Forest structure and dynamics are analysed and compared for No thofagus-dominated forests in the Andes and for forests lacking Nothofagus in the Coastal Cordillera of the Province of Valdivia (c. 400S latitude), Chile. At mid-elevation (c. 600-950 m) in the Andes, even-aged Nothofagus stands develop on sites devastated by mass movements and volcanic eruptions; with further development shade-tolerant trees such as Laurelia philippiana, Saxegothaea conspicua and Dasyphyllum diacanthoides become abundant in the Nothofagus-dominated stands. The lack of saplings and of relatively small- diameter individuals indicates that the shade-intolerant Nothofagus species are not regenerating in undisturbed old-growth stands. In contrast, the population structures and reproductive behaviours of the shade-tolerant trees suggest that in the absence of massive disturbance these species would replace the Nothofagus species at mid-elevations. However, due to the longevity of the Nothofagus (> 500 years) and the frequency of periodic catastrophic disturbance extensive Nothofagus-free stands do not occur in the Valdivian Andes. At higher evaluations in the Andes, above the upper altitudinal limit of the shade-tolerant trees, the dynamics of the pure Nothofagus forests are also greatly influenced by massive disturbances such as volcanic eruptions, mass movements, and snow avalanches which lead to the formation of extensive even-aged stands in the near-timberline zone. Here, in pure, old-growth Nothofagus stands show- ing no sign of recent massive disturbance since the establishment of the oldest trees, tree regeneration occurs in gap phases involving a subtle overstorey- understorey interaction. Large treefalls create understorey patches of less favourable micro-climate, thus reducing the size and abundance of the under- storey bamboos which otherwise impede Nothofagus regeneration. This pattern and process of regeneration creates a mosaic of even-aged patches of trees in the near-timberline Nothofagus forests. In the Coastal Cordillera natural disturbances are less frequent and less massive than in the Andes. Accordingly, the population structures of most of the common tree species in these Nothofagus-free forests indicate that they are much closer to a steady-state condition than are the Andean forests. Even though the composition of the Coastal forests is not as influenced by massive disturbances as in the Andes, the dependence for regeneration of some of the common trees on large canopy gaps, probably created by wind, indicates the influence of allogenic factors as well.