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Abstract

Macrolobium acaciifolium (Benth.) Benth. ( Fabaceae) is a dominant legume tree species occurring at low elevations of nutrient-poor black-water (igapo) and nutrient-rich white-water floodplain forests (varzea) of Amazonia. As a consequence of the annual long-term flooding this species forms distinct annual tree rings allowing dendrochronological analyses. From both floodplain types in Central Amazonia we sampled cores from 20 large canopy trees growing at identical elevations with a flood-height up to 7 m. We determined tree age, wood density (WD) and mean radial increment (MRI) and synchronized ring-width patterns of single trees to construct tree-ring chronologies for every study site. Maximum tree age found in the igapo was more than 500 years, contrary to the varzea with ages not older than 200 years. MRI and WD were significantly lower in the igapo ( MRI = 1.52 +/- 0.38 mm year(-1), WD = 0.39 +/- 0.05 g cm(-3)) than in the varzea (MRI = 2.66 +/- 0.67 mm year(-1), WD= 0.45 +/- 0.03 g cm(-3)). In both floodplain forests we developed tree-ring chronologies comprising the period 1857 - 2003 ( n= 7 trees) in the varzea and 1606 - 2003 ( n= 13 trees) in the igapo. The ring-width in both floodplain forests was significantly correlated with the length of the terrestrial phase ( vegetation period) derived from the daily recorded water level in the port of Manaus since 1903. In both chronologies we found increased wood growth during El Nino events causing negative precipitation anomalies and a lower water discharge in Amazonian rivers, which leads to an extension of the terrestrial phase. The climate signal of La Nina was not evident in the dendroclimatic proxies.