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Wetlands: Ecology, Conservation and Management 8
Paul A. Keddy
Causal Factors for Wetland Management and Restoration: A Concise Guide
Wetlands: Ecology, Conservation and Management Volume 8
Series Editor C. Max Finlayson, Albury, NSW, Australia Editorial Board Members Cui Lijuan, Institute of Wetland Research, Chinese Academy of Forestry, Beijing, China Anne A. van Dam, Dept. of Water Resources and Ecosystems, IHE, Inst for Water Education, Delft, The Netherlands Siobhan Fennessy, Kenyon College, Gambier, OH, USA Patricia Kandus, Instituto de Investigaciones e Ingeniería Ambiental, Universidad Nacional de San Martín, San Martin, Buenos Aires, Argentina Julius Kipkemboi, Department of Biological Sciences, Egerton University, Egerton, Kenya Donovan Kotze, Centre for Water Resources Research, University of KwaZuluNatal, Pietermartizburg, South Africa Ritesh Kumar, 2nd Floor, Wetlands International South Asia, New Delhi, India Tatiana Lobato de Magalhães , Autonomous University of Queretaro, Santiago de Queretaro, Querétaro, Mexico Victor Marin, Departamento de Ciencias Ecologicas, Universidad de Chile, Santiago, Chile Beth Middleton, U.S. Geological Survey, Lafayette, LA, USA Randy Milton, Dept of Natural Resources, Acadia University, Wolfsville, NS, Canada Simon Mitrovic, School of Life Sciences, University of Technology Sydney, Ultimo, NSW, Australia Nidhi Nagabhatla, Institute for Water, Environment Health, United Nations University Institute on C, Brugge, Belgium Kerrylee Rogers, School of Earth & Environmental Sci, Univ of Wollongong, Wollongong NSW, Australia Rebecca Woodward, 35 Percent, Chalford, UK
The recognition that wetlands provide many values for people and are important foci for conservation worldwide has led to an increasing amount of research and management activity. This has resulted in an increased demand for high quality publications that outline both the value of wetlands and the many management steps necessary to ensure that they are maintained and even restored. Recent research and management activities in support of conservation and sustainable development provide a strong basis for the book series. The series presents current analyses of the many problems afflicting wetlands as well as assessments of their conservation status. Current research is described by leading academics and scientists from the biological and social sciences. Leading practitioners and managers provide analyses based on their vast experience. The series provides an avenue for describing and explaining the functioning and processes that support the many wonderful and valuable wetland habitats, such as swamps, lagoons and marshes, and their species, such as waterbirds, plants and fish, as well as the most recent research directions. Proposals cover current research, conservation and management issues from around the world and provide the reader with new and relevant perspectives on wetland issues.
Paul A. Keddy
Causal Factors for Wetland Management and Restoration: A Concise Guide
Paul A. Keddy Independent Scholar Lanark County, ON, Canada
ISSN 1875-1261 ISSN 1875-127X (electronic) Wetlands: Ecology, Conservation and Management ISBN 978-3-031-21787-6 ISBN 978-3-031-21788-3 (eBook) https://doi.org/10.1007/978-3-031-21788-3 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland
Preface
For some years I have been teaching and writing about the causal factor approach to wetland ecology. My intention in doing so was to provide a logical and consistent structure for the science of wetland ecology. I have received a good deal of positive feedback on the virtues of this approach, and I used it in my textbook, Wetland Ecology (DOI: https://doi.org/10.1017/CBO9780511778179). An environmental planner in China told me that my book Wetland Ecology was “overwhelming.” I thought there was some wisdom in that observation. I had written Wetland Ecology for fellow scientists and university students, who would expect a good deal of detail, many references to scientific papers, and multiple examples. This got me wondering: just how short could a guide to wetland ecology be? Consider the audience of park managers, landscape architects, consultants, planners, and engineers who might be sincerely interested in protecting and restoring wetlands, but might not have the time to read Wetland Ecology. Could I write a concise guide for them? In this book, therefore, I have kept referencing to a minimum. If there are statements that seem insufficiently referenced, I invite you to consult Wetland Ecology for a more complete story. I have also kept examples to a minimum, mostly just two or three per section. In Wetland Ecology, I often have five or more examples, so again, if this is too short for your tastes, I recommend the larger book. I have kept what we might call classic examples in wetland ecology. Some people are of the impression that new work is always better, and I have even heard that some professors tell their students not to read work that is more than 5 years old. I disagree. I have kept “old” examples including peat bog succession (Dansereau and Segadas-Vianna 1952), changes in deltas with time (Penland et al. 1988), and effects of fire in the Everglades (White 1994). These are fine work that is still useful today. Throwing them out would be the same as throwing out a perfectly useful antique chair only to replace it with a new plastic one. We need to keep good work in circulation, and it remains useful for teaching students about landmarks in the development of wetland ecology. (I will note, too, that older work often has better artwork than modern work. Clip art is not a substitute for a talented pen and ink artist.) v
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Another book hovers in the background. The causal factor approach in this book has a broader theoretical context—the pool and filter approach to community ecology—so, those of you seeking the theoretical context might wish to consult A Framework for Community Ecology (DOI: https://doi.org/10.1017/9781009067881) recently completed with my co-author Daniel Laughlin. My intention in preparing this book was to make a positive contribution to protecting and restoring wetlands. Thus, I have concluded each chapter with implications for (1) people who are managing protected wetlands or watersheds and (2) people who are restoring wetlands. At the end of the book, I provide a further list of review questions that should help with applying this book to both sets of circumstances. So, here is my concise introduction to wetland ecology based upon causal factors. It is arranged with the most important causal factors first, so even the first half of the book will have a great deal of information that can be immediately applied to conservation and restoration. May you protect and restore extensive areas of wetland during your lifetime. Lanark County, ON, Canada
Paul A. Keddy
Acknowledgments
I must begin by thanking Marleen Moore for first suggesting this project. I also thank Li Zhang for offering me the opportunity to speak to her class in China which challenged me to consider how best to simplify wetland ecology with a focus on management. I’m particularly grateful to Cathy Keddy for her devoted assistance during a protracted period of serious illness for both of us. She helped me at every stage of the manuscript. Sadly, she herself did not live to see the book published, but Cathy’s legacy is here on every page. I also appreciate my son, Ian Keddy, for being there with software advice as needed. I’m also grateful to Max Finlayson for his effort in reviewing the manuscript. Finally, I thank the many (patient) people who have taught me these principles of wetland ecology, principles that I am now going to share with you.
