High lichen species richness but low taxonomic diversity built up on abandoned tailings heaps in a cultural landscape

We aimed to detect species distribution patterns at landscape level that have arisen following the colonisation of a mine spoil heap (MSH) by macrolichens. All taxa occurring on various substrates and the degree of occupancy by different vegetation patch types were recorded at a resolution of 50 m × 50 m within a regular square grid of 25 ha, which extended over a 60-year-old abandoned MSH and its adjacent agro-pastoral area. The fraction of MSH was the most important predictor of the lichen composition and richness at grid cell level, followed by the terrain slope and the proportion of heathland. Almost all lichen taxa positively correlated with the MSH fraction were terricolous, fruticose, oligotrophilous, acidophilous species that occurred preferentially on the steep, barren slopes. The few corticolous, nitrophilous species were negatively correlated with the MSH fraction. Except for the corticolous and saprophytic species, the proportion of MSH and the elevation range had each a positive effect on both total and terricolous lichen richness. Conversely, taxonomic distinctness displayed an opposite pattern. Such a contrast was determined by the numerous conspecific (Cladonia) lichens occurring on the steeper MSH slopes, with scarce vegetation. A conspicuous nestedness, but no pattern of species turnover, was detected along the main ecological gradient. This was due to both the corticolous/saprophytic species shared with the adjacent, tailings-free habitats and the terricolous/saxicolous lichens dispersed from proximal source-habitats. The MSH studied can be considered a hotspot for lichen species richness but not for taxonomic diversity.