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30. Improved allometric models to estimate the aboveground biomass of tropical trees.
- Author
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Chave J, Réjou-Méchain M, Búrquez A, Chidumayo E, Colgan MS, Delitti WB, Duque A, Eid T, Fearnside PM, Goodman RC, Henry M, Martínez-Yrízar A, Mugasha WA, Muller-Landau HC, Mencuccini M, Nelson BW, Ngomanda A, Nogueira EM, Ortiz-Malavassi E, Pélissier R, Ploton P, Ryan CM, Saldarriaga JG, and Vieilledent G
- Subjects
- Carbon, Models, Biological, Regression Analysis, Specific Gravity, Wood chemistry, Biomass, Environmental Monitoring methods, Models, Theoretical, Trees physiology, Tropical Climate
- Abstract
Terrestrial carbon stock mapping is important for the successful implementation of climate change mitigation policies. Its accuracy depends on the availability of reliable allometric models to infer oven-dry aboveground biomass of trees from census data. The degree of uncertainty associated with previously published pantropical aboveground biomass allometries is large. We analyzed a global database of directly harvested trees at 58 sites, spanning a wide range of climatic conditions and vegetation types (4004 trees ≥ 5 cm trunk diameter). When trunk diameter, total tree height, and wood specific gravity were included in the aboveground biomass model as covariates, a single model was found to hold across tropical vegetation types, with no detectable effect of region or environmental factors. The mean percent bias and variance of this model was only slightly higher than that of locally fitted models. Wood specific gravity was an important predictor of aboveground biomass, especially when including a much broader range of vegetation types than previous studies. The generic tree diameter-height relationship depended linearly on a bioclimatic stress variable E, which compounds indices of temperature variability, precipitation variability, and drought intensity. For cases in which total tree height is unavailable for aboveground biomass estimation, a pantropical model incorporating wood density, trunk diameter, and the variable E outperformed previously published models without height. However, to minimize bias, the development of locally derived diameter-height relationships is advised whenever possible. Both new allometric models should contribute to improve the accuracy of biomass assessment protocols in tropical vegetation types, and to advancing our understanding of architectural and evolutionary constraints on woody plant development., (© 2014 John Wiley & Sons Ltd.)
- Published
- 2014
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31. Forecasting deforestation and carbon emissions in tropical developing countries facing demographic expansion: a case study in Madagascar.
- Author
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Vieilledent G, Grinand C, and Vaudry R
- Abstract
Anthropogenic deforestation in tropical countries is responsible for a significant part of global carbon dioxide emissions in the atmosphere. To plan efficient climate change mitigation programs (such as REDD+, Reducing Emissions from Deforestation and forest Degradation), reliable forecasts of deforestation and carbon dioxide emissions are necessary. Although population density has been recognized as a key factor in tropical deforestation, current methods of prediction do not allow the population explosion that is occurring in many tropical developing countries to be taken into account. Here, we propose an innovative approach using novel computational and statistical tools, including R/GRASS scripts and the new phcfM R package, to model the intensity and location of deforestation including the effect of population density. We used the model to forecast anthropogenic deforestation and carbon dioxide emissions in five large study areas in the humid and spiny-dry forests of Madagascar. Using our approach, we were able to demonstrate that the current rapid population growth in Madagascar (+3.39% per year) will significantly increase the intensity of deforestation by 2030 (up to +1.17% per year in densely populated areas). We estimated the carbon dioxide emissions associated with the loss of aboveground biomass to be of 2.24 and 0.26 tons per hectare and per year in the humid and spiny-dry forest, respectively. Our models showed better predictive ability than previous deforestation models (the figure of merit ranged from 10 to 23). We recommend this approach to reduce the uncertainty associated with deforestation forecasts. We also underline the risk of an increase in the speed of deforestation in the short term in tropical developing countries undergoing rapid population expansion.
- Published
- 2013
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32. Competitive interactions between forest trees are driven by species' trait hierarchy, not phylogenetic or functional similarity: implications for forest community assembly.
- Author
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Kunstler G, Lavergne S, Courbaud B, Thuiller W, Vieilledent G, Zimmermann NE, Kattge J, and Coomes DA
- Subjects
- Ecosystem, France, Population Dynamics, Trees growth & development, Phylogeny, Trees classification
- Abstract
The relative importance of competition vs. environmental filtering in the assembly of communities is commonly inferred from their functional and phylogenetic structure, on the grounds that similar species compete most strongly for resources and are therefore less likely to coexist locally. This approach ignores the possibility that competitive effects can be determined by relative positions of species on a hierarchy of competitive ability. Using growth data, we estimated 275 interaction coefficients between tree species in the French mountains. We show that interaction strengths are mainly driven by trait hierarchy and not by functional or phylogenetic similarity. On the basis of this result, we thus propose that functional and phylogenetic convergence in local tree community might be due to competition-sorting species with different competitive abilities and not only environmental filtering as commonly assumed. We then show a functional and phylogenetic convergence of forest structure with increasing plot age, which supports this view., (© 2012 Blackwell Publishing Ltd/CNRS.)
- Published
- 2012
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33. A universal airborne LiDAR approach for tropical forest carbon mapping.
