Spatial Coupling of Plant Recruitment Processes; Vegetation Change and the Regeneration Ecology of Hoon Hay Valley, Port Hills, Canterbury, New Zealand
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SPATIAL COUPLING OF PLANT RECRUITMENT PROCESSES; VEGETATION CHANGE AND THE REGENERATION ECOLOGY OF HOON HAY VALLEY, PORT HILLS, CANTERBURY, NEW ZEALAND A thesis submitted in partial fulfilment of the requirements for the Degree of Master of Science lll Environmental Science from the University of Canterbury Roger John Dungan :::'" 1997 "Though I do not believe that a plant will spring up where no seed has been, I have great· faith in a seed. Convince me that you have a seed there, and I am prepared to expect wonders." Henry D. Thoreau (1817- 1862) ABSTRACT Spatial coupling of plant recruitment processes was measured during 1996 in a dynamic post-agricultural successional environment on the Port Hills of Banks Peninsula. Steps along a conceptual vegetation~seed rain~seedlings recruitment continuum were measured, and the degree of spatial coupling (as measured· by correlations of DCA ordination axis position) between each determined. Spatial coupling of recruitment processes provides a direct measure of potential vegetation change; tight coupling indicates vegetation is changing little as each recruitment step is spatially similar to the step previous, whereas weak coupling indicates dynamic change as steps 'are not spatially related. Coupling was weakest at the vegetation~seed rain and seed rain~seedlings stages, indicating that at these stages plant dispersal and vegetation change are most strongly expressed. Coupling was strongest at the vegetation~seedling stage, indicating that processes associated with seedling establishment and survival offer the strongest impediments to vegetation change. Coupling of all steps was weakest at the habitat-type level, with spatial patterns related to presumed successional age, indicating that vegetation change is proceeding in a process of within-valley succession and species migration. This result confirms those of previous studies which have investigated vegetation change on the Port Hills and Banks Peninsula. It indicates that with the removal of proximate causes of disturbance (fire, grazing, agriculture, etc.) the overwhelming trend of vegetation change in post-agricultural successional environments such as this is toward forest dominated by native species. TABLE OF CONTENTS CHAPTER 1. INTRODUCTION 1 CHAPTER2. STUDY AREA 6 1. Location 6 2. Geology and Landforms 6 3.Soils 8 4. Climate 9 5. Vegetation history 10 6. Current vegetation 13 CHAPTER 3. VEGETATION DESCRIPTION 16 1. Introduction 16 2. Method 16 a. Ordination Techniques 18 i. Detrended Correspondence Analysis 20 ii TWINSPAN- TWo Way INdicator SPecies ANalysis 20 3. Results 21 a. Characteristics of derived habitat types 29 i. Forest types 29 ii Scrub types 29 4. Discussion 30 CHAPTER 4. SEED RAIN 33 1. Introduction 33 2. Method 35 3. Results 3 8 1. Seed Rain 38 1A. Temporal distribution of seed rain. 40 1B. Spatial distribution of seed rain 40 i. Seed rain density 40 ii. Ordination 48 iii. Seed rain diversity 50 2. Seeds In Possum Faecal Clumps 51 3. Seed Predation. 54 4. Litterfall 54 4. Discussion 56 1. Error And Bias. 56 2. General Discussion. 57 . A Spatial Pattern 61 B. Possums As Seed Dispersal Mutualists. 65 C. Seed Predation 68 CHAPTER 5 SEEDLINGS 70 1. Introduction 70 2. Method 70 3. Results 71 1. Seasonal trends 72 2. Spatial pattern 74 i. Seedling density 74 ii. Ordination 75 iii. Seedling diversity 78 3. Summary 79 4. Discussion 79 a. Sources ofbias 79 b. General discussion 80 CHAPTER 6. SYNTHESIS 90 1. Introduction 90 2. Method 90 3. Results 92 a. Step 1. Vegetation ---., seed rain 93 b. Step 2. Seed rain____, seedlings 94 c. Step 3. Vegetation---., seedlings 95 d. Summary 98 4. Discussion 98 a. Sources of error 98 i. Method of overall study 98 ii. Spatial considerations - importance of scale 99 iii. Spatial considerations - autocorrelation and the 100 weakness of classical statistics iv. Spatial considerations- implications for this study 100 v. Temporal considerations 100 b. General discussion 10 1 i. Vegetation ---., seed rain 101 ii Seed rain ____, seedlings 102 iii Vegetation ---., seedlings 104 c. Implications for restoration 107 ACKNOWLEDGEMENTS REFERENCES APPENDIX 1 APPENDIX2 APPENDIX3 LIST OF FIGURES Chapter 2 Page 2.1 Location map 7 Chapter 3 3.1 Scatter plot ofDCA ordination site scores. Vegetation data. 22 3.2 Scatter plot of DCA ordination species scores. Vegetation data. 22 3. 3. Figure 3.1 plotted with first subjectively defined habitat types. 24 3. 4. Figure 3 .1 plotted with four TWINSPAN derived habitat types. 25 Chapter 4 4. 1 One of the seed traps used in this study 36 4.2 Frequency distribution of percent oftotal seed rain caught 41 by the 80 seed traps 4. 