Abstract
The analysis of the influence of edaphic finer textures, as a facilitating factor for the expansion of forest formations in the absence of fire, was possible thanks to rare characteristics found in a savanna fragment located in the State of São Paulo, Brazil. The total suppression of fire for over four decades, and the occurrence of two savanna physiognomies, cerrado sensu stricto and cerradão, allowed the conduction of this study based on the hypothesis that cerradão, a physiognomy of forest aspect consisting of fire-sensitive tree and shrubs species, is favored by fire absence and higher soil hydric retention capacity. Edaphic samples were collected from a regular grid of 200 m(2) for the production of isopletic maps of the distribution of clay, fine sand, coarse sand and silt edaphic textures by the geostatistic method of ordinary kriging. Changes in the areas occupied by both savanna physiognomies, defined on the basis of aerial photographs taken over a period of 43 years, were assessed through mean variation rates. Besides corroborating the hypothesis of edaphic hydric retention as a facilitating factor for the expansion of forest physiognomies in savanna areas, we were able to infer the positive influence of higher precipitation on the increase in cerradão expansion rates.
Highlights
In Brazil, recent studies have demonstrated the importance of periodical fires in keeping the balance among the savanna physiognomies encompassed by cerrado sensu lato, by ensuring the permanence of these physiognomies, namely campo limpo, campo sujo, and campo cerrado, which are dominated by herbaceous plants and subshrubs, often fire-resistant (Coutinho 1990, 2002, Durigan et al 1994, Hoffmann 1999)
The comparison between two intervals of equal duration, e.g., ten years (1962-1972 and 1978-1988), allows the identification of differences in the intensity of cerradão expansion into areas formerly occupied by cerrado s.s. (Fig. 3)
In their description of the Corumbataí campo limpo, Camargo and Arens (1967) mentioned Dimorphandra mollis Benth. (Fabaceae) and Ouratea spectabilis (Mart. ex Engl.) Engl. (Ochnaceae), besides species of the genera Bauhinia L., Campomanesia Ruiz and Pav., Kielmeyera Mart. and Zucc. (Clusiaceae), and Stryphnodendron Mart. (Mimosaceae), in which tree and shrub species predominate. Such a physiognomy cannot be considered as a campo limpo according to the classification systems proposed by Eiten (1977) and OliveiraFilho and Ratter (2002), unless tree and shrub individuals were small and covered by herbaceous plants across the entire area, a fact not confirmed by the aerial photographs taken at that time
Summary
The characteristics of plant formations can be influenced by different abiotic factors, such as topography, soils, climate changes (Oliveira-Filho et al 1994, Clark et al 1998, Sollins 1998, Lindenmayer et al 1999, Zeilhofer and Schessl 1999, Miyamoto et al 2003, Guilherme et al 2004) and fire (Kauffman et al 1994, Moreira 2000, Roberts 2001, Ivanauskas et al 2003). DE AZEVEDO and REINALDO MONTEIRO seem to play an critical role in determining the distribution, composition and structure of savanna forms, e.g., edaphic hydric availability (Furley 1992, Haridasan 1992, Oliveira-Filho and Ratter 2002, Quesada et al 2004, Marimon Júnior and Haridasan 2005), nearness to other remaining savanna or non-savanna areas (Ribeiro and Tabarelli 2002, Pinheiro and Monteiro 2006), besides the absence of fires (Moreira 2000, Henriques and Hay 2002, Durigan and Ratter 2006)
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