Coexistence of forest and savanna in an Amazonian area from a geological perspective

Autor(es)

Rossetti, D. F. ^[1] ; Almeida, S. ^[2] ; Amaral, D. D. ^[2] ; Lima, C. M. ^[3] ; Pessenda, L. C. R. ^[3]

Afiliação do(s) autor(es)

^[1] Inst Nacl Pesquisas Espaciais OBT DSR, BR-12245970 Sao Jose Dos Campos, SP - Brazil

^[2] Museu Paraense Emilio Goeldi, BR-66077530 Belem, PA - Brazil

^[3] Univ Sao Paulo, Lab 14C, BR-13416000 Piracicaba, SP - Brazil

• Tipo de documento: Artigo Científico
• Fonte: JOURNAL OF VEGETATION SCIENCE; v. 21, n. 1, p. 120-132, FEB 10 2010.
• Citações Web of Science: 20

Resumo

Question: How can the coexistence of savanna and forest in Amazonian areas with relatively uniform climates be explained? Location: Eastern Marajo Island, northeast Amazonia, Brazil. Methods: The study integrated floristic analysis, terrain morphology, sedimentology and delta(13)C of soil organic matter. Floristic analysis involved rapid ecological assessment of 33 sites, determination of occurrence, specific richness, hierarchical distribution and matrix of floristic similarity between paired vegetation types. Terrain characterization was based on analysis of Landsat images using 4(R), 5(G) and 7(B) composition and digital elevation model (DEM). Sedimentology involved field descriptions of surface and core sediments. Finally, radiocarbon dating and analysis of delta(13)C of soil profile organic matter and natural ecotone forest-savanna was undertaken. Results: Slight tectonic subsidence in eastern Marajo Island favours seasonal flooding, making it unsuitable for forest growth. However, this area displays slightly convex-up, sinuous morphologies related to paleochannels, covered by forest. Terra-firme lowland forests are expanding from west to east, preferentially occupying paleochannels and replacing savanna. Slack, running water during channel abandonment leads to disappearance of varzea/gallery forest at channel margins. Long-abandoned channels sustain continuous terra-firme forests, because of longer times for more species to establish. Recently abandoned channels have had less time to become sites for widespread tree development, and are either not vegetated or covered by savanna. Conclusion: Landforms in eastern Marajo Island reflect changes in the physical environment due to reactivation of tectonic faults during the latest Quaternary. This promoted a dynamic history of channel abandonment, which controlled a set of interrelated parameters (soil type, topography, hydrology) that determined species location. Inclusion of a geological perspective for paleoenvironmental reconstruction can increase understanding of plant distribution in Amazonia. (AU)

• Processo FAPESP: 04/15518-6 - Integração de dados biológicos e geológicos no Baixo Tocantins-Ilha do Marajó: chave na análise da biodiversidade
• Beneficiário: Dilce de Fátima Rossetti
• Linha de fomento: Auxílio à Pesquisa - Regular