Dinâmica de florestas alagáveis de igapó de água preta da Amazônia Central

Understanding how hydroclimatic variability modulates the structural and functional stability of igapó forests is essential for assessing their persistence under the intensification of climatic extremes and anthropogenic pressures in the Amazon. This thesis is based on a decade of continuous demographic monitoring (2013–2024) in permanent botanical plots and on the analysis of a 36-year post-fire chronosequence (1982–2017), conducted in black-water igapó forests of Jaú National Park and the Rio Unini Extractive Reserve, in Central Amazonia. The work is organised into a general introduction and two integrated chapters, addressing both contemporary forest dynamics and the long-term effects of hydroclimatic and fire-related disturbances. In Chapter 1, we analysed seven permanent 1-ha plots (7 ha in total), distributed along an inundation gradient and monitored biennially since 2013, considering trees with DBH ≥ 10 cm. Biomass demographic rates (increment, mortality, recruitment, and net balance) were estimated, and the effects of hydroclimatic variables were evaluated, including inundation duration, vapour pressure deficit (VPD), and cumulative water deficit (CWD). Linear mixed-effects models indicated that VPD was the main atmospheric driver of forest dynamics, being associated with reduced biomass increment (p = 0.002) and increased mortality (p < 0.001). During intense El Niño events (2015/2016 and 2023/2024), forest biomass balances became negative (p = 0.0136), highlighting the functional vulnerability of igapó forests to atmospheric drought. Prolonged inundation exerted a stabilising effect on biomass losses, supporting the role of igapó forests as carbon sinks, particularly in areas subjected to long flooding periods. In contrast, igapó forests located at higher topographic positions were more strongly affected by extreme droughts, which increased VPD and intensified biomass losses. In Chapter 2, we assessed a 36-year post-fire chronosequence composed of nine successional stages, based on 47 plots (2.94 ha). Abundance, species richness, floristic composition, and above-ground woody biomass (AGB) were analysed as a function of time since disturbance and soil physico-chemical properties (0–20 cm). The results demonstrate that fire acts as a severe structural disturbance and as a novel ecological filter in igapó forests, promoting high tree mortality, floristic simplification, and persistent reductions in biomass stocks. Post-fire recovery is slow and incomplete, characterised by a gradual increase in biomass and diversity over time (R² = 0.45; p < 0.001), with dominance by a few generalist species of lower wood density, even after three decades. These patterns indicate prolonged functional impairment and high vulnerability to recurrent fires. The integration of both chapters shows that severe droughts associated with strong El Niño events constitute the main source of vulnerability for igapó forests in Central Amazonia, by combining high VPD, water deficit, and reduced inundation duration. This combination triggers high mortality and negative biomass balances in less-flooded areas, while simultaneously increasing landscape flammability and fire occurrence in low-lying zones, resulting in long-lasting losses of carbon and biodiversity. Under a scenario of regional warming and intensification of hydroclimatic extremes, igapó forests are approaching a critical functional threshold, in which the decoupling of carbon and water cycles may compromise their role as carbon sinks in the Amazon Basin. These findings reinforce the urgency of integrated strategies for conservation, fire prevention, and ecological adaptation to maintain the functional integrity of these ecosystems under ongoing climate change.