RECOVERY OF TERRESTRIAL ORCHIDS IN THE POST-MINING LANDSCAPE

Abstract

Currently, Alcoa World Alumina Australia mines and rehabilitates ca. 550 ha of jarrah forest each year at two open-cut bauxite mines in Western Australia. The aim of Alcoa's rehabilitation program is to re-establish a functional and self-sustaining jarrah forest ecosystem in these mined areas. Many in- digenous geophytic plant species, however, fail to re-establish or do so very slowly. Indigenous terrestrial orchids form a significant proportion of the species difficult to re-establish. The dominant source of orchid propagules within the rehabilitation areas is wind-dispersed seed. Recruitment of new plants is dependent on availability of both viable seed and appropriate mycorrhizal fungi in the soil of suitable microhabitats at the beginning of the wet season. Flora surveys were undertaken to determine orchid species and their density in a temporal sequence of rehabilitation areas, so as to establish the sequence of species recovery. Total orchid population and clonal orchids were found to have returned to rehabilitation areas within 5 years at densities not significantly different from those of adjacent unmined forest. Numbers of total species and clonal species also were found to have returned to rehabilitation areas within 5 years at densities not significantly different from those of adjacent unmined forest. Orchid species identified as disturbance op- portunists returned to rehabilitation areas within 5 years with densities increasing during the following 10 years but dropping to numbers not significantly different from those of adjacent unmined forest after 25 years. No disturbance opportunists were found in any unmined forest. Future studies will investigate the recovery of selected individual species in rehabilitation areas, vegetation associations of these species in both unmined forest and rehabilitation areas, and the diversity of their mycorrhizal fungi.