Structural features of old-growth Australian montane ash forests

We examined structural features of montane ash stands that varied from 15 t o 300+ years of age in the Central Highlands of Victoria, south-eastern Aus tralia. Extensive field data were gathered for our investigation and were d rawn from >3700 survey plots on >625 sites located throughout the study reg ion. Much of our study focussed on understorey features because extensive p ast studies in these forests have highlighted their importance as key habit at components for wildlife. A wide range of stand features, including the a bundance of shrubs, the prevalence of tree ferns, the presence of Acacia sp p., the presence of Myrtle Beech (Nothofagus cunninghamii), and the number of vegetation strata (a measure of vertical heterogeneity) varied considera bly between age classes; most attributes were significantly (p < 0.001) les s likely to occur or were significantly less abundant in young logged fores ts. Highly significant differences in these structural features also were f ound in stands dominated by different tree species (Mountain Ash [Eucalyptu s regnans] and Alpine Ash [E. delegatensis]). The traditional view of disturbance in montane ash forests is that of high- intensity stand-replacing wildfires which produce even-aged regrowth forest s. However, our data suggest that low-intensity, non-stand-replacing fires or only partial stand-replacing fires, have occurred in many old-growth mon tane ash stands, both to create multi-aged stands and to re-juvenate compon ents of the understorey - a process leading to asynchrony in the ages of un derstorey and some elements of the overstorey. Thus, the structural variabi lity, and the patterns of natural disturbance leading to such conditions, a ppears to be more complex than often previously recognised. This has import ant implications for both nature conservation strategies and timber harvest ing practices in montane ash forests. Existing high-intensity clearfell log ging operations produce an even-aged dominant overstorey as well as underst orey and overstorey plants of the same age. If logging effects are to more closely resemble natural disturbance regimes and promote structural complex ity in stands of harvested forest to enhance wildlife habitat values, then a wider range of types of harvesting methods (in addition to clearfelling) need to be employed. (C) 2000 Elsevier Science B.V. All rights reserved.