G. M. McKeon

Learning from episodes of degradation and recovery in variable Australian rangelands

Land-change science emphasizes the intimate linkages between the human and environmental components of land management systems. Recent theoretical developments in drylands identify a small set of key principles that can guide the understanding of these linkages. Using these principles, a detailed study of seven major degradation episodes over the past century in Australian grazed rangelands was reanalyzed to show a common set of events: (i) good climatic and economic conditions for a period, leading to local and regional social responses of increasing stocking rates, setting the preconditions for rapid environmental collapse, followed by (ii) a major drought coupled with a fall in the market making destocking financially unattractive, further exacerbating the pressure on the environment; then (iii) permanent or temporary declines in grazing productivity, depending on follow-up seasons coupled again with market and social conditions. The analysis supports recent theoretical developments but shows that the establishment of environmental knowledge that is strictly local may be insufficient on its own for sustainable management. Learning systems based in a wider community are needed that combine local knowledge, formal research, and institutional support. It also illustrates how natural variability in the state of both ecological and social systems can interact to precipitate nonequilibrial change in each other, so that planning cannot be based only on average conditions. Indeed, it is this variability in both environment and social subsystems that hinders the local learning required to prevent collapse.

Simulation of Grazing Strategies for Beef Production in North-East Queensland

A simulation study was conducted to compare diverse grazing strategies for steers grazing open woodlands in northeast Queensland. Simulations included a wide range of possible stocking rates and pasture utilisation levels using 108 years (1889–1996) of daily climate data for Charters Towers. Five strategies were compared in terms of steer liveweight gain per ha, risk of weight loss, pasture availability, frequency of burning and soil loss. The strategies included constant stocking, stocking in response to available feed, and stocking in response to predicted future feed availability based on a climate forecast. For strategies achieving an average annual liveweight gain per head of about 100 kg, the simulation studies indicated that a responsive stocking rate strategy in June using a forecast of the next year’s pasture growth would increase liveweight gain per ha by about 10%, reduce the risk of liveweight loss by 57%, reduce risk of low pasture yield, but would slightly increase the risk of soil loss (4%). Maximum LWG/ha was achieved at high utilisation rates (> 35%). However, at such high levels of utilisation burning was achieved in less than 10% of years and soil loss was 30–40% more than at levels of utilisation regarded as safe (≈20%). The simulations highlighted the potential value of achieving in June, the skill from seasonal forecasting that is now available in November using average SOI in the Aug-Oct period as the indicator of season type. Assumptions in the model development are outlined and future work required is discussed. Despite the complexity of the simulation analysis, it is concluded that there is a trade-off between production and environmental damage, and that improved forecasting may improve production and/or reduce damage.

A review of the potential role of greenhouse gas abatement in native vegetation management in Queensland's rangelands

Concern about the risk of harmful human-induced climate change has resulted in international efforts to reduce greenhouse gas emissions to the atmosphere. We review the international and national context for consideration of greenhouse abatement in native vegetation management and discuss potential options in Queensland. Queensland has large areas of productive or potentially productive land with native woody vegetation cover with approximately 76 million ha with woody cover remaining in 1991. High rates of tree clearing, predominantly to increase pasture productivity, continued throughout the 1990s with an average 345,000 ha/a estimated to have been cleared, including non-remnant (woody regrowth) as well as remnant vegetation. Estimates of greenhouse gas emissions associated with land clearing currently have a high uncertainty but clearing was reported to contribute a significant proportion of Australias total greenhouse gas emissions from 1990 (21%) to 1999 (13%). In Queensland, greenhouse emissions from land clearing were estimated to have been 54.5 Mt CO2-e in 1999. Management of native vegetation for timber harvesting and the proliferation of woody vegetation (vegetation thickening) in the grazed woodlands also represent large carbon fluxes. Forestry (plantations and native forests) in Queensland was reported to be a 4.4 Mt CO2-e sink in 1999 but there are a lack of comprehensive data on timber harvesting in private hardwood forests. Vegetation thickening is reported for large areas of the c. 60 million ha grazed woodlands in Queensland. The magnitude of the carbon sink in 27 million ha grazed eucalypt woodlands has been estimated to be 66 Mt CO2-e/a but this sink is not currently included in Australias inventory of anthropogenic greenhouse emissions. Improved understanding of the function and dynamics of natural and managed ecosystems is required to support management of native vegetation to preserve and enhance carbon stocks for greenhouse benefits while meeting objectives of sustainable and productive management and biodiversity protection.

