This thesis presents a phytosociological analysis of the current vegetation communities on the western slopes of the Valdivian Coastal Range in South Chile. The goal is to describe the changes undergone by the potential vegetation in the research area, which led to the formation of non-native vegetation units and to a more diverse landscape. The data collection was carried out between the Bonifacio and Hueicolla sectors (de Los Ríos Region) and up to an altitude of 300 m a.s.l. This area corresponds to the region where the Olivillo forest used to be the dominant community. A total of 169 phytosociological relevés was used to survey the vegetation. The area of the relevés ranges between 100 and 400 m2, according to the physiognomical minimal area and to the Braun-Blanquet approach. The collected vegetation data set was used to: i) construct the related full and synoptic tables, and ii) describe the physiognomy, floristic composition, diagnostic species, ecology and distribution of the plant communities. In particular, the diagnostic species were identified by using their fidelity values based on the phi-coefficient as described in the literature. The vegetation units were then classified by means of the Ward’s method and the Euclidean distance. Finally, a detrended correspondence analysis (DCA) was performed to identify the environmental variables with the largest influence on the relevés. The analysis led to the classification of 12 plant communities (11 associations and 1 community) and to the identification of a total amount of 137 species. Out of the 137 species, 76 are endemic and 18 present among the IUCN conservation categories (1 is Endangered, 7 are Vulnerable, 4 are Near Threatened, 4 are Least Concerned, 1 is Data Deficient and 1 is Not Evaluated). The species are distributed over 5 classes, 62 families and 117 genera. The plant communities belong to 2 classes (Molinio-Arrhenatheretea and Wintero-Nothofagetea), 3 orders and 6 alliances. One alliance and 2 associations are newly described: the Libertion chilensis and Agrostio capillariae-Eryngietum paniculatae within Molinio-Arrhenatheretea, and Rubo constricto-Greigietum sphacelatae within Wintero-Nothofagetea. The results of this thesis indicate that: i) the identified units show serial relationships of anthropogenic origin, and ii) human activity favours the development of native and non-native permanent communities in the research area. Finally, they can be used for the selection of areas suitable for ecological restoration and landscape management.