Distribution of Anthriscus Sylvestris and Myrrhis Odorata Within Open Areas of Reykjavík, Iceland

Distribution of Anthriscus sylvestris and Myrrhis odorata within open areas of Reykjavík, Iceland

Mervi Orvokki Luoma

Faculty of Life and Environmental Sciences University of Iceland 2019

Distribution of Anthriscus sylvestris and Myrrhis odorata within open areas of Reykjavík, Iceland

Mervi Orvokki Luoma

60 ECTS thesis submitted in partial fulfillment of a Magister Scientiarum degree in Environment and Natural Resources

MS Committee Mariana Tamayo Snorri Sigurðsson

Master’s Examiner Borgþór Magnússon

Faculty of Life and Environmental Sciences School of Engineering and Natural Sciences University of Iceland Reykjavík, February 2019

Distribution of Anthriscus sylvestris and Myrrhis odorata within open areas of Reykjavík, Iceland Cow Parsley & Sweet Cicely in Reykjavík 60 ECTS thesis submitted in partial fulfillment of a Magister Scientiarum degree in Environment and Natural Resources

Faculty of Life and Environmental Sciences School of Engineering and Natural Sciences University of Iceland Sæmundargata 2 101, Reykjavík Iceland

Telephone: 525 4000

Bibliographic information: Mervi Orvokki Luoma, 2019, Distribution of Anthriscus sylvestris and Myrrhis odorata within open areas of Reykjavík, Iceland , Master’s thesis, Faculty of Life and Environmental Sciences, University of Iceland, pp. 101.

Printing: Háskólaprent Reykjavík, Iceland, February 2019 Abstract

The main purpose of the research was to map the distribution of cow parsley (Anthriscus sylvestris), an invasive alien plant, within four open areas in Reykjavík; Laugarnes, Vatnsmýri, Elliðaárdalur, and Ægisíða. The aim was to identify hot spot areas with high abundance of cow parsley as that may increase the risk of losing native plant species in those areas. Furthermore, the distribution of sweet cicely (Myrrhis odorata) was mapped to assess if there is overlap in the cover of these two plant species from the Apiaceae family that share similar plant traits. The total combined size of the four study areas surveyed was 158 ha. Results indicate that cow parsley covered 10% (15.5 ha) of the study areas and was most abundant near pathways, riversides and streams. Cow parsley is spreading and is a serious concern in the wildlife nature reserve of Vatnsmýri and the popular outdoor area of Elliðaárdalur. Over 30 plant taxa were found in the plots within the study areas, a third of them being alien. Species richness did not vary significantly between areas with and without cow parsley; however areas with cow parsley had significantly greater cover of alien species (p < 0,001). This is the first time that cow parsley is mapped in Reykjavík, which is essential for developing management plans and actions. Mapping the distribution of alien and invasive species, testing and adopting a multi-approach techniques via adaptive management, and conducting long-term monitoring are the key in fostering a functioning, species rich urban ecosystem.

Útdráttur

Tilgangur rannsóknarinnar var að kortleggja útbreiðslu skógarkerfils (Anthriscus sylvestris), ágengrar framandi plöntutegundar, á opnum svæðum í Reykjavík. Markmiðið var að greina hvernig útbreiðslunni var háttað á þessum svæðum og finna „heita reiti“ þar sem þéttleikinn var mestur. Skógarkerfill hefur breiðst hratt út á Íslandi og getur ógnað innlendri flóru því hann vex gjarnan í einsleitum breiðum sem bola öðrum gróðri burt en geta einnig leitt til jarðvegseyðingar og breytingum á landslagi. Útbreiðslan var könnuð árin 2017 og 2018 á fjórum opnum svæðum í Reykjavík: Elliðarárdal, Laugarnesi, Vatnsmýri og Ægisíðu. Jafnframt voru plöntusamfélög nálægt skógarkerfilsbreiðum skoðuð. Niðurstöður sýna að skógarkerfill þakti að meðaltali 10% svæðanna og var þéttleikinn mestur nálægt stígum og á árbökkum. Skógarkerfill er mjög algengur í fuglafriðlandinu í Vatnsmýri og í Elliðaárdal. Yfir þrjátíu tegundir blómplantna fundust við skoðun á plöntusamfélögum, þar af um þriðjungur framandi tegundir. Tegundaauðgi var ekki marktæk breytileg milli svæða með eða án skógarkerfils, hins vegar var marktækt meiri þekja framandi tegunda á svæðum með skógarkerfil. Í þessari rannsókn er í fyrsta sinn kortlögð útbreiðsla skógarkerfils í Reykjavík, og er um mikilvægar upplýsingar að ræða fyrir náttúruvernd og skipulag í borginni. Að greina útbreiðslu framandi ágengra tegunda er grunnforsenda fyrir ákvarðanatöku um hreinsunar- og fækkunaraðgerðir og til að móta vöktunar- og rannsóknaráætlanir á lykilvistkerfum í borginni.

Table of Contents

Abstract ...... iii

Table of Contents ...... vii

List of Figures ...... viii

List of Tables ...... x

Acknowledgements ...... xi

1 Distribution of Cow Parsley (Anthriscus sylvestris) and Sweet Cicely (Myrrhis odorata) within open areas of Reykjavík ...... 1 1.1 Introduction ...... 1 1.2 Methods ...... 4 1.2.1 Target species ...... 4 1.2.2 Study areas ...... 5 1.2.2 Mapping ...... 11 1.3 Results ...... 11 1.4 Discussion ...... 21 1.5 Conclusions ...... 25 References ...... 26

2 Potential impact of cow parsley (Anthriscus sylvestris) invasion on native plant communities in Reykjavík ...... 34 2.1. Introduction ...... 34 2.2 Methods ...... 35 2.2.1 Study areas ...... 35 2.2.2 Characterization of plant communities ...... 39 2.2.3 Statistical analysis ...... 40 2.3 Results ...... 40 2.4 Discussion ...... 45 2.4.1 Plant community associated with cow parsley ...... 45 2.4.2 Management of cow parsley ...... 48 2.5 Conclusions ...... 52 References ...... 53 Appendix A. Survey Sites ...... 60 Appendix B. Plant Illustrations ...... 72 Appendix C. Maps of Plant Communities and Mowing Areas ...... 76 Appendix D. Plot measurements datasets ...... 85 Appendix E. Tallest Plant Species in Plots without Cow Parsley ...... 89 Appendix F. Maps of Study Plots and Mowing Areas ...... 95

vii List of Figures

Chapter 1

Figure 1.1. Target species ...... 4

Figure 1.2. Study areas in Reykjavík ...... 5

Figure 1.3. Laugarnes area in Reykjavík ...... 6

Figure 1.4. Vatnsmýri area in Reykjavík ...... 7

Figure 1.5. Elliðaárdalur Valley area in Reykjavík ...... 9

Figure 1.6. Ægisiða area in Reykjavík ...... 10

Figure 1.7. Laugarnes plant distribution ...... 13

Figure 1.8. Frequency of patch size in Laugarnes for cow parsley and sweet cicely...... 14

Figure 1.9. Vatnsmýri plant distribution ...... 15

Figure 1.10. Frequency of patch size in Vatnsmýri for cow parsley and sweet cicely ...... 16

Figure 1.11. Elliðaárdalur plant distribution ...... 18

Figure 1.12. Frequency of patch size in Geirsnef and Elliðaárdalur for cow parsley and sweet cicely...... 19

Figure 1.13. Ægisiða plant distribution ...... 20

Figure 1.14. Frequency of patch size in Ægisíða for cow parsley and sweet cicely ...... 21

viii Chapter 2

Figure 2.1. Survey plots in Æegisíða and Vatnsmýri…………………………………………..36

Figure 2.2. Survey plots in Laugarnes…………………………………………………………...37

Figure 2.3. Survey plots in Elliðaárdalur………………………………………………………..38

Figure 2.4. Survey plots and tall plant species in Vatnsmýri………………………………….39

ix List of Tables

Chapter 1

Table 1.1. Distribution and cover of cow parsley and sweet cicely in the study areas ……………………………………………………….12

Table 1.2. Average patch sizes of cow parsley among the study sites……………………….12

Chapter 2

Table 2.1. Average plant cover, plant taxa richness, and tallest plant height in all survey plots……………………………………………………………..41

Table 2.2. Mean cover of plant taxa present in the plots with and without cow parsley surveyed in 2017 and 2018…………………………………...43

Table 2.3. Total number of invasive, alien, native plant species, grasses, and mosses present in the study sites and their average cover………………………………..44

Table 2.4. The average cover (%) of invasive, alien, native plant species, grasses, and mosses present in plots with and without cow parsley…………………………………………44

Table 2.5. Management recommendations for each study site………………………………..51

x Acknowledgements

I would like to thank Náttúruverndarsjóður Pálma Jónssonar for granting me funding for my field work during summer 2017. I am grateful beyond words for my supervisors Mariana Lucia Tamayo and Snorri Sigurðsson. I am thanking you both for guiding me through this process and giving me invaluable advice and input during this journey. I also want to thank my examiner Borgþór Magnússon at the Icelandic Natural History Institute for taking the time to review my work. Very special thanks to my dear friends and study colleagues, Danielle Beauchemin and Valentina Klaas for your motivation and support. Thank you Tarun Devrani for helping me with ArcGIS. Thank you Julien Achache for your support and understanding. And lastly, I want to thank my family, who have supported and encouraged me throughout my studies.

1 Distribution of Cow Parsley (Anthriscus sylvestris) and Sweet Cicely (Myrrhis odorata) within open areas of Reykjavík

1.1 Introduction

Protection of urban biodiversity is a key priority for many cities around the world. However, promoting the success of all biodiversity regardless of origin or characteristics may lead to decline of native species. Research indicates that plant invasions are the most important factor reducing local plant diversity globally (Pimentel et al., 2005; Keller et al., 2011; Vellend et al., 2013), and that alien species might benefit at the expense of natives within urban areas (Shochat et al., 2010; Aronson et al., 2014). For example, native wetland plants declined in Lake Ontario, Canada with increasing urban human population density and percent cover of alien wetland plants (Glyceria maxima and Phragmites australis) (Wei & Chow-Fraser, 2006). However, some studies, suggest that urban areas have a higher number of both native and alien plant species than rural areas due to urban areas possessing a greater habitat variability (Kühn et al., 2004; Wania et al., 2006). Furthermore, in Central European cities the larger the city the greater the number of alien and native plants species (Pyšek, 1998). Although plant richness can be high in urban areas, these areas can also be hotspots for invasions of alien species (Marco et al., 2010; Gaertner et al., 2017). It is widely recognized that alien species will be an increasing problem, not only due to the globalization of economies and the movement of people and materials, but also because of the susceptibility of disturbed ecosystems to invasions (Walker & Steffen, 1997; EEA, 2016). The invasion of alien species into new areas including cities, is a concern for policy makers, resource managers, and researchers because they can threaten agricultural productivity, native biodiversity, ecosystem functioning, human aesthetics and wellbeing, as well as overall economic and ecological health (Pimentel et al., 2005; Pejchar & Mooney, 2009; Simberloff et al., 2013). The importance of this cannot be understated as the impacts of invasive alien species often appear and affect their communities gradually, but can lead to large-scale, and irreversible consequences (Neely, 2000; Simberloff et al., 2013; EEA, 2016). Nonetheless, some studies have found that alien plant species can sometimes have positive impacts (Gleditch & Carlo, 2010; Gribben et al., 2013; Salisbury et al., 2015). For example, alien garden plants can benefit pollinators in urban habitats by supplying more consistent resources throughout the growing season (Salisbury et al., 2015). Similarily, fruits from invasive honeysuckles (Lonicera spp) show a strong positive relationship with the abundance of native frugivorous birds in central Pennsylvania, USA (Gleditsch & Carlo, 2010). Research on species invasions in habitats in the Czech Republic showed that the highest amount of invasive alien species occur in habitats that are made by humans (Pyšek, Chytrý & Jarošík, 2009). However, the there is a considerable difference in the invasibility

