Early colonization of stone by freshwater lichens of restored habitats: A case study in northern Italy

This study evaluated the effectiveness and life-strategies of freshwater lichens in colonizing newly constructed stone structures in low-elevation streams in a small nature reserve in northern Italy. Species richness, size of thalli, morphological and ontogenetic traits of the species were related to the age of restored habitats. Lichen colonization was surprisingly rapid, indicating the high potential of these organisms in colonizing restored habitats. However, the species pool found in the restored habitats was different than that found in natural sites in the same study area. The age of newly constructed habitats influenced both species richness and thallus size of the two most frequent Verrucaria species. Verrucaria aquatilis was a rapid colonizer invading the substrate by several small-sized and thin thalli which soon supported a large number of small perithecia whose development began in the earlier phase of thallus formation. V. elaeomelaena, on the contrary, developed according to a different strategy, establishing a thick thallus on which relatively large perithecia were formed much later than in V. aquatilis. As these taxa are important photoautotrophic components of freshwater ecosystems more ecological knowledge is needed to evaluate the effectiveness of different measures of river restoration on lichen communities. The main practical implication of our study is related to the value of small stone structures, such as riffles and ramps, for enhancing the establishment of pioneer freshwater lichens to rapidly colonize newly available substrata.