Olga Kotchetkoff Henriques

In a search to establish a solid base for conservation of forest fragments in Ribeirão Preto, SP, a diagnosis of the natural vegetation of the municipality was done. There are 102 forest remnants and in 99 of them an expeditious floristic survey was carried out. In this survey, 494 tree species were found belonging to 74 botanic families along with 31 exotic species. Based on the species composition of each fragment, a Detrended Correspondence Analysis (DCA) was conducted using the soil class where the fragment is found as categorical variable. This analysis indicates the existence of four vegetation groups: mesophytic forests, deciduous forests, swampy forests and cerrado, that occur respectively in purple latosol, lithosol, hydromorphic soil and dark red latossol or yellow red latossol. Each group presents its own floristic composition and typical vegetation physiognomy. The richness of species found in each fragment was from 13 to 134 species. There is a very large number of species that are very difficult to find - 275 species (52,38%) that occur in less than 5% of the fragments and 9 species (1,71%) occur in more than 50% of the remnants. There are species with rare occurrences in all fragments, but they tend to occur in larger number in the bigger ones. Each fragment presents a small percentage of the total of species, which indicates that to preserve the species diversity all the fragments are important. Generally, the initial secondary and animal dispersed species predominate in the fragments with the tendency to increase the proportion of the pioneer and wind dispersed species with the increase of the human disturbance. The majority of the fragments are small and isolated. The Principal Component Analysis (PCA) shows that the area and the core area, shape factor and fractal dimension, and the proximity index and similarity are, respectively, the main factors acting on the first three axes. The area and the core area showed significant and positively correlated with the species richness in the mesophytic and deciduous forests. The shape and the isolation did not show correlation with the species richness. Considering the biological factors (richness and proportion of species with rare occurrence) and spatial patterns (fragment area, core area proportion and similarity index), the conservation value (VC) was built, which allows us to set a hierarchy of the fragments according to their importance to conservation. The joint analysis of the result of this index and the fragments spatial distribution indicates that there are two situations that deserve attention: 1) many fragments with high conservation value are located in the urban expansion area and therefore exposed to a bigger human disturbance; 2) There is a concentration of large fragments, which are close to each other, that show a high VC in the southern region of the municipality, along the Onça creek, that includes mesophytic forests,swampy forests and cerrado. In both cases the creation of Environmental Protection Areas (APA) are suggested in order to enhance the conservation actions in these areas.

"Caracterização da vegetação natural em Ribeirão Preto, SP: bases para conservação". / Characterization of the natural vegetation in Ribeirão Preto, SP: Bases for conservation.

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