STRUCTURE, PHYSIOGNOMY AND FLORISTIC COMPOSITION OF A SCHINOPSIS-BALANSAE (ANACARDIACEAE) FOREST IN THE SOUTHERN CHACO, ARGENTINA

Amazonia and the Gran Chaco are the largest phytogeographic units of t ropical and subtropical South America. The Santa Fe Forest Wedge is th e southernmost portion of the Eastern Chaco, where the Schinopsis bala nsae forest (Quebrachal) is the most widespread and characteristic com munity. A detailed analysis of the floristic composition, physiognomy and vegetation structure was carried out in 32 10 x 10 m contiguous pl ots sampled along two transects in one of these forests near Vera, Pro vince of Santa Fe, Argentina. All woody individuals higher than 0.6 m present in the plots were recorded, identified and their height and cr own diameter measured. With these data, cartographic diagrams and vege tation profiles were drawn. Woody species were classified according to leaf size, leaf texture, presence of spines and phenology. This quebr achal is an open forest with very complex structure and heterogeneous floristic composition. Most woody species of this forest are deciduous , with small leaves and frequently with spiny structures. It has two h igher tree layers of S. balansae and Acacia praecox. and a lower tree layer of Achatocarpus praecox with younger individuals of the higher s trata species and some large shrubs. There is as well a 2 m high shrub layer. The tree canopy is discontinuous, with gaps that can be rather large, where the soil is covered by a dense grass layer. This forest is much like other S. balansae forests of the Santa Fe Forest Wedge, b ut quite different from most other forest areas of the Gran Chaco.