Study sites
The study was carried out in forest stands growing on technosols developing from three different types of substrates referred to as Clays, Sands and Ashes. Samples of Clays were taken at the external spoil heaps of the open-pit lignite mine Turów (number of sampling sites, n = 12) and the open-pit sulphur mine near Piaseczno (n = 12). Clays sampled at Turów and Piaseczno represented acid and alkaline materials, respectively. Sands were sampled in the reclaimed areas of the sand quarry Szczakowa (n = 17) and on the external spoil heap of the open-pit lignite mine Bełchatów (n = 7) while Ashes were taken at the combustion waste disposal site Lubień (n = 24). Geographic localization and basic data on climate, parent material and initial fertilization of the sampling sites are given in Table 1.