The Spatial Distribution of Alien and Invasive Vascular Plant Species on Sub-Antarctic Marion Island

The spatial distribution of alien and invasive vascular plant species on sub-Antarctic Marion Island

Tshililo Ramaswiela

Thesis presented in partial fulfillment of the requirements for the degree of Master of Science (Botany) at Stellenbosch University

Department of Botany and Zoology

Faculty of Science

Supervisor: Prof. Steven L. Chown

Co-supervisor: Dr. Justine D. Shaw

December 2010

DECLARATION

By submitting this thesis electronically, I declare that the entirety of the work contained therein is my own, original work, that I am the owner of the copyright thereof (unless to the extent explicitly otherwise stated) and that I have not previously in its entirety or in part submitted it for obtaining any qualification. Date: September 2010

i ABSTRACT

The patterns of spread of non-indigenous species and the factors influencing their distribution have been studied infrequently on Southern Ocean Islands, where the prevention and control of biological invasions is a priority for conservation management. Owing to its remoteness and relatively small size, sub-Antarctic Marion Island provides an ideal opportunity to investigate the patterns of spread of invasive species and the factors likely influencing the distribution of alien species. Therefore, this study provides a spatially explicit documentation of the alien and invasive vascular plant species on Marion Island, the change in their distribution patterns through time, an assessment of the correlates of the current distributions, documentation of species rich areas, and provides recommendations for control based on these data and life history data available for each species. To ensure comprehensive coverage for the current estimate of distributions, a combination of a systematic (spatially explicit) survey and an ad hoc data collection method was used to examine the abundance and occupancy of each alien plant species across the island. The spatially explicit survey was used to identify sampling sites on a ½ minute by ½ minute scale (926 m × 926 m) which resulted in 348 sites across the island, whereas 2356 additional presence records were added during the ad hoc sampling. The residence time of each species was also estimated from the first records reported in various literature. While it has been documented in many studies that residence time is an important factor explaining species distribution, this study showed that distribution of alien species on Marion Island is not explained by residence time. The alien plant species on Marion Island differ markedly in their occupancy, distribution and rate of expansion. Agrostis stolonifera, Cerastium fontanum, Poa annua and Sagina procumbens are all expanding their ranges, whereas the range of Stellaria media appears to be contracting. Cerastium fontanum is the most widespread species on Marion Island while Sagina procumbens is the most abundant (number of records) and most rapidly expanding species on both Marion and Prince Edward Islands. Generalized linear models demonstrated that altitude, distance to human disturbed sites, and nearest neighbour presence are all significant and often strong correlates of spatial variation in alien vascular plant species richness and individual species presences on Marion Island. In particular, alien species richness on Marion Island declines sharply with increasing elevation, and that the distribution of the most widespread species is spatially aggregated. The surroundings of the Meteorological station and Mixed Pickle hut exhibit high richness and a high likelihood of the presence of individual species. None of the models developed for this study resulted in habitat type being significant explanatory variable for the distribution of any of the alien plant species, although from the

ii records alone it is clear that the salt spray vegetation type is avoided. Together with assessments of the life history of the species, the current distribution data suggest that few alien plant species can be easily eradicated. Most are already too widespread already for cost- effective eradication. Moreover, given the current rate of spread of Agrostis stolonifera, Cerastium fontanum, Poa annua and Sagina procumbens, and their apparent lack of habitat preference, it seems likely that within the next few decades many lowland habitats will be dominated by these species. By contrast, Rumex acestosella, Agrostis gigantea, Agropyron repens, Juncus effusus, Luzula cf. multiflora and the newly established shrub species should be the subject of control or eradication efforts. This thesis provides comprehensive baseline data on alien vascular plant distributions as a benchmark for future assessments.

iii OPSOMMING

Die verspreidingspatrone van uitheemse spesies en die faktore wat hulle verspreiding beïnvloed is selde op Suidelike Oseaan Eilande bestudeer, waar die voorkoming en beheer van biologiese indringing ‘n prioriteit is vir bewaringsbestuur. Te danke aan sy afgeleëndheid en relatiewe klein grootte, voorsien sub-Antarktiese Marion Eiland ‘n ideale geleentheid om die patrone van verspreiding van indringer spesies en die faktore wat moontlik die verspreiding van uitheemse spesies beïnvloed te ondersoek. Daarom voorsien hierdie studie ‘n ruimtelik eksplisiete dokumentering van die uitheemse en indringer vaatplant spesies op Marion Eiland, die verandering in hulle verspreidingspatrone oor tyd, ‘n bepaling van die korrelasies van die huidige verspreidings, dokumentering van spesiesryke areas, en voorsien aanbevelings vir beheer gebasseer op hierdie data en die lewensloopdata beskikbaar vir elke spesie. Om omvattende dekking vir die huidige skatting van vespreidings te verseker, is ‘n kombinasie van sistematiese en ad hoc metodes gebruik om die talrykheid en besetting van elke uitheemse spesie oor die eiland te ondersoek. Die ruimtelik eksplisiete opname is gebruik om moniteringsplotte op ‘n ½ minuut by ½ minuut skaal (926 m × 926 m), met die resultaat van 348 plotte oor die eiland, terwyl 2356 addisionele voorkomsrekords bygevoeg is tydens die ad hoc versameling. Die verblyftyd van elke spesie is ook beraam vanaf die eerste rekords in die literatuur. Terwyl dit aangeteken is dat verblyftyd ‘n belangrike faktor is om spesie verspreiding te verduidelik, wys hierdie studie dat verspreiding van uitheemse spesies op Marion Eiland nie verduidelik word deur verblyftyd nie. Die uitheemse spesies op Marion Eiland verskil aansienlik in hulle besetting, verspreiding en tempo van uitbreiding. Agrostis stolonifera, Cerastium fontanum, Poa annua en Sagina procumbens brei almal hulle areas uit, terwyl die area van Stellaria media bleik te krimp. Cerastium fontanum is die mees wydverspreide spesie op Marion Eiland, terwyl Sagina procumbens die oorvloedigste (aantal rekords) en die vinnigste uitbreidende spesie is op beide Marion en Prince Edward Eiland. Veralgemeende lineêre modelle het aangetoon dat hoogte, afstand na menslike versteurde plotte, en naaste buurman teenwoordigheid almal betekenisvol is en gereeld sterk korreleer met ruimtelike variasie in uitheemse vaatplant spesierykheid en individuele spesie voorkoms op Marion Eiland. Uitheemse spesierykheid op Marion Eiland neem in besonder sterk af met ‘n toename in hoogte en die verspreiding van die mees wyduitgebreide spesies is ruimtelik saamgesteld. Die omgewing om die Weerstasie en Mixed Pickle hut toon hoë rykheid en ‘n hoë waarskynlikheid van die voorkoms van individuele spesies. Nie een van die modelle wat vir hierdie studie ontwikkel is toon ‘n belangrikheid in habitat tipe as ‘n verduidelikbare veranderlike vir die verspreiding van enige van die uitheemse plant spesies nie, alhoewel

iv vanuit die rekords alleen is dit duidelik dat soutsproei plantegroei nie verkies word nie. Tesame met ondersoeke oor die lewensloop van die spesies, stel die huidige verspreidingsdata voor dat min uitheemse plant spesies maklik uitgeroei kan word. Die meeste is eenvoudig te wydverspreid vir koste effektiewe uitroeiing. Voorts, gegewe die huidige tempo van uitbreiding van Agrostis stolonifera, Cerastium fontanum, Poa annua en Sagina procumbens en hulle skynbare gebrek aan habitat voorkeur, is dit hoogs waarskynlik dat baie van die laerliggende habitatte binne die volgende paar dekades gedomineer sal word deur hierdie spesies. In teenstelling, Rumex acestosella, Agrostis gigantea, Agropyron repens, Juncus effusus, Luzula cf. multiflora en die nuutgevestigde struik spesie moet die fokus wees van beheer/uitroeiing pogings. Hierdie tesis voorsien omvattende basislyn data oor uitheemse vaatplantverspreidings as ‘n standaard vir toekomstige ondersoeke.

v ACKNOWLEDGEMENTS

This project was funded by the South African National Antarctic Programme of the National Research Foundation (NRF – SANAP). Additional funding was provided by The Prince Edward Islands book fund. Logistical support for the project on Marion Island was provided by the Department of Environmental Affairs and Tourism (DEAT). I thank the Marion 63 team for being my family during the period I spent on Marion Island. To Jacques Deere, thanks for sending all sorts of items that I requested while I was on the island.

My gratitude goes to my supervisors, Dr. Justine D. Shaw and Prof. Steven L. Chown – thanks for your constructive criticism, guidance, and above all, your faith in me. The completion of this work would not have been possible without your support. Special thanks go to Ethel Phiri and Dr. Peter le Roux for invaluable comments and assistance with statistical analysis. Thanks to Dr. Dian Spear and Dr. Jesse Kalwij for providing useful assistance with GIS. Erika Nortje, thank you for translating the abstract for this thesis to Afrikaans. I am also grateful to Steven’s (C.I.B) research group for support throughout the writing up of this work.

I would also like to thank my fellow office mates Fulufhelo Mukhadi, Andrew Rogers and Michelle Gibson for helping me in many ways. To Nomzamo Kunene, thanks for your constant support, courage and for believing in my ability, thank you very much.

Last but not least, my gratitude goes to my family. To my parents, Abby and Grace Ramaswiela, you stood by me during tough times. To my siblings, Thendo, Gabriel, Farisani, Humbulani and Rofhiwa, you all inspire me.

vi TABLE OF CONTENTS

Declaration………………………………………………………...... i Abstract………………………………………………………...... ii Opsomming………………………………………………………...... iv Acknowledgements………………………………………………………...... vi Table of contents………………………………………………………...... vii

Chapter 1...... 1-22 GENERAL INTRODUCTION...... 1 Study location...... 10 Thesis outline...... 13 References...... 14

Chapter 2...... 23-58 THE CURRENT DISTRIBUTION OF INVASIVE SPECIES ON MARION ISLAND Introduction...... 23 Materials and methods...... 29 Results...... 33 Discussion...... 48 References...... 52

Chapter 3...... 59-87 ASSESSING THE VULNERABILITY OF VEGETATION AND VARIABLES THAT DETERMINE ALIEN SPECIES OCCURENCE ON MARION ISLAND Introduction...... 59 Materials and methods...... 61 Results...... 67 Discussion...... 73 References...... 77

Chapter 4...... 88-103 MANAGEMENT RECOMMENDATIONS Introduction...... 88 Species ranked according to their prioritization for eradication...... 91

vii Prioritizing control and eradication on Marion Island…………...…...... 92 General conclusion...... 97 References...... 98

viii Chapter 1 GENERAL INTRODUCTION

The Southern Ocean Islands (SOI), ranging from Tristan da Cunha in the north (37°S, 12°W) to South Georgia in the south (54°S, 37°W) represent the only terrestrial areas in the vast Southern Ocean (Gremmen et al. 1997). The islands that are clustered around the Antarctic Polar Frontal Zone from the sub-Antarctic Biogeographic region (De Villiers et al. 2006). The sub-Antarctic climate is oceanic and thermally stable (Smith 2002), with the low mean air- temperature, generally remaining above freezing point. For example, on Marion Island the mean annual temperature is 6.4°C (le Roux & McGeoch 2008). These remote islands have oceanic climates very different to those of the Southern Hemisphere continents, and support tundra-like vegetation (with some low tree growth on northern islands) (Gremmen 1981; Chown et al. 2008a). They also form the breeding platforms for many seabird and seal species, and are home to many endemic taxa (Gremmen 1997; Chown et al. 1998; Bergstrom & Chown 1999). In consequence, the Southern Ocean Islands are of considerable conservation significance (Dingwall 1995; Chown et al. 2001, De Villiers et al. 2006).

Despite their remoteness, the islands are not free from the introduction of species from other regions of the world (Frenot et al. 2001, 2005). The majority of the alien plant species on the SOI have been accidentally introduced (Chown et al. 1998), and most of these alien species are common in temperate regions of the northern hemisphere belonging to the European flora (Frenot et al. 2001). A relatively large number (284) of alien plant species and their impacts have been recorded from the islands (Table 1). Other taxa, for exmple introduced mammalian predators and herbivores, and invertebrates have also been well-documented (e.g. Chapuis et al. 1994; Gremmen et al. 1998; Ernsting et al. 1999; Jones et al. 2003; Chown et al. 2008b). These alien species pose a considerable threat to the species and ecosystems of most SOI islands and it is predicted that these threats will continue to increase in conjunction with climate change in the region (Frenot et al. 2005).

Changes in climate have been recorded over the past 50 years on several sub-Antarctic islands, including Macquarie (Adamson et al. 1988), Kerguelen (Frenot et al. 1997), Marion (Rouault et al. 2005; le Roux & McGeoch 2008), and Heard (Budd 2000) islands. These increases in surface temperature are typically well above the global average temperature increase, and are often coupled with a decline in annual rainfall (Smith 2002). The changing climates of the sub-Antarctic islands are having, and are predicted to have, far-reaching

1 impacts on indigenous terrestrial species and biological invasions on the islands (Bergstrom & Chown 1999; Barendse & Chown 2000; Frenot et al. 2005). Increasing temperatures are likely to promote the spread of established alien species on the islands (Frenot et al. 2005; Chown et al. 2007). Warmer climates are also likely to create suitable habitat conditions enabling species from temperate regions to establish on the otherwise cool and wet sub- Antarctic islands (Kennedy 1995; Bergstrom & Chown 1999).

Despite being governened and therefore managed by many different countries, most of the Southern Ocean islands are nature reserves of varying status (De Villiers et al. 2006). In consequence, many of the management plans of Southern Ocean islands identify the need to prevent further introductions of alien species and to control those that have already colonized and established populations (Dingwall 1995; Chown et al. 2001; Jones et al. 2003; de Villiers et al. 2006). Effective alien species control programmes require that the status of the species (i.e. indigenous or transient, established, invasive, transformer alien species – see below) be determined and their island distributions and extent be quantified. Without such information, appropriate and effective management cannot be undertaken (Davies et al. 2007). However, for most islands, such information is either non-existent, incomplete, or spatially restricted.

Therefore, the objectives of this study on Marion Island were to:

° Map the geographic distribution of alien vascular plants and determine the habitats and areas that are most susceptible to invasion, ° Determine the current status of all the invasive plant species on the island (i.e. whether they are restricted aliens or invasive species with wide distributions), ° Compare present distributions with previous information, ° Provide baseline data on alien vascular plant distributions as a benchmark for future assessments, ° Establish priorities for the control of alien vascular plants based on feasibility assessments.

In so doing, several hypotheses significant in the field of invasion biology have also been tested: ° Distribution range and abundance are positively related to residence time as suggested by Pyšek & Hulme (2005) and Wilson et al. (2007)

2 ° Areas of disturbance such as settlements (Marion Base and field huts) are more important in the invasion process. That is, disturbance may be the driver and invasion the passenger (Didham et al. 2005).

Classification and terminology for alien and invasive plants Several terms are commonly used to distinguish the status of non-indigenous species. Many of these have been used interchangeably to describe the same concept (exotic, alien nonindigenous) whereas others (naturalized, invasive, imported) have been used contradictorily to describe “alien species” (Colautii & MacIsaac 2004). Additionally it must also be considered that, alien plants, once introduced to an area can spread and change their status; they can change from alien to invasive and subsequently become transformers. Based on an extensive and critical survey of the literature, Richardson et al. (2000), Pyšek et al. (2004) and Pyšek & Richardson (2006) suggested the following terminologies, which were adopted for this study:

Alien plant Plant taxa in a given area whose presence there is due to intentional or unintentional human involvement, or which have arrived there without the help of people from an area in which they are alien.

Casual alien plants Alien plants that may flourish and even reproduce occasionally outside cultivation in an area, but that eventually die out because they do not form self-replacing populations, and rely on repeated introductions for their persistence.

Naturalized plants Alien plants that sustain self-replacing populations for at least 10 years without direct intervention by people (or in spite of human intervention) by recruitment from seed or ramets (tillers, tubers, bulbs, fragments, etc.) capable of independent growth.

Invasive plants Invasive plants are a subset of naturalized plants that produce reproductive offspring, often in very large numbers, at considerable distances from the parent plants, and thus have the potential to spread over a large area.

3 Transformers A subset of invasive plants (not necessarily alien) that change the character, condition, form or nature of ecosystems over a substantial area relative to the extent of that ecosystem.

Impact of invasive plants Invasive alien plants not only pose threat to island ecosystems, but also affect terrestrial ecosystem functioning elsewhere. Although plant invasion studies have been carried out for centuries (Richardson & Pyšek 2006), it is only over the past decade that studies have extensively assessed the ecological impact of alien plants on native plant communities (Vinton & Burke 1995; Protopopova et al. 2006). Many studies on competition have hypothesized that alien plants are superior competitors than native species (Bakker & Wilson 2001; Levine et al. 2003; Vilá & Weiner 2004). Competition often involves valuable resources such as light, water, nutrients, as well as biotic agents that pollinate and disperse seeds (Daehler 2003; Hager 2004; Bjerknes et al. 2007). Some alien plants, particularly tree species, can alter the hydrological cycle and change fire regimes (Auld & Denham 2006, Kueffer et al. 2007). Furthermore, introduced plants can also disrupt community structure in many ways, including allelopathy, nitrogen fixation, hybridization and facilitation (Milne & Abbott 2000; Ridenour & Callaway 2001; Hierro & Callaway 2003; Yelenik et al. 2007; Bulleri et al. 2008).

Alien plants in the Southern Ocean Islands The vascular plants of most Southern Ocean islands have been the subject of floristic surveys over the last 50 years. There are approximately 350 alien plant species recorded across the SOI (Shaw et al. 2010, see Table 1). Most of these species were not deliberately introduced to the islands, but were accidentally introduced on clothing, footwear or equipment (Wace 1986; Frenot et al. 2005, Whinam et al. 2005). There is a lack of detailed information on invasive alien plant species for most islands, and consequently insufficient information across the SOI to implement alien plant species management programs. This is particularly true of sub- Antarctic Marion Island, where the current management plan (Anonymous 1996) and the new proposed Environmental Management Plan for the Prince Edward Islands (Davies et al. 2007) both specify that introductions of new species should be prevented, and current introduced species should be controlled. Moreover, the South African National Environmental Management: Protected Areas Act (Act 57 of 2003) specifies that invasive alien species control plants must be developed for and implemented in Special Nature Reserves, of which the Prince Edward islands are the only Special nature Reserve in the South African

4 geopolitical region. However, to date, surveys of the alien vascular flora have not been as fully spatially comprehensive or explicit or at a fine enough resolution as might be necessary for this purpose, and are out of date (see e.g. Gremmen 1981; Bergstrom & Smith 1990; Gremmen & Smith 1999).

Some information exists on the number of alien plants in the SOI. For example, of the 81 vascular plants recorded from Gough Island, approximately 25 species were thought to be introduced to the island. However, some of these species never established populations and they have disappeared from the island (Jones et al. 2003). While explicit surveys of all the alien species on Gough Island have not been undertaken, the most aggressive species, Sagina procumbens, native to Europe, has been well mapped and is currently the subject of an eradication programme (Gremmen et al. 2001). On Gough Island, this alien plant occupies empty niches by forming a mat-like carpet that out-competes the surrounding indigenous biota (Gremmen et al. 2001; Jones et al. 2003).

Large areas of the Crozet and Kerguelen islands have been invaded by alien species, with the majority of these species being persistent aliens, rather than invasives or transformers, and their distribution is limited to certain geographical areas (Frenot et al. 2005). On Possession Island, a large proportion of the alien species are restricted to the vicinity of the research station, and only a few species are invasive species with wide distribution ranges. On this island approximately 10 species have spread beyond their initial colonisation sites; these are Cerastium fontanum, C. glomeratum, Juncus bufonius, Poa annua, P. pratensis, Rumex acetocella, Sagina procumbens, Stellaria alsine, Taraxacum erythrospermum and T. officinale (Frenot et al. 2001).

At least 56 alien plant have been recorded at Amsterdam island, with the most widely distributed species being Apium graveolens, Cirsium vulgre, Hieracium auantiacum, Mentha pulegium, Prunella vulgarise, Rumex acetosella, Senecio vulgarise, Sonchus apser and S. oleraceus (Frenot et al. 2001). At Heard Island comprehensive spatial surveys of alien vascular plants have been undertaken (Scott & Kirkpatrick 2005). Poa annua is the only alien species recorded on this island and the survey was conducted between 1987 and 2000 to measure environmental parameters of preferred sites and to map its distribution range (Scott & Kirkpatrick 2005).

5 Table 1 The numbers of indigenous and alien vascular plant species recorded across the SOI (adapted from Chown et al. 1998 and Chown et al. 2008b). Island Position Area Max. Alien vascular Indigenous (decimal degrees) (km²) Altitude plants vascular plants (m)

West Falkland 51.5 S, 60.5 W 3,500 701 66 153 East Falkland 51.5 S, 58.5 W 5,000 705 78 149 South Georgia 54.25 S, 37.0 W 3,755 2,950 53 25 Tristan da Cunha 37.1 S, 12.25 W 86 2,060 93 64 Nightingale 37.42 S, 12.5 W 4 400 6 34 Inaccessible 37.25 S, 2.75 W 12 600 20 55 Gough 40.33 S, 9.54 W 57 910 24 57 Marion 46.9 S, 36.75 E 290 1,230 18 23 Prince Edward 46.63 S, 37.95 E 44 672 3 21 Cochons 46.1 S, 50.23 E 70 775 6 18 Apotres 45.97 S, 50.43 E 3 289 2 13 Pinguoins 46.5 S, 50.4 E 3.16 360 1 13 Est 46.43 S, 52.2 E 130 1,090 5 19 Possession 46.42 S, 51.63 E 150 934 101 19 Kerguelen 46.37 S, 69.5 E 7,200 1,840 36 30 Heard 53.1 S, 73.5 E 368 2,745 1 10 McDonald 53.03 S, 72.6 E 2.6 230 0 5 Amsterdam 37.83 S, 77.52 E 55 881 81 26 St Paul 38.72 S, 77.53 E 8.1 268 10 9 Macquarie 54.62 S, 158.9 E 128 433 5 40 Snares 48.12 S, 166.6 E 3.28 152 2 20 Auckland 50.83 S, 166.0 E 626 668 33 188 Campbell 52.5 S, 169.17 E 113 567 88 140 Antipodes 49.68 S, 178.77 E 21 366 2 68 Bounty 47.72 S, 179.0 E 1.35 89 0 0

Introduced plants at the Prince Edward Islands Several alien plant species have been recorded for the Prince Edward Islands (PEI). Huntley (1971) was the first to undertake a detailed ecological study of terrestrial plant species on the islands, recording at least 37 vascular plants of which 13 were found to be alien species. It has been estimated that for the past two decades at least seven alien species of either plants or insects have colonized and established populations on Marion Island (Lee et al. 2007). To date, 23 indigenous vascular plants have been recorded on Marion Island. Eighteen alien plants have been recorded of which 6 have disappeared or have been removed (Gremmen &

6 Smith 2008). Unlike Marion Island, Prince Edward Island is free from introduced mammals, having 21 indigenous vascular plant and only three alien vascular plant species. To date 13 alien vascular plants have established on Marion Island and three at Prince Edward (Gremmen & Smith 2008).

