Part I - Version November 2012 - European...

Part I - Version November 2012 -

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Explanation of asterisks (*) in the table. • Wooded dunes, dry (H2180A): * here refers to removal of conifers and American bird cherry trees • Wooded dunes, humid (H2180B): * here refers to periodic clearing • Wooded dunes, inside dune edge (H2180C): * here refers to thinning • Humid dune slacks, open water (H2190A): * here refers to removing a forest or changing a conifer forest in the

vicinity in order to combat evaporation and promote infiltration • Humid dune slacks, lime-rich (H2190B) * here refers to removing a forest or changing a conifer forest in the

vicinity in order to combat evaporation and promote infiltration • Humid dune slacks, decalcified (H2190C) * here refers to removing a forest or changing a conifer forest in the

vicinity in order to combat evaporation and promote infiltration • Driftsand (H2330): * here refers to tilling with a rotary cultivator • Hard oligo-mesotrophic waters with benthic vegetation of Chara spp (H3140): * active biological control • Lakes with crab’s claw and Potamogeton (H3150): * active biological control • Dry heathland (H4030): * in case of expansion, removal of volunteers together with litter and, if necessary, liming

may be needed • Juniper thickets (H5130): * here refers to opening up vegetation and working in seeds until germination follows **

here refers to pruning, thinning and layering. • Grasslands on soils rich in heavy metals (H6130): * here refers to cutting forest along the Geul ** here refers to

removing zinc ore/acidulating *** here refers to discontinuing fertilisation and liming in the area **** here refers to dredging Geul tributary

• Nutrient-poor grassland with carnation sedge (H6410): * here refers to in the area • Tall herb fringe communities, dry forest fringes (H6430C): * here refers to rooting out trees and shrubs • False oat-grass and Alopecurus hay meadows, false oat-grass (H6510A): * here refers to excavating • Transitional and quaking bogs, quaking bogs (H7140A): * here refers to more dynamic seasonal level control • Transitional and quaking bogs, sphagnum reed beds (H7140B): * here refers to dephosphating of inflowing water,

** here refers to pulling up sphagnum, *** here refers to more dynamic seasonal level control • Oak-hornbeam forests, higher arenaceous soils (H9160A): * here refers to coppicing with standards • Oak-hornbeam forests, undulating landscape (H9160B): * This incudes conversion of forest onto a more diverse

age structure • Bog woodland (H91D0): * here refers to thinning • Humid alluvial forests, ash-elm forests (H91E0B): * here refers to inundations • Humid alluvial forests, riparian forests (H91E0C): * here refers to inundations • Permanent spring & slow-flowing upper course (LC01) * here refers to (additional) cleaning 3.2 Restoration measures at habitat level Restoration measures at habitat level are basically once-off and are repeated at lengthy intervals. Their aim is to restore a degenerated habitat to an earlier, better developed state. It is an inherent aspect of their scale that these measures are applied to a restricted area, which may range from a few square metres to several hectares. Measures at the habitat level intervene directly in the so-called conditional and operational factors. Conditional factors are related to the level of acidity and basicity (saturation with bases, ability to neutralise acids) and other factors in the soil, such as the redox state, and therefore codetermine the operational factors (Van Wirdum 1979). The conditional factors therefore regulate the operational factors, which are related to the availability of vegetation nutrition. Measures to reduce acidification at habitat level are directed either at the removal of acidified topsoil with a view to bringing soil layers which are richer in bases to the surface or at the


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introduction of basic substances, either in groundwater or directly by spreading lime-rich or base-rich substrates, such as lime or loam. In order to combat the overfertilising effects of nitrogen deposition, nutrients must be disposed of. This can be done by disposing of biomass and on the other hand by disposing of nitrogen-enriched soil. Measures at landscape level are often taken at the same time as measures at habitat level. For example, measures to counter dehydration on arenaceous soils are often combined with removing the degraded vegetation and the acidified and nutrient-enriched topsoil. In groundwater-independent systems, where infiltration of groundwater occurs, measures at habitat level may already suffice to (temporarily) create better circumstances for flora, vegetation and fauna. However, sometimes measures at habitat level are sufficient. Thus removal of the acidified and/or overfertilised topsoil may well temporarily expose soil layers richer in bases and depleted of nutrients, but if the groundwater regime is unfavourable, renewed acidification and accelerated mineralisation will occur soon. Then the recovery of the flora and vegetation that followed sod cutting is merely temporary: within a few years, species thriving in more acid and/or nutrient-rich conditions will regain the upper hand at the expense of the typical species bound to more buffered and low-nutrient conditions (Jansen et al. 1996; Jansen et al. 2004). This paragraph will first deal with measures that are specifically aimed at the restoration of the base situation, followed by measures aimed at the disposal of nutrients. Thus the consequences of an acidified and overfertilised past are wiped out. Lastly, measures are discussed that intervene in the succession by creating pioneering conditions. Naturally, there is a relation between restoration at habitat level and at landscape level. Their efficacy benefits if the choice of location for the restorative measures at the habitat level is based on the functioning of the landscape ecology of an area. Several examples of this approach will be provided in the subparagraphs below. Measures at habitat level or combinations can contribute to restoration at landscape level by aligning them spatially. Furthermore, the efficacy of measures at landscape level is often enhanced by combining them with measures at habitat level. One example is the combination of hydrological restoration measures and sod cutting (Van Turnhout et al. 2010). 3.2.1 Measures against acidification by adding basic substances The addition of basic substances (buffer substances) refers to the addition of lime and other calcareous substances or of base-rich substrates to the soil, or the supply of more buffered ground or surface water. The aim of this measure is to restore the buffering capacity (acid-neutralising capacity) and the pH of the soil and/or the ground and surface water. It can consist in the addition of basic substances in order to combat local soil acidification, but also to combat the soil acidification and of the groundwater and/or surface water at some distance from the place where the bases were introduced. Buffering the pH of (very) poorly buffered waters through a direct supply of buffered as well as low-nutrient ground or surface water, i.e. via water, is a third way of introducing basic substances. The addition of basic substances to combat local soil acidification also prevents an ammonium peak after sod cutting (Dorland et al. 2005). This ammonium peak is particularly harmful to many


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characteristic and endangered heath species (De Graaf et al. 1998; Van den Berg et al. 2005). At the same time, the soil is returned to the so-called calcium buffer stage (see 2.2.2). When the soil becomes acidified and the pH drops below approximately 4.5, calcium no longer buffers the pH, but aluminium. Aluminium is toxic to, for example, many characteristic higher plants of low-nutrition grasslands, but also to meadow thistle (Cirsium dissectum), a characteristic species of the blue moorland (De Graaf et al. 1998). Liming of the seepage area can be done if the addition of buffer strips is aimed at combatting the acidification of soil and of ground and surface water at some distance from the limed area. This measure can be considered when it is no longer possible to restore the buffering by means of ground or surface water by taking measures against dehydration because the ground or surface water has turned acid. Dissolving the added basic substances through seeping rainwater ultimately makes the groundwater more basic. The base-rich groundwater flows from higher to lower parts of the landscape (fens and other low-lying areas) where it emerges once again as (very) poorly buffered groundwater, thus increasing the buffering capacity and the pH of the soil and the surface water. In this way the system becomes more resistant to the effects of acid deposition. The measure is usually taken in combination with sod cutting in the seepage area and/or cleaning up the fen soil (Dorland et al. 2005; Van Duinen et al. 2009). Applying ground lime or another calcareous substance, such as dolokal, to the soil is one way of quickly recharging the soil complex in dry and humid seepage areas with basic ions which were destroyed by acid deposition. The same effect can also be achieved by loaming. However, the liming (or loaming) must be done after (shallow) sod cutting, otherwise the risk of an increased breakdown of organic material will be very high and serious encroachment may occur. EGM research (Dorland et al. 2005) showed that a once-off addition of lime or dolokal (200-300 g/m2) after sod cutting can restore and maintain soil conditions adequately for at least 10-15 years. The base content and the pH are increased and the aluminium concentration decreases. Besides, direct liming after sod cutting prevents an undesirable ammonium increase (Van Turnhout et al. 2008). At the end of the previous century, buffering the pH of (very) poorly buffered waters through a direct supply of buffered as well as low-nutrient ground or surface water was applied successfully as a survival measure in some fens with originally very poorly buffered circumstances (Bobbink et al. 2004). Now that the deposits have become less acid in recent years, this form of buffering is needed less often. In areas such as the Bergvennen, groundwater has to be pumped up less frequently to keep the pH of the system at a sufficiently high level (oral communication by J.G.M. Roelofs). 3.2.2 Anti-acidification measures by restoring the water cycle The water cycle needs to be restored not only in order to restore the groundwater regime (groundwater levels are high enough during the year). It is also important for increasing the pH and the base saturation of acidified habitats of basophilic plant communities/habitat types and species characteristic of such habitats. Whether local measures against dehydration will suffice


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for this purpose or whether such measures are needed on a (much) larger scale depends on the nature of the groundwater system that controls the local pH and base saturation. If larger groundwater systems are in control, measures must be taken in a broader area (Jansen et al. 2000; see 3.3.1 under Restoration of water cycle). If smaller or local groundwater systems (co)determine the pH and base saturation, measures within and in the vicinity of a nature area are usually sufficient (Jansen et al. 2000; see 3.3.1 under Restoration of water cycle). The preparation and execution of local hydrological restoration measures demand not only preliminary research to determine whether they are effective enough, but careful implementation as well. In sandy and clayey areas, closing off ditches is in most cases not enough. Like closed systems of earthen walls without an outlet, closed ditches keep draining; ditches must be filled up. While damming ditches and other watercourses does slow down the discharge of water and can therefore be a desirable antidehydration measure, filling up watercourses is generally more effective. In order to combat eutrophication, it is important first to remove dredgings, other dead organic material and vegetation from ditches and only afterwards fill them with clean substrate, preferably from the same area. If the ditches cut through poorly permeable loam or organic layers, the poorly permeable layer can be restored with clay or loam. Earthen wall systems are levelled by first cleaning the drainage channels and cutting sods on the sides. The remaining, mineral body of the wall is then moved into the adjacent channel. This amounts not only to an antidehydration measure, but a depression is restored more or less to its original shape at the same time. Such antidehydration measures are often the last step in a project comprising other restoration measures, such as removing volunteer trees and sod cutting or excavating. It is important to carry out work involving heavy equipment before wetting occurs, in other words before the anti-drying measures are executed. This is to prevent deep tracks and soil compaction. In Part II these measures are usually mentioned in general terms, whereas in Part III the details of the specific hydrological measures are discussed as well. 3.2.3 Measures against acidification by intervening in the species composition of the tree layer This measure refers to the cutting of groups of trees in forest complexes (structural thinning) combined with stimulation of natural rejuvenation and the planting of specific trees of species that produce mild, i.e. base-rich and more easily degradable litter, such as lime trees (Tilia species; Hommel et al. 2007). This measure aims to counter further acidification and enhance the decomposition litter. The latter prevents the accumulation of rough and acid humus on the forest floor. Not only conifers, but broad-leaf trees such as oaks (Quercus species) and beech (Fagus sylvatica) also produce acid litter that does not decompose readily. Many plant species of the old forest floors disappear as a result of this accumulation (Hommel & De Waal 2003), but the same also applies to various groups of soil fauna (Kemmers et al. 2007). Another effect of litter accumulation is that further acidification of the soil and the groundwater occurs (Stuyfzand 1993).