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Contents
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Introduction to Wetlands������������������������������������������������������������������������ 1 1.1 What Is a Wetland? �������������������������������������������������������������������������� 2 1.2 Where Do Wetlands Occur?�������������������������������������������������������������� 2 1.3 The Six Basic Types of Wetlands������������������������������������������������������ 2 1.4 Three Other Approaches to Wetland Classification�������������������������� 7 1.4.1 A Global View���������������������������������������������������������������������� 9 1.4.2 A Hydrogeomorphic View���������������������������������������������������� 10 1.4.3 A View Based on Water Sources������������������������������������������ 11 1.5 Ecoregions and Wetland Classification�������������������������������������������� 13 References�������������������������������������������������������������������������������������������������� 14
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The Causal Factor Approach to Wetland Ecology�������������������������������� 17 2.1 Causal Factors Are a Simplifying Tool for Wetland Ecology ���������� 17 2.2 The Importance of Multiple Working Hypotheses���������������������������� 19 2.3 Revisiting Protection and Restoration���������������������������������������������� 22 References�������������������������������������������������������������������������������������������������� 22
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Duration of Flooding Is the Most Important Causal Factor���������������� 23 3.1 Flood Duration Controls Wetlands��������������������������������������������������� 23 3.2 Flooding Changes Wetland Soils������������������������������������������������������ 24 3.3 Flooding Is a Stress�������������������������������������������������������������������������� 25 3.4 How Plants Cope with Flooding ������������������������������������������������������ 27 3.5 Flooding Has Secondary Effects������������������������������������������������������ 28 3.5.1 Secondary Effects in Swamps���������������������������������������������� 28 3.5.2 Secondary Effects in Marshes���������������������������������������������� 29 3.5.3 Secondary Effects in Peatlands �������������������������������������������� 30 3.5.4 Secondary Effects in Aquatic Wetlands�������������������������������� 32 3.6 Flooding Is the Main Causal Factor�������������������������������������������������� 32 References�������������������������������������������������������������������������������������������������� 33
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Flood Pulses���������������������������������������������������������������������������������������������� 37 4.1 Changes in Water Level Are Natural in Lakes, Rivers, and Wetlands ������������������������������������������������������������������������������������ 37 4.2 Flood Pulses Are a Natural—And Necessary—Occurrence������������ 40 4.3 Humans Are Interfering with Natural Flood Pulses�������������������������� 42 4.4 Flood Pulses Increase Marsh Area and Diversity: The Twin Limit Model���������������������������������������������������������������������� 45 4.5 Flood Pulses Have Other Important Effects in Watersheds�������������� 47 4.6 Vernal Pools: A Special Case of a General Principle������������������������ 48 References�������������������������������������������������������������������������������������������������� 50
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Fertility������������������������������������������������������������������������������������������������������ 53 5.1 Nitrogen and Phosphorus Control Fertility�������������������������������������� 53 5.2 Peatlands Have Relatively Low Fertility������������������������������������������ 57 5.3 The Everglades Have Extremely Low Fertility�������������������������������� 57 5.4 Fertilization Threatens a Globally Imperiled Plant Species������������� 58 5.5 Increased Fertility Causes Many Other Changes in Wetlands���������� 60 References�������������������������������������������������������������������������������������������������� 60
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Natural Disturbance�������������������������������������������������������������������������������� 63 6.1 Natural Disturbances Remove Biomass�������������������������������������������� 63 6.1.1 Duration�������������������������������������������������������������������������������� 64 6.1.2 Intensity�������������������������������������������������������������������������������� 64 6.1.3 Frequency������������������������������������������������������������������������������ 65 6.1.4 Area�������������������������������������������������������������������������������������� 65 6.2 Fire Has Many Effects upon Wetlands���������������������������������������������� 65 6.3 Natural Disturbance Is Common along Rivers �������������������������������� 66 6.4 Animals Create Natural Disturbance������������������������������������������������ 68 6.5 Wetlands Recover from Disturbance by Seeds and Rhizomes������������������������������������������������������������������������������������ 69 6.6 Humans Have Big Effects When They Alter Natural Disturbances in Landscapes�������������������������������������������������������������� 70 References�������������������������������������������������������������������������������������������������� 71
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Competition���������������������������������������������������������������������������������������������� 73 7.1 Competition Is a Biological Causal Factor �������������������������������������� 73 7.2 Large Clonal Plants Tend to Exclude Weaker Competitors�������������� 75 7.3 Competition Among Plants Drives Plant Succession ���������������������� 76 7.4 Competition Among Plants Changes Animal Habitat���������������������� 78 References�������������������������������������������������������������������������������������������������� 79