Over the past three decades a number of surveys have been carried out to assess the distribution of alien plants on the Prince Edward Islands. Surveys of alien plant distributions on the Prince Edward Islands were conducted in 1965, 1975, 1981, 1987, 1998 and 2001 (Huntley 1971; Gremmen 1975, 1981; Bergstrom & Smith 1990; Gremmen & Smith 1999; Ryan et al. 2003). Most of the surveys conducted on Marion Island concentrated on areas where alien plants had been previously recorded, i.e. known localities (Gremmen & Smith 1990). Very few researchers have conducted island-wide surveys (Slabber & Chown 2002). Based on this work a substantial, though often not fully spatially explicit, baseline of information is available on the alien vascular plants found on Marion and Prince Edward Islands.

Baseline information on the alien plants of Marion Island and Prince Edward Island Poa annua (Widespread naturalized alien) This species has spread from its centre of origin in temperate Europe, throughout the rest Europe and other regions of the world. Poa annua was recorded on Marion Island by Dike in 1948 (see Greene & Greene 1963; Gremmen 1997). Poa annua spreads easily by seeds and on Marion Island it occurs in almost all coastal habitats and in some cases extends up to 360 m above sea level (Gremmen 1981). This species was first recorded from Prince Edward Island in 1965 at Cave Bay (Huntley 1971). Currently the species is widely distributed in all the coastal areas except for the south coast of Prince Edward Island. It has spread from Cave Bay at the rate of 280 m a year on the east coast (Ryan et al. 2003).

Cerastium fontanum (Widespread naturalized alien) This species probably originated in Europe but is now found across the world. On Marion Island Cerastium fontanum was first recorded in 1873 (see Gremmen 1997). Cerastium fontanum produces an abundance of flowers and seeds (Gremmen 1981), hence it is widespread in a variety of habitats, but frequently occurs in small populations. It also occurs on the neighbouring Prince Edward Island, where it is very abundant but restricted to certain localities on the west coast. The 1998 survey revealed that the species was spreading at the

7 average rate of 170 m a year (Gremmen & Smith 1999). However, the survey in 2001 found that the species was spreading at an average rate of 370 m a year (Ryan et al. 2003).

Sagina procumbens (Widespread naturalized alien) This cushion plant is native to the temperate regions of the Northern Hemisphere (Gremmen 2001). This plant was first recorded from Marion Island in 1965 by Huntley, who found the species only limited to the Meteorological station (Huntley 1971). However since Huntley’s record, Sagina procumbens is now widespread and produces an abundance of flowers during summer (Gremmen 1975). Wherever it reaches dominance it forms a mat-like carpet and thus out-competes the native species (Gremmen 1997). At Prince Edward Island S. procumbens was first recoded only at two sites along the east coast during the 1997 survey (Gremmen & Smith 1999). Since then it has spread to other sites at an average rate of 800 m a year (Ryan et al. 2003).

Agrostis stolonifera (Widespread naturalized alien) This species originated from the Northern Hemisphere and has been introduced in most parts of the Southern hemisphere. This species was initially mis-identified as Agropyron repens (Gremmen 1975). It was first recorded on Marion Island surrounding the Meteorological station in 1965 (Huntley 1971). Currently Agrostis stolonifera is most abundant on wet coastal areas and river banks, where it displaces Acaena megallanica communities (Gremmen et al. 1998). Its spread from Kildalkey hut between 1989 and 1998 covered 100 m a year (Gremmen & Smith 1999). Gremmen (1997) suggested that given its current rate of spread, the species is predicted to occur all over the island within the next 40-100 years.

Stellaria media (Widespread naturalized alien) Stellaria media, a small European herbaceous plant, and on Marion Island it was first recorded in 1873 (Moseley 1874 in Gremmen 1997). It has also invaded other the sub- Antarctic islands i.e. South Georgia, Macquarie Island (Walton 1975). Stellaria media can dominate areas subjected to biotic disturbance, where it forms small patches (Gremmen 2004). This species is widespread on the coastal plain, but has also been recorded inland of Crawford Bay and Storm Petrel Bay (Bergstrom & Smith 1990).

Poa pratensis (Naturalized alien with restricted distribution) This species has been introduced from the Northern Hemisphere into most parts of the Southern Hemisphere, occurring on many Southern Ocean Islands (Gremmen 2004). Poa

8 pratensis was first recorded in the vicinity of Meteorological station in 1965 (Huntley 1971). During the 1975 survey on Marion Island, a few sites were recorded between Ship’s Cove and Archway Bay (Gremmen 1975). Poa pratensis has a slow dispersal rate, is abundant in the north-eastern lowlands, and rarely found in other parts of the island (Gremmen 2004).

Agrostis castellana (Naturalised alien with restricted distribution) This species is indigenous to the Mediterranean and looks very similar to Agrostis stolonifera, but the awns are present on some of the spikelets in the inflorescences of Agrostis castellana and absent in Agrostis stolonifera. Agrostis castellana spreads vegetatively by (underground) rhizomes, while A. stolonifera spreads by above-ground stolons. Owing to its similarity and difficult to distinguish from A. stolonifera, its distribution on the island is poorly known (Gremmen 2004).

Agropyron repens (Naturalised alien with restricted distribution) Agropyron repens has a native distribution throughout much of Europe and temperate Asia. On Marion Island this species was first recorded in February 1965 (Huntley 1971). Agropyron repens is a perennial grass which forms extensive and often very dense patches spread by long creeping rhizomes. This species is confined to Ship’s Cove, where it forms a small patch near a site of previous Solglimt camp (Gremmen 2004). It is currently the focus of an eradication programme.

Agrostis gigantea (Naturalised alien with restricted distribution) Native to Europe and other part of Asia, this species has been introduced in many parts of the Southern Hemisphere. The plant was first recorded in 1994 at the meteorological station (Gremmen 1997). It is also similar to Agrostis stolonifera but possesses rhizomes rather than stolons and is taller and more robust. The inflorescences are larger and looser than those of A. stolonifera. On Marion Island this grass is still restricted to a small area near the research station. After its discovery in 1994, an eradication programme was carried out to uproot, spray or prevent A. gigantea from flowering by removing all inflorescences (Gremmen 2004, De Villiers & Copper 2008). The programme is still underway.

Alopecurus geniculatus (Naturalized alien with restricted distribution) This species originated from Europe and Asia, and it has been introduced in several sub- Antarctic islands. Alopecurus geniculatus was first recorded from Mixed Pickle Cove in

9 1965, and was only restricted to the old sealer’s camp (Huntley 1971). By late 1998 it was still present, but occupying only few square metres, due to trampling by fur seals.

Juncus effusus (Naturalized alien with restricted distribution) Originating from the Northern Hemisphere the species only occurs at four localities on Marion Island; at Trypot Beach, on the western side of Van den Boogaard River, Ship’s Cove and Goney Plain. At each site this species forms dense turfs, numbering between 2 and 15 square metres. It appears to form no seeds, and the plants spread only by vegetative means. Gremmen (2004) suggested that the establishment of this species on the island is unlikely to have been influenced by human occupation.

Luzula cf. multiflora (Status unknown) The identity of this species on the island still raises some questions about its origin, although evidence indicates that it is probably a European species. Now it has been introduced to several parts of the Southern Hemisphere. This species was first discovered on Marion Island in April 1999 along the coast at Sealer’s Cave. Luzula cf. multiflora occurs in areas of 100- 150 m in length and 20-50 wide, in which it forms numerous small and larger groups. It spreads vegetatively, but can also spread from seeds (Gremmen 2004).

Rumex acetosella (Naturalized alien with restricted distribution) A European species, introduced in many parts of the Southern hemisphere especially the sub- Antarctic islands. It is a perennial herb with long, thin rhizomes with adventitious buds. Rumex acetosella was first discovered on Marion Island by van der Merwe in 1953 (see Gremmen 1975). On Marion Island this species only occurs at two sites, near Gentoo Lake, and at Goney Plain. However Bergstrom and Smith (1990) reported another population at Skua Ridge in 1989, but during later years the population has not been seen (Gremmen 2004).

Festuca rubra (Naturalized alien with restricted distribution) Festuca rubra is a perennial grass originating from Europe. On Marion Island it occurs at two sites, near Van den Boogaard River and at Ship’s Cove where it competes with Agropyron repens (Gremmen & Smith 1999). Seeds have been observed in abundance, but the grass seems to spread vegetatively (Gremmen 2004).

10 STUDY LOCATION Marion Island together with Prince Edward Island, which is only 19 km away, form the Prince Edward Island group (van Zinderen Bakker et al. 1971; Boelhouwers et al. 2008). Marion Island (46° 54’S, 37° 45’ E) is situated in the vast Southern Ocean just north of the Antarctic Convergence (Fig. 1). The island encompasses an area of 293 km2 and the interior mountains rise up to 1230 m above sea level (Boelhouwers et al. 2008). The closest landfall to Marion Island is the Crozet Islands Group located approximately 950 km to the east (Chown & Froneman 2008) while the nearest continental land mass is Africa, situated 2000 km to the northwest (Pakhomov & Froneman 1999).

Figure 1 Map showing the position of Marion Island and other Southern Ocean Islands. The blue line shows the approximate position of the Antarctic Convergence.

11 Geology Geologically, Marion Island is a relatively young oceanic island. The island is a shield volcano associated with a mantle plume, similar to the Hawaiian Islands (McDougall et al. 2001). Marion Island could have emerged during the last half million to 1 million years, and the oldest grey lava has been found to be at least 0.5 million years old (Verwoerd 1971; McDougall et al. 2001). However, the island is dominated by black lava thought to have emerged from recent volcanic eruptions (Verwoerd et al. 1981). At least five glaciations have occurred during Quaternary age resulting in the formation of high landscape topographies (Boelhouwers et al. 2008).

Climate Being situated just north of the Antarctic Convergence, the island experiences an oceanic climate which is characterized by a relatively low mean temperature of 6.4°C (le Roux & McGeoch 2008). The mean temperature difference between the warmest and the coldest month is 4.1C°, with a mean diurnal temperature variation of 2°C in winter and 3°C in summer respectively (le Roux & McGeoch 2008). The main source of precipitation is rainfall, snow and mist (Schulze 1971; Smith 2002). Precipitation in the form of rain falls throughout the year, but there is small daily variation of high rainfall at sunrise and sunset during summer months (Schulze 1971). Because of its position in the roaring forties the island experiences extremely windy conditions (le Roux 2008) and a wind gusting at 15 m sec-1 has been recorded (Schulze 1971). Records show that humidity is relatively high at about 80% (Schulze 1971).

Climate change The warming of the globe has caused considerable change over the last century (Mastrandrea et al. 2010), thus affecting a variety of ecosystems all over the world (Hughes 2000, McCarthy 2001; Walter et al. 2006). Climate has changed substantially on Marion Island (Barendse & Chown 2000), with increase on annual mean temperature from 5.4° in the 1950s to 6.4° in the 1990s (le Roux & McGeoch 2008). Similarly the rainfall has decreased from approximately 3000 mm per annum (1960s) to 2000 mm per annum (1990s) (Smith 2002; le Roux & McGeoch 2007; le Roux & McGeoch 2008). Also wind speed has increased considerably over the last few decades with a shift from north westerly winds to northerly winds (le Roux 2008). The melting and disappearing of the ice plateau is direct evidence of climate change (Summer et al. 2004). With time such changes will have serious implications for the natural biota (Barendse & Chown 2000).

12 Vegetation Marion Island is climatically and geographically isolated from nearby continental landmasses (Africa), situated in the sub-Antarctic zone which is the southern limit for growth of tress and shrubs (Gremmen 1982). Closed phanerogamic vegetation is limited to low-lying areas and at high altitudes vegetation is very sparse, mostly consisting of bryophytes and lichens (Gremmen et al. 1998). Forty-one vascular plant species have been recorded, 18 of which were considered to be aliens. To date only twelve of these eighteen introduced plants have established populations (Gremmen & Smith 2008). Ninety three species of mosses (Gremmen & Smith 2008), forty four hepatics (Gremmen 2008) and one hundred and ten species of lichen (Øvterdal & Gremmen 2008) have been recorded on the Island. The plant communities of the island can be grouped into seven community-complexes, Coastal Saltspray Complex, Biotic Complex, Mire Complex, Slope Complex, Fellfield Complex, Polar Desert and Aquatic Communities (see Gremmen and Smith 2008).

THESIS OUTLINE The main objective of this project is to provide a spatially explicit documentation of the alien and invasive vascular plant species on Marion Island, therefore enabling priorities for control to be established based on feasibility estimates. The thesis is divided into four chapters, including this first one. Chapter two assesses the residence time and rate of expansion of alien plants, while chapter three assesses the vulnerability of habitats and variables that determine alien species occurrence. Chapter four is the general conclusion and it provides feasibility assessments for the control and/or eradication of the alien vascular plant species.

13 REFERENCES

Adamson, D.A., Whetton, P. & Selkirk, P.M. 1988. An analysis of air temperature records for Macquarie Island: decadal warming, ENSO cooling and Southern hemisphere circulation patterns. Papers and Proceedings of the Royal Society of Tasmania 122, 107-112.

Anonymous 1996. Prince Edward Islands Management Plan. Department of Environmental Affairs and Tourism, Pretoria.

Auld, T.D. & Denham, A.J. 2006. How much seed remains in the soil after a fire? Plant Ecology 187, 15-24.

Bakker, J. & Wilson, S. 2001. Competitive abilities of introduced and native grasses. Plant Ecology 15, 117-125.

Barendse, J. & Chown, S.L. 2000. The biology Bothrometopus elongatus (Coleoptera, Curculionidae) in a mid-altitude fellfield on sub-Antarctic Marion Island. Polar Biology 23, 346-351.

Bergstrom, D.M. & Chown, S.L. 1999. Life at the front: history, ecology and change on Southern Ocean islands. Trends in Ecology and Evolution 14, 472-477.

Bergstrom, D. & Smith, V.R. 1990. Alien vascular flora of Marion and Prince Edward Islands: new species, present distribution and status. Antarctic Science 2, 301-308.

Bjerknes, A-L., Totland, Ø., Hegland, S.J. & Nielsen, A. 2007. Do alien plant invasions really affect pollination success in native species? Biological Conservation 138, 1-12.

Boelhouwers, J., Meiklejohn, I., Holness, S. & Hedding, D. 2008. Geology, geomorphology and climate change. In: Chown, S.L. & Froneman, P.W. (Eds.) The Prince Edward Islands. Land-Sea Interactions in a Changing Ecosystem. African Sun Media, Stellenbosch, pp. 65-95.

Budd, G.M. 2000. Changes in the Heard Island glaciers, king penguins and fur seals since 1947. Papers and Proceedings of the Royal Society of Tasmania 133, 47-60.

14 Bulleri, F., Bruno, J.F. & Benedetti-Cecchi, L. 2008. Beyond competition: incorporating positive interactions between species to predict ecosystem invisibility. PLoS Biology 6, 1136- 1140.

Chapuis, J.L., Bousses, P. & Barnaud, G. 1994. Alien mammals, impact and management in the French sub-Antarctic islands. Biological Conservation 67, 97-104.

Chown, S.L.& Froneman, P.W. 2008. The Prince Edward Islands in a global context. In: Chown S.L. & Froneman, P.W. (Eds.) The Prince Edward Islands. Land-Sea Interactions in a Changing Ecosystem. African Sun Media, Stellenbosch, pp. 1-16.

Chown, S.L., Gremmen, N.J.M. & Gaston, K.J. 1998. Ecological biogeography of Southern Ocean Islands: species-area relationships, human impacts and conservation. American Naturalist 152, 562-575.

Chown, S.L. & Klok, C.J., 2001. First record of Palirhoeus eatoni (Coleptera, Curculionidae) from Heard Island. African Entomology 9, 193-194.

Chown, S.L., Lee, J.E. & Shaw, J.D. 2008a. Conservation of Southern Ocean Island: invertebrates as exemplars. Journal of Insect Conservation 12, 277-291.

Chown, S.L., Sinclair, B.J. & van Vuuren, B.J. 2008b. DNA barcoding and the document of alien species establishment on the sub-Antarctic Marion Island. Polar Biology 12, 277-291.

Chown, S.L., Slabber, S., McGeoch, M.A., Janion, C. & Leinaas, H.P. 2007. Phenotypic plasticity mediates climate change responses among invasive and indigenous arthropods. Proceedings of the Royal Society of London B 274, 2531-2537.

Colautti, R.I., & MacIsaac, H.J. 2004. A neutral terminology to define invasive species. Diversity and Distributions 10, 135-141.

Daehler, C.C. 2003. Performance comparisons of co-occurring native and alien invasive plants: Implication for conservation and restoration. Annual Review of Ecology, Evolution, and Systematics 34, 183-211.

15 Davies, S.J. Chown, S.L. & Joubert, L.S. 2007. Renewed management system and provisions for South Africa’s sub-Antarctic Islands. Papers and Proceedings of the Royal Society of Tasmania 141, 115-120.

De Villiers, M.S. & Cooper, J. 2008. Conservation and management. In: Chown, S.L & Froneman, P.W. (Eds.) The Prince Edward Islands. Land-Sea Interactions in a Changing Ecosystem. African Sun Media, Stellenbosch, pp.301-330.

De Villiers, M.S., Copper, J., Carmichael, N., Glass, J.P., Liddle, G.M., Mcivor, E., Micol, T. & Roberts, A. 2006. Conservation management at Southern Ocean Islands: towards the development of best practice guidelines. Polarforschung 75, 13-131.

Didham, R.K., Tylianakis, J.M., Hutchison, M.A., Ewers, R.M. & Gemmell, N.J. 2005. Are invasive species the drivers of ecological change? Trends in Ecology and Evolution 20, 470- 474.

Dingwall, P.R., ed. 1995. Progress in Conservation of the Sub-Antarctic Islands. IUCN, Gland.

Ernsting, G., Brandjes, G.J., Block, W. & Isaaks, J.A. 1999. Life-history consequences of predation for sub-Antarctic beetle: evaluating the contribution of direct and indirect effects. Journal of Animal Ecology 68, 741-752.

Frenot, Y., Chown, S.L., Whinam, J., Selkrik, P.M., Convey P., Skotnicki, M. & Bergstrom, D.M. 2005. Biological invasions in the Antarctic: extent, impacts and implications. Biological Reviews 80, 45-72.

Frenot, Y., Gloaguen, J.C., Masse´, L. & Lebouvier, M. 2001. Human activities, ecosystem disturbance and plant invasions in sub-Antarctic Crozet, Kerguelen and Amsterdam Islands. Biological Conservation 101, 33-50.

Frenot, Y., Gloaguen, J.C. & Trehen, P. 1997. Climate change in the Kerguelen Islands and colonization of recently deglaciated areas by Poa Kerguelensis and P. annua. In: Battaglia, B., Valencia, J. & Walton, D.W.H. (Eds.) Antarctic Communities: Species, Structure and Survival. Cambridge University Press, Cambridge, pp. 358-366.

16 Gremmen, N.J.M. 1975. The distribution of alien vascular Plants on Marion and Prince Edward Islands. South African Journal of Antarctic Research 5, 25-30.

Gremmen, N.J.M. 1981. The Vegetation of Sub-Antarctic Islands Marion and Prince Edward. Dr.W.Junk, The Hauge.

Gremmen, N.J.M. 1982. Alien vascular plants on Marion island (sub-Antarctic). National Fránçais pour les Recherches Antarctiques 51, 315-323.

Gremmen, N.J.M. 1997. Changes in the vegetation of sub-Antarcic Marion Island resulting from introduced vascular plants. In: Bataglia, B., Valencia, J. & Walton, D.W.H. (Eds.) Antarctic Communities: Species, Structure and survival. Cambridge University Press, Cambridge, pp. 417-423.

Gremmen, N.J.M. 2004. Management of alien vascular plants on Marion and Prince Edward Islands: an Integrated Approach. Unpublished report. Data Analyse Ecologie, Diever, The Netherlands, 1-30.

Gremmen, N.J.M. 2008. Hepatics of the Prince Edward Islands. In: Chown, S.L. & Froneman, P.W. (Eds.) The Prince Edward Islands. Land-Sea Interactions in a Changing Ecosystem. African Sun Media, Stellenbosch, pp. 379-382.

Gremmen, N.J.M., Barendse, J. & Orr, I. 2001. Invasion and eradication of Sagina procumbens L. (Procumbent Pearlwort) on Gough Island. Arctic, Antarctic and Alpine Research 35, 442-446.

Gremmen, N.J.M., Chown, S.L. & Marshall, D.J. 1998. Impact of the introduced grass Agrostis stolonifera on vegetation and soil fauna communities at Marion Island, sub- Antarctic. Biological Conservation 85, 223-231.

Gremmen, N.J.M. & Smith, V.R. 1999. New records of alien vascular plants from Marion and Prince Edward Islands, sub-Antarctic. Polar Biology 21, 401-409.

17 Gremmen, N.J.M. & Smith, V.R. 2008. Terrestrial vegetation and dynamics. In: Chown S.L. & Froneman, P.W. (Eds.) The Prince Edward Islands. Land-Sea Interactions in a Changing Ecosystem. African Sun Media, Stellenbosch, pp. 215-244.

Greene, S.W. & Greene, D.M. 1963. Check list of the sub-Antarctic and Antarctic vascular flora. Polar Record 11, 411-418.

Hager, A. 2004. Competitive effect versus competitive response of invasive and native wetland plant species. Oecologia 139, 140-149.

Hierro, J.L. & Callaway, R.M. 2003. Allelopathy and exotic plant invasion. Plant and Soil 256, 29-39.

Hughes, J. 2000. Biological consequences of global warming: is the signal already apparent? Trends in Ecology and Evolution 15, 56-61.

Huntley, B.J. 1971. Vegetation. In: van Zinderen Bakker, E.M., Winterbottom, J.M. & Dyer, R.A. (Eds.) Marion and Prince Edwards Islands. Report on the South African Biological and Geological Expedition 1965-1966. A.A. Balkema, Cape Town, pp. 98-160.

Jones, A.G., Chown, S.L., Ryan, P.G., Gremmen, N.J.M. & Gaston, K.J. 2003. A review of conservation threats on Gough Island: a case study for terrestrial conservation in the Southern Oceans. Biological Conservation 112, 75-87.

Kennedy, A.D. 1995. Antarctic terrestrial ecosystem responds to global environmental change. Annual Review of Ecology, Evolution, and Systematics 26, 683-704.

Kueffer, C., Schumacher, E., Fleischmann, K., Edwards, P.J. & Dietz, H. 2007. Strong below- ground competition shapes tree regeneration in invasive Cinnamomum verum forests. Journal of Ecology 95, 273-282.

Lee, J.E., Slabber, S., Jansen van Vuuren, B., van Noort, S. & Chown, S.L. 2007. Colonisation of sub-Antarctic Marion Island by a non-indigenous aphid parasitoid Aphidius matricariae (Hymenoptera, Braconidae). Polar Biology 30, 1195-1201.

18 le Roux, P.C. 2008. Climate and climate change. In: Chown, S.L. & Froneman, P.W. (Eds.) The Prince Edward Islands. Land-Sea Interactions in a Changing Ecosystem. African Sun Media, Stellenbosch, pp. 39-64. le Roux, P.C. & McGeoch, M.A. 2007. Fine-scale in the spatial association of plant species: A test of the stress-gradient hypothesis in the sub-Antarctic. South African Journal of Botany 73, 297-298. le Roux, P.C. & McGeoch, M.A. 2008. Changes in extremes, variability and signature on sub-Antarctic Marion Island. Climate Change 86, 309-329.

