Structure and Dynamics of Old-Growth Nothofagus Forests in the Valdivian Andes, Chile

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Abstract
Analysis of the structure of old-growth Nothofagus-dominated forests in the Valdivian Andes indicates that they are not in a steady-state condition. At mid-elevations the lack of saplings and of relatively small-diameter individuals clearly shows that the shade-intolerant Nothofagus spp. are not regenerating in undisturbed old-growth stands. The population structures and reproductive behavior of the shade-tolerant Laurelia philippiana and Saxegothaea conspicua suggest that in the absence of massive disturbance these species would replace the Nothofagus spp. at mid-elevations. The failure of succession to proceed beyond the relatively early successional phase represented by the N. dombeyi- and N. alpina-dominated forests is a consequence of a long history of periodic natural catastrophes, principally landslides and volcanic eruptions. Catastrophic mass movements in the Andes of south-central Chile, such as those triggered by the devastating 1960 earthquake, periodically destroy or drastically alter thousands of square kilometers of old-growth forest, creating conditions favorable to the establishment of the rapidly growing Nothofagus spp. Models of vegetation change which assume long-term stability of site and postulate successional development towards a stable end-point are not fully consistent with the regional importance of the mid-elevation Nothofagus forests of the Valdivian Andes which are maintained by catastrophes. A kinetic scheme which does not require a stable end-point for succession and which emphasizes continuous change, even in old-growth forest, is more consistent with the dynamics described for the old-growth forests of the Valdivian Andes.