Restoration of natural hydrology in forests

UNIVERSITY OF COPENHAGEN FACULTY OF SCIENCE Master’s Thesis v Oscar Andersson Restoration of natural hydrology in forests. A map study of forest hydrology management and a case study of wetland legacy and restoration success in Gribskov, Denmark. Supervisor: Karsten Raulund Rasmussen Submitted on: 28. of June 2022

1 Name of department: Department of Geosciences and Natural Resource Management, Faculty of Science Author: Oscar Alexander Andersson (VSM164) Title and subtitle: Restoration of natural hydrology in forests. A map study of forest hydrology management and a case study of wetland legacy and restoration success in Gribskov, Denmark. Topic description: Hydrology of restored forested wetlands compared to a historic reference and map study revealing the cause and effect resulting in decline and subsequent increase of wetlands in Gribskov, Denmark Supervisor: Karsten Raulund Rasmussen Submitted on: 28 of June 2022 Front page photo: Gribskov, photo by Oscar Andersson (2022.03.03) ECTS points: 45 ECTS Number of characters: 48.901 (excluding spacing)

It was found that all three studied cases seem to have been hydrologically well restored, as the correlation between a shallow depth of ground water and presence of peat was high, indicating that the border of the wetland is situated approximately at the same location currently as it did

The historical conditions are investigated by analysing 19th century maps and by identifying peat in soil samples along transects. The current conditions are investigated through a current forest map and a GIS based rain fill model that identifies local depressions in the landscape, as well as measuring ground water depth in the field. The maps used for this study are also held up against each other and compared with the results of the field study to determine how well the delineation fits with the actual measured border of the wetlands.

An additional aspect of the field study dealt with the composition of soil horizons of the samples across the transects and across the three cases, revealing in what way soil constitutes change with increasing distance to a wetland.

An inclination analysis of the landscape surrounding the three restored wetlands was also made by a combination of field and map studies for investigating whether or not the border of wetlands are affected by the topography of the surface.

The map study was also done to investigate the timing and intensity of the management actions that have led to the steep decline of wetlands in the whole of Gribskov through time, as well as the opposite trend in recent years.

Thehistorically.inclination analysis was inconclusive, but vaguely supports the idea that topography do affect wetland borders. Method development is needed in order to reach more conclusive results in this Historicalmatter. ditching was found to have had a great effect on the decline of wetlands, and modern restoration projects also seem to be an effective measure of bringing the wetlands back.

Lastly, the soil samples consistently showed a decrease of peat with increasing distance to blank water and an increase of inorganic mineral soil with increasing distance.

This study combines a map study with a field study with the focus on wetland restoration. It investigates three restored wetlands in the forest of Gribskov and whether or not the restoration has been successful in bringing the wetlands back to historical, pre ditching conditions.

2 Abstract

3 Contents 1. Introduction 5 2. Materials and methods..............................................................................................................7 2.1. Biophysical characteristics of Gribskov 7 2.2. Maps and map analyses..........................................................................................................8 2.2.1. The GSTD maps 8 2.2.2. NST Forest map...............................................................................................................8 2.2.3. SCALGO rain fill map 9 2.2.4 Map analyses....................................................................................................................9 2.3. Field study description 10 2.4. Registration of samples........................................................................................................ 12 2.5. Transect placements 13 2.6. Analysis of collected data .................................................................................................... 15 2.6.1. Soil moisture 15 2.6.2. Soil horizon distribution............................................................................................... 15 2.6.3. Inclination on transects 15 2.6.4. Inclination map study................................................................................................... 16 2.6.5. GW depth 16 2.7. Statistical models and tools.................................................................................................. 16 3. Results 16 3.1. History of water management in Gribskov analyses of maps ........................................... 16 3.1.1. Wetlands 16 3.1.2. Ditches and canals......................................................................................................... 18 3.1.3. Peat excavation sites 19 3.2. Case studies.......................................................................................................................... 20 3.2.1. Soil wetness 20 3.2.2. Relation between wetness and peat.............................................................................. 21 3.2.3. Relation between wetness and inclination 22 3.2.4. Case specific soil wetness.............................................................................................. 22 3.2.5. Soil horizon distribution 23 3.2.6. GW depth ..................................................................................................................... 25 3.2.7. Comparing GW depth and soil horizon 25

4 3.2.8. Inclination study based on maps 28 4. Discussion............................................................................................................................... 30 4.1. Historical analysis of forest hydrology management in the whole of Gribskov 30 4.2. Comparing delineation of wetlands between the GTSD maps, NST forest map and SCALGO rain fill model with the three case areas 30 4.3. Are the three cases hydrologically restored to a pre ditching state?................................... 31 4.4. Comparing the inclination results from transect study and from the map study 32 4.5. Can the area of restored wetlands be estimated with high accuracy even before the restoration is initiated?............................................................................................................... 33 4.6. Strengths and weaknesses with this study. 33 5. References .............................................................................................................................. 35 6. Appendices 38 6.1. Equipment........................................................................................................................... 38 6.2. Field Protocol 38 6.3. Historical maps (except the GSTD maps from 1858) ........................................................... 39

Ditches for draining can also alter the water quality, as the runoff volume often increases and nutrient contamination in runoff water due to erosion is more frequent, leading to eutrophication of downstream water bodies (Blann, Anderson, Sands, & Vondracek, 2009, Remm, Löhmus, Leis, & Löhmus, 2013). Peat excavation is something that, similarly to draining, has adverse effects on water flow and water retention capacity (Menberu, et al., 2016). Ditching of wetlands with sphagnum growth also contributes to the climate crisis by aerating the peat, allowing decomposition to speed up and thereby turning those areas from a sink of atmospheric carbon into a source of it (Holden, Chapman, & Labadz, (Blann,2004). Anderson, Sands, & Vondracek, 2009) (Remm, Löhmus, Leis, & Löhmus, 2013) (Malmström, 1928) (Holmen, 1964) (Hånell, 1988) (Campeau & Rochefort, 1996) (Millennium Ecosystem Assessment, 2005)

5 1. Introduction

The purpose of this has been to make the forest soils dryer and more suitable for forest production. Drained wetlands also have the additional benefit in relation to forest production of a carbon rich and fertile soil (Malmström, 1928, Holmen, 1964, Hånell, 1988). The extensive digging of drains has resulted in a steep and substantial decline in wetlands within the forests, something that has a negative impact on species associated with those particular habitats (Campeau & Rochefort, 1996, Millennium Ecosystem Assessment, 2005)

In the last few decades decision makers have become increasingly aware of these issues and the Danish government is now taking action to try and reverse negative impacts on nature through its agency for state owned nature areas: the Danish Nature Agency, (hereafter abbreviated according to its Danish official abbreviation, NST, Naturstyrelsen) (NST (a), 2022). Efforts are now made to do more restoration of natural hydrology through blocking of drains wherever it is practically, technically and neighbourly possible, and where very specific considerations of nature do not speak against it (NST, 2021)

Digging drains has been common practice in Danish forests for the last 200 years (Rune, 2009), a tradition that is shared with most of north western Europe, especially the British Isles (Holden, Chapman, & Labadz, 2004)

If the restoration is done uncritically, there are potential negative impacts on the current infrastructure of paths that risk getting asditchessiteshypothesisthatrestorationThewhichneighbouringflooded,andnewwetareasmightextendontoprivatelandandaffectlanduse,shouldbeavoided(NST,2021).hypothesisofthisstudyisthatthebringsbackhydrologytothestateithadbeforedrainingtookplace.ThisistestedbyafieldstudyofthreeinGribskovthathavehaddrainingblockedwithinthelast15yearsand,aresult,havebecomewetter.

