Epiphyte homogenization and de-diversification on alien Eucalyptus versus native Quercus forest in the Colombian Andes: a case study using lirellate Graphidaceae lichens

In many tropical areas, monospecific tree plantations are replacing natural forest. The ecology of these plantations is quite different from that of natural forests, including the diversity and community structure of vascular and cryptogamic epiphytes. Few studies have looked at the ecology of guilds of epiphytes in plantations versus natural forest. Here, we investigated epiphytic, lirellate species of the family Graphidaceae, the largest family of tropical lichen fungi, which are widely distributed and abundant in tropical regions. We compared species richness and community structure in a monospecific plantation of the introduced tree species Eucalyptus globulus versus native oak forest dominated by Quercus humboldtii. Overall species richness was substantially higher in the natural oak forest (41 vs. 14 species, with eight shared between both stands, for a total of 47), whereas species abundance was significantly higher in the gum plantation. While species richness per tree (alpha diversity) was comparable between both stands, average species turnover between trees within each stand (beta diversity) was significantly higher in the natural oak forest, resulting in substantially higher overall species richness (gamma diversity). We conclude that the monospecific gum plantation exhibits both de-diversification (lower overall species richness) and homogenization (more similar communities between trees) of these epiphytic lichen guilds. This is not an effect of phorophyte diversity since in both stands, only a single tree species each was considered. Among the lichens identified, we detected six new to the Neotropics and 29 new records for Colombia.