School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemLooking for expansins : a molecular approach to the investigation of tylose development and heartwood formation in Eucalyptus nitens( 2006)Advanced stages of stem development in many tree species, including eucalypts, are marked by the transition of conductive sapwood to non-conductive heartwood. Heartwood formation follows a characteristic sequence of events involving the accumulation of phenolic compounds in ray parenchyma cells, the occlusion of vessels by tylose and/or gum formation, cell death and the subsequent release of phenolic compounds into the surrounding tissue. These events are dependent upon the activity of ray parenchyma cells, but the molecular processes involved, particularly with regard to tylose formation, remain largely unknown. The identification of molecular pathways leading to tylose formation might yield insights into heartwood formation. A molecular approach to the investigation of tylose formation is hampered by the paucity and inaccessibility of ray parenchyma cells and the asynchronous nature of tylose formation. Based on the assumption that wound-induced tyloses and those formed during the transition of sapwood to heartwood develop via a common mechanism, these difficulties were overcome by using the wounding response of the tree (a 12-year-old Eucalyptus nitens sapling) to induce extensive and simultaneous development of tyloses. Tylose formation involves the marked extension of a primary cell wall structure. Elsewhere, such wall extension has been closely associated with the activity of expansins. These constitute a large, multi-gene family of proteins which are widely distributed throughout higher plants and which have been shown to induce relaxation and extension of primary cell walls, often in a cell- and tissue-specific manner. It is proposed that expansins are likely to be involved in tylose formation. Ray and axial parenchyma cells are the only living cells found in sapwood, and primary cell wall extension is only possible through tylose formation. Thus, gene expression associated with wall extension occurring in sapwood is likely to be associated with tylose formation. Cellular material from outer sapwood showing extensive wound-induced tylose development was successfully harvested and partial cDNA sequences displaying significant homology with a-expansins were identified. This provides circumstantial evidence that expansin gene expression is associated with tylose formation and should encourage further investigation of the molecular pathways involved in this process.
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ItemChlorophyll fluorescence for rapid assessment of salt tolerance in eucalypts( 1999)Chlorophyll fluorescence parameters were investigated, using the OPTISCIENCES 0S5-FL fluorometer. for their potential as non-invasive rapid indices of salt stress in Eucalypts. Cloned E. camaldulensis and E. urophvlla x grandis plants were subjected to salinity (0-650mM NaCI) and chlorophyll fluorescence parameters measured. Dark-adapted and quenching parameters did not show consistent responses to salinity stress. The light-adapted parameter Fds, measured by the Yield program, showed a predictable trend in response to salinity treatment. Measurements were influenced by diurnal changes, positional effects and environmental changes. It is therefore important to measure Fd, within a controlled environment, randomising and rearranging plants during the course of the experiment. Fully expanded, green, attached leaves should be used for measurement and salt concentration should be raised slowly (e.g. 50mM/5 days) after a concentration of 300mM NaCI has been reached. Statistical analysis should be performed using non-parametric methods as chlorophyll fluorescence parameters are not normally distributed. In most cases Fds declines before the onset of visible physical symptoms, however it is affected by sudden shock. It is therefore important that results show a consistent decline in Fds and/or Fds decreases markedly (e.g. 40-50% of the control). This method allows for the objective ranking for salt tolerance of both seedlings and clones. Fds may also have the potential to detect individual responses to salinity and assist the detection of individuals with uncharacteristic responses or unsatisfactory root systems within clones.
