School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemAn analysis of radiata pine-pasture agroforestry systems( 1993)Agroforestry, the integration of forestry and agricultural production, requires an understanding of the interactions between trees, agriculture and the environment. This thesis presents an analysis of the effects of a variety of Radiata Pine-pasture agroforestry treatments on soil water, tree growth and form and pasture production together with a series of economic analyses using the FARMTREE model to simulate the various agroforestry regimes established at Carngham in western Victoria. The Carngham study site consists of a replicated randomized block design of five Radiata Pinepasture treatments. The treatments were: open pasture (no trees), 100 trees/ha (8 m x 12 m), 277 trees/ha-wide-spaced (4 m x 9 m), 277 trees/ha-5 row (5 rows, 4 x 3 m, with 10 row gap) and 1650 trees/ha (no pasture). Results, 11 years after tree establishment, show that soil water content under the various treatments has a cyclical pattern of recharge and discharge with an annual amplitude of approximately 100 mm. Within the 100 trees/ha and 277 trees/ha-5 row and 277 trees/ha-wide-spaced treatments, the soil water content was generally significantly less than under open pasture in the upper 170 cm of the upper profile. Within the 1650 trees/ha treatment, the trees utilize water to a depth of at least 270 cm. Tree form was influenced by tree density. Tree diameter decreased but height increased with tree density with the trees of largest volume produced in the 277 trees/ha-wide-spaced treatment. Variable-lift pruning was routinely applied on an annual basis from tree age 6 years, to minimize the internal knotty-core and to maximise the volume of knot-free timber produced. Pruning was virtually completed (to 6 m) after five or six annual treatments, and significant relationships between DOS (diameter over stubs) and various tree parameters were identified as predictors for determining the volume of the knotty-core. Agricultural production was assessed as net pasture production using rising-plate methodology during the major growth seasons. Trees in single rows, as in the 100 trees/ha and 277 trees/ha-wide-spaced treatments, had only a limited effect on net pasture production compared to the zone within 4.5 m from the trees in the 277 trees/ha-5 row treatment where pasture production was significantly less than in open pasture, or in the zone from 4.5 to 18 m from the tree line where there was a possible shelter benefit. Although pasture production was similar between treatments, animal production decreased with increasing tree density. Economic analyses using the FARMTREE model and progressive data from the Carngham trial showed that simulations of the agroforestry regimes at Carngham were more profitable than grazing alone using real discount rates up to 7%. The 277 trees/ha-wide-spaced regime returned the greatest net present values over the range of discount rates used. The optimum rotation length, assuming a 5% real discount rate, was 26 years. Based on the 277 trees/ha-5 row treatment, shelter benefits for agricultural production could be obtained with a distance between belts of 150 to 200 m and by leaving at least 10% of the trees unpruned. The Carngham trial represents one case study of Radiata Pine-pasture agroforestry for south west Victoria. On this basis, the data presented provides information on patterns and trends likely to be encountered in applying agroforestry to other locations in Victoria. The adoption of agroforestry requires ongoing research trials and demonstrations and the Carngham trial has been well planned and maintained and should be seen as a valuable asset for the advancement of agroforestry in Victoria.
