Is re-planting hedgerows a potential solution to reduce flood
and drought risk in the Netherlands?
A case study on the decrease of hedgerows along agricultural landscapes in Het Groene Woud in Noord- Brabant between 1900 and 2015
Source: CBS, PBL, RIVM, WUR (2009)
L. C. Huijser – 11697466 1 July 2020, Amsterdam BSc Bèta-Gamma & major Earth Sciences University of Amsterdam Dhr. Dr. K.F. Rijsdijk
Abstract. In the twentieth century a lot of hedgerows were removed from the borders of
agricultural landscapes of the Netherlands, mainly due to land consolidations and
replacement by barbed wire fences. Since 1910, the average temperature in the Netherlands
increased with 1.8 degrees Celsius and precipitation with 26 percent. With the removal of
hedgerows, soil ecosystem services that can reduce flood and drought risk, have also
vanished. The aim of this research is to investigate how many hedgerows and soil ecosystem
services that can reduce the flood and drought risk are lost in Het Groene Woud in
Noord-Brabant between 1900 and 2015. The findings implicate the following consequences due the
removal of hedgerows in Het Groene Woud between 1900 and 2015. First, the amount of
soil organic carbon was decreased with 10 percent in the soil’s top 5 centimetre. Second, the
moisture content increased with 39 percent. Third, the soil could infiltrate 3.97*10
6cubic
metres more rainwater thought a saturated soil in one hour in 1900 than in 2015. Thus,
re-planting hedgerows in Het Groene Woud should be taken into account as a potential
solution to reduce the flood and drought risk. This paper aims to encourage more research
on re-planting hedgerows across the Netherlands, to make the Netherlands more robust
against weather extremes.
Keywords: Hedgerows; Climate Change; Adaption; Soil Ecosystem Services; Soil Moisture
Content; Soil Organic Carbon; Saturated Hydraulic Conductivity
Inhoud
Introduction ... 4
Methods and Data ... 7
Map Collection ... 7
Extraction Study Region: Het Groene Woud ... 8
Selection Hedgerows 2015 ... 8
Selection Hedgerows 1900 ... 8
Calculations on Decrease Hedgerows and Soil Ecosystem Services ... 8
Results ... 11
Study Region ... 11
The Difference in Hedgerows and Soil Ecosystem Services ... 12
Discussion ... 12 Conclusion ... 14 Acknowledgements ... 15 Bibliography ... 16 Appendices ... 19 1. MATLAB script ... 19
2. Layouts of map layers ... 22
2.1 Layout of the study region Het Groene Woud ... 22
2.2 Layout of the agricultural land-use in Het Groene Woud. ... 23
2.3 Layout of soil map of Het Groene Woud ... 23
2.4 Layout of the AHN map of Het Groene Woud... 26
2.5 Layout of the hedgerows in Het Groene Woud in 2015 ... 27
2.6 Layout of the hedgerows in Het Groene Woud in 1900 ... 28
Introduction
It is expected that the world population will exceed nine billion by 2050 (Buttriss, 2010). The capacity to feed all this people will largely depend on the health of soils (Lal, 2009; Cassman, 1999). However, 33 percent of the world’s surface is currently facing soil degradation and in the tropics 500 million hectare is affected by it, this is all mainly due to intensification of agriculture (Lal, 2015; Lamb, Erskine & Parrotta, 2005). Moreover, it is indicated that soil ecosystem services were decreased by 60 percent due to degradation in the period from 1950 to 2010 (León & Osorio, 2014). Soil
degradation accelerated in the twentieth century because of livestock trampling and overgrazing, agricultural machinery, and excessive use of fertilizers and irrigation (Chyba, Kroulík, Krištof, Misiewicz & Chaney, 2014; R. Lal, 2009; Soane & van Ouwerkerk, 1995). This has depleted the soil and if nothing will be done about it, the soil will deplete further. Besides intensification of
agriculture, agricultural lands also have to cope with more extreme weather conditions. The increase in extreme weather events, like heatwaves and precipitation extremes, is a consequence of the warming climate and this trend is very likely to continue as long as greenhouse warming continues (Coumou & Rahmstorf, 2012; Solomon et al., 2007)
In the Netherlands the accelerated climate change effects are also noticeable. Here the temperature increased with 1.8 degrees Celsius and the precipitation with 26 percent since 1910. This is interrelated, because the warmer the air, the more water vapor it can hold. Furthermore, from observations of the most extreme rainfall events it is shown that precipitation increases with 12 percent per hour per increased degree (KNMI, n.d.). Due to the increase in extreme rainfall events, the Netherlands will be more vulnerable for floods (Rijksoverheid, n.d.). Moreover, between 1958 and 2013 potential evaporation increased with 12 percent and drought has become more common in the Netherlands since 1951. This trend will probably carry on in the future (KNMI, n.d.).
The increase in extreme rainfall events, evaporations, and drought affect agriculture in the Netherlands negatively, and with that also the food security. The world food system now nourishes over one billion people. And since 1961, the food supply has increased with more than 30 percent per capita (IPCC, 2019).The Netherlands is a big producer and exporter of food; in 2019 the Netherlands achieved 94,5 billion euros from exporting agricultural goods alone, and this amount increases every year (CBS, 2020). Therefore, it is important for the Dutch economy as well to protect the farmlands against floods and drought.
There is a way to improve the soil ecosystem services of agricultural lands and protect the Netherlands against floods and drought effectively. This potential solution was already used for thousands of years, but decreased tremendously in the twentieth century (Baudry, Bunce & Burel, 2000). This potential solution is re-planting hedgerows along agricultural fields in the Netherlands. This can improve the soil organic carbon content, increase the saturated hydraulic conductivity, and decrease the soil moisture content (Holden et al., 2019; Van Vooren et al., 2017). These are all important properties for the soil quality and the resilience against drought and floods.
