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Coastal sandmining and landscape rehabilitation in Eastern Australia
Landscape Planning, 6 (1979) 359-374 o Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
COASTAL EASTERN
SANDMINING AUSTRALIA
AND LANDSCAPE
REHABILITATION
359
IN
J.E. COALDRAKE director, Environmental Division, Cameron, ~~~amara R 0. Box 94, North Brisbane, Qld. 4000 ~Aus~alia~ (Accepted
& Partners e~~sul~an~ Group,
3 July 1979)
ABSTRACT Coaldrake, J.E., 1979. Coastal sandmining and landscape rehabilitation Landscape Plann., 6: 359-374.
in eastern Australia,
Extensive deposits of the heavy minerals rutile, ilmenite and zircon are scattered along the beaches and massive silicious sand dune systems of the central east coast of Australia. Mining of these minerals by open cut methods close to major centres of population has led to a need for very high standards of performance in rehabilitation by the mining companies concerned. Rehabilitation now results from an extensive program that starts with surveys of landform and vegetation before mining, and continues as a responsibility of the mining company for 7 years or more after mining. The emphasis required by public policy is on re-establishment of native species. Since mining can occur anywhere between the foredune and 100 m+ above sea-level techniques have to vary in detail for particular sites. On the foredune with its extreme exposure costly methods of surface mulching are used. Elsewhere a cover crop of short-lived crop plants supported by limited fertiliser provides initial cover for slow-growing native species. The storage and replacement of topsoil is a vital component of success with the silicious sands and vegetation involved. On land forms recreated to harmonise with the original, the plant communities achieved after 7-10 years seem assured to persist and develop into types of native vegetation satisfactory for many later uses. Extensive public conflict over allocation of land use as between mining and national park has diverted attention from the long term need for proper planning for the use and management of these dune landscapes for the many other possible and sought-after forms of land-use.
INTRODUCTION
About one third of the 19 000 km of coastline in Australia carries coastal sand dunes of significant extent, i.e. more than 50 m in width. The longest stretch of such dunal coastline is on the northeast coast between Newcastle and Gladstone, a distance of some 1 200 km between latitudes 24” and 33”s. Over this length of coastline geological patterns and geomorpholo~c~ processes have combined to produce extensive areas of massive sand dunes; these include many individual areas of over 1 000 ha where a dune massif rises
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from the shoreline to final heights of over 200 m. They also include large islands just offshore which consist essentially of masses of sand anchored by a few small rocky headlands. The largest of these sand islands, Fraser island at latitude 25”S, covers 163 000 ha over a length of 120 km and rises to a peak elevation of 235 m. The total area of dune lands on this central east coast is about 500 000 ha. The mainland adjoining this lenghy dunal section of the east coast is a provenance for the heavy minerals rutile, ilmenite and zircon; the first two of these are a primary source of titanium for which there is an extensive market around the world. The minerals reach the coast through the normal processes of weathering, erosion and river transport as a component of silicious sands. These mineral-bearing sands are moved northwards and brought onshore by wave action. Onshore deposition involves some concentration into seams of mineral-rich sand on the beaches and, in some cases, further concentration during sand-drift as dunes are built. These are old dune systems thought to have been building throughout the Pleistocene and probably longer (Coaldrake, 1962; Thorn, 1965; Thompson and Ward, 1975) so that at least some of their elevation probably relates to earlier stands of raised sea-level. As a result of these processes, commercially important deposits of heavy minerals are spread widely along this 1 200 km stretch of coastline. The processes of emplacement result in commercial concentration occurring at heights of up to 150 m above present sea level and as far as about 10 km inland from the present shoreline. Many of these have been mined since mining started about 1950, and access for mining has been sought over most of the remainder. The dune lands on the central east coast flank the part of the continent with the greatest concentration of population and the best water supply for further population growth. The beaches are used year-round for recreation with a consequent growth of extensive seaside resorts on many areas of adjoining dune land. The mineral deposits have to be mined by various forms of open-cut mining which inevitably creates temporary scars on the landscape. These scars are highly visible in dune landscape. Areas nearby are in continual use for recreation by visitors who are not directly dependent on mining for their income, and therefore less inclined to accept the visual effects. This combination of factors led to early pressure on mining companies to follow their mining with rehabilitation to acceptable types of vegetal cover. The mineral sand-miners on the east coast were the first branch of the Australian mining industry to come under such pressure. They have responded by developing successful methods based on elaboration of research and practical experience into quite detailed knowledge of reshaping land, and the use of topsoil, fertiliser, seed and mulches. This paper summarises the past experience and present knowledge which has now been applied over some 7 000 ha on the eastern coast by the sand
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mining industry over the last 20 years. It discusses some of the problems that have arisen from the need to regenerate native vegetation over most of these mined areas. No attempt is made at exhaustive coverage of the literature; the pertinent Australian literature up to 1973 was covered by Coaldrake et al., (1973) and Coaldrake and Beattie (1974), and selected later references are used as a key to the more recent literature. THE NATURAL
LANDSCAPE
Extended discussion of these sand dune landscapes is given in Coaldrake (1961) and in Stevens and Monroe (1975). There are four basic components in these coastal dune landscapes. The first is the fordune which may rise from just above high water mark to heights of up to 20 m (Fig. 1). The sea-
Fig. 1. This photograph is of a portion of a 25 km long foredune that was rebuilt and stabilised after mining. The berm in the foreground is a temporary accumulation that could be removed in 24 hours by storm waves. The size and shape of the foredune behind the berm is typical of foredunes on undisturbed Australian coast. The photograph ‘also illustrates the use of cut “brush” for windbreaks in rehabilitation of a foredune and berm. The photographer was on the beach. The brush lines about 20 m apart are made from tall shrubs and tree branches cut from other parts of the mining lease. In areas of severe exposure on both foredunes and inland dunes similar brush material is laid on the surface. The brush lasts about 1 year by which time the native spinifex grass seeded (or marram grass established from cuttings) provides enough cover for stability.
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ward face with its high exposure to wind and spray, and susceptibility to storm wave erosion is an extreme habitat with a restricted range of species in the vegetation. It normally carries a grassland or low woodland dominated by Spinifex hirsutus an Australian species which has been shown by Barr and McKenzie (1977) to be capable of responding to nitrogenous fertiliser at rates of up to 900 kg ha’ year-’ of N. With stolons up to 20 m in length it colonises vigorously in advance of associated species such as Ipomea pes-caprae and Hibbertia scandens. Common low trees on the seaward face are Casuarina equisetifolia (a nodulated nitrogen fixer), Banksia integrifolia, and a stunted shrubby form of the forest tree Tristania conferta. The second landscape component is the low dunes defined by Coaldrake and Roe (1976) as areas in which the majority of dunes do not reach heights of above 50 m. This type of dune landscape may extend for over 2 km inland from the beach, or in the case of present and former islands extend as a fringe around a central massif of high dunes (Fig. 2). These low dunes carry a dense vegetation of low forests and woodlands and heath (generally about lo-15 m in height) dominated by various species of Eucalyptus, Angophora, Tristania and Casuarina, with a dense shrub layer dominated by species of
Fig. 2. Portion of Fraser Island showing, from the right (1) a creek and adjoining swamps between stranded old foredunes. The general elevation here is less than 10 m above the beach which is 200 m beyond the right edge of the photograph. (2) Low dunes which had been partly mined; the elevation of this area of dunes lies between 5 and 50 m. The differences in toning represent rehabilitation of different ages up to 2 years old. (3) An unmined swamp with its herbfield and low shrub vegetation. (4) High dunes rising finally to 200 m. (5) A perched lake among high dunes.
