The Conservation Of Arboreal Marsupials In The Montane Ash Forests Of The Central Highlands Of Victoria, South-Eastern Australia - VII. Modelling The Persistence Of Leadbeater's Possum In Response To Modified Timber Harvesting Practices

A computer model for Population Viability Analysis (PVA) was used to simulate the relationship between the persistence of populations of the endangered species, Leadbeater's possum, Gymnobelideus leadbeateri and the implementation of a range of possible modified timber harvesting practices in two wood production blocks within the montane ash forests of the central highlands of Victoria, south-eastern Australia. The results of our analyses revealed that under the existing conservation strategies there was a high probability of extinction over the next 150 years in both blocks. Given that timber production areas comprise more than 75% of the distribution of G. leadbeateri, our findings highlight a need for additional conservation measures to enhance the survival prospects of the species. The range of upgraded conservation strategies that were examined included (1) extending the rotation time between logging operations; (2) modifying silvicultural practices to increase the amount of forest retained within each harvested coupe; and (3) permanently withdrawing areas from wood production. All of each of these approaches were found significantly to reduce the probability of extinction of populations of G. leadbeateri. However, when the relative merits of the various strategies were compared, the permanent withdrawal of potential logging coupes from timber harvesting was predicted to be the most efficient approach. Importantly, this strategy would have a number of practical advantages including that it overcomes both (1) the logistic difficulties of ensuring the long-term survival of retained trees within logged areas; and (2) human safety issues arising from implementing modified silvicultural practices. This practical application of PVA to compare the merits of different potential management options has provided new information that will enhance present efforts to conserve G. leadbeateri in wood production areas

The effects of slash burning on the mortality and collapse of trees retained on logged sites in south-eastern Australia.

Trees may be retained on logged sites in eucalypt forests for a number of reasons, such as to provide wildlife habitat, for future wood production, for aesthetic reasons, to mitigate erosion, or to provide seed for regeneration. These trees may be required to survive for a considerable period to meet these objectives. Logged sites in eucalypt forests are routinely treated with a post-logging slash-burn to reduce fuel loads and facilitate regeneration. We compared rates of mortality and collapse among trees retained on logged sites that were routinely treated with a high-intensity slash-burn with logged sites routinely treated with a low-intensity slash-burn. All observations were made 2-5 years after logging. The proportion of all retained trees that were killed after logging was 37% on sites treated with a high-intensity slash-burn and 14% on sites treated with a low-intensity slash-burn. The rate of collapse among retained trees over the same period was 1.5 and 0.5%, respectively. Results of logistic regression models indicated that trees retained on logged sites were more likely to die and collapse if the site was treated with a high-intensity slash-burn; however, trees were also more likely to die if the basal area of trees retained on the site was relatively low and the site had a northerly aspect. Mortality was similar among all diameter classes on sites treated with a high-intensity slash-burn. Some of the objectives of retaining trees on logged sites, such as perpetuating hollow-bearing trees for wildlife, may be compromised where high-intensity post-logging slash-burns are employed

Hollow selection by vertebrate fauna in forests of southern Australia and implications for forest management

We examined the types of hollows, and types of hollow-bearing trees, occupied by vertebrate fauna in temperate eucalypt forests in southeastern Australia. Hollow-bearing trees are selected for retention in wood production forests to mitigate the effects of logging on hole-nesting fauna. A total of 471 hollows was examined in 228 trees felled as part of routine logging operations. Fauna had occupied 43% of all hollows (≥2cm minimum entrance width; ≥5cm depth). Hollows with small (2-5cm), medium (6-10cm) and large (>10cm) minimum entrance widths had occupancy rates of 29, 44 and 62%, respectively. The internal dimensions of hollows, especially hollow depth, were the best predictors of hollow occupancy, even when variables measured at the tree and site levels were considered. Fauna occupied 57% of all hollow-bearing trees. In a Poisson regression model, the number of hollows in trees that contained evidence of occupancy was positively associated with: (1) the total number of hollows visible in the tree; (2) the proportion of the tree's crown that contained dead branches; and (3) tree diameter. The number of different vertebrate species that occupied trees was positively associated with the same explanatory variables except tree diameter. Thus, our results suggest that trees with multiple hollows and dead branches in the crown should be preferentially selected for occupancy by hollow-using fauna. Our results suggest that trees with the largest diameter are not the most suitable for retention. Possibly because they contain proportionally fewer hollows with small entrances, which are favoured by some vertebrate species

Hollow formation in eucalypts from temperate forests in southeastern Australia

We examined factors associated with the occurence of tree hollows in four eucalypt species from temperate forest in southeastern New South Wales and East Gippsland. A total of 1 256 standing trees and 328 felled trees was examined. The proportion of trees containing hollows with small entrances (2-5 cm) was significantly negatively associated with dbh, while the proportion of trees containing hollows with medium (5-10 cm) and large (>10 cm) entrances was positively associated with dbh. There was a significant, but weak, relationship between hollow depth and minimum entrance width that was improved with the addition to the model of the variables branch diameter and branch health. Trees of all sizes and ages contained hollows, although larger and older trees had a higher probability of doing so. For two tree species (Brown Barrel or Cuttall Eucalyptus fastigata and Messmate E. obliqua), the probability of live trees containing hollows remained below 0.5 for stems less than 180 years of age. Unlogged forest supported, on average, 22.0 hollow-bearing trees per ha - 18.5% of which were dead trees. For all values of dbh, trees were more likely to contain hollows if either dead or In poor physiological condition, indicating the potential for hollow development to be accelarted in eucalypts by killing or injuring suitably-sized trees