Prunus serotina removal by sheep in the Kennemerduinen dune

Transcription

Faculty of Earth and Life Sciences, VU Amsterdam
MSc Environment and Resource Management
Prunus serotina removal by sheep in the Kennemerduinen
dune reserve: biodiversity effects and cost-effectiveness
Richa Nanne│2121581
External supervisor: Ir. H. Kivit - Senior advisor nature and recreation - PWN
Supervisor: Prof. Dr. J.E. Vermaat – Earth Sciences and Economics at the Faculty of Earth and Life
Sciences - VU Amsterdam
Date: 06-08-2012
Research Project: 468017
18 ects
2
Foreword
This project was completed during a three month research placement at PWN regional office Zuid, in Overveen.
This project constitutes the final research thesis component of the Environment and Resource Management
(ERM) masters programme at the VU-Amsterdam. This report is intended to offer more insight in the costeffectiveness of sheep grazing management and its influence on biodiversity and P.serotina eradication. This
report can be seen as an intention for further research. The information provided is of interest for organisations
that manage natural areas dealing with alien invasive species or who are interested in sheep grazing management
as a biological management method.
Hubert Kivit is biologist and working at the department Nature and Recreation at PWN Water Company NorthHolland. Annually, PWN provides 105 milliard l. drinking water to private households, companies and
institutions in North-Holland. PWN develops purification techniques that are adopted on a world wide scale,
PWN also manages the coastal dune area between Bergen and Zandvoort (www.pwn.nl).
This report has been composed in cooperation with the advice and guidance of Dr. Jan Vermaat and Hubert
Kivit. Jan Vermaat is researcher at IVM Institute for Environmental Studies and professor in Earth Sciences and
Economics at the Faculty of Earth and Life Sciences. IVM is established in 1971 and is the oldest academic
environmental research institute in the Netherlands. The mission of IVM is to contribute to sustainable
development and care for the environment through scientific research and education (www.ivm.vu.nl).
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Abstract
Prunus serotina (Black cherry) is introduced successful in Western Europe as an ornamental shrub. Since the
1980’s it is considered a threat to native species and biodiversity. Sheep grazing management is practiced in
National Park Zuid- Kennemerland (NPZK) in order to eradicate the species. In this study the effect of sheep
grazing management on P. serotina is measured comparing differences in viability, growth and seedling
establishment between grazed areas and areas excluded from sheep grazing management. Field measurement
took place along transects situated in densely covered areas. The different parameters measured are ‘viability of
stems’, ‘type of use’, ‘ringed’, ‘number of leaves’, percentage of use’, diameter’, ‘height’, weight’, ‘coverage
percentage’ and ‘number of stems’. The effects of sheep grazing management are divided in long- and short term
effects. The long term effects cover the influence of sheep on P. serotina from 2008 to 2012. The short term
effects embrace the influence of sheep on P. serotina within one week of grazing. The effect of P. serotina on
biodiversity is assessed from vegetation relevés using the Tansley abundance score. The cost-effectiveness of the
sheep grazing management was estimated using scientific literature and information provided by PWN.
Sheep were found to be effective browsers of P. serotina influencing viability towards the desired effect, namely
eradication. This conclusion comes forward both in the short term- and long term analysis. All parameters used
to measure viability were influenced and all parts of the plant are consumed by sheep. In the short term
especially, the number of leaves are affected. The influence of sheep grazing management on the bark was not
noticeable in the short term. As a response to grazing activities, P. serotina was found to grow faster in height.
However the diameter and weight did not increase after introduction. Sheep also reduce the coverage of P.
serotina in the short and long term because of leaf removal. Trampling might also affect this parameter. Even in
the short term the herd diminished the cover of P. serotina. This reduction does not imply that the number of
individual trees decreases. Reduction in cover occurs mainly as a result of the reduction of branches and leaves.
The number of stems per tree did not change in the short term. The effect of sheep grazing management on
growth and seedling establishment was limited. Intensive grazing did not influence biodiversity within NPZK
generally whereas there are differences between the reference areas mutually and the grazed sites mutually.
Sheep grazing management does have a negative influence on indicator species since they decreased in cover
and number. The costs of sheep grazing management are constant over time and independent of coverage
percentage of P. serotina. In the long term sheep grazing management becomes expensive in comparison with
other methods as the costs of the other eradication methods diminish through time. For eradication, long term
investment is needed which makes this type of management relatively expensive, especially when P. serotina is
present with a low coverage percentage.
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Table of contents
1
1.1
1.2
1.3
2
2.1
2.2
2.3
2.4
2.5
2.6
3
3.1
3.2
3.3
3.4
3.5
4
4.1
4.2
4.3
4.4
5
5.1
5.2
5.3
6
Introduction .....................................................................................................................................................................................6
P. serotina in National Park South-Kennemerland ............................................................................................................................6
Research question ..............................................................................................................................................................................7
Chapter outline ..................................................................................................................................................................................7
Background ......................................................................................................................................................................................8
The introduction of P. serotina .........................................................................................................................................................8
Invasiveness characteristics of P. serotina ........................................................................................................................................9
Sheep grazing management and P. serotina .....................................................................................................................................9
Possible positive and negative effects of grazing on P. serotina .....................................................................................................10
The influence of grazing by large herbivores on biodiversity .........................................................................................................11
Hypotheses .....................................................................................................................................................................................12
Methodology ..................................................................................................................................................................................13
Study area ......................................................................................................................................................................................13
Data collection ................................................................................................................................................................................13
Data collection on biodiversity .......................................................................................................................................................13
Data collection on P. serotina .........................................................................................................................................................14
Statistical analyses ..........................................................................................................................................................................16
Results ...........................................................................................................................................................................................17
Long term influence of sheep grazing management on P. serotina ................................................................................................17
4.1.1
Viability ........................................................................................................................................................................17
4.1.2
Population characteristics ..............................................................................................................................................20
4.1.3
Coverage percentage of P. serotina ...............................................................................................................................22
Short term influence of sheep grazing management on P. serotina ................................................................................................24
4.2.1
Short term influences of sheep grazing management ....................................................................................................24
The influence of sheep grazing management on biodiversity .........................................................................................................26
Costs of P. serotina eradication ......................................................................................................................................................30
4.4.1
General costs of sheep grazing management .................................................................................................................30
4.4.2
Costs of sheep grazing management on P. serotina eradication ....................................................................................31
4.4.3
Costs of manual excavation ...........................................................................................................................................32
4.4.4
Costs of chemical eradication ........................................................................................................................................34
4.4.5
Costs of mechanical excavation ....................................................................................................................................34
4.4.6
Costs of excavation using horses ...................................................................................................................................35
Discussion ......................................................................................................................................................................................36
The influence of sheep grazing management on P. serotina ..........................................................................................................36
Biodiversity ....................................................................................................................................................................................39
Cost effectiveness ...........................................................................................................................................................................40
Conclusions ...................................................................................................................................................................................42
References .....................................................................................................................................................................................43
Appendix I
Appendix II
Appendix III
Appendix IV
Appendix V
Appendix VI
Appendix VII
Appendix VIII
Appendix IX
RD Coordinates transects ..............................................................................................................................................45
Parameters and motivation ............................................................................................................................................46
Costs of sheep grazing management PWN ....................................................................................................................47
Costs of sheep grazing management ..............................................................................................................................48
Costs of P. serotina eradication .....................................................................................................................................49
Overview statistics biodiversity ....................................................................................................................................50
Overview plant species inventoried ...............................................................................................................................52
Overview statistics P. serotina .....................................................................................................................................54
Statistical background short term analysis......................................................................................................................64
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1
Introduction
1.1
Prunus serotina in National Park South-Kennemerland
Invasive alien species are nonindigenous species that are spreading uncontrollably causing damage to their new
environment. They have the ability to establish themselves in new habitats, master indigenous species and
dominate their new environment. Local genes, ecosystems and biodiversity are threatened this way while they
are crucial to sustain the ecosystem services they provide. In the Netherlands, the invasive alien species Prunus
serotina (Black cherry) is especially a threat to local biodiversity (Aptroot et al, 2006)
P. serotina also became an invasive alien species in National Park South-Kennemerland (NPZK) from the 1990s
onwards, following the crash of the rabbit population. In 2008 P. serotina was driven back manually (contractor
KIPP) by sawing and the use of the chemical herbicide Glyphosate, focussing on the removal of older seed
carrying trees. Young trees were removed on smaller scale by volunteers and foresters. Main goals of removal of
P. serotina are prevention of seed dispersal and reduction of the current population. Since the 1st of September
2008 a herd of 100 sheep was deployed, owned by PWN Water Company of North-Holland (PWN). The aim of
this herd was to detract the attention of visitors from manual removal of P. serotina because that brings a lot of
visual damage to the treated area. During the first weeks of grazing it turned out that sheep also graze on P.
serotina which has lead to a management strategy adjustment. Manual repression was replaced for sheep grazing
management at sites with extremely high densities of young plants. To combat P. serotina at these sites
effectively, sheep need to graze this species multiple times hence a circulation scheme is used. In 2011 the herd
had grown to 250 sheep grazing on P. serotina three times per year. A temporary fence is used to keep the sheep
in place in dense P. serotina vegetated areas for one to two weeks per area. From April-September 6 areas with a
total surface of 30 ha are managed this way. During this period P.serotina has leaves which are browsed by the
sheep. Expectations are that the quantity of P. serotina will not diminish without the presence of sheep. Other
herbivores within NPZK are roe deer, fallow deer, konik ponies, shetland ponies and scottish highlanders
(Anonymus, 2009).
Secondary goals of PWN using sheep grazing management are reduction of shrubs on playgrounds and
management of relations with other organisations (Bloemendaal municipality) by lending the herd. Furthermore,
in 2012 mowing subsidy will end and sheep can partially replace the function of mowing activities. The grazing
regime of the herd is managed as follows: the herd grazes on P. serotina from April until September. P. serotina
contains hydrocyanic acid from which sheep can die. To complement the diet of the sheep, the herd moves to
other grazing areas four times per week. During the winter the herd is used for reduction of other shrubs and
sheep grazing management is complemented with manual control, especially so on play grounds and dense
vegetated habitats. Larger trees that aren’t grazed effectively enough by sheep are removed to prevent them
maturing and dispersing seeds. This management strategy needs to be continued until dispersed seeds lose their
viability, this takes 3-4 years. Seeds will always enter NPZK being eaten and dispersed by birds (§2.2). Until
2012 mowing of P. serotina by the contractor and volunteers continues. After this period PWN is responsible for
the development of P. serotina within NPZK (Anonymus, 2009).
Given the importance of P. serotina eradication, studying the influence of sheep grazing management on
biodiversity and on growth, mortality and reproduction of this species seems opportune. The amount of research
done on the cost-effectiveness compared to other management methods with the same purpose is scarce or not
available at all. This also accounts for the effectiveness and the effects of sheep grazing management on
biodiversity and P. serotina (Anonymus, 2009).
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1.2
Research questions
The purpose of this study is to evaluate the effectiveness and impact of sheep grazing management on P.
serotina and on biodiversity. Furthermore, a comparison of the cost-effectiveness of sheep grazing management
with other management methods is made. Therefore, the research questions are formulated as follows:
1: What influence does sheep grazing management have on local densely vegetated P. serotina in National park
Zuid- Kennemerland in the short- and long term?
2: What influence does sheep grazing management have on biodiversity in National Park Zuid- Kennemerland?
3: How cost-effective is sheep grazing management in comparison with other management methods used for
combating P. serotina?
To answer these questions a literature study, using scientific literature and literature provided by PWN has been
carried out. To complement the literature study, data about the influence sheep grazing management has on
biodiversity and P. serotina is gathered in the field and analysed statistically.
1.3
Chapter outline
This thesis is divided into the following chapters: chapter two provides background information about the
invasive characteristics of P. serotina and the motives behind introduction of this species in Europe. This chapter
also discusses the impact grazing by large herbivores might have on P.serotina growth, spread and seedling
reestablishment. A conceptual framework is included that represent possible effects and uncertainties of this
management strategy. Also, the impact of sheep grazing management on biodiversity is briefly discussed.
Chapter three describes the methods used in this report with respect to the field work done, the statistical analysis
and the literature study. An overview is provided of the research area, the locations of the transects and sheep
grazed areas, reference areas and transects. Chapter four represents the results of the statistical analysis
concerning biodiversity and P. serotina eradication and the literature study concerning the cost-effectiveness.
Chapter five discusses the results of this study. Chapter six summarises the main findings of this research and
includes possible recommendations for the future.
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2
Background
2.1
The introduction of P. serotina
Due to the expansion of trade and the increase in human mobility, dispersion of invasive alien species increased
dramatically during the last 200 years. The impact of these species become increasingly visible over the whole
world. Researchers try to identify species specific traits that account for successful invasion and try to link these
characteristics to environmental attributes. But the characteristics of these successful species often appear to be
idiosyncratic and vary under different circumstances. Research is done on the spreading range and ecological
characteristics of P. serotina within areas where this species is planted intentionally. However, research on the
population dynamics of P. serotina within areas where it has appeared unintentionally is scarce (Vanhellemont et
al, 2009).
Alien invasive woody plant species altering native plant communities cause conservation problems all over the
world within both forest and non-forest habitat types (Vanhellemont et al, 2009). P. serotina is native to North
America and was introduced as an ornamental shrub in Europe in the 17th century. During the 19th century the
use of P. serotina converted from an ornamental purpose to timber production (even on nutrient poor soils like
dunes) and soil amelioration purposes (Godefroid et al, 2003). Afforestation practises with alien species occurs
with cultural, political, economic and even ecological motives (Richardson, 1998). P. serotina was used as a
forest tree because this species enriches the soil it grows on due to fast decomposition of the leaves. P. serotina
was also used for fire prevention and was often combined with the Scottish pine (Pinus sylvestris) used for
timber production. Intensive planting of this species continued until the 1950s of the last century. During the
1980s suppression of P. serotina started to take place due to its recognition as a threat to ecosystems and
biodiversity and after introduction of subsidies. Furthermore, people believed that complete eradication was
possible. But the opposite effect occurred, management methods like uprooting or cutting stimulated
establishment of this species (Uiterweerd, 2008). From that time period, P. serotina was also named “wood pest”
(Godefroid et al, 2003).
During the last centuries P. serotina invaded forests, woody habitat types, and poor soils which often contained
rare and vulnerable native species with a less competitive character (Deckers et al, 2005). Invasion of P. serotina
does not occur in North America due to repressive function of the fungi Pythium spp. Pythium spp. causes
‘damping-off disease’ which causes growth reduction or mortality of infected trees. This fungi is not present in
European soils. Suggested is that the release of P. serotina from its native soil pathogens causes unrestrained
spreading in Europe (Reinhart et al, 2005). At present, P. serotina is spreading through most of Europe, from
France to Italy and from the North of France to Poland, Hungary and Rumania. As P. serotina is a gapdependent species, the major control of dispersion within Europe exists of restricted light availability during
sprouting (Godefroid et al, 2003). At the moment, P. serotina has not yet reached its potential range within
Europe. Seed dispersal is believed to be a limiting factor (Vanhellemont et al, 2009).
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2.2
Invasiveness characteristics of P. serotina
Due to the presence of invasive alien species basic ecological processes (e.g. hydrological processes), chemical
processes and disturbance dynamics can be influenced. This can lead to undesirable effects on local communities
and populations due to an increase of homogeneous vegetation and a decrease of species richness (Deckers et al,
2005). P. serotina is a semi-shade tolerant tree species with a high fruit production rate, even when growing in
forest undergrowth. Fruit production varies between years and is related to the growing area and tree size. The
higher the tree in open landscapes, the higher the rate of seed production. There is no correlation between the
height of trees and seed production of trees growing in forest undergrowth. Most of the fruit falls within a
distance of 5 m from the tree (Vanhellemont et al, 2009) but in general P. serotina is known as a bird dispersed
tree with opportunistic characteristics. When seeds (eaten by birds) fall and germinate in the soil its starts
colonising and spreading. P. serotina is also a great competitor for nutrients, water and light (Godefroid et al,
2003). It is considered an aggressive alien invasive species because its presence complicates forest management
significantly. This species also suppresses the development of deciduous forests and herbs (Vanhellemont et al,
2009). Adaptability is a typical trait of these invasive species. P. serotina grows rapidly because of its resistance
to frost, drought, diseases, its fast seed production and growth rate, avian seed dispersal, its tolerance towards a
wide variety of climatic conditions, low soil requirements, long life span and high germinative power (Deckers
et al, 2005). Individual plants can actively resprout during all live stages. To be more specific, three traits has
been reported by Godefroid (2003) explaining the invasion success of P. serotina: (1) the first characteristic is
called the ‘Oskar syndrome’, i.e. the ability to pre-empt space of closed canopy forests undergrowth by its long
living seed bank. Seeds are able to remain in the soil for up to four years. These seeds entered the forest through
dispersion by birds and/or mammals, (2) ‘the sit and wait strategy’ i.e. once a canopy gap occurs, seedlings start
growing rapidly to capture resources such as nutrients, water and light. Young sprouts fill in the gaps and
outcompete other native species, (3) ‘the Alice behaviour’ i.e. the ability to perpetuate on a local scale. At first,
growth of other species slows down due to diminished nutrients, water and light availability. Secondly, stumps
and roots sprout during their whole lifetime. To survive periods of threat or scarcity, P. serotina stores nutrients
in its roots making regrowth of sprouts possible. Resprouting even occurs after the tree has been felled. The
invasion success depends on different spatial factors. An area needs to contain suitable characteristics in which
these species is able to establish and survive. Natural enemies might suppress establishment and/or spreading but
are mostly not present in the new habitat (Deckers et al, 2005).
