ARE TROPICAL RAIN FORESTS NON-RENEWABLE? AN ENQUIRY THROUGH MODELLING
Keywords:Dipterocarp forests, management, non-renewable, mechanistic model, natural frequency, regeneration, poles
Much controversy surrounds the management of tropical rain forests, and arguments that they are non-renewable are gaining currency. The solutions to such arguments lie in studying the long term changes and recovery of forests following specific silvicultural regimes. Such forest areas in the tropics have all vanished. An alternative and easier approach is by modelling. A mechanistic process model was developed based on the five development stages of trees (seedling, sapling, pole and understorey layer, main canopy layer, and emergent tree), and the individual photosynthetic production at each layer. The simulations were validated satisfactorily with the stand characteristics found in nature. Following the validation, the model was used to assess two silvicultural systems, the Malayan Uniform System (a tropical sheltenvood system) and the Selective Management System (a selective felling), that have been used for managing the dipterocarp forests in Malaysia. The model's results, even with cautious acceptance, have several important implications to forest management practices. Dipterocarp forests are renewable, but only long rotations (ca. 100 years) are in step with the dynamics of the forest. This is because the recruitment process is very slow. More significantly, the model showed that the pole regeneration is ephemeral in time and space, implying that cutting dipterocarp forests when the poles are few or absent would endanger the timber sustainability of such forests.