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Abstract

Central Amazonian floodplain forests near Manaus can be divided
into two ecosystems, according to the principal flooding water types.
Whitewater floodplains (várzea) have soils with high, blackwaters (igapó)
with low nutrient content. Differences in wood specific gravities and annual
increments were investigated in 30 tree species in várzea and 35 species in
igapó. In várzea, trees had lower wood specific gravities and higher annual
wood increments than in igapó. Elevation and flood duration showed no
significant influences on wood specific gravities in both ecosystems.
Pioneer species of whitewater floodplains had significantly lower mean wood
specific gravities and higher annual increments than non-pioneer species.

Intraspecifically, two of four species occurring in both systems showed
significantly higher wood specific gravity and lower annual increments in
blackwater than in whitewater floodplains.

The significant differences in wood specific gravity and annual increments
in the whitewater and blackwater floodplain systems suggest that the type of
flooding water and the related nutrient input may directly affect tree
growth. Slow growth in blackwater floodplain forests can be considered as an
adaptation to the low nutrient status of the system and an efficient
utilization of the available nutrients.