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Aspects of the conservation biology of Helipterum albicans (Hook.) P.G. Wilson
thesisposted on 2023-05-26, 23:13 authored by Gilfedder, Louise
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¬¨‚àûC. 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.
Rights statementThesis (M.Sc.)--University of Tasmania, 1993. Includes bibliographical references (leaves 151-169)