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3.2.4 Removal of nutrients by excavation Excavation or soil removal entails removing part of the soil and is usually aimed at bringing about a nutrient availability that suits the intended vegetation. This measure is applied mainly on former agricultural land and differs from sod cutting in that more than just the organic topsoil is frequently removed. The soil of former agricultural land contains not only (many) nutrients in the topsoil, but also in the non-organic underlying layer. Former agricultural land has almost always been fertilised heavily and, in low-lying areas, has been severely dewatered as well. This fertilisation has greatly increased the nutrient concentration (Gough & Marrs 1990; Pywell et al. 1994). The development of a species-rich nature on former agricultural land requires first and foremost a substantial reduction in the nutrient content (Marrs 1993). Traditionally, the nutrient concentration was reduced by making hay (mowing and removing it without fertilising) or by grazing. But it takes decades before these forms of nutrition removal have reduced the nutrient availability sufficiently (Bakker 1989; Marrs et al. 1998). Moreover, the nitrogen availability on former agricultural lands decreases substantially as a result of nitrate wash-out and denitrification (Lamers et al. 2005). That does not apply to phosphate, however. Phosphate is strongly bound to iron and calcium in the soil, which keeps it in place (Lamers et al. 2005). When antidehydration measures are implemented, phosphate availability to the vegetation increases further. The soil becomes more anaerobic, with the result that phosphate bound to iron (hydr)oxides will be released (Lamers et al. 2005; see paragraph XX in chapter 2). Under such conditions, Pitrus (Juncus effusus) becomes dominant (Smolders et al. 2008). In order to achieve leaner conditions more quickly and to prevent additional phosphate from being released during hydration, it has become common practice over the past two decades to remove the top, phosphate-saturated layer. Together with the soil, the nutrients present in it are also removed, which creates much more nutrient-poor circumstances in the soil surface that is exposed (Marrs 1993). Before excavation, it is important to determine how deep the excavation should be in order to create a situation with a sufficiently low phosphate content for the intended vegetation. This can be done by measuring the P availability at different depths. The Olsen-P concentration is a measure of the phosphate available to plants (Lamers et al. 2005). In soils of former agricultural lands in the Netherlands, this concentration has been found to lie between 30 and 160 mg phosphorus per kg dry soil, whereas the target value for oligotrophic to mesotrophic plant communities is only about 8 mg P/kg. Verhagen (2007) evaluated a large number of nature development projects on former agricultural land in the northern Netherlands. After removal of the entire tilled layer, good conditions arise for the recovery of low-productivity plant communities. With shallower excavation, intensive follow-up management is needed to counter the effects of the nutrients then released. Most species of low-nutrient circumstances became established with a total nitrogen content below 1mg/l, less than 14 mg/100 gr total phosphate and less than 4 mg 100 gr/l interchangeable phosphate. It was also found that ten years after excavation, many target species still had not become established. Seed dissemination appears to be a strong inhibiting factor in the restoration of the well-developed vegetation. The primary succession on the bare, freshly excavated soils is


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severely impeded if there are no sources of seeds in the vicinity. Later on the species composition of the vegetation is also determined by the abiotic conditions. Similar results were found with regard to ground beetles: the colonisation of excavated former agricultural lands by large, non-flying species depends greatly on source populations in the immediate vicinity. Excavating former agricultural land can quickly reduce the availability of nutrients. Nevertheless, besides the high costs there are some points that must be considered before proceeding with excavations. For example, excavation is not always allowed because of archaeological value (Treaty of Malta, 1992), or undesirable for geographical or cultural-historical reasons. There is a risk that former agricultural land may lie so low afterwards that it begins to drain the adjacent nature reserve. This means that the groundwater levels in the existing nature area may drop or that the groundwater there no longer reaches the surface. In such cases, excavation - certainly deep excavation – is discouraged. Furthermore, much agricultural land in the Netherlands has been developed fairly recently and was levelled at the time, with the original low-lying areas being filled up. If the depth of an excavation is determined solely by the nutrient content and not by the original topography, the opportunity to restore gradients and depressions fed by groundwater will be missed (Jansen et al. 2004). Such depressions may be very important for restoring the dispersal of water above ground level (Jansen 2000). Restoring such dispersal prevents the stagnation of rainwater in the wrong places on the gradient. In addition, seeds and other plant parts can be distributed (Cappers 1993). Locally, mining out the soil can be an alternative. Mining out is the selective addition of nutrients, e.g. nitrogen and potassium, resulting in accelerated uptake of phosphate from the soil through planting and mowing. On the basis of the stock of P in the soil (measured as oxalate-extractable P) and the thickness of the soil layer sampled, the time it will take before the desired P concentrations are reached can be calculated, i.e. water-extractable P (Pw), oxalate-extractable P (Pox) and the (molar) ratio between Pox and the extent of the adsorption complex for P, measured as oxalate-extractable Fe and Al (Chardon 2008). Mining out is particularly effective where available phosphate contents are not too high. Then the desired phosphate availability can be reached within a fairly short period (Chardon 2008). 3.2.5 Removal of nutrients by sod cutting Sod cutting is the removal of nutrients and/or organic substances present in the layer of vegetation and the organic part of the soil profile by partly or completely removing the vegetation layer and partly or completely removing the organic part of the soil profile. The aim is to remove the excess of nutrients (and acids) that have accumulated in the system - the vegetation, the litter and the organic horizons - over the years as a result of nitrogen deposition and/or dehydration. Any acid topsoil is also removed, so that a base-rich soil is brought back to the surface. A third objective is to allow the vegetation succession and the soil development to start with a clean slate, i.e. on a bare surface. At the same time, the microrelief can be also be influenced by sod cutting. This is often very important to keep or restore the variation (gradients) in the system.


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In dehydrated situations it is important to cut turf in combination with hydrological measures. This also ensures the supply of basic substances and prevents the buffering capacity of the soil at the cutting locations from becoming inadequate for the retention and restoration of the prospective species and communities. The evaluation of the EGM scheme shows that this combination of measures is the most successful (Jansen et al. 2010). Sod cutting on its own can be considered if the hydrological restoration is not possible (yet), while some species and communities are seriously endangered locally. If the soil in originally weakly buffered systems is heavily acidified (pH-KCl ≤ 4,2), it is found that liming of the cutting site - with 2,000 kg lime/hectare - within one year of cutting is a sensible supplementary measure (Dorland et al. 2005; www.natuurkennis.nl). In all cases residual populations of rare plants and animals must be protected. The same applies to residual populations of plant species with a short-lived seed bank. The presence of such species will also boost the success of sod cutting considerably. Despite the many successes achieved by sod cutting, especially in the ‘wet sandy landscape’ (Jansen et al. 2010), the measure is subject to a number of risks. Working on a small scale prevents removal of the entire seed bank and populations of characteristic animal species. It also brings about a certain heterogeneity that is also important to the conservation and restoration of the fauna. Sod cutting in summer prevents the dormancy of seedlings from being ended too soon, inhibiting the growth of the seedlings. In strongly acidified locations, a high risk of poisoning by ammonium exists, which can be countered by liming once immediately after sod cutting (see 3.3.3 Measures against acidification by adding basic substances). After sod cutting, adequate follow-up management must take place. Large-scale volunteering of shrubs and trees in particular is a recurrent effect that calls for early intervention. Additional mowing and/or grazing are the most suitable means to this end. 3.2.6 Removal of nutrients by choppering Choppering is a form of deep mowing or shallow sod cutting, depending on the depth setting of the machine. Choppering is regularly done in areas with a thin layer of litter or when the vegetation contains many invasive species or is ‘felted’. The execution and risks are comparable to those of sod cutting. The risk of the seed bank being removed is lower, but choppering retains many seeds of species from acidified and overfertilised circumstances which, after this measure has been implemented, can quickly cause problems again (Verhagen 2007). Then follow-up management is essential. 3.2.7 Removal of nutrients by dredging Dredging is the removal of sludge and other organic material not embedded in the soil from permanent or temporary waters. In this way nutrients and acids are removed. It is explicitly not the intention to remove peat, in other words solid, organic soils which often have a genesis spanning centuries. Such peat packages are not only a valuable historic archive, but also serve as an anchor for plants and therefore the basis for the restoration of a well-developed community. When we refer to the measure of ‘dredging’ here, it refers not only to low-lying fens, but also to