Soil organic carbon is a component of soil organic matter, which consists of both dead and living material from organisms and plants (Moebius-Clune et al., 2017). Soil organic carbon can help the soil against dehydration and degradation, because it improves the water infiltration, holds on to water and nutrients, serves as food for soil flora and fauna, and can protect the soil against pesticides (Lehmann & Kleber, 2015; Chan, 2008; Moebius-Clune et al., n.d.). In research of Holden et al. (2019) is shown that the saturated hydraulic conductivity of soils under hedgerows is 102.4 mm per hour in comparison to soils under arable and pasture land, which were ranging between 3.4 and 20-30 mm per hour. And the soil moisture content of soils under hedgerows is lower in comparison to soils under arable and pasture land (Holden et al., 2019). Altogether, during extreme rainfall events the soil will be able to infiltrate and store more water, and during dry periods the soil will be less dehydrated because the water holding capacity is increased.
Historically, hedgerows were preferred above common woody fences, because they could put up with floods for weeks and in this way their cattle could not escape, nor unwanted predators could entry the agricultural fields. Hedgerows also kept the soil fertile, because it could hold on to sludge coming from the flooding river. Additionally, hedgerows brought along a lot of useful by-products, like food, medicine, extracting honey, fodder, charcoal, and tea (Maes, 2016; Rijkswaterstaat & Staatsbosbeheer, 2013). Despite all the benefits of hedgerows, they also required more effort in maintenance than the upcoming barbed wire fences. Therefore a lot of hedgerows which stood there for thousands of years were replaced by barbed wire fences in the twentieth century (Rijkswaterstaat & Staatsbosbeheer, 2013). After the Second World War, the Dutch
government started with promoting land consolidations. The purpose of land consolidations was to create big agricultural surfaces in order to cultivate the land better with agricultural machinery. With this land consolidations farmers could farm faster and produce more food. Around 70 percent of the rural area in the Netherlands has faced land consolidations, all in the disadvantage of the old
hedgerow fences (Van Den Bergh, 2005).
Recently, hedgerows received more attention, because it is shown that they can e.g. improve biodiversity, preserve bees, and act as natural pest controllers (Hannon & Sisk, 2009; Lecq, Loisel, Brischoux, Mullin & Bonnet, 2017; Van Rijn, 2017). However, in the Netherlands there has not yet been a lot of research on the removed hedgerows and their soil ecosystem services that can reduce the flood and drought risk. Therefore, the aim of this study is to make an approximation on the number of lost hedgerows of a case study region and calculate how many soil ecosystem services that can reduce the flood and drought risk has gone lost along with the hedgerows there since 1900. This led to the conclusion whether re-planting hedgerows in agricultural landscapes of the
Netherlands is a potential solution for reducing the flood and drought risk.
This research carried out by a case study on Het Groene Woud in Noord-Brabant in the Netherlands. This is an old nature reserve that lays in a triangle between Eindhoven, Tilburg, and ‘s-Hertogenbosch (Fig. 1). This area is chosen as case study area, because Noord-Brabant is at risk for floods and drought. Noord-Brabant is
threatened by floods, because there are a lot of rivers flowing through the province. In 1995, there was a flood that made the A2 at ‘s-Hertogenbosch impassable for two weeks (Omroep Brabant, 2018). Recently, the streets of Rijen in Noord-Brabant were flooded due to extreme rainfall events (NOS, 2020). An example that shows that Noord-Brabant is getting drier every year is that in forests in Noord-Brabant spars are falling down due to drought. Their roots can’t reach the depth of the groundwater. Adrie Bossers, head of the ZLTO, is convinced that farmers should do more to prevent drought, by increasing the water storage and holding capacity (Buijs, 2020). Moreover, due to drought there is a bigger chance that the forests of Noord-Brabant will be burned by a wildfire. Forester Erik de Jonge says that the soil will have to deal with even more drought than in the past two dry years. Although historically water
management in the Netherlands was always more focused on draining rainwater instead of holding it, this should change (Hart van Nederland, 2020).
Het Groene Woud contains a lot of different soil types (Fig. 2a). The legend of this map is shown in appendix 2.3.1. The most common soil types of this region are the ‘Veldpodzol’,
‘Beekeerdgrond’, and ‘Enkeergrond’. While the soil types are diverse, the soil texture loamy fine sand is almost everywhere present in the region. Moreover, the area is mainly flat, but the elevation goes slightly uphill further to the south (Fig. 2b).
There is chosen for a comparison of Het Groene Woud in 2015 with 1900, because after 1900 a lot of hedgerows were removed due to five reasons. First, the “rivierenwet” was implemented in 1908, this meant it was forbidden to plant hedgerows in the winter. Second, hedgerows were replaced by barbed wire fences in 1920. Third, the government started with land consolidations in 1945. Fourth, hedgerows were removed because of ‘perenvuur’ in 1970. And fifth, hedgerows were removed for the flow of rivers, or they just vanished due to a lack of management in 1980
(Rijkswaterstaat & Staatsbosbeheer, 2013).
The main research question is: Should hedgerows be re-planted in the agricultural lands of Het Groene Woud to reduce the flood and drought risk? To answers this question three sub questions have been set up. Firstly, How many hedgerows are removed in Het Groene Woud between 1900 and 2015? Secondly, How many soil ecosystem services that can reduce the flood and drought risk, are lost with the decrease of hedgerows in Het Groene Woud between 1900 and 2015? And thirdly, What will be the risk reduction effects if the removed hedgerows are re-planted in Het Groene Woud?
