5. Conclusions
Natural forest ecosystems have many indigenous pathogens associated with them, but genetic and age diversity of the host community prevents disease epidemics. This is the situation in undisturbed eucalypt forests in Australia. Disturbed ecosystems and plantations, however, are more susceptible to outbreaks because of a reduction in both genetic and age diversity and because of increased external stress. Observations and records of eucalypt pathogens and diseases in Australia are increasing. In addition, many new diseases are emerging on exotic eucalypt plantations throughout the world, especially in the tropics and sub-tropics. These emerging diseases pose a threat to native eucalypt forests in Australia. Vigilant and strictly applied quarantine measures are necessary to prevent the introduction of potentially devastating pathogens into Australia.