aliens

Invasive Species Specialist Group of the IUCN Species Survival Commission

ALIENS Number 14 2001

SPECIAL ISSUE ON ISLANDS MESSAGE FROM THE CHAIR It has become clear to most people working on alien species that islands (and other geographically and evolutionary isolated places) are different from continental situations in a number of ways. They are more vulnerable to invasions and are more likely to suffer catastrophic loss of biodiversity as a result of invasions, but they also easier to defend by border control and have greater potential for successful eradications of invasive species. As part of the focus on islands, ISSG, in cooperation with New Zealand, is developing a worldwide Cooperative Initiative on Alien Invasive Species on Islands, in the context of the global cooperation taking place under the umbrella of GISP (the Global Invasive Species Programme). The initiative is focussed firmly on biodiversity aspects. GISP, at its Phase 1 Synthesis meeting in September 2000, identified islands as a special case warranting co-operative initiatives. The Convention on Biological Diversity (CBD) also recognises the very urgent need to deal with invasive alien species issues in isolated and vulnerable ecosystems. At the March 2001 meeting of the CBD’s subsidiary body, the Plenary: “Endorse[d] the call for an islands cooperation initiative and welcomes the offer of New Zealand, the IUCN Invasive Species Specialist Group and the Global Invasive Species Programme to explore means to establish such an initiative” (VI/4, 18). Existing co-operative efforts show that even where there are major differences in climate, politics, language, etc, the experience of one island country can provide valuable input to work in other islands. There are four key areas where a co-operative initiative on island invasives may be especially valuable: • Undertaking the eradication of alien species from islands. • Undertaking management of alien species populations on islands, where eradication is not currently feasible, to low levels that allow recovery of biodiversity values. • Training and other capacity enhancement activities. • Undertaking quarantine and contingency response activities to prevent the establishment of new populations of alien species that might threaten ecosystems or species (including the control of movement within national borders). Co-operation would span the range from formal government-togovernment co-operation to informal practitioners’ or individuals’ cooperation, at whatever organisational level or scale achievements would result in enhanced conservation of biological diversity on islands. The initiative will encompass all islands that have significant biodiversity, including

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Manaaki Whenua Landcare Research

ISSN: 1173-5988

CONTENTS Message from the Chair Cooperative Initiative on Island Invasive Species Toolkit for Prevention & Management of IAS Update: Global Invasive Species Database Jamaican iguana of Hellshire Hills Meanwhile in Mauritius Report on Eradication on Islands Conference Biological control on St Helena Impact of African Land Snails on Reunion Island Publications (Hawai’i) Report on Brown Tree Snake Symposium Notes (Australia, Scotland) Hedgehogs on Scottish Islands Notes (Canary Islands) Eradicating Sagina procumbens on Gough Island Developing biosecurity Strategy for New Zealand Publications (Australia) Notes (Landcare) Aliens subscription form About Aliens , ISSG, IUCN....

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GENERAL DISCLAIMER All material appearing in Aliens is the work of individual authors, whose names are listed at the foot of each article. Contributions are not refereed, as this is a newsletter and not an academic journal. Ideas and comments in Aliens are not intended in any way to represent the view of IUCN, SSC or the Invasive Species Specialist Group or the sponsors, unless specifically stated to the contrary.

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small island states and offshore and oceanic islands of continental states. It will include both developing and developed country islands. ISSG is currently seeking funds for this new initiative. We need help from anyone with an interest in islands IAS problems and solution who would like to participate and anyone who can help us access funding. Because of their special nature, we felt it that was time that we had a special issue of Aliens focussing on islands. I hope that you enjoy reading this issue. Best wishes for a productive and peaceful 2002 from myself and the ISSG staff at Auckland. Mick Clout, ISSG Chair

