Long-Term Trends in Faunal Recolonization After Bauxite Mining in the Jarrah Forest of Southwestern Australia

Abstract Fauna serve a key role in many forest ecological processes. Despite this, few studies have considered long‐term faunal recolonization after mining and rehabilitation of forest ecosystems. In the jarrah forest of southwestern Australia, permanent fauna monitoring sites have been established in bauxite mined areas rehabilitated in 1990 and in a range of representative unmined forest control sites. At each site mammals, birds, reptiles, and ants were surveyed in 1992, 1995, and 1998. The aims of the monitoring were to develop a better understanding of faunal recolonization trends, to produce recommendations for promoting fauna return, and to consider which techniques and fauna groups are best suited for monitoring recolonization. The results showed that successional trends varied between fauna groups. Generalist foraging mammals recolonized rapidly, whereas small predators took longer. Feral mice were initially abundant and then declined. Birds gradually recolonized, and after 8 years bird communities were very similar to those in unmined forest sites. Reptile species took longer, and after 8 years numbers of species remained lower than in unmined forests. Species richness and diversity of ants in 8‐year‐old rehabilitation were comparable with those of unmined forest in some rehabilitated sites but were lower in others. The composition of ant communities was still different from that of unmined sites. Ant species that only use disturbed forest declined rapidly in abundance as rehabilitation aged. The results suggest that although the rates of faunal recolonization will vary, with time most or all mammal, bird, reptile, and ant species should inhabit rehabilitated bauxite mines. The densities of many are likely to be similar to those in unmined forest, but for others it is too early to know whether this will be the case. Techniques for promoting fauna return are discussed. This study demonstrates that no single fauna group is suitable for use as an overall “indicator” of faunal recolonization; different fauna species and groups reflect different aspects of faunal succession.     

Soil moisture dynamics and restoration of self‐sustaining native vegetation ecosystem on an open‐cut coal mine

Post‐mining landscape reconstruction on open‐cut coal mines aims to support restoration of self‐sustaining native vegetation ecosystems that in perpetuity require no extra inputs relative to unmined analogs. Little is known about the soil moisture retention capacity of the limited layer of topsoil replaced (often <30 cm deep), impacts of deep ripping of the profile, and the combined impacts of these on plant available water during the mine restoration process. We examined changes in soil moisture parameters (soil water potential, Ψ, and soil water content, Θ) daily using automated soil sensors installed at 30 and 45–65 cm depths on mine restoration sites aged between 3 and 22 years and on adjacent remnant vegetation sites following heavy rainfall events at Meandu mine, southeast Queensland, Australia. Consistent patterns in soil moisture attributes were observed among rehabilitated sites with generally marked differences from remnant sites. Remnant site soil profiles had generally higher Θ after drying than rehabilitated sites and maintained high Ψ for extended periods after rain events. There was a relatively rapid decline of Ψ on reconstructed soil profiles compared with remnant sites although the times of decline onset varied. This response indicated that vegetation restoration sites released soil moisture more rapidly than remnant sites but the rate of drying decreased with increasing rehabilitation age and increased with increasing tree stem density. The rapid drying of mine rehabilitated sites may threaten the survival of some remnant forest species, limit tree growth, and delay restoration of self‐sustaining native ecosystem.     

Widening gap between expectations and practice in Australian minesite rehabilitation

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.     

Poor recovery of woody vegetation on sand and gravel mines in the Darwin region of the Northern Territory

Summary Sand sheets near Darwin support a distinct heathland vegetation type which includes the habitat of several threatened species. Sand and gravel are extracted from shallow mines in this region. Woody vegetation recovery in 31 small, shallow former sand or gravel mine sites near Darwin that were up to 27 years old was assessed and compared to paired unmined control sites. Recovery in vegetation structure within each mine was calculated as the percentage of that in the control site. Mined sites recovered about 50% of their stem count and canopy cover, but only about 10% of basal area and mature tree count. Gravel mines showed poorer recovery than sand mines. Time since mining had no significant effect on the extent of recovery, but deeper mines had significantly poorer recovery. Only 35% of woody species in sand controls were present in mine sites, and 41% of gravel control species were present in former mine sites. It is unlikely that recovery will significantly improve in coming decades. Sand mining affects about 40 ha of land per year in this region, but is likely to increase in the future. If Darwin expands to a population of 1 million people, and mine sites are not fully rehabilitated, all of the sand‐sheet vegetation in the region could be removed in the next 100 years. Improved rehabilitation and protection is crucial for the conservation of heathland vegetation in this region.     

