School of Ecosystem and Forest Sciences - Theses

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    Chemical treatment of wood and its effect on wood/water interactions
    Hann, Jeffrey Albert ( 1999)
    Wood-water interactions including the effect of grain orientation, sample size and water potential in Pinus radiata D.Don were investigated. The influence of various chemical treatments on the wood-water interaction was also evaluated. The uptake of moisture by wood soaking in water was determined using the water soak method developed by Rowell and Banks (1985). Treatments with surfactants such as ammoniacal copper-didecyldimethylammonium chloride (DDAC-ACQ) and linoleate salts increased the initial uptake rates of the wafers, whilst treatment with copper chrome arsenic (CCA), linseed oil (LO) and a combined CCA/LO treatment reduced uptakes of moisture. The length of time used to assess the water repellent effectiveness (WRE) was found to be crucial to the test, with most of the reduction in WRE occurring in the first 15 minutes of soaking. Exposure of wax treated wafers to weathering indicated an initial gradual reduction in efficacy, which decreased more rapidly as the length of exposure time increased Tests on the effectiveness of different wood coatings subjected to high humidity illustrated the importance of a film with low permeability and some elasticity. Wood blocks coated with resorcinol-formaldehyde resin initially inhibited moisture ingress, but failed after prolonged exposure. An extra coat increased the time required before failure. Coating the wood wafer with a silicone resin slightly reduced the uptake of water into the wafer. However, this resin was more permeable than the resorcinol-formaldehyde resin and was not as efficacious. The effect of various oil treatments on the uptake of water vapour indicated that the distribution of the oil is critical to inhibiting vapour uptake. No significant difference was found between the moisture uptake of hardwood and softwood stakes. Treatment with trimethylborate (TMB), DDAC-ACQ and CCA had no significant effect on the extent of vapour taken up by the wood. An experiment designed to investigate the importance of sample size when assessing wood performance was carried out using matched samples of treated and untreated quartersawn and flatsawn Pines radiata D.Don. It was found that samples treated with DDAC-ACQ and exposed outdoors experienced a greater flux in moisture content compared to controls. CCA reduced the extent of moisture uptake, with the incorporation of oil further enhancing the short term weathering performance. Quartersawn wood exhibited a smaller moisture flux than the flatsawn timber.However, the performance of CCA/Oil treated quartersawn wood was only marginally better than the quartersawn controls. Laboratory trials gave an identical treatment ranking as the exterior trial; however the use of the smaller sample size was identified as being inappropriate for the assessment of check formation in the timber. A sample size effect was demonstrated when assessing the efficacy of treatments by the water soak method. A treatment gradient could be demonstrated when whole stakes were impregnated with CCA and linseed oil by a two-stage process. The test indicated that the significance of improvements in the water repellency of treated wafers diminishes when larger sized samples are investigated. The effect of soil water availability on wood moisture content was determined for untreated hardwood and softwood sticks. At low soil moisture contents, hardwood sticks were found to be significantly more saturated than their softwood counterparts. At higher soil water contents (100% water holding capacity (WHC)) the performance of the two species of wood became less significant. Chemical treatment was found to have a significant effect on reducing wood moisture levels when free water was available in the soil. Linseed oil was responsible for a significant reduction in moisture uptake, by blocking the pathways for water uptake as well as by decreasing the void volume available in the wood for water to occupy. Incorporation of a drying agent did not improve the quality of the film formed by the linseed oil as no significant change in water repellent performance was identified. The uptake and movement of water through a horticultural post was simulated using a procedure described by Baines and Levy (1979). The wick action of heartwood and sapwood