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fens in the arenaceous landscape, especially to the high moor habitat type (H7110B). In the brochure ‘Sleutelen aan vennen’ [Tinkering with fens], (www.natuurkennis.nl) a series of steps is set out whereby the right package of measures can be selected for fens. In practice, dredging is often done in combination with sod cutting of the (fen) banks and with the clearing of forest from the banks up to 30 m from the high-water mark. In low-nutrition systems such as fens, the sludge must be removed from the site in order to prevent overfertilisation. This is less imperative in low-lying fen waters, where the sludge used to be applied as valuable fertiliser on drying banks and other solid fen soils (often the places where similar grasslands were found). This benefitted the maintenance of varied grasslands with rough growth on the edges. In the present circumstances, the pros and cons must be carefully weighed up. Although the sludge contributes to the supply of bases (thereby countering acidification)), the often excessive phosphate contents count against such an application. It is custom work; in every case a decision must be made whether and to what extent the sludge must be removed from the fen and can be brought up. The iron/phosphate ratio in the soil water of peat lakes, for example, determines whether dredging is a sensible restoration measure (Geurts 2010). 3.2.8 Removal of nutrients by (additional) mowing This refers to additional haymaking (mowing and removing above-ground parts of plants) together with the nutrients and organic matter present in them. The removal of biomass stimulates the restoration of the former species diversity, not only by creating lower-nutrient conditions in the long term, but also by shortening and opening up the vegetation and thereby allowing less competitive species to germinate and grow. This is a regular management action to maintain hayfields. Additional haymaking is used to remove excess nitrogen that has accumulated in the system, as was done on the former agricultural lands, where the restoration of species-rich hayfields is pursued. Furthermore, haymaking combats afforestation, not only on grassfields but also in places where sod cutting used to be practised. In the open places left after sod cutting or choppering, trees and shrubs mostly take over on a massive sale. By mowing these volunteers at an early stage, trees and shrubs are prevented from becoming so large that they can be removed only by expensive uprooting and/or cutting. Especially in these humid circumstances, seedlings of trees grow into shrubs within just two to three growing seasons. Therefore, even if the production is still very low, mowing and removal often already have to start in the second growing season. Birch, willow and alder in particular rapidly colonise such soils and form deep and extensive root systems underground in which nutrients are captured or are formed through symbiosis with root nodule bacteria (alders). For maximum effect, the young trees must be cut early in the season (mid June). This early cutting also supports the envisaged removal of nutrients, most of which are still in the parts of the plant which are above ground at that time. The later in the year mowing is done, the fewer the nutrients removed and mowing increasingly becomes the removal of carbon. In the restoration of calcareous grasslands on former agricultural lands (Wylré acres), mowing was done late in the season for years (after the gentians and some orchids had been in flower), but as a results the nutrient depletion was less effective than intended (Schaminée & Hennekens 1985).


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3.2.9 Removal of nutrients by (additional) grazing Grazing refers to the use of livestock for the purpose of reducing the coverage by highly productive, strongly competitive plant species in favour of low-production, less competitive species. Grazing removes nutrients, although at a much lower rate than haymaking does (Bakker 1989; Van Uytvanck et al. 2008; Smits et al. 2007; Smits 2010). In particular, grazing redistributes nutrients within an area and thereby ensures a more varied vegetation structure (Bokdam 2003; Van Uytvanck et al. 2008). Treading on, squashing as well as watering, mud bathing, sheltering, sleeping and resting places, defecation and other forms of animal behaviour contribute to this variation as well (Kuiters 2002; Van Wieren et al. 1997). Grazing is not only a regular management measure for grasslands; it is also frequently used to combat the adverse effects of nitrogen deposition on heaths and in dunes. Nevertheless, Van Uytvanck et al. (2008) conclude that a very drastic reduction of atmospheric nitrogen deposition is needed to conserve or restore vulnerable, nutrient-poor grasslands. Given the present high atmospheric input, cattle are just as unable to remove nitrogen from forests or forested pasturage (Van Uytvanck et al. 2008). There are different types of grazing (all-year, seasonal, herd, intensive). The timing of grazing, choice of herbivores and intensity depend on the system and local circumstances as well as the objective pursued. Grazing can be used as a permanent measure, but also as a temporary one to quickly combat encroaching grasses and the extensive formation of forests and thickets (Annema & Jansen 1998). When the choice is made, attention must be given not only to the effects on the vegetation, but to those on the fauna as well. In heavily grassified, but not dehydrated areas, sod cutting before sending in the herbivores can be considered. 3.2.10 Removal of nutrients by burning Periodic burning is a traditional management method, which used to be common practice on the heaths and locally also in other landscapes (dunes, Heuvelland). This was done to rejuvenate the vegetation and combat volunteer shrubs and trees (Bobbink et al. 2009). Burning can therefore be used as a preparatory measure before grazing (heath) landscapes. Then the livestock does not have to graze off the old, often low-nutrient vegetation first. Traditionally, burning was done in winter, so that the fire could not penetrate deep into the soil. After it had been shown that burning was a less effective way of removing nutrients than sod cutting, and it also became increasingly clear that this measure can also adversely affect various groups of animals, burning was virtually discontinued. Localised burning nevertheless has positive results, for example for species of low-nutrient grasslands and for the heath bush cricket (Gampsocleis glabra; Haveman et al. 1999; Van der Berg et al. 2000). For this reason an evaluating investigation of burning was carried out (Bobbink et al. 2009). The above investigation shows that the effect of burning depends greatly on the vegetation type, the intensity of the fire and the climatic conditions during and after the fire. The loss of nitrogen in the humus and the vegetation above ground can be substantial, whereas phosphorus and many cations remain behind in the ash particles. There may also be a temporary increase in the


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available cations in the upper soil layers immediately after a fire. After one or two seasons, this effect has normally disappeared again. As expected, burning has hardly any effect on the total nutrient pool available in the soil (Bobbink et al. 2009). In winter the temperatures do not become very high, and the lower part of the humus profile remains virtually intact. An effective nutrient removal is achieved only by intensive burning, which also removes the deeper part of the organic layer. In such intensive burning, the root systems of the heath plants also die, and there is a risk that the seed bank may also be destroyed. After winter burning the plants will have to recover from the seed bank; in the other case, this is not possible, or only to a limited extent, and grasses will take over. In any case, the effects of burning greatly depend on the wind speed, the moisture content of the soil and the surface vegetation. Periodic burning of the vegetation removes - temporarily, in any case - the biomass above ground, allowing species to establish on the open patches or to germinate from the seed bank - provided it has survived the fire. Burning in winter is also advantageous to species that hibernate in the soil. They will profit from the open spaces left after burning, because favourable microclimatic conditions prevail there. The larvae of animal groups that hibernate above ground, in the vegetation, are destroyed by burning during this period. The effects of burning therefore differ significantly, and they are closely related to the characteristic of the species’ life history. The greatest risks to the fauna arise after the fire, however, when a (sometimes reduced) population has to maintain itself in a totally altered environment, with a shortage of food and a more extreme microclimate (Bobbink et al. 2009). 3.2.11 Removal of nutrients by removing litter The present forests in our country are characterised by the presence of thick layers of litter resulting from dehydration, sulphur and nitrogen deposition and a different management. One possible measure would be to remove this accumulated litter (with the nutrients stored in it). However, no experience exists of the implementation of this measure. The few studies show that in the short term, species of earlier succession stages do profit somewhat, but that this effect disappears again within five years at the most (De Vries et al. 1995; Bartelink et al. 2001). Moreover, the removal of litter (in combination with other forms of soil rehabilitation) it is quite difficult in practice. A knowledge gap exists both as regards the manner of execution (blowers?) and the efficacy of the possible measure(s). By removing only the loose litter (and a large part of the F layer) and leaving the stable humus layer (H layer) intact, strong stimulation of the mineralisation can be prevented in principle, resulting in a strong increase in grasses and other nitrophile species. By leaving the stable humus layer intact, the removal of bases can also be prevented, as this would increase the susceptibility to acidification in the long term. Once-off, small-scale litter removal (L and F layer) can be beneficial for the creation of new growth sites for old-forest plants that take root in the humus layer. In order to prevent a fresh accumulation of litter, the measure can be implemented in combination with conversion into a varied forest in which tree species with an easily decomposing “rich” litter are prominent (Hommel et al. 2007, see also 3.3.3 Intervening in the species


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composition of the tree layer). However, this does not apply to the low-nutrient habitat type Old Oak Forests, where a tree layer of oaks and birches is required. In naturally acid systems, litter removal could be combined with some liming or the introduction of moulds. The sole purpose of liming in these systems is to restore systems that have become too acidified, so that moulds can once again optimally immobilise the nitrogen by absorbing the mineralised nitrogen. In naturally more base-rich circumstances, once-off litter removal combined with liming could in acidified situations stimulate the soil bacteria and soil mesofauna (nematodes, potworms and rainworms, which can bind the excess of mineralised nitrogen (Kemmers 2011). Liming without litter removal has no positive effect in relatively acid, low-nutrient forests (Olsthoorn et al. 2006). 3.2.12 Intervening in the succession by coppice management and thinning Chopping and thinning are types of interventions in the species composition and structure of forests which in the (distant) past were practised as regular management actions. With the coming of cheap energy and timber imports, Dutch forests underwent a change of function that made this intensive practice unprofitable. The effect of this intensive management was that together with wood, nutrients were removed and much more light penetrated to the forest floor, which in turn stimulated the decomposition of litter. Leaf production also decreased in the years following chopping, and less litter was produced. Many and currently scarce plant species benefitted from the sparse and bright circumstances. In coppice management in the strict sense, the shoots are periodically cut down to the stool and the increment is removed. Coppicing with standards comprises cutting and removing only the shrubby and lower tree layer once in 7 to 20 years, leaving the higher tree layer intact. In thinning, cutting is done selectively to reduce the tree density, resulting in a more open forest environment where more light can penetrate to the forest floor. Coppicing with standards and thinning results in a very rough structure, which captures more deposits and gives nitrophile species a better chance of becoming dominant. If the additional nitrogen capture can be compensated through supplementary management measures (or the additional capture is limited), thinning or coppicing with standards in the PAS framework can be applicable. One of the major questions (knowledge gap) is how, in the present circumstances with thick nitrogen-rich litter deposits, the measures envisaged can be implemented without negative effects. When more light penetrates, the mineralisation of the nitrogen-rich litter deposit will be promoted, with all the concomitant adverse effects (flourishing of undesirable brambles and grasses). A second focus point (knowledge gap) is the possible depletion of calcium and other basic cations on poor soils (De Jong 2011).


