Dynamique de la forêt mixte à diptérocaroacées de basse altitude avant et après traitement sylvicole

As part of the STREK project, forest dynamics were analysed to assess the impact of logging, especially relatively environment-friendly techniques, and the potential benefits of silvicultural regimes that favour the growth of commercial species. The study was mainly focused on growth and mortality rates, especially concerning species of the Dipterocarpaceae family, which represents 25% of the trees in the stand and literally all of the commercial species. Productivity of the primary forest was found to be lower than 1m3/ha/year. Dipterocarpaceae species had the highest growth rates. Growth and mortality rates were dependent on the stand density, tree diameterm the size and shape of the canopy, which is an indicator of between tree-competition. The conditions were most detrimental to small-diameter trees. Two years after logging, productivity in the logged plot was as low as in the primary forest. The reforestation process in not yet under way. However, forest degradation to the benefit of Dipterocarpaceae species prompted a productivity gain of 3 to 5 m3/ha/year. (O

Growth and mortality patterns before and after logging

In the frame work of the STREK project, growth and mortality rates were analysed in both primary forest and after interventions such as logging or liberation thinning in logged-over forest. Dipterocarps, the dominant family in the upper storey and the major commercial species, were the particular focus. Before logging, the annual increment is a few millimetres per year and depends on the diameter class, linked to the social status in the stand. Dipterocarps grow faster than many other species and the stand density influences growth. The denser the stand, the higher the proportion of trees with negative or nil growth with an associated high probability of dying. After logging, growth and mortality were clearly influenced by the degree of canopy opening related to logging intensity. The data analysis therefore took into account different levels of logging intensity. A spatial approach using GIS showed that only a part of the stand suffered any harvesting impact. Two years after logging, the balance between growth, recruitment and mortality, showed no significant difference to the control plots. This suggests that the forest is not yet in a reconstitution phase but in a recovery process. Overall, the growth enhancement induced by canopy opening is balanced by a higher mortality. In the logged over areas, growth, after the silvicultural treatments, was enhanced by an average of 50%. The long-term effect of these treatments will have to be assessed over an extended period

The response of the tropical forest stand to silviculture operations

The CIRAD-Forest Research Programme on the dynamics of humid tropical forests has been in operation since 1974 in collaboration with various national forest research institutes. Research is carried out on a network of experimental plots, of which the most important are in Africa (Mopri, Irobo and La Téné in Côte d’Ivoire and M’baiki in the Central African Republic), South America (ZF2 at Manaus in Brazil and Paracou in French Guiana) and Asia (Strek at Berau in Indonesia). These plots have been designed with a common methodology and are followed up consistently. They enable study of the dynamics of humid tropical forest ecosystems and the response of different types of forest to disturbances such as commercial logging and therapeutic thinning. Much research has been carried out on these plots. Some of the results obtained have already led to the implementation of large-scale forest management projects based on the principles of sustainable management (Yapo in Côte d’Ivore, for example). The aim of this article is to present an overview of these plots and to outline the main response trends of the forest stand to sylviculture interventions. In the first part, the parameters of the average natural forest are given (in terms of growth rate, expansion and mortality). By showing how these parameters change over time after sylviculture interventions, the effect of stand density on productivity and the influence of harvesting and thinning on the recovery rate of the forest stand can be assessed

Réaction de peuplements forestiers tropicaux à des interventions sylvicoles

CIRAD-Forêt research on the dynamics of tropical moist forests has been carried since 1974, in collaboration with different tropical forest research institutes. Research is based on a worldwide network of experimental layouts whose most important sites are located in Africa ( Mopri, Irobo and La Tênê in Cote-d'Ivoire and M'baiki in Central African Republic), in South-America (ZF2 at Manaus in Brazil, Paracou in French Guiana) and in Asia (STREK in Beurau in Indonesia). the layouts have been designed with a common methodology and followed-up in a coherent way. They permit to study the dynamics of tropical moist forest ecosystem and the response of different forest types to various interventions such as logging and the silvicultural treatments. Many studies have been carried out in these permanent plots. Some results have already led to implementation of large scale forest management projects (for example Yapo in Cote-d'Ivoire). The aim of this paper is to present the average parameters of the natural forest dynamics (growth, mortality and recruitment). Then we will show the changes in these parameters following an artificial disturbance and the relationship between the stand density and its dynamics. Lastly, we will use these relations to calculate the time required for the forest stand to recover its original state after logging