Research informs the
improvement of hollow tree
retention measures in
Tasmania’s production forests
Amelia Koch and Sarah Munks
The importance of tree hollows
in Tasmania
• 42 vertebrate species use hollows
(birds, arboreal marsupials and bats)
• 35% of Tasmania’s mammals and 31%
of birds
• 12 endemic species or sub-species
• 4 threatened bird species (State and
Commonwealth legislation)
• 7 introduced species
The importance of tree hollows
in Tasmania
• Hollow availability is declining
• Management tool: Forest Practices
Code
• Habitat Tree prescriptions vague
SMALL
HOLLOW
USERS
Distribution of
hollow users
• Extra small:
1-2 species
• Small:
3-5 species
• Medium:
6-8 species
• Large:
9-11 species
• Extra large:
12-15 species
Black: Rainforest
Dark grey: Wet forest
Light grey: Dry forest
White: Non-forest
MEDIUM
HOLLOW
USERS
Distribution of
hollow users
• Extra small:
1-2 species
• Small:
3-4 species
• Medium:
5-6 species
• Large:
7-8 species
• Extra large:
9-12 species
Black: Rainforest
Dark grey: Wet forest
Light grey: Dry forest
White: Non-forest
LARGE
HOLLOW
USERS
Distribution of
hollow users
• Small:
1 species
• Medium:
2 species
• Large:
3 species
Black: Rainforest
Dark grey: Wet forest
Light grey: Dry forest
White: Non-forest
Aim
To develop a model that
can be used by forest
managers to predict the
occurrence of hollowbearing trees of use to
fauna in Tasmania’s
production forests
Eucalyptus obliqua forest
• Widely distributed
• Heavily used by forestry
• Wet and dry forest
• Tree species which provides a large
number of hollows (Munks et al. in press)
• Known tree used by fauna
(Taylor and Haseler 1993)
• Focal tree for other studies
Methods
• Study sites:
Logging
coupes
• Destructive
sampling –
advantages
Pre-felling survey
• Randomly select 10-13 trees
(50 cm dbh)
• Basic structural
measurements
• Hollow abundance
• General site measurements
• Stand structure survey
Post-felling analysis
• Measure hollows found
(2x2 cm)
• Search hollows for evidence
of use by fauna
• Tree slice for ageing
• Classification Tree analysis
Ageing trees
14
12
25
10
8
6
4
2
0
2-5
(n = 1253)
5-10
(n = 623)
Entrance width (cm)
Entrance
Entrance
width
width
(cm)(cm)
>10
(n = 402)
of hollows
% Percentage
of hollows
used used
% Percentage
of hollows
used
of hollows used
16
20
15
10
5
0
2-5
(n = 806)
10-15
(n = 293)
15-30
(n = 293)
>30
(n = 258)
Hollow
depth (cm)
(cm)
Hollow
depth
10
8
6
4
12
2
0
of hollows
%Percentage
of hollows
usedused
Percentage
of hollows
%
of hollows
usedused
5-10
(n = 576)
<10
.10-20 20-30 30-40 40-50 50-60 60-70 70-80 80-90 90-100 >100
(n=65) (n=418) (n=390) (n=263) (n=277) (n=176) (n=140) (n=109) (n=78) (n=69) (n=254)
Branch diameter (cm)
Branch
diameter (cm)
10
8
6
4
2
0
2-5
5-10
10-15
15-20
20-25
20-25
30-35
35-40
>40
(n =79) (n =238) (n =371) (n =397) (n =411) (n =318) (n =232) (n =140) (n =86)
Hollow height above ground (m)
Hollow
height above ground (m)
Rates of hollow use
5.4% all hollows
24.4% large hollows
(At the lower end of national rates)
83.6% of large hollows were deeper than they were wide
Only 46.7% were at least twice as deep as they were
wide
The hollows used by fauna were on average 5.3 ± 9.7 s.d.
times as deep as they were wide (median 2.5)
Are Tasmanian hollows too shallow and open?
Tasmania has relatively few termites
Number of hollows
Are we seeing the hollows
that are being used?
200
Seen before felling
Not seen before felling
150
100
50
0
All
Brushtail Ringtail
Sugar
Glider
Pygmy Bat spp. Bird spp.
Possum
Which trees are used?
Selecting
useful trees
Rates of tree use
All trees
21.2% dry forest (51.1%)
23.4% damp forest (60%)
24.8% wet forest (52.6%)
12 to 64 hollow-bearing trees per
hectare
(mean 40.1 ± 15.7 s.d.; 33 sites)
8-15 trees used per hectare
(using predictive models or rates of tree use)
250
60
50
No. hollows / ha
No. hole-bearing trees / ha
Tree and hollow availability and
forest type
40
30
20
10
200
150
100
50
0
0
Dry
Damp
Forest type
Wet
Dry
Damp
Forest type
Wet
Tree age, tree use and forest type
use
Dry forest
use
Damp forest
nonuse
100%
80%
80%
of trees
%.Number
of trees
100%
%. of trees
Number of trees
nonuse
60%
40%
20%
40%
20%
0%
0%
<100
n=23
100-150
n=39
150-200
n=50
200-250
n=40
250-300
n=28
300-350 >350 n=7
n=9
Tree age (years)
use
nonuse
100%
80%
60%
40%
20%
0%
100-150
n=8
150-200
n=8
200-250
n=16
250-300
n=14
Tree age (years)
Tree age
100-150
n=13
150-200
n=17
200-250
n=12
Tree age
Wet forest
<100
n=19
<100
n=21
250-300
n=9
Tree age (years)
Tree age
Number
of trees
%.
of trees
60%
300-350
n=10
>350
n=41
300-350 >350 n=2
n=2
Tree diameter, use and forest type
Dry forest
use
Damp forest
nonuse
80
%.
of trees
Number of trees
of trees
%.Number
of trees
25
60
50
40
30
20
20
15
10
5
10
0
0
nonuse
20
18
16
14
12
10
8
6
4
2
0
10
>2
0
21
119
0
19
117
0
17
115
0
15
113
0
13
111
10
-1
91
0
-9
71
0
-7
50
Tree diameter(cm)
(cm)
Tree diameter
10
>2
0
21
119
0
19
117
0
17
115
0
15
113
0
13
111
10
-1
91
use
0
-9
71
Wet forest
0
-7
50
10
>2
0
21
119
0
19
117
0
17
115
0
15
113
0
13
111
10
-1
91
0
-9
71
0
-7
50
Tree diameter
Tree diameter(cm)
(cm)
%.Number
of trees
of trees
nonuse
30
70
use
Tree diameter (cm)
Tree diameter
(cm)
Conclusions
Rates of tree and hollow use are lower in
Tasmania compared to many other areas of
Australia
Animals are selective: large hollows
Good hollows are relatively rare in Tasmania
Habitat trees need to be carefully selected
Good habitat trees contain large hollows, are
large in diameter, old in age and have lots of
dead wood
From research to management
Hollows Working Group
Considering research findings
Revise current management
Working with industry
(practical, auditable, and effective prescriptions)
Adoption by industry
Thanks
• Jamie Kirkpatrick, Don Driscoll
• University of Tasmania
• Forest Practices Authority
• W.V. Scott
• Forestry Tasmania
• Holsworth Wildlife Research Fund
• Birds Tasmania