Comparison of Post-Mine Rehabilitated and Natural Shrubland Communities in Southwestern Australia

Following mineral sand mining near Eneabba, southwestern Australia, rehabilitation managers have the difficult task of restoring shrubland communities of exceptional plant species richness. Species diversity, composition, structure, and key functional attributes in four mined sites rehabilitated 8 (R8) to 24 (R24) years ago were compared with those of typical nearby natural areas classified on the basis of substrate type (Low and High sand Dunes, shallow sand Swales, sand over Laterite, and sand over Limestone). The rehabilitated sites (except R8) had more species (about 140) than natural sites (about 100) in 40 × 40–m plots, with 12–37% species in common with natural sites. Rehabilitated sites were more similar in composition to each other than they were to the natural sites, with two strong colonizers, the fire-killed Acacia blakelyi and the fire-tolerant Melaleuca leuropoma , universally present. Dendrograms and ordinations based on composition and cover showed that rehabilitated sites grouped with each other before they did with the Dune and Swale sites (physically closest), and last with the Laterite and Limestone sites. Plant densities for R16 and R24 were about half those of the High Dune and Limestone, and about a quarter those of the Swale and Laterite. Fire resprouters were under-represented in the rehabilitated sites. Growth form distribution in rehabilitated sites was most similar to those of the dunes, with some woody shrubs up to 2.5 m tall present. Total iron and soil hardness (penetrability) were the only soil factors consistently different (higher) in the rehabilitated sites.     

Two‐tiered methodology for the assessment and projection of mine vegetation rehabilitation against mine closure restoration goal

Reinstatement of a ‘self‐sustaining native ecosystem’ is an increasingly common revegetation goal for open‐cut mines in Australia. This is usually applied as a regulatory requirement for mine closure, with some mines aiming for a high standard of ‘ecological restoration’. There is a growing appreciation that ecological restoration outcomes of mine rehabilitation are unachievable within the life of a mine and that assessment methodologies are subjective and inadequate to provide the high degree of confidence needed for mine closure. Here we elaborate on the integration of the BioCondition assessment and the Ecosystem Dynamics Simulator (EDS) trajectory methodologies. We also demonstrate an alternative early relinquishment assessment criteria similar to that used for early recruitment of regrowth native vegetation that exhibit structural characteristics of undisturbed native vegetation into remnant status in Queensland. We used ten age cohorts of rehabilitation ranging from three to 22 years at Meandu coal mine, south‐east Queensland. All the sites gained average BioCondition scores ranging from 19 to 44 out of possible score of 65. Growth trajectories indicated decline in species and basal area on all sites in the next three decades as the dense stock of short‐lived acacia species senesce and die. None of the sites are projected to meet self‐sustaining status by 2072, but there is evidence in some of a progression. All the sites except two (K2.3 and SW2) are projected to achieve remnant vegetation status by 2062. Applying the remnant vegetation criteria results in shorter timeframes and robustly evaluates whether sites are progressing towards the self‐sustaining ecosystem mine closure goal.     

Contexts,developing ideas and emerging issues in the conservation management of the RSPB Abernethy Forest Reserve

Summary

Native pinewoods are fragmentary in extent and floristic integrity. In maintaining and extending these remnants, managers should recognise the diversity of potential communities and the unique mix of species in their flora. At the RSPB Abernethy Forest Reserve management aims to develop a self sustaining forest of natural character over the potential woodland area. A present-natural forest provides one model for the attributes and processes, which this forest should contain. Habitat management experiments have recently commenced investigating ways of increasing blaeberry Vaccinium myrtillus in forest areas, and increasing tree regeneration at the forest edge. The possible wider role of management intervention in pinewoods is discussed.     