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Myrtaceae,
Proteaceae and Fubaceue (Fig. 3). Sedges are more common than grasses. Low lying areas between dunes are subject to water impoundment so that swamps and open lakes are common. Here the dominant trees are of Meluleuca while sedges and shrubs of Myrtuceae, Proteaceae, Fubaceae and Epacriduceue are profuse. The third landscape component is the high dunes in which the majority of dunes rises to heights of more than 50 m with peak heights of over 200 m being not uncommon. The vegetation is again a mixture of forest, woodland and heath, but with an overall tendency to greater height. The plant genera are largely the same as in the low dunes but different species (especially of Eucalyptus) may produce forests up to 35 m tall. These forests have been subjected to controlled logging for some 50 years following an earlier 50 year period of uncontrolled logging in which exploitation was concentrated largely on the rain-forests described later. The most striking type of vegetation in these dune areas is the sub-tropical rain forest discussed by Webb and Tracey (1975). There was originally a total area of 10 500 ha of this type of vegetation, particularly towards the northern end of the coastal dune belt, and most still exists though with some alteration due to selective logging. It is a tall closed-forest often over 30 m high growing on deep silicious sand, apparently after slow processes of succession to enable accumulation of the necessary nutrient mass. The fourth landscape component is the rolling heathlands and swamps which occur mainly at lower elevations on land of gentle topography. These Australian heaths are dense assemblages of sclerophyll shrubs generally l-2 m in height. They are dominated by genera from the families Myrtuceae, Proteuceae, Fabaceae and Epucridaceue; sedges are common in the ground layer and increase in density on wetter sites. The swamps already referred to among the low dunes can become extensive on low lying areas in units of 100 ha. In the wettest swamp areas the vegetation becomes a herbfield dominated by sedges and growing on acid bog peats up to 5 m thick. With a basic “soil material” consisting entirely of silicious sand the soils formed on these dune areas are a series of variants within the general groups of regosols, podzols and ground-water podzols. Organic cemented pan layers up to over 2 m in thickness are common in the ground water podzols. The fertility of these soils in their natural condition resides largely in the organic matter in the top 20-30 cm. The natural vegetation is well adapted to the low levels of fertility. This selective advantage can pose problems when chemical fertilisers are used to hasten the early establishment of vegetal cover during rehabilitation; some of the native species desired have evolved to the point of having a low tolerance for increased levels of phosphorus (Specht, 1975; Heddle and Specht, 1975). In addition to landform, soils and vegetation the factor of climate is also important to the conduct of successful rehabilitation. Over this long stretch of coastal dunelands the climate is mild and sub-tropical with increasing dominance of summer rainfall of high intensity from south to north. Total
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annual rainfall is from 1 000 to 1 800 mm of which 50-65s falls in the summer months of November through March; daily rainfalls of 125 mm are common while cyclonic disturbances can yield daily totals of 375 to 500 mm. Such high daily falls contribute to high variability from month to month, and high run off; both can lead to problems in the early stages of rehabilitation after mining. Temperatures are generally mild with only a few light frosts. However, when good moisture conditions occur during the high levels of solar radiation in summer, plant growth can be rapid. As with any sand dune landscape the basic trend over long periods is intermittent change of landform on any given hectare. There is the typical cycle of sand movement, colonisation of bare sand by pioneer species, seral development continuing through minor short-term oscillations, with final loss of stabilising vegetal cover leading to a new phase of sand movement. All of these stages are to be seen in these coastal dune landscapes of the east coast. One of the most striking visual aspects of this sequence is the phase of bare sand movement through blow-outs. James Cook recorded their presence from 10 km offshore in the journal of his passage along the east coast in 1770 before the arrival of Europeans. Watt (1972) measured a total area of 5 235 ha of sand drift in these dune landscapes south of latitude 28”S, while Coaldrake (unpublished data, 1972) estimated the presence of 8 500 ha north of that latitude. This is 1.8% of the total area or roughly twice the area now successfully rehabilitated by the sand mining industry. The community at large has had time to come to accept these areas of sand drift as a natural part of the landscape. Perhaps with time they will also come to regard the different vegetal cover and visual aspect of developing rehabilitation as a part of the landscape. BEACH
MINING
Mining for heavy mineral sands on the east coast commenced soon after World War II with simple scraping from the tidal zone of seams of minerals that had been concentrated by wave action. This form of mining continues with modern earth-moving equipment, but access has become increasingly restricted due to conflict with recreational use of beaches. The seams mined are commonly from 2-10 cm thick, so that even if there are multiple seams the total bulk removed is small. Again, the beaches concerned may lose a thickness of up to 30 cm in 48 h, over the whole beach from the action of storm waves; this sand is normally re-deposited during ensuing calm weather in the normal oscillatory cycle of ocean beaches. Thus this form of mining is consistent with the natural cycle of beach behaviour. The only problem in rehabilitation is the backfilling of holes at a slope conforming to that of the beach nearby. The combined effects of wave swash, tides and winds remove any evidence of mining within a few days. The small areas of vegetated land above high water mark used for depots
and tracks are rehabilitated using the same methods as those discussed for coastal sand mining below. There is argument that removal of the heavy minerals (more than twice the relative density of ordinary beach sand) affects the stability of beaches, but there is no experimental evidence to prove this. There are plenty of stable beaches with little or no content of heavy minerals. DUNE MINING
The greatest extent of mining for heavy minerals on the central east coast is on the sand dunes from high-water mark upwards. Such mining has now been carried out, together with successful rehabilitation at heights of up to 130 m above sea level. The two basic methods of mining used are outlined later with some comment on important differences they create in regard to rehabilitation. The essential difference between the two methods is in the winning of the mineral-bearing sand from the ore body. The treatment for extraction of the minerals is the same once the sand enters the treatment plant. The basis of treatment at the mine site is common separation of all minerals out of a water-borne slurry by gravity. Final sorting of the separate minerals is done in electro-static and magnetic fields at central mills remote from the mine site; caustic soda is sometimes used in these mills to remove the coating of organic matter from mineral sand grains that are won from swamp beds or the organic hardpans of ground water podzols. But with regard to rehabilitation after mining the important point is that no chemicals are used at the mine site. In “dry” mining all of the mineral bearing sand is transported to a separation plant nearby for removal of the minerals. The tailings, which comprise 98-99.5X of the sand originally mined, are returned to the open cut as a water-borne slurry. For reasons of operational efficiency in dry mining the hole of an open cut is commonly open for 1 year or more before final re-contouring and spreading of topsoil. This reduces the effectiveness of the topsoil, especially as a source of seed, since the type of operation requires long term storage of the topsoil. In “wet” mining the ore body is removed by a suction dredge with cutterwheel. The dredge floats in a moving pond and is attached directly to a floating primary separation plant. This combined mining and separation plant moves through the ore-body with the tailings discarded directly at the rear edge of the moving pond. As with dry mining the tailings constitute 98-99.5% of the sand removed by the dredge from the front of the pond. This type of wet mining is used from high-water mark upwards to any elevation at which ore bodies occur and for which a water supply can be obtained t.o maintain the water level in the pond. In one variation of this basic process of wet mining a transportable separation plant with separate holding ponds for water stood alongside the mining path; both the
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plant and the ponds were moved at intervals of a few months. This type of wet mining accounts for the majority of mineral sand mining on the east coast. With regard to rehabilitation it has the advantage that topsoil can be replaced much more rapidly than with dry mining. In some situations close to the sea, and where fresh water was in limited supply, sea water has been used for wet mining. This necessitates a delay between mining and rehabilitation to allow leaching of the salt from the sea water out of the top 30 cm or so of the new land. The delay required is purely a function of total rainfall. About 250 mm is required and it may need from 1 week upwards to achieve this total; delays of 12 weeks or more are possible in the drier months of winter. REHABILITATION
Over 20 years or so the coastal sand mining industry has developed considerable expertise in rehabilitation through a combination of its own efforts and technical advice from certain government agencies. Rehabilitation is now recognised by the industry as a separate problem requiring its own specialist professional planning and supervision. As commented on in the introduction to this paper the industry has to work under close public scrutiny, and its continuing access to ore bodies depends strongly on its performance in rehabilitation. In this paper space permits only a general discussion of the methods and problems of rehabilitation; for more detailed discussions the reader is referred to Barr and Atkinson (1970), Barr (1974), Thatcher and Westman (1975), Lewis (1976) and Brooks (1978). There are a number of distinct stages in the total process of rehabilitation after mineral sand mining. They relate primarily to the fact that the miner is, in almost every case, required to re-establish landforms and vegetation resembling the original as a condition of the mining lease that permits access to mineral on public land; and most of the mining is on public land. This requirement interacts with the fact that the sand to be stabilised is often in topographic situations where there is risk of wind-blown drift. The first stage in the whole process of rehabilitation is a survey of the contours and vegetation of the landscape before mining starts. This is accompanied by collection of seed of the commonest species of trees and tall shrubs present. The second stage is the stripping and stockpiling of topsoil including shrubs, after burning of large trees in situ so that the ashes are incorporated in the topsoil. The first two stages need to be closely related to the actual mining operation for several reasons. The requirement for a final landform that is close to the original can largely be met by the mining engineer through control of the distribution of tailings such that the use of bulldozers for final shaping and smoothing of contours is kept to a minimum. Slopes on the original dunes can be up to angles beyond the normal angle of repose of raw sand (32-34”) due to
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Fig. 3. Sclerophyll woodland typical of much of the natural vegetation on the silicious sand dunes of the central east coast of Australia. This vegetation is well adapted to periodic burning which maintains a fluctuating balance between the shrub layer and the ground layer of sedges and grasses.
