Nothofagus dombeyi regeneration in declining Austrocedrus chilensis forests: Effects of overstory mortality and climatic events

Abstract

This research examines the regeneration dynamics of . Nothofagus dombeyi and . Austrocedrus chilensis in . A. chilensis-dominated forests growing near the eastern limit of . N. dombeyi where precipitation is limiting. In these forests the widespread decline and mortality of overstory . A. chilensis trees, known as '. mal del ciprés' (cypress sickness), generates large canopy gaps in which new individuals establish. Our objective was to study the population dynamics of . N. dombeyi and . A. chilensis in these forests to investigate the influences of overstory tree death and climatic variation on establishment. We sampled 6 symptomatic . A. chilensis stands and used dendrochronological techniques to reconstruct basal area development and regeneration establishment over time. Bivariate event analysis was performed to examine the temporal relationships between tree establishment and mortality events and climatic variation. Overstory . A. chilensis trees established as post-fire cohorts, with subsequent establishment of . A. chilensis and . N. dombeyi during the past 50-60 years. Regeneration in the past two decades was primarily . N. dombeyi. The establishment of both . A. chilensis and . N. dombeyi was synchronous with overstory tree mortality events, but it was more consistent among stands and prolonged for . N. dombeyi. Establishment of . A. chilensis was not associated with climatic events but . N. dombeyi establishment was synchronous with droughts, possibly related to climate-driven mortality creating canopy gaps or reducing competition within gaps. We have demonstrated that . N. dombeyi has the ability to establish in post-fire . A. chilensis-dominated forests resulting in mixed-species, uneven-aged forests. The ongoing increase in the abundance of . N. dombeyi relative to . A. chilensis represents a shift in composition and increased complexity in stand structure driven by '. mal del ciprés' and climatic variation. © 2011 Istituto Italiano di Dendrocronologia.