The west of Santa Catarina was occupied by indigenous groups and caboclos until the arrival of other migrants and immigrants in the 20th century. The spaces occupied by fields and forests were described as "sertões" (wilderness), as they did not have a suitable agricultural practice at the time. The object of this article is to analyze the uses and occupation process of forest areas in western Santa Catarina from 1920 to 1960, when this frontier was "closed". For this, a varied typology of sources was analyzed, in dialogue with the precepts of environmental history. The advance of colonization was responsible for the reduction of spaces dominated by the forest, which is now occupied by agriculture and animal husbandry. Both were the main elements responsible for the formation and consolidation of the agro-industrial sector in the region.