Establishment of native vegetation on artificial growth mediums in the Afroalpine zone, Lesotho

Abstract

Mining is an anthropogenic activity that is not only destructive to the environment but creates imbalances between the natural integrity of the environment and human society. Letšeng Diamonds is a kimberlite diamond mining company in the mountain kingdom of Lesotho. Located in the Mokhotlong district, Letšeng Diamond Mine produces post-extraction kimberlite tailings with a sand fraction of 82.7%, clay mineral content of 9.3%, and low organic matter. Such fine material is prone to wind erosion and easily washed away by storm water runoff, necessitating rehabilitation. Vegetation cover is important for soil protection and promotes biodiversity during rehabilitation of mined areas. Native plant species are ideal for such rehabilitation processes through evolutionary adaptations to harsh local growing conditions. The aim of this study was to identify the most suitable species and soil treatment for restoration purposes. Secondary aims included to (1) test the germination response of various native species on different kimberlite and top soil treatments, (2) evaluate the establishment and growth of these selected species, and (3) assess their germination response as part of an experimental seed mix. A rapid germination trial using seeds of seven pioneer plant species acquired from the study area was used to determine the most suited plant species according to predetermined criteria. The ability of T. disticha to germinate and establish on different kimberlite and top soil treatments was compared. Furthermore, a native plant seed mix was used to determine germination responses of other plant species in the presence of T. disticha across various treatments. Additionally, the ability of forb species to establish with T. disticha was compared. The germination trial showed that T. disticha revealed highest germination ability on various kimberlite treatments. The seedling growth performance results indicated that effective seedling establishment was associated with kimberlite tailing treatments having additional topsoil. Of the nine plant species in the seed mix, only Dierama robustum, Hesperantha schelpeana and Sisymbrium turczaninowii germinated copiously in the presence of T. disticha seedlings, which suggests that these species can tolerate competition to germinate across various treatments. Addition of topsoil increased the potential of mine tailings to support germination and establishment of plant diversity. Furthermore, the emergence of 18 unsown plant species from 10 families in the trial treatments (most probably due to the soil seed bank and seed dispersal) is a positive indication that plants can naturally colonise kimberlite mine tailings.