Date of Award

1997

Degree Type

Thesis

Degree Name

Bachelor of Science Honours

Faculty

Faculty of Science, Technology and Engineering

First Advisor

Dr Ray Froend

Abstract

Two of Western Australia's most pressing land degradation problems are waterlogging and increasing soil salinity. Extensive clearing of the native. deep-rooted vegetation and its replacement with shallow-rooted crop and pasture plants has resulted in increased recharge of groundwater tables. causing them to rise. Salts stored in the soil are being brought to the soil surface with the rising watertables. Revegetation with deep-rooted native plants has been identified as the most likely strategy to achieve increased groundwater usage and a lowering of watertables. One area seriously affected by waterlogging and increasing salinity is the Western Australian central wheatbelt region. The Department for Conservation and Land Management [CALM] is conducting revegetation trials with oil producing mallee-form eucalypts. It is hoped that commercial production of cineole, a major constituent of eucalyptus oil, will prove to be an economic catalyst for large-scale revegetation of tile Western Australian wheatbelt region. Species used in the oil mallee trials include Eucalyptus horistes and E. loxaphleba subsp. lissophloia, about which very little is known. Yet site specific species selection, based on knowledge of a species' preferred site conditions for maximum productivity, is essential in reaching revegetation objectives, such as high water use and cineole production. To gain this knowledge about E. horistes and E. loxophfeba subsp. lissophloia a study was conducted on trial sites in the central wheatbelt region of Narrogin-Wickepin. A number of plant growth, water use and cineole production parameters were examined at sites representing recharge and discharge zones, and the chemical and physical characteristics of the sites were determined. It was hypothesised that any differences in species productivity and water use can be explained in terms of the species' suitability to the site conditions, and that any differences between species are physiological. Analysis of the data revealed that E. horistes prefers recharge sites, while E. loxophleba subsp. lissophloia appears to be a generalist species. Both species transpire large amounts of water, making them inherently suitable for revegetation projects aimed at controlling rising watertables and associated soil salinity. Cineole production by E. horistes plants was larger, and E. loxophleba subsp. Lissophloia showed great variability in leaf cineole content. The study highlighted the need for grazing and weed controls in oil mallee plantations, as well as the necessity to carry out further research with emphasis on species provenance selection and breeding trials for higher cineole yields and improved tolerance to waterlogged and saline site conditions.

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