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Bellairs, S. M. and Davidson, P. (1999). Native plant establishment after mining in Australian rangelands. In: Eldridge, D. and Freudenberger, D. (eds). People and Rangelands: Proceedings of the VI International Rangelands Conference. Vol. 2, 19

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Most mining operations in Australia are in the Australian rangelands and nearly all these operations require the re-establishment of native vegetation as their end land use, or are exploring this option. In some cases there are conflicts between
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  V/th International Rangeland Congress Proceedings Vol 2 Native plant establishment after mining n ustralian rangelands SEAN BELLAIRS 1•2 PHIL DAVIDSOW entrefor Mined Land Rehabilitation The University of Queensland St Lucia QLD 4072 Australia 2 School of Land and Food The University of Queensland St Lucia QLD 4072 Australia S.Bellairs@mailbox.uq.edu.au Phillip.Davidson@mailbox.uq.edu.au Introduction Most mining operations in Australia are in the Australian rangelands and nearly all these operations require the re-establishment of native vegetation as their end land use, or are exploring this option. In some cases there are conflicts between pastoral wish lists of the best foraging species and desired outcomes by regulators for ecosystem reconstmction, which is not necessarily focused on pastoral production issues. However, research associated with minesite rehabilitation over the last thirty years has greatly expanded our knowledge of the biology of the flora and fauna of rangelands and our ability to re-establish native flora and fauna on disturbed pastoral land. Mining techniques and the environments in which mining occurs varies considerably across the Australian rangelands (Mulligan 1996). Triodia grasslands which dominate about 22% of Australia's arid and semi-arid regions (Griffm 1984), include goldmines and petroleum production in central Australia, base metal mines in Queensland and iron ore mines in the Pilbara of Western Australia. In northern Australia savanna there are large bauxite mines, uranium mines and the Argyle diamond mine. Open-cut coal mining dominates the landscape of grassy woodlands in central Queensland while in the goldfields of Western Australia, gold and nickel mines are found in chenopod shrub lands and Acacia or Eucalyptus open woodlands. Mineral sand mining occurs in kwongan dry sclerophyll shrub heathland in Western Australia. The various mining processes also have different impacts on the process of native vegetation establishment. Mineral sand mining is relatively benign with relative few changes to the growing medium, the ore is only a small proportion and the remaining material can be replaced forming similar contours to the pre-mining landscape. Large scale, opencut coal and gold mining result in large spoil piles of often highly erodible material that may be saline, sodic, dispersive or extreme in pH. Iron ore and diamond mining result in large spoil piles of rough broken rock. Coal, gold and base metal mining can necessitate the use of large tailings dams containing material of poor structure often containing cyanide, arsenic and/or heavy metals. Bauxite mining can result in changes to topography and soil hydrology over large areas. While the type of environment and mining operation impose restraints on the revegetation protocols applied the other factor that needs to be taken into account is the end land use. Where native species are to be used when pastoral grazing is the end land use it m y be desirable to exclude less palatable species; however, the vegetation coriununity needs to persist under grazing pressure. Where the land has higher conservation value there is likely to be a greater effort to approximate the pre-mining community. Creating habitats for specific fauna species also increases the requirements for the rehabilitation to be successful. To maximize the efficiency of the rehabilitation process, the end land use should be defined well before the rehabilitation process commences, preferably pre-mining. There is a general requirement across mine sites that the rehabilitation show some level of sustainable ecological functioning in order to maintain a stable land surface and the rehabilitation should be sustaintainable with minimal maintenance after mine life. However, there can be a great diversity of site specific rehabilitation requirements for a particular vegetation composition or structure, faunal habitat, anthropological requirement or other criteria related to the end land use which can require consider ably different management protocols. In this paper we address the process of native vegetation establishment on mined lands through looking at a hierarchy of functional processes that need to be achieved for native plant establishment. Reasonable landform stability is required for nutrients, moisture and propagules to be