Evaluation of the Potential of Hedgerow Networks for Forest Biodiversity Restoration in an Irish Rural Landscape

Faculteit Bio-ingenieurswetenschappen

Academiejaar 2011 – 2012

Evaluation of the potential of hedgerow networks for forest biodiversity restoration in an Irish rural landscape

Litsa Bogaerts

Promotor: Prof. dr. ir. Kris Verheyen

Copromotor: Prof. dr. Geert Potters (Hogere Zeevaartschool / Universiteit Antwerpen)

Masterproef voorgedragen tot het behalen van de graad van Master in de bio-ingenieurswetenschappen: Bos- en natuurbeheer

Foreword

The realization of this thesis would not have been possible without the cooperation, advice and support of many people. I would like to thank them for that.

First supervisor Prof. dr. ir. Kris Verheyen and co-supervisor Prof. dr. Geert Potters for enabling this study and for their counsel and advice. They created the framework within which this thesis could be carried out and guided me during the investigation and processing of the data.

The advice of Prof. Olivier Thas, Kristof De Beuf and Jan De Neve on the processing of the data are greatly valued.

I also want to thank the people in Ireland, they have ensured that the fieldwork, which was associated with these thesis, could continue in a good mood. In particular, James Dungan, Frank Counihan, Peter Counihan, Eamonn Murphy and Bobby Jones gave permission to enter their premises. Also the help of Steven Dauwe, Pieter Ostermeyer and Jan Ostermeyer during the fieldwork is greatly appreciated.

I would also like to thank Erik Martens for the help and for lots of patience. Especially in wintertime, fieldwork was not always pleasant.

Finally, I also like to thank my parents Krista Janssens and Walter Bogaerts. I would like to thank them for their patience and their support and encouragement. Also my brother Kieran Bogaerts I want to thank, especially when searching for a number of historical works in the library.

A special thank is reserved for Denis O'Connor for providing the necessary accommodation and for reading my text and Iulia Klimina for the hard work and assistance during the fieldwork in Ireland. Without them, this was never successful.

Table of content

FOREWORD I

TABLE OF CONTENT II

LIST OF ABBREVIATIONS IV

LIST OF FIGURES V

LIST OF TABLES VII

LIST OF PICTURES VIII

ABSTRACT IX

SAMENVATTING X

1. INTRODUCTION 1

2. LITERATURE REVIEW 2

2.1. Hedgerows: a definition 2 2.2. Functions of hedges 4

2.2.1. On a local scale 4 2.2.1.1. Effect of hedgerows on the adjacent fields 4 2.2.1.2. Biodiversity - ecological function for fauna and flora 5 2.2.2. On a landscape scale 6 2.3. Ecosystem services 15

3. METHODOLOGY 18

3.1. Study area 18

3.1.1. General description 18

3.1.2. Origin of the hedgerows 19

3.1.3. Evolution of the hedges 20

3.2. Data collection 21

3.2.1. In general 21

3.2.2. Plant species 21

3.2.3. Explanatory variables 21

3.2.3.1. Owner (OWN) 22

3.2.3.2. Field observations 22

3.2.3.3. Cartographic information 24

3.2.3.4. Soil types (SOI) 24

3.3. Data processing 25

3.3.1. Descriptive statistics 25

3.3.2. Linear modeling 26

3.3.3. T-testing 26

3.3.4. Ordination analysis 27

3.3.4.1. PCA 27

3.3.4.2. DCA 27

3.3.5. Cluster analysis 28

4. RESULTS 30

4.1. Descriptive statistics 30

4.2. Linear modeling 37

4.3. T-testing 38

4.4. Ordination analysis 39

4.4.1. PCA 39

4.4.2. DCA 40

4.5. Cluster analysis 41

4.6. Differences between owners 41

5. DISCUSSION 43

5.1. Plant strategies 43

5.2. Explanatory variables 44

5.3. Ordination analysis 46

5.4. Owners 46

5.5. Measures to take 47

5.5.1. For existing hedgerows 47

5.5.2. For new hedgerows 48

5.5.3. Remarks 49

6. CONCLUSIONS 46

6.1. Which forest plants can be found, surviving in the hedgerows? 51 6.2. What are the variables affecting plant species richness and composition in hedgerows

within an Irish rural landscape? 51 6.3. Are there any measures the owners can take to promote the spread of forest plants on

their properties? 51

7. REFERENCES 51

APPENDIX 1: ACT OF 1721 64

APPENDIX 2: AGE OF THE HEDGES 68

APPENDIX 3: LIST OF TARGET SPECIES 73

APPENDIX 4: TOTAL LIST OF FOUND SPECIES 76

APPENDIX 5: SUBSET OF 45 HEDGES 80

Parts of the collected dataset are also used for a proceeding of the IXth World Bamboo Congress, held in Antwerp, April 10-15, 2012. The proceeding can be found at the end of this document.

III

List of abbreviations

AGE age of the hedgerow BAN presence of a bank DCA detrended correspondence analysis DED depth of the ditch DIT presence of a ditch ELE elevation above sea level GAP percentage of gaps LAN adjacent land use LED water level in the ditch LEN length of the hedgerow MEH mean height of the hedgerow ORI orientation of the hedgerow OUT outliers in height OWN owner PCA principal component analysis S presence of a shrub layer SOI soil type T presence of a tree layer VAH variation in height VAW variation in width WID width of the hedgerow

List of figures

Figure 2.1: Schematic representation of the whole colonization process as a funnel, illustrating that many diaspores are available initially, but few cam ultimately settle (adapted from Hermy and De

Blust, 1997). 8

Figure 2.2: Difference between habitat loss and habitat fragmentation (Verheyen, 2011). 9

Figure 2.3: Configuration of the different sampling plots (Tewksbury et al., 2002). 14

Figure 3.1: Localization of Ballyboughal, encircled in red (adjusted from Google maps). 18

Figure 3.2: Map of the study area (encircled in blue) and the farm of Denis O’Connor (encircled in orange) (adjusted from the GeoPortal website (gis.epa.ie) of the environmental protection agency

(EPA). 19

Figure 3.3: Field in the townland of Broomfield in 1843 (left) and in 1873 (right). 21

Figure 3.4: Visualization of the average linkage algorithm. The dissimilarity between the clusters C1 and C2 is equal to the average dissimilarity between all observations of C1 (points 1,2 and 3) and all observations of C2 (points 4 and 5). 28

Figure 4.1: Absolute frequency of the target species in the sampled hedges. 30

Figure 4.2: Distribution of the number of species (left) and the number of target species (right). 31

Figure 4.3: Different plant strategies of the target species (after Hodgson’s look-up table) (S = Stress- tolerant strategy, C = Competitive strategy and R = Ruderal strategy). 32

Figure 4.4: Different plant strategies of the 23 found species (after Hodgson’s look-up table) (S =

Stress-tolerant strategy, C = Competitive strategy and R = Ruderal strategy). 32

Figure 4.5: Different plant strategies of the abundant species (after Hodgson’s look-up table) (S =

Stress-tolerant strategy, C = Competitive strategy and R = Ruderal strategy). 33

Figure 4.6: Species-area relation for the number of species. 33

Figure 4.7: Species-area relation for the number of target species. 34

Figure 4.8: Histograms for the variables owner (OWN) and length of the hedgerow (LEN). 34

Figure 4.9: Histograms for the variables width of the hedgerow (WID) and the variation in width

(VAW). 35

Figure 4.10: Histograms for the variables percentages gaps (GAP) and mean height of the hedgerow

(MEH). 35

Figure 4.11: Histograms for the variables outliers in height (OUT) and variation in height (VAH). 31

Figure 4.12: Histograms for the variables presence of tree layer (T) and presence of shrub layer

(S). 35

Figure 4.13: Histograms for the variables presence of bank (BAN) and presence of ditch (DIT). 35

Figure 4.14: Histograms for the variables depth of the ditch (DED) and water level in the ditch

(LED). 36

Figure 4.15: Histograms for the variables elevation above sea level (ELE) and age of the hedge

(AGE). 36

Figure 4.16: Histograms for the variables orientation (ORI) and soil type (SOI). 37

Figure 4.17: Histogram for the variable adjacent land use (LAN). 37

Figure 4.18: Subset of 45 species in function of the first 2 principal components, the hedges of the bad group are encircled in blue. 39

Figure 4.19: Subset of 45 species in function of the first 2 components. 40

Figure 4.20: Dendrogram of the subset of 45 species using average linkage, the hedges of the good group are indicated in blue. 41

Figure 4.21: Boxplots for the number of species (left) and the number of target species (right) per owner. 41

Figure 4.22: Number of target species per owner. 42

List of tables

Table 2.1: Different strategies of plants in situations with stress or disturbance (Grime, 1977). 8

Table 2.2: Different ecosystem services (adapted from Millennium Ecosystem Assessment, 2005 and

Wallace, 2007). 15

Table 3.1: Number of planted and removed hedges over several periods in time. In the summer of

2011 there were 204 hedgerows, with a total length of 27847m and an average of 138.5m. 20

Table 3.2: The different owners that gave permission and whose hedges are included in the study. 22

Table 3.3: Different variables recorded during field observations. 23

Table 3.4: Categories of land use present in the study area (‘grass’ includes fields with horses, cows or sheep, ‘crops’ includes turnip, maize, corn, potato, sprout or cabbage, ‘garden’ includes gardens and a golf-course, ‘street’ includes paved and unpaved roads, ‘fragment’ includes older as well as recent fragments and ‘mixed’ includes all land use not suitable for previous categories). 23

Table 3.5: Categories of elevation present in the study area. 24

Table 3.6: Categories of orientation present in the study area. 24

Table 3.7: Categories of soil types beneath the study area. 25

Table 3.8: Sort of variables used in the linear models. 26

Table 4.1: Target species found during the study. 30

Table 4.2: Results of the linear model using the variables owner (OWN), age of the hedge (AGE), presence of a ditch (DIT) and length of the hedge (LEN). 37

Table 4.3: Results of the linear mixed model using the variables where the age of the hedge (AGE), the presence of a ditch (DIT) and the length of the hedge (LEN) are dependent on the variable owner

(OWN). 38

Table 4.4: Results of the T-tests per variable. 38

VII

List of pictures

Picture 3.1: Detail of the gradation on the self-constructed tool (left) and an example when used in the field to measure the height of a hedge (right). 22

Picture 5.1: Forest fragment with big trees on Frank’s property. 46

VIII

Abstract

Hedgerows are narrow bands of woody vegetation and associated organisms that separate fields. They can have a lot of different functions, like providing wildlife, shade for livestock, marking property boundaries, inhibiting erosion and nutrient runoff and aesthetics. They can also act as corridors, which are thought to facilitate movement between connected patches of habitat, thus increasing gene flow, promoting reestablishment of locally extinct populations and increasing species diversity within otherwise isolated areas.

The aim of the thesis is to investigate whether a hedgerow network can promote the presence and the spread of forest species in an Irish rural landscape.

This was done in a circle with a 1km radius around the farm of Denis O’Conor in Ballyboughal. In total 204 hedgerows were examined, in which 223 different species were found. Twenty-three of these species were forest species. Using different linear models the dimensions and the age of the hedgerow proved to be the most important variables affecting hedgerow flora in this research. Other factors that could have an influence are the presence of a ditch, the presence of a tree and a shrub layer, the percentage of gaps and the adjacent land use. A measure would be to keep as many hedges and ditches as possible. Not only to promote and help different species, but also to avoid flooding of your fields and consequent problems. Given the fact that hedgerow flora is heavily influenced by the dimensions of the hedge, it should be appropriate to keep the hedges as large as possible. Another important measure is to actively manage a hedge. A set of different management strategies results in a high species richness and diversity, because of the high level of spatio-temporal variability in environmental conditions.

The conclusion of this thesis is that with the right measures and with the right management hedgerows could promote the spread of forest plants.

Samenvatting

Haagkanten zijn smalle banden van houtige vegetatie op de grens tussen verschillende velden. Ze kunnen veel verschillende functies hebben, zoals het beschermen van wilde dieren, het bieden van schaduw voor vee, het markeren van grenzen, het remmen van erosie en de run-off van voedingsstoffen. Ze kunnen ook fungeren als corridors, welke verondersteld worden om de uitwisseling tussen habitat patches in een gefragmenteerd landschap te vergemakkelijken, waardoor ze het herstel van plaatselijk uitgestorven populaties bevorderen en aanleiding geven tot een de toenemende soortenrijkdom.

Het doel van deze masterproef is om te onderzoeken of een netwerk van haagkanten de aanwezigheid en de verspreiding van bosssoorten in een Iers agrarisch landschap kan bevorderen.

Dit werd onderzocht in een cirkel met een straal van een kilometer rond de boerderij van Denis O'Conor in Ballyboughal. In totaal werden 204 haagkanten onderzocht, waarbij 223 verschillende soorten werden gevonden. Drieëntwintig van deze soorten waren bossoorten. Door het gebruik van verschillende lineaire modellen bleken de afmetingen en de leeftijd van de haag, in dit onderzoek, de belangrijkste variabelen met een effect op de flora. Andere factoren die van invloed kunnen zijn, zijn de aanwezigheid van een sloot, de aanwezigheid van een boom- en een struiklaag, het percentage gaten en het aangrenzende landgebruik. Gezien het feit dat de flora van de haagkant zwaar beïnvloed wordt door de afmetingen van de haag, is het wenselijk om de haagkanten zo groot mogelijk te houden. Een andere belangrijke maatregel is het actief beheren van een haagkant. Een reeks verschillende management strategieën resulteert in een hoge soortenrijkdom en diversiteit, als gevolg van het hoge niveau aan spatio-temporele variabiliteit in milieuomstandigheden. Een andere maatregel zou zijn om zo veel mogelijk haagkanten en sloten te behouden. Niet alleen bevorderen en helpen zij verschillende soorten, maar zij voorkomen ook de overstroming van velden en de daaruit voortvloeiende problemen.

De conclusie van deze masterproef is dat met de juiste maatregelen en met het juiste management van de desbetreffende haagkanten de verspreiding van bosplanten kan bevorderd worden.

1. Introduction

I have studied seven years in Antwerp and have achieved a licentiate in Biomedical Sciences and a bachelor's degree in Bio-Engineering. For the subsequent master the UGent was elected, however there is still a good contact with different teachers from the UA.

During the first master year a topic should be chosen for the thesis, which is than prepared during the second master year. Usually this topic is elected from a list of proposals submitted by different professors. This particular proposal, however, came from a totally different angle, namely from the owner of a farm in Ireland. I was there in the summer of 2010 as part of an ongoing PhD at the UA. To lighten the fieldwork for the doctoral student, there were several students as well, who then came into contact with Denis O'Connor, the owner.

In February 2011 Denis asked me if I didn’t want to come back to Ireland and investigate how he could run his farm in a scientifically based and ecologically responsible way. The way he worked at that time was not economically profitable and not consistent with his great love for nature and his desire to take care of the environment as much as possible.

My task was therefore to advise and to propose measures for a new way of managing the farm. One of the things that Denis wanted to do was to plant more trees on his property, to create a more forest like environment and to create a good habitat for various plants and animals. Therefore it was, however, paramount to know which forest plants were already present in the region, so that the proposed measures could promote and encourage their dissemination.

After consulting Prof. dr. ir. Kris Verheyen, it was therefore decided on the following title: "Evaluation of the potential of hedgerow networks for forest biodiversity restoration in an Irish rural landscape." The existing hedgerows are indeed the only refuge for forest plants in a region with a very low forest cover and with a very intensive agriculture.

The promoter of this thesis is Prof. dr. ir. Kris Verheyen, but the direct supervision of this work is in the hands of Prof. Dr. Geert Potters, a lecturer at the UA and already familiar with the region in question, this by guiding students in various projects on the spot.

The following question are addressed in this thesis: 1) Which forest plants can be found, surviving in the hedgerows ? 2) What are the variables affecting hedgerow flora or, in other words, which explanatory variables are statistically significant in explaining patterns of plant species richness and composition in hedgerow habitats within an Irish rural landscape ? 3) Are there any measures the owners can take to promote the spread of forest plants on their properties ?

2. Literature review

2.1. Hedgerows: a definition

Hedgerows, as stated by Forman and Baudry (1984), are narrow bands of woody vegetation and associated organisms that separate fields. French and Cummins (2001) defined a hedgerow as a combination of a hedge and a hedge-bottom. A hedge is a self-supporting woody vegetation, usually forming a boundary or barrier and maintaining a linear shape. Management is most common by cutting or, less frequent, by laying, when the main stem is partly cut through and the plant bent over before interlacing the branches with stakes or adjacent plants (French and Cummins, 2001). The hedge-bottom consists of a mainly herbaceous ground flora, plus any soft-wooded species present. Hedges in Britain are usually planted and only one or two thorny species are commonly used, although additional shrubs or trees may invade later. In contrast, hedge-bottoms arise mainly by natural colonization (French and Cummins, 2001). Sometimes the terms hedgerows and hedges are used interchangeably. The term fencerow refers to those hedgerows where a fence is or was present (Forman and Baudry, 1984). French geographers use the word bocage to indicate a landscape where hedgerows are characteristic features. Such landscapes can be found in France, Britain, Spain, Denmark, Italy, Switzerland, Belgium and Germany (Baudry et al., 2000). In Ireland, field boundaries have an estimated total length of 830,000km and occupy 1.5% of the land area (Aalen et al., 1997). Hoskins (1955) describes how in medieval times the ancient enclosures were often taken out of woodland. He mentions that hawthorn (Crataegus monogyna) is the oldest species used for hedgerows and points out that it even gets its name from the old word ‘haga’, a hedge or enclosure. Despois provides the first description of tropical bocages in Africa (Lauga-Sallenave, 1997), where villages are surrounded by hedgerows to protect gardens. Hedgerows are also extensive in Ecuador and in Bolivia where they separate paddocks or gardens (Baudry et al., 2000). In China hedgerows are also found mostly around villages (Zhenrong et al., 1999). In North America hedgerows were planted by early European settlers who wanted to recreate their homeland landscapes (Hewes, 1981; Sutton, 1985) and also as a means to manage and protect soils (Nabhan and Sheridan, 1977).

Three predominant types of hedgerow origins can be recognized: planted, spontaneous and remnant. Planted hedgerows usually are dominated by a single species such as hawthorn (Crataegus) in Europe or Osage orange (Maclura) in the United States (Forman and Baudry, 1984). The shrubs or trees are generally planted in a single row. On slopes, a ditch and/or a bank with or without stones, may be constructed along with the plantings. Planted hedgerows tend to have equal-aged dominants, relative homogeneity in vertical and horizontal structure and rather low species diversity (Pollard et al., 1974). In spontaneous hedgerows, trees and/or shrubs grow along a fence, stonewall or ditch, from seeds dispersed by animals and the wind. A fence serves as an attractant for many birds which drop seeds and also limits cultivation and livestock grazing, hence permitting development of the hedgerow biota. The observations of Forman and Baudry (1984) suggest spatial diversity and species diversity, particularly of bird-dispersed plant species, tend to be high in spontaneous hedgerows. Forest remnant hedgerows (Hooper, 1976) result from the process of forest-clearing, such as a row of trees and shrubs left along a property line. Such hedgerows generally have old individuals of various species, considerable spatial heterogeneity, high species diversity and many forest species (Forman and Baudry, 1984).

A hedgerow can be planted or grow spontaneously, but always has a human component to provide control and to prevent its expansion into adjacent fields (Baudry et al., 2000). Most of the time a hedgerow is a field boundary and its management forms part of the farming activities (Baudry et al., 2000). Agriculture and hedgerows are closely related and have developed together. Today they coexist over about 10% of our planet’s land surface (Forman and Baudry, 1984). Therefore herbicides and insecticides from the field can blow into the hedgerow (Pollard et al., 1974). Pollard et al. (1974) point to a loss of hedgerow insects and nesting and a decrease in hedgerow pheasants in England. Fertilizers from fields readily enter hedgerows and favor some species, such as nitrophiles, at the expense of other species (Forman and Baudry, 1984). In short, the nature of hedgerows as narrow lines of vegetation and fauna is heavily determined by inputs from the adjacent fields.

Solar radiation, wind and precipitation are the three major inputs to a hedgerow. Relative to a field, hedgerow albedo is lower, which means more heat energy is absorbed (Damagnez, 1976; Guyot and Seguin, 1976). During the day the sunny side of the hedgerow has higher soil and air temperatures than the shady side, although air temperature differences may only be about 0.5 - 2.0°C (Pollard et al., 1974; Guyot and Seguin, 1976). A shaded ground-layer environment is generally present, with relative humidity higher than in the field. At the top of the hedgerow wind velocity exceeds that in the adjacent field, whereas at the bottom center of the hedgerow it is considerably lower than in the field (Caborn, 1976). On the windward side of the hedgerow , wind velocity is reduced near the ground. The entire leeward side has reduced wind velocity, though for dense, relatively non permeable hedgerows considerable turbulence will be present in strong winds (Pollard et al., 1974). Evaporation from the soil in a hedgerow is less than in a field, but plant respiration must be higher, due to exposure to wind (Ballard, 1979; Geiger, 1965). Snow persists longer in portions of temperate hedgerows due to accumulation by wind and subsequent shading and hence more spring soil moisture is expected (Forman and Baudry, 1984). Percolation to the ground water is considered greater if the hedgerow is on a slope where runoff is impeded by the hedgerow (Merot and Ruellan, 1980; Buson, 1979). In contrast, on flatter land, percolation is probably lower than in the field due to hedgerow evapotranspiration (Blavoux et al., 1976; Ballard, 1979).

