School of Agriculture, Food and Ecosystem Sciences - Theses

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    Studies on soil carbon and nitrogen in plantation forests using mid-infrared spectroscopy
    Madhavan, Dinesh Babu ( 2014)
    Australian forest plantations have significantly expanded in area since the mid 1990s to meet the increasing demands for wood based products and for environmental services. Establishment and management of plantations can affect soil organic matter (SOM) quantity and quality and thereby soil fertility and sustainable production. This thesis describes investigations of soil carbon (C) and nitrogen (N) in plantations, including effects of a) land-use change, b) management of harvest residues, and c) tree species in biodiverse environmental plantings. Mid-infrared (MIR) spectroscopy was used in tandem with conventional analyses to determine and characterise SOM. MIR spectra (4000-450 cm-1) and partial least squares regression (PLSR) predictions for soil properties were evaluated in land-use change soils from pasture to Eucalyptus globulus plantations (first rotation). Predictions were excellent for C, N and C:N ratio in calibration and in independent test validations, with strong relationships between measured and predicted values (R2 > 0.80) and minimum bias. Reasonable predictions were obtained for microbial biomass C and N, and total P (R2 > 0.70). While there was no significant difference in the concentrations of C and N between land-uses, the results demonstrated the potential of MIR spectroscopy-PLSR to rapidly and accurately assess soil C and N properties, and potential to improve the predictions through local calibrations (e.g., land-use, soil type, concentration range, climate). The effects of harvest residue management on C and N were investigated at two contrasting early-third-rotation Eucalyptus globulus plantations having different soil textures and fertility. Management treatments applied after the first rotation harvest included burning, removing, retaining or doubling the harvest residues; and except for the burning treatments were repeated after the second rotation harvest. Removing residues significantly reduced the mass, concentrations and stocks of organic matter, C and N in litter & residues (L&R) compared to retained or doubled treatments. The concentrations and stocks of soil C and N were not significantly affected by treatment, however there was a general trend of soil C and N increasing with the quantity of residue retained. A corresponding trend was more evident in soil respiration and potentially mineralisable N measurements. Characteristic absorption peaks in MIR spectra indicated that lignins, proteins and carbohydrates were dominant in L&R from residue retained treatments, but easily decomposable aliphatic and carbonyl groups were dominant in L&R from residue removed treatments. The peak area of the organic bands was well correlated with soil respiration. The results emphasised the importance of retaining harvest residues in plantation sites to maintain soil fertility and plant growth. The effect of tree species on soil and litter organic matter was investigated using MIR spectroscopy in five biodiverse environmental native tree plantings (Acacia implexa, A. mearnsii, Allocasuarina verticillata, Eucalyptus melliodora, E. polyanthemos). There were significant differences between litter from the species, with absorbances for proteins, carboxylic acids and carbohydrates dominant in Acacia, whereas those of lignins, cellulose and lower proteins dominant in eucalypts. Soil spectra indicated that only the aliphatic C functional group (3010-2810 cm-1) was significantly greater for A. mearnsii, and which increased with decreasing soil aggregate size. There was a strong correlation of aliphatic band intensity (2924 and 2854 cm-1) with total C indicating a higher degree of humification in soils below A. implexa and A. mearnsii. The results revealed that although there were little or no differences in soil C, there were differences in soil and litter chemical functional groups arising from different tree species. These differences may be useful in selection of species for environmental plantings and rehabilitation. The three studies improved the understanding on changes in soil C and N influenced by vegetation and management practices, and demonstrated the utility of MIR spectroscopy to characterise and interpret changes in SOM.
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    Ecosystem goods and services in production landscapes in south-eastern Australia
    BARAL, HIMLAL ( 2013)
    Ecosystem goods and services (EGS), the benefits that humans obtain from ecosystems, are vital for human well-being. As human populations increase so do demands for almost all EGS. Managing changing landscapes for multiple EGS is therefore a key challenge for resource planners and decision makers. However, in many cases the supply of different types of goods and services can conflict. For example, the enhancement of provisioning services can lead to declines in regulating and cultural services, but there are few tools available for analysing these trade-offs in a spatially-explicit way. This thesis developed approaches and tools for spatially explicit measurement and management of multiple EGS provided by production landscapes. These were used to assess the impacts of land-use change and to provide a basis for managing these trade-offs using case studies in two contrasting production landscapes in south-eastern Australia. Both landscapes have been subject to extensive clearing of native vegetation, which is now present in remnant patches. One study landscape had a concentration of commercially-valuable hardwood and softwood plantations, and the other was dominated by land traditionally focused on agricultural production that is currently being re-configured to provide for more sustainable farming practices and to increase provision of multiple ecosystem services. The study involved five components: (i) development of a novel, qualitative approach for rapid assessment of EGS in changing landscapes that was used to assess observed and potential changes in land use and land cover and their impact on the production of different EGS (Chapter 2); (ii) development and testing of an approach for assessing multiple EGS across space and time using a case study of six key EGS in a sub-catchment in Lower Glenelg Basin, south-western Victoria that demonstrated landscape-scale trade-offs between provisioning and many regulating services (Chapter 3); (iii) an economic valuation of EGS using market and non-market techniques to produce spatial economic value maps (Chapter 4); (iv) spatial assessment of the biodiversity values that underpin provision of many ecosystem services utilising a variety of readily available data and tools (Chapter 5); and (v) assessment of trade-offs and synergies among multiple EGS under current land use and realistic future land-use scenarios (Chapter 6). Results indicate that EGS can be assessed and mapped in a variety of ways depending on the availability of data, time, and funding as well as level of detail and accuracy required. A qualitative assessment can be useful for an initial investigation (Chapter 2) while quantitative and monetary assessments may be required for detailed landscape-scale planning (Chapters 3, 4). In addition, the provision of EGS by production landscapes can vary considerably depending on land use and land cover, and management choices. The study demonstrates that landscapes dedicated mostly to agricultural production have limited capacity to produce the range of ecosystem services required for human health and well-being, while landscapes with a mosaic of land uses can produce a wide range of services, although these are often subject to trade-offs between multiple EGS (Chapters 2, 3). Furthermore, the study demonstrated that spatial assessment and mapping of biodiversity value plays a vital role in identifying key areas for conservation and establishing conservation priorities to allocate limited resources (Chapter 5). There is potential for an improved balance of the multiple EGS required for human health and well-being at the landscape scale, although the economic incentive to adopt more sustainable land use practices that produce a wide range of services are compromised due to the lack of economic valuation of public ecosystem services (Chapter 6). High hopes have been placed by researchers on spatial assessment, mapping and economic valuations of ecosystem goods and services to influence policy makers for coping with the accelerating degradation of natural capital. The approaches and tools used in this thesis can potentially enhance our collective choices regarding the management of landscapes for multiple values and can help policy makers and land managers to enhance the total benefits that landscapes provide to societies through the provision of an optimal mix of goods and services.