Solos orgânicos em ambientes altomontanos no Sudeste do Brasil: formação, classificação e relações com a história da vegetação

Abstract

The research developed in this thesis aims to contribute to the understanding of the formation of non-hydromorphic organic soils in upper montane environments in the southeastern Brazil. The thesis was organized in two chapters, in Chapter I “Organic soils - definitions and use as record of paleoenvironmental changes”, a theoretical framework based on relevant bibliographical sources is presented and discussed. In addition to the environmental relevance, organic soils are important natural archives of paleoenvironmental changes, providing data for inferences about the climate and vegetation of the past and future. They have great relevance for climate regulation, water storage and maintaining biodiversity. In the Chapter II, entitled - Organic soils in upper montane environments in Southeastern Brazil: formation, classification and relations with the history of vegetation, the results obtained from the characterization of 14 soil profiles, described and collected in upper montane environments in southeastern Brazil, are presented. The following hypotheses were set: (i) the formation of organic soils under free drainage conditions is related to the history of vegetation and variations in climatic conditions in the past; (ii) the cold and humid climate of the upper montane environments in the Southeastern region of Brazil results in soils with andic (non-allophanic) properties. The objective of this research was to propose a general scheme for the formation of these soils, based on the understanding of the soil-landscape relationship and on the reconstitution of the vegetation history. As for the first hypothesis, based on records of phytoliths, δ

13C, carbon stocks derived from C3 and C4 plants, and 14C dating, it was possible to infer four environmental conditions: Phase I (before ~18,9k yr BP), markedly colder climate and drier than current one, with a predominance of subtropical grassland vegetation and the occurrence of fires; Phase II (~18,9k yr BP to ~11,1k yr BP), slight increase in humidity, decrease in fires and expansion of forest formations, with rare presence of Araucaria angustifolia; Phase III (from ~11,1k years BP) increase in humidity, with the establishment of current conditions (cold and humid climate,

typical of southeastern Brazilian highlands), and marked presence of Araucaria in upper- montane forests; Phase IV (present) environmental changes related to increased occurrence of

fires, reduction of Araucaria individuals and increase of Bambusoid, Arecaceae and C4 plants, possibly linked to human activities. On the second hypothesis, Organossolos Fólicos (Folists) in the upper montane environments of Serra da Mantiqueira are formed by the accumulation of litter (vegetation residues) and can occur in two soil environments: (i) directly on rocks in the high-altitude fields, by the processes of addition and transformation of litter, which constitute the main parental material of these soils; and (ii) in upper montane forests, with histic horizons formed over mineral horizons. In both cases, the cold and humid climate and the vegetation (organisms) are the main soil formation factors, not only reducing the decomposition of the organic matter, but influencing the physical and chemical properties of the soils. The cold and humid climate of the upper montane environments in southeastern Brazil also results in soils with andic (non-allophanic) properties.