The effects of rabbits and kangaroos, and rabbits alone, on the biomass and species composition of a
native grassland dominated by Stipa nitida/nodosa, Danthonia caespitosa and Aristida contorta, and
a grassland dominated by the exotic species Hordeum glaucum, Vulpia spp., Medicago laciniata and the
native Erodium crinitum growing at Yathong Nature Reserve in central New South Wales was monitored
between 1979 and 1985. Rabbits generally favoured the grassy component; kangaroos also favoured
grasses but less so. Changes in non-grass species composition due to grazing was generally insignificant.
Changes in species composition due to seasonal differences in rainfall was highly significant. No new
species appeared on plots exclosed from grazing for 10 years, suggesting that the grazing by livestock,
rabbits, and kangaroos in the past has determined the present species composition. The annual biomass
consumption by rabbits averaged over 6 years was 100-200 kg ha-1, which is equivalent to reducing the
carrying capacity by one sheep for every 2-4 ha rabbit-infested area. In the native grassland the spatial
pattern of rabbit grazing, as indicated by faecal pellet distribution, biomass removal, and percentage
of 'unpalatable' species in the pasture, shows greatest grazing pressure to be within 50 m of the warren,
grazing intensity dropping off from there to 300 m the greatest distance studied. From the start of the
study 'palatable' species, especially grasses, were at their lowest density within 50 m of the warren; this
appeared to be a historical effect of grazing. No patterns were discernible in the pasture dominated by
introduced species. Little change in species composition of these grasslands can be expected under a
wide range of grazing pressure, except close to rabbit warrens.