MANGROVE ECOLOGY, SILVICULTURE AND CONSERVATION Mangrove Ecology, Silviculture and Conservation by Peter Saenger Southern Cross University, Lismore, Australia • ,~ Springer-Science+Business Media, B.V. A C.I.P. Catalogue record for this book is available from the Library of Congress. ISBN 978-90-481-6050-1 ISBN 978-94-015-9962-7 (eBook) DOI 10.1007/978-94-015-9962-7 Printed on acid-free paper All Rights Reserved © 2002 Springer Science+Business Media Dordrecht Originally published by Kluwer Academic Publishers in 2002. Softcover reprint ofthe hardcover I st edition 2002 No part of this work may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without written permission from the Publisher, with the exception of any material supplied specifically for the purpose of being entered and executed on a computer system, for exclusive use by the purchaser of the work. CONTENTS Preface IX 1. Introduction: The Mangrove Environment 1 2. The Mangrove Flora 11 2.1 Introduction 11 2.2 The Mangrove Flora 11 2.3 Contemporary Biogeographical Processes 21 2.3.1 Floristic Attenuation with Latitude 21 2.3.2 Floristic Attenuation with Aridity 22 2.3.3 Floristic Changes induced by Natural Upheavals and Human Activities 23 2.4 Contemporary Biogeographic Patterns 25 2.4.1 Vicariants 26 2.4.2 Hybridizations 26 2.4.3 Discontinuities and Endemism 27 2.4.4 AtLantic and Eastern Pacific Biogeogrqaphy 28 2.4.5 Indian Ocean and East African Biogeography 32 2.4.6 Australasian Biogeography 37 2.4.7 Western Pacific Biogeography 39 2.4.8 North-East Asian Biogeography 41 2.5 Towards a Global Biogeographic History 43 3. Adapting to the Mangrove Environment 49 3.1 Introduction 49 3.2 Dealing with High Salt Concentrations 49 3.2.1 Salt Exclusion 50 3.2.2 Salt Extrusion 53 3.2.3 Storage ofS alt 57 3.2.4 Succulence 58 3.2.5 Compartmentalization 60 3.2.6 Osmocompensation 62 3.3 Conserving Desalinated Water 63 3.3.1 Xeromorphic Features 63 3.3.2 Transpiration 68 3.3.3 Optimizing Leaf Temperatures 73 3.4 Root Aeration in Waterlogged Soils 75 3.4.1 Morphological Adaptations 75 3.4.2 Physiological Adaptations 81 3.4.3 Metabolic Adaptations 83 3.5 Surviving Seawater Dispersal 84 3.5.1 Vivipary and Cryptovivipary 84 3.5.2 Propagule Production 87 3.5.3 Propagule Dispersal and Establishment 91 VI 4. Physico-chemical Factors and Mangrove Performance 101 4.1 Introduction 101 4.2 Temperature 101 4.2.1 Mangroves and Low Temperatures 102 4.2.2 Responses to High Temperatures 103 4.2.3 Inter- and Intra-specific Differences 104 4.3 Light and Photosynthesis 105 4.3.1 Photosynthetic Efficiency of Mangroves 105 4.3.2. Canopy Gaps: Gap-enhancement of Reproduction and Growth 110 4.3.3 The Mangrove Understorey and the Role of Sulfides 113 4.4 Wind and other Atmospheric Phenomena 114 4.4.1 Ambient Winds 114 4.4.2 Extreme Winds and Mangrove Vegetation 116 4.4.3 Hail 121 4.4.4 Lightning 121 4.5 Sedimentary Conditions and Processes 122 4.5.1 Mangrove Soil Development 122 4.5.2 Aeration and Drainage Properties ofM angrove Soils 128 4.5.3 Nutrients in Mangrove Soils 131 4.6 Salinity of Soil Water 137 5. Biotic Interactions and Mangrove Performance 147 5.1 Plant-Plant Interactions 147 5.1.1 Parasitism 147 5.1.2 Antagonism (Ammensalism) 150 5.1.3 Mutualism 152 5.1.4 Competition 154 5.2 Plant-Animal Interactions 160 5.2.1 Flowering and Pollination 160 5.2.2 Bioturbation of Sediments 166 5.2.3 Grazing and Trampling (Leaf Herbivory) 168 5.2.4 Other Mutualistic Interactions 176 5.2.5 Trophic Pathways 179 6. Mangrove Structure and Classification 183 6.1 Classification of Mangrove Communities 183 6.1.1 Phytosociological Classification 183 6.1.2 Classification Using Structural Attributes 184 6.1.3 Classification Using Geomorphological Settings 187 6.1.4 Classification Using Physiographic and Structural Attributes 190 6.2 Zonation of Mangroves 194 6.2.1 Shoreline Zonation 194 6.2.2 Longitudinal Upriver Zonation 201 6.2.3 Similarities and Differences in Shoreline and Upriver