Restored Bauxite Mines Research Articles

Preliminary trial of woody debris addition on the return of invertebrates to restored bauxite mines in the jarrah forest of Western Australia

SummaryWoody debris is an important component of forest ecosystems, but its use in mine site restoration has been limited and it can be slow to build up naturally. A new technique of spreading snipped wood waste onto restored mine pits prior to seeding has been subjected to a preliminary trial at Alcoa's Huntly mine site, in the northern jarrah forest of south‐western Western Australia. We examined whether the application of snipped wood during restoration encourages the return of ground‐ and litter‐dwelling invertebrates without negatively suppressing plant establishment. Invertebrates were sampled across three seasons from experimental plots treated with 0 t/ha (control), 100 t/ha or 300 t/ha snipped wood waste. Invertebrate communities in treatment plots comprised higher numbers and diversity of wood and litter decomposers such as mites, Diplopoda, Dermaptera and Blattodea than control plots. Plant responses were variable, with wood treatment resulting in lower tree and overall plant density but having no effects on plant species richness or plant cover. Wood treatment plots were associated with higher soil nitrogen than controls. We hypothesise that the use of a fine wood treatment at the lowest rate of 100 t/ha (approximately 30% wood cover) is likely to enhance the diversity and abundance of invertebrates in restored areas, with minimal effect on plant establishment. Encouraging a diverse invertebrate fauna to recolonise restoration should help speed up succession and ecosystem functions such as decomposition and nutrient cycling, and more quickly return the land to previous ecosystem values.

Banco de Sementes em Mina de Bauxita Restaurada no Sudeste do Brasil

RESUMO O objetivo deste trabalho foi caracterizar o banco de sementes do solo em mina de bauxita restaurada dez anos após implantação do projeto de restauração. O estudo foi realizado em uma área onde ocorreu exploração de bauxita e posterior restauração florestal. Foram coletadas 40 amostras de solo superficial (0,25 × 0,30 × 0,05 m) para avaliação do banco de sementes pelo método de germinação em casa de sombra durante seis meses. Emergiram 2.489 plântulas, pertencentes a 69 espécies e 23 famílias botânicas, com densidade de 830 propágulos m–2. As famílias com maior densidade foram Poaceae e Cannabaceae. Houve maior proporção de espécies e indivíduos do grupo ecológico pioneiras e da síndrome de dispersão zoocórica. Não houve semelhança florística entre as espécies do plantio e o banco de sementes. Os resultados mostram que o banco de sementes pode fornecer aporte necessário à recuperação do ambiente após perturbações.

Does coarse woody debris density and volume influence the terrestrial vertebrate community in restored bauxite mines?

Coarse woody debris (CWD) is a critical functional and structural component of forest and woodland ecosystems, providing habitat for many species, and is an important consideration in forest and woodland restoration. CWD is very slow to develop naturally so, to accelerate the return of CWD-dependent species to restored areas, CWD is commonly returned manually. However, few studies have tested the effectiveness of such a strategy. We investigated whether the provision of CWD, heaped into ‘habitat piles’ of varying density (0.4–5.7pilesha−1), was effective in accelerating recolonisation by reptiles, frogs and mammals into 3-year old restored bauxite mine-pits in south-western Western Australia. Both reptile and mammal communities, and the abundances of some individual species, differed significantly between unmined and restored forest but the provision of CWD had only a weak effect in accelerating recolonisation. Acritoscincus trilineatus abundance showed a weak positive relationship with habitat pile density and both Cryptoblepharus buchananii and Christinus marmoratus, species that are very rare in restoration, were recorded adjacent to habitat piles in two and one mine-pits respectively. The weak effects of CWD in accelerating recolonisation were likely due to the differences in vegetation between unmined and restored forest, resulting in restored forests being primarily inhabited by generalist species that did not require CWD, and the highest habitat pile densities being ⩽6% of log densities in unmined forest, suggesting that CWD-dependent species perceived all mine-pits as having similarly low levels of CWD, compared to unmined forest. Our results suggest that the provision of CWD in restored areas is critical to accelerate recolonisation of CWD-dependent fauna, but this will require consideration of both CWD spatial connectivity and temporal continuity. Spatial connectivity would be best achieved through CWD densities that approximate those in reference ecosystems, whereas temporal continuity will be harder to achieve, particularly in systems where CWD is slow to develop, and will require the development of innovative techniques and long-term management. However, ensuring the spatial connectivity and temporal continuity of CWD in restored areas should greatly increase their biodiversity value.