oversteepening when drifting sand spills under standing forest or woodland. Tailings can be stacked at the angle of repose, but there are difficulties in subsequent use of farm machinery if the final slopes to be rehabilitated exceed 15” ; Short lengths of slope of up to 25” can be worked on the basis of machinery working down the slope only. Short slopes of more than 25” can be rehabilitated by the use of spray-on mulching such as hydro-mulching or bituminous mulches. Unless there is a strict requirement to recreate identical landform (as in parts of future nature reserves) slopes are finished mainly at less than 15” so that farm machinery can be used freely in all directions. In this connection it should be noted that to the ordinary recreational visitor slopes steeper than 10” are perceptibly steep for climbing, and at 15 to 20” the effort of climbing becomes enough to dissuade many. The visual impact of a mixture of slopes of mainly less than 15” with scattered steeper areas is that of the essentially random landform of the original dune areas before mining. To all but the most determined critic these rehabilitated areas give a satisfactory blend of landform with the surrounding unmined areas (Fig. 4).
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Fig. 4. The junction of mined and unmined land on low dunes 1 km from the beach at an elevation of about 30 m. This photograph, taken 18 months after mining, shows the blending of landform and early dominance by Acacia. Fig. 5 is a close-up of the topcentre of the rehabilitated area shown here.
In the second stage the handling of topsoil becomes a crucial part of the mining plan if the full benefits are to be gained from the use of topsoil. Storage in heaps near the mine path needs to be kept to a minimum time. After a few weeks of storage the viability of included seed of most of the native species concerned drops quickly. Storage beyond about 4 months leaves viable seed of only some hard-seeded plants such as Acacia spp. in the topsoil. There can also be degenerative changes in some fractions of the soil organic matter. Practical difficulties usually preclude the theoretically ideal practice of moving topsoil direct from its source to its final destination for immediate spreading. Once emplaced the topsoil fills the normal roles of supplying nutrients and seedlings, and provides some resistance to wind drift if enough litter is present. Where mining passes through large areas of bare sand as in the blowouts that occur naturally in these dune lands, or on the foredune where organically rich topsoil is often lacking, the methods are altered to offset this disadvantage. These alterations are made before and during the third stage of rehabilitatation. The lack of topsoil and the high exposure to wind are offset by the use of mulches and windbreaks (Fig. l), and by increased dressings of nitrogenous fertiliser. The primary stabilising grasses used are the native sand spinifex (Spinifex hirsutus) and south of about latitude 31”s
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the introduced marram grass (Ammophila arenaria). Seed of other creeping herbaceous plants and seedling trees of Cusuarina and Banksiu are also planted. Away from the foredune the third stage of rehabilitation consists of seeding and fertilising into the topsoil with a mixture of species. The seed mixture commonly includes a cover crop of hybrid sorghum in warmer months, or cereal rye in cooler months; neither of these persists beyond a scattered second generation. These cover crops provide a first rapid cover while the slower growing native species establish. The seed mixture of native species used varies with the site but can be complex. It commonly includes Acacia which is a valuable pioneer species not only for its input of nitrogen to the soil but also for its litterfall. (Figs. 4 and 5). In some areas in recent years the placement of seed and fertiliser into the topsoil has been followed by the spreading of chopped mulch harvested from the shrub layer of woodland like that in Fig. 3. The early results suggest that this widens the range of native species that re-appear early, and enhances their growth. In most situations a light dressing of N-P-K fertiliser is used to stimulate the growth of the cover crop. Excessive use of phosphorus can raise prob-
Fig. 5. Close-up of portion of the area in Fig. 4. Note the dead stools of the cover crop of hybrid sorghum near the man’s right leg. The small tree he is touching is a self-sown seedling of Eucalyptus intermedia, probably from wind blown seed; the larger specimen, behind his legs is Tristania conferta from nursery stock. Both of these are major native trees. The bulky shrubs in the rear are Acacia cunninghamii from seed in the topsoil or from chopped mulch spread on this area before planting.