retained. Propagules, sufficient moisture and nutrients are required for seedling establishment to occur and toxic materials must be absent or managed to achieve tolerable levels. Nutrient cycling must occur for growth to be maintained and for future establishment. Interactions between the micro and macro flora and fauna species also need to be considered. Stability Historically, mine site closure was centred around stability issues i.e. 1 a non eroding stable landform'. n general, the greater the stability of any landfmm in relation to slope minimization, water infiltration relative to runoff, movement of substrate and organic material downslope, water harvesting, surface crusting and resistance to rainfall impact, the better it is also likely to be for plant establishment. To successfully establish native vegetation a reasonably stable landfonn and growing medium is an initial requirement to allow: maintenance of features that control water runoff and retain moisture; retention of nutrients and litter for recycling; and seedling establishment. Erosion is controlled by maintaining slope angle and length along with the establishment of adequate vegetation and litter cover to reduce surface water flow. Excessive erosion will result in the loss of nutrients, increased seedling mortality and reduced water quality. Soil characteristics, degree of slope, length of slope and ground cover all affect the extent that erosion is likely to occur. A large multi-mine project, Post-Mining Landscape Parameters for Erosion and Water Quality Control Project (So et a/. 1995), has been sponsored by the mining industry to determine slope angle and length criteria for different soil and spoil types. This project is nearing completion and also includes a PhD project which is modelling the temporal and spatial movement of salts through the soil profile (Short pers. comm.). Understorey ground cover values may need to be above a minimum value to achieve erosion control and cover crops of exotic pasture species are sown at many mine where erosion is a potential problem. As part of the Post-Mining Landscape Parameters for Erosion and Water Quality Control project, rainfall simulation has been used to dete1mine the minimum vegetation cover levels required to maintain erosion control (Loch Bourke 1996). This study showed that grass cover was extremely effective at stabilizing the site and erosion was minimal once grass cover of 50% was achieved on the slopes and soil types tested. A problem for long tenn native vegetation establishment can be the effect ofr in events as the soil and mine spoil material consolidates. Sheridan (unpubl. data) shows that erosion rates can increase as spoil consolidates because the surface can 96 Mined · l nd rehabilitation  Be/lairs Davidson ernst and while this increases soil strength, the reduction in infiltration is dominant and can lead to 50 fold increases in erosion. The presence of logs, sticks and stones can also assist in erosion control by increasing infiltration through increasing macro-pores within the soil profile, however, logs can also be the nucleus of rill erosion in contour bank systems on mine dump slopes. Wind erosion in some instances, is a major prob lem for establishment of native seedlings on rehabilitation areas, particularly in arid and semi-arid regions. Fine particle material such as that found in tailings dams near Kalgoorlie, Western Australia (Fletcher et 1989), can damage seedlings through sand blasting. It has also been a problem for mineral sand mines and a variety of treatments have used to control it, including: chip mulch, brush matting, Terolas (a bitumen compound) and grass cover crops. Wind tunnel trials catTied out on mineral sand mines near Eneabba determined that rows of oats, sparse clumps of the grass cultivar Sudax and Terolas were all effective at reducing wind erosion (Bell et a/ 1986). Careful selection of growing media, surface cover and design of the landform is vital for effective establishment and should be an integral process in the whole mine plan. ydrology Control of water movement is important for retaining water and nutrients in the landscape, and for vegetation establishment, growth and survival. The distribution of water in the landscape will affect the distribution and diversity of flora and, subsequently , fauna communities present. Hydrological considerations include infiltration, soil water storage, water movement across the landscape, sub surface flows (i.e. plumes) and water use by vegetation. They will be affected by soil surface conditions, waste mullock types, landform and the type and composition of vegetation. For conservation of water through time, landscape and site features that capture or aid water movement need to be maintained. Infiltration, tunoff, water storage capacity, transpiration and evaporation will all affect the amount of water available for plant growth. Rainfall infiltration into the soil and the duration of retention of plant available