The grassy vegetation of the Darling Downs, south-eastern Queensland, Australia. Floristics and grazing effects Original Research Article

An ordination of floristic data from the grassy vegetation of the Darling Downs in southern Queensland describes four broad vegetation types, red gum (Eucalyptus camaldulensis/E. tereticornis) woodland associated with the flood-plain of the major streams, grassland on alluvial clay, poplar box (E. populnea) on clay loam terraces and hill woodland dominated by any of E. albens, E. crebra, E. melliodora, E. orgadophila. Ten per cent of species proved sensitive to grazing intensity categories (derived largely from land tenure) in hill woodland compared to 3% of species in grassland or poplar box woodland. There were no clear trends in the relative response of native and exotic species, although overall, species richness was greatest in either the moderate or heavily grazed treatment for all broad vegetation types. It is suggested that the interaction between Themeda dominance and the inter-tussock flora may contribute to the importance of grazing as a determinant of floristic composition in hill woodland broad vegetation type. Mechanical disturbance is implicated as a means of effecting the spread of exotic plants. However, there are relatively few exotic species that appear to have the capacity to displace native species without mechanical disturbance, although a notable exception is Phyla canescens in the flood-prone habitat. Moderate domestic stock grazing is compatible with nature conservation on the Darling Downs, although it is demonstrated that a proportion of the flora is sensitive to grazing. Remnants will need to be managed under a range of grazing regimes, including light total grazing pressure that excludes domestic stock to ensure the survival of the full range of species.