Ecology and Management of Non-Native 'Poa Annua' on Sub-Antarctic Macquarie Island

Abstract

Invasive species pose one of the greatest threats to the Antarctic region and consequently control is a priority to managers. To date, all successful eradications of vascular plants in the sub-Antarctic and Antarctica have been on small, restricted populations. Eradication or control is more difficult for widespread species, largely due to established seed banks. Information on the biology of the target species and the efficacy of control can increase eradication success. It is also important to assess the impact of control on non-target species. One widespread invasive species in the Antarctic and sub-Antarctic under consideration for control is the grass 'Poa annua'. For any potential eradication or control programs to be successful, information is required on the species' ecology and response to control. Therefore with the aim of informing future management of 'P. annua', my thesis focused on quantifying the ecology of 'P. annua' on Macquarie Island and assessing the efficacy of physical and chemical control. This included assessing the impact of control on native plant species, and the mobility of glyphosate in Macquarie Island soils and potential off-target impacts. I found that 'P. annua' plants showed a perennial lifecycle, a common survival mechanism for sub-Antarctic plants, and they displayed considerable variation in growth forms across environmental gradients. 'Poa annua' plant size and seed banks varied across Macquarie Island in response to 'P. annua' cover and environmental variables. Larger plants and denser seed banks were found at low elevation sites with high 'P. annua' cover, high animal disturbance and deep, sandy soils. The high cover of 'P. annua' at these sites also suppressed native species diversity. Conversely, at high altitude, exposed sites with low 'P. annua' cover and shallow soils, 'P. annua' plants were small and seed bank densities were low or non-existent. Less than 3% of buried seed remained viable for two years. Plants from all sites allocated most of their biomass to root material (60-80%), likely to enhance persistence.