Déformation asymétrique de houppiers pour la génération de représentations paysagères réalistes

National audienceLa génération de paysage naturel virtuel réaliste a beaucoup dapplications, aussi bien en infographie quen éco- logie par exemple. Ce problème est généralement traité en deux étapes. Une distribution des plantes sur le terrain est dabord calculée en utilisant des modèles simplifiés de plantes. Puis ces modèles sont utilisés pour générer des représentations géométriques détaillées des plantes. En suivant cette méthodologie, nous présentons dans ce travail une réalisation dun tel processus sur une forêt de hêtres. Pour cela, nos proposons dutiliser une méthode de distribution stochastique darbres basée sur les processus de Gibbs. Une contribution importante de ce travail est la prise en compte la plasticité des houppiers lors de la distribution en considérant notamment des formes asymétriques de houppier

Soil variation response is mediated by growth trajectories rather than functional traits in a widespread pioneer Neotropical tree

1. Trait-environment relationships have been described at the community level across tree species. However, whether interspecific trait-environment relationships are consistent at the intraspecific level is yet unknown. Moreover, we do not know how consistent is the response between organ vs. whole-tree level. 2. We examined phenotypic variability for 16 functional leaf (dimensions, nutrient, chlorophyll) and wood traits (density) across two soil types, Ferralitic Soil (FS) vs. White Sands (WS), on two sites for 70 adult trees of Cecropia obtusa Trécul (Urticaceae) in French Guiana. Cecropia is a widespread pioneer Neotropical genus that generally dominates early successional forest stages. To understand how soil types impact resource use through the processes of growth and branching, we examined the architectural development with a retrospective analysis of growth trajectories. We expect soil types to affect both, functional traits in relation to resource acquisition strategy as already described at the interspecific level, and growth strategies due to resource limitations with reduced growth on poor soils. 3. Functional traits were not involved in the soil response, as only two traits -leaf residual water content and K content-showed significant differences across soil types. Soil effects were stronger on growth trajectories, with WS trees having the slowest growth trajectories and less numerous branches across their lifespan. 4. The analysis of growth trajectories based on architectural analysis improved our ability to characterise the response of trees with soil types. The intraspecific variability is higher for growth trajectories than functional traits for  C. obtusa, revealing the complementarity of the architectural approach with the functional approach to gain insights on the way trees manage their resources over their lifetime. Soil-related responses of Cecropia functional traits are not the same as those at the interspecific level, suggesting that the effects of the acting ecological processes are different between the two levels. Apart from soil differences, much variation was found across sites, which calls for further investigation of the factors shaping growth trajectories in tropical forests

Intégration d'outils d'optimisation sous CAPSIS : premiers éléments

National audienc

A generalized self-thinning relationship for multi-species and mixed-size forests

Introduction: The self-thinning relationship established by Reineke in 1933 assumes a relationship between the number of stems and the quadratic mean diameter in fully stocked pure stands. This rule is extensively used for management purposes, but it has been initially calibrated for pure, even-aged stands for relatively few species. Objectives: Here, we extend this relationship to mixed-species and mixed-size forests through a generalized modeling approach. Reineke’s rule can be seen as a particular case of this generalized approach. Resource sharing is taken as a starting point; thus, both site fertility and diameter heterogeneity are taken into account. Discussion: Calibration on actual inventories is made on a dataset of 82 French stands. The theoretical relationship is successfully adjusted for species in which enough data were available, namely, common beech (Fagus sylvatica L.), oak (Quercus petraea [Mattuschka] Liebl and Quercus robur L.), and Norway spruce (Picea abies [L.] Karst). Conclusion: Self-thinning exponents obtained for beech and oak (1.86 and 1.76, respectively) can be used in the mixed-species equation that we developed. These results encourage calibrating the parameters for other species if appropriate data are available

Individual seedling mortality as a function of size, growth and competition in naturally regenerated beech seedlings

International audienceYoung forest stands that are naturally regenerated are characterized by a large number of seedlings and high mortality rates. Good prediction of seedling mortality is therefore necessary to model the dynamics of young stands. We used data obtained in a natural beech (Fagus sylvatica L.) regeneration in north-eastern France, to fit logistic models to predict seedling mortality and to analyse how seedling size, seedling growth and local competition relate to seedling mortality. Good relationships were obtained with recent seedling diameter growth, and with a combination of local competition and initial seedling size. However, the relationships between the probability of mortality and recent growth appeared to be unstable and to vary substantially with local competition and among measurement years, precluding the use of these relationships in regeneration models

MODELISATION DE PROPRIETES DE BASE DU BOIS (COEFFICIENTS DE GONFLEMENT ET DENSITE DU BOIS) ET DE LEUR VARIABILITE CHEZ LE CHENE SESSILE (QUERCUS PETRAEA LIEBL.). SIMULATIONS EN VUE DE L'EVALUATION D'UNE RESSOURCE FORESTIERE

PARIS-AgroParisTech Centre Paris (751052302) / SudocSudocFranceF

Modeling tree mortality from a 20-year forest survey in the Western Ghats of India

National audienc

Fagacées : a tree-centered growth and yield model for sessils oak (Quercus petraea L.) and common beech (Fagus sylvatica L.)

International audienceIntroduction : Fagacées is a growth model that has been developed for pure Oak or Beech stand management in even-aged high forests and coppice with standards forests. It has been calibrated for the plain forests of northern France. * Objectives : This paper presents all the characteristics of this model: general structure, equations, and parameters. It can be classified as a distance-independent tree-centered model. Its main originality is that tree growth is organised according to a top-down organisation. * Result : At first, the growth is computed at the stand level. Then it is allocated between the individual trees. The paper presents and discusses successively these two parts. In addition, the model delivers the stem profile of each tree: rings and compartments within the stem. Some other additional modelling that have been defined for batch mode purposes are also briefly presented