Why are plant communities of calamine soil worthy of study?
Rich deposits of silver, zinc, and lead ores were discovered in the environs of Olkusz in the Middle Ages and mined until the end of the 20th century. Several hundred years of mining and processing ores resulted in degradation of the landscape and destruction of vegetation. The area is now covered by smaller and larger excavations and waste remaining after ore processing. Huge, dry, uncovered heaps of rocky material are one of the most hazardous by-products of open-cast mining. They contain considerable amounts of heavy metals (mainly Zn and Pb). Undergoing wind and water erosion, they pose a threat to the environment as a source of windblown and leached toxic substances.
A popular method for rehabilitating degraded post-mining areas, including the Olkusz Ore-bearing Region (OOR), is tree planting (afforestation). Recultivation practices of that kind are commonly accepted because they produce a quick and eye-pleasing effect of greening. Unfortunately, this kind of recultivation is rarely carried out properly. The most frequent errors are these: unwise selection of trees for planting (the use of species not adapted to develop in the extremely adverse soil and moisture conditions); the creation of homogenous communities dominated by one tree species; and the introduction of alien species (not only trees but also herbaceous vegetation occurring in soil brought from afar and used for recultivation) which pose a potential threat to the native flora. It is expensive and troublesome to maintain vegetation cover formed in that way; plants unable to survive die, leaving gaps that must be filled.
Artificially created forest-park communities may not satisfy the hopes placed in them for protection the environment against the harmful impact of post-mining waste. The pine that dominates the planted stands causes strong acidification of the substratum, which may promote the mobilisation of heavy metals accumulated in the soil (at low pH they become more soluble and in consequence more toxic to living organisms).
The native flora of the Olkusz region shows quite different characteristic. It is composed of grasslands and meadows of diverse species composition, which develop spontaneously near the recultivated areas. The unfavourable water regime and high heavy metal content do not hinder the development of these plants; the species (and also their varieties or ecotypes) that occur here have evolved, by natural selection lasting for up to hundreds of years, features enabling them to survive in the extremely adverse habitat. The most interesting and most valuable communities have developed in zinc- and lead-rich areas; originally these were rock outcrops of galena and calamine deposits, and are now sites of past disposal of mining waste.
Open-cast mining contributed to the spread of the calamine flora but today is indirectly leading to its destruction. The greatest threat is probably the method of recultivation. The applied recultivation measures, which are aimed at creating a substitute natural environment in the degraded terrain, paradoxically obstruct the development of valuable vegetation. Another problem is that the ostensibly useless fragments of grassland and meadows are designated for industrial development.
Conservation of the typical flora of metalliferous areas is important for many reasons. Firstly, on account of their properties, grassland and meadow communities may become not only the basis for successful restoration of degraded landscape but also the most appropriate way of protecting the environment against the harmful impact of mine spoils. Dense cover of this type of vegetation binds soil particles together, protecting the ground surface against erosion. It is not unlikely that it improves the chemical parameters of soil solutions and the activity of microorganisms. Also, the relatively high biodiversity and the ability of species to organise themselves into associations may be critical to the vegetation's resistance and durability.
Secondly, grassland and meadow communities have high aesthetic value. They are composed of small patches of herbaceous vegetation, differing in pattern and colour, and changing according to the season. Saving the most valuable fragments of grasslands and meadows in the vicinity of forests would create an attractive landscape.
Thirdly, vegetation colonising former excavations and mine spoils, including the native flora of the Olkusz region, is a very interesting subject for study, because it develops under strong selection pressure. Microevolution processes proceed quickly there, leading to the creation of new ecotypes, varieties, and even species adapted to live in the hostile habitat. These plants may prove invaluable on account of their ability to colonise heavily contaminated areas, the number of which unfortunately is increasing.
The present method of managing the natural and landscape resources of the described mining area seems at best ineffective, because the potential of the native vegetation is not employed in the recultivation work. This state of affairs is reinforced by poor knowledge of the flora of the Olkusz region and of the factors responsible for the development of plant communities in metalliferous areas, as well as insufficient understanding of the effect of different types of vegetation on the physical and chemical parameters of the substratum. The present project is an attempt to change this.