Koolan Island Flora and vegetation 
239 
ulmifolia, a small yellow flowering herb. This taxa 
has also not previously been recorded elsewhere in 
Western Australia. 
In a vegetated valley near the southern boundary 
of the town site, a small but vigorous population of 
rubber vine (Cryptostegia madagascariensis) was 
found. The creek line running south from this 
valley (Creek 4) was dominated by Leucaena 
leucocephala, Tire Poinciana (Delonix regia) was also 
found in this area and is the first time this taxon 
has been recorded as naturalised in Western 
Australia. The Leucaena leucocephala and Delonix 
regia were also found in the two smaller creek lines 
(Creeks 5 and 6) at the south west end of town. 
Eleven species of grass have become naturalised 
including buffel grass ( Cenchrus ciliaris). This 
species has become a very serious weed at Cape 
Range (near Exmouth) where it was planted along 
the coastal flats as improved pasture and has 
subsequently spread through most of the plant 
communities of the area (Keighcry and Gibson 
1993). 
Currently all the weeds are restricted to the 
settlement area (including creek lines and sewerage 
outfalls) and road verges. With closure of the town 
supplementary irrigation and sewerage output will 
cease. This is likely to lead to long term loss of 
weed taxa given the extended dry season in this 
area. Weedy tree species may persist but success of 
further recruitment is uncertain. Experience in 
areas such as Cape Range suggests some of the 
exotic grasses will persist. The current distribution 
of Cryptostegia madagascariensis elsewhere in 
Australia suggests that this species will also persist 
and spread unless efforts are made to eradicate it. 
It should be noted that of the several hundred taxa 
present in the town gardens, only 44 have become 
naturalised (Appendix 1). 
Vegetation 
Five major vegetation units were found on the 
island. There were also several minor units but 
these occupied areas too small to map (Figure 1). 
The most widespread community was the 
Eucalyptus miniata - Eucalyptus confertiflora open 
woodlands generally over Triodia hummock 
grassland. The understorey was composed of a 
diverse herb layer with species such as Tacca 
leontopelaloides and T. maculata being common. The 
density of shrubs in this community is variable but 
several species of Terminalia and Acacia are 
common (Appendix 1). This vegetation type covers 
about 80% of the non-disturbed area of the island 
and is the common vegetation type on the adjacent 
mainland (Beard 1979). The floristics of this 
community are fairly consistent, however there is 
considerable local change in dominance across the 
island. This floristic variation did not appear to be 
Figure 2 Map of the townsite showing location of creek lines and sewerage outfalls. 
