Grigg, A 2012, 'Adaptive rehabilitation management and a drying climate: unique challenges for Alcoa's bauxite mine rehabilitation in southwestern Australia', in AB Fourie & M Tibbett (eds), Proceedings of the Seventh International Conference on Mine Closure
, Australian Centre for Geomechanics, Perth, pp. 459-466, https://doi.org/10.36487/ACG_rep/1208_40_Grigg
Alcoa has been mining bauxite in Perth’s water supply catchments within the jarrah forest of southwest Australia since the late 1960s and has rehabilitated more than 15,000 ha to date. The current rehabilitation objective of restoring a sustainable jarrah forest ecosystem was implemented from 1988, utilising direct seeding of the local native tree species of jarrah (Eucalyptus marginata) and marri (Corymbia calophylla). Tree establishment densities were initially high, averaging 3,000 trees ha-1, but these have been reduced over time as an adaptive management response based on monitoring and feedback. The present day establishment target is 1,300 trees ha-1, with a maximum of 2,500 trees ha-1. Although tree densities meet past and current completion criteria agreed to by regulators, there is reluctance on the part of some government stakeholders to grant Certificates of Acceptance because of the higher water use characteristics of dense rehabilitation compared to the less dense forest it replaced. The issue has risen in prominence in recent years due to declining water yields into Perth’s water supply reservoirs, which are largely associated with a drying climate since the mid 1970s. While target tree establishment densities for future years of rehabilitation may be reviewed in renegotiated completion criteria, a legacy remains of older rehabilitation which is now regarded as over-dense. Alcoa believes that these areas may be treated by an initial cycle of thinning, which experimentation at the plot and whole-catchment scale has demonstrated: (i) increased catchment flows; (ii) potentially shortened crop rotations for future timber production; and (iii) benefits to forest conservation values including fauna. This paper describes the unique challenges faced by Alcoa and the rare example of large-scale post-establishment management of rehabilitation to address stakeholder concerns and to deliver improved rehabilitation outcomes.
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