INVASION OF ALIEN TREES IN A PRE-ANDEAN WATERSHED OF CENTRAL CHILE

Abstract

In this paper the assemblage of alien tree species inhabiting in the Río San Ramón watershed is described. This watershed is located at East border of Santiago, central Chile. Particularly, we documented the flora of alien tree species, the invasion state (not naturalized, naturalized, invader), abundance and population structure of each species. In addition, we related richness and abundance of each species with the way of access into the watershed (planted or natural immigration) and characterized species distribution through the abiotic habitats and resident vegetation patches. During 2003, a cense of all the individuals of alien tree species observed in the watershed was carried out. Fifteen alien tree species were observed. From these, eight species may be considered as invaders, two species as naturalized, and five species were planted but no natural regeneration was observed. Invader species had different abundance, being Ulmus minor the most abundant. Most of the invader species had natural regeneration and small-size individuals. The species that have become invaders, especially those that are the most abundant, were not planted in the watershed. On the other hand, the alien species had a similar environmental distribution, principally on the wettest habitats and on open sites without woody vegetation. These results suggest that the invasion process would be continuous, and that biotic and abiotic environment might be playing a role on the invasion of alien trees in central Chile, and that this role would be similar among species.