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Herbivory�������������������������������������������������������������������������������������������������� 81 8.1 Herbivory Is a Biological Causal Factor������������������������������������������ 81 8.2 Hippopotamus in Tropical Wetlands������������������������������������������������ 82 8.3 Snow Geese in Northern Marshes���������������������������������������������������� 84 8.4 Selective Grazing Can Increase or Decrease Diversity�������������������� 86
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8.5 Bottom-Up or Top-Down? The Biological Control of Herbivores������������������������������������������������������������������������������������ 87 8.6 Large Herbivores Are Declining ������������������������������������������������������ 89 8.7 Managing Herbivores May Require Case-by-Case Strategies���������� 90 References�������������������������������������������������������������������������������������������������� 92 9
Burial�������������������������������������������������������������������������������������������������������� 95 9.1 Rates of Burial Vary with Wetland Type������������������������������������������ 96 9.2 Autogenic Burial Is Usually Rather Slow���������������������������������������� 97 9.3 Allogenic Burial Is Often Rapid and Builds Wetlands �������������������� 99 9.4 Plants Can Often Regenerate After Burial���������������������������������������� 102 9.5 Animals Are Also Affected by Burial ���������������������������������������������� 105 References�������������������������������������������������������������������������������������������������� 108
10 Salinity������������������������������������������������������������������������������������������������������ 113 10.1 Salinity Reduces the Species Pool�������������������������������������������������� 113 10.2 Salinity and Rising Sea Levels�������������������������������������������������������� 117 10.3 Salinity and Facilitation������������������������������������������������������������������ 119 References�������������������������������������������������������������������������������������������������� 120 11 Roads�������������������������������������������������������������������������������������������������������� 123 11.1 Roads Are Everywhere, Expanding, and Increasing���������������������� 123 11.2 The Direct Effect: Roads Kill Animals ������������������������������������������ 124 11.3 Indirect Effects May Be More Important Than Roadkill���������������� 124 References�������������������������������������������������������������������������������������������������� 128 12 Coarse Woody Debris������������������������������������������������������������������������������ 131 References�������������������������������������������������������������������������������������������������� 134 13 Invasive Species Are an Emerging Causal Factor�������������������������������� 135 13.1 Invasive Species Are a Global Threat to Biodiversity�������������������� 135 13.2 Five Examples of Invasive Species ������������������������������������������������ 137 13.2.1 Burmese Python (Python bivittatus) in the Everglades�������������������������������������������������������������� 137 13.2.2 Emerald Ash Borer (Agrilus planipennis) in Swamps������������������������������������������������������������������������ 138 13.2.3 Nutria or Coypu (Myocastor coypus) in Marshes������������ 139 13.2.4 European Frog-Bit (Hydrocharis morsus-ranae) in Aquatics������������������������������������������������������������������������ 139 13.2.5 Giant Cane (Arundo donax) in Floodplains���������������������� 140 13.3 Risk Assessment for Invasive Species�������������������������������������������� 141 13.4 Dealing with Invasives�������������������������������������������������������������������� 142 References�������������������������������������������������������������������������������������������������� 142 14 Human Population Size �������������������������������������������������������������������������� 145 14.1 Human Population Size Drives Anthropogenic Impacts���������������� 145 Reference �������������������������������������������������������������������������������������������������� 148
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15 The Global Context for Wetland Protection and Restoration ������������ 149 15.1 Causal Factors Help Simplify Complexity ������������������������������������ 149 15.2 Putting the Pieces Together in a Global Network �������������������������� 150 References�������������������������������������������������������������������������������������������������� 152 16 Some Review Questions for Managers�������������������������������������������������� 153 16.1 Protection���������������������������������������������������������������������������������������� 153 16.2 Restoration�������������������������������������������������������������������������������������� 154 Index������������������������������������������������������������������������������������������������������������������ 155
About the Author
Paul A. Keddy has been Professor of Ecology for more than 40 years and has published over 150 scholarly papers and 6 books. His awards include a National Wetlands Award for Science Research from the Environmental Law Institute, a Lifetime Achievement Award from the Society of Wetland Scientists, and a Meritorious Service Medal from the Governor General of Canada. Dr. Keddy’s Wetland Ecology: Principles and Conservation, now entering its third edition, has won a Merit Award from SWS. Dr. Keddy lives within a nature reserve in Canada, where he continues research, writing, and public lectures (www.drpaulkeddy.com). He has served as a volunteer to organizations such as NSF, NSERC, World Wildlife Fund, and The Nature Conservancy. His work in theoretical ecology includes A Framework for Community Ecology, co-authored with Daniel Laughlin. His applied work has covered protection of wetlands and forests in areas including Nova Scotia, Louisiana, and Ontario.
