The nature and extent of environmental disturbance associated with mining commonly entails completely new and challenging combinations of climate, lithology and landform. Consequently, the outcomes of ecological processes associated with the recovery or restoration of ecosystems cannot be predicted reliably from previously known associations between their physical and biological components. For radically disturbed sites, we propose that it is not practicable to aim for the restoration of historical ecosystems. However, hybrid (reversibly different) or novel (irreversibly different) ecosystems comprising new combinations of physical and biological components, including both native and non-native species, could provide levels of stability and functionality acceptable to all stakeholders and within feasible management regimes. We propose that limiting physical conditions of the landscape can be identified and managed, and that alternative species combinations for introduction to these new landscapes may be considered with cautious optimism.

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Adopting novel ecosystems as suitable rehabilitation alternatives for former mine sites

A review of studies on sustainable development in mining life cycle

Mine land rehabilitation: Modern ecological approaches for more sustainable mining

The basic methods for rehabilitating degraded land left after mining are reasonably well-understood and there are examples across Australia of these being currently implemented. But there are many other situations where further research will be needed to achieve rehabilitation objectives. In addition, a number of mines are yet to embark on any sustained program of rehabilitation and there is a disappointing number of cases of mines ceasing operations before rehabilitation is completed leaving sites in a badly degraded state. Overall there appear to be surprisingly few examples in Australia of post- mining rehabilitation that has reached a successful conclusion. In part, this may be simply a matter of time and the problem will be resolved as more mines reach the end of their working lives. But there is an apparent trend for mines to be placed into ‘care and maintenance’ or sold to other entities, to avoid the costs of rehabilitation. Thus, we are concerned there is a widening gap between what should be possible and what is being done in practice. We review some of the experiences of rehabilitating post-mining landscapes in Australia and conclude that problems have arisen because of (i) the inherently difficult task of restoring ecosystems at highly modified mine sites, (ii) institutional and management weaknesses and (iii) loose regulatory frameworks that allow a high level of company self-regulation. A key problem is that the importance of rehabilitation appears to rank below that of production in the minds of many mine managers and is not accorded the level of priority that the community expects. The scale of the mining industry and its capacity to cause environmental damage means that there is a need to improve the way mine rehabilitation is currently undertaken. We suggest that this might be achieved by improving research programs as well as better institutional and regulatory arrangements. The present situation represents a major ecological and financial risk to the nation as a whole and regulatory authorities need to develop more rigorous approaches to ensure effective rehabilitation standards are achieved.

Widening gap between expectations and practice in Australian minesite rehabilitation

Semi-arid ecosystems contribute about 40% to global net primary production (GPP) even though water is a major factor limiting carbon uptake. Evapotranspiration (ET) accounts for up to 95% of the water loss and in addition, vegetation can also mitigate drought effects by altering soil water distribution. Hence, partitioning of carbon and water fluxes between the soil and vegetation components is crucial to gain mechanistic understanding of vegetation effects on carbon and water cycling. However, the possible impact of herbaceous vegetation in savanna type ecosystems is often overlooked. Therefore, we aimed at quantifying understory vegetation effects on the water balance and productivity of a Mediterranean oak savanna. ET and net ecosystem CO2 exchange (NEE) were partitioned based on flux and stable oxygen isotope measurements and also rain infiltration was estimated. The understory vegetation contributed importantly to total ecosystem ET and GPP with a maximum of 43% and 51%, respectively. It reached water-use efficiencies (WUE; ratio of carbon gain by water loss) similar to cork-oak trees. The understory vegetation inhibited soil evaporation (E) and, although E was large during wet periods, it did not diminish WUE during water-limited times. The understory strongly increased soil water infiltration, specifically following major rain events. At the same time, the understory itself was vulnerable to drought, which led to an earlier senescence of the understory growing under trees as compared to open areas, due to competition for water. Thus, beneficial understory effects are dominant and contribute to the resilience of this ecosystem. At the same time the vulnerability of the understory to drought suggests that future climate change scenarios for the Mediterranean basin threaten understory development. This in turn will very likely diminish beneficial understory effects like infiltration and ground water recharge and therefore ecosystem resilience to drought.

