Journal of the Royal Society of Western Australia, 86(3), September 2003 
*—Exclosures Site 1 
Figure 7. Changes in the abundance index for the seedlings and 
reshoots category as a result of rabbit grazing in the fenced and 
unfenced areas of remnant vegetation at Tomlinson's site. The 
results from rabbit exclosure plots are included for comparison. 
An abundance index scale of 1 to 7 was used to score the 5 
quadrats within each plot (see methods). Values are mean (± se) 
of the abundance index scores for the plots (n = 10) at each site. 
Sites 1 and 2 had been fenced for approximately 4-5 years and 1 
year respectively, prior to the experimental plots being 
established. 
The main effects of rabbit grazing on remnant 
vegetation when rabbits were confined within this 
vegetation are shown in Figs 6 and 7. The ANOVA (Table 
1) showed that both rabbit grazing and time (i.e. years) 
had a significant effect on the percentage vegetation 
cover for sedges and grasses (Fig 6). Although the 
abundance of sedges and grasses in the open plots and 
exclosures on each site were similar when the 
experiments were commenced in 1999, there was a 
consistent divergence over time between the ungrazed 
and grazed plots on both sites. This was presumably due 
to the cumulative effects of rabbit grazing, as percentage 
cover on the open plots was markedly reduced compared 
with the amount of vegetation within the ungrazed 
exclosures. This effect appeared to become more 
pronounced over time as there was a clear difference 
between years (Table 1). However, initially, there was 
little overall change in the percentage cover of sedges 
and grasses between 1999 and 2000, but there was a 
marked decline in this vegetation parameter between 
2000 and 2001. This change may well have been 'driven', 
at least partially, by rainfall events. The period between 
November 2000 and November 2001 had much less rain 
than the corresponding period in 1999-2000 (Fig 8). In 
fact, rainfall over the 10 months between September 2000 
and June 2001 was also considerably less than the long¬ 
term average for this period. 
The seedling and reshoots score (= abundance index), 
and the number of quadrats with seedlings and re¬ 
shooting rootstocks, also showed a significant effect of 
both year and exposure to rabbit grazing at both sites 
(Table 1; Fig 7). Like sedges and grasses, changes in these 
parameters almost certainly reflected recent preceding 
rainfall (Fig 8). However, in the absence of grazing by 
rabbits (i.e. in the exclosure plots; Fig 7) there was an 
increase in the percentage cover of the seedlings and 
reshoots from year to year. Grazing by rabbits 
diminished the numbers of seedlings and reshoots, with 
the biggest effect occurring in November 2000 after two 
months of very low rainfall. As indicated by the RAI, this 
period also corresponds with the observed peak in rabbit 
abundance (Fig 5). The impact of rabbit grazing is also 
clearly illustrated in Fig 9 which shows the effect of even 
low numbers of rabbits within the fenced bush remnant 
(~ 5 ha* 1 ) compared to the surrounding pasture with no/ 
few rabbits. 
Costs of rabbit-proof fencing 
Although the overall area of crops and pasture that 
was affected by rabbit grazing in the absence of rabbit- 
proof fencing was often small, there was usually a total 
loss of plant biomass in the affected areas. In canola 
crops, these losses ranged from $288 to $1296 (mean $972, 
J FMAMJ J ASOND 
Figure 8. Long-term average (LTA) rainfall (mm), and rainfall (mm) for each of the years during the short- and long-term studies at 
Boxwood Hill. The recording station was within 8 km of the study sites. 
102 
