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Abstract

The large rivers in central Amazonia show annual water level fluctuations of about 14 m. The life cycles of the trees growing in this environment are closely linked to the periodicity of the hydrological regime, but there are differences depending on tree position in the flooding gradient. To study the effect of flooding and precipitation on tree reproductive phenology at community and population level, we surveyed the phenological events of 29 species in a black water floodplain forest in Central Amazonia, Brazil. At community level, peak of number of trees with flowers occurred in the falling river phase and dry season, while the peak of fruiting occurred in the period of rising river level and rainy season. At population level, 72% of the species had their flowering periods significantly related with the variation of water level or precipitation, and 85% had their fruiting periods significantly related with the variation of water level or precipitation. In both cases, the trigger of reproduction was more correlated with precipitation level than with the variation of the water level. For some species there were individual variations of the onset of flowering and fruiting, and of mean flowering or fruiting periods in relation to tree position in the flooding gradient. This can indicate that the beginning of flooding as related to the position in the flooding gradient is one very strong trigger to explain variation.