Is the dry season an important driver of phenology and growth for two Brazilian savanna tree species with contrasting leaf habits?

摘要

Brazilian savanna (known as cerrado) has highly seasonal variation in rainfall yet trees have widely different phenological strategies ranging from evergreen to fully deciduous. While qualitative patterns of canopy phenology are well-known, few studies have quantitatively measured schedules of leaf and branch phenology. We measured the leaf and vegetative phenology of two widely distributed cerrado tree species Vochysia divergens Pohl., an evergreen species, and Curatella americana L., a semi-deciduous species, over a 1-year period and hypothesized that the dry season would represent a trigger for leaf abscission and leaf and branch growth. Leaf and branch emergence and leaf abscission for the semi-deciduous species were coincident with the end and beginning of the dry season, respectively, and were significantly correlated with dry season meteorology, but with time lags that varied depending on the meteorological variable. Leaf and branch emergence and leaf abscission for the evergreen species were also coincident with the dry season, but correlations with meteorological variables were weaker and seasonal patterns were more subtle. V. divergens leaves also suffered more from herbivory than C. americana, and there is evidence that herbivory may have altered patterns of leaf emergence for V. divergens. V. divergens leaves survived longer than C. americana leaves, and relative branch growth rates were significantly higher for C. americana. While our study was limited to only two tree species and 1 year, we demonstrated quantitatively that patterns of leaf and branch phenology were highly correlated with climatic variations. A strategy of leaf emergence and branch growth initiation during the dry season likely maximizes carbon gain by increasing rates of C assimilation by plants at the onset of the rainy season.