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lems in subsequent growth of native species as discussed in an earlier section of this paper. In recent years there has been a trend to steady reduction of the content of phosphorus fertiliser to a point that is just sufficient for the cover crop. In cases such as dry mining with the loss of seed that follows lengthy storage of topsoil it may be necessary to use a perennial grass to provide stabilising cover and shelter for the nursery stocks and hand seeding of native species that is necessary. The most commonly used species is Chloris gayana (Rhodes grass); this practice is declining as skill increases in the handling of topsoil and seed of native species. After about 18 months the fourth stage of rehabilitation starts. This is a transition from cover crop and early fast growing native species such as Acacia to a wider variety of slower growing native species. This transition stage lasts about five years after which the Acacias especially begin to die out and to be replaced in bulk by a variety of other shrubs. These may be from seed in the topsoil, or seed harvested elsewhere and deliberately sown, or from nursery stock. This transition stage leads slowly into the longer stages of succession towards a native woodland or forest. It is hoped that the foregoing short account of rehabilitation conveys something of the elaborate methods that have been developed to engender re-establishment of native vegetation. Under the spur of necessity this branch of the mining industry in Australia has developed a high degree of skill in nurturing a range of Australian native plants. Little was known previously about the “horticulture” of many of these species under broadfield conditions. While there has not yet been time for mature woodland to develop completely there are no known cases of broadscale failure of areas treated properly by modern methods; some failures from the earliest attempts have necessitated a second treatment but the techniques now seem assured. Comparatively little attention has been given yet to the return of wildlife to areas under rehabilitation. It is a common experience to those who work extensively on rehabilitated areas that they attract numbers of kangaroos if these are still present in the general area. Birdlife can be profuse once there is a good cover of shrubs, though the number of species may be restricted. It seems reasonable to assume that a full range of wildlife will recolonise rehabilitated areas as the necessary range of habitats develops. In this connection it is interesting to note the results of a recent study by Fox (1978) on the return of ants to a rehabilitated area. In comparisons between unmined control areas and rehabilitated areas 4-11 years old she found that “species richness values, even for the younger plots are close to those of the control; however many more individuals were trapped on the mined plots.” THE TIME FACTOR
Some harsh criticism
has been levelled at the effectiveness
of rehabilita-
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tion after coastal sand mining because, after 7-10 years, areas of rear dunes (away from the foredune) do not carry a mature woodland. It has frequently been claimed that the plant communities established will not persist. Such criticism overlooks one of the fundamental featues of a sand dune landscape - a sand dune only starts to form through drifting of bare sand. Thus any heavily vegetated dune only reaches such a state through natural processes of colonisation of bare sand by pioneer species followed by successional development of more complex communities. In the Australian situations involved the time scale is probably over 100 years. The essentials needed for these processes to continue once started are energy, water and nutrients in appropriate quantities, a stability of land surface, a source of propagules, and time for the processes to operate. The only one of these factors not in complete supply five years after rehabilitation starts is the supply of propagules of all species originally present. But the distribution of ore bodies is such that it is uncommon for the centre of a mined area to be more than 500 m from untouched vegetation in similar positions in the landscape. This is not a long distance for natural dissemination of propagules. These arguments, of course, do not apply to the complex ecosystem of sub-tropical rain forest but no large areas of this have ever been mined. In a few cases mining has removed all of a small area of a given type of vegetation so that the only native species to return are those planted by the miner. But such limited types of vegetation are now protected from mining. Except for these few special situations time is on the side of the miner once a limited range of native species has been established for 5 years. DIVERSITY
AND STABILITY
A criticism levelled strongly in recent years at the effectiveness of rehabilitation after coastal sand mining is that the reduced number of species present in the new plant communities in their early stages represents a loss of diversity that must lead to instability and eventual breakdown. This criticism, of course, rests on the concept that diversity begets stability which has been hypothesised as applying to vegetation by authors such as Margalef (1968). This theory was always difficult to accept with regard to these coastal dune landscapes. Here the seral processes start in such extreme and harsh environments as the foredune and the bare sand of blowout areas further inland; such extreme environments are not harsh to the few species adapted to them. Field work in such areas always produces evidence of the sharp reduction in number of species between mature woodland on inland dunes and the edge of the foredune, or a blowout area that is being colonised. The foredune community is as stable as anything can be on a piece of landform that comes and goes. The early communities on blow-
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outs are, of course, replaced in due course by larger numbers of species but this form of instability is a necessary part of seral development. Finally, it is interesting that the sub-tropical rain forests on these dune landscapes with their assemblage of about 160 species recorded by Webb and Tracey (1975) are more difficult to restore from human interference or catastrophic storm damage than the other types of vegetation present. Their diversity does not seem to confer communal robustness. Margalef and others associated with the concept that diversity begets stability in plant communities revised their opinions, more or less to the point of reversal, in 1974 (Van Dobben and Lowe-McConnell, 1975). But this information has been slow to reach, much less to be accepted, by many of the critics of the effectiveness of rehabilitation after coastal sand-mining. SOCIAL
A~rTUDES
AND PLANNING
About one third of the total population of Australia lives within 40 km of the sea on the 1 200 km of eastern coast where much of the shoreline is occupied by these coastal dune landscapes. An activity so conspicuous as open cut mining is inevitably under close notice. For over 100 years until about 1970 Australian mining laws gave almost total preference to mining over other forms of land use. In the process of using such laws to its advantage the ming industry accumulated a large loss of goodwill with those sectors of the public not directly dependent on mining for a living. The placement of ore bodies close to large centres of population and the coastline used by those people for recreation, and the resentments generated by the industry’s early years of preferential access to land combined to produce a public acceptance of pressure to restrict access for coastal sand mining. The detailed reasons for this conflict, basically between temporary land use and outright preservation, are not the subject of this paper. But one of the results is of concern in relation to lost opportunities for proper planning for the use and management of landscape. In the pol~sation that has developed over the conflict mentioned above it has been difficult to achieve any long range strategic planning for allocation of dune landscape to a variety of land use. Over 20% is already allocated to total preservation in the Australian form of National Park, and a further 10% seems likely to be added. The argument over this allocation distracts attention and funding from the work needed to develop comprehensive guidelines for use and management of the remainder in ways compatible with dune landscape. The largest of the offshore islands, Fraser Island, has been partitioned largely between National Park (25%) and State Forest (in which camping is increasingly permitted). Only about 0.1% of the island is currently available for the commercial accommodation centres on which most Australians prefer to base their coastal recreation. In a recent Iengthy and costly public inquiry the CommisGoners were constrained by their terms of reference
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into considering coastal sand mining simply as a separate use of land, rather than as the first use in a sequence. Brooks (1978) lists ten different forms of land use which can sensibly follow mineral sand mining and its attendant rehabilitation. On the coastal lands concerned two of these, tourism-recreation and urban development, are increasingly sought. Each is well suited to the land form and vegetal cover that can be created after mining but, with a few notable exceptions, this type of planning for a sequence of uses does not happen at present. ACKNOWLEDGEMENT
This paper condenses my experience over many years during which I have benefited from field trips and discussions with staff of many sandmining companies, government agencies and Universities. They are too numerous to thank individually.
REFERENCES Barr, D.A., 1974. Progress in Costal Sand Dune Reclamation in Queensland, Australia. Int. J. of Biometeorol., 18: 137-141. Barr, D.A. and Atkinson, W.J., 1970. Stabilisation of Coastal Sands after Mining. J. Soil Conserv. Serv. N.S.W., 26: 89-107. Barr, D.A. and McKenzie, J.B., 1977. Progress in coastal sand dune stabilisation and management experiments on South Stradbroke Island, Queensland. Proc., 3rd Australian Conference on Coastal and Ocean Engineering. Institution of Engineers of Australia, Sydney. National Conference Publ. No. 77-2, pp. 207-213. Brooks, D.R., 1978. A grave imbalance. Min. Rev. Aust. Min. Ind. Council, Canberra, pp. 5-7, 10. Coaldrake, J.E., 1961. The Ecosystem of the Coastal Lowlands (“Wallum”) of Southern Queensland. C.S.I.R.O., Melbourne, Bulletin No. 283: 138 pp. Coaldrake, J.E., 1962. The coastal sand dunes of southern Queensland. Proc. R. Sot. Queensl., 72: 101-115. Coaldrake, J.E. and Beattie, K.J., 1974. Suppl. No. 1 to Coaldrake, McKay and Roe (1973). Div. Plant. Ind., CSIRO, Canberra, 103 pp. Coaldrake, J.E. and Roe, P.A., 1976. Rehabilitation after Mining in “Moreton Island Environmental Impact Study and Strategic Plan”. Co-ordinator General’s Department, Brisbane. Part 2: 66-70. Coaldrake, J.E., McKay, M. and Roe, P.A., 1973. Annotated Bibliography on the Ecology and Stabilisation of Coastal Sand Dunes, Mining Spoils and other Disturbed areas. Div. Plant Ind., CSIRO, Canberra, 158 pp. Fox, M., 1978. Changes in an ant community of coastal heath following sand mining. Bull., Ecol. Soc.Aust., 8( 1):9. Heddle, E.M. and Specht, R.L., 1975. Dark Island Heath (Ninety-Mile Plain, South Australia). VIII. The effect of fertilisers on composition and growth, 1950-1972. Aust. J. Bot., 23: 151-64. Lewis, J.W., 1976. Regeneration of Coastal Ecosystems after mineral sand mining. Aust. Min., 68: 27-29. Margalef, R., 1968. Perspectives in Ecological Theory. University of Chicago Press, Chicago, Ill., 111 pp.