In order to answers these questions the following method is used. First, an approximation is made of the surface of hedgerows in Het Groene Woud in 1900. This number is compared to the number of hedgerows in 2015. Second, the decrease of the soil organic carbon content, moisture content, and saturated hydraulic conductivity in Het Groene Woud from 1900 to 2015 is calculated. At last, this decrease is analysed to decide whether the hedgerows of 1900 should return to reduce the flood and drought risk in Het Groene Woud, and potentially to more agricultural landscapes in the Netherlands.
Figure 2 The soil map (a) and AHN map (b) of Het Groene Woud. Credits: Esri Nederland, PDOK, AHN.
Methods and Data
Map Collection
The first step was to load all relevant map layers into ArcGIS pro. In table 1 is shown which layers were loaded into ArcGIS pro, from which site they were downloaded, and how they were named in the project. The project where all the layers were loaded into is named:
LiseHuijser_Hedgerows1900_GroeneWoud. And the map containing all the layers was named: Map of Het Groene Woud in Noord-Brabant.
Map Layer Name in Project Link Download Location Type Resolution
Historische_tijdr eis_1900 Map_NL_1900 https://www.arcgis.com/hom e/item.html?id=ae9ebc152a4 1426587fd146ba8b5a70c Tile Layer By Esri NL - Base map 15 m swf-2015-vec-NL011-fgdb Hedgerows2015 https://land.copernicus.eu/pa n-european/high-resolution- layers/small-woody- features/small-woody-features-2015?tab=download ESRI File Geodatabase - Vector 5 m World Land Cover ESA 2010 (Mature Support) agriculture_gw https://www.arcgis.com/hom e/item.html?id=7173340debc 240a9b7ee5aec230e099c Imagery layer by Esri - Raster 250 m
AHN3 5m AHN3 5m https://www.arcgis.com/hom e/item.html?id=265b16cc854 5477ea4ac2ee533171369 Imagery Layer by Esri NL – ground level grid 5m
Bodemkaart Soil_map_gw https://www.arcgis.com/hom e/item.html?id=de58bafde72 84c99836a54519fa9f3cd Feature Layer by Esri NL 25 m Gemeenten (Bestuurlijke Grenzen 2020) Groenwoud https://www.arcgis.com/hom e/item.html?id=178f5a12af3a 49f79a15dfebed113ce0 Feature Layer by Esri NL -
The Map_NL_1900 showed where hedgerows were in 1900 in Het Groene Woud. The
Hedgerows2015 map layer showed small woody features in the study region. 2015 was the most recent dataset of hedgerows. There is chosen for a vector instead of a raster map layer, because the vector’s attribute table included information about the Shape_Areas of the polygons of the
hedgerows. This was needed to calculate the sum of all hedgerows of the study region. The
hedgerows of 2015 were validated by making them transparent and checking the orthophoto of the base map: Imagery. The Soil_map_gw was used to get a general idea of the soil types and textures of the study region. This map layer distinguishes between 300 different soil types over a depth of one meter. The AHN map layer was used to get an idea of the elevation of the study region. Additionally, the layers agriculture_gw and Groenwoud were used to make outlines of the study region: Het Groene Woud. To calculate the boundaries of the grid resolution a formula from Hengl (2006) is used. According to this formula, the recommended resolution is calculated by multiplying the scale number of the coarsest dataset with 0.0005 (Hengl, 2006). Thus, the recommended resolution for this research is 250 m. Moreover, there was made sure that all map layers had the same projection
and projected coordinate system, namely Mercator Auxiliary Sphere and WGS 1984 Web Mercator (auxiliary sphere).
Extraction Study Region: Het Groene Woud
After all the maps were loaded in, the outlines of the study region were made. First, the counties of Het Groene Woud were selected. The green area in figure 3 served as example for the outlines of Het
Groene Woud. A layer including all counties of Het Groene Woud was made. The contours of this layer clipped the land-use map. With the tool “Extract by Attributes”, the four following class names were
extracted: Cropland_raindfed; Cropland,rainfed – Herbaceous cover; Grassland; and Mosaic cropland (>50%)/ natural vegetation
(Tree, shrub, herbaceous cover) (<50%). These classes represent the arable and pasture lands. At last, the different polygons of the agricultural lands in the counties of Het Groene Woud were merged together and all map layers of table 1, except the MAP_NL_1900 and AHN map layers, were clipped with the contours of the study region Het Groene Woud. The agricultural lands were extracted from the land-use map, because this research is mainly interested in the hedgerows along agricultural field borders.
Selection Hedgerows 2015
From the feature class of the hedgerows of 2015, code 1 was extracted, because this research is mainly interested in the small woody features (code 1), and not in the additional small woody features.
Selection Hedgerows 1900
To make an approximation of the number of hedgerows in Het Groene Woud in 1900 a couple of steps had to be taken. In the process of selecting hedgerows in 1900 the Map_NL_1900 served as base map, here all hedgerows are displayed, and Het Groene Woud served as the perimeter of the study region wherein the hedgerows could be selected. The hedgerows were selected according to the legend originating from a map of the Netherlands in 1897, which is quite similar to the map of 1900. This legend is shown in appendices number 4. Hedgerows, forest borders adjacent to agricultural fields, and coppice were selected with the ‘freehand’ polygon selector and turned into green polygons, these were saved into the feature class file: Hedgerows1900. After all the hedgerows were traced, hedgerows outside the perimeter were deleted.
Hereafter, layouts were made of the following map layers: Hedgerows1900, Hedgerows2015, AHN3 5m, agriculture_gw, Groene_woud, and Soil_map_gw. This map layers are displayed in the appendices number 2.
Calculations on Decrease Hedgerows and Soil Ecosystem Services
The sums of the Shape_Areas of the feature classes Hedgerows1900 and Hegderows2015 represent the surfaces of hedgerows in Het Groene Woud in 1900 and 2015. The sums were calculated by ArcGIS pro and shown at Statistics of Shape_Area. To verify the unit of Shape_Area, a random polygon of Hedgerows1900 was selected, and with the tool “Measure Features” compared to the value in the attribute table. The tool was set on the unit square metres.
