Natural establishment of forests in the Brazilian Pampa biome should occur due to soil, hydrology and climate conditions, although no significant forest expansion over grassland has been noticed, precluded mainly by human interference and lack of environmental management. In this study, we used niche-modeling distribution of the tree species Schinus molle L. based on climatic variables to access the vegetation dynamics of the Brazilian Pampa and to develop strategies that assure the conservation of this biome, concerning both grassland and forest formations. Here we show that a large area of the Brazilian Pampa is suitable for expansion of S. molle populations, supporting the forest expansion over grassland as a natural process in this biome. We propose that the current absence of tree species expansion over the grassland in these areas is a result of the resilience of the grassland and of human interferences through expansion of agriculture, ranching and forestry with exotic species. Therefore, conservationist actions should focus on establishing preservation unities that include forest populations and grassland, while environmental management should be applied just in farming areas with historical human interference. Such actions will respect the ecological dynamics of the Pampa and value the forest formations in this grassland-dominated environment.