Intensive, costly and time consuming eradication strategies exist but success rates are variable. Further insight
into the effectiveness and cost-effectiveness of eradication strategies is needed for development of an effective,
sustainable and cost-effective management method.
2.3
Sheep grazing management and P. serotina
NPZK is grazed by both cattle (konik ponies, shetland ponies and scottish highlanders) and wild herbivores
(rabbits, roe deer and fallow deer). Even though the diet of these herbivores partially overlaps, the influence on
P. serotina is limited. To combat it ecologically the decision was made to intensify grazing on this species
specifically through the introduction of sheep. Grazing of two or more species of livestock separately or together
within the same area is also known as multi-species grazing. The main characteristic of this strategy is that
consumption of one specific plant species (e.g. P. serotina) can be managed due to dietary overlap. A related
benefit of multi-species grazing, which is relatively more important with presence of cattle, is the consumption
of toxic plants. Both sheep and goat are known to graze on plant species containing toxic substances. Although
goats are known as browsers, sheep can be very efficient browsers as well. Especially when availability of other
plant species than P. serotina is limited. According to Animut and Goetsch (2008) especially the green, living
parts of shrubs and grasses are preferred against dead and woody material (Animut and Goetsch, 2008). Beside
the introduction of cattle in NPZK, wild animals also forage on P. serotina. The roe deer is known to forage on
the leaves and twigs, hares feed on young twigs and rabbits on the bark during wintertime when other food is
scarce. In the case of P. serotina only withered leaves are poisonous for cattle whereas fresh, young leaves do
not cause harm (Uiterweerd, 2008).
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2.4
Possible positive and negative effects of grazing on P. serotina
Grazing in general could have positive and negative effects on P. serotina and biodiversity. Desired effects are a
decrease or even disappearance of P. serotina, a more open canopy and an increase in species richness (increase
of biodiversity). Possible effects of sheep on P. serotina and biodiversity are shown in a conceptual framework
(figure 1) based on the framework of Uiterweerd (2008). Browsing of trees leads directly to a decrease in
biomass with possible positive effects through tree mortality. Due to an increase in light availability as a result of
less dense vegetation biodiversity may increase. But light availability also improves circumstances to grow and
for seedling reestablishment. Trampling can destroy vegetation and creates new open spaces for regeneration.
This effect also enhances new growing opportunities for native plant species. Treading could also lead to direct
physical damage to seeds and seedlings and reduce the amount of plants including P. serotina to mature. This
effect can be both positive and negative for biodiversity within a grazed area (Uiterweerd, 2008). The influence
of trampling by sheep is probably less significant than trampling of cows or horses because of their lower weight
and smaller hooves. Soil compaction as a result of trampling by sheep reaches depths of about 2-4 cm while soil
compaction by cattle is 10-15 cm (Elbersen et al, 2003). Cattle might eat the seeds which die due to mastication.
Surviving seeds disperse and dung seems to be a suitable regeneration site (Uiterweerd, 2008) for both P.
serotina and other species. The amount of seasonal fruits and berries in the diet of sheep is limited which limits
seed dispersion as well (Animut and Goetsch, 2008). If these positive effects of grazing outweigh the negative
effects is part of this study. Besides the introduced cattle in NPZK, wild animals also forage on P. serotina
(Uiterweerd, 2008).
Figure 1: Conceptual framework including possible effects of sheep grazing management on P. serotina and biodiversity. The light coloured
arrows indicate the relation between sheep grazing management, P. serotina and biodiversity which are not taken into account in this
research. The pluses indicate positive effects of grazing on P. serotina and biodiversity, the minuses indicate negative effects of grazing on
P. serotina and biodiversity. Positive and negative effects refer to effects on P. serotina or other plant species in general, these effects do not
refer to management goals. The symbols represented in red are part of the hypotheses of (Uiterweerd, 2008).
10
Research of Vanhellemont (2009) compared the development of P. serotina between Ossenbos forest and
Liedekerke forest. Both forests are located in the Belgium and grow on poor sandy soils. In the first forest the
density of ungulates (red deer, roe deer and wild boar) was relatively high and in the latter forest ungulates were
absent. Results show that P. serotina successfully invaded the Ossenbos forest while it dispersed much slower in
Liedekerke forest. For colonization patterns of the native species Q. rubra the results were contrasting. Q. rubra
showed unsuccessful regeneration in the Ossenbos forest and regenerated successfully in Liedekerke forest. A
concluding hypotheses of this study suggest that high herbivore pressure favours colonization of P. serotina
above those of native shrub and tree species. Other research (Kuiters and Slim, 2002) more or less confirms this
hypothesis. Their research shows low regeneration densities of native species due to seed consumption while
consumed seeds of P. serotina are defecated unharmed. The study of Vanhellemont (2009) also shows that P.
serotina is able to flourish under high ungulate density when other sources of food are present. The authors of
this study argue that grazing management to control P. serotina might have the opposite effect because large
herbivores might facilitate invasion of this species.
Although the results of previous studies are rather negative, there is one significant aspect that needs to be taken
into account. Grazing intensity of sheep within NPZK varies highly during the year. Each grazing area is grazed
intensively two or three times a year for a short period. This method is also known as peak-grazing management
(in Dutch: piek-, stoot-, of drukbegrazing). The general aim of this method is to create suitable growing places
for desired plant species to increase biodiversity (Elbersen, 2003). The aim of this method in NPZK is to exhaust
P. serotina (sprouts/young plants) until it diminishes and ultimately disappears.
2.5
The influence of grazing by large herbivores on biodiversity
Invasive alien species are known as the second major threat to biodiversity on a world wide scale. The primary
threat is habitat fragmentation (Vanhellemont et al, 2009). Introduction of large herbivores in conservation areas
is widely used as a management tool to enhance and preserve biodiversity. Although research on this topic in
general is available, there is still high uncertainty about the effects of large herbivores. Sheep directly affect
species richness by biomass removal and by creation of open spaces (Kohyani et al, 2008; Aptroot et al, 2006).
Light intensity increases due to a more open canopy which creates opportunities for the establishment of less
dominant species. Dung increases nutrient availability within limited space while the amount of available
nutrients on grazed places decreases. Alternatively, grazing might have negative effects on species richness
where the regrowth of plants is limited as a result of limited soil resources (Kohyani et al, 2008; Kooijman and
Smit, 2001). Other reported negative effects range from devastation to continuing impoverishment (Aptroot et al,
2006).
The influence of grazing on biodiversity also depends on the spatial scale. At a smaller scale corresponding to
individual plants and surrounding plants, grazing seems to have a positive effect independent of soil conditions.
Local colonisation increases as a result of the creation of gaps by trampling and increased light availability. Also,
local extinction of dominating species takes place resulting in growing opportunities for less combative species.
However, a decline in biodiversity is expected on a larger scale as a result of selective grazing in which grazing
tolerant species flourish. On the other hand, dominant species might be suppressed by grazing, resulting in an
increase of less dominant plant species. Due to suppression of dominant species, especially grasses, there should
be an increase of species (mainly herbs) with low cover within the grazed areas compared to areas excluded from
grazing. This hypothesis is tested in paragraph 4.2. Also, the local presence of rare species increases when
dominant plant species are suppressed through the introduction of large herbivores (Kohyani et al, 2008). Cattle
grazing in complex dune areas might influence biodiversity positively because it seems to stall succession from
pioneer- towards shrub vegetation which was retained by rabbits until the 70s and 80s. When spatial variation of
vegetation is high, large herbivores may graze in the areas with low densities characterized by vulnerable plant
species (Aptroot et al, 2006). In coastal dune areas encroachment of dominants grasses, partially resulting from
atmospheric nitrogen deposition and the collapse of the rabbit population and through eutrophication, has a
negative influence. As most grasses are intolerant to grazing, the introduction of large herbivores positively
effects species richness (Smit et al, 2000). This effect is confirmed by a study of Van Wingerden (2001) showing
stagnation in grass growth in a dune area at Vlieland. Using cattle to manage grass dominated areas lead to a
11
reduction of standing crop, an open vegetation structure and favours growth of smaller (pioneer) species. Also
mosses and lichens which disappeared from grass encroached vegetation may return (Kooijman and Van der
Meulen, 1996; Kohyani et al, 2008). Even local biodiversity that is already high might increase due to the
introduction of large herbivores (Van Wingerden et al, 2001). Research on the effects of larger ungulates on
forest rejuvenation on sandy soils shows that they prefer deciduous tree species above conifers which start
dominating. Their influence on succession is minor due to the preference for dominated species. Especially
deciduous trees growing in small open spaces in the forest were grazed intensively resulting in primary
rejuvenation of coniferous trees (Kuiters and Slim, 2000). Increased light availability due to a more open canopy
results in an increase in biodiversity and even reestablishment of disappeared lichen species (Kooijman and
Smit, 2001). Reestablishment of lichens also occurs in open dune areas as a result of extensive grazing (Van
Wingerden et al, 2001). In coastal areas shrub growth is curtailed and development of forest is expected to
decelerate. The end succession stage will consist of a partially open dune area (Van Wingerden et al, 2001).
2.6
Hypotheses
Thus, taking this all into consideration, for the present study the hypotheses are stated as follows: short term,
directed and intensive sheep grazing will not; (1) reduce the leaf canopy of P. serotina, when it reduces growth
and enhances mortality, (2) increase space available for vegetation, which will not affect P. serotina samplings
and older plants that grow in or above the canopy of the accompanying vegetation. But grazing should increase
seedling reestablishment opportunities for P. serotina. (3) Grazing should increase seedling reestablishment of
all other plant species that germinate into open soil. (4) Preferential grazing may alter abundance of the
accompanying vegetation.
12
3
Methodology
3.1
Study area
This research was carried out in National Park South-Kennemerland (NPZK), partially managed by PWN Water
Company of North-Holland. NPZK is situated in the coastal dune area north of Zandvoort and south of IJmuiden
in North-Holland (figure 2). NPZK exists of ca. 3.800 ha. containing different habitat types including (wet) dune
valleys, dune forests and dune grasslands which are valued for their rare plant- and animal species and
biodiversity. NPZK is protected by the EU Habitat- Directive and proposed as Natura 2000 site. The main goals
of NPZK are sea defence, the maintenance and development of nature, landscape and cultural history,
communication, (scientific) research, recreation and education (www.pwn.nl). P. serotina is currently considered
a threat to biodiversity in some parts of NPZK (Deckers et al, 2005). As mentioned in paragraph 1.1, NPZK
contains wild populations of roe deer, fallow deer and rabbits. Domesticated cattle grazing in NPZK are scottish
highlanders, konik- and shetland ponies.
N
Figure 2: Overview of NPZK
3.2
Data collection
Data concerning the cost-effectiveness analysis were collected by carrying out a literature study, using scientific
literature only. Area specific information was provided by PWN. The cost-effectiveness of sheep grazing
management was estimated in € per ha. per year. This outcome was compared with other management strategies
aspiring the same objective also expressed in € per ha. per year.
The study examines two environmental impacts of sheep grazing management. The influence of sheep grazing
management on biodiversity and P. serotina was researched using scientific data from literature and data
collected in the field. Field data concerning this research project was collected from April until May 2012, but
the research will continue for PWN until September 2012.
3.3
Data collection on biodiversity
For data collection on biodiversity the inventory method Tansley was applied. The advantage of using Tansley is
that it is a quick and suitable method for estimating the abundance per plant species (Van Katwijk and ter Braak,
2008). A disadvantage is its subjectivity because the number of individuals of a species were estimated. Besides,
Tansley is a relatively rough method. Minimalization of differences between grazed area and reference areas was
13
achieved by restricting the tansley relevé to the habitat type ‘dune grassland’. In the present study a more
specific Tansley method is applied (table 1) (Inberg et. al., 2008). Tansley will be used in 6 areas grazed by
sheep as well as in the 5 reference areas (figure 3). These areas are more or less comparable to the grazed areas
taking into account hydrological and geomorphological circumstances and habitat type. The former management
strategies (to eradicate P. serotina before grazing took place) were comparable to the grazed- and non grazed
sites before sheep grazing started. The grazing intensiveness by other herbivores is the same. Furthermore, the
grazed areas and its references were inventoried within the same week. By applying this method, differences in
species appearance due to time influences were restricted. The tansley relevés were restricted to the habitat type
‘dune grassland’ to increase the reliability of comparison between grazed and non grazed areas. The size of the
inventoried parts within the grazing areas was not defined specifically but covers approximately 1 ha. per area.
In the past, the grazed sites probably contained a higher coverage percentage of P. serotina and higher individual
plants (up to 1m). These characteristics were used as a criterion for the introduction of sheep grazing
management. This implies that the initial state of the research areas were not exactly the same. Both the research
areas and reference areas are grazed by scottish highlanders, rabbits, konik- and shetland ponies with the same
intensity throughout most of the year. Highlanders and ponies were excluded from the fenced areas for 2-4
weeks when the sheep were grazing within these areas. The tansley relevés were set out shortly before sheep
grazing begins in one specific area. The collected field data of the grazed- and non-grazed areas were compared
to study the influence of sheep grazing management on biodiversity in the long term.
Table 1: Inventory method Tansley, applied to research the influence of sheep grazing management on P. serotina (Inberg et. al., 2008).
Code
1
2
3
4
5
6
7
8
9
Description
Sporadic
Rare
Scarce
Local numerous
Numerous, distributed regularly
Local very numerous
Very numerous, distributed regularly
Species co-dominates
Species dominates
3.4
Data collection on P. serotina
Explanation
The area contains a few individuals (1-3)
The area contains a small number of individuals (4-10)
The area contains some groups of individuals, no more than 10-20
20-100 individuals
20-100 individuals
 100 individuals
 100 individuals
Together with other species
 50% cover
For the inventory of P. serotina, six transects were set out in the areas grazed by sheep and five in the reference
areas excluded from sheep grazing management. P. serotina was measured by applying the Line Intercept
method. This method consist of counting and measuring each individual P. serotina which hits a line
(Coulloudon, 1999). Shortly before and shortly after sheep grazing, the abundance and dimensions of P. serotina
along the transect were measured. The gained data were used to measure the long- and short term effects of
sheep grazing management. Sheep grazing started in 2008, to investigate the long term accumulated affect of
former grazing sessions, each transect was measured before grazing started. To investigate the long term affect
of sheep grazing management on P. serotina, the data obtained from the transects within the grazing areas were
compared to the data obtained from transects in the reference areas. To research the short term affects, the grazed
transects were measured shortly before and after grazing. Between these measurements, the transects were
grazed intensively for one week. Using this strategy, the influence of sheep on P. serotina within one week
(short term) was investigated. Data obtained within the grazing area and its reference area was gathered within
the same time period/week to limit changes through time (e.g. plant growth and death). By applying this method,
the development of P. serotina with and without sheep grazing management was researched. During field work
one of the reference transects (reference 2 of ‘Manege’) was included in the adjacent grazing area. This transect
was measured (to investigate the long term influence of sheep grazing management) before the first period of
grazing took place this year. It is not valid to use this reference in the future since it is already influenced by
sheep. The reference is replaced by another for measurements after this study. Nevertheless, the accuracy of the
data obtained along this reference is less reliable than the data obtained along the other four references.
14
10 different parameters were measured per individual tree. For a comprehensive overview of these parameters
and their motivation, see appendix II. Shrub mortality was used as an indicator of viability, divided in living,
dying and dead trees. The viability was measured to investigate if the amount of dying, dead and living trees
differs between the grazed and non grazed sites. This parameter included some subjectivity because viability
could be determined only by looking at the exterior of the tree. Each individual tree was measured 2 times during
this research. Therefore it was not possible to cut or break the stem to see whether it was alive. This parameter
was tested in the field by breaking some branches of trees growing near the transect. When a tree was dead it
was easy to break and the inside of the stem was coloured brown. Trees were marked as dying when some parts
of it were dead. To complement this indicator other parameters were measured; i) type of use, ii) percentage of
use and iii) number of leaves. The type of use indicates which part of the plant was affected by sheep grazing
divided in ‘branch-, leaves-, and bark eaten’. During field work, the type of use was determined by looking at
which part was affected mostly by grazing. If the bark of one tree was more affected than the branches, the type
of use was divined as ‘bark eaten’. The percentage per individual tree used or influenced by grazing included
some subjectivity. When was partially eaten it was difficult to estimate how much of the tree (leaves and
branches) was gone. This subjectivity was minimized by noting the visible damage of the plant (e.g. what
percentage of the branches, leaves and bark was affected). When the branches were noticed to be affected, some
of the leaves might have been eaten. This subjectivity results in a higher percentage of branches eaten than
leaves eaten. The percentage of use might be higher than described in this thesis. The type of use has been
measured to research the influence of sheep on P. serotina in the long and short term and if this type of grazing
is effective for eradication. The parameter ‘percentage of use’ is also part of viability, P. serotina probably needs
to be grazed with a certain intensiveness before grazing becomes effective. The parameter ‘number of leaves’
has been estimated by selecting one branch, counting the amount of leaves on that branch, then count the number
of branches and multiply this with the number of leaves. The parameter ‘height’ was not applied as a parameter
for viability because the 0-situation is not comparable since the grazed sites are selected on the height and
coverage percentage of P. serotina.
