Office for Environmental Programs - Theses
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ItemSustainability, weeds, grasslands and Melbourne Water( 2005)Melbourne Water is responsible for large tracts of land throughout metropolitan Melbourne. Management of such large areas requires thorough knowledge of vegetation communities, threats they face and the relevant legislative requirements. Sustainability of many vegetation communities is directly threatened by the possible invasion by weed species. Weeds are a plant that has or has the potential to have detrimental effect on economic, social or conservation values. There are several different pieces of legislation that specifically relate to weeds. It is the Victorian Pest Management Framework 2002 that provides the strategic direction for the development of further weed management action plans. The principle means by which biodiversity may be protected is through the removal of weeds. The historical approach taken by Melbourne Water to weed control has been practical. Attention has always been focused on high value sites where native vegetation has the potential to recolonise the area naturally. Whilst the actual cost of the impact of weeds on ecosystems cannot be quantified, it is proven that weeds have the ability to reduce farm productivity, displace native species and contribute significantly to land and water degradation. Native grasslands are a threatened ecosystem. Their main threat is weed invasion. Unfortunately Melbourne Water is not currently doing anything to prevent weed infestation of these communities. There is no policy/strategy for dealing with weed management and this has adverse implications for operational efforts. At officer level there are pockets of strong awareness and expertise in relation to weeds and their impact, unfortunately there is no continuity of management standards or communication. These all combine to have little effect on the war against weeds and on the protection of threatened ecosystems.
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ItemNiche similarity assessment for understanding sea rockets replacement in the Australian coast( 2012)Sea Rockets (Cakile: Brasssicaseae) are plant species specialized for inhabiting coastal fringes and are well known for being successful invaders worldwide. A characteristic patter of invasion in Western North America and New Zealand, has been observed in two species of this genus. Cakile edentula (Bigel.) Hook, native from eastern North America invades and colonizes a coastal area, and is then replaced by Cakile maritima Scop., native from the Atlantic coast of Europe and coast of the Mediterranean Sea. This pattern of invasion and replacement has been repeated in coastal areas of West, South, and East Australian, coast. Currently, few sites in Tasmania are the only places in which these two species coexist. A greater breeding performance of Cakile maritima is one explanation for this replacement pattern In this research, the niche of each species is determined, through ecological niche modelling with MaxEnt, and contrasted to assess the importance of environmental conditions in Cakile edentula's replacement Species' niches were determined through comparison of habitat suitability of each species in the Australian coast. Ecological niche models were developed using data and environmental variables of Cakiles' native range and extrapolated onto Australian records of both species. To compare Cakile edentula's and Cakile maritima's realized niche differences it was necessary to test the ability of each species to predict the distribution of the other. Modelling results showed there are niche differences between both species. However, contrary to what was expected from replacement dynamics, models predicted greater habitat suitability for Cakile edentula than Cakile maritima in the South and East Australian coast. This result, in addition to low model performance and unexpected environmental factors driving C. maritima's distribution, could indicate that model assumptions of equilibrium and unbiased distribution of species records are not being fulfilled. In addition, there are other factors such as the choice of environmental variables, niche similarity methods and biological knowledge of Cakile that may affect niche comparison. Therefore, modelling limitations together with potential solutions are discussed, reinforcing the importance of taking into account the assumptions of species equilibrium and unbiased records, as well as the use of relevant environmental variables.