ISSUES ASSOCIATED WITH THE RETENTION OF HOLLOW-BEARING TREES WITHIN EUCALYPT FORESTS MANAGED FOR WOOD PRODUCTION

The conservation of hollow-dependent fauna is a major forest managemen t problem in natural eucalypt forests managed for wood production. Euc alypt forests support a diverse fauna that utilise hollows in trees. H ollow-bearing trees are a component of forest structure often lost or substantially modified as a result of timber harvesting operations, es pecially those that are intensive (like clearfelling) and take place o n a short rotation (< 120 years). One approach adopted to conserve pop ulations of hollow-dependent fauna in eucalypt forests has been to ret ain suitable trees in logged areas. This paper reviews a wide range of issues associated with the retention of such trees ranging from: (1) the characteristics of trees which should be selected for retention; ( 2) the number and spatial arrangement of retained stems; (3) the need for recruitment of new hollow-bearing trees to ensure there is a perpe tual supply of such resources; and (4) how best to protect those trees that are retained. We also consider factors such as the inter-relatio nships between tree retention strategies and silvicultural requirement s, and on-site tree retention strategies and forest management at the landscape-scale. A major conclusion from our study is that the array o f issues associated with the retention of trees with hollows in eucaly pt forests is considerably more complex than reflected by current mana gement practice. Indeed, it appears that most existing prescriptions f or the retention of trees with hollows in logged sites may not ensure a perpetual supply of a range of types of hollow trees or provide the necessary habitat conditions to support viable populations of some spe cies of hollow-dependent fauna. This is because current prescriptions typically do not take account of factors such as: the prolonged period s until hollows first begin to develop in Eucalyptus trees; mortality and collapse amongst retained stems; and the need to supply trees with suitable characteristics and in a suitable configuration to meet the requirements of the full range of vertebrate tars that utilise this re source. Taking these factors into account, we conclude that only modif ied partial cutting systems would adequately provide for the needs of all cavity-using species across logged sites in eucalypt forests. A ma jor problem confounding attempts to develop more informed prescription s for the retention of trees in logged areas is a lack of data on key topics such as stem longevity and hollow ontogeny, mortality of retain ed trees on logged sites and cavity use by animals. There is scope for some of these data to be readily gathered in routine timber assessmen t and inventory, stand regeneration surveys and fauna and vegetation s urveys. We recommend that forest and wildlife management agencies revi ew their field survey methods and include some new measures among the rang of data collected. There is also considerable merit in instigatin g new tree and forest modelling projects to simulate long-term stand c onditions in wood production eucalypt forests. Such studies would guid e forest and wildlife managers in the development of tree retention st rategies needed to create and maintain stand characteristics suitable to support populations of hollow-dependent wildlife over not one, but many rotations. Given the uncertainty associated with the effects of t hese operations on hollow-dependent fauna, and continued timber harves ting operations in these forests, we recommend a strategy which mainta ins a variety of approaches to management. Such a strategy is akin to 'risk spreading' and would involve implementing a range of tree retent ion strategies within cutting areas as well as the adoption of a numbe r of strategies at the landscape level (e.g. wildlife corridors).