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Are giant eucalypt forests rain forest?

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Tng, DYP (2014) Are giant eucalypt forests rain forest? PhD thesis, University of Tasmania.

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Abstract

Forests dominated by giant eucalypts ( eucalypt species with the potential to attain
heights exceeding 70m) occur along the Australian east coast in association with rain
forest. These forests contribute significantly to the global carbon budget but their
ecological classification suffers from ambiguities around the definition of rain forest.
The belief that eucalypts are 'sclerophyllous' and therefore not rain forest is a
subjective view that has led to problems with conservation policies and management
strategies of giant eucalypt forests. Understanding these forests from a global and
functional viewpoint is paramount for their effective management. Eucalyptus
grandis-dominated giant eucalypt forests in the Wet Tropics of Australia serve as a
case study. Observing that rain forest species continuously regenerate in the
understories of these eucalypt forests and believing that rain forest incursion will
lead to the local elimination of the giant eucalypts, land managers prescribe frequent,
low intensity fires. This management strategy is contentious and not underpinned by
robust ecological understanding. To resolve these classificatory problems around
eucalypts occurring in rain forest, I take a multidisciplinary approach to address the
specific question: Are giant eucalypt forests rain forests?
To obtain an in depth understanding of the ecology of giant eucalypts and the forests
they dominate, and to provide a global context for these systems, I synthesise over a
century's worth of literature on these systems (Chapter 2). Based on these data I
propose that giant eucalypts are ecologically akin to rain forest emergent pioneers
with a unique dependence on fire for regeneration, and that their habitat should be
considered a type of secondary rain forest.
Using a GIS-based approach I investigate the landscape scale vegetation dynamics of
rain forest and E. grandis forest in the Wet Tropics, where E. grandis forests are
considered to be threatened (Chapter 3). Using a environmentally stratified sample of
sites, I show that rain forest has expanded over the past 50 years, and that this
expansion is most likely a response to a global driver such as increased atmospheric
CO2 rather than with local environmental factors. Projective modelling of this rain forest expansion predicts that, even at the fastest estimated rate known for the region,
it will be more than 2000 years before rain forest fully engulfs giant eucalypt forests.
In Chapter 4, I present a seedling growth experiment to examine if the regeneration
niche of E. grandis exhibits ecological convergence with that of well-studied
temperate giant eucalypts. I show that E. grandis seedlings grow poorly in unburnt
rain forest soils because of the unavailability of phosphorus. The addition of
phosphorus lifts phosphorus-deficiency symptoms in seedlings in rain forest soils,
and accords well with the idea of E. grandis being a rain forest pioneer with the
unique requirement of fire as a disturbance mechanism to create suitable open
habitats for regeneration.
To contextualize the rain forest- giant eucalypt forest - savanna transitions in
Australia from a functional and macroecological perspective, I present a plant
functional trait analysis of representative plants across these vegetation transitions in
both tropical and temperate Australia (Chapter 5). I show that both tropical and
temperate giant eucalypt forest are functionally convergent with rain forest and not
with savanna. These results suggest that a classification of giant eucalypt forest based
on functional attributes of the whole forest will be more useful for management
policy than the established classification based on canopy dominants
In conclusion (Chapter 6), the synthesis ofmy landscape ecology and functional
biology data supports my overarching hypothesis that giant eucalypt forests are
functionally and ecologically rain forests and should be managed as such. I discuss
the implications of my research for the management of Wet Tropics giant eucalypt
forest and recommend that E. grandis forest should be managed under a regime of
total fire suppression. Given that rare natural fires can be expected to occur under
this management, the resulting regime will mimic the inherently long fire return
times of these systems.

Item Type: Thesis (PhD)
Copyright Holders: The Author
Copyright Information:

Copyright 2014 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).

Additional Information:

Chapter 2 appears to be the equivalent of a post-print of an article published as: Tug DYP, Williamson GJ, Jordan GJ, Bowman DMJS. 2012. Giant eucalypts -
globally unique fire-adapted rain-forest trees? New Phytologist 196: 1001-1014.

Chapter 3 appears to be the equivalent of a post-print of an article published as: Tng DYP, Murphy BP, Weber E, Sanders G, Williamson GJ, Kemp J, Bowman DMJS. 2012. Humid tropical rain forest has expanded into eucalypt forest and savanna over the last 50 years. Ecology & Evolution 2: 34-45

Chapter 5 appears to be the equivalent of a post-print of an article published as: Tug DYP, Jordan GJ, Bowman DMJS. 2013. Plant traits demonstrate that giant
eucalypt forests are ecologically convergent with rain forest not savanna. PLoS
ONE 8: e84378. doi:l0.1371/joumal.pone.0084378.

Chapter 6 appears to be the equivalent, in part, of a post-print of an article published as: Tug DYP, Goosem S, Jordan GJ, Bowman DMJS. 2014. Letting giants be -
rethinking active fire management of old-growth eucalypt forest in the Australian
tropics. Journal of Applied Ecology 51: 555-559.

Date Deposited: 07 Apr 2016 05:18
Last Modified: 07 Apr 2016 05:18
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