The Paranaian forest is currently a relict of the Atlantic Mata and is the largest ecoregion of the 15 that make up it. It extends from the western fallout of Serra do Mar in Brazil, to eastern Paraguay and the province of Misiones in Argentina. Our interest is to incorporate a historical and geographical dimension that allows us to characterise the environmental changes in the last two centuries since the dynamics of the complex systems, at the Triple Border of Brazil, Paraguay and Argentina. The interaction of global economic policy models is verified locally and regionally in the social system and productive activities. Taking environmental history as a reference, border processes are described in a time frame that facilitates analysis of how the territory was structured by social, political and economic borders. This work is a preliminary approach, from the Argentinian perspective (Misiones province) and is organised in two central parts: the first with the characterisation and explanation of the triple border as a complex system and the description of its hydrographic, biogeographical, economic and spatial sub-systems; and the second, containing the environmental changes in the Atlantic Mata on the triple border between 1810 and 2020.