School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemTree growth modelling of Eucalyptus delegatensis (R. T. Bak.) and other eucalyptus species utilising early-aged stand measurements( 1999)Growth modelling methods for Eucalyptus species that can make use of minimal measurement information are scarce but necessary for those involved in small-scale forestry to make informed decisions about investment and management options. A computer program, FARMTREE, is available for evaluating the costs and benefits of trees on farms, however its growth modelling functions could be improved. This thesis achieves this for Eucalyptus delegatensis (R. T. Bak.) and provides a series of stand basal area, survival, diameter distribution and individual tree diameter increment models that could be incorporated into a FARMTREE-like program. While not a major farm forestry species, the models have been related to other Eucalyptus species and when more later-age data become available, the methods used here could be fully applied to more suitable species. A systematic series of growth predictions were made, with estimates from the earlier processes being used in the next. Initially, the Gompertz function was selected as the best of five non-linear equations and used to model stand basal area based on two, early-age measurements, while keeping the asymptotic parameter constant. Survival was modelled using a modified logistic function with basal area and age as the predictor variables. The results from the above procedures were then used to model diameter distributions using a percentile-based parameter recovery procedure. The predicted distributions were assessed by comparing them to the actual cumulative density functions. Comparing the predicted estimates of basal area, mortality and diameter distributions to those produced by FARMTREE showed that the new estimates were better, both for the stands for which the models were developed, and for an independent data set. Individual tree diameter increment models based on distance-independent competition indices were also studied. Overall, the predictions for two-year diameter increment were not as good as for the previously studied areas of growth. This was especially noticeable when observing the results for the verification data set. These poorer results for diameter increment may be because of the less flexible methods used or perhaps partially due to the accumulation of previous prediction errors. The research approaches and functions used are easy to apply, efficient, accurate and require minimal actual growth measurement information. They could be applied to other species in greater detail when more information becomes available and could be incorporated into FARMTREE or a similar package for use by owners and managers of small farm forests with the expectation of providing improved growth predictions.
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ItemA microcomputer application of the FORest PLANning (FORPLAN) model to Australian Forestry( 1994)The FORest PLANning model (FORPLAN) has been studied and applied to Australian native forests since the late 1980s. One of the most successful and typical applications of FORPLAN to Australian native forests is the Otway Forest Management Planning Project developed by the co-operation of the Department of Conservation and Natural Resources Victoria and the Centre for Resource and Environmental Studies, Australian National University. This FORPLAN model was implemented on a VAX mainframe computer system. However, FORPLAN models can also be implemented on a PC computer. A PC version of FORPLAN has recently been developed by the Land Management Planning Systems Section, USDA Forest Service, Fort Collins, CO. In order to test the implementation of FORPLAN run on a microcomputer system, a FORPLAN model was developed for the Upper Barwon forest, which is one of ten management units of the Otway forests, based on an integrated multiple-use management approach. For this purpose, both a knowledge of linear programming techniques, and a knowledge of how to implement and utilize FORPLAN on a PC computer are required. The acquisition and application of such knowledge using data consistent with the original Otway FORPLAN model forms the subject of research described in this thesis.
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ItemAustralian wheat storage : an application of dynamic programming( 1975)Research on Australian wheat policy has been mainly concerned with supply and stabilisation; little work has been done on inventory policy. This area of study has recently assumed increased importance because of the large wheat carryover held by the Australian Wheat Board during the wheat crisis of the late sixties. This thesis is an investigation and evaluation of the two main motives for holding stocks of wheat in Australia. These are: (i) Withholding wheat from the export market as part of an oligopolistic marketing strategy. (ii) Storing wheat in low price years with the aim of selling it at a higher price at a late date. Chapter 1 discusses oligopolistic pricing in the world wheat market. Two models of price formation in which the U.S.A. and Canada act as co-operative duopolists are discussed, and a third model is developed to explain the triopoly formed by Australia, Canada and the United States. The rest of the chapter is concerned with the expansion of Australian wheat production in the late fifties and sixties, and the problems of handling and storing wheat which arose from increased production and the large stocks held in the 1968/69 and 1969/70 seasons. This chapter provides background for the study. The problem of evaluating storage policy based on price movements alone was formulated as an inventory model. This model was solved by dynamic programming using sets of simulated prices. The computer solutions of the model estimate the return to storage from following optimal policies. The dynamic programming model is developed in chapter 2. The inventory model was solved using estimates of the total variable cost of storage in 1973/74. Only the variable costs were calculated because the permissible range of carryover was restricted to the excess capacity of the grain-handling system. Thus the model represents no particular period in time, but is a useful abstraction because it permits inferences about past and future wheat storage policy. Chapter 3 is concerned with the statistical analysis and simulation of the price series. The excess capacity of the grain handling system and the variable costs of storage are estimated in chapter 4. The results of the study are presented in chapter 5 and the major conclusions are summarised in chapter 6. Appendix I contains five computer solutions of the inventory model; appendix II contains the total variable cost of storage function. Appendix III contains a listing of the computer program.