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ItemVariation of some vessel characteristics of plantation Eucalyptus regnans F. Muell( 1993)Some vessel characteristics of six 15-year old plantation grown Eucalyptus regnans F. v. Muell. trees from a progeny trial in Narbethong, Victoria were studied. The within and between tree variation of vessel frequency and percent tyloses with distance from the pith, between six heights and between the six trees was examined. Vessels and vessels containing tyloses present on the cross-sectional surface of 7 mm by 7 mm wood blocks taken from pith to bark were counted using a stereo zoom microscope. Analysis of variance was used to examine the variation of vessel frequency and percent tyloses with: distance from the pith; between the north and south axes; between the base, breast height, 20%, 40%, 60% and 80% of total tree heights; and between the six trees. Data in graphical form coupled with microscopic observations were used to examine the within and between growth ring variation. The overall mean vessel frequency for the six 15-year old trees was 7.885 vessels/mm2. Variation of mean vessel frequency with distance from the pith, between heights and between trees was statistically significant. However, after area weighting the vessel frequency values, there was not a significant difference between trees. Mean vessel frequency generally increased with height, with means of 7.100 vessels/mm2 at the base and 10.722 vessels/mm2 at the 80% height, and decreased from the pith to the bark. The variation between axes and with all interactions between the main factors were not significant. Vessel frequency was observed to vary within and between growth rings. Vessel frequency was lowest in the region at the latewood to earlywood boundary and highest in the central portion of the growth ring. Vessels containing tyloses were found at all six heights of all six trees and the mean percent tyloses for the six trees ranged between about 7 to 18%. The variation of mean percent tyloses with distance from the pith, between heights, between trees and the interaction between height and tree was statistically significant. The percent tyloses was lower in the region near the pith and in the sapwood region near the bark and highest in the central region between the pith and the bark. The percent tyloses varied between about 10 and 40% in a cyclic or wave-type manner over distances of about 10 to 15 mm from pith to bark but did not appear to be related to vessel frequency. The mean percent tyloses showed a general decrease with height, with the base height having a mean of 20.387% and the 80% height a mean of 6.448%. The largest tree mean was 17.568% and the lowest was 7.219%. The relative magnitude of the mean percent tyloses at each height and the ranking between heights varied between trees. For all six trees the frequency of vessels was greater toward the top of the trees but fewer vessels contained tyloses at these upper heights. It may be that timber removed from the upper portions of the stem might be more permeable to liquids such as in the preservation and pulping processes and may release moisture upon drying more easily.
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ItemEffect of later age fertilization with superphosphate at age 24 on tree growth, mechanical properties and wood quality of Pinus radiata D. Don( 1993)Later-age fertilization with superphosphate of Pinus radiata is one of the silvicultural practices used in Australia and is employed operationally on phosphorus deficient sites found in Victoria. Later-age fertilization of radiata pine has previously been shown to give satisfactory responses in terms of growth, wood production and economic values. However, sudden increases in growth rate can lead to detrimental effects on wood properties. The present study was aimed at examining the effect of later-age fertilization with superphosphate at age 24 on the tree growth, mechanical properties and wood quality of radiata pine grown on a phosphorus deficient site. Three trees from each of three diameter classes were selected randomly from a control plot and an adjacent fertilized plot at Scarsdale, Victoria. The fertilized plot had received 504 kg ha-1 superphosphate at age 24 and all eighteen trees studied were felled at age 38. Ring width, percent latewood and tracheid length were examined using a wood disc removed at breast height. Ring width and latewood were measured for each growth ring from pith to bark along the north and south axes. Tracheid length was measured for selected growth rings along the north axis. Basic specific gravity from pith to bark for the north and south axes was determined using the maximum moisture content method at five heights including 0.3 m, 1.3 m, 3.3 m, 7.3 m and 13.3 m. Mechanical properties which included static bending and compression parallel to the grain were determined for four axes for clear specimens removed from a 1.0 m log taken near breast height. Diameter and height growth of the fertilized trees increased significantly over the fifteen year period following fertilization by 30% and 34% respectively as compared to the controls. Volume of the fertilized trees increased 212% over the same period as compared to 77% for the controls. No significant differences in the strength properties were found for the wood produced after the age of fertilization between the control and fertilized trees. Non significant reductions of 8%, 6% and 4% were found for bending properties modulus of rupture, modulus of elacticity and stress at limit proportionality respectively. Non significant reductions of 6%, 11% and 12% were found for compression properties of maximum crushing strength, modulus of elasticity and stress at limit of proportionality. Mechanical properties of both the control and fertilized trees were generally greater than previously reported values for radiata pine. Ring widths increased substantially within two to three years following fertilization with mean values of the fertilized trees around two times that of the control trees. The enhanced radial growth was maintained through to harvest at age 38 and when combined with the the second thinning at age 35 increased even further relative to the controls. The effect of fertilization on percent lateveood was not consistent but appears to be somewhat dependent on the availability of moisture. The effect of fertilization on tracheid length was not clear as there appeared to be a site effect which resulted in the tracheid lengths of the fertilized trees being greater than the controls prior to fertilization. Basic specific gravity was reduced about 4% to 9 % following fertilization and the effect appeared to last for about six to nine years. It appears that the first thinning which occurred at age 20 prior to the fertilization contributed to this reduction in basic specific gravity. Over approximately the final six years of growth the basic specific gravity of the fertilized trees was 3% to 6% greater than the control trees. In conclusion, the effect of later-age fertilization with superphosphate at age 24 on the mechanical properties and overall wood quality appears to be minimal. The large gains made in tree volume following fertrilization on the phosphorus deficient site at Scarsdale and the fact that the later-age fertilization brings a relatively unproductive site into a productive capacity would appear to far outweigh any minimal reductions in wood properties. It further appears that on the deficient site the phosphorus remains available for tree growth through to rotation age and the additional wood produced at the later-age tends to have the desirable mature wood properties as compared to the less desirable wood properties which normally accompany the juvenile growth period.
