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Disturbance and regeneration dynamics of an old‐growth North Patagonian rain forest in Chiloé Island, Chile
- GUTIÉRREZ, ALVARO G., ARMESTO, JUAN J., ARAVENA, JUAN CARLOS
- The journal of ecology 2004 v.92 no.4 pp. 598-608
- forest trees, rain forests, old-growth forests, shade tolerance, plant competition, tree growth, tree and stand measurements, forest stands, natural regeneration, growth rings, overstory, stand structure, stand composition, canopy gaps, Chile
- 1 Few studies have addressed the mechanisms of coexistence of shade‐tolerant and intolerant tree species in the canopy of old‐growth, lowland rain forests of southern South America. We explored the hypothesis that their forest dynamics result from frequent, single tree‐fall gap episodes. 2 We analysed the disturbance regime and assessed the regeneration modes of shade‐tolerant and intolerant canopy trees in a lowland, old growth North Patagonian rain forest in Chiloé Island (42° S) using dendroecological methods. 3 Dominant canopy trees were the shade‐intolerant Nothofagus nitida (Fagaceae), Drimys winteri (Winteraceae) and the tolerant Podocarpus nubigena (Podocarpaceae). The oldest individuals, however, were represented by Saxegothaea conspicua, Podocarpaceae (shade tolerant > 498 years) and Weinmannia trichosperma, Cunoniaceae (intolerant > 382 years). Shade‐tolerant species have regenerated continuously for the past 400 years, but recruitment of shade‐intolerant species has increased only in the past 50 years. These regeneration patterns suggest a lack of catastrophic disturbance, at least since 1650. 4 Analysis of tree radial growth patterns revealed frequent moderate releases of both shade‐tolerant and intolerant tree species, consistent with frequent small‐scale disturbances, such as individual tree‐fall gaps. Increased releases, peaking in 1940 and followed by enhanced recruitment, may be a consequence of individual tree‐falls induced by low‐intensity windstorms or limited selective logging. Such disturbances have occurred for at least 250 years, but have had little overall effect on stand structure and canopy composition. 5 The replacement and coexistence of shade‐tolerant and intolerant tree species in the canopy of this North Patagonian forest can be explained by frequent small‐scale disturbances (i.e. gap‐phase dynamics) and by the absence of large‐scale natural or anthropogenic disturbances over the past four centuries.