School of Agriculture, Food and Ecosystem Sciences - Theses

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    Improving species distribution models using extreme value theory and climate dataset ensembles
    Stewart, Stephen Blair ( 2020)
    The development of climate datasets at fine spatial and temporal scales has commonly been driven by the need to better understand vegetation distributions and ecological systems. While a wide range of global, national and regional climate datasets have been developed over the last two decades, they are rarely compared directly in the ecological literature. This thesis evaluates a range of climate interpolation techniques and investigates how the spatial and temporal characteristics of climate datasets may be utilised to improve the predictive performance of plant species distribution models (SDM). A series of spline-based and geostatistical methods for interpolating temperature variables are first compared across Victoria, southeast Australia. Secondary predictors (thermal remote sensing data and local topographic indices) which indirectly capture mesoscale microclimate and cold air drainage regimes were found to improve monthly mean minimum temperature interpolations by up to 39%. Thermal remote sensing data only reduced root mean square error (RMSE) by up to 6% for maximum temperature across Victoria and was most effective during the summer months. The interpolation methods used in southeast Australia were subsequently transferred to the Royal Himalayan Kingdom of Bhutan to validate their effectiveness in a novel climate. In Bhutan, the predictive performance of minimum temperature interpolations was also improved considerably (up to 23% reduction in RMSE) when using thermal remote sensing data and local topographic indices as spatial covariates. Thermal remote sensing data also reduced the RMSE for maximum temperature interpolations by up to 16% in Bhutan. Interannual variability of climate extremes were used to evaluate how the temporal characteristics of climate may be used to improve the predictive performance of SDMs. Generalised Extreme Value (GEV) distributions were fitted to monthly climate data to generate variables which account for the skewed distribution of extremes. Models incorporating interannual variability (drawn from a range of expected return intervals) improved predictive performance compared to models using seasonal extremes only for 28 of 37 species assessed. Iteratively fitting models using alternate expected return intervals typically acted on the leading and trailing edges of current distributions, indicating that such methods may be useful for model calibration and characterising climate-driven source-sink population dynamics. The impact of spatial disparities in climate on the predictive performance of plant SDMs was evaluated using three distinct datasets developed for Victoria as part of this research, in addition to two global datasets (WorldClim v1 and v2). Individual models were compared against one another and as ensembles to explore the potential for alternate predictions to complement one another. The Victorian datasets demonstrated a significant improvement over the original WorldClim dataset (up to 17.3% mean increase in D2) and trended towards an improvement relative to WorldClim v2; however, no significant differences were found when comparing the alternate Victorian datasets. Multi-model ensembles achieved a mean increase of up to 13.8% and 29.2% in D2 relative to individual models when using regional and global datasets, respectively. Ensembles provide a pragmatic method to improve the predictive performance of SDMs and allow a trade-off between the uncertainties and potential biases embedded in competing climate datasets.
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    Making the connection between history, agricultural diversity and place: the story of Victorian apples
    Christensen, Johanna Annelie ( 2016)
    Apple growing practices are embedded in a productivist mentality aiming for ever higher efficiency and productivity. And while the climate change impacts are to a large extent known, there is little attention given to the coupling of the social and the ecological effects. I use apple growing as a case study to explore the relationship between place, biodiversity and rural change in Victoria. My research is based on historical research; including an analysis of the Museum Victoria’s collection of wax apple models, and in-depth interviews with orchardists. By drawing on environmental history, social-ecological systems thinking and Bourdieu's theory of practice, I highlight the importance of a systems perspective and inform it by emphasis on the critical role of underlying power structures and individual dispositions, or the habitus, of the growers. These dispositions have been shaped and internalised by the growers’ histories and their physical surroundings. Orchardists have been able to respond to intensifying production requirements by utilizing technologies and scientific nous to keep up with the continuous aim for efficiency. Growers are caught up in a self-reinforcing cycle of satisfying the demand for perfect apples by adopting expensive techno-scientific approaches to enable ever more intensive production. The symbolic violence and amplified biophysical pressure orchardists experience has driven many to despair; resulting in a significant decline in small scale apple growing businesses over the last decade. I offer some suggestions for government policy and support measures and argue that any services or support programs need to be tailored to the appropriate level and need of each orchard business and the individuals who are involved. My analysis shows that those growers, who engage more closely with their biophysical place as well as their history and identity as apple growers in that place are (re-)creating another version of what it means to be an apple grower. In some cases this is resulting in resistance to the vortex of agricultural productivism that has been the basis of their existence for many generations.
