Regeneração natural em uma floresta atingida por tempestade convectiva na Amazônia Central: dinâmica sucessional e respostas funcionais

Abstract

Windthrows are the main disturbance agents in tropical forests, directly impacting the dynamics (recruitment, growth, and mortality) and species composition. However, in the early stages of regeneration following natural disturbances, the patterns of recovery are complex and hard to predict. Changes in environmental factors, such as air temperature and vapor pressure deficit (VPD), are crucial for understanding the species’ demographic dynamics and their physiological responses to the environment variation. When those three components are combined, they provide a greater understanding of forest establishment and recovery after disturbances. However, studies focusing on the initial phase of natural regeneration are scarce, especially in tropical forests. This study aimed to monitor the microclimatic, demographic, and physiological dynamics of natural regeneration in an area affected by windthrow in 2019 in Central Amazonia. Six permanent plots (4m x 4m) were monitored for 36 months, distributed across a disturbance severity gradient (20% to 90% tree mortality), and three permanent plots (4m x 4m) in an undisturbed forest area close to the windthrow event. Additionally, microclimatic variables were monitored using a 25-meter-tall tower installed near the experiment, along with sensors inside and outside the gap 1,3 meter above the ground. In the third year after the event, functional traits were measured for pioneer and non-pioneer species located in the gap areas. The results indicated that windthrow caused an increase in average air temperature, VPD, and a reduction in relative humidity (RH) in the gaps when compared to the intact forest (p < 0.001). However, these differences tended to decrease over time due to vegetation growth and restoration, which contributed to local microclimatic regulation (PseudoR2 = 0.73). Regarding vegetation dynamics, the degree of disturbance severity had a positive effect on recruitment and growth rates (p < 0.001), whereas the effect on mortality was less pronounced (p = 0.017). Precipitation and VPD reduced recruitment and growth rates but had a positive effect on mortality. The disturbance also promoted strong species turnover, favoring communities with lower wood density and higher growth rates, particularly in high- severity areas (r = -0.36, p = 0.012). Additionally, the analysis of functional traits between pioneer and non-pioneer species indicated that the traditional trade-off between growth and survival was not evident in the study area. Traits such as Asat (r = 0.72, p < 0.05) and Vcmax (r = 0.57, p < 0.05) explained growth, while Rdark (r = -0.72, p < 0.05) was the best predictor of survival. The results highlight that windthrows play a crucial role in secondary succession in tropical forests. The interaction between microclimatic, vital rates, and functional traits reinforces the complexity of the responses following the disturbance. Microclimatic variations act as environmental filters that, combined with allocation strategies, favor the dominance of species with acquisitive traits in the early stages of natural regeneration. However, conservative traits are essential for the continuity of succession. This information is crucial for vegetation dynamics models in order to understand the vulnerability and recovery capacity of forests in the face of the increased occurrence of windthrows associated with climate change.