This paper analyses the determinants of the optimal size of protected areas and what conducts neighboring effects. We investigate in which measure the infrastructure effect and the scarcity effect matter. We obtain several results. The size of protected area mainly depends on preferences toward forest, on the firms’ production costs and on the relation between municipalities. As far as total deforestation is concerned asymmetric regulation is better than no regulation. The infrastructure effect always leads to smaller protected areas than the scarcity effect. Under the infrastructure effect, centralized decisions do not always work in favor of larger protected areas than decentralized decisions contrary to the scarcity effect. We also show that decentralized decisions can reach the first best under the infrastructure effect without public intervention. A study of protected areas in the Brazilian Legal Amazônia corroborates our theoretical results.