Levine, J.M., Villá, M., D’Antonio, C.M., Dukes, J.S., Grigulis, K. & Lavorel, S. 2003.

Mechanisms underlying the impacts of exotic plant invasions. Proceedings of the Royal Society of London B, 270, 775-781.

Mastrandrea, M.D., Heller, N.E., Root, T.L. & Schneider, S.H. 2010. Bridging the gap: linking climate-impacts research with adaptation planning and management. Climate Change 100, 87-101.

McCarthy, J.J., Canziani, O.Z., Leary, N. Dokken, D.J. & White, K. 2001. Climate Change 2001. Impacts, Adaptation and Vulnerability. Cambridge University Press, Cambridge.

McDougall, I., Verwoerd, W. & Chevallier, L. 2001. K-Ar geochronology of Marion Island, Southern Ocean. Geological Magazine 138, 1-17.

Milne, R.I. & Abbott, R.J. 2000. Origin and evolution of invasive naturalized material of Rhododendron ponticum L. in the British Isles. Molecular Ecology 9, 541-556.

Moseley, H.N. 1874. On the botany of Marion Island, Kerguelen’s land and Young Island of the Heard group. Journal of the Linnean Society (Botany) 14,387-388.

Øvterdal, D.O. & Gremmen, N.J.M. 2008. Lichens of the Prince Edward islands. In: Chown, S.L. & Froneman, P.W. (Eds.) The Prince Edward Islands. Land Sea Interactions in a Changing Ecosystem. African Sun Media, Stellenbosch, pp. 393-397.

19 Pakhomov, E.A. & Froneman, P.W. 1999. The Prince Edward Islands pelagic ecosystem: a review of achievements 1976-1990. Journal of Marine Systems 18, 297-310.

Protopopova, V.V., Shevera, M.V. & Mosyakin, S.L. 2006. Deliberate and unintentional introduction of invasive weeds: a case study of the alien flora of Ukraine. Euphytica 148, 17- 33.

Pyšek, P. & Hulme, P.E. 2005. Spatio-temporal dynamics of plant invasions: linking pattern to process. Ecoscience 12, 345-54.

Pyšek, P. & Richardson, D.M. 2006. The biogeography of naturalization in alien plants. Journal of Biogeography 33, 2040-2050.

Pyšek, P., Richardson, D.M., Rajmánek, M., Webster, G.L., Williamson, M. & Kirschner, J. 2004. Alien plants in checklists and floras: towards better communication between taxonomists and ecologists. Taxon 53, 131-143.

Richardson, D.M. & Pyšek, P. 2006. Plant invasions: merging the concepts of species invasiveness and community invisibility. Progress in Physical Geography 30, 409-431.

Richardson, D.M., Pyšek, P., Rejmánek, M., Barbour, M.G., Panetta, F.D. & West, C.J. 2000. Naturalization and invasion of alien plants: concepts and definitions. Diversity and Distributions 6, 93-107.

Ridenour, W.M. & Callaway, R.M. 2001. The relative importance of allelopathy in interference: the effects of an invasive weed on a native bunchgrass. Oecologia 126, 444-450.

Rouault, M., Melelice, J-L., Reason, C.J.C. & Lutjeharms, R.E. 2005. Climate variability at Marion Island, Southern Ocean, since 1960. Journal of Geophysical Research 110, 1-9.

Ryan, P.G., Smith, V.R. & Gremmen, N.J.M. 2003. The distribution and spread of alien vascular plants on Prince Edward Island. African Journal of Marine Science 25, 555-562.

20 Schulze, B.R. 1971. The climate of Marion Island. In: van Zinderen Bakker, E.M., Winterbottom, J.M. & Dyer, R.A. (Eds.) Marion and Prince Edwards Islands. Report on the South African Biological and Geological Expedition 1965-1966. A.A. Balkema, Cape Town, pp. 16-31.

Scott, J.J., & Kirkpatrick, J.B. 2005. Changes in sub-Antarctic Heard Island vegetation at sites occupied by Poa annua, 1987-2000. Arctic, Antarctic and Alpine Research 37, 366-371.

Shaw, J.D., Spear, M., Greve, M. & Chown, S.L. 2010. Taxonomic homogenization and differentiation across Southern Ocean Islands differ among insects and vascular plants. Journal of Biogeography 37, 217-228.

Slabber, S. & Chown, S.L. 2002. The first record of a terrestrial crustacean, Porcellio scaber (isopoada, Porcellioniadae), from sub-Antarctic Marion island. Polar Biology 25, 855-858.

Smith, V.R. 2002. Climate change in the sub-Antarctic: an illustration from Marion Island. Climate Change 52, 245-357.

Summer, P., Meiklejohn, I., Boelhouwers, I. & Hedding, D. 2004. Climate change melts Marion’s snow and ice. South African Journal of Science 100, 395-398. van Zinder Bakker, E.M., Winterbottom, J.M. & Dyer, R.A. (Eds.) 1971. Marion and Prince Edward Islands. Report on the South African Biological and Geological Expedition 1965- 1966. A.A. Balkema, Cape Town.

Verwoerd, W.J. 1971. Geology. In: Van Zinderen Bakker, E.M., Winerbottom, J.M. & Dyer, R.A. (Eds.) Marion and Prince Edwards Islands. Report on the South African Biological and Geological Expedition 1965-1966. A.A. Balkema, Cape Town, pp. 40-53.

Verwoerd, W.J., Russel, S. & Berrti, A. 1981. 1980 volcanic eruption reported on Marion Island. Earth and Planetary Science Letters 54, 397-422.

Vilá, M. & Weiner, J. 2004. Are invasive plant species better competitors than native plant species? - evidence from pair-wise experiments. Oikos 105, 229-238.

21 Vinton, M.A. & Burke, I.C. 1995. Interactions between individual plant species and soil nutrient status in shortgrass steppe. Ecology 76, 1116-1133.

Wace, N. M. 1986. The arrival, establishment and control of alien plants on Gough Island. South African Journal of Antarctic Research 16, 95–101.

Walter, K.M., Zimov, S.A., Chanton, J.P., Verbyla, D. & Chapin, F.S. 2006. Methane bubbling from Siberian thaw lakes as a positive feedback to climate warming. Nature 443, 71- 75.

Walton, D.W.H. 1975. European weeds and other alien species in the sub-Antarctic. Weed Research 15, 271-282.

Wilson, J.R.U., Richardson, D.M., Rouget, M., Proches, S., Amis, M.A., Henderson, L. & Thuiller, W. 2007. Residence time and potential range: crucial considerations in modeling plant invasions. Diversity and Distributions 13, 11-22.

Whinam, J. Chilcott, N. & Bergstrom, D.M. 2005. Sub-Antarctic hitchhikers: expeditioners as vectors for introduction of alien organisms. Biological Conservation 121, 207-219.

Yelenik, S.G., Stock, W.D. & Richardson, D.M. 2007. Functional group identity does not predict invader impacts: differential effects of nitrogen-fixing exotic plants on ecosystem function. Biological Invasions 9, 177-125.

22 Chapter 2 THE CURRENT DISTRIBUTION OF INVASIVE SPECIES ON MARION ISLAND

INTRODUCTION When plant species are moved beyond their indigenous geographical ranges, many of them can become established, and often spread. This sometimes poses serious threats to indigenous systems (Vinton & Burke 1995; Richardson et al. 2000; Protopopova et al. 2006; Hoffmann & Haridasan 2008). Previously some inconsistencies have been associated with the assessment of invasion status (Richardson & Pyšek 2006). However, Richardson et al. (2000), Pyšek et al. (2004) and Pyšek & Richardson (2006) developed a scheme for assessing the status of alien plants and correctly categorizing them, although the topic continues to engender discussion. Part of the focus of improving current understanding of invasion has been the documentation of a positive correlation between residence time and invasion status (Becker et al. (2005; Harris et al. 2007; Wilson et al. 2007). That is to say, the longer the presence of species in an area the more likely that propagules will spread and therefore increase the likelihood of a change in the status (Pyšek & Jarošik 2005).

While in many regions much progress has been made in understanding the interactions between propagule pressure, residence time and other processes influencing the spread of non-indigenous species (Pyšek et al. 2004; Richardson & Pyšek 2006), these dynamics remain poorly explored for many other regions. For example, although plant invasions on the Southern Ocean Islands have been well explored (e.g. Dean et al. 1994; Gremmen et al. 1998; Frenot et al. 2001; Frenot et al. 2005; Scott & Kirkpatrick 2005; Lee & Chown 2009), and the role of propagule pressure increasingly so (Chown et al. 1998; Whinam et al. 2005; Lee & Chown 2009), explicit investigations of changes in status and the significance of residence time in influencing species status are rare (but see Gremmen & Smith 1999; Frenot et al. 2001; Scott & Kirkpatrick 2005). As is the case with other islands (Pickard 1984) the remoteness of the Southern Ocean Islands provides excellent opportunities to study these patterns of and processes underlying biological invasions (Lee & Chown 2009). Because of the long-term biological investigations of the Prince Edward Islands (see Chown & Froneman 2008), they make an especially useful case study.

Alien plants species and historical records on Marion Island The first attempts to explore the Prince Edward Islands date back to their discovery in 1663 (Cooper 2008). However the first recorded landing was made either in December 1803 or

23 January 1804 (Cooper 2008). From 1804 to 1930, numerous visits were made by sealers. During their stay on the island, sealers established camps in all accessible coastal areas to collect fur seal skins and elephant seal oil (Cooper 2008). The earliest existence of alien vascular plants was recorded two centuries ago (see description in Gremmen 1997) and it appears that a number of alien plant species were introduced in association with sealers’ activities (Gremmen 1975). The first voyage to study and collect botanical material was the Challenger expedition in 1873. During the expedition, Cerastium fontanum and Stellaria media were the only two alien plants to be recorded by the naturalist Henry Moseley (Moseley 1874). Where precisely Moseley went ashore is not completely clear, but his description in ‘Notes by a Naturalist’ (1879) appears to suggest he went ashore in the area just to the north of what is now known as Long Ridge.

The first comprehensive study of the island flora was carried out by Brian J. Huntley in 1965 (Huntley 1971). He recorded at least 37 vascular plant species, of which 13 were alien. Almost a decade later, Gremmen assessed the distribution of alien plants on the island in 1973. Further surveys were carried out in 1975 (Gremmen 1975), 1981 (Gremmen 1981), 1982 (Gremmen 1982), 1989 (Bergstrom & Smith 1990) and 1998 (Gremmen & Smith 1999). To date, 18 alien plants have been recorded, of which six have disappeared or have been removed (Gremmen & Smith 2008). Since Gremmen’s 1998 survey, no other studies of the distribution of alien plants have been undertaken on Marion Island, although a single survey of Prince Edward Island was undertaken in 2001 (Ryan et al. 2003). Moreover, to date, none of the studies have made any attempt to quantify the abundance of the species, formally record absences (which are important for distribution modelling studies, see e.g. Elith & Graham 2009), or examine among species the relationship between distribution and residence time. Given that the last comprehensive assessment of alien plant distributions was 20 years ago on Marion Island, the current situation is poorly understood. This is especially important for developing appropriate management responses, as is now required by South African legislation for protected areas (National Environmental Management: Protected Areas Act 57 of 2003). Indeed, an understanding of the current status of all alien species is critical for identifying conservation priorities and effective management of alien plant species (Government Gazette 2004). Therefore, I provide spatially explicit documentation of abundance and occurrence of each of the alien vascular plant species on Marion Island. In doing so, I also (i) estimate the residence time of each species from the available literature; (ii) and assess the rate of range change (mostly expansion).

24 Marion Island Marion Island (46° 54’ S, 37° 45’ E) is the larger of the two islands that constitute the Prince Edward Islands (van Zinderen Bakker et al. 1971), located in the vast Southern Ocean just north of the Antarctic Convergence (Gremmen 1997). The island encompasses an area of 293 km2 and the interior mountains rise to 1230 m above sea level (Boelhouwers et al. 2008). The closest landfall to the Prince Edward Islands is the Crozet Islands located approximately 900 km to the east (Chown et al. 2008) while the nearest continental land mass is Africa about 2000 km away (Pakhomov & Froneman 1999). The island experiences an oceanic climate which is characterized by relatively low mean temperature of c. 6.4°C (le Roux 2008; le Roux & McGeoch 2008a). Geologically, the island is a shield volcano associated with a mantle plume, similar to the Hawaiian Islands (McDougall et al. 2001). The island flora comprises 33 vascular indigenous plants species (Gremmen & Smith 2008), 90 species of mosses (Gremmen & Smith 2008), 44 hepatics (Gremmen 2008) and 110 species of lichen (Øvstedal & Gremmen 2008).

Naturalised alien plants with restricted distribution Agropyron repens (L.) Beaiv. (Poaceae) The Quack grass, Agropyron repens is indigenous to Europe and is considered a problematic weed outside its natural range (Gremmen 2004). Agropyron repens is a rhizomatous perennial grass known especially to reduce crop yield significantly because it is an aggressive competitor (Young et al. 1984). Agropyron repens was first recorded on Marion Island in February 1965 (Huntley 1971). This species only occurs at one site at Ship’s Cove occupying approximately 250 m² (Gremmen 2004). The size of the patch has not shown significant increase since its first discovery. On Marion Island this species is known to produce numerous inflorescences, but on other sub-Antarctic islands the grass appears to spread exclusively by rhizomes (Walton 1975). On Marion Island, an eradication programme for the species has been initiated (de Villiers & Cooper 2008) and is ongoing.

Agrostis castellana Boiss. Et Reut. (Poaceae) This species looks very similar to Agrostis stolonifera, but the awns are present on some of the spikelets in the inflorescences of Agrostis castellana and absent in Agrostis stolonifera. It was first recognized in 1994 from Gremmen’s 1975 collections. Agrostis castellana spreads vegetatively by (underground) rhizomes, while A. stolonifera spreads by above-ground stolons.

25 Agrostis gigantea Roth (Poaceae) The plant was first recorded in 1994 at the meteorological station (Gremmen 1997). It is also similar to Agrostis stolonifera but possesses rhizomes rather than stolons and is considered taller and more robust. The inflorescences are larger and looser than those of A. stolonifera. On Marion Island this grass is still restricted to a small area near the research station. After its discovery in 1994 eradication programme was carried out to uproot, spray or prevent A. gigantea from flowering by removing all inflorescences (Gremmen 2004).

Alopecurus geniculatus L. (Poaceae) Alopecurus geniculatus was first recorded from Mixed Pickle Cove in 1965, and it was only restricted to the old sealer’s camp (Huntley 1971). By late 1998 it was still there, but occupying only few square metres, due to trampling by fur seals. Although inflorescences have been observed, the grass seems to spread by vegetative means only (Gremmen 1975).

Juncus effusus L. (Juncaceae) The soft rush, Juncus effusus originated from the Northern Hemisphere and its status on Marion Island still raises some questions (Gremmen & Smith 2008). However, the fact that this species is considered introduced to other Southern islands (e.g. Falkland Islands, Tristan da Cunha, New Zealand) suggests that it was introduced by humans to Marion Island too (Gremmen 2004). Juncus effusus was first detected on Marion Island during the 1965-1966 survey (Huntley 1971). Gremmen (2004) suggested that the distribution of this species is unlikely to have been influenced by human occupation. Presently this species occurs at four sites on the island: two patches are found between Ships’ Cove and Sealers Beach, one at Trypot Beach and one on the north-western side of the Van den Boogaard River.

Luzula cf. multiflora (Retz.) Lej. (Juncaceae) The identity of this species has not yet been definitively confirmed, but it is though to be either L. multiflora, a European member of this widespread genus, or a species very closely allied to it (Gremmen & Smith 2008). It was first discovered by M.N. Bester and B. Stewart in April 1999 along the coast at Sealer’s Cave. The site was visited by the conservation officers at the time, S.L. Chown and A.G.A. Gabriel, and in his report, Chown (1999) reported that the sedge covered an area of approximately 100-150 m in length and 20-50 wide.

26 Rumex acetosella L. (Polygonaceae) The sheep’s sorrel, Rumex acetosella is an herbaceous perennial originating from Europe (Klimeš & Klimešova´ 1999), but has been introduced to the Southern Hemisphere and occurs on several sub-Antarctic islands (Gremmen 2004). It is a member of buckwheat family, and reproduces vegetatively and by underground rhizomes. Elsewhere, on other sub-Antarctic islands it was noted on that the species produces large number of seeds, but spread of this species appears to be exceptionally low and the species relies on repeated introduction to maintain its populations (Walton 1975). The first record of Rumex acetosella on Marion Island comes from the collection by van der Merwe in 1953. This species was then recorded by Huntley in 1971 at three sites. Currently this species only occurs in two localities, close to Gentoo Lake and on Goney Plain. The third site on Skua Ridge which was reported by Bergstrom and Smith (1990) during the 1987 survey is no longer occupied by the species.

Alien plant species with a widespread distribution Agrostis stolonifera Boiss. Et Reut. (Poaceae) The bent grass, Agrostis stolonifera is a perennial grass originating from Western Europe (Goverde et al. 2002). At present this species is among the most invasive species in the Southern Ocean islands, and occurs on a number of sub-Antarctic islands (Gremmen 2004). On Marion Island, it flowers abundantly producing many seeds, but also spreads vegetatively by stolons (Gremmen 2004). The species was probably introduced with sheep fodder and was first detected by Huntley at the meteorological station in 1965 (Bergstrom & Smith 1990). A sudden increase in the number of localities has been recorded from surveys conducted in 1981, 1987 and 1998 (Gremmen 1981; Bergstrom & Smith 1990; Gremmen & Smith 1999). Currently Agrostis stolonifera is most abundant on wet coastal areas and river banks, where it competes with the indigenous Acaena magellanica (Gremmen et al. 1998, Phiri et al. 2008).

Cerastium fontanum Baumg. (Caryophyllaceae) The mouse-ear chickweed, Cerastium fontanum is a herbaceous species originating from the Northern Hemisphere (temperate Asia, North Africa, Europe), and is one of the most widespread alien species on the sub-Antarctic islands (Walton 1975) and occurs in a broad array of habitat types (Gremmen 2004). On Marion Island, this species produces abundant flowers throughout the growing season and it appears to be spreading by means of seeds (Gremmen 1975), and seeds could live for over 40 years in the soil (Salisbury 1961). Cerastium fontanum was first discovered on Marion Island by Moseley in 1873 (Moseley 1874). Since its first detection, there has been an increase in its recorded localities in the 1975,

27 1981 and 1987 surveys (Gremmen 1975; Gremmen 1981; Bergstrom & Smith 1990). The species also occurs on Prince Edward Island (Ryan et al. 2003), where it was first discovered in 1987 and re-recorded in 2001(Ryan et al. 2003).

Poa annua L. (Poaceae) The annual bluegrass, Poa annua is species of European origin and one of the most widely distributed plants in the world (Chwedorzewska 2008). The species is well adapted to a wide range of climatic conditions ranging from polar to equatorial regions (Vargas & Turgeon 2003). This species is known to colonize areas altered by human activities or pioneer zones (Frenot et al. 1997). The ability of Poa annua to produce large numbers of viable seeds appears to be an important feature of the biology of this species (Roberts & Stokes 1966). Seeds may remain viable for several years, forming a persistent seedbank (Gremmen 2004). Among 108 alien vascular species currently found in the sub-Antarctic region, only Poa annua occurs on all major sub-Antarctic islands (Frenot et al. 2005). On Marion Island Poa annua was first recorded by Dike in 1948 (as cited by Greene & Greene 1963). However it is assumed that this species was introduced by sealers in the 1800s as is the case with its first discovery in 1874 on Kerguelen Island (Frenot et al. 2001). Further records of this species on Marion Island were made in surveys carried out in 1975, 1981, and 1987 (Gremmen 1975; Gremmen 1981; Bergstrom & Smith 1990). At the neighbouring Prince Edward Island, Poa annua was first recorded in 1965 and further with continued detection in 1987, 1998 and 2001 (Huntley 1971; Bergstrom & Gremmen 1990; Gremmen & Smith 1999; Ryan et al. 2003).

Poa pratensis L. (Poaceae) The Kentucky bluegrass, Poa pratensis is a perennial grass native to Eurasia, Gremmen (2004) describes it as a potential invasive to many sub-Antarctic islands. Poa pratensis is commonly used for golf courses and sports fields (Ke & Lee 1996). Although P. pratensis often produces viable seeds (Walton 1975), the species seems to spread vegetatively rather than by seed on Marion Island (Gremmen 2004). Poa pratensis was first noticed in 1965 on Marion Island at Ship’s Cove and at the meteorological station (Huntley 1971). Data from surveys conducted in 1975, 1981, 1998 indicate that the species is restricted to the eastern part of the island (Gremmen 1975; Gremmen 1981; Gremmen & Smith 1999). On other sub- Antarctic islands, (e.g. Kerguelen Island) the species is very abundant and is displacing native plant communities (Frenot et al. 2001).

28 Sagina procumbens L. (Caryophyllaceae) The procumbent pearlwort, Sagina procumbens is a small herb native to the Northern Hemisphere. This species has become one of the most aggressive invasive species on the sub- Antarctic islands (Walton 1975). This species spreads vegetatively and by seed dispersal and usually forms a large mat-like carpet (Gremmen et al. 2001). Sagina procumbens produces many seeds and once germinated, seedlings start producing seeds within a few months (Gremmen et al. 2001). On Marion Island, Sagina procumbens is very widespread, colonizing nearly all major habitat types. Sagina procumbens was first detected at the meteorological station by Huntley in 1965 (Huntley 1971). Repeated surveys in 1975, 1981 and 1987 on Marion Island revealed that S. procumbens had spread to new localities (Huntley 1971; Gremmen 1975; Gremmen 1981; Bergstrom & Smith 1990). Sagina procumbens also occurs on Prince Edward Island and was first observed at two localities in 1997 (Gremmen & Smith 1999).

Stellaria media (L.) Vill. (Caryophyllaceae) Common chickweed, Stellaria media is a small herbaceous plant, native to Europe. At present Stellaria media has invaded a number of sub-Antarctic Islands (Walton 1975). The species rarely occupies dry ground, preferring biotically disturbed habitats; particularly wetter environments (Walton 1975). Stellaria media flowers and produces abundant seeds, and it appears to spread by seed on Marion Island (Gremmen 2004). This species was first discovered by Moseley in 1873 (Moseley 1874). It was then recorded by Huntley at 12 localities in 1965 (Huntley 1971). This species was found to be widespread from surveys undertaken in 1975, 1981 and 1989 (Gremmen 1975; Gremmen 1981; Bergstrom & Smith 1990). To date Stellaria media is not very abundant and is only restricted to coastal habitats (Gremmen 2004).

MATERIALS AND METHODS 2006/7 Field Survey Field work was carried out on Marion Island between April 2006 and May 2007. To ensure comprehensive coverage, different techniques were used to examine the distribution of each alien plants species across the island (Table 1). Surveys were conducted at regular intervals (or continuously) throughout the year except in winter when harsh weather conditions and heavy snow prevented sampling. To ensure comprehensive coverage, the spatially explicit survey was used to identify sampling sites on a ½ minute by ½ minute scale which resulted in 348 sites across the island (Fig. 1). The blank highland (above 800 m) area was not sampled

29 due to plants being restricted by altitude to varying extents (Fig. 2). Huntley (1970) recorded the altitudinal limit of indigenous plants at 765 m a.s.l, while Hedding (2006) found an Azorella selago cushion at 840 m a.s.l, and Gremmen (1981) confirmed that indigenous plants were sparse above 600 m a.s.l.