About 500-600 vascular plant species are known to grow in hedgerows in England, although only half this number occurs frequently enough to be thought of as hedgerow plants (Pollard et al., 1974). Apparently, at least in England, France and New Jersey and elsewhere in the USA, no plant species is limited to hedgerows. All species are found in other nearby habitats. Some plants are predominantly open-field species, some forest-interior species, but many are forest-edge species. In general, hedgerows are similar in vegetation to forest edges (Forman and Baudry, 1984). Interestingly, the wider the hedgerow, the more forest herb species were present. The predominant species of hedgerow trees and shrubs in temperate-zone landscapes differ, though the genera, such as Fraxinus, Prunus, Quercus, Ulmus, Acer, Rubus and Rosa are rather similar (Forman and Baudry, 1984).

In view of the high proportion of plants in most hedgerows that are bird-dispersed, a positive feedback system involving plants and birds is evident. The plants produce fruits that attract large numbers of birds and the birds disperse the seeds, which in turn produce more of the plants (McDonnell and Stiles, 1983). Mammals using hedgerow cover include rabbits, squirrels (Harmon, 1948), red-back voles (Sinclair et al., 1967), hedgehogs, moles, common shrews, pygmy shrews,

water shrews, harvest mice and house mice (Pollard et al., 1974). Many hedgerow faunal studies show high diversity, apparently due to the microhabitat heterogeneity in the hedgerow (Lefeuvre et al., 1976). The high species diversity of hedgerows applies to invertebrates as well as vertebrates. For example, summer insect diversity was higher in an English hedgerow than in an adjoining bean field and pasture (Lewis, 1969). Animal distribution in hedgerows have been correlated with vegetation structure, plant species diversity and plant species composition (Constant et al., 1976; Pollard et al., 1974).

As discussed above, individual hedgerows differ markedly in internal structure. But a hedgerow network has also other characteristics like the type of connection where lines intersect or end. The types are L’s, T’s, +’s, ends and connections with woods (Forman and Baudry, 1984). Another network property is the presence and length of breaks in lines. In some hedgerow landscapes the + connection is rather uncommon and experience in New Jersey suggests that T and + connections generally have short breaks near the intersection, caused by the movement of farm equipment (Forman and Baudry, 1984). The area immediately surrounding a connection may be expected to have a somewhat different microenvironment than that along a line. Indeed, Constant et al. (1976) reported more bird species at hedgerow connections than along lines. Presumably micro- environmental conditions would vary with connection type.

Mesh size is another structural property of a network (Forman and Baudry, 1984). This may be measured as the distance between network lines or the area of landscape elements enclosed by the lines. Mesh size is important in relation to the grain size of a species, that is, the distance or area the species is sensitive to in carrying out its functions, such as foraging, defending a nesting territory or absorbing sunlight and water. Mesh size is also relevant to agricultural economics. Farmers observe that it requires more time to cultivate small fields than a large field. An economist concluded that 4ha appeared to be the minimum field size from an economic perspective (Le Clezio, 1976).

2.2. Functions of hedges

2.2.1. On a local scale

2.2.1.1. Effect of hedgerows on the adjacent fields

Microclimate. Essentially all microclimate variables are modified downwind of a hedgerow. Shade modifies the environment in a narrow band next to the hedgerow, but wind is the driving force controlling all other microclimate variables (Forman and Baudry, 1984). Relative to an open area without hedgerows, some environmental factors are elevated, including day temperature, soil and atmospheric moisture and others, such as wind speed, evaporation and night temperatures, reduced. Two environmental factors are modified a long distance downwind. For evaporation the effect extends downwind about 16 times the hedgerow height (=h) and for wind speed 28 times the hedgerow height (Forman and Baudry, 1984). In many agricultural landscapes, hedgerows are interconnected to form a network. In such cases the second hedgerow modifies the normal wind attenuation pattern. Wind speed near the ground is reduced for a considerable distance downwind of a hedgerow, is higher in the 6 to 8 h distance and is reduced again on the windward side of the second hedgerow (Forman and Baudry, 1984).

Water, erosion and mineral nutrients. On gentle slopes where precipitation soaks into the soil, lateral movement of water is a subsurface process. Subsurface water may be absorbed by deep and/or dens roots of hedgerow plants. Tall hedgerow plants are exposed to high levels of sun and wind, which accelerate evapotranspiration (Ballard, 1979; Geiger, 1965). The presence of a ditch or bank in the hedgerow would further increase the process. Hedgerows in such area are thus active sites of soil water depletion and atmospheric moisture enrichment. Soil erosion on slopes is undoubtedly reduced with hedgerows along the contours (Forman and Baudry, 1984). Indeed, the deposition of soil particles, including organic matter, on the upslope side of a hedgerow may be pronounced, producing a terrace like effect. The distance between hedgerows here again is important in inhibiting soil erosion. Pihan (1976) estimates 40% more erosion with a doubling of the distance between hedgerows. Similar patterns of mineral nutrient runoff may be expected.

Animals and plants. Hedgerows affect the organisms in adjacent fields in two basic ways: first, indirectly, by modifying the microclimate and secondly, directly, by the movement of organisms from hedgerow to field (Forman and Baudry, 1984). Immediately adjacent to hedgerows, the hedgerow plants shade the field and send out roots that extract water and nutrients (Bates, 1937; Steavenson et al., 1943). Many types of animals move from hedgerow into fields, including mice (Pollard and Relton, 1970; Saint-Girons, 1976), birds and insects (Pollard et al., 1974). Some animals may cause economic damage by feeding on crops. But it is also been hypothesized that hedgerow maintain predators that feed in fields and reduce agricultural crop loss by dampening pest population fluctuations (Forman and Baudry, 1984).

Crop production. On the negative side, hedgerows decrease the crop area and produce shade and competition for soil moisture and nutrients between hedgerow and crop plants. Balanced against this is the pattern of microclimate over the field discussed above. Especially productive zones in the field may be expected from 3 to 6 times the hedgerow height downwind and 2 to 6 times the hedgerow height upwind of a second hedgerow (Forman and Baudry, 1984). Forman and Baudry (1984) hypothesize that there is little difference for a small area in the presence or absence of hedgerows. Therefore the decision of the farmer whether to have hedgerows by fields, hinges largely on the other functions of hedgerows, such as providing wildlife, inhibiting potentially damaging maximum wind velocities, providing sites for potential predators on crop pests, shade for livestock, marking property boundaries, inhibiting erosion and nutrient runoff, biological conservation and aesthetics.

2.2.1.2. Biodiversity - ecological function for fauna and flora

Hedgerows control biodiversity being habitats, refuges, corridors or barriers. These functions are critical for many plants and animals that otherwise could not exist in in agricultural landscapes (Burel, 1996). Indeed, landscape elements can have different functions for living organisms (Hermy and De Blust, 1997):

- permanent residence - a location during a particular life stage or used for a specific function - the route that organisms use for their regular journeys through the landscape - the places where they spread along in search of new habitats

For many organisms small landscape elements are the habitat where they spend their entire lives. In the first place this is true for the flora. The botanical richness of the hedgerows or hedgerow landscapes is well-known (Pollard et al., 1974). There, in areas that are otherwise poor in forest, true forest species can still be found. They are the remnant of what once were contiguous populations of forest vegetation (Hermy and De Blust, 1997). This also applies to many animal species. Quite a lot of real forest invertebrates still live in ancient hedgerows. This is especially well researched for ground beetles (Burel, 1992; Burel and Baudry, 1990b). The biodiversity in hedgerows may be large. Often this has to do with the large food supply, because there are many plant species early in leaf, at least before the fruits in the field (Hermy and De Blust, 1997). For many animals a given landscape element is only part of their habitat. Their range is much greater. It has a very specific function or they use the element only for a certain period in the year or in their lives. Quite a few mammals and birds have their nest in hedges and seek food in the open field. Outside the breeding season or in case of danger small landscape elements are a place to rest and shelter for many animals. And for their daily movement through the landscape many animals follow the network of landscape elements. They are quite selective, so a suitable element for one species, might not necessarily work for another (Hermy and De Blust, 1997). See for example Broekhuizen (1986) for stone martens, polecats and badgers, Wegner and Merriam (1979) and Van Dorp (1996) for birds and Helmer and Limpens (1988) for bats.

Two network properties may be hypothesized to be significant. Connectivity, the degree of spatial linkage, provides a measure of the number of breaks in hedgerows, which in turn must inhibit the flow along hedgerows. Second, the presence of loops, or alternative pathways, in the network provides options to an organism or species to avoid breaks, as well as predators or disturbances at a point (Forman and Baudry, 1984). In contrast, the movement of field species across a hedgerow landscape would presumably be less efficient in a fine-mesh network, since hedgerow lines would act as partial or full barriers. Here, breaks in hedgerows would favor movement of such open-field species (Forman and Baudry, 1984). Note that both types of movement would be affected by the orientation of the network relative to the direction of the movement (Forman and Baudry, 1984).

The structural diversity of hedgerows plays an important role, as shady and sunny conditions as opposed to wet and dry situations may be present (Baudry et al., 2000). The single hedgerow approach does not generally include the cyclical management of hedgerows, which is partly responsible for the diversity of conditions. Although tree cover may decrease from time to time due to pollarding, most authors (e.g. Petit and Burel, 1998) assume that dense hedgerows, at a given time, are efficient corridors for forest species movement. Biodiversity must be assessed at the landscape scale not only because of the diversity of hedgerows, but also because of landscape scale processes (Baudry et al., 2000). The corridor function of networks of hedgerows has been demonstrated in various conditions: for plants by Baudry (1988) and Marshall and Arnold (1995); for insects by Burel (1989) and Duelli et al. (1990); for birds by Dmowski and Koziakiewicz (1990) and Clergeau and Burel (1997).

2.2.2. On a landscape scale

The pollination of plants is done primarily by animals (zoophily, entomophily) and by the wind (anemophily). About 80% of the Northwest European plant species is pollinated by insects (Holm,

1978). In addition, self-pollination (autogamy) and pollination by water (hydrogamy) also exist. Cross- pollination of plants is important to reduce the loss of genetic variation (Hermy and De Blust, 1997). For plants that are pollinated by insects, the spatial arrangement of the flower blooming groups can be of interest. This determines the probability of flower visit by the insects. It is clear that the problem of fertilization is strongly linked to the mobility and behavior of pollinators. The extent to which the landscape (micro) structure is able to influence them, will therefore also be determining for the degree of isolation of the plant population (Hermy and De Blust, 1997).

Dissemination of diaspores usually happens through one of the following processes (Van der Pijl, 1969): - Anemochory. Spread by the wind whereby very large distances of tens of km can be bridged. The diffusion occurs across the whole landscape. - Epizoochory. Spreading by hooking to animals. Here, the distance over which a seed is transported, depends on the activity of the animal. The spread is usually focused. - Endozoochory. Spread by animals after the fruit is eaten. After digestion of the fruit, the seeds are excreted. The distance over which a seed is transported, is dependent on the activity of the animal. The spread is usually focused. As a special form spread by birds is distinguished (ornithochory). - Myrmecochory. Displacement by ants. In this manner, only very small distances in the order of centimeters are traveled. The spread is quite focused. - Hydrochory. Spread through water. Depending on the buoyancy of the seed, the intensity of the water current and the absence of obstacles, very large distances may be traveled. - Autochory. Spreading without special equipment. Seeds are sometimes thrown out, others fall and roll away with gravity (barochory). In this way, there are only very small distances traveled. The spread is not focused, except in hilly areas. - Agestochory. Transport by humans and their vehicles. In this way the seeds can be moved for a great distance.

The colonization capacity strongly depends on the number diaspores produced by the plant. When this is very little, then the probability of a (remote) dissemination is also very small. The amount of diaspores diminishes rapidly with increasing distance from the mother plant (Hermy and De Blust, 1997).

The entire process of colonization is shown schematically in figure 2.1. We need to distinguish two stages in the propagation process: in phase 1, the seeds of the mother plant land on a surface, phase 2 includes the movements of the diaspores after the completion of phase 1 (Hermy and De Blust, 1997). This secondary horizontal and/or vertical movement of the seeds is likely to be much more important than is usually thought (Chambers and MacMahon, 1994). The type of movement and the distance traveled, depends, inter alia, on the slope and the exposition in relation to the wind. Especially where there is little vegetation, the wind plays a large role in this secondary spread. Individual plants and other structures act as seed traps. Animals can also play a large role in this secondary spread (Hermy and De Blust, 1997).

Figure 2.1: Schematic representation of the whole colonization process as a funnel, illustrating that many diaspores are available initially, but few can ultimately settle (adapted from Hermy and De Blust, 1997).

In the establishment phase, the germinated species struggle with competitors who have targeted the same area. Competition is both an above-ground and an underground matter (Hermy and De Blust, 1997). When the available soil is rich in nutrients, it will be especially competitive species who gradually gain ascendancy, because of their rapid growth, their large biomass production and their often extensive network of roots and rhizomes. If people do not intervene, a relatively species-poor vegetation will occur (Hermy and De Blust, 1997).

Besides competitive plant species, which live in situations with low intensities of stress and disturbance, there are also plants with a ruderal or a stress-tolerant strategy as shown in table 2.1. Ruderals have a rather slow growth rate and a high nutrient retention rate and live in areas with a high intensity of disturbance, but a low intensity of stress (Grime, 1977). Stress-tolerators, on the other hand, live in conditions with a high intensity of stress and a low intensity of disturbance, are fast-growing and are often annuals (Grime, 1977). There is no viable strategy is situations with a high intensity in stress as well as in disturbance.

Table 2.1: Different strategies of plants in situations with stress or disturbance (Grime, 1977). Intensity of stress Low high low competitive strategy stress-tolerant strategy Intensity of disturbance high ruderal strategy no viable strategy

Fragmentation can be seen as an extreme form of disturbance and is characterized by a decrease in the amount of habitat, an increase in the number of patches, a decrease in the mean size of the

patches, an increase in the amount of edge and an increase in the distance between several patches (Vancoillie, 2012; Verheyen, 2011).

Definition: “habitat fragmentation is a process during which a large expanse of habitat is transformed into a number of smaller patches of smaller total area, isolated from each other by a matrix of habitats unlike the original” (Wilcove et al. 1986). Habitat fragmentation occurs when a large, fairly continuous tract of a vegetation type is converted to other vegetation types such that only scattered fragments of the original type remain. These remnants (also called isolates, habitat islands, fragments, patches, etc.) obviously occupy less area than the initial condition, are of variable size, shape, and location and are separated by habitats different from the original condition (Faaborg et al., 1995).

It is necessary to make a distinction between biodiversity effects of habitat loss on the one hand and on habitat fragmentation per se (i.e. the breaking apart of habitat) on the other (Verheyen, 2011).

Figure 2.2: Difference between habitat loss and habitat fragmentation (Verheyen, 2011).

Problems associated with habitat fragmentation include overall habitat loss, increase in edge habitat and edge effects (particularly higher parasitism and nest predation rates) and isolation effects (Faaborg et al., 1995).

Habitat fragmentation results in a qualitative loss of habitat for species originally dependent on that habitat type (Temple and Wilcox, 1986), but the most obvious effect of is an outright quantitative loss of habitat. Groups of species directly impacted by habitat loss through fragmentation include those with large home range requirements, very specific microhabitat requirements and poor dispersal abilities (Wilcove et al., 1986, Wilcove, 1988). As a consequence, the abundance and the diversity of species originally present often declines and losses are most noticeable in smallest fragments (Faaborg et al., 1995).

As an area is fragmented, there is an increase in amount of edge relative to interior area and an increase in “edge effects” (Temple, 1986). The ratio of edge to interior is determined by fragment shape, with the ratio largest for long, narrow fragments and smallest for circular or square fragments (Faaborg et al., 1995). Faaborg et al. (1995) defined an edge as the junction between two dissimilar habitat types or successional stages. “Edge effects” are ecological characteristics associated with this

junction that affect any number of biological traits (Harris, 1988; Yahner, 1988; Saunders et al., 1991) and which may extend great distances into a forest.

Traditionally, edge effect has been defined as an increase in abundance and diversity of wildlife found along the boundary between two habitat types (Leopold, 1933). Because many game species are more abundant near edges, wildlife managers were generally taught that “edge” was good for wildlife and in many cases, wildlife management was considered synonymous with creating edge habitat (Harris, 1988). The concept of edge and edge effect has changed for a number of reasons (Faaborg et al., 1995). First, the definition of wildlife has expanded to include non-game species, many of which evolved within extensive area of unfragmented habitat away from edges (Temple and Cary, 1988). In addition, our way of defining edge effects has changed; instead of merely looking at number and abundance of species, we are using demographic parameters such as reproductive success (Faaborg et al., 1995). This is important, because misleading conclusions can be reached by using only abundance as a measure of habitat quality (Van Horne, 1983). For example, an apparent consequence of the increase in abundance and diversity of wildlife along edges is an increase in biotic interactions, such as nest predation, brood parasitism and interspecific competition (Faaborg et al., 1995).

Initial predictions about the genetic consequences of habitat fragmentation focused on the reduced size and increased spatial isolation of populations occupying habitat remnants (van Treuren et al., 1991; Young et al., 1993). Theoretically, such population changes lead to an erosion of genetic variation and increased interpopulation genetic divergence through: (1) increased random genetic drift, (2) elevated inbreeding, (3) reduced interpopulation gene flow, and (4) increased probability of local extinction of demes within a metapopulation (Gilpin, 1991; Raijmann et al., 1994). Such effects have serious implications for species persistence (Young et al., 1996). In the short term, a loss of heterozygosity can reduce individual fitness and lower remnant population viability (Young et al., 1996). In the longer term, reduced allelic richness may limit a species’ ability to respond to changing selection pressures (Frankel et al., 1995). For plants, the genetic effects of habitat fragmentation are likely to be complicated by their sessile habit, interspecific differences in longevity, generation time and pre-fragmentation abundance, their wide variety of sexual and asexual reproductive systems, the possibility of gene flow by both pollen and seed, the storage of genetic material as seed, and their interactions with animal pollination and dispersal vectors, which may themselves be affected by fragmentation events (Young et al., 1996).

Current empirical results clearly show that habitat fragmentation has population genetic consequences for plants (Young et al., 1996). However, these would appear to be more varied than predicted from simple population genetics models (Young et al., 1996). It is obvious that not all fragmentation events lead to reduced genetic variation for plants. The data from Eucalyptus albens point to the possible existence of fragmentation thresholds up to which genetic variation is not lost (Prober and Brown, 1994). Perhaps the most surprising results have been the apparent increases in interpopulation gene flow observed for Acer sacchavum populations that have been subject to fragmentation (Young et al., 1993; Foré et al., 1992). These findings are counterintuitive and raise new conservation and evolutionary questions about the effects of a breakdown of local population genetic structure due to habitat fragmentation (Young et al., 1996).

To the extent that dispersal capabilities and the character of habitat separating fragments limit movement, relative isolation of a fragment may be detrimental to population survival. All other

things being equal, theory suggests that isolated fragments might support fewer species or lower densities than less isolated fragments (MacArthur and Wilson, 1967; Shafer, 1990).

Recognizing the relationship between species-area patterns on oceanic islands and the equilibrium model, early researchers in habitat fragmentation censussed birds on habitat fragments of varying size within a region (Bond, 1957; Galli et al., 1976; Whitcomb et al., 1976; Robbins, 1979; Hayden et al., 1985 and others). They found the number of species on a habitat island increased with increasing habitat size. A number of studies (reviewed by Askins et al., 1990) verified that area per se has the greatest influence on species number in a given area. Factors such as habitat heterogeneity, degree of isolation and vegetation structure were relatively unimportant compared to habitat size.

Most importantly, these studies have noted “area sensitive” species, species which tend to occur in or achieve their highest densities only on large fragments. These patterns suggest the possibility of regional extinctions without preservation of large enough habitats.

With recognition that some species seemed to “require” large areas to exist, attempts were made to determine minimum area requirement (MAR) of each species within a region. MAR was defined in a variety of ways, ranging from “size class of habitat at which the frequency of occurrence undergoes a sharp decline” (Robbins, 1979) to “the area in which young can be produced in sufficient numbers to replace adult attrition under the poorest conditions of weather, food availability, competition from other wildlife and other disturbances” (Robbins et al., 1989).

A consequence of fragmentation is that species are more frequently present in smaller and separated populations. Depending on the surrounding landscape and on the spreading capacity of the species, a more or less regular exchange of individuals between these populations may still exist (Hermy and De Blust, 1997). Such fragmented populations between which exchange occurs, are called metapopulations or network populations (Opdam, 1987). If a local segment of the population dies out, the empty habitat can be repopulated through immigration. Of course this requires sufficient individuals to reach the liberated areas. This can occur via binding linear features, the corridors or via habitat patches, such as stepping stones or because of individuals directly bridging the intervening space (Hermy and De Blust, 1997). The intensity of exchange between sub-populations of a species depends not only on the abundance of the species in an area, but also on the number of suitable habitat and the mutual distance between them and on the resistance the intermediate region has for the species. Landscape elements can reduce this resistance (Opdam, 1987). Through migrations a metapopulation finds itself in a dynamic equilibrium. In one place a subpopulation dies out; the habitat remains unoccupied for a while and is then colonized again. The probability of local extinction is greatest in small sub-populations and the chance of repopulating is smallest in habitats with a peripheral location (Hermy and De Blust, 1997).

