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.