Recolonization by Collembola of rehabilitated bauxite mines in Western Australia

Abstract The collembolan faunas of 30 bauxite mines rehabilitated by a range of different methods between 1966 and 1977, and three forest plots were surveyed in the spring and summer of 1978–79 with the aim of studying the restoration of decomposer activity in degraded areas. The rehabilitation methods included seeding and planting with a variety of native or exotic plant species. Physical and botanical parameters of the plots were also measured. Sixty species of Collembola were collected from the rehabilitated areas; nine of the 28 species found in the forest plots were not present on the mined sites. Principal components analysis suggested that the species richness of the collembolan community in rehabilitated areas is positively correlated with plot age. A parametric correlation analysis using a number of collembolan community characteristics revealed that, among other factors, the development of a species rich collembolan fauna is positively correlated with plant species richness and diversity, and also with percentage plant cover. These results provide directions for improving rehabilitation practices.     

Comparison of Post‐mining Rehabilitation with Reference Ecosystems in Monsoonal Eucalypt Woodlands,Northern Australia

Rehabilitation of post‐mining lands frequently aims to create “self‐sustaining” systems. Where native vegetation is the designated post‐mining land use, it is generally assumed that rehabilitation that is similar to local native ecosystems is more likely to be sustainable. I compared landscape functionality, plant community composition, and vegetation structure in (1) reference sites representing pre‐mining native forest; (2) reference sites representing potential landscape analogues for the post‐mining landscape; and (3) a 23‐year chronosequence of post‐mining rehabilitation on the Weipa bauxite plateau, Cape York Peninsula, Australia. The trends across the post‐mining chronosequence indicate that vegetation growth is rapid in the first 5–8 years, and then slows with mean height approaching an asymptote after approximately 15 years. Landscape function indices showed a response that coincided with vegetation growth. Vegetation composition was significantly different from reference native forest. Most importantly, from the perspective of creating self‐sustaining ecosystems, the contribution of local framework species to vegetation in rehabilitation was significantly lower than in reference native forest. I discuss the results in relation to theoretical models of succession and conclude that without management intervention, differences between post‐mining rehabilitation and native forest are likely to be persistent.     

Using forest growth trajectory modelling to complement BioCondition assessment of mine vegetation rehabilitation

The standard rehabilitation objective for open‐cut mines in Queensland is to establish a self‐sustaining native forest ecosystem. Consequently, mine regulators and managers need tools to project whether sites are likely or not to meet agreed completion criteria and to ensure timely remedial interventions. The Ecosystem Dynamics Simulator (EDS) is such a tool capable of modelling forest dynamics and projecting long‐term growth of woody species only. Here, the model was applied to rehabilitation sites aged between 5 and 22 years in Meandu open‐cut coal mine in southeast Queensland. EDS projected structural characteristics for trees (height, diameter, basal area, foliage projective cover and stem density) and tree species composition as a function of rehabilitation age. Projected stand growth attributes were assessed against BioCondition benchmarks developed from eucalypt (Eucalyptus/Corymbia) remnant forests adjacent to the mine. Growth trajectories indicated that sites with >30% eucalypt basal area composition were more likely to develop into eucalypt‐dominated self‐sustaining ecosystems compared with sites that were initially dominated by acacias (Acacia spp.). Projections suggested that some benchmark attributes such as number of large eucalypt trees would take more than 70 years to be met. The application of EDS provided a framework to support decisions on early remedial intervention and assess the risk associated with lease relinquishment.     