The climate change risk management matrix for the grazing industry of northern Australia

The complexity, variability and vastness of the northern Australian rangelands make it difficult to assess the risks associated with climate change. In this paper we present a methodology to help industry and primary producers assess risks associated with climate change and to assess the effectiveness of adaptation options in managing those risks. Our assessment involved three steps. Initially, the impacts and adaptation responses were documented in matrices by ‘experts’ (rangeland and climate scientists). Then, a modified risk management framework was used to develop risk management matrices that identified important impacts, areas of greatest vulnerability (combination of potential impact and adaptive capacity) and priority areas for action at the industry level. The process was easy to implement and useful for arranging and analysing large amounts of information (both complex and interacting). Lastly, regional extension officers (after minimal ‘climate literacy’ training) could build on existing knowledge provided here and implement the risk management process in workshops with rangeland land managers. Their participation is likely to identify relevant and robust adaptive responses that are most likely to be included in regional and property management decisions. The process developed here for the grazing industry could be modified and used in other industries and sectors. By 2030, some areas of northern Australia will experience more droughts and lower summer rainfall. This poses a serious threat to the rangelands. Although the impacts and adaptive responses will vary between ecological and geographic systems, climate change is expected to have noticeable detrimental effects: reduced pasture growth and surface water availability; increased competition from woody vegetation; decreased production per head (beef and wool) and gross margin; and adverse impacts on biodiversity. Further research and development is needed to identify the most vulnerable regions, and to inform policy in time to facilitate transitional change and enable land managers to implement those changes.

Global change impacts on native pastures in south-east Queensland, Australia

Increases in atmospheric concentrations of greenhouse gases such as carbon dioxide (CO2) are likely to impact on grazing industries through direct effects on plant growth and through possible changes in climate. Assessment of the likely direction and magnitude of these impacts requires development of appropriate modelling capacities linked with experimental work. This paper documents the adaptation of an existing soil–pasture–livestock model, GRASP, to simulate system responses to changes in CO2. The adapted model is then used to compare these responses under current climate and CO2 conditions with four possible future scenarios: (1) doubled CO2; (2) doubled CO2 and increased temperature; (3) as in the previous scenario but with a drier climate; and (4) as in (2) but with a wetter climate. These studies suggest that CO2 changes alone are likely to have beneficial effects, with increased pasture growth, increased and less variable liveweight gain, and increased ground cover. However, subsoil drainage is likely to increase. Growth responses to CO2 are likely to be greater in drier years than in wetter years partly due to nitrogen limitations in the soils of the region. Increases in temperature in combination with CO2 further increased animal production due to the increased number of growing days in the cooler months. The increased rainfall scenario had few additional positive effects but further increased subsoil drainage. In contrast, the drier scenario had reduced plant and animal production when compared with current conditions even though seasonal transpiration efficiency was increased by 20% due to increased CO2.

Global change and the mulga woodlands of southwest Queensland: greenhouse gas emissions, impacts, and adaptation

The possibility of trading greenhouse gas emission permits as a result of the Kyoto Protocol has spurred interest in developing land-based sinks for greenhouse gases. Extensive grazing lands that have the potential to develop substantial woody biomass are one obvious candidate for such activities. However, such activities need to consider the possible impacts on existing grazing and the possible impacts of continuing CO2 buildup in the atmosphere and resultant climate change. We used simulation models to investigate these issues in the mulga (Acacia aneura) woodlands of southwest Queensland. The simulation results suggest that this system can be managed to act as either a net source or a net sink of greenhouse gases under current climate and CO2 and under a range of global change scenarios. The key component in determining source or sink status is the management of the woody mulga. The most effective means of permanently increasing carbon stores and hence reducing net emissions is to exclude both burning and grazing. There are combinations of management regimes, such as excluding fire with light grazing, which, on average, allows productive grazing but transient carbon storage. The effects of increased CO2 on ecosystem carbon stores were unexpected. Carbon stores increased (7-17%) with doubling of CO2 only in those simulations where burning did not occur, but decreased when burnt. This occurred because the substantial increases in grass growth with doubling of CO2 (34-56%) enabled more fires, killing off the establishing cohorts needed to ensure continued carbon accumulation. On average, the doubling of atmospheric CO2 concentration increased grass growth by 44%, which is identical with mean literature values, suggesting that this result may be applicable in other ecosystems where fire has a similar function. A sensitivity analysis of the CO2 response of mulga showed only minor impacts. We discuss additional uncertainties and shortcomings.

Methods for exploring management options to reduce greenhouse gas emissions from tropical grazing systems

