Monitoring leaf loss and possum impact on New Zealand beech mistletoes A thesis submitted in partial fulfilment of the requirements for the . Degree of Master of Science in Botany at the University of Canterbury by Laura A. Sessions "",,;:f University of Canterbury 1999 THESIS v. 11 TABLE OF CONTENTS Table of Contents .............................................................................................................. ii List of Tables ................................................................................................................. viii List of Figures ................................................................................................................ xiii List of Plates ................................................................................................................... xv ABSTRACT ................................................................................................................... xvi CHAPTER 1: INTRODUCTION .................................................................................... 1 1.1. IMPORTANCE OF HERBIVORY TO PLANT DEMOGRAPHY AND PERFORMANCE ........... 1 1.2. HERBIVORY IN NEW ZEALAND ............................................................................... 2 1.2.1. The rata example ............................................................................................. 4 1.2.2. The importance o/herbivory to native mistletoes ........................................... 5 1.3. PROJECT GOALS ...................................................................................................... 5 CHAPTER 2: STUDY ORGANISMS AND SITES ........................................................ 7 2.1. NEW ZEALAND BEECH MISTLETOES ........................................................................ 7 2.1.1. Alepisflavida ................................................................................................... 9 2.1.2. Peraxilla colensoi ............................................................................................ 9 2.1.3. Peraxilla tetrapetala ..................................................................................... 10 2.1.4. Causes o/mistletoe decline ........................................................................... 11 2.2. AUSTRALIAN BRUSHTAIL POSSUM (TRICHOSURUS VULPECULA KERR) ................... 12 2.2.1. General characteristics ................................................................................. 12 2.2.2. Possunl diet ................................................................................................... 13 2.2.3. Possum colonization and spread in New Zealand ........................................ 14 -. 2.2.4. Current distribution and abundance in New Zealand .................................. 15 111 2.2.5. Effects o/possums on native flora ................................................................. 16 2.3. STUDY SITES ......................................................................................................... 18 2.3.1. Site descriptions ............................................................................................ 18 2.3.1.1. Craigieburn ............................................................................................. 21 2.3.1.2. Lake Ohau ............................................................................................... 23 2.3.1.3. Eglinton Valley ....................................................................................... 25 2.3.1.4. Waipori Gorge ........................................................................................ 30 2.3.2. Possum densities ........................................................................................... 32 2.3.2.1. Methods .................................................................................................. 32 2.3.2.2. Results ..................................................................................................... 33 2.3.2.3. Conclusions ............................................................................................. 35 CHAPTER 3: EVIDENCE FOR POSSUM DAMAGE ON NATIVE MISTLETOES. 38 3.1. MT. MISERY: FIRST EVIDENCE AGAINST POSSUMS ................................................. 38 3.1.1. 1978-1984 ..................................................................................................... 38 3.1.2. 1984-1997 ..................................................................................................... 39 3.1.3. Conclusionsfrom Mt. lv.fisery ........................................................................ 40 3 .2. ANECDOTAL EVIDENCE ......................................................................................... 41 3.2.1. Coinciding possum colonisation and mistletoe decline ................................ 41 3.2.2. Changes in plant health afterprotectionfrom browse ................................. 42 3.3. DEPARTMENT OF CONSERVATION MONITORING PROGRAMS ................................. 42 3.3.1. Eglinton Valley Mistletoe Monitoring ........................................................... 42 3.3.1.1. Methods .................................................................................................. 43 3.3 .1.2. Results ..................................................................................................... 44 3.3.1.3. Conclusions ............................................................................................. 45 3.3.2. Hurunui Mainland Island j\1onitoring Programme ...................................... 46 3.3 .2.1. Project background and methods ............................................................ 46 3.3.2.2. Results and conclusions .......................................................................... 46 3.4. EVIDENCE AGAINST POSSUMS AS THE PRIMARY AGENT OF DECLINE ...................... 47 3.5. CONCLUSIONS ...................................................................................................... 49 IV CHAPTER 4: PATTERNS OF MISTLETOE LEAF LOSS AND IMPLICATIONS FOR PLANT HEALTH .................................................................................................. 50 4.1. INTRODUCTION ..................................................................................................... 50 4.2. METHODS ............................................................................................................. 51 4.2.1. Identifying types of leaf damage ................................................................... 51 4.2.2. Experimental design ...................................................................................... 54 4.2.3. Data analysis ................................................................................................. 55 4.2.3.1. Meanleaf1oss ......................................................................................... 55 4.2.3.2. Variation in leaf loss ............................................................................... 56 4.2.3.3. Annual flux in leaf area .......................................................................... 57 4.3. RESULTS ............................................................................................................... 57 4.3.1. Plant and branch loss .................................................................................... 57 4.3.2. Mean leaf loss ............................................................................................... 59 4.3.3. Variation in leafloss ........: ............................................................................ 64 4.3.4. Annual flux in leaf area .. ............................................................................... 65 4.4. DISCUSSION .......................................................................................................... 68 4.4.1. Mean leafloss ............................................................................................... 68 4.4.1.1. Insect loss ................................................................................................ 68 4.4.1.2. Possum damage and associated abscission ............................................. 69: 4.4.1.3. Other causes of abscission ...................................................................... 70 4.4.2. The importance ofheterogeneity .................................................................... 71 4.4.3. Annual flux in leaf area: implications for plant health ................................. 73 4.5. CONCLUSIONS ...................................................................................................... 76 CHAPTER 5: FACTORS INFLUENCING HERBIVORY AND LEAF ABSCISSION77 5.1. INTRODUCTION ..................................................................................................... 77 5 .2. VARIATION BETWEEN LEAVES .............................................................................. 77 5.2.1. Methodsfor leaflevel analyses ..................................................................... 77 5.2.2. Results ........................................................................................................... 79 5.2.2.1. Effect ofleaf age on probability of abscission ....................................... 79 5.2.2.2. Effect ofleaf age on insect damage ........................................................ 82 5.2.2.3. Effect ofleaf age on possum browse ........... ~: ......................................... 85 5.2.2.4. Summary of effects of leaf age on leaf area loss .................................... 88