J.M. Sarrailh and N. Ayrault
Jean Michel Sarrailh is Programme
Leader at the Institut agronomique
néo-Calédonien (IAC), Nouméa,
Nathalie Ayrault is an intern from
the École Supérieure d'Agro-Économie
assisting the Programme Leader for
Mining Rehabilitation in
Tonghoué-Dumbéa, New Caledonia.
Although rehabilitation of open-pit mines is not yet required by law in New Caledonia, mining companies are revegetating nickel mining sites in response to popular environmental concern.
New Caledonia, a South Pacific archipelago, has the fourth largest nickel deposits in the world, with 11 percent of the world's reserves (International Nickel Study Group, 2000). Today, with major mining companies moving into the country and large tracts being worked with open-pit methods, mining rehabilitation is a subject of major concern to New Caledonians. New Caledonia has an exceptional endemic plant and animal wildlife, and needs to bring the rush for the green gold - "King Nick" as it is called in the islands - under control.
The government, mining companies and research centres are studying the major problems involved in mining rehabilitation, in a context that is sometimes economically, environmentally, scientifically and politically difficult.
Mining of steep terrain, in the absence of environmental regulations, led to siltation of streams (lower left) that carry the wastes downhill; a new mining site is visible on the upper crest (Monastir, New Caledonia)
- J.M. SARRAILH
New Caledonia's land area of 19 000 km2 is spread over an area 500 km long by 50 km wide. Half the main island, Grande-terre, is made up of ultrabasic rocks (rocks very low in silica and rich in ferromagnesian minerals), witnesses to the sliding of the Caledonian plate over the Earth's crust. This rock layer is made up mainly of peridotite, which becomes nickel ore, making New Caledonia the eighth largest producer of this metal in the world (after the Russian Federation, Japan, Canada, Australia, Norway, Finland and China) (International Nickel Study Group, 2000).
Since 1950, the mechanization of mining processes has allowed a considerable increase in extraction. The deposits, lying under a covering of laterite soil, have become accessible, and there is now large-scale production of waste material (tailings). Until the mid-1970s, in the absence of any regulations, the mining companies burned the vegetation when prospecting and systematically tipped the tailings downhill (Jaffre and Pelletier, 1992).
The inhabitants of New Caledonia tolerated the environmental damage caused by mining for a long time. The areas where nickel is found are fairly infertile, with soil unfavourable to traditional farming methods, so that until the 1970s the village or tribal way of life was barely affected by mining activities. However, people became more concerned when pollution began to infringe on their way of life. Sediments began to block rivers until farmland downstream was impoverished or even swallowed up, and finally polluted the lagoon. Large columns of red smoke hang in the air above Nouméa. The open wounds on the sides of mountains that used to be seen as signs of economic wealth are now seen as a major problem. People's concern has particularly been demonstrated through community action.
The tourism sector has also played a large part in pressing the mining companies to take environmental action. Tourism is economically important in New Caledonia, and the red sediments from the nickel mines began to be a threat to its white coral sands. With the development of both the mining industry and tourism (and the tertiary sector that goes with it), these two economic poles have entered into conflict.
Pressure has grown steadily. People are concerned over damage expected to result from the establishment, in a very brief interval, of two mining sites: one by the Canadian company Falconbridge in association with SMSP (Société Minière du Sud Pacifique), and the other by Inco. Each has an annual extraction capacity of 60 000 tonnes, on average 80 percent ferronickel and 20 percent matte (a mixture of nickel and iron sulphides formed during smelting). The Inco project, Goro Nickel, is located close to a protected zone. An outcry over wastewater discharged into the lagoon by the Inco factory, which uses hydrometallurgic processes, is a clear sign of local people's concern.
In the 1970s, after people started to protest, the mining companies were forced to stabilize wastes and to seek new prospecting and extraction techniques. For some years now, the mining methods used have been more respectful of nature. New techniques developed for opening up mines and storing wastes now protect sites against erosion (Jaffre and Pelletier, 1992). Bulldozers are no longer used. Topsoil is set aside for future use in revegetation. The main companies have been implementing revegetation programmes, although as yet no legal constraints force them to do so. Thus companies are adopting various rehabilitation strategies to improve their environmental image and to avoid conflicts with the communities where they carry out their activities.
A project to police mining activities for compliance with New Caledonian laws (still awaiting passage) is currently being developed under the Mining and Industry Service. A legal framework needs to be set up as quickly as possible so that this control can also apply to mining revegetation activities.