Plant dimensions were investigated measuring i) diameter of the stem, ii) height of each tree and iii) weight of 12
plants along each transect. To quantify the effectiveness of sheep grazing management i) the number of sprouts
resprouting off one stump and ii) the percentage of cover was measured. The cover was defined by considering a
surface of 2m2 along each site of the transect line. Of this surface the cover of P. serotina was estimated. Each
transect contained 12-13 estimations, the average of these estimations was noted as the cover of P. serotina
along a transect. The plants weighed were selected on their height varying between 15-20 cm. The plant
dimensions might be influenced by former management since the grazed sites where selected on the coverage of
P. serotina. The most dense areas became grazed areas. Trees higher than one meter were removed manually or
mechanically, this accounts for the grazed areas and the control areas.
Each transect was 25 m long and was marked with two poles. The beginning of the transect was identified with a
green pole, the end was marked with a blank pole. The RD (Rijksdriehoek) coordinates of each transect
(appendix I) were measured with GPS (Global Position System) with 5 m accuracy, represented in figure 3. The
transects of the grazing areas 5 and 6 have the same reference due to scarce presence of P. serotina in the
surrounding area. These areas have comparable characteristics in terms of habitat type (both grazed- and non
grazed transect exist of dune grassland), geomorphological and hydrological circumstances. The reference
transects where also selected on their relatively high abundance of P. serotina. The abundance of P. serotina
within the grazed areas was comparable to P. serotina within the non grazed areas. The parameters used to
investigate the effectiveness of sheep grazing management on P. serotina are the same for each transect.
15
5 6
5+6
4
3
3
4
2
2
1
2
3
4
5
6
Name
Zevenbosjes
Manege
Eiland Noord
Eiland Zuid
Noorderweg west
Noorderweg oost
1
1
Figure 3: The black numbers represent the order hence the areas are grazed throughout the year, starting with the most southern grazing area.
The white numbered areas represent references for the grazing areas concerning biodiversity inventories. Grazing area 5 and 6 have one
reference area and one reference transect.
3.5
Statistical analyses
For primary data storage and processing Microsoft Excel 2007 was applied and for further analysis SPSS
statistics 20 for Windows. The Chi-Square test was used to determine whether nominal variables were dependent
on each other. This method was applied in combination with crosstabs to compare viability, growth and
reestablishment between sheep grazed areas and their references. To investigate the direct influence of sheep
grazing management in the short term, the Chi-Square test and the Paired T-Test were applied. The Paired TTest tests whether the averages of two related groups (two measurements within the same area) differ (Huizingh,
2006) and is applicable if a comparison contains measurements of different variables over time. Table 2 gives an
overview of the measured parameters, the statistical method used and its applicability.
Table 2: overview of the different parameters, the corresponding subjects and the statistical methods used
Subject
Timing
Parameters
Method used
Biodiversity
Comparison of biodiversity between
Inventory shortly before
Cover of species
Chi-Square
grazed and non-grazed areas in the long term
grazing starts
Prunus serotina
Difference in viability between grazed and non-grazed Inventory shortly before
Viability of stems,
Chi-Square
areas in the long term
grazing starts
Type of use, Ringed,
Number of leaves, % of use
Difference in growth between grazed and non-grazed Inventory shortly before
Diameter, Height, Weight
Chi-Square
areas in the long term
grazing starts
Difference in seedling reestablishment between grazed Inventory shortly before
Coverage %
Chi-Square
and non-grazed areas in the long term
grazing starts
Number of stems
Difference in plant damage of grazed areas in the short Inventory shortly before and Type of use, Ringed,
Chi-Square
term (shortly before and after grazing)
after grazing
Number of leaves,
Paired T-test
% of use, % of cover
16
4
Results
4.1
Long term influence of sheep grazing management on P. serotina
The parameters are measured prior to grazing to investigate the long term affect of sheep grazing management.
During each week, starting at the 1st of April, one grazed area and its reference was measured. The first area
(Zevenbosjes) was measured during the first week of Aril, the second area was measured during the second week
of April etc. Differentiation is made between the grazed areas to get an impression of the impact of sheep
grazing management in these areas specifically. The outcomes can be seen as guidelines for future management
of P. serotina. For further insight in the statistical background, see appendix VIII.
4.1.1
Viability
Viability of P. serotina is analysed using the parameters ‘viability of stems’, ‘type of use’, ‘ringed’, ‘number of
leaves’ and ‘percentage of use’. The first parameter ‘viability of stems’ measures if individual P.serotina
seedlings and shrubs are alive, dying or dead. Results are represented in figure 4. Grazed transects contain 172
living individual seedlings and shrubs, 113 dying individuals and 39 dead individuals (53%, 34%, 12%
respectively). Transects excluded from grazing contain 401 living, 38 dying and 1 dead individual (91%, 9%,
0,2% respectively). This difference proves to be significant (P < 0,05). The viability of P. serotina is also
significant between the different transects in the grazed areas (P = < 0,05) (figure 5). The transects
‘Zevenbosjes’, ‘Manege’ and ‘Eiland Noord’ contain high percentages of living plants (93%, 60% and 74%
respectively). Most of them are young plants between 6-30 cm of height (§4.3.2). The transects ‘Eiland Zuid’,
‘Noorderweg Oost’ and ‘Noorderweg West’ contain a high number of dying (66%, 40% and 5%) and dead
plants (17%, 27% and 21%). Using regression analysis, this variable is also compared with the variables
‘ringed’, ‘type of use’ and ‘number of leaves’ to test whether these parameters influence viability. Regression
analysis shows that all of these have a significant influence on viability (P = < 0,05 in all cases).
Figure 4: difference in number of P.serotina individuals and their
viability concerning the grazed areas (left) and the non grazed
areas (right)
viability along each grazed transect
The type of use between the grazed- and reference areas differs significantly (P = < 0,05) (fig. 6). In the grazing
areas 14% of the trees are not used and 86% of is affected by sheep. Of the grazed trees, 12% is debarked, 84%
are ‘branch eaten’ and 4% are ‘leaf eaten’. In the areas excluded from grazing these numbers account for 41% of
the trees are not affected by sheep and 59% shows grazing marks (of other herbivores). Of the grazed trees 0,5%
are debarked, 97% are branch eaten and 3% are leaf eaten. The type of use also differs significantly between de
grazed transects (P = < 0,05) (figure 7). At ‘Zevenbosjes’, 21% of the trees measured is not affected by sheep
grazing. Of the trees grazed, 6% is debarked and 94% is branch eaten, there are no leaves eaten. Along the
17
transect of ‘Manege’ 23% of the trees does not show signs of grazing. Among the trees grazed, 2% is debarked,
92% is branch eaten and 6% is leaf eaten. Within the grazed areas ‘Éiland Noord’ 21% if the plants is not grazed.
Of the grazed trees 10% is debarked, 89% are branch eaten and 1% are leaf eaten. Along the transect of ‘Éiland
Zuid’ 29% of the trees are not grazed by sheep, 9% of the affected trees are debarked, 84% are branch eaten and
7% are browsed on their leaves. At ‘Noorderweg Oost’, 52% of the trees are not affected, among the grazed
trees 6% is debarked, 90% are eaten by their branches and 4% are affected on their leaves. At ‘Noorderweg
West’ 10% of the trees are not grazed. Of the grazed trees 13% are debarked, 87% are branch eaten and there are
no trees browsed on their leaves.
type of use concerning the grazed areas (left) and the non grazed
areas (right)
type of use along each grazed transect
The parameter ‘ringed’ is measured because this way of browsing could have a more direct effect on the viability
of a plant than the other parameters used to measure viability. Along the grazed transects, 7% of the trees
measured are ringed while 0,5% are ringed along the references (figure 8). The difference in ringing between the
grazed transects and its references is significant (P = < 0,05). This parameter also differs significantly between
the grazed transects mutually (P = < 0,05) (figure 9). There are no plants ringed along the transects of
‘Zevenbosjes’ and ‘Manege’ whereas the others contain a relative low number of plants ringed (10% at ‘Eiland
Noord’, 22% at ‘Eiland Zuid’, 5% at ‘Noorderweg Oost’ and 10% at ‘Noorderweg West’). These bar charts
confirm the impression that sheep browse on the bark of P.serotina effectively. Furthermore, comparison of this
variable with the variable ‘viability’ shows that ringed plants are often dying or dead (P = < 0,05).
Figure 8: difference in number of P.serotina individuals ringed
between the grazed areas (left) and the non grazed areas (right)
Figure 9: difference in number of P.serotina individuals ringed
between the grazed transects
18
‘Browsing on leaves’ is a parameter that did not appear in the previous analysis although it is part of the
parameter ‘type of use’. The parameter ‘number of leaves’ gives more insight into the effect of sheep grazing
management on viability. It is difficult to see whether the leaves are eaten or not because they (or a part of the
leaf) are not present anymore. As described in §3.4, leaves eaten might be part of the parameter ‘branch eaten’.
The grazing effect of sheep on the leaves can be measured by comparing the grazed areas with their references,
this accounts for all parameters measured. The number of leaves is measured by counting (or estimating) the
leaves present at the vertical slope of the transect. The difference in number of leaves appears to be significant (P
= < 0,05) between the grazed transect and the references (figure 10). Between April- June, the trees at the grazed
sites contain 2 leaves on average. Along the references, the trees contained 7 leaves on average. The trees along
the references contain 3,5 times as much leaves as the trees along the grazed transects. Along the grazed
transects, 49% of the individual trees where bare. The number of leaves of one individual tree ranged from 0-14
while this was 0-90 for the references. There are more trees with a high number of leaves along the references
compared to the grazed transects. Also, the number of trees with a small number of leaves is higher in de grazed
transects. Generally this means that sheep browse on the leaves effectively. The difference in browsing on leaves
also varies significantly between the grazed transects (P = < 0,05) (figure 11). Trees growing at ‘Noorderweg
Oost’ have a relatively high number of leaves (ranging from 1-14 leaves per tree) in comparison with the other
transects (ranging from 1-10 leaves per tree). The trees along this transect and ‘Eiland Noord’ account for half
(51%) of the total amount counted. The field work started in the first week of April, at that time there were no
leaves present so that it was not possible to measure this parameter for ‘Zevenbosjes’. This transect is not
included in the bar chart.
Figure 10: difference in number leaves between P.serotina
individuals between the grazed areas (left) and the non grazed
areas (right)
Figure 11: difference in number of leaves between P.serotina
individuals between the grazed transects
The parameter ‘percentage of use’ defines how much of the tree has been damaged by sheep (including all parts
of the tree growing above the ground). Also in this case, it is difficult to estimate this parameter when branches
or leaves are eaten and gone which makes comparison with the references necessary (figure 12). Along the
grazed transects 51% of the individual trees are affected by sheep for 0-5%, 47% are affected for 5-25%, 2% are
affected for 25-75% and 0,3% are affected for 75-100%. Along the references 74% of the trees are affected for
0-5% and 26% for 5-25%. This difference is significant (P = < 0,05) showing that sheep grazing management
influences the percentage of use towards the expectations. Namely, browsing of P.serotina within the grazed
area. This parameter also varies significantly between the grazed sites (P = < 0,05) (figure 13). Most (84% and
76%) of the plants of ‘Noorderweg Oost’ and ‘Noorderweg West’ are grazed for 1-5% while most (62%, 77%
and 68%) of the plants growing in the areas ‘Manege’, ‘Eiland Noord’ and ‘Eiland Zuid’ are browsed more
intensively (5-25% usage). This parameter is also compared to the parameters ‘type of use’, ‘ringed’ and
‘number of leaves’ to get an impression of their mutual influence. The former two parameters do influence the
19
percentage of use significantly (P = < 0,05). The number of leaves does not influence the percentage of use (P =
> 0,05).
Figure 12: difference in percentage of use of P.serotina
individuals between the grazed areas (left) and the non grazed
areas (right)
Figure 13: difference in percentage of use of P.serotina
individuals between the grazed transects
4.1.2
Population characteristics
Figure 14 shows the difference in diameter of all individual plants measured along the grazed- and non grazed
sites. Although this figure suggest that the non grazed areas contained higher numbers of seedlings with a small
stem diameter in comparison with the grazed sites, this difference was not significant (P = > 0,05). This also
account for the median diameter which is 0,3 cm for both the grazed- and reference transects. However, the
diameter does differ (P = < 0,05) between the grazed transects mutually (figure 15). All transects contain a high
number of individual seedlings with a small diameter ranging from 0,1-0,5 cm. The areas ‘Zevenbosjes’, Eiland
Noord’, and ‘Noorderweg Oost’ contain plants with a larger diameter varying between 1-3 cm. The overall
conclusion is that sheep grazing management does not influence the diameter of P. serotina growing on a large
scale within NPZK.
Figure 14: difference in diameter of P. serotina individuals within
the grazed (left) and non grazed areas (right)
Figure 15: difference in diameter of P. serotina individuals
between grazed areas
The measured plants along the grazed transects are significantly higher than the ones growing along the non
grazed transects (P = < 0,05) (figure 16). The plants growing along the grazed transects have a median height of
22 cm and the trees along the reference transects have a median height of 19 cm. At the grazed sites 88% of the
individual trees have a height between 1-50 cm and 12% has a height between 50-161 cm. In the reference areas
95% of the trees has a height between 1-50 cm and 5% varies between 50-161 cm. There is also a significant
20
difference in height between the grazed transects mutually (P = < 0,05) (figure 17). At ‘Zevenbosjes’, 81% of the
trees have a height between 1-50 cm, 17% between 51-100 cm and 2% between 101 and 120 cm. At ‘Manege’
96% have a height between 1-50 cm, 4% between 51-100 cm. At ‘Eiland Noord’ 57% have a height between 150 cm, 31% between 51-100 cm and 7% between 101-120 cm. At ‘Eiland Zuid’ 95% have a height between 1-50
cm and 5% between 51-100 cm. At ‘Noorderweg Oost’ and ‘Noorderweg West’ all plants measured have a
height between 1-50 cm.
Figure 16: difference in height of P. serotina individuals between
the grazed and non grazed areas
Figure 17: difference in height P. serotina individuals between
the grazed areas mutual
There was no significant difference in weight (of trees between 15-20 cm of height) between the grazed areas
and the areas excluded from sheep grazing management (P = > 0,05) (figure 18). Nevertheless, there is a
significant difference in weight between the grazed transects mutually (P = < 0,05) (figure 19). Relatively heavy
trees are weighed at the site of ‘Manege’ (weighing up to 39 gr.) in comparison with the trees weighed at
‘Zevenbosjes’ and ‘Eiland Noord’ (weighing up to 2 gr.). The weight of the plants growing in the other grazing
areas varies between 0,3-6 gr.
Figure 18: difference in weight of P. serotina individuals between
the grazed and non grazed areas
Figure 19: difference in weight of P. serotina individuals between
the grazed areas
The correlation of height versus diameter showed an increasing trend (figure 20). The highest regression
coefficient is found for the areas grazed by sheep and the lowest for the areas excluded from sheep grazing
management (respectively 54 for the grazed areas and 40 for the non grazed areas). These results imply that
grazed P.serotina grows faster than P.serotina excluded from sheep grazing management. This can be seen as
21
confirmation for the results of the parameter ‘height’ (figure 16). The relationship between height and diameter
is significant (P= < 0,05). This means that the diameter depends on the height of a plant and that sheep do not
significantly affect this parameter. The correlation of weight versus diameter results in a slightly increasing trend
(figure 21) with the highest regression coefficient for grazed areas implying that P.serotina individuals of the
sampled height growing in sheep grazed areas weigh slightly more than individuals growing in reference areas
but this effect proves to be insignificant.
120,0
180,0
Grazed
Non grazed
160,0
100,0
140,0
120,0
Tree height (cm)
Tree height (cm)
80,0
60,0
40,0
100,0
80,0
60,0
40,0
20,0
20,0
y = 22,787ln(x) + 55,045
R² = 0,5122
0,0
0,0
0,5
1,0
1,5
2,0
2,5
3,0
y = 17,506ln(x) + 47,256
R² = 0,5085
0,0
3,5
0,0
1,0
Stem diameter (cm)
2,0
3,0
4,0
Stem diameter (cm)
Figure 20: Correlation of individual P. serotina height versus diameter subject to grazed areas and non grazed areas.
180,0
120,0
Grazed
Non grazed
160,0
100,0
Tree height (cm)
Tree height (cm)
140,0
80,0
60,0
40,0
120,0
100,0
80,0
60,0
40,0
20,0
y = -0,0197x2 + 0,8504x + 22,85
R² = 0,0077
0,0
0
10
20
30
40
y = 0,226x + 21,616
R² = 0,0032
20,0
0,0
50
0
5
10
15
20
25
30
Weight (gr)
Weight (gr)
Figure 21: Correlation of individual P. serotina height versus weight subject to grazed areas and non grazed areas.
4.1.3
Coverage percentage of P. serotina
The coverage percentage along the grazed transects is 5% on average. The coverage percentage along the
transects excluded from sheep grazing management is significantly higher with 9% on average (P = < 0,05)
(table 3). Overall, P. serotina cover of grazed- and reference transects differs mutual. This parameter varies
between 2% (Eiland Zuid) and 10% (Zevenbosjes) (P = < 0,05).
