Structural and other adaptation to long-term flooding by trees in Central Amazonia

Cross section discs were taken from 66 tree species at two sites in the Central Amazonian inundation forest, near Manaus (Brazil) and analysed macroscopically with respect to the occurrence and formation of growth zones. Dendroclimatological investigation and a succesfully applied dating survey using the 14C method (nuclear arms effect) showed, that trees in the igapó and várzea produce more or less distinct annual rings. The boundaries of the growth zones are marked mainly by marginal parenchyma bands and by the decreasing size and thickened walls of the fibre cells. These formations indicate deceleration, followed by suspension, of cambial activity as a reaction to unfavourable climatic conditions such as drought, low temperature or, in the present case, long term flooding. Adaptative strategies of trees to long term inundation are discussed. The formation of growth zones and the distinctiveness of the annual ring boundaries are related to defoliation behaviour, peculiar to each species