School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemControl of thinning operations for maximum production( 1998)Thinning of plantations is a recognised practice for concentrating growth onto selected trees while providing an intermediate return from the thinnings. A great deal of work has been done on methods for estimating optimum time and weight of thinning for the particular stand. However, the selection of individual trees to be thinned in the forest has relaxed in recent years to make thinning more flexible, reduce costs and to better facilitate mechanised harvesting. Some plantations are now being thinned by the harvesting machine operator selecting the trees to be thinned while harvesting. A series of field trials were undertaken in Pinus radiata plantation at Rennick, Victoria, to compare conventional tree marked thinning with operator selected thinning (OST) where the harvesting machine operator selected trees while harvesting. The results indicate good control of tree selection by the operators: thinning to the same density and diameter distribution as the tree marked treatment while removing all required defect trees. Operator tree selection did not affect harvesting productivity, however, it improved log processing time in a second thinning by an experienced tree selecting operator, it also improved falling and work cycle time (approach tree, fall and process) in first thinning on a high site quality. Thinning trials at an operational level, about 6 ha, tested operator selection thinning to two different sets of guidelines: a diameter limit; and spacing requirements for residual trees. These OST thinning operations were no worse than the conventional tree marked thinning and resulted in less residual tree damage and more trees harvested per hour in second thinning. A simple economic analysis, based on data from the field trials, showed each operator selection thinning to be similar to the conventional tree marked thinning for revenue from thinnings and PNV of the rotation taken through to final harvest by a computer model. Of the trials, first thinning on high site quality by a relatively inexperienced operator selecting trees was the least favourable for stand production.
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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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ItemEffects of mulching logging residue on soil water relations, soil temperature and early growth of Pinus radiata on sandy soils in south-west Victoria( 1990)The timber industry in Australia is becoming increasingly dependent on plantations of exotic softwoods, with Pinus radiata D. Don (Monterey pine) the most important species planted in Victoria and South Australia. In general, these plantations have been highly productive in the first rotation. However, in the second rotation there is evidence of a decline in productivity on relatively infertile sandy soils, particularly where the litter and logging residue remaining after clearfelling is burnt. Research has indicated that this decline can be arrested by careful control of cultural inputs, such as chemical weed control, fertiliser and planting of legumes, or by mulching the litter and logging residue. This thesis reports on a study that examined the interacting effects of mulch, weed control and fertiliser on soil and plant water relations, weed biomass, soil temperature, root development, tree growth, and biomass and nutrient accumulation during the first five years following re-establishment of a P. radiata plantation. Mulch, weed control and fertiliser were applied (present, absent) in a 2 x 2 x 2 split-plot factorial design, resulting in eight treatment combinations. Mulch was applied prior to planting; weed control prior to planting and at regular intervals thereafter to age two years; fertiliser at 1.5, 10 and 14 months after planting, a total of 58.1 kg ha-1 of nitrogen and 19.1 kg ha-1 of phosphorus (as part of a complete mineral mix, including zinc). During the first two years after planting, soil and plant moisture levels, soil temperature and tree growth were monitored at four-weekly intervals, and weed biomass three-monthly. Annual growth was also monitored to age five years. Root development, tree biomass and nutrient accumulation were examined in detail at age two years. In the absence of mulch and weed control, soil moisture was significantly reduced during the first two summers after planting due to evapotranspiration losses, with a consequent reduction in tree growth. Both mulch alone and weed control alone were similarly effective in conserving soil moisture in the surface 10 cm of soil, through a reduction in evaporation and transpiration losses respectively. There was evidence that transpiration losses from weeds in mulch had a greater impact than evaporation losses from bare soils at depths from 10 to 40 cm. Maximum soil moisture levels during the summer months occurred where the mulch and weed control treatments were applied together. Mulch reduced weed biomass on average by half for the first two years after planting compared to that on bare soils with no weed control, though weed biomass by mid- to late- summer was similar for both treatments. Weeds which establish in the mulch treatment benefit from improved soil moisture availability as do the P. radiata trees. Mulch