Agricultura itinerante e manejo de recursos: impactos para uma floresta secundária tropical.

Abstract

The expansion of secondary forests in tropical ecosystems due to post-shifting cultivation abandonment is a reality driven by decreased productivity resulting from improper management practices. Natural regeneration often plays a major role in restoring these ecosystems, but its effectiveness is limited by various factors, including the degree of degradation, the source of propagules, and proximity to adjacent forests. The Manipulation of Water and Nutrients in Secondary Forests in Eastern Amazonia (MANFLORA) project was developed over eight years (1999-2007) to understand the factors influencing the dynamics of these ecosystems. The experiment was conducted in an ecosystem with a 40-year history of shifting agriculture and included irrigation during drier periods and the removal of nutrients through litter. Treatments consisted of irrigation, litter removal, and a control group. Sixteen years after the conclusion of MANFLORA, this dissertation is divided into three chapters aiming to comprehend the overall context of shifting agriculture in Amazonia and the long-term impacts of resource management on secondary forests in the region. In the first chapter, a literature review on shifting agriculture in Amazonia was conducted, highlighting its importance for rural populations and emphasizing negative impacts such as reduced biota, soil fertility, and soil aggregation, as well as impacts on flora and fauna. The next two chapters evaluated the long-term effects of the MANFLORA experiment. The second chapter examined indicators of vegetation composition and structure, showing differences in floristic composition among treatments but without significant impacts on vegetation structure. The third chapter focused on soil and litter nutrient dynamics, highlighting residual effects on nutrient availability such as K, Ca, Mg, and P. Irrigation positively influenced K availability, while litter removal negatively impacted pH and monthly production of Ca, Mg, and P. These results suggest that resource management can have lasting effects on nutrient dynamics in secondary forests. In summary, the study underscores the importance of shifting agriculture for Amazonian communities but emphasizes the need for sustainable practices to balance food production with forest conservation. The long-term results of MANFLORA provide valuable insights into post-shifting cultivation dynamics, highlighting the influence of water and nutrient manipulations over time. Therefore, this work contributes to understanding the role of these ecosystems and emphasizes the importance of management approaches that consider long-term resilience and sustainability.