To understand the regional dynamics of populations in fragments, a variety of source-sink models have been developed (Brown and Kodric-Brown, 1977; Pulliam, 1988). A sink population is one that does not produce enough young to replace adult mortality and which exists because of continued colonization from elsewhere. A source produces enough young to replace breeding adults and perhaps even enough to populate other fragments through dispersal.

Since habitat loss has much stronger effects on biodiversity than habitat fragmentation per se, the focus for conservation should in the first place be on the maintenance (and expansion) of suitable habitat to levels that are sufficient for persistence of the most vulnerable species (cursus ecotechniek).

In the second place, the permeability of the landscape matrix should be improved as well, to counteract the effects of habitat fragmentation sensu strictu. (Verheyen, 2011).

Strategies to increase the permeability of the landscape matrix: 1) Create ‘stepping stones’ or ‘landscape corridors’ e.g. agri-environment schemes 2) Create linear corridors to connect habitat patches e.g. hedgerows

The concept of connectivity was introduced by Gray Merriam (Merriam, 1984). Connectivity is a fairly complex concept for which there is no widely accepted measure or unit. In nature, one can define connectivity as the degree of connectedness of habitats of the same type and for specific organisms. This degree of connectedness is not only dependent on the distance between the habitats. Besides internal habitat features also the presence or absence of connecting structures and corridors, the quality of these corridors and even the nature of the landscape where the corridors are located (the scenic background matrix) play a role (Hermy and De Blust, 1997). Corridors are landscape features and structures that allow connections between habitats. These are of better quality than the surrounding landscape and hence migrating organisms will preferably use them. Moreover, it is only meaningful to study the relationship between two habitats if one has a suitable organism or group of organisms in mind, that can use the present connections to search adjacent similar habitats (Hermy and De Blust, 1997). For example, in landscape ecology one makes a distinction between functional and structural connectivity. The connectivity between habitats is called functional only when it is actually shown that an organism uses the available elements and structures in the landscape between two habitats on its travels. A high structural connectivity may not always coincide with high functional connectivity. The functionality of a corridor is therefore species-specific: a corridor for one species may act as a barrier for another species (Hermy and De Blust, 1997).

Corridors are thought to facilitate movement between connected patches of habitat, thus increasing gene flow, promoting reestablishment of locally extinct populations and increasing species diversity within otherwise isolated areas (Tilman et al., 1997; Gonzalez et al., 1998; Aars and Ims, 1999, Hale et al., 2001). But the utility of corridors in conservation and management has generated extensive controversy because the case for corridors has been built more on intuition than on empirical evidence (Hobbs, 1992; Simberloff et al., 1992; Beier and Noss, 1998). Although recent studies suggest that corridors increase movement rates between patches for a broad range of animal species (Gonzalez et al., 1998; Haas, 1995; Fahrig and Merriam, 1985; Saunders and Hobbs, 1991; Haddad, 1999; Coffman et al., 2001), other studies show no such response (Rosenberg et al., 1998; Bowne et al., 1999; Haddad and Baum, 1999; Collinge, 2000).

Many hypothesize that hedgerows are basically corridors where movement of plants and animals is facilitated (Sinclair et al., 1967; Pollard et al., 1974; Helliwell, 1975; Forman and Godron, 1981; Forman 1981 and 1983).

For forest species, it remains to be seen whether hedges and hedgerows really function as a propagation path (Hermy and De Blust, 1997). Forest species can be found in hedges and hedgerows and the density of the forest plants is often high. This is the case especially close to the adjacent forest or in the nodes of the landscape elements. The first suggests a possible dissemination from the forest. The second can, however, indicate that it is a remaining population, which could survive in the node, because there is - by the larger dimensions - a more forest-like climate. For forest plants whose seeds are easily spread, those nodes can also serve as stepping stones, which means there is actual spreading (Hermy and De Blust, 1997). If spread is possible, then however, it will be particularly slow for most real forest plants. On the other side, this won’t be a problem for plants of clearcut zones and forest edges, who carry berries. Because they often are spread by birds, they are far less susceptible to isolation (Van Ruremonde and Kalkhoven, 1991).

Forman and Baudry (1984) conclude that, rather than forest herbs moving progressively down the hedgerow as a corridor, somehow a species disperses to a point in the hedgerow and spreads in that immediate area. MacClintock et al. (1977) found more bird species in point samples within woodlots connected by a wooded corridor to other woods than in isolated woodlots and hypothesized that the corridor was important. There is some indication that wide tree-shrub hedgerows are more effective corridors than shrub hedgerows. Finally, in landscapes with few woodlots, hedgerows are probably critical in the long-term for survival and dispersal of a wide range of species.

In general, too little evidence is available to definitively evaluate hedgerow effectiveness. Different taxa show different response: - Mammals (most studies use rodents as study species): generally positive - Birds: generally positive - Invertebrates: little info available (only carabids), positive trend - Plants: unclear, but probably mostly beneficial for animal pollinated and dispersed species (see also Tewksbury et al., 2002)

There is a general positive effect of higher structural complexity in hedgerows.

A unique corridor experiment performed by Tewksbury et al. (2002) had some promising results.

Tewksbury et al. (2002) stated two major problems in research concerning corridors. First, linking two patches of habitat with a corridor increases the area of those patches (Tewksbury et al., 2002). If corridors function by increasing patch area, the population dynamics within a patch connected by a corridor should be identical to the dynamics of a patch that is increased in area by the size of the corridor (Haddad and Baum, 1999; Rosenberg et al., 1997; MacArthur and Wilson, 1967). A second complication is that corridors affect patch shape in ways that may alter their function in unexpected ways. For example, they may act as “drift-fences”, intercepting individuals moving through matrix habitat and diverting them into connected patches (Haddad and Baum, 1999).

Figure 2.3: Configuration of the different sampling plots (Tewksbury et al., 2002).

Using the configuration of the sampling plots shown in figure 2.3 Tewksbury et al. (2002) found that movement from the center patch to peripheral patches connected by corridors was higher than movement to unconnected patches for all taxa studied. The Common Buckeye (Junonia coenia) was three to four times more likely to move from center patches to connected patches than to unconnected patches and the Variegated Fritillary (Euptoieta claudia) was twice as likely to move down corridors than through forest when moving from the center patch (Tewksbury et al., 2002). Neither butterfly was more likely to move to winged patches than to rectangular patches. The corridors thus facilitated the movement of both butterfly species between connected patches, even after controlling for patch size and shape, but did not function as drift fences (Tewksbury et al., 2002). Pollen movement mirrored the movement of the butterflies studied. A significantly higher proportion of flowers produced fruit in connected patches than in the unconnected patches, with fruit set increasing averaging 69% in connected patches compared with unconnected patches (Tewksbury et al., 2002).

Holly (Ilex vomitoria) flowers in the patches were visited by flies, wasps, bees and butterflies, including both the Common Buckeye and the Variegated Fritillary. The results of Tewksbury et al. (2002) confirm that corridors are used preferentially by at least some of those insects, presumably resulting in higher fruit set in connected patches. Ilex vomitoria seeds were more than twice as likely to be found in connected patches than in isolated patches and a significantly greater proportion of fecal samples collected in connected patches contained fluorescent powder compared with fecal samples from unconnected patches (an increase of 18%) (Tewksbury et al., 2002).

These results provide a large-scale, experimental demonstration that habitat corridors facilitate movement of disparate taxa between otherwise isolated habitat patches, even after controlling for area effects (Tewksbury et al., 2002).

Increased fruit set and seed movement between connected patches have additive effects on gene flow and population dynamics. Given that plants producing more fruit are likely to attract more frugivores (Blake and Hoppes, 1986), plants in connected patches are likely to contribute more to

gene flow both within and between patches due to increases in pollen movement, fruit removal and seed movement down corridors (Tewksbury et al ., 2002).

The ability of plant populations to persist, expand and colonize habitat in fragmented landscapes is determined in large part by pollination and seed dispersal (Kearns et al., 1998; Cordeiro and Howe, 2001; Levey et al., 2001). The results of Tewksbury et al. (2002) provide evidence that corridors can have substantial effects on these processes and thereby help overcome the depressed reproduction frequently reported for isolated plant populations (Aizen and Feinsinger, 1994; Cunningham, 2000; Groom, 2001).

These results clearly suggest a role for corridors in connecting populations of both plants and insects.

2.3. Ecosystem services

Ecosystem services (Table 2.2) are defined as the benefits people obtain from ecosystems (Millennium Ecosystem Assessment, 2005). These services include provisioning services such as food, fresh water, wood and fiber; regulating services such as the regulation of climate, floods, disease, air quality and erosion; cultural services such as recreation, aesthetic enjoyment and spiritual fulfillment; and supporting services such as soil formation, photosynthesis and nutrient cycling (Millennium Ecosystem Assessment, 2005, Wallace 2007).

Table 2.2: Different ecosystem services (adapted from Millennium Ecosystem Assessment, 2005 and Wallace, 2007). ECOSYSTEM SERVICES supporting services provisioning services regulating services cultural services nutrient cycling food climate regulation aesthetic soil formation fresh water flood regulation spiritual primary production wood and fiber disease regulation educational photosynthesis fuel water purification recreational water cycling genetic resources air quality regulation … … ornamental resources erosion regulation bio-chemicals pest regulation natural medicines pollination … …

Provisioning services of hedgerows. Hedgerows provide more than protection; they provide resources. Firewood is usually the most important product of hedgerows and is often critical in times of war and fuel shortages. In traditional rural societies wood was the only source of energy for cooking and heating and peasants therefore needed to have access to such a resource. Often farm hedgerows were the only available source of wood to them, as woodlands were often owned by large landowners (Baudry et al., 2000). Hedgerow wood is also used for fence posts, furniture and building (Forman and Baudry, 1984). Elm (Ulmus spp.) and oak (Quercus spp.) in Britain, Osage orange (Maclura pomifera) and red cedar (Juniperus virginiana), in the Great Plains, USA and chestnut (Castanea spp.) and oak (Quercus spp.) in France are especially valuable (Pollard et al., 1974; Shelterbelt Project, 1934; Steavenson et al., 1943;

Harmon, 1948). With abundant light and limited tree competition, hedgerow productivity is high. Furthermore, coppicing of many species is possible and particularly increases the productivity of the last two trees (Forman an Baudry, 1984). Pollarding of trees such as ash (Fraxinus excelsior) and elm (Ulmus spp.) is also done to provide food for livestock (Rackham, 1976; Pollard et al., 1974). Such species thus may be especially abundant in hedgerows near villages. The different usages of the wood lead to contrastingly different forms of trees (Baudry et al., 2000).

Apple trees (Malus spp.) have often been included in temperate-zone hedgerows. Windbreaks planted with species for fruit production, thus provide a double economic value (Forman and Baudry, 1984). Fruits of bird-dispersed shrubs like blackberries, raspberries and elderberries (Rubus spp. and Sambucus spp.) are also harvested as food for people (Forman and Baudry, 1984). Other products may be medicinal plants e.g. nettles (Urtica dioica), materials for tools e.g. ash (Fraxinus excelsior) and even vegetables (Baudry et al, 2000). Finally, wildlife is especially abundant in hedgerows and is a source of meat (Forman and Baudry, 1984).

Regulating services of hedgerows. Hedgerows have often been constructed or maintained for their fence effect (Forman and Baudry, 1984). The boundary function can be both physical and symbolic, as a row of shrubs around a garden with an open gate or as stock-proof fences (Baudry et al., 2000). Such structures can either keep livestock in a pasture or protect the crop in a field against livestock or wild herbivores roaming in surrounding woods or heathland (Forman and Baudry, 1984). The planted hedgerows are generally made of non-palatable species such as hawthorn (Crataegus monogyna) in Europe and spurges (Euphorbia spp.) in Ecuador or shrubs e.g. willow (Salix spp.), hazel (Corylus avellana) and blackthorn (Prunus spp.) (Baudry et al., 2000). Hedgerows are managed in many ways, for example, by laying, mechanically pollarding, clipping and clearing of undergrowth (Pollard et al., 1974; Yahner, 1982). European hedgerows tend to have one or few dominant species that may be either tree or shrub height. Thorns, layering, wire or stone in any hedgerow may produce the basic fence effect of inhibiting the passage of animals (Forman and Baudry, 1984).

In open areas dense and high hedges continue to serve as windbreaks (Hermy and De Blust, 1997). Jensen (1954) found average wind speed to be 15% less in a hedgerow landscape than a comparable open-field landscape in Denmark.

The hedgerow network can be expected to decrease soil loss by wind (Shelterbelt Project, 1934).

Great attention is paid to the role that landscape elements can play in erosion control. In hilly areas and on the edge of valleys rainfall erosion is an increasing problem. Besides an adaptation of the cultivation techniques, landscape elements such as densely vegetated grafting, can reduce the erosion power of running water and hence limit the transport of soil material (Burel et al., 1993; Gulinck, 1985). Merot and Ruellan (1980) compared two nearby landscapes in Brittany, France, one with and one without a hedgerow network. In winter, which is the rainy season, stream flow was lower in the hedgerow landscape than in the open landscape, yet in summer the opposite was observed.

Research on the role of hedgerows as a buffer against nitrates and for water protection is growing (Caubel-Forget and Grimaldi, 1999).

Uncultivated, narrow strips in the middle of the fields may play an important role in biological control of pests (Hermy and De Blust, 1997). Delattre et al. (1999) found that predators in hedgerows can buffer cyclic-pest outbreaks of species such as voles.

Cultural services of hedgerows. In addition to their direct economic and general agricultural use, great importance is now also attached to their recreational function. A variety of landscape features make a landscape attractive and gives it a high amenity (Hermy and De Blust, 1997).

Finally, for many people, hedgerows play a critical role in the aesthetics of the agricultural landscape (Forman and Baudry, 1984).

3. Methodology

3.1. Study area

3.1.1. General description

The area of interest is situated in Ballyboughal in county Dublin, Ireland (encircled in red on Figure 3.1) (53°31’N, 6°15’W).

Figure 3.1: Localization of Ballyboughal, encircled in red (adjusted from Google maps).

Ballyboughal, or Baile Bachaille in Irish, is a small town with approximately 800 inhabitants and different townlands like Ballyboghil, Mainscourt and Grange.

Baile means town or community and Bachaille means staff. So Baile Bachaille is ‘Town of the staff’. The staff mentioned is the one carried by Saint-Patrick, which was stolen from the Archdiocese of Dublin by order of the Archdiocese of Armagh and placed in the old church in Baile Bachaille. This was the furthest point south of the Archdiocese of Armagh, before the Archdiocese of Dublin. By doing so Baile Bachaille became some sort of a place of pilgrimage and is thus already inhabited for a very long time. The staff was venerated there until about the end of the twelfth century when it was given place of worship in St Patricks Cathedral. It was there until the sixteenth century when Protestant Reformation Bishop of Dublin Bishop Browne had it burnt to destroy its symbolic power as a Catholic icon (pers. comm. D. O'Connor).

In this village, a circle with a 1km radius was drawn (in blue on Figure 3.2), centered on the farm of Denis O’Connor (encircled in orange on Figure 3.2).

ELLISTOWN WIMBLETOWN CLONSWORDS BETTYVILLE

BROOMFIELD BALLYBOGHIL

MAINSCOURT

GRANGE

Figure 3.2: Map of the study area (encircled in blue) and the farm of Denis O’Connor (encircled in orange) (adjusted from the GeoPortal website (gis.epa.ie) of the environmental protection agency (EPA).

3.1.2. Origin of the hedgerows

An individual hedgerow was defined as a discrete segment between two different nodes of the hedgerow network. If necessary, these segments were subdivided further using adjacent land use, management of the hedge and the dominant plant species in that part of the hedge as criteria.

The origin of the hedges in Ireland can be explained using the 1721 document ‘An act to oblige proprietors and tenants of neighbouring lands to make fences between their several lands and holdings’. This is an act of the Parliament of Ireland, under reign of George 1 and is referred to as 8 Geo. 1 c. 5 or as the ‘Boundaries Act 1721’.

In this act the following sentence gives an idea about the reason why the hedges were needed: “Whereas it is found by experience that many trespasses happen and frequent disputes arise between proprietors of lands about mears and bounds of lands, which is in a great measure occasioned by the proprietors and tenants neglecting to make fences between their several lands and holdings … “ (lines 1 till 3 in [1] in Appendix 1).

Moreover, the Act also stipulates the rules to be followed: “… and where no sufficient fences or only dead and dry fenceless ditches then shall be, that the proprietor or proprietors, occupier or occupiers, or tenant or tenants of such neighbouring lands on reasonable request to him, here or them made, shall be and is hereby obliged to be at equal expence in making between such several lands and holdings good and sufficient ditches of six foot wide and five foot deep at least where the same is practicable well and sufficiently quicked in good husbandlike manner with white thorn, crab, or other quicksets where the same will grow, and in ground where such quicksets will not grow with

furz, and where furz will not grow, or where ditches cannot be made of the said depth and wideness instead of a ditch, with a dry stone wall where a stone be conveniently had, and where stone cannot conveniently be had, with a clay or mud wall not under five foot high and two foot and a half thick at the bottom, and one foot and a half thick at the top, and in wet low ground with sufficient trenches or drains, the banks thereof to be planted with sallows, alder, or other aquatick trees where such aquaticks will grow … “ (lines 8 till 19 in [2] in Appendix 1)

This act even mentions the species to be used when planting, namely whitethorn (Crataegus monogyna), crab (Malus spp.), furze (Ulex spp.), sallow (Salix spp.) and alder (Alnus spp.), which are all still present nowadays.

The complete act is found in appendix 1.

3.1.3. Evolution of the hedges

In Trinity College historical maps of 5 different times were found, dating from 1760, 1843, 1873, 1909 and 1937. The map op 1760 doesn’t seem to be accurate according to field boundaries and is therefore neglected in the following parts.

This series of maps could be used to estimate the age of the hedges. This was done by searching every hedge on every map and noting presence or absence. In this way hedge number 1 was present on every map and is probably older than 168 years (=2011-1843). Hedge number 3 wasn’t present in 1937, but was recorded in 2011. So therefore the age of hedge number 3 is equal to 37 years (=(2011-1937)/2). The age of every hedge is given in appendix 2.

An overview of the evolution and the age of all the hedges in the study area is given in appendix 2. A short summary in shown in table 3.1.

Table 3.1: Number of planted and removed hedges over several periods in time. In the summer of 2011 there were 204 hedgerows, with a total length of 27847m and an average of 138.5m. planted removed period number period number 1873->1909 5 1843->1873 27 1909->1937 3 1873->1909 8 1937->2011 15 1937->2011 7 total 23 total 42

In general there is a decrease in the number of hedges, because 42 removed hedges were replaced by only 23 new ones. Most of the newly planted hedges appeared between 1937 and 2011 (15 hedges) and most of the hedges disappeared between 1843 and 1873 (27 hedges).

An example is given in figure 3.3. The area concerned is one of the fields in the townland of Broomfield. The hedges in this field disappeared between 1843 and 1873 . According to people using the field nowadays this has led to a much wetter field with problems for heavy machinery. Probably the loss of the ditches that accompanied the hedges lead to a decrease in carrying off capacity.

Figure 3.3: Field in the townland of Broomfield in 1843 (left) and in 1873 (right).

3.2. Data collection

3.2.1. In general

There have been three field campaigns with in total approximately nine weeks of field - and research work in Ireland. The first campaign (± six weeks) was in July and the beginning of August 2011 and was used to collect all the data concerning plant presence or absence and a small part of the explanatory variables that needed field observation. In August a first check of the data was done and during the second campaign in September 2011 (± 1 week) the observed blanks concerning plants were filled up, together with another part of the explanatory variables with field observation. The last field observations were done in the Christmas holiday (± 2 weeks), together with a search for historical maps in the library of Trinity College in Dublin. Spare time during this weeks was used to talk to as many people as possible, with special attention to the older inhabitants of the village, to gather as much information as possible about the area.

3.2.2. Plant species

One of the questions addressed in this thesis was to identify the forest plants which were present in the hedges. The list in appendix 3 (Butaye et al., 2001) was used as a reference to know which plant should be considered a forest plant and therefore a target species for this research.

The first step towards this goal was the establishment of a complete list of all the species present in the hedges.

The hedges were defined as mentioned in part 3.1.2. Once a hedgerow was identified, a complete list of plant species was recorded, by walking the two sides of the hedge and noting presence or absence. When a species could not be immediately identified in the field, the necessary parts were collected and identified in the evening using a book of plant determination (Rose and O’Reilly, 2006; Heimans et al., 1909) and a binocular when needed.

3.2.3. Explanatory variables

A second question of this thesis was to investigate which variables affect the flora in hedges. So besides presence/absence data of all the plants present, a whole set of possible explanatory variables was recorded.

3.2.3.1. Owner (OWN)

Denis O’Connor identified 8 bigger and several smaller owners in the study area. Before doing any field observations these owners were contacted and asked for permission to set foot upon their land. Two of the bigger owners did not grant permission, leading to a gap in the circle where no data were collected. The other owners (listed in table 3.2) all wanted to cooperate with the study. The several smaller properties are grouped together in category 7.

Table 3.2: The different owners that gave permission and whose hedges are included in the study. category owner 1 Denis O'Connor 2 James Dungan 3 community 4 Frank Counihan 5 Eamonn Murphy 6 Bobby Jones 7 others

3.2.3.2. Field observations

When permission was granted the following field observations were made, namely measuring length (LEN), width (WID), variation on width (VAW), mean height (MEH), outliers in height (OUT), variation on height (VAH) and the percentage of gaps (GAP) of each hedge, the presence of a tree and/or a shrub layer (T, S), the presence of a bank (BAN), the presence of a ditch (DIT), the depth of the ditch (DED), the water level in the ditch (LED) and the adjacent land use (LAN).