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Chapter 1
Introduction to Wetlands
Abstract There are six basic kinds of wetland in the world: swamp, marsh, bog, fen, wet meadow, and aquatic. These six types are mostly caused by differences in flooding and nutrient supply. The particular kinds of plants and animals in the wetland will depend upon the ecoregion in which the wetland occurs. Keywords Wetland · Marsh · Swamp · Bog · Fen · Wet meadow · Aquatic · Mangroves · Classification · Ecoregions · Species pools This textbook is about the ecological communities that occur where land meets water—wetlands—and the environmental factors that create them. My intention is to provide a concise guide for busy managers, conservation biologists, landscape architects, and anyone else who deals with wetlands. For readers with broader interests in wetlands as a whole, and topics beyond causal factors, there is my book, Wetland Ecology: Principles and Conservation (Keddy 2010), with many more examples and a broader range of topics. Wetlands have always influenced humans. Early civilizations first arose along the edges of rivers in the fertile soils of floodplains in Asia and the Middle East. One of the world’s earliest written stories, the Epic of Gilgamesh, describes a flood. Wetlands continue to produce many benefits for humans—along with fertile soils for agriculture, and they provide food such as fish, as well as many other kinds of wild animals. Additionally, wetlands have other vital roles that are less obvious— they produce oxygen, store carbon, and process nitrogen. For thousands of years, human cities in low areas have flooded during periods of high water. Yet, people continue to build in floodplains, which, if nothing else, makes work for environmental educators and planners. And, now, we are at the point where humans are having an enormous impact upon wetlands. This book is a guide on how to better coexist with wetlands and their wildlife. Better still, it is also a guide to how we can restore wetlands to enhance their services, expand our wild places, and create more habitat for wild species.
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 P. A. Keddy, Causal Factors for Wetland Management and Restoration: A Concise Guide, Wetlands: Ecology, Conservation and Management 8, https://doi.org/10.1007/978-3-031-21788-3_1
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1 Introduction to Wetlands
1.1 What Is a Wetland? A wetland is an ecosystem that arises when inundation by water produces soils dominated by anaerobic processes, which, in turn, forces the biota, particularly rooted plants, to adapt to flooding. This broad definition includes everything from tropical mangrove swamps to subarctic peatlands. This single sentence of definition has a complex structure: there is a cause (inundation by water), a proximate effect (reduction of oxygen levels in the soil), and a secondary effect (the biota must tolerate both the direct effects of flooding and the secondary effects of low oxygen levels). It is not the only definition, and maybe not even the best, but it shall get us started. Of course, other definitions are possible and are used in other books, and by other agencies, such as the Ramsar Convention on Wetlands (Gardner and Finlayson 2018). It is important to have clear definitions for science to proceed; on the other hand, a great deal of time can be consumed in scholastic debates. Here, my intention is to take an avowedly pragmatic approach to wetland ecology. For broader views of wetland definitions and wetland classifications, one can consult the overview in my own book (Keddy 2010) or other sources such as Dugan (1993) or Finlayson et al. (2018a, b).
1.2 Where Do Wetlands Occur? Figure 1.1 shows the approximate global distribution of global wetlands. Such a map has many limitations. It is difficult to map wetlands at the global scale for at least three reasons. Firstly, wetlands are often a relatively small proportion of the landscape. Secondly, they are often distributed in small patches or strips and therefore cannot be mapped at a scale suitable for reproducing in a book. Thirdly, they are very variable, and one area may have several different types of wetlands. To offer an alternative to the map, Table 1.1 lists the largest wetland areas in the world. These provide an important priority list for research and conservation. Given the global variation in wetlands, it is not surprising to find that many different wetland classification schemes have been developed. They vary, for example, by geographic region, the intended use of the classification, and the scale at which classification is undertaken. We will start with a simple classification system that distinguishes six wetland types largely on the basis of location and hydrology.