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3.2.13 Intervening in the succession by felling trees and clearing fen banks Felling and then transporting out trees (and bush) along the banks of fens is done for several reasons. Firstly, eutrophication of the environment is limited by falling and wind-blown leaves, pollen and litter. Fens are opened up in the landscape, allowing wind to act on the water. Consequently the organic matter produced in the fen itself is deposited on one bank, while on the upwind bank bare sandy soils remain for lengthy periods. And that is precisely where the typical littoral vegetations can develop and persist in the long term. Lastly, removing forest reduces evaporation, resulting in water levels remaining high for longer and fen banks not remaining dry for too long. The reduction in evaporation is greatest in stands of ‘dark conifers’ (Christmas tree, Douglas fir); Buishand & Velds 1980; Schaminée & Jansen 1998). Fen banks should not have their turfs cut if there is a poorly permeable organic layer (liquefied humus, water hard, bonded ß horizon) just below the bank. This is often the case in acid fens (H3160) and high moor fens (H7110B). Such places can often be identified in the landscape by the presence of a belt of nests made of purple moor grass (Molinia caerulea). After bush has been cut on the banks proper, sod cutting is possible in order to create new habitats for a varied vegetation gradient from heath to littoral vegetation communities. It is important to maintain the original relief during sod cutting. Where overfertilisation of the fen vegetation has occurred through the transport of nutrient-rich surface water, other methods - besides cleaning the soil - must be taken to prevent the inflow of such water, but not to the point where the fen becomes hydrologically isolated. Besides clearing bush on the fen borders as set out above, volunteer shrubs and trees in other open vegetations (high moors and heaths) resulting from acidification, overfertilising and/or dehydration must be kept within limits. In high moors, the removal of (dense) volunteer birches not only raises the summer groundwater levels (Limpens 2011), it also limits the capture of nitrogen deposits and the supply - through falling leaves – of large amounts of phosphorus (as much or twice as much phosphorus on the fen surface as via the precipitation; Limpens 2009). In high moors birch trees are removed best by felling large areas at a time (preferably at compartment level) in order to curb the rate of regrowth (Limpens 2009). If still present, the removal of birch trees can best be combined with the filling-up of channels and ditches. Cutting birch trees down is the most practical method. The best way is to saw off the trunk at some height. Sawing them down at the bottom of the trunk appears to stimulate the formation of new shoots. In any case, it is best not to allow the birch trees to become too thick in order to counter the sprouting of the stools. Birch trees are best cut when they are about 2 m high and/or the trunk has a diameter of 3 cm. Depending on the growth rate of the trees, this implies cutting once in 5-15 years. For places with bulging sphagnum species, cutting once every 5 years is best (Limpens 2009).


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3.2.14 Intervening in the succession by digging peat trenches and restoring drying banks In the low moor landscapes, peat was cut on a large scale in the past, after which extensive complexes of peat trenches were formed which locally expanded into lakes by the action of wind and waves. During the conversion of the peat trenches and lakes into land, species-diverse plant communities develop in the course of the succession, ranging from vegetations with crab’s claw (Stratiotes aloides) and other water plants to small floating islands (rafts), quaking bogs, (sphagnum) reed fields, march heaths, reed thickets, wet grasslands, thickets and swamps. The course of the succession is codetermined by the ion supply in the water. In sweet water, the succession differs from the succession in brackish water. For many years now, no new peat trenches have been cut; in the remaining lakes, the water plant and floating island vegetation has degraded seriously due to the severely deteriorated surface water quality. This deterioration was not only the result of a much higher supply of nutrients (see restoration of the food web), but also of the inflow of water from the large rivers that had become very rich in sulphates as a result of pollution. By way of a complex chain of chemical reactions, this higher sulphate concentration causes decomposition of the peat and reduction of iron phosphate, in the course of which much phosphate is released. This form of eutrophication is called internal eutrophication. At the same time, ever increasing surfaces of the landscape were no longer being mown, resulting in further development into swampland on a large scale. In this way the landscape was metamorphosed and became rigid (Stortelder et al. 1998; Lamers et al. 1998b; Lamers et al. 2009). In the past few decades, new peat trenches have been cut in an attempt to interrupt this development. Earlier peat trenches which had become overgrown were re-excavated on order to create open water for (renewed) peat formation. Other interventions concerned partial filling of existing peat trenches which were too deep with peaty material in order to create favourable initial conditions for peat growth. As meadow management of the drying banks (the peatless parts on which the excavated peat was laid out to dry) had been discontinued in most places, they became overgrown with trees (especially alders and willows). The peat decomposition due to internal eutrophication has led to weakening of the edges of the lakes as well as of the banks of drying banks (Jansen et al. 2011). Trees are blown over by storms and entire sections of the weakened banks are dragged along. The end result of internal eutrophication and the degradation of banks and drying banks is - once again – open peat lakes, now with weakened soils, where underwater vegetations no longer occur and with insufficient protection for conversion into land to occur. In order to recreate protected environments, which are essential for getting the conversion of open low moors into land going, local measures have been taken to repair or reinforce drying strips and their banks (Jansen et al. 2011). This comprises cutting bush and reintroducing meadow management for the remaining drying strips, erecting wave screens, planting young helophytes (reed, mat-rush, lesser bulrush) and protecting them against geese.


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3.3 Restoration measures at landscape level

The processes controlling the habitat may operate at the landscape level. The measures required can be implemented partly within nature areas, but interventions beyond them may also be called for. The extent and the distance from the nature area depend on the nature of the landscape system. For the water cycle, a distinction is made between local and larger-scale groundwater systems. If local groundwater systems determine the habitat conditions, antidehydration measures in and near the nature area are usually sufficient. The measures at landscape level must often be combined with measures at habitat level. For example, on mineral soils hydrological restoration is often accompanied by removal of the topsoil, degraded by dehydration, by means of sod cutting or excavation at habitat level. In the Netherlands, wind and water most often determine – directly or indirectly – the conditions affecting plants and animals. These factors also ensure that there is sufficient dynamism within the landscapes for the different succession stages – from pioneer to climax – to coexist. In order to guarantee that plants and animals are able to complete their full life cycle, and are therefore able to continue to exist, the nature areas will have to be sufficiently large or linked together. This ‘linking’ implies not only being spatially connected, but also the promotion of the action of dispersion factors via wind, water, animals and man. In some cases, isolation is precisely what is needed to counter the dissemination of highly competitive species. This is not only a matter of invasive exotics only, but also of preserving populations of animal species that have since time immemorial lived in locations difficult to reach. A known example is the tundra vole (root vole) (Microtus oeconomus ssp. arenicola), which is sensitive to competition with other root vole species such as the Alexander Archipelago tundra vole (Microtus arvalis) and the field vole (Microtus agrestis). Where territories overlap, the Alexander Archipelago tundra vole forces the root vole out of the grasslands and the field vole forces it out of relatively drier thickets and the somewhat higher-lying reed fields. The species can maintain itself only in refuges and in some isolated areas where no competitors occur (Janssen & Schaminée 2008). Interactions between plants and animals in the food web also take place at the landscape level. Acidification, overfertilisation, dehydration and fragmentation have in many cases destroyed links in the food web, upsetting the balance of the system and preventing it from returning to its original state by itself even after the abiotic circumstances have been restored. To restore this balance, active intervention in food chains is essential – what is called active biological management (i.a. Lamers 2006). Little experience of such measures is available to date (see 3.3.4). 3.3.1 Measures aimed at restoring the water cycle The adverse effects of dehydration can be countered by restoring the water cycle. This does not only involve raising groundwater levels, but also the restoration of groundwater flows (seepage or the prevention of excessive seeping away to combat loss of bases in the root zone). It also counters the indirect effects of dehydration, i.e. acidification caused by the increased influence of rainwater and over-fertilisation due to increased mineralisation.


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The restoration of the water cycle comprises a whole range of possible measures. A hydro-ecological system analysis (preliminary research) must point out which (combination of) these measures will be necessary. At the regional level, for example, it involves stopping or decreasing the extraction of groundwater for the supply of potable or industrial water, making deep main watercourses such as brooks and canals shallower and transforming high-evaporation (dark conifer) forests into open vegetations. On the one hand, these measures supplement the groundwater reserves (sponge effect); on the other they increase the rise of the deeper groundwater and thereby of the mean lowest groundwater level (MLGL). Diversification of land use in the seepage area is desirable if an inflow of groundwater enriched with fertilisers and/or sulphate causes over-fertilisation in the nature area. On high moors, high nitrogen deposition can lead to birch trees becoming undesirably dominant. Compared with fens without birches, evaporation increases with volunteer birch vegetation (Limpens 2009, 2011). Removing birch trees on active high moors has positive effects on the water balance (Limpens 2011). These effects usually filter down to the groundwater regime, in other words the water level does not drop as low in summer. Only in open water or in places with a large lateral water inflow will the effect on the water balance not be noticeable in the groundwater regime. At the local level, often within the nature areas, the filling-in of ditches and channels, the provision of culverts for watercourses with a feed-through function, the removal of earthen walls and sealing or removal of pipe drains can be considered. Removing bush and tickets and possibly dams that impede the natural discharge of water across the surface can have a positive impact on the operation of local groundwater systems (Jansen et al. 1996). These measures bring about higher groundwater levels and raise the highest groundwater level (HGL) in the longer term. Measures that were aimed at water retention, but in the end caused acidification, can be reversed, preferably in combination with measures that restore the supply of base-rich(er) groundwater to the surface. The filling in of dams can be considered in this regard. Digging channels in acidified areas in order to dispose of stagnant rainwater should be done with great circumspection (Van der Hoek 2005; Jansen et al. 2007). Above all, measures should be taken that promote the supply of bases via the groundwater. Digging channels in low-lying areas with little or no surface discharge have the opposite effect (Jansen 2001). Floating vegetation islands in low fens, which have already been dependent on a supply of clean, base-rich surface water for a long time are a different matter (Van Wirdum 1990). Digging and maintaining channels to promote the penetration of base-rich surface water originating elsewhere below and under floating islands is a measure that can be successful if seepage into the substrate is not to great (Beltman et al. 2001). No exact figures can be given in this regard, but with seepage of more than 1 mm/day the success of this measure seems to be limited; in other words species of more base-rich circumstances can survive only at the edges of ditches and channels near the inlet of the incoming surface water (Barendregt et al. 2004). In this case some species of more buffered circumstances will only colonise the banks of the channels (Beltman & Barendregt et al. 2007). Liming of the seepage area of the local groundwater systems is a useful restoration measure if the water cycle has been restored, but the soil has been acidified fairly deeply. Before this measure is resorted to, a preliminary investigation is needed to determine the level of acidification. Liming experiments in the Vecht lakes has shown that restoration occurs only in moderately acidified circumstances. In highly acidified circumstances, there is hardly any recovery, whereas in slightly acidified circumstances disturbance actually occurs (Barendregt et al. 2004).


