Wijesuriya, Wipulal Sardha (1999) Investigation of the relationships between biomass reduction, soil disturbance, soil nutrients and weed invasion in basalt plains native grassland remnants in Victoria, Australia. PhD thesis, Victoria University of Technology.

Abstract

The investigations reported in this thesis examined the relationships between biomass reduction (burning and mowing), soil disturbance, soil nutrient levels (N, P and K) and weed invasion in native grassland remnants in Victoria, Australia. The study was carried out at three native grassland remnant sites, Derrimut grassland reserve, Laverton grassland reserve and Victoria University of Technology, St. Albans campus grassland reserve on the westem edge of Melboume, Australia. These grassland remnants belong to the Western Basalt Plains grassland community which is listed as threatened in Victoria, and which forms part of the lowland temperate grasslands which once extended across south eastern Australia. A major threat to the survival of these communities is invasion by a variety of weeds. Weed invasion is often markedly enhanced by disturbance of the soil due to ploughing and overgrazing. It is known that some type of biomass reduction (burning, mowing or grazing) is required to prevent the dominant native perennial tussock grasses from over shadowing the diversity of forbs that grow between the tussocks, but the effects of various biomass reduction methods on weediness, and the underlying causes of weediness, have not been studied in any depth. The outcomes of the investigation are currently being applied to the management and rehabilitation of lowland grassland remnants. Most previous studies of lowland grassland rehabilitation and management have assumed that the key determinant of competition between native and exotic plant species in lowland grasslands is above-ground cover. The results reported in this thesis clearly show that below-ground competition for nutrients is also important in determining the extent of exotic and native plant growth in intact and disturbed areas. The successful establishment of native species during revegetation, with low levels of weed growth, will depend on the extent to which below ground growth of natives is achieved to lower available nutrient levels quickly, and prevent large scale growth of exotics. The management of lowland grassland remnants with low levels of flatweeds and annual grasses will likewise depend on the maintenance of a healthy sward of native vegetation which can keep available nutrients in the soil at low levels, especially when above-ground cover is removed by biomass reduction actions such as burning, mowing and grazing.

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