1 of habitats (i.e. vulnerability of habitats to invasion), where habitats with fluctuating availability of resources, especially nutrients, are most susceptible to invasion. These habitats are also frequently or strongly disturbed (Pyšek, Chytrý & Jarošík, 2009). Cadotte et al. (2017) identified four general categories of potential causes that make urban areas suitable for alien species to thrive. The first one is propagule pressure, which occurs when „individuals or propagules of alien species are purposefully introduced into urban areas“ (Cadotte et al., 2017). Plant invasions can start from ornamental plantings (Lee et al. 2015), which has in fact been suspected as one of the reasons for the spread of the alien plant cow parsley (Anthriscus sylvestris) in Iceland (Magnússon, 2011). A second category is about reduced negative interactions, e.g. reduced species competition among plants usually mediated by gardeners, which alters the negative interactions such as competition and predation of species. The third category, resource supply, is a factor that is either reduced or enhanced in urban areas. Lastly, urban areas provide a unique and altered combination of environmental conditions that are typically different than those in unmodified, natural state landscapes (Cadotte et al., 2017). An example of this is the abundance of light with the open ground cover, which can enable the growth of alien species within urban areas. The city of Reykjavík, Iceland, like many other cities worldwide is committed to urban biodiversity and recognizes invasive species as a focus area in its biodiversity policy (City of Reykjavík, 2016a). Reykjavík’s northern location limits its biodiversity as it is geographically isolated, has a short growing season and conditions for plant species growth are generally challenging (Haraldsson & Ólafsdóttir, 2003; Gretarsdottir et al., 2004). The city’s biodiversity policy recognizes that alien animal species are increasing in Reykjavík, and that there is a high diversity of alien plant species in the city (City of Reykjavík, 2016a). Part of Reykjavík‘s biodiversity strategy includes identifying and mapping invasive species, developing management actions, and public outreach (City of Reykjavík, 2016a). Invasive plants, such as hogweed (Heracleum spp) have already presented a severe public health issue (Sigurgeirsdóttir & Hilmarsdóttir, 2017; City of Reykjavík, 2018a), and Nootka lupine (Lupinus nootkatensis) seems to be a threat to insect pollinators (Willow, Tamayo & Jóhannsson, 2017). The city is also concerned about cow parsley, which has been spreading throughout Reykjavík and Iceland (Magnússon, 2011). Cow parsley is a biennial or short-lived perennial plant, native to Europe and Asia but not to Iceland (Magnússon, 2011; Elmarsdóttir et al., 2011; Wasowicz, Przedpelska- Wasowicz & Kristinsson, 2013; Swearingen & Bargeron, 2016). The plant has been introduced in Canada (Darbyshire et al., 1999), the United States (USA) (USDA, 2018a), and is even found in the Arctic in Svalbard, where it is now considered as potentially invasive (Gederaas et al., 2012; Alsos, Ware & Elven, 2015). The states of Vermont and New York, USA have declared cow parsley as an invasive weed (USDA, 2018a), and have included it in their prohibited species list (New York State Department of Environmental Conservation, 2014). Cow parsley has been first recorded in Iceland in 1927 in Akureyri (Òskarsson, 1932). The plant may have been introduced to Iceland in wildflower mixtures or as an ornamental plant. After being introduced to Iceland, cow parsley became widely established in Reykjavik during World War II particularly in gardens and army camps. This plant spread quickly throughout Iceland from 1940 to 1965 (Davidsson, 1967). Cow parsley was not considered as an invasive species in Iceland until fairly recently (in the last 10-15 years) when its distribution and abundance increased in many areas (Magnússon, Björnsson & Guðleifsson, 2006; Magnússon, 2011). Currently, cow parsley is widely spread throughout Iceland, often growing in monocultures (Magnússon, 2011). Unlike Nootka lupine, cow parsley does very little to enrich the soil, and it undercuts biodiversity by replacing other flora (Hansson & Persson,

2 1994). It can also enhance soil erosion and enable invasion of other alien plants (Godefroid & Koedam, 2003). Cow parsley spreads rapidly and degrades the habitats for native plant species in Iceland (Magnússon, 2011; Miller & D'Auria, 2011), and elsewhere such as in species rich nature reserve areas in Sweden, hay fields and pastures in Vermont, and pastures, roadsides and forest edges in British Columbia, Canada (Hansson& Persson, 1994; Bosworth, 2000; The Ministries of Transportation and Infrastructure, and Forests, Lands, and Natural Resource Operations, 2016). Although the plant often spreads in areas formerly used as pasture land, the negative impacts it has in urban areas cannot be undermined (Magnússon, 2011; Pilto, 2012). Degradation of the cultural landscape is emphasized by the difficulty of eradicating cow parsley once it has become established (Hansson & Persson, 1994; Magnússon, 2011; Jørgensen et.al., 2013). Preserving the native vegetation in Iceland is especially important as the country has the lowest vegetation cover in all of Europe with only 45% cover in total; over 40% of land is covered by deserts (Arnalds, 2015). Cow parsley is a growing concern in Iceland and globally as it can drastically change landscapes and has proven to be very hard to eradicate (Darbyshire et al., 1999; Jørgensen et al., 2013; Førde & Magnussen, 2015). Tourism in Iceland has grown at a fast rate in recent years, and Reykjavik is a popular destination for tourists arriving both by plane and cruise ships (Icelandic Tourist Board, 2018). The number of tourists has increased significantly from 488,600 in 2010 to 2,224,600 tourists in 2017 (Icelandic Tourist Board, 2018). This greater traffic of people and transportation modes is a potential pathway for alien species introductions and their dispersal in Reykjavik and other areas in Iceland. Wacsowicz (2016) found that the dispersal by humans through the road network contributes to the movement of plant propagules, as well as the spread of plant species used in restoration in Iceland.The study also indicated that areas with tourist attractions, geothermal activity, hiking huts and shelters along the highlands host very high numbers of alien species, and this number has increased dramatically within the last two decades. Increased human activities in Reykjavík, as well as increased construction work, can also enable the spread of alien species as there is more exposed land space and construction work requires movement and storage of large masses of soil (Þórsson, 2017). Although cow parsley has spread throughout Iceland, there is limited information about its distribution in urban areas, especially in Reykjavík (Wasowicz, Przedpelska- Wasowicz & Kristinsson, 2013). In recent years, cow parsley has been monitored and managed using pesticides (glyphosate spraying), cutting, pulling out individual plants and grazing in parts of the western and northern Iceland with mixed results (Elmarsdóttir et al., 2011; Jónsson & Þórðarson, 2018). Currently, it is unclear where cow parsley is most abundant and what its distribution patterns in Reykjavík are. Similarly, there is a lack of information on the plant community associated with cow parsley in urban areas, and whether it overlaps with other alien plants such as sweet cicely (Spánarkerfill = Myrrhis odorata). Both cow parsley and sweet cicely belong to the carrot family (Apiaceae). They have a very similar appearance, both forming small white flowers that are arranged into a flat umbrella- like head, and having a similar height range (Kristinsson, 2013). Sweet cicely is native to central and southern Europe and is classified as an alien species in Iceland, but so far it has not been evaluated with regards to invasiveness (Anderberg, 2008; von Schmalensee, 2010). This study addresses several data gaps by assessing the distribution and abundance of both cow parsley and sweet cicely in Reykjavik. Specifically, areas where these species are growing were mapped and categorized in terms of distribution (dense stands versus scattered plants), type of land (e.g., grasslands, wetland, riversides), and other plant species present. This information will be useful for invasive species management and land planning actions,

3 and contribute to the conservation of urban biodiversity, which is a priority for Reykjavík and other cities around the world. 1.2 Methods

1.2.1 Target species

Cow parsley is a herbaceous biennial or a short-lived perennial plant, which can usually grow 0.3–1.5 m tall; however personal observation shows that in Iceland they can grow up to 2 meters in height. The flowers are small, white and arranged into compound umbels. In Iceland, the mature plants start flowering in early June and spread seeds in late July or even later (Magnússon, 2011; Elmarsdóttir et al., 2011; Swearingen & Bargeron, 2016). Each plant may produce up to 10,000 seeds, but it can also reproduce from the root buds at the top of the root (Darbyshire et al., 1999). The plant does not have a particular obvious dispersal method, as the seeds usually fall close to the mother plant. However, seeds can be spread through wind and water, and human activities can also mediate the dispersal of cow parsley (Hansson & Persson, 1994; Magnússon, 2011). For example, seeds can be transported by shoes, vehicles and agricultural activities, and often cow parsley grows along waterways, pathways, and streets (Hansson & Persson, 1994; Magnússon, 2011). Sweet cicely is a perennial plant that can easily be confused with cow parsley; however, sweet cicely has lighter green leaves. Also, the seeds of sweet cicely are much larger in size, and the plant species has a very distinctive, anise-like odor (Kristinsson, 2013). Like cow parsley, sweet cicely regenerates by seeds and taproot (Penny, 2018). Sweet cicely is found throughout Iceland in woodlands, farms and along streams. It is common in gardens in the capital area, in the north, and also in villages in Westfjords and Eastfjords (Icelandic Institute of Natural History, 2018). Photos of both plant species are shown below in Figure 1.1.

Figure 1.1. Target species. On the left, sweet cicely in Laugarnes on June 22, 2017. On the right, cow parsley in Elliðaárdalur on June 5th, 2018.

4 1.2.2 Study areas

The distribution and abundance of cow parsley was assessed in four study sites in Reykjavik, located in Laugarnes, Vatnsmýri, Elliðaárdalur, and Ægisíða (Figure 1.1). The sites were all open, public spaces rich in vegetation.

Figure 1.2. Study areas in Reykjavík are highlighted in red. 1. Laugarnes, 2. Vatnsmýri, 3. Elliðaárdalur, 4. Ægisíða. Basemap: Léttkort af Reykjavík, 2016 drawn by Mervi Luoma with ArcGIS (ESRI, 2017a).

5 Laugarnes Laugarnes is in the northern part of Reykjavik by the coast and is currently a popular outdoor area hosting Sigurjón Ólafsson Museum and a few residential buildings. Laugarnes also has many archaeological sites, two of which are protected. In the past, the area was more densely populated, and was also used as a pasture land, as well as hosting a military community during World War II (Guðmundsdóttir, 2003). The study area in Laugarnes was 12,3 ha in size, and the area type can be described as being a grassland. Invasive plants such as giant hogweed and lupin as well as other species that characterize disturbed areas are very common in the area. Figure 1.3 shows an aerial photo of Laugarnes.

Figure 1.3. Laugarnes area in Reykjavík. Protected area is outlined red with shaded green horizontal lines and archaeological sites are indicated with blue stars. Source: LUKR, Borgarvefsjá, aerial photo July 28, 2017.

6 Vatnsmýri Vatnsmýri is located in the western part of Reykjavik next to the University of Iceland and in close proximity to the Reykjavik Airport. It is a large, mostly wetland area encompassing 3,7 ha. The study area included the surrounding grassland area next to the wetland and was in total 8,7 ha. This area is a wildlife nature reserve, which is closed during the summertime as it serves as nesting ground for migrating and resident birds, including ducks, waders, and a colony of arctic terns (Sterna paradisaea) (Palsson, 2003; Sigurðsson, 2015). A survey in 2003, recorded a total of 83 vascular plant species in the area of which 65 were native to Iceland (Pálsson, 2003). The nature reserve is a water source for Tjörnin Lake, and is located in an area that is undergoing extensive changes due to new residential areas planned to replace the Reykjavík Airport (City of Reykjavik, 2014). In recent years, the wetland area was also changed with an aim to improve the habitat for nesting birds. The water level was increased and the elevation of some of the islands in the wetland was decreased through plant and soil removal in order to manage the abundance of cow parsley and other alien plants (S. Sigurðsson, personal communication, January 22, 2019). An aerial view of Vatnsmýri and surrounding area are shown in Figure 1.4. The study area in Vatnsmýri consists only of the outer edges of the nature reserve, because the inner part of the nature reserve was closed during the survey period for birds nesting in the area. However, as the plant survey in the area was conducted in early June, it was possible to see the inner parts of the study area for descriptive data (Appendix A; Figure 5).

Figure 1.4. Vatnsmýri area in Reykjavík. The protected area in Vatnsmýri is outlined red with shaded green horizontal lines. Source: LUKR, Borgarvefsjá, aerial photo July 28, 2017.

7 Elliðaárdalur Elliðaárdalur is one of the largest green areas in Reykjavik, popular for various outdoor activities including hiking, fishing, and biking. This area is in the eastern part of Reykjavik and previously hosted sheep farms, as well as summer houses, and also used for forestry (City of Reykjavik, 2016b). Nowadays the area is characterized by varied landscapes, terrain and vegetation, with the Elliðaár River forming the center of the area. The land type is a mixture of forest and grassland. Elliðaár River starts at Elliðavatn Lake in the south and flows down the valley northwards between Breiðholt and Selás and Ártúnsholt and eventually forks (City of Reykjavík, 2016b; Pálsson, 2004). A variety of plants, including a forest can be found in Elliðaárdalur Valley, which hosts a rich bird community of approximately 25 different species. At least 315 vascular plants species are present in the area, of which 179 (56,82%) are native species (Pálsson, 2004). The study area was 116,2 ha in size and consists also of Geirsnef, an open area popular for dog owners, located north of Elliðaárdalur Valley as well as Háubakkar, a geologically significant protected area located west of Geirsnef (City of Reykjavík, 2018b). The Elliðaárdalur Valley study area is shown in Figure 1.5. The study area includes an open area above Geirsnef near industrial buildings.

Figure 1.5. Elliðaárdalur Valley area in Reykjavík. The protected area in the valley is outlined red with shaded green horizontal lines. Háubakkar, geologically significant protected area is outlined red with bright green color. Source: LUKR, Borgarvefsjá, aerial photo July 28, 2017.

9 Ægisiða Ægisiða is a long residential street located in Vesturbær, in the north western part of Reykjavik by the shoreline. The study area is the open area between the street and the shoreline, which is protected (Figure 1.6). The study area was 20,7 ha in size. This grassland area is mostly covered by grass, although there are large patches of cow parsley and garden angelica (Angelica archangelica) growing at the southern end of the area close to a residential building. Grass fields have been created for football and to some extent to make hay in the past when the area was used for farming. An aerial photo from 1954 reveals that the study area used to have more houses, and also some industrial buildings (Borgarvefsjá, 1954). The area along the street nowadays is flat and has both pedestrian and cycling paths running next to the main street. There is also a picnic area, an old fishermen‘s hut, and a separate, narrow path for walking right next to the shoreline. The area is popular for walking a dog, jogging, and cycling. Reykjavík airport is within very close vicinity of the street.

Figure 1.6. Ægisiða area in Reykjavík. The protected area by the shoreline is outlined red with shaded green horizontal lines. Source: LUKR, Borgarvefsjá, aerial photo July 28, 2017.

