Phytophthora Root and Collar Rot in Rehabilitated Bauxite Mines and the Adjacent Eucalyptus Marginata (jarrah) Forest of Western Australia

Western Australia is unique in its botanical diversity. There are over 7000 species of native vascular plants of which over 3000 are endemic (Keighery 1992). Phytophthora cinnamomi has a major impact on this diverse flora and directly effects over 2000 species from a diverse range of plant families (Wills 1993). Its indirect effects in terms of botanical impact through the loss of vertebrate and invertabrate pollinators, and loss of canopy and litter cover has not been measured. The pathogen was probably introduced into the state with the importation of nursery plants in particular fruit trees at the turn of the 20 century. The pathogen was then spread into the natural ecosystems principally by road building, forestry and other humankind activities. This spread has had a major impact in the jarrah forest, banksia woodlands and heathlands in the lower southwest of the state. The pathogen is an excellent example of an introduced pathogen with a wide host range causing considerable damage to a diverse community made of many susceptible plant species. In Western Australia, the majority of past and current research on this pathogen has been conducted in the jarrah forest. This has been because P. cinnamomi has had a considerable impact on the ecology and management of the jarrah forest (Shearer and Tippett, 1989). The research was concentrated in the jarrah forest, since jarrah is an economically important hardwood species. However, more recently, research activities have also centered on the rehabilitation of bauxite mines. The jarrah forest in Western Australia is also the location of one of the largest and most productive bauxite mines in the world (Colquhoun and Hardy, 2000). The bauxite mining and alumina refining company, Alcoa Worldwide Alumina-Australia, supplies 22% of the world’s alumina. In the jarrah forest, Alcoa mines and rehabilitates approximately 500 ha of forest annually. Although P. cinnamomi is estimated to only impact on 14% of the forest (Davison and Shearer 1990); many of Alcoa’s ore bodies encompass areas of forest free of the pathogen. Since, P. cinnamomi is spread in soil and water the management of this pathogen between pathogen-free and pathogen-infested pits is daunting.