Recovery strategies for nitrogen-sensitive habitatsec.europa.eu/.../part-i...1_nov-2012_2013-09-10_en.pdf · best available knowledge and form the ecological foundations of the measures,

Recovery strategies for

nitrogen-sensitive habitats

Version: November 2012

Ecological underpinnings of the

Programmatic Approach to Nitrogen (PAN)

Alterra Wageningen UR &

Natura 2000 Programme Directorate of the Ministry of Economic Affairs, Agriculture and Innovation

Part I - version: November 2012 – 2


Authors Part I Editors: N.A.C. Smits & D. Bal Authors: D. Bal, D. Brunt, R. Bobbink, W. de Vries, A.J.M. Jansen, M. Nijssen, H. Siepel, J.H.J. Schaminée, N.A.C. Smits, A.J.P. Smolders & H.F. van Dobben Part II Editors: N.A.C. Smits, A.S. Adams, D. Bal & H.M. Beije Authors: A.S. Adams, C. Aggenbach, G.H.P. Arts, A. Aptroot, A.M. Arens, D. Bal, A. Barendregt, H.M. Beije, B. Beltman, R. Bobbink, J. Bouwman, E. Brouwer, A. Corporaal, H. de Mars, J. den Ouden, H. de Vries, R.W. de Waal, D. Groenendijk, A.P. Grootjans, R. Haveman, A.M.M. van Haperen, P.W.F.M. Hommel, M.A.P. Horsthuis, H.P.J. Huiskes, A.J.M. Jansen, A.M. Kooijman, G. Kooijman, L.P.M. Lamers, E.C.H.E.T. Lucassen, D. Melman, M. Nijssen, M. Riksen, H.N. Siebel, N. Schotsman, Q.L. Slings, H. Sluiter, J. Smits, N.A.C. Smits, L.B. Sparrius, K.V. Sýkora, H.B.M. Tomassen, H.F. van Dobben, G.A. van Duinen, W. van Steenis, R. van ’t Veer, L. van Tweel-de Groot, G. van Wirdum & M.F. Wallis de Vries Part III Editors: A.J.M. Jansen, H.F. van Dobben, D. Bal & N.A.C. Smits Authors: B. Arends, A. Barendregt, B. Beltman, R.J. Bijlsma, R. Bobbink, I. Borkent, J. Bouwman, E. Brouwer, H. van Dobben, H. Everts, F. Eysink, A. Grootjans, G. ter Heerdt, A.J.M. Jansen, G. Kooiman, G. Maas, M. Nijssen, E. Remke, J. Sevink, N.A.C. Smits, R. Slings, F. Smolders, L. Sparrius, B. Takman, H. Weinreich, R. van der Burg, A. van Haperen, H. van Kleef, T. van Noordwijk, B. van Tooren



Foreword BACKGROUND AND PURPOSE OF THE RECOVERY STRATEGIES Natura 2000 is the European network of valuable habitats and is also the name of the European policy protecting the nature in those areas. In the Netherlands, more than 160 nature reserves have been designated under Natura 2000. In more than 130 of these areas there are plants and animals - defined as habitat types and species - which suffer from the effects of the deposition of nitrogen from the air. The purpose of the recovery strategies for nitrogen-sensitive habitats is the retention and restoration of nature, which is sensitive to precipitation of nitrogen from the air, the atmospheric nitrogen deposition. In order to achieve the nature targets in these areas, the precipitation of nitrogen from mainly agriculture, traffic and industry needs to be reduced. This is a big task. It calls for innovations in various fields, which take a long time to come to a broad application in practice. The deposition of nitrogen has been declining for decades, through cleaner cars, cleaner industry and several emission-limiting measures that have been implemented in cattle breeding. Between 1980 and 2007, the emission of nitrogen oxide in the Netherlands dropped from 550 kilotons to 300 kilotons, a decrease of 45%. A slightly higher decline was noted for the emission of ammonia between 1990 and 2008. In recent years, the decline has stagnated. Nevertheless, a further reduction of emissions is foreseen for the period up to and including 2030, and in its wake of the deposition. That is in part (about one third) determined abroad, but also there is a downward development, so that the downward deposition trend is not hampered. This is good for nitrogen-sensitive nature, but in some circumstances not good enough. It can take a long time before the deposition is reduced to such a level, whereby certain habitats of plants and animals can revive again. In some cases, it is even unlikely that this level will completely be reached. Natura 2000 asks that the decline of valuable nature is stopped and that a concrete prospect of improvement occurs. Improvements should be determined within one, two or three management periods of six years, and which are consolidated or continued in the period after 2030. Recognizing that it will take a long time to bring back the nitrogen deposition enough, the recovery strategies have been developed. The recovery strategies contain all possible impact-oriented measures to in any case maintain, and, if possible, recover the different habitat types in the Natura 2000 areas during the period when the deposition of nitrogen is (still) too high. The effects of many of the remedial measures are temporary and some restoration work cannot be repeated frequently. Moreover, it sometimes concerns costly interventions. It therefore remains essential that the reduction of nitrogen emissions continues. To achieve this, the Programmatic Approach Nitrogen (PAN) was created in the summer of 2009.


THE PROGRAMMATIC APPROACH NITROGEN (PAN) The core of the PAN is to make the preservation and restoration of the nature quality possible without jeopardizing economic development. Within the PAN, binding agreements are made about remedial measures in the Natura 2000 areas and reduction of the nitrogen load. The PAN is an integral program of the government and the joint provinces, which also relies on the cooperation and involvement of many, such as the Association of Dutch Municipalities, the Association of Water Boards, the agricultural and horticultural organisations, the employers' organisation VNO-NCW and the various land management organisations. In 2009, the government at that time decided that the Programmatic Approach Nitrogen had to be developed (Advisory group Huys (Parliamentary document 31700 XIV 160) & the Trojan Commission (Parliamentary document 30654, No. 51) and in 2012 the PAN will enter into force. Part of the PAN approach is moving from the one-sided emphasis on lowering the deposition to the realisation of a widely supported range of measures for the conservation and restoration of habitats. This involves the quality and the surface of these habitats. If a certain effect of nitrogen on this quality can be (temporarily) reduced by measures that are themselves not focused on nitrogen deposition, then such a measure can be characterised as a mitigation measure. Mitigation measures are, as long as the deposition is still too high, often of great importance. For this reason, measures aimed at hydrological restoration have, amongst others, gotten a prominent place within the recovery strategies. APPLICATION OF THE RECOVERY STRATEGIES The recovery strategies have been prepared for the habitat types and species based on the best available knowledge and form the ecological foundations of the measures, which need to be taken in practice. From the available recovery measures, a package of (local, field level) management measures need to be compiled for a specific Natura 2000 area, where nitrogen-sensitive nature occurs. The area-specific information needs to be added. Information on the location, differences in space and time and environmental factors (e.g. air and groundwater quality) are, in addition to, for example, historical analyses with which the trend can be determined, the basis for an area-specific landscape ecological analysis (LESA; Van der Molen 2010). The information from the current project must help the writers of the management plans to get to an optimal package of management measures against the effects of atmospheric nitrogen deposition. In addition, this information forms the foundation for a possible authorization of new economic activities. The strategies therefore offer guidance in achieving concrete measures to protect vulnerable habitats in specific areas. This can involve measures at the location where the habitat types are present, such as removing the present nitrogen supply by mowing, turf cutting or digging, or adjusting the water level locally. But there may also be measures under discussion relating to an entire landscape, both inside and outside the Natura 2000 area concerned. Think of, for example, the improvement of the groundwater quality in the catchment area, the increase of the local groundwater level and of interventions in the landscape that contribute to sand drift. The knowledge is made available through a computer application (web tool), whereby the user sees the nitrogen problem on the spot from a specific Natura 2000 area. Everts & De


