ORTHOGONAL EFFECTS OF MICROMETEOROLOGICAL VARIABLES ON TWO AMAZONIAN SPECIES OF CONTRASTING GROWTH RATES

Abstract

Intra-annual micrometeorological variability leads to a mild dry season in the central Amazon, but how rainfall seasonality affects tree growth is still unclear. This study aimed to determine the collinearity-free (orthogonal) effect of microclimatic variability on stem growth of Eschweilera bracteosa (slow-growing species) and Tachigali venusta (fast-growing species). Stem growth in diameter was measured from January 2008 to December 2012, at monthly intervals. Irradiance, air temperature, rainfall and vapour pressure deficit data were also recorded. Principal component regression was used to assess the effect of micrometeorological variability on stem growth. In the fast-growing species, stem growth increased with increasing precipitation, but it decreased with increases in mean and maximum temperature and vapour pressure deficit. The slow-growing species was only responsive to variations in mean temperature and mean and maximum vapour pressure deficit. Irradiance variability has no effect on stem growth. This study demonstrated the orthogonal effect of the mean and maximum vapour pressure deficit on stem growth, and showed that fast and slowgrowing species could respond differently to microclimatic variability. Therefore, if the dry season becomes longer and dryer, trees more sensitive to micrometeorological variability can be the most affected by climate changes.