stakes of Pinus radiata D.Don was investigated with distinct moisture distribution and behaviours found. Heartwood, being less permeable, showed a reduction in the volume of vapour that moved through the wood, as well as a much lower stake moisture content compared to the sapwood. This difference was most pronounced above the air/water interface and helps to explain the difference in decay resistance exhibited by the two wood types. End sealing the stakes with silicone resin was found to have no significant effect on the wick action of the stake. Lumen filling treatments with wax, oil and alkyd resins were found to significantly alter the wick action of the stakes. Treatment with low concentrations of surface active compounds such as DDAC-ACQ and linoleate soaps were found to increase the rate of water uptake. At higher concentrations the presence of the surfactant increased the hydrophobicity of the wood and reduced moisture uptake. Biological testing using a fungal cellar determined that treatment of the wood with CCA/LO, CCA, DDAC-ACQ/LO, LO and DDAC-ACQ significantly improved the resistance of the wood to decay. The incorporation of linseed oil did not cause a significant improvement to the decay resistance of the stakes over the trial period
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    The potential for non-target soil fungi to compromise a wood preservative
    Collett, Olga ( 1998)
    Increased environmental concerns associated with currently used wood preservatives have seen a trend in the development of biocides that include inorganic-organic binary mixtures. One such mixture is the ammoniacal copper quaternary ammonium system (ACQ) which contains copper as the primary biocide and didecyldimethylammonium chloride (DDAC) as the co-biocide. In view of experience in agriculture and horticulture, where similar changes from inorganic to organic formulations resulted in failure through the development of tolerance to the organic compounds in target organisms, the present investigation set out to determine if a similar fate awaits these binary wood preservatives which are exposed continuously to a wide range of microorganisms in soil. Soil fungi tolerant of DDAC, copper and a combination of both were isolated from liquid medium inoculated with soil and from treated blocks of Pinus radiata sapwood which had been buried in soil for 26 weeks. Matric potentials of soil and blocks were determined and treated blocks were buried in soil to give two moisture contents. More species of fungi were isolated from blocks at the higher moisture content than at the lower one. All were Hyphomycetes and included species of Verticillium, Paecilomyces and Gliocladium. Growth of selected tolerant isolates, measured as extension of colony diameters on PDA, was not sensitive to pH. Variation in growth rates among isolates was not related to tolerance of DDAC. Isolates of Verticillium were the most tolerant. Toxic thresholds of DDAC and copper to selected soil isolates and two wood-decay fungi were determined in liquid media. The fungi varied widely in their responses. Species of soil fungi were more tolerant of these chemicals than were wood-decay species. V. lecanii was the most tolerant of DDAC and was able to grow in medium containing 250 ppm DDAC, while the brown-rot fungus, Antrodia vaillantii was able to tolerate only 2.5 ppm. V. lecanii was also much more copper tolerant than A. vaillantii and grew in medium containing 12000 ppm elemental copper. Growth of V. lecanii, measured as biomass, was not affected by test concentrations of DDAC. Bioassays in liquid medium showed that the fungus was able to reduce the concentration or activity of DDAC to levels permitting growth of other more sensitive isolates, including wood-decay fungi. None of the soil isolates examined was able to utilise DDAC as a sole source of carbon. Growth rate and biomass production were not affected by 500 ppm copper but at 3000 ppm reduction of both was observed. Inductive coupling plasma (ICP) emission spectroscopy analyses showed that V. lecanii reduced the concentration of soluble copper in the growth media. Combinations of DDAC and copper were much more effective against V. lecanii than either component alone and in certain ratios these combinations were synergistic. The amount of copper required to control V. lecanii was substantially less when it was combined with DDAC which could have economic as well as environmental benefits.