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In Part II these measures are usually mentioned in general terms, whereas in Part III the details of the specific hydrological measures are discussed as well. 3.3.2 Measures aimed at restoring wind and water dynamics At the landscape level, wind and water dynamics are the main processes countering stagnation and senescence, because they ensure that through erosion and sedimentation pioneer circumstances are constantly created. These processes are significant in ‘wet’ as well as ‘dry’ landscapes, for example along the coast, along the rivers and in Pleistocene arenaceous areas and stream valleys. Nitrogen deposition furthers stagnation and senescence, not only through the increased supply of nutrients and the accompanying accumulation of biomass and humus, but also through accelerated leaching of bases in the topsoil. Wind and water counter these effects in two ways: one the one hand by mechanical action, which brings mineral substrates to the surface, and on the other by supplying buffering agents (bases) in water and supplying fresh substrate (sand, loam or clay). Measures aimed at the restoration of wind and water dynamics have in the past two decades been put on trial especially in the coastal dunes, the aeolian sand deposits in the interior and along the large rivers (as part of the ‘Plan Ooievaar’ and ‘Ruimte voor de Rivier’). Along the large rivers the removal of summer dykes, bank protection (rock dumps) and of breakwaters (groynes), but also the construction of free-flowing side channels have reactivated erosion and sedimentation processes. Erosion has created new steep slopes, and thin sand and mud layers have again been deposited locally. In some places, thicker sand deposits have even been formed which started drifting, forming new river dunes. However, the scale on which these landscape-forming processes can occur is limited because Dutch rivers are dyked in in the interest of safety, shipping and the need to disperse high tides quickly. Other geomorphological processes in and along rivers, such as the formation of point bars, of islands in the river bed, meandering and the formation of raised river beds are no longer possible because of these interests. Although the driftsands will no longer become nearly as large as in the first half of the 19th century, some sands that had settled down virtually completely have again become active since 1990. Although the matter seems simple - cut the bush, remove litter and humus deposits and leave the wind to do its work – it is not quite that simple in practice. For example, there needs to be an upwind supply of wind-erodible soil. Furthermore, wind erosion depends on the force of the wind and the erodibility of the sand. Wind strength increases with the fetch. The fetch is determined largely by the openness of the terrain. Especially on the south-western side - from the direction of the prevailing winds – the wind must therefore regain free play. The erodibility of the sand is severely reduced by soil moisture, humus and the presence of clay, loam, rocks and roots in the soil. A proper understanding of the earlier land forms in drift sand areas that have now become consolidated also is a precondition for successful driftsand restoration (Hermy et al. 1989). In a preliminary study in which these aspects are mapped out, the areas qualifying for re-


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establishing aeolian erosion are determined. The vegetation and the organic topsoil must be removed to such a depth that the roots of grasses cannot sprout again. The removal of bush and bush volunteers is often part of the measures, not only on the drift sand surface but also in the vicinity in order to increase the fetch of the wind, bring enough erodible sand to the surface and reduce the capture of nitrogen deposits. The excavation of soil on the highest parts of the south-facing slopes is found to increase water erosion, thus assisting the exposure of erodible sand, which in turn creates new sand pits. If the soil has been disturbed by earlier human activity such as small-scale tillage, the layer of organic matter is much thicker. Then this thicker layer must be removed to allow wind erosion or sustainable regeneration of a vegetation adapted to low-nutrient circumstances. What applies to inland driftsand also applies in essence to coastal dunes. 3.3.3 Measures aimed at restoring connectivity The Dutch landscape has undergone profound changes in the past century, as a result of which plants and animals are much less able to survive in their habitats or to colonise new, suitable areas. As indicated, several issues are important in this regard. First of all, many of the remaining nature areas are too small. This increases the risk that populations of plant and animal species may become locally extinct. To mitigate this risk, nature areas must be enlarged. In larger areas, and certainly if they are characterised by heterogeneous structures, there are more alternatives when unfavourable situations occur, and the chances of being struck by adverse events are smaller. A second important factor is the poor integration with other nature areas. This makes it impossible, or much more difficult, for species to expand to other areas. For these two reasons (increasing size and restoring connectivity), the Ecological Main Structure consisting of core areas, nature development areas and corridors (some of which were subsequently upgraded to Robust Corridors) was designed in the Nature Policy Plan (Ministerie van LNV 1990) [Ministry of Agriculture, Nature and Food Quality] A third cause is that many dissemination mechanisms are less active than before. In the past, there used to be a much greater exchange of seeds and other diaspores via water (think of inundation and irrigation), wind (open landscapes) and man (shepherded livestock, transport of manure end straw). The same goes for many small animals. So far, nature policy has focused more on establishing connections in order to remedy fragmentation and less on the restoration of these dispersal vectors (Ozinga 2008). Lastly, terrain heterogeneity has often decreased. In other words, the cohesion between the different habitats within and between areas. Influenced by dehydration, acidification and overfertilisation, but also by ever- increasing afforestation, the delicate mosaic of the surface has given way to coarse-grained patterns. Many species need different parts of the landscape for completing the different phases of their full life cycle (e.g. egg-larva-pupa-imago) and to meet their different needs (resting, searching for food, mating, breeding). The disappearance of the small-scale variations of (vegetation) structures (micro and meso scale) and living areas (meso and macro scale) has led to the local extinction of species and to the fragmentation of species populations. Within the nature areas and in the zones connecting these nature areas, organisational and management measures must be implemented to promote this heterogeneity of the terrain in order to enhance the quality of the connections. In that regard the restoration or


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creation of gradients is desirable, not only because they are inhabited by many animal species, but also because quite a few plant species can migrate up and down them in reaction to variations in habitat conditions over time. 3.3.4 Measures aimed at restoring the food chain As pointed out earlier, links in the food chain have often disappeared because of acidification, dehydration and fragmentation. This has thrown the system out of kilter, and even after the abiotic conditions have been restored it does not return to its original state by itself. Restoring the often complex food chains in affected landscapes is therefore one of the most difficult tasks confronting the restoration of nature. There is insufficient knowledge in many areas, certainly where plant-animal interactions are concerned. This is also true of the availability of minerals in ecosystems and the mineral balances in animal diets. To date, little experience has been gained of active intervention in food chains (active biological management). The most striking examples concern the restoration of the food web in lakes (Lamers 2006; Jaarsma et al. 2008; Jansen et al. 2011). Earlier eutrophication has turned many waters murky. Although the phosphate contents have been substantially reduced, the water has not regained its former clearness yet. It remain turbid. This was found to be caused by disturbance of the bottom by whitefish, notably bream and also bluegill and carp, and the absence of algae-eating zooplankton. The aim of intervention in the food chain - catching the whitefish population - is to clarify waters so that subaqueous plants can flourish again. These water plants are refuges for algae-eating zooplankton and predatory fish eating whitefish, especially pike. Because of the complexity of the food web that is manipulated by active biological control, the chances of recovery in the long term are slim (Gulati & Van Donk 2002). Supplementary measures such as dredging and curbing the resupply of nutrients from the soil (internal eutrophication) increase the chances of success (Gulati et al. 2008). 3.4 Conclusions In the past twenty years, the Effectgerichte Maatregelen [effect-oriented measures] (EGM) scheme has carried out many of the measures described above. This has benefited many plant species on the Red List (more than 30 %) (Jansen et al. 2010). The fauna has so far profited less from these measures. The vascular plants of wet heathlands, fens, dune valleys and wet low-nutrient soils in particular have done very well. In other ecosystems, including dry heaths, low-nutrient grasslands and low fens, the results have been (much) less positive, for numerous reasons (Jansen et al. 2011).

The challenge of future restoration management lies in the development of successful measures for the ecosystems that have not benefited from all efforts so far. Furthermore, it is important to secure and strengthen the positive results achieved with restoration management by, on the one hand, decreasing environmental pollution – including nitrogen deposition – and dehydration further, and on the other hand by consistent, detailed terrain management. In order to cancel out


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the heritage of accumulated nitrogen (and other nutrients) and acid, effect-oriented measures must remain in place while nitrogen deposition and dehydration are decreased further. It is still often not clear how often specific restoration measures must and can be repeated. Measures such as liming the seepage area can have a prolonged, positive effect (Dorland et al. 2005). On fens a sustainable recovery is also found over the longer term, partly as a consequence of the lower deposition of atmospheric sulphur and nitrogen (Brouwer et al. 2009a, 2009b). In their assessment of the EGM scheme, Jansen et al. (2010) found that effect-oriented measures are effective over the longer term as well. This is deduced from the larger number of red-listed species that profited from the effect-oriented measures compared with the Red List with Green Dot, 1000 (Bekker & Lammerts 2000). It was also found that the majority of the species that received a green dot then retained it. It can also be seen from the total list of species with a Green Dot that not only pioneers and other Red List species from early succession stages received a Green Dot, but also many Red List species from older succession stages. The efficacy of some other restoration measures, such as dredging and digging peat trenches, will probably only become apparent in a few decades’ time. Research and practical experience will have to show how resilient the different ecosystems are. The development of effect-oriented restoration measures demands much knowledge and experience in an intensive collaboration between researchers and site managers. This is the lesson that can be learnt from the successful EGM scheme. The development of knowledge for restoration strategies currently lies with the Bosschap [Dutch Forestry Board] organised within the network of Ontwikkeling en Beheer Natuurkwaliteit (O+BN) [Knowledge network Development and Management Nature Quality]. The expert teams constitute the core of this network. Together researchers and managers investigate, in laboratory and field research, the controlling factors and processes surrounding acidification, overfertilisation and dehydration in many situations. On the basis of the outcomes of this research, effect-oriented and restoration measures are developed and successfully put into practice (Jansen et al. 2010). In the first instance the expert teams focus on the restoration of vegetation and flora by investigating the habitat conditions of specific ecosystems such as fens, wet nutrient-poor grasslands, quaking bogs, nutrient-poor grasslands, dry dune grasslands and high moors. Over time, two crucial developments took place. Firstly, increasing attention was given to the fauna and the requirements it sets for its habitat. By adapting the scale and the manner of execution of the measures, animals began to benefit from the restoration measures. Secondly, the approach changed from the scale of ecosystems (habitat level) to the landscape level. In 2005 the expert teams were therefore grouped according to landscape types. This laid a firm foundation for the research of the restoration measures at the landscape scale. But the preparation and the execution of the new, often complex measures also demands much knowledge. For such complex measure the site manager needs specific prior knowledge of the nature area in question. That is why, as part of the effect-oriented measures scheme (EGM), preliminary investigations were carried out. On instructions from the site managers, hydro-ecological analyses were done, or the chances of restoring the action of wind transport in the dunes or in overgrown inland driftsands were explored. The execution of so many measures obviously also demands the documentation and evaluation of the results (monitoring). This was