Figure 1 Half-minute by half minute basis Figure 2 Satellite map of Marion Island, the green for regular sampling of alien vascular plant colour indicates vegetation and the dark grey species on Marion Island. indicates bare ground (www.earth.google.com).

All the sampling sites (348 sites) were physically located using a hand-held GPS (Garmin E- trex Vista-C®). At each site an 8 m x 8 m grid was laid and the presence/absence of alien plant species recorded. For consistency the grid was laid with the bottom left-hand corner on the grid intersection point facing south west. Where the size of a patch was larger than 64 m2 the extent of occurrence was measured by mapping the outer limit of the patch with a GPS every 50 m. At each site, the following were recorded: GPS location, altitude, slope, aspect, vegetation type and lava type (Table 2). En route to the sampling sites ad hoc observations of alien plant species were recorded and a species was not recorded again until seen 10 m away. However, if a different species was observed within 10 m of recording, then it was recorded and notes taken for environmental variables as above. Site-specific recording or targeted surveys were also used to confirm the presence or absence of those alien species known to occur at few specific sites. Alien plant distribution data from Prince Edward Island was derived from the 2008 survey conducted by S.L Chown, J.D Shaw and P.G. Ryan who surveyed a relatively large part of the island.

30 Table 1 Methods for providing relative abundance and distribution of alien plants on Marion Island.

Species General island Ad hoc Spatially Targeted Extent of distribution explicit survey occurrence Gremmen (1997) survey Monocotyledonae Agropyron repens V

Agrostis gigantea Restricted V

Agrostis stolonifera Widespread V V V

Alopecurus Appears to be geniculatus trampled -not recorded Juncus effusus Restricted V

Luzula cf. multiflora Restricted V

Poa annua Widespread V V V

Poa pratensis Widespread V V V

Dicotyledonae Cerastium fontanum Widespread V V

Rumex acetosella Restricted V V V

Sagina procumbens Widespread V V

Stellaria media Widespread V V

Fig 2 List of vegetation types and other environmental variables recorded at each site

Habitat complex Substrate Slope Aspect

Biotic herbfield Vegetated lava Flat North Coastal saltspray Black lava Gentle East Fellfield complex Grey lava Moderate South Mire complex Scoria Undulating West Slope Complex Steep Polar desert

31 Data analysis All the records obtained from systematic and ad hoc survey were compiled and scaled up to a 500 m x 500 m grid. Occupied cells were taken as presences while unoccupied cells were considered absences. The number of separate records in each grid cell was taken as a measure of relative abundance. Then the current distribution and relative abundance were mapped at 500 m x 500 m resolution for both Marion and Prince Edward Islands. The change in surface area was determined by first digitising and georectifying old distribution maps of alien species into Arc GIS, and then scaling them up to 500 m x 500 m (0.25 km2) resolution. The change in occupancy was then calculated as the difference in number of grid cells occupied between two time periods (e.g. 1975 -1989 grids), and quantified in m2. In addition, rate of spread between different periods was also calculated by dividing the number of grids occupied by the number of years between time periods. For both islands each available map was assessed separately (see Table 3 for the years for which data were available).

Table 3 Sources of data on alien plant distributions at the Prince Edward Islands.

Author/source Year of Island Species recorded Nature of survey survey Agrostis stolonifera The first detailed survey of Cerastium fontanum the distribution of alien Gremmen 1975 1975 Marion Poa annua plants that covered most of Poa pratensis Marion Island. Sagina procumbens Stellaria media The area covered included the northern part of the Gremmen 1981 1981 Marion Cerastium fontanum island especially the Poa pratensis vicinity of Meteorological Stellaria media station where a number of alien species were previously recorded. Large parts of Marion and Agrostis stolonifera Prince Edward Island were Bergstrom & 1987 Marion & Prince Cerastium fontanum covered. However, on Smith 1990 Edward Poa annua Marion Island the survey Sagina procumbens concentrated largely on Stellaria media areas were alien had been previously recorded (e.g. Base & field huts) On Marion Island except Agrostis stolonifera for the south coast, the Gremmen & 1998 Marion & Prince Poa pratensis entire coastlines were Smith 1999 Edward Sagina procumbens covered. At Prince Edward, the east and the west coast as well as the interior were surveyed. Cerastium fontanum Coverage included all Ryan et al. 2003 2001 Prince Edward Poa annua accessible coastline and Sagina procumbens, much of adjacent interior Stellaria media

32 Residence time of alien plant species on Marion Island was also calculated. However, acquiring the data on the exact date the species was first introduced is often difficult if not impossible. The data on species records was not only collected from the published literature, but also from other reliable sources and these included herbarium specimens and unpublished records (Dike herbarium specimen; van der Merve unpublished data; Bergstrom & Smith 1999; Gremmen, 1975, 1981, 1997; Gremmen and Smith 1990; Huntley 1971; Moseley 1874). Residence time was then calculated by subtracting the year the species was first detected from the year of current survey (e.g. 2006 – 1965). Ordinary least squares linear regression was used to test the relationship between occupancy and residence time.

RESULTS Current alien species range

A total of 1271 mapping squares (500 m × 500 m) cover Marion Island, and approximately 236 squares (22%) are occupied by alien plants (Fig. 3). The smaller Prince Edward Island has a total of 219 squares, 45 of which are occupied by the three alien plant species that currently occur on the island (Fig. 4). On Marion Island, the number of grids occupied by alien plants sharply declines from the coastal habitats to high altitude habitats with significant numbers occurring around the settlement site (Marion Base). Of the 283 mapping squares invaded, Cerastium fontanum occupies 172, Poa annua 161, Sagina procumbens 151, Agrostis stolonifera 45, Poa pratensis 30 and Stellaria media 24. Other alien species (Agropyron repens, Juncus effusus, Luzula multiflora and Rumex acetosella) occupy less than 10 squares each.

Alien plant species also differ markedly in their abundance. The term relative abundance was used to refer to the number of separate records in each grid cell. In consequence, 2356 records were obtained from ad hoc recording and only 29 records derived from the spatially explicit survey, with Agrostis stolonifera, Cerastium fontanum, Poa annua, Poa pratensis and Sagina procumbens having more than 100 records each (see Fig. 5). Although Cerastium fontanum is the most widespread species on Marion Island, Sagina procumbens has the most records (relative abundance) of all the alien species on Marion Island with a total of 842 records. Other species with high number of records include Poa annua (555), Cerastium fontanum (503), Poa pratensis (233) and Agrostis stolonifera (162).

Figure 3 Current distribution of all alien species on Marion Island.

Figure 4 Current distribution of Cerastium fontanum, Poa annua and Sagina procumbens at Prince Edward Island.

Figure 5 Relative abundance of widespread alien plant species on Marion Island. (a) Agrostis stolonifera; (b) Cerastium fontanum; (c) Poa annua; (d) Poa pratensis; (e) Sagina procumbens; (f) Stellaria media. Black dots indicate individual records and a hatched area indicates patches larger than 64 m².

36 Extent of occurrence of alien species Some species have gradually expanded their range and some have not moved beyond their point of introduction. The distribution range of some species seems to be contracting since the last survey was undertaken on Marion Island. For example, Agropyron repens and Luzula multiflora each continue to occupy a single grid cell. Juncus effusus and Rumex acetosella are still restricted to a few grids, occupying three and two of the grids, respectively (Table 4).

Other species, however, are widely distributed. Agrostis stolonifera occupied 12 grids in 1975, but by 2006, it had spread on the east coast of Marion Island particularly in the vicinity of the Meteorological station and now occupies 45 grids.

Cerastium fontanum occupied only 33 grid cells in 1975. The species has since extended its distribution considerably (Fig. 6a). At present Cerastium fontanum is the most widespread species on Marion Island, occupying a total number of 175 grid cells. The number of grids occupied by this species clearly indicates that it occurs in a broader range of habitats than any other alien plant species on the island. Cerastium fontanum also occurs on the neighbouring Prince Edward Island where the number of grids increased from one grid cell in 1987 to nine grids in 2008 (Fig. 6b).

Poa annua has gradually increased its distribution range, and is the second-most widespread species on Marion Island (Fig. 6a). This species occupied approximately 80 grid cells in 1975. By 2006, this species was widely distributed, occupying a total of 163 cells. Poa annua is the only gramminoid alien species occurring at Prince Edward Island. Its distribution has declined from 21 grids in 2001 to 12 grids by 2008. The decline in number of grids occupied can be explained by an incomplete survey that was undertaken in 2008 (Fig. 6b).

Poa pratensis has slowly, but steadily increased its range. This species occupied seven grid cells in 1975 and 30 grid cells in 2006 (Fig. 6a). The grid cells occupied by this species are restricted to the east coast.

Sagina procumbens is the most rapidly expanding species on both Marion and Prince Edward Island. Sagina procumbens has increased its range on Marion Island from four grid cells in 1975 to 152 cells by 2006 (Fig. 6a). Likewise, Sagina procumbens is also doing well at Prince Edward Island and it appears to be the most widespread species on this island. Initially,

37 Sagina procumbens occupied only two grid cells during its first record in 1997, but increased to 41 cells in 2008 (Fig. 6b).

The first record of Stellaria media dates back to 1873 (Moseley 1874). This species occupied 59 grids in 1975. By 2006 (Fig. 6a), Stellaria media occupied only 25 grids. Despite its earliest record on Marion Island the distribution of Stellaria media seems to be contracting.

Table 4 Occupancy of alien invasive species since their first discovery on the Prince Edward Islands.

Year of Original Spread since Rate of Occupancy discovery Collector Occupancy discovery spread (m²) (m²) (m²/yr) 2006 (MI) 2008 (PEI) (m²)

Marion Island

A. stolonifera 1965 B.J. Huntley < 250 000 11 000 000 268 293 11 250 000

A. repens 1965 B.J. Huntley < 250 000 0 0 250 000

C. fontanum 1873 H.N.Moseley < 250 000 42 750 000 321 429 43 000 000

J. effusus 1965 B.J. Huntley < 250 000 500 000 12 195 750 000 M.N. Bester L. multiflora 1999 & B. Stewart < 250 000 0 0 250 000

P. annua 1948 Dike < 250 000 40 000 000 689 655 40 250 000

P. pratensis 1965 B.J. Huntley < 500 000 7 000 000 353 659 7 500 000 J.J. Van der R. acetosella 1953 Merve < 250 000 250 000 4 717 500 000

S. procumbens 1965 B.J. Huntley < 250 000 37 500 000 914 634 37 750 000

S. media 1873 H.N. Moseley < 250 000 5 750 000 43 233 6 000 000

Prince Edward Island D.M. C. fontanum 1987 Bergstrom & < 250 000 2 000 000 95 238 2 250 000 V.R. Smith

P. annua 1966 B.J.Huntley < 250 000 2 750 000 65 476 3 000 000 N.J.M. S. procumbens 1997 Gremmen & < 500 000 9 750 000 1 818 181 10 250 000 V.R. Smith

38 180

d Cerastium fontanum e i 160 Poa annua p

u Sagina procumbens c c 140 Agrostis stolonifera o

s Stellaria media t a

r 120 Poa pratensis d a u q

100 m

0 80 5

x 60 m

0 0

5 40

f o

o 20 N 0 1860 1880 1900 1920 1940 1960 1980 2000 2020 Year

Figure 6 a The occupancy of the six major invasive alien plant species (Cerastium fonatnum Sagina procumbens, Stellaria media, Agrostis stolonifera, Poa annua and Poa pratensis) over time at Marion Island.

45 Cerastium fontanum d

e 40 Poa annua i

p Sagina procumbens u

c 35 c o

s t

a 30 r d a

u 25 q

m 20 0 0 5

x 15

0 0 5

10 f o . o 5 N

0 1960 1970 1980 1990 2000 2010 Year

Figure 6 b The occupancy of the three invasive alien plant species (Cerastium fontanum, Poa annua and Sagina procumbens) at Prince Edward Island. 39 Rate of spread of widespread alien plants It is assumed that when first discovered, all alien species occupied only one grid, unless specific sites were given by the works first reporting the species. There is no clear pattern of expansion from the point of introduction for alien plant species on the Prince Edward Islands. Nevertheless the spread of alien species appears to be directed to the coast. Approximately 80 of 162 grid cells along the coast have been invaded on Marion Island, while 20 of grids cells have been invaded along the coast of Prince Edward Island. Almost all of the species have increased their area of occupancy at different rates between different time periods (Fig. 7).

Since its first discovery in 1965 (presumably occupying a single grid), Agrostis stolonifera has expanded over 41 years, at a rate of 268 293 m²/yr. However, this rate of spread has changed over time. Between 1965 and 1975 the rate of expansion was 275 000 m²/yr. It reached 625 000 m²/yr between 1975 and 1981. Between 1981 and 1987 the expansion rate was 291 666 m²/yr. The expansion between 1987 and 1998 was 250 000 m²/yr however, between 1998 and 2006 there was no further increase in the number of grid occupied by A. stolonifera.

After its first detection in 1873 on Marion Island, the rate of spread of Cerastium fontanum has been 321 429 m²/yr. However, its expansion has occurred at different rates during different periods. Between 1873 and 1975 the rate of spread was 75 980 m²/yr. From 1975 to 1981 the expansion rate was 83 333 m²/yr. The rate of spread increased to 333 333 m²/yr between 1981 and 1987, and accelerated to 1 750 000 m²/yr between 1987 and 2006. The average rate of C. fontanum since discovery at Prince Edward Island has been 95 238 m²/yr.

The rate of spread of Poa annua since its discovery on Marion Island in 1948 has been 689 655 m²/yr. From 1948 to 1975 this species expanded at a rate of 731 481 m²/yr. Between 1975 and 1987 the expansion rate was 104 166 m²/yr. The period of rapid expansion occurred between 1987 and 2006 with the expansion rate of 1 026 315 m²/yr. At the neighbouring Prince Edward Island the rate of expansion since its discovery has to date been 65 476 m²/yr.

Since its first discovery in 1965 (occupying two grids), Poa pratensis has expanded over 41 years at a rate of 353 659 m²/yr. Similarly, the expansion occurred at different rates during different periods. From 1965 to 1975 the rate of expansion was 200 000 m²/y and between 1975 and 1981, the expansion was relatively slow at 83 333 m²/yr. However, the rate of

40 spread increased to 250 000 m²/yr between 1981 and 1998. It again proceeded slowly at a rate of 125 000 m²/yr between 1998 and 2006.

After its first detection in 1965 on Marion Island, the rate of spread of Sagina procumbens has been an alarming rate of 914 634 m²/yr. However, this rate of spread has changed over time. From 1965 to 1975 its rate of expansion was 75 000 m²/yr. Between 1975 and 1981 the rate of spread was 41 666 m²/yr. It reached 750 000m²/yr between 1981 and 1987, and increased to 1 795 454 m²/yr between 1987 and 1998. Between 1998 and 2006, the rate of expansion was 1 562 500 m²/yr. The average spread rate of S. procumbens since discovery at Prince Edward Island has been 1 818 181 m²/yr.

Stellaria media has expanded over 133 years, at a rate of 43 233 m²/yr since its discovery in 1873 on Marion Island. The rate of expansion has varied between years. From 1873 to 1975 the rate of expansion was 105 392 m²/yr. Between 1975 and 1981 the rate of spread was 41 666 m²/yr. The highest rate of expansion of Stellaria media occurred between 1981 and 1987 spreading at a rate of 583 333 m²/yr. However, by 2006 no further expansion of this species was observed and its range seems to be contracting.

Figure 7 a Expansion of the range of Agrostis stolonifera over time.

Figure 7 b Expansion of the range of Cerastium fontanum over time.

Figure 7 c Expansion of the range of Poa annua over time.

Figure 7 d Expansion of the range of Poa pratensis over time.

Figure 7 e Expansion of the range of Sagina procumbens over time.

Figure 7 f Expansion and then contraction of the range of Stellaria media over time.

47 Finally, residence time was calculated. However, it was not a significant factor explaining the extent of alien vascular plant species distribution on the island (Fig. 8). There was no relationship between residence time and occupancy (r² = 0.149, p = 0.27). Species such as Stellaria media and Rumex acetocella occupied few grids despite their long residence time on the island. However, a species, such as Sagina procumbens, have a wide island distribution despite their relatively short residence time.

180 d e i

p 160 u c c

o 140

s t a r 120 d a u q

100 m

0 80 5

x 60 m

0 40 5

f o

. 20 o N 0 0 20 40 60 80 100 120 140 Residence time (years)

Figure 8 The non-significant (r² = 0.149, p = 0.27) relationship between residence time of alien plant species and occupancy on Marion island.

DISCUSSION This study assessed the current distribution of alien plant species on the sub-Antarctic Prince Edward Islands. The results demonstrated significant increase in occupancy of Cerastium fontanum, Poa annua and Sagina procumbens. This increase is in keeping with the trend documented and discussed by previous authors (e.g. Gremmen 1981; Gremmen & Smith 1999). For example, data from the survey undertaken by Gremmen and Smith in 1987 shows a remarkable increase in species range from the previous survey undertaken by Gremmen in 1981. Recent surveys undertaken on Marion Island also show a steady increase in the occupancy of species such as Agrostis stolonifera and Poa pratensis (Gremmen & Smith

48 1999). Gremmen et al. (1998) reported that the rate of spread of Agrostis stolonifera on Marion Island between 1987 and 1998 has been 150-400 m/yr-¹.

This increase has also been noticeable on Prince Edward Island. In particular, Sagina procumbens has rapidly increased its range since its discovery on the island. Ryan et al. (2003) suggested that the average rate of spread of this species has been 800 m/yr-¹ between 1997 and 2001. This is likely due to its habit of colonizing disturbed habitats and large number of seals and sea birds are responsible for such disturbances (Bester et al. 2003). Similarly Poa annua is widespread and has been observed growing around the nest of burrowing birds, particularly on fernbrake slopes. The rate of spread of Poa annua on Prince Edward Island has been 280 m/yr-¹ between 1966 and 2001 (Ryan et al. 2003). Similar trends of expansion of Poa annua and Sagina procumbens were observed on sub-Antarctic Possession Island in the Crozet archipelago between 1989 and 1996 (see Frenot et al. 2001).

Cerastium fontanum has also spread at a substantial rate, and must now be considered as one of the most significant invasive vascular plants on Marion Island. Cerastium fontanum is the most widespread species on the island and has invaded nearly all coastal habitat communities. On Marion Island Cerastium fontanum occurs in a broad array of habitats, ranging from Wet mires to nutrient-poor Fellfield communities. Previously this species was only found on Marion Island, but was later found at the neighbouring Prince Edward Island in 1987. It has been estimated that the rate of spread of this species at Prince Edward has been 370 m/yr-¹ between 1998 and 2001 (Ryan et al. 2003). Cerastium fontanum also occurs on several sub- Antarctic islands including Crozet Islands, Kerguelen, Macquarie and Possession (Walton 1975; Frenot et al. 2001).

Apart from natural disturbances from birds and seals, human activities might have led to the spread of alien plants on Marion Island. After the first documented landing in either December 1803 or January 1804, there have been a number of activities that have taken place. Among those activities are the sealing era between early 1800 and 1930, annexation of Marion Island in 1948, construction of field huts in 1971, a cat hunting campaign between 1986 and 1990, the construction of a new research base since 2003 and finally, the ongoing research projects (Copper 2008; De Villiers & Copper 2008). The number of visits by early settlers was infrequent but there has been an increase in number of expeditions since the annexation of the island in 1948. As was documented by Chown et al. (1998), there is a link between number of alien plants present on the island and the number of visitors.

49 The results (Fig. 6a) also demonstrate a noticeable increase in the distribution and occupancy of alien plants species after 1987 on Marion Island. This may have resulted from the extensive cat hunting campaign, which commenced in August 1986. The operation involved a team of 16 members each year (in addition to normal station and science personnel) and ran until 1990, during which time poisoning, night-shooting and trapping were techniques used to eradicate cats (De Villiers & Copper 2008). During the operation it is believed that propagules might have been inadvertently spread across the island. This study shows that there has been a considerable increase in the presence of alien plant species since the cat eradication programme.

Given the current rate of spread of Agrostis stolonifera, Cerastium fontanum, Poa annua and Sagina procumbens it is not hard to predict that within the next 20 years all coastal habitats will be dominated by these species. Additionally the rapid climate change on the island might facilitate the expansion of widespread species, especially the colonization of higher elevations by Cerastium fontanum, Poa annua and Sagina procumbens given that le Roux & McGeoch (2008b) found most indigenous vascular plants have been increasing their altitudinal ranges since the first records in the 1960s. Gremmen and Smith (1999) also suggested that a warmer climate is likely to make the island conducive for alien species, resulting in the production of more seeds and some species may even start to produce viable seeds.

Distribution of alien species on Marion Island is not explained by residence time. In other studies, residence time is an important factor explaining species distribution. For example, Scott and Panetta (1993), Rejmaneck (2000), Becker et al. (2005), Castro et al. (2005) and Hamilton et al. (2005) found positive relationships between residence time and occupancy. Additionally, La Sorte and Pyšek (2009) suggested that residence time seemed to be the important factor determining the success and distribution of European archaeophytes in North America. Nevertheless, a few studies have demonstrated that residence time did not explain the distribution of alien plant species, consistent with the findings for Marion Island’s alien plants. For example, Mihulka and Pyšek (2001) found a negative relationship between number of localities of alien plant species in Europe and the year of the first introduction. Similarly, Wu et al. (2003) reported that in Taiwan Fabaceae species with similar residence time show different distribution ranges.

In conclusion, this study demonstrated that alien plant species on Marion Island differ markedly in their occupancy, distribution and rate of expansion. Agrostis stolonifera,

50 Cerastium fontanum, Poa annua and Sagina procumbens are all expanding their ranges, whereas the range of Stellaria media is contracting. Cerastium fontanum is the most widespread species on Marion Island while Sagina procumbens is the most abundant (number of records) and most rapidly expanding species on both Marion and Prince Edward Islands. Moreover, S. procumbens is a very aggressive invader species on the island and is currently transforming the landscape by forming a mat-like carpet, especially along rivers.

51 REFERENCES

Becker, T., Dietz, H., Billeter, R., Buschmann, H., Edward, P.J. 2005. Altitudinal distribution of alien plant species in the Swiss Alps. Perspectives in Plant Ecology, Evolution and Systematics 7, 173-183.

Bester, M.N., Ryan, P.G. & Dyer, B.M. 2003. Population numbers of fur seals at Prince Island, Southern Ocean. African Journal of Marine Science 25, 549-554.

Bergstrom, D. & Smith, V.R. 1990. Alien vascular flora of Marion and Prince Edward Islands: new species, present distribution and status. Antarctic Science 2, 301-308.

Castro, S.A, Figueroa, J.A. Muñoz-Schick, M, Jaksic, F. M. 2005. Minimum residence time, biogeographical origin, and life cycle as determinants of the geographical extent of naturalized plants in continental Chile. Diversity and Distributions 11, 183-191.