There are, however, uncertainties on how exactly thisactionwillaffectthehydrology of the individual restoration sites. Other studies on restoration of forested wetlands have had focus on the development of wetland vegetation (Timmermann, Margóczi, Takács, & Vegelin, 2006), but less focus has been on the actual wetness of restored sites. It cannot be assumed that hydrology conditions will return to a pre ditching state if ditches are blocked. Other factors, such as tree species compositions and historical peat excavations also play a role in the water balance of the forests, as well as changed weather patterns over the years. Ground water extraction for drinking water might also influence surface water balance. (Henriksen, et al., 2003)

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Related research questions were: Are these restoration sites hydrologically restored to a pre ditching state? How well do the shape and area of the rewetted area correspond with the topography of the landscape? Can the boundary of the rewetted area be estimated with high accuracy even before the restoration is initiated?

A map based analysis of the whole of Gribskov is carried out to assess both the change in area of wetlands through time, and timing and intensity of the management actions that have affected this, namely ditching and peat excavation, and in recent years also ditch blocking. The maps from 1858 by General staff topographic department, hereafter abbreviated as the GSTDmaps, are used for historical reference (The Danish Agency for Data Supply and Efficiency (a), 2022). The maps that are used or the current situation, are the current forest map from the NST (NST (b), 2022) and a rain fill modelled map by SCALGO (SCALGO, 2022) which is based upon, and integrated with, the elevation model of Denmark (The Danish Agency for Data Supply and Efficiency (b), 2022) What can be assessed through investigating historical and modelled maps is neither an exhaustive, nor a fully legitimate, representation of the extent of past and restored wetlands. Therefore, a field study of three restored wetlands in Gribskov is performed in order to investigate the historical legacy of these wetlands on site In the field study, samples of the soil adjacent to wetlands are extracted and traces of old wetland legacy in the form of peat can be studied with high accuracy The legacy can then be held up against the current hydrological situation post restoration and the success of the restoration can be assessed.

Figure1:MapofDenmarkshowingtheposition andshapeofGribskov. by approximately 0.1°C per decade (DMI, 2021, The Ministry of Environment in Denmark, 2022). The landscape of today is largely formed during the late Weichsel ice age as the edge of the Scandinavian ice sheet pushed forward over and retreated from the area, in a time span of hundreds of years beforeretreating completely by theendof the ice age. What was left behind was a landscape system of north northeast south southwest going terminal moraines with parallel ridges and valleys, mainly consisting of glaciofluvial sand and gravel. This landscape is scattered with over a thousand smaller depressions, so called kettleholes, originally forming shallow lakes, most of them developing into wetlands over time. Only the largest ones have remained as lakes to this day: Store Gribsø, Lille Gribsø and Hjortesøle (Rune, 1997, Rune, 2009, NST (d), 2022) Due to the uneven landscape filled with wetlands, the area that is now Gribskov was never extensively farmed and has remained forested to this day, making it an area of extraordinarily long forest continuity (Rune, 2009, Overballe Petersen, Nielsen, Hannon, Halsall, & Bradshaw, 2013). (Rune, 1997) (NST (c), 2022) (DMI, 2021) (TheMinistryof Environmentin Denmark, 2022). (Rune, 1997) (Rune, 2009) (NST (d), 2022) (Rune, 2009) (Overballe Petersen, Nielsen, Hannon, Halsall, & Bradshaw, 2013)

7 2. Materials and methods

2.1. Biophysical characteristics of Gribskov Gribskov is the largest forest on Zealand, measuring 5650 hectares (fig 1) This study includes the state owned part of Gribskov only, so the parts conventionally considered as parts of Gribskov, Rankeskov and Strødam Plantage, are left out. The forest is situated centrally in northern Zealand, approximately 40 km north of Copenhagen with the highest and lowest points being 89 m and 9 m above sea level respectively, making it rather hilly in a Danish context (Rune, 1997, NST (c), 2022) Average annual precipitation in the area is about 650 mm per year and has been

alsotemperaturelastincreasingwithapproximately1mm/yforthe150years.(DMI,2021).Theannualmeanisapproximately9°Candhasbeenincreasingforthelast150years

The GSTD maps covering northern Zealand are from 1858 and have a resolution of 1:20 000 (fig 2) (The Danish Agency for Data Supply and Efficiency (a), 2022) The GSTD map of Gribskov is the earliest map of the forest where all wetlands are delineated somewhat accurately. The map was made by the Danish military to have a superior overview of the landscape in case of a foreign invasion. Having detailed information of the location of all wetlands enables Danish army troops avoid them in order to advantage over the enemy by being able to navigate and move more swiftly through the terrain (Svenningsen, 2021) Drainage digging had already begun by thetimethismap wasmade, but the effect on the wetlands was still only

Figure2:GSTDmapfrom1858. minor. Therefore, this map is studied in detail as adocumentedandnearly pristine reference state for wetland distribution in Gribskov. Although highly accurate for its time, the 19th century maps do not live up to the accuracy of modern topographical maps. Thus, the delineation of the wetlands in those maps cannot stand on their own as reference to an original hydrology, as they are not accurate enough on a smaller scale.

The forest map from NST (fig 3) (NST (b), 2022), divides the forest into management units of single species forest stands and unforested areas The map is partly based on older maps from when the areas that are now restored wetlands, were still drained and planted with trees, so the delineation of wetlands is sometimes a poor fit. This map, however, is what the nature agency uses as the basis for registration of areas with restored hydrology, so it’s thereby also the basis map used in this project for choosing case areas

The main maps studied are the GSTD maps (The Danish Agency for Data Supply and Efficiency (a), 2022), the forest map from NST (NST (b), 2022) and a GIS based analysis of flooded areas by SCALGO (SCALGO, 2022)

8 2.2. Maps and map analyses

Figure3:TheNSTforestmapwithmanagementunits.