10 1.2.2 Mapping

Surveys were conducted between May 31st to October 25th, 2017 using AllTrailsPro and ArcGIS mobile applications (AllTrails, 2017; ESRI, 2017b). These mobile applications were used to record the GPS locations of cow parsley and sweet cicely plants in the four study areas. In addition, polygon shapes were also drawn using the ArcGIS mobile application to indicate the distribution and extent of cow parsley and sweet cicely in the survey sites. The area of distribution was then calculated by identifying the polygon area with each species using the SHAPE_Area feature (ESRI, 2017b). Furthermore, the distribution of cow parsley and sweet cicely was characterized by classifying it either as dense plant stands/patches or scattered plants. A dense plant stand/patch was one with 3 or more individual plants over a m2 area on average. In contrast, scattered plants referred to a plant patch larger than 0,5 m2 but with 2 or less individual plants, over a m2 on average. In the case of sweet cicely, a scattered distribution usually indicated a single plant that encompassed a polygon that was 1 m2 or less in size. The distribution of sweet cicely was assessed and mapped to see if there were any synergies in distribution with cow parsley. Photos of both cow parsley and sweet cicely communities present were also taken at all the study sites for reference. Distribution maps of cow parsley and sweet cicely were generated with ArcGIS software’s ArcMap 10.4.1. (ESRI, 2017a). The geographic coordinate system used for data gathering was GCS_WGS_1984 with a Prime Meridian set for Greenwich. All data used in the mapping was projected as WGS_1984_Web_Mercantor_Axiliary_Sphere with metric linear unit. Due to the similar appearance of other plant species, the surveys of cow parsley and sweet cicely were done on foot. Although a drone can be useful for mapping plants such as Nootka lupin which is easily distinguished from other plants due to its distinctive color, cow parsley can easily be mistaken with sweet cicely and ground elder (Aegopodium podagraria) when not identified at a close distance (Appendix B).

1.3 Results

Overall, nearly 10% of the study areas were covered with cow parsley. Vatnsmýri, with over 23% of cow parsley plant cover, had the largest cover of cow parsley. Sweet cicely coverage was fairly low in all study areas except for Laugarnes, where it was double that of cow parsley, covering over 8% (Table 1.1). Cow parsley cover, however, was not significantly different among the study sites [F(3, 16) = 0,119, p = 0,947]. Cow parsley covers the greatest area in Elliðaárdalur, where it encompassed about 12.8 ha (Table 1.1). This was followed by Vatnsmýri, occurring in approximately 2 ha. In Laugarnes, cow parsley was present in about 0.5 ha, and in Ægisíða in 0.2 ha. The largest cover of sweet cicely was recorded in Laugarnes, occurring in approximately 1 ha (Table 1.1). The second largest cover of sweet cicely among the study sites was in Elliðaárdalur with 0.46 ha. Ægisíða and Vatnsmýri had a fairly low distribution of sweet cicely, both having less than 0.05 ha. However it is worth noting that due to the bird nesting season, the inner area of Vatnsmýri was restricted from access, and the entire wetland area could not be mapped. Overall, the total area mapped in 2017 for all four sites was 158 ha, of which cow parsley and sweet cicely covered approximately 11%.

11 Table 1.1. Distribution in hectares (ha) and mean percent cover (%) of cow parsley and sweet cicely in the study areas in 2017. Total area (distribution) where sweet cicely and cow parsley was present is shown, as well as the total area surveyed for each site. In addition, the percentage of each area surveyed that was covered by sweet cicely, cow parsley, and both plant species is presented.

Total area Total Total surveyed distribution distribution CP SC & CP Study site per site (ha) of CP (ha) of SC (ha) SC % % %

Ægisíða 20,72 0,24 0,03 0,1 1,2 1,3

Elliðaárdalur 116,19 12,77 0,46 0,4 11 11,4

Laugarnes 12,31 0,51 1,01 8,3 4,1 12,4

Vatnsmýri 8,73 1,99 0,04 0,5 22,8 23,3 CP= Cow Parsley, SC = Sweet Cicely

A total of 396 cow parsley patches were recorded for all study sites, of which 34 were scattered plant patches. The average cow parsley patch was 392 m2 (SE ± 55), however the size of the patches varied greatly and ranged from less than 1 m2 up to 12251 m2 (Table 1.2). Sweet cicely was recorded in 98 patches in total, also varying in size from less than 1 m2 to a large, dense stand of 3875 m2. The average patch size of cow parsley varied significantly among the study sites [F(3, 392) = 5,584, p = 0,001] (Table 1.2). Overall, Laugarnes had significantly smaller patches of cow parsley than Elliðaárdalur (p = 0,001) and Vatnsmýri (p = 0.041) (Table 1.2). Furthermore, there was a significant difference among the patch sizes within the Elliðaárdalur study area [F(5, 239) = 11,948, p = 0,000]. The post doc Bonferroni test indicated that there were significantly smaller cow parsley patches in Háubakkar (area shown in Figure 1.4.) (p < 0,001; patch size = 106 m2 ± 57) than in the area east of Geirsnef (patch size = 2425 m2 ± 780). The study site below Geirsnef also had significantly smaller cow parsley patches (241 m2 ± 44) than the eastern (p < 0.001) and north eastern (p = 0,017; patch size = 1428 m2 ± 644) areas of Geirsnef. Additionally, the cow parsley patches found in Geirsnef were significantly smaller (p < 0,001; patch size = 574 m2 ± 168) than those located in the east of Geirsnef.

Table 1.2. Average patch sizes (m)2 of cow parsley among the study sites in 2017.

Number Mean patch Smallest Largest Site of patches size (m2) ± SE Patch (m2) patch (m2) Ægisída 11 221,8 ± 117,8 0,57 1254,4

Elliðaárdalur 245 521,1 ± 85,0 0,001 12251,5

Laugarnes 109 46,7 ± 10,1 0,02 520,5

Vatnsmýri 31 641,9 ± 136,3 0,88 3312,2

12 Laugarnes The distribution of cow parsley and sweet cicely in Laugarnes are shown in Figure 1.7. Cow parsley occured in dense stands and scattered patches as well as single plants scattered around the area, rarely overlapping with sweet cicely. Laugarnes also had three very large sweet cicely patches, two of which were located on the western corner of the area, where there was formerly a building, suggesting it has been planted there in the past. There was also a few large sweet cicely patches next to the cow parsley patches near the current residential buildings in Laugarnes. The majority of the patches (64%) of cow parsley and sweet cicely were under 10 m2 in size (Figure 1.8).

Figure 1.7. Laugarnes plant distribution, Summer 2017. Source: Data collection by Mervi Luoma with Collector for ArcGIS (ESRI, 2017a). Basemap: Léttkort af Reykjavík (2016).

13 3 > 1000 m2 -Very large patch

6 100 -999.9 m2 - Large patch 17

10-99.9 m2 - Medium patch 26 Sweet Cicely 17 Cow Parsley

20 1-10 m2 - Small patch 32

28 <1 m2 - Less than 3 plants 43

0 10 20 30 40 50

Figure 1.8. Frequency of patch size in Laugarnes for cow parsley and sweet cicely. The number of patches per size category and plant species are shown.

14 Vatnsmýri Vatnsmýri had a single, very large sweet cicely patch that was growing with cow parsley on the north eastern part of Vatnsmýri by the pathway next to heavily trafficked Hringbraut street (Figure 1.9). Most patches (77%) of cow parsley were dense and large, over 100 m2 in size, and scattered all around the area near the water and next to the walking paths (Figure 1.10).

Figure 1.9. Vatnsmýri plant distribution, Summer 2017. Source: Data collection by Mervi Luoma with Collector for ArcGIS (ESRI, 2017a). Basemap: Léttkort af Reykjavík (2016).

15 > 1000 m2 -Very large patch 8

1 100 -999.9 m2 - Large patch 16

10-99.9 m2 - Medium patch Sweet Cicely 5 Cow Parsley

1-10 m2 - Small patch 1

<1 m2 - Less than 3 plants 1

0 2 4 6 8 10 12 14 16 18

Figure 1.10. Frequency of patch size in Vatnsmýri for cow parsley and sweet cicely.The number of patches for each size category are shown.

16 Elliðaárdalur In Elliðaárdalur the area in and around Geirsnef had both dense and scattered cow parsley patches that were large in size right next to the downstream of the Elliðaár river. The distribution was also clearly visible along the walking paths in Geirsnef. Sweet cicely, however, was absent in this area (Figure 1.11). An example of scattered patches in Geirsnef is shown in Appendix A; Figure 9. In contrast, sweet cicely occurred in dense patches in the inner areas of Elliðaárdalur next to the walking paths but it did not overlap with cow parsley (Figure 1.11). The areas inside Elliðaárdalur had mostly dense patches of cow parsley occurring next to the walking and cycling paths as well as along the riverbed. In general, the majority (75%) of patches of cow parsley and sweet cicely in Elliðaárdalur were at least 10 m2 or larger (Figure 1.12). The most common patch size for both species was over 100 m2.

Figure 1.11. Elliðaárdalur plant distribution; Summer 2017. Source: Data collection by Mervi Luoma with Collector for ArcGIS (ESRI, 2017a). Basemap: Léttkort af Reykjavík (2016).

18 1 > 1000 m2 -Very large patch 26

7 100 -999.9 m2 - Large patch 88

2 10-99.9 m2 - Medium patch Sweet Cicely 69 Cow Parsley

1 1-10 m2 - Small patch 41

<1 m2 - Less than 3 plants 21

0 20 40 60 80 100

Figure 1.12. Frequency of patch size in Geirsnef and Elliðaárdalur for cow parsley and sweet cicely. The number of patches for each patch size category are shown.

Ægisíða The nortwestern and southern parts of Ægisíða had both dense and scattered patches of cow parsley and sweet cicely (Figures 1.13), and there was no overlap between the species. Overall, cow parsley was more prevalent in Ægisíða than sweet cicely. Most patches (71%) of cow parsley and sweet cicely were over 10 m2 in size (Figure 1.14).

Figure 1.13. Ægisiða plant distribution; Summer 2017. Source: Datacollection by Mervi Luoma with Collector for ArcGIS (ESRI, 2017a). Basemap: Léttkort af Reykjavík (2016).

> 1000 m2 -Very large patch 1

1 100 -999.9 m2 - Large patch 3

1 10-99.9 m2 - Medium patch Sweet Cicely 4 Cow Parsley

1-10 m2 - Small patch 1 2

<1 m2 - Less than 3 plants 1

0 1 2 3 4 5

Figure 1.14. Frequency of patch size in Ægisíða for cow parsley and sweet cicely. The number of patches in each patch size categery are shown.

1.4 Discussion

The overall abundance of cow parsley was more widespread than expected, with cow parsley patches encompassing 10% of the areas surveyed in Reykjavík. In all study sites, except in Ægisíða, cow parsley was spreading as a large scattered plant community in close proximity to existing cow parsley populations. Æegisíða had several dense cow parsley populations, but only a few very small patches of 1 to 3 cow parsley plants were recorded outside them. Large areas in Ægisíða are mown 4 times during the summer by the city (Appendix C; Figures 6, 7). It is possible that this mowing frequency keeps individual plants of cow parsley and sweet cicely from forming larger stands and patches, as it has been found that when the mowing begins early enough in the season it prevents seed dispersal. However, according to recent studies, mowing alone does not eradicate cow parsley, it only affects the spread of seeds (Ministries of Transportation and Infrastructure, and Forests, Lands, and Natural Resource Operations, 2016). This may explain why in Ægisíða there are only a few individual plants and two cow parsley communities present in the area where the grass is cut, while larger populations of cow parsley and sweet cicely occur outside the grass cutting range. One potential way of controlling cow parsley is to dig out individual seedlings of cow parsley with their tap roots early in the season before the flowering phase in areas where the grass is mowed (e.g. Ægisíða) as well as in places where small patches of cow parsley are encountered (Department of Agriculture, 2003). For large patches of cow parsley, resource managers in Canada recommend either mowing early in the summer season either just before blooming or at full bloom and repeating in two weeks interval to prevent seed production in sites where herbicides cannot be used, and using herbicides where it is permitted as a

21 management strategy (Department of Agriculture, 2003; Ministries of Transportation and Infrastructure, and Forests, Lands, and Natural Resource Operations, 2016). In addition, Miller and D'Auria (2011) found that a combination of mowing before flowering, herbicides, tillage and native grass seeding generated the best control results of cow parsley. There are similar conclusions from Iceland, when the management objective is to eliminate cow parsley in an area to preserve native species (Jónsson & Þórðarson, 2018). Jónsson and Þórðarson (2018) suggest that based on management experiments in Eyjafjörður in 2011,having herbicide treatments 3-4 times could be the most effective way of eradicating cow parsley; however, they also suggest that grazing could be a more environmentally friendly option. Moreover, as dense and large patches of cow parsley can distinctly affect the aesthetics of the landscape, as seen in Ægisíða (Appendix A; Figure 11), it is recommended that at least in Ægisíða the mowing area be expanded to include the large patches of cow parsley and sweet cicely recorded in 2017. Even without using herbicides, mowing frequently (at least three times) and starting in early summer before the flowering period may help control current populations of cow parsley including those in Ægisíða (van Mierlo & van Groenendael, 1991; Darbyshire et al., 1999). This method may also prove to be effective in controlling the only large sweet cicely population found in Æegísiða near a residential building. The surveys in Reykjavík indicate that cow parsley grows well in urban areas, especially near buildings, pathways, roads, and waterways. These distribution patterns have also been found in northwest Iceland (Hvammstangi), the United States, Canada, and the Netherlands (van Mierlo & van Groenendael, 1991; Darbyshire et al., 1999; The Nature Conservancy, 2010; Jónsson & Þórðarson, 2018). Cow parsley is becoming a prevalent species in Reykjavík, particularly in Vatnsmýri where nearly 23% of the nature reserve surveyed was covered by cow parsley in 2017. Furthermore, the scattered patches recorded indicate that this invasive plant is increasing its distribution throughout the reserve. The management efforts implemented a few years ago in Vatnsmýri of raising the water level and removing plants and soil layers from some of islands to improve bird habitat and reduce the abundance alien plants, may have had limited long-term success regarding cow parsley given the plant’s current distribution. However, it is worth noting that the distribution of cow parsley was concentrated on the outer edges of the wetland area, not the inner parts of the reserve. Currently, the grass is cut four times during the summer in areas next to the Vatnsmýri wildlife nature reserve. However, due to the restricted access to the inner area of the reserve and the wetland habitat during the summer, mowing cannot be expanded further. Although most cow parsley and sweet cicely patches are located outside the grass cutting areas in Vatnsmýri, a scattered cow parsley community was present in a mowed area close to the University of Iceland´s parking lot. Similarly, large patches of cow parsley and sweet cicely occurred next to mowed areas along the pedestrian pathway near Hringbraut Street suggesting that mowing four times per summer next to Vatnsmýri is not enough to reduce the abundance of cow parsley (Appendix C, Figures 3, 4). A potential strategy is to start mowing the area earlier in the summer before cow parsley plants bloom to prevent seed production, and pull out individual plants with roots to reduce spreading (Ministries of Transportation and Infrastructure, and Forests, Lands, and Natural Resource Operations, 2016). The presence of cow parsley in Vatnsmýri is of great concern as it can become a dominant plant species where it occurs, by taking over soil space due to its tall height and shading other plant species in the area, leading to a loss of biodiversity (Hansson & Persson, 1994; Darbyshire et al., 1999). Vatnsmýri is an important area for migratory and resident birds, and >60 native plants have been recorded in the reserve (Palsson, 2003). Furthermore,