Natural regeneration in a restored bauxite mine in southeast Brazil

Votorantim Metais, Setor de Meio Ambiente, CEP: 36790000, Mirai, MG, Brasil.SUMMARYThe objective of the present study was to verify if, in floristic terms of natural regeneration, a restored bauxite mine in southeast Brazil can be considered successfully restored. Forty plots of 3.0 x 3.0 m were allocated in the area. All shrubs and trees with height ≥ 0.30 m and diameter at 1.30 m height (DBH) ≤ 5.0 cm were identified and classified into successional categories and dispersal syndromes; DSL (diameter at soil level) and height were measured. We use the canonical correspondence analysis (CCA) to verify the correlations between environmental variables (canopy openness, litter decomposition, soil penetration resistance) and vegetation. We found 705 individuals, 80 species and 30 families. The families with the highest species richness were Fabaceae and Melastomataceae. The specie with the highest importance value (IV) was

Effectiveness of plant guards in reducing grazing of Tetraria capillaris in restored bauxite mines in Western Australia

Herbivores can exert significant impacts on vegetation composition, particularly in open, newly established restored sites where plants are visible and often represent high quality forage. While tree species can potentially outgrow herbivores, understorey plants are unable to do so and may remain prone to herbivory in developing restored sites. We assessed the effectiveness of various mechanical and biological guards (Acacia companion plants) against grazing of the palatable dryland sedge Tetraria capillaris (hair sedge), in sites restored after bauxite mining in the jarrah forest of Western Australia. Six months after planting, grazing was severe and repetitive, and affected plant survival. Grazing intensity and severity reduced over time (from 95% to 64% of surviving plants grazed after six and a half years). No method of guarding entirely prevented grazing. Plants with plastic sleeves and Polynet mesh tubes showed significantly higher survival rates in short and longer term compared with unprotected controls (62% survival for both treatments compared with 30% survival of controls after six and a half years). Plastic sleeves were most effective at guarding T.capillaris against grazing although they were less cost-effective than Polynet tubes. While companion planting also reduced grazing it was less effective than artificial guards and not cost-effective. These data indicate that plant guards can have a positive impact on plant performance, even 6.5years after planting.

Contrasting physiological responses of two co-occurring eucalypts to seasonal drought at restored bauxite mine sites

This study describes the physiological response of two co-occurring tree species (Eucalyptus marginata and Corymbia calophylla) to seasonal drought at low- and high-quality restored bauxite mine sites in south-western Australia. Seasonal changes in photosynthesis (A), stomatal conductance (g(s)), leaf water potential (ψ), leaf osmotic potential (ψ), leaf relative water content (RWC) and pressure-volume analysis were captured over an 18-month field study to (i) determine the nature and severity of physiological stress in relation to site quality and (ii) identify any physiological differences between the two species. Root system restriction at the low-quality site reduced maximum rates of gas exchange (g(s) and A) and increased water stress (midday ψ and daily RWC) in both species during drought. Both species showed high stomatal sensitivity during drought; however, E. marginata demonstrated a higher dehydration tolerance where ψ and RWC fell to -3.2 MPa and 73% compared with -2.4 MPa and 80% for C. calophylla. Corymbia calophylla showed lower g(s) and higher ψ and RWC during drought, indicating higher drought tolerance. Pressure-volume curves showed that cell-wall elasticity of E. marginata leaves increased in response to drought, while C. calophylla leaves showed lower osmotic potential at zero turgor in summer than in winter, indicating osmotic adjustment. Both species are clearly able to tolerate seasonal drought at hostile sites; however, by C. calophylla closing stomata earlier in the drought cycle, maintaining a higher water status during drought and having the additional mechanism of osmotic adjustment, it may have a greater capacity to survive extended periods of drought.

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.

Assessing the success of mine restoration using Hemiptera as indicators

Understanding trends in assemblage composition of key invertebrate groups can provide important insight into the ‘condition’ of, or changes in, the environment. Species density, abundance and composition of Hemiptera (true bugs) were assessed in jarrah (Eucalyptus marginata) forest and a chronosequence of restored bauxite mine pits near Boddington, Western Australia, in order to evaluate how restoration was progressing. A significant difference was uncovered for hemipteran species density between the youngest restored treatment and forest. In contrast, hemipteran composition was distinct between the forest and all restored treatments. Hemipteran composition was associated with the presence of the plant species Conostylis setigera and Trichocline spathulata, and plant structure between 160–180 cm and 260–280, plus soil pH. Restoration was successful in returning Hemiptera with respect to species density, but restoration was yet to attain a similar composition of Hemiptera to that of unmined forest, despite some of the restored sites being almost 20 years old. These results are similar to those of other studies that have assessed the response of Hemiptera to disturbance, and highlight the need to wait for considerable periods in order to achieve restoration goals. This study also confirms the utility of Hemiptera as bioindicators of environmental ‘condition’ and change.