Measuring length (LEN), width (WID) and percentage of gaps (GAP) was done using a measuring tape of 30m and a self-constructed tool with a gradation of 10cm was used to measure mean height (MEH) and outliers in height (OUT). This tool is shown in picture 3.1.

Picture 3.1: Detail of the gradation on the self-constructed tool (left) and an example when used in the field to measure the height of a hedge (right).

Variation on width (VAW), variation on height (VAH) and water level in the ditch (LED) were estimated using a 4 point scale (no-low-medium-high), presence of tree (T) and shrub layer (S) and presence of bank (BAN) and ditch (DIT) using a 2 point scale (absence-presence).

The different types of land use (LAN) present in the study area include woody or other fragments, fields with cattle, crops or lying fallow, gardens, a golf-course and a water purification plant, traversed by paved or unpaved roads. For example, when a crop was present on a field, the land use category of that field was category 3. So if there was a hedge with crops on both sides, the hedge will have combination 33.

An overview of this observed field variables is given in tables 3.3 and 3.4.

Table 3.3: Different variables recorded during field observations. Variable abbreviation unit accuracy length LEN m per 0,5m width WID m per 0,5m variation on width VAW 0-1-2-3 no - low - medium - high mean height MEH m per 0,5m outliers in height OUT m per 0,5m variation on height VAH 0-1-2-3 no - low - medium - high percentage of gaps GAP % per 5% (except <5%) presence of tree layer T 0-1 presence-absence presence of shrub layer S 0-1 presence-absence presence of bank BAN 0-1 presence-absence presence of ditch DIT 0-1 presence-absence depth of ditch DED m per 0,5m water level of ditch LED 0-1-2-3 no - low - medium - high

5 H2O purification 6 fallow 7 street 8 unknown A fragment B mixed

3.2.3.3. Cartographic information

As mentioned in part 3.1.3. several historical maps were found in Trinity College in Dublin. During the analysis of these maps contour lines were found on the map of 1873. These lines were used to divide the studied area in 5 different categories of elevation (ELE) shown in table 3.5.

This series of maps could also be used to estimate the age of the hedges. As already stated in part 3.1.3. this was done by searching every hedge on every map and noting presence or absence. In this way hedge number 1 was present on every map and is probably older than 168 years (=2011-1843). Hedge number 3 wasn’t present in 1937, but was recorded in 2011. So therefore the age of hedge number 3 is equal to 37 years (=(2011-1937)/2). The age of every hedge is given in appendix 2.

Table 3.5: Categories of elevation present in the study area. category unit elevation 1 feet <100 2 feet ±100 3 feet >100 but <150 4 feet ±150 5 feet >150 but <200

It was also possible to deduce the orientation (ORI) of the different hedges. The fields in the study area consist of boundaries in north-south and east-west direction (categories 1 and 2 in table 3.6). Only a few of the hedges have a mixed orientation, meaning there is a turn or twist (category 4 in table 3.6). The woody or other fragments in the area are put together in category 3 in table 3.6.

Table 3.6: Categories of orientation present in the study area. category orientation 1 north-south 2 east-west 3 fragment 4 mixed

3.2.3.4. Soil types (SOI)

A map indicating the soil types present in the study area was found on the GeoPortal website (gis.epa.ie) of the environmental protection agency (EPA). Four different soil types were found, namely BminPD, AlluvMIN, BminDW and AminPD, where BminPD stands for surface water gleys/ ground water gleys (basic), AlluvMIN means mineral alluvium, BminDW means grey brown podzolics/ brown earth basics and AminPD is equal to surface water gleys/ ground water gleys (acidic). The possible combinations are shown in table 3.7.

Table 3.7: Categories of soil types beneath the study area. category soil type 1 BminPD 2 AlluvMIN 3 BminDW 4 AminPD 5 1 + 2 6 1 + 3 7 1 + 4 8 2 + 3 9 2 + 4 10 3 + 4 11 1 + 2 + 3

This way, a dataset with 204 samples, 223 different species and 19 explanatory variables was constructed. Thirty-eight of these species are still unknown. Since they don’t have a positive identity, they are given a combination of a letter and a number instead of a species name. For example, species 1A is the first unknown plant on the first property and species 2C is the third unknown plant on the second property. Four of these unknown species were found on different properties and are indicated by a letter. For example, species B is found on the properties 2, 4, 5 and 7.

Some of the values indicating the dimensions of the hedges are not available. For example, hedge number 141 was removed between September and December and doesn’t have a value for the variables LEN, WID, VAW and GAP.

Some of the hedges didn’t have any outliers in height and don’t have a value for the variable OUT.

Some of the hedges were in fact small woody fragments, probably old remnants of a former forest and already indicated on the map of 1843. The forest cover is rather low in the entire country, but especially in county Dublin (2.8-5%), which is mainly an agrarian and an urban region.

3.3. Data processing

3.3.1. Descriptive statistics

Excel and the Analysis ToolPak was used to do the basic descriptive statistics and to make some histograms.

Based on the dataset it was also possible to count the total number of species in a hedgerow and to calculate the area of each sampling site. Doing so, a species-area relation was drawn up, using the standard equation S = cAz (MacArthur and Wilson, 1967).

3.3.2. Linear modeling

Linear modeling was done using R and the package NLME (Pinheiro et al., 2012).

The first linear model contained all the possible variables (Table 3.8). After a first round of calculations, the non-significant ones were deleted, retaining the variables that did have a significant effect (p-value < 0.05) on the number of target species present in the hedge.

Since the owner (OWN) is also used as one of the variables, there is a possible influence of this variable on the other ones. Supposing that the values of the variables are more similar between hedges on the same property then between hedges on different properties, this effect was tested using a linear mixed model.

Table 3.8: Sort of variables used in the linear models. variable abbreviation sort of variable owner OWN categorical length LEN continual width WID continual variation on width VAW ordinal mean height MEH continual outliers in height OUT continual variation on height VAH ordinal percentage gaps GAP continual presence tree layer T categorical presence shrub layer S categorical presence bank BAN categorical presence ditch DIT categorical depth of ditch DED continual water level in ditch LED ordinal adjacent land use LAN categorical age AGE continual elevation ELE ordinal orientation ORI categorical soil type SOI categorical

3.3.3. T-testing

T-testing was done using R.

Because of the complexity of the dataset the choice was made to do the methods for more complex testing on a part of the dataset, for which only 45 of the 204 sampled hedgerows were used. These 45 hedges consist of 20 hedges containing 2,3 or 4 target species and 25 hedges containing 10, 11 or 12 target species. So, in fact the extremes of the dataset are used to get a clear image in the subsequent analysis.

The 20 hedges with the least forest species (2, 3 or 4) is referred to as the ‘bad group’ and the 25 hedges with the most forest species (10, 11 or 12) present is called the ‘good group’.

Since the 2 groups were not of the same size, 20 hedges compared to 25 hedges, the test was not paired.

The test were done using the following code and a confidence interval of 95%. -> t.test(group1,group2,alternative="two.sided",mu=0,paired=F,conf.level=0.95)

The null hypothesis of the T-test is that there is no difference between the means of the two compared groups (H0 : µ1 = µ2). When the p-value of the test is smaller than 0.05, we reject this null hypothesis.

3.3.4. Ordination analysis

The ordination analysis was done using R and the package VEGAN (Oksanen et al., 2012).

Since the length of gradient was 3.0085, 2.75951, 2.94175 and 2.21374 for axes 1, 2, 3 and 4 respectively, both a principal component analysis (PCA) and a detrended correspondence analysis (DCA) were performed on the same subset of 45 hedges.

3.3.4.1. PCA

Principal component analysis uses orthogonal transformation to convert a set of variables to a set of principal components, which are linear and uncorrelated. The goal of this analysis is to reduce a multivariate dataset in such a way that someone only uses a few of the principal components to explain the variability in the dataset. This is possible because the first component has the largest possible variance, as well as all the succeeding components, as long they are orthogonal to each other.

A negative fact about PCA is the sensitivity to the relative scaling of the original variables, but this isn’t a problem in this subset since it only contains presence and absence data without any units used.

3.3.4.2. DCA

Detrended correspondence analysis is an iterative algorithm that has shown itself to be a highly reliable and useful tool for data exploration and summary in community ecology and is used to suppress two artifacts inherent in most other multivariate analyses: - the ordination scores of the samples will exhibit the edge effect, i.e. the variance of the scores at the beginning and the end will be considerably smaller than that in the middle - when presented as a graph the points will be seen to follow a horseshoe shaped curve rather than a straight line (arch effect), even though the process under analysis is a steady and continuous change that human intuition would prefer to see as a linear trend.

DCA starts by running a standard ordination (CA or reciprocal averaging) on the data, to produce the initial horse-shoe curve in which the 1st ordination axis distorts into the 2nd axis. It then divides the first axis into segments (default = 26), and rescales each segment to have mean value of zero on the 2nd axis - this effectively squashes the curve flat. It also rescales the axis so that the ends are no longer compressed relative to the middle, so that 1 DCA unit approximates to the same rate of turnover all the way through the data: the rule of thumb is that 4 DCA units mean that there has been a total turnover in the community.

A drawback is that there are no significance tests available with DCA, although there is a constrained (canonical) version, called DCCA, in which the axes are forced by multiple linear regression to correlate optimally with a linear combination of other (usually environmental) variables; this allows testing of a null model by Monte-Carlo permutation analysis.

3.3.5. Cluster analysis

Cluster analysis was also done using R and the package VEGAN.

The goal of cluster analysis is to assign an object to a group in such a way that objects in the same cluster are more similar to each other than to those in other clusters.

Hierarchical clustering is based on the distance between objects and results in a dendrogram. A distinction is made between agglomerative and divisive clustering. The former starts from each individual observation and sequentially merges them, until there is only one cluster left. Divisive clustering starts with one cluster and thus works the other way around.

1 5 2

3 C2 C1

Figure 3.4: Visualization of the average linkage algorithm. The dissimilarity between the clusters C1

and C2 is equal to the average dissimilarity between all observations of C1 (points 1,2 and 3) and all

observations of C2 (points 4 and 5).

The choice was made to use the average linkage algorithm.

Average linkage clustering is a method of calculating distance between clusters in hierarchical cluster analysis. The linkage function specifying the distance between two clusters is computed as the average distance between objects from the first cluster and objects from the second cluster. The averaging is performed over all pairs (x,y) of observations, where x is an object from the first cluster and y is an object from the second cluster.

Mathematically the linkage function - the distance between clusters C1and C2 - is described by the following expression :

( ) ∑ ( ) | || |

where

 d (x1,x2) is the distance between objects x C1 and y C2  C1 and C2 are two sets of objects (clusters)  |C1| and |C2| are the numbers of objects in clusters C1 and C2 respectively

4. Results

4.1. Descriptive statistics

A total number of 204 hedgerows were examined. 223 different plant species were recorded, of which 158 were herbs, 32 were shrubs and 33 were trees. The total species list is found in appendix 4. Seventeen of these 223 species were present in more than half of the hedges. Twenty-three target species were found, of which 14 were herbs, 8 shrubs and 1 tree species (Table 4.1). Seven of these 23 were present in more than half of the hedges (Figure 4.1).

Table 4.1: Target species found during the study. group species abbreviation group species abbreviation Herb Athyrium filix-femina Ath fil Herb Stellaria holostea Ste hol Herb Chamerion angustifolium Cha ang Herb Vicia sepium Vic sep Herb Geum urbanum Geu urb Shrub Corylus avellana Cor ave Herb Hedera helix Hed hel Shrub Crataegus spp. Cra spp Herb Hypericum maculatum Hyp mac Shrub Ilex aquifolium Ile aqu Herb Lapsana communis Lap com Shrub Ligustrum vulgare Lig vul Herb Lonicera periclymenum Lon per Shrub Prunus spinosa Pru spi Herb Prunus spinosa Pru spi Shrub Salix caprea Sal cap Herb Rosa rubiginosa Ros rub Shrub Sambucus spp. Sam spp Herb Rubus fruticosus Rub fru Shrub Ulex europaeus Ule eur Herb Scrophularia nodosa Scr nod Tree Malus sylvestris Mal syl Herb Stachys sylvatica Sta syl

Figure 4.1: Absolute frequency of the target species in the sampled hedges.

An average of 28 species was recorded in the hedgerows, with a minimum of 7 and a maximum of 60. The mean number of target species in every hedgerow is 7, with a minimum of 2 and a maximum of 12.

The distribution of the number of species and number of target species is shown in figure 4.2.

Figure 4.2: Distribution of the number of species (left) and the number of target species (right).

As seen before, only 17 of the total 223 species and 7 of the 23 target species were present in more than half of the hedgerows. Normally there should only be 1,75 target species (= 17/223) in more than half of the hedges, but there are 7, so in fact the target species are doing quite good compared to the other plants.

The plant strategies (Grime, 1977 and table 2.1) of this 23 species were compared with those of the intended target species that haven’t been encountered during the survey, using Hodgson’s look-up table (Hodgson et al., 1999). Some of the species were excluded since they didn’t had any value mentioned in the table and when two strategies were given the primary was elected. For example, Athyrium filix-femina had an SC-strategy as well as a C-strategy, so the C-strategy was used. Percentages were calculated and are shown in figure 4.3.

Most of the encountered species had an SC-strategy, while most of the absent species had an S- strategy (Figure 4.3), but all strategies were present.

The same procedure was used to compare the 7 target species found in more than half of the hedges with those found in less than half of the hedges. These results are shown in figure 4.4.

In both cases (more than half or less than half) the SC-strategy is the most abundant one, but the percentage for species present in more than half of the hedges is even higher, 67% compared to 43%. It is also clear that the less abundant species have a broader range of strategies then the abundant ones, namely 6 out of 7 compared to 2 out of 7. The only strategy that isn’t used by the plants in the SR-strategy.

Figure 4.3: Different plant strategies of the target species (after Hodgson’s look-up table) (S = Stress- tolerant strategy, C = Competitive strategy and R = Ruderal strategy).

One might conclude that the SC-strategy is the most favourable strategy for plants in the present conditions. But when the same procedure is used a third time comparing abundant target species with abundant other species it seems that the SC-strategy is only followed by the target species and not by the other species (Figure 4.5).

Figure 4.4: Different plant strategies of the 23 found species (after Hodgson’s look-up table) (S = Stress-tolerant strategy, C = Competitive strategy and R = Ruderal strategy).

Figure 4.5: Different plant strategies of the abundant species (after Hodgson’s look-up table) (S = Stress-tolerant strategy, C = Competitive strategy and R = Ruderal strategy).

In cases like these, it is necessary to make a correction for the area in which the plants were situated. For this purpose, a species-area relation was constructed (Figure 4.6). The standard equation used was S = cAz. In the case of the total number of species c was 5.2481 and z was 0.262 which gave us S = 5.2481 A 0.262 with an R² of 0.3657.

Figure 4.6: Species-area relation for the number of species.

A parallel calculation for the target species alone gave us the following results: S = 2.3385 A 0.1779 with an R2 of 0.2627 (Figure 4.7).

Figure 4.7: Species-area relation for the number of target species.

To get an insight in the distribution of the different explanatory variables a set of histograms was made.

As mentioned before there were 6 different owners with a bigger property (categories 1 till 6), separated by several smaller properties, which were grouped together in category 7. Owner 1 had 41 hedgerows, owner 2 had 42 hedges and owners 3, 4, 5 and 6 had respectively 25, 25, 20 and 17 hedges. In category 7 there were 34 hedges (Figure 4.8 left).

Figure 4.8: Histograms for the variables owner (OWN) and length of the hedgerow (LEN).

Most of the hedges were less than 100m long (79 hedges on Figure 4.8 right) or between 100 and 200m (82 hedges on Figure 4.8 right). In 134 hedges the width is smaller than 5m (Figure 4.9 left) and the variation on the width is rather low (127 hedges on Figure 4.9 right). In most of the hedges were no gaps (129 hedges on Figure 4.10 left). Most of the hedgerows had a mean height less or equal to 5m (189 hedges on Figure 4.10 right), with outliers around 7m (69 hedges on Figure 4.11 left). The variation in height is low (81 hedges on Figure 4.11 right) to medium (93 hedges on Figure 4.11 right).

Figure 4.9: Histograms for the variables width of the hedgerow (WID) and the variation in width (VAW).

Figure 4.10: Histograms for the variables percentages gaps (GAP) and mean height of the hedgerow (MEH).

Figure 4.11: Histograms for the variables outliers in height (OUT) and variation in height (VAH).

Figure 4.12: Histograms for the variables presence of tree layer (T) and presence of shrub layer (S).

In almost all the hedges there was a tree (191 hedges on Figure 4.12 left) and a shrub layer (202 hedges on Figure 4.12 right) present. A bank was not present in most of the cases (191 hedges on Figure 4.13 left). Beneath 156 hedges was a ditch (Figure 4.13 right), with a depth of 1 (47 hedges), 1,5 (55 hedges) or 2m (41 hedges) (Figure 4.14 left), but in most ditches there was no water present (134 hedges on Figure 4.14 right).

Figure 4.13: Histograms for the variables presence of bank (BAN) and presence of ditch (DIT).

Figure 4.14: Histograms for the variables depth of the ditch (DED) and water level in the ditch (LED).

Most of the hedges had an elevation (Figure 4.15 left) in category 3 (79 hedges) or category 5 (79 hedges) and had an age equal or older than 168 years (181 hedges on Figure 4.15 right). There is more or less an equal amount of hedges with north-south (104 hedges) or east-west orientation (88 hedges) (Figure 4.16 left). The soil type (Figure 4.16 right) was mostly type 3 (77 hedges), followed by type 4 (57 hedges). The adjacent land use (Figure 4.17) was predominantly combination 33 (31 hedges), followed by combinations 13 (27 hedges), 11 (24 hedges) and 17 (20 hedges).

Figure 4.15: Histograms for the variables elevation above sea level (ELE) and age of the hedge (AGE).

Figure 4.16: Histograms for the variables orientation (ORI) and soil type (SOI).

Figure 4.17: Histogram for the variable adjacent land use (LAN).

4.2. Linear modeling

Using the 19 different variables a linear model was created to explain the number of target species present in a hedgerow. As stated in part 3.3.2. the non-significant ones were deleted after a first round of calculations, retaining the variables that did have a significant effect (p-value < 0.05) on the number of target species present in the hedge.

The model consists therefore of the variables owner (OWN), age of the hedge (AGE), presence of a ditch (DIT) and length of the hedge (LEN). More information about the model is given in table 4.2.

Table 4.2: Results of the linear model using the variables owner (OWN), age of the hedge (AGE), presence of a ditch (DIT) and length of the hedge (LEN). Df F-value estimated coefficient OWN 1 13.054 *** 3.713149 AGE 1 21.267 *** 0.167669 DIT 1 22.997 *** 0.009097 LEN 1 15.423 *** 1.401310 residuals 156 0.004970 Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

Even when using a linear mixed model, where AGE, DIT and LEN are dependent of OWN, they prove to be significant. This is shown in table 4.3.

Table 4.3: Results of the linear mixed model using the variables where the age of the hedge (AGE), the presence of a ditch (DIT) and the length of the hedge (LEN) are dependent on the variable owner (OWN). numDF F-value (intercept) 1 804.3586 *** AGE 1 15.5039 *** DIT 1 21.0921 *** LEN 1 10.7357 ** Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

4.3. T-testing

As mentioned in part 3.3.3. a subset of 45 hedges is used, of which 20 hedges contain 2, 3 or 4 target species (the bad group) and 25 hedges contain 10, 11 or 12 target species (the good group). This subset is found in appendix 5.

Since the tests are done using a confidence interval of 95%, the test is significant when the p - value is smaller than 0,05. This is the case in 9 of the tested variables, namely LEN, MEH, VAH, T, DIT, DED, LED, ELE and AGE (Table 4.4).

Table 4.4: Results of the T-tests per variable. mean of bad group mean of good group p - value < 0,05 LEN 58.42 241.94 0.000073 yes WID 7.34 7.74 0.84 no VAW 1.05 1.40 0.081 no MEH 4.03 2.50 0.0054 yes OUT 7.79 7.25 0.43 no VAH 0.90 1.56 0.00096 yes T 0.75 1.00 0.021 yes S 0.90 1.00 0.16 no GAP 2.68 2.16 0.77 no BAN 0.05 0.12 0.40 no DIT 0.45 1.00 0.00012 yes DED 0.53 1.64 0,00000078 yes LED 0.15 0.56 0.0064 yes LAN 41.25 42.24 0.92 no ELE 3.90 3.24 0.040 yes SOI 3.05 3.96 0.12 no AGE 122.15 164.80 0.0085 yes ORI 2.00 1.60 0.091 no

For example the variable length (LEN) has a p - value of 0.000073 (Table 4.4), which means there is a difference in the means of the bad group (column 2 in table 4.4) and the good group (column 3 in table 4.4).

4.4. Ordination analysis

On the same subset of 45 hedges both a principal component analysis (PCA) and a detrended correspondence analysis (DCA) were performed.

4.4.1. PCA

29% of the variation present in the subset is explained by the first 2 principal components.

PC1 is explained by the following plants: Athyrium filix-femina, Lapsana communis, Lathyrus pratensis, Rosa rubiginosa, Rumex crispus, Scolopendrium vulgare, Vicia cracca and Vicia sepium.

