Global Change Biology (2004) 10, 545-562, doi: 10.1111/j.l529-8817.2003.00751.x Variation in wood density determines spatial patterns in Amazonian forest biomass TIMOTHY R. BAKER*t, OLIVER L. PHILLIPSf, YADVINDER MALHIJ, SAMUEL ALME1DA§, LUZMILA ARROYO^, ANTHONY Dl FIORE|| , TERRY ERWIN**, TIMOTHY J. KILLEENtt, SUSAN G. LAURANCEJi, WILLIAM F. LAURANCEH, SIMON L. LEWISt, JON LLOYD*, ABEL MONTEAGUDO§§,§§§, DAVID A. NEILLHt. SANDRA PATIÑO*||||, NIGEL C. A. PITMAN***, J. NATALINO M. SILVA 111 tíí and RODOLFO VÁSQUEZ MARTÍNEZ§§§ *Max Planck Institut für Biogeochemie, ]ena, Germany, ^Earth and Biosphere Institute, School of Geography, University of Leeds, Leeds, UK, ^School of GeoSciences, University of Edinburgh, Edinburgh, UK, §Museu Paraense Emilio Goeldi, BeUm, Brazil, *\Museo Noel Kempff Mercado, Santa Cruz, Bolivia, \\Department of Anthropology, New York University, New York, USA, **Smithsonian Institution, Washington, DC, USA, i^Center for Applied Biodiversity Science, Conservation International, Washington, DC, USA, WSmithsonian Tropical Research Institute, Balboa, Panama, §%Herbario Vargas, Universidad Nacional San Antonio Abad del Cusco, Cusco, Peru, '¡'¡¡Missouri Botanical Garden, c/o Herbario Nacional del Ecuador, Quito, Ecuador, IIII Alexander von Humboldt Biological Research Institute, Bogota, Colombia, ***Center for Tropical Conservation, Duke University, Durham, USA, tttC7f OR, Tapajos, Brazil, I'^^EMBRAPA Amazonia Oriental, Belém, Brazil, %%%Proyecto Flora del Perú, jardin Botánico de Missouri, Oxapampa, Peru Abstract Uncertainty in biomass estimates is one of the greatest limitations to models of carbon flux in tropical forests. Previous comparisons of field-based estimates of the above- ground biomass (AGB) of trees greater than 10 cm diameter within Amazonia have been limited by the paucity of data for western Amazon forests, and the use of site-specific methods to estimate biomass from inventory data. In addition, the role of regional variation in stand-level wood specific gravity has not previously been considered. Using data from 56 mature forest plots across Amazonia, we consider the relative roles of species composition (wood specific gravity) and forest structure (basal area) in determining variation in AGB. Mean stand-level wood specific gravity, on a per stem basis, is 15.8% higher in forests in central and eastern, compared with northwestern Amazonia. This pattern is due to the higher diversity and abundance of taxa with high specific gravity values in central and eastern Amazonia, and the greater diversity and abundance of taxa with low specific gravity values in western Amazonia. For two estimates of AGB derived using different allometric equations, basal area explains 51.7% and 63.4%, and stand-level specific gravity 45.4% and 29.7%, of the total variation in AGB. The variation in specific gravity is important because it determines the regional scale, spatial pattern of AGB. When weighting by specific gravity is included, central and eastern Amazon forests have significantly higher AGB than stands in northwest or southwest Amazonia. The regional-scale pattern of species composition therefore defines a broad gradient of AGB across Amazonia. Keywords: AGB, Amazonia, carbon, permanent plot, tropical forests, wood specific gravity Received 13 December 2002; revised version received and accepted 28 March 2003 Introduction Correspondence: T. R. Baker, Earth and Biosphere Institute, School Accurately quantifying the role of tropical forests in the of Geography, University of Leeds, Leeds LS2 9JT, UK, tel. +44113 global carbon cycle is one of the key requirements to 343 3361, fax + 44 113 343 3308, e-mail: t.baker@geog.leeds.ac.uk improve our understanding of current patterns of © 2004 Blackwell Publishing Ltd 545