School of Ecosystem and Forest Sciences - Theses
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ItemEffects of adding nutrients on soil chemistry and tree growth in native Eucalyptus forests of south-eastern Australia( 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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ItemEffects of salinity on growth and wood and fibre properties in eucalypts( 2001)Salinity, the presence of soluble salts in soils or waters, can be separated into naturally occurring primary salinity, and secondary salinity resulting from human activities such as land development and agriculture. Secondary salinity involving high, saline water-tables affects large areas, estimated between 4.7 and 6.1 'ha (Williamson 1990, Robertson 1996), of agricultural land in Australia, and tree planting is one approach to lower saline watertables. Such plantations could become a significant fibre source for the pulp and paper industry, but it is not known whether growth in salt-affected environments influences key fibre properties important in paper production. This work therefore examined the wood and fibre properties of Tasmanian blue gum, Eucalyptus globulus ssp. globulus, and river red gum, E. camaldulensis, grown under various conditions of soil salinity. Eucalyptus globulus was studied in trial plantations in the Shepparton region of north-central Victoria. The plantations were established in 1993, and field sampling was carried out from 1995 to 1997. Salinity in the top 20 cm of soil over the period of study (1994 to 1997), according to the soil salinity classes set lutin Marcar et al. (1995), ranged from non-saline at the fresh-channel water-irrigated plot to slightly saline for the saline groundwater-irrigated plots. Tree size generally did not differ significantly between plots at any age. Differences in foliar [Na±], {K±] and [Cl-] occurred between the field plots but were not consistent between years. The highest concentrations of foliar ions were also not always associated with the plot receiving the highest salinity irrigation water, suggesting that in only some years was the soil salt level sufficient to cause a plant response. Wood basic density differed between the plots, but it could not be attributed to salinity, and may have reflected other site-specific effects. Fibre morphology parameters did not differ significantly between the plots. There were some differences between the plots in the increase in fibre length from year to year but the differences were not consistent over the entire survey period and could not conclusively be attributed to differences in soil salinity. A pilot salinity pot trial was conducted on E. camaldulensis plants, as a precursor to a more elaborate experiment planned for potted E. globulus plants. The E. camaldulensis pot trial comprised a single concentration salt (NaCl) treatment and a control (freshwater) treatment applied over a 60 day period. A marked reduction of growth occurred with salt-treated seedlings relative to control seedlings. Concomitant with the reduction in growth, salt-treated seedlings produced significantly shorter, thicker-walled fibres than the control seedlings. The pot-trial on 18-month-old Eucalyptus globulus ssp. globulus trees applied different concentration salt (lRlaCi) solutions over a 10-week period. The salinity of the potting mixture increased markedly in the salt-treated trees relative to the controls. Foliar chloride and sodium were also significantly greater in trees on the higher salt treatments than in the control trees. Diameter growth decreased with the higher salt treatments, and five trees under high salt treatments had to be harvested prior to the planned completion of the experiment, due to their poor state of health. These results indicated the salt treatments had influenced some aspects of tree physiology. A wound made to the cambium allowed pre-treatment fibres (fibres formed prior to the start of the experiment) to be distinguished from post-treatment fibres (fibres formed during the experiment) in the E.globulus pot trial. Trees on higher salt treatments produced significantly longer, thinner-walled fibres compared to controls, but this pattern also occurred in fibres formed before treatments were imposed, implying that these differences were due to preexisting differences in the trees unrelated to the salt treatment. Statistical analysis of fibres formed during treatments, taking account of pre-existing differences, found that there was no significant effect of salt treatment on fibre length or wall thickness, although this was possibly because of the low sample size relative