water are likely to be important (Aronson et 1993). Ground cover and vegetation conditions that assist to stabilize the landforms tend to slow above groundwater flow and allow greater infiltration. Vegetation density, cover and rooting stmcture will affect water flows, transpiration and evaporation. Hydrology will be strongly influenced by surface stability as this is important for maintenance of landscape and site features that control water runoff and the dish·ibution of water in the landscape. At the more inland mines rainfall generally becomes more inegular and less predictable. Within the rangeland landscape, rainfall is typically not uniformly distributed, rather it tends to flow across areas of poor infiltration and concentrates in smaller zones of high infiltration. Stmchu·es to concenh·ate water are important for successful vegetation establishment in arid areas. At the BHP Cannington mine seed is broadcast across the rehabilitation areas but tends to only successfully establish in the base ofriplines. At the Hill 50 mine at Mt Magnet in Western Australia, there were 3.5 times as many plants growing in riplines as in unripped soil between contour banks (Jennings et 1993 . Jetmings et al ( 1993) found that increasing plant numbers were associated with increased frequency of contour riplines and recommended that spacings be 3m to maximize water ha t vest- ing on 20° mine batters while minimizing erosional forces. However at the Blair Athol minesite in Central Queensland, seedlings also successfully establish on top of the ridges between the riplines and the microtopographic position of Acacia seedlings has little effect on subsequent smvival (Bellairs unpubl. data). In areas of the north-eastern goldfields, it is critical for plants to establish within the first few rainfall seasons as the Vlth International Rangeland Congress Proceedings Vol 2 water havesting structures tend to collapse due to the nature of the slaking and dispersive topsoils. Seeds that do not germinate while water harvesting structures (i.e. contour banks and riplines) are working at their maximum capacity, become sequentially buried in the rip lines too deep to emerge from the soil. The micro-climates, water harvesting, nutrient pooling fi:om areas ofmnoffto areas ofmnon and provision of suitable seed bed characteristics are particularly important for revegetation programs in the a id pastoral regions of Australia. On a larger scale, ponding or moonscaping of waste dumps can be carried out. At Oaky Creek in central Queensland overburden is reshaped into a series of internally draining ponds of area about0.25 ha (McNamara 1999). These ponds are topsoiled on the slopes and in strips on the floor of the ponds and then aerial seeded with a range of native and exotic grass and tree species. This technique ensures that there is little offsite mnoff and infiltration potential is maximized. The stability of the structures has been tested under a sinmlated exh·eme rainfall event of 1250 mm on a 0.25 ha pond over I 03 hours which is in excess ofthe average annual rainfall for the area. The structures have been effective at promoting establishment over the last six years with the vegetation establishing deep root systems, surviving drought conditions and Eucalyplus and Acacia species have flowered and set seed on several occasions, resulting in seedling establishment (Burns 1998). Contour ripping, moonscaping, and water ponding banks all focus not only on minimizing erosion but on the interception of rainfall and nutrients fi·om areas of relatively low infiltration and high mnoff. In effect, a rainfall event of only 10 - 20 mm can provide the equivalent of > I 00-150 nun rainfall through the interception of surface flows via a contour bank with a 3 m run-off area. This provides enough water to instigate a germination event which usually requires somewhere in the order of 40-80 mm incident rainfall with no runon in mo st rangeland plant communities. Another hydrological problem on some minesite rehabilitation areas is surface crusting from sadie spoils. Some mine sites have high sodium levels within the surface mine spoils creating an imbalance at the cation exchange sites of the soil particles. This then translates into high levels of soil clay dispersion particularly during high rainfall periods, subsequently fmming hard crusts. Harwood (1998) found lower levels of seedling emergence from a range of grasses in mine spoils compared to topsoil in central Queensland. This was attributed to surface sealing as a result of higher salinity and ESP levels in the spoil increasing the osmotic potential of the soil water, hence slowing seed imbibition and concurrent rapid dtying of the soil surface resulting in a crust trapping emergent seedlings. At the Mt Owen mine site in NSW chips of wood mulch spread over the surface of the spoil greatly reduce surface crusting and increase infiltration (Read unpubl. data). In the north-eastern goldfields several mining