2.2.2. NST Forest map

2.2.1. The GSTD maps

9 2.2.3. SCALGO rain fill map In SCALGO (SCALGO, 2022), a web hosted workspace, GIS analyses of flooded areas in case of rain events can be made, taking the topography and water flows into consideration. The analysis uses the elevation model of Denmark by the Agency for Data supply and Efficiency, which has a 0 4 m*0.4 m grid (The Danish Agency for Data Supply and Efficiency (b), 2022). The model is a so called “glass model”, meaning it does not work with parameters other than the topography and precipitation. It is possible to make local models of seepage, but the standard form is the glass model, where the precipitation modelled accumulates in all localdepressionsuntilitflowsoverinto lower local depressions until it reaches the ocean. The actual dynamics of the water regime is muchmorecomplex, but theSCALGO model gives an estimate of locations for plausible wetlands. Due to the high resolution grid of the elevation model, the resulting image appears as very precise Difference in the blue colours in the map represents different projected water depths as a result of the rain event (fig 4) 2.2.4 Map analyses With the help of aforementioned maps, as well as an array of additional historical maps, analyses on wetland area, ditching and peat excavation could be carried out in QGIS For thewetlandarea analysis,theGSTDmapsand a topographical map from 1994 was used as historical references of a near pristine state as well as a degraded state The NST forest map was used as reference to the current state. Polygons were drawn and numberand area of wetlandscould becalculated. For theditching analysis, the GSTD maps and the The Danish “Høje Målebordsblade” (HMB) map set were used as historical references from 1858 and 1898, and the NST forest map was used as the current state. Line elements were drawn and the total length could be calculated for all three maps

GSTD map from 1830 (1:80 000)

Figure4:SCALGOmodelledmapshowingrainfillareasfora15mmrainevent.

Through analysing seven different historical maps dating from 1830 to 1994, the distribution of areas where peat extraction has been performed in Gribskov in the last circa 200 years were found and plotted out as point elements. The maps studied for this investigation are:

GSTD maps from 1858 (1:20 000) HMB maps from 1898 (1:20 000) LMB maps from 1915 (1.20 000) LMB maps from 1960 (1:20 000) 4 cm maps from 1968 (1:25 000) 4 cm maps from 1994 (1:25 000) (LMB = Lave Målebordsblade)

Figure5:Thethreestudycasesoverviewanddetail.NSTforestmapasbackground

Three restored wetlands of which the restoration was carried out between 2009 and 2016 by NST were chosen for the field study

Case 1 Case 2 Case 1 Case 3

10 2.3. Field study description

The three sites range in size of 0.8 to 2 hectares and are positioned in proximity to each other, with all three sites fitting well within a circle with a radius of 500 m The three sites are hereafter named Case 1, Case 2 g and Case 3 respectively. All three sites have been heavily ditched out and drained, with the majority of existing ditches having been dug out by the turn of the 20th century. According to studied maps none of the cases have had peat excavation on them. The delineation of the case areas is based on the forest map by NST (fig 5).

At each individual case transects were positioned out along the expected border of blank water,pointingaway fromitincardinal directions, four transects at Case 1, seven at Case 2 and six at Case 3. The innermost sample spot was chosen to be at the border of blank water and the rest were at equal cnnnncc distances in a straight line farther and farther away from the blank water (fig 6 and fig 7)

On site hydrology investigations through soil sampling were made to estimate both the current and the historical wetland extent of the three cases. When comparing the results of the on site investigations to the GSTD maps and with the SCALGO model it was possible to evaluate to what degree the restoration has been successful and if any of the mapping tools were reliable and/or useful in terms of a delineation of the actual restored wetland The investigation was done by carefully choosing transects around the expected border of each of the restored areas.

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A smartphone app called GPS Logger© by Basic Air Data was used to register geo reference locations for each sample spot. Because the comparably poor precision of this app of approximately 4 metres, it was necessary to manually adjust all sample points in QGIS upon finishing the field work. By doing the sampling in the wintertime, which is the wettest season in Denmark, it was expected that the water level was close to its annual maximum. The month of February 2022 was also the second wettest February in Denmark since official measurements on precipitation started in 1874. (DMI, 2022) 93 samples in total were taken at the three cases, distributed on 17 transects on February 22., 23., 25. and 28, as well as March 1., 3., 7. and 14. transectFigure6and7:Picturetakenattheinnermostspotoftransect2.6facingtheblankwaterandalongtherespectively(Mar14,2022).

removedFigure9and10:Picturestakenatsample2oftransect3.3showingtheaugerfilledwithsoilandwithsoilfromtheaugerrespectively(Mar.3,2022).

measuringshowingFigure8:Picturetakenatsample5oftransect3.5theaugerfilledwithsoilwiththestickbesideit.Theperforatedplasticpipeisalsoshowninsidethehole.(Mar.7,2022).

At each sampling site a hole was made with a soil sampling auger with a depth of 95cm and soil was pulled out. A manually perforated PVC pipe Ø25 mm was then pushed into the hole made by the auger. After a few minutes, when the water had set inside the pipe, the depth was measured with a water depth logger device consisting of a measuring tape by WEISS MESSWERKZEUGE GmbH with an accompanying metal piece attached to the end The metal piece makes a sound when it hits a water surface and the depth can be noted. A measuring stick was laid down beside the soil filled auger, so depth specific registrations could be made (fig 8). Registrations of wetness, texture and organic matter of the soil and ground water (GW) depths for each sample was made on a field protocol. In addition to the protocol, many photographs were taken of each soil sample, both while still inside the auger and also whentaken out forregistering thesoiltexture and wetness (fig 9 and 10).

12 2.4. Registration of samples

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The organic matter of the soil samples is also evaluated qualitatively and divided into distinct horizons, which were categorised within following four categories: O horizon (forest floor litter) H horizon (peat soil) A horizon (organic mineral soil) B horizon (inorganic mineral soil)

By giving the categories numerical classes, it was possible to do calculations on the soil wetness. However, registration is made through qualitative estimations, not measurements (as a soil moisture sensor would provide), so the results regarding soil moisture in this study should also be considered as estimations.

A few samplesappeared withoutan unbroken coherent soil profile. This might be explained by air pockets from decomposed roots or from burrows. However, since it’s unknown what soil horizon that should have been there, the hollows are referred to as “Missing data” when analysing the samples.

Depending on the wetness, the forest floor litter, in time, turns into either slowly decomposing and accumulating peat or quickly decomposing organic mineral soil. If the wet, peat forming conditions change through drainage digging, the peat starts decomposing. This is still a very slow process and most peat will remain in the soil profile for many years (Chadburn, et al., 2022).

Soil wetness was evaluated through the qualitative method of observing and touching the soil. Values from 1 to 4 were attributed to sections of the soil sample according to following categories: Soaked (4). Soil is over saturated with water anddoesn’thaveafirm structure. Wet (3). Soil feels wet and is easily kneaded. It has a semi firm structure. Moist (2). Soil smoulders between fingers, but can also be kneaded. Dry (1). Soil looks and feels dry. It smoulders and cannot be kneaded.