Table 3: the cover per grazed- and non grazed transect
Transect
Cover
Reference
10%
Reference Zevenbosjes
Zevenbosjes
7%
Reference Manege
Manege
4%
Reference Eiland Noord
Eiland Noord
2%
Reference Eiland Zuid
Eiland Zuid
3%
Reference Noorderweg Oost and West
Noorderweg Oost
5%
Noorderweg West
5%
Average
Cover
8%
12%
8%
5%
10%
9%
22
The number of stems per individual tree is also used as a variable for growth (figure 22). The number of trees
with one stem is equal among the grazed sites and its references mutual. Although the figure shows a higher
number of trees with one stem in the areas excluded from sheep grazing management than in the grazed areas,
there is no marked difference (P = > 0,05).
400
One stem
350
Multiple stems
Number of individuals
300
250
200
150
100
50
0
Grazed
Non grazed
Transect
Figure 22: difference of number of stems of plants between the
grazed- (left) and non grazed areas (right)
Both grazed- and reference areas contain equal percentages of trees with multiple stems (raging from 2 to >6
stems) (figure 23). Within the grazed areas 39% of the trees with multiple stems have 2 stems, 31% has 3 stems,
10% have 4 stems, 6% have 5 stems, 7% have 6 stems and 7% of the trees have more than 6 stems (up to 17
stems counted). Within the areas excluded from sheep grazing 49% of the trees with multiple stems have 2
stems, 20% has 3 stems, 10% have 4 stems, 4% have 5 stems, 7% have 6 stems and 10% of the trees have more
than 6 stems. The difference in the number of stems per tree is not significant (P = > 0,05).
40
2 stems
Number of individuals
35
3 stems
4 stems
30
5 stems
25
6 stems
20
> 6 stems
15
10
5
0
Grazed
Non grazed
Transect
Figure 23: difference in number of stems of plants between the
grazed- (left) and non grazed areas (right)
23
4.2
Short term influence of sheep grazing management on P. serotina
The parameters are tested on their significance, differentiating between two grazing moments with one week
time intervals. For further insight in the statistical background, see appendix IX.
4.2.1
Short term influences of sheep grazing management
The variables ‘ringed’, ‘height’ and ‘percentage of use’, did not change significantly within one week of
intensive grazing in the researched areas (P = > 0,05), (appendix IX). A significant difference did occur between
the number of leaves per tree before (2 leaves per tree) and after grazing (1 leaf per tree), (P = < 0,05) (figure
24). Before grazing started, the number of trees without leaves was relatively high already but increased after
sheep grazing took place. The number of trees without leaves became twice as high after one week of grazing.
The number of trees with high numbers of leaves was higher before grazing started. The statistical analysis
showed that the number of trees with 0-3 leaves increased after grazing while the number of trees with four
leaves and more decreased. This outcome shows that sheep are excellent browsers.
The diameter is part of this analysis to see whether plant growth accelerates or decelerates in the short term. The
difference in diameter is just significant (P = 0,044) (figure 25). The number of trunks with a small diameter (up
to 0,3 cm) increased after one week of grazing, this is probably the result of growth of seedlings during the
spring. Sheep grazing management does decrease the number of leaves per trees. Also, the percentage of cover
(figure 26) does significantly diminish after sheep grazing (P = < 0,05). Especially high coverage percentages
have decreased and the number of transects with mediocre coverage percentages (of 5%) increased. There is a
marked difference noticed in the type of use in the short term (P = < 0,05) (figure 27). The number of trees that
are not affected by grazing decreased with 59%. The number of trees whose bark or branches were affected did
barely change while the number of trees that were browsed for their leaves quadrupled. The difference in
viability is also significant in the short term (P = < 0,05) (figure 28). The number of living trees decreased by
11%, dying trees increased by 67% and dead trees increased by 21% after one week of grazing.
The Principal component analysis is used to test which of the measured parameters are correlated to each other.
In the short term, correlated parameters are ‘viability of stems’ with ‘number of leaves’ and ‘diameter’ with
‘height’. Principal component analysis shows that when the diameter grows 1 mm, height increases with 6 cm.
Figure 24: difference of number of leaves per individual tree
before and after grazing
Figure 25: difference in diameter per individual tree before
and after grazing
24
Figure 26: difference in percentage of cover before
and after grazing
Figure 27: difference in type of use of individual
trees before and after grazing
Figure 28: difference in viability of the trees
measured before
25
4.3
The influence of sheep grazing management on biodiversity
To get an impression of the structural differences, the number of species between the grazed areas and the
references are represented in figure 29. The grazed areas ‘Noorderweg Oost and West’ are combined because
they have the same reference. These areas contained 54 and 53 species respectively. Three of the five grazed
areas do contain slightly more species (up to seven) than their references while two grazed sites contain slightly
less species (less than seven). Furthermore, this figure shows an increasing trend in numbers of species from the
first areas inventoried to the last areas. These differences in total number of species does not prove to be
significant since P = > 0,05.
60
Grazed
Reference
Number of species
50
40
30
20
10
0
Zevenbosjes
Manege
Eiland
Noord
Eiland Zuid Noorderweg
Transect Name
Figure 29: number of species in each Tansley relevé represented in pairs; grazed and non grazed areas.
To get an impression of the difference in cover of P. serotina between the grazed- and non grazed areas, see
table 4. This table shows that the cover at ‘Eiland North’ differs from its reference. In the grazed area, P.
serotina is distributed regularly (20-100 individuals). Within the reference, this species is locally present in high
numbers (>100 individuals). There are no differences found in cover between the other areas inventoried.
Table 4: Cover of P. serotina within the research areas
Area
Zevenbosjes
Manege
Eiland Noord
Eiland Zuid
Noorderweg Oost and West
Cover
of P. serotina
Local very numerous
Very numerous, distributed
regularly
Local very numerous
Local very numerous
Cover of P. serotina
Reference
Zevenbosjes
Reference Manege
Reference
Eiland
Noord
Reference
Noorderweg Oost and
West
Local very numerous
Local very numerous
Local very numerous
Local very numerous
In total, 121 different species were observed in the grazed areas and its references (see appendix VII) (with an
average of 47 species in the grazed areas and 45 species in the non grazed areas). For all calculations the ChiSquare (x2) test was applied. There is a significant (P = < 0,05) difference between the variables ‘cover’ and
‘area’. This means that the cover of the plant species inventoried differs per area (grazed and excluded from
grazing) (figure 30). In comparison to the other areas, the grazed area ‘Zevenbosjes’ scores high on species (13
species respectively) with sporadic appearance (1-3 individuals inventoried) including mosses and pioneer
species. This areas also has a relatively high number of species with ‘rare’-, ‘scarce’-, and ‘very numerous,
26
distributed regularly’ appearance. ‘Zevenbosjes’ has a low number of species distributed under the other scales
of Tansley. All other areas score low on species with sporadic appearance. The non grazed ‘Reference
Zevenbosjes’ has a lot of species with scarce appearance (10-20 species) and a low number of species that are
locally numerous or dominating. The grazed area ‘Manege’ scores high (16 individuals) on species with scarce
appearance (10-20 species), this also applies to its reference (13 species). ‘Manege’ has a low number of species
with sporadic-, locally very numerous-, and dominating appearance which also applies to its reference. ‘Eiland
Noord’ contains a high number of species with rare- and scarce appearance (12 and 16 species respectively) and
a low number with sporadic- and dominating cover, this also applies to its reference. The grazed area ‘Eiland
Zuid’ has a relatively high number that are distributed locally or regularly (10 species locally and 11 species
regularly) and a low number that have a sporadic-, rare-, or dominating coverage. This also applies to its
reference. The coverage of species with a locally numerous or regularly numerous appearance is also high within
the grazing areas ‘Noorderweg Oost’ (18 and 11 species) and ‘Noorderweg West’ (13 and 13 species). The
reference areas of ‘Noorderweg’ are characterized by species that are distributed regularly throughout the area.
Figure 30: species number in each cover class for each Tansley relevé; grazed areas on the left, non grazed areas (referred to as ‘reference’)
on the right.
This result is also noticed when clustering the grazed areas and the references and comparing these variables
with cover (figure 31). The grazed areas contain 18 plant species with a sporadic cover while the reference areas
represent only four with a sporadic cover. There is no difference concerning ‘rare species’ and ‘species
dominating’ (24 rare- and 3 dominating species in the grazed- and non grazed areas respectively). There is a
slight difference between ‘scarce’ and ‘local numerous’ species (49 and 43, 38 and 36). The differences between
the grazed sites and the references concerning the variables ‘numerous, distributed regularly’ (36 and 43), ‘local
very numerous’ (51 and 28), ‘very numerous, distributed regularly’ (48 and 39) and ‘species co-dominates’ (14
and 7)) are larger although the results do not prove large enough to be significant (P = 0,073).
27
Figure 31: species number in each cover class including the grazed areas (left) and the non grazed areas (right)
To gain more information about the effects of sheep grazing management on biodiversity the plant species
inventoried are clustered into a ‘moss’, ‘herb’, ‘shrub’, ‘tree’ and ‘grass’ layer. A comparison is made between
the grazed and non grazed areas (figure 32). This comparison also does not prove to be significant (P = > 0,05)
which means that sheep grazing management does not influence biodiversity within the different layers of the
research areas.
80
Moss
70
Grass
Herbs
60
Number of species
Shrubs
Trees
50
40
30
20
10
0
Grazed
Non grazed
Area
Figure 32: species number in each layer representing the grazed areas (left) and the non grazed areas (right)
The inventories took place in the week before the sheep started grazing, the reference areas were inventoried the
same day to exclude environmental changes through time. There is no data gathered to investigate influences of
sheep grazing management in the short term. The effect of sheep grazing management could differ per plant
species. For more insight in the statistical background see appendix VI. Appendix VII provides an overview of
the plant species inventoried between Aril and May 2012.
28
PWN provided a list with plant species that represent the quality of dune grasslands. The higher the number and
abundance of these species, the better the state of the dune grassland. In total there are 121 plant species
inventoried containing 15 indicator species (12%). To investigate the affect of sheep grazing management on
these species, an overview of these species and their abundance is provided (table 5). In total, 17 indicator
species are inventoried. The cover of ‘Noorderweg’ represents the average cover of the grazed sites
‘Noorderweg Oost and West’, to make comparison with their references possible. Both the grazed sites and the
references contain 15 indicator species. The average cover of the indicator species within the grazed sites is
lower (3 = 10-20 individuals) than in the references (4 = 20-100 individuals). There is no difference in the
abundance of indicator species between ‘Zevenbosjes’ and its reference, but the cover is clearly higher in the
reference. The grazed area ‘Manege’ contain more indicator species than its references but the cover of these
species is higher in the reference area than at the grazed site. ‘Eiland Noord’ and ‘Eiland Zuid’ contain only 2-3
indicator species while their references contain 5-6. Also the cover of these species is clearly higher within the
references. ‘Noorderweg’ contains 8 indicator species, its reference has 7 but with a higher average cover. In
total, the references contain a higher number of indicator species (27) than the grazed sites (25).
2
1
1
6
3
2
3
2
3
2
3
5
Ref.
Noorderweg
Oost and West
Noorderweg
Oost and West
Ref.
Eiland
Zuid
5
Eiland Zuid
Ref.
Noord
2
Eiland
Eiland Noord
Ref. Manege
Manege
Area
Sonchus arvensis
Viola curtisii
Lithospermum officinale
Thymus pulegioides
Viola canina
Leontodon saxatilis
Sanguisorba minor
Ajuga reptans
Vicia lathyroides
Viola odorata
Arabis hirsuta subsp. hirsuta
Viola hirta
Myosotis ramosissima
Verbascum densiflorum
Scrophularia vernalis
Polygonatum odoratum
Anisantha tectorum
Ref.
Zevenbosjes
Zevenbosjes
Table 5: overview of indicator species and its cover per grazing area and its reference
Scientific name
3
3
4
3
4
4
4
5
4
5
3
7
2
3
1
2
3
2
2
3
5
5
2
5
7
5
6
7
7
6
5
1
4
3
3
2
5
7
Dutch
name
Akkermelkdistel s.l.
Duinviooltje
Glad parelzaad
Grote tijm
Hondsviooltje
Kleine leeuwentand
Kleine pimpernel
Kruipend zenegroen
Lathyruswikke
Maarts viooltje
Ruige scheefkelk
Ruig viooltje
Ruw vergeet-mij-nietje
Stalkaars
Voorjaarshelmkruid
Welriekende salomonszegel
Zwenkdravik
29
4.4
Costs of P. serotina eradication
Spread of P. serotina within Dutch and European nature reserves is considered as an increasing problem that
nature conservation organisations are dealing with (Straatsma and Jansen, 2005). There is no default eradication
method practiced. The different methods used have their own advantages and disadvantages in terms of
efficiency, damage to the direct environment, effectiveness and costs. For organisations dealing with the
management of natural areas it is of interest to gain insight into the costs of the various methods practiced. The
management methods ‘ringing’ and ‘thinning’ of trees are disregarded because they proved to be ineffective to
eradicate or control spreading. This also holds for biological eradication using a native pathogenic fungus
Biochon. Use of Biochon proved to be moderately effective under very specific circumstances. In practice
Biochon seemed difficult to use and disappeared from the market. Introduction of Pythium spp. is not an option
due to possible undesired side effects (Straatsma and Jansen, 2005).
The use of shadow providing trees is not explained in this research because this method for eradication of
unwanted species is not applicable to P. serotina eradication (Elbersen, 2003).
4.4.1
General costs of sheep grazing management
At PWN, the fixed costs of sheep grazing management are estimated on a basis of reviews of internal meetings
and a cost/benefit overview of 2011 (table 6). The shepherd receives travel expenses of €0,17 per km with a
maximum of 80 km. The shepherd also receives a monetary compensation of €22,50 per hour. The expenses for
the shepherd are the largest part of the costs made, amounting for €22.478,76 in 2011 (63% of the total costs).
During the winter the herd is kept permanently on one place which results in lower costs. During this period
expenses consist of controlling the herd on health and basic needs. Supervision of the herd takes approximately
three hours on a daily basis annually. During the summer the herd grazes three times per week under supervision
of a paid shepherd because it is more reliable than using volunteers only. Furthermore, the herd needs to graze
under supervision five times a week for five hours to be eligible for a subsidy of €8,500. The herd is also active
within the borders of Bloemendaal municipality which accounts for an income generation of €10,800. In 2011,
the costs for food including grass silage and chunk accounted for €7.276,64 (20%). Cost concerning health care
are relatively high: €3.459,32 (10%). The costs made for food and healthcare vary due to their dependence on the
weather and resilience of the herd. Though, these costs do return annually and are considered fixed in this report.
Other incurred costs are shearing of sheep twice a year accounting for €2 per sheep (2%). Volunteers are also
part of sheep grazing management, they place fences and function as shepherd for four days per week. They
receive travel compensation of €0,17 per km (4%). Table 4 provides a overview of the general annual cost made
by PWN. For an overview of all cost and revenues made by PWN in 2011, see appendix III. Notice that the costs
of sheep grazing management are not specifically made for combating P. serotina.
Table 6: fixed general cost and revenues made by PWN on sheep grazing management in 2011.
Unit
Travel reimbursement shepherd
Salary shepherd
Volunteers
Food
Health
Contributions/charges
Shearing of sheep
Dutch Breeders Association 2011
Charge Animal Health Fund 2011
Charge 2010
Total costs
Subsidy
Bloemendaal municipality
Revenue
Net Total costs
Total grazed ha
Net Costs per ha. per year:
Costs/€
2.568,16
19.910,60
1.501,5
7.276,64
3.459,32
265,10
586
50,00
181,60
33,50
35.823,42
8.500
10.800
19.300
16.532,42
30
551,08
30
A study by Schouteden (2009) provides a financial overview of five Belgian companies keeping sheep for
landscape grazing management. For PWN and these Belgian companies shepherd salary is the most important
component of the total costs followed by costs for food and health. In general the cost of keeping sheep exceeds
income, in Belgium this loss is compensated by a subsidy provided by the government. This subsidy accounted
for 65% of the total income in 2009 (Schouteden, 2009). For PWN the net costs made in 2011 per sheep account
for €65,07 assuming a herd of 250 sheep. According to the study by Schouteden (2009) the total costs per sheep
accounts for €85,93 including wage costs (39%), costs on food (26%) and costs according to animal health (4%)
and excluding variable costs (vet, buildings and materials). For PWN food costs are minimized because the
sheep feed primarily on dune vegetation. Extra food is provided when natural resources are scarce due to
snowfall, these costs can be considered variable.
A study by Elbersen (2003) confirms that most of the fixed costs (in the case of foundations and an average herd
of 230 sheep) consist of wage costs (58% of the total costs), food (13%), buildings (8%) and depreciations (1%)
(figure 33). Speaking of private companies with an average herd of 370 sheep, fixed costs consist of food (29%),
buildings (6%) and depreciations (15%). Other costs including variable costs account for 20% (foundations) and
49% (private companies). The total annual costs for private companies are €74.051 which account for €175,06
per ha. per year managing 423 ha on average. For PWN the total costs per ha. per year are €551. Making a
comparison between the costs made by PWN and private companies is not realistic in this case. PWN has high
labour costs and a relative small grazing area of 30 ha. where sheep are used to graze on P.serotina primarily.
For Elbersen (2003) it was not possible to make an overview including the total costs made by foundations,
private companies and nature organisations due to a lack of data availability. This report provides such an
overview, see appendix IV (Elbersen, 2003).
Others
Elbersen 2003, the Netherlands,
private companies
Depreciations
Buildings
Source
Shearing
Elbersen 2003, the Netherlands,
foundations
Charges
Health
Food
Schouteden 2009, Belgium
Wages
PWN 2011
0
10
20 30 40 50 60 70
Percentage of total costs ⤍
80
Figure 33: overview of general costs (€/per ha/per year) made on sheep grazing management (Elbersen, 2003; Schouteden, 2009; PWN).