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done by means of policy monitoring, for which the site managers used a maximum of five per cent of their EGM budget. The outcomes were reported to the Ministry and created insight into the efficacy of the EGM scheme. The data also illustrated what species and systems were supported (or not) effectively by which measure (Jansen et al. 2010). The results of the policy monitoring also revealed knowledge gaps, which were further elaborated into knowledge questions by the expert teams. In this way the policy monitoring strengthened the close relation between policy, execution and research. Together with the Advisory Committee Knowledge, the expert teams constitute the knowledge leg within the O+BN network. This committee of policymakers, managers and researchers advises the Ministry of Economic Affairs, Agriculture and Innovation on the desirability and quality of research and the practical applicability of measures, with the policy-making context having been shifted from effect-oriented policy to questions concerning the organisation of the Ecological Main Structure, the species policy, Natura 2000 and the Programmatic Nitrogen Approach (PAS). The deployment of the substantive and organisational knowledge and experience in the policy, research, execution and monitoring cycle that has been gained within the EGM will definitely contribute to the continued and successful tackling of these problems. 3.5 Literature Annema, M. & A.J.M. Jansen 1998. Het herstel van het vroongrondengebied Midden- en

Oostduinen op Goeree. Stratiotes 17: 20-60. (Translation: Restoration of the Middle and East dune grasslands on Goeree.)

Bakker, J.P. 1989. Nature management by grazing and cutting. PhD thesis University of Groningen. Kluwer Academic Publishers, Dordrecht.

Barendregt, A. B. Beltman, E. Schouwenberg & G. van Wirdum 2004. Effectgerichte maatregelen tegen verdroging, verzuring en stikstofdepositie op trilvenen (Noord-Holland, Utrecht en Noordwest- Overijssel). Expertisecentrum LNV, Ede. (Translation: Effect-oriented measures against dehydration, acidification and nitrogen deposition on quaking bogs (North Holland, Utrecht and North-west Overijssel.)

Bartelink, H.H., H.F. van Dobben, J.M. Klap & Th.W. Kuyper 2001. Maatregelen om effecten van eutrofiering en verzuring in bossen met bijzondere natuurwaarden tegen te gaan: synthese. OBN rapport 13. Expertisecentrum LNV, Ministerie van Landbouw, Natuurbeheer en Visserij, Ede. (Translation: Measures to counter effects of eutrophication and acidification in forests with special natural value: synthesis. OBN report 13.)

Bekker, R.M. & E.J. Lammerts 2000. Naar een Rode Lijst met Groene Stip voor hogere planten in Nederland; eindrapport 1e en 2e fase. Dienst Landelijk Gebied/IKC Natuurbeheer, Ede. (Translation: Towards a Red List with a Green Dot for higher plants in the Netherlands; final report 1t and 2nd phase.)

Bekker, R.M. 2009. 20 jaar ontgronden voor natuur op zandgronden. De Levende Natuur 110: 9-15. (Translation: 20 years of excavating for nature on arenaceous soils.)

Bekker, R.M., J.H.J. Schaminée, J.P. Bakker & K. Thompson 1998. Seed bank characteristics of Dutch plant communities. Acta Botanica Neerlandica 47: 15-26.

Beltman, B., T. van den Broek, A. Barendregt, M.C. Bootsma & A.P. Grootjans 2001. Rehabilitation of acidified and eutrophied fens in The Netherlands: Effects of hydrologic manipulation and liming. Ecological Engineering 17: 21-31.


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Beltman, B.G.H.J. & A. Barendregt 2007. Herstelmaatregelen in verzuurde schraallanden in laag-Nederland. De Levende Natuur 108: 87-92. (Translation: Rehabilitation measures in acidified low-nutrient soils in the low Netherlands.)

Bobbink, R., E. Brouwer, J. ten Hoopen & E. Dorland 2004. Herstelbeheer in het heidelandschap: effectiviteit, knelpunten en duurzaamheid. In: In: G.J. van Duinen, R. Bobbink, Ch. van Dam, H. Esselink, R. Hendriks, M. Klein, A. Kooijman, J. Roelofs & H. Siebel (red.). Duurzaam natuurherstel voor behoud van biodiversiteit; 15 jaar herstelmaatregelen in het kader van het Overlevingsplan Bos en Natuur. Rapport Expertisecentrum LNV nr. 2004/305, Ministerie van Landbouw, Natuur en Voedselkwaliteit, Ede, pag. 33-70. (Translation: Restoration management on the heath: efficacy, bottlenecks and sustainability. In: Sustainable restoration of nature for conserving biodiversity.15 years of restoration measures as part of the Forest and Nature Survival Plan).

Bobbink, R., M. Weijters, M. Nijssen, J. Vogels, R. Haveman & L. Kuiters 2009. Branden als EGM maatregel. Rapport DK nr. 2009/dk117-O. (Translation: Burning as an EGM measure.)

Bokdam, J. 2003. Nature conservation and grazing management: free ranging-cattle as a driving force for cyclic vegetation succession. PhD thesis Wageningen University.

Bossuyt, B., O. Honnay & M. Hermy 2003. An island biogeographical view of the successional pathway in wet dune slacks. Journal of Vegetation Science 14: 781-788.

Brouwer, E., G.H.P. Arts, H. van Dam & H. van Kleef 2009a. Duurzaamheid venherstel: evaluatie van herstelmaatregelen in vennen. Rapport Directie Kennis-LNV, Ede. (Translation: Sustainable fen restoration: evaluation of restoration measures in fens).

Brouwer, E., H. van Kleef, H. van Dam, J. Loermans, G.H.P. Arts, & J.D.M Belgers 2009b. Effectiviteit van herstelbeheer in vennen en duinplassen op de middellange termijn. Directie Kennis en Innovatie, Ministerie van Landbouw, Natuur en Voedselkwaliteit, Ede. (Translation: Efficacy of restoration management on fens and dune lakes in the medium term.)

Buishand, T.A. & C.A. Velds 1980. Klimaat van Nederland 1: Neerslag en verdamping. Koninklijk Nederlands Meteorologisch Instituut, De Bilt, pp. 66-67. (Translation: Climate of the Netherlands I: Precipitation and evaporation.)

Cappers, R.T.J. 1993. Seed dispersal by water: a contribution to the interpretation of seed assemblages. Vegetation history and Archeobotany 2: 173-186.

Chardon, W.J. 2008. Uitmijnen of afgraven van voormalige landbouwgronden ten behoeve van natuurontwikkeling. Een studie in het kader van ‘Bodemdiensten’. Rapport 1683. Alterra, Wageningen. (Translation: Mining out or excavating former agricultural soils for nature development. A study in the Soil Services framework.)

De Deyn G.B., C.E. Raaijmakers & W.H. van der Putten 2004. Bodemfauna bevordert herstel van soortenrijke graslanden. De Levende Natuur 105: 10-12. (Translation: Soil fauna promotes restoration of species-rich grasslands.)

De Deyn, G.B., C.E. Raaijmakers, H.R. Zoomer, M.P. Berg, P.C. de Ruiter, H.A. Verhoef, T.M. Bezemer & E.H. van der Putten 2003. Soil invertebrate fauna enhances grassland succession and diversity. Nature 422: 711-713.

De Graaf, M.C.C., R. Bobbink, J.G.M. Roelofs & P.J.M. Verbeek 1998. Differential effects of ammonium and nitrate on three heathland species. Plant Ecology 135: 185-196.

De Jong, J.J. 2011. Effecten van oogst van takhout op de voedingstoestand en bijgroei van bos. Alterra-rapport 2202, Wageningen. (Translation: Effects of harvesting branchwood on the nutritional state and forest increment.)

De Vries, B.W.L., E. Jansen, H.F. van Dobben, Th.W. Kuyper 1995. Partial restoration of fungal and plant species diversity by removal of litter and humus layers in stands of Scots pine in The Netherlands. Biodiversity and Conservation 4: 156-164.


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Del Moral, R., J.H. Titus, & A.M. Cook 1995. Early primary succession on Mount St. Helens, Washington, USA. Journal of Vegetation Science 6: 107-120.

Dorland, E. R. Bobbink & E. Brouwer 2005. Herstelbeheer in de heide: een overzicht van maatregelen in het kader van OBN. De Levende Natuur 106: 204-208. (Translation: Restoration management on the heath: an overview of measures in the OBN framework.)

Fenner, M. 1985. Seed ecology. Chapman and Hall, London/New York. Galatowitsch, S.M. & A.G. van der Valk 1995. Natural revegetation during restoration of

wetlands in the Southern Prairie Pothole Region of North America. In: Wheeler, B.D., S.C. Shaw, W.J. Foyt & R.A Robertson (eds.), Restoration of temperate wetlands, pp. 129-142. Wiley and Sons, Chichester.

Geurts, J.J.M. 2010. Restoration of fens and peat lakes: a biogeochemical approach. PhD thesis, Radboud University Nijmegen.

Gough, M.W. & R.H. Marrs 1990. A comparison of soil fertility between semi-natural and agricultural plant communities: implications for the creation of species-rich grassland on abandoned agricultural land. Biological Conservation 51: 83-96.

Grootjans, A.P., J.P. Bakker, A.J.M. Jansen & R.H. Kemmers 2002a. Restoration of brook valley meadows in the Netherlands. Hydrobiologia 478: 149-170.