Increasing atmospheric concentrations of ‘greenhouse gases’ are expected to result in global climatic changes over the next decades. Means of evaluating and reducing greenhouse gas emissions are being sought. In this study an existing simulation model of a tropical savanna woodland grazing system was adapted to account for greenhouse gas emissions. This approach may be able to be used in identifying ways to assess and limit emissions from other rangeland, agricultural and natural ecosystems.GRASSMAN, an agricultural decision-support model, was modified to include sources, sinks and storages of greenhouse gases in the tropical and sub-tropical savanna woodlands of northern Australia. The modified model was then used to predict the changes in emissions and productivity resulting from changes in stock and burning management in a hypothetical grazing system in tropical northeastern Queensland. The sensitivity of these results to different Global Warming Potentials (GWPs) and emission definitions was then tested.Management options to reduce greenhouse gas emissions from the tropical grazing system investigated were highly sensitive to the GWPs used, and to the emission definition adopted. A recommendation to reduce emissions by changing burning management would be toreduce fire frequency if both direct and indirect GWPs of CO2, CH4, N2O, CO and NO are used in evaluating emissions, but toincrease fire frequency if only direct GWPs of CO2, CH4 and N2O are used. The ability to reduce greenhouse gas emissions from these systems by reducing stocking rates was also sensitive to the GWPs used. In heavily grazed systems, the relatively small reductions in stocking rate needed to reduce emissions significantly should also reduce the degradation of soils and vegetation, thereby improving the sustainability of these enterprises.The simulation studies indicate that it is possible to alter management to maximise beef cattle production per unit greenhouse gases or per unit methane emitted, but that this is also dependent upon the emission definition used. High ratios of liveweight gain per unit net greenhouse gas emission were found in a broadly defined band covering the entire range of stocking rates likely to be used. In contrast, high values of liveweight gain per unit ‘anthropogenic’ greenhouse gas emission were found only at very low stocking rates that are unlikely to be economically viable.These results suggest that policy initiatives to reduce greenhouse gas emissions from tropical grazing systems should be evaluated cautiously until the GWPs have been further developed and the implications of emission definitions more rigorously determined.

The dynamics of grazed woodlands in southwest Queensland, Australia and their effect on greenhouse gas emissions

This study outlines the development of an approach to evaluate the sources, sinks, and magnitudes of greenhouse gas emissions from a grazed semiarid rangeland dominated by mulga (Acacia aneura) and how these emissions may be altered by changes in management. This paper describes the modification of an existing pasture production model (GRASP) to include a gas emission component and a dynamic tree growth and population model. An exploratory study was completed to investigate the likely impact of changes in burning practices and stock management on emissions. This study indicates that there is a fundamental conflict between maintaining agricultural productivity and reducing greenhouse gas emissions on a given unit of land. Greater agricultural productivity is allied with the system being an emissions source while production declines and the system becomes a net emissions sink as mulga density increases. Effective management for sheep production results in the system acting as a net source (approximately 60-200 kg CO2 equivalents/ha/year). The magnitude of the source depends on the management strategies used to maintain the productivity of the system and is largely determined by starting density and average density of the mulga over the simulation period. Prior to European settlement, it is believed that the mulga lands were burnt almost annually. Simulations indicate that such a management approach results in the system acting as a small net sink with an average net absorption of greenhouse gases of 14 kg CO2 equivalents/ha/year through minimal growth of mulga stands. In contrast, the suppression of fire and the introduction of grazing results in thickening of mulga stands and the system can act as a significant net sink absorbing an average of 1000 kg CO2 equivalents/ha/year. Although dense mulga will render the land largely useless for grazing, land in this region is relatively inexpensive and could possibly be developed as a cost-effective carbon offset for greenhouse gas emissions elsewhere. These results also provide support for the hypothesis that changes in land management, and particularly, suppression of fire is chiefly responsible for the observed increases in mulga density over the past century.

Assessing the historical frequency of drought events on grazing properties in Australian rangelands

Abstract Using a simulation model of sheep and cattle grazing systems in different regions of the Australian rangelands, we tested the use of different measures and analyses for identifying an ‘exceptional circumstances’ drought event, defined as occurring once in 20 years in the long term. Over the century-long simulations, all measures (rainfall, various soil moisture measures, pasture growth, liveweight gain and an economic productivity index) identified the major drought periods in each region. However, the measures differed considerably in the identification of marginal events, because economic and biological hardship are not always synchronised. Total soil moisture seems to be the best single measure, providing it is properly calculated, but there is a strong case for considering more than one measure. Periods perceived as exceptional are also greatly affected by the choice of averaging technique, moving window, and assumptions about baseline management strategies. Hence the choice of index has implications for sustainability. We also show that revocation criteria are as important as the criteria for declaring a drought, and discuss the difficult balance between objectivity and equity.

Managing Climate Variability in Grazing Enterprises: A Case Study of Dalrymple Shire, North-Eastern Australia

In this paper we examine approaches to managing climate variability in the Dalrymple Shire of north-east Queensland. We use the forage-animal production model Grasp to evaluate the production and resource implications of grazing management and seasonal climate forecasting strategies. In this study, five forecasting strategies were assessed at each of nine test rainfall stations in Dalrymple Shire. Forecasting strategies used were: (a) spring SOI, (b) spring SOI phases, (c) an SOI phase system “tuned” to Charters Towers rainfall, (d) winter Pacific Ocean sea surface temperatures (EOF analyses), and (e) winter Pacific and Indian Ocean sea surface temperatures (EOF analyses). Stocking rates were adjusted annually according to analogue year types provided by the forecasts. In forecast “dry” years stock numbers were reduced by 50% and in “wet” years they were increased by 30%. Stocking rate changes were made in either November, when all forecasts were available, or in June, which assumes some improvement in forecasting lead time, particularly for the SOI.