Zonation 204 Vll 7. The Value of Mangroves 207 7.1 Introduction 207 7.2 Components 209 7.2.1 Plant Resources 209 7.2.2 Fisheries Resources 213 7.2.3 Wildlife Resources 21S 7.2.4 Water Supply Resources 21S 7.2.S Agricultural Resources (including Salt Production and Aquaculture) 21S 7.2.6 Forage Resources 21S 7.2.7 Water Transport Resources 216 7.2.8 Recreational Resources 217 7.2.9 Energy Resources 217 7.2.10 Pharmaceutical Resources 218 7.3 Functions 219 7.3.1 Shoreline Protection 219 7.3.2 Windbreak and Stonn Protection 219 7.3.3 Sediment Regulation 219 7.3.4 Nutrient Retention 220 7.3.S Water Quality Maintenance 220 7.3.6 External Support 221 7.3.7 Groundwater Discharge and Recharge 222 7.3.8 Local Microclimatic Stabilization 223 7.4 Attributes 223 7.4.1 Biodiversity 223 7.4.2 Uniqueness and Heritage 224 7.5 An Economic Perspective 225 8. Mangrove Silviculture and Restoration 229 8.1 Introduction 229 8.2 Objectives for Mangrove Planting 229 8.2.1 Setting the Objectives 230 8.2.2 Timber Production 231 8.2.3 Shoreline Protection. Channel Stabilization and Stonn Protection 237 8.2.4 Fisheries and Wildlife Enhancement 238 8.2.S Legislative Compliance 239 8.2.6 Social Enrichment 240 8.2.7 Ecological Restoration 241 8.3 Macropropagation of Mangroves 243 8.3.1 Direct Planting of Propagules collected from the Wild 243 8.3.2 Outplanting of up to One Year old Nursery-raised Propagules 244 8.3.3 Outplanting of small Seedlings after Nursery-raising 244 8.3.4 Direct Transplanting ofS eedlings and Shrubs 244 8.3.S Raising ofA ir-layered Material 24S 8.3.6 Use of Stem Cuttings 24S 8.3.7 Use of Propagule Segments 246 8.4 Tissue Culture or Micropropagation of Mangroves 247 Vl11 8.5 Site· Species Matching 249 8.5.1 Some General Principles 249 8.5.2 Nursery and Planting Techniques 250 8.5.3 Field Trials 252 8.6 Silvicultural Management of Planted Areas 252 8.6.1 Objectivesfor Management 252 8.6.2 Site Management 253 8.6.3 Natural and Assisted Regeneration 253 8.6.4 Cost ofA ssisted Regeneration 255 8.7 Plantation Performance 256 8.7.1 Optimal Planting Season 256 8.7.2 Optimal initial Spacing 257 8.7.3 Survival 257 8.7.4 Standing Stock 257 8.7.5 Mean Annual increment 265 8.7.6 Rotation and Thinning Schedules 268 8.8 Indices of 'Health' in Mangrove Communities 269 9. Conservation and Management of Mangroves 271 9.1 The Need for Mangrove Management 271 9.2 Management Frameworks 275 9.3 Some Specific Management Issues 277 9.3.1 Excessive Extractive Use 277 9.3.2 Discharge of Wastes 278 9.3.3 Hydrocarbon Contamination 282 9.3.4 Reclamation and Foreshore Development 286 9.3.5 Mangroves and Global Climate Change 291 9.4 Management Tools 294 9.4.1 The Reserves 294 9.4.2 Zoning ofM angrove Areas 297 9.4.3 Ecosystem Modelling 298 9.4.4 Raising Public Awareness 298 9.5 Future Prospects of Mangroves 299 10. References 303 Index 351 Preface Historically, there has not been a greater appreciation for natural environments than exists today. Indeed, most of the emphasis of today's world is on sustainable development and the re-establishment of natural systems! And, mangroves are no exception. Considering that mangroves occupy less than I % of the world's surface, they appear from the publication record to have occupied a 'figure-head' place in the scientific literature. This trend seems to be continuing. Personally, I have advocated the use and conservation of mangroves for many years, and I have often been dismayed by the thoughtless destruction of mangroves. Believing, as I do, that raising public awareness of mangroves is a major step for their conservation, this book is intended to inform resource managers and decision makers on the capabilities and values of mangroves, and the processes governing their continued existence. I have included a chapter on silviculture and restoration to assist with restoring damaged systems, and to provide information on the sustainable use of mangrove forests. While preparing the book has been