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    Effects of adding nutrients on soil chemistry and tree growth in native Eucalyptus forests of south-eastern Australia
    Severino, Dean Christopher ( 2007)
    The decreasing area available for timber extraction in south-eastern Australia, due largely to social pressure to reserve greater areas of forest, has led to the consideration of fertiliser-application to increase wood output from the remaining available forest. Potentially deleterious effects of fertilising on water quality must be assessed before implementation on a wide scale. This is in accordance with relevant forest management policies. This study examined the effects of applying fertilisers containing nitrogen and phosphorus, on soil and soil-water chemistry in two pole-sized stands of mixed Eucalyptus spp in the Wombat Forest, in the Midlands Forest Management Area, Victoria, Australia. The findings are synthesised and discussed in relation to management of regenerating mixed-eucalypt forests in south-eastern Australia. Fertiliser treatments were none (R); 400 kg N ha-1 as ammonium-sulphate (N); or 400 kg ha-1 plus 202 kg P ha-1 as triple superphosphate coated with 10% sulphur (NP). It was calculated that incidental additions of S were 1371 kg ha -1 (N treatments), and 1696 kg ha-1 (NP treatments). It was expected that P would be principally adsorbed on soil surfaces; N immobilised in the soil organic pool and that metallic cations would enter the soil solution to varying degrees. Fertiliser-addition increased both plot-basal-area (BA) growth and the rate of stand self-thinning. In 3.8 years, BA in reference (R) plots at two sites increased by 7.3% and 23.4%. Where N alone was added, BA increased by 14.2% and 27.1%, while in NP plots BA increased by 17.1% and 42.7% respectively. Mortality was 9% in untreated plots compared to 14% in NP plots. Estimated increases in biomass growth equated to additional above-ground nutrient accumulation of 0.4 to 1.5 kg ha-1 of P, and 5.5 to 20.8 kg ha-1 of N. This represented only 0.2 to 0.7% of added P, and 1.4 to 5.2% of added N. Soil solution was extracted from 10 and 50 cm with porous-ceramic-cup tension-lysimeters (-0.6 kPa). Concentrations of P and N were low both before and after adding fertiliser. Across all treatments the maximum median PO43- concentration in soil-water at 50 cm was 0.12 ppm (mean 0.28 ppm). Typically PO43- concentrations were not higher than 0.03 ppm. The 400 kg ha-1 of added N was rapidly immobilised in the soil organic pool. The greatest mean NH4' concentration from a single sampling occasion was 1.1 ppm. The mean NO3 concentration at 50 cm was never higher than 0.26 ppm. After adding N in fertiliser the proportion of NO3- relative to NH4* in soil-water increased and was correlated with decreasing soil-water pH. Less than 1% of added P and N was recovered from soil solution at 50 cm. The largest pool of added P recovered was PO43- adsorbed to soil between 0 and 20 cm, due to the soil adsorption capacity being well in excess of the applied 202 kg P ha-1. Phosphate desorption using sequential extractions with a mild acid extractant (0.3M NH4F, 0.1M HCI) recovered between 25% and 116% of added P. Differences were attributed to both the amount of P added and the effect of time since treatment at different sites. Soil disturbance during sampler installation was found to be more likely to raise soil-water P concentrations at 50 cm than would adding up to 202 kg P ha-1. Among the ions in solution. SO42- and CI' were the dominant anions while Cat+ dominated the cation chemistry. In untreated forest 5042- in soil-water ranged from 7.7 to 16.0 ppm at 10 cm and 7.9 to 12.2 ppm at 50 cm. In fertilised plots up to 100.5 ppm SO42 was measured in soil-water at 50 cm depth. In the N treatment at 50 cm, SO42- in soil-water accounted for 9.4 % of applied S. compared to 14.0 % in NP. In untreated forest, soil-water Cl- and SO42- accounted for over 98% of the total soil-water anions, in roughly equal proportions at 10 cm, and CI- slightly higher at 50 cm. Following fertiliser-application soil-water pH at 10 cm fell from 6.3 in R to as low as 4.81 (N) and 4.45 (NP). At 50 cm pH never dropped below 6 and there were no visible departures from reference concentrations. Relative activities of K+ and Mg2+ in solution increased with decreasing pH, indicating increased leaching potential. Sulphate in soil-water increased total anion charge further in NP than in N. Total charge (cmolc L-1) for cations followed anions. A slight deficit in anion charge was likely due to the unquantified contribution of organic anions. These results confirm that despite the quantity of fertilisers added in this trial being double likely operational quantities, the forest and associated soils had the capacity to retain these nutrients through a variety of processes. The study validates the environmental sustainability of proposed intensive management practices including fertiliser-application in this forest type. It also emphasises the importance of understanding fundamental forest nutrient cycling processes when aiming to carry out intensive forest management practices in an environmentally sensitive manner.