Using Dominance-Diversity Curves to Assess Completion Criteria After Bauxite Mining Rehabilitation in Western Australia

Abstract Dominance‐diversity curves have been previously constructed for a range of ecosystems around the world to illustrate the dominance of particular species and show how their relative abundances compare between communities separated in time or space. We investigate the usefulness of dominance‐diversity curves in rehabilitated areas to compare the floristic composition and abundance of “undisturbed” areas with disturbed areas, using bauxite mining rehabilitation in Western Australia as an example. Rehabilitated pits (11–13 years old) subjected to prescribed fire in autumn and spring were compared with unburned rehabilitated areas and the native jarrah (Eucalyptus marginata) forest. Dominance diversity curves were constructed by ranking the log of the species density values from highest to lowest. Species were categorized according to a variety of functional responses: life form (trees, shrubs, subshrubs, and annuals), fire response syndrome (seeder or resprouter), nitrogen fixing capability, and origin (native or adventive). Exponential functions showed extremely good fits for all sites (r² = 0.939–0.995). Dominance diversity graphs showed that after burning of rehabilitated areas, sites exhibited a more similar dominance‐diversity curve than before burning. This was emphasized in a classification (UPGMA) of the regression equations from the dominance‐diversity curves that showed that sites burned in spring were more similar to the native forest than sites burned in autumn. There was no significant segregation of the nitrogen‐fixing and species origin categories, although the life form and fire response groupings showed significant segregation along the dominance‐diversity curve. Resprouters tended to be over‐represented in the lower quartiles and under‐represented in the upper quartiles of post‐burn sites. It is suggested that using dominance‐diversity curves in the monitoring of rehabilitated areas may be a useful approach because it provides an easily interpretable visual representation of both species richness and abundance relationships and may be further utilized to emphasize categories of plants that are over‐ or under‐represented in rehabilitated areas. This will assist in the post‐rehabilitation management of these sites.     

State-and-Transition Successional Model for Bauxite Mining Rehabilitation in the Jarrah Forest of Western Australia

Alcoa World Alumina Australia has been rehabilitating bauxite mines in the jarrah (Eucalyptus marginata) forest of western Australia for more than 35 years. Completion criteria were developed in the 1990s for native species rehabilitation, with various desirable characteristics described as the rehabilitation ages. Successional models can be useful in mining rehabilitation for predicting whether sites are developing along the desired trajectory toward the rehabilitation objective. The current rehabilitation objective is to establish a self‐sustaining jarrah forest ecosystem, planned to enhance or maintain water, timber, recreation, and conservation values. The major objective of this study was to present a state‐and‐transition successional model that assists Alcoa to identify sites that will and will not meet identified completion criteria. Agreed completion criteria and vegetation data collected from native species rehabilitation from 9 months to 15 years old were used to construct a state‐and‐transition model. The model identified the various desired and deviated successional states and factors that cause transitions between these states. Five desirable and nine deviated states were identified and described in detail. Key indicators relating to desired and deviated states include eucalypt density, species richness, legume density, topsoil cover, vegetation structure, ripping depth, and tree health and form. Identified management manipulations to return deviated states to the desired successional trajectory include ripping, reseeding, replanting, weed control, and tree thinning. Some of the identified thresholds between desired and deviated states will require significant management input (e.g., reripping), whereas others require little or no input (e.g., recovery following wildfire). Of the 6,429 ha of native species rehabilitation undertaken between 1991 and 2002, 98% is on or above the desired successional trajectory. More than half of the rehabilitated area is regarded as being above the desired trajectory because of high tree density. Although these sites meet the existing completion criteria, management input may be required in the future, emphasizing the importance of identifying maximum and minimum completion criteria. The state‐and‐transition model of successional development is a practical but rigorous land management tool that has the potential to be applied in a wide variety of ecosystems and wide range of land uses.     

