Rippey & Hobbs: Effects of fire and quokkas on Rottnest Island vegetation 
dominate. Acacia rostellifera is a favoured food for 
quokkas, and Callitris and Melaleuca are very palatable, 
and a large quokka population would destroy shoots and 
seedlings as they appeared so that these species would 
die out with the death of the mature plants. 
The transitions from one stable state to another have 
been precipitate over the past 200 years, brought about 
by human intervention. It is postulated that there were 
occasional large fires before human occupation in 1838, 
and that these were associated with Melaleuca/Callitris 
forests. These gave way to Acacia rostellifera scrub 
between 1840 and the 1920s/1930s, when frequent fires 
took place and the quokka population was kept low by 
hunting. After this the quokka population was protected 
and burgeoned; the population probably reached 
saturation point by the mid twentieth century. Heathland 
predominated with this heavy grazing, and the 
prevention or control of fires after 1955. 
It is possible that the Acanthocarpus/Austrostipa heath 
is not stable, but is becoming increasingly degraded by 
invasion by Trachyandra divaricata and by overgrazing 
and damage by quokkas. The stable state concept does 
not preclude the possibility that future changes might 
occur to the vegetation, associated with changes in the 
island environment or invasion by other species. 
It would seem that virtually all of the natural old 
growth trees on Rottnest must be drawing towards the 
end of their life span. Quokkas were protected from 1917 
and there had been some limitations on quokka hunting 
prior to this (CSO File 2047/1900 in Joske et al. 1995), 
with the result that presumably little regeneration of trees 
could have taken place for 80 years. Melaleuca/Callitris 
forest thins out rapidly from 80 years of age and the trees 
disappear within about thirty years. Similarly, if quokka 
grazing prevents regeneration of Acacia rostellifera , then 
Acacia scrub senesces and dies in 20-40 years. 
The exploitation of the vegetation of Rottnest Island 
for two centuries releases environmental managers to 
some extent of expectations that they should restore the 
vegetation to any 'original' state. This gives considerable 
freedom of action, but in practice severe constraints are 
imposed by the island's gazetted purpose of 'public 
recreation', and by the threatened status of quokkas, 
which are a Western Australian icon. Both of these 
factors restrict the use of fire as a management tool, and 
it is interesting to note that the Draft Management Plan 
for the island for 2002-2007 states that 'fire is a threat to 
all habitats ... particularly ... to woodland communities'. 
However from our study, it is clear that fire remains an 
important factor shaping the vegetation and that its 
occurrence (or that of a suitable alternative disturbance), 
in conjunction with local control of quokka grazing may 
be essential for the maintenance of some of the major 
vegetation types (outside plantations) on the island. 
Acknowledgements : We are grateful to the staff of the Rottnest Island 
Authority for providing information about the recent fire, especially to C 
Wright and C Hansen. Thanks are also due to J Dodd, Department of 
Agriculture, for information on Trachyandra. Warm appreciation is 
expressed to M Hazelton of the Department of Mathematics, University 
of Western Australia, who gave advice on the statistics and performed 
the ANOVA and Kruskal-Wallis tests on the data we provided. 
Acknowledgment is also given to the Department of Land Administration 
for permission to use aerial photograph WA 4544C, Run 41: 5139, taken 
14/12/00, scale 1:25,000 as the basis for Fig 7. 
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