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    Effects of organic applicants in a southern Victorian vineyard
    Lakey, Vincent G ( 2007)
    Mulch is a material applied to the surface of the soil to reduce weed growth and reduce soil moisture loss through evaporation from the soil surface. The use of organic mulches will alter the soil environment. This alteration may include reducing soil temperature fluctuations, increasing soil organic matter, increasing soil microflora populations modifying soil chemical properties and increasing soil moisture retention. An experiment was conducted to compare composted green waste mulch and barley straw mulch with herbicide as alternative means of maintaining the undervine strip in a cool climate vineyard. Plant and soil responses to the different undervine treatments were monitored. Grapevine budburst was retarded, however, by the fourth week of vine growth there were no observable differences in grapevine growth stage. Both mulches stimulated grapevine growth and increased yield, with the compost mulch increasing vegetative growth with respect to fruit yield. The fruit quality parameters juice pH and titratable acidity were not significantly altered by the different undervine treatments. In the second year of the experiment the juice soluble solids were lower on the straw mulched grapevines. The compost mulch increased soil pH and carbon levels. The straw mulch improved soil water retention and the mass of soil fungal hyphae. Both mulches increased soil cation exchange capacity. The straw mulch increased soil exchangeable Mg to a greater extent than was predicted from straw nutrient content. The significant variations seen in soil cation content under the mulch treatments were not observed in the tissue analysis. Mulch can be used in a cool climate vineyard to increased yield without deleterious side effects.
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    Investigation of boron toxicity in lentil
    Hobson, Kristy Bree ( 2007)
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    An evaluation of management by objectives as a planning system in a government veterinary service
    Wroth, Robert Harold ( 197-?)
    The need, for field officers, of State Departments of Agriculture to plan their work has been recognized for many years. In the last 10 years particular attention has been paid to program planning by Extension officers. However, it has become apparent that program planning is not being used effectively. Reasons for this range from the lack of defined organizational objectives to difficulties associated with planning at the individual level. The purpose of this study was to test the feasibility of introducing MBO into a Department of Agriculture and its effectiveness in overcoming planning difficulties. In order to test this a MBO system was used to plan for the eradication of bovine Brucellosis by two country regions of the Division of Animal Health in the Victorian Department of Agriculture. Two other regions acted as controls and prepared plans without MBO. The effectiveness of MBO was evaluated on the criteria of involvement and participation of field officers, their job satisfaction, job dissatisfaction, understanding of the plans and the MBO process and the importance of aspects for planning. The major finding was the difference in response of Officers at higher and lower levels of authority and responsibility. Those at higher levels viewed MBO more favourably than those at lower levels, and consequently considered they had significantly more involvement and participation than previously. The study also highlighted deficiencies that existed, such as confusion as to lines of responsibility and lack of two way communication between Regional and Head Office staff, and showed how this can lead to increased job dissatisfaction. The work to be performed was not seen as personally satisfying, thus lowering job satisfaction, and so reduced the apparent success of MBO. However, the overall conclusion was that MBO was a realistic system to use for planning by Department of Agriculture personnel and that it did overcome problems associated with program planning. General and specific recommendations on the use of MBO are made.
