The spatial and temporary position of the swampy Loto-Cyperetum eragrostidae and Caricetum ripariae and prairie Juncetum procerii and Centello-Anthoxanthetum utriculatae plant associations, in the degradation of the swampy Forest of Temo-Pitra (Blepharocalyo-Myrceugenietum exsuccae) vegetation dynamics was studied, comparing the taxonomic, origin and biological spectra of the flora and applying multivariate statistical analysis of classification (cluster analysis) and ordination (principal components and constellation of plant species and associations) using the floristic similarity between them. The study was accomplished in the inferior basin of the Valdivia river and in the coastal region of the homonimuous province in the X Region of Chile, with 48 vegetation samples lifted with phytosociological methodology, in homogeneous stands of these swampy and prairie associations. With exception of the Centello-Anthoxanthetum utriculatae, in all the others associations dominated alochtonous plant species. It was found a great floristic affinity and similar site requirements between the swamp Loto-Cyperetum eragrostidae and the prairie Juncetum procerii associations. It is concluded that the swampy associations would be primary communities, while the prairie would correspond to secondary communities of antropic origin and dependent as such by grazing and cultivation as human intervention. It is proposed a series of degradation that is going from the Loto-Cyperetum eragrostidae to the Centello-Anthoxanthetum utriculatae, going through the intermediate stage of Juncetum procerii prairie.