The potential role of tree plantations in providing habitat for lichen epiphytes

The extension of native forests has been reduced worldwide and their distribution is increasingly fragmented. In contrast, tree plantations have expanded, and currently constitute an important element of the matrix of semi-natural habitats surrounding native forest fragments. The objective of this study is to evaluate the suitability of tree plantations to harbor epiphytic lichen flora typical of native forests, thus increasing landscape connectivity. We focus especially on Eucalyptus globulus plantations, which have dramatically expanded in the last decades in the study area (NW Spain). We surveyed epiphytic lichen diversity and composition of species and functional groups in the most common forested habitats in the area: eucalypt plantations of three ages (young, intermediate and mature), pine plantations (Pinus pinaster) and native oak (Quercus robur) forests. Lichen diversity and abundance was highest in oak forests and pine plantations and lowest in eucalypt plantations, particularly in young plantations. Oak forests were associated with the most shade tolerant and hygrophytic species, whereas those requiring more light and the most xerophytic were associated with eucalypt plantations. Oaks and pines were associated with species requiring acidic substrates, whereas eucalypts were associated with lichens of basic substrates and eutrophicated sites. In eucalypt plantations, there was a higher predominance of sexual reproduction and crustose lichens in younger eucalypts and of asexual reproduction and foliose lichens in the older eucalypts. Native forests had a very distinctive species composition. They had the highest percentage of unique species and were associated with the species of higher conservation concern (e.g. cyanolichens and members of the Lobarion community). The low abundance and diversity together with the differences in species composition show that eucalypt plantations are a poor habitat for lichens and can hardly provide connectivity among oak forests patches. Pine plantations harbor higher lichen abundance and diversity but differ markedly with oak forests in composition, in both species and functional types. Thus they cannot provide connectivity to the lichen flora typical of native oak forests, especially for the most vulnerable. (C) 2012 Elsevier B.V. All rights reserved.