4.4.2 Costs of sheep grazing management on P. serotina eradication
Previous text focuses on the costs made on sheep grazing management in general. The next part concentrates on
the costs made by PWN specifically applied for P.serotina eradication. Costs of sheep grazing management with
other purposes are not taken into consideration in this section, this makes comparison with other management
methods aspiring to the same purpose possible. Costs on P.serotina eradication using sheep are the costs made
from April-September. During this time period the sheep are used to combat P.serotina exclusively. The main
fixed costs are made on travel expenses €1.428 (€13,60 per day*3 times per week*35 weeks), labour €11.812,50
(€112,50 per day* 3 times per week*35 weeks) and health care €2.328,39, they account for 77%, 6% and 14% of
the total costs respectively (figure 34). The total costs for the shepherd is €13.240,50 during the summer. The
31
other costs (with exclusion of grass silage and chunk) are divided by 52 weeks times 35 weeks (the time period
sheep consume P.serotina). The fixed net costs of P.serotina eradication using sheep accounted for €144,68 per
ha. in 2011 (table 7; figure 35).
Table 7: fixed cost and revenues made by PWN on P.serotina
eradication with sheep grazing management in 2011.
1%
2%
Shepherd
14%
Volunteers
6%
Health
Charges
77%
Shearing
Figure 34: costs of P. serotina abatement with
sheep, made by PWN in 2011
Unit
Travel reimbursement shepherd
Salary shepherd
Volunteers
Health
Contributions/charges
Shearing of sheep
Costs/€
1.428
11.812,50
1.010,63
2.328,39
178,43
394,42
Charge 2010
33,65
122,23
22,55
Fixed costs
Subsidy
Total revenue
Net result
Total grazed ha
Costs per ha. per year:
17.330,89
5.721,15
7.269,23
12.990,38
-4.340,51
30
144,68
According to a manual for sheep farming (Handboek Schapenhouderij) developed by Wageningen UR, the
annual costs of a herd of 250 sheep kept for management of natural areas is €204 per day per ha. (€25.50 per
hour including wages, travel reimbursement and overhead). The costs for keeping the herd fenced is €127.50 per
day including 5 hours of work. Then the total cost for sheep grazing management to combat P.serotina (taking
the management scheme of PWN into account) would be (€25.5 * 5 hours of work per day * 3 days per week *
35 weeks per year) €13.387,50 per ha. per year. The herd is fenced two days per week which costs (€25.5 * 3
hours of work per day * 2 days per week * 35 weeks per year) €5.355 per ha. per year. The total costs of sheep
grazing management to combat P.serotina would be €18.742,50 per ha. per year (Handboek Schapenhouderij,
2002).
500
Costs (€/ha)
450
Sheep grazing management
Regrowth 2nd year
400
Regrowth 1st year
350
Initial removal
300
250
200
150
100
50
0
0-5%
5-25%
25-50%
50-75%
75-100%
Cover
Figure 35: the cost per treatment per ha/per year of sheep grazing management to eradicate P. serotina
4.4.3
Costs of manual excavation
Scientific study by Oosterbaan (2003) provides an estimation of costs of the most effective methods practiced for
eradication of unwanted tree species, including P. serotina. These costs include primary and secondary (aftercare) eradication costs. In case of P. serotina, the seed viability is prolonged so that sprouts will germinate years
after the first treatment. Follow-up management is needed to suppress these seedlings. This estimation is based
32
on ‘Normenboek Staatsbosbeheer’ 2001-2002, including a deduction of 20% overheads and an hourly net wage
of €26,33 (Staatsbosbeheer, 2001). Revenues are disregarded although they can be considered important in
choosing a management strategy (Oosterbaan et al, 2003).
Manual excavation exists of pulling the trees out of the ground, this is only possible when trees are younger than
two years because at this point the root system is not fully developed yet. This method is only effective when
repeated on a regular basis. Important is that the roots are excavated completely during removal to prevent
further regrowth (Straatsma and Jansen, 2005). Annual cost of manual excavation depends on the cover and the
height of the tree. When individual seedling lower than one meter are growing dispersed within a certain area
(cover 0-5%), eradication costs €39 per ha. per year (figure 36). Individual seedling with low cover can be
excavated by hand. Because low numbers are present, after- care is considered unnecessary. When considering
groups of P. serotina with a cover of 5-25%, the cost of primary eradication is €130 per ha. per year. In this case
follow-up treatment is needed which costs €39 per ha. per year. At this density, seedlings probably re-establish
themselves from the roots left, covering 0-5% of the surface (Oosterbaan et al, 2003). The costs of eradication
increases when cover increases. With a cover of 25-50% the costs of the first treatment are €442 per ha. per year
including 17 hours of work. After care is needed for two years accounting for €39 per ha. per year. When
assuming a cover of 50-75% the costs per ha. per year are €1.170 including 45 hours of work. The total costs
including after-care are €1.248 per ha. per year (Staatsbosbeheer, 2001). In case of a cover of 75-100% the cost
of eradication are €1.820 per ha. in the first year, €130 per ha. in the second year and €39 per ha. in the third year
accounting for €1.989 per ha. in total. The first year after the seedlings are removed, they will re-establish with a
cover of 5-25%. The second year after removal seedlings will re-establish with a cover of 0-5%, so after-care is
needed for several years (Oosterbaan et al, 2003). As mentioned in section 2.5, the disadvantages of manual
excavation is local soil disturbance creating suitable places to grow for which after-care is needed (Straatsma and
Jansen, 2005).
Manual excavation of seedlings higher than one meter is included in this paragraph even though they probably
can’t be eradicated using sheep grazing management exclusively. This management strategy can be practiced to
complement sheep grazing management. Seedling (>1m) eradication with a cover of 0-5% costs €52 per ha. per
year including two hours of work. When the cover is 5-25% the costs are €195 per ha per year including aftercare and 6 hours of work. When seedling cover 25-50% the total costs are €689 per ha. per year including 25
hours of work. When P. serotina covers 50-75% the costs are €1.638 per ha per year including 60 hours of work.
When the cover accounts for 75-100% the costs are €2.418 per ha. per year including costs on wages (90 hours
of work) and after-care (Staatsbosbeheer, 2001).
2500
Manual excavation
Regrowth 2nd year
Regrowth 1st year
2000
Costs (€/ha)
Initial removal
1500
1000
500
0
0-5%
5-25%
25-50%
50-75%
75-100%
Cover
Figure 36: the cost per treatment per ha/per year of manual excavation to eradicate P. serotina
33
4.4.4
Costs of chemical eradication
In the past, different chemical substances (e.g. hydrochloric acid and ammonium sulphate) where used to
eradicate P. serotina. Use of these substances stopped due to health issues and glyphosate have been entered the
market. Glyphosate is sprayed or lubricated on sawn off stems (Straatsma and Jansen, 2005). Eradication of
dispersed individuals lower than one meter using chemical substances (glyphosate/Roundup) costs €30 per ha.
(figure 37). Seedlings can be sprayed with glyphosate in which after-care is not needed when performed
properly. For this calculation one working hour and 0.1 l of glyphosate is used. Because NPZK is used for the
extraction of drinking water, use of glyphosate is avoided as much as possible but was used in the past
(Oosterbaan et al, 2003). Eradication of dispersed individuals higher than one meter costs €169 per ha. per year
including 3 hours of work and the use of 0.1 l of glyphosate (Straatsma and Jansen, 2005). When P. serotina has
a coverage percentage of 5-25% and is lower than 1m, the use of glyphosate costs €170 per ha. during the first
year of treatment and €30 per ha. in the second year of after-care. For this calculation six working hour and 0.4 l
of glyphosate are included (Oosterbaan et al, 2003). When the seedlings are higher than one meter, use of
glyphosate costs €287 per ha. per year including 5 hours of work and the use of 0.4 l glyphosate (Straatsma and
Jansen, 2005).
The costs of P. serotina higher than one meter with a cover of 25-50% and 50-75% without mechanical
excavation are €464 per ha. per year and €698 per ha. per year including 8-12 working hours and 0.9-1.5 l of
glyphosate (Straatsma and Jansen, 2005). When it is lower than one meter and covers 75-100%, the first
treatment costs €522 per ha., €170 per ha. during the second year and €33 per ha. during the third year of aftercare, accounting for €725 in total, including 18 hours of work and 4 l of glyphosate. During treatment some of
the seedlings will be missed and survive. The second year P. serotina covers approximately 5-25% and the third
year of after-care consist of treatment of individual trees (Oosterbaan et al, 2003). In case of seedlings higher
than one meter treatment costs €862 per ha per year. including 15 hours of work and the use of 2 l glyphosate per
ha (Straatsma and Jansen, 2005).
800
Chemical eradication
Regrowth 2nd year
700
Regrowth 1st year
Costs (€/ha)
600
Initial removal
500
400
300
200
100
0
0-5%
5-25%
25-50%
50-75%
75-100%
Cover
Figure 37: the cost per treatment per ha/per year of chemical eradication of P. serotina
4.4.5
Costs of mechanical excavation
Mechanical excavation is applied on shrubs of one meter and higher. Shrubs are pulled out of the ground using
machines. Sheep grazing management is probably not effective enough to combat shrubs of this size.
Nevertheless, this method is discussed in this section because it might be applied before grazing with (large)
herbivores starts. PWN used mechanical removal of P. serotina as preparation before the implementation of
sheep grazing management. This management technique is included in this report because it is often combined
with the implementation of herbivores or chemical eradication.
Mechanical removal of dispersed individual shrubs costs €168 per ha. in the first year and €39 per ha. during the
second year of treatment accounting for €207 per ha. in total (figure 38). After-care consist of manual excavation
of seedlings. When shrubs cover 5-25% of the total area mechanical excavation costs €431 per ha. during the
34
first year of treatment and €39 per ha. during the second year of after-care which is €470 per ha. in total. After
excavation of shrubs there is a high chance of reestablishment for which after-care is needed consisting of
manual excavation (Oosterbaan et al, 2003). When the cover is 25-50% the total costs are €976 per ha. per year
including wages and after-care (Staatsbosbeheer, 2001). Mechanical excavation costs €1.514 per ha. per year
with a cover of 50-75% including wages and after-care (Oosterbaan et al, 2003). With a cover of 75-100% the
area needs to be treated for three continuous years. The first year of treatment costs €1.684 per ha., the second
year €130 per ha. and the last year costs €39 per ha, €1.853 per ha. in total (Oosterbaan et al, 2003).
Disadvantages of mechanical removal are (re)growth of sprouts, this method is only suitable to control P.
serotina, but not for effective eradication (Straatsma and Jansen, 2005). After- care consists of manual
excavation of seedlings (Oosterbaan et al, 2003).
2000
Costs (€/ha)
1800
Mechanical eradication
Regrowth 2nd year
1600
Regrowth 1st year
1400
Initial removal
1200
1000
800
600
400
200
0
0-5%
5-25%
25-50%
50-75%
75-100%
Cover
Figure 38: the cost per treatment per ha/per year of mechanical eradication to combat P. serotina
4.4.6
Costs of excavation using horses
Another way to combat P. serotina is to eradicate individual trees using horses. Excavation with horses is known
to be an effective method in general but it is also a timeconsuming method which makes it relatively expensive.
In this case information concerning after-care is not available but is assumed to be €39 (the annual cost for
manual excavation) for the following 2 years. Excavation using horses is practised when trees have a height of
0.5-3 meters and a circumference of 5 cm. When P. serotina covers 0-5% the costs are €162 per ha. per year
including 5 hours of work. With 5-25% of cover the costs are €390 per ha. per year for 12 hours of work. If P.
serotina covers 25-50 the annual costs are €813 per ha. for 25 hours of work. The annual costs per ha. per year
according to a cover of 50-75% and 75-100% are €1.300 and €1.625 (figure 39). These costs include 40 and 50
hours of work (Staatsbosbeheer, 2001). For a complete overview of the costs of the different management
strategies described, see appendix V.
1800
1600
Excavation with horses
Regrowth 2nd year
Regrowth 1st year
Costs (€/ha)
1400
Initial removal
1200
1000
800
600
400
200
0
0-5%
5-25%
25-50%
50-75%
75-100%
Cover
Figure 39: the cost per treatment per ha/per year of excavation with horses to eradicate P. serotina
35
5
Discussion
5.1
The influence of sheep grazing management on P. serotina
The individual trees at the grazed sites are affected/damaged for 0-25% while ¾ of the trees growing in the
control areas are affected for 0-5%. These results show that sheep browse on P. serotina. The difference in
grazing intensiveness does have influence on the viability of P. serotina. The plants growing within the non
grazed areas are barely suffering from extensive grazing and are viable for 90%. Within the grazed sites almost
halve of the plants are dying or dead as a result of browsed leaves, branches and bark. The introduction of
periodic intensive grazing by sheep does influence P. serotina viability in the desired direction which proves
sheep to be effective browsers although the effect differs per grazing area. Half of the grazed areas contain more
living than dying and dead plants. Within the other areas most of the plants are suffering from grazing but are not
yet dead. This difference in grazing effectiveness might be influenced by the availability of other food sources
and the amount of P. serotina growing in the grazing areas. Assuming that the diet of sheep primary exists of
grasses and partially of P. serotina, it might be possible that this species is avoided when there is alternative
food available. If this impression is valid, grazing of P. serotina can be intensified by reducing other food
sources. This can be accomplished by diminishing the time the herd is grazing outside the grazing area, but then
the subsidy will be discontinued. Keeping the herd in one grazing area for a longer period might also be an
effective method to intensify browsing on the bark and branches. This strategy does not conflict with the current
subsidy. It is important that intensified grazing is not introduced during the late summer and autumn when
weathered leaves of P. serotina contain toxic substances.
The branches are most affected by browsing, followed by the browsing of the leaves and bark. This outcome
holds for the grazed- and non grazed areas and might be influenced by the time of the year the inventories
started. The first inventories took place at the beginning of April, at that period the trees measured did not had
leaves hence sheep grazed primary on the branches and bark. The amount of leaves eaten increases later in
spring and summer. At the control sites almost half of the plants measured did not show any signs of grazing.
Sheep appear to ring the trees and during field work it was visible that all of the trees ringed were dying or dead.
This implies that this type of browsing does affect the viability of P. serotina significantly. But less than 10% of
the trees within the grazing areas are affected this way. In the non grazed areas the number of individually ringed
trees is close to zero. At the moment sheep do not graze on P. serotina during the winter and early spring when
the trees are still bare while the bark and branches are grazed more intensively at these times. Since browsing on
the bark is an effective way to decrease the viability of P. serotina, implementation of sheep grazing
management when trees are bare might complement current management. Furthermore, bare trees do not contain
toxic substances hence the herd might be fenced in more specific and densely P. serotina vegetated areas to
intensify grazing pressure.
Sheep do browse on the leaves effectively. Almost half of the trees measured along the grazed transects are bare
or contain only a few leaves. This decrease of leaves results in a decrease of cover of P. serotina within the
grazing areas. This results reject the 1st hypothesis: ‘the leaf canopy of P. serotina will not be reduced through
sheep grazing management’. Sheep reduce the cover of P. serotina through grazing (primary) and trampling
(secondary), based on field observations. Especially seedlings seem to be vulnerable for grazing because their
leaves are young and their stems do not yet consist of woody material which makes them attractive to eat. When
seedlings are grazed, they are often eaten as a whole instead of partially as older, woody plants. This diminishes
seedlings chance of survival. During fieldwork I noticed that some older, woody plants were broken, probably as
a result of trampling. These trees were not situated along the transects and not part of the data gathered. But
trampling does occur on a small scale with minor affect. Despite that the grazed sites were selected on the basis
of their high cover in comparison with other areas, the cover diminished significantly and is even lower than at
the control sites. These findings reject the 2nd hypothesis partially: ‘sheep grazing management does not increase
openness of the vegetation, which will not affect P. serotina samplings and older plants that grow in or above the
canopy of the accompanying vegetation. But grazing should increase seedling reestablishment opportunities for
P. serotina.. Seedling reestablishment might be increased during grazing due to more open spaces in the soil. But
36
grazing itself does outweigh this affect since seedlings are grazed intensively. Sheep do not influence the number
of stems per individual tree although scientific literature (§2.2) describes resprouting as a survival mechanism of
P. serotina. This is probably the effect of extensive grazing throughout NPZK. Extensive grazing might be
intensive enough to stimulate resprouting and influences the outcome towards a non significant difference.
Sheep grazing management was applied in 2008 and since then, the cover of P. serotina has decreased with 4%
assuming a comparable cover of the grazed areas and their references (note that in 2008, the cover was higher
within the grazing areas than in the areas excluded from grazing). These findings show that the cover decreases
with 1% annually. If the cover was , for instance, twice as high at the grazed sites than at their references in
2008, the cover has decreased with 3%. With these short estimations it becomes clear that sheep grazing
management does have the desired effect on the cover of P. serotina but it takes years to eradicate this species
and long term investment is needed. Another point is that the grazed areas still contain seedlings and resprouting
stumps and the references are dense P. serotina vegetated areas hence eradication seems impossible with the
current grazing intensity/herd. Also, the trees growing at the references are relatively high (>140 cm). Reduction
of P. serotina towards a cover between 1-5% should be feasible. An adjusted and combined management
strategy like grazing and manual excavation is recommended to combat P. serotina increasingly effectively.