rehabilitation projects (MERIWA) have focused on applications of gypsum or lime, soil mulches and several surface treatments in order to ameliorate the soil and surface micro-topography to enhance water infiltration, minimize dispersion and surface crusting, and minimize evaporative losses of upper soil profile (Jetmings el 1993; Fletcher e/ a/ 1989). Propagules Sources of propagules for rehabilitation include the soil seed bank, collected broadcast seed, seed in mulch applied to the site, wind bome seeds and seeds dispersed onto to the site by fauna. Depending on the age of the mine site and historical mining practices, various seed sources may have been used. Generally, older minesites would not have used topsoil resources as a source of seed as at time of mining, the topsoil resource was not seen as important in respect to the economics Mined land rehabilitation 963  Vlth International Rangeland Congress Proceedings Vol 2 of the mining process. This has now changed with mine sites now aware that rehabilitation costs can be significantly re duced in respect to plant establishment by the conservation of soil seed banks within topsoil resources. Provision ofpropagules to rehabilitation sites can be a prob lem when re-establishing species rich communities such as the kwongan heathlands near Eneabba in Western Australia but it needs to be considered for all sites. The kwongan heathlands near Eneabba are extremely diverse with 338 species within 8.7 ha (Hnatiuk Hopkins 1981 ), mainly Fabaceae, Myrtaceae, Proteaceae shrubs and Cyperaceae and Restionaceae xerophytic sedges less than a metre high. Many of the species at the site do not release mature seeds but rather are bradysporous or serotinous, storing the mature seeds in woody fruits for many years, often until death of the branch or until after fire. Ten km south ofEneabba, RGC operates a mineral sands mine which has been operating since 1974. Seeds are provided to the rehabilitation sites through three sources: soil stored seeds in the topsoil, seeds in a mulch of the native vegetation containing the woody fruits, and broadcast seeds collected by site environ mental staff. Good management can retum a diverse range of species to the site. In 1984 topsoil tended to be stockpiled and together with mulch application resulted in an average of 12 species per 28 m 2 or a total of about 120 species in a whole rehabilitation block. Mulch collection techniques were im proved, topsoil stockpiling time was reduced, a cover crop was sown to prevent tailings being blown over the topsoil, topsoil was double stripped and the number of species included in the broadcast seed mix was increased. In a 1989 rehabilitation area, 149 native species emerged from within120 m 2 of monitoring area (Bellairs 1992). The sources from which these plants were derived were quantified through assessment of the species composition and germinable seed density in the topsoil, mulch and broadcast seed mix. Over 80 of he seeds were of perennial species and the mulch supplied 89 of the seed density, the topsoil 9 and native species in the broadcast seed mix less than I . However in tenns of species riclmess 51 species were included in the broadcast seed mix, 31 species had seeds in woody fruits in the mulch and between 113 to 139 species had seeds in the soil seed bank (Bella rs Bell 1993 . The results at this site demonstrate the importance of maximizing the viability of seeds in the topsoil and other sources for maximizing species diver sity on rehabilitated mined lands. n spite of considerable effort involved in collecting large quantities of seeds from a wide range of native species the broadcast seed mix did not approach the soil stored seed reserves in tetms of richness or density. However the broadcast seed mix is useful for increasing the species richness of the other sources as species may be patchily distributed across the landscape or it may be desirable to increase the abundance of some groups of species. At Eneabba, species that resprout after fire tend to produce fewer seeds than species which reseed after fire. Including resprouting spe cies in the broadcast seed mix increases the establishment of resprouting species to ratios closer to that in the unmined land scape. This illustrates the importance of considering the functional attributes of species that are to be re-established to create a functioning community. Typically seeds are concentrated in the surface layer of topsoil, sometimes just in the surface few centimeters (Tacey Glossop 1980). Many of the smaller seeded species are not able to emerge from deeper than two centimeters. Double strip ping topsoil, that is removing and replacing the surface few centimetres separately from the underlying subsoil and then replacing the upper layer back on the surface, can increase seedling establishment through reducing dilution of the seeds with subsoil material and by reducing the depth of burial of the seeds (Tacey Glossop 1980). Be lairs Davidson At