Natural Recolonization by Riparian Forest on the Left Bank of the Salto Grande Reservoir

Identification of Pioneer Species

Abstract

The reservoir of Salto Grande, formed in 1979 when the building of the homonymous dam was completed, covers the last stretch of the middle section of the Uruguay river. These works caused the flooding of numerous hectares in the departments of Salto and Artigas in Uruguay, and in the province of Entre Ríos in Argentina, destroying woods of great diversity on the riverside and on the islands. After more than three decades of this disruption, it has been possible to observe natural regeneration of wooded strips on the banks. The composition of the flora and the characters of the vegetation in these woods have been thoroughly studied on rounds of observation and samplings performed on 16 places on the banks of the reservoir and statistical analysis of the data have been done. One hundred woody species have been counted all over the area: 83 native ones and 17 exotic ones belonging to 34 families. Nevertheless, the number of species listed in each location is much less, with a minimum of 10, 12, 17 species per observation round; two, seven, nine species per sampling in some small woods; and a maximum of 48 and 33 species (per round and per sampling, respectively) in the most northern location. In the communities of the reservoir which were studied Erythrina crista-galli, Vachellia caven (Acacia caven), Sesbania virgata, Sebastiania schottiana, Terminalia australis and others recognized as pioneers or early successional species are recurrent and predominant. The predo-minant family is Fabaceae. On the islands near Bella Unión, to the north of the reservoir, the forest vegetation remains with few alterations, thus being a source of propagules.