Within the references P. serotina spread is increasing. It might be useful to make a systematic inventory of dense
P. serotina vegetated areas every few years and adjust the management strategy when needed. Currently, P.
serotina vegetated areas are partially managed effectively. To combat this species, all dense covered areas need
to be managed this way.
The growth of P. serotina is beside grazing influenced by other variables, including environmental factors such
as: eutrophication; nutrient availability; light availability and soil disturbance. These factors are not included in
this research. Assumed is that these variables promote spread of P. serotina within NPZK since numbers are
increasing without management. Further research might give more insight into the influence of environmental
characteristics in combination with sheep grazing management on the development of P. serotina. Growth,
viability and reproduction are also influenced by trampling and grazing activities of other herbivores. Other large
herbivores are temporarily excluded from the areas where the sheep are fenced. This management method makes
comparison with the control sites possible. According to scientific literature (§2.2), increase of weight (through
nutrient storage in the root system) would be a logical reaction of P. serotina to sheep grazing management. This
effect is visible especially in the grazing areas. At these sites the part of the root that is growing just above the
ground, is clearly thicker than the rest of the stem. But this effect could not be confirmed through measuring the
diameter and weight of the stems. Further research might give more insight into the affect of sheep grazing
management on nutrient storage in the roots. This might give more insight into when P. serotina gets exhausted
and how high grazing pressure should be to be effective. The diameter and weight of P. serotina are not
influenced by sheep grazing management. The height does increase after the introduction of sheep which is
probably a strategy to survive environmental pressure. A fast growth rate is one of the characteristics of P.
serotina and ensures survival through outcompeting other plant species. This trait is increasing visible under a
grazing regime. On average, the plants that are affected by sheep are 3 cm higher than the plants excluded from
sheep grazing management. It might be possible that intensive grazing accelerates growth hence plants increase
their change on survival. Grazing must be intensive enough to prevent recovery of P. serotina. For investigating
how intensive grazing should be to prevent recovery, further research is necessary.
The outcomes of the long term analysis are included in the conceptual framework (figure 40). The growth of P.
serotina is influenced by sheep grazing management positively and negatively since the height increases and the
weight and diameter does not change. The viability is negatively influenced since grazing on leaves, branches
and bark does increase the numbers of dead and dying P. serotina individuals. Regrowth is positively and
negatively influenced because the total cover of P. serotina decreases but the number of resprouting stems are
not influenced by grazing.
37
Figure 40: overview of the conceptual framework including the results of this research. The lighter green arrows are not included in this
research.
For the short term analysis a comparison is made between the grazed areas before, and after the implementation
of grazing. The outcomes of the short term analysis shows that the cover, the number of leaves and the viability
of P. serotina decreased as a result of the introduction of sheep. These findings are in line with the results of the
long term analysis. The decrease in viability especially, is important to manage P. serotina spread within NPZK.
Young trees that have a limited number of leaves are suffering when most of their leaves are eaten. They seem to
be less viable than older trees because they do not yet consist of woody material (as explained earlier in this
chapter). Browsing activity is a prominent result of this research, both appearing in the short term- as well as in
the long term analysis. Especially browsing on the bark influences viability. In the long term sheep browsing is
restricted on the bark. This browsing is not noticeable in the short term. Browsing on the bark is probably
increasingly noticeable when other sources of food are scarce during the early spring and winter (as described in
§5.1). During the time the short term inventories took place, sheep preferred grazing on young leaves. The leaves
are favourite during spring, and browsed intensively. The percentage of trees eaten had increased during one
week of grazing. Browsing on the leaves is correlated to the reduction of the cover of P. serotina as a result of a
decrease of leaf canopy. This outcome is related to the amount of leaves of all trees since the number of stems
does not significantly decrease in the short term. In the long term the number of stems diminish resulting in a
larger decrease in cover. The short term reduction of cover is of temporary nature (because leaves grow back)
but becomes visible in the long term resulting in a decrease in cover of 4% since 2008. This implies that,
although the cover diminishes in the long term, there is no significant decrease of P. serotina individuals in the
short term. The amount of P. serotina individuals and the cover of this species depends on the viability of the
trees and the time period sheep grazing management is applied. The results show that short term grazing is not
affective to eradicate P. serotina. To reach the desired effect, long term management is necessary.
38
The stem diameter slightly increases within one week of intensive grazing. This increase is minimal and might
be influenced by the time of the year (sprouts starts growing during spring). It might be possible that this result
changes after the data set is added to data gathered during the second round of grazing. The diameter increase
must be received with some precaution. The height and weight do not change after one week of grazing.
5.2
Biodiversity
Half of the grazed sites do contain more species than their control sites, the other half contain less species than
their references. The differences in number of species between the grazing areas and their references are minor.
These findings show that sheep grazing management does not influence the number of species. The difference in
cover of P. serotina is also negligible when comparing the grazed sites and their references. This is a remarkable
outcome since the results of the former paragraphs of this chapter show that sheep grazing management does
reduce cover of P. serotina. This contradictory outcome is probably a result of the selection criteria of the
grazing areas in the initial situation, namely a high cover of P. serotina. Currently, after four years of intensive
grazing, the cover of P. serotina is comparable within the grazed- and non grazed areas. These findings could
indicate that, on the one hand P. serotina cover is reduced at the grazed sites since grazing started. Or, on the
other hand, the cover in the control areas increased toward the same level as the initial cover of P. serotina at the
grazed sites. The former impression seems to be self-evident since the other results of this theses show that sheep
grazing management does reduce the cover.
There is a significant difference in cover between all areas researched with the most remarkable difference of
species with sporadic appearance. Three of the five reference areas do not contain species with sporadic
appearance. All grazed areas do contain species with sporadic appearance which is probably a result of an
increase of light availability, less dense vegetation and creation of more open spaces. The type of species with
sporadic appearance differs per area varying from mosses to pioneer species to species growing on eutrophicated
soil. The effect of sheep grazing management on different vegetative layers (mosses, grasses, herbs, shrubs and
trees) is insignificant. These findings show that sheep grazing management does not have a significant influence
on biodiversity in NPZK during the past four years of grazing. Follow-up research may give more insight in the
long term affects of sheep grazing management on biodiversity. It might be possible that development or
decrease of biodiversity takes more than four years of management before it becomes measurable. It is important
that changes are noticed in time, especially when biodiversity is negatively influenced and adjustment of this
method is needed.
This management strategy does influence the cover and attendance of indicator species. On average, the cover of
indicator species is lower at the grazed sited than at the references. This also holds for the total number of
species although this difference is minor. These species are probably sensitive for (both) trampling and/or
grazing activities. Some of these species might be attractive for sheep and are grazed intensively. Further
research to indicate which indicator species are sensitive to trampling, are grazed intensively by sheep and are
sensitive to grazing might provide further insight in this topic. This can be carried out through inventory the
indicator species shortly before and after grazing to investigate short term affects. Since these species are
characteristic for the coastal dune habitat and are valued for their appearance, protection or an adjusted
management strategy might be necessary when they are suffering from grazing. Intensive grazing is applied
since four years, it might be possible that the disappearance of indicator species takes longer than four years. But
since these species seem to be influenced negatively already, it might be possible that they are the first ones
disappearing.
Hypothesis 3 and 4: ‘Grazing should increase seedling reestablishment of all other plant species that germinate
into open soil’ and ‘preferential grazing may alter abundance of the accompanying vegetation’ are rejected since
there is no difference in number of species and cover between the grazed- and non grazed areas. And above all,
the cover of indicator species decreased at the grazed sites.
39
As described in chapter 3 the inventory method Tansley is applied which is a relatively rough method including
some subjectivity. By applying another more exact inventory method, like a series of vegetation recordings using
permanent quadrants (PQ’s) the objectivity of this would be increased.
5.3
Cost-effectiveness
Information concerning the cost-effectiveness of sheep grazing management is restricted, especially when
speaking of availability of scientific literature. Most of the information (including scientific sources) is based on
data derived from nature management organisations (Staatsbosbeheer and PWN). Costs are also obtained from
interviews (Elbersen et al, 2003) and insight in business statistics to make comparison possible. Furthermore,
scientific information about the costs-effectiveness of sheep grazing management to combat P. serotina
specifically is not available. Nevertheless, since sheep grazing was introduced as a management strategy to
combat (spread of) P. serotina, insight in monetary data becomes increasingly important. This report
complements previous research concerning this topic due to insight in financial overviews of sheep grazing
management in NPZK provided by PWN.
In the long term, costs of sheep grazing management are relatively high compared to other methods. Although
the benefits of sheep grazing management are excluded from this research, it is an important aspect to be
considered. The monetary benefits prove to be relatively low (appendix III), but sheep grazing management also
comprises aesthetic- and educational values. Whereas mechanical and chemical excavation might cause
environmental harm, use of sheep minimizes damage. A herd of sheep, with or without shepherd, is a sight
valued by visitors of NPZK. Besides, the herd is used as an educational tool to make visitors more aware of the
impact sheep have on the environment (this report will be converted in a poster used to inform visitors of
NPZK). Furthermore, PWN combines nature conservation with the extraction of drinking water. The use of
chemicals to eradicate P. serotina is not very appropriate in terms of environmental protection and safety of
drinking water. By applying biological eradication techniques, PWN protects its environmental friendly image.
These benefits are not included in the calculations made for this thesis due to time restrictions. Further research
on the aesthetic-, educational- and image supporting monetary value of sheep grazing management is
recommended and gives insight into the benefits of this method. Furthermore, the revenues from the provided
subsidy are also not taken into consideration. When including the subsidy in the calculations, the costs of sheep
grazing management would be lower.
Sheep grazing management becomes more expensive in the long term because the costs are constant over the
years it takes place, while costs of other management methods diminish (figure 41) .
160
Costs (€)
1st year
140
2nd year
120
3rd year
100
80
60
40
20
0
Sheep grazing management
Manual excavation
Chemical treatment
Management method
Figure 41: average costs of sheep grazing management, manual excavation and chemical treatment including two years of after-care
40
The cost-effectiveness of grazing depends on the time period applied. To combat P.serotina effectively, long
term management is needed (to suppress reestablishment of young sprouts and seedlings) continuing relatively
high costs (chapter 4). Especially hiring a shepherd is accompanied by high costs, other costs are made on food
and health care. Costs of manual excavation and chemical treatment depend on the coverage percentage of P.
serotina and the time period applied. The cover does not influence the costs of sheep grazing management in
itself. The higher the coverage percentage of P. serotina, the lower the cost of sheep grazing management are
comparable to the other management methods. The coverage percentage might influence the management
method chosen and/or practiced. The coverage percentage of P. serotina within NPZK varies between 0-25%,
making eradication using sheep relatively expensive in comparison with the other methods (table 7). The costs of
sheep grazing management compared to the costs of manual excavation concerning a coverage percentage of 05% and 5-25% are 61-91% higher. The costs of sheep grazing compared to chemical treatment is 54-93% higher.
This means that sheep grazing management is relatively expensive considering a coverage percentage of P.
serotina between 0-25%. For an overview of the costs of sheep grazing of trees > 1m, see appendix V.
The costs represented in table 8 are the costs of total eradication of invasive trees/shrubs. The question is
whether this is possible. Since sheep grazing management is practised, the cover of P. serotina, as described in
§5.1, reduced with 1-3% annually at a cost of €145 per ha. Assuming that total eradication of P. serotina is not
realistic and after-care is needed, the total costs of manual excavation and chemical treatment after three year of
management are significantly higher (represented in red in table 8). A realistic goal, when considering the
invasive characteristics of P. serotina, is suppression towards a cover of 0-5%. The yearly costs (per ha) of sheep
grazing management will always be higher than the costs of manual excavation and chemical treatment. But this
method does reach the desired goal in the long term and is inherent to aesthetic, educational and image
protecting values.
Table 8: Comparison of the annual costs of P. serotina eradication of different management strategies in euro’s per ha. discussed in chapter 4
(Staatsbosbeheer, 2001; Oosterbaan et al, 2003; Straatsma and Jansen, 2005; PWN). Only three years of treatment of trees <1 m are included
in this table to make comparison with other management methods possible. The purple number represent the costs assuming that total
excavation is possible within three years of time. The red number represent the costs assuming that total excavation is impossible and aftercare is needed annually.
Appearance
<1m
Management
strategy
Costs treatment 1st
year (€)
Costs after-care 2nd
year (€)
Costs after-care 3rd
year (€)
Unspecified
Sheep grazing
management
Manual
excavation
Manual
excavation
Chemical
treatment
Chemical
treatment
145
145
145
Costs after 3
years of
treatment
(€)
435
39
39
39
39/127
130
39
39
169/208
30
30
30
30/90
170
30
30
200/230
<1m
Coverage 0-5%
<1m
Coverage 5-25%
<1m
Coverage 0-5%
<1m
Coverage 5-25%
41
6
Conclusions
The aim of this study was to research the effectiveness and impact of sheep grazing management on P. serotina
and biodiversity. Besides, a comparison of the cost-effectiveness of sheep grazing management with other
management methods is made. Therefore, this thesis addressed the following research questions:
1: What influence does sheep grazing management have on locally dense vegetated P. serotina in National park
Zuid- Kennemerland in the short- and long term?
2: What influence does sheep grazing management have on biodiversity in National Park Zuid- Kennemerland?
3: How cost-effective is sheep grazing management in comparison with other management methods used for
combating P. serotina?
1) Research on the short term effect of sheep grazing management is done to investigate how sheep graze on P.
serotina, which parts of the trees are favourite and if reduction of this species is already visible. The short term
analysis showed that the leaves are temporarily removed resulting in a decrease of viability, leaf canopy and
cover. Sheep browse on the leaves and branches intensively, leading to increased numbers of dead and dying
plants. Especially young leaves are browsed during the spring. Grazing activities on the stem are not noticed in
the short term. Young resprouting stems are barely grazed and do not diminish. The number of individual trees
does not diminish during short term grazing activities and the reduction of cover is of temporary nature but
becomes visible as the years progress resulting in a decrease in cover. These finding show that sheep graze on P.
serotina in the short term although the effects are limited and of temporary nature.
Research on the long term effect of sheep grazing management is done to investigate if this method does reduce
P. serotina growth, cover and viability in locally dense vegetated areas. The long term analysis shows that sheep
browse on the branches and leaves of P. serotina resulting in reduction of cover. Browsing activities on the bark
are limited. The grazing regime applied results in increased numbers of dying and dead plants. Half of the plants
within the grazing areas are suffering or already dead. Although these finding are promising, total eradication
does not seem to be possible since NPZK does contain numerous dense P. serotina vegetated locations, that are
not grazed intensively. Especially the references contain dense P. serotina covered parts. Besides, the results
vary between the grazed sites and P. serotina has several affective survival mechanisms hindering total
eradication. One of these traits that became visible under the current grazing regime is an increase of height
(while the diameter and weight stay the same). Although total eradication is probably not possible, sheep grazing
management is an effective method to diminish the viability and cover within NPZK.
2) Since sheep grazing management started, there is no measurable difference in biodiversity based on the fact
that the number of species and their cover does not differ between the grazing areas and their references.
However, the cover and attendance of indicator species within NPZK is negatively influenced through this
management strategy.
3) Sheep grazing management is relatively expensive in comparison with other methods because after-care is
needed for several years. Costs of other methods diminish during the years after-care is needed. The costs of
keeping a herd are high because a shepherd is needed, the herd needs extra food during the winter and healthcare
expenses. Furthermore, the costs of other management methods applied depend on the percentage of cover of
P.serotina while the herd grazes with the same intensiveness independent of the cover. Because after-care and
long term management are essential to eradicate P.serotina effectively, intensive grazing needs to be applied
every year. Grazing might even be intensified since NPZK contains several densely P.serotina vegetated areas
that need management and are not grazed at the moment. Sheep grazing management is an relative expensive
method but probably more sustainable than the other methods used for eradication. Therefore, this method might
be more effective in the long term.
42
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Biowetenschappen, Landbouwkunde Natuur en Milieu: 75: 5-75. Katholieke Hogeschool Kempen
Smit A., A.M. Kooijman, J. Sevink, 2000. “Impact of grazing on litter decomposition and nutrient availability in
a grass-encroached Scots pine forest”, Forest Ecology and Management: 158: 117-126.
Staatsbosbeheer, 2001.”Normenboek Staatsbosbeheer 2001-2002”, Normen voor de uitvoering van
werkzaamheden in Bosbouw, Natuurbeheer en Landschapsverzorging
Straatsma W. and P. Jansen, 2005. “Amerikaanse Vogelkers: bestrijden of beheren”, Vakblad Natuur, Bos,
Landschap: 3: 1-3
Uiterweerd W.S.H., 2008. “Browse effects of cattle on Black cherry (Prunus serotina Ehrh) in the Oxbøl
District, Denmark”, Resource Ecology Group: 21: 5-6. Wageningen UR
Van Katwijk M.M. and C.J.F. ter Braak, 2008. “Handleiding voor het gebruik van multivariate
analysetechnieken in de ecologie”, Ecoscience, Afdeling Milieukunde Radboud Universiteit: 36: 5-6. Nijmegen
Van Wingerden W.K.R.E., M. Nijsen, P.A. Slim, J. Burgers, R.J.M. van Kats, H.F. van Dobben, A.P. Noordam,
G.F.P. Martakis, H. Esselink and G.A.J.M. Jagers op Akkerhuis, 2001. “Grazers in Vlielands duin: Evaluatie van
runderbegrazing in duinvalleien op Vlieland. Deel 2: Onderzoek in 2001”, Research Instituut voor de Groene
Ruimte. 100: 1-100. Alterra, Wageningen
Van Wingerden W.K.R.E., M. Nijsen, P.A. Slim, J. Burgers,. G.A.J.M. Jagers op Akkerhuis, A.P. Noordam,
G.F.P. Martakis, H. Esselink, W.J. Dimmers, R.J.Mvan Kats, 2001. “Evaluatie van zeven jaar runderbegrazing in
duinvalleien op Vlieland”, Research Instituut voor de Groene Ruimte. 100: 1-100. Alterra, Wageningen
Vanhellemont M., K. Verheyen, L. De Keersmaeker, K. Vandekerkhove, M. Hermy, 2009 a. “Does Prunus
serotina act as an agressive invader in areas with low propagule pressure”, Biological Invasions 11:1451-1462.
