Table of Contents. Monitoring of Spartina References Table of Figures

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1 Table of Contents Monitoring of Spartina Mapping Methodology and results... 1 Potential errors and limitations... 1 Re-mapping Methodology... 2 Errors and limitations... 2 Results... 2 Additional observations... 3 Conclusion... 7 References... 8 Table of Figures Fig. 1 Spartina field 2014: Grazing right of the fence with few short Spartina shoots visible along the fence.. 4 Fig. 2 Spartina field July 2014: short Spartina shoots in grazed area vs. Flowering Spartina on other side of the fence... 4 Fig. 3 Spartina invading low salt marsh at Sønder Nyland... 6 Fig. 4 Continuous ribbon of sea clubrush with single Spartina patches which was only Spartina in 2010 mapping... 7

2 Monitoring of Spartina Mapping 2010 Methodology and results The initial mapping of invasive Spartina anglica at Læsø has been conducted in The observed area ranges from the south-western to the south-eastern part of the island, including small islands located south of the main island. The team used high resolution orthographic pictures of the area to mark new seedlings less than 20x20cm- with a dot in the map while out in the field. For larger areas the team tried to draw the circumference of the affected area. This data was digitized on a laptop right away but no GPS-coordinates have been taken or used for the mapping. Based on this procedure the total area invaded by Spartina has been calculated to be 12,96 ha. The map shows that Spartina is more established in the south-western part of the island and that there is hardly any Spartina east of Hornfiskrøn. Also it is well noticeable that the largest and most established Spartina fields occur around Stokken and Sønder Nyland where we find sheltered, estuary- like conditions. The fact that Spartina seems more successful at Lœsø in less exposed areas is in line with findings from other places (Cottet, de Montaudouin, Blanchet, & Lebleu, 2007; Nehring & Hesse, 2008; Vinther, Christiansen, & Bartholdy, 2000). Other areas with larger Spartina fields are near Fannemands Færge and on some of the small islands near Hornfiskrøn. Those areas are also well protected from wave erosion and are characterized by a habitat mix of lower salt marsh vegetation and open salt pans. Potential errors and limitations As the data has been drawn manually to a map, it is possible that some areas are accidentally misplaced on the map. Additionally, drawing polygons manually carries the risk of drawing the areas too large/wide. Due to the fact that some of the polygons are 25-50m wide, I assume this to be very likely. Also, it is not clear whether circumferences have been drawn around areas with a complete Spartina coverage and/or around areas where many smaller patches of Spartina are scattered in a larger area. Considering the size (area) of many of the polygons from 2010, I assume that the latter is the case. All this might have lead to an overestimation of the whole area covered with Spartina in Lastly, it is not known if the team has not observed some areas within the mapping- range. Re-mapping 2014 Four years after the initial mapping of Spartina a re-mapping has been conducted between September and November 2014, in order to get a better idea of the invasiveness of Spartina and to see how the situation has developed. 1

