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The ecological biogeography of Callitris vent. in Tasmania

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Harris, S (1989) The ecological biogeography of Callitris vent. in Tasmania. Research Master thesis, University of Tasmania.

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Abstract

Callitris rhomboidea and Callitris oblonga have a parapatric
distribution in Eastern Tasmania. C. rhomboidea occurs on the
East Coast and C. oblonga is mainly confined to a few coastal
and inland river valleys between Launceston and the East
Coast.
C. rhomboidea is capable of continuous gap-phase regeneration.
Natural stands are often multi-aged but even-aged cohorts
often reflect burning. C. oblonga regenerates after fire or
after mechanical damage to cone bearing branches (usually
during floods). It is therefore an episodic regenerator which
does not appear to regenerate continuously in the absence of
exogenous disturbance.
The two species are ecologically differentiated by frost
tolerance, waterlogging and shade tolerance. C. oblonga is
more tolerant of frost and waterlogging but C. rhomboidea still
occupies a very wide ecological amplitude, although it
possibly has a competitive advantage on the driest sites.
C. oblonga is well adapted to a riparian and floodplain niche,
a distribution which is reinforced by the higher fire
frequency in non riparian habitats. Hybrids between the two
taxa are rare because timing of their peak pollen release is asynchronous.
Climatically suitable areas apparently occur for both species
beyond their present range but a temperature reduction during
the Last Glacial may have limited C. rhomboidea to the east of
the Eastern Tiers and C. oblonga to a small glacial refuge
within the northern part of the Eastern Tiers. Expansion
beyond these palaeogeographically determined limits has been
retarded by the slow overland migration rates of both species,
and by the onset of anthropogenic burning. Limited post-glacial dispersal of C. oblonga has been aided by downstream
spread of propagules.
An increase in fire frequency with the arrival of Aboriginal
man about 30,000 years ago may have not only constrained the
expansion of Callitris but also caused the extinction of
C. rhomboidea in the far north east of Tasmania. A further
increase in burning from the early nineteenth century, has
caused a decline in the extent of Callitris. Frequent burning
has forced C. rhomboidea into fire protected habitats such as
cliffs, deep gullies and rocky knolls, and C. oblonga into
areas protected by anastomosing channels, cut off meander
loops or rocky benches and cliffs.
Prior to human colonisation of the "Tasmanian peninsula",
C. rhomboidea was probably found on more xeric sites in
juxtaposition with rainforest and wet sclerophyll forest on
other sites. Frequent burning is hypothesised to have caused
a shift in forest patterns.
C.oblonga is inadequately reserved. Management of the species
should aim to protect the most upstream stands, which provide
sources of propagules for downstream habitats. C. oblonga
conservation would be helped by fire prevention, enrichment
planting and weed control. C. rhomboidea is adequately
reserved but fire frequency should be reduced throughout its
range, and outlying stands, especially on islands, should be
reserved and protected.

Item Type: Thesis (Research Master)
Keywords: Conifers
Copyright Holders: The Author
Copyright Information:

Copyright 1990 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).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 1990. Bibliography: p. 159-168

Date Deposited: 08 Dec 2014 23:59
Last Modified: 11 Mar 2016 05:55
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