Date of Award

1998

Degree Type

Thesis

Degree Name

Bachelor of Science Honours

Faculty

Faculty of Communications, Health and Science

First Advisor

Dr Ray Froend

Abstract

The planting of "Oil malices" have a number of implications in terms of environmental management within Western Australia. Firstly, the incorporation of perennial trees on a large scale into the agricultural landscape can assist in balancing the hydrological cycle and other land degradation problems (Bird et. al. 1992; Western Australian Salinity Action Plan, 1996). Secondly, harvesting the above-ground biomass can produce an economic return because of the oil contained within the leaves. This oil has the potential to replace ozone damaging solvents (Barton and Knight, J997; Wildy, 1996). Finally, "oil mallees" have the potential to offset greenhouse gas emissions, because mallee Eucalypts have a sizeable carbon sink, in the form of a root system that continues to grow after harvesting the above-ground growth (James, 1984). These sinks can potentially be traded, providing the landowner with another income source. For "oil mallees" to realise the potential outlined above, there is a need to obtain information on their growth characteristics, particularly that of the below-ground structures. The aims of the research presented in this thesis were to determine the biomass and amount of carbon being sequested by the below ground organs of E. kochii subsp. plenissima at four different ages, and of E. loxophleba subsp. lissophloia at two ages and to compare these differences to the above ground growth. In addition, the impact of harvesting of the above ground biomass for oil production on the carbon sequestration and growth of the below ground organs was also determined. E. plenissima and E. lissophloia present contrasting stories about the effects harvesting has on biomass sequestration. E. plenissima displayed no significant difference between unharvested and harvested trees for lignotuber biomass. Annual re-growth of the above ground biomass for the harvested trees was 4.3 tonnes per hectare per year and unharvested trees recorded only slightly higher average annual growth (5.2 tonnes/km hedge). At age 2.5 years, E. plenissima has enough carbon reserves within the lignotuber to fund rapid re-growth after harvesting and establish a leaf area that is large enough to restock the Iignotuber and maintain above ground growth.

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