3 Overall seed rain trend 41 4.4 Seed rain trend: Melicytus ramiflorus 42 4.5 Seed rain trend: Clematisfoetida 42 4.6 Seed rain trend: Cytisus scoparius 43 4. 7 Seed rain trend: Aristotelia serrata 43 4.8 Seed rain trend: Coprosma virescens 44 4.9 Seed rain trend: Parsonsia spp. 44 4.10 Seed rain trend: Hoheria spp. 45 4.11 Seed rain trend: Leycesteriaformosa 45 4.12 Seed rain trend: Sambuccus nigra 46 4.13 Seed rain trend: Dodonea viscosa 46 4.14 Seed rain trend: Meuhlenbeckia australis 47 4.15 Scatter plot of DCA ordination site scores. Seed rain data. 49 4.16 Scatter plot ofDCA ordination species scores. Seed rain data 49 4.17 Relationship between total possum faecal weight and 53 number of possum-dispersed seeds 4.18 Seeds as a porportion of total faecal weight 53 4.19 Temporallitterfall trend 55 Chapter 5 5.1 Seasonal trend in seedling density 72 5.2. Scatter plot of DCA ordination site scores. 77 November seedling survey data 5.3 Scatter plot ofDCA ordinaiton species scores. 77 November seedling survey data Chapter 6 6.1 Relationship between vegetation and seed rain DCA ordination 93 site scores 6.2 Relationship between seed rain and seedling DCA ordination 94 site scores. 6.3 Relationship between vegetation and seedling DCA ordination 95 site scores. LIST OF TABLES Chapter 3 Page 3. 1 Cover classes used in vegetation survey 17 3.2 Vegetation survey tiers with tier-height corrections 18 3. 3 Summary of DCA ordination of vegetation data 23 3.4 Correlations between vegetation ordination and 24 species abundance scores 3.5 Weighted species abundance scores in each habitat type 27 3.6 Mean vegetation biomass and species diversity in each habitat type 28 Chapter 4 4.1 Seed trap results; whole and damaged fruit and seeds 39 4.2 Seed species contributing> 1% oftotal whole seed rain 38 4. 3 Differences in seed rain per trap between the four habitat types 40 4.4 Habitat type differences in seed rain for Table 4.2 species 48 4. 5 Seed rain DCA ordination summary 48 4.6 Correlations between species seed rain counts and site DCA axis position 50 4.7 Seed rain diversity in each habitat type 50 4.8 Whole seeds from possum faecal clumps 51 4.9 Weight and number of seeds extracted from possum faecal clumps 52 Differences between habitat types 4.10 Seed predation(% total seed rain damaged) for Table 4.2 species 54 4. 11 Litterfall weight. Differences between habitat types by trap date 55 4.12 Summary of Ahuriri Bush seed rain data. From Burrows 1994b. 59 4.13 Summary comparison ofvegetation score and seed rain. 64 Data from Tables 3.5 and 4.3 4.14 Summary of possum diet. From O'Cain 1997. 66 4.15 Fruit species in possum diet. From O'Cain 1997. 66 4.16 Pre-dispersal insect predation of 13 seed species. 69 From Sullivan eta!. (1995) Chapter 5 5 .I Seedlings counted at each measurement period 71 5.2 Mean seedling density at each measurement period. 72 Differences between habitat types 5.3 Seasonal seedling density for 10 most abundant seedling species 73 5. 4 Differences in seasonal seedling density between habitat types 74 5.5 Between habitat type differences in seedling density for Table 5.3 species 74 5.6 Duncan's Multiple Range Test for between-habitat type 75 differences ofTable 5.3 species 5.7 Summary ofDCA ordination ofNovember seedling data 76 5.8 Correlations between seedling counts and site DCA ordination axis position 76 5. 9 Correlations between seedling counts and vegetation score for 78 Table 5.3 species 5.10 Between habitat-type differences in seedling diversity at each measurement 79 period 5.11 Germination requirements of27 species. From Burrows (various) 83 Chapter6 6.1 Correlation between DCA Axes 92 6.2 Regressions between axes for vegetation and seed rain DCA ordinations 93 6.3 Regressions between axes for seed rain and seedling DCA ordinations 94 6.4 Regressions between axes for vegetation and seedling DCA ordinations 96 6.5 Correlations between species score for vegetation, seed rain, and 97 seedlings for Table 4.2 species 6.6 Mean Table 6.5 correlations for each species, separated by dispersal mode 97 6.7 Summary oftables 6.2, 6.3, and 6.4. 98 CHAPTER 1 INTRODUCTION To walk through any part of the New Zealand landscape which is easily accessible is to experience a landscape which owes more to the actions of human settlement than it does to any 'natural' ecology. Several short centuries of human occupation have left their indelible imprint on the ecology of lowland New Zealand to the point where essentially all the easily accessible land has been converted to 'productive' use, and is as modified as any landscape in the world. As Park (1995) describes, the full consequence of this "total, deliberate extermination from New Zealand's plains" has never been really been grasped. When the smoke of the colonists fires cleared in the early twentieth century New Zealand had become a different country.