significantly reduced soil temperatures compared to those under bare soils during the spring and summer months, particularly in the surface 10 cm of soil. This is likely to have led to less favourable conditions for root growth and mineralisation of soil nitrogen under mulch during spring, when soil moisture availability is not limited by any of the treatments. During summer however, conditions were more favourable under mulch due to higher soil moisture availability. Where mulch and weed control were both applied, root length at age two years was almost twice compared to that for weed control alone. This difference occurred in the surface 10 cm of soil, and is attributed to the combined effect of higher soil moisture availability and stable temperatures within the optimum range for root growth under mulch during the summer months. Roots were also found in the mulch, which indicates that P. radiata roots can either extract nutrients, water or both from the mulch itself. All growth parameters show that in the absence of fertiliser, the responses to mulch alone and weed control alone were similar up to age five years, and that growth was significantly increased when both treatments were applied. These responses were however confounded, as severe zinc deficiency was induced on the weed control alone treatment. In the presence of fertiliser, the responses to mulch alone, weed control alone and both treatments combined were similar by age four years. The largest response to fertiliser was for the weed control alone treatment, probably due to the correction of zinc deficiency. A fertiliser response was initially found where both the mulch and weed control treatments were applied, but by age four years this response was no longer detectable. Growth at age five years was a maximum on, and not significantly different between, the mulch and weed control, mulch and fertiliser, weed control and fertiliser, and mulch, weed control and fertiliser treatment combinations. The nitrogen concentration in needles less than one year-old was at or below the critical level of 14 g kg-1 for all treatment combinations at age two years, except for the weed control alone treatment which was affected by severe zinc deficiency. Despite this, foliage on the treatments associated with good growth did not show obvious nitrogen deficiency symptoms. It is likely that there was net immobilisation of nitrogen under the mulch treatment during the first two years, but subsequent to this it is considered that the mulch would have been a source of nitrogen to the P. radiata trees. Foliar concentrations of both phosphorus and potassium were adequate for all treatment combinations. Foliar concentrations of zinc were at or below the critical level of 10-11 mg kg-1 for those treatments showing maximum growth, which indicates that demands were just being met. They were well below the critical level for the weed control alone treatment. There is clear evidence that the mulched litter and logging residue is a source of zinc to the replanted P. radiata. Relationships between concentration of nutrients in biomass components and tree diameter were generally weak and not significant, and thus nutrient accumulation closely mirrored the pattern of biomass production. The results show that mulching of the litter and logging residue in situ has the beneficial effects of conserving soil moisture, which in combination with more favourable soil temperature conditions during summer, resulted in satisfactory early growth. The results also indicate that mulch is a source of nutrients to the re-established crop. Although care must be taken in extrapolating these results, forest managers should consider mulching as an alternative site preparation technique to burning, particularly on infertile sandy soils.
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ItemThe effects of fertilisation and wastewater irrigation on the biomass and nutrient content of Pinus radiata D. Don( 1985)Detailed measurements were made of soil and stand characteristics before experimental plots were designed and laid out by collaborators from CSIRO. Fertiliser and irrigation were applied in a 2 x 2 factorial design, giving four treatment combinations. Irrigation commenced when the stand was 15 years old, and continued for 29 months; phosphorus at the rate of 5 g m- 2 was evenly broadcast as superphosphate when the stand was 16 years old. The study of biomass and nutrient uptake was comprehensive. Above-ground biomass was estimated by regression analysis of weights and dimensions of 24 sample trees, six trees being selected from each treatment. Standing litter was sampled, and root biomass estimated from core samples and by excavating the roots of one tree per treatment. Uptake of nine nutrients was estimated after measuring their concentrations in all components of the stand. Fertilisation with phosphorus had no effect on total above-ground biomass over a two-year period. Foliar analysis at the start of the study indicated that the trees were mildly deficient in phosphorus, but there was no increase in foliage biomass after fertilisation, despite substantial uptake of the applied nutrient. The lack of growth response was attributed to limiting soil moisture. This finding reinforces results of studies elsewhere that fertiliser responses are site-specific. (From Summary)