NOTHOFAGUS REGENERATION DYNAMICS IN SOUTH‐CENTRAL CHILE: A TEST OF A GENERAL MODEL

Abstract

Studies in Southern Hemisphere temperate forests have yielded a general model of how the successional status of shade‐intolerant Nothofagus is related to site conditions and disturbance. According to model predictions, regeneration of most Nothofagus species is dependent on coarse‐scale disturbance at favorable sites where shade‐tolerant rain forest species co‐occur. In contrast, at suboptimal sites where tree species richness is low, regeneration is not dependent on coarse‐scale disturbance. We used variation in forest composition and structure as well as disturbance patterns in the forests of Puyehue National Park, Chile, to test several predictions from this general model. The study area presents a complex mosaic of disturbance patterns, including the effects of the strong 1960 earthquake as well as fire and wind disturbance. We reconstructed stand development on sites affected by these disturbances, and compared these patterns with the structure of old‐growth forests along an elevation gradient from species‐rich montane rain forest to monotypic subalpine Nothofagus forests.Tree age data indicate that both the Nothofagus and many of the rain forest tree species are long‐lived, often reaching ages greater than 600 years. Regeneration of Nothofagus was abundant in stands recently disturbed by landslides, fire, or blowdown across the entire elevation gradient, and Nothofagus also regenerated in old‐growth high‐elevation forests. In contrast, regeneration of Nothofagus was scarce or absent in undisturbed stands and at lower elevation. In comparison with the rain forest species, Nothofagus species are more tolerant of the unfavorable site conditions associated with increasing elevation. Thus, there is a gradient of decreasing interspecific tree competition with increasing elevation, so that the dependence of regeneration of Nothofagus on coarse‐scale disturbance is much less at higher elevation. This study confirms that changes in forest composition may be explained by simple processes occurring in accordance with the main predictions of the general model of Nothofagus forest dynamics: At low elevations, coarse‐scale disturbance is required for Nothofagus regeneration; at higher elevations under decreasing competition the regeneration of Nothofagus is less dependent on coarse‐scale disturbance. Thus, for the Puyehue landscape, patterns of forest structure and disturbance history are congruent with the major features of the general model of Nothofagus dynamics.