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
paper session 29: Molecular biology - forage quality. In: Proc. XVII International Grassland Congress, pp. 1105-6. Keeling and Mundy Ltd., Palmerston North, New Zealand. United States Department of Agriculture. (1980). Report and recommendations on organic farming. U.S. Government Printing Office, Washington, DC. VanTassel, L. W., Heitschmidt, R.K. and Conner, J.R. (1987). Modeling variation in range calf growth under conditions of environmental uncertainty. J. Range. Manage. 40: 310-4. Walker, B.H. (1993). Stability in rangelands: ecology and economics. In: Proc. XW International Grassland Congress, pp. 1885-90. Keeling and Mundy Ltd., Palmerston North, New Zealand. Walker, J.W. (1994). Multispecies grazing: the ecological advantage. Sheep Res. J. Special Issue: 52-64. Walker, A.B., Frizelle, J.A. and Morris, S.D. (1994). The New Zealand policy framework for sustainable agriculture and some implications for animal production research. Proc. N. Z. Soc. Anim Prod. 54: 369-72. Walker, J.W., Heitschmidt, R.K., DeMoraes, E.A., Kothmann, M.M. and Dowhower, S.L. (1989). Quality and botanical composition of cattle diets under rotational and continuous grazing treatments. J. Range Manage . 42: 239-42. Whitson, R.E., Heitschmidt, R.K., Kothmann, M.M. and Lundgren, G.K. (1982). The impact of grazing systems on the magnitude and stability of ranch income in the Rolling Plains of Texas. J. Range Manage .35: 526-32. Wight, J.R. and Hanson, C.L. (1993). Simulation models as decision aids for management of rangeland ecosystems. In: Proc. XVII International Grassland Congress, pp. 770-1. Keeling and Mundy Ltd., Palmerston North, New Zealand. Wilson, A.D., Harrington, G.N. and Beale, I.F. (1984). Grazing management. In: Management of Australia's rangelands (Eds G.N. Harrington, A.D. Wilson and M.D. Young) pp. 129-40. Commonwealth Scientific and Industrial Research Organization, Australia. Wood, W.R. and Thiessen, T.D. (Eds) (1985). Early fur trade on the Northern Plains: the narratives of John Macdonnell, David Thompson, Francois-Antoine Laraocque and Charles McKenzie. University of Oklahoma Press, Norman, Oklahoma. Manuscript received 4 April 1996, accepted 30 July 1996. Rangel. J. 18(2) 1996, 216-43 EVALUATING STOCKING RATE IMPACTS IN RANGELANDS: ANIMALS DON'T PRACTICE WHAT WE PREACH A.J. Ash1 and D.M. Stafford Smith2 'CSIRO Division of Tropical Crops and Pastures, PMB, Aitkenvale, Qld 4814 2CSIR0 Division of Wildlife and Ecology, PO Box 2111, Alice Springs, NT 0871 Abstract Stocking rate is the most important management variable affecting productivity and stability in rangelands. In this paper we examine the relevance of stocking rate research to the complex and highly variable ecosystems that make up most rangeland enterprises. We review a number of stocking rate experiments that have been conducted in both rangelands and more intensively grazed, improved pastures and demonstrate a fundamental difference in the nature of the stocking rate - animal production relationship between the two environments. Animal production in rangelands is less sensitive to increases in utilisation rate than in improved pastures, at least in the short to medium time frame of most experiments. These differences can largely be explained by factors relating to the much greater spatial and temporal variability of rangelands such as: inter-annual and seasonal fluctuations in vegetation composition and quality; long-term vegetation changes; and spatial and temporal patterns of diet selection in complex vegetation. Together, these factors limit the application of linear stocking rate models to complex rangeland environments for prediction of animal production responses. We suggest that dynamic simulation models, which incorporate the spatial and temporal variability of rangelands, may be the best way of developing simple but useful management principles for setting stocking rates that are more appropriate than simplified regression relationships.
Managing rangeland enterprises requires balancing socio-economic goals within a production environment characterised by ecological complexity and large climatic variability. Trafalgar Station in north-east Queensland, has been trying to maintain this balance over a period of 80 years and three generations of the one family. This paper explores how management on Trafalgar Station has gone through four evolutionary phases and examines the advantages and disadvantages of each of these stages of development. The first 50 years of management was a technologically constrained era of low stock numbers and poor productivity but there were few resource management problems. Next followed a 20 year period of production maximisation which was made possible by improved cattle genetics and nutritional technologies. With drought feeding occurring more frequently and loss of perennial grasses and soil becoming more evident, there came the realisation that this high stocking strategy was unsustainable. The management of Trafalgar then embarked on a new philosophy based on conservative stocking (similar to historical levels) and increased emphasis on herd, pasture and financial management. This new management philosophy required a transitional phase where stock numbers. and income, were very low to allow pasture condition to improve. Current herd management focuses on maintaining quality rather than quantity, strategic use of supplements for production, and developing a diverse range of markets for sale cattle. Conservative stock numbers have increased opportunities in pasture management with 15 to 20% of the property now annually rested from grazing. Fire has been reintroduced to restrict "thickening" of native woody plants and to control exotic woody weeds. Together with long-term financial planning, these improvements in management are reducing economic risk. The perceived benefits of the current management philosophy are supported by simulation modelling studies of pasture and animal production and analyses of property economics.
SummaryElimination of the rumen anaerobic fungi from sheep fed chemically-treated barley straw diets resulted in elevated proportions of propionic acid in rumen liquor (fromca. 0·15 to 0·30). Subsequent inoculation of these sheep with a pure culture of fungus decreased propionate concentrations within 3 days to the levels observed in control animals that possessed abundant fungal populations throughout the experiment.Confirmation that propionate itself was not responsible for the elimination of the fungi was provided by the results of a second experiment in which intraruminal infusions of propionic acid failed to reduce fungal growth or prevent recolonization in sheep previously rendered fungi-free.In a third experiment with sheep fed untreated barley straw, monensin supplementation produced the well known elevation of propionate concentrations. However, this treatment also resulted in the elimination of rumen anaerobic fungi from the animals. The magnitude of the increased concentration of rumen propionic acid, resulting from the elimination of the anaerobic fungal flora, indicates an important role for the fungi in the fermentation of high-fibre diets. In addition, these findings indicate that the well known elevation of propionate levels produced by monensin may likewise be effected directly by removal of the rumen anaerobic fungi.
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