Building Grass Castles: Integrating Ecology and Management of Australia's Tropical Tallgrass Rangelands.

Abstract

The tropical tallgrass rangelands of Australia are declining in condition in response to increased grazing pressure. However, large areas are still in good condition and many of the deteriorated areas are not yet irreversibly damaged. Increases in grazing pressure have been associated with the loss of perennial grasses, woody weed invasion, and increased run-off and soil loss in some areas. The population dynamics, diet selection patterns, defoliation responses of the perennial grasses and impacts of fire are outlined and ways this understanding can be incorporated into management are presented. The perennial grasses are sensitive to defoliation and can only be lightly utilised. Annual utilisation rates should not exceed 25% in areas of moderate and high fertility and this threshold 'safe' level decreases to 15% on infertile soils in the monsoon zone of the north and north-west. Spelling pastures during the wet season, when they are particularly sensitive to defoliation, may enable utilisation during the rest of the year to be increased. Such a grazing regime allows fuel accumulation, increasing the opportunity for use of fire in managing exotic woody weeds and the treetshrub layer. Fire can also be used to improve animal distribution and reduce the formation of patches which are prone to soil degradation. Sown pastures and tree clearing can be used to increase carrying capacity and improve flexibility in the management of native pastures but careful consideration needs to be given to these improvements to prevent problems such as salinisation and unwanted spread of exotic pasture plants. One of the difficulties in developing recommendations relevant to management is that most of the ecological understanding is at the plant and plant community scale but most problems occur at the paddocWlandscape scale where our knowledge base is limited. Future work should focus at this large spatial scale so that ecological principles derived from a range of scales can be better integrated into guidelines more appropriate to extensive management of tropical tallgrass rangelands. Key words: grazing, population dynamics, defoliation, diet selection, fire, grass decline