Grazing Effects in Fragmented E. salmonophloia Woodlands in Southwestern Australia: Implications for

1
Grazing Effects in Fragmented E. salmonophloia
Woodlands in South-western Australia
Implications for Restoration
Brett Johnson, Department of Biological and
Physical Sciences, University of Southern
Queensland, Australia
Introduction Eucalypt woodlands in temperate
southern Australia have been extensively cleared
for agriculture and now occur as isolated patches
that are often disturbed by livestock grazing.
The most obvious effect of livestock grazing is a
change to vegetation structure and composition.
Generally, as livestock grazing pressure
increases, native plant species become less
abundant and are replaced by exotic species. This
study aims to ? assess the effect of long term
livestock grazing by sheep on native plant
species cover, and ? provide information for
developing strategies that restore and sustain
native plant species in degraded woodlands.
Conversely the percentage cover of native
perennials was significantly higher in rarely
grazed/ungrazed woodlands than in heavily grazed
woodlands (t2.639, d.f.118, Plt0.008). The mean
percentage cover of native perennials in rarely
grazed/ungrazed woodlands was 9.1 and in heavily
grazed woodlands was 3.6 (Figure 2). No
significant differences in native annual cover
were observed between different grazing regimes
(Figure 2).
Figure 2 Mean percentage cover in 1 m2 quadrats
(n60) of exotic annuals, native annuals and
native perennial herbs and shrubs in rarely
grazed/ungrazed and heavily grazed remnant E.
salmonophloia woodlands. Vertical bars represent
standard errors of means.
Discussion Livestock grazing is a composite
disturbance that encompasses the effects of
defoliation, trampling, defecation and urination.
The results presented here demonstrate that
livestock grazing in remnant E. salmonophloia
woodlands has a significant impact on vegetation
structure and composition, in particular the
reduction in cover of native perennial species.
It was also observed in this study that the
cover of plant stems, grass tussocks and woody
material was consistently less in the heavily
grazed woodlands than in the rarely
grazed/ungrazed woodlands. These features, along
with native vegetation cover, form important
components of resource sinks. Resource sinks are
vital for conserving
Methods This study was conducted
in remnant E. salmonophloia woodlands
approximately 200 km east of Perth (figure 1).
Three woodlands regularly grazed by sheep
(heavily grazed) and three woodlands very
occasionally or never grazed by sheep (rarely
grazed/ungrazed) were chosen for comparisons of
vegetation cover. The heavily grazed and rarely
grazed/ungrazed woodlands were strikingly
different visually. At each site two 50 m
transects spaced 5 m apart were established, and
ten 1 m2 quadrats at 5 m intervals were located
in each transect. At each site in September 1996
the percentage cover of exotic annuals, native
annuals and native perennial herbs and shrubs was
assessed visually in each quadrat. Comparisons
of vegetation cover were made with unpaired two
tailed t-tests.
limited resources within an ecosystem. Livestock
grazing in remnant woodland has removed the
landscape patchiness and reduced the probability
of these

resource sinks forming. Thus lowering the
levels of resources found within grazed
woodlands.
Study area north of Kellerberrin and east of
Merredin in the central wheatbelt of WA
Conclusion Livestock grazing in E. salmonophloia
woodland changes conditions and disrupts
ecosystem processes resulting in the external
loss of scarce resources from within remnants.
Effective restoration of degraded woodlands will
require strategies that allow recapture and
retention of resources, the subsequent formation
of resource sinks, and the overall improvement of
the microclimate of remnants not just the
removal of livestock from degraded woodland.
Figure 1 Map of Western Australia showing
location of study area.
Results The percentage cover of exotic annuals
was significantly higher in heavily grazed
remnant E. salmonophloia woodlands than in rarely
grazed/ungrazed woodlands (t -6.608, d.f.118,
Plt0.0001). The mean percentage cover of exotic
annuals in heavily grazed woodlands was 29.7
and in rarely grazed/ungrazed woodlands was 0.5
(Figure 2).
Acknowledgements Adapted from Yates, C.J.,
Norton, D.A. and Hobbs, R.J. (2000) Grazing
Effects on Plant Cover, Soil and Microclimate in
Fragmented Woodlands in South-western Australia
Implications for Restoration. Austral Ecology 25
36-47.
Completed as part of BIO3314 Terrestrial Ecology
assessment - October, 2003