Climate change impacts on northern Australian rangeland livestock carrying capacity: a review of issues

Abstract

Grazing is a major land use in Australia’s rangelands. The ‘safe’ livestock carrying capacity (LCC) required to maintain resource condition is strongly dependent on climate. We reviewed: the approaches for quantifying LCC; current trends in climate and their effect on components of the grazing system; implications of the ‘best estimates’ of climate change projections for LCC; the agreement and disagreement between the current trends and projections; and the adequacy of current models of forage production in simulating the impact of climate change. We report the results of a sensitivity study of climate change impacts on forage production across the rangelands, and we discuss the more general issues facing grazing enterprises associated with climate change, such as ‘known uncertainties’ and adaptation responses (e.g. use of climate risk assessment). We found that the method of quantifying LCC from a combination of estimates (simulations) of long-term (>30 years) forage production and successful grazier experience has been well tested across northern Australian rangelands with different climatic regions. This methodology provides a sound base for the assessment of climate change impacts, even though there are many identified gaps in knowledge. The evaluation of current trends indicated substantial differences in the trends of annual rainfall (and simulated forage production) across Australian rangelands with general increases in most of western Australian rangelands (including northern regions of the Northern Territory) and decreases in eastern Australian rangelands and south-western Western Australia. Some of the projected changes in rainfall and temperature appear small compared with year-to-year variability. Nevertheless, the impacts on rangeland production systems are expected to be important in terms of required managerial and enterprise adaptations. Some important aspects of climate systems science remain unresolved, and we suggest that a risk-averse approach to rangeland management, based on the ‘best estimate’ projections, in combination with appropriate responses to short-term (1–5 years) climate variability, would reduce the risk of resource degradation. Climate change projections – including changes in rainfall, temperature, carbon dioxide and other climatic variables – if realised, are likely to affect forage and animal production, and ecosystem functioning. The major known uncertainties in quantifying climate change impacts are: (i) carbon dioxide effects on forage production, quality, nutrient cycling and competition between life forms (e.g. grass, shrubs and trees); and (ii) the future role of woody plants including effects of fire, climatic extremes and management for carbon storage. In a simple example of simulating climate change impacts on forage production, we found that increased temperature (3°C) was likely to result in a decrease in forage production for most rangeland locations (e.g. –21% calculated as an unweighted average across 90 locations). The increase in temperature exacerbated or reduced the effects of a 10% decrease/increase in rainfall respectively (–33% or –9%). Estimates of the beneficial effects of increased CO2 (from 350 to 650 ppm) on forage production and water use efficiency indicated enhanced forage production (+26%). The increase was approximately equivalent to the decline in forage production associated with a 3°C temperature increase. The large magnitude of these opposing effects emphasised the importance of the uncertainties in quantifying the impacts of these components of climate change. We anticipate decreases in LCC given that the ‘best estimate’ of climate change across the rangelands is for a decline (or little change) in rainfall and an increase in temperature. As a consequence, we suggest that public policy have regard for: the implications for livestock enterprises, regional communities, potential resource damage, animal welfare and human distress. However, the capability to quantify these warnings is yet to be developed and this important task remains as a challenge for rangeland and climate systems science.

Adaptation to climate change – exploring the potential of locally adapted breeds

“…Already during the last decade, a high number of extreme heat waves affected major food crop growing by drought (Fischer, 2011; World Bank, 2012). McKeon et al (2009) observed that in Australia, current yearto-year variability exceeds projected changes in temperature and rainfall, but that climate change is projected to affect forage and animal production and ecosystem functioning.…”

“…The models developed by Fischer (2011) assume full agronomic adaptation by farmers, whereas McKeon et al (2009) foresee challenges for important managerial and enterprise adaptations even in a developed country such as Australia. Vermeulen et al (2012) note that low-income producers will be more vulnerable to climate change owing to their limited ability to invest in adaptive institutions and technologies.…”

“…Nonetheless, their reliance on local natural resources makes them vulnerable to local disasters or problems such as declines in the quantity or quality of forage or the emergence of unfamiliar diseases or parasites. For rangelands, the major uncertainties in quantifying climate change impacts are the CO 2 fertilization effect on forage production and quality, species assemblages (competition between grass, shrubs, trees) and the role of woody plants (McKeon et al, 2009). Changes in fodder quality and diet composition also affect digestibility and rumen functioning (Gauly et al, 2013).…”

“…Already during the last decade, a high number of extreme heat waves affected major food crop growing by drought (Fischer, 2011; World Bank, 2012). McKeon et al (2009) observed that in Australia, current yearto-year variability exceeds projected changes in temperature and rainfall, but that climate change is projected to affect forage and animal production and ecosystem functioning.The models developed by Fischer (2011) assume full agronomic adaptation by farmers, whereas McKeon et al (2009) foresee challenges for important managerial and enterprise adaptations even in a developed country such as Australia. Vermeulen et al (2012) note that low-income producers will be more vulnerable to climate change owing to their limited ability to invest in adaptive institutions and technologies.…”

Sustainable management for rangelands in a variable climate: evidence and insights from northern Australia

“…Runoff water quality has also declined threatening key downstream ecosystems like the Great Barrier Reef lagoon (Furnas, 2003). With climate change projections of a hotter, drier and potentially more variable climate, sustainable management of northern Australian rangelands is likely to become even more challenging (McKeon et al, 2009). …”