COMPARATIVE SEED AND REGENERATION BIOLOGY OF TWO THATCIDNG REED SPECIES (THAMNOCHORTUS INSIGNIS AND T. ERECTUS, RESTIONACEAE) Jaana-Maria Ball UniversitySeptember of Cape 1995 Town A thesis submitted to the Faculty of Science, University of Cape Town, in fulfilment of the requirements for the Degree of Master of Science The copyright of this thesis vests in the author. No quotation from it or information derived from it is to be published without full acknowledgement of the source. The thesis is to be used for private study or non- commercial research purposes only. Published by the University of Cape Town (UCT) in terms of the non-exclusive license granted to UCT by the author. University of Cape Town ii SUM:MARY The effect of harvesting on the seed and seedling ecology and the effect of fire and harvesting on the population dynamics of two thatching reed species, namely Thamnochortus insignis and Thamnochortus erectus were studied. The study species are both perennial hemicryptophytes each with a different regeneration mode, the former being a non-sprouter and the latter a resprouter. Despite being increasingly harvested in the agriculturally marginal areas of the southern Cape coast, no information exists on population dynamics and population processes that depend on the distribution and behaviour of seeds. Furthermore, Restionaceae which are physiognomically and floristically characteristic of the fynbos have generally been poorly studied. Thus, this study aimed to increase our understanding of the effect of harvesting on the seed bank dynamics and the effect of fire and harvesting on population dynamics of these species, as well as to provide managers of thatch stands with guidelines for the sustainable utilization of the resource. Seed bank dynamics and response of the species to disturbance were the focus of this study, but were placed in the context of their whole life cycles. Soil seed bank densities of both species were high; with that of T. insignis being approximately two times larger than that of T. erectus. This was attributed to greater seed production of T. insignis compared to T. erectus, rather than to longer survival of seed in the soil. Both species produced considerably more seeds than were incorporated into the seed bank and it was during this life history stage that the largest seed losses were observed. The seed bank densities of both species were distinctly seasonal, with direct seed counts for T. insignis varying between 1633 ± 2601 (mean± standard deviation) seeds per m2 before dispersal and 3773 ± 6027 seeds per m2 after dispersal. Seed counts for T. erectus varied between 1134 ± 2644 seeds per m2 before dispersal and 2530 ± 3482 seeds per m2 after dispersal. Seed bank estimates from germination were lower. Annual seed production and seed bank densities of both species showed large inter-annual variations, as well iii asdifferencesbetween species. Harvesting resulted in a drastic decline in both seed production and post-dispersal seed bank density. Active dispersal of seed during harvesting resulted in an increase in pre-dispersal seed bank density. Both species have seasonally persistent seed banks, and seed losses over the year following seed input were moderate. An accumulation of seeds in the soil over the two years was observed for both species. Seed burial showed that seed persistence and losses in seed banks differed between species and experimental seed bank type. Thamnochortus erectus showed greater seed persistence and T. insignis showed greater seed losses. These results conflict with actual observations of seed bank densities. Burial bags showed greater seed persistence and burial boxes showed greater seed losses for both species. Recruitment and seedling survival in mature vegetation was Umited for both species, although T. insignis appeared to have more potential than T. erectus for recruitment in this environment. In contrast. T. in.signis seedling recruitment was massive in the post-disturbance environment, indicating that the dormancy breaking may be mediated through cue " mcreasect resources in the disturbed environment. Moreover, germination appears to be cued by fire, although post-fire recruitment was not confmed to the first germination season after fire. Thamnochortus erectus seedling density was variable after disturbance and showed no large differences in the post-disturbance environment compared to mature vegetation, indicating that germination was not stimulated by environmental stimuli in the post-disturbance environment. The "open" microhabitat was favoured by seedlings of both species. Fire appeared to have a greater impact than harvesting on the population structure of both species. Culm production and resumption of seed production was rapid for both species, although reproductive output was both larger and increased more rapidly with time for T. in.signis compared to T. erectus. A single disturbance