314 Specht, R.L., 1975. The effect of fertilisers on sclerophyll (Heath) vegetation. The problems of revegetation after sand mining of high dunes. Search, 6: 459-461. Stevens, N.C. and Monroe, R.W., 1975 (Editors). Stradbroke Island Symposium. Proc. R. Sot. Queensl., 86: l-146. Thatcher, A.C. and Westman, W.E., 1975. Succession following mining on high dunes of coastal south-east Queensland. Proc. Ecol. Sot. Aust., 9: 17-33. Thorn, B.G., 1965. Late Quaternary coastal morphology of’the Port Stephens-Myall Lakes area, N.S.W. J. R. Sot. N.S.W., 98: 23-36. Thompson, C.H. and Ward, W.T., 1975. Soil landscapes of North Stradbroke Island. Proc. R. Sot. Queensl., 86(18): 9-14. Van Dobben, W.H. and Lowe-McConnell, R.H., 1975. Unifying Concepts in Ecology. W. Junk, The Hague, 302 pp. Watt, B.G., 1972. An assessment of coastal sand drift in New South Wales. J. Soil Conserv. Serv. N.S.W., 28: 7-21. Webb, L.J. and Tracey, J.G., 1975. The Cooloola Rain Forests. Proc. Ecol. Sot. Aust., 9: 317-321.
COASTAL EASTERN
SANDMINING AUSTRALIA
AND LANDSCAPE
REHABILITATION
359
IN
J.E. COALDRAKE director, Environmental Division, Cameron, ~~~amara R 0. Box 94, North Brisbane, Qld. 4000 ~Aus~alia~ (Accepted
& Partners e~~sul~an~ Group,
3 July 1979)
ABSTRACT Coaldrake, J.E., 1979. Coastal sandmining and landscape rehabilitation Landscape Plann., 6: 359-374.
in eastern Australia,
Extensive deposits of the heavy minerals rutile, ilmenite and zircon are scattered along the beaches and massive silicious sand dune systems of the central east coast of Australia. Mining of these minerals by open cut methods close to major centres of population has led to a need for very high standards of performance in rehabilitation by the mining companies concerned. Rehabilitation now results from an extensive program that starts with surveys of landform and vegetation before mining, and continues as a responsibility of the mining company for 7 years or more after mining. The emphasis required by public policy is on re-establishment of native species. Since mining can occur anywhere between the foredune and 100 m+ above sea-level techniques have to vary in detail for particular sites. On the foredune with its extreme exposure costly methods of surface mulching are used. Elsewhere a cover crop of short-lived crop plants supported by limited fertiliser provides initial cover for slow-growing native species. The storage and replacement of topsoil is a vital component of success with the silicious sands and vegetation involved. On land forms recreated to harmonise with the original, the plant communities achieved after 7-10 years seem assured to persist and develop into types of native vegetation satisfactory for many later uses. Extensive public conflict over allocation of land use as between mining and national park has diverted attention from the long term need for proper planning for the use and management of these dune landscapes for the many other possible and sought-after forms of land-use.
INTRODUCTION
About one third of the 19 000 km of coastline in Australia carries coastal sand dunes of significant extent, i.e. more than 50 m in width. The longest stretch of such dunal coastline is on the northeast coast between Newcastle and Gladstone, a distance of some 1 200 km between latitudes 24” and 33”s. Over this length of coastline geological patterns and geomorpholo~c~ processes have combined to produce extensive areas of massive sand dunes; these include many individual areas of over 1 000 ha where a dune massif rises
360
from the shoreline to final heights of over 200 m. They also include large islands just offshore which consist essentially of masses of sand anchored by a few small rocky headlands. The largest of these sand islands, Fraser island at latitude 25”S, covers 163 000 ha over a length of 120 km and rises to a peak elevation of 235 m. The total area of dune lands on this central east coast is about 500 000 ha. The mainland adjoining this lenghy dunal section of the east coast is a provenance for the heavy minerals rutile, ilmenite and zircon; the first two of these are a primary source of titanium for which there is an extensive market around the world. The minerals reach the coast through the normal processes of weathering, erosion and river transport as a component of silicious sands. These mineral-bearing sands are moved northwards and brought onshore by wave action. Onshore deposition involves some concentration into seams of mineral-rich sand on the beaches and, in some cases, further concentration during sand-drift as dunes are built. These are old dune systems thought to have been building throughout the Pleistocene and probably longer (Coaldrake, 1962; Thorn, 1965; Thompson and Ward, 1975) so that at least some of their elevation probably relates to earlier stands of raised sea-level. As a result of these processes, commercially important deposits of heavy minerals are spread widely along this 1 200 km stretch of coastline. The processes of emplacement result in commercial concentration occurring at heights of up to 150 m above present sea level and as far as about 10 km inland from the present shoreline. Many of these have been mined since mining started about 1950, and access for mining has been sought over most of the remainder. The dune lands on the central east coast flank the part of the continent with the greatest concentration of population and the best water supply for further population growth. The beaches are used year-round for recreation with a consequent growth of extensive seaside resorts on many areas of adjoining dune land. The mineral deposits have to be mined by various forms of open-cut mining which inevitably creates temporary scars on the landscape. These scars are highly visible in dune landscape. Areas nearby are in continual use for recreation by visitors who are not directly dependent on mining for their income, and therefore less inclined to accept the visual effects. This combination of factors led to early pressure on mining companies to follow their mining with rehabilitation to acceptable types of vegetal cover. The mineral sand-miners on the east coast were the first branch of the Australian mining industry to come under such pressure. They have responded by developing successful methods based on elaboration of research and practical experience into quite detailed knowledge of reshaping land, and the use of topsoil, fertiliser, seed and mulches. This paper summarises the past experience and present knowledge which has now been applied over some 7 000 ha on the eastern coast by the sand
361
mining industry over the last 20 years. It discusses some of the problems that have arisen from the need to regenerate native vegetation over most of these mined areas. No attempt is made at exhaustive coverage of the literature; the pertinent Australian literature up to 1973 was covered by Coaldrake et al., (1973) and Coaldrake and Beattie (1974), and selected later references are used as a key to the more recent literature. THE NATURAL
LANDSCAPE
Extended discussion of these sand dune landscapes is given in Coaldrake (1961) and in Stevens and Monroe (1975). There are four basic components in these coastal dune landscapes. The first is the fordune which may rise from just above high water mark to heights of up to 20 m (Fig. 1). The sea-
Fig. 1. This photograph is of a portion of a 25 km long foredune that was rebuilt and stabilised after mining. The berm in the foreground is a temporary accumulation that could be removed in 24 hours by storm waves. The size and shape of the foredune behind the berm is typical of foredunes on undisturbed Australian coast. The photograph ‘also illustrates the use of cut “brush” for windbreaks in rehabilitation of a foredune and berm. The photographer was on the beach. The brush lines about 20 m apart are made from tall shrubs and tree branches cut from other parts of the mining lease. In areas of severe exposure on both foredunes and inland dunes similar brush material is laid on the surface. The brush lasts about 1 year by which time the native spinifex grass seeded (or marram grass established from cuttings) provides enough cover for stability.