Vries (2011) have developed an application for this use. Through a roadmap the user gets the right information at his disposal and the relevant measures will become visible. DISCLAIMER The documents provide an overview of possible effective recovery measures for the selected nitrogen-sensitive habitats and thus serve as handles to protect the vulnerable habitats in specific areas. By means of the status of the stated measures their (proven) effectiveness is shown. The three distinct categories are: rule of thumb (V), hypothesis (H) and proven (B). The effect of a control measure in a specific field situation can deviate due to the great variety and complexity of ecosystems. ACCOUNTABILITY To access the best available knowledge, a wide range of experts from policy, practice and research in the Netherlands were asked to contribute to the recovery strategies. The documents were drawn up in a partnership of the Natura 2000 Programme Directorate of the Ministry of EL&I and Alterra (Wageningen UR). Also, ample use was made of the skills in the knowledge network Development and Management of Nature Quality (kennisnetwerk Ontwikkeling en Beheer Natuurkwaliteit, O+BN). This network consists of experts from practice, policy and research in the field of ecological restoration. The project "Recovery strategies for nitrogen-sensitive habitats" was financed by the Natura 2000 Programme Directorate of the Ministry of EL&I and was conducted in the period 2010-2012, with the aim of bringing together the best available knowledge on possible remedial measures and of unlocking this knowledge in a systematic manner for application in practice.


Structure The ecological underpinnings of the recovery measures in practice have led to three coherent parts:

I. General introduction to recovery strategies: policy, knowledge and measures II. Recovery strategies for nitrogen-sensitive habitats III. Landscape ecological embedding of the recovery strategies

The first part (Part I) is the general introduction to the strategies by habitat and provides basic information about the effects of nitrogen deposition and the underlying biogeochemical processes. This introductory report explains the effects of nitrogen deposition on the structure and the functioning of ecosystems. Following this, it discusses the remedial measures to minimise the adverse effects of nitrogen deposition. The second part (Part II) forms the core of the research and describes the specific recovery strategies for the nitrogen-sensitive habitats (habitat types and habitats of species). It starts by giving an overview of the current state of knowledge about the effects of nitrogen deposition on the habitat concerned, whereby, if possible, a distinction is made between the acidifying effects and the fertilizing effects. Also any toxic effects and effects on fauna (typical species and species of the Birds and Habitats Directives) are included. Other relevant processes that affect the quality of the habitat type, such as hydrology and management, are also included. Measures against the effects of nitrogen deposition and other conditions affecting it, form the core of the recovery strategies. These are divided into measures against the effects of nitrogen deposition (impact-oriented measures in the strict sense) and measures for functional recovery. The choice (and combination) of the necessary measures is generally area-specific, and should therefore be developed for a specific area. The third part (Part III) deals with the ecological embedding of recovery strategies. In Part II, the recovery strategies are elaborated in detail at the level of the location of each habitat. When one "zooms out" from the local level to the landscape level, however, there appears to be a significant degree of correlation between the positions of the individual habitats. Each position is, as it were, embedded in a spatial gradient, of which character and direction are determined through the landscape. As a result, recovery measures taken for one habitat often also affect other habitats, which are connected with this one type through landscape gradients. This influence can be positive: what is good for one habitat is also good for another in the same habitat gradient, but this need not always be the case. It is therefore necessary to take the landscape context into consideration when planning restorative measures. Therefore, Part III considers the processes and measures again, but now per landscape gradient, indicating what measures are needed at the landscape level to recover degraded landscape gradients.



Table of contents Foreword 5 Structure 8 Part I General introduction to recovery strategies:

Policy, knowledge and measures 18 Chapter 1 General introduction 20 1.1 Background & aim 20 1.2 The different effects of nitrogen deposition and their connection 20

1.2.1 Direct toxicity of gases on individual plant species 22 1.2.2 Eutrophication by gradual increase of the N-availability 22 1.2.3 Acidification of soil and water 22 1.2.4 Negative effects of increased availability of reduced N 23 1.2.5 Increased sensitivity to secondary stress factors as pests and frost or drought damage 23 1.2.6 Long-term effects 23

1.3 Critical deposition values (CDV) 25 1.4 Policy context 26

1.4.1 Natura 2000 26 Conservation objectives habitat types 26

1.4.2 Nitrogen deposition and Natura 2000 29 1.4.3 Programmatic Approach Nitrogen (PAN) 30 1.4.4 Preconditions of the project 30

Definition habitat types 30 Critical deposition values 31 Impact-oriented measures vs source-based measures 31 Abiotic preconditions 31

1.5 Recovery strategies 31 1.5.1 Impact-oriented measures 31 1.5.2 Operation of the recovery strategies in connection with the PAN 33

1.6 Method 34 1.6.1 Part I: General introduction recovery strategies 34 1.6.2 Part II: Recovery strategies for nitrogen-sensitive habitats 35

1. Habitat types 35 2. Habitats of species of the Birds and Habitats Directives 35

1.6.3 Part III: Landscape ecological embedding of the recovery strategies 35 1.7 Literature 36


Chapter 2 The effects of nitrogen deposition on the structure and functioning of ecosystems 39 2.1 Introduction 39 2.2 Emission, transport and deposition of nitrogen compounds 40

2.2.1 Chemical conversions in the atmosphere 40 2.2.2 Transport and deposition 40 2.2.3 The influence of vegetation on the deposition process 44

Edge Effect 45 2.3 Different effects of nitrogen deposition 46

2.3.1 N-eutrophication 46 Shifts in competition 47 Decrease in species richness 49 Disturbed nitrogen cycle and nitrogen leaching 51

2.3.2 Acidification 53 Buffering capacity of the soil 54 Buffering mechanisms and soil acidification 55 Sensitivity to acidification: a world of difference 57 Effects of soil acidification: a complex of factors 59 Acidification of surface waters 59 Acidification and fauna 60

2.3.3 The negative effects of reduced nitrogen 60 Ammonium toxicity 61 A crucial role: the nitrification rate of the soil 62

2.4 Effects on the habitats of fauna 63 2.4.1 Cooler and damper microclimate (1) 66 2.4.2 Decrease in opportunity to reproduce (2) 66 2.4.3 Decrease in quantity of food plants (3) 67 2.4.4 Decrease in quality of food plants (4) 68 2.4.5 Physiological problems (5) 69 2.4.6 Reduction in availability of prey animals and host species (6) 70

2.5 Literature 71 Intermezzo I Biogeochemical mechanisms in wet ecosystems 80

I-1 Introduction 80 I-2 Redox processes and anaerobics 81 I-3 Biogeochemistry of nitrogen 83 I-4 Biogeochemistry of phosphorus 85 I-5 Biogeochemistry of iron 88 I-6 Biogeochemistry of sulphur 89 I-7 Hardening soft water 92 I-8 Literature 93

Intermezzo II Effects of former sulphur deposition and other sulphate loads 96

II-1 Introduction 96 II-2 Processes in supply of sulphate or presence of pyrite 97 II-3 Other causes of sulphate-rich groundwater 98 II-4 Conclusions 99


II-5 Habitat types and habitats where sulphur loads play a role 101 II-6 Literature 107

Chapter 3 Restoration measures 108 3.1 Introduction 108 3.2 Restoration measures at habitat level 116