3 Methodology In contrast to the initial mapping in 2010, the data has been collected with a Garmin GPSMAP 62s tool in the field. After the data collection the GPS data (gpx) was converted to be properly displayed in the GISsoftware MapInfo. Due to the fact that the amount of Spartina must have enlarged quite a bit over the past four years the area indicated by a dot on the map had, for practicability reasons, to be enlarged to clumps smaller than 3x3m. Those clumps have been tracked with the waypoint function of the GPS-tool. All areas larger than 3x3m have been tracked with the measuring areas - function. This means that all areas completely covered by Spartina have been walked around, taking the exact GPS positions, which make up the circumference of the area. The same has been done in areas which do not show a complete Spartina coverage but are heavily invaded with many clumps and new seedlings. All these areas have then been converted into respectively sized polygons in MapInfo. In addition to that, all Spartina clumps less than 1.5m apart from each other along the coastline are considered continuous ribbons and are also indicated by polygons on the map. The GPS based mapping should be more accurate when it comes to calculating the total area affected by Spartina. The total area affected by Spartina in 2014 has been calculated by adding up the area of all polygons and waypoints. For the polygons the respective areas are precisely given by MapInfo; for the waypoints only a rough calculation could be made based on the total number of waypoints multiplied by a median area. Large parts of Stokken have not been tracked with a GPS-tool, but based on previous visits this year, polygons could be drawn onto areas that are knowingly affected by scattered or complete Spartina coverage. Also some of the small islands off Rønnerne and Hornfiskrøn have not been tracked with the GPS-tool this year. As it is very unlikely that the Spartina out there has disappeared, while it has increased in all other areas around, data from 2010 has been utilized to include those areas into the calculation. Errors and limitations For the polygons indicating continuous ribbons the same errors and limitations are true in terms of size as already mentioned for Also, the data generated by the GPS tool might not be 100% accurate either. Moreover, time and weather constraints during the re-mapping period caused that not unexceptionally all areas in the respective range from 2010 could be tracked with the GPS-tool. As already mentioned, this accounts specifically for some parts of Stokken and some islands south of the main island at Rønnerne and around Hornfiskrøn. To at least optionally include these areas into this year s calculation of the total area affected, data from 2010 and manually drawn polygons have been utilized. Of course, this data is less reliable and less accurate than the newly generated GPS data from Results The most significant result is the strong eastwards expansion of Spartina over the past four years. Also it has further established in most of the areas where it was already present in While in 2010 areas larger than 20x20cm have only been present around Stokken, Sønder Nyland and on some of the small islands at Rønnerne as well as around Hornfiskrøn, these small seedlings have vastly grown into clumps up to 3x3m. 2

4 Especially along the coastline ranging from Sønder Nyland to Hornfiskrøn those single new seedlings found in 2010, have developed into a large continuous ribbon with very few interruptions. East of Hornfiskrøn continuous ribbons are not present yet but many single clumps are present nearly along the entire coastline. Furthermore, the re-mapping shows that Spartina does not only spread on bare mudflats along the coastline, but also expands further inland. Here it invades predominantly lower salt marshes, open salt pans and ditches. In the low salt marsh it is likely to displace native vegetation (Roberts & Pullin, 2007). Additionally, the expansion of Spartina negatively changes the feeding grounds for shorebirds (Chandrasekara & Davey, 1999; Hammond, 2001; Paramor & Hughes, 2007; Raybould, 2005). But also for the inland expansion differences between the south-western and south-eastern part of Læsø are clearly visible. While from the most south-western edge of the observed area near Fannemands Færge to Hornfiskrøn a strong inland expansion is evident almost everywhere where the described habitat conditions are present, it is still rather limited in those areas east of Hornfiskrøn. Although even here some early stages of an expansion into the lower marsh, ponds and ditches exist. Besides the remarkable expansion of Spartina on a large scale, there are also hints for a significant regional decrease/ dieback in the far south-western part. According to the initial mapping in 2010 there were extensive Spartina fields on both sides of the tidal inlet between the main island and Stokken as well as along the coastline east and west of the parking lot at Sønder Nyland. In 2014 only a few single clumps were found here. While this can be stated with absolute certainty for the respective sections off the main island, there is a bit uncertainty for the section on Stokken because this part has not been tracked with a GPS-tool in However, from this year s observation of the area, the presence of such a large Spartina field as indicated in the map 2010 can be excluded. The phenomenon of natural diebacks is discussed in more detail in the Experiment Report. All in all, when taking only those areas into consideration which have been tracked with a GPS tool, the total area affected by Spartina in 2014 sums up to 10,4 ha. When including those areas, which have not been tracked by GPS but are knowingly, affected by Spartina (not completely covered) this number increases to 15,2 ha. Lastly, when including the data gathered in 2010 for those areas which have not been tracked this year by GPS but have already been affected 2010, it sums up to 22.9 ha. Additional observations In the course of the data collection in the field some additional interesting observations were made regarding the presence of Spartina in grazed areas and in competition with native vegetation. Grazing In all areas where Spartina has spread into fenced areas, it is evident that cattle as well as horses (Icelandic horses)like to graze Spartina plants. This can be nicely seen in Fig. 1 and Fig. 2. On one side of the fence are many fully developed Spartina plants and on the grazed side the plants are significantly shorter. The fact that the Spartina close to the fence on the ungrazed side also is significantly shorter, leads to the assumption 3