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    Beef-cattle production in the Western District of Victoria : technical and economic relationships between beef cattle and sheep
    Wills, I. R ( 1965)
    Sheep-and-wool production and beef-cattle production are combined on many grazing properties in the Western District of Victoria. In the past beef cattle have generally been regarded as less profitable than sheep as a sole enterprise on a per-acre basis. In previous surveys it has been found that graziers believe that sheep and beef-cattle complement one another in a variety of circumstances because of the different effects of the two types of animal on pasture. It has also been found that sheep and beef cattle on grazing properties are frequently supplementary with respect to labour. The thesis has two main objectives. First it investigates whether the currently available analytical models based on static economic theory are adequate to solve problems of resource allocation between sheep and beef cattle grazing the same pasture. Second, it investigates whether many graziers carry beef cattle partly or solely to satisfy goals other than profit maximisation. The method of achieving the first objective was to compare the static economic theory relating to enterprise combination, and published work dealing with the problem of selecting the optimum combination of two enterprises, with the real situation existing on grazing properties carrying both sheep and beef cattle. The second objective was investigated by means or an interview survey of graziers running both sheep and beef cattle in six Western District parishes. A considerable amount of technical information about beef-cattle production in the Western District was collected in the course of the survey, and the more important points are summarised in the thesis. Of particular interest are the findings that very few graziers purchased cattle for fattening purposes, and that beef cattle were relatively more important on large properties than on small properties. It was concluded that static economic theory does not provide an adequate basis for the description of the situation where sheep and cattle graze the same pasture, or for the determination of the optimum allocation of resources between sheep arid beef cattle grazing together. Sheep and cattle graze pasture differently, and therefore different pastures result as the sheep-cattle ratio is altered. In this situation, the postulates on which the iso-resource function is based, that the shared input or inputs should remain homogeneous and constant in quantity as the outputs of the products change, are violated. Thus strictly speaking it is not possible to derive a valid iso-resource function relating the sheep and beef-cattle enterprises with respect to pasture when the sheep and the cattle graze the same pasture. However, if the changes in the pasture are disregarded, it is possible to design experiments to produce practical approximations of iso-resource curves relating sheep and beef cattle. Information obtained from graziers in this and other surveys, and the results of experiments, strongly suggest that for practical purposes it is reasonable to think of an iso-resource curve for sheep and cattle with respect to pasture as being concave towards the origin, that is, the sacrifice rate of sheep for cattle increases as more cattle are added on a sheep property. Farmer estimates and experimental evidence suggests that the marginal sacrifice rate on most properties may be lower than is generally assumed (nutritional standards imply a linear rate of eight merino whethers per 1,000 lb. steer). Almost all the survey graziers believed that the overall relationship between their sheep and their beef cattle with respect to their total feed supply over the whole year was a competitive one. Most estimated that their sheep and their cattle were complementary or supplementary with respect to pasture over a part of the year, including the Spring, and that their sheep and their cattle competed for scarce pasture at some time in the autumn and winter. The survey results showed that the most important reason for the presence of beef cattle on the survey properties was the value of cattle in controlling and utilising pasture and weed growth. However the value 0f cattle for that purpose appeared to decline as the sheep stocking rate increased. It appeared that on many properties the importance of beef cattle in pasture control was a consequence of a desire on the part of the grazier to maximise profits within the restrictions imposed by limitations on sheep numbers including the grazier's desire to limit his personal effort. Beef cattle were also frequently carried for the reason that they provided a means of stabilising income from year to year. Although the survey results tended to confirm previous findings that sheep and beef cattle are supplementary with respect to labour at certain times during the year, and that beef cattle generally require less labour per unit of return than sheep, few graziers said that they carried beef cattle for those reasons. It was concluded that substantial minority of the survey graziers did carry beef cattle partly or solely to satisfy goals other than profit maximisation. The most important of these goals was the minimisation of personal effort, which was shown not by giving labour as a reason for carrying beef cattle, but indirectly in the affirmation of the value of cattle (rather than additional sheep) in pasture control. A few graziers were motivated by a personal preference for beef cattle. In the situation where the available economic theory is inadequate to solve problems of resource allocation between sheep and beef cattle, and where a substantial proportion of graziers carry beef cattle partly or solely for reasons other than profit maximisation, there is little scope for sophisticated economic procedures. Given additional experimental data to provide indicators of probable "substitution rates", it seems that the allocation of resources between sheep and beef cattle on properties such as those in the survey can best be improved by budgeting possible adjustments.
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