362
ward face with its high exposure to wind and spray, and susceptibility to storm wave erosion is an extreme habitat with a restricted range of species in the vegetation. It normally carries a grassland or low woodland dominated by Spinifex hirsutus an Australian species which has been shown by Barr and McKenzie (1977) to be capable of responding to nitrogenous fertiliser at rates of up to 900 kg ha’ year-’ of N. With stolons up to 20 m in length it colonises vigorously in advance of associated species such as Ipomea pes-caprae and Hibbertia scandens. Common low trees on the seaward face are Casuarina equisetifolia (a nodulated nitrogen fixer), Banksia integrifolia, and a stunted shrubby form of the forest tree Tristania conferta. The second landscape component is the low dunes defined by Coaldrake and Roe (1976) as areas in which the majority of dunes do not reach heights of above 50 m. This type of dune landscape may extend for over 2 km inland from the beach, or in the case of present and former islands extend as a fringe around a central massif of high dunes (Fig. 2). These low dunes carry a dense vegetation of low forests and woodlands and heath (generally about lo-15 m in height) dominated by various species of Eucalyptus, Angophora, Tristania and Casuarina, with a dense shrub layer dominated by species of
Fig. 2. Portion of Fraser Island showing, from the right (1) a creek and adjoining swamps between stranded old foredunes. The general elevation here is less than 10 m above the beach which is 200 m beyond the right edge of the photograph. (2) Low dunes which had been partly mined; the elevation of this area of dunes lies between 5 and 50 m. The differences in toning represent rehabilitation of different ages up to 2 years old. (3) An unmined swamp with its herbfield and low shrub vegetation. (4) High dunes rising finally to 200 m. (5) A perched lake among high dunes.
363
Myrtaceae,
Proteaceae and Fubaceue (Fig. 3). Sedges are more common than grasses. Low lying areas between dunes are subject to water impoundment so that swamps and open lakes are common. Here the dominant trees are of Meluleuca while sedges and shrubs of Myrtuceae, Proteaceae, Fubaceae and Epacriduceue are profuse. The third landscape component is the high dunes in which the majority of dunes rises to heights of more than 50 m with peak heights of over 200 m being not uncommon. The vegetation is again a mixture of forest, woodland and heath, but with an overall tendency to greater height. The plant genera are largely the same as in the low dunes but different species (especially of Eucalyptus) may produce forests up to 35 m tall. These forests have been subjected to controlled logging for some 50 years following an earlier 50 year period of uncontrolled logging in which exploitation was concentrated largely on the rain-forests described later. The most striking type of vegetation in these dune areas is the sub-tropical rain forest discussed by Webb and Tracey (1975). There was originally a total area of 10 500 ha of this type of vegetation, particularly towards the northern end of the coastal dune belt, and most still exists though with some alteration due to selective logging. It is a tall closed-forest often over 30 m high growing on deep silicious sand, apparently after slow processes of succession to enable accumulation of the necessary nutrient mass. The fourth landscape component is the rolling heathlands and swamps which occur mainly at lower elevations on land of gentle topography. These Australian heaths are dense assemblages of sclerophyll shrubs generally l-2 m in height. They are dominated by genera from the families Myrtuceae, Proteuceae, Fabaceae and Epucridaceue; sedges are common in the ground layer and increase in density on wetter sites. The swamps already referred to among the low dunes can become extensive on low lying areas in units of 100 ha. In the wettest swamp areas the vegetation becomes a herbfield dominated by sedges and growing on acid bog peats up to 5 m thick. With a basic “soil material” consisting entirely of silicious sand the soils formed on these dune areas are a series of variants within the general groups of regosols, podzols and ground-water podzols. Organic cemented pan layers up to over 2 m in thickness are common in the ground water podzols. The fertility of these soils in their natural condition resides largely in the organic matter in the top 20-30 cm. The natural vegetation is well adapted to the low levels of fertility. This selective advantage can pose problems when chemical fertilisers are used to hasten the early establishment of vegetal cover during rehabilitation; some of the native species desired have evolved to the point of having a low tolerance for increased levels of phosphorus (Specht, 1975; Heddle and Specht, 1975). In addition to landform, soils and vegetation the factor of climate is also important to the conduct of successful rehabilitation. Over this long stretch of coastal dunelands the climate is mild and sub-tropical with increasing dominance of summer rainfall of high intensity from south to north. Total
364
annual rainfall is from 1 000 to 1 800 mm of which 50-65s falls in the summer months of November through March; daily rainfalls of 125 mm are common while cyclonic disturbances can yield daily totals of 375 to 500 mm. Such high daily falls contribute to high variability from month to month, and high run off; both can lead to problems in the early stages of rehabilitation after mining. Temperatures are generally mild with only a few light frosts. However, when good moisture conditions occur during the high levels of solar radiation in summer, plant growth can be rapid. As with any sand dune landscape the basic trend over long periods is intermittent change of landform on any given hectare. There is the typical cycle of sand movement, colonisation of bare sand by pioneer species, seral development continuing through minor short-term oscillations, with final loss of stabilising vegetal cover leading to a new phase of sand movement. All of these stages are to be seen in these coastal dune landscapes of the east coast. One of the most striking visual aspects of this sequence is the phase of bare sand movement through blow-outs. James Cook recorded their presence from 10 km offshore in the journal of his passage along the east coast in 1770 before the arrival of Europeans. Watt (1972) measured a total area of 5 235 ha of sand drift in these dune landscapes south of latitude 28”S, while Coaldrake (unpublished data, 1972) estimated the presence of 8 500 ha north of that latitude. This is 1.8% of the total area or roughly twice the area now successfully rehabilitated by the sand mining industry. The community at large has had time to come to accept these areas of sand drift as a natural part of the landscape. Perhaps with time they will also come to regard the different vegetal cover and visual aspect of developing rehabilitation as a part of the landscape. BEACH
MINING
Mining for heavy mineral sands on the east coast commenced soon after World War II with simple scraping from the tidal zone of seams of minerals that had been concentrated by wave action. This form of mining continues with modern earth-moving equipment, but access has become increasingly restricted due to conflict with recreational use of beaches. The seams mined are commonly from 2-10 cm thick, so that even if there are multiple seams the total bulk removed is small. Again, the beaches concerned may lose a thickness of up to 30 cm in 48 h, over the whole beach from the action of storm waves; this sand is normally re-deposited during ensuing calm weather in the normal oscillatory cycle of ocean beaches. Thus this form of mining is consistent with the natural cycle of beach behaviour. The only problem in rehabilitation is the backfilling of holes at a slope conforming to that of the beach nearby. The combined effects of wave swash, tides and winds remove any evidence of mining within a few days. The small areas of vegetated land above high water mark used for depots
and tracks are rehabilitated using the same methods as those discussed for coastal sand mining below. There is argument that removal of the heavy minerals (more than twice the relative density of ordinary beach sand) affects the stability of beaches, but there is no experimental evidence to prove this. There are plenty of stable beaches with little or no content of heavy minerals. DUNE MINING
