Gradientes edáficos e sua relação com as fitofisionomias do semi-árido meridional brasileiro / Edaphic gradients and their relationship with the vegetation types of semi-arid southern Brazil

Daniel Meira Arruda

The semi-arid region in Brazil represents a significant territorial extension, where the climate is markedly seasonal, with low rainfall, high evapotranspiration and higher temperatures. Its southern portion comprises the northern boundary between the states of Minas Gerais and Bahia. This region is dominated by dry forest vegetation type, however, different cerrados vegetation type are also present. The different portions of the landscape and its edaphic variation are responsible for the establishment of different vegetation type. However, studies approach these relationships and seeking to understand the edaphic-vegetational gradients are scarce in the landscapes semi-arid. Thus, the objective was to characterize the soils and plant communities of different landscape segments (top, slope and low) and test the following hypotheses: (1) soils of the same segment of the landscape, subject to the same climatic conditions and vegetation types, are similar even in different locations, (2) the plant communities on the same segment are similar floristically and (3) the most abundant species show preference to certain segments of the landscape. For this, we sampled soils and plant communities in 14 different environments on segments Januária (MG), Porteinha (MG), Guanambi (BA) and Ibiassucê (BA). The variables of the analyzed soils were subjected to Principal Components Analysis, in order to verify the existence of gradient (Chapter 1). The species sampled in different segments were subjected to similarity analysis, and the most abundant were correlated with the variables of soils through of canonical correspondence analysis to observe trends along the gradient (Chapter 2). A gradient of soil fertility could be observed, in which the same segments grouped according to their soil characteristics, confirming the hypothesis of edaphic similarity. At one extreme of the gradient, the tops were more dystrophic with high aluminum levels and low base saturation. In this portion, was concentrated cerrados vegetation type. The other end of the gradient presented eutrophic, with higher values of saturation. In this portion, was concentrated vegetation types of dry forest associated with different slopes. The center of the gradient showed median values of soil characteristics, the portion being considered mesotrophic. In this portion, concentrated segments of the lowland associated with dry forest. The slopes of the interior of Espinhaço differed edaphically from the other landscapes of the middle São Francisco basin, due to orographic influences and quartzite. The floristic similarity analysis did not group the communities of similar segments, but the greater geographical proximity, rejecting the hypothesis of floristic similarity. The communities of the low and eastern slope of Ibiassucê, formation shrubs-trees previously characterized as savanna hypoxerophytic showed floristic similarities with other dry forests of the San Francisco river basin, and therefore considered a state of succession of dry forests. However, the dry forest of the western slope showed great dissimilarity of the other communities. The most abundant species of each community showed preference segments of the gradient after associated with soil characteristics, confirming the hypothesis of the preference of the species. In general, the communities of the slopes were denser, with lower basal area and greater dominance of one species, especially Myracrodruon urundeuva and Handroanthus ochraceus. These characteristics of the slopes were associated with constant disturbances, naturally predominant, which these environments are submitted.

Gradientes edáficos e sua relação com as fitofisionomias do semi-árido meridional brasileiro / Edaphic gradients and their relationship with the vegetation types of semi-arid southern Brazil

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