Ecology of Dunes, Salt Marsh and Shingle J.R

ECOLOGY OF DUNES, SALT MARSH AND SHINGLE J.R. Packham Emeritus Professor of Ecology, University of Wolverhampton, UK

and A.J. Willis Emeritus Professor of Botany University of Sheffield, UK

The assistance of Dr N.J.W. Clipson (part-author of Chapter 3 and section 10.3) and of Dr R.A. Stuttard (part-author of sections 2.7 and 2.8) is gratefully acknowledged.

CHAPMAN & HALL E3 London • Weinheim • New York • Tokyo • Melbourne • Madras CONTENTS

Preface xiii

1 Introduction and primary concepts 1 1.1 At the edge of the sea 1 1.1.1 A local example 1 1.1.2 The objects of study 2 1.2 Geomorphology of coastal dunes, shingle systems and salt marshes 3 1.2.1 Detached beaches 5 1.2.2 Barrier islands 6 1.3 Substrate material and movement: winds, tides and plants 9 1.3.1 Substrate particle size 9 1.3.2 Substrate movement 9 1.3.3 Origin, transport and erosion of water-borne sediments 11 1.3.4 Tidal cycles 12 1.4 Environmental variation in a coastal ecotone 13 1.5 Grazing, decomposition and renewal 16 1.5.1 Energy flow 18 1.5.2 Nutrient cycling 18 1.6 Patterns in space and time 20 1.6.1 Fluctuations and phenology 25 1.7 Stability, selection and strategy 25 1.7.1 Development and vegetational history of the Berrow salt marsh, 26 North Somerset \ 1.7.2 Stability and species diversity 28 1.7.3 Selection and strategy 28 1.7.4 Plant strategies in response to competition, disturbance and stress 30

2 Primary and secondary production: the autotrophs and their associates 33 2.1 Plant life forms 33 2.1.1 Life forms of terrestrial bryophytes 34 2.1.2 Algae 34 2.2 Biological spectra 35 2.3 Processes of primary production 40 2.3.1 Limiting factors " 43 2.4 Climate, limiting factors and dispersal 43 2.4.1 Climatically determined species 44 2.4.2 Edaphic factors 45 2.4.3 Dispersal 46 viii Contents 2.5 Soils 49 2.5.1 Composition and properties of soil 49 2.5.2 Soil formation 50 2.5.3 Soil variation in the Cefni Marsh, Anglesey, UK 51 2.5.4 Soil-landform relationships on the Romney Marshes, Kent, UK . . 52 2.5.5 Pedogenesis and the soils of dunes, slacks and pine woodlands at 53 Ainsdale (Merseyside), Northern Ireland and Wales 2.5.6 Buried soils and coastal aeolian sands 55 2.6 Microbial ecology of coastal ecosystems 55 2.6.1 Mycorrhizal relations of coastal vegetation 56 2.6.2 Nitrogen fixation in coastal sites 56 2.7 Heterotrophs, secondary production and ecosystem processes 57 2.7.1 Characteristics of estuarine heterotrophs 58 2.7.2 Microarthropods and other biota of beaches and dunes 59 2.8 Coastal birds 59 2.8.1 Availability and selection of prey items 62 2.8.2 Bird migration and its impact on intertidal invertebrates 63 2.8.3 Coastal birds: predation and breeding in a Scottish dune/estuary 64 2.8.4 Conservation and management of coastal habitats 64

3 Water and ionic relationships: plant adaptations to coastal environments 67 3.1 Limiting environmental factors 67 3.1.1 Environmental impacts on salt-marsh plants 67 3.2 Halophyte water relations 69 3.3 Adaptive mechanisms in halophytes 74 3.3.1 Growth responses in halophytes 74 3.3.2 Intracellular compartmentalization of solutes 76 3.3.3 Adaptation at the whole-plant level 78 3.3.4 Regulation of uptake at the root 79 3.3.5 Regulation of uptake at the shoot 79 3.3.6 Molecular regulation of halophyte salt tolerance \ 80 3.4 Waterlogging and soil anaerobiosis 81 3.5 Plant adaptation on sand dunes 83 3.5.1 Transpiration in dune plants 85

