Journal of the Royal Society of Western Australia, 86(2), June 2003 
6500 years ago. Fossil pollen of native species dominant 
on the coastal plain today, such as fire tolerant 
Eucalyptus , Casuarina, Banksia, Macrozamia and 
Xanthorrhoea, have been found in the swamps on Rottnest 
Island, dating back to the early Holocene (Storr et al. 1959; 
Churchill 1960; Backhouse 1993). All of these genera 
became extinct on Rottnest after separation when a 
different set of influences came into operation. 
There has been some uncertainty as to whether there 
were fires on Rottnest after the island was separated from 
the mainland and before European settlement. Abbott et 
al. (2000) suggested that the islands off Perth escaped 
anthropogenic disturbance, especially fire, for at least 
5000 years, as the Aboriginal people did not use 
watercraft in this area (Abbott 1980). However occasional 
fires do appear to have occurred. Core samples taken 
from Barker Swamp reveal that layers of charcoal, which 
could only have resulted from fires, were deposited in 
the sediments. Backhouse (1993) discovered 14 charcoal 
bands laid down in the 1200 years between about 6850 
and 5645 years before present indicating that fires 
occurred more than once per century. The frequency of 
the bands thereafter decreased to one per 350-400 years. 
The pollen record indicates that this decrease is because 
the fire-prone Callitris and Eucalyptus that had dominated 
the area disappeared from the catchment of the swamp 
and were replaced by a comparatively sparse low cover 
of Pimelia and Asteraceae. Other fires could have 
occurred elsewhere on Rottnest during this period. 
Groves (2001) separated large charcoal fragments (>1 
mm) from small fragments (5-150 mm) in sediment cores 
from Barker Swamp, assuming that large fragments 
would indicate local fires on Rottnest Island while small 
fragments may have been transported on the wind from 
fires on the mainland. He concluded that major local fire 
events on Rottnest over the past 5300 years occurred 
about every 210 years while major regional fires 
(probably on the mainland) occurred about every 120 
years. Unfortunately it is now difficult to resolve the 
question of the frequency of fires on Rottnest Island by 
studying cores from other catchments, because most of 
its swamps have been bulldozed to obtain marl for 
roadbuilding (Playford 1988; J Dodson, University of 
Western Australia, personal communication). 
Today many of the native plant species on Rottnest 
and Garden Islands are killed by fire, including Callitris 
and Melaleuca , with regeneration only taking place 
through germination of seeds (Bell et al. 1987). In the 
absence of very frequent fires, the critical factors for 
vegetation are exposure to wind and salt, lower rainfall 
than the mainland with summer drought, and grazing by 
quokkas. Reports on the vegetation of Rottnest Island by 
visitors in the 17 lh and early 19 th century mention the 
wooded nature of the island. In 1822 the botanist 
Cunningham reported that Callitris was abundant on the 
island To the point of monotony... occasionally relieved 
by ... Melaleuca ... and the more elegant Pittosporum' 
(quoted by Pen & Green 1983). Early reports of Garden 
Island described a similar picture. In 1827 Fraser reported 
areas Thickly covered with cypress [Callitris preissii] and 
... extensive thickets of arborescent metrosiderous' 
[Melaleuca lanceolata ], and in 1829 Fremantle noted that 
the vegetation was '... covered in a small kind of pine 
[Callitris] .... from the thickness of the trees and 
underwood it was impossible to move' (quoted by 
Wykes & McArthur 1995). However, Wilson described a 
very different landscape after a visit to the central 
southern part of Rottnest in 1829; '... miserably barren. 
The hummocks are sand hills, many of which are entirely 
destitute of any kind of herbage, in the valleys are some 
stunted trees and shrubs and very little grass' (quoted by 
Marchant & Abbott 1981). He had probably described the 
large blowout at Barnett's Gully, but his description also 
fits the desolation that follows fire on Rottnest Island. 
In 1831 settlers started farming on Rottnest Island. In 
1838 the prison was established and farming was 
intensified, with the introduction of pigs, horses, rabbits, 
sheep and cattle, and crops of wheat, barley, rye, stock 
fodder, fruit and vegetables, even tobacco and castor oil at 
times (Somerville 1976; Ferguson 1986). Wood was taken 
for fuel, and buildings and roads were constructed. 
Quokkas became scarce. The Aboriginal prisoners used 
fire to hunt them for food, and vice-regal parties hunted 
them for sport towards the end of the 19 ,h century, as did 
tourists in the early 20 th century (Storr 1963). The 
vegetation changed under the new regime of frequent 
fires, low wallaby numbers and removal of trees. In 1855, 
Jewell reported areas of dense scrub. Acacia rostellifera 
(quoted by Marchant 1977). In 1905, Lawson wrote that 
the interior of the island was covered with very dense 
Acacia scrub, quite impenetrable apart from the 'rides' that 
had been cut through it, and that trees were absent except 
in the settlement at the eastern end of the island and most 
of these were introduced (Lawson 1905). By 1919, Weir 
estimated that two thirds of the island (1200 hectares) was 
covered by Acacia scrub (Storr 1963), and in 1929 Glauert 
wrote that 'much of the island is clothed in dense wattle 
[Acacia] scrub' (quoted by Pen & Green 1983). 
In 1917, legislation was passed prohibiting shooting 
on the island (Anon 1917), but shooting apparently 
persisted because in 1926 J B Stark was appointed 
Honorary Guardian under the Game Act 1912-13 (Storr 
1963). New laws were promulgated in 1933 prohibiting 
firearms on the island altogether (Anon 1933). The 
quokka population recovered during this period, with an 
abundant food supply of nutritious Acacia rostellifera and 
palatable introduced plants associated with crops and 
improved pastures. By 1932 it was reported that quokkas 
were more numerous than before and were damaging 
crops (Storr 1963). 
Overgrazing by quokkas prevented the regeneration 
of Acacia scrub, which by 1941 was fragmented and 
covered only 400 ha (Pen & Green 1983), one third of the 
area it had occupied 22 years earlier. In the mid-1950s. 
Acacia was even more restricted, to sheltered valleys and 
slopes (Storr et al 1959). Here it was 3-6 m high, and 
often associated with the climber Clematis linearifolia. 
Callitris had apparently become so rare that it was not 
mentioned at all. The scrub was replaced by grassy heath 
consisting mainly of Acanthocarpus preissii and tussock 
grass Austrostipa flavescens. 
In 1955 a major fire burnt two thirds of Rottnest 
Island, and a year later there was a widespread fire on 
Garden Island. The recovery of the vegetation on both 
islands was documented (Storr 1963; Baird 1958) and the 
effects of fire on the vegetation of the islands have been 
widely discussed since this time (White & Edmiston 1974; 
O'Connor et al 1977; Hesp et al 1983; Osborne et al 1985* 
McArthur 1996a, b; 1998; Abbott et al 2000). 
50 
