Afshin Ghahramani

Climate change and broadacre livestock production across southern Australia. 2. Adaptation options via grassland management

Abstract. Climate change is predicted to cause a significant reduction in the productivity of grasslands and the livestock industry across southern Australia. We have used the GRAZPLAN biophysical simulation models to assess a range of pasture management practices as adaptation options under the SRES A2 global change scenario. The modelling analysis spanned four dimensions: space (25 representative locations), time (2030, 2050, 2070, and a historical reference period of 1970–99), livestock enterprises (five), and management (four adaptation options at different levels). Climate projection uncertainty was taken into account by considering climates from four global climate models. The effectiveness of adaptation options varied widely among enterprises and locations, over time, and under the four projected future climates. Increased soil fertility by adding phosphorus and addition of an area of lucerne to the feed-base were predicted to have the greatest effect in recovering from the negative impact of climate change on profitability. In high-rainfall zones in particular, and compared with the historical period, the most profitable option could return the profitability of livestock production systems to historical levels at 68%, 52%, and 32% of the representative locations at 2030, 2050, and 2070, respectively. At 2030, increased soil fertility, adding lucerne to the feed-base, and confinement feeding in summer recovered overall profit fully at 52%, 28%, and 12% of locations. Removing annual legumes in an attempt to preserve ground cover was ineffective as an adaptation to changing climate. For the majority of location × livestock enterprise combinations, there was at least one individual incremental adaptation that could recover the declines in the profitability at 2030, but effectiveness decreased over time after 2030. It is unlikely that the examined single climate change adaptations to the feed-base of southern Australian livestock production systems can return them to profitability in the second half of the century.

Climate change and broadacre livestock production across southern Australia. 3. Adaptation options via livestock genetic improvement

Climate change is predicted to reduce the productivity of the broadacre livestock industries across southern Australia; to date there has been no formal evaluation of the potential of genetic improvement in cattle or sheep to ameliorate the impacts of changing climates. We used the GRAZPLAN simulation models to assess selection of five traits of sheep and cattle as adaptation options under the SRES A2 global change scenario. Analysis of the breeding strategies was carried out for 25 representative locations, five livestock enterprises and three future years (2030, 2050, 2070). Uncertainty in future climates was taken into account by considering projected climates from four global circulation models. For three sheep enterprises, breeding for greater fleece growth (at constant body size) was predicted to produce the greatest improvements in forage conversion efficiency, and so it was the most effective genetic adaptation option. For beef cow and steer enterprises, breeding for larger body size was most effective; for beef cows, however, this conclusion relied on per-animal costs (including provision of bulls) remaining stable as body size increases. Increased conception rates proved to be less effective but potentially viable as an adaptation in beef cow and crossbred ewe enterprises. In the southern Australian environments that were analysed, our modelling suggests that breeding for tolerance to heat stress is unlikely to improve the performance of livestock production systems even at 2070. Genetic improvement of livestock was able to recover much less of the impact of climate change on profitability at drier locations where the need for adaptation is likely to be greatest. Combinations of feedbase and livestock genetic adaptations are likely to complement one another as the former alter the amount of forage that can be consumed, while the latter affect the efficiency with which consumed forage is converted to animal products. Climate change impacts on pasture production across southern Australia are likely to have only small effects on methane emissions intensity, as are a range of candidate genetic and feedbase adaptations to climate change; methane emissions per hectare in future climates will therefore be driven mainly by changes in livestock numbers due to alterations in pasture productivity.

Sheep greenhouse gas emission intensities under different management practices, climate zones and enterprise types

Greenhouse gas emissions (GHG) from broadacre sheep farms constitute ~16% of Australia’s total livestock emissions. To study the diversity of Australian sheep farming enterprises a combination of modelling packages was used to calculate GHG emissions from three sheep enterprises (Merino ewe production for wool and meat, Merino-cross ewes with an emphasis on lamb production, and Merino wethers for fine wool production) at 28 sites across eight climate zones in southern Australia. GHG emissions per ha, per dry sheep equivalents and emissions intensity (EI) per tonne of clean wool or liveweight sold under different pasture management or animal breeding options (that had been previously determined in interviews with farmers) were assessed relative to baseline farms in each zone (‘Nil’ option). Increasing soil phosphorus fertility or sowing 40% of the farm area to lucerne resulted in the smallest and largest changes in GHG/dry sheep equivalents, respectively (–66%, 113%), though both of these options had little influence on EI for either clean wool or liveweight sold. Breeding ewes with greater body size or genotypes with higher fleece weight resulted in 11% and 9% reductions, respectively, in EI. Enterprises specialising in lamb production (crossbred ewes) had 89% lower EI than enterprises specialising in fine wool production (Merino wethers). Thus, sheep producers aiming for lower EI could focus more on liveweight turnoff than wool production. Emissions intensities were typically highest in cool temperate regions with high rainfall and lowest in semiarid and arid regions with low aboveground net primary productivity. Overall, animal breeding options reduced EI more than feedbase interventions.