to the variation of the experimental material. The controlled application of salt for 10 weeks during the E. globulus pot trial thus had some effect on tree physiology, but no significant effects on fibre dimensions or wood formation. This was consistent with the observation in the field trial that fibre dimensions and wood formation were not influenced by factors that did not also reduce tree growth, at least in trees up to 4 years old. Higher levels of salt could cause rapid tree decline due to the inability of the trees to exclude the salt, and processes associated with fibre formation would then also cease. The combined results from the field and pot trials indicated that E. globulus, a slightly to moderately salt-tolerant species, suffered negligible or minor growth reductions on soils irrigated to a slightly saline level, and produced fibres of similar morphology to trees grown under non-saline conditions. If soil salinity increased above the moderate level, the trees would continue to grow provided sufficient water is still available, but internal salt levels would increase to the point where tree death would result. Based on the pot trial, where such internal salt levels were achieved, the decline and death of the trees would occur before the salt affects fibre morphology. Eucalyptus camaldulensis adopted a different strategy to cope with salt stress than E. globulus. Eucalyptus globulus continued to grow provided it was supplied with water, despite its saline nature. Finally, when salt levels within the plant reached a critical level, plant health rapidly declined. When E. camaldulensis was watered with solution of a similar salinity to the highest salt treatments in the E. globulus pot trial, there was a rapid cessation in extension growth, but there was no other sign of a deterioration in plant health. The mechanism by which E. camaldulensis was able to quickly cease shoot growth, which presumably allowed it to tolerate saline conditions by restricting salt uptake, was not investigated here. Material from Eucalyptus camaldulensis that had been growing for 14 years on a dryland plantation site in southwest Western Australia was also investigated. Trees from the high salinity area did not differ significantly in average height, diameter and volume from those from the low salinity area. Basic density were significantly greater in the high salinity group of trees than in the low salinity group, but no relationship with tree growth was established. The absence of a relationship between growth and basic density was not unusual, as natural variation in basic density makes it difficult to establish environmental or experimental effects (Downes and Raymond 1997). Fibre fractional wall coverage was greater in the high salinity group of trees than in the low salinity group, as was also the case for the E. camaldulensis pot trial. In the pot trial, however, a significant growth reduction due to salinity was recorded. There were no other differences in fibre morphology between the high and low salinity groups of the Western Australian plantation. Eucalyptus globulus is less salt and waterlogging tolerant than E. camaldulensis (Bennett and George 1995a; Bennett and George 1995b) but in the field studies the growth and wood and fibre properties for each species was similar across the range of salinities encountered. The exception was basic density and fibre fractional wall coverage in the 14-year-old E. camaldulensis, both of which were greater in the high salinity group of trees. It was expected that the growth of E. globulus would be adversely affected if irrigation with the saline groundwater continued for several more years, allowing a build up in soil salinity. Based on the results from the E. globulus pot trial, once soil salinity levels exceed the tolerance limits of this species, a rapid decline in tree health will occur, and fibre formation will cease. Eucalyptus camaldulensis, with its greater salt and waterlogging tolerance, will grow in areas where other commercial species, such s E. globulus, would not thrive. However, E. camaldulensis has disadvantages for farm forestry in Australia, due to low percentage pulp yields by comparison with E. globulus (Arnold et al. 1999), and poor growth rates and tree form (Mazanec 1999). In the USA, E. camaldulensis has equalled the pulp yield of the commercially proven E. globulus (Arnold et al. 1999). Further research into improving pulp yields, growth rates and tree form of E. camaldulensis in Australia, would allow expansion of eucalypt plantations for pulp and wood production, as well as land and water care, onto previously unsuitable land.