Vanhellemont M., R. Wouters, L. Baeten, R.J., Bijlsma, P. De Frenne, M. Hermy, K. Verheyen, 2009 b. “Prunus
serotina unleashed: invader dominance after 70 years of forest development”, Biological Invasions 12: 1-12.
44
Appendix I
RD Coordinates transects
This table represents the RD coordinates of the researched transects measured with GPS
Area
RD Coordinates begin transect
RD Coordinates end transect
101029/491043
101050/491039
Zevenbosjes
100890/491232
100912/491238
Reference Zevenbosjes
100544/492211
100557/492228
Manege
100552/492076
100584/292051
Reference Manege
100995/492903
100977/492911
Eiland Noord
101416/493023
101394/493020
Reference Eiland Noord
101047/492830
101026/492811
Eiland Zuid
101277/493033
101255/493018
101199/493929
101178/493915
Noorderweg West
101238/493899
101219/493914
Noorderweg East
101694/493767
101682/493791
Reference Noorderweg W/E
45
Appendix II
Parameters and motivation
An overview of the parameters used during inventory of P.serotina and its motivation
Parameter
Number of stems
Description parameter
Number of sprouts of one
plant/tree
Viability of stems
1= Life: stem is fully alive
2= Dying: stem is dying, not
dead yet
3= Dead: Stem is fully dead
Diameter in cm of stem of one
of the sprouts of one tree at
50% height of the tree
Maximum height of one tree
in cm
Diameter
Height
Type of use
Ringed
Number of leaves
Weight of plant
Percentage of use
% of cover
0= No use
1= Debarked
2= Branch eaten
3= Leaf eaten
4= Bud eaten
5= Other
1= Yes
2= No
The number of leaves of one
plant at the point where the
plant intersects with the
transect line.
Weight of complete individual
plants (with a height between
15-20 cm) along the transect
at one meter of distance from
the rope each two meters
How much of the tree has
been affected by sheep.
1= 0-5%
2= 5-25%
3= 25-50%
4= 50-75%
5= 75-100%
Estimates
the
coverage
percentage of P.serotina along
a transect.
Motivation/usefulness parameter
Represents how many resprouting sprouts one stem
has. If one plants has two or more stems, one will
be measured. This stem is marked (with tape) in the
field to prevent confusion during following
inventories1. This parameter is measured to
investigate the effectiveness of sheep grazing1
management on regeneration of P. serotina.
Measures the influence sheep1 grazing has on the
viability of P.serotina. The more stems are
dying/dead after sheep grazing, the more effective
this management method is.
Measures if sheep grazing management influences
the thickness of stems1.
Measures if sheep grazing management influences
the height of stems1. If it does, management of
P.serotina might be adjusted to combat larger
plants.
Measures which part(s) of the plant is eaten the
most/least. This information may give some
valuable information about the grazing behaviour
of sheep1. These parameter also influences viability
of P. serotina.
If plants are ringed all around the stem, it will die.
Then sheep grazing is very effective to combat
P.serotina. This parameter has a relationship with
viability1.
This is measured because to investigate its
relationship with viability1. Sheep are known to
browse young leaves specifically.
If the foot of the stem and the root are thicker than
the rest of the tree, the tree is storing reserves. This
might be an effect of grazing management1.
Defines grazing behaviour1. A correlation can be
made with viability of stems to see how much
P.serotina needs to be affected before it dies.
This parameter is used to see whether the
effectiveness of sheep grazing1 management
influences the reproduction of P.serotina.
1
Might also be influenced by grazing of cattle, rabbits and deer.
46
Appendix III
Costs of sheep grazing management PWN
Costs of sheep grazing management, made by PWN in 2011
Company/person
Type of cost
Contributions etc.
Productship V&V
Dienst Regelingen
Total contributions/Charges
Travel costs
Total travel costs
Remaining costs
Keizer-de Hoef
Rendac
P. Nijsen
Spaanderman
Stad & Lande Dierenkliniek
G. Kouprie
Nijssen Fourages
H. Ebelaar
NFDH
K bd Bijl
Totaal remaining costs
Remaining
Beljaars Schapenpraktijk
De Groot
Veno
Mulder Media Groep
Totaal Overige Kosten
Totaal remaining costs 2011
Revenues
Total revenues 2011
Net costs 2011
30 ha
Total costs per ha
Cost/revenue/€
Charge 2010
50,00
181,60
33,50
G. Kouprie
Y. Duijn
Reeuwijk
Bronsdijk 2010
Vrolijk
2.568,16
327,60
253,20
475,20
445,50
Total costs/revenue/€
265,10
4.069,66
Rupromin Medicines
Dispose of carcasses
Grass silage
Chunk
Control/section/medicines
Work 2011
Grass silage
Shearing of sheep
Inspection fees sheep
Breeding
845,00
276,71
1.500,00
1.394,24
2.650,32
19.910,60
4.382,40
586,00
90,00
120,00
31.755,27
Software package
Work Rietvlak
Rack
Signage
1.507,50
1.052,38
453,50
355,00
3.368,38
39.458,41
Province NH, subsidy 2011
Sale sheepskin
10.800,00
8.500,00
29,41
19.329,41
20.129,00
670,97
47
Appendix IV
Costs of sheep grazing management
Costs of sheep grazing management of PWN, private companies and foundations.
Type of cost
PWN
Private companies Foundations
Charge 2010
Depreciations
Travel costs
Rupromin Medicines
Land costs
Buildings
Dispose of carcasses
Food
Control/section/medicines
Labour costs
Shearing of sheep
Inspection fees sheep
Breeding
Software package
Work Rietvlak
Rack
Signage
Other costs
Loan entrepreneur
Total costs
Revenue
Subsidy
Sale sheepskin
Accretion and sale
Ewe premium
Other income
Total revenues
50,00
181,60
33,50
Net result
4.707
459
706
2.058
177
4.950
9.470
7.593
21.210
43.376
14.900
21.000
74.051
12.433
9.177
38.816
19.329,41
18.353
7.877
8.021
43.338
10.011
5.133
12.411
66.372
-20.129
-30.713
-2.616
4.069,66
845,00
276,71
7.276,64
2.650,32
19.910,60
586,00
90,00
120,00
1.507,50
1.052,38
453,50
355,00
39.458,41
10.800,00
8.500,00
29,41
68.988
48
Appendix V
Costs of P. serotina eradication
Comparison of the annual costs of p. serotina eradication of different management strategies in euro’s per ha. discussed in chapter 4 . The
costs of trees > 1m are also included (Staatsbosbeheer, 2001; Oosterbaan et al, 2003; Straatsma and Jansen, 2005; PWN).
Appearance
<1m
Management strategy
Costs treatment 1st year (€)
Costs after-care 2nd year (€)
Costs after-care 3rd year (€)
Unspecified
Sheep grazing
management
Manual excavation
145
145
145
Manual excavation
130
39
Manual excavation
442
39
39
520
Manual excavation
1.170
39
39
1.248
Manual excavation
1.820
130
39
1.989
<1m
Coverage 0-5%
<1m
Coverage 5-25%
<1m
Coverage 25-50%
<1m
Coverage 50-75%
<1m
Coverage 75-100%
<1m
Coverage 0-5%
<1m
Coverage 5-25%
<1m
Coverage 25-50%
<1m
Coverage 50-75%
<1m
Coverage 75-100%
>1m
>1m
Coverage 0-5%
>1m
Coverage 5-25%
>1m
Coverage 25-50%
>1m
Coverage 50-75%
>1m
Coverage 75-100%
>1m
Coverage 0-5%
>1m
Coverage 5-25%
>1m
Coverage 25-50%
>1m
Coverage 50-75%
>1m
Coverage 75-100%
>1m
Coverage 0-5%
>1m
Coverage 5-25%
>1m
Coverage 25-50%
>1m
Coverage 50-75%
>1m
Coverage 75-100%
>1m
Coverage 0-5%
>1m
Coverage 5-25%
>1m
Coverage 25-50%
>1m
Coverage 50-75%
>1m
Coverage 75-100%
39
Costs after 3 years
of treatment
(€)
435
39
169
Chemical treatment
30
Chemical treatment
170
30
30
200
Chemical treatment
346
30
376
Chemical treatment
434
30
30
494
Chemical treatment
522
170
33
725
Manual excavation
52
Manual excavation
156
39
Manual excavation
650
39
Manual excavation
1.560
39
39
1.638
Manual excavation
2.340
39
39
2.418
Chemical treatment
169
169
Chemical treatment
287
287
Chemical treatment
464
464
Chemical treatment
698
698
Chemical treatment
862
Mechanical removal
168
39
Mechanical removal
431
39
Mechanical removal
898
39
39
976
Mechanical removal
1.436
39
39
1.514
Mechanical removal
1.684
130
39
1.853
Horse excavation
162
39
Horse excavation
390
39
39
468
Horse excavation
813
39
39
891
Horse excavation
1.300
39
39
1.378
Horse excavation
1.625
39
39
1.703
52
195
689
862
207
470
201
49
Appendix VI
Overview statistics biodiversity
Crosstabs Area * Cover
Case Processing Summary
Cases
Valid
N
Missing
Percent
N
Total
Percent
N
Percent
Area * Layer
1331
100,0%
0
0,0%
1331
100,0%
Area * Cover
508
38,2%
823
61,8%
1331
100,0%
Chi-Square Tests
Value
df
Asymp. Sig. (2sided)
Pearson Chi-Square
275,749a
80
,000
Likelihood Ratio
258,032
80
,000
13,281
1
,000
Linear-by-Linear Association
N of Valid Cases
508
a. 41 cells (41,4%) have expected count less than 5. The minimum expected count is ,41.
Grazed * Layer
Cases
Valid
N
Missing
Percent
N
Total
Percent
N
Percent
Grazed * Layer
1331
100,0%
0
0,0%
1331
100,0%
Grazed * Cover
508
38,2%
823
61,8%
1331
100,0%
Chi-Square Tests
Value
df
Pearson Chi-Square
a
,000
3
1,000
Likelihood Ratio
,000
3
1,000
,000
1
1,000
N of Valid Cases
1331
a. 0 cells (,0%) have expected count less than 5. The minimum expected count is 45,00.
50
Grazed * Cover
Chi-Square Tests
Value
df
Pearson Chi-Square
14,357a
8
,073
Likelihood Ratio
15,057
8
,058
,034
1
,854
N of Valid Cases
508
a. 2 cells (11,1%) have expected count less than 5. The minimum expected count is 2,68.
Crosstabs Area * Layer
Cases
Valid
N
Area * Layer
Missing
Percent
1331
N
Total
Percent
100,0%
0
N
0,0%
Percent
1331
100,0%
Chi-Square Tests
Value
df
Pearson Chi-Square
,000a
30
1,000
Likelihood Ratio
,000
30
1,000
,000
1
1,000
N of Valid Cases
1331
a. 0 cells (0,0%) have expected count less than 5. The minimum expected count is 9,00.
51
Appendix VII Overview plant species inventoried
SHORTNAME
FIRST_NATI
Ribres rubrum
Cerastium arvense
Sonchus arvensis
Convolvulus arvensis
Prunus serotina
Gladomia spp
Betula ssp
Senecio inaequidens
Fragaria vesca
Scirpus sylvaticus
Senecio sylvaticus
Plantago major herba
Pinus nigra v. maritim
Rubus caesius
Carlina vulgaris
Hippophae rhamnoides
Seneci jacoba s. dunen
Taraxacum erythrospermum
Erodiu cicuta s. dunen
Calamagrostis epigejos
Rosa pimpinellifolia
Viola curtisii
Stellaria pallida
Crataegus monogyna
Rosa rubiginosa
Eurhynchium spp
Festuca filiformis
Anthriscus sylvestris
Lophocolea heterophyll
Geum urbanum
Galium verum
Holcus lanatus
Lotus corniculatus
Veronica chamaedrys
Acer pseudoplatanus
Cerast fontan s. vulga
Anchusa officinalis
Lotus cornic v. cornic
Luzula campestris
Sambucus nigra
Arenaria serpyllifolia
Hypochaeris radicata
Brachytheciu rutabulum
Achillea millefolium
Dicranum scoparium
Mnium hornum
Lithospermu officinale
Galium mollugo
Drepanocladu polygamus
Populus x canescens
Salix cinerea
Syntri rurali v. areni
Urtica dioica
Thymus pulegioides
Pinus sylvestris
Polytrichum spp
Bryonia dioica
Euphorbia esula
Ammophila arenaria
Glechoma hederacea
Rosa canina
Viola canina
Saxifraga tridactylite
Silene conica
Galium aparine
Urtica urens
Leontodon saxatilis
Sanguisorba minor
Cardamine hirsuta
Senecio viscosus
Bryum species
Aalbes
Akkerhoornbloem
Akkermelkdistel s.l.
Akkerwinde
Amerikaanse vogelkers
Bekertjesmos
Berk
Bezemkruiskruid
Bosaardbei
Bosbies
Boskruiskruid
Brede weegbree
Corsikaanse den
Dauwbraam
Driedistel
Duindoorn
Duinkruiskruid
Duinpaardenbloem
Duinreigersbek
Duinriet
Duinroosje
Duinviooltje
Duinvogelmuur
Eenstijlige meidoorn
Egelantier
Laddermos
Fijn schapengras
Fluitekruid
Gedrongen kantmos
Geel nagelkruid
Geel walstro
Gestreepte witbol
Gewone en Rechte rolklaver
Gewone ereprijs
Gewone esdoorn
Gewone hoornbloem
Gewone ossentong
Gewone rolklaver
Gewone veldbies
Gewone vlier
Gewone zandmuur
Gewoon biggenkruid
Gewoon dikkopmos
Gewoon duizendblad
Gewoon gaffeltandmos
Gewoon sterrenmos
Glad parelzaad
Glad walstro
Goudsikkelmos
Grauwe abeel
Grauwe en Rossige wilg
Groot duinsterretje
Grote brandnetel
Grote tijm
Grove den
Haarmos
Heggerank
Heksenmelk
Helm
Hondsdraf
Hondsroos
Hondsviooltje
Kandelaartje
Kegelsilene
Kleefkruid
Kleine brandnetel
Kleine leeuwentand
Kleine pimpernel
Kleine veldkers
Kleverig kruiskruid
Knikmos (G)
Area
1
Area 2
Area 3
Area 4
Area 5
Area 6
Area 7
2
7
6
1
2
6
2
2
8
8
7
3
6
Area 8
Area 9
Area 10
5
6
5
6
3
6
2
4
6
6
4
6
4
4
4
3
4
4
3
1
5
2
7
7
3
7
7
7
4
7
7
4
8
7
7
7
6
8
4
7
7
6
8
4
6
7
7
4
6
3
3
7
7
7
7
3
7
9
5
5
3
9
9
8
3
2
2
3
3
1
3
3
4
5
9
6
7
7
8
8
5
8
7
4
3
2
2
4
1
2
8
3
5
3
2
2
3
6
3
8
5
7
5
4
6
2
5
5
8
5
2
3
5
7
7
7
7
6
7
3
6
6
7
5
8
4
7
7
7
7
7
6
4
6
7
6
3
7
5
4
6
5
8
3
8
5
5
8
4
6
7
7
6
6
3
3
2
2
5
6
7
6
8
1
7
7
5
5
4
3
3
3
5
7
2
4
2
2
7
2
5
4
5
3
3
9
4
6
3
3
6
3
6
4
1
4
4
6
2
4
4
4
6
6
3
1
1
6
6
1
6
7
4
6
6
2
1
8
3
1
1
6
6
2
3
3
3
6
3
2
2
7
2
3
6
5
1
1
1
6
6
4
4
2
4
4
3
7
6
4
2
5
6
5
5
7
5
7
5
7
6
6
7
7
2
52
Area
11
Galinsoga quadriradiata
Ajuga reptans
Ranunculus repens
Salix repens
Vicia lathyroides
Alliaria petiolata
Viola odorata
Veronica officinalis
Dryopteris filix-mas
Sedum acre
Taraxacum species
Lamium purpureum
Pastinaca sativa
Daucus carota
Cladina
Geranium robertianum
Arabis hirsuta subsp. hirsuta
Viola hirta
Myosotis ramosissima
Rumex acetosella
Echium vulgare
Plantago lanceolata
Cirsium vulgare
Verbascum densiflorum
Poa annua
Taxus baccata
Teucrium scorodonia
Veronica arvensis
Cynoglossum officinale
Rumex acetosa
Viola species
Linaria vulgaris
Prunus padus
Ste me + S. pa + S. ne
Erophila verna
Scrophularia vernalis
Polygonatum odoratum
Lonicera periclymenum
Euonymus europaeus
Ligustrum vulgare
Trifolium repens
Geranium molle
Cerastium semidecandru
Tarax. sect. Erythr.
