Orchid species succession in rehabilitated bauxite mines in Western Australia

Twenty-three orchid species were recorded in Alcoa's permanent vegetation-monitoring plots in unmined and rehabilitated jarrah forest. Of these, 22 were identified in the unmined jarrah forest and 20 were recorded in rehabilitated areas of between 1 and 31 years old. Three species (Cyrtostylis ovata, Lyperanthus serratus and Prasophyllum elatum) were only recorded in the unmined forest and one species was only recorded in rehabilitated areas (Diuris carinata). The overall density of native orchids in the forest was 13 755 plants ha–1, 10 times greater than the density in rehabilitated areas (1381 plants ha–1). The most abundant species in the forest were Cyrtostylis robusta, Caladenia flava, Pterostylis nana and Thelymitra crinita, all with densities greater than 1000 plants ha–1. The most abundant species in the rehabilitated areas were Microtis media, Disa bracteata (an introduced species), Caladenia flava, Pterostylis nana, Diuris longifolia and Pterostylis vittata, all with densities greater than 60 plants ha–1. In rehabilitation older than 10 years, the density of orchids increased to 2685 plants ha–1. Burning in rehabilitated areas resulted in large increases in orchid densities. It is believed that orchid colonisation of rehabilitated bauxite mines is dependent on symbiotic mycorrhiza, which are in turn dependent on development of an organic litter component in the soil.