Mick Clout, Maj De Poorter, Michael Browne, Souad Boudjelas, Carola Warner

Invasion and eradication of Sagina procumbens L. (Procumbent pearlwort) on Gough Island Gough Island (South Atlantic, 40o21’S, 9o53’W) is one of the least disturbed major cool-temperate island ecosystems in the world. It is part of the Tristan-Gough group of islands and is ca. 300 km removed from the other islands of this group. Administratively Gough is part of the Dependency of Tristan da Cunha. The island was designated a wildlife reserve in 1976 and placed on the World Heritage list in 1995. Invasions by introduced plants and animals form a major threat to the integrity of the ecosystems of oceanic islands like Gough (Smith & Smith 1998, Chown et al. 1998). Such introductions often result in the replacement of native, often endemic species, by introduced, cosmopolitan species and can lead to significant changes in species composition and structure of native plant and animal communities (Ernsting et al. 1995; Gremmen 1997; Gremmen et al. 1998). In 1998 an invasive weed, Sagina procumbens L. (Procumbent Pearlwort), was recorded at Gough Island. Sagina procumbens is a small herb, spreading vegetatively and by seed. Once established, it can form large, very dense mats and on cold, oceanic islands is a serious threat to native vegetation and to soil fauna communities in many habitat types. Characteristic is the short time (a few months) for Sagina seedlings to reach maturity and produce seeds, the large number of very small, easily dispersed seeds produced per plant, and the longevity of the seeds in the soil. On subantarctic Marion Island it was found that Sagina spreads on average by 300m per year, with occasional jumps of several km (Gremmen & Smith 1999).

Gough Island Gough Island measures ca. 6 by 14 km and is very mountainous. The highest peak reaches 910m above sea level and much of the island is above 400m. On most sides the uplands fall away to the coast very steeply, but the high coastal escarpments are dissected by numerous steep and narrow valleys. The climate is cool and wet, with a mean temperature at sea level of ca. 11oC, mean annual precipitation in excess of 3000mm and frequent gale-force winds. The island was visited by sealers and whalers during the 19th century, as well as by egg-collectors and diamond prospectors but it was never permanently inhabited. In 1955 a scientific station was established at The Glen, which was subsequently taken over by the South African Weather Bureau as a meteorological station. In 1963 a new weatherstation was built above Transvaal Bay and the old one was abandoned. The Gough population of Sagina appears to be the result of a recent, accidental introduction at the site of the Meteorological Station. The lowlands of Gough are covered in a lush vegetation,

dominated by the island tree (Phylica arborea), tree ferns (Blechnum palmiforme), numerous other ferns and grasses, sedges and rushes. Coastal areas are covered in over 2m high, dense tussock grassland. More elevated areas are covered by thick heath and grassy vegetation, rich in bryophytes. In flat upland areas mires and bogs developed, dominated partly by Sphagnum, partly by other mosses and hepatics. The slopes, which make out the larger part of the island, are characterised by a cyclic succession, where vegetation develops from pioneer moss and lichen communities to a climax stage of Phylica bush or fernbush vegetation, or in upland areas to Empetrum heathland or mountain grassland (cf. Wace 1961). During the vegetation succession thick organic soils build up. At some stage, presumably triggered by high rainfalls, water saturated peat soils start slipping down the steep slopes. After such peatslips little or no soil is left on the slopes, and succession starts again on the rocky substratum. The flora of Gough consists of 36 flowering plants, of which 21 are endemic to the Tristan da Cunha - Gough island group and 4 are restricted to Gough Island. Twentyseven species of fern are known from the island, of which 15 are endemic to the Tristan-Gough group. Although a large number of bryophytes and lichens are known from Gough (Wace 1961), the knowledge of the non-vascular flora is very incomplete. Despite our incomplete knowledge of the island’s flora and fauna, it is clear that the island’s biota is unique, containing a large proportion of endemic species. Unique also is the small number of introduced species (Wace 1986), which makes Gough one of the very few, if not the only major cool-temperate oceanic island which still is in a nearly pristine state.

Sagina invasion In September 1998, during the annual relief expedition to the weather-station, Sagina procumbens was discovered in the logistic zone near the weather-station. In September 1999, Sagina was found still to occur only within an area of ca. 1ha near the weather-station. Within this area Sagina occurred in all habitat types and communities characterised by disturbance and/or by the presence of bare soil. From this, and from the behaviour of the species in other areas, notably on subantarctic Marion Island (Gremmen 1997, Gremmen & Smith 1999), it was expected that Sagina would be able to invade all habitat types on Gough Island characterised by disturbance and/or the presence of bare soil. Because of the vast numbers of burrowing and ground-breeding birds disturbance occurs on Gough Island in a wide range of habitats. Also the cyclical vegetation succession patterns on the island’s slopes provide ample habitats for Sagina to colonise, especially in the early successional stages, where the vegetation is