At Poya, New Caledonia, efforts have been made to reduce the environmental impact of mining, with construction of holding pools, site reconstruction and stabilization of wastes
- J.M. SARRAILH
The New Caledonian flora is rich in over 3 000 species of flowering plants and has an exceptionally high endemicity level: two-thirds of the area's species fall in the endemic category. Such a variety concentrated in so small a space is a source of great vulnerability, and some species have vanished even before being catalogued or studied. In all, 1 137 species are endemic both to the country and to the mining areas.
There is a risk of extinction for 32.4 percent of the species forming the "mining scrub", the shrubby formation found on soils formed from ultrabasic rocks (peridotite and serpentinite). Thus, even if there are a number of plant and animal wildlife reserves, management of this heritage depends essentially on the protection measures that the mining companies take with regard to the vegetation (Jaffre, Rigault and Sarrailh, 1994).
It is hard to regenerate the destroyed vegetation over nickel mining sites, since the soil is fairly infertile (generally deficient in phosphorus, potassium and nitrogen), as well as being high in toxic elements (nickel, magnesium) and very vulnerable to erosion. The natural process of recolonization by degraded species is extremely slow and sometimes simply does not happen. However, research carried out mostly by the Insitut de recherche pour le développement (IRD) and the International Cooperation Centre on Agrarian Research for Development (CIRAD) has facilitated the development of techniques necessary for revegetation.
Large-scale revegetation work did not start until the mid-1990s, by SLN (Société Le Nickel) in 1993 and by SMSP in 1997. In the absence of any legal obligation, each mining company has been developing its own strategy, bearing in mind its financial constraints.
With a view to reducing the damage caused to slopes by runoff, the companies carrying out revegetation have been using exotic species such as acacias or Graminaceae in order to produce a fast and inexpensive groundcover that will check erosion. However, it is hard to prevent introduced species from competing with endemic species, which ensure longer-term revegetation.
Fast-growing native species such as Acacia spirorbis and Casuarina collina are nitrogen-fixing species and improve environmental conditions. The behaviour of these species is well known and easily managed from planting to harvesting, so they are the most widely used. At least in the early stages, however, they prevent regeneration of the pioneer species of the mining scrub.
The present trend is increasingly towards revegetation by planting endemic New Caledonian scrub species suited to the substratum in order to recreate the original biodiversity. About 30 species can now be propagated, although their slow growth sometimes necessitates a high planting density (10 000 plants per hectare) in order to give sufficient ground cover. Certain faster-growing shrubs - such as Proteaceae (Grevillea spp.), Myrtaceae (e.g. Carpolepis laurifolia) and various species of the Casuarinaceae family (e.g. Gymnostoma deplancheanum) - allow more reasonable densities (2 500 plants per hectare).
Hydroseeding - a technique using a mixture of mulch, vegetable glue, nutrients, mineral and organic fertilizers and seeds of different species, projected by a hydroseeder (a pump mounted on a truck) - is now starting to be used on the slopes, with a mixture of fast-growing Graminaceae and endemic Cyperaceae whose germination is often slow (e.g. Costularia comosa, Schoenus juvenis). This approach is still in its very early stages and is badly hampered by excessive costs and difficulties in obtaining seeds (with 5 000 seeds needed per square metre).
Hydroseeding on the Koniambo site, New Caledonia, carried out by an Australian company for Falconbridge/SMSP; the hydroseeding mixture includes a biodegradable paint toindicate where mulch has been applied
- J.M. SARRAILH
The main problem is the harvesting of seeds. The process has so far not been properly organized, and harvesting dates are variable. Moreover, conservation methods have not yet been perfected, so that the germination rate falls very rapidly and seeds quickly become useless. This problem acts as a constraint on every system of revegetation, hydroseeding and planting.
In addition, slow-growing seedlings have to be kept in the nursery for over a year. Another constraint is that planting is always done by hand, since the seedlings are produced in large polythene bags. This laborious work accounts for half the price of a planted seedling.
When added together, all these factors make the cost of revegetation exorbitant.
In the absence of any legal framework, the mining companies have developed different strategies and priorities.
SLN carries out rehabilitation through a private company that uses both planting and hydroseeding methods and covers every process from harvesting to planting, using a wide variety of species. The company's revegetation budget is limited, so only small areas are treated; the company explains this by claiming that it has a voluntary policy of species protection. Since 1993 the company has planted a total of 300 000 seedlings, which represents treatment of less than 10 percent of the mined surface.
