L The vegetation ecology of Tasmanian dry closed-forest by Thomas John Olegas Pollard (BSc Hons UQ) Submitted in fulfilment of the requirements for the Degree of Doctor of Philosophy University of Tasmania (September, 2006). t r i Declarations Declarations I declare that this thesis contains no material wliich has been accepted for a degrye or diploma by the University of Tasmania or any other institution, except by way of background information and duly acknowledged in. th~ thesis, and to the best of my knowledge and belief no material previously published or written by another person except where due acknowledgement is macfe in the text of the thesis, nor does the thesis contain any material that infringes 'Copyright. This thesis may be made available for loan and limited copying in accordance with the Copyright Act 1968. Signed: TLfJ~ Thomas John Olegas Pollard i - Abstract Abstract The subject of this study is a poorly known closed-forest community that occurs as small, disjunct stands in eastern Tasmania. This community has affinities with dry rainforest, a formation that occurs extensively in mainland Australia. There is ongoing debate as to what constitutes Australian rainforest, with most definitions based on the regeneration requirements of the constituent species. A species must be capable of self-replacement in the absence of exogenous disturbance to qualify as a rainforest species. The present study aims to answer the questions: 1. Where does dry closed-forest occur in Tasmania and what environmental factors influence this distribution? 2. How does the floristic composition of this community vary across its range? 3. What are the modes ofregeneration of the major tree species of this community and why is Eucalyptus absent? 4. What are the conservation management and reservation requirements of the community? Additionally, an overarching aim concerns whether the study community can be considered rainforest. To achieve these aims the study: documents the geographic variation of dry closed­ forest stands and test the hypothesis that distributional characteristics are related to fire-avoidance by mapping the location and characteristics of stands and measuring variables of the local stand environment; documents the floristic variation of dry closed-forest in relation to environmental variables by conducting a survey of the vascular plant species composition and stand environment; determines if this community requires exogenous disturbance for perpetuation, by studying the spatial arrangement and regeneration-characteristics of major canopy species within stands; and investigates why Eucalyptus is absent from this community by conducting experiments of the germination and growth of Eucalyptus and some comparative dry closed-forest species in a number of soil treatments. 11 Abstract One hundred and eighty three stands were mapped. Stands occupied a number of different topographic and edaphic situations that afford protection from fire. Six floristic sub-communities were differentiated, and a number of environmental variables shown to significantly influence this variation. Floristic similarities were shown to exist between this community and other Australian rainforest and wet­ forest communities. Stands not recently disturbed proved to be dominated by self­ replacing species, while early-successional stands consisted mainly of species requiring exogenous disturbance for regeneration. There was no significant segregation of individuals either within or between species, however seedlings of bird-dispersed species were clustered around large trees. The germination experiments indicated that limitations on Eucalyptus establishment are related to soil properties (particularly damping-off fungi) and competition with dry closed­ forest species. Tasmanian dry closed-forest appears to be a community that has some affinity with rainforest in terms of distribution, floristic composition, structural attributes and regeneration strategy. However, the identification of a number of successional stages of this vegetation type, that require fire for the establishment of a number of key species, brings into question the status of this vegetation as rainforest. This only highlights the challenges present in attempting to define Australian rainforest vegetation. iii Acknowledgements Acknowledgments Foremost, my thanks go to Prof. Jamie Kirkpatrick, my primary supervisor, for providing invaluable advice on aspects of my study and comments on the thesis, and for directing me towards asking the right questions. I would also like to thank a number of people who gave me substantial assistance during my study and in completing this thesis. Dr Mick Russell for help with aspects of GIS, aerial photograph rectification, and light environment analysis. Denis Charlesworth, for analysing soil samples and providing field equipment. David Somerville for help with technical equipment. Darren Turner for computer-based assistance and particularly ~or writing the Excel Macro to analyse nearest neighbour relationships. Kate Charlesworth, for assistance with obtaining maps, aerial photographs and associated interpretation equipment. Dr Rob Anders for help with aerial photograph rectification. Dr Peter McQuillan for advice on aspects of analysis in PC-ORD. Dr Emma Pharo, for her advice on collecting Bryophytes. The Dunbabbin family for allowing me access to their properties Bangor and The Quoin, and the Department of Primary Industries, Water and Environment (DPIWE), Forestry Tasmania, and Norske Skogg for access to various areas managed by them. DPIWE for use of digital layers compiled in the Land Information System Tasmania (LIST). Special thanks to my father for editing parts of the thesis and to friends and family who helped motivate me during this study. lV Table of Contents Table of Contents Declarations ........................................................................................................ i Abstract. .. .' .......................................................................................................... ii Acknowledginents ............................................................................................ iv Table of Contents ............................................................................................... v List of Figures .................................................................................................... x List of Tables .................................................................................................. xiii List of Plates ................................................................................................... xvi List of Appendices ........................................................................................ xviii Chapter 1 - General Introduction .......................................................................... 1 Australian rainforests ..................................................................................... 1 What determines patterns of Australian rainforest distribution? ................... 2 Floristic composition of Australian dry closed-forests .................................. 4 Regeneration of rainforest species ................................................................. 4 Is Tasmanian dry closed-forest rainforest? .................................................... 5 Absence of Eucalyptus from rainforest ......................................................... 7 Aims and approaches of this study ................................................................ 8 Chapter 2 - The nature and distribution of Tasmanian dry closed-forest stands ································································································································· 10 Abstract ............................................................................................................ 10 Introduction ..................................................................................................... 11 v Table of Contents Methods ........................................................................................................... 16 The physical characteristics of stands ......................................................... 17 Influences on the physical nature of stands ................................................. 21 Influences on the location of stands ............................................................ 22 Results ............................................................................................................. 23 The physical nature of stands ...................................................................... 23 'Stands are protected from fire by NW topography' hypothesis ................. 28 Influences on the physical nature of stands ................................................. 30 Influences on the location of stands ............................................................ 33 Discussion ........................................................................................................ 35 Chapter 3 - Floristic variation of Tasmanian dry closed-forest ........................ 44 Abstract. ........................................................................................................... 44 Introduction ..................................................................................................... 45 Methods ........................................................................................................... 48 Data collection ............................................................................................