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Abstract

The straw daisy Helipterum albicans ssp. albicans var. incanum (Hook.)
P.G.Wilson forme incanum is endangered, and is in serious risk of
disappearing from the wild within one or two decades if present land use and
other causal factors continue to operate. H. albicans may have been a
naturally rare species, but its current endangered status is the result of
anthropogenic processes. It is a species that occurs in temperate grassy
ecosystems, the vegetation type most altered for grazing and agriculture.
H. albicans was once more widespread in its distribution, but currently it is
restricted to a small number of fragmented and scattered populations in north
west and central Tasmania on land that is managed for grazing. Floristic data
were collected from 24 sites where H. albicans occurs, and five floristic
groupings were recognized. These were from sites at altitudes ranging from
60 m to 1200m on soils derived from basalt, mudstone, glacial and lateritic
deposits, and in areas with both high and low mean annual rainfall.
Genotypic and phenotypic variation were established for different populations
of H. albicans in terms of morphology, germination and response to
experimental treatments.
H. albicans has a high rate of seed production, and the seeds have virtually no
dormancy period and require no special treatment to stimulate germination.
Moderate to high germination success is achieved at a range of temperatures
from 5-30°C. H. albicans has an achene with a well developed pappus suited
to wind dispersal, and the wind dispersal of large quantities of seed which
form a transient and short-lived seedbank appears to be a more critical strategy
for regeneration than seed stored in the soil. Germinates of H. albicans
represented less than 2% of the total number of individuals that germinated
from the soil seed bank.
H. albicans is not palatable to domestic stock, and there was little evidence of
insect or animal predation. Exclosure studies revealed that H. albicans was a
species that benefits from stock grazing in two principal ways. Grazing results
in the soil disturbance necessary for regeneration, and reduces the biomass of
the dominant grasses, allowing the establishment and growth of herbaceous
species. The exotic composite Hypochoeris radicata is abundant in the soil
seed bank and germinates earlier than Hypochoeris, giving it a competitive
advantage. Glasshouse studies established Hypochoeris is able to supress the
growth of H. albicans when they are grown together.
H. albicans will require active conservation management in the form of weed
control, grazing and a suitable fire regime to ensure its survival in the wild.

Item Type:	Thesis - Unspecified
Authors/Creators:	Gilfedder, Louise
Keywords:	Endangered plants, Daisies, Plant conservation
Copyright Holders:	The Author
Additional Information:	Thesis (M.Sc.)--University of Tasmania, 1993. Includes bibliographical references (leaves 151-169)
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