SMSP has its own environmental department and works with small companies that are mainly concerned with planting seedlings. Initially this company focused on the use of rapid-growing local species (Acacia spirorbis and Casuarina collina) to recolonize large areas. Endemic species are also used (Sarrailh, 1997). Since 1997, SMSP has planted nearly 50 000 seedlings on mining sites. The company also carried out hydroseeding tests at the end of 2000.
Inco's Goro Nickel project has to cope with another problem: its smelter is located on a site where many species endemic to the zone grow. These species are not found anywhere else in New Caledonia or the world, and they must therefore be conserved at any cost. Goro Nickel has thus launched a programme of "advance revegetation" to propagate rare species ( Retrophyllum minor and Araucaria muelleri) that will be destroyed on the site.
Falconbridge-SMSP has started mining exploration with a view to setting up a smelter in the north of New Caledonia. Anticipating that there will be large areas to be rehabilitated, it is seeking a low-cost revegetation method in order to restore the original biodiversity. It has shown a clear interest in hydroseeding, with a policy of introducing Graminaceae in order to create a favourable environment for the artificial and natural reintroduction of endemic species.
Harvesting of seeds of Grevillea exul var. exul, Koniambo site, New Caledonia
- N. AYRAULT
Most of the old (pre-1975) mines have been "orphaned" - the companies that worked them no longer exist. These older mines are therefore being rehabilitated by local communities. The South Province rehabilitated 8 ha at the De Rouvray mine in 1993, and 13 ha in 1999. The Odette mine was totally rehabilitated in 2000, accounting for an area of 10 ha. There are, however, still 900 ha of old mines scattered around the country.
For a long time, mining extraction disfigured certain regions of New Caledonia without causing much reaction from the inhabitants. New Caledonia now has a new Constitution (under the Nouméa Accord of 5 May 1998) which allows for the establishment of new mining regulations. Rehabilitation of mining sites will probably be made obligatory. Such revegetation must reconcile limited budgetary means with a minimum of environmental restoration and the treatment of large areas. Rehabilitation is already starting to take account both of the variety of species in the original environment and of the conservation of rare species found around the mines.
In view of the variety of plant life in the mining scrub, the preferred strategy is to initiate the normal ecological succession using low-cost techniques, so that the environment can then enrich itself naturally in terms of biodiversity, and plant and animal wildlife can be progressively restored.
The use of Acacia spirorbis and Casuarina collina brings fast results, but the Mine and Energy Service of New Caledonia has realized that these species should not be planted unmixed with others or too close together. They are therefore now used mainly on the edges of slopes for landscaping purposes.
Slower-growing species from the mining scrub, such as Grevillea exul, Carpolepis laurifolia, Dodonea viscosa, Arillastrum gummiferum and Alphitonia neocaledonica, are usually used on the flat parts of open-pit mines. The price of these seedlings is now not much higher than that of Guaiacum officinale and Casuarina collina. This approach is thus a good compromise to bring about the relatively fast reconstitution of the original vegetation (Sarrailh, 2001).
Despite the steady fall in the price of seedlings, planting is still costly. Direct sowing through hydroseeding seems the only real means of reducing the costs of revegetation. At present there is still the problem of obtaining enough seeds of local species, but this problem could be solved by setting up seed orchards and improving harvesting techniques.
Jaffre, T. & Pelletier, B. 1992. Plantes de Nouvelle-Caledonie permettant de revégétaliser des sites miniers. Nouméa, New Caledonia, ORSTOM (IRD) & SLN.
Jaffre, T., Rigault, F. & Sarrailh, J.M. 1994. La végétalisation des anciens sites miniers. Bois et Forêts des Tropiques, 242(4): 44-55.
International Nickel Study Group. 2001. Current statistics on nickel. Internet document: www.insg.org
Sarrailh, J.M. 1997. Native or exotic plants for mining sites. Experiments in New Caledonia. In Forage production and rehabilitation of mine sites, NAPPEC Regional Workshop, p. 41-44. Nouméa, New Caledonia, Commission Pacifique Sud.
Sarrailh, J.M. 2001. Bilan des recherches menées par l'IAC sur la revégétalisation des sites miniers. Nouméa, New Caledonia, Institut agronomique néo-Calédonien (IAC) Forêt.