- Author
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Asner GP, Mascaro J, Muller-Landau HC, Vieilledent G, Vaudry R, Rasamoelina M, Hall JS, and van Breugel M
- Subjects
- Calibration, Hawaii, Madagascar, Panama, Peru, Tropical Climate, Carbon analysis, Conservation of Natural Resources methods, Models, Theoretical, Remote Sensing Technology methods, Trees chemistry
- Abstract
Airborne light detection and ranging (LiDAR) is fast turning the corner from demonstration technology to a key tool for assessing carbon stocks in tropical forests. With its ability to penetrate tropical forest canopies and detect three-dimensional forest structure, LiDAR may prove to be a major component of international strategies to measure and account for carbon emissions from and uptake by tropical forests. To date, however, basic ecological information such as height-diameter allometry and stand-level wood density have not been mechanistically incorporated into methods for mapping forest carbon at regional and global scales. A better incorporation of these structural patterns in forests may reduce the considerable time needed to calibrate airborne data with ground-based forest inventory plots, which presently necessitate exhaustive measurements of tree diameters and heights, as well as tree identifications for wood density estimation. Here, we develop a new approach that can facilitate rapid LiDAR calibration with minimal field data. Throughout four tropical regions (Panama, Peru, Madagascar, and Hawaii), we were able to predict aboveground carbon density estimated in field inventory plots using a single universal LiDAR model (r ( 2 ) = 0.80, RMSE = 27.6 Mg C ha(-1)). This model is comparable in predictive power to locally calibrated models, but relies on limited inputs of basal area and wood density information for a given region, rather than on traditional plot inventories. With this approach, we propose to radically decrease the time required to calibrate airborne LiDAR data and thus increase the output of high-resolution carbon maps, supporting tropical forest conservation and climate mitigation policy.
- Published
- 2012
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34. Growth strategies of tropical tree species: disentangling light and size effects.
- Author
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Rüger N, Berger U, Hubbell SP, Vieilledent G, and Condit R
- Subjects
- Trees radiation effects, Light, Trees growth & development, Tropical Climate
- Abstract
An understanding of the drivers of tree growth at the species level is required to predict likely changes of carbon stocks and biodiversity when environmental conditions change. Especially in species-rich tropical forests, it is largely unknown how species differ in their response of growth to resource availability and individual size. We use a hierarchical bayesian approach to quantify the impact of light availability and tree diameter on growth of 274 woody species in a 50-ha long-term forest census plot in Barro Colorado Island, Panama. Light reaching each individual tree was estimated from yearly vertical censuses of canopy density. The hierarchical bayesian approach allowed accounting for different sources of error, such as negative growth observations, and including rare species correctly weighted by their abundance. All species grew faster at higher light. Exponents of a power function relating growth to light were mostly between 0 and 1. This indicates that nearly all species exhibit a decelerating increase of growth with light. In contrast, estimated growth rates at standardized conditions (5 cm dbh, 5% light) varied over a 9-fold range and reflect strong growth-strategy differentiation between the species. As a consequence, growth rankings of the species at low (2%) and high light (20%) were highly correlated. Rare species tended to grow faster and showed a greater sensitivity to light than abundant species. Overall, tree size was less important for growth than light and about half the species were predicted to grow faster in diameter when bigger or smaller, respectively. Together light availability and tree diameter only explained on average 12% of the variation in growth rates. Thus, other factors such as soil characteristics, herbivory, or pathogens may contribute considerably to shaping tree growth in the tropics.
- Published
- 2011
- Full Text
- View/download PDF
35. Individual variability in tree allometry determines light resource allocation in forest ecosystems: a hierarchical Bayesian approach.
- Author
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Vieilledent G, Courbaud B, Kunstler G, Dhôte JF, and Clark JS
- Subjects
- Bayes Theorem, France, Italy, Phenotype, Picea anatomy & histology, Picea classification, Picea growth & development, Species Specificity, Switzerland, Time Factors, Ecosystem, Light, Photosynthesis physiology, Picea physiology, Trees
- Abstract
Tree species differences in crown size and shape are often highlighted as key characteristics determining light interception strategies and successional dynamics. The phenotypic plasticity of species in response to light and space availability suggests that intraspecific variability can have potential consequences on light interception and community dynamics. Species crown size varies depending on site characteristics and other factors at the individual level which differ from competition for light and space. These factors, such as individual genetic characteristics, past disturbances or environmental micro-site effects, combine with competition-related phenotypic plasticity to determine the individual variability in crown size. Site and individual variability are typically ignored when considering crown size and light interception by trees, and residual variability is relegated to a residual error term, which is then ignored when studying ecological processes. In the present study, we structured and quantified variability at the species, site, and individual levels for three frequently used tree allometric relations using fixed and random effects in a hierarchical Bayesian framework. We focused on two species: Abies alba (silver fir) and Picea abies (Norway spruce) in nine forest stands of the western Alps. We demonstrated that species had different allometric relations from site to site and that individual variability accounted for a large part of the variation in allometric relations. Using a spatially explicit radiation transmission model on real stands, we showed that individual variability in tree allometry had a substantial impact on light resource allocation in the forest. Individual variability in tree allometry modulates species' light-intercepting ability. It generates heterogeneous light conditions under the canopy, with high light micro-habitats that may promote the regeneration of light-demanding species and slow down successional dynamics.
- Published
- 2010
- Full Text
- View/download PDF
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