School of Ecosystem and Forest Sciences - Theses
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ItemImproving species distribution models using extreme value theory and climate dataset ensembles( 2020)The development of climate datasets at fine spatial and temporal scales has commonly been driven by the need to better understand vegetation distributions and ecological systems. While a wide range of global, national and regional climate datasets have been developed over the last two decades, they are rarely compared directly in the ecological literature. This thesis evaluates a range of climate interpolation techniques and investigates how the spatial and temporal characteristics of climate datasets may be utilised to improve the predictive performance of plant species distribution models (SDM). A series of spline-based and geostatistical methods for interpolating temperature variables are first compared across Victoria, southeast Australia. Secondary predictors (thermal remote sensing data and local topographic indices) which indirectly capture mesoscale microclimate and cold air drainage regimes were found to improve monthly mean minimum temperature interpolations by up to 39%. Thermal remote sensing data only reduced root mean square error (RMSE) by up to 6% for maximum temperature across Victoria and was most effective during the summer months. The interpolation methods used in southeast Australia were subsequently transferred to the Royal Himalayan Kingdom of Bhutan to validate their effectiveness in a novel climate. In Bhutan, the predictive performance of minimum temperature interpolations was also improved considerably (up to 23% reduction in RMSE) when using thermal remote sensing data and local topographic indices as spatial covariates. Thermal remote sensing data also reduced the RMSE for maximum temperature interpolations by up to 16% in Bhutan. Interannual variability of climate extremes were used to evaluate how the temporal characteristics of climate may be used to improve the predictive performance of SDMs. Generalised Extreme Value (GEV) distributions were fitted to monthly climate data to generate variables which account for the skewed distribution of extremes. Models incorporating interannual variability (drawn from a range of expected return intervals) improved predictive performance compared to models using seasonal extremes only for 28 of 37 species assessed. Iteratively fitting models using alternate expected return intervals typically acted on the leading and trailing edges of current distributions, indicating that such methods may be useful for model calibration and characterising climate-driven source-sink population dynamics. The impact of spatial disparities in climate on the predictive performance of plant SDMs was evaluated using three distinct datasets developed for Victoria as part of this research, in addition to two global datasets (WorldClim v1 and v2). Individual models were compared against one another and as ensembles to explore the potential for alternate predictions to complement one another. The Victorian datasets demonstrated a significant improvement over the original WorldClim dataset (up to 17.3% mean increase in D2) and trended towards an improvement relative to WorldClim v2; however, no significant differences were found when comparing the alternate Victorian datasets. Multi-model ensembles achieved a mean increase of up to 13.8% and 29.2% in D2 relative to individual models when using regional and global datasets, respectively. Ensembles provide a pragmatic method to improve the predictive performance of SDMs and allow a trade-off between the uncertainties and potential biases embedded in competing climate datasets.
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ItemMaking the connection between history, agricultural diversity and place: the story of Victorian apples( 2016)Apple growing practices are embedded in a productivist mentality aiming for ever higher efficiency and productivity. And while the climate change impacts are to a large extent known, there is little attention given to the coupling of the social and the ecological effects. I use apple growing as a case study to explore the relationship between place, biodiversity and rural change in Victoria. My research is based on historical research; including an analysis of the Museum Victoria’s collection of wax apple models, and in-depth interviews with orchardists. By drawing on environmental history, social-ecological systems thinking and Bourdieu's theory of practice, I highlight the importance of a systems perspective and inform it by emphasis on the critical role of underlying power structures and individual dispositions, or the habitus, of the growers. These dispositions have been shaped and internalised by the growers’ histories and their physical surroundings. Orchardists have been able to respond to intensifying production requirements by utilizing technologies and scientific nous to keep up with the continuous aim for efficiency. Growers are caught up in a self-reinforcing cycle of satisfying the demand for perfect apples by adopting expensive techno-scientific approaches to enable ever more intensive production. The symbolic violence and amplified biophysical pressure orchardists experience has driven many to despair; resulting in a significant decline in small scale apple growing businesses over the last decade. I offer some suggestions for government policy and support measures and argue that any services or support programs need to be tailored to the appropriate level and need of each orchard business and the individuals who are involved. My analysis shows that those growers, who engage more closely with their biophysical place as well as their history and identity as apple growers in that place are (re-)creating another version of what it means to be an apple grower. In some cases this is resulting in resistance to the vortex of agricultural productivism that has been the basis of their existence for many generations.
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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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ItemThe water and nitrogen dynamics of a lucerne-based farming system in the Victorian Wimmera( 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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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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