ASPECTOS DA VEGETA\uc7\uc3O ARB 3REA EM FRAGMENTO DE ESTEPE ESTACIONAL SAVAN\ucdCOLA, BARRA DO QUARA\ucd-RS, BRASIL

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 \u2018Parque do Espinilho\u2019, in Barra do Quara\ued, 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 65 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\u2019) 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 quebrachoblanco 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 affinisand Vachellia caven, constituting a unique combination of species in Brazil, presenting question of rarity in terms of species composition and structure.O presente estudo teve por objetivo avaliar a composi\ue7\ue3o flor\uedstica, a estrutura horizontal e vertical, bem como os padr\uf5es de distribui\ue7\ue3o espacial do componente arb\uf3reo e agrupamento de esp\ue9cies em uma amostra de Estepe Estacional Savan\uedcola localizada no Parque do Espinilho, Barra do Quara\ued - RS. Para o levantamento flor\uedstico e an\ue1lise fitossociol\uf3gica foi instalada, em uma \ue1rea de ocorr\ueancia de Aspidosperma quebracho-blanco , uma unidade permanente de 4 ha (200 x 200 m), onde todos os indiv\uedduos com circunfer\ueancia (C) 65 15,7 cm a 30 cm do n\uedvel do solo foram amostrados e medidas a circunfer\ueancia e altura total. Foram encontrados 145 indiv\uedduos/ha, distribu\ueddos em 11 esp\ue9cies, 10 g\ueaneros e 8 fam\uedlias, com \ue1rea basal de 4,06 m2/ha. A vegeta\ue7\ue3o arb\uf3rea apresentou \ucdndice de Diversidade de Shannon estimado em 1,86, sendo que as esp\ue9cies com os maiores valores de import\ue2ncia foram Prosopis nigra (25,86%), Aspidosperma quebracho-blanco (24,57%), Prosopis affinis (24,30%) e Vachellia caven (10,51%), representando 85,26% do total. A vegeta\ue7\ue3o arb\uf3rea apresenta dois estratos bem definidos, o inferior com 93,3% das \ue1rvores e o superior com apenas 6,7% do total de \ue1rvores amostradas. Neste a esp\ue9cie Aspidosperma quebracho-blanco predomina com 70,0% das \ue1rvores. Com rela\ue7\ue3o ao padr\ue3o de distribui\ue7\ue3o espacial das esp\ue9cies, Aspidosperma quebracho-blanco apresentou tend\ueancia ao agrupamento, de acordo com o \ucdndice de Payandeh, enquanto que as demais esp\ue9cies apresentaram-se agrupadas. Aspidosperma quebracho-blanco e Prosopis nigra tendem a ocorrer associadas, enquanto Prosopis affinis e Vachellia caven formam grupos individuais. A associa\ue7\ue3o estudada constitui-se de uma forma\ue7\ue3o de esp\ue9cies \ufanica no Brasil, apresentando quest\ue3o de raridade em termos de composi\ue7\ue3o de esp\ue9cies e estrutura