Impacts of a two degree increase in temperature on pasture growth in the Northern Tablelands of New South Wales

Abstract

Sheep production is the major contributor to the agricultural economy of the Northern Tablelands of New South Wales. In 1996/97 $109.1 million was derived from sheep production. There is a pressing need for agricultural industries to reduce their carbon footprint and global warming is a major concern. This study has simulated a sheep production system of a 36 ha research station called 'Trevenna' located at the University of New England, Armidale (30° 30'S 151° 40' E). The 'Trevenna' site has been set up as a demonstration site for producers, advisers, students, and researchers to gain insight into how to estimate and measure livestock enteric methane emissions. The Sustainable Grazing Systems (SGS) model was used to simulate, over 50 years, pasture growth on the 'Trevenna' demonstration site. Simulations contrasted the impacts of a 2°C change in temperature on herbage mass (t/ha) and pasture growth rate (kg C/ha/day). A validation check indicated that the predicted values from 1st Sep 2010 to 30th March 2011 fell within 10% of the observed values. There was no effect of the 2°C increase in temperature on green herbage mass (P > 0.05) but a significant difference for dead herbage mass and pasture growth rate (P < 0.05). The increase in dead herbage mass is discussed. A significant effect of temperature on botanical composition (P < 0.05) was found with an increase in C4 native grasses (e.g. kangaroo grass, red grass, and wire grass) at the expense of other pasture species present in the sward. The impact of a 2°C increase in temperature reduced the number of frosts (defined as mornings below 2°C) and number of severe frosts (defined as mornings below 0°C). In conclusion, a 2°C increase in temperature on the Northern Tablelands of New South Wales can be expected to increase pasture growth, particularly of C4 species, so supporting an increase in herbage mass.