Northern Australian pasture and beef systems. 1. Net carbon position

Abstract

The beef industry in northern Australia manages ~15 million cattle, grazed on 250 million hectares of grassland and savanna woodland. The large size of the beef industry results in significant quantities of greenhouse gases being emitted to the atmosphere through ruminant livestock enteric methane production. However, livestock emissions are only one component of the carbon cycle in which grazing businesses operate. Livestock grazing also affects carbon stocks and fluxes in pasture, woody vegetation, soil and from fire through the consumption of forage and other landscape impacts. Little knowledge is available on the impact of different grazing management strategies on the ‘net carbon position’ incorporating carbon stocks and greenhouse gas emissions when grazing savanna woodlands. The Wambiana grazing trial in northern Queensland, Australia, provides an opportunity to assess carbon stocks and greenhouse gas emissions (reported as t CO2-e) associated with livestock, pasture, woody vegetation, soil and fire under alternative grazing management strategies (moderate and heavy stocking rate) over a 16-year period. The results indicate that tree biomass and woody vegetation dynamics dominate the carbon stocks and fluxes in grazed savanna woodlands. During the trial, both moderate and heavy stocking rate treatments had a positive net carbon balance, with the moderate stocking rate treatment having a better ‘net carbon position’ (19 t CO2-e per ha) than the heavy stocking rate treatment (9 t CO2-e per ha), primarily due to less livestock emissions and greater pasture biomass and soil C. These results add to the previously published benefits on land condition and economic return of grazing at moderate stocking rates, compared with heavy stocking rates.