Architectural plasticity in young Eucalyptus marginata on restored bauxite mines and adjacent natural forest in south-western Australia

The aboveground architecture of Eucalyptus marginata (Jarrah) was investigated in chronosequences of young trees (2.5, 5 and 10 m height) growing in a seasonally dry climate in a natural forest environment with intact soils, and on adjacent restored bauxite mine sites on soils with highly modified A and B horizons above an intact C horizon. Compared to forest trees, trees on restored sites were much younger and faster growing, with straighter, more clearly defined main stems and deeper, narrower crowns containing a greater number of branches that were longer, thinner and more vertically angled. Trees on restored sites also had a higher fraction of biomass in leaves than forest trees, as indicated by 20-25% thicker leaves, 30-70% greater leaf area, 10-30% greater leaf area to sapwood area ratios and 5-30% lesser branch Huber values. Differences in crown architecture and biomass distribution were consistent with putatively greater soil-water, nutrient and light availability on restored sites. Our results demonstrate that under the same climatic conditions, E. marginata displays a high degree of plasticity of aboveground architecture in response to the net effects of resource availability and soil environment. These differences in architecture are likely to have functional consequences in relation to tree hydraulics and growth that, on larger scales, is likely to affect the water and carbon balances of restored forest ecosystems. This study highlights substrate as a significant determinant of tree architecture in water-limited environments. It further suggests that the architecture of young trees on restored sites may need to change again if they are to survive likely longer-term changes in resource availability.

Vertebrate Fauna Recolonization of Restored Bauxite Mines—Key Findings from Almost 30 Years of Monitoring and Research

Abstract Studies into the processes of vertebrate fauna colonization of Alcoa’s restored bauxite mines began around 1975. This recognized the key role of vertebrate fauna in jarrah forest ecosystem processes, and also the fact that some species were rare, so priority was given to determining their status in unmined forest, and promoting their return to restored areas following mining. Long‐term studies have since taken place on mammals, birds, and reptiles both in unmined forest and in restored areas of varying ages and techniques. Mammal recolonization varies between species depending on species’ food and shelter requirements and their distribution and abundance in the surrounding forest. Birds rapidly recolonize and 95% of species have been recorded in restoration. Bird community structure changes with restoration type and age, and in current restoration, it is similar to that of unmined forest by the age of 10 years. Studies on reptiles have shown that 21 of 24 species have recolonized. The remaining three include one legless lizard and two snakes, all of which feed on small vertebrates (e.g., skinks) and require shelter in the form of logs, stumps, and coarse woody debris. Some other reptile species consistently occur in restoration in lower densities than in unmined forest, and current studies are investigating the causes of this. Together, studies on these three vertebrate fauna groups have provided valuable, complementary information on their habitat requirements, and the extent to which Alcoa’s restoration program has been successful in reestablishing this important component of the jarrah forest’s biodiversity.

Root Architecture of Jarrah (Eucalyptus marginata) Trees in Relation to Post‐Mining Deep Ripping in Western Australia

Abstract This research aimed to investigate coarse root systems of Jarrah (Eucalyptus marginata Donn ex Sm.) trees at a 13‐year‐old restored bauxite mine site in south‐western Australia. Excavations in an area with small trees (low‐quality site) revealed that deep ripping equipment failed to penetrate the cemented lateritic subsoil, restricting coarse roots (roots &gt;5 mm in diameter) to the top 0.5 m of the soil profile, resulting in fewer (1,344 stems/ha) and smaller (mean height 4.5 m) Jarrah trees. An adjacent area within the same pit (high‐quality site), with a stand density of 3,256 stems/ha and a mean height of 8.0 m, had a kaolinitic clay subsoil which coarse roots penetrated to the average ripping depth (1.5 m). Trees at the low‐quality site did not penetrate the subsoil with their taproot, relying instead on a large number of lateral (5.3–8.0/tree) and sinker (12.0–16.5/tree) roots. Taproots of trees on crests at the high‐quality site also did not penetrate the subsoil, and in contrast to trees at the low‐quality site, they produced fewer lateral and sinker roots (2.3 and 2.0/tree, respectively). Taproots of trees in riplines at the high‐quality site directly penetrated the ripline and these trees also produced fewer lateral and sinker roots (5.0 and 3.7/tree, respectively) than those at the low‐quality site. Jarrah trees appear to have opportunistic root systems capable of responding to a variety of soil conditions encountered in the post‐mining landscape.

