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Phyllocladus aspleniifolius (Labill.) Hook. f. and Anodopetalum biglandulosum (A. Cunn.) ex Endl. : a comparative autecology of coexisting wet forest trees in Tasmania

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Barker, Philip C J (1993) Phyllocladus aspleniifolius (Labill.) Hook. f. and Anodopetalum biglandulosum (A. Cunn.) ex Endl. : a comparative autecology of coexisting wet forest trees in Tasmania. PhD thesis, University of Tasmania.

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Abstract

This thesis describes and compares the autecology of two coexisting wet forest trees.
It demonstrates temporal, spatial and biological differentiation of the reproduction,
regeneration and growth characteristics which allow these taxa to coexist in
superficially similar environments.
The distributions of the species and the environmental correlates of the communities
in which they exist are compared and contrasted. The climatic range of P.
aspleniifolius is greater than A. biglandulosum but this may be attributed to the greater
vagility of P. asplennfolius allowing it to occupy areas that are dimatically susceptible
to repeated disturbance by fire. It is determined that both are most important in
poorly structured and diverse rainforest communities which are often associated with
low fertility substrates. The physiological basis for this correlation was tested
experimentally and by field measurements. A. biglandulosum performed best under
add conditions while P. aspleniifolius was relatively insensitive to fertility. These
responses are manifest in the absence of both species from the most fertile sites which
support floristically simple tall Nothofagus cunninghamii dominated forests. The
preference of A. biglandulosum for acid sites and the insensitivity of P. aspleniifolius
allow these species to take advantage of the decline in the performance of the
important canopy dominant, Nothofagus cunninghamii, and hence increase their
abundance on such sites. Other than possible exclusion from pure Nothofagus
cunninghamii forest their geographic range and phytosociological associations are not
limited by edaphic conditions. Field performance of both A. biglandulosum and P.
aspleniifolius does, however, reflect the physiological growth response measured
under experimental conditions.
The photosynthetic responses of A. biglandulosum and P. aspleniifolius were
investigated in the contrasting micro-environments of the canopy, a gap and the
understorey of a rainforest in Tasmania. Measurements were made using a portable
infra-red gas analyser. Both species displayed the highest light saturation levels at
the canopy but both produced the highest rates of photosynthesis in the gap
environment. Diffuse light on cloudy days was important in the understorey
environment. The rate of photosynthesis was affected considerably by low levels of
stomatal conductance two days after rain. The results indicate that both species are
"sun" plants and that their dependance upon high levels of light to maintain
competitive growth rates would influence their regeneration opportunities and may
induce competition for sites. The phenological and demographic strategies of both species were compared. The
timing of foliar and sexual development of Phyllocladus asplenhfolius and
Anodopetalum biglandulosum were recorded at Mt Field in Tasmania. Seed production,
seed predation, germination and survival were monitored in different regions of
Tasmania. The wind dispersed A. biglandulosum suffered an extremely high level of
fruit predation by a moth and by birds. The resultant low seed production is
reflected in the poor seed regeneration in this species.
The timing of pollen release and female cone development in P. asplenhfolius indicates
that outcrossing between populations is likely. Outcrossing may provide the species
with a high degree of genetic fitness but may not necessarily explain its wide
ecological amplitude as this situation contrasts with the poorly dispersed and
possibly genetically limited A. biglandulosum which also has a broad ecological range.
P. asplenhfolius produced spatially variable amounts of seed and is a mast seeder. The
number of germinants two springs after seed fall reflected the variation in annual
seed production and suggests that pulses in regeneration are likely although soilstored
seed and immigrant seed may offset this effect.
The consequences of the phenological differentiation on regeneration opportunities
was explored. The contrasting strategies required different approaches, as A.
biglandulosum dependsiargely upon vegetative regeneration and proliferation while
P. asplenhfolius is an obligate seed regenerator.
A growth-form/disturbance typology of A. biglandulosum based on data from 48 sites
was produced. A multivariate data set from each site summarizes a stands' growth-form
as stem types, densities and diameters. A canonical correlation indicates a
significant relationship between the growth-form data set and community floristics.
The basic architecture associated with a particular forest is modified by proliferation
in response to exogenic disturbances, such as fire and heavy snow-falls, or as a result
of community processes such as crown senescence and tree-fall.
This study aimed to determine the range of the P. asplenhfolius regeneration niche in
terms of differential microsite occupation, population structure and dispersion
pattern at 52 forest sites. The distribution and sizes of stems were mapped on belt
transects to within 0.5 m, and the microsites of seedlings and saplings were recorded.
A variety of population structures exist and are related to community floristics and
structure. Community variation provides different microsite opportunities. P.
asplenhfolius showed a preference for elevated sites, including logs, buttresses and old
stump mounds. Aggregation of seedlings is common and determined by microsite
distribution and dispersal characteristics. It is concluded that niche differentiation between P. aspleniifolius and A. biglandulosum
is demonstrated in edaphic responses and reproductive biology, and niche overlap is
evident in their use of the light environment. Although their coexistence is
theoretically dependent upon niche differentiation, stochastic events producing
opportunities for regeneration appear to be more important and therefore the results
conform with the theory of non-equilibrium coexistence of species. The broad and
common phytosociological associations may reflect Tertiary species extinctions which
have produced an environment of low competition with few specialists. The extant
species experience niche broadening via more opportunities for regeneration and
hence greater levels of coexistence which are expressed as low beta diversity in
Tasmanian wet forests.

Item Type: Thesis (PhD)
Keywords: Phyllocladus aspleniifolius, Anodopetalum biglandulosum, Rain forest ecology, Rain forest plants
Copyright Holders: The Author
Additional Information:

Thesis (Ph.D.)--University of Tasmania, 1994. Includes bibliographical references (leaves 218-236)

Date Deposited: 25 Nov 2014 00:44
Last Modified: 11 Mar 2016 05:55
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