3.2.1 Measures against acidification by adding basic substances 117 3.2.2 Anti-acidification measures by restoring the water cycle 118 3.2.3 Measures against acidification by intervening in the species composition of the tree layer 119 3.2.4 Removal of nutrients by excavation 120 3.2.5 Removal of nutrients by sod cutting 121 3.2.6 Removal of nutrients by choppering 122 3.2.7 Removal of nutrients by dredging 122 3.2.8 Removal of nutrients by (additional) mowing 123 3.2.9 Removal of nutrients by (additional) grazing 124 3.2.10 Removal of nutrients by burning 124 3.2.11 Removal of nutrients by removing litter 125 3.2.12 Intervening in the succession by coppice management and thinning 126 3.2.13 Intervening in the succession by felling trees and clearing fen banks 127 3.2.14 Intervening in the succession by digging peat trenches and restoring drying banks 128

3.3 Restoration measures at the landscape level 129 3.3.1 Measures aimed at restoring the water cycle 129 3.3.2 Measures aimed at restoring wind and water dynamics 131 3.3.3 Measures aimed at restoring connectivity 132 3.3.4 Measures aimed at restoring the food chain 133

3.4 Conclusions 133 3.5 Literature 135 Intermezzo III Additional expansion measures 142

III-1 Introduction 142 III-2 Intervention mainly on the abiotic conditions 142 III-3 Intervention mainly on the biotic conditions 144 III-4 Literature 146

Literature Part I 148 Glossary 168 Appendices Part I 173 Appendix 1 Overview of the habitats for which recovery strategies were prepared 175 Appendix 2 Composition of the review commission 178 Appendix 3 Composition of the Task Force Ecological Underpinnings (Taakgroep Ecologische Onderbouwing) 180 Appendix 4 Participants Expert meetings Part II 182 Appendix 5 Review knowledge network Development and Management Nature Quality (kennisnetwerk O+BN) Part II 186


Appendix 6 Cross tabulation of habitat types and landscape types Part III 188 Appendix 7 The members of the writing teams for each landscape type Part III 190 Appendix 8 List of external experts Part III 192 Appendix 9 Development of soil and vegetation over a period of 60 years for three deposition scenarios: expectations based on a model simulation 194 Part II Recovery strategies for nitrogen-sensitive habitats (external document) Structure Part II

1 Nitrogen-sensitive habitat types

Silty pioneer vegetation, glasswort (H1310A) Silty pioneer vegetation, sea pearlwort (H1310B) Spartina fields (Spartinion maritimae) (H1320) Salt marshes and silty grass fields, outside the dyke (H1330A) Salt marshes and silty grass fields, inside the dyke (H1330B) Embryonic dunes (H2110) White dunes (H2120) Grey dunes, lime-rich (H2130A) Grey dunes, lime-deficient (H2130B) Grey dunes, nutrient-poor soil (H2130C) Dune heath with crowberry, humid (H2140A) Dune heath with crowberry, dry (H2140B) Dune heath with crowberry (H2150) Dune with thorny scrub (H2160) Creepy willow thickets (H2170) Wooded dunes, dry (H2180A) Wooded dunes, wet (H2180B) Wooded dunes, inside dune edge (H2180C) Humid dune slacks, open water (H2190A) Humid dune slacks, lime-rich (H2190B) Humid dune slacks, decalcified (H2190C) Driftsand heathland (H2310) Inland crowberry heathland (H2320) Drift sand (H2330) Oligotrophic waters containing very few minerals of sandy plains (H3110) Oligotrophic to mesotrophic peat bogs (H3130) Hard oligo-mesotrophic waters with benthic vegetation of Chara spp. (H3140) Lakes with crab’s claw and Potamogeton (H3150) Acid fens (H3160) Humid heathland, elevated sandy soils (H4010A) Humid heathland, fenland (H4010B) Dry heathland (H4030) Juniper thickets (H5130)


Pioneer vegetation on rocky soil (H6110) Brook valley grasslands (H6120) Grasslands on soils rich in heavy metals (H6130) Calcareous grassland (H6210) Xeric sand calcareous grasslands (H6230) Nutrient-poor grassland with carnation sedge (H6410) Tall herb fringe communities, dry forest fringes (H6430C) False oat-grass and Alopecurus hay meadows, false oat-grass (H6510A) False oat-grass and Alopecurus hay meadows, meadow foxtail (H6510B) Active raised bogs, high raised bogs (H7110A) Active raised bogs, small heathland moors (H7110B) Recovering raised bogs (H7120) Transitional and quaking bogs, quaking bogs (H7140A) Transitional and quaking bogs, sphagnum reed beds (H7140B) Pioneer vegetations with white beak-sedge (H7150) Cladium mariscus marshes (H7210) Petrifying springs with tufa formation (H7220) Calcium-rich springwater-fed fens (H7230) Woodrush-beech forests (H9110) Beech-oak forests with Ilex (H9120) Oak-hornbeam forests, higher arenaceous soils (H9160A) Oak-hornbeam forests, undulating landscape (H9160B) Old oak forests (H9190) Bog woodland (H91D0) Humid alluvial forests, ash-elm forests (H91E0B) Humid alluvial forests, riparian forests (H91E0C) Dry riparian hardwood forests (H91F0) Literature Part II-1

2. Nitrogen-sensitive habitats

1. Permanent spring & slow-flowing upper course 2. Isolated meander and peat trench 3. Poorly buffered ditch 4. Acid fen 5. Large-sedge swamp 6. Marsh-marigold meadow of stream valleys 7. Marsh-marigold meadow of turf and clay 8. Wet, moderately nutrient-rich grassland 9. Dry agrostis field 10. Dog’s-tail grass & multifloral meadow-bird grassland of the sand and fen area 11. Dog’s-tail grass & multifloral meadow-bird grassland of the riverine and marine clay

area 12. Edge, mantle and dry thicket of the dunes 13. Forest on poor sandy soils 14. Oak and beech forest on loamy arenaceous soils


Literature Part II-2 Appendices Part II Appendix 1 Habitats Directive species and the sensitivity to nitrogen of the habitat

1. Vascular plants 2. Mosses 3. Molluscs 4. Dragonflies 5. Butterflies 6. Beetles 7. Fish 8. Amphibians 9. Mammals

Appendix 2 Birds Directive species and the sensitivity to nitrogen of the habitat Appendix 3 List of target nature types, which are used in appendices 1 and 2 for the characterization of the habitats Part III Landscape ecological embedding of the recovery strategies (external document) Structure Part III Fauna in landscape gradients Table 1: the distinguished landscapes and gradients Table 2: key to determining the gradient type Landscapes and gradient types Hills 1. Slopes with limestone outcrops 2. Slopes without limestone outcrops Dry sand landscape 1. Shifting sands landscape 2. Ground moraine- and terraces landscape 3. Moraine landscape 4. Cover sand landscape Wet sand landscape 1. Raised bog without alkaline-rich fen 2. Raised bog with alkaline-rich fen 3. Hollows with perched water table 4. Acid hollows without perched water table 5. Very weakly and weakly buffered hollows 6. Alkaline-rich non-draining hollows