2.5. Transect placements When preparing the field work, finding sampling spots that were representative was of high importance This was guarded by making sure transects are plotted in all four cardinal directions for each case area. A variety of inclination steepness of transects was also sought for, as the selection of transects should be representative of the true terrain surrounding each case area. A tool in SCALGO, where it’s possible to draw transects and thus, clearly see the inclination was used to find representative positions of transects (fig 11), as well as a combination of the SCALGO modelled map and the delineation made on the NST forest map.

Figure11:ProfiletoolinSCALGOinuseshowingtheprofilefortransectnumber2.1.

Preliminary, the innermost sample spot was chosen to be at the border of blank water according to the rain fill model in SCALGO and when performing the sampling in the field, the innermost sample spot was adjusted to the actual border of blank water. In the following two figures of Case 2, the chosen transects with pre meditated sampling points and the actual sampling points are shown respectively Three of the transects at Case 2 (2.2, 2.3 and 2.5) were adjusted considerably from long (20 m) to short (10 m) due to proposed starting point being submerged in water and inclination being steeper from new starting point (fig 12 and 13)

discrepancyFigure12:Case2withproposedsamplespotsbasedonanalysisoflocalinclinationsofthelandscapeandindelineationbetweenSCALGOtoolandtheforestmapbyNST.

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Two different lengths of transects were chosen for this study. Either the transects were 10 metres with a sample spot every second meter or 20 metres with a sample spot every fourth meter The length of each transectdepended on whetherthe inclination was flat or steep. A flatter inclination would grant the longer transect, as the expectation was that a wetland stretches farther from blank water in a flat terrain than in a steep terrain. One exception was transect number 2.1, where the 20 metre transect here is justified by the big discrepancy in delineation between the SCALGO model and the NST forest map at this particular location, despite a rather steep inclination (visible on fig 11)

2.6.2. Soil horizon distribution

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Across all samples there were great variations of colour and texture, but the main characteristics of the soil horizons in relation to this study is the presence or absence of peat Peaty soils reveal the legacy of the location in terms of water saturation. In this study it was used as the most important inclusion criterion for whether a location should be considered as having been part of a wetland historically or not When analysing the data, the presence or absence of a H horizon werehighlightedas themain two soil horizon types.

2.6.1. Soil moisture

In relation to soil moisture, it was also noted that there was a variation of wetness in the soil samples. This wetness variation was analysed superficially and there was variation both inthesoilcolumn of individualtransects and in between transects

2.6. Analysis of collected data By comparing the registrations of moisture, texture and organic matter between depths, transects and case areas, several conditions of the samples can be extracted and analysed.

Figure13:Case2withthetruepositionsofthesamplespots.

In most cases the wetness varied with depth, so the depth specific registrations were put together and a mean wetness value was calculated. The mean value laid between 1 and 4, where those values were the absolute extremes of the chosen registration method.

2.6.3 Inclination on transects

Tools for measuring the inclination of the terrain on site was not used for this study Instead, thestudy was reliant on the elevation model of Denmark, as well as an accurate pin pointing of the transect locations.

Table1:ThechangeinwetlandareaandrelativechangeinGribskovaccordingtothreemaps.

2.7. Statistical models and tools Analysis of the collected data was made in Microsoft Excel. Statistical analysis of testing the significance of regression models and t Tests were made using Excel’ s Data Analysis tool.

2.6.5. GW depth

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The inclination data was, thus, derived from a model rather than measurements. All inclinations were calculated in relation to the innermost point of each transect, giving all those sample points an inclination value of 0. 2.6.4. Inclination map study

A study from Finland uses a GW level of 30 cm as a threshold of what they consider to categorise as a mire (Menberu, et al., 2016). The same threshold was used for this study, meaning a measured GW depth of less than 30 cm could be considered as a sample spot inside of a restored wetland.

The total wetland area in Gribskov was found to having decreased considerably between 1858 and 1994 and is now increasing again as a result of restoration projects and ceased maintenance of drainage ditches (table 1). Accordingto theGSTD maps, morethan1700 wetlands were found to having been scattered all over Gribskov in 1858, covering 1235 hectares (fig 14). By 1994, according to the topographical maps from that time, the total wetland area inGribskov was found to having declined to 82 hectares (fig 15). In the latest available forest map by NST (2018), it was found that the wetland area had again increased to 308 hectares (fig 16).

The GW depth was analysed as a measure of whether the location should be considered inside or outside the area of restored wetland.

An additional case specific map study on inclination based on the SCALGO rain fill model was made to complement the transect inclination data. The study was made by plotting the rain fill area for each of the three cases inQGISand registerthearea. Afterthat, areas of a hypothetical situation where the depth of the rain filled areas are increased by 10 cm were plotted. By doing this, a smaller area, corresponding with the SCALGO rain fill model and a larger area, forming a SCALGO rain fill model +10 cm was found. The difference in size between these areas gave an indication of how great of an inclination there is in the immediate surroundings of the wetlands. In order to enable calculating an approximate mean inclination between the border of the smaller area and the border of the larger area, an assumption of a circular shape of all areas was made. By making this assumption, the inclination (%) could be calculated using the following formula: 0.1 √��2 π √��1 π Where A1 represents the area (m2) of the rain fill model and A2 represents the area (m2) of the rain fill model if the water is raised by 10 cm (0.1 m).

3. Results

3.1. History of water management in Gribskov analyses of maps 3.1.1. Wetlands

17 Figure 14:MapofGribskovwithwetlandareaas background.Figureitwasin1858.(QGIS)GSTDmapsasbackground.16:MapofGribskovwithwetlandareaasitwasin2018.(QGIS).NSTforestmapas initFigure15:MapofGribskovwithwetlandareaaswasin1994.(QGIS).Topographicalmapdrawn1:25000from1994asbackground.

Figure18:MapofditchesinGribskovby1898(QGIS).

Gribskovaccordingtothreemaps.

Figure (QGIS).17:MapofditchesinGribskovby1858 had increased to 439 km and in the latest available forest map by NST (2018), the total length was 489 km. Note that the newest length also includes non functioning ditches due to either blocking as a restoration measure or due to ceased maintenance (Table 2 and fig 17, 18 and 19).

The total length of dug out drainage ditches was found to having increased through time Most notably, the length was found to have

havelengthandincreasedby245kmin40yearsbetween18581898Throughmapanalysis,thetotalofditchesin1858wasfoundtobeen194km.In1898thetotallength

18 3.1.2. Ditches and canals

Table2:Thechangeinlengthofdug outditchesandrelativechangein

Figure19:MapofditchesinGribskovby2018(QGIS).

