Abstract
Across the savannas of northern Australia, many native vertebrates, especiallymammals, are experiencing widespread population declines. Many declining species rely on
tree hollows as habitat, yet these critical resources themselves are threatened by land clearing
and inappropriate fire regimes. In order to ensure the ongoing provision of habitat for
threatened species, it is important to understand how our management is affecting tree hollows.
In these savannas, prescribed early dry season fire is a key management tool for reducing the
risk and extent of severe late dry season wildfires. The broad aim of my research was to
understand how various fire regimes affect tree hollow abundance and development when they
are maintained over the long-term.
Using a long-term (18-year) fire experiment, I surveyed for tree hollows using both
ground-based surveys (aided by binoculars), and through the novel application of drone
technology. I also sampled for termites, which are key creators of tree hollows in these
ecosystems. My study represents the first use of drones to survey for tree hollows, as well as
the first in Australia to investigate the long-term effects of fire on both termites and tree
hollows.
The results of my termite surveys supported the recently developed hypothesis that
faunal responses to fire are primarily indirect, through changes in vegetation structure. I found
that frequent, high-intensity fires were associated with reduced termite abundance and activity,
largely due to related reductions in woody cover. As frequent, high-intensity fires are
associated with reduced woody cover, management that decreases the occurrence of such fires
would likely increase termite abundance and activity. These termite surveys were the first to
use both baiting and reduced transect sampling methods in the tropical savannas of Australia,
and I was able to compare and evaluate the efficacy and costs of these methods
By surveying for hollow using drone imagery, I found that drone-based hollow surveys
improved estimates of tree hollow abundance and accessibility. I observed that ground-based
surveys underestimated potential habitat hollows by at least 15%, and that drone-based surveys
also provided more information on hollow accessibility, identifying that 38% of hollows were
inaccessible to fauna due to being blind or blocked by termite material.
Interestingly, I did not find a significant effect of fire or termites on hollow abundance
at the individual tree level, despite previous research highlighting these factors as key drivers.
It is likely that the effects of both fire and termites on hollow abundance are more evident at
the stand- and landscape-level, where overall tree demographics come into play and greater
variation in termite communities may be present. I found that tree size (diameter at breast
height) was a strong predictor of hollows and thus fire regimes that maintain and promote large
trees in the landscape are likely to also preserve and increase hollow numbers. High-intensity
late dry season fires are associated with reduced recruitment, growth and survival of trees, and
consequently avoiding such fires would likely assist in maintaining large trees.
Overall, I highlight that contemporary fire management – which aims to reduce the
occurrence of high-intensity late dry season wildfires and therefore helps promote the
recruitment, growth and survival of trees – is likely to be supporting termite communities and
hollow development and abundance in northern Australian savanna landscapes. However,
careful consideration is still required to avoid any negative effects of high-frequency early dry
season fires.
| Date of Award | 2025 |
|---|---|
| Original language | English |
| Awarding Institution |
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| Supervisor | Brett Murphy (Supervisor), Anna Richards (Supervisor), Shaun Levick (Supervisor) & Alyson Stobo-Wilson (Supervisor) |