Biomass and Net Primary Production of Central Amazonian Floodplain Forests

In this chapter the existing knowledge on biomass in floodplain forests and the compounds that contribute to their net primary production (NPP) are presented and discussed in comparison with data from non-flooded upland (terra firme) forests. Fine litterfall in old-growth floodplain forests are similar to litterfall data from terra firme forests. The few existing estimates of root biomass in nutrient-rich white-water floodplain forests (varzea) indicate lower belowground biomasses in floodplain forests than in terra firme forests due to regular flooding which limits the development of deep roots. Along the chronosequence, C-storage in the aboveground coarse live wood biomass (AGWB) of varzea forests indicates a strong increase during the first 50–80 years of successional development, but afterwards no increase in AGWB can be observed. On the other hand C-sequestration in the AGWB of varzea forests declines more than threefold along the successional gradient. In comparison to terra firme forest, the varzea forests have lower C-stocks, but a higher C-sequestration in the AGWB. The estimated aboveground NPP in young successional stages of the central Amazonian varzea is among the highest NPP known for tropical forests, while the NPP of the late succession in the varzea is in the upper range of the NPP of old-growth forests in the terra firme. The available database for nutrient-poor floodplain forests (igapo) is insufficient to estimate their NPP. Climate-growth relationships of tree-ring chronologies of species from central Amazonian terra firme and floodplain forests indicate opposing signals during El Nino years. During these events large areas of terra firme forests release carbon to the atmosphere due to the warmer and drier climate conditions, while the weakened flood-pulse favours tree growth in the floodplain forests which might therefore sequester parts of the climate-induced carbon emissions of terra firme forests.