Figure 3 The counties and perimeter of Het Groene (Het Groene
The numbers representing the surfaces of hedgerows in 1900 and 2015 were put into MATLAB R2019b in the script: Matlab_calculations_hedgerows.m. Other soil properties that were also put into the script were: mean bulk densities, mean SOC proportions, mean moisture content proportions, and the median values of the Ks (Table 2). All these soil properties were derived from the article of Holden et al. (2019, because all the measured soil properties in the article are also interesting for this research. In the research of Holden et al. (2019) the soil under hedgerows was compared to soils under arable and pasture land, and this is also needed for the calculations on the decrease of soil ecosystem services in Het Groene Woud between 1900 and 2015. In figure 4, the elevation of the two study sites are shown. An overview of all pros and cons for using the soil properties of Holden et al. (2019) is shown in table 3.
Pros Cons
Both the United Kingdom and the Netherlands have a temperate maritime climate
(Klimaatinfo, n.d.-a, n.d.-b)
The studied area of Holden et al. (2019) is situated on a gentle slope, while Het Groene Woud is more flat (Holden et al. (2019; Fig. 4) There is measured with a variety of hedgerow
types (Holden et al., 2019)
The soil texture is loam, while in Het Groene Woud it is loamy fine sand (Holden et al., 2019; Fig. 2a)
Measurement of soils under hedgerows as well as under arable and pasture land were made (Holden et al., 2019)
The main soil type is a Calcaric Endoleptic Cambisol, while Het Groene Woud consists of several other soil types (Holden et al., 2019; Fig. 2a)
The moisture content, saturated hydraulic conductivity, bulk density, and the soil organic carbon content are all measured, and this are all parameters needed for this research (Holden et al., 2019)
The moisture content, saturated hydraulic conductivity, bulk density, and soil organic carbon content are very likely to be different than they would have been when measured in Het Groene Woud
Soil under Mean
Bulk Density [g/cm3] depth: 0 – 50 cm Mean SOC content [%] depth: 2– 7 cm Mean Soil Moisture Content [%] Depth: 5 cm Mean Soil Moisture Content [%] Depth: 20 cm Mean Soil Moisture Content [%] Depth: 50 cm Median Ks [mm/hour] Hedgerows 1.259 3.1 12.4 11.9 10.8 102.4 Pasture land 1.422 2.9 22.0 18.2 17.0 20-30 (25) Arable land 1.540 1.9 14.4 15.5 14.3 3.4
Table 2 Soil properties derived from Holden et al. (2019)
Before starting with the calculations on the parameters for the soil ecosystem services, the units of the
parameters were converted. Bulk density was converted to g/m3 and the Ks to m3/m2/hour. The percentages of the soil organic and moisture content were converted to proportions.
Hereafter, the surface of cropland (arable land) and grassland (pasture land) had to be calculated for the sites where in 1900 were hedgerows and in 2015 not anymore. This was achieved by first making an approximation of the ratio cropland and grassland in Het Groene Woud. This ratio was then converted to the surface of lost hedgerows since 1900. Explained in more detail: the ratio was calculated in ArcGIS pro by extracting the crop- and arable lands from the
agriculture_gw raster map layer with the tool “Extract by Attributes”. Thereafter they were turned into polygons to see the sum of the Shape_Areas. The sums of the Shape_Areas were put into MATLAB R2019b and subsequently the ratio of the crop- and arable land was calculated for the total area of Het Groene Woud. These proportions were multiplied with the surface of the lost hedgerows between 1900 and 2015. The script of this calculation is shown in the appendices number 1.
Hereafter the difference in the soil organic carbon content, saturated hydraulic conductivity, and soil moisture content were calculated for Het Groene Woud between 1900 and 2015. For calculating the decrease in the soil organic carbon content in Het Groene Woud between 1900 and 2015 Equation 1 is used. For calculating the lost soil moisture content Equation 2 is used. And for calculating the difference in the saturated hydraulic conductivity equation 3 is used.
Equation 1: 𝑆𝑂𝐶𝐺𝑊 = 𝐴(𝑥) ∗ 𝐷(𝑥) ∗ 𝐵𝐷(𝑥) ∗ 𝑃𝑠𝑜𝑐(𝑥)
Equation 2: 𝑆𝑜𝑖𝑙𝑀𝑜𝑖𝑠𝑡𝑢𝑟𝑒𝐺𝑊= 𝐴(𝑥) ∗ 𝐷(𝑥) ∗ 𝐵𝐷(𝑥) ∗ 𝑃𝑚𝑜𝑖𝑠𝑡𝑢𝑟𝑒(𝑥)
Equation 3: 𝑊𝑎𝑡𝑒𝑟𝐹𝑙𝑜𝑤𝐺𝑊= 𝐴(𝑥) ∗ 𝐾𝑠(𝑥)
With:
SOCGW : The soil organic carbon content of Het Groene Woud [g]
A : Surface of measured land [m2]
D : Depth of measurement [m]
BD : Bulk density [g/m3]
Psoc : The proportion of the soil organic carbon content [-]
SoilMoistureGW : The soil moisture content of Het Groene Woud [g]
Pmoisture : The proportion of the soil moisture content [-]
WaterFlowGW : The water that flows vertically through saturated soil of Het Groene Woud [m3/hr]
Ks : Saturated hydraulic conductivity [m3/m2/hr]
Figure 4 Elevation map of North-West Europe. The red arrow shows the study region of Holden et al. (2019) and the blue arrow shows the site of Het Groene Woud (European Environment Agency, 2009).