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ItemSpatial and temporal morphological changes in McHugh's Gully measured using aerial photogrammetry and geographic information systems( 1993)The study addresses the need for the quantitative analysis of gully growth which is one of the neglected dimensions of erosion studies. Gully growth is reflected in the spatial and temporal morphological changes of the gullies. In addition, the influence of causal factors on gully morphology is likewise vital in examining the growth of the gullies. The fast detection of the extent of gully erosion and the rapid acquisition of data is vital in designing measures to stabilise the gullies, control the formation of incipient gullies, and monitor the growth of gullies over time. It was envisioned that the integration of aerial photogrammetry and geographic information systems (GIS) would serve this purpose. Data extracted from aerial photographs can provide important inputs for a GIS database dedicated for monitoring gully systems and providing information to assist erosion control measures. The gully system used for the study was McHugh's Gully which is situated north of Ballarat, Victoria. The morphological characteristics considered in this study were length, width, and order of the gullies and the fractal dimension of the entire gully system. Photo-interpretation of stereoscopic pairs of large-scale aerial photographs (1: 15 840 and 1:25 000) enabled the delineation of the gully outline, classification of the vegetation cover, and measurement of the gully width. Gully outlines and other spatial features were digitised to form the thematic layers for a GIS database. Elevation data was measured from topographic maps and was used to derive the slope and aspect classes. A grid with a cell size of 100 x 100 m was generated to store the attribute data. A PC Version of ARC/INFO and IDRISI were used to manipulate both raster- and vector representation of the data. The findings indicate that the total length of the gully system increased by 0.30 km/yr and affected an additional three hectares of land each year between 1946 and 1980. The majority of the gullies have widths of less than 6.25 m although some gullies were more than 18.75 m wide. McHugh's Gully can be measured to the seventh gully order following Strahler's stream ordering scheme. The branching out of first and second order gullies profused after 1946. The complexity of the gully system was also measured using the concept of fractals. The gully system has a fractal dimension that increased from 1.26 in 1946 to 1.55 for the period 1972-1991. Results also indicate that interrelationships among the gully morphological parameters exist. Evidence show, in general, that longer gullies have shorter widths and the first and second order gullies are longer than the higher order gullies. The study confirmed that rainfall, vegetation cover, slope, and aspect of maximum slope influenced the morphology of the gullies. Gullying increases with more frequent rain events. The amount of rainfall in the McHugh's Gully area was not linearly correlated with the year but the frequency of annual, autumn, winter and spring rainfall showed strong positive correlation with the year of record. Gullies found in the dense vegetated areas were longer with narrower widths. Moreover, the non-uniformity of the topographic characteristics of the area induce the formation of incipient gullies and the growth of existing ones. Most gullies developed on 10-19 per cent slopes and the direction of the flow of sediments is towards the north-east and north-west. The dynamic nature of gully processes is associated with difficulties in modelling and simulating the growth of gullies as reflected in the contrasting patterns in gully morphology. However, the monitoring of the growth of the gullies and the fast detection of gullied areas is facilitated through the integration of aerial photogrammetry with geographic information systems. Additional research towards the improvement of the methods described in this thesis are therefore encouraged.