Return of Ecosystem Function to Restored Bauxite Mines in Western Australia

AbstractA critical aspect of reestablishing a self‐sustaining Jarrah (Eucalyptus marginata) forest ecosystem to bauxite‐mined areas is to ensure that vital ecosystem functions such as litter decomposition and nutrient cycling are returned. Significant research has been undertaken over the past 20 years relating to litter decomposition and nutrient cycling. Studies have shown that litter accumulates rapidly in restored areas (1–4 ton ha−1yr−1) and the accumulated litter tends to be richer in nitrogen due to intentionally elevated densities of nitrogen‐fixing species. This leads to a lower (carbon:nitrogen) C:N ratio (60:1 compared to 130:1 in unmined forest) that may promote mineralization of organic N to inorganic forms in restored areas. The major nutrient store in the unmined forest is in the soil and returning soil during the restoration process largely conserves this resource, particularly in relation to P. Short‐term plant macronutrient requirements for growth are readily restored by fertilizer application. Studies on the reaccumulation of nutrient pools in the successional development of restored areas have shown that pools equivalent to the unmined forest are established within 10–20 years. Ongoing research is focusing on the rates of cycling processes in burnt and unburnt restored areas, and comparing these to the unmined forest to ensure that key functions have been reestablished. To date, all measured ecosystem function parameters are indicating that restored areas have achieved or are on a trajectory toward a self‐sustaining Jarrah forest ecosystem.

Fire and Silvicultural Management of Restored Bauxite Mines in Western Australia

Abstract To be self‐sustaining in the longer‐term and meet defined completion criteria, it is important that the management of restored bauxite mines can be integrated with the surrounding unmined Jarrah (Eucalyptus marginata) forest. A number of research projects relating to fire management have been undertaken in restored areas over the past 15 years. The broad objectives of these studies have been to assess the resilience of different‐aged restored sites to fire and define the most suitable fire regime (season, intensity, and frequency) to utilize in the management of these areas. Restored areas were found to be a low fire risk up to five years of age because litter fuel was discontinuous and could not normally carry the fire. Between the ages of five and 12–15 years, restored areas were very susceptible to fire due to high fuel loads and a prominent midstory of senescent legume species. However, if burnt at this age, restoration areas were extremely resilient. Restored areas that are older than 12–15 years can be integrated with prescribed burning of the surrounding unmined forest because the midstory layer has collapsed and the overstory is now separated from the understory fuel. The most suitable fire regime to utilize in restored areas is low‐ to moderate‐intensity spring burns. Silvicultural management of restored areas has recently been investigated incorporating noncommercial thinning and commercial harvesting operations in association with prescribed burning. Restored areas of suitable ages appear to be able to be integrated with the management regimes commonly used in the Jarrah forest.

Grazing by Kangaroos Limits the Establishment of the Grass Trees Xanthorrhoea gracilis and X. preissii in Restored Bauxite Mines in Eucalypt Forest of Southwestern Australia

Abstract This study examined factors affecting germination, survival, and growth of the grass trees Xanthorrhoea gracilis and X. preissii on newly rehabilitated bauxite mine pits in the jarrah forest of southwestern Australia. Grazing by kangaroos (Macropus fuliginosus) was the major factor in reducing survival and growth of both species during the first 2 years. Provision of artificial grazing protection increased survival and growth (plant mass) of both species by 3‐fold. Grazing by native vertebrates has not previously been identified as affecting mine restoration in Western Australia. Initial germination rates from sown seeds of X. preissii at eight replicate sites ranged from 25 to 64% with a mean of 42%. Corresponding figures for X. gracilis were 5–42% with a mean of 17%. Germination of X. gracilis was greater on heavier, moister soils, but X. preissii germinated better on sandier soils. High levels of initial germination did not ensure high survival. Plants of both species grew bigger and survived better on the lighter, sandy soils. Xanthorrhoea seedlings located in the depressions created by the ripping process grew larger than seedlings on the slopes of the riplines. The presence of plants of other species did not have a significant effect on survival. However, these plants facilitated the growth of both species when artificial grazing protection was unavailable. Plants of other species reduced the growth rates of Xanthorrhoea seedlings where artificial grazing protection was provided. Artificial shade by itself had no significant effect on growth of either species. In rehabilitated bauxite mines in the jarrah forest, the provision of grazing protection is recommended to ensure successful establishment and early survival of Xanthorrhoea spp.

