This paper aims to analyze the economic impact of the legal reserve on the gross margin of different types of farms located in the watershed of the Oriçanga River – in São Paulo state, Brazil. In order to reach such purpose, a typology of farmers was elaborated for the watershed. Two farmer types were selected for a detailed study: small farmers with low technology and citrus producers. The productive structure of both types was modeled through the recursive programming method, comprising the period between 2002/03 and 2008/09. The current farm system adopted by each type was confronted with two scenarios for legal reserve compensation: I) through the reallocation of productive areas within the farms and sustainable management of natural vegetation recovery in order to explore the production of timber; II) through the spontaneous growth of natural vegetation. Results highlight the importance of policies aimed to obtain a more equitable distribution of environmental conservation costs in the society, as well as the importance of locational adjustments of the legal reserves, in order to reach a better equilibrium between the preservation of biodiversity and the opportunity cost of land.