Estratégias silviculturais aplicadas ao manejo sustentável de florestas de crescimento secundário na Amazônia Central

Abstract

Secondary forests are representative landscapes in the Brazilian Amazon, covering about 20% (~16,000,000 hectares) of the region's previously deforested area. However, these forests suffer from high rates of deforestation. Sustainable forest management has been promoted as a strategy to encourage owners of secondary forests to conserve them. Silvicultural management systems, based on methods of improvement of natural stands and enrichment with commercial species, are important management options for this forest typology. However, there is a lack of scientific knowledge to support the formulation of silvicultural protocols for the management of secondary forests through these systems. In this sense, the main objective of this thesis is to evaluate how different silvicultural strategies contribute to the sustainable management of later successional secondary forests. To this end, silvicultural diagnoses were carried out in 2021 in two later successional secondary forests in the Central Amazon. These forests were found to have a floristic composition and trees with stem quality suitable for timber production. However, the growth conditions of desirable species require the application of silvicultural treatments (Chapter 2). Subsequently, in 2021, an experiment of improvement of secondary forest through liberation silvicultural treatments was installed in a 35-year-old secondary forest. Five blocks were established consisting of two plots of one hectare each. In one of the plots, individuals of commercial tree species benefited from liberation silvicultural treatments and in the other they did not receive silvicultural treatments. Individuals of Goupia glabra (the dominant species in the forest) had superior growth when benefiting from liberation treatments, but the magnitude of the response depended on the individual tree traits and the growth conditions (Chapter 3). In 2016, an enrichment experiment with a split-plot design was established in a secondary forest (19 years old at the time). Six levels of basal area reduction (0, 20, 40, 60, 80, and 100%), combined or not with understory slashing (understory slashed and control), were applied to the planting of six commercial tree species (Cedrela fissilis, Tabebuia rosea, Swietenia macrophylla, Carapa guianensis, Bertholletia excelsa, Hymenaea courbaril). Silvicultural treatments affected the microclimate of the forest, but temporal changes were observed that caused a reduction in light availability. However, light availability varied among species. Furthermore, the microclimatic conditions caused by the treatments are not harmful to the planted species (Chapter 4). Silvicultural treatments affected survival, biomass, stem quality, and carbon accumulation of planted species. Wood quality was also affected, but for a minority of species (Chapter 5). Survival and biomass productivity of planted species were related to traits measured in various organs of planted species, providing a broad view of the mechanisms that determine species responses to silvicultural treatments and providing valuable information for selecting suitable species for enrichment plantings, such as Bertholletia excelsa, Carapa guianensis, and Hymenaea courbaril (Chapter 6). The results obtained are important for the formulation of silvicultural protocols for the sustainable management of secondary forests, contributing to the generation of income for their owners and, consequently, to the conservation of this forest typology and its essential ecosystem services.