Revegetation of old mining sites in New Caledonia.
The extraction of nickel ore from open cast mines in New Caledonia results in the removal of several hundred hectares of surface substrate. The different types of exposed substrate on mined sites lack essential plant nutrients such as N, P, K and Ca. They have a low pH and often high Ni and Mg concentrations. Data are presented for afforestation trials carried out at various sites in New Caledonia. On desaturated ferralitic soils (low in Ni), a single application of NPK fertilizer at time of planting allowed exotic tree species (Pinus caribaea, Acacia dealbata) and kikuyu grass (Pennisetum clandestinum) to establish; two indigenous nitrogen-fixing species (Acacia spirorbis and Casuarina collina) gave the best results. On substrates dominated by yellow laterite, all exotic species tested gave mediocre results; of local species tested, only C. collina and A. spirorbis showed significant growth. On saprolitic substrates, encouraging results have been obtained for approximately 20 indigenous species, notably in the families Cyperaceae (Baumea deplanchei, Costularia comosa, Schoenus juvenis and S. neocaledonicus), Casuarinaceae (G. deplancheanum and C. collina), Myrtaceae (Carpolepis laurifolia), Verbenaceae (Oxera neriifolia), Proteaceae (Grevillea exul) and Euphorbiaceae (Phyllanthus aeneus, P. buxoides and Longetia buxoides [?Austrobuxus sp.]). There have also been promising results for about 10 other species. The overall results obtained for numerous endemic ultramafic plant species grown on a variety of sites with different edaphic conditions, indicated the potential importance of local species for the revegetation of old mine sites.