Mineral deposits are finite and will eventually be exhausted (Jowitt et al., 2020). Mining of minerals is a temporary land use change that alters the original soil strata and produces large amounts of soil remains (Johnson et al., 1994; Basommi et al., 2016). The increasing demand for minerals is causing expansions in mining areas; at present, 57,277 km² is being used for mining operations on a global scale (Maus et al., 2020). In many mining operations, waste production, and its disposal can cause extensive and long-lasting disturbances on the natural ecological processes such as changes in species composition, primarily due to unstable substrates for plant growth (Ballesteros et al., 2014; Virah-Sawmy et al., 2014; Reta et al., 2018; Sonter et al., 2018). On a large scale, mining operations impact both the abiotic and biotic components of particular ecosystems (Hester et al., 1994; Millennium Ecosystem Assessment, 2005). The abiotic impacts include changes in soil profile, nutrients, texture, and other physicochemical properties such as pH electrical conductivity and production of particulate matter due to crushing of rocks. The assessment of the physicochemical properties of solid waste is essential to understand its fertility status. Khan et al. (2020) and Okereafor et al. (2020) found that some mining operations can release toxic elements such as arsenic, lead, and nickel, which can pollute the soil and water. Mining can impact on ecology through habitat loss and fragmentation (Gajic et al., 2018). Ntshane and Gambiza (2016) reported 20–30% habitat loss due to mining in South Africa. Sonter et al. (2015) found that a significant amount of carbon emissions ascribed to deforestation was linked with charcoal mining. Similarly, mining in Indonesia resulted in a sixfold increase in habitat loss (Paull et al., 2006).

The utilization of large amounts of mining waste for establishing vegetation in mining areas depends on its physicochemical properties. As a general rule, only a few stress-tolerant plant species are able to grow in postmining substrates (Zhang et al., 2017). This is mainly due to high concentration of minerals, scarce availability of organic matter, and moisture and disruption of soil strata (Zeleznik and Skousen, 1996; Gorman et al., 2001; Grant and Koch, 2007; Skousen and Zipper, 2014). Furthermore, the mining areas can also be inhabited by some exotic species, such as Monty et al. (2019), who recorded the significant invasion of alien plants on limestone quarry wastes, which resulted in indigenous species habitat loss. Additionally, limestone quarries can cause soil erosion and dereliction of mined sites (Langer, 2001). A rapid solution for avoiding soil erosion and plant invasion is the plantation of native species for rehabilitating postmining landscapes. Native plant species can repopulate these postmining landscapes and eventually restore native vegetation.

The social and legislative context in many parts of the modern world means that some form of postmining land use and natural ecosystem reestablishment goals will be set before the permission is granted for a new mine (Skousen et al., 1994; Skousen and Zipper, 2014). Species reestablishment and sustainability are the major factors that determine the success of ecological restoration (Rodríguez-Seijo and Andrade, 2017; Li et al., 2018; Song, 2018). Species selection for restoration can be based on the chemical analysis of plant tissues, which can be indicative of species capacities to uptake the minerals in the solid waste of mining sites. Species more apt at mineral uptake can be effective in site restoration and more easily established (Marcus et al., 2018) such plant-tissue analyses that can be helpful in predicting plant growth. Minerals in mining waste can have positive or negative impacts on plant growth, e.g., plant height and branch sprouting (Jim, 2001; Gajic et al., 2018).

Restoration actions should aim to reestablish ecosystem services through species diversity and survival (Montoya et al., 2012). Appropriate measures, such as the possible solid waste amelioration with fertile soil and the selection of suitable species for mineral uptake, should be taken for the utilization of mining solid waste to revegetate the mining site. These cannot only reduce the impacts of mining on such transformed habitats but also increase the population sizes of the selected species (Macdonald et al., 2015; Gentili et al., 2020). Such species are suitable for ground stabilization and to green a barren anew (Bengson, 1995; Yirdaw and Luukkanen, 2003). Furthermore, being adaptive to local environmental and edaphic conditions, these native species can be established as self-sustaining plant communities. Therefore, the use of native plant species for landscape restoration in mining areas or to replace exotic plants can help to reverse the trend of species loss (Richards et al., 1998; Román et al., 2015).

Pakistan has extensive deposits of limestone in the provinces of Punjab, Sindh, Balochistan, and northern areas. These deposits are located in geological formations that range in age from the pre-Cambrian to the Eocene (Hamid et al., 2012). The presence of these deposits attracts mining companies, resulting in accelerated habitat change for the indigenous plants (Drewes et al., 2007). In the limestone quarry, Acacia modesta forms a bi-species climatic climax community with Olea cuspidata, while Adhatoda vasica and Dodonea viscosa both are understory shrubs (Champion et al., 1965). All of these species are valuable sources of livelihood for the local community as they are a source of traditional medicines, fodder, and animal grazing and control soil erosion (Khan, 2013; Khan et al., 2019). Considering the ongoing acceleration of mining impact on natural vegetation, there is a need to utilize the mining solid waste. As the quarry sites with waste heaps become barren, revegetation may begin by planting more productive species such as herbs and shrubs of the area, capable of using the existing postmining solid waste (Swanson et al., 2010). The present study was designed with the following objectives:

As the restoration of an abandoned site with limestone waste may follow the natural succession, we hypothesized that the shrub A. vasica being the early colonizer may accumulate more minerals in its tissues than A. modesta.