The calculations with the equations 1, 2, and 3 were conducted in MATLAB R2019b. In appendix number 1 the elaboration of the equations is shown in the MATLAB Script. These equations were used for four different surfaces, namely the hedgerow surface in 1900 and the one in 2015, and the crop- and pasture land surface in 2015. Thus, for 2015 the soil properties consisted of the sum of the hedgerows, crop- and pasture land surface. Afterwards, the difference of the lost hedgerows and the lost soil ecosystem services parameters were calculated by subtracting the values of 1900 and 2015 from each other. After the calculations were conducted, the differences in the numbers of the surface of the hedgerows, soil organic carbon content, soil moisture content, and saturated hydraulic conductivity in Het Groene Woud between 1900 and 2015 were visualised and analysed. Note: this research only calculates the soil ecosystem services of the field borders, because the main interest is the difference in the number hedgerows and their soil ecosystem services of Het Groene Woud between 1900 and 2015. Thereby, it is assumed that the agricultural fields minus the field borders did not change in land-use.
Results
Study Region
In figure 5 all hedgerows along agricultural fieldborders in Het Groene Woud in 1900 and 2015 are shown. In 1900 the surface of the hedgerows was 70.89 square kilometres. In 2015 the surface of the hedgerows was 26.92 square kilometres. Thus, 44 square kilometres of hedgerows were lost.
The ratio between pasture and arable land in Het Groene Woud is 39/61. Therefore, the approximation was made that the surface of the number of lost hedgerows was converted to 27 square kilometres of arable land and 17 square kilometres of pasture land. In the appendices number 2.2 the map of agricultural land-use in Het Groene Woud is shown.
The Difference in Hedgerows and Soil Ecosystem Services
The surface containing hedgerows in Het Groene Woud has decreased with 62 percent between 1900 and 2015 (Fig. 6a). In 1900 there were 2.6 times more hedgerows along agricultural field borders than in 2015. The percentage of surface covered by hedgerows in Het Groene Woud in 1900 was 14 percent, while in 2015 this was only 5 percent.
Between 1900 and 2015 the soil organic carbon content decreased with 1.39*107 Kg in the top 5 centimetres of the soil of Het Groene Woud (Fig. 6b). This is a decrease of 10 percent. The soil moisture content of Het Groene Woud increased with 1.77*109 Kg between 1900 and 2015, this is 38 percent (Fig. 6c). Moreover, in 1900 the saturated hydraulic conductivity was 2.2 times bigger than in 2015 in Het Groene Woud (Fig. 6d). In one hour the saturated soil under hedgerows in 1900 could move vertically 3.97*106 cubic metres more rainwater through Het Groene Woud than in 2015.
Discussion
In this discussion a couple of things are discussed. First of all, the results are analysed whether they answer the research questions asked in the introduction. Secondly, some points to improve this study are named. And third, there is analysed how re-planting hedgerows can be best introduced in the Netherlands.
The results point out that Het Groene Woud was more vulnerable for drought and floods in 2015 than in 1900. This is due to the loss of 44 square kilometres hedgerows. Together with the
hedgerows, the potential water storage, the amount of soil organic carbon, the infiltration rate, and the saturated hydraulic conductivity decreased in Het Groene Woud. If the hedgerows of 1900 would be re-planted, the flood and drought risk in Het Groene Woud would also reduce. During extreme rainfall events the soil would take in 3.97*106 cubic metres more rainwater, and have more potency to store this water. Besides, the water holding capacity of the soil would improve due to the increase in soil organic carbon. And this increase also improves the holding capacity of nutrients which can make the soil more fertile for flora and fauna, and by that increasing the permeability of the soil and
Figure 6 Bar plots of number of hedgerows (a), soil organic carbon contents (b), soil moisture contents (c), and saturated hydraulic conductivities (d) in Het Groene Woud in 1900 and 2015
improving the infiltration rate. Altogether, Het Groene Woud would be more robust against floods and drought if the hedgerows of 1900 are re-planted.
Although the results only account for the area of Het Groene Woud, they do show the potency of re-introducing hedgerows in other agricultural landscapes of the Netherlands.
Re-introducing hedgerows on a larger scale would definitely have more impact than re-Re-introducing them on a small scale. Nevertheless, before re-introducing them on a large scale, more research should be conducted at more places. And different hedgerow types on dissimilar soil- types and textures should be researched. For follow-up research that is also interested in doing research to hedgerows in another time, it is recommended to use the Deep Learning Method in ArcGIS pro to detect hedgerows in old maps. This can save a lot of time and manual work.
There is no other research conducted that examined the decrease of hedgerows and their influence on soil ecosystem services that can reduce the flood and drought risk in Het Groene Woud between 1900 and 2015. So, a comparison with another study could not have been made. However, there is research that examined how the Netherlands can be made more climate change robust. An example is the initiative to water down peat landscapes. This can reduce atmospheric carbon dioxide enormously, and with that putting a hold on the increasing weather extremes the Netherlands is facing (Bromet, 2018). Another way to reduce flood risk is to let canalised rivers reshape back to their natural course by removing obstacles from the floodplain (Rijksoverheid, n.d.). The combination of re-introducing hedgerows, watering down peat landscapes, and reshape rivers would be the best solution to reduce the flood and drought risk in the Netherlands.
There are some points to improve this study. First of all, there was assumed that the soil properties in Het Groene Woud in 1900 and 2015 equal the soil properties of the research of Holden et al. (2019). This assumption was made, because there is no data of soils under hedgerows in the Netherlands or Het Groene Woud in 1900 or 2015. Therefore the results consists of an
approximation of the soil ecosystem services in Het Groene Woud in 1900 and 2015, rather than exact facts. Hence, it is recommended for follow-up research to do fieldwork in the study region and measure the bulk densities, soil organic carbon contents, soil moisture contents, and the saturated hydraulic conductivities of soils under hedgerows, and arable- and pasture land. Although this cannot be done for the soil hundred years ago, the approximation of the soil ecosystem services will be closer to reality than if the data comes from another place or land.
