ARBOREAL VEGETATION ASPECTS ON A SEASONAL STEPPE SAVANNA REMAINING, IN BARRA DO QUARAÍ, RS STATE, BRAZIL

ABSTRACT

The purpose of this study was to evaluate the floristic composition, the horizontal and vertical structures, as well as the spatial distribution patterns of the tree component in a Steppe Savanna Park located at 'Parque do Espinilho', in Barra do Quaraí, Rio Grande do Sul state, Brazil. Floristic composition and phyto-sociological analysis were carried out in a four (04) ha permanent plot (40 000 m²), where all individuals which circumference (C) was ≥ 15.7 cm, measured 30 cm from the ground, were sampled and had their circumference and total height measured. A mean of 145 individuals/ha was found, distributed in 11 species, 10 genera and eight (08) families, with basal area of 4.06 m²/ha. The Shannon Diversity Index (H') for the tree vegetation was 1.86, and the species with the highest importance values were Prosopis nigra (25.86%), Aspidosperma quebracho-blanco (24.57%), Prosopis affinis (24.30%) and Vachellia caven (10.51%), representing 85.26% of the total. The tree vegetation has two strata, the lower one with 93.3% of the trees and the upper one with only 6.7% of total. The species Aspidosperma quebracho- blanco dominated with 70.0% of trees in this stratum. Regarding the spatial distribution pattern of the species, Aspidosperma quebracho-blanco presented a grouped tendency, whereas the other ones were grouped. The savannah steppe park studied is mainly characterized by the occurrence of Aspidosperma quebracho-blanco, Prosopis nigra, Prosopis affinis and Vachellia caven, constituting a unique combination of species in Brazil, presenting question of rarity in terms of species composition and structure.

Keywords:
Parque do Espinilho; Prosopis; Aspidosperma quebracho-blanco; Vachelia caven