Effects of eucalyptus plantations on avian and herb species richness and composition in North-West Spain

Eucalyptus plantations have been established in many areas of the world due to their fast growth and profitability. In NW Spain, Eucalyptus plantations now cover a larger area than native forests. Although Eucalyptus plantations have been shown to affect biodiversity, relatively few studies have compared their effect on multiple taxonomic groups and different aspects of biodiversity. We compared herb and bird species richness and bird abundance between 14 paired patches of native deciduous forest and Eucalyptus plantations in a heterogeneous agro-forest region of NW Spain. We also investigated whether Eucalyptus plantations contribute to shifts in community composition by analysing species nestedness and turnover. We found that species richness of both herbs and birds was consistently lower in Eucalyptus plantations compared to native forests. Furthermore, the abundances of bird species characteristic of agricultural, forest, scrubland and other habitats, were all much lower in Eucalyptus plantations than in native forests. Herb and bird communities were also significantly dissimilar between the two habitats, but as a result of different ecological processes. Species turnover explained variation between habitats in herb composition, such that species present in native forests were typical for both farmland and forest habitats, whereas those present in Eucalyptus plantations were typical for scrub and farmland habitats. In contrast, bird assemblages showed a significant nested subset pattern, with fewer species in Eucalyptus plantations compared to native forests. In total, the relative abundance of cavity-nesting forest birds was at least 64% higher in native forests. Our results show that Eucalyptus plantations cannot replace native forests as they harbour different herb species and only a subset of the bird species found in native forests. Considering the current rate of increase of Eucalyptus plantations and the fragmentation of native forests in NW Spain, a lack of conservation of native forests could result in future loss of biodiversity in general and forest specialist species in particular