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3.1.3. Peat excavation sites

Different wetlands were found to having been excavated at different points in time (table 3 and fig 20). Only four (albeit large) wetlands were found to having been continuously utilised for peat excavation through time: Tokkerup mose, Grøftemose, Bøndernes Tørvemose and Hovmose.

The total number of excavation sites was found to have varied through time and according to the map study it peaked around 1898. Individual excavation sites were found to only seldomly having being in use for longer periods of time and most of them disappeared between one map and the next.

Table3:ThechangeinnumberofpeatexcavationsitesandrelativechangeinGribskovaccordingtosevenmaps.

excavationFigure20:MapofGribskovwithlocationsforpeat(QGIS).NSTforestmapasbackground.

The soil was generally wetter closer to the blank water than it was farther away (fig 21). The variation at each distance was big, which means the different transects across the three cases differed quite a lot in relation to the wetness of the soil. The trend of soil moisture distance was clear and through a linear regression analysis, the negative correlation of wetness over distance from blank water was found to be highly statistically significant (p < 0.001, fig 21) from blank water (m)

over

20 3.2. Case studies 3.2.1. Soil wetness

Relation between wetness index and distance

4321 0 2 4 6 8 10 12 14 16 18 20 (1Wetness4) Distance

Figure21:Chartshowingtherelationbetweenwetnessindexanddistancetoblankwater.Alineartrendlineisadded.

21 3.2.2. Relation between wetness and peat Itwasfoundthrough at Testthat soilsamples with an H horizon present were significantly wetter than soil samples without an H horizon present. (p < 0.001, Table 4 and fig 22). wetness of the soil. The trend of soil moisture over distance was clear and through a linear regression analysis, the negative correlation of wetness over distance from blank water was found to be highly statistically significant. (p < 0.001, fig 21). Table 4: t Test: TwoSampleAssumingEqual Variances between soils with or withoutanH horizon. 4321 0 2 4 6 8 10 12 14 16 18 20 (1Wetness4) Distance from blank water (m) Relation between wetness index and distance Peat present Peat absent Figure22:Chartshowingtherelationbetweenwetnessindexanddistancetoblankwaterdividedbetweenthetwomajorsoilhorizonsfound,onewherepeatsoilispresentinthesoilcolumnandonewhereitisnot.

22 3.2.3. Relation between wetness and inclination Since inclination was calculated in relation to the starting point of each transect (0 m from blank water), the data at that distance were given zero as value and thus, excluded ssvsvvvvvvs 3.2.4. Case specific soil wetness An analysis of the correlation of wetness and distance between the three cases showed that Case 3 had generally wetter soils than both Case 1 and Case 2 across all distances The negative correlation of wetness over c from this particular chart. No significant correlation between mean soil wetness and inclination was found, meaning the shape of the terrain did not seem to have an effect on the wetness of the soil (p = 0.73, fig 23) distancesvvvvvvs from blank water was highly statistically significant for all three cases (pindividually.<0.001for all three cases, fig 24) 4321 -1% 4% 9% 14% 19% 24% (1Wetness4) Inclination (%) Relation between wetness index and inclination Figure23:Chartshowingtherelationbetweenwetnessindexandinclinationoftheground. Alineartrend Figurelineisadded.24:Chartshowingtherelationbetweenwetnessindexanddistancetoblankwaterdividedbetweenthethreecases.Lineartrendlinesfortheindividualcasesareadded. 4321 0 2 4 6 8 10 12 14 16 18 20 (1Wetness-4) Distance from blank water (m) Relation between wetness index and distance Case 1 Case 2 Case 3 Linear (Case 1) Linear (Case 2) Linear (Case 3)

23 3.2.5. Soil horizon distribution For all three cases it was observed that the distribution of the H horizon decreased with greater distance to blank water and the distribution of the B horizon increased with greater distance to blank water (fig 25, 26 and 27). Through regression analyses it was found that these observations were highly s statistically significant for Case 2 and Case 3 (p < 0.001). For Case 1, B horizon distribution correlated positively with distance, but not significantly (p = 0.073). Also at Case 1, H horizon distribution correlated negatively with distance, but not strongly significant (p = 0.014). 50%40%30%20%10%0% 60% 100%90%80%70% 0 2 4 6 8 10 12 14 16 18 20 Distance to blank water (m) Soil horizon distribution at each distance to blank water: Case 1 O-horizon A-horizon B-horizon H-horizon Missing data 100%90%80%70%60%50%40%30%20%10%0% 0 2 4 6 8 10 12 14 16 18 20 Distance to blank water (m) Soil horizon distribution at each distance to blank water: Case 2 O-horizon A-horizon B-horizon H-horizon Missing data Figure25:ColumnchartshowingsoilhorizondistributionateachdistancetoblankwateratCase1.Figure26:ColumnchartshowingsoilhorizondistributionateachdistancetoblankwateratCase2

24 6 out of 46 samples farther away than 0 m from blank water at Case 1 and Case 2 had peat soil present and 9 out of 30 samples farther away from 0 m from blank water at Case 3, had peat soil present, showing that peat was not prevalent away from blank water at Case 1 and Case 2, but more so at Case 3 (table 5). 100%90%80%70%60%50%40%30%20%10%0% 0 2 4 6 8 10 12 14 16 18 20 Distance to blank water (m) Soil horizon distribution at each distance to blank water: Case 3 O-horizon A-horizon B-horizon H-horizon Missing data TableFigure27:ColumnchartshowingsoilhorizondistributionateachdistancetoblankwateratCase25:Fractionofsampleswherepeatysoilispresentateachcaseandforeachdistance,aswell as percentageacrossallcases

25 3.2.6. GW depth GWdepth was found to bemost shallow close to blank water, with all 31 sample points that had a GW depth of less than 30 cm being at 8 m from blank water or closer 20 of all vvvvvvvv 3.2 7 Comparing GW depth and soil horizon It was found that in all but four samples, either GW was above 30 cm depth and had peat present, or GW was below 30 cm depth vvvv sample points had a GW depth below the maximum depth of the auger, giving those samples an unspecified depth of > 95 cm (fig with28)peat being absent (table 6 and fig 29, 30, 31 and 32). 9060300 0 2 4 6 8 10 12 14 16 18 20 (cm)depthGW Distance from blank water (m) Relation between GW depth and distance Samples with GW below auger depth (> 95 cm): 2 5 5 2 3 3 Figure28:ThemeasuredGWdepthateachsamplespotacrossallthreecases The30cmthresholdchosen forconsideringtheparticularsiteasbeingpartofawetlandismarkedwithabluelineonthechart.SampleswhereGWwastoodeeptobemeasuredareshownasnumbersunderneaththechartateachrespectivedistance.Table6:Comparisonbetweenpresence/absenceofpeatversusGWdepthofabove/below30cmofallsoilsamples

26 0.90.60.30 0 2 4 6 8 10 12 14 16 18 20 (m)depthGW Distance to open water (m) Relation between GW depth and distance Peat present Peat absent Samples with GW below Auger depth (> 95 cm): 2 5 5 2 3 3 cmFigure29:RelationbetweenGWdepthanddistancealsoshowingwhetherornotpeatispresent.The30thresholdchosenforconsideringtheparticularsiteasbeingpartofawetlandismarkedwithabluelineonthechart.SampleswhereGWwastoodeeptobemeasuredareshownasnumbersunderneaththechartateachrespectivedistance.Figure30:MapofCase1showingsoilandGWcharacteristicsofeachsamplespot.GSTDmapasbackground.

