Variable retention harvesting influences biotic and abiotic drivers of regeneration in Nothofagus pumilio southern Patagonian forests

Abstract

Understanding regeneration processes is important for implementing new silvicultural treatments that rely on natural regeneration from seed. Nevertheless, integrated, flower-to-sapling studies of the regeneration cycle evaluating the effect of management factors operating at each reproductive stage are scarce. We analyzed the influence of variable retention harvesting on the biotic and abiotic drivers of regeneration of Nothofagus pumilio forests of Southern Patagonia (Argentina). We quantified losses in reproductive potential caused by biotic and abiotic factors within the landscape mosaic generated by variable retention, including harvested stands with aggregated retention and dispersed retention, and in primary unharvested forests. Overall, pre-dispersal losses were caused by wind and insect predation acting on flowers and developing fruits, whereas post-dispersal losses resulted from stratification during winter, and impact of microclimate and rodent predation upon seeds. Dispersed retention areas modified the main drivers of regeneration as compared to aggregates and control areas. Flowering and fruiting was favored in the dispersed retention treatment, whereas seed and seedling survival were more successful in aggregates and control stands. Aggregates retained within harvested areas maintained most of reproductive processes of primary unharvested forests. The most critical step of the reproductive cycle is associated with the seedling stage to the extent that complete regeneration failure can occur in certain years independently of flower and seed crops.