Effects of exotic pasture grasses on biodiversity in the Mary River catchment, Northern Territory

  • Kerry Elizabeth Beggs

    Student thesis: Doctor of Philosophy (PhD) - CDU


    The Mary River catchment, Northern Territory, is a multiple-use region which has significance not only as highly productive pastoral land but also for conservation values. Concerns have been raised in recent years regarding the spread of exotic pasture grasses, particularly gamba grass (Andropogon gayanus) and para grass (Urochloa mutica), from pastoral properties into natural habitats and their possible threat to biological diversity. The comprehensive field surveys of terrestrial vertebrate fauna in the floodplain and savanna woodland habitats within the catchment provide the first quantitative evidence on the ecological effects of para grass and gamba grass. 

    The findings of my research indicate that the conversion of native vegetation to communities dominated by dense para grass or gamba grass, could lead to a substantial loss of plant and animal biodiversity, as well as reductions in the size of some animal populations currently present in the catchment. In the floodplain habitat, 87% of native plant and 66% of native animal species were not recorded in areas where para grass cover was greater than 40%. In the savanna woodland habitat, a similar although less pronounced result was observed, with 47% of native plant, 18% of native vertebrate species not recorded in either woodland areas with a dense gamba grass understorey (i.e. >70% of the total ground-level plant cover) or paddocks of gamba grass. Many individual species (mostly small reptiles and birds) were shown to decline in abundance as the cover of para grass or gamba grass increased. 

    Management responses at a range of levels, in conjunction with monitoring to assess the efficacy of any action, are required if conservation goals for the catchment are to be realised. The eradication of para grass and gamba grass on conservation reserves within the Mary River catchment should become a high priority. Efforts to contain these exotic pasture grasses on unreserved land, particularly pastoral properties bordering conservation reserves, need to be intensified. A monitoring program that involves a combination of direct monitoring of the exotic grasses (e.g. aerial surveys), and on-ground flora and fauna surveys (possibly streamlined to target indicator groups only) is recommended.
    Date of AwardMar 2010
    Original languageEnglish
    SupervisorPeter Whitehead (Supervisor) & John Woinarski (Supervisor)

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