22 cow parsley is difficult and costly to eradicate once it becomes established as the habitats where it grows require different kinds of management treatments, and eradication of individual plants requires manual labor (Department of Agriculture. 2003; Pálsson, 2003; Jørgensen et al., 2013). Currently, the distribution of cow parsley in Vatnsmýri is concentrated along the waterway. A dense and tall cow parsley patch was already visible in early June 2017 (Appendix A; Figures 4-6). Should be noted that cow parsley in general did not overlap with sweet cicely except in Vatnsmýri, where both plants were growing together in dense stands between Hringbraut Street and the waterway. Further research is needed to understand why the heavily trafficked roadside by Vatnsmýri appears to be an ideal habitat for sweet cicely and cow parsley to coexist. Regular monitoring of the plant community in the area would also help detect changes in species composition, as well as potential effects on the bird community. In some areas of Laugarnes, cow parsley and sweet cicely grew in close proximity to each other but did not overlap as much as in Vatnsmýri. Perhaps the presence of other invasive alien species prevents the overlapping of cow parsley and sweet cicely . In Laugarnes cow parsley was growing together with two other invasive and potentially invasive plants in Iceland, Nootka lupin and giant hogweed (Appendix A; Figures 1 and 3). The presence of these other plants may explain why cow parsley had significantly smaller patch sizes in the area. Giant hogweed is a serious concern in Laugarnes, in addition to being a potentially invasive plant that is very tall and has large leaves that threaten native flora, it also presents a major health hazard for humans. The sap of the plant can cause serious burns to the skin when exposed to ultraviolet radiation (Nielsen et al., 2005; EEA, 2012). Laugarnes also had the lowest native plant species cover. Additional loss of biodiversity here and in other sites is alarming, as several central European studies show that vegetation types where cow parsley occurs are vulnerable to further invasion of alien species (Hansson & Persson, 1994; Godefroid & Koedam, 2003; Pyšek, Chytrý & Jarošík, 2009). This means that sites containing cow parsley can also enable invasion of other alien species, especially those that favor nutrient rich soils. Magnússon (2011) recommends paying attention to areas in Iceland where Nootka lupin has brought about a higher nitrogen status in the soil as they may be invaded by cow parsley. Nootka lupin was abundant in Elliðaárdalur and Geirsnef (Appendix A; Figures 8 and 10). A large area of Nootka lupin was also growing next to cow parsley patches in Laugarnes. Monitoring whether cow parsley is spreading further into the Nootka lupin communities is advisable. Surprisingly, cow parsley was also present in Háubakkar (Elliðaárdalur) growing with creeping buttercup (Ranunculus repens), another alien plant, in soil that seemed to be barren and nutrient poor (Appendix A; Figure 7). Another factor that may drastically increase the abundance of cow parsley in the future, is climate change. Wasowicz, Przedpelska-Wasowicz & Kristinsson (2013) predicted that the climatic niche for cow parsley will grow significantly, allowing it and other plant species to colonize new areas in Iceland that will have more favorable growing conditions in the future. Overall, sweet cicely cover was not as high in Reykjavík as that of cow parsley. Laugarnes, however, had a large patch of sweet cicely on the hill near Sæbraut and Klettagarðar Streets, with individual plants and small patches scattered around (Appendix A; Figure 2). The area where sweet cicely formed a large community used to have buildings. The size and location of the patch suggests that sweet cicely was likely planted there several decades ago, and as no control methods have been implemented it has become a very large population. In 2018, however, the area was mowed once during the summer, but the mowing took place late in the season (mid-August), which is probably not enough to control and reduce the presence of sweet cicely (Appendix C; Figures 6, 7). Moreover, the previous land use in the area, e.g. hosting farms and residential buildings, may enable alien plant species

23 to thrive (National Museums Northern Ireland, 2010). In Laugarnes sweet cicely and cow parsley were growing together in smaller patches with other alien species, some invasive and potentially invasive (Nootka lupin and giant hogweed) and others naturalized such as creeping buttercup and orange hawkweed (Pilosella aurantiaca). In Ægisíða sweet cicely was only recorded next to a residential building, suggesting that it was a garden escape. Continuous monitoring of sweet cicely distribution in Reykjavík is recommended to see if the species spreads further. The distribution of sweet cicely has increased in the UK and Northern Ireland, and it has been introduced into some northern states in the US as well as into some parts of Canada (USDA, 2018b). Similar to cow parsley, sweet cicely is abundant in roadsides close to residential buildings, and is suspected to have spread from gardens (National Museums Northern Ireland, 2010; Reznicek, Voss & Walters, 2011; Gederaas et al., 2012; BRC, 2018; USDA 2018b). However, it has not been classified as invasive in Europe or in Iceland, except in Norway where it is listed as an alien species under the severe impact category (i.e. possessing a high potential to spread, threaten native species, and alter habitat ecology) (Gederaas et al., 2012). Pyšek et al. (2012) categorized sweet cicely as being purposely cultivated in the past, and currently it has escaped cultivation and forms stable populations in the wild. Sweet cicely is a common plant in gardens in Reykjavík and it has also become abundant elsewhere, including in Stykkishólmur, west Iceland (von Schmalensee & Stefánsson, 2009). Although it does not seem to be spreading as fast as cow parsley, monitoring the distribution and abundance of sweet cicely is important, especially to help conserve native biodiversity in urban areas. The distribution maps of sweet cicely in Reykjavík show where single plants and small patches occur, which could be managed by digging them out with relatively low effort early in the season to discourage further expansion of sweet cicely. Public awareness campaigns focusing on the edible and medicinal use of the plant could also be a way of educating people about sweet cicely. The strong smell and taste of the plant makes it easily recognizable, and the whole plant is edible and can be used e.g. as a sweetener, in salads, or as a spice. (Hussain et al., 1990; Róbertsdóttir, 2013; Lim, 2015). While urban areas, especially cities, often have higher species richness than less densely populated areas, this usually happens at the expense of the native species (Czech, Krausman & Devers, 2000; McKinney, 2008). Alien species can find their way into urban areas through horticultural practices, such as part of seed mixtures, which is suspected how both cow parsley and sweet cicely were originally brought to Iceland (Magnússon, 2011; Mayer et al., 2017; Icelandic Institute of Natural History, 2018). Even a single alien plant species can pose a threat by increasing its distribution and abundance in an invaded community and thereby decreasing native plant diversity (Vilà et al., 2011). This pattern has been seen in several central European cities indicating that over time alien species play a major role in biotic homogenization, becoming especially problematic in highly urbanized areas (Lososová et al., 2012). Although this process takes time, it is still a concern for Reykjavík. Cadotte et al. (2017) suggests that urban areas may provide ideal habitats for alien species to thrive, as the alien species are often capable of forming large populations in disturbed urban habitats. They also stress the importance of monitoring and controlling invasive species in urban areas, in order to prevent them from spreading to new areas outside the cities. Understanding the scale of alien species abundance and behavior in a city is crucial for urban planning and management of green areas. In terms of cow parsley management, this study provides important insights on the timing and frequency of mowing for it to be an effective management tool. Pilot studies testing different management strategies for both cow parsley and sweet cicely would be useful to take into account the differences between various habitats within the city.

24 Caujapé-Castells et al. (2010) highlight several factors threatening the plant diversity in oceanic islands. In addition to habitat alteration and destruction, invasive alien plant species were identified most frequently as having a major role in affecting the success of native plants survival. Furthermore, their study suggests that invasive species outcompete native species especially in open and disturbed environments. Similarly, Kueffer et al. (2010) found that species invasions are primarily driven by human disturbance on oceanic islands. These invasion patterns in islands seem applicable to Reykjavík as well, where all the study sites have undergone some kind of human mediated alteration over the past decades and centuries. Although there are currently a few residential buildings and a museum in Laugarnes, it formerly hosted farms, a church with a graveyard, a leprosy hospital, and a World War II military camp (Hið íslenzka Fornleifafélag, 1997; Ísberg, 2014). Elliðaárdalur is a popular outdoor area with a variety of habitats for plants and animals but the area has also been changed enormously in the last decades (Pálsson, 2004). In the past, the area was used for forestry cultivation and was popular for holiday homes; it is now a recreational area providing various activities from a dog park, hiking routes and fishing. Æegisíða is a residential street with an open area between the sea shore and paths for walking and biking. This area consists of grass that is regularly mowed, as well as a large area covered with both native and alien plants. Vatnsmýri is a large wetland nature reserve, within close vicinity of the Reykjavík Airport and the University of Iceland, situated also next to a high-traffic road. The walking path crosses the area with small wooden bridges and benches built along the path. Dispersal of seeds can be mediated both by pedestrian and car traffic in all of the study sites, in addition to grass cutting machinery. Large, dense patches of cow parsley alter not only the landscape aesthetics (Førde & Magnussen, 2015), but also threaten native plant forage communities for animals (e.g. insect pollinators), thus potentially altering the functioning of ecosystems (Willow, 2017).

1.5 Conclusions

Cow parsley is becoming a prevalent species in Reykjavík and is reaching a substantial cover in the study sites, especially in Laugarnes, Elliðaárdalur and Vatnsmýri. Open areas of Reykjavík seem to offer an ideal habitat for cow parsley to further spread, which is why it is important to plan and implement management actions to prevent this species from expanding its distribution and altering the ecosystems where it is present. In order to fully understand and properly record the current state of cow parsley distribution, it is recommended that mapping be conducted by foot. Although this method is time consuming, it reduces the risk of mistaking cow parsley with similar looking species. Sweet cicely distribution appears to be more limited than that of cow parsley, however, future monitoring is recommended especially in Laugarnes, where the species is most abundant. As sweet cicely distribution is so far limited to a few areas, a priority should be given to target these areas in order to eradicate it when possible, and increase the frequency of mowing to control the expansion of sweet cicely. Ultimately, a proactive, long term, and adaptive management strategy, involving monitoring, public awareness and participation, and a variety of management actions, will be more effective in addressing invasive species and promoting biodiversity in urban areas such as Reykjavík.

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33 2 Potential impact of cow parsley (Anthriscus sylvestris) invasion on native plant communities in Reykjavík

2.1. Introduction

The invasion of alien species is often characterized by a time lag between the date of first introduction of a species, its naturalization, and whether it increases its distribution (Kowarik, 1995a; Crooks, 2005; Aikio et al., 2010). Problems emerge, for example, when alien species that are naturalized and currently rare have the ability to spread quickly when climatic conditions become more favorable, enabling these species to expand rapidly to new regions and habitats (Aikio et al., 2010). Hence, the importance of surveying areas with alien taxa lies in detecting if currently rare alien species are increasing their abundance and distribution. Moreover, establishing baseline data on the distribution of invasive species is essential in order to control their spread and impacts before they become a major threat to native taxa and cause other negative effects such as the degradation of cultural landscapes and ecosystem functions (Hansson & Persson, 1994 ; Hejda, Pyšek & Jarošík, 2009; Pyšek, & Richardson, 2010; Vilà et al., 2011). One important factor determining the success of alien species establishment into native plant communities is environmental filtering, which requires alien species to possess functional traits that are similar to native species (Divíšek, et al. 2018). However, the established alien species need to possess a trait that out-competes native species and helps them to occupy novel niche space, in order to become invasive (Divíšek, et al. 2018). Research in central Europe, indicates that plant height is a key trait for an invasive alien species to gain a competitive advantage over native plant species (Divíšek et al., 2018). Both the cover and height of invasive species, as well as the differences in height and cover between invasive and dominant native species, are also major determinants in reducing Shannon diversity and evenness (Hejda et al., 2009). Similarly in Australia, Gallagher et al. (2014) found that in addition to a long flowering period, the maximum height of invasive plant species is one of the determining factors giving them advantage over other alien taxa. Furthermore, invasive plants species in general have significantly higher values for performance related traits such as physiology, leaf area allocation, shoot allocation, growth rate, size and fitness than non-invasive (both alien and native) plant species (van Kleunen et al., 2010). These differences in traits are even greater between invasive plants species and native plant species. What makes naturalized alien species different from invasive species is that although their populations are self-sustaining, they are also not (yet) spreading (Gallagher et al., 2014). However, the ecological and environmental conditions under which naturalized alien plants have established, play an important role, as these conditions influence the role of traits in determining a plant's ability to become invasive (Kueffer, Pyšek & Richardson, 2010; Gallagher et al., 2014). In northern latitudes climate change is creating major changes in plant communities (Root, 2003; Post et al., 2009). Bjorkman et al. (2018), for example, found that as the temperature increased in the last 30 years, so did the plant height in the tundra. This rapid increase in community height was mostly due to the movement of tall plant species (i.e.,

