fire and silvicultural management of restored Bauxite Mines in western australia

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.

return of ecosystem function to restored Bauxite Mines in western australia

A 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−1 yr−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.

vertebrate fauna recolonization of restored Bauxite Mines key findings from almost 30 years of monitoring and research

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.

effectiveness of plant guards in reducing grazing of tetraria capillaris in restored Bauxite Mines in western australia

Abstract 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 6.5 years after planting.

arthropods in coarse woody debris in jarrah forest and rehabilitated Bauxite Mines in western australia

• Coarse woody debris (CWD) is returned to Alcoa’s rehabilitated mined areas in the jarrah forest as potential vertebrate fauna habitat, however, its value for invertebrate fauna has not been investigated. We sought to determine if CWD in rehabilitated areas supported a similar arthropod fauna to that on fallen logs in the adjacent unmined jarrah forest.

• Using emergence tents, sampling from logs in 5-year old and 15-year old rehabilitated forest, and in unmined forest, yielded 2266 specimens from 187 taxa. Collembola (43% of total) and Acarina (32%) were the most abundant groups, followed by Diptera (11%), Araneae (4%) and Coleoptera (3%).

• There were no significant differences in either taxa richness or overall abundance among the three forest types. However, community composition varied significantly. Species richness from the Araneida, Coleoptera and Diptera was highest in the 5-year old rehabilitated forest, while Collembola and Acarina were better represented in the unmined forest; this was related to changes in the environment surrounding the logs as rehabilitated forest develops, and to log condition. The composition of arthropods on logs in the 15-year old rehabilitated forest was intermediate, indicating a trend of increasing similarity to the unmined forest in arthropod fauna as the rehabilitated forest ages.

• We suggest that over longer time periods, CWD in rehabilitated forest will support arthropod communities similar to those found in unmined forest. Future work should determine if returning logs to mined areas facilitates the return of CWD-dependent taxa.

Vegetation succession after Bauxite mining in western Australia

Alcoa World Alumina Australia has been rehabilitating Bauxite Mines in the jarrah forest of Western Australia for more than 35 years. An experiment was established in 1988 using three different seed treatments (legume and small understorey mix, small understorey mix only, and no seed) and two fertilizer treatments (N and P, and P only). The objectives of this study were to (1) document vegetation changes in the first 14 years after Bauxite mining; (2) assess whether the vegetation is becoming more similar to the unmined forest; and (3) gain a better understanding of successional processes. Seed treatments significantly affected 13 of the 14 measured vegetation characteristics. Native species richness was higher in seeded than in unseeded sites at 1, 2, and 5 years of age, whereas diversity and evenness were generally higher at all assessment ages. Exotic species density was higher in unseeded than in seeded sites from 5 years onward, whereas richness was higher from 8 years onward. Nitrogen fertilizer significantly increased exotic species richness, density, and cover. Ephemerals dominated plant density in all rehabilitation treatments over time, whereas seeder species dominated cover. In contrast, resprouting species dominated density and cover in the unmined forest. Orchids were the only species that were not present in the first year in rehabilitated sites but increased in abundance over time. Vegetation composition in rehabilitated areas did not become more similar to the unmined forest during the 14 years since seeding, instead strongly reflected the initial species mix. Rehabilitated Bauxite Mines appear to follow the initial floristic composition model of succession.

ectomycorrhizal fungal communities of rehabilitated Bauxite Mines and adjacent natural jarrah forest in western australia

Abstract Species richness and species composition of ectomycorrhizal (EM) fungi were compared among rehabilitated mine sites and unmined jarrah forest in southwest Western Australia. Species richness, measured in 50 m × 50 m plots, was high. In the wetter, western region, mean species richness per plot in 16-year-old rehabilitated mine sites (63.7 ± 2.5, n  = 3) was similar to that of unmined jarrah forest (63.6 ± 9.6, n  = 9). In the drier, eastern region, species richness in 12-year-old rehabilitated mine sites (40.3 ± 2.1, n  = 3) approached that of nearby forest (52.4 ± 9.3, n  = 9). Species composition was analysed by detrended correspondence analysis. Rehabilitated sites of similar age clustered together in the analysis and species composition was closer to the native jarrah forest in the older rehabilitated plots. In unmined forest, species composition of fungal communities in the wetter, western region was different from communities in the drier, eastern region.

fire management implications of fuel loads and vegetation structure in jarrah forest restoration on Bauxite Mines in western australia

Abstract 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 ( 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.

the effects of burning on the understorey composition of rehabilitated Bauxite Mines in western australia community changes and vegetation succession

Abstract The first 2 years of post-burn vegetation succession of 11–13-year-old rehabilitated Bauxite Mines in Western Australia is compared to the native jarrah ( Eucalyptus marginata ) forest using the techniques of ordination (CANOCO TM ) and classification (TWINSPAN TM ). Analyses of understorey species density and cover values showed consistent patterns of composition and abundance between the native jarrah forest and the rehabilitated areas, both before and after burning. These patterns resulted from the intentional establishment of high densities of legume species in the initial rehabilitation process and proliferation of high densities of seeding species and non-native eucalypt seedlings following burning of the rehabilitated areas, features not characteristic of native jarrah forest. Burnt sites showed larger changes in species abundance and composition than unburnt control sites as indicated by their relative shift of position in the ordination hyper-space. This shift in position was generally less for sites burnt in spring than sites burnt in autumn. The first two divisions of the site classifications separated the unburnt sites and early spring post-burn sites from the forest and the remainder of the post-burn sites. The species classification showed that each of these groups was associated with a specific suite of species. Pit age (i.e. 11, 12 or 13 years-old at time of burning) was an important determinant of species composition in both the ordinations and classifications. Although species densities recovered more rapidly than live plant cover in the rehabilitated areas following burning, the vegetation of these rehabilitated sites exhibited little evidence of returning to their pre-fire species composition and abundance after 2 years. However, the high species similarity (75–79%) between the pre-burn (including species only present as seed in the topsoil) and post-burn vegetation indicates the importance of the initial floristic composition in determining the potential direction of the post-fire succession.