5 P that grazers must very much like Spartina. Both areas shown on the pictures were grazed by cattle, but the same observation has been made at areas grazed by Icelandic horses. Fig. 1 Spartina field 2014: Grazing right of the fence with few short Spartina shoots visible along the fence Fig. 2 Spartina field July 2014: short Spartina shoots in grazed area vs. Flowering Spartina on other side of the fence 4

6 Another interesting observation in this context is that east of Hornfiskrøn there are areas where Spartina is clearly on the forefront of spreading inland but visible plants stop right outside the fenced area, even though conditions inside the fenced area are very much in favor of Spartina as well. This might be complete coincidence, but it might also be an indicator that especially in the early stages of a Spartina invasion, grazing is an effective controlling technique because it prevents new seedlings from establishing. The latter is supported the findings of Scholten M.C.T. & Rozema J. (1990) who found out that clipping almost completely suppressed the growth of young Spartina (anglica) shoots, whereas Puccinellia was less affected, especially on brackish dry sand. Another observation vaguely supporting this was made even further east, where there is a distinctive section along the coastline not showing any presence of Spartina, even though there are clumps east and west of this section. On first sight there are no territorial reasons that would explain the lack of Spartina. However, this section is grazed by cattle and the fence line is almost continuously in the water or at least extremely close to the water line. In summary there are some indicators pointing towards grazing as an effective and very practical controlling technique. Even though, grazing has so far not proven effective in eradicating Spartina and is seen quite controversial in literature (Shaw & Falls, 1999)(Hammond, 2001), there is clear evidence that in areas where Spartina is already well established grazing at least keeps the plant short and therewith limits further spread of Spartina through seeds. Furthermore, it might limit Spartina in establishing in new areas. Nonetheless, all this is very vague information at this point of time with a big need and potential for further research. Competition with native vegetation (very briefly more detailed in thesis) Along the coastline in the so called pioneer zone marsh samphire (Salicornia europaer) is the only native plant capable of dealing with the conditions in this zone. It is likely that in most areas Spartina negatively impacts marsh samphire as previous research has shown that the density of Salicornia is lowered with increasing shoot density of Spartina. Moreover there is reason to fear that the vegetation of the lower salt marsh will not be able to compete against Spartina invasion in the long term (Scholten M.C.T. & Rozema J., 1990). Fig. 3 shows a low salt marsh area at Sønder Nyland where Spartina has already built a large sward with many single clumps and new seedlings scattered in the remaining native vegetation. 5

7 Fig. 3 Spartina invading low salt marsh at Sønder Nyland Even though on first sight it seems as if Spartina is a threat to native vegetation in low salt marsh areas at Lœsø, it needs to be considered that we are talking about a highly dynamic and complex system in which Spartinas role is not fully understood yet. At the International Spartina Conference 2014 e.g. it was reported that Spartina had integrated into native vegetation of the French salt marsh and therefore is not considered a threat anymore. Also Spartina enhances sediment accretion and stabilization and therewith promotes large scale salt marsh creation (Balke et al., 2012; Paramor & Hughes, 2007). In addition, Spartina anglica is found in mixed stands with native sea clubrush (Bolboschoenus maritimus (L.) Palla) as seen in Fig. 4. Especially when considering the fact that one of the areas indicated with a continuous ribbon of Spartina in 2010, is dominated by a continuous ribbon of sea clubrush with only very few Spartina clumps in Previous research has shown that Bolboschoenus maritimus performs poorly in salt marshes and the same is true for Spartina anglica in freshwater marshes (Engels J.G., & Jensen K., 2010). Under brackish conditions there is controversial information regarding Spartinas competetiveness (Gray, Marshall, & Raybould, 1991; Roberts & Pullin, 2007). 6