27 Figure31:MapofCase2showingsoiland GWcharacteristicsofeachsamplespot. GSTDmapas background.Figure32:MapofCase3showingsoiland GWcharacteristicsofeachsamplespot. GSTDmapas background.

28 3.2.8. Inclination study based on maps

levelTable7:TheincreaseofareaofwatercoveredlandaccordingtoSCALGOrainfillmodelifwaterisraisedby10cm.Table8:Assumingacircularshapeofrainfilledareaandtherainfill+10cmarea.Thereaftercalculatingtheinclinationbetweentheinnerandoutercircle.Figure33:OrthophotoofCase1showingtherainfillareaaccordingtoSCALGOmodelasitisandifraisedby10cm.

Itwas found that thegreatestrelative increase in area if the SCALGO rain fill model would have water level increase of 10 cm was at Case 3, and it was found that the lowest mean vvvvv inclination between the two areas, with the assumptionof theshapeofthe areas isacircle, was at Case 2 (table 7 and 8 and fig 33, 34 and 35)

29 ifFigureifFigure34:OrthophotoofCase2showingtherainfillareaaccordingtoSCALGOmodelasitisandraisedby10cm.35:OrthophotoofCase3showingtherainfillareaaccordingtoSCALGOmodelasitisandraisedby10cm.

Conversely, the restoration efforts that have been ongoing since 1986, when the first project for restoring natural hydrology in Gribskov, named Toggerup Tørvemose was carried out, have also started proving to be successful According to the newest available maps, the overall wetland area of Gribskov has yet again started increasing considerably The intensity of peat excavation in Gribskov was found to have varied through time, with the number of peat excavation sites marked on the maps studied varied between 4 to 106.

Similar to (Norstedt, Hasselquist, & Laudon, 2021), where land use change from mires to agricultural land was investigated through a series of historical maps, this study also presented how management interventions have gradually changed the hydrological infrastructure in Gribskov. It was found that the extensive ditching of the forest and the subsequent planting of trees was a successful method in terms of reducing the wetland area by over 90% and thus making the land more effective in terms of wood production.

30 4. Discussion 4.1. Historical analysis of forest hydrology management in the whole of Gribskov

By thoroughly studying historical maps and registering specific attributes, such as ditches and wetlands, it was possible to get a detailed understanding of the changes through time for these attributes individually and analyse the consequences of historical interventions.

The existence of an individual site was relatively temporary with only few sites reappearing in subsequent maps, which is illustrated by the total number of sites across all seven historical maps together adding up to 258 This indicates that there might have been sites that were dug out and abandoned in between two maps, and thus not registered on either.

4.2. Comparing delineation of wetlands between the GTSD maps, NST forest map and SCALGO rain fill model with the three case areas

The delineation of the mapped wetlands did not strictly follow the topography of the landscape in the NST forest map and in the GTSD maps. In both those maps wetlands positioned several metres uphill was included in some places and areas near the bottom of a local depression were excluded in other places On the other hand, the delineation of the SCALGO rain fill map, which is completely based on the elevation model, did strictly follow the topography. When comparing the delineation of the different maps with the results of the in field sampling, it was found that the SCALGO rain fill map was a superior fit to the size and shape of the actual wetland at all three cases compared to the other two maps This implies that wetlands are restricted to depressions in the landscape and that the SCALGO rain fill model can be of great help when making maps that show wetlands with accurate Indelineationasomewhat similar study by Timár, et al. (2008), where areas in Romania and Serbia, that were flooded by a storm in 2005, were investigated through bothhistoricalmaps and an elevation model It was found that, although the delineation of the historical maps was rather unprecise, it could be determined that thearea that was floodedwas certainly part of a former wetland In this study, the results of the map study strongly indicatesthat the GTSD maps isa trustworthy source as a reference to a historical and near pristine distribution of wetlands, but, just like the aforementioned study, lacks precision in the fine scale delineation. (Timár, et al., 2008),

Figure36:MapofpartofGribskovthatincludesallthreecaseareas, showingthedelineationofSCALGO rainfilloverlayingwetlanddelineationoftheGTSDmaps.

Many similarities can be found between the wetland delineation of the GTSD maps and the SCALGO rain fill model, which indicates 4.3. Are the three cases hydrologically restored to a pre ditching state?

When analysing soil samples alone, soil samples rarely contained peaty soil farther away than 0 m from blank water at Case 1 and Case 2. This indicated that these two cases have not been wetter historically than they are now and thus, they seemed to be hydrologically well restored. At Case 3, peat present in soils were common at longer distances from blank water. This indicated that the water table could have been higher in pre ditching times. thatmost wetlands including thethreecases in this study were indeed identified and drawn onto the maps to a manageable degree of accuracy for the time (fig 36)

It was found that the soils at Case 3 were generally wetter than at the other two cases Instead of the presence of peat several metres from blank water being an indication that Case 3 is supposedly not as well restored as the other two cases, the wet soil samples instead indicates that a larger portion of the wetland might be on dry land here. This observation contradicts the claim of the previous observation, as it explains how the current extent of blank water can be sufficient for Case 3 to be considered well restored.

31

A larger relative difference does roughly correspond with a lower general inclination. The relative difference was largest at Case 3, suggesting that areahaving thelowestgeneral However,inclination.sincethealtitudedifferenceis fixed on 10 cm, the scaling of the area affects the inclination. This means that a large area has a lower inclination than a small area if the relative difference in size is the same. Case 2 has the largest area out of the three cases, and when calculating the general inclination here, it was found to have been lower than it was at Case 3. The calculation performed to get to this result made use of the assumption of areas with circular shape. However, none of the three cases have a shape that is remotely circular, so the calculations do not correspond well with the actual situation

The calculated inclination of the map study was found to be approximately 1/10 of the mean transect inclinations (table 9).