Stream valleys 1. Stream valleys with local seepage in the upper course 2. Stream valleys with regional seepage in the middle course 3. Flooded stream valleys of the lower course 4. Relief-rich stream valleys of the higher sandy soils with alkaline-poor sloped fens 5. Relief-rich stream valleys of the higher sandy soils (lateral moraines, terrace and valley edges) 6. Relief-rich stream valleys in the hills River landscape 1. Small sand rivers 2. Floodplains in the transport zone of large rivers (river terraces Meuse) 3. Floodplains in the deposition zone of large rivers (Upper Rhine/IJssel/Lower Rhine and Bedijkte Maas) 4. Basins (large rivers inside the dike) 5. Lower course rivers with weak tide 6. Lower course rivers with strong tides (freshwater tidal areas) Bog landscape 1. Fens with supply of buffered water from the higher sandy soils 2. Fens bordering the river and sea clay landscape 3. Brackish fens Dry dunes 1. Growing, lime-rich dunes 2. Growing, lime-poor dunes 3. Eroding, lime-rich dunes 4. Eroding, lime-poor dunes 5. Eroding, lime-rich dunes: landscape with seaside villages Wet dune and coast landscape 1. Lime-rich dune valleys with sweet-salt gradient (Groen Strand) 2. Lime-rich dune valleys in lime-rich dunes 3. Lime-rich dune valleys in lime-rich dunes 4. Decalcified inner dune edge with lime-rich groundwater 5. Lime-rich shallows in closed off sea branches 6. Tidal marshes and salty grasslands inside the dike



Part I General introduction to recovery strategies: policy, knowledge and measures Foreword The first part (Part I) is the general introduction to the strategies by habitat and provides basic information about the effects of nitrogen deposition and the underlying biogeochemical processes. This introductory report explains the effects of nitrogen deposition on the structure and the functioning of ecosystems. Following this, it discusses the remedial measures to minimise the adverse effects of nitrogen deposition. Part I consists of three chapters and three intermezzos: Chapter 1 General introduction

• The cause for the recovery strategies • The policy context • Nature and purpose of the recovery strategies: effect-oriented measures • Description of the method

Chapter 2 Effects of nitrogen deposition

• Emission, transport en deposition of nitrogen compounds • Different effects of nitrogen deposition: eutrophication, acidification, negative

effects of reduced nitrogen • Effects on fauna

Intermezzo I Biogeochemical mechanisms in wet ecosystems Chapter 3 discusses the specific remedial measures. There are often also other biogeochemical mechanisms underlying the various recovery measures for damp and wet ecosystems. These are described in intermezzo I as an introduction to Chapter 3. Intermezzo II Effects of former sulphur deposition and other sulphate load Although the atmospheric sulphur deposition is now much smaller than before, remnants could still be present or stream into the bottom of fens, peat bogs and aquatic and terrestrial environments under the influence of (local) seepage. Effects of this (former) deposition and due to other causes of sulphate-rich groundwater are discussed in Intermezzo II. Intermezzo III Additional expansion measures The measures currently included in the recovery strategies focus mainly on recovery. In addition to the measures listed in parts II and III, there are other conceivable expansion measures that could mitigate the decrease in habitat surface area due to nitrogen deposition. In this intermezzo, these additional measures are roughly worked out. Chapter 3 Recovery measures

• Recovery measures at local scale • Recovery measures at landscape scale


These three chapters form the introduction and background information for the other two parts (Part II: Recovery Strategies for habitats; Part III: Landscape ecological embedding of the recovery strategies).


1 General introduction Smits, N.A.C., D. Bal, R. Bobbink, H.F. van Dobben, J.H.J. Schaminee, A.J.M. Jansen & D. Brunt 1.1 BACKGROUND & AIM The biodiversity of the earth is found in natural and semi-natural ecosystems, both in aquatic and terrestrial environments. Human activities threaten the structure and functioning of these ecosystems in many ways, and thus also the natural variety of plant and animal species. One of the main anthropogenic threats is increased air pollution by both reduced and oxidized nitrogen compounds in the form of NHx and NOy (e.g. Sala et al. 2000; Galloway & Cowling 2002; Bobbink et al. 2010a). In the Netherlands it is recognized that high nitrogen deposition is a major limiting factor maintaining or restoring favourable conservation status in sensitive natural areas. To cope with this nitrogen problem, the government has chosen a Programmatic Approach Nitrogen (PAN) aimed at allowing sustainable economic development and recovery to go together with the realisation of the nature objectives as set at European level in the context of Natura 2000 (Ministry of Agriculture, Nature and Food Quality 2010). Nitrogen (N) itself is not a problem. On the contrary, it is one of the essential building blocks for life on earth. The problem lies in the extent to which this element is added to our environment in reactive form. For centuries, only organic fertilizer (manure, etc.) was used to increase agricultural production. Later, guano or ‘Chile saltpeter', recovered from bird droppings and consisting mainly of NaNO3, was used. This situation only changed after the invention of synthetic conversion of the inert molecular nitrogen (N2) into the reactive ammonia by Fritz Haber in 1909 and the industrial scaling of that by Carl Bosch (both got the Nobel Prize). This 'Haber-Bosch process’ made large-scale fertilizer production possible and its use very much increased after 1920. In the course of the twentieth century, increasing amounts of fertilizer were used to increase agricultural production. Along with a refinement of agricultural varieties, this, for example, led to an increase in grain yields from some 1,500 kg / ha about 1950 to some 10,000 kg / ha nowadays (Strijker 2000). The downside was that more and more nitrogen disappeared from the agricultural system to ground or surface water or through air emissions. The purpose of the recovery strategies is to gather up-to-date and well-founded knowledge of all effect-oriented measures, which contribute to preserving and restoring nitrogen-sensitive habitats (habitat types and species) in relation to atmospheric nitrogen deposition. The documents, which are drawn up under the PAN, are applicable at the local level in the specific Natura 2000 areas and provide a basis for judicial reviews. 1.2 THE DIFFERENT EFFECTS OF NITROGEN DEPOSITION AND THEIR CONNECTION The availability of plant nutrients is a factor, which is very important for the composition of the vegetation. Nitrogen compounds are limiting for plant growth in many natural and semi-natural ecosystems in the temperate and boreal zone of Europe. Quite a few plant species have adapted to nutrient-poor conditions and can only successfully continue to exist on soils with low N levels. The effects of an excessive supply of nitrogen compounds


on ecosystems are diverse and complex (eg Bobbink & Lamers 1999; Kros et al. 2008) (Diagram 1.1).

Diagram 1.1 Diagram with an overview of the ecological effects of N deposition (according to Bobbink & Hettelingh 2011). Toename = increase Afname = decrease Toename N-depositie = increase of N-deposition Verstoring en stressfactoren = disruption and stress factors Directe toxiciteit = direct toxicity Beschikbaarheid van N = availability of N N-mineralisatie = N-mineralisation Productiviteit = productivity Strooisel productie en kwaliteit = plant litter production and quality Bodemverzuring = soil acidification Vatbaarheid voor pathogenen en herbivoren = Susceptibility to pathogens and herbivores Concurrentie om licht = competition for light N gelimiteerd/ P gelimiteerd = N-limited / P-limited Onderdrukte nitrificatie, verlies van basische kationen = Suppressed nitrification, loss of alkaline cations Ophoping van ammonium en toename van metalen = Accumulation of ammonium and increase of metals Soortenrijkdom = species richness