Chown, S.L. 1999. Relief conservation officer's report to the Prince Edward Islands Management Committee, June 1999. Unpublished report, Department of Environmental Affairs & Tourism.

Chown, S.L. & Froneman, P.W. 2008. The Prince Edward Islands in a global context. In: Chown, S.L. & Froneman, P.W. (Eds.) The Prince Edward Islands. Land-Sea Interactions in a Changing Ecosystem. African Sun Media, Stellenbosch, pp. 1-16.

Chown, S.L., Gremmen, N.J.M. & Gaston, K.J. 1998. Ecological biogeography of southern ocean islands: Species-area relationships, human impacts, and conservation. American Naturalist 152, 562-575.

Chown, S.L., Sinclair, B.J. & van Vuuren, B.J. 2008. DNA barcoding and the document of alien species establishment on the sub-Antarctic Marion Island. Polar Biology 12, 277-291.

52 Chwedorzewska, K.J. 2008. Poa annua L. in Antarctic: searching for the source of introduction. Polar Biology 31, 263-268.

Cooper, J. 2008. Human History. In: Chown S.L. & Froneman, P.W. (Eds.) The Prince Edward Islands. Land-Sea Interactions in a Changing Ecosystem. African Sun Media, Stellenbosch, pp. 331-350.

Dean, W.R.J., Milton, S.J., Ryan, R.G. & Moloney, C.L. 1994. The role of disturbance in the establishment of indigenous and alien plants at Inaccessible Nightingale islands in the South Atlantic Ocean. Vegetatio 113, 13-23.

Elith, J. & Graham, C.H. 2009. Do they? How do they? Why do they differ? - On finding reasons for differing performances of species distribution models. Ecography 32, 66-77.

Frenot, Y., Gloaguen, J.C., Massé, L. & Lebouvier, M. 2001. Human activities, ecosystem disturbance and plant invasions in sub-Antarctic Crozet, Kerguelen and Amsterdam Islands. Biological Conservation 101, 33-50.

Goverde, M., Arnone, III. & Erhardt, A. 2002. Species-specific reactions to elevated CO2 and nutrient availability in four grass species. Basic and Applied Ecology 3, 221-227.

53 Government Gazette 2004. Republic of South Africa: National Environmental Management: Protected Areas Act of 2003 464, 1-50.

Greene, S.W. & Greene, D.M. 1963. Check list of the sub-Antarctic and Antarctic vascular flora. Polar Record 11, 411-418.

Gremmen, N.J.M. 1975. The distribution of alien vascular plants on Marion and Prince Edward Islands. South African Journal of Antarctic Research 5, 25-30.

Gremmen, N.J.M. 1981. The Vegetation of the sub-Antarctic Islands Marion and Prince Edward. Dr.W.Junk. The Hauge.

Gremmen, N.J.M. 1982. Alien vascular plants on Marion island (sub-Antarctic). National Fránçais pour les Recherches Antarctiques 51, 315-323.

Gremmen, N.J.M. 1997. Changes in the vegetation of sub-Antarctic Marion Island resulting from introduced vascular plants. In: Bataglia, B., Valencia, J. & Walton, D.W.H. (Eds.) Antarctic Communities: Species, Structure and Survival. Cambridge University Press, Cambridge pp. 417-423.

Gremmen, N.J.M. 2004. Management of alien vascular plants on Marion and Prince Edward Islands: an Integrated Approach. Unpublished report. Data Analyse Ecologie, Diever, The Netherlands, 1-30.

Gremmen, N.J.M., Chown, S.L. & Marshall, D.J. 1998. Impact of introduced Agrostis stolonifera L. on vegetation and soil fauna of drainage communities at Marion Island, sub- Antarctic. Biological Conservation 85, 223-231.

Gremmen, N.J.M. & Smith, V.R. 1999. New records of alien vascular plants from Marion and Prince Edward Islands, sub-Antarctic. Polar Biology 21, 401-409.

54 Gremmen, N.J.M. & Smith, V.R. 2008. Terrestrial vegetation and dynamics. In: Chown S.L. & Froneman, P.W. (Eds.) The Prince Edward Islands. Land-Sea Interactions in a Changing Ecosystem. African Sun Media, Stellenbosch, pp. 215-244.

Hamilton, M.A, Murray, B.R., Cadotte, M.W, Hose, G.C., Baker, A.C., Harris, C.J. & Licari, D. 2005. Life- history correlates of plant invasiveness. Ecology Letters 8, 1066-1074.

Harris, C.J., Murray, B.R., Hose, G.C. & Hamilton, M.A 2007. Introduction history and invasion success in exotic vines introduced to Australia. Diversity and Distributions 13, 467- 475.

Hedding, D.W. 2006. Geomorphology and geomorphological responses to climate change in the interior of sub-Antarctic Marion Island. M.Sc thesis, University of Pretoria, South Africa.

Hoffmann, W.A., & Haridasan, A. 2008. The invasive grass, Melinis minutiflora, inhibits tree regeneration in a Neotropical savanna. Austral Ecology 33, 29-36.

Huntley, B.J. 1970. Altitudinal distribution and phenology of Marion Island vascular plants. Tydskrif vir Natuurwetenskap 10, 255-262.

Huntley, B.J. 1971. Vegetation. In: van Zinderen Bakker, E.M., Winterbottom, J.M. & Dyer, R.A. (Eds.) Marion and Prince Edward Islands. Report on the South African Biological and Geological Expedition 1965-1966. A.A. Balkema, Cape Town, pp. 98-160.

Ke, S. & Lee, C.W. 1996. Plant regeneration in Kentucky bluegrass (Poa pratensis L.) via coleoptile tissue cultures. Plant Cell Reports 15, 882-887.

Klimeš, L. & Klimešová, J. 1999. Root sprouting in Rumex acetosella under nutrient levels. Plant Ecology 141, 33-39

La Sorte, F.A. & Pyšek, P. 2009. Extra-regional residence time as a correlate of plant invasiveness: European achaeophytes in North America. Ecology 90, 2589-2597.

Lee, J.E. & Chown, S.L. 2009. Temporal development of hull-fouling assemblages associated with an Antarctic supply vessel. Marine Ecology Progress Series 386, 97-105.

55 le Roux, P.C. 2008. Climate and climate change. In: Chown, S.L. & Froneman, P.W. (Eds.) The Prince Edward Islands. Land Sea Interactions in a Changing Ecosystem. African Sun Media, Stellenbosch, pp. 39-64. le Roux, P.C. & McGeoch, M.A. 2008a. Changes in climate extremes, variability and signature on sub-Antarctic Marion Island. Climate Change 86, 309-329. le Roux, P.C. & McGeoch, M.A. 2008b. Rapid range expansion and community reorganization in respond to warming. Global Change Biology 14, 2950-2962.

McDougall, I., Verwoerd, W. & Chevallier, L. 2001. K-Ar geochronology of Marion Island, Southern Ocean. Geological Magazine 138, 1-17.

Mihulka, S. & Pyšek, P. 2001. Invasive history of Oenothera congeners in Europe: a comparative study of spreading rates in the last 200 years. Journal of Biogeography 28, 597- 609.

Moseley, H.N. 1874. On the botany of Marion Island, Kerguelen’s land and Young Island of the Heard group. Journal of the Linnean Society (Botany) 14, 387-388.

Øvterdal, D.O. & Gremmen, N.J.M. 2008. Lichens of the Prince Edward islands. In: Chown, S.L. & Froneman, P.W. (Eds.) The Prince Edward Islands. Land-Sea Interactions in a Changing Ecosystem. African Sun Media, Stellenbosch, pp. 393-397.

Pakhomov, E.A. & Froneman, P.W. 1999. The Prince Edward Islands pelagic ecosystem: a review of achievements 1976-1990. Journal of Marine Systems 18, 297-310.

Pickard, J. 1984. Exotic plants on Lord Howe Island: distribution in space and time, 1853- 1981. Journal of Biogeography 11, 181-208.

Phiri, P.P. 2008. Species occupancy, distribution and abundance: indigenous and alien invasive vascular plants on sub-Antarctic Marion Island. M.Sc. Thesis, University of Stellenbosch, South Africa.

56 Protopopova, V.V., Shevera, M.V. & Mosyakin, S.L. 2006. Deliberate and unintentional introduction of invasive weeds: a case study of the alien flora of Ukraine. Euphytica 148, 17- 33.

Pyšek, P. & Jarošik, V. 2005. Residence time determines the distribution of alien plants. In: Inderjit, S. (Eds) Invasive Plants: Ecological and Agricultural Aspects. Birkhäuser Verlag, Basel, pp.77-86.

Pyšek, P. & Richardson, D.M. 2006. The biogeography of naturalization in alien plants. Journal of Biogeography 33, 2040-2050.

Rejmánek, M. 2000. Invasive plants: approaches and predictions. Austral Ecology 25, 497- 506.

Richardson, D.M. & Pyšek, P. 2006. Plant invasions: merging the concepts of species invasiveness and community invisibility. Progress in Physical Geography 30, 409-431.

Roberts, H.A. & Stokes, F.G. 1966. Studies on the weeds of vegetable crops. VI. Seed populations of soil under commercial cropping. Journal of Applied Ecology 3, 181-190.

Ryan, P.G., Smith, V.R. & Gremmen, N.J.M. 2003. The distribution and spread of alien vascular plants on Prince Edward Island. African Journal of Marine Science 25, 555-562.

Salisbury, E.J. 1961. Weeds & Aliens. New Naturalist Series. Collins, London.

Scott, J.J. & Kirkpatrick, J.B. 2005. Changes in sub-Antarctic Heard Island vegetation at sites occupied by Poa annua, 1987-2000. Arctic, Antarctic and Alpine Research 37, 366-371.

57 Scott, J.K. & Panetta, F.D. 1993. Predicting the Australian weed status of Southern African plants. Journal of Biogeography 20, 87-93. van Zinderen Bakker, E.M., Winterbottom, J.M. & Dyer, R.A. 1971. Marion and Prince Edward Islands. Report on the South African Biological and Geological Expedition 1965- 1966. A.A. Balkema, Cape Town.

Vargas, J. M., & Turgeon, A. J. 2003. Poa annua: Physiology, Culture and Control of Annual Bluegrass. Wiley, Hoboken, New Jersey.

Vinton, M.A. & Burke, I.C. 1995. Interactions between individual plant species and soil nutrient status in shortgrass steppe. Ecology 76, 1116-1133.

Walton, D.W.H. 1975. European weeds and other alien species in the sub-Antarctic. Weed Research 15, 271-282.

Whinam, J. Chilcott, N. & Bergstrom, D.M. 2005. Sub-Antarctic hitchhikers: expeditioners as vectors for introduction of alien organisms. Biological Conservation 121, 207-219

Wu, S., Chaw, S. & Rajmánek, M. 2003. Naturalised Fabaceae (Leguminosae) species in Taiwan: the first approximation. Botanical Bulletin of Academia Sinica 44, 61-66.

Young, F.L., Wyse, D.L. & Robert, J.J. 1984. Quackgrass (Agropyron repens) interference on corn (Zea mays). Weed Science 32, 226-234.

58 Chapter 3 ASSESSING THE VULNERABILITY OF VEGETATION AND VARIABLES THAT DETERMINE ALIEN SPECIES OCCURENCE ON MARION ISLAND

INTRODUCTION The vulnerability of regions to invasion varies considerably. At the broadest scale, islands appear to be more vulnerable to invasion than mainlands (Elton 1958; Denslow 2003; Gimeno et al. 2006). Nonetheless, in terrestrial ecosystems, temperate regions are considered to be more susceptible to invasion than the tropics (Lonsdale 1999; Pyšek & Richardson 2006). Despite variation in vulnerability amongst regions, the degree of susceptibility of habitats within a region also differs (Chytrý et al. 2008a; Chytrý et al. 2008b). For instance, riverine ecosystems are generally prone to invasion by alien plant species (Richardson et al. 2007; Truscott et al. 2008; Jacquemyn 2010). Many studies have been carried out to identify habitats that are susceptible to invasion (Alpert et al. 2000) after it was realized that species attributes are by no means the only determinant factor of invasion success (Richardson & Pyšek 2006). However, the habitat requirements of a species (physical characteristic of an area) largely influences invasibility (Andrew & Ustin 2009). As it was well documented by Chytrý et al. (2009) and Walter et al. (2005) habitat type appears to be the main predictor of invasion success at a particular locality. Currently, a great deal of effort is devoted to modelling areas or habitats where alien plant species might potentially flourish (Thuiller et al. 2006; Zhu et al. 2007; Nielson et al. 2008; Elith & Leathwick 2009; Smolik et al. 2010). Even though it has been proven fairly straightforward to predict habitat likely to be invaded, it is often difficult to identify traits associated with invasiveness (Alpert et al. 2000; Evangelista et al. 2008).

It is rather challenging to single out individual variables that explain invasion, and the best prediction can only be achieved by combining both species traits and environmental variables (Gassó et al. 2009). Despite vegetation type being the main predictor of invasion by alien plants species, alien plants also show differences in distribution along the altitudinal gradient (Pauchard & Alaback 2004; Arévalo et al. 2005). The harsh climatic conditions at high altitude can limit the distribution of alien plants. However, high propagule pressure and disturbance can help species overcome the high-altitude barrier (Richardson et al. 2000). Becker et al. (2005) suggested that the altitudinal distribution of alien plant species is mostly influenced by residence time. In addition studies by Silva & Smith (2004) and Wilson et al. (2007) revealed that variation in altitude, landscape structure and aspect play a significant role 59 in distribution of alien plant species. It has also been shown that climate, slope, aspect and geology can explain the distribution patterns of alien plants (Bashkin et al. 2003; Kalkhan et al. 2007).

The occurrence of alien plant species in a particular place also either shows spatial aggregation or segregation patterns (Sebert-Cuvillier 2008; Wilson et al. 2009; Gulezian & Nyberg 2010). Such pattern of occurrence may result from disturbance regimes or availability of suitable habitats, and human agency also plays a significant role in dispersing propagules (Nathan et al. 2003; Dullinger et al. 2009). Spatially aggregated population structure may also be a result of diffusion or short-distance dispersal (McCay et al. 2009). Spread through diffusion is relatively slow, expanding with a regular pattern over short distance (Wilson et al. 2009). The other dispersal mechanism is jump dispersal or long-distance dispersal (Suarez et al. 2000; von der Lippe & Kowarik 2007; Wilson et al. 2009). With jump dispersal, propagules are randomly dispersed over long distance to establish new populations thereby covering the entire area of suitable habitat within a short time period (Nehrbass et al. 2007; Zechmeiter et al. 2007). Human settlements act as sources of introduction (Sax & Brown 2000; Alston & Richardson 2006; Niggemann et al. 2009), while trails and road networks act as corridors for dispersal (Hood & Naiman 2000; Harrison et al. 2002; Lu & Ma 2006; Kalwij et al. 2008). It is assumed that the distribution and abundance of alien plant species tends to be highest in proximity to human-inhabited areas.

Similar challenges to predicting habitats and areas susceptible to invasion have been realized for the Southern Ocean Islands. Owing to their remoteness and relatively small sizes, the Southern Ocean Islands provide ideal opportunities to investigate the processes that limit the spread of alien species (Lee & Chown 2009a). Management plans for many of the Southern Ocean Islands (e.g. Davis et al. 2007) require that distribution of alien plants be determined and habitats most susceptible to invasion be identified for appropriate and effective management (Andrew & Ustin 2009). For example, several studies have investigated the distribution of alien plant on sub-Antarctic Marion Island (Gremmen 1975; Bergstrom & Smith 1990; Gremmen & Smith 1999). While the expansion of alien plant species on Marion Island has been fairly well documented, little has been done to asses the influence of settlement (base and field huts) and other environmental variables that might explain the occurrence of alien species. Therefore this study sought to understand the correlates of the distribution of alien plants on Marion Island. I therefore determined whether the distribution of six widespread species on Marion Island shows any pattern, such that they are aggregated

60 or discrete. The main goals are to determine whether alien plants correlate with a particular variable and also to identify invasion hotspots. The point data for presence and absence for each species (see Chapter 2) were used to determine (i) minimum distance to the closest record of the same species, (ii) minimum distance to the Meteorological station (Marion base), (iii) minimum distance to the nearest field hut, (iii) which habitats are most and least invaded. The Meteorological station is the site of likely species introduction, and is situated on the east coast.

MATERIALS AND METHODS Study site The study was carried out on the sub-Antarctic Marion Island (46° 54’S, 37° 45’ E) between April 2006 and May 2007. This volcanic island is located in the Roaring Forties of the vast Southern Ocean just north of the Antarctic Convergence (Gremmen 1997). The island encompasses an area of 293 km2 and the interior mountains rise up to 1230 m above sea level (Boelhouwers et al. 2008). The interior is characterised by a number of perennial streams, rock outcrops, ridges and steep valleys. At least three types of basalt lava occur on Marion Island: the oldest grey lava, the young and dominant black lava, and scoria, which forms about 130 scoria cones (Boelhouwers et al. 2008). The island experiences an oceanic climate which is cool, wet and windy (Bergstrom & Chown 1999). However, the island has experienced rapid climate change over the last five decades, with the annual temperature increasing by 1.5 °C (le Roux & McGeoch 2008a). Marion Island has both a temporary and permanent human history. The earliest settlers on the island were sealers in the early 1800s until 1930 (Cooper 2008). After the annexation of the island by the South African government in 1947, a research station was established in 1948. Since then, various research expeditions have been made annually to island. In the early 1970s field huts were constructed around the island exclusively for research purposes (Gremmen & Smith 1999). To date, a total of nine new field huts have been erected to replace the old small huts. In addition, the construction of a new station is nearing completion. Since it’s commencement in 2003 there has been an increase in number of voyages and this is associated with increase in number of personnel and cargo containers which are major vectors of alien species (De Villiers & Cooper 2008; Lee & Chown 2009a, b).

Study species Six alien plants species were selected for analysis because they are widely distributed on the island

61 Agrostis stolonifera Agrostis stolonifera is a perennial grass originating from Western Europe and commonly used on golf courses (Beam et al. 2006). Agrostis stolonifera belongs to a genus that includes about 200 species around the world (Soreng et al. 2003). This genus is well-adapted to cool climatic regions, but can also thrive in warmer regions (Warnke 2003). Moreover, A. stolonifera can tolerate soil with high levels of salinity and acidity (Beard 1973). This species flowers abundantly, producing viable seeds (Lush 1988), but also spreads vegetatively by stolons (Reichman et al. 2006). On Marion Island Agrostis stolonifera is mostly abundant on wet coastal areas and river banks, where it competes with the indigenous Acaena magellanica (Gremmen et al. 1998).

Cerastium fontanum This is a small, herbaceous species originating from the Northern Hemisphere (temperate Asia, North Africa, Europe), but is one of the most widespread alien species on the sub- Antarctic islands (Walton 1975). Cerastium fontanum is a member of the pink family (Caryophyllaceae) and occurs in a broad array of habitat types (Wyse Jackson 2001). Stems or branches can erect up to 60 cm, and are covered with dense glandular hairs (Healy & Edgar 1980). This genus is known to produce abundant flowers throughout the growing season and it appears to spread by seeds (Gremmen 1975). Flowering begins in early April and continues until late September (Clapham et al. 1987) and seeds could live for over 40 years in the soil (Salisbury 1961).

Poa annua This small grass species is native to Europe and belongs to one of the most widely distributed family in the world (Chwedorzewska 2008). Poa annua is well adapted to a wide range of climatic conditions ranging polar to equatorial regions (Vargas & Turgeon 2003). This species is known to colonize areas altered by human activities or pioneer zones (Frenot et al. 1997). Flowering begins in early spring and continues throughout the season (Chwedorzewska 2008). The ability of Poa annua to produce large numbers of viable seeds appears to be an important feature of the biology of this species (Roberts & Stokes 1966). Seeds may remain viable for several years, forming a persistent seedbank (Lush 1989). The seeds of this genus germinate rapidly and the species has the ability to tolerate heavy mowing, thus making it difficult to control or eradicate (Lush 1989).

62 Poa pratensis Poa pratensis is a perennial grass native to Eurasia, but now a potential invasive to many sub- Antarctic islands (Walton 1975). Poa pratensis is commonly used for golf courses and sports fields (Warnke 2003). This species thrives well in cold to moderate climatic conditions (Duel 1985). As like in most species from Poa family, the new leaf blades are flat and folded (Gremmen 2004). Under favourable environmental conditions, this species can produce up to 200 seeds per panicle (Sather 1996). Although Poa pratensis produces viable seeds quite often (Walton 1975), on Marion Island the species seems to spread vegetatively rather than by seed.

Sagina procumbens Sagina procumbens is a small herb, and a native of the Northern Hemisphere. This species has become one of the most aggressive invasive species on the sub-Antarctic islands (Walton 1975). It produces small greenish flowers and spreads vegetatively and by seed dispersal (Grime et al. 1990). Under favourable conditions adult plants usually forms a large mat-like carpet (Gremmen et al. 2001). Sagina procumbens produces a profusion of seeds and once germinated, the young plant starts producing seeds within few months (Gremmen et al. 2001). On Marion Island, Sagina procumbens is very widespread colonizing nearly all major habitat types.

Stellaria media Stellaria media is a small herbaceous plant, native to Europe. At present Stellaria media has invaded a number of sub-Antarctic Islands (Walton 1975). The species hardly occupies dry ground, but prefers biotic disturbed habitats; particularly wetter environments (Walton 1975). This species can be distinguished from other species from the same genus by having single row of hairs along the internodes (Saunders 1922). Stellaria media flowers and produces an abundance of seeds, and it appears to spread by seed on Marion Island (Gremmen 2004). Under favourable conditions germination of seeds occurs throughout a year (Sobey 1981).

Vegetation types The vegetation types follow the description by Gremmen & Smith (2008). The plant communities of the island can be grouped into seven community-complexes containing twenty three habitats.

63 Coastal Saltspray Complex This community occurs up to at least 50 m of the shore, and covers an area of about 1 km² of the island. The complex is strongly influenced by saltspray, and is dominated by Crassula moschata near the shoreline, whereas Cotula plumosa in some instances is dominant, but more often is co-dominant. Bryophytes play only a minor role in these communities. Coastal Fellfield occurs on areas with relatively shallow soil with expose rock structure, and mostly dominated by Azorela selago in some cases Colobanthus kergulensis and Poa annua occur. Where lichens such as Mastodia tesselata are found close to the interdial zone, Coastal Rock Habitat occurs. Coastal Herbfield only occurs where the soil is very wet along the shoreline, whereas Saline Mires occur where the soil is wet along the coast.

Biotic Complex These complexes occur in areas strongly influenced by animals especially seals and seabirds. Soil is relatively rich in nutrient due to guano deposition from burrowing birds, penguins and seals. The complex is mostly dominated by Poa cookii, Callitriche antarctica, Cotula plumosa, Montia fontana or Poa annua. Biotic complex covers at least 4.5 km2 of the coastal lowland. The Pedestalled Tussock Grassland occurs in areas trampled by penguin and seals and bryophytes usually play a minor role in the vegetation. Because of severe trampling effect the area does not allow the growth of most species, only Calitriche antarctica and in some areas Poa annua. The bryophyte species, Marchantia berteroana, can tolerate animal trampling. Coastal Tussock Grassland occurs on relatively gently undulating areas where erosion is minimal. Bryophytes found growing in this area include, Clasmatocolea vermicularis, Leptodontium gemmascens and Brachythecium rutabulum. On upper slopes Inland Tussock Grassland occurs and the abundance of vascular plant is relatively high due to reduced trampling effect. The most common species in Tusscok Grassland include Acaena magellanica, Montia fontana, Blechnum penna-marina and Agrostis stolonifera. Of all coastal habitat communities on the island, Cotula Herbfield Habitat is dominant, occurring in large stands that can extend up to a kilometer inland, where there is minimal trampling effect.