The soil texture of Het Groene Woud consists mainly of fine loamy sand, and the soil texture of the soil of Holden et al. (2019) consists of loam. Loamy sand consists of 80 percent sand and 10 percent clay, while loam consists of 45 percent sand and 15 percent clay (Saxton, Rawls, Romberger, & Papendick, 1986). According to Saxton et al. (1986) the moisture content of a loamy sand soil is smaller than of a loam soil. Therefore it is expected that the soil of Het Groene Woud probably has a smaller moisture content than is calculated. Moreover, loamy sand soil has a higher soil water conductivity than a loam soil (Saxton et al., 1986). Hence, the soil in Het Groene Woud can drain rainwater well, but is also more vulnerable for drought than the soil of Holden et al. (2019). Therefore, it is extra important to increase the soil organic carbon content in Het Groene Woud to increase the water holding capacity and be more robust against dry periods.
When selecting the hedgerows of 1900, there could have been made mistakes. For example, an object on the map may looked like a hedgerow, while in fact it was something else, or vice versa. Moreover, the Map_NL_1900 base map consisted of different layers. The most detailed map with the scale 1:6.000 consisted of different maps that were made per county. So, there is a possibility that some counties used a different symbol for the same object. Besides, not all maps had the same resolution or coordinates in Het Groene Woud.
Another point to improve this study is by using a land-use map with a higher resolution. Because in this research the resolution of the agricultural land-use raster was not very high.
However, a more detailed land-use raster of the Netherlands was not available. So, for follow-up research it is recommended to use a land-use raster with a high resolution.
In this research is the decrease of atmospheric carbon dioxide by the increase of soil carbon stocks in Het Groene Woud not examined. However, this would be interesting to examine in follow-up research, because a significant reduction in atmospheric carbon dioxide can put a hold on global warming, and with that on the increase in weather extremes (Soussana et al., 2019; Coumou & Rahmstorf, 2012; Joos, Plattner & Stocker, 1999).
To re-introduce hedgerows in not only Het Groene Woud, but also in other agricultural landscapes of the Netherlands, collaboration is needed between scientists, the government, and farmers. Currently, farmers are more discouraged to plant hedgerows on their landscapes than encouraged. Because Dutch farmers don’t receive subsidy for hedgerows or wooded banks on their lands, but they do receive subsidy if they remove them and make cultivable land from it.
Consequently, to receive more subsidy farmers remove hedgerows or woody banks from their lands (Hakkenes, 2018). A possible solution for this issue is ‘carbon credits’, this are tradable certificates that companies, individuals, or other parties can buy to compensate their carbon dioxide emissions. Another solution is planting-subsidy for planting hedgerows along agricultural field borders (Van Druenen & Vastrick, 2020). Re-planting hedgerows should be made attractive for farmers to do, because they do lose cultivable land.
Conclusion
The aim of this research was to make an approximation on the number of lost hedgerows and calculate how many soil ecosystem services that can reduce the flood and drought risk has gone lost together with the hedgerows in Het Groene Woud between 1900 and 2015. The examined soil ecosystem services were calculated with the following parameters, namely the soil organic carbon content, the soil moisture content, and the saturated hydraulic conductivity.
The results showed that re-introducing hedgerows is a potential solution to reduce the flood and drought risk in Het Groene Woud, because Het Groene Woud was more robust against weather extremes in 1900 than it was in 2015. If the 44 square kilometres of lost hedgerows would be re-planted in Het Groene Woud, the soil could infiltrate 3.97*106 cubic metres more rainwater, and also have the capacity for an extra soil moisture content of 1.77*109 Kg. The increase of 1.39*107 Kg soil organic carbon content in the top five centimetres of the soil can improve the infiltration rate during a rainstorm, and improve the water holding capacity, which is needed during dry periods.
A point to improve this study is conducting fieldwork on the research area of Het Groene Woud, to obtain data of soils under hedgerows, pasture- and arable land. Another point that can be improved is the resolution of the map. Hopefully this case study research will encourage more and bigger research on the effect of hedgerow loss on the soil ecosystem services at different agricultural landscapes in the Netherlands.
To re-introduce hedgerows along agricultural field borders in the Netherlands, collaboration between scientists, farmers, and the government is needed. Scientist should bring their knowledge to the wider public and make it more accessible. The government should encourage farmers to re-plant hedgerows along agricultural fields by giving re-plant- subsidy or carbon-credits. And farmers should re-plant or let other people re-plant hedgerows on the borders of their lands.
Acknowledgements
First of all, I would like to thank my supervisor Dhr. Dr. K.F. Rijsdijk for all the feedback and support he gave me in the past months. Moreover, I would like to thank the following people for their help, namely: Marius Grutters, Dhr. Dr. W.M. de Boer, Esther Vastrick, Jaap Dirkmaat, Bert Maes, Dr. Ir. E.E. van Loon, Dhr. Dr. A.C. Seijmonsbergen, de Kadaster, Andrew Dawson, Wijnand Sukkel, and Egbert Jaap Mooiweer.
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Appendices
In these appendices the MATLAB script, layouts of used maps, and the legend of the map of the Netherlands in 1900 is shown.
1. MATLAB script
Below the Matlab script: Matlab_calculations_hedgerows.m is shown. The script was made in MATLAB R2019b and last-updated at 28-6-2020. It includes the calculations on the decrease of hedgerows and the parameters for the soil ecosystem services of Het Groene Woud between 1900 and 2015. It also includes initialisations of the used soil properties of Holden et al. (2019), the number of hedgerows in 1900 and 2015, and the script of the visualisation of figure 6.
