Basin-wide variations in Amazon forest structure and function are mediated by both soils and climate
- 1School of Geography, University of Leeds, LS2 9JT, UK
- 2Instituto Nacional de Pesquisas da Amazônia, Manaus, Brazil
- 3Ecoservices, 07743 Jena, Germany
- 4Max-Planck-Institut fuer Biogeochemie, Jena, Germany
- 5Centre for Ecology and Hydrology, Wallingford, UK
- 6Instituto Venezolano de Investigaciones Científicas, Caracas Venezuela
- 7Museu Paraense Emilio Goeldi, Belém, Brazil
- 8Jardin Botanico de Medellin, Medellin, Colombia
- 9Karlsruhe Institute of Technology, Institute for Meteorology and Climate Research,Garmisch-Partenkirchen, Germany
- 10Museo Noel Kempff Mercado, Santa Cruz, Bolivia
- 11Smithsonian Institution, Washington, DC 20560-0166, USA
- 12Department of Anthropology, New York University, New York, NY 10003, USA
- 13IIAP, Apartado Postal 784, Iquitos, Peru
- 14Universidad Nacional de Colombia, Leticia, Colombia
- 15Centre for Applied Biodiversity Science, Conservation International, Washington DC, USA
- 16Faculdad de Ciencias Forestales y Ambientales, Univ. de Los Andes, Merida, Venezuela
- 17Integer Wealth Management, Camberwell, Australia
- 18School of Geography and the Environment, University of Oxford, Oxford, UK
- 19Herbario Vargas, Universidad Nacional San Antonio Abad del Cusco, Cusco, Peru
- 20Proyecto Flora del Perú, Jardin Botanico de Missouri, Oxapampa, Peru
- 21Herbario Nacional del Ecuador, Quito, Ecuador
- 22Centre for Tropical Conservation, Duke University, Durham, USA
- 23Depto de Fisica, Universidade Federal do Mato Grosso, Cuiabá, Brazil
- 24Instituto de Ciencias Naturales, Universidad Nacional de Colombia, Bogotá, Colombia
- 25Depto de Ecologia, Universidade de Brasilia, DF, Brazil
- 26Empresa Brasileira de Pesquisas Agropecuárias, Belém, Brazil
- 27Depto de Ciências da Natureza, Universidade Federal do Acre, Rio Branco, Brazil
- 28Centre for Tropical Environmental and Sustainability Science (TESS) and School of Earth and Environmental Sciences, James Cook University, Cairns, Queensland 4878, Australia
Abstract. Forest structure and dynamics vary across the Amazon Basin in an east-west gradient coincident with variations in soil fertility and geology. This has resulted in the hypothesis that soil fertility may play an important role in explaining Basin-wide variations in forest biomass, growth and stem turnover rates.
Soil samples were collected in a total of 59 different forest plots across the Amazon Basin and analysed for exchangeable cations, carbon, nitrogen and pH, with several phosphorus fractions of likely different plant availability also quantified. Physical properties were additionally examined and an index of soil physical quality developed. Bivariate relationships of soil and climatic properties with above-ground wood productivity, stand-level tree turnover rates, above-ground wood biomass and wood density were first examined with multivariate regression models then applied. Both forms of analysis were undertaken with and without considerations regarding the underlying spatial structure of the dataset.
Despite the presence of autocorrelated spatial structures complicating many analyses, forest structure and dynamics were found to be strongly and quantitatively related to edaphic as well as climatic conditions. Basin-wide differences in stand-level turnover rates are mostly influenced by soil physical properties with variations in rates of coarse wood production mostly related to soil phosphorus status. Total soil P was a better predictor of wood production rates than any of the fractionated organic- or inorganic-P pools. This suggests that it is not only the immediately available P forms, but probably the entire soil phosphorus pool that is interacting with forest growth on longer timescales.
A role for soil potassium in modulating Amazon forest dynamics through its effects on stand-level wood density was also detected. Taking this into account, otherwise enigmatic variations in stand-level biomass across the Basin were then accounted for through the interacting effects of soil physical and chemical properties with climate. A hypothesis of self-maintaining forest dynamic feedback mechanisms initiated by edaphic conditions is proposed. It is further suggested that this is a major factor determining endogenous disturbance levels, species composition, and forest productivity across the Amazon Basin.