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Stable oxygen isotope and flux partitioning demonstrates understory of an oak savanna contributes up to half of ecosystem carbon and water exchange

Assessing the development of rehabilitated grasslands on post-mined landforms in north west Queensland, Australia

This study depicts broad-scale revegetation patterns following sand mining on North Stradbroke Island, south-eastern Queensland, Australia. Based on an ecological timeline spanning 4–20 years post-rehabilitation, the structure of these ecosystems (n = 146) was assessed by distinguishing between periods of ‘older’ (pre-1995) and ‘younger’ (post-1995) rehabilitation practices. The general rehabilitation outlook appeared promising, whereby an adequate forest composition and suitable levels of native biodiversity (consisting of mixed-eucalypt communities) were achieved across the majority of rehabilitated sites over a relatively short time. Still, older sites (n = 36) appeared to deviate relative to natural analogues as indicated by their lack of under-storey heath and simplified canopy composition now characterised by mono-dominant black sheoak (Allocasuarina littoralis) reaching up to 60% of the total tree density. These changes coincided with lower soil fertility parameters (e.g., total carbon, total nitrogen, and nutrient holding capacity) leading us to believe that altered growth conditions associated with the initial mining disturbance could have facilitated an opportunistic colonisation by this species. Once established, it is suspected that the black sheoak’s above/belowground ecological behaviour (i.e., relating to its leaf-litter allelopathy and potential for soil-nitrogen fixation) further exacerbated its mono-dominant distribution by inhibiting the development of other native species. Although rehabilitation techniques on-site have undergone refinements to improve site management, our findings support that putative changes in edaphic conditions in combination with the competitive characteristics of some plant species can facilitate conditions leading to alternative ecological outcomes among rehabilitated ecosystems. Based on these outcomes, future studies would benefit from in depth spatio-temporal analyses to verify these mechanisms at finer investigative scales.

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Structural development of vegetation on rehabilitated North Stradbroke Island: Above/belowground feedback may facilitate alternative ecological outcomes

Completion Criteria for Native Ecosystem Rehabilitation at RTA Weipa – Report to Rio Tinto Alcan – Weipa Operations, September 2008

A requisite corollary of mineral sand mining on North Stradbroake Island (Queensland (Qld), Australia) has been the progressive rehabilitation of post-mined lands for the revegetation of native subtropical Eucalypt communities. Since 2005, rigorous environmental monitoring has been undertaken to verify the annual development of post-rehabilitated sites. From these longterm analyses, a chronosequence of land revegetation (ranging from three to 26 years postrehabilitation) was developed to examine the rehabilitation trajectories of various post-mined sites in relation to proximal undisturbed locations. Here, we identifi ed that some sites may be deviating from the intended natural analogues as evidenced by the opportunistic colonisation and otherwise ‘invasive’ behaviour of a regionally native species (Black Sheoak − Allocasuarina littoralis), which appear to be displacing the intended Eucalypt varieties. Although it is recognised that the broader data trends correspond to distinct periods of adaptive modifi cations to the implementation of rehabilitation (ie pre- and post-1995), this analysis focuses on further identifying potential above- and belowground feedback mechanisms underlying these divergent ecological outcomes.

H. Vickers

Papers

Assessing the development of rehabilitated grasslands on post-mined landforms in north west Queensland, Australia

Structural development of vegetation on rehabilitated North Stradbroke Island: Above/belowground feedback may facilitate alternative ecological outcomes

Completion Criteria for Native Ecosystem Rehabilitation at RTA Weipa – Report to Rio Tinto Alcan – Weipa Operations, September 2008

Above/belowground feedback may facilitate and sustain mono-dominance on rehabilitated North Stradbroke Island