Estudo floristico e fitossociológico de três comunidades vegetais em San Ignacio, provincia de Misiones, Argentina

Abstract

This study aims to gain a better understanding of the floristic and phytosociological tree component of three plant communities. Those are forest, savannah and rock outcrop vegetation. The study was conducted in the Osununú Private Reserve (RPO), Teyú Cuaré Provincial Park (PPTC) and a sector of savannah, in the department of San Ignacio, Misiones, Argentina. The phyto-physiognomy forest vegetation was compartmentalized in: I) located at the bottom of the valley and the river banks; II) at the base of the slopes; III) steepest slopes; IV) at the tops; and V) was characterized by high density of Eugenia psidiiflora. Sample units were allocated in clusters consisting of four sub- units of 100 m2 within each compartment. A total of 13 clusters and 51 plots were installed inside the RPO, while in the PPTC seven clusters and 28 plots. In each plot soil depth and slope were measured. Canonical Correspondence Analysis was used to analyze the correlation between these variables with coverage value of the species. All trees with a circumference at breast height equal or greater than 10 cm were measured. For the savannah phyto-physiognomy 12 square plots of 400 m2 each were used. However, for that the areas with vegetation on rock outcrops seven rectangular plots of 200 m2 each were installed. For these two communities all trees with perimeters up to the neck equal or greater than 10 cm were included. For all types of plant communities their height were measured, the number of stem per individual was recorded, and, their sociological position was defined. In forest vegetation 83 species were measured. The following species presented a higher percentage of importance in the RPO: Calophyllum brasiliense and Myrsine balansae (I), Rheedia brasiliensis and Myrsine balansae (II), Rheedia brasiliensis and Qualea cordata (III), Rheedia brasiliensis and Eugenia psidiiflora (IV) and Eugenia psidiiflora (V). In the case of the PPTC predominated Helietta apiculata and Luehea divaricata (I), Diatenopteryx sorbifolia and Rheedia brasiliensis (II), Syagrus romanzoffiana and Matayba elaeagnoides (III), Rheedia brasiliensis and Guarea macrophylla (IV). Results show that the soil depth and slope parameters are significant correlated with coverage values. These forests imposes its uniqueness in the territory, considering that much of the structure was expressed by species with restricted distribution, or rare for national flora. In savannah vegetation type were detected 17 species, where Acosmium subelegans had the highest percentage of importance. The diameter distribution of this specie did not demonstrate inconvenient for regeneration, showing up adapted to environments where the fire was recurrent. The vegetation on rock outcrops growing under fragile geomorphic and soil conditions, where the flora was represented by 32 species, where Qualea cordata, Monvillea euchlora and Ocotea lancifolia showed the highest percentage of importance. In each plant communities both structural and diversity difference were detected. The forest stands with the highest species richness and diversity indices, followed by vegetation on rock outcrop, and the savannah.