34 species turnover). In addition, Bjorkman et al. (2018) suggest that the changes in plant traits such as plant height may alter ecosystem functions and feedback effects (e.g., soil temperature, decomposition, and carbon cycling). Given this, climate change is also very likely to impact plant communities in northern latitude urban areas. Species that are able to adapt to a wider range of biotic conditions may have an advantage over native species with lower abilities to adapt to these environmental changes (Kueffer , Pyšek & Richardson, 2010). This is a concern in Reykjavík, Iceland, which is the most northern capital in the world and seems to be a hotspot for both casual and naturalized alien plant taxa (Wasowics et al., 2013). One alien species that has become invasive recently in Iceland, including Reykjavík, is cow parsley (Anthriscus sylvestris) (Magnússon, 2011; Wasowics et al., 2013). Cow parsley is a tall, herbaceous biennial or a short-lived perennial plant, which can grow up to 2 meters in height. (Magnússon, 2011; Elmarsdóttir et al., 2011; Swearingen & Bargeron, 2016). This height trait increases cow parsley’s ability to expand its distribution and impact on native plant communities (Hejda et al., 2009; Gallagher et al., 2014; Divíšek et al., 2018). Moreover, this plant can produce up to 10,000 seeds, as well as reproduce from the root buds at the top part of the root (Darbyshire et al., 1999). Cow parsley’s ability to reproduce from the root bud is problematic as it makes the management of this species hard (Jørgensen et al., 2013). In western and northern Iceland cow parsley has been mapped and managed in recent years with mixed results; the techniques used include cutting, pulling individual plants, using herbicides, and grazing (Elmarsdóttir et al., 2011; Jónsson & Þórðarson, 2018). The potential effects of cow parsley on native plant communities cannot be underestimated, as the species is spreading rapidly and once it has established large communities it is very difficult to eradicate (von Schmalensee & Stefánsson, 2009; Jørgensen et al., 2013; Bjarnadóttir, Sigurðsson & Guðleiffson, 2018; Jónsson & Þórðarson, 2018). Although cow parsley is spreading in Reykjavík (Wasowics et al., 2013) and its distribution has been mapped recently in several hot spots of the city, there is a data gap on the plant community associated with cow parsley. This information is essential for developing a management plan for cow parsley and other potential invasive species. To address this important data gap, the plant community associated with cow parsley was surveyed in four open areas in Reykjavík. Taxa richness and cover were measured, and plants were classified as native, alien or invasive. In addition, in an effort to help guide the management of cow parsley in urban areas such as Reykjavík, a literature review was conducted on management strategies for cow parsley in Europe and North America. This is more important now than ever, as climate warming may accelerate the abundance of cow parsley and other alien and invasive species into latitudes that were previously unsuitable for these species to thrive.

2.2 Methods

2.2.1 Study areas

Four study sites in Reykjavík were surveyed and they included Laugarnes, Elliðaárdalur, Vatnsmýri, and Ægisíða. They are all open areas, rich in vegetation, and located in different parts of the city. Laugarnes is a grassland area that has undergone many changes in the past decades. Currently it has a small residential area with a large open green space, but in the past it hosted farms, a church with a graveyard, a leprosy hospital, and a World War II military camp (Hið íslenzka Fornleifafélag, 1997; Ísberg, 2014). Elliðaárdalur is a large popular outdoor area with a variety of habitats for plants and animals but, like Laugarnes, it

35 has also undergone major changes in the past decades (Pálsson, 2004). Nowadays it is a recreational area with grasslands and forests providing various activities such as a dog park, hiking routes and fishing, however in previous years it was used for forest cultivation and as an area for holiday homes (Pálsson, 2004). Æegisíða is a residential street with an open grassland area between the sea shore and paths for walking and biking. Vatnsmýri is a wetland nature reserve located between the Reykjavík Airport and the University of Iceland, and is surrounded by highly trafficked roads on two sides. A series of experimental plot surveys were conducted in all four study areas during the summer in 2017 and 2018. Data was collected by using AllTrails and ArcGIS mobile applications (AllTrails, 2017; ESRI, 2017). These mobile applications recorded the GPS locations of the plots, which were then mapped with ArcGIS software ArcMap 10.4.1. The geographic coordinate system used for the plots with cow parsley was GCS_WGS_1984 with a Prime Meridian set for Greenwich. In contrast, the plots without cow parsley used GCS_INS_1993 with a Prime Meridian set for Greenwich. All data was projected as ISN_1993 Lambert_1993 with metric linear unit. Plot locations are shown in Figures 2.1 - 2.3.

VC1

Plot 2

Figure 2.1. Survey plots in Æegisíða and Vatnsmýri. Black stars indicate plots with cow parsley (Plot 1-5), while plots without cow parsley are indicated with purple stars (AC1-5, VC1-5). Source: Data collection by Mervi Luoma with Collector for ArcGIS, 2017 and 2018. Basemap: Léttkort af Reykjavík (2016).

Figure 2.2. Survey plots in Laugarnes. Black stars indicate plots with cow parsley (Plot 1- 5), and plots without cow parsley are shown by the purple stars (LC1-5). Source: Data collection by Mervi Luoma with Collector for ArcGIS, 2017 and 2018. Basemap: Léttkort af Reykjavík (2016).

Figure 2.3. Survey plots in Elliðaárdalur. Black stars represent the plots with cow parsley (Plot 1-5), comparison plots without cow parsley are shown by the purple stars (EC1-5). Source: Data collection by Mervi Luoma with Collector for ArcGIS, 2017 and 2018. Basemap: Léttkort af Reykjavík (2016).

38 2.2.2 Characterization of plant communities

In each of the study areas, 10 grid plots measuring 2 x 2 m were haphazardly placed to capture the plant taxa in each study area. Overall, 20 plots with cow parsley were surveyed from July 20th to the 22nd, 2017, and 20 plots without cow parsley were surveyed the following year, from July 26th to August 2nd, 2018. Given the large size of the cow parsley plants, 2 x 2 m plots were used instead of a standard 1 x 1 m plot to properly capture the variability of the plant community (Figure 2.4).

1 2

3 4

Figure 2.4. Survey plots and tall plant species in Vatnsmýri. (1) Marsh horsetail (Equisetum palustre), a native plant species sometimes associated with cow parsley. (2) Alpine Burnet (Sanguisorba alpina) an alien species present in some of the cow parsley plots. (3) Creeping thistle (Cirsium arvense), an alien species found in some plots without cow parsley. (4) Cow parsley (Anthriscus sylvestris) present in a 2 x 2 m survey plot.

39 The plant taxa present and their cover (%) was visually estimated, using wooden measurement sticks with centimeter lines that marked the plot borders (Figure 2.4) to help estimate the percent cover of each species. Additionally, photos were taken for each plot. The plants in each plot were identified to species level, with the exception of grasses and mosses that were classified as Poaceae and Bryophyta (family level). Species classification was based on Kristinsson (2013) and species status (native, alien, or invasive) based on Kristinsson (2013) and Wasowicz et al. (2013). The height of the tallest cow parsley plant was measured in all the plots with cow parsley, which often was the tallest plant present. In Laugarnes, however, giant hogweed was present in the area but not in the study plots and it was taller than cow parsley. In addition, garden angelica (Angelica archangelica), and northern dock (Rumex longifolius) were present and may have been taller than cow parsley in some of the plots with cow parsley in Ægisíða (Plot 3 and 5) and Laugarnes (Plot 2 and 5), but unfortunately their plant height was not measured. Plant height measurements were also collected for the tallest plant present in the plots without cow parsley in all four sites.

2.2.3 Statistical analysis

Plant richness (taxa count), native and alien plant cover, and plant height were compared among the sites using one-way analysis of variance (ANOVA) and a Bonferroni correction for the post-hoc test. Although the plots with,- (n = 20 plots) and without (n = 20 plots) cow parsley were surveyed in different years, 2017 and 2018 respectively, they were compared to assess potential differences in their plant communities. Independent sample t-tests were conducted to see if there were significant differences in plant richness and cover between the plots with,- and without cow parsley. In addition, the height of the tallest cow parsley plant was compared with the tallest plant present in the plots without cow parsley. All statistical analyses were conducted with SPSS 24, with a significance level of 0,5.

2.3 Results

Species richness did not vary significantly between plots with and without cow parsley (Table 2.1). However percent cover of alien plants was significantly higher in the cow parsley plots (p = 0,000) than in the plots without cow parsley. In contrast, the plots without cow parsley had significantly more native plant cover (p = 0,021) (Table 2.1). Plant height was significantly higher (p > 0.001) in plots with cow parsley (125,6cm ± 5,3), than those without it (80,5cm ± 8,8). The height of cow parsley varied between 86 to 162cm. The tallest plant species found in plots without cow parsley were northern dock (Rumex longifolius), creeping thistle (Cirsium arvense), and garden angelica (Angelica archangelica), all of which ranged from 102-137cm depending on the study site (Appendix E, Figures 1-4). Both northern dock and creeping thistle are alien species, while garden angelica is native.

40 Table 2.1. Average plant cover (%), plant taxa richness, and tallest plant height (cm) in the survey plots (n = 40 plots). Note that native and alien species cover (%) and richness excludes grasses and mosses, while total plant taxa includes them both. * Indicates variables that were significantly different. The mean standard error are shown. CP = Cow parsley.

Characteristics CP present CP not present Native species cover (%)* 23,2 ± 3,9 39,8 ± 5,7 Alien species cover (%)* 56,2 ± 5,0 24,5 ± 5,6 Native species richness 2,2 ± 0,3 1,7 ± 0,2 Alien species richness 2,6 ± 0,2 3,3 ± 0,4 Total plant taxa richness 5,9 ± 0,4 6 ± 0,5 Highest plant species measured (cm)* 125,6 ± 5,3 80,5 ± 8,8

Native plant cover among the cow parsley plots ranged on average from 11-32%, and was not significantly different across the sites [F(3, 16) = 1,478, p = 0,258]. Furthermore, the plots with cow parsley in Vatnsmýri had the highest native plant cover, and Laugarnes the lowest. In terms of alien plants, their mean cover ranged from 42-72% in plots with cow parsley and did not vary significantly among the sites [F(3, 16) = 2,249, p = 0,122]. On average, Ellidaárdalur had the highest alien plant cover (72% ± 10), while Vatnsmýri had the lowest (42% ± 11). The mean alien plant cover (%) in the cow parsley plots when cow parsley itself is excluded is 25,1% ± 0,7, which is similar to the average in the plots without cow parsley (Table 2.1). Should be noted that comparisons of alien and native plant cover or species did not include mosses or grasses as they were not identified to species level. Mosses were only recorded in one cow parsley plot with 27% cover in Laugarnes. Grasses were found in all the cow parsley plots ranging from 2% to 48% cover, and it was on average 19% ± 4. A total of 24 plant species were found in the plots with cow parsley, of which 10 species were alien and 14 were native (Table 2.2). Species richness was not significantly different among the sites, and it varied on average from 5-7 plant species [F(3, 16) = 2,404, p = 0,105]. Overall, the average number of plant taxa (including mosses and grasses) for areas with cow parsley was greatest in Elliðaárdalur (7 taxa ± 0,9), and lowest in Ægisída (5 taxa ± 0,3). Native plant cover among the plots without cow parsley ranged on average from 34- 49%, and was not significantly different across the sites [F(3, 16) = 1,639, p = 0,220]. The highest native plant cover for plots without cow parsley was found in Elliðaárdalur, and the lowest in Ægisíða. Moreover, the cover of alien plants in these plots ranged on average from 6-44% and did not vary significantly among the sites [F(3, 16) = 2,978, p = 0,063]. Laugarnes had the highest alien plant cover (44% ± 16), while Ægisíða had the lowest (6% ± 3). Mosses were only found in one plot without cow parsley in Vatnsmýri covering 12% (Appendix D). In contrast, grasses were present in all plots without cow parsley having a mean cover of 35,2% ± 5,1. A total of 29 plant species (without moss and grasses) were found in the plots without cow parsley, of which 9 species were alien and 20 were native. The taxa richness (mosses and grasses included) was significantly different among the sites, varying from 4- 8 plant taxa on average [F(3, 16) = 5,492, p = 0,009]. In the areas without cow parsley, Elliðaárdalur had significantly higher taxa richness (8 taxa ± 0,6) than Ægisída (4 taxa ± 0,5) (p = 0,006). Similarly, there was also significantly more alien species (p = 0,034) in the areas not containing cow parsley in Elliðaárdalur (5 species ± 0,5) than in Ægisíða (2 species ± 0,8). Overall, 36 plant taxa (including mosses and grasses) were found in the study sites (Table 2.2; Appendix D). Cow parsley cover ranged from 27-36 % on average depending on

41 the site and the total mean average was 31% in cow parsley plots. Grasses represented on average 19% in plots with cow parsley and 35% in plots without cow parsley. Garden angelica had the highest recorded cover of the all the native taxa in both plots with and without cow parsley, ranging from 7-8%. In Vatnsmýri, the plants with the highest cover in the plots containing cow parsley were cow parsley and grasses. In contrast, grasses and the native plant species silverweed (Argentina anserina), yellow-rattle (Rhinanthus minor), and colt‘s-foot (Tussilago farfara) covered the largest areas within the Vatnsmýri plots without cow parsley (Table 2.2). Overall, cow parsley occurred throughout Vatnsmýri, while creeping thistle, alpine burnet, and garden angelica were only present in a few locations (Appendix D). In Laugarnes cow parsley covered 27% of the cow parsley plots. Another alien invasive species found in Laugarnes was Nootka lupin (Lupinus nootkatensis), which occurred in areas with and without cow parsley In addition, creeping buttercup (Ranunculus repens) was among the most common alien species present in Laugarnes (Table 2.2, Appendix D). In Elliðaárdalur, cow parsley cover was 31% on average, and Nootka lupin was also present in the area, especially where cow parsley occurred (26% on average). Creeping buttercup was the most frequently found alien species in Elliðaárdalur (Table 2.2, Appendix D). In terms of native plants, meadowsweet (Filipendula ulmaria) had the highest cover on average both in areas with and without cow parsley in Elliðaárdalur. Finally, in Ægisíða cow parsley had a 36% cover on average, And of all the native plants detected, garden angelica had the highest mean cover both where cow parsley was present and absent. Overall, grasses were more prevalent in areas of Ægisíða without cow parsley (Table 2.2).