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ItemThe relative value of tagasaste and lucerne as supplementary feeds for sheep( 1993)Chamaecytisus palmensis (Tagasaste) is a leguminous perennial shrub which grows well in a range of climatic zones. Tagasaste was introduced from the Canary Islands to Australia in 1879 and a number of farmers are growing the shrub for fodder production and soil conservation. The most economical means of utilizing tagasaste in Australia appears to be direct grazing by sheep. This thesis reports on a study of tagasaste and lucerne as a supplementary summer feed for sheep in the Strathfieldsaye Research Station, East Gippsland, Victoria. The purpose of the present study was to investigate the relative value of feeding tagasaste and lucerne (Medicago sativa) as a supplementary feed for sheep during summer. Growth performance of sheep, dry matter consumed and the chemical composition of feeds were examined over the four months of the experimental period. The 240 two year old Merino sheep were divided into 12 groups for grazing eight plots of tagasaste and four plots of lucerne as a supplement to summer pasture. Each plot had been fenced into four or six subplots for tagasaste or lucerne respectively, to allow stock to be rotated in four months. The estimation of the dry matter consumed in each subplot was done by selecting 50 sample quadrats before and after grazing for each experimental month. The mean liveweight gain for all sheep in the lucerne plots (11.3 kg/head) was not significantly different from tagasaste (10.6 kg/head) at the end of the experiment. The mean total change in standing dry matter due to grazing in the tagasaste treatment (5360 kg/ha) over the four months was greater than for the lucerne treatment (3384 kg/ha). The overall daily growth efficiency over the daily dry matter (LW (g)/DM (g)) eaten by sheep in tagasaste was 0.20% and 0.34% for lucerne over the experimental period. In both treatments the pattern of pasture dry matter consumption did not resemble the pattern of liveweight gain. The digestibility and total nitrogen content of feed types were not significantly different between trial months. However, the leaf part of tagasaste had significantly greater values than other feed types during the trial although lucerne leaf was not measured. During the trial there was no loss of liveweight in sheep fed tagasaste or lucerne as a supplement. A second experiment indicated that tagasaste regrowth after grazing was significantly better in lightly grazed plots than in heavily grazed plots suggesting that farmers remove stock before all leaf has been eaten. In conclusion, the results of this study suggest that there is scope for the summer grazing tagasaste as a supplement to dry pasture however lucerne remains a better feed than tagasaste on this site. The high quality of tagasaste foliage (leaf) and low rate of liveweight gain of the experimental sheep suggest that further study is necessary to identify the cause of low stock performance.
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ItemRoot-shoot interactions in the growth of irrigated white clover( 1993)White clover pastures support the dairy industry in the irrigated area of northern Victoria. However, pasture production is low because conditions for root growth are sub-optimal, particularly under flood irrigation. This thesis investigated the possibility that the growth of white clover can be increased by reducing the limitations to root growth. A series of experiments examined the response of white clover plants to various soil-based treatments and quantified relationships between root and shoot growth. Plants were grown in intact soil cores in the greenhouse with shoot and root growth measured by destructive harvest. The cores were collected from a range of field sites that were characterised by their different soil physical properties and the variation in pasture yield they supported. Other cores contained a sand-based potting mix in which the conditions for root growth were superior to the most productive field soil. Despite the large effects of soil treatment on white clover production, the growth of shoots and roots was highly correlated (R2>0.95). A prerequisite of high shoot yield is, therefore, a large root system. In one experiment, soil drying or defoliation perturbed the correlation but this disruption was only temporary. In another,experiment, the repeated cycles of drought stress that accompanied a series of extended irrigation intervals had no effect on the relationships between shoot and root growth. In field soils, the restrictions to root growth could not be overcome by intensive irrigation and fertiliser management. However, plants in the treatments in which the soil physical properties had been modified produced 4.0 - 6.5 times as much shoot DM compared with the least productive treatment. This suggests that the potential to improve pasture yield by amelioration of the soil physical properties is very large. Two further experiments were conducted in which either the soil texture or the frequency of irrigation varied between the upper and lower sections of the soil cores. In both cases the production of shoots was correlated with total root production. However, when `unfavourable' conditions restricted the growth of roots in one layer, extra growth of roots in the `favourable' layer was not sufficient to compensate. As a consequence, both total root and shoot growth were reduced. Taken together, these results suggest that there is a large scope to improve the yield of white clover by removing the restrictions to root growth that currently exist in field soils. This will probably entail both amelioration of the soil physical properties and careful management with respect to water and fertiliser applications. However, if the experiments reported here accurately reflect the field situation, then the growth of white clover pastures can only be maximised if the entire root zone is modified.