4 Salt marshes: tides, time and function 87 4.1 Marshes and mangrove forests . 87 4.1.1 Mangrove associations 87 4.1.2 Salt marsh origin and form 88 4.1.3 Transitions from salt marsh to tidal woodland 91 4.2 Tidal cycles, inundation and accretion 91 4.2.1 Tidal range and exposure 93 4.2.2 Measurements of* tidal flows 94 4.2.3 Sampling patterns for nutrient flux determination 95 4.2.4 Drainage and pore water 95 4.2.5 Inundation, soil aeration and redox potential 96 4.2.6 Patterns of accretion and erosion 99 Contents ix 4.2.7 Biotic influence on the stability of salt-marsh sediments 99 4.2.8 Subsidence and changes in marsh elevation 100 4.3 Topography: creeks and salt pans 101 4.3.1 Microrelief 105 4.4 Development, zonation and age of salt-marsh ecosystems 105 4.4.1 Salt-marsh floras 105 4.4.2 Zonation 107 4.4.3 Developmental zonation and succession 110 4.4.4 Allogenic versus autogenic factors 110 4.4.5 Cyclic change in a tropical salt marsh 112 4.5 Nutrient flux and salt-marsh chemistry 114 4.5.1 Nitrogen flux in a Spartina alterniflora marsh in New England 116 4.5.2 Influence of soil sulphide on the distribution of higher plants 117 4.6 Succession, stability and palaeoecology 118

5 Salt-marsh dynamics and communities 123 5.1 Autecology of major plant species 123 5.2 Plant and animal communities 128 5.2.1 Interactions between plant and animal communities 129 5.2.2 Influence of Spartina anglica on salt-marsh communities 129 5.2.3 Loss of Spartina anglica marsh 129 5.2.4 Salt-marsh animals 130 5.3 Seasonal changes 132 5.3.1 Germination and seedling establishment 132 5.3.2 Seasonal growth patterns in plants 133 5.3.3 Rainfall, salinity and survival 137 5.3.4 Seasonal behaviour in animals 138 5.4 Plant-herbivore relationships in an evolving sub-Arctic salt marsh 138 5.4.1 Influence of grazing geese on plant productivity, species diversity and 139 microtopography 5.4.2 Growth responses of Arctic graminoids following grazing 139 5.4.3 Influence of grazing on succession in emergent vegetation in the Hudson 141 Bay lowlands: an uncertain future 5.4.4 Environmental degradation, food limitation and the cost of philopatry 142 5.5 Biomass, productivity and energy flow 142 5.5.1 Primary production 143 5.5.2 Productivity and tidal gradients . 145 5.5.3 Secondary production by an avian herbivore 146 5.6 Ecology of the Sapelo Island salt marshes, South Georgia, USA 147 5.6.1 Ecological processes in the marsh water 148 5.6.2 Ecological processes in the marsh sediments 149 5.6.3 Tidal transport of organic matter and a simulation model of carbon flux 150

6 Sand dunes: initiation, development and function 153 6.1 Blown sand and its fixation 153 6.1.1 Classification of dunes 154 6.1.2 Sand supply for coastal dune formation 155 x Contents 6.1.3 Plant habit and dune formation 155 6.1.4 Initiation of saltation 156 6.1.5 Saltation boundary layer 157 6.1.6 Rate of sand transport 158 6.1.7 Embryo dune formation - . 158 6.1.8 Influence of vegetation on sand movement 159 6.1.9 Maintenance of dunes and slacks 159 6.1.10 Older dune ridges and slacks 160 6.1.11 Topographic change and parabolic coastal blowout dunes 160 6.2 The strandline and general zonation: embryo dunes 162 6.2.1 Scottish strandline vegetation 165 6.2.2 Extent of the growth zone 167 6.2.3 Pioneer dune grasses and differential grazing 167 6.2.4 Accretion rates and survival of dune grasses 168 6.2.5 Embryo dune formation by Elytrigia juncea 168 6.3 Influence of land form, soil and water regime on dune plants 169 6.3.1 Composition of dune soils and changes with time 172 6.3.2 Domed water tables in dune systems 173 6.3.3 Dew formation 174 6.3.4 Wet slacks, dry slacks, dunes and the water table 175 6.3.5 Effects of water on plant distribution 176 6.3.6 Influence of weather 177 6.4 The role of non-vascular plants in dune systems 178 6.4.1 Dune bryophytes and their growth forms 179 6.4.2 Dune lichens 180 6.4.3 Ecophysiology of two dominant lichens in Dutch coastal dunes 181 6.4.4 Fungi of dune systems 181 6.5 Two contrasting dune systems 182 6.5.1 Braunton Burrows, North Devon 182 6.5.2 The South Haven dune system and its development 184 6.5.3 Lichens of South Haven dunes '? 188 6.6 Grazing, nutrients and diversity 190 6.6.1 Rabbits and the influence of grazing on primary producers 190 6.6.2 The impact of myxomatosis 191 6.6.3 Nutrient additions in the absence of grazing 192 6.6.4 Calcium and micronutrient deficiencies in dune soils 194 6.6.5 Nutrient additions in the presence of grazing 195 6.6.6 Use of Oenothera as an indicator species in a Japanese dune system 196