32 Correspondingly to Menberu, et al., (2016), GW depth of 30 cm was considered the threshold for whether a location is currently wet enough to be considered as part of a wetland, and peat present in the soil, an indication that the location has been wet enough to support wetland vegetation in the past. These two parameters were found to correlate to a high degree across all three cases and this strong correlation is thus an indication that all three cases have been successfully restored to a pre ditching state. 4.4. Comparing the inclination results from transect study and from the map study No measurements of inclination were made for this study. Instead, the elevation model of Denmark (The Danish Agency for Data Supply and Efficiency (b), 2022) was used. Aligning this model with measurements in the field proved to be impossible to do accurately with the chosen tools. The accuracy of the GPS logger was too unprecise, so manual adjustmentof thegeo references of the transects was needed. The use of compass and 20 m measuring tape in the field study was an assertion that the transects were positioned in cardinal directions and that sample spots were at the designated distances from each other, but their accurate position on a map could not be assured. It was expected to find a clear relation, where a lower inclination would result in a more wet soil No such relation was found, but because of the uncertainty of the inclination data, vvvvvvv the results of the transect inclination are Theinconclusivemapstudy of inclination of the whole case areas was made as an alternative method to the unprecise method of plotting inclination of the transects onto the elevation model, as well as to study the inclination of the case areas as a whole. By making polygons

inQGISof theSCALGO rainfillandusing the elevation model to make polygons at a 10 cm higher altitude in QGIS, the difference and relative difference in size between the two polygon areas was found for the three cases.

Table9:Comparisonofinclinationresultsfromthetwodifferentmethods. “Differencebetweenmethods (%)”showshowmuchgreatertheinclinationofthetransectstudyiscomparedtothemapstudy.

There are evident weaknesses with both methods and in regards to the inclination both provide inconclusive results. However, the map study does provide a fuller understanding of the local depression that constitutes the delineation of the wetland.

Using a linear trendline to describe how soil wetness decreases with increased distance to blank water, when the wetness definition has a defined maximum and minimum value is not feasible. It is believed that a logistical function would act as a better description of this relation. This study lacks the tools and knowledge necessary to make that type of Thecalculation.inclination data regarding profiles of the transects were not based on measurements, but on the elevation model of Denmark. The lack of precision of the location data makes the inclination data uncertain. Even though the aim when choosing the locations for sampling was for them to be as representative of the individual wetlands as possible, the lack of randomness contradicts that aim. The GW depths were only measured once for each sample location, providing a snapshot of the GW depth at that particular time, not revealing any information on seasonal fluctuations. It is believed that the sampling was madeat thewettest time of theyear. That claim is supported by weather data, but the method used for this study makes it impossible to know for sure. Most similar studies make use of long time series of measurement to count for seasonal variation (Menberu, et al., 2016, Faubert, 2004, Wilson, et al., 2010).

33

When looking specifically at Case 2, most of the increased area between the rain fill and the rain fill +10 cm is placed centrally in the wetland and thus, it cannot be concluded that it has the lowest inclination around its (outer) border out of the three cases It’s a difficult mathematical task to make a valid calculation to portray what is visually tangible, namely that when studying the maps, Case 3 does visually seem to have the lowest overall inclination around its outer border

More research is needed to investigate this question further.

The SCALGO rain fill gives a rather fragmented image of each of the case areas, where the rain fill + 10 cm provides a more coherent outline shape of the area. It can be speculated that the rain fill + 10 cm can be a rather accurate fit to the true border of the three wetlands. The sampling of this study held together with the rain fill + 10 cm suggests that this speculation might be viable. It calls for further research.

4.6. Strengths and weaknesses with this study.

4.5. Can the area of restored wetlands be estimated with high accuracy even before the restoration is initiated? The results from this study are promising in terms of feasibility of the SCALGO rain fill toolas a ratheraccuratemeasureof predicting the size and shape of wetlands. All three studied cases had blank water in almost the same area as was covered by the SCALGO rain fill map when conducting the field study. It’s uncertain if the results from this study’ s three cases can be extrapolated to other cases, but this study does not reject that possibility

There are several weaknesses in the methodology of this study: Registrations in the field of soil moisture and soil horizons were made on visual and tactile evaluations and not measurements, thus the division into classes was subjective.

There are also strengths in this study. The combination of map studies and field studies as done in this project is rarely seen in other studies, which gives this study the possibility to cross check and validate map information with in field sampling data.

Through on site soil sampling it was possible to identify the limit of the former wetland in 16 out of 17 transects, as presence of peat at the innermost sample locations and absence of peat at the outer sample locations are undeniable evidence of a historical wetland border. This could not have been achieved from solely studying maps.

34

(Menberu, et al., 2016) (Faubert, 2004) (Wilson, et al., 2010)

35 5. References Blann, K. L., Anderson, J. L., Sands, G. R., & Vondracek, B. (2009). Effects of Agricultural Drainage on Aquatic Ecosystems: A Review. CriticalReviews Fritzbøger,Faubert,DMI.DMI.Chadburn,Campeau,Technology,inEnvironmentalScienceand39(11),pp.9091001.S.,&Rochefort,L.(1996).Sphagnumregenerationonpeatsurfaces:fieldandgreenhouseresults.JournalofAppliedEcology33(3),pp.599608.S.E.,Burke,E.J.,GallegoSala,A.V.,Smith,N.D.,BretHarte,M.S.,Charman,D.J.,...Pawlak,W.(2022).Anewapproachtosimulatepeataccumulation,degradationandstabilityinagloballandsurfacescheme(JULESvn5.8_accumulate_soil)fornorthernandtemperatepeatlands.GeoscientificModelDevelopment,15,16331657.(2021).DenmarkDMIHistoricalClimateDataCollection17682020DMIReportNo.2102.Copenhagen:DanishMeteorologicalInstitute.(2022,0621).www.dmi.dk.RetrievedfromDanishMeteorologicalInstitute(Danish):https://www.dmi.dk/fileadmin/user_upload/Afrapportering/Maanedssammendrag/Sammendrag_2022_februar.pdfP.(2004).THEEFFECTOFLONGTERMWATERLEVELDRAWDOWNONTHEVEGETATIONCOMPOSITIONANDCO2FLUXESOFABOREALPEATLANDINCENTRALFINLAND.Chicoutimi:UniversityofQuébec.B.,&Odgaard,B.(2022,0329).Skovenideseneste6.000åriNatureniDanmark(Danish).RetrievedfromNatureniDanmark:https://naturenidanmark.lex.dk/Skoven_i_de_seneste_6.000_%C3%A5r