1.3 The Six Basic Types of Wetlands Each type of wetland can be visualized as a set of plant and animal associations that recur. This recurrence probably means that the same causal factors are at work. In trying to name the kinds of wetlands, we run into a problem at the very start: the
1.3 The Six Basic Types of Wetlands
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Fig. 1.1 The major wetland areas on Earth. Mangrove swamps are shown as triangles. (Compiled from Dugan 1993 and Groombridge 1992) Table 1.1 The world’s largest wetlands (areas rounded to the nearest 1000 km2) Rank Continent 1 Eurasia 2 3 4 5 6 7 8 9 10 11
South America North America Africa North America South America North America Africa Africa North America South America
Wetland Description West Siberian Bogs, mires, fens lowland Amazon River basin Floodplain forest and savanna, marshes, mangal Hudson Bay Bogs, fens, swamps, marshes lowland Congo River basin Swamps, riverine forest, wet prairie Mackenzie River Bogs, fens, swamps, marshes basin Pantanal Savannas, grasslands, riverine forest
Area (km2) 2,745,000 1,738,000 374,000 189,000 166,000 138,000
Mississippi River basin Lake Chad basin River Nile basin Prairie potholes
Bottomland hardwood forest, swamps, marshes Grass and shrub savanna, marshes Swamps, marshes Marshes, meadows
108,000
Magellanic moorland
Bogs
44,000
106,000 92,000 63,000
From Fraser and Keddy (2005)
terminology for describing wetlands varies both among human societies and among scientists. Thus, one finds an abundance of words used to describe wetlands—bog, bayou, carr, fen, flark, hochmoore, lagg, marsh, mire, muskeg, swamp, pocosin, pothole, quagmire, savanna, slough, swale, turlough, yazoo—in the English language
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1 Introduction to Wetlands
alone. Many of these words can be traced back centuries to Old Norse, Old Teutonic, or Gaelic origins (Gorham 1953). Now add in other world languages, and the problem is compounded. To bring order to this confusion, we need to identify just a few types of wetlands that occur around the world. To keep the terminology simple, we will begin with four types of wetlands and then add two to extend the list to six. Swamp A wetland that is dominated by woody plants that are rooted in hydric soils, but not usually in peat (Fig. 1.2). The most widespread examples are the many kinds of floodplain forests that occur along rivers, such as the ash and willow swamps of the Rhine River, or the cypress and tupelo swamps along the Mississippi River. Swamps with trees may be distinguished from swamps with shrubs. If organic matter accumulates, swamps may eventually become peatlands. Marsh A wetland that is dominated by herbaceous plants that are usually emergent through water and rooted in hydric soils, but not usually in peat (Fig. 1.3). Examples would include sedge (Carex lacustris) marshes around the Great Lakes and reeds (Phragmites australis) around the Baltic Sea. Marshes often have dense reserves of buried seeds to regenerate during periods of low water. Bog A wetland dominated by Sphagnum moss, sedges, ericaceous shrubs, or evergreen trees rooted in deep peat with a pH less than 5 (Fig. 1.4). Examples would include the blanket bogs which carpet mountainsides in northern Europe, the vast peatland of the West Siberian Lowland in central Russia, and the peat bogs that stretch across the boreal regions of North America. Peatlands also occur in tropical areas, where they may have rainforest vegetation. Fen A wetland that is usually dominated by sedges and grasses rooted in shallow peat, often with considerable groundwater movement, and with pH greater than 6 (Fig. 1.5). Many occur on calcareous rocks, and most have brown mosses in genera including Scorpidium or Drepanocladus. Fens are often mixed with bogs and occur within the extensive peatlands of northern North America and Europe, as well as in many smaller seepage areas throughout the temperate zone, particularly in high altitude valleys. Other wetland types could be added to these four. Two important ones follow. Wet Meadow A wetland dominated by herbaceous plants rooted in occasionally flooded soils (Fig. 1.6). These wetlands depend upon natural water level fluctuations and are often found along lakes and rivers. Temporary flooding drowns the terrestrial plants and trees. Subsequent dry periods then allow emergence of many species from buried seeds, producing plant communities in moist soils. Examples would include wet prairies along river floodplains and meadow marshes on the shorelines of large lakes. Since these wetlands are produced by periodic flooding, they are easily overlooked if visited during a dry period.
1.3 The Six Basic Types of Wetlands
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Fig. 1.2 Swamps. (a) Pterocarpus swamp (Guadeloupe, Wikimedia Commons). (b) Mangrove swamp (Thailand, Shutterstock)
Aquatics A wetland community dominated by mostly aquatic plants growing in and covered by at least 25 cm of water (Fig. 1.7). Examples include the littoral zones of lakes, bays in rivers, and the more permanently flooded areas of prairie potholes. The water surface may be covered by floating-leaved plants, such as many species of water lilies.
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Fig. 1.3 Marshes. (a) Riverine marsh (Bellows Bay, Ottawa River, Canada; courtesy D. Brunton). (b) Salt marsh (Petpeswick Inlet, Canada)
Any attempt to sort the diversity of nature into only six categories will have its limitations. Rather than worry further about how to name wetlands, we should probably admit that wetlands show great variation and agree to not get stalled or diverted by too many debates over terminology. As Cowardin and Golet (1995) say, “No single system can accurately portray the diversity of wetland conditions world- wide. Some important ecological information inevitably will be lost through classification.”
1.4 Three Other Approaches to Wetland Classification
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Fig. 1.4 Bogs. (a) Lowland continental bog (Algonquin Park, Canada). (b) Upland bog with pools (Newfoundland, Canada)
1.4 Three Other Approaches to Wetland Classification The system I presented above has the advantage of simplicity and generality. There are four wetland types, six if you wish to expand it slightly. (I prefer the six categories, because otherwise wet meadows and aquatic communities tend to be overlooked. Moreover, the organisms in these habitats have distinctive features.) You should be aware that there are far more elaborate systems and that these vary around the world. Each wetland classification system tries to describe the major types of
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Fig. 1.5 Fens. (a) Patterned fen (northern Canada; courtesy C. Rubec). (b) Shoreline fen (Lake Ontario, Canada)
wetland vegetation and then relate them to environmental conditions. Here are three more examples. I have selected them because of their global scale and because they provide some insight into the control exerted by flooding. But there are, of course, many other systems that classify wetlands into types: international, national, state, ecoregion, and even local systems can be found. While you explore wetland types using this book, you will likely need to learn one more classification system—the specific system that is used in your own political and ecological region. However, by the time you finish this section, and certainly this book, you will understand the small set of ecological factors that underlie all these classification systems.