the Blair Athol minesite in central Queensland the local vegetation is Eucalyptus and Acacia dominated woodland with a grass understorey. The scale of disturbance and the cost of transporting topsoil around the mining front result in the topsoil being stockpiled, often for several years. The broadcast seed mix is important for increasing the density of perennial shtub and tree species. Often shrubs and grasses are able to establish on the topsoil stockpiles and continue to provide some seeds but this can result in increased weed establishment. Hard seeded legume species are often able to persist in the stockpiled topsoil for many years. Seed germin tion Not only must seeds be supplied to the site but, in particu lar, supplementing sites with broadcast seeds relies on effec tive germination and establishment of those seeds when favourable conditions occur. As the broadcast seeds have not undergone natural conditioning and priming for germination, there has been a need to understand the seed biology and the mechanisms inhibiting gennination and establishment on rehabilitation areas. Many Australian species have seed dormancy mechanisms to prevent premature germination when conditions are not optimal for establishment under the regime to which the plant has adapted. Bell et a/. (1995) suggest that only a third of Western Australian species genninate readily when moisture is applied. An additional one third require simple treatments to stimulate germination and the final third have complex or unknown seed dormancy mechanisms. The identi fication of seed donnancy mechanisms and ways to alleviate these have been a major focus of he mining industry in order to re-introduce endemic plant species to their respective minesites Many species in semi-arid Australia only establish successfully after disturbance, especially fire. One of the difficulties in using topsoil seed banks in the restoration process is that disturbance, i.e. clearing and grubbing and physical re moval of topsoil, is not a natural disturbance that the endemic plant community has adapted to. Hence, the nmmal stimulation of the soil seed bank by such natural disturbances as fire, does not occmT and many of the propagules within the seed bank remain dmmant. Knowing that fire plays an important role in the germination stimulation of many Australian plant communities has enabled mining companies to routinely apply heat treatments to native legume species. Acacia species dominate the seed mix applied to many mine sites (Langkamp 1987) and most species are hard seeded and respond to boiling water treatments (Auld O'Connell 1991). Recently smoke derived from burnt plant material has been found to stimulate seed germination of many native Australian species from a wide range of families (Dixon el a/. 1995). t has been found to be particularly effective in stimulating native grass species (Read Bellairs 1998). Davidson & Adkins ( 1997) and Davidson (unpubl.) have found plant derived smoke to be the key environmental stimulant to the germination ofTriodia hummock grass species which dominate much of arid Australia. These hummock grasses form the corner stone of rehabilitation programs at iron ore mines in the Pilbara, the Argyle diamond mine in the Kimberley, at gold mines throughout the Tanami Desett region in central Australia, gold mines in the eastern part of the north-eastern goldfields and at numerous mine sites in north-westem Queens land. The findings of this research will not only benefit mine site rehabilitation programs but also be valuable to the manage ment of pastoral leases in the hummock grasslands in respect to pasture manipulation. Another product of fire, charrate from burnt wood, has also been shown to stimulate germination of Burchardia umbel/a/a Belle/ a . 1987). The seed coat of some species consists of hard, tough tissues (shells, pits, stones etc) which offer considerable resistance to the 964 Mined land rehabilitation  Be lairs Davidson expansion of the embryo and emergence of the radicle and so mechanically prevent growth of the seed until they are degraded. This includes many important rangeland shrubs and trees including Eremophila, Scaevola, Owenia and Santalwn (Dixon 1985; Richmond Ghisalberti 1994). In general, breakdown of the woody fruit coats may take several years depending on the species and seasonal conditions in natural seed banks. There is still no reliable method to simulate this with broadcast seeding programs. Many studies have been carried out looking at the influence of enviromnental temperatures on germination (Bella irs Bell 1990; Mott 1972, 1978; Plummer Bell 1995). Tempera ture is particularly important for determining the season in which a species will germinate. Mott ( 1972) found distinct optimum temperature ranges that that coincided with winter and sunm1er germinating a1muals in the Murchison goldfields region of Western Australia. Seeds at unfavourable temperatures can remain donnant, particularly at lower temperatures, but may be killed at high temperattu·es i moist (Bella rs Belll990) . The light environment influences the germination of many seeds through the phytochrome system. Some seeds may require light to avoid germination when buried at depth or under canopies of existing vegetation. Other species only germinate in the dark to avoid genninating on the soil surface. Thls changes the optimum sowing conditions required for seeds but for most species tested the light or dark requirement only affects a proportion of the seed lot Belll993; Bell eta . 