Rippey & Hobbs: Effects of fire and quokkas on Rottnest Island vegetation 
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Acacia 
Site of 1997 fire 
Fenced plots 
Figure 6. A: Distribution of Acacia rostellifera in 1942. B: Distribution of Acacia rostellifera in 1955. C: 
Young growth of Acacia rostellifera in the enclosures. The only acacia in the area between 1956 and 
1997 was in plantations. 
Heath species 
Additional native species recorded in burnt areas but 
not in the unburnt heath were Rhagodia baccata, Olearia 
axillaris and Lepidosperma pubisquameum only within 
enclosures, and Solarium symonii (a fire ephemeral, mostly 
dead by the time of the survey), Lepidosperma gladiatum 
and Carex preissii within and outside enclosures (Table 1). 
The increased coverage by native species in enclosures 
was at the expense of Acanthocarpus preissii, the 
introduced Trachyandra divaricata and (to a lesser extent) 
small introduced annuals, notably Euphorbia peplus and 
the grass Lagurus ovatus. Trachyandra was an important 
component of the vegetation in unbumed and unfenced 
heath (Table 2; Fig 8) but little Trachyandra persisted 
within enclosures (Kruskal-Wallis test, PcO.OOl). 
Discussion 
The vegetation recovery sequence proposed by Noble 
& Slatyer (1980) seems applicable to the dominant 
communities on Rottnest Island. The 1997 fire was 
followed by germination or regeneration of all dominant 
communities within fenced areas. 
Melaleuca! Callitris. 
The only germination observed of these species was 
beside a burnt Melaleuca within an enclosure, despite the 
fact that Melaleuca and Callitris trees were growing in 
plantations, which had not been burned, within 50 m of 
the fenced plots. Four and a half years after the fire the 
slender saplings reached 2 m high but were far 
outstripped by young Acacia rostellifera. It was anticipated 
that Acacia would overshadow these trees for another 
twenty or thirty years. At Woodman Point thirty years 
after a fire, a stand of senescent 5 m Acacia rostellifera was 
still taller than Callitris preissii trees but the Callitris were 
young at 30 years of age, and would shortly displace the 
Acacia (Powell & Emberson 1981). On Garden Island, 
progress of the forest trees could be traced over their life 
span as the ages of various stands of Callitris/Melaleuca 
trees were known from the dates of fires that stimulated 
their germination. It was found that forty year old trees 
numbered approximately 16 per 25 sq m, 75 year old 
trees numbered 6, and hundred year old trees only 1 per 
25 sq m. As the decline progressed the forest was 
replaced by Acanthocarpus preissii heath (McArthur 1998). 
Acacia rostellifera 
This dominated parts of the Research Site enclosures, 
reaching 3-4 m. The changing distribution patterns of this 
species since 1942 have been mentioned. The decrease in 
Acacia rostellifera between 1942 and 1955 (Figs 6A,B) 
accords with Storr's report of major and continuing 
fragmentation of Acacia rostellifera scrub from the 1930s 
onwards (Storr 1963). The disappearance of Acacia from 
around Barker Swamp after the fire of 1955 was 
explained by Storr (1963) who recorded that there had 
been an abnormally high number of quokkas in this area 
after the fire. Small pockets of scrub had escaped the fire 
here, and within two years the quokkas surviving in 
these nodes had eaten all regenerating Acacia , and the 
scrub had been completely replaced with Acanthocarpus 
heath. The only Acacia in the area at the time of 1997 fire 
was in surrounding plantations, established between 
1964 and 1972. The resemblance between the distribution 
patterns of Acacia rostellifera in 1942 and 2001 suggests 
that after the fire Acacia had grown from seed in the soil, 
55 
