Forest Pathology Special Issue on ‘Root‐rot diseases in acacia and eucalypt plantations in Indonesia: their biology, field behaviour and management’

Abstract

Various species of Australian acacia and eucalypt trees have been widely planted in plantations and smallholder woodlots throughout South-East Asia. With over 7 M ha now planted, these non-native trees have become an important part of the wood supplies for Asian forest industries and generate very substantial livelihoods for smallholders in many parts of Asia. In Indonesia, the pulp and paper industries and their associated plantations combined directly employ around 1.5 M people and contribute around 1.8% of GDP. Maintaining the health of the plantations and sustaining their productivity are of critical importance as these resources form a crucial part of the wood supply to large pulp mills and many furniture industries.As these exotic plantations estates age, their viability is increasingly threatened by insect pests and pathogens. These include those that are introduced accidentally, as well as 'new encounter' insect pests and pathogens that are undergoing host shifts to attack the acacia and eucalypt trees. Two of the most important pathogens that have shifted to non-native trees are basidiomycetes (Ganoderma and Phellinus spp.), which cause root-rot disease. In this case, these root-rot fungi are present in the native forest and remain in infected stumps and roots as inoculum sources when this original forest is cleared for plantations. Root-rot disease build-up in acacia and eucalypt plantations is rather similar to that observed in oil palm and rubber plantations from one rotation to the next. However, because pulpwood rotations are generally only 5 to 6 years, compared with 25 years for oil palm and rubber, there is accelerated disease development, such that in some areas, tree death can exceed 50% within 20 years of establishing the first pulpwood plantation.The Government of Indonesia has an ambitious plan to expand the area of smallholder plantations by 5.4 M ha to provide wood resources for the expanding pulp and paper industries. Growth rates of Acacia mangium in Sumatra, where the majority of the industrial plantations have been established, ranged between 22-35 m 3 /ha/years before being impacted by root-rot disease. However, studies have shown that smallholders currently achieve yields of only around 50% of potential yield from their first-rotation plantations, due to lack of knowledge and/or application of appropriate management, including disease management. More recently, another disease Ceratocystis has also had significant impact on the productivity of A. mangium plantations through widespread tree death. Together these diseases have reduced A. mangium plantation productivity to unacceptably low levels, forcing a switch to Eucalyptus pellita. However, E. pellita is also vulnerable to root-rot as well as other diseases, so this may not be a viable long-term strategy.The Australian Centre for International Agricultural Research (ACIAR), through its Forestry Program, has invested in collaborative research on the management of forestry pests and diseases in South-East Asia since the early 1990s. ...