1995). Many seed coat dormancy mechanisms have been described in Austt·alian native species including mechanical, chemical and permeability dormancy mechanisms in seed coats and physiological mechanisms in the embryo of the seeds. To further complicate treating seeds to maximize germination it is common for a species to have several of these mechanisms. n some examples, seeds have both a coat-imposed and an embryo dormancy, while in others it can be shown that as one form of dormancy is removed another is formed (Adkins Bellairs 1997). Understanding the role that natural distttrbances such as fire play in the germination stimulation of Austt·alian native species, has now enabled mine sites to pre-treat broadcast seed with either heat or smoke to enhance germination and establishment. New research within Australia is even showing that whole stockpiles or areas of spread topsoil can be treated with plant derived 'smoke water'. Much of our understanding of seed dormancy in Australian native plants and of the mechanisms such as smoke stimulation of natives, has occurred as a result of mining induslly funding. The Australian Centre for Mining Environmental Research has sponsored two national workshops on the seed biology of Australian native species for revegetation (Bellairs Bell 1995; Bellairs Osborne 1997). Soil toxicity and deficiency Several studies have documented ciitical concentrations of nutrients for plant growth on mine soils, spoils and industrial waste (Aitken et . 1984; Olsen Bell 1990). Generally nitrogen and phosphorus fertilizers are applied when seed is sown. Cormnonly applied levels of fertilizer on mined lands in central Queensland are 400 kg/ha of superphosphate and I 00 kg/ha of ammonium nitrate (Kelly 1987). Fertilizer levels have to be carefully managed. Where reasonable quality topsoil from unmined native vegetation sites is available, low levels of fertilizer are applied to reduce weed invasion. On waste rock dumps in semi-arid Westem Australia good establishment has been achieved with 45 kg/ha or no fertilizer application (Osborne et a . 1993). A number of minesites in the north-eastern goldfields and Murchison areas of Western Australia (WA) have stopped using fertilizer altogether with rehabilitation work. Jennings et . (1993) were advised by several minesite rehabilitators around Kalgoorlie (WA) that optimum rates were Vlth International Rangeland Congress Proceedings Vol 2 more likely in the range of I 00-200 kg/ha for A triplex and A1aireana species while one source stated that rates greater than 200 kg/ha reduced establishment in Acacia and Eucalyptus species in the Kambalda region ofWA. In arid regions of Australia the nutrient levels of the ancient, infertile soils are low (Johns eta . 1984). While available nutrients are not unifonnly distributed but tend to be concentrated in run on areas. These run on areas tend to concentrate nutrients, seeds and moisture providing more favourable conditions for seedling establishment. Spoils of marine srcin in central Queensland are often of high salinity and sodicity (Kelly 1987) as are rock waste dumps in the goldfields ofWestem Australia (Osborne eta . 1993). On these highly saline materials halophytic speci~ s are typically sown. In the Western Australian goldfields, chenopods are widely used especially Atriplex, Maireana, and Scleroleana species. At the two sites assessed by Osborne l a . (1993) Chenopodiaceae made up 79 and 59 of the seed mix by weight, the sown seed contributed 70 of he establishing plants and over 80 of the plants established on the dumps were Chenopodiaceae. In the central Queensland coal fields there has been a effort to select species from more arid western regions near saltpans to revegetate more difficult sites. Competition Competition with weeds and grasses can inhibit native plant establishment. Cover crops of exotic grasses are used on many mine sites as the fibrous root systems provide effective initial soil erosion control and add organic matter. Almual species including Sa/sola kali and saltbushes have also been used. Rhodes grass, Kikuyu and Buffel grass establish rapidly and are effective are controlling erosion, however they can also retard tree growth and eliminate native grasses when densely established. Low levels of exotic grass cover can increase tree growth rates compared to bare soil (Forster 1995). In the Western Australian goldfields, cover crops of cereal rye grass were