Authors: Schreiner, GO; Pienaar, E; van Eeden, JD; Hoffman, MT; Carrick, PJ

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DOI https://doi.org/10.36487/ACG_repo/852_74

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Schreiner, GO, Pienaar, E, van Eeden, JD, Hoffman, MT & Carrick, PJ 2008, 'An Ecological Evaluation of Rehabilitation Interventions on Phosphate Mined Land in the West Coast Fossil Park from 1996–2008', in AB Fourie, M Tibbett, I Weiersbye & P Dye (eds), Mine Closure 2008: Proceedings of the Third International Seminar on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 799-807, https://doi.org/10.36487/ACG_repo/852_74

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Abstract:
From the early 1940s until 1993, the 600 hectare West Coast Fossil Park (WCFP) was mined for phosphate. In 1996, plots were established to determine the most cost-effective approach to restore the exposed phosphate beds, as well as sites in the tailings dam area. Three replicates of control and treated plots were established. Treatments at the phosphate beds site included fertilizer addition, brushpacking and topsoiling. Seed was added to all treatments on the phosphate beds. In tailings dam plots, the treatments included adding seeds, or planting seedlings of different grass and early-succession species with and without brushpacking. We resurveyed the plots between March and April 2008. Our objectives were to record species richness and the percentage cover of species and growth forms within treated plots, and to compare them to the control plots and to plots from an undisturbed reference site. Species richness was determined by counting all the species in a plot. Species cover was determined using a point intercept method. We also measured the cover of litter and bare ground using this approach. Comparisons between plots were visually assessed, using a DCA ordination analysis. Species richness, plant, litter and bare ground cover, as well as plant cover of the major growth forms were compared with ANOVA and Student-Newman-Keuls tests for the phosphate bed and tailings dam sites separately. Results show that all control and treated plots had significantly fewer species and lower cover than the reference plots. Tree and succulent plant cover was also generally higher in the reference plots. The absence of restios in the control and treated plots was a significant difference between previously-mined and reference sites. There were few significant differences between treated and control plots at the tailings dam site for all variables. The main difference between treated and control plots at the phosphate beds was the increase in short-lived shrubs at sites which received topsoil prior to seeding. The dramatic differences between previously-mined sites and reference sites are primarily attributed to the comprehensive transformation of the substrate available for plant growth on previously-mined sites. Three reasons for the lack of difference between treated and control plots are suggested. First, after twelve years, the initial impact of the treatments might be obscured. Second, significant substrate differences between plots and low replication might make it difficult to find statistically meaningful differences. Third, greater intervention effort in terms of labor and seed or seedling quantity might have produced a different result. We conclude by acknowledging the significant role that the rehabilitation project has played in the region.

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