Tree ring studies related to carbon uptake in Amazon lowland forests: Tree Growth and Climate
Marco
Sack, Institute for Forest Botany, University of Göttingen, Büsgenweg 2, 37077 Göttingen, Germany, msack@gwdg.de
Wolfgang
Johannes
Junk, Max-Planck-Institute for Limnology, Tropical Ecology, P.O. Box 165, 24302 Plön, Germany, wjj@mpil-ploen.mpg.de
Maria
Teresa
Piedade, Instituto Nacional de Pesquisas da Amazônia, Av. André Araújo 1756, Cx. P. 478, 69011-910, Manaus/AM, Brasil, maitepp@internext.com.br
Jochen
Schoengart, Max-Planck-Institute for Limnology, Tropical Ecology, P.O. Box 165, 24302 Plön, Germany, jschoen@gwdg.de
(Presenting)
Martin
Worbes, Institute of Agronomy in the Tropics, University of Göttingen, Griesebachstraße 6, 37077 Germany, mworbes@gwdg.de
In contrast to popular belief, the annual dry season induces temporary cambial dormancy of many tree species in non-flooded terra-firme forests near Manaus and leads to the formation of annual tree rings. This allows individual tree age determination and provides detailed information about aboveground wood biomass allocation and carbon fixation by ring width measurements. For tree ring analysis we chose the genus Eschweilera due to its high relative abundance, importance and value as main sample tree. Tree rings of this genus are well defined by alternating tissues of fibres and parenchyma and allow an accurate age determination. From a total of sixteen trees the ring-width curves of nine individuals were statistically and visually cross-dated to develop a mean chronology, which was indexed by a five-year running mean to eliminate long term growth trends. The indexed ring-width curve correlated significantly with November to June rainfall. This correlation was indicated by the percentage of parallel run (p.p.r.=74.6%), the Student's t-value (t=4,0) and the correlation coefficient (r=0,47). El-Niño causes exceptional droughts during the rainy season in central Amazonia (Sombroeck 2001). On the other hand, in the last 30 years the intensity of El-Niño has increased dramatically (Trenberth 1997) and for the twelve El-Niño events since 1970 significantly lower growth rates (mean ring-width index: 85,7) were observed in comparison with other years (mean ring-width index: 105,2; t-value: -2,57; p<0,01). This indicates an increasing impact of the El-Niño phenomenon on tree growth in the central Amazonian terra-firme in the latter part of the 20th century.
References:
SOMBROEK, W. (2001): Spatial and temporal patterns of Amazon rainfall. Ambio 30, 388-396.
TRENBERTH, K. E. (1997): The definition of El Niño. Bulletin of the American Meteorological Society 78, 2771-2777.