Restauração ativa de floresta secundária: Estabelecimento inicial de espécies florestais em resposta a tratamentos silviculturais durante o El Niño 2023/24

Abstract

Deforestation in the Legal Amazon has two main causes: illegal logging and the expansion of the agricultural frontier in the biome. Following deforestation, another important characteristic is the lack of adequate management to maintain the productive capacity of the site for agricultural activities, resulting in the abandonment of the area and the deforestation of other forests. As a result of this abandonment, a new vegetation known as secondary forest (capoeira) emerges. Secondary forests occupy approximately 17 million hectares in the Legal Amazon and provide a wide range of ecosystem services, especially acting as important carbon sinks. However, these forests are seen as unproductive and lack specific legal protection, resulting in a high probability of recurrent deforestation. Proper management with the implementation of silvicultural systems suited to the characteristics of the forest constitutes an important conservation strategy for these areas, generating income from timber and non-timber forest products. However, the current scenario of climate change and the intensification of extreme weather events in the Amazon, such as El Niño, which has altered rainfall patterns in the region and increased tree mortality, pose new challenges to the implementation of more sustainable forest production systems. In this context, we implemented a secondary forest enrichment silvicultural system with six forest species (Aniba rosaeodora, Copaifera sp., Dipteryx odorata, Euterpe oleracea, Theobroma cacao, and Theobroma grandiflorum) under different fertilization treatments: (T1) liming; (T2) liming + organic fertilization with chicken manure; (T3) liming + mineral fertilization; and (T4) liming + combined organic and mineral fertilization. The overall objective of this thesis was to evaluate the functional performance and initial establishment of six forest species in a secondary forest enrichment silvicultural system under different fertilization treatments during El Niño 2023/24. The specific objectives were divided into two chapters: I) to investigate the differences in the microclimate of the secondary forest understory and full sun environment during El Niño 2023/24; II) to evaluate whether the functional performance of seedlings planted in the secondary forest understory is influenced by the species and the type of soil management (fertilization) (Chapter 1); and III) to evaluate whether there is a short-term effect of fertilization treatments on the survival and growth of economically important tree species in enrichment plantings in secondary forests; IV) to evaluate whether fertilization treatments promote greater biomass accumulation in the species; V) to evaluate whether fertilization treatments improve the nutritional status of the species (Chapter 2). The understory of the secondary forest, even during severe drought events, exhibited microclimatic characteristics (relative air humidity, temperature, and vapor pressure deficit) that contributed to the initial establishment of the seedlings. The survival rate of all species in all treatments was greater than 90%. Treatments with organic fertilization (T2 and T4) improved nutritional status, especially of the species T. cacao, which also showed greater biomass accumulation in these treatments. The data indicated that the seedlings presented stomatal and non-stomatal limitations to carbon assimilation in response to water deficit. Seedlings from the treatment that combined organic and mineral fertilization (T4) showed greater recovery capacities to water stress, especially D. odorata. On the other hand, A. rosaeodora showed less recovery. Our results demonstrate that the silvicultural enrichment system of secondary tropical forests is a promising adaptive silviculture strategy against the effects of the climate crisis. Despite the significant effects of extreme drought events on the functional performance of the species, in general, the seedlings exhibited good establishment indicators, which were influenced by soil fertility management practices and the species planted.