Lu, P & Meek, I 2019, 'Harnessing ecological processes in the Ranger Uranium Mine revegetation strategy', in AB Fourie & M Tibbett (eds), Proceedings of the 13th International Conference on Mine Closure
, Australian Centre for Geomechanics, Perth, pp. 719-732.
Energy Resources of Australia Ltd’s (ERA) Ranger Uranium Mine, surrounded by Kakadu National Park (KNP) in Australia’s Northern Territory, ceased mining in 2012 after 31 years of operation. All rehabilitation activities, including revegetation, shall be completed by 2026, followed by a post-closure monitoring and maintenance period. A detailed Mine Closure Plan for Ranger was published online in 2018 and will be updated annually (Energy Resources of Australia Ltd & Eco Logical Australia [ERA & ELA] 2018).
At ERA Ranger Mine, the final landform made of waste rock will be revegetated using local native species to establish a self-sustaining ecosystem, similar to the eucalypt savanna woodlands that dominate the adjacent area of the KNP. The waste rock substrate dictates fairly harsh conditions, with high temperatures, irradiance and surface reflectance, relatively low water holding capacity (at least until weathering and other soil development processes progress), and low or no soil organic matter, microbial activity or nutrients. Together with the long dry seasons in the monsoonal wet–dry tropics, and the high fire frequencies in the KNP, this poses great challenges for the Ranger mine’s ecosystem restoration.
Taking into account the above challenges and based on the learnings from extensive studies and revegetation trials at Ranger over the last three decades undertaken by ERA and other research agencies (e.g. CSIRO, ERISS), a revegetation strategy was developed and endorsed by key stakeholders in 2004. Following this, ongoing research and monitoring of the revegetation established by applying this strategy has continued to develop the science underpinning this strategy.
The revegetation strategy is to initially establish framework overstorey species, or K-strategists (sensu MacArthur & Wilson 1967), along with a subset of important and reliable midstorey and understorey species. These species form the ‘framework’ for the ecosystems, controlling much of a site’s nutrient and water resources, providing many of the core habitat values for other plants and animals, and contributing substantially to both the overall functioning and long-term stability of the plant communities.
As the initial plantings establish and develop, a process expected to take five or more years based on trial landform experience, the soil and litter layer will develop, canopy should increase providing shade, and plants will develop attributes resilient to fires (e.g. stem diameter, lignotubers). It is at this stage that introductions of additional species are planned to improve the composition and structure of the ecosystem. These species are generally those that risk being too competitive or, alternatively, too sensitive to introduce at the earlier (initial) stage.
This two-stage approach to species establishment harnesses ecological processes such as vegetation community and soil development, and species-specific environmental preferences, to underpin the Ranger revegetation strategy. Well-intended aspirations to introduce all target species at the initial revegetation establishment stage should defer to an appreciation of ecological processes that will increase the likelihood that revegetation efforts will result in success. Ongoing planning, research, monitoring and adaptive management should ensure the best possible revegetation outcome at Ranger mine.
This paper reviews the natural ecological processes that govern the eucalypt-dominated ecosystems of the region and discusses the current Ranger revegetation strategy and its validation by a 10-year-long ongoing field test on the Ranger trial landform. The trial landform studies have demonstrated that the key overstorey species of the target vegetation communities can establish and mature on the waste rock substrate. Current research is focused on the establishment of understorey species.
Keywords: revegetation strategy, framework species, tropical woodland, uranium mining, waste rock
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