Flora of spoil heaps after hard coal mining in Trzebinia (southern Poland): effect of substratum properties

The aim of the present study was to investigate the composition of spontaneous plant cover and the physicochemical properties of the substratum of spoil heaps of the Siersza hard coal mine in Trzebinia (southern Poland) abandoned in 2001. Floristic and soil analyses were performed in 2011. The substratum was very diverse in terms of texture (sand: 55-92 %, clay: 6-38 %), nutrient content (total C: 1.3-41.0 %, total N: 0.05-0.49 %, total Ca: 0.5-7.3 %) and pH (3.7-8.7). Moreover, total thallium concentration in the substratum was high, ranging from 6.0 to 14.6 mg kg(-1). Plant cover varied from 50 to 95 %. The number of plant species per 4 m(2) varied from 6 to 29 and correlated negatively with total carbon content (r = -0.85, p < 0.01), and positively with sand content in the substratum (r = 66, p < 0.05). The highest number of species per area unit was observed on a humus substratum, where initial soil has developed on the part of carboniferous waste rock spoil under 20-30 year old trees, and the lowest on carbon shale with coal and culm. Among 197 plant species, most belong to Asteraceae, Fabaceae, Poaceae and Rosaceae families. Hemicryptophytes (49%) and terophytes (18%) predominated. The investigated area was primarily colonized by native species spread by the wind. However, invasive alien species also had a significant share (8%) in the plant cover.