Profundidade do lençol freático: efeitos na dinâmica, estrutura e resposta da floresta às secas intensas na Amazônia

Abstract

Water availability is one of the main influences on the structure, dynamics and response of tropical forests to extreme events. However, little is known about the relationship between the water availability provided by the groundwater, modulated by depth to the water table, and forest functioning. In this research, aiming to understand the natural forest functioning, I investigated how the structure of the Amazon forest varies according to the water table depth, historical average of climatic water deficit and soil properties (chapter 1). Then, I evaluated forest functioning in years of strong drought, investigating how water table depth and soil properties interact with climatological droughts to influence tree and palm dynamics (chapter 2). Water provided by both precipitation and soil affected the structure and dynamics of the Amazon forest, but in different ways. Forests with shallow water table (depth <5 m) had lower aboveground biomass productivity and aboveground biomass stock than those with deep water table. Forests located in drier climates (maximum cumulative water deficit < -160 mm) also had lower productivity and biomass stocks than those located in wetter climates. Productivity (AGWP) was affected by interactions between climatic water deficit, water table depth and soil texture. In drier climates, shallow water table forests had lower AGWP than deep water table forests. However, the combination of shallow water table and clayey soil reduced the limitation imposed by the dry climate on productivity, while the combination of shallow water table and sandy soil caused the opposite. Therefore, in this first chapter I have separated the relative contribution of water table and climate, improving the understanding of the functioning of tropical ecosystems. When it comes to strong droughts, forest responses to climate change are of global importance and are critically determined by patterns of water availability. There was no change in stem mortality rate and biomass loss in response to drought in forests dominated by shallow water-table. Instead, there was an increase in recruitment rates compared to rates in the pre-El-Niño. In addition, there was a significant increase in tree biomass for the analyzed period (2010-2016). Therefore, in this chapter 2 I have shown that forests that grow on shallow water table are remarkably resistant to drought, thus enhancing our understanding of the integrated effects of drought, encompassing climate, local hydrology and soil, on tropical forest dynamics.