1CSIRO Forestry and Forest Products, PO Box E4008 Kingston, Canberra, ACT 2604, Australia; 2University of the Orange Free State, PO Box 339, Bloemfontein 9300, South Africa

Plantation forestry is expanding in many countries as future availability of wood from native forests is declining through deforestation, reservation for conservation purposes and improved sustained yield management. Expansion of plantations can provide alternative sources of wood for fibre and solid timber products to meet worldwide demand. In addition, plantation establishment on former farm or pastoral land can assist in amelioration of land degradation.

Australian native trees, especially Eucalyptus, Acacia and Casuarina, have proved to be extremely useful plantation species in many parts of the world, with several million hectares of exotic plantations established in tropical, sub-tropical and temperate regions, especially during the past three decades. Pinus spp., native to the Northern Hemisphere, are also widely grown as exotics, especially in the Southern Hemisphere. Plantation expansion has been accompanied by the appearance of a range of disease problems. Some of these have threatened the continuing productivity of plantations in some areas and influenced the choice of species in others.

Examples are given to illustrate the likely origins of epidemics in exotic plantations of these species. Examples include adaptation of pathogens from related indigenous hosts, transfer of pathogens with a broad host range from locally grown crops to plantation trees, and the possibility of movement of pathogens in germplasm.

Australia benefits from its geographic isolation, which reduces the risk of incursions of exotic pests and pathogens. The establishment of major plantation resources based on Australian trees in the Asia-Pacific region and elsewhere has increased incursion risk by providing dispersal pathways for newly encountered pathogens. Such pathogens, if they breach quarantine barriers, could severely impact on both conservation and commercial values of native forests.

Large quantities of seed are currently being moved internationally to meet the demands of plantation establishment. There is a potential for pathogen movement in tree germplasm that is largely unrecognized. The shrinking global village demands that forest pathologists take a pro-active approach to the definition and prevention of future problems.