Fire management implications of fuel loads and vegetation structure in jarrah forest restoration on bauxite mines in Western Australia

Bauxite mines being restored to native jarrah ( Eucalyptus marginata)-dominated forest in Western Australia have accumulated substantial fuel loads. Assessment of fire management aspects is necessary for the effective integration of restored areas into forest-wide management. Fuel characteristics, vegetation structure and fire behaviour of young (5- and 8-year-old) restored bauxite mines in Western Australia were examined. Pre-burn fuel loads were moderate in 5-year-old restoration (15.0 t ha −1) and high in 8-year-old restoration (29.8 t ha −1). Large ranges in available fuel load estimates of sample sites (2.2–60.8 t ha −1) indicated the heterogeneous nature of fuel distribution leading to variable fire behaviour. The vegetation structure of restored areas differed from that of the unmined jarrah forest due to the presence of a prominent mid-storey layer composed of number of acacias ( Acacia pulchella, A. celastrifolia, A. extensa, A. drummondii and A. lateriticola). This mid-storey layer contributed 49% of the total fuel load in 5-year-old restoration, although the high proportion of live material (73.6%) inhibited fire development. In 8-year-old restoration the mid-storey layer contributed 46% of the total fuel load. The lower proportion of live material in these sites (27.9%), due to the senescence and death of the relatively short-lived acacias, led to increased fire intensities, flame heights and higher levels of crown scorch and defoliation. Prescribed burns were conducted in early summer 1997. Burns in 5-year-old restoration were of low intensity (<250 kW m −1) while burns in 8-year-old restoration were of very high intensity (>7000 kW m −1). Fuel re-accumulation was rapid in the first 2 weeks post-burn, with litter-fall rates 2–3.5 times that of unburnt control sites. Thereafter, litter-fall and fuel accumulation in burnt restored and unmined sites was comparable to that of unburnt control sites. Analysis of 1 and 2 years post-burn 5-year-old restoration indicated that the prescribed burns had failed to remove the mid-storey acacia layer and actually increased the proportion of dead standing material, whereas in the 8-year-old restoration, the prescribed burns removed the mid-storey layer of acacia shrubs and stimulated an increase in the proportion of live plant material, particularly near ground level. Maximum soil temperatures recorded by heat sensitive crayons exceeded 300 °C in 8-year-old restoration burns but were less than 100 °C in 5-year-old restoration burns. Hard-seeded species were stimulated to germinate in the top 2–3 cm of the soil following burns in 8-year-old restoration and only in the top 0.5 cm of the soil following burns in 5-year-old restoration. Some seeds in the top 1 cm of the soil may also have been killed by the high temperatures generated in burns in the 8-year-old sites. Fire management of jarrah forest restoration will have to be different to that employed in unmined jarrah forest due to differences in fuel characteristics, vegetation structure and fire behaviour.

Practical method of germination for a key jarrah forest species: Snottygobble (Persoonia longifolia)

Summary Snottygobble (Persoonia longifolia) is an ecologically and economically important species in the jarrah forest in Western Australia but is not well represented in jarrah forest restoration projects because it is difficult to germinate. In restored bauxite mines the establishment density of Snottygobble from the soil seed bank is variable and often inadequate. Alcoa considers it a priority to re‐establish such key species at adequate densities in its restored mine areas The aims of the present research were: (i) to determine if the species could be cued to germinate; and (ii) to develop a practical method to re‐establish the species in restored bauxite mines. We found that fresh Snottygobble seed has high viability (&gt; 90%) but seed stored at 4°C rapidly loses viability over the first year after seed fall. We obtained up to 40% germination using fresh seed that had been treated with gibberellic acid (GA3) after having part of the endocarp chipped away, sown on the soil surface and watered twice daily in an ambient temperature glasshouse in winter/spring. We found that the key to successful germination was combining surface sowing, endocarp chipping and GA3 treatment. Germination involved the breakdown of mechanical and, probably, chemical dormancy. There also appears to be a cool temperature requirement for germination. Practical recommendations to germinate Snottygobble are made. This germination method will have application to land managers, restoration practitioners and the horticultural industry. Alcoa will continue work to translate this success into an adequate stocking of Snottygobble in restored bauxite mines.Key words bauxite mine, dormancy, endocarp chipping, endogenous, germination, gibberellic acid, Persoonia longifolia, restoration, Snottygobble.