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Conservation biology of the critically endangered Western Australian shrub Calytrix breviseta Lindl. subsp. breviseta

Nield, Andrew (2008) Conservation biology of the critically endangered Western Australian shrub Calytrix breviseta Lindl. subsp. breviseta. Honours thesis, Murdoch University.

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Abstract

Calytrix breviseta Lindl. subsp. breviseta is a critically endangered, obligate-seeder shrub within fire-prone kwongan of southwest Western Australia. Little is known about the species’ reproductive biology and how threatening processes, particularly altered fire regimes and exotic species invasion, will impact the long-term viability of the species. This study aims to elucidate the species’ reproductive biology and patterns of seedling recruitment during succession after fire. This work also describes general changes in floristic structure of the kwongan community in which the species resides, including an examination of species diversity and changes in dominant life-forms during succession after fire. This facilitates a determination of whether exotic species are competitively displaced during the successional process. The effects of changes to the fire return interval and exotic species invasion on the long-term viability of the species is also described.

The species exhibits abundant recruitment following fire and the application of a smoke treatment significantly improves germination, similar to many other Western Australian shrubs. However, significant inter-fire recruitment was observed up to 10 years following fire, leading to the presence of multi-aged subpopulations, although seedling recruitment was negligible > 20 years after fire. The juvenile period is short at 3 years to first flowering. While shrub species displaced perennial herbs during post-fire succession, exotic annual herbs, graminoids and geophytic perennial herbs are consistently observed during post-fire years, reflecting the susceptibility of the community to invasion by exotic species. Population viability analysis (PVA) predicted that the optimal fire return interval to maintain C. breviseta subsp. breviseta was dependent on the carrying capacity (K) of the community and the number of individuals present. Interpretation of carrying capacity will be influenced by site quality and competition from invasive species. PVA suggested that if K remains high, then the optimal fire return interval is approximately 15-20 years but under lower carrying capacity, (i.e. weed competition) fires decrease the likelihood of population survival.

The management implications of this study are that fire should be used, rather than excluded from the landscape, and exotic species monitored and controlled to ensure the continued persistence of C. breviseta subsp. breviseta. Ongoing demographic monitoring should also occur to validate the results of the PVA and to provide the basis for future analysis.

Item Type: Thesis (Honours)
Murdoch Affiliation: School of Environmental Science
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: repository@murdoch.edu.au. Thank you.
Supervisor(s): Ladd, Phil and Yates, Colin
URI: http://researchrepository.murdoch.edu.au/id/eprint/51889
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