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ItemShelterbelt effects on microclimate and cereal crops( 1993)The 1980's saw a rapidly expanding community interest in re-establishing trees and other natural vegetation in the largely cleared rural environments in Australia. This culminated in Prime Minister Bob Hawkes' pledge to establish one billion trees in Australia by the year 2000. Tree growing became a major focus for many of the hundreds of Landcare groups which established in this period. The Landcare movement, which has at its foundation the objective of achieving sustainable land use, grew rapidly. Landcare encompasses a broad range of land management issues including soil erosion and salinity, pest plants and animals, declining soil fertility and nature conservation. Tree planting became one of the most popular landcare activities as trees are directly or indirectly related to the majority of landcare issues. Involvement in tree planting can lead an individual into a myriad of more complex aspects of land management. Indeed, many of today's Landcare groups started as Farm Tree groups. The motivation for people to re-establish trees varies greatly and reflects the heterogeneity of the population (such as their needs, their level of understanding and their values) and the multiple benefits that trees can provide. Some are motivated by what they see as the tragedy of the insidious loss, due to tree decline, of quintessential Australian rural landscapes which have resulted from the attractive combination of remnant eucalypts, acacias and other trees and shrubs with agricultural pursuits. Others recognise the importance of rural vegetation in maintaining the biodiversity of Australia's flora and fauna. There is increasing evidence that deep rooted perennial vegetation is important for sustainable agricultural production from many agro-ecosystems. Tree-establishment, in addition to the adoption of other conservation farming practices, is prominent in many strategies to control land degradation. For example, salinity management plans in Victoria are proposing the establishment of trees at low and medium densities over tens of thousands of hectares of land with high ground water recharge to control dryland salinity (Goulburn Broken Salinity Pilot Program Advisory Council 1989). Well planned, integrated revegetation programs may indeed provide combinations of these and other benefits (Burke and Voul 1988). Revegetation projects are generally costly with many long term benefits which are often difficult to measure in monetary terms. In recognition of the public benefit flowing from rural tree growing projects, state and federal governments have provided modest financial incentives such as those under the Tree Victoria Program, and the One Billion Trees Program. These programs at their current levels however only fund a small percentage of the tree growing component of the strategy needed to seriously address some of the land degradation problems present. Most farms in south-eastern Australia are family-owned small businesses. Regardless of the motivation for undertaking tree growing projects, given the modest level of financial incentives and subsidies available, these must largely be funded from the income generated from the farm. There is increasing recognition that "landcare should be able to pay for itself'. For this reason, tree growing projects are particularly compelling which have, at least as one of their benefits, enhanced short-term farm productivity. Shelterbelts are generally rows of trees and shrubs established to ameliorate the effects of the wind. Increased farm productivity from the provision of shelter is widely cited as one of the major benefits of trees on farms in the media and popular literature. This study aims to investigate some of the effects that shelterbelts can have on cereal crop production in south-eastern Australia and thereby help determine the feasibility of some tree growing projects to be at least partially "self funding".
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ItemEfficiency of mechanised ash thinning( 1993)This is a study of the fully mechanised thinning of young (15 to 25 years old), regrowth stands of high quality ash species. The study quantifies the productivity of the harvesting operation, the amount and distribution of traffic across the coupes, as well it describes the changes that occur to components of the forest floor. Strategies are put forward, that if implemented would provide gains in the economic and environmental efficiency of similarly executed ash thinning operations.