1.4 Three Other Approaches to Wetland Classification
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Fig. 1.6 Wet meadows. (a) Sand spit (Long Point, Lake Ontario, Canada; courtesy A. Reznicek). (b) Gravel lakeshore (Tusket River, Canada; courtesy A. Payne)
1.4.1 A Global View Figure 1.8 provides a summary that puts different classification systems into a unified whole. It begins with “water regime,” from permanently waterlogged on the left to permanent shallow water on the right. Combining these three hydrological regimes with “nutrient supply,” one obtains peatlands on the left, swamps in the middle, and marshes and aquatic systems on the far right. Further, this scheme then goes on to address the main types of plants that will occur.
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Fig. 1.7 Aquatics. (a) Lake (Lake Burtnieki, Latvia, Anda Mikelsone, Shutterstock). (b) Pond (Interdunal pools on Sable Island, Canada)
1.4.2 A Hydrogeomorphic View The location or setting of a wetland often has important consequences for duration of flooding and water chemistry. One example is the widely used Cowardin classification system (Table 1.2). Setting may be particularly important for fens, since it affects so many aspects of hydrology and chemistry (Godwin et al. 2002), but wetlands along rivers also vary a great deal with local conditions (Tockner et al. 2008; Merritt 2013).
1.4 Three Other Approaches to Wetland Classification
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Fig. 1.8 The kinds of wetlands can be related to two sets of environmental factors: water regime and nutrient supply (upper left). The term “water regime” refers to hydrological factors including depth and duration of flooding, while “nutrient supply” refers to chemical factors including available nitrogen, phosphorus, and calcium. (From Gopal et al. 1990. Republished by permission of Backhuys Publishers)
1.4.3 A View Based on Water Sources There are three main sources of water for wetlands—precipitation, groundwater, and water moving across the surface (Brinson 1993a, b). Raised bogs are almost completely dependent upon the first, whereas floodplains are largely dependent upon the third. In practice, nutrient levels are often closely correlated with water sources, since rainfall tends to be low in nutrients, whereas water that flows across the surface or through the ground picks up dissolved nutrients and particulate matter. Wetlands can be classified according to the relative proportions of these three water sources. Each of the above three views provides a certain perspective on wetlands and will be useful for certain purposes. It is not that one system is right and the other is wrong. Deciding which is best for a particular project requires that you know the purpose of your work and the nature of your audience, as well as the geographical and political situation in which you are working.
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Table 1.2 Cowardin classification of wetlands and deepwater habitats System Marine
Subsystem Subtidal
Intertidal
Estuarine
Subtidal
Intertidal
Riverine
Tidal
Lower perennial
Upper perennial
Intermittent
Class Rock bottom Unconsolidated bottom Aquatic bed Reef Aquatic bed Reef Rocky shore Unconsolidated shore Rock bottom Unconsolidated Bottom Aquatic bed Reef Aquatic bed Reef Streambed Rocky shore Unconsolidated shore Emergent wetland Scrub–shrub wetland Forested wetland Rock bottom Unconsolidated bottom Aquatic bed Rocky shore Unconsolidated shore Emergent wetland Rock bottom Unconsolidated bottom Aquatic bed Rocky shore Unconsolidated shore Emergent wetland Rock bottom Unconsolidated bottom Aquatic bed Rocky shore Unconsolidated shore Streambed (continued)
1.5 Ecoregions and Wetland Classification
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Table 1.2 (continued) System Lacustrine
Subsystem Limnetic Littoral
Palustrine
Class Rock bottom Unconsolidated bottom Aquatic bed Rock bottom Unconsolidated bottom Aquatic bed Rocky shore Unconsolidated shore Emergent wetland Rock bottom Unconsolidated bottom Aquatic bed Unconsolidated shore Moss–lichen wetland Emergent wetland Scrub–shrub wetland Forested wetland
From Cowardin et al. (1979)
1.5 Ecoregions and Wetland Classification Swamps, marshes, bogs, fens, wet meadows, and aquatics provide a simple classification. This approach to wetlands allows us to understand some of the patterns we see in the landscape around us. It allows us to communicate with one another. It also has its limits. The useful simplicity needs to be balanced by an awareness of complexity. I must re-emphasize that the small set of causal factors presented in this guide will apply around the world—but at the same time, the visible consequences of these factors will depend somewhat upon the region in which you live. Different regions of the world have different climates, soils, and species pools. Therefore, you have the professional responsibility to be familiar with these local circumstances. How local is local, you may reasonably ask? I suggest you start with the ecoregion in which you live and work. Olson et al. (2001) define ecoregions as “relatively large units of land containing a distinct assemblage of natural communities and species, with boundaries that approximate the original extent of natural communities prior to major land-use change.” Their map (Fig. 1.9) recognizes a total of 867 ecoregions, nested within 14 biomes and 8 biogeographic realms. It seems reasonable to expect that each of us should know the ecoregion in which we are working, and become somewhat familiar with the landscape of this ecoregion and the kinds of species that inhabit this landscape. There is also a complementary global map of freshwater ecoregions (Abell et al. 2008). This classification has 426 units and is based primarily upon fish. Since wetlands occur where terrestrial ecosystems meet aquatic ecosystems, this freshwater ecoregion map may also be useful, particularly in permanently flooded wetlands.
