Chilean historiography states Araucanian territory kept its pristine conditions until the republican period beginning. However, the presence of border military enclaves would have produced an early environmental disturbance in the Araucania. To validate this hypothesis, a study of the Spanish chronicles, old documents and historiographical studies was done. Results indicate there was significant environmental disturbance on the Araucanian ecological system, as a result of the intercultural contact during the Arauco war and the Spanish-Creole settlement. Native species extinction, exotic species introduction, Mapuche crops substitution, natural resources mistreatment, land use changes, Mapuche culture modification, and Araucanian mortality and migration rising are among the environmental effects occurred under the area influenced by the forts.