42 Table 2.2 Mean cover (%) of plant taxa present in the plots with (n = 20) and without cow parsley (n=20 ) surveyed in 2017 and 2018. Standard error is shown. 3 ± 1,3 ± 3 4,5 ± 1 1 ± 0,3 0 ± 1,3 0 ± 1,9 0 ± 0,3 0 ± 0,3 0 ± 0,2 0 ± 0,2 0 ± 0,8 0 ± 0,4 1 ± 0,6 0 ± 0,6 3 ± 14,1 ± 3 14 ± 2,4 10 ± 1,8 10 ± 5,4 2,4 ± 4,1 ± 2,4 7,6 ± 5,4 1,5 ± 0,4 0,5 ± 0,2 1,9 ± 0,7 7,9 ± 8,4 6,2 ± 3,6 1,4 ± 1,3 0,6 ± 0,7 2,7 ± 3,8 8,1 ± 12,1 ± 8,1 19,5 ± 2,6 21,1 ± 4,6 5,1 ± 35,2 without CP without Total 1 ± 0 ± 1 5 ± 2 0 ± 2 0 ± 1 6,5 ± 5 ± 6,5 6 ± 1,2 0 ± 0,1 1 ± 2,1 0 ± 0,3 0 ± 0,3 9 ± 1,2 0 ± 0,1 0 ± 0,4 0 ± 0,2 0 ± 1,4 with CP with 2,9 ± 1,3 5,4 ± 1,7 5,6 ± 3,2 1,3 ± 5,3 0,3 ± 0,3 4,5 ± 1,3 2,8 ± 3,9 2,4 ± 4,8 ± 2,4 31,2 ± 4,8 ± 31,2 3,6 ± 19,3 10,8 ± 12,2 ± 10,8 3 ± 0 ± 3 0,6 ± 0 ± 0,6 1,8 ± 4 0,5 ± 1 0 ± 1,6 8,8 ± 14 ± 8,8 2,2 ± 3,5 ± 2,2 25,6 ± 26 ± 25,6 53,2 ± 13,7 ± 53,2 without CP without Ægisíða 4 ± 0 ± 4 3,6 ± 0 ± 3,6 3,5 ± 8 0 ± 0,8 with CP with 8,1 ± 9,4 35,8 ± 6,1 ± 35,8 6,2 ± 24,6 13,8 ± 3,5 ± 13,8 1 ± 0 ± 1 0 ± 1 2,4 ± 0 ± 2,4 0 ± 2,4 0 ± 5,2 4,2 ± 2 4 ± 2,4 0 ± 0,4 0 ± 2,6 7 ± 20,5 ± 7 3,8 ± 6,4 ± 3,8 1,4 ± 1,2 1,5 ± 1,4 7,8 ± 3,8 0,7 ± 1,4 1,4 ± 2,4 2,8 ± 2,7 ± 2,8 32,6 ± 8,9 ± 32,6 11,4 ± 19,5 ± 11,4 11,6 ± 12,8 without CP without Elliðaárdalur 8 ± 5 ± 8 1,4 ± 0 ± 1,4 0 ± 4,4 0 ± 1,2 9 ± 4,8 0 ± 0,2 1 ± 1,2 0 ± 0,8 with CP with 5,5 ± 5,4 3,1 ± 4,8 1,5 ± 4,8 1,6 ± 6,2 30,6 ± 14,4 ± 30,6 13,6 ± 26,2 5 ± 1,3 ± 5 0 ± 0,4 0 ± 0,6 1 ± 1,6 4,7 ± 9 0 ± 8,6 14,4 ± 0 ± 14,4 14 ± 9,6 5,7 ± 22 10,2 ± 19,5 ± 10,2 17,4 ± 18,6 without CP without Laugarnes 4 ± 0 ± 4 0 ± 4 0 ± 1 0,2 ± 0 ± 0,2 0 ± 0,4 0 ± 1,4 4,5 ± 5 0 ± 5,4 with CP with 0,5 ± 0,6 8,5 ± 4,6 1,8 ± 5,4 2,2 ± 3,4 27 ± 10,1 ± 27 30,5 ± 17 20,6 ± 7,6 ± 20,6 1 ± 0 ± 1 4 ± 3,5 ± 4 5,8 ± 7 0 ± 7,6 0 ± 0,2 0 ± 0,6 0 ± 0,6 0 ± 0,8 0 ± 3,6 0 ± 0,2 0 ± 2,4 4,2 ± 4,2 ± 4,2 11,8 ± 9,4 ± 11,8 8,6 ± 32,8 12,8 ± 11,3 ± 12,8 15,3 ± 10,4 without CP without Vatnsmýri 8 ± 0 ± 8 0 ± 4 1,2 ± 0 ± 1,2 0 ± 6,8 0 ± 1,2 2,8 ± 6 6 ± 2,8 with CP with 4,4 ± 4,6 7,5 ± 6,2 1,5 ± 1,4 6,8 ± 5,4 ± 6,8 25,8 ± 9,2 ± 25,8 31,2 ± 9,5 ± 31,2 Sea MayweedSea ᴬ /Rosebay ᴬ Willowherb Chickweed Willowherb Willowherb Chickweed Garden Angelica Garden Wood Crane's-bill Dandelion Meadowsweet Yarrow Yarrow Lady's-mantle Hairy ᴬᴵ /Nootka ᴬᴵ Lupin Silverweed Silverweed MarshHorsetail ᴬ / Orange Hawkweed ᴬ IcelandicHawkweed PlantainSea ᴬᴵ / Cow Parsley /Cow ᴬᴵ ᴬ /Alpine Burnet ᴬ Yellow-rattle Yellow-rattle Field Forget-me-not Field Thrift Thrift ᴬ /CreepingButtercup ᴬ Colt´s-foot Groundsel ᴬ /Northern ᴬ Dock ᴬ /Lady´s-mantle ᴬ NorthernBedstraw Common Chickweed Chickweed Common Common Sorrel Sorrel Common ᴬ / Sweet Cicely /Cicely Sweet ᴬ ᴬ* /Whiteᴬ* Clover ᴬ /CreepingThistle ᴬ Lady´sBedstraw Tufted Vetch WaterAvens Moss Grassspecies

Speciesname Achilleamillefolium / Alchemillafilicaulis / Alchemillamollis Angelicaarchangelica / Anthriscussylvestris Argentinaanserina / Armeriamaritima / Chamaenerionangustifolium Cirsiumarvense Equisetumpalustre / Epilobicumalsinifolium / Filipendulaulmaria / Galiumboreale / Galiumverum/ Geraniumsylvaticum / rivale Geum / Lupinusnootkatensis Myosotisarvensis / Myrrhisodorata Pilosellaaurantiaca Pilosellaislandica / Plantagomaritima / Ranunculusrepens Rhinanthusminor / Rumexacetosa / Rumexlongifolius Sanguisorbaalpina Seneciovulgaris / Stellariamedia / Taraxacumofficinale / Trifoliumrepens Tripleurospermummaritimum subsp. Phaeocephalum / Tussilago/farfara Viciacracca / Bryophytes/ Poaceae/ native the in InvasivenorthAlien Common ᴬᴵ ᴬ* elsewhereAlien Iceland,ofalien naturalized ᴬ

43 Vatnsmýri had the highest number of alien species, whereas the highest number of native species was recorded in Elliðaárdalur (Table 2.3). However, the average cover of invasive alien species was highest in Laugarnes and Elliðaárdalur where both Nootka lupin and cow parsley were present. The highest naturalized alien species cover was also seen in Laugarnes. Although Elliðaárdalur had the highest number of native taxa, the highest average cover of native species was found in Vatnsmýri. (Table 2.3.)

Table 2.3. Total number of invasive, alien, and native plant species in the study sites. Also shown in parentheses is the cover (%) of each species category, as well as for grasses and mosses which were excluded from the categories

Study area Invasive alien species Alien species* Native species Grasses Mosses Vatnsmýri 1 (15,6) 7 (13,4) 12 (40,5) (29,3) (1,2) Laugarnes 2 (29,2) 5 (24,3) 9 (22,5) (21,3) (2,7) Elliðaárdalur 2 (30,3) 5 (21,6) 16 (28,7) (19,4) Æegisíða 1 (17,9) 3 (9,1) 7 (34,1) (38,9) Total 2 (23,3) 9 (17,1) 23 (31,5) (27,3) (1) *Naturalized

Native species cover was higher in plots without cow parsley in all the sites than in plots with cow parsley (Table 2.4). The same was true for mean grass cover. Similarly, all the sites except Ægisíða, had a higher cover of naturalized alien species in plots without cow parsley than in plots with cow parsley (Table 2.4).

Table 2.4. The average cover (%) of invasive, alien, and native plant species present in plots with and without cow parsley in the study sites. For reference the mean cover for mosses and grasses are also shown.

Invasive alien Alien Native Study area species species* species Grasses Mosses Vatnsmýri

Plots with cow parsley 31,2 10,8 32,2 25,8 0

Plots without cow parsley 0 16 48,8 32,8 2,4 Laugarnes

Plots with cow parsley 44 18,8 11,2 20,6 5,4

Plots without cow parsley 14,4 29,8 33,8 22,0 0 Elliðaárdalur

Plots with cow parsley 56,8 15,4 21,6 6,2 0

Plots without cow parsley 3,8 27,8 35,8 32,6 0 Æegisíða

Plots with cow parsley 35,8 12,0 27,6 24,6 0

Plots without cow parsley 0,0 6,2 40,6 53,2 0 *Naturalized

44 2.4 Discussion

Four open areas within Reykjavík were surveyed during summer season in 2017 and 2018. Over 30 plant taxa were found in these areas, of which nearly one third were alien species. How does this urban plant richness compare to Iceland in general? A total of 489 vascular plants are currently documented in Iceland (Kristinsson, 2008). Presently only two plant species are listed as alien invasive, cow parsley, and Nootka lupin, and one as potential alien invasive, giant hogweed (Heracleum mantegazzianum), and all three species are present in Reykjavík including the study sites (Nobanis, 2006; Wasowicz et al., 2013; Icelandic Institute of Natural History, 2018c; Icelandic Institute of Natural History, 2018d). Overall, 336 alien plant taxa have been recorded in Iceland between 1840 and 2012, of which approximately half have been suggested as being deliberately introduced and the rest as accidental introductions (Wasowicz et al., 2013). Urban areas in Iceland are major hotspots for plant diversity, including alien species (Wasowicz et al., 2013). Given Iceland´s remote location, alien plants were introduced into the country more or less infrequently until 1900; this, however, has changed and the current rate of alien plant introductions is 3 taxa per year (Davíðsson, 1967, Wasowicz et al., 2013). Despite the steady rate of new alien taxa being introduced each year to Iceland, the presence of already naturalized alien plants also poses a serious threat to native plants given climate change. Climate change with warming temperatures may play an important role in affecting the native taxa survival in northern latitudes like in Iceland, as the resident species tend to be adapted to colder temperatures. In addition, Wasowicz et al. (2013) suggest that climate change heavily impacts the alien taxa in Iceland, giving the current invasive species a potential to colonize further into new areas within Iceland. Moreover, research in Greenland suggests that the climatic changes in the Arctic have a strong effect on individual species and ecological communities, with implications for trophic interactions (Høye et al., 2013).

2.4.1 Plant community associated with cow parsley

Of the study sites, Elliðaárdalur was the largest area surveyed in Reykjavík (116.2 ha), and it had the highest number of native species and overall species richness, but on average the lowest cover of native species, which suggests higher diversity. The area has undergone a lot of changes in the past and is in the vicinity of residential areas, so it is possible that the high number of taxa is a result of previous horticultural practices and/or recent garden escapes. In addition, the variety of geological and hydrological features in Elliðaárdalur may also explain the higher species diversity, as this has been seen in several German cities where ecological diversity contributes to higher plant diversity (Kühn et al., 2004). Although Vatnsmýri was the smallest study site (8.7 ha) it had the second highest species richness and the highest number of naturalized alien species. These high richness numbers may be due to more habitat heterogeneity in the wetland that allows different species to thrive. Also, as the area hosts a variety of bird species, it is possible that some of them may be dispersing plant species. Laugarnes, on the other hand was found to host the highest invasive and naturalized alien species cover. Although it is a relatively small area, the previous land use as an old farmland and a residential area, among others, means that it is also a highly disturbed habitat, hence vulnerable to invasion of alien plant species (Kowarik, 1995b). The presence of giant hogweed in Laugarnes in addition to other alien plants that have raised concern, cow parsley and nootka lupin, creates not only a distinctive appearance in the landscape, but also poses a serious threat to human health. In general, invasive alien species had the highest plant cover in all the sites, ranging