Mire Complex Communities of oligotrophic mires occupy the lowland areas and are dominated by bryophytes species Blepharidophyllum densifolium. The most common graminoids include Agrostis magellanica, Uncinia compata and Juncus scheuchzerioides. High moisture content is the main factor that influences the mire habitat, while soil type determines the type of mire that can grow. On very wet and peat soils the Wet Mire Habitat develops and the dominant

64 vascular species are J. scheuchzerioides and Ranunculus biternatus, with the following bryophytes species: Sanionia uncinata, Distichophyllum fasciculatum and B. densifolium. Dry Mire Habitats are found on dry peat and bryophytes (Jamesoniella colorata, Racomitrium lanuginosum and Ptychomnion densifolium) are the major component of the stratum. Agrostis stolonifera and Uncinia compacta are the dominant species representing the vascular group. The Mesic Mire Habitat has relatively low soil moisture content. The most dominant bryophytes species is J. colorata although some water-loving bryophyte species such as B. densifolium can also be found. All the mire habitats make up 22 km² total area of the island.

Slope complex Well-drained lowland slopes are mostly dominated by dense sward of Blechnum penna- marina. The community is not influenced by animals, or saltspray. This is because it occurs at upper altitude slopes but not higher than 300 m. Soil moisture is the main factor that influences this community. Open Fernbrake occurs on dry shallow slopes and flat areas. The dominant species is Blechnum penna-marina wherein it grows together with lichens and other vascular plants mainly Azorella selago, Acaena magellanica and Agrostis magellanica. Closed fernbrake habitat is the most common plant community on the slope, where it forms a mat like carpet of Blechnum penna-marina with a few bryophytes and vascular plants are rare. Mesic Fernbrake, Spring and Flush, Slope Drainage Line, and Dwarf Fernbrake habitats also form important components of the Slope Complex.

Polar Desert Polar desert only occurs at high altitude, comprised of sparse communities of bryophytes and lichens. The sub-Antarctic Polar Desert is similar to those found on the Northern Hemisphere. On rare occasions A. selago can be found growing on some scoria surfaces. The most common bryophytes species include Ditrichum strictum, Bucklandiella orthotrichacea, Guembellia kidderi, Hymenoloma antarticum, Philonotis scabrifoli and Notoligotrichum australe. This community covers about 109 km2 and together with Fellfield habitat they encompass 246 km2, which is about 80% of the island surface area.

Fellfield Complex Azorella selago and cushion-forming mosses are major components of Fellfield vegetation. The soil is infertile, rich in mineral content and contains large propotion of scoria rocks. At low altitude, less than 300 m Mesic Fellfield Habitat occurs with about 50% cover plant. The Xeric Fellfield can be found at low altitude, but it normally dominates the high terrain with

65 roughly 10% plant cover. The Fellfield complex occupies about 137 km2, which is equivalent to 47% of Marion Island.

Aquatic communities These include all the open water bodies that are found on the island. The most common fresh water bodies are lakes, lava-lakelets, crater lakes, wallows and streams. The most likely plants are Agrostis magellanica, A. stolonifera, J. scheuchzerioides, and R. biternatus. Limosella australis and Ranunculus moseleyi on rare occasion has been found growing at the bottom of the ponds.

Sampling Extensive field work was conducted on Marion Island between April 2006 and May 2007. Gridline intersections were identified on a ½ minute scale across the island with the exception of the high altitude areas. The area above 700 m elevation was not surveyed because it only supports sparse communities of bryophytes and lichens. The ½ minute lat/long gridline intersections were visited and an 8 m x 8 m square was placed at the centre point to asses the present/absent of all alien plant species. The total of 348 points were identified and the following environmental variables were noted, habitat type (discussed in detail above), volcanic lava type (black, grey or scoria), altitude, slope (flat, gentle, moderate, undulating or steep) and aspect (eight directions). The position was determined using a hand-held GPS

(Garmin E-trex Vista-C®) and a digital camera was used to photograph each site. En route to the sampling sites alien plant species were recorded ad hoc whenever sighted, and a species was not recorded again until seen 10 m away. However, if a different species was observed within 10 m of recording, then it was recorded and notes taken of the environmental variables as set out above.

Data analysis The GPS coordinates for presence/absence were imported into ArcGIS 9.2 to produce the distribution map of all alien plant species on the island. The point data for each species was used to calculate the nearest distance to a population of the same species, scientific station and/or field hut using ESRI ArcGIS 9.2 ‘hawths’ tools. Generalized linear models (GLZ with a Poisson distribution and log link function, Type 3 model, see Quinn & Keough 2006) were used to examine the relative significance of elevation, slope and nearest neighbour in distribution of alien species. Because slope was insignificant it was then omitted from the second model, as was nearest neighbour because it confound with nearest distance to base and

66 field huts. For the second model, altitude, base and all field huts were selected to examine whether any of these could explain difference in plant distribution.

RESULTS Distribution patterns of species richness Scatterplots of altitude and species richness (no. species per 500 m × 500 m plot) show many sites with zeros at all altitudes (Fig. 1a). It appears that the maximum number of species declines with elevation. Therefore quantile regression was used to provide an estimate of the rate of this decline (using BLOSSOM statistical software W2008.04.02 (USGS, Fort Collins, CO, USA; Cade & Richards 2005). However, fits were poor at the 90 and 95% quantiles, perhaps because the upper quantile is curvilinear (Fig. 1a). So altitude was log-transformed (base 10) to provide a straight line upper quantile (Fig. 1b). The 0.9 quantile estimate shows a strong and significant relationship between altitude and species richness (p < 0.00001), with richness declining on average by 0.7 species per 100 m (i.e. a slope of 4.17)

In a generalized linear model using only data where species number was more than zero (i.e. zeros excluded), both habitat and vegetation type were excluded because they are subsets, and all neighbours used because the nearest neighbour is a subset of all neighbours. So, using this approach the generalized linear model indicated that both altitude and nearest neighbour are important and significant predictors of alien species richness in a given grid cell (Table 1). This model has an AIC weight of 0.851 and the next best model (e.g. including lava type) has an AICw of 0.102. The altitude and all neighbour model appeared to be the best perfoming model. Thus, the number of species of alien in an occupied cell is a declining function of altitude and increasing function of the number of neighbouring cells occupied by any alien species.

Table 1 Best fit generalized linear model (Poisson distribution, log-link function, AICw = 0.851) for alien vascular plant species richness showing the negative effect of altitude and positive effect of the presence of an alien species in a neighbouring grid square.

Model Wald Chi-square p Estimate

Altitude 10.54 0.0012 -0.0019

All neighbours 20.29 0.0073 0.064

Deviance/df = 148.5/282 = 0.527

67 8

7 t o l p

6 m

0 5 5

0 4 0 5 / s

e 3 i c e p

s 2

f o

. 1 o N 0

-1 -100 0 100 200 300 400 500 600 700 800

Altitude (m) Figure 1 a Relationship between species richness (no. species per 500 m × 500 m plot) and altitude

7 t o l

p 6

0 5 0 5

x 4 0 0 5 /

s 3 e i c e

p 2 s

f o .

o 1 N 0

-1 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0

Log altitude Figure 1 b Relationship between species richness (no. species per 500 m × 500 m plot) and altitude (logarithmic fit).

68 Distribution pattern of individual species For the purpose of these analyses, only continuous predictors were used to implement a logistic regression model. Using logit model in Statistica, binomial model with logit link function was performed. First, the occurrence (presence /absence) of species with respect to altitude, slope and nearest neighbour was examined. Except for a significant but, negative estimate on Poa annua, slope has no effect on alien plant occurrence. However, highly significant but rather weak positive estimates were found between altitude and nearest neighbour across the species. This means that occurrence of species is a function of altitude and its nearest neighbour (Table 2 see model 1).

But, how important is the distance to base and distances to all field huts? (see Fig. 2 for locality). Huts and nearest neighbour are confounded at some extent. So, to re-run the analysis slope was removed, and so was nearest neighbour, but altitude, hut distances and distance to base were included. The sign of estimate was important for model 2 (base and field huts). Positive estimates mean that the closer to base or huts the more likely that the species will be present. Negative estimates mean that the closer a site is to a hut the more likely a species is to be absent. The probability of finding Agrostis stolonifera increases with proximity to base and significantly decreases towards Katedraal hut (Table 2a). Cerastium fontanum is more likely to be found at Mixed Pickle hut and not likely to be found at Greyheaded hut (Table 2b). The positive estimate for Mixed Pickle hut means that the closer to Mixed Pickle hut the more likely that Poa annua will be present and negative for Cape Davis and Swartkop huts means closer to these huts more likely to be absent (Table 2c). Poa pratensis showed a preference for sites close to the Meteorological station (base) and is not likely to be found at any of the field huts (Table 2d). Sagina procumbens is more likely to be found at Swartkops hut but its occurrence decreases towards Rooks hut (Table 2e). The probability of finding Stellaria media is predicted to increase closer to base and Mixed Pickle hut but, but unlikely to be found at Katedraal hut (Table 2f).

Figure 2 Map showing the location of Marion base, field huts and alien plants with restricted distribition

Table 2 a Outcome of General Linear Models (binomial distribution, logit link function) for the presence/absence of Agrostis stolonifera.

Model Wald Chi-square p Estimate

Model I Altitude 26.27 0.00001 0.04 Slope 2.10 0.147 -0.23 Nearest record 22.25 0.00001 0.0016 Deviance/df = 207.6/496 = 0.419

Model II Altitude 19.75 0.00001 0.041 Base 10.41 0.0013 0.897 Cape Davis 3.12 0.077 -1.639 Greyheaded 0.0007 0.98 -0.345 Katedraal 13.74 0.0002 -3.955 Kildalkey 4.62 0.032 0.644 Mixed Pickle 1.71 0.191 4.110 Repettos 6.49 0.0108 2.033 Rooks 0.296 0.586 -5.006 Swartkop Point 0.021 0.882 -0.869 Watertunnel 0.680 0.410 5.23 Deviance/df = 200.5/488 = 0.411 70 Table 2 b Outcome of General Linear Models (binomial distribution, logit link function) for the presence/absence of Cerastium fontanum.

Model Wald Chi-square p Estimate

Model I Altitude 19.85 0.00001 0.0041 Slope 0.0025 0.959 0.0039 Nearest record 122.29 0.00001 0.0035 Deviance/df = 753.9/837 = 0.901

Model II Altitude 48.66 0.00001 0.0077 Base 2.52 0.113 -0.194 Cape Davis 2.73 0.099 -0.236 Greyheaded 3.96 0.047 -0.585 Katedraal 1.20 0.274 0.259 Kildalkey 1.58 0.209 -0.131 Mixed Pickle 7.33 0.0068 0.213 Repettos 0.216 0.642 -0.072 Rooks 0.156 0.693 0.070 Swartkop Point 1.53 0.216 -0.132 Watertunnel 2.48 0.115 0.320 Deviance/df = 878.1/829 = 1.059

Table 2 c Outcome of General Linear Models (binomial distribution, logit link function) for the presence/absence of Poa annua.

Model Wald Chi-square p Estimate

Model I Altitude 28.87 0.00001 0.0054 Slope 10.65 0.0011 -0.291 Nearest record 129.63 0.00001 0.0046 Deviance/df = 660.2/885 = 0.746

Model II Altitude 56.46 0.00001 0.010 Base 1.39 0.239 -0.133 Cape Davis 8.48 0.0036 -0.376 Greyheaded 2.31 0.129 0.283 Katedraal 0.0070 0.933 -0.021 Kildalkey 5.72 0.017 -0.271 Mixed Pickle 17.62 0.00001 0.318 Repettos 1.78 0.182 0.182 Rooks 2.50 0.114 -0.219 Swartkop Point 12.93 0.00001 -0.395 Watertunnel 0.205 0.651 0.070 Deviance/df = 825.8/877 = 0.942

71 Table 2 d Outcome of General Linear Models (binomial distribution, logit link function) for the presence/absence of Poa pratensis.

Model Wald Chi-square p Estimate

Model I Altitude 9.18 0.0025 0.024 Slope 2.51 0.113 -0.306 Nearest record 31.40 0.00001 0.0043 Deviance/df = 150.8/566 = 0.266

Model II Altitude 0.17 0.680 -0.0056 Base 10.42 0.001 1.795 Cape Davis 0.15 0.703 -20.720 Greyheaded 0.22 0.640 15.525 Katedraal 0.04 0.851 2.049 Kildalkey 0.11 0.745 3.870 Mixed Pickle 0.18 0.672 8.420 Repettos 0.09 0.770 12.483 Rooks 0.0004 0.983 -0.253 Swartkop Point 0.01 0.903 -1.340 Watertunnel 0.23 0.628 -22.010 Deviance/df = 119.5/558 = 0.214

Table 2 e Outcome of General Linear Models (binomial distribution, logit link function) for the presence/absence of Sagina procumbens.

Model Wald Chi-square p Estimate

Model I Altitude 19.65 0.00001 0.0080 Slope 1.33 0.248 0.118 Nearest record 124.39 0.00001 0.0056 Deviance/df = 581/1163 = 0.499

Model II Altitude 60.19 0.00001 0.022 Base 0.136 0.713 -0.045 Cape Davis 1.80 0.180 -0.201 Greyheaded 4.73 0.030 0.698 Katedraal 2.22 0.136 0.453 Kildalkey 0.406 0.524 -0.071 Mixed Pickle 0.0094 0.923 -0.0095 Repettos 0.539 0.463 -0.120 Rooks 11.11 0.0009 -1.193 Swartkop Point 10.58 0.0011 0.495 Watertunnel 0.017 0.897 0.022 Deviance/df = 773.9/1155 = 0.670

72 Table 2 f Outcome of General Linear Models (binomial distribution, logit link function) for the presence/absence of Stellaria media.

Model Wald Chi-square p Estimate

Model I Altitude 13.11 0.0003 0.018 Slope 0.59 0.442 -0.120 Nearest record 20.62 0.00001 0.0014 Deviance/df = 185.8/389 = 0.478

Model II Altitude 8.01 0.0047 0.017 Base 4.29 0.038 0.814 Cape Davis 1.09 0.296 -0.371 Greyheaded 0.896 0.344 -0.572 Katedraal 4.64 0.031 -2.674 Kildalkey 0.198 0.656 0.123 Mixed Pickle 7.84 0.0050 0.571 Repettos 3.20 0.074 0.987 Rooks 0.266 0.870 -0.069 Swartkop Point 0.181 0.670 0.098 Watertunnel 9.72 0.0018 1.445 Deviance/df = 184.4/380 = 0.485

These models demonstrate the significance of altitude, distance to human disturbed sites, and nearest neighbour presence in influencing patterns of distribution of the alien vascular plant species on Marion Island. Although it is clear from other work that species may show habitat preferences (such as A. stolonifera for river banks, Gremmen et al. 1998), none of the models developed here resulted in significance of habitat type as explanatory variables for the alien plant species distributions. Rather, it appears that all of the species have quite wide habitat preferences, limited perhaps locally (a scale not investigated) by conditions such as water availability, but more regionally limited only by environmental severity represented by elevation, and by human movement and disturbance (distance to base and huts) and by propagule pressure (nearest neighbour distances).

DISCUSSION The results show that the occurrence of six widespread alien species on Marion Island are a function of altitude and nearest neighbour, with vegetation type being much less important at least as far as inspection of data could reveal. Elevation was the best predictor of occurrence irrespective of species status. Overall, species richness declines exponentially with increasing altitude (Fig. 1). However, alien species exhibit high occurrences below 100 m a.s.l. and they are absent above 500 m a.s.l. This altitudinal trend could also be attributed to other 73 environmental factors. Harsh climatic conditions above 500 m might be the factor limiting the growth and establishment of alien plants. More importantly, at higher altitude the soil is dry, nutrient poor and only dotted cushions of Azorella selago can be found (Gremmen & Smith 2008; Phiri 2008). At the elevation of above 600 m Polar Desert occurs and it only supports bryophytes and lichens (Gremmen & Smith 2008). At low altitude there is a variety of vegetation communities. Collectively, the Fernbrakes, Mires, Coastal herbfield and the biotic influenced habitat represent about 90 % of the low altitude vegetation communities and are generally rich in nutrient content (Smith 2008). The decline of alien species with increasing altitude is not a new phenomenon as it has been well documented on oceanic islands (Arévalo et al. 2005) and other mainland regions (McDougall et al. 2005; Morgan & Carnegie 2009). It also mirrors the decline in indigenous diversity documented above and also shown by le Roux & McGeoch (2008b).

Clearly the proximity to the nearest neighbour is also a factor influencing occurrence of alien plants on Marion Island. It appears, then that the presence of an alien species in a grid cell increases the likelihood that the neighbouring grid will also be occupied by an alien plant. The significance of distance to the nearest population is clearly a consequence of both disturbance and propagule pressure. The results show that alien plant species on Marion Island exhibit a high spatial aggregation where they occur. A similar pattern was observed along Marion Island’s rivers where the distributions of Agrostis stolonifera and Sagina procumbens are spatially aggregated (Phiri 2008). The diversity of suitable habitat types at low altitude is usually an important factor determining the distribution pattern of alien plants. Hamill & Wright (1986) suggested that species are often non-randomly distributed in the wider landscape but, will be distributed according to their habitat preferences. Studies in other ecosystems have also reported that habitat preference is an important factor underpinning alien species distribution (Mandák & Pyšek 1998; Jakobs et al. 2004; Chytrý et al. 2005). However, at Marion Island, habitat preference seems to be a less notable feature determining species richness and individual distribution of alien vascular plant species. This may reflect both the generalized weedy nature of the species (see Frenot et al. 2005), as well as the fact that in many species the distributions have not yet reached equilibrium, i.e. they are still expanding (see Chapter 2).

The results from the second set of models indicate that species occurrence is influenced by distance to the base and field huts in most species. The prediction was that most alien species would be found in the vicinity of the base because it is characterized by high human traffic

74 which is linked with considerable disturbance and dispersal of alien plants (Gremmen & Smith 1999; Chown et al. 2008). However, the model indicates that the base was only significantly associated with the occurrence of Agrostis stolonifera, Poa pratensis and Stellaria media but, it had no effect on the occurrence of widespread species such as Cerastium fontanum, Poa annua and Sagina procumbens. Gremmen et al. (2003) similarly found no significant relationship between occurrence of alien species and distance to base. The lack of influence of distance to the base on these three species may be a consequence of them having reached an equilibrium spatial distribution on the island (at the resolution investigated) following very rapid increases in range (see Chapter 2).

Although the analyses could not reveal the significant influence of habitat type on distributions, the maps of species distribution (see Chapter 2) show that the occurrence of Agrostis stolonifera, Poa pratensis and Stellaria media is restricted to the eastern part of the island closer to base and suggest that the factor limiting the occurrence or the abundance of C. fontanum, and P. annua around Meteorological station may be habitat preference rather than disturbance regime. The wet mire surrounding the base might not be an ideal habitat for the majority of alien species. Cerastium fontanum, Poa annua and Stellaria media were at greater frequency at the vicinity of Mixed Pickle hut. The proximity of the hut to the breeding colony of seals and high density of burrowing birds on fernbrake slope, would to some extent explain the occurrence of these species closer to the hut. Sagina procumbens was the only common species around Swartkop and Greyheaded huts and this may be attributed to its ability to colonize various habitats on Marion Island (Gremmen 2001). The significant but negative estimate for P. annua at Swartkop hut is likely to be the effect of unsuitable Salt-spray habitat.

The models also show that the likelihood of finding alien species decreases with increasing proximity to Katedraal hut, the only hut located at high altitude. Several studies have revealed that degree of disturbance, visitation and propagule pressure facilitate invasion by alien plants (Williamson & Harrison 2002; Colautti et al. 2006; Britton-Simons & Abbott 2008, Eschtruth & Battles 2009). This, however, may not be the case with Katedraal hut because harsh climatic conditions there are likely to be the factor preventing the germination and growth of alien species at this site. At low altitude the distribution of alien plants is influenced by disturbance regime and propagule pressure. Large numbers of seals and high density of sea birds are responsible for such disturbances at lowland coastline communities (Bester et al. 2003). Human trampling especially walking tracks facilitates the establishment and spread of

75 alien species on Marion Island (Gremmen et al. 2003). Scott and Kirkpatrick (1994) also documented the negative impact of human trampling and tracks association with the establishment of alien species on sub-Antarctic Macquarie Island. To date, huts are regularly visited by a small, annually rotated group of researchers (Gremmen et al. 2003) but, the highest visitation occurs during annual relief. Such visits aid propagule dissemination and disturbance via trampling. The occurrence of alien species at field huts might have occurred as a series of jump dispersals during hut construction and with the helicopters used for resupply. This has been suggested for an alien slug species, Deroceras panormitanum (see Lee et al. 2009).

In conclusion, this study has demonstrated that alien species richness on Marion Island declines sharply with increasing elevation, and that the distribution of the most widespread species is spatially aggregated. The surroundings of the Meteorological station and Mixed Pickle hut exhibit high richness and presence likelihood of invasiveness. Although the higher elevations are free of alien and invasive vascular plant species (as is also true of invasive invertebrates, see e.g. Gabriel et al. 2001; Lee et al. 2009), it would be an error to assume that high altitude sites are not susceptible to invasion, as changing climates (le Roux & McGeoch 2008a) are likely to improve the favourability of high altitude sites for alien species.

76 REFERENCES

Alpert, P., Bone, E. & Holzapfel, C. 2000. Invasiveness, invasibility and the role of environmental stress in the spread of non-native plants. Perspectives in Plant Ecology, Evolution and Systematics 3, 52-66.

Alston, K.P. & Richardson, D.M. 2006. The roles of habitat features, disturbance, and distance from putative source populations in structuring alien plant invasions at the urban/wildland interface on the Cape Peninsula, South Africa. Biological Conservation 132, 183-198.

Andrew, M.E. & Ustin, S.L. 2009. Habitat suitability modelling of an invasive plant with advanced remote sensing data. Diversity and Distributions 15, 627-640.

Arévalo, J.R., Delgado, J.D., Otto, R., Naranjo, A., Salas, M. & Fernández-Palacios, J.M. 2005. Distribution of alien vs. native plant species in roadside communities along an altitudinal gradient in Tenerife and Gran Canaria (Canary Islands). Perspectives in Plant Ecology, Evolution and Systematics 7, 185-202.

Bashkin, M., Stohlgren, T.J., Otsuki, Y., Lee, M., Evangelista, P. & Belnap, J. 2003. Soil characteristics and plant exotic species invasions in the Grand Staircase- Escalante National Monument, Utah, USA. Applied Soil Ecology 22, 67-77.

Beam, J.B., Barker, W.L. & Askew, S.D. 2006. Selective creeping bentgrass (Agrostis stolonifera) control in cool-season turfgrass.Weed Technology 20, 340-344.

Beard, J.B. 1973. Turfgrass: Science and Culture. Prentice-Hall, Englewood Cliffs, New Jersey.

