Effects of grazing management on botanical composition of native grass-based pastures in temperate south-east Australia

Grazing management strategies to alter botanical composition of native past ures were investigated at 4 locations in the high rainfall zone of south-ea st Australia, including Tasmania. These studies were conducted as part of t he Temperate Pasture Sustainability Key Program, which evaluated the effect s of grazing management on a wide range of pasture types between 1993 and 1 996. Pastures in this study were based on Aristida ramosalBothriochloa macr a, Microlaena stipoides-Austrodanthonia spp. or Themeda triandra-Austrodant honia spp. Seasonal rests, increased grazing pressure in spring, mob stocki ng and cutting for hay were compared to continuous grazing at all sites. In addition, specific local treatments were tested at individual sites. Chang es in composition resulting from the treatments were minimal at most sites. This may have been due to a combination of the inherent stability of the p astures, the relatively short duration of the experiments, and the drought conditions experienced, which minimised differences between treatments. Som e strategies to alter composition of natural pastures are suggested. In the Aristida-Bothriochloa pasture there was a general decrease in Aristida and an increase in Bothriochloa, which was largely unaffected by the type of g razing management applied. The combination of drought conditions and increa sing grazing pressure was sufficient to alter composition without specific management strategies being necessary. In the Themeda-Austrodanthonia pastu re, resting in spring, 12-month rests or cutting for hay (which involved a spring rest) allowed Themeda to increase in the pasture. The Microlaena-Aus trodanthonia pastures were very stable, especially where annual grass conte nt was low. However, certain treatments allowed Microlaena to increase, a r esult which is regarded as being favourable. The major effects in these lat ter pastures were on undesirable species. Vulpia spp. were reduced by resti ng in autumn and increased spring grazing pressure, while Holcus lanatus wa s increased dramatically by resting in spring and was also increased by res ting in autumn or winter, but only when conditions were suitable for growth of this species. In many cases, treatment differences were only expressed following recovery from drought, showing that timing of grazing management to achieve change is critical.