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    The effect of process variables on the dimensional stability of particleboard
    Ho, Siew Kheng ( 1998)
    The work undertaken in this thesis aim at improving the dimensional stability of particleboards caused by water absorption and stress relaxation both of which often occur simultaneously in finished composite board products. Dimensional instability was quantified by measuring the board percent thickness increase resulting from: i) springbuck on press opening; ii) reversible swelling subjected to moisture or solvent absorption and, iii) irreversible swelling due to stress release The reversible swelling was measured after a complete wetting or a humidity cycle from low to high humidity levels. The irreversible swelling was assessed after a complete drying or a humidity cycle from high to low humidity levels. Chemical modification of wood aimed at reducing the reversible swelling due to moisture absorption was attempted after the sequential replacement of water in wood by solvents. P. radiata and E. Obliqua blocks saturated with water were sequentially treated with polar followed by non-polar solvents in order to replace the water in the woods. Both species showed about 30 % retention of their original (green) volume after the final stage of treatment. The partially swollen P. radiata blocks were then chemically treated with the wood cell wall-bulking and cross-linking agents, i.e. acetic anhydride and paraformaldehyde respectively. Wood thickness swell was monitored through cyclic wetting and drying tests. The results showed that the dimensional stability of neither the acetylated nor the paraformaldehyde treated sample were improved as quantified by the anti-swelling efficiency (ASE). The presence of a catalyst (ferric chloride) was necessary to enhance the cell wall cross-linking and to improve the wood dimensional stability. This work identified that a chemical reaction between the reagents and the wood is necessary for achieving dimensional stability. Stress relaxation from springbuck and irreversible recovery are inherent in wood particles which have been stressed. Much of this work focused on reducing this stress in situ during wood composite panel consolidation. Chemical conditioning of wood materials by ammonia in situ during consolidation was studied using phenolic-based resin systems. Ammonium hydroxide (source for ammonia) was found to accelerate the curing of phenol-resorcinol-formaldehyde (PRF). Accelerated curing was also found for 50:50 (w/w) mixtures of PRF and phenol-urea-formaldehyde (PUF) at low temperatures between 45 C and 75 C and in the presence of formaldehyde. The PRF:PUF (50:50) resin system showed a significantly faster cure than the PRF resin in the presence of ammonium hydroxide at all levels of temperatures investigated. The resin system also showed shorter gel times than those of the PRF at different weight portions of ammonium hydroxide additions. Preliminary chemical structural analysis of both resin systems catalysed by ammonium hydroxide using Infrared (IR) analyser showed evidence for the presence of an azomethine group which indicated that the ammonia was being incorporated into the resin structure. Single layer particleboards were manufactured at low temperatures using the PRF binder and ammonia. Gaseous injection of ammonia in situ during board consolidation was achieved by using a laboratory press fitted with perforated plattens. An optimum pressing schedule was established whereby the ammonia was injected after the mat had reaching its final thickness in a sealed press system. The effects of pressing temperature, PRF resin loading and gas pressure on board vertical density profile, MOR, MOE, IB and thickness swell were studied. The results showed that the ammonia gas-injected boards consolidated at both temperatures of 50 C and 100 C had more uniform density profiles than those of the hot-pressed boards at the temperature of 180 C, however, the MOR, MOE, IB and thickness swell were less satisfactory. The MOR, MOE, IB and thickness swell of the ammonia gas-injected boards were bench marked against the requirements for standard grade High Moisture Resistant (HIR) particleboards in accordance with the AS/NZS 1859.1: Part 1 (1997), and were found to be below the acceptable standard. Particleboards bonded with PRF:PUF 50:50 (w/w) resin catalysed by ammonia gas were also produced. The board MOR, MOE, lB and thickness swell were less superior than those bonded with PRF, although ammonia was found to accelerate the cure of both resin systems. This was thought to be attributable to a curing reaction that was too rapid between the ammonia and the resin system. The pressing time and temperature may need to be shortened and lowered respectively for board property improvement. The effect of wood particle size on the properties of ammonia gas-injected particleboards was investigated. Large size particles were found to increase the MOR and MIE irrespective of pressing methods. However, boards made from small size particles were found to have higher lB's than those of large size particles. This was thought to be due to better gas penetration. Recommendations are provided for further work to enhance the properties of ammonia-catalysed PRF boards.
