Variação em diâmetro do tronco de 30 espécies de árvores florestais em função de variáveis ambientais em floresta de terra firme na Amazônia central

Abstract

Changes in the dynamics of the Amazon rainforest may affect the concentration of atmospheric CO2 and the climate on a regional and global scale. The characterization of factors influencing carbon fixation and the gain of biomass are essential for building models to predict the primary productivity of a forest ecosystem. The aim of this work was to investigate the monthly growth in trunk diameter as well as to determine the effect of climate factors on trees growth in central Amazonia. The variation in the trunk diameter of 138 trees (30 species) was measured monthly by using stainless steel dendrometer bands from 2008 to 2012. In the same period, climate data were collected on the top of a 40-m-tall observation tower. On a daily basis, were collected data of rainfall, temperature, relative humidity and photosynthetically active radiation (RFA) and a monthly mean for each of these climate variables obtained. The maximum vapor pressure deficit (DPV) was obtained using minimum relative humidity and maximum temperature data, while the potential evapotranspiration was estimated by using the method of Hargreaves and Samani. The monthly tree growth was determined by measuring the variation in monthly diameter increment (IMD). Analysis of variance (ANOVA) for repeated measurements was used to evaluate differences in IMD between species and the effect of time (months and years) on tree growth. Before assessing the effect of the climate variables on IMD, the temporal trend of IMD was removed. During the study, the average rainfall was 2854 mm, mean temperature and mean relative humidity were 25.3 °C and 84% respectively. Mean RFA was 25.7 mol m–2 day–1, whereas the mean maximum DPV was 1.61 kPa. On average the potential evapotranspiration was 123 mm month–1. With regard to the IMD of trees, there was significant difference between tree species (p < 0.001). The largest increase in diameter was observed in T. venusta (0.81 mm month–1) and the smallest in T. sylvestre with 0.009 mm month–1. The ANOVA also showed that there was a significant effect of time (months and years) on IMD (p < 0.001). In 50% of species, tree growth varied over years. Across species, the mean annual tree growth of the 30 species was lower in 2009 (1.08 mm year–1), and greater in 2012 (1.92 mm year–1). The IMD was positively affected by monthly rainfall in 56% of species, whereas it was negatively affected by mean temperature in 27% of them. In 40% of species, the IMD was negatively affected by the DPV. Trees with greater diameter at breast height (DBH) and with the canopy more exposed to the sun had greater IMD, but on the other hand, they were more sensitive to variations in weather conditions. In the majority of tree species, the IMD tended to decrease in the months when the precipitation did not compensate the water lost through evapotranspiration. These results show that if the dry period becomes more pronounced, as predicted by climate models for some parts of the Amazon, the negative effect of the dry season on trees growth can be substantially increased.