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ItemAn evaluation of fuel-reduction burning in the dry sclerophyll Wombat State Forest( 1994)Each year, between one and three per cent of the total forested area in Victoria is fuel-reduced as a part of the Department of Conservation and Natural Resources' program to implement its overall fire protection policy. The dry sclerophyll Wombat State Forest has been fuel-reduced since the 1960's, - a practise considered important because of its susceptibility to fire and its highly flammable plant community. This thesis presents the results of an evaluation of fuel-reduction burning in the Wombat State Forest, commencing with a review of forest conditions, principles of fuel-reduction burning, fire behaviour and fire effects. This is followed by observations and measurements in the field to document current practices of fuel-reduction burning, to select an appropriate fire-behaviour prediction model, to identify time-intervals between successive burns and to evaluate the effects of fuel-reduction burning on forest trees. Historical data of wildfires were used to evaluate the effectiveness of fuel-reduction burning in limiting the number, area and losses from wildfires. "Multi-criteria analysis" was then applied to select priority areas for fuel-reduction burning. The fuel-reduction burning program which is conducted 'every year during autumn and spring requires detailed planning and preparation, because it can only be carried out under certain prescriptions for weather, fuel and fire behaviour. Depending on the extent and conditions of each area, either ground or aerial ignition is applied. Large areas ignited from the air often result in variations of fire behaviour and intensity that leave many un-burnt patches within the broad areas of burnt forest. In order to predict fire-behaviour, comparisons were made between the Control Burning Meter, the McArthur Fire Danger Meter and the Fire Behaviour Tables for Western Australia (the Red Book). From a study of small trial plots, it was shown that the fire behaviour model incorporated in the Control Burning Meter for messmate-gum or silvertop forest type provided quite realistic predictions of low-intensity prescribed fires compared with predictions based on the McArthur Forest Fire Danger Meter and the Fire Behaviour Tables for Western Australia. Since its inception, fuel-reduction burning in the Wombat State Forest has decreased the quantity of litter and twigs, but it has had no significant effect on the quantity of humus and coarse fuels. This reduction of flammable fuels has reduced the potential for major fires and the study showed that a fuel-reduction burning cycle of less than five years is required to restrict the build up of fine fuels to acceptable levels. With regard to the impact of fuel-reduction burning, it was shown that it causes scorches on most trees, and that there is a significant relationship between scorch-height and tree diameter for the two dominant species, messmate (Eucalyptus obliqua L'Herit) and peppermint (E. radiata Sieb. ex. DC.). However, because of their different bark types, average scorch height was higher for messmate. Due to the considerable variation in the severity of fire seasons, hence in the frequency and severity of fire, no significant differences were detected in the number of wildfires and the extent of areas burnt, before and after the application of fuel-reduction burning in the Wombat State Forest. However, analysis of the historical fire data led to the conclusion that fuel-reduction burning has achieved its objective of limiting the severity of wildfires. Most of the wildfires occurred on areas that either had never been fuel-reduced or that had been fuel-reduced for more than five years. The costs of fuel-reduction burning have been relatively modest in comparison with the potential losses. Therefore, when properly planned and implemented, fuel-reduction burning is a valuable management tool for protecting forests and wider community values. This study has also provided a general idea on the applicability of "multi-criteria analysis" for identifying priority areas for fuel-reduction burning in the Wombat State Forest, with priority areas being selected on the basis of level of fire hazard (fuel, weather and topographical conditions) and values of particular sites (significant values, timber quality, distance from the nearest township and extent of the area). The result was a ranking of areas according to their priorities for burning.
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ItemAnalysis of growth and yield in uneven-aged, mixed species eucalypts at Mt. Cole State Forest( 1994)Continuous forest inventory (CFI) is an effective method for studying forest changes over time; it provides growth and yield information which forest planners and managers can use for planning and managing forests to meet long-term sustained yield. This thesis reports results from a 30 year series of successive CFI measurement at Mt. Cole State Forest in west-central Victoria, commencing in 1963. With an area of 12,352 ha, Mt. Cole State Forest consists of three sub areas; the northern and southern Blocks totalling 11,250 ha, and the Mt. Lonarch Block comprised of 1,102 ha. Permanent sample plots (CFI plots) were first established in the Mt. Cole Blocks in 1963 and these have been measured on seven occasions, including the most recent 1994 assessment. During this period, various changes to the inventory data-base have occurred, which have impacted on the analysis and interpretation of the data. Since 1983 the forest area of the Mt. Cole Blocks have been classified according to land