8 Fig. 4 Continuous ribbon of sea clubrush with single Spartina patches which was only Spartina in 2010 mapping Conclusion Summarizing the findings of the initial mapping in 2010 and the re-mapping in 2014, Spartina is more established in the south-western part of the Lœsø but has progressively expanded eastwards. In the worst case scenario it needs to be feared that the total area affected by Spartina has almost doubled over the past four years. In addition, three main areas for further research have been identified. First of all, grazing has been recognized as a potential limiting factor for a further uncontrolled spread of Spartina with a big need for further research on its actual potential as a controlling technique. Secondly, there are hints that Spartina is a threat to native low salt marsh vegetation. However, the dynamics of the system need to be further researched before coming to a hasty conclusion. Lastly, along the coastline Spartina is frequently found in mixed stands with native sea clubrush where it is also uncertain at this point whether these two species will coexist or which species will outcompete the other one in the long run. 7

9 References Balke, T., Klaassen, P. C., Garbutt, A., van der Wal, D., Herman, P. M. J., & Bouma, T. J. (2012). Conditional outcome of ecosystem engineering: A case study on tussocks of the salt marsh pioneer Spartina anglica. Geomorphology, , doi: /j.geomorph Chandrasekara, W. U., & Davey, P. (1999). The restoration of mud flats inuaded by common cord- grass (Spartina anglica, CE Hubbard) using mechanical disturbance and its effects on the macrobenthic fauna. AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, 9, Cottet, M., de Montaudouin, X., Blanchet, H., & Lebleu, P. (2007). Spartina anglica eradication experiment and in situ monitoring assess structuring strength of habitat complexity on marine macrofauna at high tidal level. Estuarine, Coastal and Shelf Science, 71(3-4), doi: /j.ecss Gray, A. J., Marshall, D. F., & Raybould, A. F. (1991). A Century of Evolution in Spartina anglica. Advances in Ecological Research, 21, doi: /s (08) Hammond, M. E. R. (2001). THE EXPERIMENTAL CONTROL OF SPARTINA ANGLICA AND SPARTINA X TOWNSENDII IN ESTUARINE SALT MARSH. Nehring, S., & Hesse, K.- J. (2008). Invasive alien plants in marine protected areas: the Spartina anglica affair in the European Wadden Sea. Biological Invasions, 10(6), doi: /s z Paramor, O. A. L., & Hughes, R. G. (2007). Restriction of Spartina anglica (C.E. Hubbard) marsh development by the infaunal polychaete Nereis diversicolor (O.F. Müller). Estuarine, Coastal and Shelf Science, 71(1-2), doi: /j.ecss Raybould, A. (2005). The Ecology of Poole Harbour. Proceedings in Marine Science (Vol. 7, pp ). Elsevier. doi: /s (05) Roberts, P. D., & Pullin, A. S. (2007). The effectiveness of management interventions for the control of Spartina species: a systematic review and meta- analysis. AQUATIC CONSERVATION- MARINE AND FRESHWATER ECOSYSTEMS. Retrieved from N= &site=eds- live&scope=site Scholten M.C.T. & Rozema J. (1990). The competitive ability of Spartina anglica on Dutch Salt Marshes. In: Gray, A.J., & Benham, P.E.M. (eds) Spartina anglica - A research review.london. Shaw, W., & Falls, O. (1999). Options for Spartina control in Northland. Retrieved from and- technical/casn253.pdf Vinther, N., Christiansen, C., & Bartholdy, J. (2000). Colonisation of Spartina on a tidal water divide, Danish, (Figure 1),