THE GRASSY VEGETATION OF THE DARLING DOWNS, SOUTH-EASTERN QUEENSLAND,AUSTRALIA - FLORISTICS AND GRAZING EFFECTS

An ordination of floristic data from the grassy vegetation of the Darl ing Downs in southern Queensland describes four broad vegetation types , red gum (Eucalyptus camaldulensis/E. tereticornis) woodland associat ed with the flood-plain of the major streams, grassland on alluvial cl ay, poplar box (E. populnea) on clay loam terraces and hill woodland d ominated by any of E. albens, E. crebra, E. melliodora, E. orgadophila . Ten per cent of species proved sensitive to grazing intensity catego ries (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 heav ily grazed treatment for all broad vegetation types. It is suggested t hat the interaction between Themeda dominance and the inter-tussock fl ora may contribute to the importance of grazing as a determinant of fl oristic composition in hill woodland broad vegetation type. Mechanical disturbance is implicated as a means of effecting the spread of exoti c plants. However, there are relatively few exotic species that appear to have the capacity to displace native species without mechanical di sturbance, although a notable exception is Phyla canescens in the floo d-prone habitat. Moderate domestic stock grazing is compatible with na ture conservation on the Darling Downs, although it is demonstrated th at a proportion of the flora is sensitive to grazing. Remnants will ne ed to be managed under a range of grazing regimes, including light tot al grazing pressure that excludes domestic stock to ensure the surviva l of the full range of species. (C) 1998 Elsevier Science Ltd. All rig hts reserved.