enjoyable, I have experienced some difficulties which I have dealt with by arbitrary, but consistent, decisions. The first is the problems of 'units': the sheer multiplicity of units has, at times, been overwhelming. Even salt concentrations, one of the fundamental parameters of mangrove ecology, can be expressed in a range of units depending on the particular interest; salinity (in %0 or without units as required by the Practical Salinity Scale) is commonly used although it is only an approximate, density-based measure of salt concentrations. Similarly, conductivity (in S m-I, IlS em-lor mmhos cm-1) is often used for easy field measurements and, while it is correlated with salt concentration and salinity, the linear relationship breaks down at high salinities such as are found on saltflats. Elsewhere, salt concentration (in g L-1, mM NaCl, mmol m-3, or meq L- 1) or osmolality (in mmol kg-1) may be more appropriate. For osmotic pressure equivalence, salt concentrations are in MPa. An equally diverse array of units is used for virtually all other measurements. For the most part, I have retained the units of the original source but have provided more common equivalents for rarely used units. Second, I have also had some difficulties with spelling and the use of accents; in the reference section, all citations are given as they were in the original. In the body of the text, I have adopted mostly the English form of spelling rather than the American - hence, centre rather than center, and kilometre rather than kilometer. Where quotes have been used, their original spelling have been retained except where the incorrect spelling of taxonomic binomials might lead to confusion. In terms of place names, I have usually given the original version as reported in the research report I have drawn on, but where different names are now in use, the altered names have been given in brackets as close to the first use of the name as possible. Third, wherever possible, I have tried to summarize information into tables. Even though this practice breaks the continuity of the text, I have persevered as many readers may not have access to the necessary library resources to locate the individual publications. I have also freely cited 'references' to enable the reader to follow up on any specific points. Last but not least, I sifted through huge numbers of papers and databases in an attempt to provide an overall synthesis of the material, only to find that many state the obvious, repeat what has long been known, or simply rephrase, sometimes with IX x little, novel philosophical twists, what has been previously reported by someone else. Personally, I know of few measures of information redundancy, but I would be happy to wager a beer or two, that by most measures, information redundancy in the mangrove literature is extremely high compared with most other areas of the natural sciences. All of these factors have made my task all the harder. Nevertheless, I have tried to be impartial and I have always tried to give credit for any specific ideas or advances where that credit was due. I have been conscientious in terms of acknowledging all authors of ideas, points of view or approaches - and, if I have not, then, it is entirely accidental. I should also l¥kl that several of my colleagues have read and commented on earlier versions of the various chapters (see acknowledgements), but, at the end of the day, the views and comments expressed here are my responsibility. Let me make the final comment, that the mangrove literature today is so vast, and it is becoming increasingly difficult to provide the sort of overview that I have attempted. More importantly, if I have managed to introduce some questions that give rise to further detailed investigation or critical review, I will have fulfilled my role. That has been my approach! I hope that it stimulates and enhances your interest in mangroves; if it does, my objectives have been met.