Efecto del retamo espinoso (Ulex europaeus) sobre las aves de borde en un bosque altoandino

The impact of invasive species is one of the most important threats to biodiversity. Gorse (Ulex europaeus) is one of the worst invasive species of plant in the world. It has been introduced in high Andean regions, with a considerable impact on the composition and structure of vegetation. However, its effect on high Andean birds is unknown. Gorse does not have birdpollinated flowers nor fruit consumed by birds, as opposed to most native shrubs. In addition, its foliage is spiny and has a different structure than that of native shrubs. Therefore, gorse invasion is likely to affect food availability for birds. We characterized vegetation composition and structure in high Andean forest edges with and without gorse, as well as species richness and relative abundance of bird species. Shrub density was twice as high in edges invaded by gorse than in those without gorse, whereas abundance of native shrubs was severely reduced in invaded edges. On the other hand, the overall abundance of birds was not affected by gorse, but at the species level we found that Colaptes rivolii avoids edges with gorse, and the presence of this plant had a negative impact on Turdus fuscater. In contrast, Diglossa humeralis and Basileuterus nigrocristatus were more abundant in forest edges invaded by gorse. These results give evidence of a moderate effect of the invasion on the avifauna as a whole, likely as a result of the composition of the community. The avifauna in the study area is depauperate because almost all groups sensitive to landscape transformation are gone; accordingly, it is composed by generalist species that are likely resilient to habitat changes.