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Tree hollows in Tasmanian Eucalyptus obliqua forest and their use by vertebrate fauna

Koch, AJ 2007 , 'Tree hollows in Tasmanian Eucalyptus obliqua forest and their use by vertebrate fauna', PhD thesis, University of Tasmania.

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Tree hollows provide an essential resource for a range of fauna, both in Australia and worldwide. There is concern over the future availability of the hollow resource in forests managed for timber harvesting because the time required for hollows to form is generally longer than the interval between harvest rotations. One of the strategies used to maintain the hollow resource is to retain specific trees to provide habitat for fauna.
The overall aim of this thesis was to assess the tree hollow resource and its use by fauna in
Tasmania, in order to inform the revision of management prescriptions for the conservation
of the hollow resource in production forest areas. It was also to assess whether different
prescriptions are required for different forest types. As part of this work, two methods of
studying tree hollows were assessed for their accuracy and utility. To achieve these aims,
391 trees were examined before and after felling in forestry coupes throughout Tasmania.
Data were collected on tree growth rings, hollow occurrence and whether the trees were
being used by fauna. Estimates of hollow abundance on felled trees were corrected by the
amount of tree that had been successfully surveyed. The trees were located at 39 sites in two
broad forest types important to the Tasmanian forest industry, wet and dry Eucalyptus
obliqua forest. The main factors associated with both hollow presence and abundance were the number of
hollows observed on the standing tree, tree diameter and the amount of dead wood in the
canopy. While tree age was strongly associated with hollow presence, it had less bearing on
hollow abundance. An increase in the maximum size o f hollow found in a tree was related to
greater tree senescence, as indicated by higher values of the afore-mentioned factors.
Although significantly more hoiJows of all sizes were found in wet forest than drier forest,
the age at which trees began to produce hollows was similar between the different forest
types. Trees grow slightly more slowly in dry forest than wet, meaning that trees need to be
slightly larger in wet forest before they are hollow-bearing. The difference in hollow
abundance between the different forest types was largely a result of the history of logging in
dry E. obliqua forest which has resulted in trees being smaller and younger in the areas
studied. Although hollow-using fauna are a major component of vertebrate fauna in Tasmania, the
number of hollow-using species found in Tasmania (42) is at the lower end of the range
found in other areas of Australia. The rate at which trees were used by vertebrate fauna in
Tasmania was also at the lower end of the scale found in other areas of Australia, with only
28% of hollow-bearing trees examined showing evidence of usc. The variables most strongly related to the use of a tree were hollow abundance, tree size and senescence. The likelihood
of a hollow being used increased with hollow size; hollow depth in particular. There was a
slight increase in the proportion of trees that showed evidence of use with increasing forest
wetness, which corresponded with an increase in the availability of hollows. The rate of
hollow use was very low (5%) and it is proposed that this was due to the often shallow and
open nature of the hollows observed in this study. This observation may relate to the low
numbers of arboreal termites in Tasmania. It was recommended that trees identified for retention of habitat in logging coupes be
selected primarily based on the presence of large hollows. Despite the difficulties in
observing hollows in standing trees, ground-based surveys are one of the most effective
ways of establishing hollow presence. In wet forest areas, large hollows are most likely to
occur in trees that are at least 125 em in diameter and have at least six visible hollows. In dry
forest areas, large hollows are most likely to occur in trees at least 100 em in diameter with
at least six visible hollows.
It was estimated that between 8 and 15 trees per hectare were used, on average, by hollowusing
fauna. This is significantly more than the rate at which trees are currently being
retained in production forests in Tasmania (0.4 to 0.6 per hectare). It is therefore
recommended that the rate of retention and type of trees being retained be reviewed in order
to more adequately meet the requirements of hollow-using fauna.

Item Type: Thesis - PhD
Authors/Creators:Koch, AJ
Copyright Information:

Copyright 2007 the Author

Additional Information:

Chapter 2 later published with the same title in Australian journal of zoology, 2008, 56, 323-349

A version of chapter 3 was later published as Estimating the accuracy of tree ageing methods in mature eucalyptus obliqua forest, Tasmania, Australian forestry, 2008, 71 (2), 147-159

Chapter 4 later published with the same title in Forest ecology and management, 2008, 255, (3-4), 674-685

A version of chapter 5 was later published as Does hollow occurrence vary with forest type? A case study in wet and dry Eucalyptus obliqua forest, Forest ecology and management, 2008, 255 (12), 3938-3951

Chapter 6 later published with the same title in Wildlife research, 35 (8), 727-746

A version of Appendix 1 was later published in Tasmanian naturalist, 2007, 129, 37-64

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