A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...

Where are the oldest of the forest? Radiocarbon use to determine the age andgrowth rate of trees from the Brazilian Amazonian ForestSimone A. Vieira 1 , Plínio B. de Camargo 1 , Susan E. Trumbore 2 , Diogo Selhorst 3 ,Niro Higuchi 4 , Luiz A. Martinelli 1 , John Southon 5savieira@cena.usp.br,pcamargo@cena.usp.br,setrumbo@uci.edu,selhorst@bol.com.br, niro@inpa.gov.br, zebu@cena.usp.br, southon@llnl.gov(1)Centro de Energia Nuclear na Agricultura/USP, Av. Centenário 303,Piracicaba, SP 13416-000 – Brazil (2) University of Califórnia, Irvine, CA, USA (3)Parque Zoobotânico-UFAC-Brazil (4) Instituto Nacional de Pesquisas da Amazônia –Manaus - Brasil (5) Center for Accelerator Mass Spectrometry, Lawrence LivermoreNational Laboratory, Livermore, CA, USAIt has been reported that trees can survive over 1000 years in the Amazonian tropicalforest. This fact apparently contradicts the idea that tropical rain forests are highlydynamic systems. This contradiction can be clarified by determining the age structureof the forest through the residence time of the Carbon in the vegetation. The first stepto estimate the C residence time in the forest is to determine the amount of 14 C oftrees. We followed the diameter tree growth at three sites in the Amazonian tropicalforest in order to provide a better understanding of the carbon dynamics in this regionand its variations according to the climate gradient. We also collected trunk samplesfrom 100 individuals and the radiocarbon measurements of tree cores purifiedcellulose were used to determine the ages and radial growth rates of various species oftrees with different diameter classes. The studied sites were located in the Tapajósforest (FLONA) near Santarém (PA), the EEST-ZF2 site near Manaus (AM) and theCatuaba Experimental Farm near Rio Branco (AC). The amount and distribution ofthe precipitation, the tree diameter distribution and the aboveground biomass aredifferent among the studied areas. The dry biomass is 360 t.ha -1 , 281 t.ha -1 and244 t.ha -1 in Manaus, Santarém and Rio Branco, respectively. The DHB of thesampled trees ranged from 11 to 143 cm. The maximum age obtained fromradiocarbon was 760 years and the minimum was 20 years. The annual diametergrowth rate ranged between 0.01 and 0.9 cm.year -1 . It seems that the bigger trees tendto have higher growth rates than smaller trees in all studied sites.