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The population genetics of two temperate rainforest trees, Lagarostrobos franklinii (Hook f.) Quinn (Huon pine), and Atherosperma moschatum Labill. (Sassafras)

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Shapcott, Alison (1993) The population genetics of two temperate rainforest trees, Lagarostrobos franklinii (Hook f.) Quinn (Huon pine), and Atherosperma moschatum Labill. (Sassafras). PhD thesis, University of Tasmania.

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Abstract

The population genetics of two temperate rainforest tree species endemic to south
eastern Australia were studied. Both species are long-lived and members of ancient
families. There are parallels between the two species even though one was a
gymnosperm and the other an angiosperm. For example, both species reproduce both
vegetatively and sexually. Lagarostrobos franklinii (Huon pine) (Podocarpaceae) is
mostly dioecious and wind pollinated, while Atherosperma moschatum (sassafras)
(Monimiaceae), is monoecious or dioecious and insect pollinated. Both have
potential for long distance seed dispersal, L.franklinii by water and A. moschatum by
wind.

The population genetics of both species was studied from stands throughout their
geographic range using isozyme analysis. Most genetic diversity was found within
rather than among sites. Genetic diversity among sites was low but generally
consistent with expectations for each species (Hamrick and Godt 1979).
Atherosperma moschatum had much more diversity among sites than Huon pine,
with its mainland sites differentiating significantly from its Tasmanian ones. In Huon
pine, most differentiation was found in isolated sites. Diversity within sites was also
low in Huon pine but was much greater in sassafras. The structure of genotypes
within stands was examined using spatial autocorrelation. In both species trees of
like genotypes were found to be clustered at short distances. This genetic
substructuring was found regardless of population size, density, distance from other
stands, level of inbreeding, history, etc. Most sites deviated from Hardy-Weinberg
expectations with deficiencies of heterozygotes, and high levels of allelic fixation,
and were effectively inbred.

The size structure and floristics within stands were investigated and used to assist in
the interpretation of the patterns of genetic variation, inbreeding and stand dynamics
found in each species. There was much variation in size structures and regeneration
modes between sites in both species and neither appeared to require large scale
disturbances for regeneration. The two species varied in the relationships between
site environmental/ecological similarity and genetic similarity. In both species there
was as much diversity in genetic variability and size structure in small isolated stands
as there was in stands within larger assemblages.

The proportion of trees contributing to the reproductive population, as well as the
proportion of each gender type within that population, were estimated for Huon pine
stands. On average thirty percent of Huon pine trees greater than one metre tall were
reproductively active in the mast year recorded, and overall there were equal
proportions of male and female trees. The relationships between reproduction and
gender expression, with size structure, density, floristics, inbreeding and genotypes
were investigated. Stands were also compared to identify if there were geographical
or climatic trends in the distribution of these characteristics. Reproduction was found
to increase with increasing tree size and also with more open canopies. Sites with
similar proportions of females were found to also have similar species compositions.
The distribution of reproductive trees and gender types within stands was
investigated using spatial autocorrelation. The results were compared with genotypic
distributions within the same stands. Although there was no direct correlation
between gender type and genotype, both genotype and gender type were clustered at
the same spatial scale, suggesting that such clustering may have a strong vegetative
component.

Huon pine seed production was estimated at one site and seed dispersal was
investigated. Very large quantities of seed were shed. Seed dispersal laterally was
negligible, but potential for dispersal down water courses was great as it stayed
afloat for extended periods. Huon pine seed germination was investigated both in the
field and under experimental conditions. Germination generally was slow, and with a
low success rate. However seed in the field germinated at particular daylengths
(regardless of temperature) in two consecutive seasons.

Both species showed evidence that vegetative reproduction and localised pollen and
seed dispersal have led to the development of family clusters, leading to inbreeding,
and local fixation of allelic proportions. However infrequent long distance gene flow
has probably reduced population differentiation. The population viability of each
species was discussed.

Item Type: Thesis (PhD)
Keywords: Forest genetics, Huon pine, Sassafras
Copyright Holders: The Author
Copyright Information:

Copyright 1993 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:

Includes bibliographical references (leaves 154-171). Thesis (Ph.D.)--University of Tasmania, 1994

Date Deposited: 03 Feb 2015 03:21
Last Modified: 11 Mar 2016 05:55
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