## 2 Study Area  
The research area (Figure 1[33]) is located in Southeast Poland close to Tarnobrzeg county, in the municipality of Grebow. The former sulfur mine called Jeziorko is located at 50\({}^{\circ}\)32\({}^{\prime}\)N; 21\({}^{\circ}\)47\({}^{\prime}\)E. The study site covers 216.72 ha of the reclaimed and reforested area after sulfur exploitation via the Frasch process (borehole exploitation/underground sulfur melting). Forestry reclamation has also been applied in the area.  
The former Jeziorko sulfur mine occupied more than 2140 ha, and more than half of the area (1179 ha) was reclaimed in 2010. For forestry, an area of about 700 ha was reclaimed, and the state forests (pl. PGL Lasy Paristwoe) were granted land occupying a total area of 374 ha. The studied area is a forest complex located in a forestry district, occupying an area of over 216.72 ha.  
Reclamation of this area consisted of, e.g., removing the infrastructure of the mine, improving the hydrographic and landscape conditions, neutralizing the pH of the sulfuric and highly acidic soils through liming (around 500 Mg ha\({}^{-1}\) on average), fertilization (70 kg ha\({}^{-1}\) P\({}_{2}\)O\({}_{5}\), 60 kg ha\({}^{-1}\) K\({}_{2}\)O), and sowing grass seeds [34]. Then, the area was developed for forestry. The area was mainly aforested with one-year-old seedlings of Scots pine (_Pinus sylvestris_ L.) and with a smaller share of silver birch (_Betula pendula_ Roth) and boreal oak (_Quercus rubra_ L.) [35]. According to the forest management plan, the tree stands in the area are currently about 25 years old.  
Reclamation of the land after sulfur extraction is generally characterized by a high degree of difficulty, especially in the case of land used for borehole mining, which causes large-scale environmental transformations, including overlapping chemical, geomechanical, and hydrological transformations [36]. The former Jeziorko sulfur mine is a very problematic area for plant adaptation because of the borehole sulfur exploitation method (Figure 2 [33]).  
In the area of the former Jeziorko sulfur mine, chemical transformations were a large challenge for reclamation, which is a typical phenomenon for mines that use the Frasch method, which is accompanied by numerous spills of liquid sulfur, resulting from technological failures within the holes and pipelines (transmission installations [36]). Moreover, the liquefied sulfur spilled out uncontrollably from the technological landfills, strongly contaminating the adjacent areas [36]. Although the reclamation treatment was carried out with many expensive technical methods, the restored forest ecosystem still has hot spots (with a complete absence, or low degree, of vegetation cover) where the degree of sulfur contamination is high (up to 45,000 mg kg\({}^{-1}\)) [36]. The plants are thus forced to function in unnatural habitat conditions caused by soil, and surface and groundwater contamination caused by high sulfur concentrations. However, research in such areas offers an exceptional  
Figure 1: The research area: (**a**) general map of Poland with the localization of the study area; (**b**) analyzed area (red polygon) as a part of the former sulfur mine Jeziorko terrain (PlanetScope imagery, 2019).  
chance to expand our knowledge about the reactions of trees and stands, as well as other ecosystem components (including herbaceous plants) to environmental stress in the broad context of assessing the dynamics of forest ecosystems undergoing restoration [6; 37; 38; 39].