Becker, T., Dietz, T. Billeter, R., Buschmann, H. & Edwards, P.J. 2005. Altitudinal distribution of alien plant species in the Swiss Alps. Perspective in Plant Ecology, Evolution and Systematics 7, 173-183.

Bergstrom, D.M. & Chown, S. L. 1999. Life at the front: history, ecology and change on southern ocean islands. Trends in Ecology and Evolution 14, 472-477.

77 Bergstrom, D.M. & Smith, V.R. 1990. Alien vascular flora of Marion and Prince Edward Islands: new species, present distribution and status. Antarctic Science 2, 301-308.

Bester, M.N., Ryan, P.G. Dyer, B.M. 2003. Population numbers of fur seals at Prince Edward Islands, Southern Ocean. African Journal of Marine Science 25, 549-554.

Britton-Simons, K.H. & Abbott, K.C. 2008. Short-and long-term effect of disturbance and propagule pressure on a biological invasion. Journal of Ecology 96, 68-77.

Cade, B. S. & Richards, J. D. 2005. User manual for BLOSSOM statistical software. USGS, Fort Collins, CO.

Chown, S.L, Lee, J.E. & Shaw, J.D. 2008. Conservation of Southern Ocean Islands: invertebrates as exemplars. Journal of Insects Conservation 12, 277-291.

Clapham, A.R., Tutin, T.G. & Moore, D.M. 1987. Flora of the British Isles. Cambridge University Press, Cambridge.

Chytrý, M., Jarosík, V., Pyšek, P., Hájek, O., Knollová, I., Tichy, L. & Danihelka, J. 2008a. Separating habitat invasibility by alien plants from the actual level of invasion. Ecology 89, 1541-1553.

Chytrý, M., Maskell, L.C., Pino, J., Pyšek, P., Vilà, M., Font, X. & Smart, S.M. 2008b. Habitat invasions by alien plants: a quantitative comparison among Mediterranean, subcontinental and oceanic regions of Europe. Journal of Applied Ecology 45, 448-458.

Chytry, M., Pyšek, P., Tichy, L., Knollová, I. & Danihelka, J. 2005. Invasions by alien plants in the Czech Republic: a quantitative assessment across habitats. Preslia 77, 339-354.

78 Chytrý, M., Pyšek, P., Wild, J., Pino, J., Maskell, L.C. & Vilà, M. 2009. European map of alien plant invasions based on the quantitative assessment across habitats. Diversity and Distributions 15, 98-107.

Chwedorzewska, K.J. 2008. Poa annua L. in Antarctic: searching for the source of introduction. Polar Biology 31, 263-268.

Colautti, R.I. Grigorovich, I.A. & MacIsaac, H.J. 2006. Propagule pressure: a null model for biological invasions. Biological Invasions 8, 1023-1037.

Cooper, J. 2008. Human History. In: Chown S.L. & Froneman, P.W. (Eds.) The Prince Edward Islands. Land-Sea Interactions in a Changing Ecosystem. African Sun Media, Stellenbosch, pp. 331-350.

Davies, S.J., Chown, S.L. & Joubert, L.S. 2007. Renewed management system and provisions for South Africa’s sub-Antarctic islands. Papers and Proceedings of Royal Society of Tasmania 14, 115-120.

Denslow, J.S. 2003. Weeds in paradise: Thoughts on the invasibility of tropical islands. Annals of the Missouri Botanical Garden 90, 119-127.

De Villiers, M. & Cooper, J. 2008. Conservation and management. In: Chown, S.L & Froneman, P.W. (Eds.) The Prince Edward Islands. Land Sea Interactions in Changing Ecosystem. African Sun Media, Stellenbosch, pp.301-330.

Duell, R. W. 1985. The bluegrasses. In: Heath, M. E., Barnes, R. F. & Metcalfe, D. S. (Eds.) Forages, The Science of Grassland Agriculture. Iowa State University, Ames, IA, pp. 188- 197.

Dullinger, S., Kleinbauer, I., Peterseil, J., Smolik, M. & Essl, F. 2009. Niche based distribution modeling of an invasive alien plant: effect of population status, propagule pressure and invasive history. Biological Invasions 11, 2401-2414.

79 Elith, J. & Leathwick, J.R. 2009. Species distribution models: Ecological explanation and prediction across space and time. Annual Review of Ecology, Evolution, and Systematics 40, 677-697.

Elton, C.S. 1958. The Ecology of Invasions by Animals and Plants. Methuen, London, UK.

Eschtruth, A.K, & Battles, J.J. 2009. Assessing the relative importance of disturbance, herbivory, diversity, and propagule pressure in exotic plant invasion. Ecological Monographs 79, 265-280.

Evangelista, P.H., Kumar, S., Stohgren, T.J., Jarnevich, C.S, Crall, A.W., Norman III, B.J & Barnett D.T. 2008. Modelling invasion for habitat generalist and specialist plant species. Diversity and distributions 14, 808-817.

Gabriel, A.G.A., Chown, S.L., Barendse, J., Marshall, D.J., Mercer, R.D., Pugh, P.J.A., et al. 2001. Biological invasions on the Southern Ocean islands: the collembola of Marion Island as a test of generalities. Ecography 24, 421-430.

Gassó, N., Sol, D., Pino, J., Dana, E.D. Lloret, F., Sanz-Elorza, Sobrino, E. & Vilà, M. 2009. Exploring species attributes and site characteristics to assess plant invasions in Spain. Diversity and Distributions 15, 50-58.

Gimeno, I., Vilà, M. & Hulme, P.E. 2006. Are islands more susceptible to plant invasion than continents? A test using Oxalis pes-carpae L. in the western Mediterranean. Journal of Biogeography 33, 1559-1565.

80 Gremmen, N.J.M. 1975. The distribution of alien vascular plants on Marion and Prince Edward Islands. South African Journal of Antarctic Research 5, 25-30.

Gremmen, N.J.M. 2004. Management of alien vascular plants on Marion and Prince Edward Islands: an Integrated Approach. Unpublished report. Data Analyse Ecologie, Diever, The Netherlands, 1-30.

Gremmen, N.J.M., Barendse, J. & Orr, I. 2001. Invasion and eradication of Sagina procumbens L. (Procumbent pearlwort) on Gough Island. Aliens 14, 19-20.

Gremmen, N.J.M. & Smith, V.R. 1999. New records of alien vascular plants from Marion and Prince Edward Islands, sub-Antarctic. Polar Biology 21, 401-409.

Gremmen, N.J.M. & Smith, V.R. 2008. Terrestrial vegetation and dynamics. In: Chown S.L. & Froneman, P.W. (Eds.) The Prince Edward Islands. Land-Sea Interactions in a Changing Ecosystem. African Sun Media, Stellenbosch, pp. 215-244.

Gremmen, N.J.M., Smith, V.R. & Van Tongeren, O.F.R. 2003. Impact of trampling on the vegetation of sub-Antarctic Marion Island. Arctic, Antarctic, and Alpine Research 35, 442- 446.

Grime, J.P. Hodgson, J.G. & Hunt, R. 1990. The Abridged Comparative Plant Ecology. Chapman and Hall, London.

Gulezian, P.Z. & Nyberg, D.W. 2010. Distribution of invasive plants in a spatially structured urban landscape. Landscape and Urban Planning 95, 161-168.

81 Hamill, D.N, Wright, S.J. 1986. Testing the dispersion of juveniles relative to adults: a new analytic method. Ecology 67, 952–957.

Harrison, S., Hohn, C. & Ratay, S. 2002. Distribution of exotic plants along roads in a peninsular nature reserve. Biological Invasions 4, 425-430.

Healy, A.J.; Edgar, E. 1980. Flora of New Zealand, Volume III. Adventive cyperaceous, petalous and spathaceous monocotyledons. Government Printer, Wellington, New Zealand.

Hood, W.G, Naiman, R.J.2000.Vulnerability of riparian zones to invasion by exotic vascular plants. Plant Ecology 148, 105-114.

Jacquemyn, H., Looy, K.V., Breyne, P. & Honnay, O. 2010. The Meuse River as a corridor for range expansion of the exotic plant species Sysymbrium austriacum: evidence for long- distance seed dispersal. Biological Invasions 12, 553-561.

Jakobs, G., Weber, E. & Edwards, P.J. 2004. Introduced plants of the invasive Salidago gigantean (Asteraceae) are larger and grow denser than conspecifics in the native range. Diversity and Distributions 10, 11-19.

Kalkhan, M.A., Stafford, E.J., Woodly, P.J. & Stohlgren, T.J. 2007. Assessing exotic plant species invasions and associated soil characteristics: A case study in eastern Rocky Mountain National Park, Colorado, USA, using the pixel nested plot design. Applied Soil Ecology 35, 622-634.

Kalwij, J.M., Milton, S.J. & McGeoch, M.A. 2008. Road verges as invasion corridors? A spatial hierarchical test in an arid ecosystem. Landscape Ecology 23, 439-451.

Lee, JE. & Chown, S.L.2009a. Breaching the dispersal barrier to invasion: quantification and management. Ecological Applications 19, 1944-1957.

Lee, J.E. & Chown, S.L. 2009b. Constructing an invasive pathway in Antarctica. Antarctic Science 21, 471-475.

82 Lee, J.E., Janion, C., Marais, E., Jansen van Vuuren, B. & Chown, S.L. 2009. Physiological tolerances account for range limits and abundance structure in an invasive slug. Proceedings of the Royal Society of London B 275, 1459-1468. le Roux, P.C. & McGeoch, M.A. 2008a. Changes in climate extremes, variability and signature on sub-Antarctic Marion Island. Climate Change 86, 309-329. le Roux, P.C. & McGeoch, M.A. 2008b. Rapid range expansion and community reorganization in respond to warming. Global Change Biology 14, 2950-2962.

Lonsdale, W.M. 1999.Global patterns of plant invasions and the concept of invasibility. Ecology 80, 1522-1536.

Lu, Z. & Ma, K. 2006. Spread of the exotic croftonweed (Eupatorium adenophorum) across southwest China along roads and streams. Weed Science 54, 1068-1072.

Lush, W.M. 1988. Biology of Poa annua in a temperate zone golf putting green (Agrostis stolonifera/Poa annua). Journal of Applied Ecology 25, 977-988.

Lush, W.M. 1989. Adaptation and differentiation of golf course populations of annual bluegrass (Poa annua L.). Weed Science 37, 54-59.

Mandák, B. & Pyšek, P. 1998. History of spread and habitat preferences of Atriplex sagittata (Chenopodiaceae) in the Czech Republic. In: Starfinger, U., Edwards, K., Kowarik,I. & Williamson, M.(Eds.) Plant Invasions: Ecological Mechanisms and Human Responses, Backhuys Publishers, Leiden, pp. 209-224.

McCay, T.S., McCay, D.H., Caragiulo, A.V. & Mandel, T.L. 2009. Demography and distribution of the invasive Rhamuns cathertica in habitats of a fragmented landscape. Journal of the Torrey Botanical Society 136, 110-121.

McDougall, K.L., Morgan, J.W., Walsh, N.E. & Williams R.J. 2005. Plant invasions in the treeless vegetation of the Australian Alps. Perspectives in Plant Ecology, Evolution and Systematics 7, 159-171.

83 Morgan, J.W. & Carnegie, V. 2009. Backcountry huts as introduction points for invasion by non-native species into sub-alpine vegetation. Arctic, Antarctic, and Alpine Research 41, 238- 245.

Nathan, R., Schurr, F.M., Spiegel, O., Steinitz, O., Trakhtenbrot, A. Tsoar, A. 2008. Mechanisms of long-distance seed dispersal. Trends in Ecology and Evolution 23, 638-647.

Nehrbass, N., Winkler, E. Müllerová, J., Pergl, J. & Pysk, P. 2007. A simulation model of plant invasion: long-distance dispersal determines the pattern of spread. Biological Invasions 9, 383-395.

Nielsen, C., Hartvig, P. & Kollmann, J. 2008. Predicting the distribution of the invasive alien Heracleum mantegazzianum at two different spatial scales. Diversity and Distributions 14, 307-317.

Niggemann, M., Jetzkowitz, J., Brunzel, S., Wichmann, M.C. & Bialozyt, R. 2009. Distribution patterns of plants explained by human movement behaviour. Ecological Modelling 220, 1339-1346.

Pauchard, A. & Alaback, P.B. 2004. Influence of elevation, land use, and landscape context on patterns of alien plant invasions along roadsides in protected areas of south-central Chile. Conservation Biology 18, 238-248.

Phiri, P.P. 2008. Species occupancy, distribution and abundance: indigenous and alien invasive vascular plants on sub-Antarctic Marion Island. M.Sc. Thesis, University of Stellenbosch, South Africa.

Pyšek, P. & Richardson, D.M. 2006. The biogeography of naturalization in alien plants. Journal of Biogeography 33, 2040-2050.

Quinn, G.P. & Keough, M.J. 2006. Experimental Design and Data Analysis for Biologists. Cambridge University Press, Cambridge.

84 Reichman, J.R. Watrud, L.S., Lee, E.H., Burdick, C.A., Bollman, M.A., Storm, M.J., King, G.A. & Mallory-Smith, C. 2006. Establishment of transgenic herbicide-resistant creeping bentgrass (Agrostis stolonifera L.) in nonagronomic habitats. Molecular Ecology 15, 4243- 4255.

Richardson, D.M., Holmes, P.M., Esler, K.J., Galatowitsch, S.M., Stromberg, J.C., Kirkman, S.P., Pyšek, P. & Hobbs, R.J. 2007. Riparian vegetation: degradation, alien plant invasions, and restoration prospects. Diversity and Distributions 13, 126-139.

Richardson, D.M, Pyšek, P.2006. Plant invasions: merging the concepts of species invasiveness and community invasibility. Progress in Physical Geography 30, 409-431

Roberts, H.A. & Stokes, F.G. 1966. Studies on the weeds of vegetable crops. VI. Seed populations of soil under commercial cropping. Journal of Applied Ecology 3, 181-190.

Salisbury, E. 1961. Weeds and Aliens. Collins, London.

Sather, N. 1996. Element Stewardship Abstract for Poa pratensis, Poa compressa Kentucky Bluegrass, Canada Bluegrass. The Nature Conservancy. Arlington, VA.

Saunders, E.R. 1922. The leaf skin theory of the stem: a consideration of certain anatomico physiological relations in the spermophyte shoot. Annals of Botany 36, 135-165.

Sax, D.F. & Brown, J.H. 2000. The paradox of invasion. Global Ecology and Biogeography 9, 363-371.

Sebert-Cuvillier, E., Simon-Goyheneche, V., Paccaut, F., Chabrerie, O., Goubet, O. & Decocq, G. 2008. Spatial spread of an alien tree species in a heterogeneous forest landscape: a spatially realistic simulation model. Landscape Ecology 23, 787-801.

85 Scott, J. J. & Kirkpatrick, J.B., 1994. Effects of human trampling on the sub-Antarctic vegetation of Macquarie Island. Polar Record 30, 207-220.

Silva, L. & Smith, C.W. 2004. A Characterization of the non-indigenous flora of the Azores Archipelago. Biological Invasions 6, 193-204.

Smith, V.R. 2008. Terrestrial and freshwater primary production and nutrient cycling. In: Chown S.L. & Froneman, P.W. (Eds.) The Prince Edward Islands. Land-Sea Interactions in a Changing Ecosystem. African Sun Media, Stellenbosch, pp. 181-214.

Smolik, M.G., Dullinger, S., Essl, F., Kleinbauer, I., Leitner, M., Peterseil, J., Stadler, L.M. & Vogl, G. 2010. Integrating species distribution models and interacting particle systems to predict the spread of an invasive alien plant. Journal of Biogeography 37, 411-422.

Sobey, D.G. 1981. Biological flora of the British Isles. Stellaria media (L.) Vill. Journal of Ecology 69, 311-335.

Soreng, R.J, Peterson, P.M., Davidse, G., Judziewicz, E.J., Zuloaga, F.O. Filgueiras, T.S. & Morrone, O. 2003. Catalogue of new world grasses (Poaceae): IV. Subfamily Pooideae. Contributions from the United States National Herbarium 48, 42-89.

Suarez, A.V., Holway, D.A. & Case, T.J. 2000. Pattern of spread in biological invasions dominated by long-distance jump dispersal: Insight from Argentine ants. Proceedings of the National Academy of Sciences of the U.SA. 98, 1095-1100.

Thuiller, W., Midgley, G.F., Rouget, M. & Cowling, R.M. 2006. Predicting patterns of plant species richness in megadiverse South Africa. Ecograghy 29, 733-744.

Truscott, A.M., Palmer, S.C.F., Soulsby, C. & Hulme, P.E. 2008. Assessing the vulnerability of riparian vegetation to invasion by Mimulus guttatus: relative importance of biotic and abiotic variables in determining species occurrence and abundance. Diversity and Distributions 14, 412-421.

Vargas, J. M., & Turgeon, A. J. 2003. Poa annua: Physiology, Culture and Control of Annual Bluegrass. Wiley, Hoboken, New Jersey.

86 Walter, J., Essl, F., Englisch, T. & Kiehn, M. 2005. Neophytes in Austria: habitat preferences and ecological effects. Neobiota 6, 13-25. von der Lippe, M.& Kowarik, I. 2007. Long-distance dispersal of plants by vehicles as a driver of plant invasions. Conservation Biology 21,986-996.

Walton, D.W.H. 1975. European weeds and other alien species in the sub-Antarctic. Weed Research 15, 271-282.

Warnke, S.E. 2003. Creeping bentgrass (Agrostis stolonifera L.). In: Casler, M.D., Duncan, R.R (Eds.) Turfgrass Biology, Genetics, and Breeding. Wiley, Hoboken, pp. 175-185.

Williamson, J. & Harrison, S. 2002. Biotic and abiotic limits to the spread of exotic revegetation species. Ecological Applications 12, 40-51.

Wilson, J.R.U. Dormontt, E.E. Prentis, P.J., Lowe, & Richardson, D.M. 2009. Something in the way you move: dispersal pathways affect invasion success. Trends in Ecology and Evolution 24, 137-144.

Wilson, J.R.U., Richardson, D.M., Rouget, M., Procheİ, ğ., Amis, M.A., Henderson, L. & Thuiller, W. 2007. Residence time and potential range: crucial considerations in modelling plant invasions. Diversity and Distributions 13, 11-22.

Wyse Jackson, M.B. 2001. Typifications and new nomenclatural combinations in Nordic Cerastium fontanum taxa (Caryophyllaceae). Nordic Journal of Botany 20, 531-535.

Zechmeiter, H.G. Dietmar, M. & Milasowszky, N. 2007. Spatial distribution patterns of Rhynchostegium megapolitaum at the landscape- an expanding species? Applied Vegetation Science 10, 111-120.

Zhu, L., Sun, O., Sang, W., Li, Z. & Ma, K. 2007. Predicting the spatial distribution of an invasive plant species (Eupatorium adenophorum) in China. Landscape Ecology 22, 1143- 1154.

87 Chapter 4 MANAGEMENT RECOMMENDATIONS

INTRODUCTION Alien species and their control are significant conservation concerns that are receiving much attention globally. Once established, alien plants are difficult, and in most cases, expensive to control or eradicate (Sheley et al. 1999). Control entails continued action to reduce the abundance of the species concerned (Nehring & Hesse 2008). Eradication involves complete removal of the whole population from the specific area, and the larger the area invaded the more difficult the task (Hulme 2006). Both tasks require considerable investment. In consequence, the best strategy to address alien plants invasions is to prevent the introduction of non-indigenous species. Preventing establishment of alien plants in a new region is a far more cost effective strategy and therefore, more desirable than actions undertaken after introduction (Leung et al. 2005). However, where alien plants have already established they need appropriate methods for control (Byers et al. 2002). To date, no single approach has been proven in effective control of alien plants, and as a result integrated control is considered the best strategy. Integrated control combines a number of approaches, including early detection, and eradication, mechanical control, chemical control, biological control and rehabilitation (Courchamp et al. 2003; Clout & de Poorter 2005; Sheppard et al. 2006; Esler et al. 2010). Early detection and eradication is often recommended because alien plants expand their range usually in an exponentially fashion after a period of delay (Clout & De Poorter 2005). For established alien plant invasions, knowing the extent of occurrence and the rate of expansion is critical for prioritizing management and control. Many invasive alien species have been eradicated worldwide, preventing impacts on biological diversity (Simberloff 2003).

Conservation implications for sub-Antarctic Islands Sub-Antarctic islands are geographically and climatically isolated from continental landmasses and they present substantial environmental challenges for the growth and development of any foreign propagule (Convey et al. 2005). However, the invasion of both plants and animals has taken place, some with far reaching impacts on indigenous species and ecosystem processes (Costin & Moore 1960; Gremmen et al. 1998; Chown & Klok 2001; Bergstrom et al. 2009; Phiri et al. 2009). In most cases alien plants are introduced unintentionally to the islands, and Chown et al. (1998) demonstrated a correlation between alien species and numbers of human visitors over the last two centuries. Many species were

88 introduced by early inhabitants of the islands during sealing era (Copper 2008). Despite increased knowledge about introduction pathways to many Southern Ocean islands (e.g. Lee & Chown 2009a), introduction of alien plant species has continued to occur (De Villiers et al. 2006). For instance access to Prince Edward Island is limited and visitation is infrequent (Ryan et al. 2003). Despite this, several plant species have been introduced to this island, including Sagina procumbens, Cerastium fontanum and Poa annua (Gremmen & Smith 1999, 2008). Other recent introductions include Sagina procumbens on Gough Island in 1998 (Gremmen et al. 2000) and Cardamine hirsuta discovered at South Georgia in 2002 (Pasteur & Walton 2006). Propagules can become attached to clothing and equipment, and this includes work boots, camera tripods and daypacks previously used elsewhere during field work (Whinam et al. 2005; Lee & Chown 2009b). Cargo and food supplies can act as vectors for the introduction of alien species (Curry et al. 2005; Whinam et al. 2005, Lee & Chown 2009a). Cargo, containers and cargo nets used by helicopter and resupply vessels are a potential pathway for inter island transfer by moving seeds from one island to the other i.e. Gough Island to Marion Island (Gremmen et al. 2001).

Among all major sub-Antarctic islands, only Pingouins (Crozet archipelago) and McDonald islands remain free from alien plants (Jenkin 1997; Chown et al. 1998; Shaw et al. 2010). The alien species richness of each sub-Antarctic island varies considerably (Frenot et al. 2005). For example, Possession Island supports 101 alien plant species while Marion Island has 17 alien plant species despite being much larger in size. Of the 284 alien plant species occurring across the Southern Ocean Islands (Shaw et al. 2010), Poa annua is the only species found in all major sub-Antarctic islands (Frenot et al. 2005). However species such as Agrostis stolonifera, Cerastium fontanum, Poa pratensis, Rumex acetocella, Sagina procumbens and Stellaria media are widely distributed across the sub-Antarctic regions but most are restricted to few localities on the island they have invaded (Frenot et al. 2005). On Marion Island, le Roux & McGeoch (2008) found that most of the indigenous vascular plants have been increasing their altitudinal ranges since the first records in the 1960s. So, it is also likely that changing climate might create suitable conditions enabling restricted species to expand their range and potentially colonize high elevation habitats.