The greatest extent of mining for heavy minerals on the central east coast is on the sand dunes from high-water mark upwards. Such mining has now been carried out, together with successful rehabilitation at heights of up to 130 m above sea level. The two basic methods of mining used are outlined later with some comment on important differences they create in regard to rehabilitation. The essential difference between the two methods is in the winning of the mineral-bearing sand from the ore body. The treatment for extraction of the minerals is the same once the sand enters the treatment plant. The basis of treatment at the mine site is common separation of all minerals out of a water-borne slurry by gravity. Final sorting of the separate minerals is done in electro-static and magnetic fields at central mills remote from the mine site; caustic soda is sometimes used in these mills to remove the coating of organic matter from mineral sand grains that are won from swamp beds or the organic hardpans of ground water podzols. But with regard to rehabilitation after mining the important point is that no chemicals are used at the mine site. In “dry” mining all of the mineral bearing sand is transported to a separation plant nearby for removal of the minerals. The tailings, which comprise 98-99.5X of the sand originally mined, are returned to the open cut as a water-borne slurry. For reasons of operational efficiency in dry mining the hole of an open cut is commonly open for 1 year or more before final re-contouring and spreading of topsoil. This reduces the effectiveness of the topsoil, especially as a source of seed, since the type of operation requires long term storage of the topsoil. In “wet” mining the ore body is removed by a suction dredge with cutterwheel. The dredge floats in a moving pond and is attached directly to a floating primary separation plant. This combined mining and separation plant moves through the ore-body with the tailings discarded directly at the rear edge of the moving pond. As with dry mining the tailings constitute 98-99.5% of the sand removed by the dredge from the front of the pond. This type of wet mining is used from high-water mark upwards to any elevation at which ore bodies occur and for which a water supply can be obtained t.o maintain the water level in the pond. In one variation of this basic process of wet mining a transportable separation plant with separate holding ponds for water stood alongside the mining path; both the
366
plant and the ponds were moved at intervals of a few months. This type of wet mining accounts for the majority of mineral sand mining on the east coast. With regard to rehabilitation it has the advantage that topsoil can be replaced much more rapidly than with dry mining. In some situations close to the sea, and where fresh water was in limited supply, sea water has been used for wet mining. This necessitates a delay between mining and rehabilitation to allow leaching of the salt from the sea water out of the top 30 cm or so of the new land. The delay required is purely a function of total rainfall. About 250 mm is required and it may need from 1 week upwards to achieve this total; delays of 12 weeks or more are possible in the drier months of winter. REHABILITATION
Over 20 years or so the coastal sand mining industry has developed considerable expertise in rehabilitation through a combination of its own efforts and technical advice from certain government agencies. Rehabilitation is now recognised by the industry as a separate problem requiring its own specialist professional planning and supervision. As commented on in the introduction to this paper the industry has to work under close public scrutiny, and its continuing access to ore bodies depends strongly on its performance in rehabilitation. In this paper space permits only a general discussion of the methods and problems of rehabilitation; for more detailed discussions the reader is referred to Barr and Atkinson (1970), Barr (1974), Thatcher and Westman (1975), Lewis (1976) and Brooks (1978). There are a number of distinct stages in the total process of rehabilitation after mineral sand mining. They relate primarily to the fact that the miner is, in almost every case, required to re-establish landforms and vegetation resembling the original as a condition of the mining lease that permits access to mineral on public land; and most of the mining is on public land. This requirement interacts with the fact that the sand to be stabilised is often in topographic situations where there is risk of wind-blown drift. The first stage in the whole process of rehabilitation is a survey of the contours and vegetation of the landscape before mining starts. This is accompanied by collection of seed of the commonest species of trees and tall shrubs present. The second stage is the stripping and stockpiling of topsoil including shrubs, after burning of large trees in situ so that the ashes are incorporated in the topsoil. The first two stages need to be closely related to the actual mining operation for several reasons. The requirement for a final landform that is close to the original can largely be met by the mining engineer through control of the distribution of tailings such that the use of bulldozers for final shaping and smoothing of contours is kept to a minimum. Slopes on the original dunes can be up to angles beyond the normal angle of repose of raw sand (32-34”) due to
367
Fig. 3. Sclerophyll woodland typical of much of the natural vegetation on the silicious sand dunes of the central east coast of Australia. This vegetation is well adapted to periodic burning which maintains a fluctuating balance between the shrub layer and the ground layer of sedges and grasses.
oversteepening when drifting sand spills under standing forest or woodland. Tailings can be stacked at the angle of repose, but there are difficulties in subsequent use of farm machinery if the final slopes to be rehabilitated exceed 15” ; Short lengths of slope of up to 25” can be worked on the basis of machinery working down the slope only. Short slopes of more than 25” can be rehabilitated by the use of spray-on mulching such as hydro-mulching or bituminous mulches. Unless there is a strict requirement to recreate identical landform (as in parts of future nature reserves) slopes are finished mainly at less than 15” so that farm machinery can be used freely in all directions. In this connection it should be noted that to the ordinary recreational visitor slopes steeper than 10” are perceptibly steep for climbing, and at 15 to 20” the effort of climbing becomes enough to dissuade many. The visual impact of a mixture of slopes of mainly less than 15” with scattered steeper areas is that of the essentially random landform of the original dune areas before mining. To all but the most determined critic these rehabilitated areas give a satisfactory blend of landform with the surrounding unmined areas (Fig. 4).
368
Fig. 4. The junction of mined and unmined land on low dunes 1 km from the beach at an elevation of about 30 m. This photograph, taken 18 months after mining, shows the blending of landform and early dominance by Acacia. Fig. 5 is a close-up of the topcentre of the rehabilitated area shown here.
In the second stage the handling of topsoil becomes a crucial part of the mining plan if the full benefits are to be gained from the use of topsoil. Storage in heaps near the mine path needs to be kept to a minimum time. After a few weeks of storage the viability of included seed of most of the native species concerned drops quickly. Storage beyond about 4 months leaves viable seed of only some hard-seeded plants such as Acacia spp. in the topsoil. There can also be degenerative changes in some fractions of the soil organic matter. Practical difficulties usually preclude the theoretically ideal practice of moving topsoil direct from its source to its final destination for immediate spreading. Once emplaced the topsoil fills the normal roles of supplying nutrients and seedlings, and provides some resistance to wind drift if enough litter is present. Where mining passes through large areas of bare sand as in the blowouts that occur naturally in these dune lands, or on the foredune where organically rich topsoil is often lacking, the methods are altered to offset this disadvantage. These alterations are made before and during the third stage of rehabilitatation. The lack of topsoil and the high exposure to wind are offset by the use of mulches and windbreaks (Fig. l), and by increased dressings of nitrogenous fertiliser. The primary stabilising grasses used are the native sand spinifex (Spinifex hirsutus) and south of about latitude 31”s
369
the introduced marram grass (Ammophila arenaria). Seed of other creeping herbaceous plants and seedling trees of Cusuarina and Banksiu are also planted. Away from the foredune the third stage of rehabilitation consists of seeding and fertilising into the topsoil with a mixture of species. The seed mixture commonly includes a cover crop of hybrid sorghum in warmer months, or cereal rye in cooler months; neither of these persists beyond a scattered second generation. These cover crops provide a first rapid cover while the slower growing native species establish. The seed mixture of native species used varies with the site but can be complex. It commonly includes Acacia which is a valuable pioneer species not only for its input of nitrogen to the soil but also for its litterfall. (Figs. 4 and 5). In some areas in recent years the placement of seed and fertiliser into the topsoil has been followed by the spreading of chopped mulch harvested from the shrub layer of woodland like that in Fig. 3. The early results suggest that this widens the range of native species that re-appear early, and enhances their growth. In most situations a light dressing of N-P-K fertiliser is used to stimulate the growth of the cover crop. Excessive use of phosphorus can raise prob-
Fig. 5. Close-up of portion of the area in Fig. 4. Note the dead stools of the cover crop of hybrid sorghum near the man’s right leg. The small tree he is touching is a self-sown seedling of Eucalyptus intermedia, probably from wind blown seed; the larger specimen, behind his legs is Tristania conferta from nursery stock. Both of these are major native trees. The bulky shrubs in the rear are Acacia cunninghamii from seed in the topsoil or from chopped mulch spread on this area before planting.