Carex arenaria
Quercus robur
Populus nigra
Verbascum nigrum
Anisantha tectorum
Knopkruid
Kruipend zenegroen
Kruipende boterbloem
Kruipwilg
Lathyruswikke
Look-zonder-look
Maarts viooltje
Mannetjesereprijs
Mannetjesvaren
Muurpeper
Paardenbloem (G)
Paarse dovenetel s.s.
Pastinaak
Peen
Rendiermos
Robertskruid
Ruige scheefkelk
Ruig viooltje
Ruw vergeet-mij-nietje
Schapenzuring
Slangenkruid
Smalle weegbree
Speerdistel
Stalkaars
Straatgras
Taxus
Valse salie
Veldereprijs
Veldhondstong
Veldzuring
Viooltje (G)
Vlasbekje
Vogelkers
Vogelmuur
Vroegeling
Voorjaarshelmkruid
Welriekende salomonszegel
Wilde kamperfoelie
Wilde kardinaalsmuts
Wilde liguster
Witte klaver
Zachte ooievaarsbek
Zandhoornbloem
Zandpaardenbloemen
Zandzegge
Zomereik
Zwarte populier
Zwarte toorts
Zwenkdravik
3
4
2
4
5
3
2
3
3
3
5
4
5
4
5
7
4
4
4
4
6
6
5
6
5
6
4
1
5
6
6
5
3
3
5
3
2
2
3
1
1
2
2
2
3
2
3
3
3
1
2
1
1
5
3
5
5
4
3
5
5
7
6
7
6
6
4
4
3
2
2
2
5
3
5
3
3
3
3
2
3
4
6
5
6
7
7
5
5
5
4
7
7
6
6
7
5
7
5
5
3
7
7
6
7
2
5
3
2
3
6
3
4
2
4
3
4
3
3
3
3
6
4
5
4
3
5
9
3
3
5
3
4
8
3
3
4
3
3
3
7
3
1
4
3
4
4
6
7
7
6
5
3
5
4
7
6
6
5
6
7
4
6
4
7
3
7
5
3
5
4
2
53
Appendix VIII Overview statistics P. serotina
Crosstabs
Cases
Valid
N
Missing
Percent
N
Total
Percent
N
Percent
Transect * Viability of stems
764
99,9%
1
0,1%
765
100,0%
Transect * Type of use
764
99,9%
1
0,1%
765
100,0%
Transect * Ringed
764
99,9%
1
0,1%
765
100,0%
Transect * No. of leaves
657
85,9%
108
14,1%
765
100,0%
Transect * % Used
764
99,9%
1
0,1%
765
100,0%
Transect * Viability of stems
Chi-Square Tests
Value
df
a
2
,000
Likelihood Ratio
161,503
2
,000
146,768
1
,000
Pearson Chi-Square
150,734
N of Valid Cases
764
a. 0 cells (,0%) have expected count less than 5. The minimum expected
count is 16,96.
Transect * Type of use
Chi-Square Tests
Value
df
Pearson Chi-Square
Likelihood Ratio
N of Valid Cases
a
3
,000
114,516
3
,000
46,008
1
,000
102,056
764
count is 8,06.
54
Transect * Ringed
Chi-Square Tests
Value
df
Asymp. Sig. (2-
Exact Sig. (2-
Exact Sig. (1-
sided)
sided)
sided)
a
1
,000
Continuity Correction
23,968
1
,000
Likelihood Ratio
28,583
1
,000
Pearson Chi-Square
26,025
b
Fisher's Exact Test
,000
25,991
N of Valid Cases
1
,000
,000
764
a. 0 cells (,0%) have expected count less than 5. The minimum expected count is 10,60.
b. Computed only for a 2x2 table
Transect * No. of leaves
Chi-Square Tests
Value
df
Pearson Chi-Square
a
34
,000
164,987
34
,000
61,950
1
,000
141,651
Likelihood Ratio
N of Valid Cases
657
a. 47 cells (67,1%) have expected count less than 5. The minimum
expected count is ,40.
Transect * % Used
Chi-Square Tests
Value
df
a
3
,000
Likelihood Ratio
51,025
3
,000
47,758
1
,000
Pearson Chi-Square
N of Valid Cases
48,871
764
55
Crosstabs
Cases
Valid
N
Missing
Percent
N
Total
Percent
N
Percent
Transect * Diameter
764
99,9%
1
0,1%
765
100,0%
Transect * Height
764
99,9%
1
0,1%
765
100,0%
Transect * Weight of plant
134
17,5%
631
82,5%
765
100,0%
Transect * Diameter
Chi-Square Tests
Value
df
Pearson Chi-Square
a
18
,065
31,042
18
,028
8,263
1
,004
27,782
Likelihood Ratio
N of Valid Cases
764
Transect * Height
Chi-Square Tests
Value
df
Pearson Chi-Square
Likelihood Ratio
N of Valid Cases
a
12
,010
28,754
12
,004
3,998
1
,046
26,222
764
56
Transect * Weight of plant
Chi-Square Tests
Value
df
a
26
,224
38,539
26
,054
,555
1
,456
N of Valid Cases
134
Pearson Chi-Square
31,117
Likelihood Ratio
Crosstabs
Cases
Valid
N
Missing
Percent
N
Total
Percent
N
Percent
Transect * % Cover
764
99,9%
1
0,1%
765
100,0%
Transect * No. of stems
764
99,9%
1
0,1%
765
100,0%
Transect * % Cover
Chi-Square Tests
Value
df
a
7
,000
Likelihood Ratio
663,464
7
,000
263,011
1
,000
Pearson Chi-Square
N of Valid Cases
493,482
764
count is 17,39.
57
Transect * No. of stems
Chi-Square Tests
Value
df
Pearson Chi-Square
Likelihood Ratio
a
9
,053
19,587
9
,021
4,291
1
,038
16,752
N of Valid Cases
764
Univariate Analysis of Variance
Tests of Between-Subjects Effects
Dependent Variable: Weight of plant
Source
Type III Sum of
df
Mean Square
F
Sig.
Squares
a
11
206,252
13,947
,000
Intercept
425,799
1
425,799
28,794
,000
Diameter
69,992
1
69,992
4,733
,032
Transect
7,695
1
7,695
,520
,472
1891,122
5
378,224
25,577
,000
193,668
4
48,417
3,274
,014
Error
1804,109
122
14,788
Total
6526,520
134
Corrected Total
4072,881
133
Corrected Model
Transectcode
Transect * Transectcode
2268,772
a. R Squared = ,557 (Adjusted R Squared = ,517)
UNIANOVA Height BY Transect Transectcode WITH Diameter
/METHOD=SSTYPE(3)
/INTERCEPT=INCLUDE
/CRITERIA=ALPHA(0.05)
/DESIGN=Diameter Transect Transectcode Transect*Transectcode.
58
Univariate Analysis of Variane
Tests of Between-Subjects Effects
Dependent Variable: Height
Source
Type III Sum of
df
Mean Square
F
Sig.
Squares
a
11
140,697
67,464
,000
Intercept
1219,948
1
1219,948
584,960
,000
Diameter
1235,970
1
1235,970
592,643
,000
56,498
5
11,300
5,418
,000
182,103
4
45,526
21,829
,000
Error
1568,313
752
2,086
Total
11903,000
764
3115,983
763
Corrected Model
1547,670
Transectcode
Transect * Transectcode
Corrected Total
a. R Squared = ,497 (Adjusted R Squared = ,489)
Crosstabs
Cases
Valid
N
Code grazed transects *
Viability of stems
Type of use
Ringed
Code grazed transects * No.
of leaves
Code grazed transects * %
Used
Missing
Percent
N
Total
Percent
N
Percent
324
42,4%
440
57,6%
764
100,0%
324
42,4%
440
57,6%
764
100,0%
324
42,4%
440
57,6%
764
100,0%
266
34,8%
498
65,2%
764
100,0%
324
42,4%
440
57,6%
764
100,0%
59
Code grazed transects * Viability of stems
Chi-Square Tests
Value
df
Pearson Chi-Square
a
10
,000
118,287
10
,000
67,001
1
,000
104,103
Likelihood Ratio
N of Valid Cases
324
a. 1 cells (5,6%) have expected count less than 5. The minimum expected
count is 4,94.
Code grazed transects * Type of use
Chi-Square Tests
Value
df
Pearson Chi-Square
a
15
,000
75,110
15
,000
,221
1
,638
77,384
Likelihood Ratio
Linear-by-Linear
Association
N of Valid Cases
324
expected count is 1,39.
Code grazed transects * Ringed
Chi-Square Tests
Value
df
Pearson Chi-Square
Likelihood Ratio
N of Valid Cases
a
5
,000
25,984
5
,000
5,336
1
,021
23,160
324
expected count is 2,91.
60
Code grazed transects * No. of leaves
Chi-Square Tests
Value
df
a
52
,013
88,861
52
,001
,231
1
,631
N of Valid Cases
266
Pearson Chi-Square
77,459
Likelihood Ratio
Code grazed transects * % Used
Chi-Square Tests
Value
df
Pearson Chi-Square
Likelihood Ratio
a
15
,000
101,961
15
,000
21,923
1
,000
103,883
N of Valid Cases
324
Crosstabs
Cases
Valid
N
Diameter
Height
Weight of plant
Missing
Percent
N
Total
Percent
N
Percent
324
42,4%
440
57,6%
764
100,0%
324
42,4%
440
57,6%
764
100,0%
72
9,4%
692
90,6%
764
100,0%
61
Code grazed transects * Diameter
Chi-Square Tests
Value
df
Pearson Chi-Square
94,978
a
70
,025
Likelihood Ratio
100,292
70
,010
11,704
1
,001
N of Valid Cases
324
Code grazed transects * Height
Chi-Square Tests
Value
df
Pearson Chi-Square
a
55
,000
133,967
55
,000
15,203
1
,000
126,702
Likelihood Ratio
N of Valid Cases
324
Code grazed transects * Weight of plant
Chi-Square Tests
Value
df
Pearson Chi-Square
Likelihood Ratio
N of Valid Cases
a
80
,003
105,713
80
,029
3,540
1
,060
119,886
72
62
Crosstabs
Cases
Valid
N
Code grazed transects * %
Cover
Code grazed transects * No.
of stems
Missing
Percent
N
Total
Percent
N
Percent
324
42,4%
440
57,6%
764
100,0%
324
42,4%
440
57,6%
764
100,0%
Code grazed transects * % Cover
Chi-Square Tests
Value
df
Pearson Chi-Square
a
25
,000
1145,370
25
,000
185,874
1
,000
1620,000
Likelihood Ratio
N of Valid Cases
324
a. 0 cells (0,0%) have expected count less than 5. The minimum expected
count is 5,19.
Code grazed transects * No. of stems
Chi-Square Tests
Value
df
a
40
,018
61,138
40
,017
,142
1
,706
N of Valid Cases
324
Pearson Chi-Square
Likelihood Ratio
61,045
expected count is,13.
63
Appendix IX
Statistical background short term analysis
Crosstabs
Cases
Valid
N
Before
or
after
grazing
*
Missing
Percent
N
Total
Percent
N
Percent
714
100.0%
0
.0%
714 100.0%
714
100.0%
0
.0%
714 100.0%
714
100.0%
0
.0%
714 100.0%
656
91.9%
58
8.1%
714 100.0%
714
100.0%
0
.0%
714 100.0%
Before or after grazing * Height 714
100.0%
0
.0%
714 100.0%
714
100.0%
0
.0%
714 100.0%
714
100.0%
0
.0%
714 100.0%
714
100.0%
0
.0%
714 100.0%
Number of stems
Before
or
after
grazing
*
or
after
grazing
*
grazing
*
grazing
*
Ringed
Before
Viability of stems
Before
or
after
Number of leaves
Before
or
after
Diameter
Before or after grazing * Type
of use
Before
or
after
grazing
*
grazing
*
Percentage of use
Before
or
after
Percentage of cover
Before or after grazing * Percentage of cover
Chi-Square Tests
Asymp. Sig. (2Value
df
sided)
Pearson Chi-Square
2.746E2
5
.000
Likelihood Ratio
338.505
5
.000
28.877
1
.000
N of Valid Cases
714
a. 0 cells (.0%) have expected count less than 5. The minimum expected count is
18.61.
64
Symmetric Measures
Asymp. Std. Errora
Value
Interval by Interval
Pearson's R
Ordinal by Ordinal
Spearman Correlation
Approx. Tb
Approx. Sig.
-.201
.035
-5.482
.000c
.007
.042
.175
.861c
N of Valid Cases
714
a. Not assuming the null hypothesis.
b. Using the asymptotic standard error assuming the null hypothesis.
c. Based on normal approximation.
Before or after grazing * Percentage of use
Chi-Square Tests
Asymp. Sig. (2Value
df
sided)
a
3
.063
Likelihood Ratio
7.657
3
.054
5.617
1
.018
Pearson Chi-Square
7.280
N of Valid Cases
714
a. 2 cells (25.0%) have expected count less than 5. The minimum expected count
is .45.
Symmetric Measures
Asymp. Std. Errora
Value
Approx. Tb
Approx. Sig.
Pearson's R
-.089
.037
-2.378
.018c
Ordinal by Ordinal
-.089
.037
-2.385
.017c
N of Valid Cases
714
65
Before or after grazing * Type of use
Chi-Square Tests
Asymp. Sig. (2Value
df
sided)
a
4
.000
Likelihood Ratio
27.962
4
.000
20.595
1
.000
Pearson Chi-Square
25.857
N of Valid Cases
714
is .91.
Symmetric Measures
Asymp. Std. Errora
Value
Approx. Tb
Approx. Sig.
Pearson's R
.170
.035
4.602
.000c
Ordinal by Ordinal
.170
.036
4.597
.000c
N of Valid Cases
714
Before or after grazing * Height
Chi-Square Tests
Asymp. Sig. (2Value
Pearson Chi-Square
Likelihood Ratio
N of Valid Cases
df
sided)
a
12
.441
12.902
12
.376
2.357
1
.125
12.062
714
is .91.
66
Symmetric Measures
Asymp. Std. Errora Approx. Tb Approx. Sig.
Value
Pearson's R
-.057
.038
-1.537
.125c
Ordinal by Ordinal
-.051
.037
-1.368
.172c
N of Valid Cases
714
Before or after grazing * Diameter
Chi-Square Tests
Asymp. Sig. (2Value
Pearson Chi-Square
df
a
17
.044
32.682
17
.012
5.971
1
.015
28.082
Likelihood Ratio
N of Valid Cases
sided)
714
is .45.
Symmetric Measures
Value Asymp. Std. Errora Approx. Tb Approx. Sig.
Pearson's R
-.092
.036
-2.452
.014c
Ordinal by Ordinal
-.131
.037
-3.516
.000c
N of Valid Cases
714
67
Before or after grazing * Number of leaves
Chi-Square Tests
Asymp. Sig. (2Value
df
sided)
a
13
.000
Likelihood Ratio
57.228
13
.000
33.113
1
.000
Pearson Chi-Square
53.607
N of Valid Cases
656
is .41.
Symmetric Measures
Value
Pearson's R
-.225
.038
-5.901
.000c
Ordinal by Ordinal
-.196
.039
-5.106
.000c
N of Valid Cases
656
Before or after grazing * Viability of stems
Chi-Square Tests
Asymp. Sig. (2Value
Pearson Chi-Square
Likelihood Ratio
N of Valid Cases
df
sided)
a
3
.001
16.466
3
.001
7.902
1
.005
16.017
714
is .45.
68
Symmetric Measures
Value
Pearson's R
.105
.034
2.825
.005c
Ordinal by Ordinal
.117
.037
3.143
.002c
N of Valid Cases
714
Before or after grazing * Ringed
Chi-Square Tests
Value
df
Asymp. Sig. (2-sided) Exact Sig. (2-sided) Exact Sig. (1-sided)
.134a
1
.715
Continuity Correctionb
.047
1
.829
Likelihood Ratio
.133
1
.715
Pearson Chi-Square
Fisher's Exact Test
.765
.134
N of Valid Cases
714
1
.413
.715
a. 0 cells (.0%) have expected count less than 5. The minimum expected count is 21.78.
b. Computed only for a 2x2 table
Symmetric Measures
Value Asymp. Std. Errora Approx. Tb Approx. Sig.
Pearson's R
.014
.038
.365
.715c
Ordinal by Ordinal
.014
.038
.365
.715c
N of Valid Cases
714
69
Before or after grazing * Number of stems
Chi-Square Tests
Asymp. Sig. (2Value
Pearson Chi-Square
df
sided)
a
9
.268
12.382
9
.193
2.103
1
.147
11.110
Likelihood Ratio
N of Valid Cases
714
is .45.
Symmetric Measures
Value
Pearson's R
-.054
.036
-1.451
.147c
Ordinal by Ordinal
-.046
.038
-1.219
.223c
N of Valid Cases
714
Component Matrixa,b
Component
1
2
Number of stems
0,469637
0,102864
Viability of stems
0,262783
-0,75486
Number of leaves
-0,32432
0,73372
Diameter
0,828641
0,261014
Height
0,832632
0,094538
Percentage of use
0,548436
0,346129
Percentage of cover
-0,23577
0,410636
Extraction Method: Principal Component Analysis.
a. 2 components extracted.
b. Only cases for which Grazed non grazed = Grazed are used in the analysis phase.
70
71

Prunus serotina removal by sheep in the Kennemerduinen dune

Transcription

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