University of Tasmania
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The ecology and biogeography of Athrotaxis D. Don.

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posted on 2023-05-26, 22:42 authored by Cullen, Philip J.(Philip James)
The coniferous tree species Athrotaxis cupressoides and Athrotaxis selaginoides and a probable hybrid, A. laxifolia, form the genus Athrotaxis, which is endemic to Tasmania. These species are found in a wide range of cool temperate rainforest, subalpine scrub, and alpine heath communities in central, western, and southern Tasmania. Athrotaxis species are slow growing, extremely long lived, and very fire sensitive. The floristic composition, site characteristics, and demographic structure of Athrotaxis populations were investigated at 57 rainforest and subalpine scrub stands dominated by either A. cupressoides or A. selaginoides. The distribution of A. cupressoides largely coincides with those areas occupied by trees where extreme frosts are most common. In areas where both species occur, A. cupressoides is more likely to be found at higher altitudes or in cold valley bottoms. Subsequent trials demonstrated that A. cupressoides seedlings are more frost resistant than A. selaginoides seedlings. Field observations and preliminary experimental investigations indicated that neither differences in drought resistance nor tolerance to waterlogging are important in determining the relative distributions of these two species. For both species seed dispersal is restricted to areas within a few tens of metres of parent trees, except when seeds fall into flowing water. The demographic structure of Athrotaxis populations is strongly related to the floristic composition of the communities in which they are found. A. selaginoides relies on gap formation or catastrophic disturbance for regeneration opportunities in forests dominated by evergreen species (thamnic and callidendrous rainforests). However, in forests containing a high proportion of the deciduous tree, Nothofagus.gunnii, (implicate rainforests) and in subalpine scrub communities A. selaginoides regenerates continuously. A. cupressoides regenerates continuously in open montane rainforests, often by producing root suckers. This species is also capable of regeneration following catastrophic disturbance. However, stands of A. cupressoides on the Central Plateau of Tasmania have no, or low, numbers of seedling sized individuals. Trials suggest that this regeneration failure is due to grazing by both introduced and native mammals. In undisturbed thamnic and implicate rainforests the species cannot regenerate successfully. Demographic structure and floristic composition of these communities indicates that they are seral stages in a succession from open montane to thamnic and implicate communites without A. cupressoides. It is probable that the colder conditions and a higher incidence of catastrophic disturbance during full glacial and interstadial climates would have been advantageous to Athrotaxis species. However, the loss of Athrotaxis populations and lack of regeneration in many cases must be attributed to the activites of Europeans in Tasmania and not to an inability to survive under the present climate.


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Copyright 1987 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s). Thesis (M.Sc.)--University of Tasmania, 1988. Bibliography: leaves 135-149

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