Analyses of floristic composition of the abandoned Cu-dump field Piesky (Staré Hory Mountains, Slovakia)

Abstract

The Cu-dump field Piesky is an important historical abandoned mining area in the region of central Europe, well known for the high content of heavy metals in its soil, especially copper, the content of which varies from 933.40 to 1485.40 mg kg-1. Floristic and phytosociological research was carried out here during the vegetation seasons in 2011-2014. Altogether a total of 156 taxa of vascular plants were found. The most common species were Acetosella vulgaris, Agrostis capillaris, A. stolonifera, Arabidopsis arenosa and Festuca rubra, which were important constituents of all mine heaps in central Slovakia. We examined a total of 11 phytosociological relevés at various sites, which were selected to capture the variability of plant communities throughout topographical and ecological variability, various successional stages and impacts from humans. They were classified into five habitats: initial successional stages, grasslands, forest stands, wetland and feeding grounds for wild animals. Each site was evaluated in terms of its species richness, index of diversity and the representation of metallophytic, alien invasive species, synanthrophytes and native non-apophytes. This representation is based on species number and abundance, and their ratios to all taxa abundance and species richness are reflected by several indicators, which we have called indexes of metallophytization, synanthropization and naturalness of the vegetation (community) composition. In addition, indexes of invasive alien taxa and native non-apophytes proportion were used. Furthermore, each of the 11 sites was characterized by its basic topographic properties and climatic and edaphic variables, using the phytoindication approach based on the Ellenberg indicator values. The correlation analysis has uncovered several important and significant associations between some of these indicators and the climatic and edaphic variables. The negative correlations between the number of native non-apophytes and temperature (and between their relative abundances in the individual habitats and light) partially confirm that on mine heaps the numbers of synanthrophytes retreat into climax forest stands. Other correlations confirm that synanthropisation of the vegetation at a site is also higher in more eutrophic and less acidic soils for mine heaps. The species richness was highest in the grasslands and wetland and lowest in the initial succession stages, while beta diversity decreased in an opposite direction. Most synanthrophytes were found on grasslands, attracted by higher amount of nutrients in the soil, brought by sewage sludge from water treatment plants during partial recultivation of this mine heap in the years 2000 and 2010. The idea behind it was to support and accelerate the succession, however the use of the sludge may not have been the best option. Despite strict control of its chemical content, a high input of nutrients inevitably increases numbers of synanthrophytes in the vegetation cover. Finally, planting deciduous trees on young mine heaps as a method of directed succession is a better option than planting coniferous ones. The latter trees create acidic litter, increasing heavy metal mobility in the soil. We have found the dump heap Piesky to be a very suitable locality for studying processes of primary and directed succession in extreme environments and their impacts on the floristic composition of vegetation.