use and management zoning, resulting in a reduction of the net productive area available for sawlog production to 2,758 ha. This area has also been stratified into four homogenous areas (strata) and the number of CFI plots has been reduced from an initial 114 to 66 plots. In the latest (1994) remeasurement, the 66 permanent sample plots for the four strata of the Northern and Southern Mt. Cole Blocks were rechecked and the data has been analysed to determine current growth and yield, and to estimate future volume growth and an available cut for the forest. The above analyses show that the structure and yield of the forest have changed from time to time, with a trend towards decreasing levels of available growing stock over time. The current (1994) growing stock levels of the Mt. Cole Blocks are approximately 80,676 m2�27% (P=0.95) or 28.6�3.7 m2 /ha for basal area, and 237,684 m3�36% (P=0.95) or 83.7�13.9 m3/ha for 'sawlog plus potential sawlog volume'. The current available sawlog volume is approximately 177,672 m3�44% (P=0.95) or 63.5�12.5 m3/ha. Additional analyses of periodic and annual growth rates of the growing stock for each stratum and the whole forest (Mt. Cole Blocks) show that the average diameter increment (underbark) of the forest is approximately 0.51�0.03 cm/yr; the net annual increment including ingrowth (Gn+i) of the growing stock in the Mt. Cole Blocks is approximately 0.63�0.11 m2 /ha/yr for basal area, 2.16�0.75 m3 /ha/yr for sawlog, and 1.78�0.68 m3/ha/yr for sawlog plus potential sawlog. The net annual changes in growing stock levels (Gd) are approximately 0.11�0.29 m2 /ha/yr for basal area, -0.15�1.52 m3 /ha/yr for sawlog, and -0.65�1.52 m3/ha/yr for sawlog plus potential sawlog. Models for predicting the current and future growing stock levels were developed using multiple regression based on the three parameters of initial basal area (BO), initial volume (Yo), and the interval of time between successive measurements (t ). Regulating forests to obtain long-term sustained yields requires a continuous flow of information on growth and yield and the development of comprehensive management strategies based on this information. In this study, such growth and yield information have been used to determine an annual available cut for the Mt. Cole Blocks of approximately 5,364�1,854 m3/yr.
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ItemThe effects of interspecific competition from Eucalyptus obliqua on young stands of Pinus radiata( 1991)The growth and stand development of even-aged Pinus radiata stands invaded by Eucalyptus obliqua were investigated for the period during which stands of P. radiata were 10 to 15 years of age. Population dynamics of P. radiata and E. obliqua stands were assessed and then used as a basis to describe the past competitive relationships and predict the future . of these mixed stands. The growth rate of P. radiata was also assessed in relation to its initial size and to neighbouring E. obliqua to reveal the 'most important factors that determined the growth of P. radiata. The study was carried out in 6 stands in which density of P. radiata was constant whereas that of the E. obliqua varied. Population dynamic parameters studied included mortality, size distribution and size hierarchy. Size distribution and size hierarchy were concerned only with DBH and height but not weight or volume. Size distribution was measured by skewness of. the distribution and size hierarchy was measured by the Gini coefficient and Lorenze curve. Mortality was found only within populations of E. obliqua. This mortality also increased with increasing density and was confined mainly to E. obliqua trees which had small DBH and height. Size distribution of both DBH and height of P. radiata in almost every stand was negatively skewed and increased with stand age. The distribution of height showed more negative skewness than did DBH. Skewness of DBH (but not height) increased the increasing density of E. obliqua and became positively skewed more quickly than did height distribution. Mean DBH, height and volume of P. radiata stands decreased with increasing density of E. obliqua. Size hierarchy in DBH and height in P.radiata increased with stand age. There was less variation in height than in DBH. Size hierarchy for DBH, but not for height, also increased with increasing density of E. obliqua. Initial size of P. radiata was found to be more closely related to relative growth rate of P. radiata during the study period than the presence of E. obliqua. The result also showed that DBH growth of P. radiata trees was affected by more strongly than was height growth by the presence of E. obliqua under its canopy during the early growth stage.
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ItemBiometric studies of some eucalypt plantations in South China( 1987)Biometrical studies Of introduced tree species in the Dongmen area are presented in two parts. In the first part, a number of tree volume functions were fitted to data for E. exserta. A simple weighted regression model was found to be most appropriate. This model proved to be better than that recommended by local mensurationists in Guangxi. In the second part, fertilizer trials are reported for eighteen seed strains under five fertilizer regimes. These strains were finally clustered into four groups in terms of performance. All strains of E. camaldulensis proved most successful for all levels of fertilizer used. Further analysis showed that E. camaldulensis responded best with highest levels of nitrogen, phosphorus and potassium plus trace elements used, and that the addition of trace elements did not significantly improve response.