% Lise Huijser Bachelorproject Earth Sciences % last updated: 28-6-2020
% Hedgerows on the borders of agricultural landscapes of Het Groene % Woud in 1900 and 2015
clc clear close all
% initialisations
hedg_1900 = 70887512.9796687 ; % surface covered by hedgerows in 1900[m2]
hedg_2015 = 26927388.0262016 ; % surface covered by hedgerows in 2015[m2]
sum_cropland = 306273485.616047; % crop/arable land in het groene Woud [m2]
sum_grassland = 193040563.002495 ; % grassland/ pasture land in het groene Woud [m2]
bulk_dens_h_cm = 1.259 ; % mean bulk density over 0-50 cm of soil under hedgerows[g/cm3]
bulk_dens_p_cm = 1.422 ; % "..." under pasture/grasland[g/cm3]
bulk_dens_a_cm = 1.540; % "..." under arable/cropland[g/cm3]
depth_soc = 0.05 ; % depth of the measurement[m]
Ks_h = 102 ; % [mm/h] equal [L/m2/hour], saturated hydraullic conductivity, hedgerows
Ks_a = 3.4 ; % [mm/h], arable
Ks_p = 25 ; % [mm/h], pasture % convertion of units
% amount of SOC, percentage --> proportion
prop_soc_h = 3.1/100 ; %hegderow
prop_soc_p = 2.9/100 ; %pasture
prop_soc_a = 1.9/100 ; %arable
% moisture content, percentage --> proportion
mois_5_h = 12.4/100 ; % 5 cm depth, hedgerows
mois_5_a = 14.4/100 ; mois_5_p = 22.0/100 ; mois_20_h = 11.9/100 ;
mois_20_a = 15.5/100 ; % 20 cm deep, arable land
mois_20_p = 18.2/100 ; mois_50_h = 10.8/100 ; mois_50_a = 14.3/100 ;
mois_50_p = 17.0/100 ; % 50 cm deep, pasture land % bulk denisty g/cm3 --> g/m3: 1 m3 = 1.000.0000 cm3
bulk_dens_h= bulk_dens_h_cm*1000000 ; % mean bulk density over 0-50 of soil under hedgerows[g/m3]
bulk_dens_p = bulk_dens_p_cm*1000000 ; % under pasture/grasland[g/m3]
bulk_dens_a = bulk_dens_a_cm*1000000; % under arable/cropland[g/m3] % Ks mm/hr --> m3/m2/hour: 1 mm = 1L/m2/hr = 1*10^-3 m3/m2/hr
Ks_h_m3 = Ks_h/1000 ;%convert [L/m2] to [m3/m2]
Ks_a_m3 = Ks_a/1000; Ks_p_m3 = Ks_p/1000;
% calculations on the different hedgerow surfaces in 1900 and 2015
lost_hedg = hedg_1900 - hedg_2015 ; % lost hedgerow surface [m2]
lost_hedg_km2 = lost_hedg/1000000 ;
bigger = hedg_1900/hedg_2015 ; % in 1900 there were 2.63 more hedgerows than in 1500
total_area = sum_cropland + sum_grassland; % surface of the study region [m2]
perc_1900 = (hedg_1900/total_area)*100 ; %percentage of the amount of hedgerows in 1900 over the whole area
perc_1500 = (hedg_2015/total_area)*100 ; % "..." 2015
perc_hedg = ((hedg_2015-hedg_1900)/hedg_1900)*100 ; %decrease of the amount of hedgerows
% calculations on the percentage of hedgerows in 2015 on agricultural land [%]
perc_grassland = (sum_grassland/total_area)*100 ; %percentage of grassland vs cropland
perc_cropland = 100 - perc_grassland ;
% calculations on the land where in 1900 were hedgerows and in 2015 not anymore
surf_crop = (perc_cropland/100) * lost_hedg ; % percentage --> surface [m2]
surf_grass = (perc_grassland/100) * lost_hedg ;
% check
surf_crop+surf_grass == lost_hedg ; %1 = true
% calculations on SOC in 1900 and 2015 i top 5 cm soil
soc_1900 = hedg_1900*bulk_dens_h*depth_soc*prop_soc_h ; %[g]
soc_2015_h = hedg_2015*bulk_dens_h*depth_soc*prop_soc_h ; %[g]
soc_2015_a = surf_crop*bulk_dens_a*depth_soc*prop_soc_a ; %[g]
soc_2015_p = surf_grass*bulk_dens_p*depth_soc*prop_soc_p ; %[g]
soc_2015 = soc_2015_h + soc_2015_a + soc_2015_p ; %[g] % difference of SOC in 1900 vs 2015
diff_hedg_soc = soc_1900 - soc_2015 ; %[g]
diff_soc_kg = diff_hedg_soc/1000 ; %[kg]
% calculate the decrease percentage from 1900 --> 2015
perc_soc = ((soc_2015 - soc_1900)/soc_1900)*100 ;
% calculations on soil moisture content % 1900
mois_1900_5 = hedg_1900*bulk_dens_h*0.05*mois_5_h ; % [g]
mois_1900_20 = hedg_1900*bulk_dens_h*0.15*mois_20_h ; mois_1900_50 = hedg_1900*bulk_dens_h*0.25*mois_50_h ;
tot_mois_1900 = mois_1900_5 + mois_1900_20 + mois_1900_50 ;
% 2015 hedgerows
mois_2015_5_h = hedg_2015*bulk_dens_h*0.05*mois_5_h ; mois_2015_20_h = hedg_2015*bulk_dens_h*0.15*mois_20_h ; mois_2015_50_h = hedg_2015*bulk_dens_h*0.25*mois_50_h ;
tot_mois_2015_h = mois_2015_5_h + mois_2015_20_h + mois_2015_50_h;
% 2015 arable
mois_2015_5_a = surf_crop*bulk_dens_a*0.05*mois_5_a ; mois_2015_20_a = surf_crop*bulk_dens_a*0.15*mois_20_a ; mois_2015_50_a = surf_crop*bulk_dens_a*0.25*mois_50_a ;
tot_mois_2015_a = mois_2015_5_a + mois_2015_20_a + mois_2015_50_a;
% 2015 pasture