370
lems in subsequent growth of native species as discussed in an earlier section of this paper. In recent years there has been a trend to steady reduction of the content of phosphorus fertiliser to a point that is just sufficient for the cover crop. In cases such as dry mining with the loss of seed that follows lengthy storage of topsoil it may be necessary to use a perennial grass to provide stabilising cover and shelter for the nursery stocks and hand seeding of native species that is necessary. The most commonly used species is Chloris gayana (Rhodes grass); this practice is declining as skill increases in the handling of topsoil and seed of native species. After about 18 months the fourth stage of rehabilitation starts. This is a transition from cover crop and early fast growing native species such as Acacia to a wider variety of slower growing native species. This transition stage lasts about five years after which the Acacias especially begin to die out and to be replaced in bulk by a variety of other shrubs. These may be from seed in the topsoil, or seed harvested elsewhere and deliberately sown, or from nursery stock. This transition stage leads slowly into the longer stages of succession towards a native woodland or forest. It is hoped that the foregoing short account of rehabilitation conveys something of the elaborate methods that have been developed to engender re-establishment of native vegetation. Under the spur of necessity this branch of the mining industry in Australia has developed a high degree of skill in nurturing a range of Australian native plants. Little was known previously about the “horticulture” of many of these species under broadfield conditions. While there has not yet been time for mature woodland to develop completely there are no known cases of broadscale failure of areas treated properly by modern methods; some failures from the earliest attempts have necessitated a second treatment but the techniques now seem assured. Comparatively little attention has been given yet to the return of wildlife to areas under rehabilitation. It is a common experience to those who work extensively on rehabilitated areas that they attract numbers of kangaroos if these are still present in the general area. Birdlife can be profuse once there is a good cover of shrubs, though the number of species may be restricted. It seems reasonable to assume that a full range of wildlife will recolonise rehabilitated areas as the necessary range of habitats develops. In this connection it is interesting to note the results of a recent study by Fox (1978) on the return of ants to a rehabilitated area. In comparisons between unmined control areas and rehabilitated areas 4-11 years old she found that “species richness values, even for the younger plots are close to those of the control; however many more individuals were trapped on the mined plots.” THE TIME FACTOR
Some harsh criticism
has been levelled at the effectiveness
of rehabilita-
371
tion after coastal sand mining because, after 7-10 years, areas of rear dunes (away from the foredune) do not carry a mature woodland. It has frequently been claimed that the plant communities established will not persist. Such criticism overlooks one of the fundamental featues of a sand dune landscape - a sand dune only starts to form through drifting of bare sand. Thus any heavily vegetated dune only reaches such a state through natural processes of colonisation of bare sand by pioneer species followed by successional development of more complex communities. In the Australian situations involved the time scale is probably over 100 years. The essentials needed for these processes to continue once started are energy, water and nutrients in appropriate quantities, a stability of land surface, a source of propagules, and time for the processes to operate. The only one of these factors not in complete supply five years after rehabilitation starts is the supply of propagules of all species originally present. But the distribution of ore bodies is such that it is uncommon for the centre of a mined area to be more than 500 m from untouched vegetation in similar positions in the landscape. This is not a long distance for natural dissemination of propagules. These arguments, of course, do not apply to the complex ecosystem of sub-tropical rain forest but no large areas of this have ever been mined. In a few cases mining has removed all of a small area of a given type of vegetation so that the only native species to return are those planted by the miner. But such limited types of vegetation are now protected from mining. Except for these few special situations time is on the side of the miner once a limited range of native species has been established for 5 years. DIVERSITY
AND STABILITY
A criticism levelled strongly in recent years at the effectiveness of rehabilitation after coastal sand mining is that the reduced number of species present in the new plant communities in their early stages represents a loss of diversity that must lead to instability and eventual breakdown. This criticism, of course, rests on the concept that diversity begets stability which has been hypothesised as applying to vegetation by authors such as Margalef (1968). This theory was always difficult to accept with regard to these coastal dune landscapes. Here the seral processes start in such extreme and harsh environments as the foredune and the bare sand of blowout areas further inland; such extreme environments are not harsh to the few species adapted to them. Field work in such areas always produces evidence of the sharp reduction in number of species between mature woodland on inland dunes and the edge of the foredune, or a blowout area that is being colonised. The foredune community is as stable as anything can be on a piece of landform that comes and goes. The early communities on blow-
372
outs are, of course, replaced in due course by larger numbers of species but this form of instability is a necessary part of seral development. Finally, it is interesting that the sub-tropical rain forests on these dune landscapes with their assemblage of about 160 species recorded by Webb and Tracey (1975) are more difficult to restore from human interference or catastrophic storm damage than the other types of vegetation present. Their diversity does not seem to confer communal robustness. Margalef and others associated with the concept that diversity begets stability in plant communities revised their opinions, more or less to the point of reversal, in 1974 (Van Dobben and Lowe-McConnell, 1975). But this information has been slow to reach, much less to be accepted, by many of the critics of the effectiveness of rehabilitation after coastal sand-mining. SOCIAL
A~rTUDES
AND PLANNING
About one third of the total population of Australia lives within 40 km of the sea on the 1 200 km of eastern coast where much of the shoreline is occupied by these coastal dune landscapes. An activity so conspicuous as open cut mining is inevitably under close notice. For over 100 years until about 1970 Australian mining laws gave almost total preference to mining over other forms of land use. In the process of using such laws to its advantage the ming industry accumulated a large loss of goodwill with those sectors of the public not directly dependent on mining for a living. The placement of ore bodies close to large centres of population and the coastline used by those people for recreation, and the resentments generated by the industry’s early years of preferential access to land combined to produce a public acceptance of pressure to restrict access for coastal sand mining. The detailed reasons for this conflict, basically between temporary land use and outright preservation, are not the subject of this paper. But one of the results is of concern in relation to lost opportunities for proper planning for the use and management of landscape. In the pol~sation that has developed over the conflict mentioned above it has been difficult to achieve any long range strategic planning for allocation of dune landscape to a variety of land use. Over 20% is already allocated to total preservation in the Australian form of National Park, and a further 10% seems likely to be added. The argument over this allocation distracts attention and funding from the work needed to develop comprehensive guidelines for use and management of the remainder in ways compatible with dune landscape. The largest of the offshore islands, Fraser Island, has been partitioned largely between National Park (25%) and State Forest (in which camping is increasingly permitted). Only about 0.1% of the island is currently available for the commercial accommodation centres on which most Australians prefer to base their coastal recreation. In a recent Iengthy and costly public inquiry the CommisGoners were constrained by their terms of reference
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into considering coastal sand mining simply as a separate use of land, rather than as the first use in a sequence. Brooks (1978) lists ten different forms of land use which can sensibly follow mineral sand mining and its attendant rehabilitation. On the coastal lands concerned two of these, tourism-recreation and urban development, are increasingly sought. Each is well suited to the land form and vegetal cover that can be created after mining but, with a few notable exceptions, this type of planning for a sequence of uses does not happen at present. ACKNOWLEDGEMENT
This paper condenses my experience over many years during which I have benefited from field trips and discussions with staff of many sandmining companies, government agencies and Universities. They are too numerous to thank individually.
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314 Specht, R.L., 1975. The effect of fertilisers on sclerophyll (Heath) vegetation. The problems of revegetation after sand mining of high dunes. Search, 6: 459-461. Stevens, N.C. and Monroe, R.W., 1975 (Editors). Stradbroke Island Symposium. Proc. R. Sot. Queensl., 86: l-146. Thatcher, A.C. and Westman, W.E., 1975. Succession following mining on high dunes of coastal south-east Queensland. Proc. Ecol. Sot. Aust., 9: 17-33. Thorn, B.G., 1965. Late Quaternary coastal morphology of’the Port Stephens-Myall Lakes area, N.S.W. J. R. Sot. N.S.W., 98: 23-36. Thompson, C.H. and Ward, W.T., 1975. Soil landscapes of North Stradbroke Island. Proc. R. Sot. Queensl., 86(18): 9-14. Van Dobben, W.H. and Lowe-McConnell, R.H., 1975. Unifying Concepts in Ecology. W. Junk, The Hague, 302 pp. Watt, B.G., 1972. An assessment of coastal sand drift in New South Wales. J. Soil Conserv. Serv. N.S.W., 28: 7-21. Webb, L.J. and Tracey, J.G., 1975. The Cooloola Rain Forests. Proc. Ecol. Sot. Aust., 9: 317-321.