Journal of the Royal Society of Western Australia, 86:49-60, 2003 
The effects of fire and quokkas (Setonix brachyurus) on the vegetation 
of Rottnest Island, Western Australia 
Rippey M E 1 & Hobbs R J 2 
1 Department of Geography, University of Western Australia, Nedlands WA 6009 
El jjrippey@cyllene.uwa.edu.au 
2 School of Environmental Science, Murdoch University, Murdoch, WA 6150 
El rhobbs@murdoch.edu.au 
(Manuscript received March 2002; accepted November 2002) 
Abstract 
Three different plant communities have dominated the vegetation of Rottnest Island over the 
past two centuries; low forest, Acacia rostellifera scrub, and sclerophyllous heath. In 1997 a fire burnt 
90 ha of heathland and provided an opportunity to examine the relationships between dominant 
vegetation types, fire and grazing by quokkas (Setonix brachyurus). Our study and the literature 
indicated four major findings. 
• Burnt heath recovered slowly if grazed. If not grazed, heath regenerated rapidly to become 
dense, tall and weed-free compared with the surrounding heathland, and the number of native 
species increased. 
• Where there was no grazing, all three vegetation communities were able to become established 
immediately after the fire. Four and a half years after the fire. Acacia thickets dominated in 
some areas and reached 3-4 m in height, overshadowing a group of self-seeded Melaleuca 
seedlings and outcompeting heath species. It is anticipated that the Melaleuca will emerge and 
dominate when the shorter-lived Acacia declines, and that heath will continue to occupy open 
areas. 
• The three dominant vegetation communities can be regarded as stable state alternatives. Heath 
will dominate if there is heavy grazing, as the young trees and Acacia are palatable and so 
cannot regenerate. Low forest dominates if there are only occasional widespread fires. Fire 
triggers the release of seed stored in tree canopies, and also temporarily reduces the local 
quokka population, giving seedlings a chance to become established. Acacia dominates if there 
are frequent fires and little grazing. Frequent fires stimulate Acacia to sucker from underground 
parts, while competition from tree species disappears, as trees are killed by fire, and if a second 
fire occurs before young trees set seed, they are eliminated locally. 
• It appears that occasional widespread hot fires, presumably started by lightning, are likely to 
have occurred on Rottnest Island over the millennia before European settlement for Melaleuca/ 
Callitris forest to have persisted. 
Key words: Rottnest Island, vegetation, fire, quokkas, vegetation dynamics 
Introduction 
A row of islands lies off the coast of Perth, Western 
Australia, the largest of which are Rottnest Island (1900 
ha) and Garden Island (1200 ha). These aeolianite 
limestone islands are remnants of Pleistocene dune 
ridges, left above sea level after the last post-glacial 
marine transgression. The vegetation of Rottnest and 
Garden Islands has strong similarities (Marchant & 
Abbott 1981). The majority of their native plant species 
are common to both islands, including the three tree 
species, Melaleuca lanceolata, Callitris preissii and 
Pittosporum ligustrifolium , as well as the tall shrub Acacia 
rostellifera. Small wallabies graze both islands, quokkas 
(Setonix brachyurus) on Rottnest Island and tammars 
(Macropus eugenii) on Garden Island. Over the past 200 
years, the vegetation of Rottnest Island has been heavily 
exploited by humans to the point where the concept of 
© Royal Society of Western Australia 2003 
'natural' vegetation is almost irrelevant. However, fossil 
pollen data and historical reports over the last two 
centuries make it possible to trace changes in the 
vegetation types that have dominated the island, and the 
processes associated with the changes. The parallel with 
Garden Island, which has suffered less disturbance, 
serves as an additional check or reference point. 
We attempt to find a conceptual framework for 
changes in the vegetation of Rottnest Island. The 
dynamics are studied from three aspects; the historical 
information is reviewed, the vital attributes of dominant 
species are assessed using criteria established by Noble & 
Slatyer (1980) with a view to predicting their response to 
a disturbance event, and the recovery of the vegetation 
after a fire in 1997 is examined. 
Vegetation history 
There have been significant changes in the vegetation 
of Rottnest Island since separation from the mainland 
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