Protecting the rain forest in Madagascar is essential to conserve biodiversity on the island. However, regulations must take into account the development of the local population. The aim of this paper is to determine if there are viable solutions which lead to the conservation of the forest and the development of the inhabitants of the forest corridor of Fianarantsoa. We will also determine what decisions must be taken in accordance with the two aspects of the problem; by elaborating a model and studying it with the mathematical tools of the viability theory. This theory deals with controlled dynamical systems and consists in finding controls which keep the evolutions governed by these systems in a defined constraint set. The set which gathers all the situations for which such controls exist is called the viability kernel. The computation of the viability kernel with a condition on equity between the different generations excludes a large part of situations. However adding monetary transfers enables to increase the size of the viability kernel.