Edaphic optimum niche for some pioneer rangeland plants in coal mine wastes in Karmozd mines, Mazandaran province, Iran

Background and objectives: Mineral exploration is an important factor in rangeland ecosystem degradation in Iran. The first priority in mine site restoration is to use native plants as they can resist the stress caused by heavy metals and nutrients deficiency and also the harsh environmental situation. Vegetation restoration in polluted mining area depends on how plants can respond to phisycal and chemical properties of mine waste. This study aimed to assess the responses of five pioneer species (Glaucium fimbrilligerum, Melica persica, Hordeum vulgare, Polygonum aviculare and Silybum marianum) in secondary succession to the phisyco-chemical properties of coal mine waste in Karmozd coal mine, Mazandaran, Iran. Methodology: The waste generated from the coal mining was heaped into different dumps in Karmozd coal mine site in Savadkoh county, Mazandaran province, Iran. This mine is one of the oldest and major coal mining site in central Alborz coal zone. Three dumps of coal waste were selected which were abandoned for more than three decades. All dumps had similar elevation above sea level and geographical aspect. During underground mining large volumes of coal wastes were heaped in one of the waste dump but in the other two dumps waste materials were deposited outside of tunnels. Plant species were sampled in 138, 1 m2 plots using random-systematic methods along transects. In each plot the cover percentage of each plant species were estimated visually. A soil samples were taken from the center of each plot at depth of maximum 20 cm. Then soil samples were kept in the plastic bags until chemical analysis time. The soil samples were air-dried at room temperature. Then Soil texture, pH, EC, OC, N, P, Cu, Zn, Ni, and Pb were measured in the laboratory. Plant species responses and the ecological niches were determined using eHOF model in R 3.5.3. The best model was selected using AIC index. Results: Results of this study showed that plant species responded to coal wastes properties in a variety of models. Among them the sysmetrical unimodal and bimodal with unequal two optima were more common. In response to the amount of sand in the soil all plant species except H. vulgare had an optimum in 49-88%. S. marianum showed an optimum in the lowest amount of clay while P. aviculare and H. vulgare had a broad ecological niche along the gradient of clay. G. fimbrilligerum and H. vulgare had a broad ecological niche than other plant species in response to the soil pH even with an optima in low soil pH. For soil minerals the dominant response was bimodal with unequal two optima. The upper optima for soil total nitrogen was found for P. aviculare and the upper optima for soil available P was detected for P. aviculare and H. vulgare. Two plant species (S. marianum and M. persica) responded to all heavy metals with symmetrical unimodal while the other species showed a verity of responses. S. marianum showed optimum in greater amount of heavy metal levels and its optima was 255.24, 53.74, 180.59, and 151.87 for Cu, Pb, Zn, and Ni, respectively. Conclusion: In this study the three forb species showed more divers responses to the measured coal waste properties than that in two grass species. The studied plant species had different life spans and life forms. According to their responses and the ecological niches it can be concluded that all of these plant species have the potential for establishment and growth on coal waste dumps. Therefore, they can be used for mine site restoration with a priority to S. marianum and M. persica. Further studies are needed to assess the facilitation of these plant species growth and establishment under different remediation treatments.