event increases the successful establishment of the non-sprouter, T. insignis, largely by massive seedling recruitment, although many plants survive and resprout from a subterranean base after harvesting. Population expansion of T. erectus after iv fire is probable, although not after harvesting. This was largely due to the ability of the resprouter, T. erectus, to maintain population size by adult plant survival and vegetative growth after a disturbance event, as :well as recruiting seedlings. Thamnoehortus insignis can, thus, be seen as a pioneer a species and T. erectus can be seen asApersistent species. This study contributes to the understanding of soil seed bank dynamics in fynbos and is the first comprehensive study of the seed and seedling biology of African Restionaceae. The implications of these results for commercial harvesting of the study species are discussed. V ACKNOWLEDGEMENTS I wish to express my appreciation to my supervisor Professor Richard Cowling for his generous academic and moral support throughout this study. Without fail I would leave each discussion more enthusiastic and enlightened. His dedication to and love for his work, and balanced outlook on life is an inspiration to all. Thanks also to my colleagues in the Institute for Plant Conservation and Botany Department at the University of Cape Town for their friendship, support and encouragement over the years. It was a privilege to have worked in such an environment. Special thanks is also due to Desmond Barnes, Henry Botha, Raymond Carelse, Hilary Cochrane, Robert Jacobs, Wendy Paisley and Sandy Smuts for their invaluable assistance. Prof. June Juritz of the Department of Statistical Sciences, University of Cape Town is thanked for assistance with the statistical analyses. I am most grateful to Angie Beuka, Bogart Butler, Raynn Bruce, Janette Du Tait, Michelle Forcioli, Alan Fransman, Carol Green, Leigh Gurney, Brandon Hurd, Petra Jobst, Alasdair Keen, Bridgit Klump, Chris Lotz, Cecilia Makua, Pieter Martin, Carl Morrow, Anton Noffke, Barry Page, Megan Page, Myles Prothero, Alison Pudney, Michael Richards, Anthony Smith, Jean Smith, Jenny Tomalin, Torbian Wiborg and Russel Wise for a great deal of hard work and patience, sometimes under extreme conditions, during the many field trips and processing of samples in the laboratory. Many friendships have been borne or strengthened during this time spent together. Access to the field study sites was kindly granted by the van Breda and Albertyn families, owners of the farms Zoetendalsvallei and Zeekoeivlei. Thanks also to Diana Durrant and Mr and Mrs Geldenhuys for accommodation at Springfield and Renosterkop during field trips. Their enthusiasm, generosity, desire to conserve natural areas, appreciation of nature and love of the area that they live in will be remembered. Whenever I vi reached the Agulhas Plain, after a long and frantic buildup to each field trip, an inner calm crept into me. I have truly come to love the area. Thanks also to the many farmers and thatch harvesters of the Stilbaai and Agulhas areas, for their willingness to discuss the practical aspects of thatch farming. Finally, I gratefully acknowledged the financial support of the Botanical Society, Department of Agriculture, Foundation for Research Development, Institute for Plant Conservation and University of Cape Town. vii CONTENTS PAGE SUMMARY ii ACKNOWLEDGEl\fENTS V CHAPTER 1: GENERAL INTRODUCTION 1 1. 1 Thesis rationale 2 1.2 Specific aims 5 1.2.1 Seed banks 5 1.2.2 Life cycle dynamics 7 1.2.3 The effects of disturbance 8 1.2.4 Practical significance 9 1.3 Study area and study sites 9 1.3.1 Physiography, climate and vegetation of the Agulhas Plain 9 1.3.2 Study sites 10 1.4 Study species and thatching industry 14 1.5 Methodology 18 1.6 Thesis structure and outline 19 1. 7 References 42 CHAPTER 2: SOIL STORED SEED BANKS OF TWO THATCIDNG REED SPECIES: PERSISTENCE AND DYNAMICS IN RESPONSE TO HARVESTING 55 2.1 Abstract 56 2.2 Introduction 58 2.3 Study species and study sites 64 2.4 Methods and materials 67 2.4.1 Seed characteristics 67 2.4.2 Population structure 67 2.4.3 Pre-dispersal seed losses 69 viii 2.4.4 Seed production 69 2.4.5 Post-dispersal seed predation 71 2.4.5.1 Cafeteria experiment 71 2.4.5.2 Observations 72 2.4.6 Soil seed bank size and dynamics 72 2.4.6.1 Pilot study 74 2.4.6.2 Physical separation technique 76 2.4.6.3 Seedling emergence technique 76 2.4.7 Seed storage and burial 77 2.4.7.1 Field study 77 a) Burial bag experiment 78 b) Burial box experiment 79 2.4.7.2 Laboratory study 80 2.4.8 Seedling dynamics 80 2.4.9 Seed budget 82 2.5 Results 84 2.5.1 Seed characteristics 84 2.5.2 Population structure 84 2.5.3 Pre-dispersal seed losses 89 2.5.4 Seed production 90 2.5.5 Post-dispersal seed predation 95 2.5.6 Soil seed bank size and dynamics 96 2.5.7 Seed storage and burial 107 2.5.8 Seedling dynamics 110 2.5.9 Seed budget 116 2.6 Discussion 155 2.