Modélisation économique de la dynamique des forêts tropicales : une revue de la littérature

Résumé En Fr

Economie modelling of tropical forests dynamics : a survey of the literature Numerous econometric analysis have tried to precise the dependency of forests dynamics on variables like demography, income, agricultural productivity or tropical timber production and trade. Making these analysis significant, despite the historical and geographic specificity of each situation, can be improved through the choice of the dependant variable (preferably the absolute level of deforestation). It is delicate to compare the weight of an explaining variable in distinct models, but some significant ideas of general validity can nevertheless be drawn from this exercise, (i) Numerous analysis show a strong relation between population and forest area dynamics. It is nevertheless difficult to anticipate the impact of the growth of demographic pressure without referring to the technical and institutional environment, (ii) There is no clear-cut relation between deforestation and the various income indicators, namely the growth of the income per capita has multiple and contradictory effects on the demand for timber and agricultural land. (iii) The increase in agricultural productivity has two opposite effects : on the one side, it diminishes the need of land to reach a given level of production ; on the other side, it makes the local agriculture more competitive and may lead to the development of the production in the area, (iv) Tropical timber international trade does not appear as a significant factor of deforestation (6 % of the total timber volume). But the opening of new roads for the cutting pave the way for the settlement of landless farmers. Defining conservation policy imply a better understanding of the behaviours of the main deforestation agents. The farmers behaviours are influenced both by general variables like the level of wages, interest rates, agricultural and timber prices, and others factors more specifically related to the expanding agricultural frontier like the existence of roads or the promotion of anti-erosion techniques. The foresters' strategies appear to be strongly dependant upon the security of the rights they may get on the land, and the existence of rent seeking opportunities. The analysis of the impact of national and international conservation policies has been noticeably improved by the use of computable general equilibrium models that allow to take more precisely into account the behaviours of the main agents of the process, and to simulate more comprehensively the simultaneous impact of policy tools. The main results of several models are presented. It must be emphasised that their scope is more heuristic than practical.

La modélisation économique constitue une approche pertinente pour plusieurs dimensions de l'étude des dynamiques anthropiques des forêts tropicales qui renvoient à des phénomènes complexes et mal connus. De nombreuses analyses économétriques ont tenté de préciser la dépendance de ces évolutions vis-à-vis de variables telles que la population, le revenu, la productivité agricole ou le commerce international des bois tropicaux. De multiples difficultés et controverses méthodologiques limitent cependant sensiblement la portée de ces travaux. L'analyse des politiques nationales ou internationales de conservation a sensiblement bénéficié du développement de modèles d'équilibre général calculable qui permettent de mieux prendre en compte les comportements des principaux agents de la déforestation et de simuler de façon plus compréhensive l'impact de mesures simultanées. On doit souligner que leur portée reste plus heuristique que pratique.