Planning mine restoration through ecosystem services to enhance community engagement and deliver social benefits

Mining companies are expected to return land to a stable, productive, and self‐sustaining condition by rehabilitating degraded areas to also deliver social benefits, an essential dimension of sustainable land management. This research aimed to develop a framework for mine rehabilitation planning based on an integrated analysis of the social‐ecological system provided by the ecosystem services concept to facilitate community engagement and the delivery of social benefits. An Ecosystem Services Assessment for Rehabilitation framework was tested at two bauxite mines undergoing ecological restoration. The mines are operated by the same company in two countries. Key results showed that the framework can help companies, regulators, and community members alike identify whether biophysical restoration efforts translate into key human benefits. Overall the framework provides a means for enhancing community engagement to explicitly address social benefits that, with a business as usual focus on ecological goals, may not be delivered. The ecosystem services concept provides a practical approach to link ecological and social outcomes of mine restoration.     

The longevity of constructed log pile fauna habitats in restored bauxite mines in relation to recurrent wildfire in the jarrah forest of Western Australia

Coarse woody debris (CWD) is often returned to rehabilitated areas after mining to provide specific habitat features for fauna that might otherwise take many decades to develop naturally. The CWD, typically constructed into log piles, is assumed to persist for comparable periods of time to fulfil their role. In the fire‐prone jarrah forest in Western Australia, these structures will be subject to recurrent wildfire, but there is little information on their survival. In January 2006, a wildfire burnt through 310 ha of rehabilitation at Alcoa’s Willowdale bauxite mine, 140 km south east of Perth, enabling the first estimates of the longevity of log pile fauna habitats to be made. Reductions in numbers of logs were greatest for small (<30 cm diameter) logs (48%), intermediate for large (>30 cm diameter) logs (37%) and least for stumps (17%). Assuming an exponential decay pattern, half‐lives of 1.1, 1.5 and 3.7 wildfires were calculated for small logs, large logs and stumps respectively, from which we estimate a useful ‘life’ of a typical log pile fauna habitat of 57–73 years. Increasing fire intensity was associated with greater reductions in the number of large logs, significantly greater surface charring and, at the highest intensity, significantly fewer crevices compared to unburnt log piles. Implications of these findings for the management of log piles in rehabilitation and CWD in the adjacent unmined forest, and of the role of prescribed fire, are discussed.     

Ant Community Development on Rehabilitated Ash Dams in the South African Highveld

Ant communities have been widely used as indicators of minesite rehabilitation in Australia and are beginning to play a similar role in other parts of the world. Here we examine ant communities on rehabilitated ash dams associated with a coal‐fired power station on the highveld of South Africa, to improve our understanding of ecosystem development on these substrates. Ants were sampled using pitfall traps at 11 ash‐dam sites, ranging from unrehabilitated to 9‐year‐old rehabilitated sites, as well as two adjacent natural grassland sites. Sampling was conducted on 12 occasions from March 1997 to January 1999. Forty‐nine ant species from 19 genera were recorded during the study. Site species richness was positively correlated with rehabilitation age, ranging from 10 to 25 at ash‐dam sites, compared with 28 and 34 at the two natural grassland sites. There was a humped relationship between total ant abundance and rehabilitation age, with abundance peaking after 5–7 years at levels far higher than those at natural sites. Ordination analysis showed clear separation between ash‐dam and natural sites along the first axis. The unrehabilitated ash‐dam site was also separated from rehabilitated sites along the first axis. Sites of different rehabilitation age were separated along the second axis. Individual ant species showed clear successional patterns across the rehabilitation gradient. Although there was a clear successional trend for the development of ant communities on rehabilitated ash dams, this trend was not toward natural grassland. The lack of convergence toward ant communities of natural grasslands reflects the markedly different substrate and plant composition on ash dams and supports the widely held view that restoration of natural grassland communities is not a realistic goal of ash‐dam rehabilitation. However, the development of species‐rich ant communities, containing at least some late‐successional species, indicates the potential for rehabilitated ash dams to support diverse and complex ecosystems.     

