Modeling tree architecture and forest dynamics. A research project in the dense moist evergreen forests of the Western Ghats (South India)

This working paper presents a research programme which aims at modelling the dynamics of the dense moist evergreen forests of the Western Ghats (India) from analysing, modelling and simulating tree architecture. The paper first reviews various approaches to modelling the dynamics of heterogeneous forests, either temperate or tropical: demographic matrix models, distance-dependent tree growth models, gap models, cellular automata and multiagent systems. The advantages and drawbacks of the architectural approach are then discussed. The proposed study site is then briefly presented and a programme is outlined: selection of some species which are both frequent and representative of the different forest strata, sampling strategy and measurements, methods used for modelling and computer simulation. The preliminary results obtained since the project was started in early 1995 are then briefly reviewed; a more detailed account will soon be published in another paper of this series

Stochastic 3D Tree Simulation Using Substructure Instancing

Tree growth is simulated using a stochastic model of organogenesis that is faithful to botanical knowledge. This model is based on the concept of bud "physiological age", on the statistical description of the transition from one physiological age to another as well as of bud death, bud growth and branching processes. In order to enhance simulation efficiency, a recurrent algorithm based on stochastic substructure instancing is proposed. The tree is hierarchically decomposed into substructures that are classified according to their physiological age, and a library of random substructure instances is constructed: the recurrent simulation starts with the simplest peripheral substructures, which are also the physiologically oldest; these substructures are then progressively assembled into more complex substructures, until the tree is completely simulated. When the size of the library of substructure instances is small, the time needed to build a single stochastic tree is much shorter than for a usual tree simul tion that operates on a bud-by-bud basis. in computing a group of trees, the speed gain is even much greater, because the library of substructure instances is built for the first tree, and then is reused for computing subsequent trees. A preliminary sensitivity analysis is carried out according to the size of the library: when the library is large, the simulated distribution of the number of organs fits well with the theoretical mean and variance; the algorithm can thus be tuned in order to obtain accurate predictions. On the other hand, a small library (e.g., with only 2 or 3 instances for each substructure class) is sufficient for generating visually realistic trees. A few examples illustrate the high performance of this algorithm which paves the way for the fast simulation of large forest scenes

Fitting a Functional-Structural growth model with plant architectural data

GreenLab is a recurrent discrete-time functional-structural model of plant growth and architecture. A method is presented estimating its parameters: the model is fitted to plant morphological and architectural data observed at one point of time. Since GreenLab output variables (number, size and fresh mass of organs) implicitly and nonlinearly depend on the model parameters, the fitting problem is solved by minimizing a generalized least-squares criterion and by implementing an iterative procedure. Fitting is satisfactorily performed on unbranched plants (cotton, maize, sunflower) using real data. The method is extended to more complex plants (i.e. with branches): a preliminary test on a virtual tree shows that the fitting algorithm also applies to such structured plants

Dynamics of the dense moist evergreen forests. Long term monitoring of an experimental station in Kodagu (Karnataka, India)

This working paper reviews the various research activities undertaken in a permanent experimental field station near Uppangala village at the foot of the western slope of the Western Ghats. Three forest compartments, all situated in a lowelevation moist evergreen dense forest type dominated by dipterocarps, are being monitored since the mid-80s and early 90s. Different types of research projects are being carried out in these compartments on: the impact of selective logging on forest composition, structure and dynamics; the forest structure and diversity and their local variation in relation to topography and silvigenesis; tree architecture and growth; phenology and litterfall; relationships between forest composition and pollen rain; impact of human activities on the vegetation around the village. This station thus provides a common field for new methodological developments and for various ecological and socio-ecological studies

A functional model of tree growth and tree architecture.

A new approach for modelling plant growth using the software AMAPpara is presented. This software takes into consideration knowledge about plant architecture which has been accumulated at the Plant Modelling Unit of CIRAD for several years, and introduces physiological concepts in order to simulate the dynamic functioning of trees. The plant is considered as a serial connection of vegetative organs which conduct water from the roots to the leaves. Another simple description of the plant as a network of parallel pipes is also presented which allows an analytical formulation of growth to be written. This recurring formula is used for very simple architectures and is useful to understand the role of each organ in water transport and assimilate production. Growth simulations are presented which show the influence of modifications in architecture on plant development

Préface

Dans son ouvrage de 1992, Forêts. Essai sur l’imaginaire occidental, Robert Harrison cite Gianbattista Vico dans La Science nouvelle (1744) :« Les choses se sont succédé dans l’ordre suivant : d’abord les forêts, puis les cabanes, les villages, les cités et enfin les académies savantes ». Forêts d’hier et de demain : en matière forestière, plus encore que pour d’autres écosystèmes ou dans d’autres secteurs socioéconomiques, le temps, auquel le titre de l’ouvrage fait explicitement référence, ..