The consequences that may occur concern 1) Direct toxicity of high concentrations of gases on individual plant species, 2) Eutrophication by a gradual increase in N availability; 3) Acidification of soil and water; 4) Negative effects of the increased availability of reduced N (ammonium); 5) Increased susceptibility to secondary stress factors, such as fungal and insect pests and frost or drought damage, and finally 6) Changes in the chemical composition (e.g. amino acid composition) of plants under the influence of a higher N availability. Therefore the quality of plants as food for herbivores changes with various effects higher in the food chain. The main consequences are explained below. 1.2.1 DIRECT TOXICITY OF GASES ON INDIVIDUAL PLANT SPECIES At high concentrations of air pollution gaseous components can have direct toxic effects on plants. However, the current concentrations of NH3, NOx and SO2 in the Netherlands are so low that this hardly occurs, and this mechanism will therefore not be discussed further here. Fungi, lichens and mosses in particular are very sensitive to direct toxicity of SO2 and perhaps also NOx. The decrease of concentrations of these substances during the last decades led to a significant recovery of the diversity of, in particular, lichens growing on trees. 1.2.2 EUTROPHICATION BY GRADUAL INCREASE OF THE N-AVAILIBILITY An increase in atmospheric nitrogen deposition in a previously unburdened area initially leads to an increase in the availability of nitrogen in soil or water, and thus to an increased uptake of nitrogen compounds by the vegetation. This process is called eutrophication. Due to an increased supply and accumulation of N compounds, the availability of nitrogen will gradually increase. This leads to supplanting of less competitive species by nitrophilous species. In many cases this is at the expense of characteristic species, since a large part of the species in semi-natural and natural ecosystems is adjusted to a low nitrogen availability in the soil. An increased supply of nitrogen can cause a sharp decline in species diversity, especially in nutrient-poor and moderately nutrient-rich systems (eg Bobbink et al. 1998; Clark & Tilman 2008). With an increased supply of nitrogen, the number of species could slightly increase on extremely nutrient-poor soils, but the original and characteristic vegetation that was adjusted to the extreme situation, disappears. 1.2.3 ACIDIFICATION OF SOIL AND WATER Acidification, or reduction in the buffering capacity, is a long-term process that also occurs naturally through carboxylic acid or organic acids, but which can be accelerated (very strongly) through the supply of acid or acidifying substances from the atmosphere. Depending on the soil composition, this complex process can lead to a lower pH, increased leaching of cations (calcium, magnesium or potassium), increased concentrations of toxic metals (particularly aluminum), and changes in the ratio between nitrate and ammonium in the soil (Van Breemen et al. 1982; Ulrich 1983, 1991). In this situation, plant species which are resistant to such acidic conditions will dominate and many species from an environment with a more neutral pH will disappear.


1.2.4 NEGATIVE EFFECTS OF INCREASED AVAILABILITY OF REDUCED N In many areas with high N-deposition, reduced N has a large part in the total N-deposition. This can result in ammonium being the predominant N-form in the soil. This is especially true in soils with a naturally low conversion of nitrate into ammonium (pH < 4.5) or when the soil is acidified by atmospheric deposition. The conversion of nitrate into ammonium is a microbial process, which is called nitrification. Elevated concentrations of ammonium in the soil or in the water can have all kinds of negative effects on plant growth. These effects are greatest in areas with formerly moderately buffered soil conditions (pH 4.5 - 6.8) (Stevens et al 2011). Precisely such conditions are often rich in Red List species, so that their number will soon decrease (e.g. Kleijn et al. 2008). 1.2.5 INCREASED SENSITIVITY TO SECONDARY STRESS FACTORS AS PESTS AND FROST AND DROUGHT DAMAGE By increased atmospheric deposition of nitrogen compounds, the sensitivity of plants to attack by pathogens may be greatly affected. Air pollution can reduce the vitality of species, making them more susceptible to attack by fungi, bacteria, viruses or insects. Also the increased nitrogen levels in the leaves or roots can cause increased damage by herbivore (pest) insects such as the heather beetle (Berdowski 1987). Due to changes in the physiology or growth, the tolerance of plant species to drought or frost can also change. 1.2.6 LONG-TERM EFFECTS The effects of deposition for the long-term can be estimated by means of model simulation. The model SMART-SUMO (Kros 2002 Wamelink et al. 2009) contains quantitative descriptions of soil and vegetation processes as they happen occur in the course of time. Such processes are, for example, weathering, nutrient uptake, growth, litterfall, etc. The model distinguishes different 'functional types' (e.g. herbs, shrubs, trees) that compete for nutrients (in this case only nitrogen) and light. Based on the biomass per functional type, statements can be made about the vegetation structure and therefore changes over time. Appendix 9 provides a detailed description of SMART-SUMO and examples of model simulations.

Diagram 1.2: simulated N availability at three deposition levels (700, 1500 and 3000 mol ha-1j-1 for respectively the lower, middle and upper line), and the critical (maximum admissible) value for the given soil - vegetation combination (dry grassland on loamy soil) (dotted line). This critical value is merely approximate and varies in reality by vegetation type (association). See Appendix 9 for technical details.


Diagram 1.3: simulated soil pH at three deposition levels (700, 1500 and 3000 mol ha-1j-1 for respectively the upper, middle and lower line), and the critical (minimum admissible) value for the given soil - vegetation combination (dry grassland on poor sandy soil) (dotted line). This critical value is merely approximate and varies in reality by vegetation type (association). See Appendix 9 for technical details.

Important preconditions for preventing vegetation types under stress of deposition are the pH of the soil and the availability of nitrogen: this is the amount of nitrogen that becomes available for the plant in an ingestible form (NH4 or NO3) per unit of time. This available nitrogen comes from mineralization of organic matter in the soil and from deposition. Preconditions for both pH and nitrogen availability can be determined by vegetation type with measurements in places where the relevant vegetation types occur. In a simulation run, the development of a large number of relevant variables was estimated over a period of 60 years at various combinations of vegetation type, soil type and hydrology. This was done for three deposition levels. Details about this are given in Appendix 9. Diagram 1.2 shows an example for the development of the nitrogen availability. Although the N-availability appears to decrease slightly on the long-term, only at the lowest deposition (700 mol ha-1j-1 = about 10 kg N ha-1j-1) it remains below the critical value at any time. Please note that the critical level of nitrogen availability is well above the CDV, because a part of the available nitrogen comes from mineralization, and thus does not count in the CDV. Diagram 1.3 shows an example of the development of the pH. The pH has a rising trend at all deposition levels, and it seems that it will eventually transcend the critical level at the highest deposition, although this happens much sooner at a low deposition level. Apart from that, this data should not be interpreted too absolutely, because the initial pH is set fairly low and by weathering - even in poor sand - some neutralization will occur in the end. When interpreting the simulated CDV one should realise that the CDV is that value at which, based on current average conditions across the Netherlands, in the long term (for the simulated values in Van Dobben & Van Hinsberg 2008 this is 100 years) either the critical pH is undershot or the critical N-availability is exceeded. Both conditions can thus determine the final CDV, but which of these two will varies by vegetation type.


1.3 CRITICAL DEPOSITION VALUES (CDV) Critical deposition values (CDV) were used to define which habitats could be considered as nitrogen-sensitive in this project. The critical deposition value for nitrogen was defined as "the limit, beyond which the risk can not be excluded that the quality of the habitat type is significantly affected as a result of the acidifying and / or fertilizing influence of the atmospheric nitrogen deposition" (Van Dobben & Van Hinsberg 2008). The critical deposition values, which are taken as a starting point in the recovery strategies, are established in Van Dobben et al. (2012) specific to habitat types in the Netherlands. In that report, several knowledge sources regarding critical deposition values were combined using a fixed protocol (Van Dobben et al. 2012). Those knowledge sources are:

- empirical critical deposition values for nature types according to the EUNIS classification, with a bandwidth, as published in Bobbink & Hettelingh (2011) and adopted by the UN-ECE (of which the Netherlands is also a member);

- model-specific critical deposition values per vegetation type according to Van Dobben et al. (2012);

- expert opinion of the authors In short, it means that the concrete CDV for a habitat (sub) type must lie within the bandwidth of a comparable EUNIS-type. The concrete CDV is (under that precondition) the average of the model-specific critical deposition values of the constituent types of vegetation. The expert opinion was applied for the selection of useful model results (also for those cases in which no empirical values were available) and for adding critical deposition values for habitat types for which no model results were available. Habitats of protected species sometimes also encompass types of nature, which are not covered by habitat types. In order to still be able to determine a CDV, Bal et al. (2007) was used, which exactly follows the same procedure for the determination of critical deposition values for target nature types. The definition of CDV therefore applies mutatis mutandis also for (elements of) habitats of species, called 'habitat of the species' in the regulations. In total 45 of the 51 habitat types have a CDV which is lower than 2400 mol of N / ha / year. These habitat types are considered ‘sensitive to nitrogen deposition' (Van Dobben et al. 2012) and for all of these types a recovery strategy is outlined in Part II. In addition, 49 protected species have a habitat that is (fully or partially) nitrogen-sensitive. The habitat types largely cover these habitats, but for 14 (additional) nitrogen-sensitive habitats a recovery strategy was prepared. Appendix 1 provides an overview of the habitats for which recovery strategies were prepared.


