Wetlands in mining sites–harbour for threatened species or source of non-native troublemakers?

The occurrence of threatened plant species on mining sites has been previously nearly exclusively examined in terrestrial habitats, where it was found that such sites often harboured threatened species of plants, especially in younger stages. In this study, we focused on aquatic and littoral habitats only. We collected and analysed vegetation samples from differently aged spontaneous successional stages in sandpits, stone quarries, clay quarries, black coal subsidences, and brown coal spoil heaps across the Czech Republic, Central Europe. The age since mining cessation ranged from 1 to 89 years. We asked what the potential of wetlands on post-mining sites to harbour threatened plant species is and if it varies between individual types of mining sites and successional stages. Altogether we recorded 251 vascular plant species and 7 charophytes, of which nearly 20 % were considered endangered in the national flora. Different types of mining sites did not differ in the proportion of threatened species. However, they differed in their conservation potential which also takes into account the cover of threatened species, not only their presence. The highest conservation potential was found in black and brown coal regions. The proportion of threatened species did not differ between successional stages, however, their cover increased with successional age. On the other hand, the presence and cover of non-native species was generally very low. Spontaneous succession at aquatic and littoral sites can lead to valuable seminatural stages rich in threatened species and can generally be recommended as a passive restoration option in disused mining sites.