Grootjans, A.P., L. Geelen, A.J.M. Jansen & E.J. Lammerts 2002b. Restoration of coastal dune slacks in the Netherlands. Hydrobiologia 478: 181-203.

Gulati, R.D. & E. van Donk 2002. Lakes in the Netherlands, their origin, eutrophication and restoration: state of the art review. Hydrobiologia 478: 73-106.

Gulati, R.D., L.M.D. Pires & E. van Donk 2008. Lake restoration studies: failures, bottlenecks and prospects of new ecotechnological measures. Limnologica 38: 233-247.

Harris, J.A. & R. van Diggelen 2006. Ecological restoration as a project for gobal society. In: J. van Andel & J. Aronson Restoration ecology: the new frontier, pp. 3-15. Blackwell Publishing, Oxford.

Haveman, R., W. van Dijk & P.A.M. van Winden 1999. Heischrale graslanden op het infanterieschietkamp Harskamp - branden als natuurbeheersmaatregel. Stratiotes 18: 3-9. (Translation: Low-nutrient grasslands on the Harskamp artillery shooting range camp - burning as a nature control measure.)

Hermy, M., G. de Blust & M. Slootmaekers 1989. Natuurbeheer. Davidsfonds, Leuven. (Translation: Nature management.)

Hommel, P.W.F.M. & R.W. de Waal 2003. Boomsoort bepaalt bostype op verzuringsgevoelige bodem. Stratiotes 26: 3-19. (Translation: Tree species determines forest type on acidification-sensitive soil.)

Hommel, P.W.F.M., R.W. de Waal, B. Muys, J. den Ouden & Th. Spek 2007. Terug naar het lindewoud - strooiselkwaliteit als basis voor ecologisch bosbeheer. KNNV Uitgeverij, Zeist. (Translation: Back to the linden forest - litter quality as a basis for ecological forest management.)

IUCN 1998. Internationale richtlijnen voor herintroducties. Gland, Zwitserland. www.iucnsscrsg.org.images/English.pdf. (Translation: IUCN Guidelines for Re-introductions.)

Jaarsma, N., M. Klinge, & L. Lamers 2008. Van helder naar troebel en weer terug. Utrecht: STOWA. (Translation: From limpid to turbid and back again.)

Jansen, A,J,M, C.J.S. Aggenbach, A.T.W. Eysink & D. van der Hoek 2007. Herstel van natte schraallanden op minerale gronden. De Levende Natuur 108: 96-102. (Translation: Restoration of wet low-nutrient lands on mineral soils.)

Jansen, A.J.M. & J.G.M. Roelofs 1996. Restoration of Cirsio-Molinietum wet meadows by sod cutting. Ecological Engineering 7: 279-298.

Jansen, A.J.M. & P.C. Schipper 1997. Tips voor herstel van natte schraallanden. De Levende Natuur 98: 304- 309. (Translation: Tips for the restoration of wet low-nutrient lands.)


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Jansen, A.J.M. 2000. Hydrology and restoration of wet heathland and fen meadow communities. Thesis, Rijksuniversiteit Groningen.

Jansen, A.J.M., Eysink, A.Th.W. & C. Maas 2001. Hydrological processes in a Cirsio-Molinietum fen meadow: implications for restoration. Ecological Engineering 17: 3-20.

Jansen, A.J.M., G. ter Heerdt & G. Koopmans 2011. Laagveen: Terra Nova, levend water in Loenderveen. In: M.I. Kamphuis, A.J.M. Jansen & J.Bouwman; Werken aan natuur, 20 jaar effectgerichte maatregelen, p. 115-128. KNNV Uitgeverij/Unie van Bosgroepen, Driebergen/Ede. (Translation: Low fen: Terra Nova, living water in Loenderveen. In: Working on nature.)

Jansen, A.J.M., Grootjans, A.P. & M.H. Jalink 2000. Hydrology of Dutch Cirsio-Molinietum meadows: prospects for restoration. Applied Vegetation Science 3: 51-64.

Jansen, A.J.M., L.F.M. Fresco, A.P. Grootjans & M.H. Jalink 2004. Effects of restoration measures on plant communities of wet heathland ecosystems. Applied Vegetation Science 7: 243-252.

Jansen, A.J.M., M.C.C. de Graaf & J.G.M. Roelofs 1996. The restoration of species-rich heathland communities in The Netherlands. Vegetatio 126: 73-88.

Jansen, A.J.M., R.M. Bekker, R. Bobbink, J.H. Bouwman, R. Loeb, H. van Dobben, G.A. van Duinen & M.F. Wallis de Vries 2010. De effectiviteit van de regeling Effectgerichte Maatregelen (EGM) voor Rode-Lijstsoorten. De Tweede Rode Lijst met Groene Stip voor vaatplanten en enkele diergroepen in Nederland. Rapport Unie van Bosgroepen, Directie Kennis en Innovatie Ministerie Landbouw, Natuur en Voedselkwaliteit. 222 pp. (Translation: The efficacy of the Effect-Oriented Measures scheme (EGM) for Red List species. The Second Red List with Green Dots for vascular plants and some animal groups in The Netherlands.)

Janssen, J.A.M. & J.H.J. Schaminée (red.) 2008. Europese natuur in Nederland: soorten van de Habitatrichtlijn. Tweede herziene en uitgebreide druk. KNNV Uitgeverij, Zeist. (Translation: European nature in The Netherlands: species of the Habitats Directive.)

Kardol, P., A. van der Wal, T.M. Bezemer, W. de Boer & W.H. van der Putten 2009. Ontgronden en bodembeestjes: geen gelukkige combinatie. De Levende Natuur 110: 57-61. (Translation: Excavation and soil inhabitants: not a happy combination.)

Kemmers, R.H. 2011. Effecten van verzuring op bodemleven en stikstofstromen in bossen. Alterra rapport 2204. Alterra, Wageningen UR, 42p. (Translation: Effects of acidification on soil life and nitrogen flows in forests.)

Kemmers, R.H., H. van Dobben, W. Wamelink & A.J.M, Jansen 2007. Effecten van het generieke milieubeleid op het terugdringen van de verzuring en het herstel van natuurwaarden in multifunctionele bossen op arme zandgronden. Alterra-rapport 1521, Alterra, Wageningen. (Translation: Effects of the generic environmental policy on the reduction of acidification and restoration of natural values in multifunctional forests on poor sandy soils.)

Klimkowska, A., R. van Diggelen, A.P. Grootjans & W. Kotowski 2010. Prospects for fen meadow restoration on severely degraded fens. Perspectives in Plant Ecology, Evolution and Systematics 12: 245–255.

Klimkowska, A., R. van Diggelen, S. den Held, R. Brienen, S. Verbeek & K. Vegelin 2009. Seed production in fens and fen meadows along a disturbance gradient. Applied Vegetation Science 12: 304–315.

Klooker, J., R. van Diggelen & J.P. Bakker 1999. Natuurontwikkeling op minerale gronden. Ontgronden nieuwe kansen voor bedreigde plantensoorten. Rapport Rijks Universiteit Groningen (met Engelse samenvatting). (Translation: Nature development on mineral soils, Soil removal: New opportunities for threatened plant species?)

Kros, J., B.J. de Haan, R. Bobbink, J.A. van Jaarsveld, J.G.M. Roelofs & W.de Vries 2008. Effecten van ammoniak op de Nederlandse natuur. Wageningen, Alterra-rapport 1698, 132 p. (Translation: Effects of ammonia on Dutch nature.)


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Kuiters, A.T. 2002. Hoofed animals in nature areas: theory and practice versus research. Vakblad Natuurbeheer 41: 21-23.

Lamers, L. (ed.) 2006. Onderzoek ten behoeve van het herstel en beheer van Nederlandse laagveenwateren. Eindrapportage 2003-2006. Directie Kennis, Ministerie van Landbouw, Natuur en Voedselkwaliteit; DK nr. 2006/057-O. (Translation: Research concerning the restoration and management of Dutch low-fen waters.)

Lamers, L.P.M., E.C.H.E.T. Lucassen, A.J.P. Smolders & J.G.M. Roelofs 2005a. Fosfaat als adder onder het gras bij “nieuwe natuur”. H2O 17: 28-30. (Translation: Phosphate: the snake in the grass in “new nature”.)

Lamers, L.P.M., H.B.M. Tomassen & J.G.M. Roelofs 1998b. Sulfate-induced eutrophication and phytotoxicity in freshwater wetlands. Environmental science Technology 32:199-205.

Lamers, L.P.M., W.C.E.P. Verberk, J. Schouwenaars, M. Klinge, W.J. Rip, J.T.A. Verhoeven & G. Kooijman 2009. Laagveenherstel: soorten turven of het landschap boetseren? De Levende Natuur 110: 153-157. (Translation: Low-fen restoration: counting species or moulding the landscape?)

Limpens, J. 2009. De rol van de berk bij herstel en beheer van hoogveen. Gecombineerde resultaten van ‘Vervolg OBN Hoogveenonderzoek’ & ‘Effecten van berkenopslag en dichtheid op hoogveenvegetaties behorende tot het natte zandlandschap’. Rapport DK nr. 2009/dk119-O, Ministerie van LNV, Ede. (Translation: The role of birch in the restoration of high moors. Combined results of ‘Follow-up OBN high-moor research’ & ‘Effects of volunteer birch growth and density on high-moor vegetations belonging to the wet sand landscape’.)

Limpens, J. 2011. Onderzoek ten behoeve van herstel en beheer van Nederlandse hoogvenen. Concept eindrapportage OBN Hoogveenonderzoek 2009-2010; -Verlenging onderzoek naar effecten van berkenopslag en dichtheid op hoogveenvegetaties behorende tot het natte zandlandschap-. Rapport Wageningen Universiteit in opdracht van het ministerie van LNV. (Translation: Research concerning the restoration and management of Dutch low-fen waters. Draft final repor OBN high-moor research 2009-2010; Extension of the research on effects of volunteer birch growth and density on high-moor vegetations belonging to the wet sand landscape.)

Marrs, R.H. 1993. Soil fertility and nature conservation in Europe: Theoretical considerations and practical management solutions. Advances in Ecological research 24: 241-300.