Although the sub-Antarctic islands are governed by many different countries, most of these islands are nature reserves of varying status (De Villiers et al. 2006). The major island groups are governed as follows, Prince Edward and Marion Islands are South African, Heard and McDonald Islands are Australian, South Georgia and the South Sandwich Islands are British,

89 Iles Kerguelen and Iles Crozet are French, Bouvetoya is Norwegian and both the Auckland Islands and Campbell Islands belong to New Zealand (De Villiers 2006). Some of these island groups have been declared as World Heritage Areas (Chown et al. 2001; De Villers et al. 2006) and some are classified as Special Nature Reserves (Davis et al. 2007). There is no specific international legislation agreement that govern these islands, however most islands are territories of nations that have ratified the Convention on Biological Diversity (Chown et al. 2008). Regardless of different legislation among the countries that govern the islands, alien management and control strategies form part of the conservation or management plans for most of the islands. For example, a plan for the eradication of rabbits and rodents on sub- Antarctic Macquarie Island was drawn up and implemented (Macqure Island pest eradication plan 2009). There have been successful eradication programs for alien vertebrates on several other islands (Bester et al. 2000; Chapuis et al. 2001; Towns & Broome 2003). A set of management actions for alien vascular plant on the Prince Edward Islands (Gremmen 2004) has been written and put in place as part of the Special Nature Reserve’s Management Plan (Anonymous 1996).

Prioritizing control and eradication on Marion Island Marion Island’s natural biota, like other sub-Antarctic islands, is at threat from invasive alien plants (see De Villiers & Cooper 2008). Several alien species on Marion Island are already well-established and increasing their range, while some are still restricted to their point of introduction. Moreover, attempts have been made on Marion Island to eradicate localized alien plants. Eradication of Agrostis gigantea at the vicinity of meteorological station has been on-going for the past few years and the population has been greatly reduced in size. Attempts to eradicate a small isolated patch of Agropyron repens at Ships Cove have not been as successful, as the population appears to be persisting through resprouting after treatment. To improve the prioritization of control, a systematic approach to identifying the species most likely to be successfully eradicated or controlled is required. A start at doing so was made by Gremmen (2004) based on the systematic assessment procedure developed by Hiebert (1997). However, at the time, an explicit assessment of the distribution and number of populations of the alien vascular plant species had not been completed for several years (see Gremmen & Smith 1999). In consequence, the assessment by Gremmen (2004) can be considered an excellent first start, but incomplete owing to the lack of appropriately modern data on distribution and abundance. Therefore, this final chapter of the thesis provides a re-assessment of the control priorities for the alien vascular plant species of the Prince Edward Islands based on the information provided elsewhere in the work.

90 SPECIES RANKED ACCORDING TO THEIR PRIORITIZATION FOR ERADICATION The system of prioritizing alien plant species for management is based on Hiebert (1997) and Gremmen (2004) as shown below. Not all the criteria were given equal weight, so each criterion was weighted according to its importance for prioritizing eradication as indicated by the variable scores for each criterion. The maximum possible score varies from 5 to 25 and the minimum score is zero. For each species the criterion scores were then summed to produce the total score to rank the species for control. Because the highest scores are associated with desirable eradication characteristics, species with the highest total score should be prioritized for control or eradication. Because of the difficulties involved in quantifying the actual level of effort required for control, and the side effects of treatment, it is assumed that species with few and small populations would require least effort for control and the side-effects would be smallest.

Criterion (element) of the prioritization system 1. Number of populations (sites) 1 = 5 or more 15 = 2-4 25 = 1

2. Aerial extent of populations / size of population 1 = > 1000 m² 2 = 100-1000 m² 3 = 10-100 m² 5 = < 10 m²

3. Seed banks 0 = Seeds forming persistent seedbank in the soil 5 = Seeds viable in the soil for 2-3 years 15 = Seeds viable in the soil for 1 year or less

4. Vegetative regeneration 0 = Any part is a viable propagule 5 = Sprout from roots or stumps 15 = No resprouting following removal of aboveground growth

5. Level of effort required 1 = Repeated chemical or mechanical control measures required 5 = One or two chemical or mechanical treatments required 10 = Can be controlled with one chemical treatment 15 = Effective control can be achieved with mechanical treatment

6. Abundance and proximity of propagules 0 = Many sources of propagules on the island 5 = Few sources of propagules near the sites, but these are readily dispersed

91 10 = Few sources of propagules near the sites, but these are not readily dispersed 15 = No sources of propagules are in close proximity

7. Side effects of chemical/mechanical control 0 = Control measures will cause major impact to community 5 = Control measures will cause moderate impact to community 15 = Control measures will cause little or no impact on community

8. Known level of impact in natural areas 0 = Not known to cause impact in other natural area 1 = Known to cause impact in natural areas, but in other habitat and different climate 3 = Known to cause low impact in natural areas in similar habitats and climate zones 5 = Known to cause moderate impact in natural areas in similar habitat and climate 10 = Known to cause high impact in natural areas in similar habitats and climate

Outcomes: priorities for control of alien plants at the Prince Edward Islands The scoring outcome for each of the species considered here is provided in Tables 1 and 2, with the first table indicating the area of occupancy and number of populations, for Marion Island and for Prince Edward Island (the latter based on unpublished information collected by S.L. Chown, P.G. Ryan, J.D. Shaw and others in 2008-2010 and on Ryan et al. 2003). These data then provide the information for the initial scoring for criteria 1 and 2, whilst the assessments for the remainder of the criteria are based on the literature as indicated in Table 2. Following these semi-quantitative assessments each species is then discussed separately.

PRIORITIZING CONTROL AND ERADICATION ON MARION ISLAND High priority species Agropyron repens This species is restricted to one site at Ship’s Cove occupying approximately 250 m² (Gremmen 2004). The patch is within walking distance (approximately 3 km) of the main research base. Over 12 months, between April 2006 and April 2007 glyphosate applications of herbicide were sprayed directly on to the leaves of the entire population. However, it resprouted four months after the treatment. The problem really amounted to follow-up and the control programme is now underway again with success. Although some underground materials were dug up, mechanical removal may still provide a solution. Given the size of the patch, mechanical removal of Agropyron repens is feasible involving cutting the above ground material and digging out and removing all of rhizomatous material from the soil.

92 Table 1 The number of populations and area of occupancy for each of the species of alien vascular plants found on the Prince Edward Islands.

Species Marion Island Prince Edward Island No. of records Occupancy (m²) No. of records Occupancy (m²)

Agrostis 162 11 250 000 Not present Not present stolonifera Agropyron 1 250 000 Not present Not present repens Cerastium 503 43 000 000 14 2 250 000 fontanum Festuca 2 500 000 Not present Not present rubra Juncus 4 750 000 Not present Not present effusus Luzula cf. 1 250 000 Not present Not present multiflora Poa 555 40 250 000 28 3 000 000 annua Poa 233 7 500 000 Not present Not present pratensis Potamogeton 1 250 000 Not present Not present nodosus Rumex 2 500 000 Not present Not present acetosella Sagina 842 37 750 000 77 10 250 000 procumbens Stellaria 54 6 000 000 Not present Not present media Unknown 1 250 000 Not present Not present shrub

Agrostis gigantea This species is restricted to the research station and efforts to eradicate it have been underway for some years (see de Villiers & Cooper 2008). Again, the largest problem has been sustained follow-up of mechanical removal and glycophosphate applications, but continuation thereof should lead to eradication. Perhaps the most significant issue with regard to this species is the lack of appropriate instruction of the team and relief conservation officers, who often seem almost completely ignorant of the problem and the need for ongoing eradication efforts. Little thought seems to be going into appropriate instruction about plant identification and control requirements, and the team conservation officers undertake the work part-time and are frequently more inclined to complete their science projects. So, despite ease of

93 eradication on the scoring system, the efforts are hampered by insufficient conservation investment, small as is this requirement.

Potamogeton nodosus This species only occurs in one of the Albatross Lakes, and since its discovery no inflorescences have been observed. Because of its proximity to human settlement this will make the eradication much easier. Eradication of this species may be achieved by pulling up the plants by hand or by digging up all plants from the lake.

Table 2 The ranking of alien plant species for each of the criteria used for prioritization for Marion Island only. Note that species underlined are those that should be prioritized for eradication. For Prince Edward Island, the species are now all widespread enough to make eradication problematic (see text). Species Criterion Criterion Criterion Criterion Criterion Criterion Criterion Criterion Total 1 2 3 4 5 6 7 8

Agropyron 83 repens 251 31 03 53 151 151 151 55 Agrostis 83 gigantea 252 32 03 53 152 152 152 56 Agrostis 29 stolonifera 11 11 03 53 11 11 101 106 Cerastium 29 fontanum 11 11 03 103 11 11 101 56 Festuca 77 rubra 152 22 153 153 52 152 52 56 Juncus 75 effusus 151 51 04 53 151 101 151 106 Luzula 82 multiflora 251 21 02 53 151 151 151 56 Poa 29 annua 11 11 03 53 11 11 101 106 Poa 49 pratensis 21 21 03 53 101 101 151 56 Potamogeton 83 nodosus 252 32 152 57 152 152 52 0 Rumex 63 acetosella 151 31 03 53 101 101 151 56 Sagina 29 procumbens 1 1 11 03 53 11 11 101 106 Stellaria 59 media 11 31 03 103 151 51 151 106

Note: 1 see Table 1, 2 Gremmen 2004, 3 Gremmen 1997, 4 Smolders et al. 2008, 5 Walton 1975, 6 Frenot 2001, Spencer et al.2000.

94 Festuca rubra Festuca rubra only occurs at two sites, north of Van den Boogaard River, and at Ship´s Cove where it mixed with Agropyron repens. Removing the species can be done by digging up small patches of this grass, but for lager patches eradication can be achieved by herbicide. After treatment, regular monitoring may be necessary.

Luzula cf. multiflora This species was first discovered in April 1999 along the coast at Sealer’s Cave. At the site this sedge forms numerous small (1 x 1 m) and large (400 m²) patches. Eradication can be achieved by mechanical removal of the above ground. Digging at the site could remove all the underground material as it is shallow rooting. The site would require continued monitoring to check for any signs of regrowth, through root fragments or seeds.

Juncus effusus This species occurs at four sites; Trypot Beach, the north-western side of Van den Boogaard River and two patches between Ships’ Cove and Sealers Beach. All four sites are accessible from the research base (< 4 km). For this species eradication can be achieved by cutting the above ground stem and then digging up the undergoing roots. The root system of this rush might be a little bit deeper, but given the small size of each patch, eradication can achieved. If some rhizomatous material persists re-sprouts could be sprayed with a glycophophate herbicide. It is unlikely to regenerate from a seedbank as no viable seed has been detected for the species on the island (Gremmen 2004). All plant materials should be incinerated in South Africa after transport away from the research station. For all species care should be taken when transporting the plant to base to prevent infestation of this plant in previously unaffected areas.

Intermediate priority species Rumex acetosella Currently this species only occurs in two localities, close to Gentoo Lake and on Goney Plain. Both patches are relatively small (< 50 m²) and in recent years large number of seeds have been produced (Gremmen 2004). The patch at Gentoo Lake is very close to the research base and can be used as a trial to determine an effective of herbicide and appropriate application for the species. Foliar spraying could be the best method to treat the plant. Herbicide should be applied only during the growing season when new shoots are developing for better

95 absorption of the chemical by its broad leaves (Gremmen 2004). Continued monitoring of the sites after treatment is very important.

Lower priority species given distribution Stellaria media This species was found to be widespread from surveys undertaken in 1975, 1981 and 1989. However range of this species seems to be retreating. At present Stellaria media is not very abundant and is restricted to coastal habitats. Although this species is widespread, it occurs in small populations. This species can be uprooted and the vegetative part taken to base, however there may still be a persistent seedbank. Whenever a new site is observed anywhere on the island plants would needs to be pulled and destroyed, and the site monitored for resprouting. Given its widespread occurrence and potentially extensive seedbank, eradicating this species will require high level of effort.

Poa pratensis Data from the recent surveys conducted in 2006 indicate that the species is restricted to the eastern part of the island with most patches adjacent to the research station. Given the number and size of the patches, mechanical control is not feasible. Herbicide application would be the only effective way of treating this grass however this will require a high level of effort. If one treatment is sufficient, then eradication of this grass is possible.

Unknown shrub This species is thought to be related to Zizyphus sp. from South Africa. Although it may well be an introduced species, it is not yet clear whether this is the case. Given that a single plant exists eradication should be straightforward through mechanical removal. It is recommended that at this point nothing be done until an identification is provided and based on life history characteristics an estimate made of natural colonization. If after five years such information is not forthcoming the species should be removed. Likewise, annual monitoring should be undertaken of the site and if the species appears to be starting to spread it should be removed. Both actions are in keeping with the precautionary principle.

Remaining species The work undertaken is this study has produced distribution maps (Chapter two) which clearly indicated that Cerastium fontaum, Poa annua, Sagina procumbens and Agrostis stolonifera are very widespread. On Prince Edward Island Poa annua and Sagina procumbens

96 are widespread and only Cerastium fontanum might be possible to control. Based on the distribution and abundance of these species neither mechanical nor chemical treatment are feasible options. Effective control, or eradication, of these species may be possible through biological control, but the introduction of further species to the islands is not recommended.

GENERAL CONCLUSION The main objective of this project was to provide a spatially explicit assessment of the abundance and occurrence of each of the alien vascular plant species on Marion Island. In doing so, I have calculated the residence time of each species, assessed the rate of range change and identified variables that explain the occurrence of alien species on the island. This study found that alien plant species on Marion Island differ markedly in their occupancy, distribution and rate of expansion. Agrostis stolonifera, Cerastium fontanum, Poa annua and Sagina procumbens are all expanding their ranges, whereas the range of Stellaria media is contracting. Cerastium fontanum is the most widespread species on Marion Island while Sagina procumbens is the most abundant (number of records) and most rapidly expanding species on both Marion and Prince Edward Islands. Distribution of alien species on Marion Island is not explained by residence time. Furthermore, this study has demonstrated that alien species richness on Marion Island declines sharply with increasing elevation, and that the distribution of the most widespread species is spatially aggregated. Feasibility assessments in this study have demonstrated that some alien plant species on Marion Island are suitable for eradication efforts. In conclusion, this thesis provides comprehensive baseline data on alien vascular plants distributions on the Prince Edward Islands as a benchmark for future assessments and monitoring. Future studies may investigate how walking trails and river systems influence the distribution of alien plants.

97 REFERENCES

Anonymous. 1996. Prince Edward Islands Management Plan. Department of Environmental Affairs and Tourism, Pretoria, South Africa.

Bergstrom, D.M., Lucieer,A., Kiefer, K., Wasley, J., Belbin, L., Pedersen, T.K. & Chown, S.L. 2009. Indirect effects of invasive species removal devastate World Heritage Island. Journal of Applied Ecology 46, 73-81.

Bester, M.N., Bloomer, J.P., Bartlett, P.A., Muller, D.D., Van Rooyen, M. & Buchner, H. 2000.Final eradication of feral cats from sub-Antarctic Marion Island, southern Indian Ocean. South African Journal of Wildlife Research 30, 53-57.

Byers, J.E., Reichard, S., Smith, C.S., Parker, I.M., Randall, J.M., Lonsdale, W.M., Atkinson, I.A.E., Seasted, T., Chornesky, E., Hayes, D. & Williamson, M. 2002. Directing research to reduce the impacts of non-indigenous species. Conservation Biology 16, 630-640.

Chapuis, J.L., le Roux, V. Asseline, J., Lefèvre, L. & Kerleau, F. 2001. Eradication of rabbits (Oryctolagus cuniculus) by poisoning on three islands of the sub-Antarctic Kerguelen Archipelago. Wildlife Research 28, 323-331.

Chown, S.L., Gremmen, N.J.M. & Gaston, K.J. 1998. Ecological biogeography of Southern Ocean Islands: species-area relationships, human impacts and conservation. American Naturalist 152, 562-575.

Chown, S.L. & Klok, C.J., 2001. First record of Palirhoeus eatoni (Coleptera, Curculionidae) from Heard Island. African Entomology 9, 193-194.

Chown, S.L, Lee, J.E. & Shaw, J.D. 2008. Conservation of Southern Ocean Islands: invertebrates as exemplars. Journal of Insect Conservation 12, 277-291.

Chown, S.L, Rodrigues, A.S.L, Gremmen, N.J.M. & Gaston, K.J. 2001. World Heritage status and conservation of Southern Ocean Islands. Conservation Biology 15, 550-557.

Clout, M. N. & De Poorter, M. 2005. International initiatives against invasive alien species. Weed Technology 19, 523-527.

98 Convey, P., Frenot, Y., Gremmen, N.J.M. & Bergstrom, D.M. 2006. Biological invasions. In: Bergstrom, D.M., Convey, P. & Huiskes, AH.L. (Eds.) Trends in Antarctic Terrestrial and Limnetic Ecosystems. Antarctica as a global indicator, Springer, Dordrecht, pp 193-220.

Cooper, J. 2008. Human History. In: Chown S.L. & Froneman, P.W. (Eds.) The Prince Edward Islands. Land-Sea Interactions in a Changing Ecosystem. African Sun Media, Stellenbosch, pp. 331-350.

Costin, A.B. & Moore, D. M. 1960. The effects of rabbit grazing on the grasslands of Macquarie Island. Journal of Ecology 48,729-732.

Courchamp, F., Chapuis, J.L. & Pascal, M. 2003. Mammal invaders on islands, impact, control and control impact. Biological Review 78, 347-383.

Curry, C.H., McCarthy, J.S., Darragh, H.M., Wake, R.A., Churchill, S.E., Robins, A.M. & Lowen, R.J. 2005. Identification of an agent suitable for disinfecting boots of visitors to the Antarctic. Polar Record 41, 39-45.

Davies, S.J., Chown, S.L. & Joubert, L.S. 2007. Renewed management system and provisions for South Africa’s sub-Antarctic islands. Papers and Proceedings of Royal Society of Tasmania 14, 115-120.

Esler, K.J., van Wilgen, B.W., te Roller, K.S., Wood, A.R. & van der Merwe, J.H. 2010. A landscape-scale assessment of the long-term integrated control of an invasive shrub in South Africa. Biological Invasions 12, 211-218.

99 Gremmen, N.J.M. 1997. Changes in the vegetation of sub-Antarctic Marion Island resulting from introduced vascular plants. In: Bataglia, B., Valencia, J. & Walton, D.W.H. (Eds.) Antarctic Communities: Species, Structure and Survival. Cambridge University Press, Cambridge, pp. 417-423.

Gremmen, N. J. M. 2000. Eradication of Sagina procumbens (procumbent pearlwort) in the Gough Island Wildlife Reserve. Tristan da Cunha Administration, Edinburgh, Tristan da Cunha.

Gremmen, N.J.M. 2004. Management of alien vascular plants on Marion and Prince Edward Islands: an Integrated Approach. Unpublished report. Data Analyse Ecologie, Diever, The Netherlands, 1-30.

Gremmen, N.J.M., Barendse, J. & Orr, I. 2001. Invasion and eradication of Sagina procumbens L. (Procumbent pearlwort) on Gough Island. Aliens 14, 19-20.

Gremmen, N.J.M., Chown, S.L. & D.J. Marshall, D.J. 1998. Impact of the introduced grass Agrostis stolonifera on vegetation and soil fauna communities at Marion Island, sub- Antarctic. Biological Conservation 85, 223-231.

Gremmen, N.J.M. & Smith, V.R. 1999. New records of alien vascular plants from Marion and Prince Edward Islands, sub-Antarctic. Polar Biology 21, 401-409.

100 Heibert, R.D. 1997. Prioritizing invasive plants and planning for management. In: Luken, J.O. & Thieret, J.W. (Eds.) Assessment and management of plant invasion. Springer, New York, pp. 195-212.

Hulme, P.E. 2006. Beyond control: wider implications for the management of biological invasions, Journal of Applied Ecology 43, 835-847.

Jenkin, J.F.1997. Vegetation of the McDonald Islands, sub-Antarctic. Polar Biology 18, 260- 272.

Lee, J.E. & Chown, S.L. 2009a. Constructing an invasion pathway in Antarctica. Antarctic Science 21, 471-475.

Lee, J.E. & Chown, S.L. 2009b. Breaching the dispersal barrier to invasion: quantification and management. Ecological Applications 19, 1944-1957. le Roux, P.C. & McGeoch, M.A. 2008. Rapid range expansion and community reorganization in respond to warming. Global Change Biology 14, 2950-2962.

Leung, B., Finnoff, D., Shogren, J.F. & Lodge, D. 2005. Managing invasive species: rules of thumb for rapid assessment. Ecological Economics 55, 24-36.

Macquarie Island pest eradication plan. 2009. Department of Primary Industries, Parks, Water and Environment – Parks and Wildlife Service Macquarie Island Pest Eradication Project. Part C – Environmental Impact Statement.

Nehring, S. & Hesse, K. 2008. Invasive alien plants in marine protected areas: the Spartina anglica affair in the European Wadden Sea. Biological Invasions 10, 937-950.

Towns, D. & Broome, K. 2003. From small Maria to massive Campbell: forty years of rat eradications from New Zealand islands. New Zealand Journal of Zoology 30, 377-398.

101 Sheley, R. L., M. Manoukian, and G. Marks. 1999. Preventing noxious weed invasion. In: Sheley, R.L & Petroff, J.K.(Eds.) Biology and Management of Noxious Rangeland Weeds. Corvallis, OR: Oregon State University Press, pp. 69-72.

Sheppard, A. W., Shaw, R. H. & Sforza, R. 2006. Top 20 environmental weeds for classical biological control in Europe: a review of opportunities, regulations and other barriers to adoption. Weed Research 46, 93-117.

Simberloff, D. 2003. Confronting introduced species: a form of xenophobia? Biological Invasions 5, 179-92.

Smolders, A.J.P, Lucassen, E.C.H.E.T., van der Aalt, M., Lamers, L.P.M. & Roelofs, J.G.M. 2008. Decreasing the abundance of Juncus effusus on former agricultural lands with noncalcareous sandy soils: Possible effects of liming and soil removal. Restoration Ecology 16, 240-248.

Spencer, D.F. Ksander, G.G., Madsen, J.D. & Owens, C.S. 2000. Emergence of vegetative propagules of Potamogeton nodosus, Potamogeton pectinatus, Vallisneria americana, and Hydrilla verticillata based on accumulated degree-days. Aquatic Botany 67, 237-249.

Pasteur, L. & Walton, D.W. 2006. South Georgia: plan for progress. Managing the environment: 2006-2010. the British Antarctic Survey and the Government of South Georgia and the South Sandwich Islands, Howlett Design, Cambridge, pp.1-17.

Phiri, E.E, McGeoch, M.A. & Chown, S.L. 2009. Spatial variation in structural damage to a keystone plant species in the sub-Antarctic: interactions between Azorella selago and invasive house mice. Antarctic Science 21, 189-196.

Ryan, P.G., Smith, V.R. & Gremmen, N.J.M. 2003. The distribution and spread of alien vascular plants on Prince Edward Island. African Journal of Marine Science 25, 555-562.

Walton, D.W.H. 1975. European weeds and other alien species in the sub-Antarctic. Weed Research 15, 271-282.

102 Whinam, J., Chilcott, N. & Bergstrom, D.M. 2005. Sub-Antarctic hitchhikers: expeditioners as vectors for the introduction of alien organisms. Biological Conservation 121, 207-219.

103