The Effect of Timing of Rehabilitation Procedures on the Establishment of a Jarrah Forest After Bauxite Mining

The restoration of the high botanical diversity of the premining jarrah (Eucalyptus marginata) forest is a major priority of rehabilitation following bauxite mining in southwestern Australia. This study investigated the effects of different ripping, seeding, and scarifying dates on the establishment of plants from propagules stored in the topsoil and from applied seed on areas being rehabilitated after mining. Seed stored in the topsoil, rather than applied seed, was the major contributor to plant diversity. Ripping late (April) or scarifying in June significantly reduced the number of species and numbers of individual plants that established from propagules in the topsoil. Species originating from broadcast seed were most numerous when the seed was broadcast in April or after scarifying in June. Scarifying before seeding, particularly in June, increased the establishment of species from the broadcast seed. To make best use of the applied seed, without jeopardizing the establishment of species from the topsoil, pits should be ripped and sown by April. We list a number of strategies that can help maximize plant numbers and botanical diversity on rehabilitated bauxite mines, which may also be of more general application for restoring the original native vegetation on disturbed sites.     

Comparative Study of Ant Communities of Rehabilitated Mineral Sand Mines and Heathland, Western Australia

We conducted a survey of ants in April 1997 in seven rehabilitated (2- to 20-year-old) and three native heathland reference sites of the Renison Goldfields Corporation (RGC) Mineral Sands operations at Eneabba, Western Australia. We employed a variety of collecting methods, including pitfall trapping, litter and soil sampling, sweeping and beating of vegetation, and collecting by hand in the day and after dark, replicating those used by previous researchers in a similar study conducted in the same area in 1980. We found a total of 96 ant species representing 30 genera in 1997, compared with 46 species from 18 genera in 1980. Ant species richness increased with age of rehabilitation and exceeded that of heath controls by the time it reached 11 years. Ant species richness related to rehabilitation age was represented by a logarithmic curve, and the slope for current rehabilitation was steeper than that for the earlier rehabilitation studied in 1980. This probably reflects improved rehabilitation practices. Ordination of the sites in terms of ant species composition indicated differences between ant species in the rehabilitated sites studied in 1980 and 1997, and also between all rehabilitated sites and heath controls. Classification of the sites in terms of the distribution of ants across functional groups also indicated differences between rehabilitation and heath control sites. According to species composition and functional group profiles from rehabilitated and control sites, we concluded that although the current rehabilitation allows for a rapid return of ant species, even after 20 years the fauna still had not attained the composition of the original heath fauna.     

Potential ‘Ecological Traps’ of Restored Landscapes: Koalas Phascolarctos cinereus Re-Occupy a Rehabilitated Mine Site

With progressively increasing anthropogenic habitat disturbances, restoration of impacted landscapes is becoming a critical element of biodiversity conservation. Evaluation of success in restoration ecology rarely includes faunal components, usually only encompassing abiotic and floral components of the ecosystems. Even when fauna is explicitly included, it is usually only species presence/absence criteria that are considered. If restoration is to have a positive outcome, however, populations in restored habitats should exhibit comparable survival and reproductive rates to populations found in undisturbed surroundings. If a species recolonises restored areas but later experiences decreased fitness, restored areas could become ecological sinks or traps. We investigated this possibility in a case study of koalas Phascolarctos cinereus occupying rehabilitated mining areas on North Stradbroke Island, Australia. Our holistic approach compared rehabilitated and undisturbed areas on the basis of their vegetation characteristics, of koalas'' body condition, roosting trees, diet, as well as predator index. Koalas using rehabilitated areas appeared to be able to access an adequate supply of roosting and fodder trees, were in good condition and had high reproductive output. We did not find any significant differences in predator density between rehabilitated areas and undisturbed surroundings. The results presented in this study showed there was no evidence that the post-mining rehabilitated areas constitute ecological sinks or traps. However, to reach a definitive conclusion as to whether areas rehabilitated post-mining provide at least equivalent habitat to undisturbed locations, additional research could be undertaken to assess foliar nutrient/water/toxin differences and predation risk in rehabilitated areas compared with undisturbed areas. More generally, the evaluation of whether restoration successfully produces a functional ecological community should include criteria on the fitness of faunal populations reoccupying such sites, so as to ensure functioning ecosystems, rather than ecological sinks or traps, are the outcome.