dominated by bryophytes, lichens and low-growing vascular plants. When unchecked, Sagina is expected to spread widely over the island and invade a large number of habitats and native communities. In several habitats Sagina is expected to form large, dense mats, outcompeting native species. This will result in a reduction of the local diversity of native species in the vegetation and to a significant change in the structure of the vegetation (Gremmen 1997). This in turn may be expected to affect also the faunal component of these ecosystems (cf. Gremmen et al. 1998). Eventually biodiversity on a whole-island scale may be affected. Sagina eradication programme Funded by the British Foreign and Commonwealth Office, through the Environmental Fund for the Overseas Territories, an eradication programme for this weed was designed and implemented during 2000. The first stage of this programme was to contain Sagina to the area near the weather-station until a full-scale eradication effort could be started. This work was admirably undertaken by the weather-station personnel who removed all Sagina plants they saw and stored them in strong plastic bags for later removal from the island.

eradication of Sagina on Gough will have been a waste of time, effort and money. This third stage involves a careful monitoring of the area and the immediate eradication of any new Sagina plants that are found. Equally important is a strict adherence to quarantine measures in order to prevent new introductions. Even though the total effort involved in the monitoring and continued eradication of Sagina on Gough is estimated to be only a few weeks per year, the short time between germination and seed production in Sagina requires that this work be spread out throughout the year and not be limited to a single, short period such as the annual relief expedition to the weather-station. Therefore, personnel with the necessary skills will have to be present on the island throughout the year and continue to monitor and eradicate Sagina on a regular basis. This means that the monitoring and eradication of Sagina (combined with other environmental monitoring and conservation tasks) have to be official tasks of the weather-station personnel. This requires specialist knowledge and the allocation of dedicated manpower within the Gough weather-station personnel, as well as the continuous support from the authorities operating the weather-station. But, with proper care, the total eradication of Sagina on Gough could be achieved within a decade or so. References

In May 2000 the second stage of the eradication programme was implemented, by sending down a fourperson team to Gough to complete the removal of the plants and to try and destroy as much of the seedbank in the soil as possible. To this end the whole area around the weatherstation, including the sea cliffs, was searched meticulously and every Sagina plant was removed, together with the soil around it, to a depth of ca. 15cm. As most Sagina seeds fall close to the parent plants many seeds were removed with this soil. Subsequently the soil of areas colonised by Sagina was treated with boiling water. Germination experiments showed that the hot water treatment reduced the number of viable Sagina seeds in the soil by more than 99%. As a backup, herbicides were used to quickly kill Sagina plants in inaccessible places. Of course, these areas were later treated with hot water, and whenever feasible the soil was removed. The eradication effort so far has been successful. We have achieved the virtual elimination of all Sagina plants in the treated area and an enormous reduction in the number of viable Sagina seeds present in the soil. It is inevitable, however, that some of the seeds in the soil are still viable and will germinate into new Sagina plants. However, without a third stage to the eradication programme the start that has been made with the Niek Gremmen Data Analyse Ecologie 7981 AP Diever, The Netherlands email: [email protected]

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 Ernsting, G, Block W., MacAlister H. & Todd C.(1995). The invasion of the carnivorous carabid beetle Trechisibus antarcticus on South Georgia (sub-Antarctic) and its effect on the endemic herbivorous beetle Hydromedion sparsatum. Oecologia 103: 34-42 Gremmen N.J.M. (1997) Changes in the vegetation of sub-Antarctic Marion Island resulting from introduced vascular plants. In: Battaglia 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., Chown S.L. & Marshall D.J. (1998) Impact of the introduced grass Agrostis stolonifera L. on vegetation and soil fauna of drainage line 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. Polar Biology 21: 401-409 Smith V.R. & Smith R.I.L. (1987). The biota and conservation status of sub-Antarctic islands. Environment International 13, 95-104 Wace N.M. 1961. The vegetation of Gough Island. Ecological Monographs 31: 337-367

Jaco Barendse MRI Whale Unit c/o South African Museum Cape Town 8000, South Africa Email: [email protected]

Iain Orr Environment Policy Department Foreign & Commonwealth Office London SW1A 2AH, UK e:[email protected]