Live Oral Presentation delivered remotely as part of National Virtual Conference AFSS Conference 2020

Wetland lawn – temporal and spatial distribution and controls of lippia, an invasive weed species in the Gwydir Wetlands, Moree NSW. (#18)

Mark R Southwell 1 , Ben E Vincent 1 , David Preston 2 , Jane Humphries 3
  1. University of New England, Armidale, NSW, Australia
  2. Environment Energy and Science, NSW Planning Industry and Environment, Moree, NSW, Australia
  3. Commonwealth Environmental Water Office, Department of Agriculture, Water and the Environment, Moree, NSW, Australia

Lippia (Phyla canescens) an introduced plant, is now a pastoral weed that has spread through large parts of the Murray-Darling Basin severely degrading both the environmental and economic integrity of the system. Lippia’s prostrate growth form, extensive root system, multiple recruitment methods (seeds, plant segments and rhizomes), low palatability and fast growth rate provide it with a competitive edge, resulting in reduced biodiversity where it occurs. In wetland systems, inundation history plays a central role in the distribution of Lippia, both through suppression of growth in areas of sufficient depth  and duration of inundation, and promoting the growth of native species such as Water Couch (Paspalum distichum), that can outcompete lippia. Vegetation monitoring over 6 years in the Gwydir Wetland system near Moree in northern NSW has allowed us to assess changes in the distribution of lippia within study plots, and the potential drivers of these changes. Lippia was present in 90% of survey plots across the 6 years of monitoring and was more prominent in vegetation communities higher in the landscape, especially within Coolibah Woodland sites.  Lippia tended to be more prominent across the landscape during drier periods, except during spring 2019 following severe drought when it was at very low abundance. In line with this, time since inundation was shown to be a dominant factor influencing the cover of lippia, with deeper inundation and sufficient length of inundation later in and over spring/summer supressing growth and advantaging other wetland species. Overall, our observations support the literature, showing that wetland inundation is an important tool for managing lippia in this wetland system.