The planting density of Acacia mangium influences the rehabilitation of a waste rock dump in Papua New Guinea (original) (raw)

Arabian Journal of Geosciences

Abstract

The waste rock dumps (WRD) in mining operations and post-mining activities pose environmental challenges unless rehabilitated with vegetation. The optimal planting density for the re-vegetation of WRD with forest tree species is unknown. This study determined the effective planting density for a native forest species Acacia mangium. Acacia seedlings were in-situ established on a WRD of a mining site at planting densities 3 m × 3 m, 2.5 m × 2.5 m, and 2 m × 2 m with an unplanted plot. The treatments were assigned to plots in a Completely Randomized Design and replicated six times. The pre-plant and post-planting physicochemical properties of the soil on the WRD were assessed. The experimental site had very low organic C content (0.07–0.95%), slight to strongly acidic reaction (pH, 2.82–6.65), moderate levels of exchangeable Mg (0.34–1.44 cmol/kg), and K (0.03–0.32 cmol/kg) in the top 30 cm of the WRD. WRD material also had appreciable amounts of toxic elements such as Al, Cu, Fe, Mn, and Cd. The post-planting results indicated that rehabilitation of WRD with Acacia at a density of 2.5 m × 2.5 m significantly (p < 0.05) increased organic C (100%), exchangeable K (124%), and Mg (55%) contents and enhanced extractable Cu contents (by 5-folds) compared to unplanted WRD. Other physicochemical characters of WRD such as pH, exchangeable Ca content, extractable P and toxic metals such as extractable Al, Fe, and Mn, and total Cd concentrations were unaffected by the planting density. The study recommended the Acacia mangium re-vegetation of WRD at a planting density of 2.5 m × 2.5 m to potentially improve the chemical fertility, nutrient recycling, and re-establishment of microbial ecosystem services.

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