7 Sand-dune dynamics and communities 199 7.1 Marram: the Oregon Dunes, machair and dumped sea sand 199 7.1.1 Marram: form, distribution and growth 199 7.1.2 Establishment, occurrence and vigour of marram 199 7.1.3 Sand stabilization with marram 201 7.1.4 Influence of marram on the Oregon Dunes 201 7.1.5 Scottish sand dune systems 203 Contents xi 7.1.6 Inland dune floras on dumped sea sand 205 7.2 Phenology and plant population biology 205 7.2.1 Seasonal activity of reptiles at Studland Heath NNR, Dorset, UK 205 7.2.2 Plant population biology of winter annuals, a rhizomatous sedge and a 206 tussock-forming grass 7.2.3 Salt marsh and sand dune annuals 212 7.3 Plant and animal communities 213 7.3.1 Environmental change, disease and biodiversity 214 7.4 Productivity, energy flow and nutrient cycling 215 7.4.1 Biomass and nutrient accumulation in a Dutch dune system 216 7.4.2 Cation fluxes at the Ainsdale Dunes, UK 218

8 Coastal shingle 221 8.1 Location and formation of shingle structures 221 8.2 Characteristics of shingle vegetation 223 8.2.1 Influence of abiotic factors 226 8.2.2 Hydrological conditions and particle size 229 8.2.3 Sources of water available to shingle plants 230 8.2.4 Successional relationships on shingle 230 8.2.5 Shingle ridge succession at Dungeness 231 8.2.6 Generalized pattern of plant succession on shingle sites in Britain 231 8.3 Shingle vegetation of a boulder bank in New Zealand 232 8.4 Two outstanding British shingle beaches 235 8.4.1 Orfordness and Dungeness 236 8.4.2 Plant communities of Dungeness 237 8.4.3 Lichen communities and lichenicolous mites at Dungeness 237 8.4.4 Other Dungeness invertebrates 239 8.4.5 Environmental degradation at Dungeness and Orfordness 239 8.4.6 A sandy cuspate foreland in the Baltic 240 8.5 Spits, bars, barrier islands, lagoons and salinas 240 8.5.1 Blakeney Point and Scolt Head Island, UK . 241 8.5.2 Lagoons • 242 8.5.3 TheWaddensee 243 8.5.4 Chesil Beach and the Fleet 244 8.5.5 Salinas 247 8.6 Dynamics of a US northern barrier spit 249

9 Environmental impacts 253 9.1 Pollution, reclamation and mineral extraction 253 9.1.1 Reclamation and mineral extraction schemes 256 9.2 Drainage and water abstraction 256 9.3 Mowing, grazing, trampling and damage by vehicles 259 9.3.1 Trampling and path1 formation 260 9.3.2 Damage by vehicles ,• 261 9.4 The influence of invasive plants 262 9.4.1 Realized niches in exotic populations 265 xii Contents 10 Variation in sea level and climatic change 267 10.1 Evidence of previous changes in sea levels 267 10.1.1 Palaeoenvironmental studies of Fenland, UK, involving sea level change 267 10.2 Evidence of contemporary change 269 10.2.1 Increases in atmospheric CO2 269 10.2.2 Measurement of sea level changes 269 10.2.3 Changes in distribution and behaviour of coastal organisms 270 10.2.4 Scale of change 270 10.3 Implications of future changes in sea level and climate 270 10.3.1 Coastal dune development in relation to sea level rise 271 10.3.2 Non-linear threshold effects 271 10.3.3 Effects of climatic change on coastal systems 273

11 Coastal management and conservation 275 11.1 Resource potential, present use and habitat creation 275 11.1.1 Habitat creation 276 11.2 Monitoring change 278 11.2.1 New communities associated with sea defence works 278 11.2.2 Loss of sand dune habitat and its compensation 279 11.2.3 Monitoring erosion and vegetation change in salt marshes 280 11.3 Management of dunes, shingle ridges and barrier islands 280 11.3.1 Effect of different sand accumulators on resultant dune form 284 11.3.2 Sediment transport in relation to coastal protection 285 11.3.3 Barrier islands 285 11.4 Objectives of salt-marsh management 286 11.5 Sea defence and planned retreat 288 11.5.1 Sea defence: the policy options 288 11.5.2 Planned retreat and salt marsh creation 289 11.5.3 Retreats on the Essex marshes 292

References \ 297