Future roles for native woody species in Australian agricultural landscapes

Abstract

Australian broadacre agricultural lands are dominated by annual crop and pasture species with relatively shallow root depths compared to perennial species and low accumulation of above ground biomass. Deterioration of the environment in these landscapes by dryland salinity, nutrient losses, soil degradation, emission of greenhouse gases and loss of biodiversity may be averted by phases of native woody species and shrubs. Recently, lucerne and other herbaceous perennials have begun to be incorporated into broadacre cropping systems for hydrological control. There are indications, however, that lucerne may not be as efficient as woody species in dewatering the soil profile. Some recent studies in America have shown that mitigation of net global warming potential by lucerne was significantly less than woody species, due to nitrous oxide emissions and lime requirements in the lucerne and resistance of woody species to decomposition in the soil. Pastures such as lucerne have different biodiversity values compared with native woody species. Phases of different ages of native woody species are likely to provide multiple niches for enhanced biodiversity, provided biological assets are maintained when cropping and/or pasture phases are resumed. Problems perceived with use of woody species often centre on loss of income during the early years of their growth. However, forecast markets for emerging bio-energy industries, and ecosystem services incentives could provide worthwhile returns. This hypothetical approach using native woody species is untested scientifically and research is needed to ascertain their utility in a range of Australian environments. The selected examples we have shown focus on environmental outcomes and would depend on favourable socio-economic structures for implementation. We envisage that optimisation of overall environmental gains could be achieved in a six year time frame.