1.4 POLICY CONTEXT 1.4.1 NATURA 2000 Natura 2000 is the name of a European network of nature areas, in which important flora and fauna occur, seen from a European perspective. Through Natura 2000 we want to protect this flora and fauna. The Natura 2000 sites in the Netherlands contain nature of European significance and they have a strict protection regime. The European network of Natura 2000 sites has been established following the Habitats Directive (1992) and the Birds Directive (1979). It concerns areas in which many habitat types and species occur that must be protected on a European scale. Because of the protection regime for these areas different functions, such as housing, recreation and business, are regularly caught up in conflict with the natural values, which need protection. The stakeholders come forward with questions about the goals and measures required by the Birds and Habitats Directives and the opportunities, which are left open for all kinds of activities. The starting points of the Birds and Habitats Directives are that measures are implemented which are ecologically necessary to prevent a deterioration of the areas and which eventually restore and maintain the favourable conservation status of species and habitat types which need to be protected. Compliance with these guidelines is a major challenge, as many habitat types and species have an unfavourable conservation status in the Netherlands and because the Netherlands is a densely populated and economically active country.

CONSERVATION OBJECTIVES HABITAT TYPES Within Natura 2000, there are four types of conservation objectives for the habitat types and habitats of species: quality preservation, area conservation, quality improvement and area expansion. In all cases, preservation or improvement is pursued. In some cases this may be about maintaining moderate quality. See Box 1 for the definition of quality within the policy context. The conservation objectives for each habitat type are set in designation decrees for the individual Natura 2000 sites (http://www.synbiosys.alterra.nl/natura2000). For each Natura 2000 site a management plan is set in which the conservation objectives are then further elaborated.


BOX 1. QUALITY OF HABITAT TYPES For the interpretation of the terms mentioned, it is essential that the definition and quality aspects of the habitat types, as published in the Natura 2000 profile document (Ministry of Agriculture, Nature and Food Quality 2008), be taken as a basis. In the profiles, four quality aspects of habitat types have been elaborated with respect to content: vegetation types, abiotic preconditions, typical species and other characteristics of good structure and function. The summary of the profile document provides an explanation of these aspects and their development. The text below, which has previously been prepared by the Ministry of Agriculture, Nature and Food Quality, explains the meaning of the terms in the designation decrees. The terms themselves are an elaboration of the European legal framework. The definitions and articles from the Habitats Directive serve as the legal framework for the quality aspects of habitat types in the profile document. In accordance with the definitions of the Habitats Directive, the quality of habitat types is about 'structure and function' and 'typical species' (Article 1e). Article 6, paragraph 2 refers to 'ecological requirements' of habitat types. The habitat types themselves are linked to vegetation units through a European "Interpretation Manual". VEGETATION TYPES Maintaining quality at local level for vegetation types means maintaining the level of quality, elaborated in the degree of variation in the vegetation types and their distribution over the surface; under these conditions one type of vegetation may be replaced by another. Maintaining quality for vegetation types concretely means: o no decrease in the number of good vegetations (indicated by 'G' in the profile

document); o no decrease in the surface jointly occupied by the good vegetations; o no decrease in the number of moderate vegetations (indicated with an 'M' in the

profile document) unless that decrease benefits the good vegetations; o no decrease in the surface jointly occupied by the moderate vegetations, unless

that decrease benefits the good vegetations. Note: sometimes a characteristic species makes use of vegetation, which is seen as moderate vegetation (e.g. a Viper in a Purple Moor Grass vegetation within H4010 – Wet heaths). In that case, that vegetation may be considered good on that location (as it contributes to a good quality).

Improving quality means that a shift occurs from moderate to good vegetation: in number (variation) and / or surface.


ABIOTIC PRECONDITIONS Maintaining quality at area level for abiotic preconditions maintaining the variation within the core range of each aspect and its distribution over the surface; the various aspects are not interchangeable. Conservation concretely means: o for each of the six abiotic preconditions, the surface area that complies with the

core range does not decrease; o for each of the six abiotic preconditions, the number of classes of the core range

does not decrease (therefore no narrowing of the abiotic variation occurs at class level);

o the surface complying with the additional range does not decrease, unless that decrease benefits the surface complying with the core range;

o for each of the six abiotic preconditions, the number of classes of the additional range does not decrease, unless that decrease leads to an increase in the number of classes in the core range.

Improving quality means that a shift occurs from additional range to core range for the different factors: in number of classes (variation) and / or surface. The vegetation types and characteristic species can serve as a good indicator of abiotic quality. When developing conservation objectives in management plans, this connection can be used. When the vegetation types and characteristic species are determined in size and space, this also means that the associated abiotic preconditions can be derived (to some extent). This can be used to localize the desired quality of habitat types (in terms of abiotic aspects such as acidity and the like). CHARACTERISTIC SPECIES Maintaining quality at area level for characteristic species means preservation of the present variation in characteristic species and their average distribution in the area, the characteristic species and their densities are interchangeable. Conservation concretely means: o the total number of different characteristic species that was present at the time

of designation of the area does not decrease; o the possible disappearance of a characteristic species can be compensated by

the establishment of another characteristic species; o the extent of spread of the charasteric species (as a whole) in the habitat type

does not decrease on average; o if the national conservation of a characteristic species hinges on the

conservation of this species in a given area, then the conservation of that particular species in that area is necessary.

Improving quality means that more characteristic species settle in the area and / or are found more scattered in the area.


At area level an ecologically relevant level of scale can be chosen at which the average spread of characteristic species can be viewed. For example, the presence over one square kilometre. OTHER CHARACTERISTICS OF GOOD STRUCTURE AND FUNCTION Maintaining quality at area level for the other characteristics of good structure and function means continuing to meet the mentioned conditions (if they were already met); the various aspects are not interchangeable. Improving quality means better compliance with these conditions.

Note: If "preferably ..." is stated next to a particular characteristic feature, then it is only a suggestion for the management (plan) and there is no need for it to be tested (the characteristic feature is not essential for the quality).

1.4.2 NITROGEN DEPOSITION AND NATURA 2000 Nitrogen has a relevant effect to Natura 2000 if the quality and / or the surface of habitats (habitat types and species of the Birds and Habitats Directives) is affected. To that end, the effects need to be compared with the quality aspects, as mentioned for habitat types in Box 1. Summarised that means: 1. Nitrogen deposition causes acidification and / or eutrophication in the soil and in the

water. This means that the quality aspects 'acidity' and 'nutrient-richness’, part of the 'abiotic conditions', are adversely affected. The surface with optimal values (classes of the 'core range') decreases and is replaced by suboptimal values (classes of the ‘additional range’) or even values that are completely outside the range of the habitat type.

