Strip-mine rehabilitation in Namaqualand

[摘要] ENGLISH ABSTRACT:Namaqualand has a very unusual diversity of plant life, with many endemic plant species. Thefundamental question of this thesis is how this system, damaged by strip-mining activities, canbe rehabilitated. The aim was to base the rehabilitation methods on ecological processes.In order to answer this question an overview of the relevant literature was needed inorder to identify possible research needs and also to evaluate the work that has been done inthe field of strip-mine rehabilitation in arid areas. An understanding of community andecosystem dynamics would help to establish aims and methods for site-specific rehabilitation.In Namaqualand, South Africa, there is also a need for experimentation to establish which of themany factors is most limiting to long-term ecosystem recovery.It is important to have a good knowledge of the successional processes and disturbancehistory of the land which needs to be rehabilitated. The vegetation on unmined areas andmined areas of different ages and treatments after mining, were sampled. It was shown thatsome areas could be expected to show a large degree of recovery in the space of a few years,whilst others would show little or no recovery over a period of decades. It is important torecognise rehabilitation as a gradual process that takes place at different rates in different areasand in different years. The planting of Atriplex nummularia and sowing of Atriplex semibaccatadid not facilitate the return of indigenous, perennial species, but rather seem to inhibit theirreturn.In view of the importance of topsoil in terms of the fertility of the soil and the seed bankpresent in the topsoil, the influence of topsoil removal and stockpiling due to strip-miningactivities were tested. The soil fertility was tested by means of radish bioassays and soillaboratory analysis, whilst species diversity and richness were tested with seedling emergencetrials. As expected a higher plant species diversity was found on the unmined soils andradishes grew larger on these soils. The topsoil deteriorated in terms of plant species richness,diversity and soil fertility whilst it was stockpiled. Direct replacement of topsoil would ensure aplanting medium closer to the pre-disturbance level that could lead to fairly rapid and successfulrecolonization of the mined area.Successful plant recruitment also depends on the microsites to which seeds aredispersed. The effect that different microsites had on seed germination, seedling growth andsurvival was tested. It was found that micro catchments always yielded the highest numbers.The establishment and survival of seedlings in the other microsite types (under single shrubs,under clumped shrubs and in the open) varied, depending on the amount of rainfall received inthe particular year. Lastly, I experimented with the translocation of three local, indigenous,succulent plant species. These plants were transplanted either in clumps of three together oralone, since I hypothesized that planting them together would facilitate their survival. However,it was found that it depended largely on the morphology of the plant and the amount of rainfallreceived in a particular year, whether these plants will compete with each other for limitingresources or facilitate each other's survival.The thesis contributes to the understanding of vegetation dynamics in the SucculentKaroo after strip-mining has taken place. Guidelines are provided based on ecologicalprocesses, for strip-mine rehabilitation in the Succulent Karoo.

[发布机构] Stellenbosch University