Effects of exotic conifer plantations on the biodiversity of understory plants, epigeal beetles and birds in Nothofagus dombeyi forests

Plantations of exotic conifers are a potential threat to natural ecosystems in the Argentinean Patagonia and a major cause of native forest loss in Chile. We examined species diversity and composition of three different functional groups: understory vascular plants, epigeal beetles, and birds, in paired stands of relatively undisturbed Nothofagus dombeyi forest and coniferous plantations. We also characterized the structure of each stand. Exotic plantations generated significant impacts on biodiversity, diminishing species richness, abundance and diversity, and generating modifications in assemblage composition. Replacement of N. dombeyi forests by conifer plantations led to a homogenization of habitat structure at the stand scale. The largest impact was detected on understory plants, followed by the beetle and bird assemblages, supporting the view that the least vagile assemblages are most affected by habitat replacement. The most relevant modifications caused by the plantations on the structure and composition of the studied assemblages were a reduction in evenness in plants and beetles, an increase of exotic species richness from 16 to 29% in plants and from none to one species in birds, and a loss of rare and specialist species in all three assemblages. Our findings suggest that plantations with more open canopy could favor biodiversity by increasing individual abundance and species richness of all three assemblages.