Abdul-Rahman-whole.pdf (6.86 MB)
Spatiotemporal characteristics and causes of damage to Azorella macquariensis cushions
thesisposted on 2023-05-26, 02:22 authored by Abdul-Rahman, J
Azorella macquariensis is a perennial cushion-forming herb that is endemic to Macquarie Island. During the 2008/09 austral summer, widespread dieback in A. macquariensis was observed, and is regarded by many to be a new phenomenon. The dieback is perceived to have spread across the entire island, affecting up to ~0 % of cushions in some areas. As a result of this perception the species has been listed as critically endangered under the Environment Protection and Biodiversity Conservation (EPBC) Act 1999. Although there have been speculations about potential contributing factors, a definite cause has not been determined. The spatiotemporal characteristics of three dominant damage types affecting the cushion plant were investigated to help determine the cause/s of the putative increasing damage. In the austral summer of 2009/10, data were collected in the course of four studies: a cushion profile study; mapping of the spatial variation of cushion health; monitoring of temporal variation in cushion health; and ¬¨‚àëa study relating soils to health. There was no significant relationship between overall cushion health and environmental variables apart from health decreasing with increasing exposure to strong winds. Type 1 damage was found to be more concentrated on the windward sectors of cushions, was significantly related to cushion exposure, substrate and vegetation community and did not display any major temporal variability. Type 2 damage was found to be more concentrated on the leeward sectors of cushions, was significantly related to cushion exposure, substrate and vegetation community and also did not display any major temporal variability. Type 3 damage was not significantly related to any particular sectors of cushions,nor to the environmental variables with the exception of cushion substrate, and expanded rapidly during the warm season. This suggested that the spatially restricted Type 3 damage might be responsible for the perception of increased dieback. Its cause is uncertain, although many of the symptoms are similar to those of a pathogen. Future monitoring should concentrate on this type of damage.
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