2. Deterioration of the quality of soil and water then causes deterioration of the quality aspect ‘vegetation types’. The surface with good quality vegetations decreases and is replaced by vegetations of moderate quality. Also, the ecological variation in the form of the number of different vegetations can decrease. The deterioration may take such forms that vegetations arise that are not part of the definition of the habitat type. In that case, the surface of the habitat type decreases.

3. In addition, deterioration of the quality of soil and water also partly causes deterioration of the quality aspect 'other characteristics of a good structure and function’. That is particularly true where there is an overlap with point 2 (deterioration of the vegetation structure or no longer meeting the optimal functional range). Sometimes it is about additional aspects (such as reduction of dynamics in certain habitat types). Some of these characteristic features are not adversely affected by nitrogen.

4. Deterioration of the aspects mentioned under the first three points, often manifests itself in the disappearance of characteristic species (both plants and animals), which also determine the quality of the habitat type. However, some characteristic species do not


react negatively to nitrogen, because they only depend on habitat characteristics that are not affected by nitrogen.

Also habitats of species (plants, birds and other animals) may be affected by nitrogen deposition. This works, in fact, in the same way as the disappearance of characteristic species from habitat types (the necessary qualities of habitats are only not described as categorically as those of the habitat types). In principle, the recovery strategies for habitat types can therefore also be used for these species, insofar those habitat types are part of the habitats. The habitat of most species consists of several types of nature, which often also have varying degrees of sensitivity to nitrogen. For a number of species, a significant portion of the habitat is even not at all sensitive to nitrogen. When implementing recovery strategies this should be given attention. 1.4.3 PROGRAMMATIC APPROACH NITROGEN (PAN) Within the PAN the local nitrogen deposition (both current as projections for 2020 and 2030) is placed next to the critical deposition value of the nitrogen-sensitive habitat types. Using the recovery measures, which can be used on habitat and landscape level, it is checked whether “scientifically speaking, there reasonably is no doubt that the conservation objectives are not jeopardised, whereby preservation is guaranteed and, if relevant, an improvement or expansion can also take place”. This formulation is based on statements by the Dutch Council of State, whereby permit applications were held to the light of the Nature Protection Act (Natuurbeschermingswet). The fact that “scientifically speaking there may reasonably be no doubt", among other things means that the best available scientific knowledge and views should have been used in determining the recovery measures.

For the PAN to work properly, three instruments, with which the foundation is laid to determine whether and how much space there is to issue permits for new economic activities, will soon need to be used in the Natura 2000 areas.

Those three instruments are: • the calculation tool Aerius to map the nitrogen deposition per area, including future

scenarios; • the web tool recovery strategies, which helps the authors of the management plans to

find the proper measures to maintain and restore nitrogen-sensitive habitats; • a tool to calculate the development space, both national and provincial and per area. 1.4.4 PRECONDITIONS OF THE PROJECT DEFINITION HABITAT TYPES The Dutch habitat types (as defined in the profile documents) are the Dutch interpretation of the European definitions. These are a starting point for the report and these definitions have been accepted by both the European Commission and the Dutch Council of State.


CRITICAL DEPOSITION VALUES In this report the CDV, which is applied in the Netherlands (Van Dobben et al. 2012), is used, with reference to the international review of the report by Bobbink & Hettelingh (2011). IMPACT-ORIENTED MEASURES VS SOURCE-BASED MEASURES The ecological underpinnings (this project) only address the impact-oriented measures. Source-based measures are not included in this assignment for the ecological underpinnings and are discussed elsewhere in the PAN (Aerius, see also 1.3.3). ABIOTIC PRECONDITIONS The abiotic preconditions (paragraph 2: acidity, nutrient-richness and moisture levels) are given as a precondition in the project. Hereby, the study of Runhaar et al (2009) is applied in all cases. In this study, preconditions are calculated based on the vegetation types, which are mentioned in the profile documents (definition of habitat types). 1.5 RECOVERY STRATEGIES The information from this part of the PAN (the ecological underpinnings) is intended to help the writers of the management plans to come to an optimal package of management measures for the effects of atmospheric nitrogen deposition. The recovery strategies hereby offer an, as far as possible complete, overview of impact-oriented measures for a habitat type or habitat. The knowledge from the individual recovery strategies (Part II and III) must be applied in a specific area. For this local application, the user should carry out some preparatory work: the area-specific information needs to be added by the user. Information on the location, differences in space and time and environmental factors (eg air and groundwater quality) are, in addition to eg historical analyses with which the trend can be determined, the basis for a landscape ecological analysis concentrated on the area (LESA; Van der Molen 2010). From this area-specific information the package of recovery measures must then be chosen, which specifically has the best effect for the area concerned, with respect to stopping the decline and achieving the conservation objectives. 1.5.1 IMPACT-ORIENTED MEASURES The excessive nitrogen deposition intervenes mainly under two area conditions, namely the basicity or buffering capacity of soil and groundwater, and the availability of nutrients and minerals for the plants and their dependent fauna (Diagram 1.4). The nitrogen deposition creates more acidic (acidity) and nutrient-richer (eutrophication) conditions. In order to cope with these attacks, two main strategies are available in connection with restoration, namely (1) removal of the extra accumulated nitrogen from the by N-deposition eutrophicated systems, and (2) increasing the buffering capacity in acidified systems, such


that the soil adsorption complex is recharged with leached cations (especially Ca-K-Mg) and the weathering of aluminium hydroxides is stopped. Removal of the extra accumulated nitrogen from ecosystems can, depending on the system, happen in several effective ways, such as through making extra hay, turf cutting or dredging. These measures are especially (well) feasible in semi-natural plant communities. To reverse the acidification process two groups of measures are basically available. On the one hand a direct gift of buffer substances through liming (after turf cutting) in dry ecosystems, on the other hand restoration of the flow of bicarbonate-rich and basic and cation-rich ground or surface waters. Depending on the landscape, the second recovery strategy is carried out in different ways in surface water or groundwater affected sites, for example by increasing the influence of buffered ground water through the recovery of seepage into the root zone, flood with buffered, clean surface water or liming of the infiltration area. An insight that has emerged with increasing emphasis in recent years is that sustainable recovery of the abiotic conditions in many cases requires an approach on landscape scale. In addition, it has become clear that successful recovery of the abiotic conditions does not always lead to a return of the desired species. In our highly fragmented landscape species appear to have great difficulty reaching the restored places, partly because the suitable habitats are too far apart, partly because the distribution mechanisms (disperse vectors) no longer function (Ozinga 2007). Also the importance of heterogeneity, whereby the various life stages and environmental needs of the animals are served within a small area, requires intact landscapes with a full range of successional stages of the there occurring systems. In natural landscapes this heterogeneity remains to exist through the occurrence of dynamics by wind, fire, ground and surface water and large herbivores and their predators. In our semi-natural landscapes, the role of these processes has been largely taken over by humans.


