Influence of biotic and abiotic factors on the growth of pre- and post-harvest regeneration in a Nothofagus pumilio forest

Abstract

To propose new silvicultural practices, it is necessary to understand the involved ecosystem processes and the impact that they produce. The proposed practices generated several questions related to remnant tree stability, the seedling bank, seed production, regeneration dynamic and the influence of biotic and abiotic damages. The objective was to determine the influence of biotic (forest structure, seedling bank, seed production and browsing by Lama guanicoe) and abiotic factors (damages by freezing or drought) in the growth of pre- and post-harvest regeneration in a Nothofagus pumilio stand under shelterwood cutting over 20 years. Monitoring surveys of forest structure and regeneration dynamics were conducted in ten permanent plots. Results showed that the remaining overstory trees reduce their basal area after harvesting (22.3 to 10.7 m² ha^-1), varying their crown cover/basal area ratio (1.1 to 6.5). Also, this study suggest that: (i) recruitment, survival and growth of pre- and post-harvest regeneration is a result of the interaction of several factors, e.g. pre-existing seedling bank, post-harvest seeding production, and the biotic and abiotic damages, being more sensitive during the first four years; (ii) pre- and post-harvest plants are the responsible for generating the future forests; and (iii) abiotic factors (freezing or drought) produce higher growth loss than that produced by biotic ones (browsing). In this sense, permanent plots for long-term monitoring allow identifying the risk factors of the proposed silvicultural practices.