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.
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