Diagram 1.4 Schematic rendering of the effects of nitrogen deposition and the possible recovery measures on landscape and area scale. The nitrogen deposition intervenes on two main processes, namely acidification and eutrophication, both on area scale and landscape scale. Eutrophication and acidification are as such directly influenced by factors such as desiccation, rigidity (loss of dynamics) and aging (succession). It is possible to compensate the effects of nitrogen deposition, whereby different measures can be taken at landscape and area level. In the diagram this is indicated by arrows, decreasing and increasing in size. Stikstofdepositie = nitrogen deposition Vermesting = eutrophication Verzuring = acidification Verdroging = desiccation Verstarring = rigidity Veroudering = aging Landschap = landscape Standplaats = local area Herstel wind- en waterdynamiek = restoring wind and water dynamics Herstel connectiviteit / behoud isolatie = restoring connectivity / maintaining isolation Herstel waterhuishouding = restoring hydrology Herstel voedselketen / biologische netwerken =restoring food chain / biological networks Herstel basentoestand = restoring base situation Verwijderen nutriënten via biomassa = Removing nutrients through biomass Verwijderen nutriënten via bodem = Removing nutrients through soil 1.5.2 OPERATION OF THE RECOVERY STRATEGIES IN CONNECTION WITH THE PAN The recovery strategies list the possible impact-oriented measures with respect to the atmospheric nitrogen deposition. To determine whether it is indeed necessary to take additional recovery measures in a particular area in connection with the PAN, the checklist below (Table 1.1) was developed. To then arrive at measures to manage the effects of atmospheric nitrogen deposition, an individual recovery strategy for each of the 55 nitrogen-sensitive habitat(sub)types has been inserted in Part II. It builds on explorations by the Bargerveen Foundation (headed by P.C. de Hullu and J. Vogels). In addition, 14 recovery strategy documents have been prepared for nitrogen-sensitive habitats for species of the Birds and Habitats Directives. The list is given in appendix 1. Table 1.1 Checklist conservation goals, state, CDV and recovery measures in connection with the PAN.

Goal State* CDV Recovery measures PAN

Maintaining quality

Good CDV not exceeded no

CDV exceeded, but there are no effects of N-deposition

not yet


Moderate CDV not exceeded not through PAN


not yet

CDV exceeded and there are effects of N-deposition

yes

Maintaining surface

CDV not exceeded not through PAN


not yet


yes

Improving quality

Moderate CDV not exceeded not through PAN


not yet


yes

Expanding surface

CDV not exceeded not through PAN

CDV exceeded yes

• To be derived from the criteria from the profile document: vegetation; abiotic preconditions; characteristic species; other characteristics of good structure and function.

1.6 METHOD The information for the chapters in the three parts were assembled by different (combinations of) authors. Here, various methods were followed. This section outlines how the texts have been established. 1.6.1 Part I: General introduction A large number of experts worked on the realization of the general chapters (Part I). Led by the first author, each chapter was prepared in draft, after which it was submitted to the Advisory Committee of the knowledge network Development and Management Nature Quality (Adviescommissie van het kennisnetwerk Ontwikkeling en Beheer Natuurkwaliteit). The comments from the knowledge network Development and Management Nature Quality and from the area processes (where the draft texts have already been used) were then processed into a final draft, which was sent to the review committee (see appendix 2 for its composition). This final concept was adjusted based on findings by the review committee into the present 'version 1.0'.


1.6.2 Part II Recovery strategies for nitrogen-sensitive habitats 1. Habitat types To realise the current recovery strategies, the following process was followed, guided from the beginning by the Task Force Ecological Underpinnings (Taakgroep Ecologische Onderbouwing, see appendix 3 for the commission’s composition). Starting point are the 55 habitat types (including subtypes), as mentioned in Chapter 1. These habitat types were edited into a so-called '60%' version according to a fixed format, mostly led by one of the authors of the project team. Subsequently, this ‘60% version’ was upgraded to a ‘80%’ version through consultation of experts (mostly through expert meetings, see appendix 4 for the complete list of experts). A number of specific types were agreed through bilateral consultations with experts (researchers / managers). The '80% 'version was then submitted to the knowledge network Development and Management Nature Quality for a quality review. Here, the habitat types, associated with the concerning landscapes, were submitted to the individual experts team (see appendix 5). The comments from the knowledge network Development and Management Nature Quality (individual expert teams) and from the area processes (where the draft texts have already been used) were then processed into a final draft, which was sent to the review committee (see appendix 2 for its composition). As many consulted experts as possible have been included as co-authors. This final concept was adjusted based on findings by the review committee into the present 'version 1.0'. 2. Habitats of species of the Birds and Habitats Directives Although in recent years, the focus has increasingly been on the effects on habitat types, legal precedents have shown that the effects on (conservation objectives of) species of the Birds and Habitats Directives and their habitats need to be determined. Because for habitats there was no systematic classification, which could be linked to the nitrogen sensitivity, a separate analysis was carried out for this aspect.

This analysis was started later than the habitat types and took place in phases. In step 2 of the Habitat types (80% version), the new habitats were developed (initiator: Marijn Nijssen) and the species of the Birds and Habitats Directives were inserted into existing habitat type texts. These were submitted to specific fauna experts and on the basis of these 'version 1.0' was drawn up. 1.6.3 Part III: Landscape ecological embedding Eight landscapes were defined (Wet sand landscape, Dry sand landscape, Stream valleys, Wet dunes, Dry dunes, Bogs, Hills, and Rivers including estuaries). Within each landscape, two to six gradient types were distinguished, and for each gradient type the habit types, which occur there were determined. Appendix 6 shows a cross tabulation of habitat types and gradient types per landscape. For each landscape a writing team was formed of research and management experts. The writing teams have drawn up the descriptions of the gradients in mutual consultation and according to a fixed format.


After an editorial debate, these descriptions were first marginally reviewed by the OBN expert teams on the concerned landscapes (together with the recovery strategies of the habitat types), and then by two external experts per landscape. The members of the writing teams can be found in the text as authors alongside the separate landscape types and are added as appendix 7. The list of external experts is provided in appendix 8. After processing the comments of the external experts, the core team tested the texts for internal consistency between the gradients within each landscape (especially for the bottlenecks and recovery measures: have these been treated in a uniform manner for all gradients for which they are relevant? and do the recovery measures solve the bottlenecks mentioned for a gradient type?) and for consistency with Part II (are the recovery measures mentioned for a gradient not inconsistent with the remedial measures specified for the habitat types present in this gradient?). Then the texts were submitted to the Program department Natura 2000 of the Ministry of Economic Affairs, Agriculture and Innovation for comments. After processing these comments, the texts were presented to the initiators of each writing team for final agreement. The texts, which were agreed by these initiators, are presented to the international review committee. 1.7 LITERATURE Bal, D., H.M. Beije, H.F. van Dobben & A. van Hinsberg 2007. Overzicht van kritische

stikstofdeposities voor natuurdoeltypen Ministerie van LNV, Directie Kennis. (Translation: Overview of critical nitrogen deposition for target nature types, Ministry of LNV, Department of Knowledge)

Berdowski, J J M. 1987. The catastrophic death of Calluna vulgaris in Dutch heathland. Dissertatie Utrecht, 132 p.

Bobbink, R. & Hettelingh J.P. (eds.) 2011. Review and revision of empirical critical loads and dose response relationships . Proceedings of an expert workshop, Noordwijkerhout, 23-25 June 2010. CCE/RIVM, Bilthoven.

Bobbink, R. & Lamers, L.P.M. 1999. Effecten van stikstofhoudende luchtverontreiniging op vegetaties; een overzicht. Rapport R13 Technische Commissie Bodembescherming, Den Haag. (Translation: The effects of nitrogen pollution on vegetation: an overview.)

Bobbink, R., Hornung, M. & Roelofs, J.G.M. 1998. The effects of air-borne nitrogen pollutants on species diversity in natural and semi-natural vegetation - a review. Journal of Ecology 86: 717-738 .

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Documents

Recovery strategies for nitrogen-sensitive habitatsec.europa.eu/.../part-i...1_nov-2012_2013-09-10_en.pdf · best available knowledge and form the ecological foundations of the measures,