often used to stabilize dump slopes as it was unlikely to reach maturity and set seed. Dalton ( 1992), investigating establishment techniques in low rainfall areas, found that fortnightly watering and residual weed control for a 1 5 m radius were most important for successful establishment. Removal of weed competition at planting without continued weed control or residual weed control within a 0.5 m radius were not effective, nor were bitumen or organic mulches. The species composition on mine site rehabilitation sites in Australia tends to be strongly influenced by the initial floristic composition. After mineral sand mining near Eneabba in Western Australia, 90 of seedlings established in the first wet season, and mortality of seedlings establishing in later years was considerably higher (Bella irs 1992). After five years, seed ling establishment was only observed if a mature plant died. Long distance dispersal mechanisms tend to be poorly developed in the south-western Australian flora. In central Queensland most species also establish in the first year of rehabilitation and dispersal of new species onto the rehabilitation sites is slow. However some bird dispersed species are regularly dis persed onto rehabilitation areas and do successfully colonize, including Acacia salicina,Airiplex semibacca/a andEnchylaena tomentosa. These species all have red fruits or arils attached to the seeds and are bird dispersed. Some native grasses also have seeds which tend to be blown or carried by animals into the rehabilitation areas. These species can successfi.tlly establish where trees shade out exotic pasture grasses. In some instances in Australia, woody weeds or exotics have been introduced to minesites with devastating results in te1ms of competing with native species. Rumex vesicaria (Middle East srcin) has dominated some minesites in Western Australia after initial use as a cover crop. A triplex lentiform is and Mined land rehabilitation 965  Vlth International Rangeland Congress Proceedings Vol 2 Cenchrus ciliaris (Buffel grass) show promise as colonizers of disturbed lands. There is debate about whether these species are detrimental or not due to their grazing potential for stock. Nutrient cycling While plants must be established on a medium that is chemically and physically fertile to ensure that the vegetation persists, biological fertility must also be re-established (Jasper 1999). Soil microbes play a major role in the biological fertility of he soil. Soil fungi and bacteria are involved in breaking down organic matter to release nutrients for plant uptake, mycorrhizae are important in low nutrient Australian soils in assisting nutrient uptake of plants and Rhizobia and Frankia are involved in symbiotic relationships to fix nitrogen Lamont 1982). Mycorrhizae and return of soil microbial biomass has been assessed at several minesites across Australia, including mineral sand mines near Eneabba and at Stradbroke Island in cen n·al Queensland, at bauxite mines in nm·them Australian, and in the jarrah forest and eastern goldfields of Western Australia (Jasper eta . 1987). Mycorrhizae are important for rehabilitation as they: (i) enhance establishment and growth of plants by increasing nun·ient uptake, (ii) increase diversity as they enhance the host plant's ability to compete, (iii) contribute to efficient recycling of nutrients and long term sustainability, and (iv) assist in soil stabilization through their extensive hypha network (Jasper 1994). Mycorrhizal survival and infectivity are reduced by soil stockpiling without host plants and by soil disturbance. Jasper eta . (1987) has found that myconhizal infectivity generally increases to pre-disturbance levels within five years of revegetation in productive ecosystems and under direct return topsoil management practices. Stockpiled topsoil tends to lose its mycorrhizal viability within a period of8 - 12 months if it is not exposed to host root systems (Jasper eta . 1987). All Ji-iodia hummock grasses measured to date (Davidson, unpubl.) have been found to be highly mycorrhizal despite their highly arid environments, many typified by highly skel etal soils. In some cases there appear to be not only ectomycorrhizal associations but also endomyconhizal associations making it quite unique in the grass family. Soil microbial biomass generally is also reduced by disturbance and stockpiling (Ranis eta . 1993). Jasper (1999) and Bellairs (1998) have found it to gradually increase during revegetation; but even in well vegetated rehabilitation areas on benign soil and spoil with abundant litter, soil microbial activity can take up to eight years to achieve levels similar to those in unmined communities. Andersen ( 1997) shows that increases in soil microbial biomass tends to parallel increases in ant biodiversity across different aged rehabilitation areas at the Ranger Uranium mine east of Darwin. Microbial activity in rangeland soils would appear to follow the source sink pattem typical across the landscape, i.e. maximum colonization appears to be in the highly productive zones where runon water and nutrients concentrate, while being low in inter-hurnmock/sluub zones or limited to mulga groves relative to intergroves (Ludwig eta . 