mois_2015_5_p = surf_grass*bulk_dens_p*0.05*mois_5_p ; mois_2015_20_p = surf_grass*bulk_dens_p*0.15*mois_20_p ;
mois_2015_50_p = surf_grass*bulk_dens_p*0.25*mois_50_p ;
tot_mois_2015_p = mois_2015_5_p + mois_2015_20_p + mois_2015_50_p;
% total 2015 moisture content
tot_mois_2015 = tot_mois_2015_h + tot_mois_2015_a + tot_mois_2015_p ;
% total difference in moisture content 1900 vs 2015
diff_mois = tot_mois_2015 - tot_mois_1900 ; %[g]
diff_mois_kg = diff_mois/1000 ; %[kg] % calcualtion on the increase percentage
perc_mois = ((tot_mois_2015 - tot_mois_1900)/tot_mois_1900)*100 ;
% calculations on the saturated hydraulic conductivity (Ks)
soil_wat_1900 = hedg_1900*Ks_h_m3; % [m3] rain infiltrated on the total surface of the saturated soil under hedgerows in Het Groene Woud in 1900 in one hour
soil_wat_2015_h = hedg_2015*Ks_h_m3;%[m3]
soil_wat_2015_a = surf_crop*Ks_a_m3; soil_wat_2015_p = surf_grass*Ks_p_m3;
soil_wat_2015 = soil_wat_2015_h + soil_wat_2015_a + soil_wat_2015_p ; diff_Ks = soil_wat_1900 - soil_wat_2015 ; % difference in saturated hydraullic conductivity between 1900 and 2015.
% calcutions on how much bigger the saturated hydraullic conductivity is in 1900 than in 2015
rain_more = soil_wat_1900/soil_wat_2015 ;
% visualisations in one figure
% visualisation of hedgerow surfaces Groene Woud
figure(1)
sgtitle('Het Groene Woud') subplot(2,2,1)
y = [hedg_1900 hedg_2015]; x = [1900 2015];
b1 = bar(x,y);
title('a. Number of Hedgerows');
ylabel('Total surface of hedgerows [m2] ');
% set colours b1.FaceColor = 'flat'; b1.CData(1,:) = [255/356 17/356 33/356]; b1.CData(2,:) = [9/242 0/242 255/242]; % visualisation soc subplot(2,2,2) y2 = [soc_1900 soc_2015]; b2=bar(x,y2);
title('b. Soil Organic Carbon'); ylabel('Soil organic carbon [g]'); b2.FaceColor = 'flat';
b2.CData(1,:) = [255/356 17/356 33/356]; b2.CData(2,:) = [9/242 0/242 255/242];
% visualisation moisture content
subplot(2,2,3)
y3 = [tot_mois_1900 tot_mois_2015]; b3=bar(x,y3);
title('c. Soil Moisture Contents'); ylabel('Soil moisture [g]');
b3.FaceColor = 'flat';
b3.CData(1,:) = [255/356 17/356 33/356]; b3.CData(2,:) = [9/242 0/242 255/242];
% visualisation saturated hydraulic conductivity
subplot(2,2,4)
y4 = [soil_wat_1900 soil_wat_2015]; b4 = bar(x,y4);
ylabel('Water [m3]'); b4.FaceColor = 'flat';
b4.CData(1,:) = [255/356 17/356 33/356]; b4.CData(2,:) = [9/242 0/242 255/242];
2. Layouts of map layers
The layouts were made in the project: LiseHuijser_Hedgerows1900_GroeneWoud. All layouts show map layers that were used in this research.
2.1 Layout of the study region Het Groene Woud
This map shows the contour of Het Groene Woud in Noord-Brabant with a topographic
background. This layout was used in the introduction to show the position of Het Groene Woud, namely between the three big cities: Eindhoven, ‘s-Hertogenbosch, and Tilburg.
2.2 Layout of the agricultural land-use in Het Groene Woud.
This map layout shows the agricultural lands of Het Groene Woud. Three categories show the arable land, namely: Cropland, rainfed; Cropland, rainfed – Herbaceous cover, Mosaic
cropland (>50%)/natural vegetation (Tree, shrub, herbaceous cover)(<50%). The category Grassland represents the pasture land.
2.3 Layout of soil map of Het Groene Woud
2.3.1 Legend of Soil Map
The legend of the soil map of Het Groene Woud is showed below. It did not fit in the layout of the soil map, because it consists of more than 300 soil types.
2.4 Layout of the AHN map of Het Groene Woud
Below the layout of the AHN map with the contours of Het Groene Woud (pink) are shown. This layout was made to show the differences in elevation in Het Groene Woud.
2.5 Layout of the hedgerows in Het Groene Woud in 2015
2.6 Layout of the hedgerows in Het Groene Woud in 1900
Below the self-made map is shown which displays all hedgerows along agricultural fieldborders present in Het Groene Woud in 1900.
3. Legend of Map_NL_1900
Below the legend of the map of the Netherlands in 1897 is shown. Bouwland met heggen shows agricultural lands with hedgerows, the hedgerows are represented as small globules. Openingen in stroken hakhout and Bosschen along agricultural fields were also selected. The source of this legend is: De Kadaster. The legend was received via the mail after handing in an application form in