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Fig. 1.9 There are 867 world ecoregions, each one having a distinctive set of species and natural communities. (From Olson et al. 2001. Republished by permission of Oxford University Press on behalf of the American Institute of Biological Sciences. For an interactive version of this map, use https://databasin.org/maps/new/#datasets=68635d7c77f1475f9b6c1d1dbe0a4c4c)
As with wetland classifications, you may find that your own country has a map of ecoregions which has some discrepancies with the global map in Fig. 1.9. We may expect such discrepancies to be resolved with time. Meanwhile, the world ecoregion map provides a context and setting for our wetland conservation and restoration activities. Each ecoregion has its own species pool; that is, the list of species that provide the raw material from which wetland plant communities are assembled (Keddy and Laughlin 2021). Ecoregions also provide a convenient framework for communicating with other professionals. Too often we are left guessing in which ecoregion a particular piece of research or management case study was located.
References Abell R, Thieme ML, Revenga C et al (2008) Freshwater ecoregions of the world: a new map of biogeographic units for freshwater biodiversity conservation. Bioscience 58:403–414 Brinson MM (1993a) Changes in the functioning of wetlands along environmental gradients. Wetlands 13:65–74 Brinson MM (1993b) A hydrogeomorphic classification for wetlands, Technical report no. WRP-DE-4. U.S. Army Corps of Engineers, Washington, DC Cowardin LM, Golet FC (1995) US fish and wildlife service 1979 wetland classification: a review. Vegetatio 118:139–152 Cowardin LM, Carter V, Golet FC et al (1979) Classification of wetlands and deepwater habitats of the United States, FWS/OBS-79/31. U.S. Department of the Interior Fish and Wildlife Service, Washington, DC Dugan P (ed) (1993) Wetlands in danger. Oxford University Press, New York
References
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Finlayson CM, Everard M, Irvine K, McInnes RJ, Middleton BA, van Dam AA, Davidson NC (eds) (2018a) The wetland book I: structure and function, management and methods. Springer, Dordrecht Finlayson CM, Milton GR, Prentice RC, Davidson NC (eds) (2018b) The wetland book II: distribution, description and conservation. Springer, Dordrecht Fraser LH, Keddy PA (eds) (2005) The world’s largest wetlands: ecology and conservation. Cambridge University Press, Cambridge Gardner RC, Finlayson M (2018) Global wetland outlook: state of the world’s wetlands and their services to people. Ramsar Convention Secretariat, Gland Godwin KS, Shallenberger J, Leopold DJ et al (2002) Linking landscape properties to local hydrogeologic gradients and plant species occurrence in New York fens: a hydrogeologic setting (HGS) framework. Wetlands 22:722–737 Gopal B, Kvet J, Loffler H et al (1990) Definition and classification. In: Patten BC (ed) Wetlands and shallow continental water bodies, vol 1: Natural and human relationships. SPB Academic Publishing, The Hague, pp 9–15 Gorham E (1953) Some early ideas concerning the nature, origin and development of peat lands. J Ecol 41:257–274 Groombridge B (ed) (1992) Global biodiversity: status of the earth’s living resources. Chapman and Hall, London Keddy PA (2010) Wetland ecology: principles and conservation, 2nd edn. Cambridge University Press, Cambridge Keddy PA, Laughlin DC (2021) A framework for community ecology: species pools, filters and traits. Cambridge University Press, Cambridge Merritt DM (2013) Reciprocal relations between riparian vegetation, fluvial landforms, and channel processes. In: Wohl E (ed) Treatise on geomorphology. vol 9: Fluvial geomorphology. Academic, San Diego, pp 219–243 Olson DM, Dinerstein E, Wikramanayake ED et al (2001) Terrestrial ecoregions of the world: a new map of life on Earth. Bioscience 51:933–938. https://doi.org/10.1641/0006-3568(2001)05 1[0933:TEOTWA]2.0.CO;2 Tockner K, Bunn SF, Gordon C et al (2008) Flood plains: critically threatened ecosystems. In: Poulin N (ed) Aquatic ecosystems. Cambridge University Press, Trends and global prospects, pp 45–61
Chapter 2
The Causal Factor Approach to Wetland Ecology
Abstract We can simplify our study of wetlands by focusing our attention on the small set of causal factors that create wetlands and control their characteristics. For any particular wetland, one has to know which causal factors are the most important, for it is these factors which can be used to manage the wetland wisely. Management may have two main goals. In some areas, such as parks and nature reserves, management will maintain the existing causal factors in order to keep the wetland in its present condition. In other areas, such as damaged landscapes, management will change the causal factors in order to restore the wetland to a more desirable state. In either case, it is important to focus upon causal factors. Finally, causal factors can provide multiple working hypotheses, which provide a useful tool for ecosystem management overall. Keywords Environmental factors · Consequences · Dependent variables · Independent variables · Management · Conservation · Protection · Restoration · Multiple working hypotheses
2.1 Causal Factors Are a Simplifying Tool for Wetland Ecology Now that you have had a brief introduction to wetlands, let me introduce the causal factor framework used in this book. Too often, wetland ecology is treated as a huge collection of facts about wet places. And, you can find such books, filled with a great many facts and lots of photos of wetland species, particularly animals, and many drawings of biogeochemical cycles. The complexity can be overwhelming. This book is different. Here, the focus is upon a handful of simple principles that unify a great many facts. Wetland ecology has a simple, logical structure with just two parts: causal factors and consequences. Our first challenge in protecting or restoring a wetland is to identify these causal factors and rank them in order of their
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 P. A. Keddy, Causal Factors for Wetland Management and Restoration: A Concise Guide, Wetlands: Ecology, Conservation and Management 8, https://doi.org/10.1007/978-3-031-21788-3_2