1997). This poses some challenges when hying to maintain orre-inn·oduce these organisms into rehabilitation areas. Nitrogen fixation by Acacia and other legumes can provide a substantial imput of nitrate into the ecosystem which is important as nitrogen is required in larger amounts than any other mineral nutrient for healthy plant growth. Acacia shrubs and n·ees are often an abundant component of the unmined community and may be the dominant tree species. In a mixed Eucalyptus forest, nitrogen fixation following fire has been found to be ve1y low for the first twelve months and was only 121 g/ha after 27 months; however, the Acacia density of the study site was fairly low. For an Acacia holosericea plantation in Senegal, it has been calculated that about 4 kg N/ha/year would be fixed Be lairs Davidson from a density of 2000 trees/ha. This density of Acacia is achieved in Australia at some minesite rehabilitation areas (Bellairs unpubl. data). Sustainability There is little information on long term development and sustainability of native ecosystems established on rehabilitated mine sites. Most long tenn studies of vegetation development on mining rehabilitation areas have focused on bauxite mining in the jarrah forest of Western Australia and on mineral sands mines on the east coast of Australia. To be sustainable all components of the ecosystem have to be re-established or develop at the site, recruitment needs to occur and the community needs to develop resilience to future disturbance at similar unmined connnunities. The latter can be a challenge because in fire prone communities of Australia many species resprout after fire, yet these species can be the most difficult to establish because oflow seed production and sometimes poor viability (Bellairs 1992; Bell 1993). In woodlands in Queensland initial establishment of Eucalyptus can be successful but a dense grom1d cover of exotic grasses present at some sites may make fi. ture recruitment difficult. On waste rock dumps in the goldfields ofWestem Aush·alia recmitment of the saltbush connnunity has been shown to be successful at some long tenn monitoring sites (Osborne pers. comm. ). A major issue that needs to be addressed, in respect of the decommissioning of minesites in the arid pastoral regions, is the resilience to grazing on these modified mine landscapes. Little work has been conducted on the grazing tolerance of rehabilitation areas after mine decommissioning. This is in part due to the low number of current decommissioned minesites that have undergone extensive rehabilitation work. Generally, stock are still being excluded and the full impact of grazing pressure has not been properly evaluated. There is also some debate as to whether these areas, which are relatively small in respect to the overall grazing lease, should in fact ever be returned to grazing. onclusion Silcock (1991) in a review of minesite rehabilitation in Queensland identified that the government must set measurable standards of rehabilitation and organize an acceptable system of monitoring. Projects in several states of Australian are investigating criteria to indicate that native rehabilitation communities are successful in tem1s of meeting end land use criteria and in terms of ecological functioning. The Australian Centre for Mining Environmental Research has just held a national workshop on indicators of ecosystem rehabilitation success. There needs to be further research in this area to develop a model and indicators to ensure that native vegetation establishment on rehabilitation areas is successful. To maintain a sustainable native vegetation community the site needs to be stable, and moisture, nutrients and propagules for vegetation need to be present; nuh·ient cycling needs to occur and the flora and fauna established need to reproduce and persist through disturbance. Research into all these areas is required including strategic research programs and applied research at particular sites. Stability is a major issue and research is needed on the relationship between erosion and vegetation cover and at older rehabilitation sites. Hydrology is particularly an issue in more arid environments. Only a few Australian native species establish reliably from seed, more research is required to overcome seed dormancy mechanisms and to promote high quality seed. Seed provenance is an issue which clouds the availability of seed. Very little is known about the long term success of native vegetation establislunent on mined lands in Australia and the ability of the rehabilitated vegetation to cope with future disturbances. New operations with improved long term planning 966 Mined land rehabilitation
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