Figure 1.
Stages of hollow formation, death and decay of mountain ash trees (Eucalyptus regnans).
The trees surveyed in this study were characterised according to five tree form (TF) categories pictured from left to right: TF1: live trees with no visible hollows (typically young trees); TF2: live trees with visible hollows (typically older, senescing trees); TF3: dead trees in the early stages of decay; TF4; dead trees in the mid-stages of decay; and TF5: highly decayed dead trees. Live trees do not begin to form hollows suitable for arboreal marsupials until they reach an age of at least 120 years.
Figure 2.
The map shows the spatial extent of the Cambarville study site affected by fire in February 2009. The coloured dots represent hollow trees to which mountain brushtail possums (Trichosurus cunninghami) were radiotracked (different colours represent separate individuals). The X and Y axes are Eastings and Northings UTM coordinates in metres (Geodetic Datum of Australia). The pale yellow area in the centre of the site is a grassy clearing, the red area is the area burnt in the 2009 fire and the grey shaded area was not burnt.
Figure 3.
The duration over which each study animal was fitted with a proximity-logging radiotransmitter.
Black bars represent individuals carrying transmitters for all three study periods, blue bars represent individuals carrying transmitters for two of the three periods and light grey bars represent individuals carrying transmitters for one study period. The vertical line shows the date that the Black Saturday wildfires commenced (7 February 2009). The collars fitted to animals in February 2009 were attached over the four days immediately preceding the fires. Individuals 1–6 were located in the unburnt section of the study site and individuals 7 to 26 were located in the burnt area of the study site (see Figure 2 for map).
Figure 4.
The number of mountain brushtail possums captured at the Cambarville study site before and after the February 2009 Black Saturday wildfires. The timing of the15 trapping sessions over this period are indicated with a “+” sign.
Figure 5.
Effects of fire on mountain ash trees at different stages of hollow formation and decay.
The chart shows the probability of a tree being scorched (no structural damage), partly consumed (tree is still standing and potentially has some utility as a den site), or completely consumed (tree has collapsed or has lost all utility as a den site) as predicted by ordinal regression.
Figure 6.
Pre and post-fire shifts in the tree forms used as shelter by mountain brushtail possums.
These graphs show the predicted probabilities (and 95% confidence intervals) of an occupied tree being of a form greater than Tree Form 2 (Figure 6a), greater than Tree Form 3 (Figure 6b) or greater than Tree Form 4 (Figure 6c) before and after the fire unburnt and unburnt habitat. See Figure 1 for details of Tree Form (TF) categories. These predictions were from generalised linear mixed models of the types of trees used by individuals radiotracked before and after the fires. See Table 1 for fitted model statistics.
Table 1.
Logistic mixed models testing for upward shifts in the tree forms (TF2–5, see Figure 1 for details) selected as den sites by mountain brushtail possums at Cambarville before and after the February 2009 Black Saturday fires.