Our results showed the enhanced growth of the two selected species grown in the mining waste which provides novel information about habitat restoration by utilizing the two selected woody species A. modesta and A. vasica on mining wastelands. Furthermore, our hypothesis regarding the comparative mineral uptake between the two species was partially supported. The biomass of A. vasica accumulated more Mg, P, and Na and less N and K than A. modesta, while both species accumulated similar amounts of Ca. Such species-specific mineral uptake behavior improves our understanding of the ecological restoration of mining sites with varying mineral concentrations. The enhanced growth of both species in the quarry waste, could be due to the high Ca content (2.37%) along with other nutrients such as N, P, K, and Mg and their uptake by the plants, as shown by their significant correlation with the total biomass. Furthermore, the presence of gravel in the mining soil can lower the substrate water-holding capacity, which could prevent the invasion of Prosopis juliflora (Khan et al., 2019).

Although mining changed the original soil strata inhabited by these species, the solid waste did not have an adverse impact on plant growth, and the treatments seemed likely to have fertilization effect. The treatment efficiency in the long terms was also observed on the growth of both species, indicating the suitability of both species for restoration of solid waste with the mentioned physiochemical properties of soil. Our findings support Richardson and Evans (1986), who utilized grasses for the restoration of limestone quarrying landscapes. They also found that the waste did not contain any toxic elements and promoted the growth of the selected species. Furthermore, our study also revealed that the solid waste areas can be converted into green patches using indigenous species without ameliorating the existing soil; some other exotic species capable of growing in soils with high Ca content could be planted to establish vegetation. These findings can help improve ecosystem restoration in limestone mining activities where habitats have been altered due to excavation.

Our results are also consistent with prior ones reporting that limestone quarry waste is mainly composed of calcium carbonate, which could promote plant growth (Jim, 2001; Elsayed et al., 2017; Marcus et al., 2018). Calcium is a necessary micronutrient and is linked with various ion movements in the plasma. Its uptake can also regulate photosynthesis, carbohydrates, nitrogen assimilation, and the enzymes involved in it (Singh et al., 2018), which can enhance not only the performance of cellular mechanisms but also stress tolerance (Marschner, 1995; Konno et al., 2002; Matthew et al., 2011; Saito and Uozumi, 2020). Ecologists have classified plant species into calcifuges, which occur in soils with low Ca content, and calcicoles, which grow on calcareous soils (Lee, 1999). A. modesta and A. vasica are indigenous to the study area and have the potential to grow better in calcareous soils. However, we found that the Ca content was not uniform in both above- and belowground organs, as the roots had less Ca than shoots, which could be due to the utilization of calcium in the aerial parts for various metabolic processes (Clarkson, 1984).

Our results were consistent with those of Fu et al. (2004), in which Pteroceltis tatarinowii seedlings were grown in Hoagland nutrient solutions with three Ca concentrations (5, 10, and 15 mmol L^–1) or without Ca (control). Their results showed that the Ca content in the roots, leaves, and bark of P. tatarinowii increased with increasing Ca concentrations, and higher Ca content was found in leaves than in roots (Marschner, 1995). Kuznetsova et al. (2010) reported that indigenous Pinus sylvestris grew better with high Ca concentrations, and could be a candidate species for mining sites with high calcium content. The inverse correlation of total biomass with sodium concentration supports the findings of Bethke and Drew (1992) and Karim et al. (1993). As in non-halophytic species, high concentrations of sodium ions can reduce plant growth by disturbing plant water relations, unbalancing plant nutrition, and affecting several plant physiological and biochemical processes, which lead to a reduction in plant growth (Misra et al., 2006; Taffouo et al., 2009). Furthermore, the garden soil had more sodium than the solid waste, hence, the decrease in sodium content with the decrease in garden soil in the three treatments, resulted in increased biomass.

Compared with A. modesta, A. vasica absorbed higher amounts of all minerals from the mining waste, as shown in Figures 5A–F. Kasowska et al. (2018) reported some species that could uptake comparatively more minerals from mining waste. A. vesica being the shrubby species and considered to be the initial colonizer could have the potential for higher uptake of minerals, except calcium, as both species had similar uptake of Ca. Although an inverse relationship was found between the biomass and the Na uptake, A. vasica had a larger uptake of Na than A. modesta in a given treatment, indicating its potential to uptake the growth-reducing minerals more than the later colonizers such as trees. The results of the present study show that both A. modesta and A. vasica will be helpful for establishing vegetation on limestone quarry sites with high calcium content.

Both native species (A. modesta and A. vasica) showed increased growth in limestone quarry waste compared with the control. Adaptive to the mining substrate, both of these species can be utilized for the restoration of such mined landscapes without any soil amelioration. Planting these species will not only provide an ecological solution for the disposal of the limestone quarry waste but will also create opportunities for other environmental goods and services, such as timber production, habitat formation, carbon sequestration, erosion control, and natural ecosystem functioning.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

MH, ZS, and AK designed the experiment. MH and ZS did the field work. MH and RM conducted the laboratory analysis. MH, ZS, AK, and K-FC analyzed and interpreted the data. All authors contributed the manuscript writing.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.