Coastal reclamation constitutes a world trend and can result in new ecosystems adapted to the new coastal configuration. In Buenos Aires City, the “Ciudad Universitaria - Costanera Norte” Ecological Reserve (RECU-CN) constitutes one example of the expansion of the coastline in the Río de la Plata sector, carried out in the late 1960s. Given the lack of published works generated systematically that cover the entire area, we set as the objective to describe the RECU-CN vascular plant vegetation. For this, a systematic sampling was carried out in 79 plots of 25 m2, where the coverage of each of the vascular plant species present was registered. We identified 154 taxa, corresponding to 144 species, 123 genus and 58 families, and the total richness was estimated as 238 species. Trees and herbs had the highest coverage of all life forms. Through multivariate analysis, three vegetation units (Wetland, Forest and Grassland with groves) and 10 vascular plant communities were recognized. Vegetation was ordered according to two gradients: one of flood and another of anthropization. From the comparison with the typical plant communities of the region, similarities were found only with those registered in the Wetland unit. Results highlight that both the coexistence of physiognomically diverse vegetation units, as well as the native composition found in the plant communities of the Wetland unit, constitute main conservation values of the protected area.

Th e native forests once occupying the coastal levees of the Lower Delta islands of the Paraná River (in Argentina) have been replaced by commercial forests. Many of those forests have been abandoned, resulting in secondary forest formation that is subject to numerous invasive exotic species. A priori observations suggest that successional trends do not lead to recovery of the original forest. Th e aim of the present study was to analyze the role of invasive exotic species in these environments and the likelihood of recovery of the original forest cover. Th erefore, we examined the composition of the seed bank and of the standing vegetation, as well as the population structure of tree species. Secondary forests are described as being in an intermediate successional stage, with few exotic species (mainly trees) but with a high abundance of standing vegetation and seed banks. Th ese exotic species will likely continue to successfully predominate in diff erent forest strata over the next stages. Because of the low density of native tree species, it is diffi cult to predict their future persistence. In conclusion, ecological restoration strategies will be needed in order to increase native tree species richness and biodiversity of the forests in the Lower Delta of the Paraná River. Acta Botanica Brasilica 27(1): 40-49. 2013.

Composición y estructura de los bosques de albardón del delta frontal del río Paraná, ArgentinaComposition and structure of levee forests in the frontal Paraná River Delta, Argentina

This study adds information on the dynamics of pioneer forest trees in the face of frequent fire. In particular, effects of fire on the regeneration dynamics and ecological attributes of a Tessaria integrifolia forest and a Cortaderia selloana grassland, located in the Costanera Sur Ecological Reserve, Buenos Aires, are analyzed. Based on the study of ten transects along a forest-grassland gradient, a considerable incidence of fire and resilient response to it were observed on grasslands. On the other hand, the forest proved resistant to fire, not showing evidence of its action. Despite its invasive tendencies, C. selloana was unable to establish itself in the forest or in the forest-grassland ecotones. Conversely, following the action of fire, T. integrifolia could be found in areas previously dominated by grassland, leading to an expansion of the forest. Replacement of grasslands with a T. integrifolia forest indicates a reduction in the incidence of and surface area susceptible to fire, as well as an increase in biodiversity. The post-fire colonization observed for T. integrifolia has not been previously described for this widely distributed South American species.