45 from 30-36%. In terms of native species cover, Ægisíða had more than twice the cover than Elliðaárdalur, but also had the lowest number of native species, as well as total species richness. The area is mainly dominated by vast area of grass that is mowed regularly, and there are a few distinctive large patches of cow parsley and garden angelica that have formed dense stands next to each other. The study areas host habitats that contain a variety of plant species in different successional stages, which also may explain the differences in the number and cover of native and alien species between the study sites. Knapp et al. (2008) argue that there are differences between the species found in typical urban areas and in urban protected areas that are considered as semi-natural habitats. These semi-natural habitats especially, are at risk of losing species richness with increasing urbanization. When the goal is to promote urban diversity, this calls for a broad range of management strategies. A variety of urban areas can be used for preserving and promoting urban diversity, such as green areas in abandoned lots and roads, that even on a temporary basis offer an ideal habitat for a variety of urban flora to thrive (Knapp et al., 2008). Size of the area is usually the most important factor in determining species richness (MacArthur & Wilson, 1967; Knapp et al., 2008). Various habitats that are often found within larger areas provide ideal conditions to host more species. If the area is small, there is a higher risk of local extinctions (MacArthur & Wilson, 1967; Knapp et al., 2008). Urban areas have been found to provide ideal niches for many alien species to thrive (Kowarik, 1995b). According to North American and European studies roadsides (in general), serve as dispersal corridors for invasive alien plants (Follak et al., 2018). When examining the species diversity Knapp et al. (2008) found that the conservation success regarding species richness is reduced by high human impact in urban areas. Globally, plant invasions have an impact on resident biota survival, and taller plant species (higher than 1.2m) in particular seem to have a major impact on resident plant and animal communities (Pyšek et al., 2012). In addition, plant invasions can change soil characteristics (e.g. soil nutrient composition), which is a concern as it may enable further invasions. A closer look of the plant species found in the four study sites in Reykjavík, indicates that the only native plants with similar height characteristics to cow parsley were meadowsweet, and garden angelica (Icelandic Institute of Natural History, 2018a and 2018b). Meadowsweet was only found in four plots in Elliðaárdalur and one plot in Ægisíða, whereas garden angelica was found in all of the study sites. However, garden angelica has a tendency to become a dominant species often leading to monocultures where it is present, therefore caution and management is needed if cow parsley is replaced with or by garden angelica (Daniel & Lerner, 2018; Icelandic Institute of Natural History, 2018b). This is true for Reykjavík, especially in Elliðaárdalur and Ægisíða where it was found that garden angelica had already established large communities (including some monoculture stands) in these two areas. It would be good to monitor garden angelica in Ægisíða and Elliðaárdalur to assess changes in plant community and dynamics. Several alien species present in the study areas in Reykjavík warrant attention. For example, giant hogweed was present in Laugarnes although not in the study plots. Beauchemin (2018) mapped the distribution of giant hogweed in Reykjavík in 2017 and found the plant was spreading and was often one of the dominant species where it was present, such as in Laugarnes. This alien species native to Russia and Georgia is currently listed as invasive in the European Union and as potentially invasive in Iceland (Nielsen et al., 2005; European Union, 2017; Icelandic Institute of Natural History, 2018c; Icelandic Institute of Natural History, 2018d). Giant hogweed is of great concern, due to its phototoxicity posing a serious health hazard to humans (Nielsen et al., 2005), as well as the plant´s capability to establish dominant communities and transform landscapes where ever

46 it is present. It grows very tall in height, and in similar areas to cow parsley; most often along traffic routes or flowing waters that are either open or partly shaded (Thiele, Otte, & Eckstein, 2007). Currently in Reykjavík, giant hogweed is found mostly in private gardens and more densely vegetated areas (Beauchemin, 2018); however, research in Germany and Norway show that abandoned grasslands are also vulnerable to invasions of both giant hogweed and cow parsley (Thiele, Otte, & Eckstein, 2007; Jørgensen et al., 2013). Management of giant hogweed and cow parsley, as well as other invasive species present in urban areas. is very important to prevent them from spreading into neighboring rural and wilderness areas. Another alien species of concern that was found in the study sites was creeping thistle, which is currently classified as invasive in many states in the United States (Global Invasive Species Database, 2018; USDA, 2018). Like cow parsley, it also reproduces primarily by root, but also by seeds. Creeping thistle can change habitat structure and compete with native species often to the point of replacing them (Moore, 1975; Global Invasive Species Database, 2018). This species was found covering fairly large share of plots both in Laugarnes and in Vatnsmýri (see Table 2.2 and Appendix D). Given that Vatnsmýri is an important wetland nature reserve in the city, the distribution and potential effects of creeping thistle to plant and wildlife communities should be monitored over time. Nootka lupin is another problematic invasive species in the study sites and in Iceland (Magnússon, 2010). This species is also listed as a species of concern and is in a watchlist in Helsinki, Finland (Ylikotila, 2018), although it is not listed as an invasive species in the European Union (European Union, 2017). Magnússon (2011) suggests that areas originally invaded by Nootka lupin act as potential areas suitable to cow parsley invasions, as cow parsley tends to prefer nutrient rich soils. Hence, monitoring and managing areas with Nootka lupin may be a useful strategy to detect and slow the spread of cow parsley and other potentially invasive species. In addition to managing known invasive plants, long-term monitoring of alien species would be beneficial for assessing changes in urban plant communities. The latter is especially relevant for alien species that are still rare but rapidly spreading, and may potentially have large impacts based on modelling, empirical evidence from other regions where they have been introduced, species traits, and/or high-impact congeners (Jeschke et al., 2014). Cow parsley has already been spreading throughout Iceland, and therefore mapping the distribution of this species in Reykjavík is important to evaluate its potential effects on urban biodiversity (Magnússon, 2011; Wasowicz et al., 2013). Primack et al. (2018) point out that without baseline data and long-term monitoring, the assessment of local changes in species richness provides useful insights about the ecology and conservation of local areas but is limited regarding changes in community structure and function, population size, and species richness at larger scales (e.g. gamma diversity). Furthermore, they highlight that some studies (e.g. Dornelas et al., 2014; Hillebrand et al., 2017), have found that local species richness (alpha diversity) is not necessarily declining in many places because native species are being replaced by other native and alien species, often leading to biotic homogenization, which in turn may affect not only the ecological processes (e.g. nutrient cycling, interactions among species) in local areas, but also other aspects of biodiversity (e.g. genetics, function), as well as cultural and intrinsic values (Olden, 2006; Pearson, 2016; Primack et al., 2018). By adopting comprehensive and long-term monitoring strategies that look at species richness, abundance, species interactions, different spatial scales, and other components of diversity, they enable a deeper understanding of the patterns of urban biodiversity as well as helping to detect both local and regional changes. Setting up clear management goals may be challenging but necessary, as climate change

47 affects the native species survival and accelerates their replacement by better adapting alien species.

2.4.2 Management of cow parsley

Drenovsky et al. (2012) point out that understanding the functional traits of successfully established alien plant species may help in controlling the spread of invasive species by choosing native species with similar characteristics, creating the opportunity and conditions to establish stable native communities that prevent further invasions of alien species. This may happen at the expense of maintaining biodiversity but can in turn recover crucial ecological functions. Garden angelica, for example, is a native species that can be seeded fairly easily to replace cow parsley, as it is also a tall plant and thrives in similar habitats, such as riversides (Icelandic Institute of Natural History; 2018b). However, careful management is needed if garden angelica is used to restore areas invaded by cow parsley, as garden angelica can also establish monoculture communities (Icelandic Institute of Natural History, 2018b). One way to prevent monocultures would be to harvest periodically garden angelica plants for local consumption. Garden angelica can be used for various medicinal purposes and also as a spice (Chauhan et al., 2016; Icelandic Institute of Natural History, 2018b). Hejda, Pyšek & Jarošík (2009) suggest that the most negative effects on species diversity and evenness is caused by tall invading species, as they are capable of forming populations with a larger cover thereby outcompeting native dominant species in this regard. These tall invasive species can also have a serious impact on the landscape. Field observations in Reykjavík suggest that cow parsley flowers earlier than some native plants, such as garden angelica, which would help reduce potential negative effects to native plants if control actions such as herbicide treatments and/or repetitive mowing are implemented earlier in the growing season. Hansson & Persson (1994) found that cutting cow parsley once during the growing season does not affect the abundance of cow parsley or the size of the communities. Only cutting the plant three times during summer was found to decrease the abundance of cow parsley. However, cutting several times may be detrimental to some species that are dependent on seed dispersal (Hansson & Persson, 1994). Also in areas such as Vatnsmýri and Elliðaárdalur, mowing is not possible along the river and inside the bird nesting reserve. One option that could be tested in Vatnsmýri would be to dig out cow parsley plants inside the reserve early in the season before the plants form seeds and without disturbing nesting birds. In addition, mowing in areas where it is feasible should be conducted early in the season, by the time the flowering begins, as this reduces the risk of strong vegetative spread through the taproot (van Mierlo & van Groenendael, 1991). Experiments to control cow parsley and sweet cicely have been conducted in northern Iceland (Svavarsdóttir, 2016), and since 2010, the municipality of Stykkishólmur in western Iceland has been taking measures against invasive plants. The West Iceland Nature Research Centre (Náttúrustofa Vesturlands), studied the distribution of several plant species that were invasive or potentially invasive, and developed an eradication plan for all them (von Schmalensee & Stefánsson, 2009). In the town of Stykkishólmur, the municipality has been conducting eradication efforts by cutting all the cow parsley 2-4 times every summer since 2010. These efforts have slowed down the spread and distribution of the species, but unfortunately they do not seem to be enough to considerably reduce the size of the areas with cow parsley. However, the latter assessment is based on personal observations and warrants quantification as the West Iceland Nature Research Centre does not have any recent direct measurements of cow parsley cover in the area (R. Stefánsson, personal

48 communication, April 13, 2018). It is very important to map and monitor the cover of cow parsley and other invasive species before and after management efforts are implemented. This allows to assess the efficiency and success of these efforts and whether they need to be modified in the future. Using adaptive management could be beneficial when managing invasive species as it helps to deal with uncertainties regarding the invasive species and the ecosystems being managed, as well as fostering „learning by doing“ through an iterative process (Walters and Holling, 1990; Park, 2004; Zalba and Ziller, 2007). In order to effectively control and eradicate invasive species, the distance over which the invasive species is being dispersed must be taken into account. This means that the eradication efforts may need to include an area that goes beyond the currently affected invasion patch (Fletcher & Westcott, 2013). Moreover, applying herbicides (e.g., glyphosate) and hand pulling has proved in many cases to be a winning combination in eradicating and controlling invasive plant species (Jørgensen et al., 2013; MacDonald et al., 2013). For example, in Hawaii, this method was used to successfully control and eradicate an invasive grass species Cenchrus echinatus (Flint, & Rehkemper, 2002). Researchers in Norway found that removing the upper 4-5 cm of the root may be sufficient for controlling cow parsley (Jørgensen et al., 2013). Furthermore, they also found in trial studies that using herbicides (mecoprop-P, thifensulfuron-methyl) in 2 consecutive years was effective in controlling cow parsley when spraying was either done in spring, or the treatment was combined with cutting the plants in spring and applying herbicides in July or August. However, regarding mowing, Jørgensen et al. (2013) showed that mowing twice in the spring and summer or once in the late summer did not reduce the abundance of cow parsley. Additionally, their results suggest that mouldboard ploughing and removing the aboveground shoots including the upper 4-5 cm of the roots by hand in small areas can be an effective method to control cow parsley. Downside of this method is that it is very labor intensive and costly, which is why of all the study sites in Reykjavík, Vatnsmýri (Appendix F; Figure 2) is likely the best area to implement and test this method to avoid disturbing nesting bird populations. Also, the accessible parts of Vatnsmýri are already being mowed four times per year, which seems to be controlling cow parsley from spreading further; however, it is recommended that mowing begins earlier in the season to prevent seed dispersal. All the study sites in Reykjavík have large patches of cow parsley. One way of managing these patches is to follow the recommendations of Canadian resource managers of mowing early in the summer season either just before blooming or at full bloom and repeating it every two weeks to prevent seed production in sites where herbicides cannot be used, and using herbicide treatments where it is permitted (Department of Agriculture, 2003; Ministries of Transportation and Infrastructure, and Forests, Lands, and Natural Resource Operations, 2016). Another approach is using a combination of mowing before flowering, herbicide treatments, tillage and native grass seeding, which has also been effective in generating the best control results of cow parsley (Miller and D'Auria, 2011). This multi approach is in line with recommendations from Jónsson & Þórðarson (2018) in northern Iceland. Bjarnadóttir et al. (2018), however, do not recommend the use of herbicides at all based on their 6-year experimental trials in Eyjafjörður. Their results indicate that repetitive spraying of herbicides (glyphosate) 3-4 times per season only gives short-term results and does not appear effective in eradicating cow parsley on a long-term basis. Instead of herbicides, they mention grazing combined with mowing, and seeding other plant species as a control method that may be more environmentally friendly option (Bjarnadóttir et al. 2018). In areas such as Laugarnes (Appendix F; Figure 1), expanding the mowing area as well as mowing several times during summer, starting early in the summer before the peak

49 flowering season, may be an effective way to control cow parsley and other alien species such as sweet cicely, Nootka lupin, and giant hogweed that are abundant in the area. In addition, the Laugarnes area would be ideal for experimental trials of different management methods such as rotated grazing and repetitive mowing. For example, biological control of cow parsley could be tested by using targeted goat (or sheep) grazing. This grazing method has already been tested in Europe and in the United States to control invasive plants like Phragmites australis in marshes (Silliman et al., 2014) and Centaurea solstitialis in canyon rangelands (Goehring, Launchbaugh, & Wilson, 2010). In regards to Ægisíða, expansion of the mowing area is also recommended, as cow parsley was found growing mostly outside the currently mowed areas (Appendix F; Figures 5-6). The Elliðaárdalur area is somewhat problematic in terms of controlling cow parsley, as the species is mainly found forming communities along the river, that are both inaccessible and cannot be controlled by using herbicides. Experimental trials with different control methods including grazing, mowing and hand pulling could be implemented in some of the areas in Elliðaárdalur to identify best management actions for this site. Further research to improve the knowledge base on control methods of invasive plants such as cow parsley, is necessary to prevent it from spreading further in Reykjavík and elsewhere in Iceland. A mixture of management methods depending on the habitat type and land-use in the area, which are tested and monitored using an adaptive management framework is recommended (Table 2.5). The lack of both funding and political will for long-term planning is what makes invasive species management often a reactive rather than proactive process (Larson et al., 2011; Simberloff et al., 2013). However, other examples like the rapid eradication response in California for the marine alga Caulerpa taxifolia in 2000 to protect coastal ecosystems, show that collaboration between different stakeholders is the key in fighting invasive species (Anderson, 2005). Kowarik (2005) emphasizes that prevention and early detection are effective measures to be taken against invasive species. Additionally, the combination of legal regulations, as well as voluntary codes of conduct (e.g. controlling invasive species, communicating this information to a wider audience), and sharing the regional knowledge of best management practices among researchers, resource managers, and city gardeners in using native and alien plants, can bring about positive changes in promoting urban biodiversity. This is essential, as the problem with invasive plants is manyfold, often leading to changes in habitat and ecosystem functioning (Kowarik, 2005; Vilà et al., 2011; Schirmel et al., 2015), thereby impacting ecosystem services and human well‐being (Pyšek & Richardson, 2010).

