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 Qing Wang
Faculty of
Science, Quaternary Earth and Water Systems
Thesis Title: Impacts of climate, topography, and weathering profile on vadose zone hydrology and coastal pine plantations management – a multi-scale investigation, southeast Queensland, Australia
Current Thesis Abstract: Exotic pine plantations are a major landuse within the coastal lowlands of southeast Queensland. Environmental factors play an important role in vadose zone hydrology, which, in turn, has a great impact on tree growth. This research project consists of three linked studies that analyses the variability of climate, topography and weathering profile at different scales, and aims to develop scientific knowledge to support forest management.
Firstly, a multiple regression model was successfully developed to spatially predict and compare forest productivity for two major species for the entire Tuan Toolara State Forest (TTSF). The independent variables were derived from ?-ray spectrometry, a digital elevation model and interpolated rainfall, which were considered to laterally control the soil water distribution. The model confirmed the low productivity in the northern TTSF.
This low productivity was because of water-logging and soil salinisation, for which the mechanisms were analysed with the focus on the vertical controls of deep weathering profiles. A network of groundwater bores was set up within the weathering profile. Water-logging was caused by perched groundwater formed on top of the ferricrete or mottled saprolite. Localised salinisation was related to the discharge of brackish groundwater occurring within the mottled saprolite. The deep aquifer was fresh and not responsible for salinisation, which differed from many other settings in Australia.
To assess the occurrence of wet conditions in the long term, the soil water balance in a selected catchment in the TTSF was simulated for 30 years using the Soil and Water Assessment Tool (SWAT). This catchment had available high-resolution elevation and soil information and years of monitoring data including stream flow, weather and groundwater levels. The model suggested that the risk of water-logging was the greatest in the humus podzols, followed by the gleyed podzolic soils and the yellow podzolic soils.
The outcomes of this research will provide foresters with guidance in regards to species planning, site treatment and harvesting. The introduced models and analysis tools can be applied to similar forested settings.
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