Factors affecting the survival of post-fire germinants in mallee communities,
in central western New South Wales, were examined. Experiments compared the
relative effects of native and introduced herbivores (kangaroos, goats,
rabbits), after small- and large-scale fires (20–50 and > 10 000 ha,
respectively), with particular emphasis on edge effects, seedling clustering,
topography and eucalypt canopy presence. The experiments (1985–1997)
focused on common understorey species Acacia rigens
Cunn. ex Don, A. wilhelmiana F.Muell. and
Triodia scariosa N.T.Burb. subsp.
scariosa, in mallee dominated by
Eucalyptus species. Following a large fire (1985), high
spring rainfall and rabbit grazing on A. rigens only,
survival of Acacia species and
T. scariosa remained relatively high 4 years later
(60–70%). After small burns (1987, 1988), low spring rainfall and
grazing by rabbits and kangaroos, survival of Acacia
species declined to between 0 and 30% of the germinants by the second
summer. In most cases, local extinction had occurred within 8 years. After
small burns (1988, 1989) and low spring rainfall, the survival of
T. scariosa declined to between 0 and 35% of
germinants by the second summer (effect of grazing unknown). No consistent
effect of edge, topography and eucalypt canopy was found. Survival of
clustered Acacia seedlings was between 10 and 20%
lower than unclustered seedlings. Given the high frequency of low rainfall and
its interaction with grazing, prescribed burning of mallee for wildfire
control and nature conservation may require the local elimination of rabbits
and a reduction in kangaroo numbers, especially in the first spring and summer
following seedling germination.
Precipitation of Calcium, Magnesium, Strontium and Barium in Tissues of Four Acacia Species (Leguminosae: Mimosoideae)