In most cases, attempts to alleviate the effects of mining on the environment have been limited to physical and chemical stabilization of mine wastes. Particularly in metal mines, the approach has been to mimic what was observed in ecosystems occurring on substrates naturally rich in metals, such as ore outcrops. On such substrates, plants are found that have adapted to tolerate the presence of high metal concentrations in the soils. Few such plant species, for example, Viola calaminaria and Pearsonia metallifera, are obligate metallophytes, which occur strictly on soils with high available metal concentrations. More common, however, are facultative metallophytes, such as Agrostis capillaris, Agrostis stolonifera, Festuca rubra, Silene vulgaris, Mimulus guttatus, and Armeria maritima. Most populations of these species occur on soils that are low in metal concentrations and are not tolerant to high available metal concentrations in the soil. However, those species do contain the genes for metal tolerance and so have the innate ability to develop metal-tolerant populations when the seeds germinate on substrates with high metal availability. It was this observation that led to the use of plants for revegetation of metal mine wastes. One of the best-known examples of this was the use of the grass F. rubra 'Merlin' for revegetation of copper and zinc tailings around Britain and Ireland during the 1970s and 1980s. In most cases with the help of amendments, such as limestone to alleviate acidity and fertilizers, revegetation has been successful - it stabilizes mine wastes and reduces the occurrence of erosion and dust blows. However, it hardly is restoration to the situation that occurred before mining activities commenced. Even if the postmining habitat was similar to the predominant habitat before mining commenced, such as revegetation with metal tolerant grasses to recreate grassland, it would be difficult to go back to the uses it had in the past. Grazing and hay production, for example, would not be advisable because of the possible transfer of toxic substances into the food chain. More importantly, from the perspective of this article, mine tailings revegetated with metal-tolerant plants are not ecologically the same as the natural grassland that existed on the site before mining commenced. One reason is that relatively few plant species have the innate ability to form metal-tolerant populations and so plant diversity on such sites, and subsequently biodiversity in general, will be much lower compared to the preexisting situation. Due to lower biodiversity, revegetated mine wastes are unlikely to perform the same 'ecological services' as the habitat that existed before mining.
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