Marrs, R.H., C.S.R. Snow, K.M. Owen & C.E. Evans 1998. Heathland and acid grassland creation on arable soil at Minsmere: identification of potential problems and a test of cropping to impoverish soils. Biological Conservation 85: 69-82.

Ministerie van Landbouw, Natuurbehoud en Visserij 1990. Natuurbeleidsplan. Regeringsbeslissing. Tweede Kamer, vergaderjaar 1989-1990, 21149, nrs 2-3. (Translation: Nature policy plan.)

Mouissie, A.M. 2004. Seed dispersal by large herbivores. PhD thesis University of Groningen. Odland, A. & R. del Moral 2002. Thirteen years of wetland succession following a permanent

drawdown, Myrkdalen, Norway. Plant Ecology 162: 185-198. Olsthoorn, A.F.M., C.A. van den Berg & J.J. de Gruijter 2006. Evaluatie van bemesting en

bekalking in bossen en de ontwikkeling in onbehandelde bossen; Alterra rapport 1337, 39 pp. (Translation: Evaluation of fertilising and liming in forests and the development in untreated forests.)

Ozinga, W.A, J.H.J. Schaminée, J.H.J., R.M. Bekker, S. Bonn, P. Potschlod, O. Tackenberg, J.P. Bakker & J.M. van Groenendael 2005. Predictability of plant species composition from environmental conditions is constrained by dispersal limitation. Oikos 108: 555-561.

Ozinga, W.A. 2008. Dispersal strategies of plants in Dutch landscapes. PhD Thesis, Radboud University Nijmegen.

Ozinga, W.A., S.M. Hennekens, J.H.J. Schaminée, N.A.C. Smits, R.M. Bekker, C. Römermann, L. Klimeš, J.P. Bakker & J.M. van Groenendael 2007. Local aboveground persistence of


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vascular plants: life-history trade-offs and environmental constraints. Journal of Vegetation Science 18: 489-497.

Pywell, R.F., N.R. Webb & P.D. Putwain 1994. Soil fertility and its implications for the restoration of heathland on farmland in southern Britain. Biological Conservation 70: 168-181.

Schaminée, J.H.J. & A.J.M. Jansen (red.) 1998. Wegen naar natuurdoeltypen. Ontwikkelingsreeksen en hun indicatoren ten behoeve van herstelbeheer en natuurontwikkeling (sporen A en B). Rapport 26, IKC-Natuurbeheer, Wageningen, 320 pp. (Translation: Ways towards target nature types. Development series and their indicators for restoration management (tracks A and B).)

Schaminée, J.H.J. & S.M. Hennekens 1985. Bodem en vegetatie van de Wylré-akkers (Zuid-Limburg): van bouwland naar krijthellinggrasland. De Levende Natuur 86: 53-60. (Translation: Soil and vegetation of the Wylré acres (South Limburg): from agricultural land to chalk slope grassland.)

Schouwenaars J.M., H. Esselink, L.P.M. Lamers & P.C. van der Molen 2002. Ontwikkelingen en herstel van hoogveensystemen: bestaande kennis en benodigd onderzoek. Rapport EC-LNV nr. 2002/084 O, Expertisecentrum LNV, Ministerie van Landbouw, Natuurbeheer en Visserij, Ede. (Translation: Development and restoration of high-moor systems: present knowledge and research required.)

Sival, F.P. & W.J. Chardon 2004. Natuurontwikkeling op fosfaatverzadigde gronden: fosfaatonttrekking door een gewas. Rapport 1090. Alterra, Wageningen. (Translation: Nature development on phosphate-saturated soils: phosphate extraction by a crop.)

Smits, N.A.C. 2010. Restoration of nutrient-poor grasslands in Southern Limburg: vegetation development and the role of soil processes. Proefschrift Rijksuniversiteit Utrecht, 148 pp.

Smits, N.A.C., R. Bobbink, J.H. Willems & J.H.J. Schaminée 2007. Evaluatie van een kwart eeuw schapenbegrazing op de Bemelerberg. Natuurhistorisch Maandblad 96: 114-121. (Translation: Evaluation of a quarter of a century of sheep grazing on the Bemelerberg.)

Smolders, A.J.P., E.C.H.E.T. Lucassen, M. van der Aalst, L.P.M. Lamers & J.G.M. Roelofs 2008. Decreasing the abundance of Juncus effusus on former agricultural lands with noncalcareous sandy soils: possible effects of liming and soil removal. Restoration Ecology 16: 240-248.

Smolders, A.J.P., M. Moonen, E.C.H.E.T. Lucassen, L.P.M. Lamers & J.G.M. Roelofs 2006b. Changes in pore water chemistry of desiccating freshwater sediments with different sulphur contents. Geoderma 132: 372-383.

Smolders, A.J.P., L.P.M. Lamers, E.C.H.E.T. Lucassen & J.G.M. Roelofs 2006a. Internal eutrophication: how it works and what to do about it - a review. Chemistry & Ecology 22: 93-111.

Stortelder, A.H.F., P.W.F.M. Hommel, R.W. de Waal, K.W. van Dort, J.G. Vrielink & R.J.A.M. Wolf 1998. Broekbossen. Bosecosystemen van Nederland deel 1. KNNV, Utrecht. (Translation: Swamps. Forest ecosystems of The Netherlands I.)

Strykstra, R.J. 2000. Reintroduction of plant species: shifting setting. PhD Thesis University of Groningen.

Stuyfzand, P.J., 1993. Hydrochemistry and hydrology of the coastal dune area of the Western Netherlands. Thesis. Vrije Universiteit, Amsterdam.

Van Andel, J. & A.P. Grootjans 2006. Concepts in restoration ecology. In: J. van Andel & J. Aronson (eds.), Restoration Ecology; the new frontier, pp. 16-28. Blackwell Publishing, Melbourne/Oxford/Victoria.

Van den Berg, L.J.L., Dorland, E., Vergeer, P., Hart, M.A.C., Bobbink, R. & Roelofs, J.G.M. 2005. Decline of acid-sensitive plant species in heathland can be attributed to ammonium toxicity in combination with low pH. New Phytologist 166: 551-564.


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Van der Berg, A., R. Haveman & M. Hornman 2000. De Kleine wrattenbijter Gampsocleis glabra herontdekt in Nederland (Orthoptera: Tettigoniidae). Nederlandse Faunistische Mededelingen II: 1-12. (Translation: The heath bush cricket Gampsocleis glabra rediscovered in The Netherlands (Orthoptera: Tettigoniidae).)

Van der Hoek, D. 2005. The effectiveness of restoration measures in species-rich fen meadows. PhD Thesis, Wageningen University.

Van Duinen, G.J., E. Brouwer, A.J.M. Jansen, J.G.M. Roelofs & M.G.C. Schouten 2009. Van hoogveen- en venherstel naar herstel van een ‘compleet’ nat zandlandschap. De Levende Natuur 110: 118-123. (Translation: From high moor and fen restoration to restoration of a ‘complete’ wet sand landscape.)

Van Turnhout, C., E. Brouwer, M. Nijssen, S. Stuijfzand, J. Vogels, H. Siepel & H. Esselink 2008. Herstelmaatregelen in heideterreinen; invloed op de fauna. Samenvatting OBN onderzoek en richtlijnen met betrekking tot de fauna. Rapport DK nr. 2008/042-O, Directie Kennis Ministerie van Landbouw, Natuur en Voedselkwaliteit, Ede. (Translation: Restoration measures in heath areas, influence on the fauna. Summary OBN research and guidelines for the fauna.)

Van Uytvanck J., T. Milotic & M. Hoffmann 2008. Effecten van extensieve begrazing op spontane verbossingsprocessen – middellange en lange termijneffecten. Rapporten van het Instituut voor Natuur- en Bosonderzoek 2008 (INBO.R.2008.53). Instituut voor Natuur- en Bosonderzoek, Brussel. (Translation: Effects of extensive grazing on spontaneous afforestation processes – medium and long-term effects.)

Van Wieren, S.E. 2006. Populations: re-introductions. In: J. van Andel & J. Aronson (eds.), Restoration Ecology; the new frontier, pp. 82-92. Blackwell Publishing, Melbourne/Oxford/Victoria.

Van Wieren, S.E., G.W.T.A. Groot Bruinderink, I.T.M. Jorritsma & A.T. Kuiters 1997. Hoefdieren in het boslandschap. Backhuys, Leiden. (Translation: Hooved animals in the forest landscape.)

Van Wirdum, G. 1979. Ecoterminologie en grondwaterregime. W.L.O.-mededelingen 6: 19-24. (Translation: Ecoterminology and groundwater regime.)

Van Wirdum, G. 1990. Vegetation and hydrology of floating rich-fens. Thesis Universiteit van Amsterdam.

Verberk, W.C.E.P. & H. Esselink 2003. Faunaherstel vereist de integratie van landschapsecologie en dierecologie. Landschap 20: 3-7. (Translation: Fauna restoration requires the integration of landscape ecology and animal ecology.)

Verberk, W.C.E.P., A.P. Grootjans & A.J.M. Jansen 2009. Natuurherstel: van standplaats naar landschap. De Levende Natuur 110: 105-110. (Translation: Restoring nature: from habitat to landscape.)

Verhagen, H.M.C. 2007. Changing Land Use Restoration perspectives of low production communities on agricultural fields after top soil removal. PhD Thesis, University of Groningen.

Wheeler, B.D. 1995. Introduction: restoration and wetlands. In: Wheeler, B.D., S.C. Shaw, W.J. Foyt & R.A Robertson (eds.), Restoration of temperate wetlands, pp. 1-18. Wiley and Sons, Chichester.

Whittaker, R.J., S.H. Jones, & T. Partomihardjo 1997. The rebuilding of an isolated rain forest assemblage: how disharmonic is the flora of Krakatau? Biodiversity Conservation 6: 1671-1696.

Wouters, B., M. Nijssen, J. Vogels & R. Verdonschot 2009. Eindrapport Voorbereidingsplan Kustduinen. Rapport Stichting Bargerveen, Nijmegen. (Translation: Final report: preparatory plan for coastal dunes.)

www.natuurkennis.nl. Website Ontwikkeling + Beheer Natuurkwaliteit. (Translation: Knowledge network: Development and Management of Nature Quality)

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