Ecology of the threatened herb Brunonia australis in Tasmania

This thesis investigates major factors influencing the ecology of the threatened species Brunonia australis in Tasmania. Brunonia is listed as vulnerable under Tasmanian Threatened Species legislation, being restricted to depleted forest communities in the central north of the state. At the commencement of this study in 1998, the species was very poorly reserved and threatened by land clearing, inappropriate grazing regimes and logging. Existing information about the response of Brunonia to various management impacts was limited to anecdotal observations. Five main areas of investigation were undertaken: 1) Known populations were surveyed to validate conservation status and determine habitat requirements, 2) Reproductive characteristics were examined to improve understanding of population dynamics, 3) Effects of grazing by domestic stock were examined in a 2 year trial in a typical population, 4) Impacts of selective logging and three silvicultural techniques in a typical forest type were assessed, 5) Success of eucalypt regeneration in relation to the silvicultural treatments is reported. 58 populations were identified in the study, 35 more than previously reported. Most occurred in Inland Eucalyptus amygdalina forest. More than half contained less than 1000 plants, but several had more than 100,000 plants. The species could be downgraded from vulnerable to rare under Tasmanian threatened species guidelines, but should not be delisted due to continuing threats. Brunonia has an efficient reproductive capacity. Flowering was profuse in sunny situations and pollination effected by common insect vectors. Germination was found to occur readily (80%) without any apparent dormancy mechanisms. Several findings are reported for the first time including Brunonia's poor dispersal capability and inability to store seed in the soil. Season of grazing influenced Brunonia populations. Winter grazing significantly benefited populations compared to grazing in other seasons. Winter grazing reduced understorey competition during Brunonia's dormant period but direct grazing of plants during summer reduced reproductive ability. Understorey competition restricted germination and reduced survival of adult plants in ungrazed plots. Selective logging benefited Brunonia in the first year after logging, except in heavily scarified plots. After three years, the recovery of Brunonia was significantly poorer in burnt and scarified areas compared to logged-only areas and controls. The increase in understorey density in logged areas, including wattle and bracken in the burnt areas reduced the survival of Brunonia and restricted recruitment. In contrast, eucalypt regeneration was most successful following the logging/scarification treatment (84% plots stocked), compared to logging/burning (77%) and logging only (57%) treatments. The logging only treatment produced unacceptable regeneration rates in terms of the adopted Tasmanian stocking standard (65% of plots stocked). Browsing by native and introduced animals influenced the success of regeneration. Moderate disturbance is important in most populations. Lack of appropriate disturbance allows more competitive understorey species to eventually inhibit the growth and establishment of Brunonia. Various management techniques are proposed.