PC2 is explained by: unknown species B, Primula spp., Sonchus arvensis and Viola spp.

Plotting the 45 hedgerows in function of the first 2 principal components gives figure 4.18.

Figure 4.18: Subset of 45 species in function of the first 2 principal components, the hedges of the bad group are encircled in blue.

In figure 4.18 all hedges of the bad group are clustered on the left side (encircled in blue), with a negative value for the first principal component.

4.4.2. DCA

DCA1 is explained by the following plants: Corylus avellana, Sorbus aucuparia, Sorbus intermedia, Sorbus spp., Acer platanoides, Aesculus hipocastanum and Quercus rubra.

DCA2 is explained by: Buxus spp., Fraxinus excelsior, Ilex aquifolium, Larix spp., Prunus laurocerasus and Ribes spp.

The following plant species have a high total value: Cirsium arvense, Hedera helix, Heracleum spondylium, Rubus fructicosus, Rumex crispus, Urtica spp., Vicia sepium, Crataegus spp. and Fraxinus excelsior.

Plotting the 45 hedgerows in function of the first 2 components gives figure 4.19.

Figure 4.19: Subset of 45 species in function of the first 2 components.

In figure 4.19 all hedges of the bad group are spread out to the more positive values of the DCA- components. The hedges of the good group are more or less clustered around the origin of the plot.

4.5. Cluster analysis

The use of average linkage as a distance measure leads to the construction of the dendrogram in figure 4.20. All hedges of the good group are clustered (rectangle in blue in Figure 4.20).

Figure 4.20: Dendrogram of the subset of 45 species using average linkage, the hedges of the good group are indicated in blue.

4.6. Differences between owners

A set of boxplots was made to investigate whether there was a difference in number of species and number of target species between the owners. The results are shown in figure 4.21.

Figure 4.21: Boxplots for the number of species (left) and the number of target species (right) per owner.

To have a more numerical proof of the existence of differences between the owners, a number of T- tests were performed comparing the owners two by two. The results are indicated by letters in figure 4.21.

In most cases, there is no significant difference in terms of the numbers of species per area, but there is a difference between Denis and Frank, James and Frank, community and Frank, Frank and Eamonn, Frank and Bobby, Frank and others and Eamonn and others. There is also no significant difference in number of target species per area, except between Denis and Frank, James and Frank, James and Eamonn, James and Bobby, community and Frank, Frank and Eamonn, Frank and Bobby, Frank and others, Eamonn and others and Bobby and others.

Having a closer look on the subset containing the best and the worst hedges, we come to the following conclusion.

Denis had 9 hedgerows with only 2, 3 or 4 target species, while Frank on the other hand had 14 hedges containing 10, 11 or 12 target species (Figure 4.22).

Figure 4.22: Number of target species per owner.

5. Discussion

5.1. Plant strategies

Looking at the agricultural environment where the plants are present, an environment with enough resources and regular disturbances, a more competitive or ruderal strategy seems logic. But since most forest plants (= target species) have a stress-tolerant strategy, only these forest plants with a more combined stress-tolerant and competitive strategy will be encountered in the hedgerows. Hermy et al. (1999) also found that the stress-tolerant plant strategy type is significantly more abundant under the ancient forest species than expected when compared with other forest plant species and vice versa for the competitive plant strategy.

McCollin et al. (2000) compared environmental indicators of forest species of hedgerows and woodlands and found some differences in ecological requirements. The plant species composition of hedgerows is consistent with a habitat that has a more continental and dryer climate with a higher soil nitrogen status and lower soil acidity, in comparison to woodland and using Ellenberg’s R, N, T and K values (McCollin et al., 2000). There were also significant differences in the frequencies of dispersal modes of plant species within woodland, but not within hedgerows or between woodland and hedgerows. The three most commonly represented modes of dispersal were anemochores, epizoochores and unspecified (autochores or uncertain) (McCollin et al., 2000). McCollin et al. (2000) concluded that hedgerows contain only a narrow range of woodland types and that environmental conditions in hedgerows were probably not suitable for several woodland species, a conclusion also reached by Fritz and Merriam (1993).

The reasons why certain woodland plant species either do not occur, or occur with a limited frequency, in hedgerows are probably the same as the reasons put forward to explain why ancient woodland indicators are seldom found in secondary woodlands (see Hermy et al., 1999). First, some hedgerows probably owe their origin to the clearance of woodland (see also part 2.a)) and since the dominant plant species of temperate woodlands are long-lived perennials which are effectively confined to sites which have had a long continuity of tree cover (Bierzychudek, 1982; Rackham, 1980; Peterken and Game, 1984; Inghe and Tamm, 1985; Dzwonko and Loster, 1989 and Dzwonko, 1993), remnant populations of woodland plant species could conceivably have survived in such hedgerows (McCollin et al., 2000). Second, because of the dependence upon vegetative spread or myrmecochory they are inherently poor colonizers (Dzwonko and Loster, 1992) or else climatic change since plants first colonized now prevents them from setting good seed (Rackham, 1976; Pigott and Huntley, 1981). Third, they may be inhibited from colonizing new sites by the higher nutrient status of the soils, especially phosphate levels, which makes hedgerows unsuitable, or encourages the growth of highly competitive plants which could also effectively exclude ancient woodland indicators (Peterken and Game, 1984; Honnay et al., 1998 and Hermy et al., 1999)

Corbit et al. (1999) highlighted the similarity of composition between forest herbs of hedgerows and proximate woodlands. They also found, however, that some taxa were notably infrequent in hedgerows. Other studies also mentioned species unique to woodlands or forest edges, but not found in hedgerows (Fritz and Merriam, 1994; Jobin et al., 1996; Boutin and Jobin, 1998). These

findings also suggest that hedgerows may serve as surrogate habitats in the landscape for a subset of woodland species but, given their structural characteristics, hedgerows may not provide the proper conditions for those species most likely to be affected by the loss of undisturbed interior habitats in farmlands (de Blois et al., 2002).

5.2. Explanatory variables

As seen in part 4.2. the variables LEN (length of the hedge), DIT (presence of a ditch) and AGE (age of the hedge) proved to be significant in the linear mixed model using all the available hedges and as seen in part 4.3. the variables LEN (length of the hedge), MEH (mean height of the hedge), VAH (variation in height), T (presence of a tree layer), DIT (presence of a ditch), DED (depth of the ditch), LED (water level in the ditch), ELE (elevation above sea level) and AGE (age of the hedge) were significantly different in the T-test using the subset of 45 hedges.

Explaining plant species distribution in a hedgerow, a central place is taken by the three spatial dimensions of the hedgerow formation, affecting possibilities for niche differentiation and controlling the extent to which the narrow linear habitat patches with a small interior to edge ratio are buffered against intruding effects of the surrounding agricultural landscape matrix (Deckers, 2005). As seen before the length (LEN) of the hedge had an influence as well as the height (MEH) and the variation in height (VAH). The width (WID), the variation in width (VAW) and the outliers in height (OUT) had no influence. The positive correlation between species richness on the one hand and hedgerow length on the other hand confirms the results of Deckers (2005), Helliwell (1975), Forman and Baudry (1984), Burel and Baudry (1994) and Hegarty et al. (1994). Although they also mention a positive correlation with the width of the hedgerow, this isn’t found here. Boatman et al. (1994) and Hegarty et al. (1994) mention the role of hedgerow height.

The presence of gaps (GAP) in the hedge had no influence at all, which is in contrast with the findings of Hegarty et al. (1994), McAdam et al. (1994) and Moonen and Marshall (2001). A possible explanation can be found in a more differentiated influence found by Deckers (2005), where the number of herbaceous species was positively and the number of woody species was negatively correlated with this variable. Additional habitat niches resulting from the creation of gaps in the hedgerow formation probably account for the higher herbaceous species richness, while the establishment of tree and shrub species is possibly impeded by an invasion of fast-growing, competitive grassland species (Deckers, 2005).

Deckers (2005) and Le Coeur et al. (1997) found a proportionally larger impact of the shrub layer in comparison with the tree layer affecting hedgerow plant communities. In their opinion this reflects the greater role of a good developed shrub layer instead of a simple row of more widely spaced trees in creating a temperate forest-like microclimate within the hedgerow habitat. In contrast, in Ireland the presence of a tree layer (T) had an influence, but not the presence of a shrub layer (S), which is probably linked with the low variability of this variable within the studied landscape (Figure 4.9).

The water level in the ditch (LED) had an influence and confirms hereby the results of Deckers (2005).

Deckers (2005) found a differentiated influence where the number of herbaceous species was positively and the number of woody species was negatively correlated with the water level in the ditch.

Adjacent land use significantly influenced the number of herbaceous and woody species as well as the total number of species (Deckers, 2005). The prominent role of adjacent land use can be explained by the fact that this factor determines to a great extent the level of human-induced disturbances by more or less frequent practices of tillage, mowing, harvesting, etc. (Boutin and Jobin, 1998) and alters plant competitive interactions in hedgerow ecosystems by processes of pesticide drift and nutrient enrichment (Jobin et al., 1997; Tsiouris and Marshall, 1998). Although the importance of adjacent land use is clearly confirmed by existing evidence (see for instance Le Coeur et al., 1997; Boutin and Jobin, 1998; Mercer et al., 1999 and de Blois et al., 2002), the assumed negative relationship between hedgerow species richness and intensity of neighboring agricultural practices as mentioned by Bunce et al., (1994) and Hegarty et al., (1994), is only partially supported by the results of Deckers (2005). Looking at these former studies the adjacent land use (LAN) was expected to have an influence, but as seen before it had no influence at all in this rural Irish landscape. This difference in results could possibly be explained by the fact that Deckers (2005) considered each side of the hedgerow separately, where combinations of both sides were used in the present study.

The elevation (ELE) above sea level had an influence, which confirms the results found by Deckers (2005). Despite the relatively flat topography of the studied area, elevation significantly affected hedgerow species richness (Deckers, 2005), but he thought this was most probably a drainage effect rather than an effect of elevation per se.

The orientation (ORI) of the hedge had no influence at all, so this was a confirmation of the results found by Deckers (2005).

The age (AGE) of the hedge used in this study had a major influence and would be comparable to two variables comprised in the study of Deckers (2005), namely hedge type and hedge origin. The observed effect of hedgerow type on plant species richness and composition, supported by the results of Marshall and Arnold (1995) and Boutin et al. (2002), is linked with the fact that the present day appearance of a hedgerow is largely the result of its historical background and former management practices, affecting contemporary distribution patterns of plant species in hedgerow habitats as the outcome of a succession process strongly embedded in history (Deckers, 2005). The specific effect of former management practices is addressed explicitly by de Blois et al. (2002), who showed a unique and significant contribution of this variable to hedgerow species variation. Authors quoting hedgerow origin as an essential organising principle of hedgerow vegetation include Pollard (1973), Forman and Baudry (1984), Burel and Baudry (1990a) and Boutin et al. (2002). The results found by Deckers (2005) show that planted hedgerows are characterized by a significantly lower plant species richness than spontaneous hedgerows, as found by Pollard (1973) and Boutin et al. (2002). This pattern is assumed to be caused by the frequent presence of single species equal-aged dominants in combination with a more uniform and intensive management strategy resulting in a lower level of spatial heterogeneity and temporal stability for planted hedgerows in comparison with natural hedgerows (Deckers, 2005).

5.3. Ordination analysis

Hedgerow vegetation organization is a complex process with a wide range of different factors significantly affecting hedgerow species richness and composition and most of the variation still remains unexplained. As seen in part 4.4. only 29% of the variation present in the subset of 45 hedgerows is explained by the first 2 principal components.

In a comparable study by Deckers (2005) only 18% of the variation in species data was explained using a (partial) canonical correspondence analysis with forward selection, in which 41 significant variables were retained out of the total of 63 different variables. Le Coeur et al. (1997) also used a partial CCA and the total variation explained based on the 21 significant variables (out of 28 variables) reached 18,6%. De Blois et al. (2002) used a (partial) CCA and different sets of possible explanations and could explain a total of 33,6% of the variation.

5.4. Owners

As seen in part 4.6. and figure 4.21 there is a big difference in the number of target species between the different properties and especially between Frank and the other owners. For example, where Denis had 9 hedgerows with only 2, 3 or 4 target species, Frank had 14 hedges containing 10, 11 or 12 target species (Figure 4.22).

Picture 5.1: Forest fragment with big trees on Frank’s property.

The two major differences between the owners are the ways in which they manage their hedgerows and the presence of small forest fragments on some of the properties, like on Bobby’s and Frank’s (Picture 5.1). Denis and James are the ones respecting their hedges and besides some cattle occasionally damaging the hedges, there is practically no management at all. On the other side is Eamonn who drastically has cut back his hedges in favor of his crops and who has even removed

some of them between the visits in September and December. You also had the so called community fields, where a lot of hedges were removed in the past, where a lot of gaps were present and where the connection between hedges was lost in some places.

The importance of hedgerow management is linked with the fact that current management practices, typically characterized by a specific frequency and intensity of (cyclical) interventions in the hedgerow habitat, strongly affect the level of human-induced disturbances, resulting in changes in physical and biological environment and resource availability (Deckers, 2005). Confirming evidence regarding the effect of management on hedgerow vegetation is provided by, amongst others, McAdam et al. (1994), Moonen and Marshall (2001), de Blois et al. (2002) and Garbutt and Sparks (2002). The assumption that the adoption of a set of different management strategies results in a high species richness and diversity, as stated by Moonen and Marshall (2001), is clearly supported by the results of Deckers (2005). The basic reason for the observed relationship is thought to be the high level of spatio-temporal variability in environmental conditions created under a combination of various management practices (Deckers, 2005). The number of plant species increased from hedgerows with no management over pruning, pollarding and coppicing to hedgerows subjected to a combination of different management practices (Deckers, 2005). The lower species richness of neglected hedgerows lacking any form of (recent) management in comparison with actively managed hedgerows, as found by McAdam et al. (1994), is also neatly confirmed by the findings of Deckers (2005).

Deckers (2005) found that the presence of connection to forest and distance to the nearest forest were important for the number of woody species in hedgerow habitats, but not for the number of herbaceous species and the total number of species. Most of the forests present within the area studied by Deckers (2005) were relatively young, planted, homogeneous forest stands and were therefore unlikely to function as a source of forest plants for the gradual colonization of surrounding hedgerows (Peterken and Game 1981), except for some common woody species (Boots 2001). The forest fragments included in the present study were also relatively young and planted, but were not homogeneous. They were too small to be seen as real forests and so they were included in the study as hedgerows. But since they will be wider then a normal hedge, they will have a slightly other plant species composition and will have a positive influence on the hedges nearby and on the overall view of that property.

5.5. Measures to take

5.5.1. For existing hedgerows

As seen in part 5.2. the dimensions of the hedgerow play a crucial role in explaining the patterns of plant species richness and composition in hedgerow habitats and in affecting the interior to edge ratio. To promote the spread of forest species and especially the spread of ancient woodland species, a higher amount of interior is needed and so people could try to adjust the dimensions of a hedge. The bigger the area occupied by a hedge, the better for forest species.

The larger a hedgerow is, the better the interior is buffered against the intrusion of fertilizer and pesticides, used on the adjacent fields, but a more active strategy is recommended. Try to minimize the amounts of products used and prevent eutrophication and competition with other plants.

A set of different management strategies results in a high species richness and diversity, because of the high level of spatio-temporal variability in environmental conditions. The number of plant species increased from hedgerows with no management over pruning, pollarding and coppicing to hedgerows subjected to a combination of different management practices (Deckers, 2005). So a hedge needs management!

Most hedges are accompanied by a ditch and the presence of that ditch and the water level in the ditch had an influence. So if one has a choice, keep as many hedges and ditches as possible. Not only to promote and help different species, but also to avoid flooding of your fields and consequent problems.

A thing worth mentioning here is the Hooper hypothesis: “the older the hedge, the more species it would have” (Pollard et al., 1974). To test this hypothesis two studies were conducted by Hooper and his associates, one in Devon, Lincolnshire, Cambridgeshire, Huntingdonshire and Northamptonshire and one on the Northamptonshire/ Huntingdonshire border (Barnes and Williamson, 2006). The first study comprised 227 hedges and produced the following equation with 72% of the variation explained. ( )

The second study, with 95 hedges and 85% of the variation explained had the following equation.

( )

The number of species mentioned, is the number of shrubs encountered in 30 yards of a hedge, including trees and roses, but excluding climbers like bramble and bryony.

So one species for every 100 years can be used as a rule of thumb, keeping in mind that not all variation is explained using age as the only variable (Pollard et al., 1974).

The most important measure is just to keep your hedgerows, because once you remove them and once your forest species have disappeared or have declined, they only recover extremely slowly (Hermy et al., 1999). Woodland plants have slow colonization abilities and their rates of migration in northern temperate forests vary from 0 to 5,5 m year-1 (Matlack, 1994; Cain et al., 1998; Honnay et al., 1998; Bossuyt et al., 1999 and Hermy et al., 1999) with rates often much less than 1 m year-1 (Grashof-Bokdam, 1997; Brunet and von Oheimb, 1998 and Honnay et al., 1999).

5.5.2 For new hedgerows

The species richness of planted hedgerows was significantly lower than that of spontaneous hedgerows (Deckers, 2005). Hedgerows with a combination of planted and spontaneous elements harbored the highest number of plant species. Furthermore, obvious differences in species richness

could be observed for different hedgerow types, with rows of trees and spontaneous regeneration characterized by a low species richness, while coppice and coppice with standards carried a higher number of plant species (Deckers, 2005). The hedgerows with the highest species richness, however, were the double equivalents of the former types, i.e. strips of woody vegetation on both sides of a small pathway (width < 1 m), acting as one functional habitat element (Deckers, 2005).

Spontaneous hedgerows harbor more species and as seen in part 2.a) in spontaneous hedges, trees and/or shrubs mostly grow along a fence, stonewall or ditch, from seeds dispersed by animals and the wind. A fence serves as an attractant for many birds which drop seeds and also limits cultivation and livestock grazing, hence permitting development of the hedgerow biota. To create new species rich hedgerows an owner could thus place a fence or another attractant and let nature develop in a spontaneous way.

5.5.3. Remarks

Careful considerations should be made by the owner. For example when giving hedgerows more space and sacrificing productive land for a wider or longer hedgerow or when using less or no fertilizer and have a possible smaller harvest. The owner should find a compromise between earning money and promoting forest plants and hedges, with functions such as providing wildlife, shade for livestock, marking property boundaries, inhibiting erosion and nutrient runoff and aesthetics.

As said in the introduction Denis wasn’t working in an economically profitable way and with the suggested measures he risks to loose even more of his harvest, so what I would like to suggest is to establish a co-operative. In my opinion this would help the different owners in finding that compromise between earning money and promoting forest plants and hedges. In a co-operative they can work ecologically responsible and yet have an economically profitable farm.

A definition of a co-operative is found on the website of the United Nations (http://www.un.org/en/events/coopsyear/) and states that a co-operative is an autonomous association of persons united voluntarily to meet their common economic, social, and cultural needs and aspirations through a jointly-owned and democratically-controlled enterprise. Co-operatives are based on the values of self-help, self-responsibility, democracy, equality, equity and solidarity. In the tradition of their founders, co-operative members believe in the ethical values of honesty, openness, social responsibility and caring for others.

The co-operative principles are guidelines by which co-operatives put their values into practice. - Voluntary and Open Membership - Democratic Member Control - Member Economic Participation - Autonomy and Independence - Education, Training and Information - Co-operation among Co-operatives - Concern for Community

In this co-operative the members could produce and sell locally or regionally made products, like wood, honey, berries, jam and liqueur.

To promote the spread of forest species it would be good to have wider and more regularly managed hedgerows (see also part 5.2.). If wood could be regularly harvested from the hedgerows, it could be sold as fire wood or processed into different tools. Especially ash (Fraxinus excelsior) is very useful and abundant in the neighborhood.

There were already a lot of flowers present in the hedges, but if some of the members could lay out or sow beds of wild flowers, then there would be plenty of nectar for honeybees to gather. Some of the members could install beehives and become part time apiarists and collect honey.

Wild fruits and berries, for example from blackthorn (Prunus spinosa) could be harvested and sold or used to make jams or liqueurs.

An advantage of a co-operative is that it can aggregate purchases, storage and distribution of farm inputs for their members. By taking advantage of volume discounts and utilizing other economies of scale, co-operatives bring down members' costs. Co-operatives may provide seeds, fertilizers, chemicals, fuel and even farm machinery, for example for plowing and harvesting.

Co-operatives can also provide the services involved in moving a product from the point of production to the point of consumption, which includes a series of inter-connected activities involving planning production, growing and harvesting, grading, packing, transport, storage, food processing, distribution and sale. Agricultural co-operatives are often formed to promote specific commodities, like regional products.

A co-operative also has an advantage for the consumer and for the climate. Nowadays people tend to use and eat more local products, to minimize their footprint. If everything that is locally produced, is gathered at the same place, people can make one trip to buy whatever they want, instead of buying one thing in one place and another 5 kilometers down the road. In this way people loose less time and emit less gasses.

A co-operative has thus advantages for everyone involved and for nature as well.

6.Conclusions

6.1. Which forest plants can be found, surviving in the hedgerows ?

- In the 204 examined hedgerows a total of 223 different plant species were recorded, with an average of 28, a minimum of 7 and a maximum of 60 species per hedgerow. Seventeen of these 223 species were present in more than half of the hedges.