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ItemPhysiological aspects of root growth of Eucalyptus pauciflora, subsp. pauciflora and Eucalyptus nitens( 1997)This thesis examined i) morphological and physiological effects of low soil temperatures on root growth of subalpine Eucalyptus pauciflora Sieber ex Sprengel subsp. pauciflora and montane Eucalyptus nitens (Deane & Maiden) Maiden, ii) determined the variability, and in particular the day/night variability, in root elongation, and iii) explored the physiological basis for such variability. A series of experiments were undertaken with seedlings of E. pauciflora and E. nitens grown at soil temperatures of 3, 7, and 13C, and where seedlings were transferred from one temperature to another. E. nitens grew faster than E. pauciflora at 7 and 13C, but E. pauciflora grew faster than E. nitens at 3C. E. pauciflora always produced greater total and white root length than E. nitens. E. nitens roots browned faster in response to lowering soil temperatures than E. pauciflora. The osmotic potential of the roots decreased with soil temperature, but more so in E. pauciflora than E. nitens. Proline was a prominent osmoregulant in roots of E. pauciflora and arginine in E. nitens roots. It is suggested that E. pauciflora is better adapted than E. nitens to root growth at low soil temperatures because it can keep roots white longer and can maintain lower root osmotic potentials. Root growth of E. pauciflora was examined for 31 months (December 1992 - June 1995) in a mature stand at an elevation of 1545 m on Mt Stirling, Victoria, Australia. Greater night than day root elongation was recorded from eight in situ rhizotrons during the summer and early autumn of 1993. Shoot growth was also monitored during part of this study (April 1994 - June 1995). It was found that root growth commenced in the spring at soil temperatures 5 1.5C, under 550 mm of snow, at least one month before the onset of shoot growth and continued at least two months longer that shoot growth during the autumn. A period of root dormancy for at least one month a year occurred in roots of E. pauciflora. The seasonal variability in root numbers of E. pauciflora appeared to be related mainly to soil temperature and to a lesser extent to soil water content. Moreover, there appeared to be some internal periodicity in root growth which was independent of the external environment on Mt Stirling. Greater night than day root elongation was recorded in seedlings of both eucalypts in a glasshouse. Root elongation rates were greatest in E. nitens, and root elongation of both eucalypt seedlings were greater than that of the mature E. pauciflora on Mt Stirling. The zones of day and night elongation were determined in root marking experiments. Histological studies of the zone of elongation showed that cell division occurred mainly during the day and cell elongation mainly at night. Night root elongation rates were increased by increasing day-time air temperatures, light-period, and light intensity; and by decreasing water stress during the night. The turgor pressure of the root tips was greater during the night than the day. It is suggested that the amount of root growth during the night is determined directly by turgor pressure during the night and indirectly by processes during the day (light duration and intensity, and temperature during the light period) which determine the extent of cell division during the day. A greater rate of cell division during the day will be translated into a greater rate of root elongation, especially in the night.
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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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ItemA study on damping-off in a regeneration mixed eucalypt forest( 1986)Although damping-off is known to cause considerable loss before and after emergence of seedlings in forest nurseries, little is known of its role in seedling mortality after direct seeding in artificial regeneration of mixed eucalypt forests. Findings reported in this thesis are the result of a survey for the presence of damping-off fungi in soils and dying seedlings, and tests of their pathogenicity to a range of eucalypts found in the Wombat State Forest of Victoria. This study was carried out in conjunction with a research programme established by the Victorian Department of Conservation, Forests and Lands to determine which factors govern the successful establishment of E. obliqua and E. radiata in three seed-bed types under five levels of overwood. Propagule counts for Pythiaceous fungi in burnt and unburnt soils from field experiment, plots prior to sowing indicated that the inoculum level was low and differed with levels of overwood retained following site preparation in summer (Chapter 2). Baiting the soils with E. sieberi cotyledons, apples or directly sowing E. sieberi seed in samples of the field soil showed that both burnt and unburnt soils were variably infested with Pythium spp., Fusarium spp., and Cylindrocarpon destructans. A small portion of the seed to be sawn in the field plots without any fungicidal pre-treatment was found to harbour a range of fungi, sane of which had the potential to inhibit germination of the eucalypts sown on the plots (Chapter 3). The fungi having this ability were however not isolated from damped off seedlings in the experimental plots. Field studies showed that the proportion of germinated seedlings killed as a result of damping-off was lower than that attributable to frost heave, droughting following freezing and insect damage (Chapter 4). Damping-off was found to be widespread over the entire study site and the rate of damping-off to differ with seed-bed type. Overwood density did not affect the disease level. Although Pythium spp. were responsible for most deaths, Cylindrocarpon destructans and Fusarium spp. also caused some mortality. Pathogenicity tests (Chapter 5) confirmed that the fungi associated with seedling mortality in the field can cause significant pre- and post-emergence damping-off in a range of eucalypts found at the study site. The fungi differed in their pathogenicity to the eucalypts and sane induced feeder root necrosis after the two leaf stage of seedling development. No differences in susceptibility to post-emergence damping-off were found between the tree species sown on the plots and others of economic importance in the forest. The overall findings and their implications for direct sowing as a management option in future field regenerations are discussed in Chapter 6.