James Cook University: Completed
Cenchrus ciliaris L. (buffel
grass) (Poaceae) is recognized as one of Australia’s most
serious environmental weeds. This introduced grass is associated
with loss of native species and alteration of fire regimes. However
there is considerable controversy regarding its weed status as it
is also highly valued as a pasture species for arid and semi-arid
zones. Quantitative studies are needed to determine its ecological
effects. In addition, its spread into non-target areas, including
conservation reserves, means that there is considerable interest in
strategies for containing or eliminating C. ciliaris. These
two issues, the effects of C. ciliaris on native species and
strategies for managing C. ciliaris, were the focus of
The relationship between C.
ciliaris and herbaceous species richness was investigated in
two studies at a range of scales up to 64 m2 in open
woodlands in north-eastern Queensland. In the first study, the
herbaceous species composition of sites with and without C.
ciliaris were compared. Cenchrus ciliaris-dominated
sites had fewer herbaceous species than non-C. ciliaris
sites at all scales investigated and this pattern was found for the
major plant groups (perennial grasses, legumes and other forbs)
present. In the second study, the relationship between varying
levels of C. ciliaris biomass and species richness was
investigated at one site. The relationship between varying levels
of a dominant native grass, Bothriochloa ewartiana (Domin)
C.E. Hubb. (Poaceae), and species richness was also determined for
comparison with the C. ciliaris biomass-richness
relationship. In this study, species richness was negatively
associated with increasing C. ciliaris biomass at some
scales and it appeared that C. ciliaris had a greater effect
on richness than B. ewartiana. No relationships between
B. ewartiana and total herbaceous species richness were
found. The negative association between C. ciliaris and
species richness is consistent with the view that invasion by C.
ciliaris poses a threat to biodiversity. However, the precise
cause of the relationship has yet to be determined.
The strategic use of fire offers
potential to control unwanted species. To evaluate fire as a tool
for reducing C. ciliaris abundance, the effects of season of
burning on two C. ciliaris-dominated communities in north
Queensland were investigated. Three treatments were imposed in
small plots at both sites: early dry season burn, late dry season
burn and control (no burn). These treatments were selected to
exploit differences in fire characteristics and vegetation
responses to fire associated with different season of burning.
The herbaceous species present and
their cover were recorded before and after the fires and post-fire
seedling emergence was monitored. To help understand the mechanisms
by which fire may alter community composition, burning treatment
effects on the availability of establishment sites and propagules
were also investigated. Fire affects establishment site
availability by reducing resident plant competition, by altering
nutrient availability and by altering soil surface condition.
Three studies were conducted to
investigate treatment effects on establishment sites: (1) C.
ciliaris plants were monitored to determine mortality, (2) a
bioassay technique was used to assess plant nutrient availability
and (3) a ‘pot’ experiment was conducted to examine the
effects of different soil surface cover on seedling emergence to
help predict the effects of litter removal on emergence patterns.
Fire effects on propagule supply were investigated by monitoring
flowering in C. ciliaris. A germination method was used to
determine soil seed bank composition.
Overall, burning had little effect on
these communities. The intensities of the fires were low to
moderate (300-3030 kWm-1).
At Dalrymple there was an unexpected
reversal of intensities; the mean intensity of early dry season
fires was higher than that of late dry season fires. The fires
caused no major changes in composition, few C. ciliaris
plants were killed and no changes in nutrient availability or seed
bank composition were detected. Although these short-term studies
of single fires do not allow definitive recommendations regarding
the use of fire to manage C. ciliaris, they provide
information that will aid future research. I found that fire could
kill C. ciliaris plants and reduce C. ciliaris
This contrasts with the positive fire
feedback model generally proposed for C. ciliaris.
Cenchrus ciliaris mortality was higher with early dry season
burning at Dalrymple, suggesting that higher intensity fires will
be more effective in eliminating C. ciliaris plants and/or
that C. ciliaris plants may be more susceptible to fire at
this time because they have not fully senesced. Apparent low
densities of perennial grass seeds in the seed banks of these
communities may be exploited: over-sowing with native perennial
grasses after fire may encourage shifts in perennial grass
There is an urgent need for management strategies that reduce,
prevent or contain invasive weed invasion. Further work is required
to investigate the application of fire regimes in C.
ciliaris-dominated communities. Of particular interest are
differences in growth and/or phenology between C. ciliaris
and native species in these grasslands that may be exploited to
disadvantage C. ciliaris.
Impacts and management of Cenchrus ciliaris (Buffel Grass) as an invasive species in northern Queensland
Jackson, J. (2004) "Impacts and management of Cenchrus ciliaris (Buffel Grass) as an invasive species in northern Queensland." PhD thesis, James Cook University
Invasion of native vegetation by Buffel Grass on Hillgrove Station in the Einasleigh Uplands was associated with a decline in species richness of the ground layer. Neither early dry season fire nor late dry season fire were found to control Buffel Grass.