- Twenty-three forest species were found, of which 7 were present in more than half of the hedges. The mean number of forest species in every hedgerow is 7, with a minimum of 2 and a maximum of 12.

- The SC-strategy is the most favourable strategy for forest plants in the present conditions, while more competitive and ruderal strategies are followed by the other plants.

6.2. What are the variables affecting plant species richness and composition in hedgerows within an Irish rural landscape ?

- The dimensions and the age of the hedgerow proved to be the most important variables affecting hedgerow flora in this research.

- Other factors that could have an influence are the presence of a ditch, the presence of a tree and a shrub layer, the percentage of gaps and the adjacent land use.

6.3. Are there any measures the owners can take to promote the spread of forest plants on their properties ?

- The dimensions of the hedgerow play a crucial role in explaining the patterns of plant species richness and composition in hedgerow habitats. The bigger the area occupied by a hedge, the better to promote the spread of forest species.

- Another important measure is to actively manage a hedge. A set of different management strategies results in a high species richness and diversity, because of the high level of spatio- temporal variability in environmental conditions.

- If one has a choice, keep as many hedges and ditches as possible. Not only to promote and help different species, but also to avoid flooding of your fields and consequent problems.

- Spontaneous hedgerows harbor more species then planted ones. To create new species rich hedgerows an owner could thus place a fence, which serves as an attractant for many birds and limits cultivation and livestock grazing, and let nature develop in a spontaneous way.

7. References

Aalen F.H.A., Whelan K. and Stout M. (1997) Atlas of the Irish rural landscape. Cork University Press. Cork.

Aars J. and Ims R.A. (1999) The effect of habitat corridors on rates of transfer and interbreeding between vole demes. Ecology 80, 1648-1655.

Aizen M.A. and Feinsinger P. (1994) Forest fragmentation, pollination and plant reproduction in a chaco dry forest, Argentina. Ecology 75, 330-351.

Askins R.A., Lynch J.F. and Greenburg R. (1990) Population declines in migratory birds in eastern North America. Pages 1-58 in D.M. Power, ed., Current ornithology 7. Plenum Press. New York.

Ballard J.T. (1979) Fluxes of water and energy through the Pine Barrens ecosystems. Pages 133-146 in R.T.T. Forman, ed., Pine Barrens: ecosystem and landscape. Academic Press. New York

Barnes G. and Williamson T. (2006) Hedgerow history: Ecology, history and landscape character. Windgather Press. Macclesfield.

Bates G.H. (1937) The vegetation of wayside and hedgerow. Journal of ecology 25, 469-481.

Baudry J. (1988) Structure et fonctionnement écologique des paysages: cas des bocages. Bulletin d’écologie 19, 523-530.

Baudry J., Bunce R.G.H. and Burel F. (2000) Hedgerows: An international perspective on their origin, function and management. Journal of environmental management 60, 7-22.

Beier P. and Noss R.F. (1998) Do habitat corridors provide connectivity? Conservation biology 12, 1241-1252.

Bierzychudek P. (1982) Life histories and demography of shade-tolerant temperate forest herbs. New phytologist 90, 757-776.

Blake J.G. and Hoppes W.G. (1986) Influence of resource abundance on use of tree-fall gaps by birds in an isolated woodlot. Auk 103, 328-340.

Blavoux B., Dray M. and Merot P. (1976) Comparaison des écoulements sur deux bassins versants élémentaires, bocager et “ouvert”, a l’aide du traçage par 018. Pages 153-158 in Les bocages: Histoire, écologie économie. University of Rennes. Rennes.

Boatman N.D., Blake K.A., Aebischer N.J. and Sotherton N.W. (1994) Factors affecting the herbaceous flora of hedgerows on arable farms and its value as wildlife habitat. Pages 33-46 in T.A. Watt and G.P. Buckley, eds., Hedgerow management and nature conservation. Wye College Press. Ashford.

Bond R.R. (1957) Ecological distribution of breeding birds in the upland forests of southern Wisconsin. Ecological monographs 27, 351-384.

Boots A.J. (2001) The effect of connection to woodlands on the woody species composition of hedgerows: a case study on the Mendip Hills plateau, North Somerset. Pages 157-162 in C. Barr and S. Petit, eds., Hedgerows of the world: their ecological functions in different landscapes. Proceedings of the 2001 annual IALE(UK) Conference. Birmingham.

Bossuyt B., Hermy M. and Deckers J. (1999) Migration of herbaceous plant species across ancient- recent forest ecotones in central Belgium. Journal of ecology 87, 628-638.

Boutin C. and Jobin B. (1998) Intensity of agricultural practices and effects on adjacent habitats. Ecological applications 8, 544-557.

Boutin C., Jobin B., Bélanger L. and Choinière L. (2002) Plant diversity in three types of hedgerows adjacent to cropfields. Biodiversity and conservation 11, 1-25.

Bowne D.R., Peles J.D. and Barrett G.W. (1999) Effects of landscape spatial structure on movement patterns of the hispid cotton rat (Sigmodon hispidus). Landscape ecology 14, 53-65.

Broekhuizen S. (1986) De betekenis van kleine landschapselementen voor marterachtigen. Pages 45- 52 in P. Opdam, T.A.W. van Rossum and T.G. Coenen, eds., Ecologie van kleine landschapselementen. Rijksinstituut voor natuurbeheer. Leersum.

Brown J.H. and Kodric-Brown A. (1977) Turnover rates in insular biogeography: effects of immigration on extinction. Ecology 58, 445-449.

Brunet J. and von Oheimb G. (1998) Migration of vascular plants to secondary woodlands in southern Sweden. Journal of ecology 86, 429-438.

Bunce R.G.H., Howard D.C. and Barr C.J. (1994) Botanical diversity in British hedgerows. British crop protection council monographs 58, 43-52.

Burel F. (1989) Landscape structure effects on carabid beetles spatial patterns in Western France. Landscape ecology 2, 215-226.

Burel F. (1992) Effect of landscape structure and dynamics on species diversity in hedgerow networks. Landscape ecology 6, 161-174.

Burel F. (1996) Hedgerows and their role in agricultural landscapes. Critical review in plant sciences 15, 169-190.

Burel F. and Baudry J. (1990a) Hedgerow network patterns and processes in France. Pages 99-120 in I.S. Zonneveld and R.T.T. Forman, eds., Changing landscapes: an ecological perspective. Springer- Verlag. New York.

Burel F. and Baudry J. (1990b) Structural dynamic of a hedgerow network landscape in Brittany France. Landscape ecology 4, 197-210.

Burel F. and Baudry J. (1994) Control of biodiversity in hedgerow network landscapes in Western France. Pages 47-57 in T.A. Watt and G.P. Buckley, eds., Hedgerow management and nature conservation. Wye College Press. Ashford.

Burel F., Baudry J. and Lefeuvre J.C. (1993) Landscape structure and the control of water runoff. Pages 41-47 in R.G.H. Bunce, L. Ryszkowski and M.G. Paoletti, eds., Landscape ecology and agroecosystems. Lewis publishers. London. Buson C. (1979) Une approche pédologue du problème de l’épandage: caractérisation hydrique des sols Bruno sur schistes briovériens de la région de Vire (Calvados). Effet des épandages de laiterie sur les sols et les eaux. Thèse doctorale ingénieur. Rennes.

Butaye J., Jacquemyn H., Honnay O. and Hermy M. (2001) The species pool concept applied to forest in a fragmented landscape: Dispersal limitation versus habitat limitation. Journal of vegetation science 13, 27-34.

Caborn J.M. (1976) Changements du paysage et protection contre le vent. Pages 109-114 in Les bocages: Histoire, écologie, économie. University of Rennes. Rennes.

Cain M. L., Damman H. and Muir A. (1998) Seed dispersal and the Holocene migration of woodland herbs. Ecological monographs 68, 325-347.

Caubel-Forget V. and Grimaldi C. (1999) Fonctionnement hydrique et géochimique du talus de ceinture de bas-fond: conséquences sur le transfert et le devenir des nitrates. Pages 169-189 in Actes du colloque bois et forêts des agriculteurs. Edition Cemagref. Paris.

Chambers J.C. and MacMahon J.A.(1994) A day in the life of a seed: movements and fates of seeds and their implications for natural and managed systems. Annual review of ecology and systematics 25, 263-292

Clergeau P. and Burel F. (1997) The role of spatio-temporal patch connectivity at the landscape level: an example in a bird distribution. Landscape and urban planning 38, 37-43.

Coffman C.J., Nichols J.D. and Pollock K.H. (2001) Population dynamics of Microtus pennsylvanicus in corridor-linked patches. Oikos 93, 3-21.

Collinge S.K. (2000) Effects of grassland fragmentation on insect species loss, colonization and movement patterns. Ecology 81, 2211-2226.

Constant P.M., Eybert C and Mahed R. (1976) Avifaune reproductrice du bocage de l’Ouest. Pages 327-332 in Les bocages: Histoire, écologie, économie. University of Rennes. Rennes.

Corbit M., Marks P.L. and Gardescu S. (1999) Hedgerows as habitat corridors for forest herbs in central New York, USA. Journal of ecology 87, 220-232.

Cordeiro N.J. and Howe H.F. (2001) Low recruitment of trees dispersed by animals in African forest fragments. Conservation biology 15, 1733-1741.

Cunningham S.A. (2000) Depressed pollination in habitat fragments causes low fruit set. Proceedings of the royal society London 267, 1149-1152.

Damagnez J. (1976) Bioclimatologie: rapport de synthèse. Pages 105-108 in Les bocages: Histoire, écologie, économie. University of Rennes. Rennes. de Blois S., Domon G. and Bouchard A. (2002) Factors affecting plant species distribution in hedgerows of southern Quebec. Biological conservation 105, 355-367.

Deckers B. (2005) Linear, woody habitats in agricultural landscapes: spatio-temporal dynamics, plant community assembly and invasive species spread. Doctoraatsproefschrift. Gent Delattre P., De Sousa B., Fichet-Calvet E., Quéré J.P. and Giraudoux P. (1999) Vole outbreaks in a landscape context: evidence from a 6-year study of Microtus arvalis. Landscape ecology 14, 401-412.

Dmowski K. and Koziakiewicz M. (1990) Influence of a shrub corridor on movements of passerine birds to a lake littoral zone. Landscape ecology 4, 98-108.

Duelli P., Studer M., Marchland I. and Jakob S. (1990) Population movements of arthropods between natural and cultivated areas. Biological conservation 54, 193-207.

Dzwonko Z. (1993) Relations between the floristic composition of isolated young woods and their proximity to ancient woodland. Journal of vegetation science 4, 693-698.

Dzwonko Z. and Loster S. (1989) Distribution of vascular plant species in small woodlands in the Western-Carpathian foothills. Oikos 56, 77-86.

Dzwonko Z. and Loster S. (1992) Species richness and seed dispersal to secondary woods in Southern Poland. Journal of biogeography 19, 195-204.

Faaborg J., Brittingham M., Donovan T. and Blake J. (1995) Habitat fragmentation in the temperate zone: perspective for managers. Pages 357-380 in T.E. Martin and D.M. Finch, Ecology and management of neotropical migratory birds: a synthesis and review of critical issues. Oxford University Press.

Fahrig L. and Merriam G. (1985) Habitat patch connectivity and population survival. Ecology 66, 1762- 1768.

Foré S.A., Hickey J., Vankat J.L. Guttman S.I. and Schaefer R.L. (1992) Genetic structure after forest fragmentation: a landscape ecology perspective on Acer saccharum. Canadian journal of botany 70, 1659-1668.

Forman R.T.T. (1981) Interaction among landscape elements: a core of landscape ecology. Proceedings of the international congress of the Netherland society for landscape ecology, 35-48.

Forman R.T.T. (1983) Corridors in a landscape: their ecological structure and function. Ekologia (CSSR) 2, 375-387.

Forman R.T.T. and Baudry J. (1984) Hedgerows and hedgerow networks in landscape ecology. Environmental management 8, 495-510.

Forman R.T.T. and Godron M. (1981) Patches and structural components for a landscape ecology. BioScience 31, 733-740.

Frankel O.H., Brown A.H.D. and Burdon J.J. (1995) The conservation of pIant biodiversity. Cambridge University Press. Cambridge.

French D.D. and Cummins R.P. (2001) Classification, composition, richness and diversity of British hedgerows. Applied vegetation science 4, 213-228.

Fritz R. and Merriam G. (1993) Fencerow habitats for plants moving between farmland forests. Biological conservation 64, 141-148.

Fritz R. and Merriam G. (1994) Fencerow and forest edge vegetation structure in eastern Ontario farmland. Ecoscience 1, 160-172.

Galli A.E., Leck C.F. and Forman R.T. (1976) Avian distribution in forest islands of different sizes in central New Jersey. Auk 93, 356-364.

Garbutt R.A. and Sparks T.H. (2002) Changes in the botanical diversity of a species rich ancient hedgerow between two surveys (1971-1998). Biological conservation 106, 273-278.

Geiger R. (1965) The climate near the ground. Harvard University Press, Cambridge.

Gilpin M. (1991) The genetic effective size of a metapopulation. Biological journal of the Linnean society 42, 165-175.

Gonzalez A., Lawton J.H., Gilbert F.S., Blackburn T.M. and Evans-Freke I. (1998) Metapopulation dynamics, abundance and distribution in a microecosystem. Science 281, 2045-2047.

Grashof-Bokdam C. (1997) Forest species in an agricultural landscape in the Netherlands: effects of habitat fragmentation. Journal of vegetation science 8, 21-28.

Grime J.P. (1977) Evidence for the existence of three primary strategies in plants and its relevance to ecological and evolutionary theory. The American naturalist 111, 1169-1194.

Groom M.J. (2001) Consequences of subpopulation isolation for pollination, herbivory and population growth in Clarkia concinna concinna (Onagraceae). Biological conservation 100, 55-63.

Gulinck H. (1985) Landbouw, bodembescherming en landschapszorg. Landbouwtijdschrift 38, 37-47.

Guyot G. and Seguin B. (1976) Influence du bocage sur le climat d’une petite region. Pages 121-130 in Les bocages: Histoire, écologie, économie. University of Rennes. Rennes.

Haas C.M. (1995) Dispersal and use of corridors by birds in wooded patches on an agricultural landscape. Conservation biology 9, 845-854.

Haddad N.M. (1999) Corridor and distance effects on interpatch movement: a landscape experiment with butterflies. Ecological applications 9, 612-622.

Haddad N.M. and Baum K.A. (1999) An experimental test of corridor effects on butterfly densities. Ecological applications 9, 623-633.

Hale M.L., Lurz P.W., Shirley M.D., Rushton S., Fuller R.M. and Wolff K. (2001) Impact of landscape management on the genetic structure of red squirrel populations. Science 293, 2246-2248.

Harmon W.H. (1948) Hedgerows. American Forestry 54, 448-450.

Harris L.D. (1988) Edge effects and conservation of biotic diversity. Conservation biology 2, 330-332.

Hayden T.J., Faaborg J. and Clawson R.L. (1985) Estimates of minimum area requirements for Missouri forest birds. Transactions of the Missouri academy of science 19, 11-22.

Hegarty C.A., McAdam J.H. and Cooper A. (1994) Factors influencing the plant species composition of hedges - implications for management in environmentally sensitive areas. British crop protection council monographs 58, 227-234.

Heimans E., Heinsius H.W. and Thijsse J.P. (1909) Geïllustreerde flora van Nederland. Handleiding voor het bepalen van de naam der in Nederland in het wild groeiende en verbouwde gewassen en van een groot aantal sierplanten. W. Versluys. Amsterdam.

Helliwell D.R. (1975) The distribution of woodland plant species in some Shropshire hedgerows. Biological conservation 7, 61-72

Helmer W. and Limpens H.J.G.A. (1988) Echo’s in het landschap: over vleermuizen en oecologische infrastructuur. De levende natuur 89, 2-6.

Hermy M. and De Blust G. (1997) Punten en lijnen in het landschap. Marc Van de Wiele. Brugge.

Hermy M., Honnay O., Firbank L., Grashof-Bokdam C. and Lawesson J.E. (1999) An ecological comparison between ancient and other forest plant species of Europe, and the implications for forest conservation. Biological conservation 91, 9-22.

Hewes L. (1981) Early fencing on the western margin of the Prairie. Annals of the association of American geographers 71, 499-526.

Hobbs R.J. (1992) The role of corridors in conservation: solution or bandwagon? Trends in ecology and evolution 7, 389-392.

Hodgson J.G., Wilson P.J., Hunt R., Grime J.P. and Thompson K. (1999) Allocating C-S-R plant functional types: a soft approach to a hard problem. Oikos 85, 282-294.

Holm E. (1978) Bloembiologie. W.J. Thieme. Zutphen.

Honnay O., Degroote B. and Hermy M. (1998) Ancient-forest plant species in western Belgium: a species list and possible ecological mechanisms. Belgian journal of botany 130, 139-154.

Honnay O., Hermy M. and Coppin P. (1999) Impact of habitat quality on forest plant species colonization. Forest ecology and management 115, 157-170.

Hooper M.D. (1976) Historical and biological studies on English hedges. Pages 225-227 in Les bocages: Histoire, écologie, économie. University of Rennes. Rennes.

Hoskins W.G. (1955) The making of the English landscape. Penguin. New York.

Inghe O. and Tamm C.O. (1985) Survival and flowering of perennial herbs. 4. The behavior of Hepatica nobilis and Sanicula europaea on permanent plots during 1943-1981. Oikos 45, 400-420.

Jensen M. (1954) Shelter effect: investigations into aerodynamics of shelter and its effects on climate and crops. Danish technical Press. Copenhagen. Jobin B., Boutin C. and DesGranges J. (1996) Habitats fauniques du milieu rural québécois: une analyse floristique. Canadian journal of botany 74, 323-336.

Jobin B., Boutin C. and DesGranges J. (1997) Effects of agricultural practices on the flora of hedgerows and woodland edges in southern Quebec. Canadian journal of plant science 77, 293-299.

Kearns C.A., Inouye D.W. and Waser N.M. (1998) Endangered mutualisms: the conservation of plant- pollinator interactions. Annual review of ecology and systematics 29, 83-112.

Lauga-Sallenave C. (1997) Le cercle des haies. Paysages des agroéleveurs peuls du Fouta-Djalon (plaine des Timbis, Guinée). Thesis. Paris, Nanterre.

Le Clezio P. (1976) Les ambigüités de la notion de maille optimale. Pages 551-554 in Les bocages: Histoire, écologie, économie. University of Rennes. Rennes.

Le Coeur D., Baudry J. and Burel F. (1997) Field margins plant assemblages: variation partitioning between local and landscape factors. Landscape and urban planning 37, 57-71.

Lefeuvre J.L., Missonnier J. and Robert Y. (1976) Caractérisation zoologique: écologie animale (des bocages). Rapport de synthèse. I.N.R.A. p315-326.

Leopold A. (1933) Game management. Scribners. New York.

Levey D.J., Silva W.R. and Galetti M. (2001) Seed dispersal and frugivory: ecology, evolution and conservation. CAB international. Wallingford, UK.

Lewis T. (1969) The diversity of the insect fauna in a hedgerow and neighboring fields. Journal of applied ecology 6, 453-458.

MacArthur R.H. and Wilson E.O. (1967) The theory of island biogeography. Princeton University Press. Princeton.

MacClintock L., Whitcomb R.F. and Whitcomb B.L. (1977) Evidence for the value of corridors and minimization of isolation in preservation of biotic diversity. American birds 31, 6-16.

Marshall E.J..P. and Arnold G.M. (1995) Factors affecting field weed and field margins flora on a farm in Essex, UK. Landscape and urban planning 31, 205-216.

Matlack G.R. (1994) Plant species migration in a mixed-history forest landscape in eastern North America. Ecology 75, 1491-1502.

McAdam J.H., Bell A.C. and Henry T. (1994) The effect of restoration techniques on flora and microfauna of hawthorn-dominated hedges. Pages 25-32 in F.A. Watt and G.P. Buckley, eds., Hedgerow management and nature conservation. Wye College Press. Ashford.

McCollin D., Jackson J.I., Bunce R.G.H., Barr C.J. and Stuart R. (2000) Hedgerows as habitat for woodland plants. Journal of environmental management 60, 77-90.

McDonnell M.J. and Stiles E.T. (1983) The structural complexity of old field vegetation and the recruitment of bird-dispersed plant species. Oecologia 56, 109-115.

Mercer C., Cherrill A., Tudor G. and Andrews M. (1999) Hedgerow plant communities: relationships with adjacent land use and aspect. Aspects of applied biology 54, 345-352.

Merot A. and Ruellan A. (1980) Pédologie, hydrologie des bocages: caractéristiques et incidences de de l’arasement des talus boises. Bulletin technique d'information 353-355, 631-656.

Merriam G. (1984) Connectivity: a fundamental ecological characteristic of landscape pattern. Proceedings 1st international IALE seminar on methodology on landscape ecological research and planning 1, 5-15.

Millennium Ecosystem Assessment (2005) Ecosystems and human well-being: biodiversity synthesis. World resources institute. Washington, D.C.

Moonen A.C. and Marshall E.J.P. (2001) The influence of sown field margin strips, management and boundary structure on herbaceous field margin vegetation in two neighboring farms in Southern England. Agriculture, ecosystems & environment 86, 187-202.

Nabhan G.P. and Sheridan T.E. (1977) Living fencerows of the Rio San Miguel, Sonora, Mexico: traditional technology for floodplain management. Human ecology 5, 97-111.

