Regional and large-scale patterns in Amazon forest structure and function are mediated by variations in soil physical and chemical properties
1Earth and Biosphere Institute, School of Geography, University of Leeds, LS2 9JT, UK
2Ecoservices, 07743 Jena, Germany
3Instituto de Investigación de Recursos Biológicos, Alexander von Humboldt, Bogotá, Colombia
4UMR-ECOFOG, INRA, 97310, Korou, French Guiana
5Max-Planck-Institut fuer Biogeochemie, Jena, Germany
6Centre for Ecology and Hydrology, Wallingford, UK
7Instituto Venezolano de Investigaciones Científicas, Caracas, Venezuela
8Geography and Ecosystem Analysis, Lund University, Lund, Sweden
9School of Geography and the Environment, University of Oxford, Oxford, UK
10Institito Nacional de Pesquisas da Amazônia, Manaus, Brazil
11Museo Noel Kempff Mercado, Santa Cruz, Bolivia
12Depto de Ciências da Natureza, Universidade Federal do Acre, Rio Branco, Brazil
13Depto de Fisica, Universidade Federal do Mato Grosso, Cuiaba, Brazil
14Universidad Nacional de Colombia, Lecticia, Colombia
15Secretaria M.de Desenvolvimento e Meio Ammbiente, Pref. M. de Maués, Maués, Brazil
16Museu Paraense Emilio Goeldi, Belém, Brazil
17Herbario Nacional del Ecuador, Quito, Ecuador
18Empresa Brasileira de Pesquisas Agropecuárias, Belem, Brazil
19Herbario Vargas, Universidad Nacional San Antonio Abad del Cusco, Cusco, Peru
20Proyecto Flora del Perú, Jardin Botanico de Missouri, Oxapampa, Peru
21Instituto de Ciencias Naturales, Universidad Nacional de Colombia, Bogotá, Colombia
22Faculdad de Ciencias Forestales y Ambientales, Univ. de Los Andes, Merida, Venezuela
23E Alvarez Dávila, Gestion Ambiental, interconexion eletrica S.A., Medellin, Colombia
24Smithsonian Institution, Washington, D.C. 20560-0166, USA
25Department of Anthropology, New York University, New York, NY 10003, USA
26IIAP, Apartado Postal 784, Iquitos, Peru
27Centre for Applied Biodiversity Science, Conservation International, Washington D.C., USA
28Centre for Tropical Conservation, Duke University, Durham, USA
Abstract. Forest structure and dynamics have been noted to vary across the Amazon Basin in an east-west gradient in a pattern which coincides 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.
To test this hypothesis and assess the importance of edaphic properties in affect forest structure and dynamics, soil and plant samples were collected in a total of 59 different forest plots across the Amazon Basin. Samples were analysed for exchangeable cations, C, N, pH with various P fractions also determined. Physical properties were also examined and an index of soil physical quality developed.
Overall, forest structure and dynamics were found to be strongly and quantitatively related to edaphic conditions. Tree turnover rates emerged to be mostly influenced by soil physical properties whereas forest growth rates were mainly related to a measure of available soil phosphorus, although also dependent on rainfall amount and distribution. On the other hand, large scale variations in forest biomass could not be explained by any of the edaphic properties measured, nor by variation in climate.
A new 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 forest disturbance levels, species composition and forest productivity on a Basin wide scale.