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importance. Our second challenge is to determine the consequences these causal factors are having upon the various characteristics of this wetland. Using even more general terms, causal factors are independent variables while the consequences are dependent variables. The list of dependent variables in wetlands is a long list of all the properties of that we might be able to measure, beginning with species composition. Then, there are many other properties that might also be measured such as carbon storage, or primary productivity, or oxygen production. Many of the scientific papers and talks in wetland ecology are descriptions of how one or more causal factors (independent variables) affect one or more properties (dependent variables). Once you understand this cause-and-effect structure in wetland ecology, it follows that one of the best ways to measure our progress in scientific understanding is the success with which we can predict properties from the causal factors (Peters 1992; Rigler and Peters 1995). For applied ecology, we have a different measure of success. If we are responsible for protecting a wetland, our measure of success will be how closely we can maintain the existing species composition and services of the wetland for which we are responsible. If we are getting the causal factors right, the existing species composition and services should continue through time. If we are responsible for restoring a wetland, our measure of success will be how closely we attain our targets for species composition and services of the wetland. These targets need to be stated explicitly, during the planning phase; monitoring will then determine how close the restored wetland comes to our target values. This is a good time to explain the use of the words protection and restoration as they will be used in this guide. I assume that there will be two general groups of people using this book, each group with its own priority for management: Protection: Some users will be responsible for parks, nature reserves, and other kinds of protected areas that are part of the growing global network of natural areas. In this case, the principal challenge is to maintain the characteristics of these protected areas that led to their recognition and designation in the first place. That is to say, your first responsibility is probably to maintain existing species composition and existing services. This will require maintaining the appropriate balance of causal factors. Of course, the term protection does not imply stasis: wetlands are dynamic systems. Changes caused by succession and competition (Chap. 7) are often natural and so too are counterbalancing factors of natural disturbance (Chap. 6) and herbivory (Chap. 8). A mixture of these causal factors will usually result in a mosaic of habitats, and the protection challenge is often to maintain a habitat mosaic with the desired array of species and services. Restoration: Some users will be responsible for repairing wetlands or landscapes that have been degraded by human use, say, wetlands with drainage canals, or wetlands that have been isolated from rivers by artificial levees. In this case, the management challenge is to shift the degraded composition and services toward more desirable states. It is vital that the desirable states be explicitly stated in the restoration plan. There is little point in beginning “restoration” until you know what it is that you are trying to accomplish. Once you know your targets, the
2.2 The Importance of Multiple Working Hypotheses
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principal way to achieve them is by creating the appropriate mix of causal factors. Causal factors, then, are the principal tool for restoration. It is my view that we can usually achieve restoration by learning to work with nature, that is, working with the natural causal factors that create wetlands. In this book, I will illustrate how causal factors will allow you to successfully protect and restore wetlands. When I need a more general word that describes both categories—a term for either protection or restoration—I will use the word management. Managers may have the goal of maintaining existing composition and services (sometimes called “passive management”), or they may have the goal of changing composition and services (sometimes called “active management”). That is why every natural area needs a management plan that sets out the goals explicitly. Sometimes, of course, you may find yourself responsible for a mixture of the two activities. You may be responsible for protecting a state park, but the management goal may include restoration projects such as reintroducing an endangered species, increasing the populations of certain rare species, or recreating a rare habitat. Similarly, you may be responsible for restoring a wetland, which may involve making large changes in composition, but you may simultaneously have the challenge of protecting small areas that already have high natural value, or protecting some existing populations of rare species that still use the degraded wetland.
2.2 The Importance of Multiple Working Hypotheses This is also a good time to remind you about the importance of multiple working hypotheses. All too often in science, or in life in general, it is easy to leap to a conclusion and assume that one knows which causal factor is producing which consequences. Certainly, we can say with a great deal of confidence that flooding is the most important factor in nearly all wetlands. However, flooding is rarely the only factor. Other factors that may affect wetlands include the availability of nitrogen and phosphorus (“fertility”), the frequency of fire or intensity of grazing (“natural disturbance”), or biological interactions such as competition and predation. We have to be able to keep an open mind about the role of other, possibly unknown, or at least overlooked, causal factors. It is not always clear which of these other causal factors is important in a particular wetland. One of the best ways to keep this open mind is to remember that there are always multiple causal factors acting in ecological communities. Our task as managers is to sort out which ones are most important. This requires us to first explicitly make a list of all the causal factors that might be operating and then collect observations or design experiments to increase our confidence about which ones are the most important. Table 2.1 gives a list of some of the principal causal factors in wetlands, and my best guess as to their relative importance overall. You might think of this as a sort of shopping list. While flooding will be important in all wetlands, the relative importance of the other factors may change in order and weighting. The task of
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Table 2.1 The estimated relative importance of environmental factors that determine the characteristics of wetlands in natural settings Environmental factor Hydrology (Chaps. 3 and 4) Fertility (Chap. 5) Natural disturbance (Chap. 6) Competition (Chap. 7) Herbivory (Chap. 8) Burial (Chap. 9) Salinity (Chap. 10) Roads (Chap. 11) Coarse Woody debris (Chap. 12) Invasive species (Chap. 13)
Relative importance (%) 50 15 15 10