The ecological consequences of Douglas-fir (Pseudotsuge menziesii) plantations in the south of Chile and their impact on the native vegetation and soil chemistry were studied. The study area was a private forest property close to Villarrica (39 degrees 19'S, 72 degrees 18'W) in southern Chile. Vegetation samples and transect methods were used to assess floristic structure. Samples from four typical soil profiles under native forest and Douglas-fir plantations were analyzed to evaluate the impact of plantations on soil chemistry. Large differences in species diversity and vegetational structure were found between native forest and Douglas-fir plantations. Native forests are rich in epiphyts, climbers and endemic species, the top layer is formed by emergent Nothofagus obliqua, N. alpina or N. dombeyi, the layers below are formed by evergreen tree species from Valdivian rainforest. Douglas-fir plantations are caracterized by non-native species (mostly european species of meadows or disturbed sites) and they are extremely poor in native plant species. In addition to the negative influences on the diversity of native flora, the Douglas-fir plantations show changes in soil chemistry compared with soil profiles under native forest. The upper soil horizons under Pseudotsuga menziesii show the tendency to be impoverished in base cations, their base saturation is lower and they have lower levels of phosphorus. From an ecological point of view the Douglas-fir plantations are not sustainable because of their destructive influences on the native vegetation. Therefore the Douglas-fir plantations should not be extended to areas with a high ecological value.