Investigations into the ecology and management of the invasive plant Galenia pubescens within the native temperate grasslands of Victoria, Australia AKO H. MAHMOOD This thesis is submitted in total fulfillment of the requirements for the degree of Doctorate of Philosophy Faculty of Science and Technology Federation University Australia PO Box 663 Mt Helen, Ballarat, Victoria 3353, Australia July 2016 Abstract Abstract Plant invasions of natural ecosystems are one of the major threats to the conservation of biological diversity across nearly all biogeographical regions in the world. This thesis focuses on Galenia pubescens (Carpet weed) as a case study of possible approaches to the potential management of environmental weed species. G. pubescens is a woody prostrate perennial plant that is becoming a serious threat to Australian temperate grasslands, surrounding agricultural areas and conservation reserves. It is indigenous to South Africa and was first recorded in Australia in the early 1900s, and it is an aggressive competitor against native species. It is difficult to control, and little information exists about its effects on natural ecosystems, and aspects of its biology and ecology. This study has investigated some important ecological characteristics of G. pubescens’ seeds and has experimented with different management strategies in combination with chemical control. It has also considered the potential for the expansion of the distribution of this species across suitable habitat in Australia under predicted elevated CO2 and drought conditions. Seeds of G. pubescens are shown to be able to germinate over a broad range of temperatures, but short bursts (5 minutes) of high temperatures (80oC to 120oC replicating possible exposures to a fire) reduced seed germination. Seed germination was positively favored by light and declined rapidly in darkness, decreasing by > 80% at a depth of only 0.5 cm in soil. This suggests that fire regimes might be useful in removing mature plants and controlling seed numbers on the surface, and that subsequent native seeding of undisturbed areas may assist in the long-term management of this noxious weed. i Abstract A trial was conducted to determine the effect of treatment with a plant essential oil (pine oil) to limit the seed germination and seedling emergence of G. pubescens. This trial showed that the effects of pine oil application were significant (P<0.05). Germination was completely inhibited by application of pine oil at 5% or higher concentrations directly to seeds, and seedling emergence was reduced by between 90 and 100% in pot trials. These outcomes demonstrate the potential viability of pine oil as a long-term control option for this species. In field-based experiments, control strategies including herbicide control with glyphosate, organic herbicide control with pine oil, the application of mulch, and the addition of native seeds to the available seedbank (and all possible combinations of these techniques), were tested. The study showed that one single treatment of a G. pubescens infestation without undertaking a secondary treatment is insufficient to control the G. pubescens infestation or to encourage native regeneration, but that a combined strategy, employing all the aforementioned techniques, is more effective. It is however suggested that full regeneration of the area may not be possible unless further restoration programs are instituted after the cycle of G. pubescens’ treatment has been completed. The thesis also assessed the control effects of chemical control combined with a prescribed spring burning. Assessment of the resulting aboveground vegetation of G. pubescens has shown that a combination of chemical control and late-spring burning can reduce the cover of non-native species such as G. pubescens, suggesting that this could be a useful tool in their management. Finally, this study has supported the view that the growth of G. pubescens will be significantly enhanced in a future climate with an enriched atmospheric CO2 concentration. These climatic changes will have important implications for management of this noxious weed in the future. ii Statement of Authorship Statement of Authorship Except where explicit reference is made in the text of this thesis, this thesis contains no material published elsewhere or extracted in whole or in part from a thesis by which I have qualified for or been awarded another degree or diploma. No other person’s work has been relied upon or used without due acknowledgement in the main text and bibliography of the thesis. Signed: Signed: Dated: Dated: Ako H. Mahmood Singarayer K. Florentine Candidate Principal Supervisor iii Acknowledgements Acknowledgements This thesis would not have reached completion without significant guidance, advice, encouragement and assistance of a number of people whom I wish to acknowledge. I would like to begin by thanking The Higher Committee for Education Development in Iraq for financial support. I would also like to give my special thanks for my supervisors Assoc. Prof. Singarayer Florentine, Dr. Grant Palmer, and Assoc. Prof. Wendy Wright (Centre for Environmental Management, Faculty of Science and Technology at Federation University Australia) and Dr. David McLaren (Department of Economic Development, Jobs, Transport and Resources) for their advice and direction in formulating and completing this project. I thank Dr Steve Sinclair for his time spent on herbaceous vegetation identification and his helpful advice and encouragement of the research program. I also thank Certified Organics Pty Ltd. for supplying their advice on the pine oil products tested in this project and Parks Victoria for allowing access to the field site at Cobbledicks Ford Road. I am grateful to my fellow graduate students Sandra Weller, Rachael Martin and Shakir Bahaddin, who have shared my trials and tribulations through this entire endeavor, for their support and encouragement. Thanks go out to all other students who listened to my complaints. Special thanks to other staff at Federation University Australia: Assoc. Prof. Jim Sillitoe, Mr. Allan Adair, and Dr. Janis K. Webb from (Research Services) for their time spent in reviewing earlier versions of this thesis, and Wendy Cloke (Lab technician) for her generous provision of time and laboratory equipment. iv Acknowledgements I am also thankful to the Collaborative Research Network (CRN) – Federation University Australia for providing financial support. Last, but certainly not least, I want to express my utmost gratitude for the support and encouragement given my wonderful wife (Hero Kareem) as well as my son (Anas) and my daughter (Alenia), who were all instrumental in getting me through this program. For that I will be forever grateful. v Table of contents Table of Contents Abstract .................................................................................................................................... i Statement of Authorship .................................................................................................... iii Acknowledgements .............................................................................................................iv Table of Contents .................................................................................................................vi List of Figures .......................................................................................................................xi List of Tables ...................................................................................................................... xiv Chapter 1: General introduction .................................................................................... 15 Background ......................................................................................................................... 15 1.0 The context of this research ................................................................................ 16 1.1 The concept and meaning of the term ‘Weed’ ................................................. 16 1.2 A brief review of the problem of weeds ............................................................. 17 1.3 Current concepts of weed invasion processes ............................................... 19 1.4 Characteristics of invasive species.................................................................... 22 1.5 Exotic plants in temperate Australian grasslands ......................................... 23 1.6 A description of the invasive species Galenia pubescens .......................... 24 1.6.1 Origin ...................................................................................................................... 24 1.6.2 Morphology ............................................................................................................ 24 1.6.3 Propagation ............................................................................................................ 25 1.6.4 Climatic conditions ............................................................................................... 25 1.6.5 Habitat ..................................................................................................................... 26 1.7 Historical and current distribution of Galenia pubescens in Australia .... 28 1.8 The main features that may predict the invasion success of Galenia pubescens ........................................................................................................................ 30 1.9 The Western Grassland