Henriksen, H. J., Troldborg, L., Nyegaard, P., Sonnenborg, T. O., Refsgaard, J. C., & and Madsen, B. (2003). Methodology for construction, calibration and validation of a national hydrological model for Denmark. JournalofHydrology280, 52 Holden,71. J., Chapman, P., & Labadz, J. (2004). Artificial drainage of peatlands: hydrological and hydrochemical process and wetland restoration. Progressin PhysicalGeography,28(1)., pp. 95 123. Holmen, H. (1964). Forest ecological studies on drained peat land in the province of Uppland, Sweden. Parts I III. Stud.For. Suec.14,, pp. 1 236. Hånell, B. (1988). Postdrainage forest productivity of peatlands in Sweden. Norstedt,MillenniumMenberu,Malmström,CanadianJournalofForestResearch18,pp.14431456.C.(1928).Våratorvmarkerurskogsdikningssynpunkt.(Englishsummary:Ourpeatareasfromthepointofforestdraining).Meddelandenfrånstatensskogsforskningsinstitut24,251372.M.W.,Tahvanainen,T.,H.Marttila,M.I.,Ronkanen,A.K.,Penttinen,J.,&Kløve,B.(2016).Watertabledependenthydrologicalchangesfollowingpeatlandforestrydrainageandrestoration:Analysisofrestorationsuccess.WaterResourcesResearch,37423760.EcosystemAssessment.(2005).ECOSYSTEMSANDHUMANWELLBEING:WETLANDSANDWATERSynthesis.Washington,DC:WorldResourcesInstitute.G.,Hasselquist,E.M.,&Laudon,H.(2021).FromHaymakingtoWood

36 Production: Past Use of Mires in Northern Sweden Affect Current Ecosystem Services and Function. Rural OverballeNST.NSTNSTNSTNSTNSTHistory,Landscapes:Society,Environment,8(1):,2,115.(a).(2022,0513).TheDanishNatureAgency.RetrievedfromNaturstyrelsen.dk:https://eng.naturstyrelsen.dk/(b).(2022,0329).SkovkortNaturstyrelsen.Retrievedfromhttps://www.skyfish.com/sh/388e6d0239f56573f0798cd4e705095d65d05797/1a5f038a/1017670(c).(2022,0329).Gribskov(Danish)Retrievedfromnaturstyrelsen.dk:https://naturstyrelsen.dk/naturoplevelser/naturguider/gribskov/(d).(2022,0523).OmrådeplanGribskov(Danish).Retrievedfromnaturstyrelsen.dk:https://naturstyrelsen.dk/driftogpleje/driftsplanlaegning/nordsjaelland/omraadeplaner/gribskov/(e).(2022,0328).Gribskovvandettilbage(Danish).Retrievedfromhttps://naturstyrelsen.dk/naturbeskyttelse/naturprojekter/vandettilbagetilgribskov/(2021).Overordnederetningslinjerforforvaltningafurørtskov(Danish).RandbølOnlineon:https://naturstyrelsen.dk/media/245332/overordnederetningslinjerforskovtilbiodiversitetsformaal.pdf:DanishNatureAgency,.Petersen,M.V.,Nielsen,A.B.,Hannon,G.E.,Halsall,K.,&Bradshaw,R.H.(2013).LongtermforestdynamicsatGribskov,easternDenmarkwithearlyHoloceneevidenceforthermophilousbroadleavedtreespecies.TheHolocene23,243254. Remm, L., Löhmus, P., Leis, M., & Löhmus, A. (2013). Long Term Impacts of Forest Ditching on Non Aquatic Biodiversity: Conservation Perspectives for a Novel Ecosystem. PLoSONE8(4), pp. 1 13. Rune, F. (1997). Declineofmiresinfour TheTheTheSvenningsen,SCALGO.Rune,20thDanishstateforestsduringthe19thandcentury.Copenhagen:ForskningscentretforSkov&LandskabUniversityofCopenhagen.F.(2009).Gribskov(Danish).Fredensborg:EsrumSø.(2022,0329).SCALGOLiveRetrievedfromhttps://scalgo.com/live/denmark?res=409.6&ll=11.503535%2C56.167039&lrs=datafordeler_skaermkort_daempet&tool=zoomS.(2021).Historiskekortsomkildetilkortlægningenshistorie.FraGeneralstabensmålebordsbladetilsovjetiskehærkortfraDenKoldeKrig(Danish).GEOFORUMPERSPEKTIVn.38,3146.DanishAgencyforDataSupplyandEfficiency(a).(2022,0329).Historiskekort(Danish).Retrievedfromhistoriskekort.dk:https://historiskekort.dk/?kortvaerk=Generalkvartermesterstaben&pagesize=25&offset=0DanishAgencyforDataSupplyandEfficiency(b).(2022,0509).TheDanishElevationModel.RetrievedfromAgencyforDataSupplyandEfficiency:https://eng.sdfe.dk/productsandservices/thedanishelevationmodeldkdemDanishForestandNatureAgency.(1992).Strategifordedanskenaturskove(Danish).Copenhagen:Miljøministeriet.

Timmermann, T., Margóczi, K., Takács, G., & Vegelin, K. (2006). Restoration of peat forming vegetation by rewetting species poor fen grasslands. Applied VegetationScience9, pp. 241 250. Wilson, L., Wilson, J., Holden, J., Johnstone, I., Armstrong, A., & Michael Morris. (2010). Recovery of water tables in Welsh blanket bog after drain blocking: Discharge rates, time scales and the influence of local conditions. Journalof Hydrology(391), 377 386.

37 The Ministry of Environment in Denmark. (2022, 05 23). Timár,klimaforandringerTemperaturog(Danish).Retrievedfrommilkøtilstand.nu:https://xnmiljtilstandyjb.nu/temaer/klimaforandringer/temperaturogklimaforandringer/G.,Székely,B.,Molnár,G.,Ferencz,C.,Kern,A.,Galambos,C.,...LászlóZentai.(2008).CombinationofhistoricalmapsandsatelliteimagesoftheBanatregionReappearanceofanoldwetlandarea.GlobalandPlanetaryChange62,2938.

38 6. Appendices 6.1 Equipment The sampling method required a specific set of equipment: Hammer and auger (circa 27 mm Ø and 95cm deep) Plastic pipe with holes for free water movement Measuring tape + water depth logger device - Second measuring tape (20 m) Folding meter stick Coloured chalk Map with proposed position of transects (Google My maps) Mobile phone with camera, compass and GPS Logger - Protocol for soil analysis sheets Note folder and pencils Warm clothing and rubber boots Lunch Backpackpacklarge enough to fit all the equipment 6.2. Field Protocol Figure37:Fieldprotocoltobefilledoutateachsamplelocation.

39 6.3. Historical maps (except the GSTD maps from 1858) vagueFigure38:MapofGribskovfrom1830.Thereisadelineationofwetlands,butmuchtoounprecisetouseasahistoricalreference.Thereisalsonodelineationofditches. Figure39:HMBmapfrom1898.1:20000.

40

Figure42:4cmmapfrom1968.1:25000.

Figure41:LMBmapfrom1960.1:20000.(Fourmapchartsfrom1959,60,63and65).

Figure43:4cmmapfrom1994.1:25000.

Figure40:LMBmapfrom1915.1:20000.