Oksanen J., Blanchet F.G., Kindt R., Legendre P., Minchin P.R., O'Hara R.B., Simpson G.L., Solymos P., Henry M., Stevens H. and Wagner H. (2012) vegan: Community Ecology Package. R package version 2.0-3. http://CRAN.R-project.org/package=vegan

Opdam P. (1987) De metapopulatie: model van een populatie in een versnipperd landschap. Landschap 4, 289-306.

Peterken G.F. and Game M. (1981) Historical factors affecting the distribution of Mercurialis perennis in central Lincolnshire. Journal of ecology 69, 781-796.

Peterken G.F. and Game M. (1984) Historical factors affecting the number and distribution of vascular plant species in central Lincolnshire. Journal of ecology 72, 155-182.

Petit S. and Burel F. (1998) Connectivity in fragmented populations: Abax parallelepipedus in a hedgerow network landscape. Comptes rendus académie des sciences Paris. Science de la vie 32, 55- 61.

Pigott C. D. and Huntley J. P. (1981) Factors controlling the distribution of Tilia cordata at the northern limits of its geographical range. III. Nature and causes of seed sterility. New phytologist 87, 817-839.

Pihan J. (1976) Bocage et érosion hydrique des sols en Bretagne. Pages 185-192 in Les bocages: Histoire, écologie, économie. University of Rennes. Rennes.

Pinheiro J., Bates D., DebRoy S., Sarkar D. and the R Development Core Team (2012) nlme: Linear and Nonlinear Mixed Effects Models. R package version 3.1-103.

Pollard E. (1973) Hedges VII. Woodland relic hedges in Huntingdon and Peterborough. Journal of ecology 61, 343-352.

Pollard E. and Relton J. (1970) Hedges. V. A study of small mammals in hedges and cultivated fields. Journal of applied ecology 7, 549-557.

Pollard E., Hooper M.D. and Moore N.W. (1974) Hedges. W. Collins and sons. London.

Prober S.M. and Brown A.H.D. (1994) Conservation of the grassy white box woodlands: Population genetics and fragmentation of Eucalyptus albens. Conservation biology 8, 1003-1013.

Pulliam H.R. (1988) Sources, sinks and population regulation. American naturalist 132, 652-661.

Rackham O. (1976) Trees and woodland in in the British landscape. Dent and sons. London.

Rackham O. (1980) Ancient Woodland. Arnold. London.

Raijmann L.E.L., Van Leeuwen N.C., Kersten R., Oostermeyer J.G.B., Den Nijs H.C.M. and Menken S.B.J. (1994) Genetic variation and outcrossing rate in relation to population size in Gentiana pneumonanthe L. Conservation biology 8, 1014-1026.

Robbins C.S. (1979) Effect of forest fragmentation on bird populations. Pages 198-212 in R.M. DeGraaf and K.E. Evans, eds., Management of north-central and northeastern forests for nongame birds. General technical report NC-51. St.-Paul, MN: US department of agriculture, forest service, north central forest experiment station.

Robbins C.S., Dawson D.K. and Dowell B.A. (1989) Habitat area requirements of breeding forest birds of the Middle Atlantic States. Wildlife monographs 103, 3-34.

Rose F. and O’Reilly C. (2006) The wild flower key. How to identify wild flowers, trees and shrubs in Britain and Ireland. Frederick Warne. London.

Rosenberg D.K., Noon B.R. and Meslow E.C. (1997) Biological corridors: form, function and efficacy. BioScience 47, 677-687.

Rosenberg D.K., Noon B.R., Megahan J.W. and Meslow E.C. (1998) Compensatory behavior of Ensatina eschscholtzii in biological corridors: a field experiment. Canadian journal of zoology 76, 117- 133.

Saint-Girons M.C. (1976) Les petits mammifères dans l’écosystème du bocage. Pages 343-346 in Les bocages: Histoire, écologie, économie. University of Rennes. Rennes.

Saunders D.A. and Hobbs R.J. (1991) Nature conservation 2: the role of corridors. Surrey Beatty and sons. Chipping Norton. New South Wales, Australia.

Saunders D.A., Hobbs R.J. and Margules C.R. (1991) Biological consequences of ecosystem fragmentation: a review. Conservation biology 5, 18-32.

Shafer C.L. (1990) Nature reserves: island theory and conservation practice. Smithsonian Institution Press. Washington D.C.

Shelterbelt Project (1934) (published statements by numerous separate authors) Journal of forestry 32, 952-991.

Simberloff D., Farr J.A., Cox J. and Mehlman D.W. (1992) Movement corridors: conservation bargains or poor investments? Conservation biology 6, 493-504.

Sinclair N.R., Getz L.L. and Bock F.S. (1967) Influence of stone walls on the local distribution of small mammals. University of Connecticut occasional papers biological science series 1, 43-62.

Steavenson H.A., Gearhart H.E. and Curtis R.L. (1943) Living fences and supplies of fence posts. Journal of Wildlife Management 7, 256-261.

Sutton R.K. (1985) Relict rural planting in Eastern Nebraska. Landscape journal 4, 106-115.

Temple S.A. (1986) The problem of avian extinctions. Current ornithology 3, 453-485.

Temple S.A. and Cary J.R. (1988) Modeling dynamics of habitat-interior bird populations in fragmented landscapes. Conservation biology 2, 340-347.

Temple S.A. and Wilcox B. (1986) Predicting effects of habitat patchiness and fragmentation. Pages 261-262 in J. Verner, M.L. Morrison and C.J. Ralph, eds., Wildlife 2000: Modeling habitat relationships of terrestrial vertebrates. University of Wisconsin Press. Madison, WI.

Tewksbury J.J., Levey D.J., Haddad N.M., Sargent S., Orrock J.L., Weldon A., Danielson B.J., Brinkerhoff J., Damschen E.I. and Townsend P. (2002) Corridor affect plants, animals, and their interactions in fragmented landscapes. Proceedings of the national academy of sciences 99, 12923-12926.

Tilman D., Lehman C.L. and Karieva P. (1997) Pages 3-20 in D. Tilman, ed., Spatial ecology: the role of space in population dynamics and interspecific interactions. Princeton University Press. Princeton.

Tsiouris S. and Marshall E.J.P. (1998) Observations on patterns of granular fertilizer deposition beside hedges and its likely effects on the botanical composition of field margins. Annals of applied biology 132, 115-127.

Vancoillie F. (2012) Landinformatiesystemen: toepassingen. University of Ghent. Gent

Van der Pijl L. (1969) Principles of dispersal in higher plants. Springer-Verlag. Berlin.

Van Dorp D. (1996) Seed dispersal in agricultural habitats and the restoration of species-rich meadows. Proefschrift. Wageningen.

Van Ruremonde R.H.A.C and Kalkhoven J.T.R. (1991) Effect of woodlot isolation on the dispersion of plants with fleshy fruits. Journal of vegetation science 2, 377-384. van Treuren R., Bijlsma R., van Delden W. and Ouborg N.J. (1991) The significance of genetic erosion in the process of extinction. 1. Genetic differentiation in Saluia pratensis and Scabiosa columbaria in relation to population size. Heredity 66, 181-189.

Verheyen K. (2011) Ecotechnique and nature construction. University of Ghent. Gent.

Wallace K.J. (2007) Classification of ecosystem services: problems and solutions. Biological conservation 139, 235-246.

Wegner J.F. and Merriam G. (1979) Movements by birds and small mammals between a wood and adjoining farmland habitats. Journal of applied ecology 16, 349-358.

Whitcomb R.F., Lynch J.F., Opler P.A. and Robbins C.S. (1976) Island biogeography and conservation: strategy and limitations. Science 193, 1030-1032.

Wilcove D.S. (1988) Changes in the avifauna of the Great Smoky Mountains: 1947-1983. Wilson bulletin 100, 256-271.

Wilcove D.S., McClellan C.H. and Dobson A.P. (1986) Habitat fragmentation in the temperate zone. Pages 237-256 in M.E. Soule, ed., Conservation biology: the science of scarcity and diversity. Sinauer associates. Sunderland, MA.

Yahner R.H. (1982) Avian use of vertical structures and plantings in farmstead shelterbelts. Journal of wildlife management 46, 50-60.

Yahner R. (1988) Changes in wildlife communities near edges. Conservation biology 2, 333-339.

Young A., Boyle T. and Brown T. (1996) The population genetic consequences of habitat fragmentation for plants. Trends in ecology and evolution 11, 413-418.

Young A.G., Merriam H.G. and Warwick S.I. (1993) The effects of forest fragmentation on genetic variation in Acer saccharum Marsh. (sugar maple) populations. Heredity 71, 277-289.

Zhenrong Y., Baudry J., Baoping Z., Hao Z. and Shouqiao L. (1999) Vegetation components of a subtropical rural landscape in China. Critical review in plant sciences 18, 381-392.

Appendix 1: Act of 1721.

An act to oblige proprietors and tenants of neighbouring lands to make fences between their several lands and holdings.

Chap. V

[1] Whereas it is found by experience that many trespasses happen and frequent disputes arise between proprietors of lands about mears and bounds of lands, which is in a great measure occasioned by the proprietors and tenants neglecting to make fences between their several lands and holdings which heretofore could not be done at equal expence without the mutual consent and concurrence of the respective proprietors or tenants of such contiguous lands.

[2] Be it therefore enacted by the kings most excellence Majesty, by and with the advice and consent of the lords spiritual and temporal and commons in this present parliament assembled, and by the authority of the same, that from and after the first day of February in the year of our Lord one thousand seven hundred twenty one, if any proprietor, occupier or tenant of any lands in this kingdom shall be desirous to make ditches or fences between his, her or their lands and holdings, and the lands next contiguous and immediately adjoining thereto, where no dispute then shall be or shall have been for three years then last past about the mears between the said lands or holdings so intended to be fenced, and where no sufficient fences or only dead and dry fenceless ditches then shall be, that the proprietor or proprietors, occupier or occupiers, or tenant or tenants of such neighbouring lands on reasonable request to him, here or them made, shall be and is hereby obliged to be at equal expence in making between such several lands and holdings good and sufficient ditches of six foot wide and five foot deep at least where the same is practicable well and sufficiently quicked in good husbandlike manner with white thorn, crab, or other quicksets where the same will grow, and in ground where such quicksets will not grow with furz, and where furz will not grow, or where ditches cannot be made of the said depth and wideness instead of a ditch, with a dry stone wall where a stone be conveniently had, and where stone cannot conveniently be had, with a clay or mud wall not under five foot high and two foot and a half thick at the bottom, and one foot and a half thick at the top, and in wet low ground with sufficient trenches or drains, the banks thereof to be planted with sallows, alder, or other aquatick trees where such aquaticks will grow, and if any proprietor, occupier or tenant of any neighbouring lands shall refuse to settle and ascertain the mears and bounds between his, her or their lands and holdings and the lands and holdings of such person or persons requiring the same in order to have fences made as aforesaid, than and in that case such proprietor, occupier or tenant of such lands so refusing shall be compellable by bill in equity or commission of perambulation to fix, adjust, settle and ascertain the mears and bounds between his or her lands and holdings, and the lands and holdings of the person or persons requiring such fence to be made, and such neighbouring proprietors, occupiers or tenants shall join and be at equal expence in making and preserving, scowring and repairing such ditches, trenches, drains or fences as aforesaid, with such proprietor, occupier or tenant of the neighbouring lands requiring the same, and if such neighbouring proprietor, occupier or tenant refuse, or for the space of one whole year neglect so to do, then and in such case it shall and may be lawful for the proprietor, occupier or tenant of such neighbouring lands requiring the same, to make the said ditches, wall, trench, drain or other fence as aforesaid, and the tenant or tenants, occupier or occupiers of such neighbouring lands

who shall refuse or neglect to make such ditches, drains or fences as aforesaid, shall be answerable for, and shall pay to the person or persons who shall make or cause the same to be made, one full moiety of what he, she or they shall reasonably bona fide and without fraud or malice lay out in making such ditches, walls, drains, trenches or fences, and in planting such quicksets and weeding them and securing the same as aforesaid, together with legal interest for such moiety of such sum so laid out as aforesaid, to be recovered by action of debt in any of his Majesties courts of record in Ireland, or if the sum expended be under ten pounds, then by a civil bill before the justices of assize and general goal delivery for the county or liberty where such fences shall be made as aforesaid, and in the county of Dublin before the justices of the peace at their general quarter sessions of the peace to be held in and for the said county, with treble costs.

[3] Provided always , that there shall not be demanded above one shilling and six pence per perch of such stone or other wall of the height and thickness aforesaid, or above one shilling per perch for such ditch, trench, drain, or other fence made and planted as aforesaid by the person or persons who shall make or cause the same to be made, and if it shall happen that after such ditches and fences are made as aforesaid, the person or persons whose lands the same lie on and who ought to keep up the same do not weed such quickset, and mend, preserve and keep up such fences, or his part thereof as they ought to do, that then and in that case the person or persons so neglecting or refusing to weed such quicksets, and to mend, preserve and keep up his part of the said fence, shall have no remedy for any involuntary trespass committed by the cattle of the proprietor, occupier or tenant of any the neighbouring lands for any trespass on his, her or their lands, or occasioned by his, her or their default in mending, preserving or keeping up his, her or their part of such fence or fences a aforesaid.

[4] And whereas the tenant or occupier of such lands who shall be obliged by this act to ditch and fence as aforesaid, or pay for the same, may be only tenant at will or sufferance, or have a very short term in the said lands so held by him or her.

[5] Be it further enacted by the authority aforesaid, that every person or persons compellable by this act to ditch and fence as aforesaid , or to pay for the same, who shall not have an estate for life or eleven years in his, her or their lands to be fenced and ditched between as aforesaid at the time the proprietor or tenant of the neighbouring lands shall request him or her to ditch or fence as aforesaid, that then and in such case such tenant shall be and is hereby impowered to deduct out of the rent due to his, her or their landlord or lessor what he, she or they shall so lay out, expend or pay, and such landlord or lessor shall and is hereby required to allow the same, such tenant or tenants first proving on oath before the justices of the peace of the county where such lands lie, at their general quarter sessions (which oath such justices are hereby impowered to administer) what he, she or they so laid out, expended or paid.

[6] Provided always, that no tenant or farmer for life or years shall be obliged to ditch or fence above one fifth part of his, her or their lands or holdings in any one year.

[7] And whereas the bounds and mears between lands do often run in crooked lines, and sometimes through places inconvenient for making of such ditches or fences as aforesaid , and it would be most convenient for the occupiers and proprietors of such neighbouring lands to make the fence between them in a streight line, and to exchange the lands left out on one side of such streight line for the lands of equal value worth and purchase took in on the other side thereof, which may happen to be

impracticable for want of a sufficient estate in the proprietors of such neighbouring lands, or one of them to make such exchange.

[8] Be it therefore enacted by the authority aforesaid, that in such cases the persons whose lands are so contiguous and to be bounded by a fence between them as aforesaid may, and they are hereby impowered and enabled by consent of the tenant or tenants of such lands, and the immediate owner and proprietor thereof in reversion expectant on the lease then in being appearing by writing under hand and seal attested by three credible witnesses at least to make the boundaries in streight lines in more convenient places, and to exchange the lands on one side of such streight line or fence for the lands of equal value, worth and purchase on the other side of such right lines, so as such reversioner be seized of the lands which he shall so grant in exchange at the least for term of his own life, with remainder limited over to the sons of his body forgotten in tail male, and if it shall happen that the lands left out on one side of such streight line or fence shall be of greater value, worth and purchase than the lands took in on the other side thereof, then and in such case the proprietor to whom the greater proportion shall fall shall be enabled to charge the same with a perpetual rent charge sufficient to countervail such difference or disproportion, which rent charge shall go to such person and persons, and for such estate and estates, and to and for the same uses as the land so charged ought to have gone, and the lands received in exchange shall go to such person and persons, and for such estate and estates, and to and for the same uses as the lands given in exchange ought to have gone in case no such exchange had been made, provided always, that no house, garden, orchard, wood or grove be included in such lands so to be exchanged as aforesaid.

[9] And be it also enacted by the authority aforesaid, that all such exchanges or agreements shall be binding to all persons, any devise, settlement or limitation of use to the contrary notwithstanding provided the lands so exchanged to the intent aforesaid do not exceed the quantity of two acres plantation measure in every one hundred perches of such line or fence, each perch in this act mentioned containing twenty one foot and no more.

[10] And be it further enacted by the authority aforesaid, that in case any person shall refuse to fence or plant according to the true intent and meaning of this act so as in default of so doing, the proprietor, possessor or tenant of the adjoyning land shall fence and ditch between his land or holding and the neighbouring lands or holdings, the person or persons to ditching and fencing as aforesaid shall and may ascertain and set out an equal proportion of such fence which the tenant or tenants, or occupier or occupiers of the adjoining lands shall be obliged from time to time to keep in good order and repair as his part of the said fence, and to weed and preserve the quicksets (if any planted thereon,) provided always, that nothing herein contained shall extend to avoid any covenants or contracts made between landlord or tenant for fencing, ditching, draining and inclosing lands.

[11] Provided likewise, and be it further enacted, that where the landlord or landlords are obliged to allow his, her or their tenant or tenants for ditching or fencing between their holdings and their neighbours as aforesaid, such tenant and tenants respectively to whom such allowance shall be made, shall at the time of making such allowance give security by his or their own bonds of the penalty of the whole sum so allowed to such landlord and landlords conditioned for the due and effectual weeding of such quicksets planted, and the preserving and keeping up the said ditches and fences for which they shall be so allowed during their respective terms in the said lands in good

tenantable order and condition, and in case of refusal to give such bond as aforesaid, such tenant so refusing shall not have the benefit of such allowance, anything herein contained to the contrary notwithstanding.

[12] Provided always, that nothing in this act contained shall extend to oblige any proprietor, occupier or tenant of any lands to fence or ditch between any lands, whereof the plantation acre shall not at the time when request shall be made for the doing thereof be worth, and which shall not really pay the landlord two shillings per annum over and above quit or crown rent.

[13] Provided also, that no proprietor or lessor of such lands shall be obliged to pay or allow in any one year for ditching or fencing as aforesaid in pursuance of this act more than the twentieth part of the annual rent payable out of such land to such proprietor or lessor, and that the tenant or tenants of such proprietor or lessor shall not be obliged to expend more in any one year in making such fences than the twentieth part of his or their rent payable to such proprietor or lessor.

[14] Provided always, that no proprietor, tenant or occupier of land shall by virtue of this act be obliged to fence in or enclose any parcel of land or ground in any one park or inclosure which shall not contain at least ten acres plantation measure, with a ditch or fence of above six foot wide and five foot deep, and that the most usual ways and passages to and from intermixed lands surrounded by other proprietors be left open and passable as formerly, anything herein contained to the contrary notwithstanding.

[15] Provided always, that no mears between lands belonging to several proprietors inclosed or ditched by virtue of this act shall be binding or conclusive so as finally to settle the mears and bounds between such lands, unless the proprietors of the said lands do agree to the same in writing under his, her or their hand and seal attested by three or more credible witnesses before or after the time of such ditching, fencing or bounding, or shall suffer the said mears so ditched and inclosed to stand for the space of five years after the determination of such lease or leases of the said lands as are or shall be then in being, and in case of infancy, coverture being beyond sea or of insane memory, or where a remainder shall be claimed by any settlement or will five years after attaining the age of one and twenty years becoming discovert returning from beyond sea or becoming of sane memory, or from and after such remainder shall take place.

Appendix 2: Age of the hedges.