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    Nutritional physiology of eucalyptus grandis and pinus radiata irrigated with municipal effluent
    O'Brien, Nicholas David ( 1998)
    The aim of this study is to compare the processes of accumulation and use of N, P, K, Mg and Ca between two and four years of age in plantations of Eucalyptus grandis and Pinus radiata irrigated at several rates with municipal effluent, and with bore water. A series of five harvests over two years was used to estimate above-ground biomass and nutrient content. Growth rate was greater in E. grandis than in P. radiata. Total biomass at 34 months ranged from 34 to 45 t ha-1 in E. grandis and from 21 to 26 t ha-1 in P. radiata, with a trend towards higher rates of growth with increased irrigation rate. Foliage mass and leaf area index (LM) were initially greater in E. grandis than P. radiata. However, the rate of increment in foliage mass and LAI in E. grandis decreased after canopy closure (at about 20 months). At 34 months foliage mass averaged 5.9 t ha-1 in E. grandis and 7.4 t ha-1 in P. radiata. Nutrient accumulation was primarily a function of growth rate, in particular the rate of canopy development. Rate of nutrient accumulation in E. grandis was greatest prior to canopy closure, decreasing thereafter, and in P. radiata it was greatest in the last year. As a result, mean annual increment of nutrient accumulation was maximum in E. grandis at 28 months, and in P. radiata at the end of the study. Implications for management of effluent-irrigated plantations are discussed. The mass of each nutrient accumulated varied greatly and decreased in the order Ca
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    The water and nitrogen dynamics of a lucerne-based farming system in the Victorian Wimmera
    McCallum, Matthew Harvie ( 1998)
    The water and nitrogen (N) dynamics of a lucerne-based farming system (grazed lucerne-annual medic-ryegrass pastures grown in rotation with crops) was compared to continuous cropping (cereal, pulse and oilseed crops) in the Victorian Wimmera. The growth dynamics and CO2-exchange behaviour of lucerne in the pasture phase was also investigated. Soil profiles under lucerne-based pastures remained consistently drier during the year as compared to annual cropping. The amount of plant-available soil water (0.0 to 2.0 m) after 3 to 4 years of pasture was on average 48 mm less than after annual crops (wheat, field pea), most of which (81%) was extracted at depth (1.0 to 2.0 m). In the field, crop yields (canola, wheat) after lucerne were not reduced because water use by these crops was predominantly in the top 1.0 m of the soil profile. A wheat simulation study predicted that a small median yield loss of 0.4 t ha-1 (15%) could be expected for the first wheat crop grown after lucerne, although this yield penalty varied from 0 to 0.87 t ha-1 depending upon seasonal rainfall. The risk of a large yield penalty (>0.8 t ha-1) was low (5 years in 100). From simulation studies, the time taken to fully recharge the soil profile after lucerne to levels equivalent to that under continuous cropping was estimated to occur within 4 to 5 years. The contributions of N2 fixation by the legumes (lucerne, annual medic, field pea) to the N economy of the farming systems in this study depended upon the amount of dry matter production. N2 fixation by field pea (121-175 kg N ha-1 yr-1) was greater than pasture legumes (40-95 kg N ha-1 yr-1), although a large amount of N was removed in grain at harvest (115-151 kg N ha-1 yr-1). N2 fixation by lucerne (19-90 kg N ha-1 yr-1) was consistently greater than annual medic (2-56 kg N ha-1 because the effects of seasonal rainfall patterns on dry matter production were more pronounced for annual medic. Winter-cleaning of ryegrass in the pasture before cropping resulted in both a high legume content (85%) and generally increased N2 fixation (up to 55 kg N ha-1 yr-1 ). Despite some benefits in N fertility, large responses to N fertiliser were still observed in crops following pastures; in grain yield (increases of 0.33-0.55 t ha-1 for canola, 1.0 t ha-1 for wheat), protein (0.7-2.3% for canola, 1.3% for wheat) and oil yield in canola (124-205 kg ha-1). The growth pattern of lucerne was similar to that of annual species (annual medic, ryegrass) contained in the pasture, with the majority (70%) of growth occurring between July and November. The small amount of lucerne growth from summer to early autumn (December to March) was due to the small supply of water (rainfall and stored in soil) during this period. A more detailed study of two lucerne pastures during summer revealed that the plant was under considerable water stress; leaf:stem ratios increased (from 0.9-1.6 to 2.6-3.2), leaf folding and paraheliotropic movement decreased the amount of leaf area exposed to incoming radiation in the middle of the day (by 14-29%), and it was estimated that the some 75-83% of assimilated carbon was partitioned below-ground to roots and crowns.
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    Physiological aspects of root growth of Eucalyptus pauciflora, subsp. pauciflora and Eucalyptus nitens
    Halter, Reese ( 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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    Multiple resources planning and inventory
    Spencer, Raymond Douglas ( 1995)
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