50 Table 2.5. Management recommendations for each study site

Total area Total Total Suggested Management method surveyed distribution distribution Study site per site (ha) of CP (ha) of SC (ha) Expand the mowing area to include areas with CP. Start repetitive mowing (minimum of 3 times during summer) early, before CP is flowering in late May. Ægisída 20,72 0,24 0,03 Handpulling individual plants including top parts of root. Possible site for testing experimental management methods (sheep/goat, and repetitive mowing).

Repetitive mowing (minimum 3 times during summer) in all the areas where mowing is possible. Start mowing before CP is flowering Elliðaárdalur 116,19 12,77 0,46 in late May. Seeding GA on the riverbeds where there are currently CP communities. Important to monitor both CP and GA.

Expand mowing area to include hill with SC. Repetitive mowing recommended, starting in late May. Handpulling of individual CP plants Laugarnes 12,31 0,51 1,01 including top parts of root. Possible site for testing experimental management methods (sheep/goat, and repetitive mowing).

Drastic eradication measures needed. Handpulling individual plants removing top rootbuds. Large communities could be removed Vatnsmýri 8,73 1,99 0,04 by completely digging out the plants and changing the soil. Management needs to be done before bird nesting season.

CP= Cow Parsley, SC = Sweet Cicely, GA= Garden Angelica

51 2.5 Conclusions

Alien species invasions are very problematic as they tend to alter not only species interactions, but also many important ecosystem functions. It is important to survey areas with alien taxa, as species that currently seem to be covering only a small portion of an area, may spread rapidly especially when climatic conditions become more favorable for them to thrive. Urban areas often serve as hotspots for alien species, as movement of people and cultivation of alien species in the gardens enable these species to move into surrounding areas fairly easily. Establishing a baseline on the distribution of invasive species is important in order to control their spread and impact before they become a major threat to native taxa. The results from the plots within the study sites in Reykjavík show that invasive alien species are a concern in the city as they had the highest plant cover in all the sites, ranging from 30- 36%. Degradation of cultural landscapes and alteration of ecosystem functions are often irreversible consequences of alien invasions. Long-term monitoring, as well as experimental test trials in various habitats in order to establish what is the best way to control invasive species, such as cow parsley, is recommended if the aim is to preserve native taxa and cultural landscape. Co-operation between researchers and decision makers is also essential, to establish the best practices in controlling invasive species.

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59 Appendix A. Survey Sites

Figure 1. Cow parsley growing in Laugarnes with sweet cicely (Myrrhis odorata), nootka lupine (Lupinus nootkatensis) and giant hogweed (Heracleum mantegazzianum). June 22, 2017.

Figure 2. A large colony of sweet cicely (Myrrhis odorata) growing with creeping buttercup (Ranunculus repens) in Laugarnes. June 8, 2017.

Figure 3. Cow parsley growing with garden angelica (Angelica archangelica), giant hogweed (Heracleum mantegazzianum) and nootka lupine (Lupinus nootkatensis) in Laugarnes. June 22, 2017.

Figure 4. Cow parsley growing with sweet cicely (Myrrhis odorata) in Vatnsmýri study area along the waterway next to Hringbraut. June 1, 2017.

Figure 5. Cow parsley (outlined with red) growing in Vatnsmýri along the waterway in the inner part of the nature reserve. June 1, 2017.

Figure 6. Dense patch of cow parsley growing in Vatnsmýri along the waterway next to Njarðargata. June 1, 2017.

Figure 7. Cow parsley growing next to creeping buttercup (Ranunculus repens) in Háubakkar, near Geirsnef in greater Elliðaárdalur study area. June 27, 2017.

Figure 8. Cow parsley growing in Geirsnef with nootka lupine (Lupinus nootkanensis) and creeping buttercup (Ranunculus repens). June 28, 2017.

Figure 9. Scattered cow parsley community in Geirsnef. Cow parsley seems to be spreading along the hill upwards away from the walking path. June 28, 2017.

Figure 10. Cow parsley growing with lupine along river Elliðaár (Figure 1.12). June 8, 2017.

Figure 11. Dense cow parsley community in Ægisíða growing with garden angelica (Angelica archangelica). June 1, 2017.

71 Appendix B. Plant Illustrations

Figure 1. Cow parsley (Skógarkerfill = Anthriscus sylvestris). Photo credit: Franz Eugen Köhler (1898).

Figure 2. Sweet cicely (Spánarkerfill = Myrrhis Odorata). Photo credit: C. A. M. Lindman (1917-1926).

Figure 3. Ground elder (Geitakál = Aegopodium podagraria). Photo credit: Otto Wilhelm Thomé (1888).

75 Appendix C. Maps of Plant Communities and Mowing Areas

Figure 1. Laugarnes grass mowing area 2018. Light green area was mowed once on August 13th, 2018. Blue area was mowed 4 times during summer, latest on August 15th, 2018. Source: Borgarvefsjá (2018).

Figure 2. Laugarnes grass mowing area 2016, marked with green color. Blue color indicates sweet cicely communities recorded in Summer 2017, dense and single cow parsley patches are marked with red color, scattered cow parsley communities are marked with purple color. Source: Datacollection by Mervi Luoma with Collector for ArcGIS, 2017 and LUKR (2016). Basemap: Léttkort af Reykjavík (2016).

Figure 3. Vatnsmýri grass mowing area 2018. Blue area was mowed 4 times during summer, latest on August 1st, 2018. Source: Borgarvefsjá (2018).

Figure 4. Vatnsmýri grass mowing area 2016, marked with green color. Blue color indicates sweet cicely communities recorded in Summer 2017, dense and single cow parsley patches are marked with red color, scattered cow parsley communities are marked with purple color. Source: Datacollection by Mervi Luoma with Collector for ArcGIS, 2017 and LUKR (2016). Basemap: Léttkort af Reykjavík (2016).

Figure 5. Ægisíða grass mowing area 2018. Blue area was mowed 4 times during summer, latest either on July 30th or August 7th, 2018 depending on the area. Source: Borgarvefsjá (2018).

Figure 6. Ægisíða grass mowing area 2016, marked with green color. Blue color indicates sweet cicely communities recorded in Summer 2017, dense and single cow parsley patches are marked with red color, scattered cow parsley communities are marked with purple color. Source: Datacollection by Mervi Luoma with Collector for ArcGIS, 2017 and LUKR (2016). Basemap: Léttkort af Reykjavík (2016).

Figure 7. Elliðaárdalur grass mowing area 2018. Light green area (Geirsnef) was mowed once on June 30th, 2018. Red area was mowed twice, latest on July 25th or July 31st depending on the area. Blue area was mowed 4 times during summer, latest either on August 15th or 27th, 2018 depending on the area. Source: Borgarvefsjá (2018).

Figure 8. Elliðaárdalur grass mowing area 2016, marked with green color. Blue color indicates sweet cicely communities recorded in Summer 2017, dense and single cow parsley patches are marked with red color, scattered cow parsley communities are marked with purple color. Source: Datacollection by Mervi Luoma with Collector for ArcGIS, 2017 and LUKR (2016). Basemap: Léttkort af Reykjavík (2016).

84 Appendix D. Plot measurements datasets

85 Site CP_AI LM_A HLM_N Y_N D_N GA_N CF_N CB_A NL_AI CT_A OH_A VC1 15 38 VC2 8 6 5 2 VC3 48 VC4 23 13 18 VC5 4 1 1 2 V1 15 22 16 5 1 V2 54 6 2 V3 17 7 1 23 V4 55 5 8 13 V5 15 20 EC1 5 50 EC2 12 10 3 2 15 EC3 3 6 13 11 EC4 1 6 1 EC5 14 4 4 E1 15 20 3 44 E2 8 4 2 7 3 67 E3 4 3 6 20 E4 46 10 E5 80 4 2 LC1 1 75 LC2 7 8 12 LC3 9 3 43 2 LC4 6 27 4 38 LC5 3 6 72 10 L1 33 4 6 L2 8 1 10 3 5 L3 64 2 3 4 12 2 L4 15 73 L5 15 20 12 20 AC1 AC2 AC3 3 38 AC4 9 AC5 2 90 2 A1 20 20 30 8 A2 25 15 20 A3 36 2 38 4 A4 52 8 A5 46 31

86 Site SP_N WA_N T_N CS_N ND_A CWWH_N MS_N WC_AR FW_A WCB_N SW_N AB_A VC1 3 VC2 40 VC3 23 VC4 1 VC5 5 1 V1 V2 V3 40 V4 V5 6 6 EC1 3 EC2 2 EC3 2 9 2 EC4 48 26 5 EC5 4 32 E1 1 15 E2 3 E3 21 25 6 E4 22 E5 4 LC1 5 LC2 LC3 3 LC4 LC5 L1 20 L2 7 1 17 L3 L4 L5 8 AC1 36 AC2 2 AC3 5 8 AC4 10 3 AC5 3 A1 A2 2 A3 A4 2 A5 18

87 Site MHT_N SMW_N CCW_N YR_N GR_N SC_A FMN_N IHW_N LBS_N NBS_N TV_N Grass Moss VC1 1 43 VC2 30 4 5 VC3 29 VC4 3 30 12 VC5 28 1 57 V1 41 V2 34 4 V3 12 V4 19 V5 53 EC1 10 8 24 EC2 2 5 5 44 EC3 54 EC4 5 8 EC5 2 7 33 E1 2 E2 2 4 E3 10 5 E4 12 10 E5 10 LC1 2 17 LC2 45 28 LC3 3 37 LC4 25 LC5 6 3 L1 5 5 27 L2 48 L3 13 L4 12 L5 25 AC1 64 AC2 8 15 75 AC3 46 AC4 78 AC5 3 A1 22 A2 38 A3 20 A4 38 A5 5

88 Appendix E. Tallest Plant Species in Plots without Cow Parsley

Figure 1. Northern Dock (Rumex longifolius), height 137cm, measured in Elliðaárdalur plot 3 without cow parsley. August 2, 2018.

Figure 2. Northern Dock (Rumex longifolius), height 102cm, measured in Laugarnes plot 3 without cow parsley. July 27, 2018.

Figure 3. Creeping Thistle (Cirsium arvense), height 128,5cm, measured in Vatnsmýri plot 1 without cow parsley. July 27, 2018.

Figure 4. Garden Angelica (Angelica archangelica), height 136cm, measured in Ægisíða plot 5 without cow parsley. July 27, 2018.

94 Appendix F. Maps of Study Plots and Mowing Areas

Figure 1. Laugarnes area in Reykjavík with plant distribution and plot data. Figure includes plots with cow parsley (Plot 1-5), and plots without cow parsley (LC1-5). Areas where the grass is mowed by the city once during summer on August 13th are included (large bright green on the right with sweet cicely distribution). Areas right next to the Særbraut street are mowed four times during summer. Sources: Borgarvefsjá (2018), Datacollection by Mervi Luoma with Collector for ArcGIS, 2017, LUKR (2016). Basemap: Léttkort af Reykjavík (2016).

96 VC 1

Figure 2. Vatnsmýri wildlife nature reserve area in Reykjavík with plant distribution and plot data. Figure includes plots with cow parsley (Plot 1-5), and plots without cow parsley (VC1-5). Areas where the grass is mowed by the city 4 times during summer are included (bright green). Sources: Borgarvefsjá (2018), Datacollection by Mervi Luoma with Collector for ArcGIS, 2017, LUKR (2016). Basemap: Léttkort af Reykjavík (2016).

Figure 3. Geirsnef and Elliðaárdalur area in Reykjavík with plant distribution and plot data. Figure includes plots with cow parsley (Plot 1 and 5), and plots without cow parsley (EC1- 3). Areas where the grass were mowed by the city 1-4 times during summer 2018 are included (bright green). Large area with Plot 5 and comparison plot 1 was mowed once at the end of June, 2018. Area on directly above, and on the right of comparison plot 2 was mowed twice during summer 2018. The areas close to the road and comparison plot 3 were mowed 4 times during summer 2018. Sources: Borgarvefsjá (2018), Datacollection by Mervi Luoma with Collector for ArcGIS, 2017, LUKR (2016). Basemap: Léttkort af Reykjavík (2016).

Figure 4. Elliðaárdalur area in Reykjavík with plant distribution and plot data. Figure includes plots with cow parsley (Plot 1-4), and comparison plots without cow parsley (EC3- 5). Areas where the grass were mowed by the city 4 times during summer 2018 are included (bright green). Sources: Borgarvefsjá (2018), Datacollection by Mervi Luoma with Collector for ArcGIS, 2017, LUKR (2016). Basemap: Léttkort af Reykjavík (2016).

Figure 5. Ægisiða area in Reykjavík with plant distribution and plot data. Figure includes Plot 1 with cow parsley and plots without cow parsley (AC1-2). Areas where the grass is mowed by the city 4 times during summer are included (bright green). Sources: Borgarvefsjá (2018), Datacollection by Mervi Luoma with Collector for ArcGIS, 2017, LUKR (2016). Basemap: Léttkort af Reykjavík (2016).

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Figure 6. Ægisiða area in Reykjavík with plant distribution and plot data. Figure includes plots without cow parsley (AC3-5) and plots with cow parsley (Plot 2-5) Areas where the grass is mowed by the city 4 times during summer are included (bright green). Sources: Borgarvefsjá (2018), Datacollection by Mervi Luoma with Collector for ArcGIS, 2017, LUKR (2016). Basemap: Léttkort af Reykjavík (2016).

101