ID owner 1843 1873 1909 1937 2011 period number period number since age 1 1 1 1 1 1 1 1843 168 2 1 1 1 1 1 1 1843 168 3 1 0 0 0 0 1 4->5 1 1974 37 4 1 1 1 1 1 1 1843 168 5 1 1 1 1 1 1 1843 168 6 1 0 0 0 0 1 4->5 1 1974 37 7 1 1 1 1 1 1 1843 168 8 1 0 0 1 1 1 2->3 1 1891 120 9 1 1 1 1 1 1 1843 168 10 1 1 1 1 1 1 1843 168 11 1 1 1 1 1 1 1843 168 12 1 0 0 0 0 1 4->5 1 1974 37 13 1 1 1 1 1 1 1843 168 14 1 1 1 1 1 1 1843 168 15 1 1 1 1 1 1 1843 168 16 1 1 1 1 1 1 1843 168 17 1 1 1 1 1 1 1843 168 18 1 1 1 1 1 1 1843 168 19 1 1 1 1 1 1 1843 168 20 1 1 1 1 1 1 1843 168 21 1 1 1 1 1 1 1843 168 22 1 1 1 1 1 1 1843 168 23 1 1 1 1 1 1 1843 168 24 1 1 1 1 1 1 1843 168 25 1 1 1 1 1 1 1843 168 26 1 1 1 1 1 1 1843 168 27 1 1 1 1 1 1 1843 168 28 1 1 1 1 1 1 1843 168 29 1 0 0 0 0 1 4->5 1 1974 37 30 1 1 1 1 1 1 1843 168 31 1 1 1 1 1 1 1843 168 32 1 1 1 1 1 1 1843 168 33 1 1 1 1 1 1 1843 168 34 1 1 1 1 1 1 1843 168 35 1 1 1 1 1 1 1843 168 36 1 1 1 1 1 1 1843 168 37 1 0 0 0 0 1 4->5 1 1974 37 38 1 1 1 1 1 1 1843 168 39 1 0 0 0 0 1 4->5 1 1974 37 40 1 1 1 1 1 1 1843 168

ID owner 1843 1873 1909 1937 2011 period number period number since age 41 1 0 0 0 0 1 4->5 1 1974 37 42 2 1 1 1 1 1 1843 168 43 2 1 1 1 1 1 1843 168 44 2 1 1 1 1 1 1843 168 45 2 1 1 1 1 1 1843 168 46 2 1 1 1 1 1 1843 168 47 2 1 1 0 0 1 4->5 1 2->3 3 1974 37 48 2 1 1 1 1 1 1843 168 49 2 1 1 1 1 1 1843 168 50 2 1 1 1 1 1 1843 168 51 2 1 1 1 1 1 1843 168 52 2 1 1 1 1 1 1843 168 53 2 1 1 1 1 1 1843 168 54 2 1 1 1 1 1 1843 168 55 2 1 1 1 1 1 1843 168 56 2 1 1 1 1 1 1843 168 57 2 1 1 1 1 1 1843 168 58 2 1 1 1 1 1 1843 168 59 2 1 1 1 1 1 1843 168 60 2 1 1 1 1 1 1843 168 61 2 1 1 1 1 1 1843 168 62 2 1 1 1 1 1 1843 168 63 2 0 0 0 1 1 3->4 1 1923 88 64 2 0 0 0 1 1 3->4 1 1923 88 65 2 1 1 1 1 1 1843 168 66 2 1 1 1 1 1 1843 168 67 2 1 1 1 1 1 1843 168 68 2 1 1 1 1 1 1843 168 69 2 1 1 1 1 1 1843 168 70 2 1 1 1 1 1 1843 168 71 2 1 1 1 1 1 1843 168 72 2 1 1 1 1 1 1843 168 73 2 1 1 1 1 1 1843 168 74 2 1 1 1 1 1 1843 168 75 2 1 1 1 1 1 1843 168 76 2 1 1 1 1 1 1843 168 77 2 1 1 1 1 1 1843 168 78 2 1 1 1 1 1 1843 168 79 2 0 0 1 1 1 2->3 1 1891 120 80 2 1 1 1 1 1 1843 168 81 2 1 1 1 1 1 1843 168 82 2 1 1 1 1 1 1843 168

ID owner 1843 1873 1909 1937 2011 period number period number since age 83 2 1 1 1 1 1 1843 168 84 3 1 1 1 1 1 1843 168 85 3 1 1 1 1 1 1843 168 86 3 1 1 1 1 1 1843 168 87 3 1 1 1 1 1 1843 168 88 3 1 1 1 1 1 1843 168 89 3 1 1 1 1 1 1->2 4 1843 168 90 3 1 1 1 1 1 2->3 4 1843 168 91 3 1 1 1 1 1 4->5 2 1843 168 92 3 1 1 1 1 1 1843 168 93 3 0 0 1 1 1 2->3 1 1891 120 94 3 0 0 1 1 1 2->3 1 1891 120 95 3 1 1 1 1 1 1843 168 96 3 1 1 1 1 1 1843 168 97 3 0 0 0 0 1 4->5 1 1974 37 98 3 1 1 1 1 1 1843 168 99 3 1 1 1 1 1 1843 168 100 3 1 1 1 1 1 1843 168 101 3 1 1 1 1 1 1843 168 102 3 1 1 1 1 1 1843 168 103 3 1 1 1 1 1 1843 168 104 3 1 1 1 1 1 1843 168 105 3 1 1 1 1 1 1843 168 106 3 1 1 1 1 1 1843 168 107 3 1 1 1 1 1 1843 168 108 3 1 1 1 1 1 1843 168 109 4 1 1 1 1 1 1843 168 110 4 1 1 1 1 1 1843 168 111 4 1 1 1 1 1 1843 168 112 4 1 1 1 1 1 1843 168 113 4 1 1 1 1 1 1->2 12 1843 168 114 4 1 1 1 1 1 1843 168 115 4 1 1 1 1 1 1843 168 116 4 1 1 1 1 1 1843 168 117 4 1 1 1 1 1 1843 168 118 4 1 1 1 1 1 1843 168 119 4 1 1 1 1 1 1843 168 120 4 1 1 1 1 1 1843 168 121 4 1 1 1 1 1 1843 168 122 4 1 1 1 1 1 1843 168 123 4 1 1 1 1 1 1843 168 124 4 1 1 1 1 1 1843 168

ID owner 1843 1873 1909 1937 2011 period number period number since age 125 4 1 1 1 1 1 1843 168 126 4 1 1 1 1 1 1843 168 127 4 1 1 1 1 1 1843 168 128 4 1 1 1 1 1 1843 168 129 4 1 1 1 1 1 1843 168 130 4 1 1 1 1 1 1843 168 131 4 1 1 1 1 1 1843 168 132 4 1 1 1 1 1 1843 168 133 4 1 1 1 1 1 1843 168 134 5 1 1 1 1 1 1843 168 135 5 1 1 1 1 1 1843 168 136 5 1 1 1 1 1 1843 168 137 5 1 1 1 1 1 1->2 11 1843 168 138 5 1 1 1 1 1 1843 168 139 5 1 1 1 1 1 1843 168 140 5 1 1 1 1 1 1843 168 141 5 1 1 1 1 1 1843 168 142 5 1 1 1 1 1 1843 168 143 5 1 1 1 1 1 1843 168 144 5 1 1 1 1 1 1843 168 145 5 1 1 1 1 1 1843 168 146 5 1 1 1 1 1 1843 168 147 5 1 1 1 1 1 1843 168 148 5 1 1 1 1 1 1843 168 149 5 1 1 1 1 1 1843 168 150 5 0 0 0 1 1 3->4 1 1923 88 151 5 1 1 1 1 1 1843 168 152 5 1 1 1 1 1 1843 168 153 5 1 1 1 1 1 1843 168 154 6 1 1 1 1 1 1843 168 155 6 1 1 1 1 1 1843 168 156 6 1 1 1 1 1 1843 168 157 6 1 1 1 1 1 1843 168 158 6 1 1 1 1 1 1843 168 159 6 1 1 1 1 1 1843 168 160 6 1 1 1 1 1 1843 168 161 6 1 1 1 1 1 1843 168 162 6 1 1 1 1 1 1843 168 163 6 1 1 1 1 1 1843 168 164 6 1 1 1 1 1 1843 168 165 6 1 1 1 1 1 1843 168 166 6 1 1 1 1 1 1843 168

ID owner 1843 1873 1909 1937 2011 period number period number since age 167 6 1 1 1 1 1 1843 168 168 6 1 1 1 1 1 1843 168 169 6 1 1 1 1 1 1843 168 170 6 1 1 1 1 1 1843 168 171 7 1 1 1 1 1 1843 168 172 7 1 1 1 1 1 1843 168 173 7 1 1 1 1 1 1843 168 174 7 1 1 1 1 1 4->5 5 1843 168 175 7 1 1 1 1 1 1843 168 176 7 0 0 0 0 1 4->5 1 1974 37 177 7 1 1 1 1 1 1843 168 178 7 0 0 0 0 1 4->5 1 1974 37 179 7 1 1 0 0 1 4->5 1 2->3 1 1974 37 180 7 1 1 1 1 1 1843 168 181 7 0 0 0 0 1 4->5 1 1974 37 182 7 0 0 0 1 1 2->3 1 1923 88 183 7 1 1 1 1 1 1843 168 184 7 1 1 1 1 1 1843 168 185 7 1 1 1 1 1 1843 168 186 7 1 1 1 1 1 1843 168 187 7 1 1 1 1 1 1843 168 188 7 1 1 1 1 1 1843 168 189 7 1 1 1 1 1 1843 168 190 7 1 1 1 1 1 1843 168 191 7 1 1 1 1 1 1843 168 192 7 1 1 1 1 1 1843 168 193 7 1 1 1 1 1 1843 168 194 7 1 1 1 1 1 1843 168 195 7 1 1 1 1 1 1843 168 196 7 0 0 0 0 1 4->5 1 1974 37 197 7 1 1 1 1 1 1843 168 198 7 1 1 1 1 1 1843 168 199 7 1 1 1 1 1 1843 168 200 7 1 1 1 1 1 1843 168 201 7 0 0 0 0 1 4->5 1 1974 37 202 7 1 1 1 1 1 1843 168 203 7 1 1 1 1 1 1843 168 204 7 1 1 1 1 1 1843 168

Appendix 3: List of target species (Butaye et al., 2001).

Adoxa moschatellina Corydalis solida Agrimonia eupatoria Corylus avellana Agrimonia repens Crataegus laevigata Ajuga reptans Crataegus monogyna Alliaria petiolata Crepis paludosa Allium ursinum Cruciata laevipes Anemone nemorosa Dactylorhiza fuchsii Arum maculatum Deschampsia cespitosa Asperula odorata Deschampsia flexuosa Athyrium filix-femina Digitalis purpurea Blechnum spicant Dipsacus pilosus Brachypodium sylvaticum Dryopteris affinis Bryonia dioica Dryopteris carthusiana Calamagrostis canescens Dryopteris dilatata Calamagrostis epigejos Dryopteris filix-mas Callitriche spp. Elymus caninus Calluna vulgaris Epilobium angustifolium Campanula trachelium Epilobium montanum Cardamine amara Epipactis helleborine Cardamine flexuosa Equisetum sylvaticum Carex divulsa Equisetum telmateia Carex elongata Euonymus europaeus Carex pallescens Euphorbia amygdaloides Carex pendula Festuca gigantea Carex pilulifera Fragaria vesca Carex remota Frangula alnus Carex spicata Gagea lutea Carex strigosa Gagea spathacea Carex sylvatica Galanthus nivalis Centaurium erythraea Galium saxatile Chaerophyllum temulentum Geranium phaeum Chrysosplenium alternifolium Geum urbanum Chrysosplenium oppositifolium Gnaphalium sylvaticum Circaea lutetiana Hedera helix Cirsium oleraceum Helleborus viridis Clematis vitalba Hieracium lachenalii Colchicum autumnale Hieracium laevigatum / H. subaudum Convallaria majalis Hieracium murorum Cornus sanguinea Hieracium spp. Corydalis claviculata Hippophae rhamnoides

Holcus mollis Ornithogalum umbellatum Humulus lupulus Osmunda regalis Hyacinthoides non-scripta Oxalis acetosella Hypericum dubium/ H. maculatum Paris quadrifolia Hypericum hirsutum Peplis portula Hypericum humifusum Phyteuma nigrum Hypericum pulchrum Phyteuma spicatum Hypericum quadrangulum Picris hieracioides/echioides Ilex aquifolium Platanthera chlorantha Impatiens noli-tangere Poa nemoralis Impatiens parviflora Polygonatum multiflorum Knautia arvensis Polygonum bistorta Lamium galeobdolon Polypodium vulgare Lapsana communis Polystichum aculeatum Lathraea clandestina Potentilla sterilis Lathyrus sylvestris Primula elatior Ligustrum vulgare Prunus spinosa Listera ovata Pteridium aquilinum Lonicera periclymenum Pulmonaria montana Luzula multiflora Pulmonaria officinalis Luzula pilosa Pyrus pyraster Luzula sylvatica Ranunculus auricomus Lysimachia nemorum Ranunculus ficaria Maianthemum bifolium Rhamnus catharticus Malus sylvestris Ribes nigrum Melampyrum pratense Ribes rubrum Melandrium dioicum Ribes uva-crispa Melica uniflora Rosa arvensis Mercurialis perennis Rosa pimpinellifolia Mespilus germanica Rosa rubiginosa Milium effusum Rosa spp. Moehringia trinervia Rosa tormentosa Mycelis muralis Rubus caesius Myrica gale Rubus fruticosus coll. Narcissus pseudonarcissus Rubus idaeus Neottia nidus-avis Rumex sanguineus Ophioglossum vulgatum Salix aurita Orchis mascula Salix caprea Orchis purpurea Salix cinerea Origanum vulgare Salix repens

Sambucus nigra Sambucus racemosa Sanicula europaea Scirpus sylvaticus Scrophularia nodosa Sedum telephium Senecio ovatus Serratula tinctoria Solidago virgaurea Sorbus torminalis Stachys officinalis Stachys sylvatica Stellaria holostea Stellaria neglecta Stellaria nemorum Stellaria uliginosa Succisa pratensis Tamus communis Teucrium scorodonia Thelypteris palustris Torilis japonica Ulex europaeus Vaccinium myrtillus Veronica montana Viburnum lantana Viburnum opulus Vicia sepium Vinca minor Viola odorata Viola palustris Viola reichenbachiana / Viola riviniana Viscum album

Appendix 4: Total list of found species. group species abbreviation goal species Herb Achillea millefolium Ach mil no Herb Aegopodium podagraria Aeg pod no Herb Ammi majus Amm maj no Herb Anagallis arvensis Ana arv no Herb Anthriscus caucalis Ant cau no Herb Anthriscus sylvestris Ant syl no Herb Apium nodiflorum Api nod no Herb Arabidopsis thaliana Ara tha no Herb Arctium minus Arc min no Herb Arctium pubens Arc pub no Herb Arctium spp. Arc spp no Herb Artemisia vulgaris Art vul no Herb Athyrium filix-femina Ath fil yes Herb Barbarea vulgaris Bar vul no Herb Bellis perennis Bel per no Herb Brassica napus Bra nap no Herb Calystegia sepium Cal sep no Herb Capsella bursa-pastoris Cap bur no Herb Cardamine hirsuta Car hir no Herb Centaurea jacea Cen jac no Herb Chamerion angustifolium Cha ang yes Herb Chenopodium album Che alb no Herb Chelidonium majus Che maj no Herb Chenopodium polyspermum Che pol no Herb Chrysanthemum segetum Chr seg no Herb Chrysanthemum vulgare Chr vul no Herb Cirsium arvense Cir arv no Herb Cirsium palustre Cir pal no Herb Cirsium vulgare Cir vul no Herb Clinopodium acinos Cli aci no Herb Convolvulus arvensis Con arv no Herb Convolvulus spp. Con spp. no Herb Daucus carota Dau car no Herb Epilobium hirsutum Epi hir no Herb Epilobium palustre Epi pal no Herb Equisetum arvense Equ arv no Herb Erysimum orientale Ery ori no Herb Euphorbia helioscopia Eup hel no Herb Fagopyrum esculentum Fag esc no Herb Filipendula ulmaria Fil ulm no Herb Fumaria capreolata Fum cap no Herb Galium aparine Gal apa no Herb Galium palustre Gal pal no Herb Galeopsis tetrahit Gal tet no

group species abbreviation goal species Herb Galium verum Gal ver no Herb Geranium dissectum Ger dis no Herb Geranium endressii Ger end no Herb Geranium lucidum Ger luc no Herb Geranium pusillum Ger pus no Herb Geranium pyrenaicum Ger pyr no Herb Geranium robertianum Ger rob no Herb Geranium spp. Ger spp no Herb Geum urbanum Geu urb yes Herb Glechoma hederacea Gle hed no Herb Hedera helix Hed hel yes Herb Helianthemum nummularium Hel num no Herb Heracleum sphondylium Her sph no Herb Hypericum maculatum Hyp mac yes Herb Hypericum tetrapterum Hyp tet no Herb Iris pseudacorus Iri pse no Herb Juncus effusus Jun eff no Herb Juncus inflexus Jun inf no Herb Lamium purpureum Lam pur no Herb Lapsana communis Lap com yes Herb Lathyrus pratensis Lat pra no Herb Laurus nobilis Lau nob no Herb Leucanthemum vulgare Leu vul no Herb Lonicera periclymenum Lon per yes Herb Lotus spp. Lot spp no Herb Luzula spp. Luz spp no Herb Malva spp. Mal spp no Herb Matricaria discoidea Mat dis no Herb Medicago lupulina Med lup no Herb Myosotis discolor Myo dis no Herb Petasites hybridus Pet hyb no Herb Phragmites communis Phr com no Herb Plantago lanceolata Pla lan no Herb Plantago major Pla maj no Herb Polygonum aviculare Pol avi no Herb Polygonum convolvulus Pol con no Herb Polygonum persicaria Pol per no Herb Potentilla anserina Pot ans no Herb Potentilla reptans Pot rep no Herb Primula spp. Pri spp no Herb Prunus spinosa Pru spi yes Herb Prunella vulgaris Pru vul no Herb Ranunculus acris Ran acr no Herb Ranunculus repens Ran rep no Herb Ranunculus sardous Ran sar no Herb Ranunculus sceleratus Ran sce no Herb Rheum rhaponticum Rhe rha no

group species abbreviation goal species Herb Rorippa nasturtium-aquaticum Ror nas no Herb Rosa canina Ros can no Herb Rosa rubiginosa Ros rub yes Herb Rubus fruticosus Rub fru yes Herb Rumex acetosa Rum ace no Herb Rumex crispus Rum cri no Herb Rumex obtusifolius Rum obt no Herb Scolopendrium vulgare Sco vul no Herb Scrophularia auriculata Scr aur no Herb Scrophularia nodosa Scr nod yes Herb Scrophularia spp. Scr spp no Herb Senecio jacobaea Sen jac no Herb Senecio vulgaris Sen vul no Herb Sisymbrium officinale Sis off no Herb Sium latifolium Siu lat no Herb Solanum dulcamara Sol dul no Herb Sonchus arvensis Son arv no Herb Sonchus asper Son asp no Herb Stachys arvensis Sta arv no Herb Stachys palustris Sta pal no Herb Stachys sylvatica Sta syl yes Herb Stellaria graminea Ste gra no Herb Stellaria holostea Ste hol yes Herb Stellaria media Ste med no Herb Taraxacum spp. Tar spp no Herb Trifolium pratense Tri pra no Herb Trifolium repens Tri rep no Herb Tussilago farfara Tus far no Herb Typha latifolia Typ lat no Herb Urtica spp. Urt spp no Herb Veronica anagallis-aquatica Ver ana no Herb Veronica arvensis Ver arv no Herb Veronica chamaedrys Ver cha no Herb Veronica persica Ver per no Herb Vicia cracca Vic cra no Herb Vicia sepium Vic sep yes Herb Viola arvensis Vio arv no Herb Viola spp. Vio spp no Shrub Acer pseudoplatanus Ace pse no Shrub Aesculus hipocastanum Aes hip no Shrub Buddleja davidii Bud dav no Shrub Buxus spp. Bux spp. no Shrub Carpinus betulus Car bet no Shrub Chamaecyparis nootkatensis Cha noo no Shrub Corylus avellana Cor ave yes Shrub Cotoneaster lacteus Cot lac no Shrub Crataegus spp. Cra spp yes

group species abbreviation goal species Shrub Fraxinus excelsior Fra exc no Shrub Ilex aquifolium Ile aqu yes Shrub Larix spp. Lar spp no Shrub Ligustrum vulgare Lig vul yes Shrub Prunus laurocerasus Pru lau no Shrub Prunus spinosa Pru spi yes Shrub Ribes spp. Rib spp. no Shrub Salix caprea Sal cap yes Shrub Sambucus spp. Sam spp yes Shrub Sorbus aucuparia Sor auc no Shrub Sorbus intermedia Sor int no Shrub Sorbus spp. Sor spp no Shrub Symphoricarpos albus Sym alb no Shrub Taxus baccata Tax bac no Shrub Ulex europaeus Ule eur yes Shrub Ulmus procera Ulm pro no Tree Acer campestre Ace cam no Tree Acer platanoides Ace pla no Tree Acer pseudoplatanus Ace pse no Tree Aesculus hipocastanum Aes hip no Tree Alnus cordata Aln cor no Tree Alnus incana Aln inc no Tree Alnus spp. Aln spp no Tree Betula pendula Bet pen no Tree Betula pubescens Bet pub no Tree Betula spp. Bet spp. no Tree Chamaecyparis nootkatensis Cha noo no Tree Fagus sylvatica Fag syl no Tree Fraxinus excelsior Fra exc no Tree Larix spp. Lar spp no Tree Malus spp. Mal spp no Tree Malus sylvestris Mal syl yes Tree Picea abies Pic abi no Tree Pinus sylvestris Pin syl no Tree Populus canescens Pop can no Tree Prunus avium Pru avi no Tree Quercus cerris Que cer no Tree Quercus petraea Que pet no Tree Quercus robur Que rob no Tree Quercus rubra Que rub no Tree Salix alba Sal alb no Tree Salix caprea Sal cap no Tree Tilia platyphyllos Til pla no Tree Tilia spp. Til spp no Tree Ulmus minor Ulm min no Tree Ulmus procera Ulm pro no Tree Ulmus spp. Ulm spp. no

Appendix 5: Subset of 45 hedges.

the bad group the good group hedge number of goal species owner hedge number of goal species owner 2 4 Denis 49 11 James 6 3 Denis 110 10 Frank 12 4 Denis 111 11 Frank 24 4 Denis 117 11 Frank 27 3 Denis 118 10 Frank 29 3 Denis 119 10 Frank 31 3 Denis 120 10 Frank 34 4 Denis 121 11 Frank 41 2 Denis 124 11 Frank 65 4 James 125 12 Frank 95 2 community 127 11 Frank 97 4 community 128 11 Frank 107 4 community 131 11 Frank 108 4 community 132 10 Frank 122 4 Frank 133 10 Frank 153 4 Eamonn 139 10 Eamonn 179 3 others 146 10 Eamonn 181 3 others 156 11 Bobby 189 4 others 157 11 Bobby 194 3 others 159 10 Bobby 165 10 Bobby 174 12 others 175 10 others 180 10 others 182 10 others