S. Afr. J. Antarct. Res., Vol. 16, No. 3, 1986 95 The arrival, establishment and control of alien plants on Gough Island
N. Wace Department of Biogeography and Geomorphology Research School of Pacific Studies Australian National University, Canberra Australian Capital Territory 2601
Twenty-three species of alien vascular plants had been re Introduction corded growing wild on Cough Island until November 1984. Eight species, which have all been present for at least 30 Along with the other two smaller islands of the Tristan da years, are naturalised and wide~pread. Five adventive species Cunha Group in the South Atlantic, Gough Island is prob have been found only at sires of human habitation on the ably the only remaining temperate oceanic island of any size coasts. These 13 species are alf forbs (7) or f!,tasses (6) hm•ing and ecological diversity, which has retained its native plant c, photosynrhetic carbon pathways, and they include no and animal life more or less intact, and little affected by hu woody or large tussock-forming plants. A further 10 casual man activities. The few other oceanic islands in the Southern species have been found only once on the island: Five of these Hemisphere near the subtropical convergence zone, which were discoveretl in October 1984 growing near a recently support woody vegetation, have been settled by breeding erected hut, and inclutling two soft-woody shrubs recognised and self-sustaining human populations, or had their native as weeds in South Africa, whence they came. ecosystems variously modified by man (Holdgate & Wace Burrowing and excreta-deposition by seaf>irds, and peat 1961, Clark & Dingwal! 1985). avalanches 11re the most important nmural processes giving This paper summarises what is known about the arrival rise to regeneration sites, which are preferentially colonised by and establishment of alien plants on Gough Island until the alien plants. There is very little human disturbance of the end of 1984; the degree to which the native vegetation has plant cover. Control of alien plants on Cough Island requires been disrupted by natural and man-induced processes (thus protection of the peat mal!tles and the nath•e vegetation, espe enhancing opportunities for alien species to become estab cially from fire. Quarantine sun·eillance, to exclude the im lished); and the management that is necessary to prevent port of plants or animals (particularly rats), and regular sur alien plants from establishing themselves in future as part of veillance of the plant life are most important in monitoring the naturalised flora. Records of the introduction and estab and maimaining the integrity of the native ecosystems, and lishment of alien animals are also summarised, because of thus excluding alien plants from the island in future. their possible effects on the native and alien flora of the is land. Drie-en-twimig spesies vreemde vaatpla/1/e wat wild op Cough-eiland groei, is sedert November 1984 aangetekcn. The arrival of alien plants Agt spesies, wat almaf reeds minstens 30 jaar daar ••oorkom, is genawraliseer en kom algemeen versprei >'oor. V>f advcn The only known introductions of domesticated plants and tiewe ~pesies is slegs aan die kus naby mense se verblyfplekke animals to Gough Island have been: (l(mgetref. Dir! 13 spesies is a/mal Of ll'eireldkruide (7) bf I. Cultivation of vegetables at various sites around the grasse (6) me/ C-fotosintetiese koo/stofroetes, en sluit nie coasts, from about 1800 AD. The first documented ac homerige of groat poltoormende spesies in nie. Nog 10 roeval counts describe '·potatoes and other vegetables" grown in /ige spesies is slegs een keer op die eiland aangetref en vyf 1811 by American sealers then living on the north coast hiermn is in Oktober 1984 ontdek naby 'n hut wattoe pas op (Tagart 1832). But Yankee sealers were known to be liv gerig is. Onder tlie plame was twee sagtehowagtige stmike ing ashore from 1804 (Wace 1969), and did so intermit \\'at in Suid-Afrika, >marvandaan !wile gekom het, as on tently until the collapse of the industry by 1888, when po kmid beskou word. tatoes were still noted as "growing wild" (Verrill1895). Seevoiils se agterlating van uitskeidings en die resu!rare van hul grawery, asook rurflawirtes, is die vemaamste natrwrlike 2. Some attempted cultivation of potatoes and vegetables oorsake ••mt regenerasieterreine wat by voorkeur deur (lettuce, carrots, cabbage. onions, radish) by N.M. Wace vreemde plame geko!oniseer word. Die mens ••ersteur se/de and J.J. van der Merwe from 1955-57; and at the present die plantbedekking. Vir die beheer van vreemde plame moet weather station in Transvaal Bay, between 1963 and 1970. die turfmantel en die inheemse plalllegroei op Cough-eiland 3. Attempts to keep sheep and poultry in small number~ dur beskerm word, ••era! teen brande. Kwarantymoesig om le ing the first years of the South African weather station at voorkom dat vreemde p!an/e of tliere (vera{ rotte) inge••oer The Glen (1956-57 - Van der Merwe, in litt.). Poultry word asook die gereelde waarneming \'an die plantfewe is were also kept at the Transvaal Bay weather station from uiters belangrik by die beheer en ham/hawing l'all die onges 1963-1970. Some fodder was probably landed with the kondenheid van die inheemse ekosisteme, en om vreemde sheep, and the poultry were fed with imported g~ain at plante in die toekoms van die eiland weg te hou. these times. 96 S. Air. T. Nav. Antarkt., Oeel16, No. 3, 1986
Except for potatoes, none of these intentionally intro land with sand or stone chippings from the Cape. After the duced ~pccics has persisted or become naturalised on Gough but wa~ built. in April 1983. the surplus sand, which had Island. Since 1970. no alien plants or animals are known to been imported to make cement for the hut foundation~. was have been taken ashore. Under the terms of the British lease spread about over the surface of the peat in the region round of part of Gough Island to South Africa for use as a weather the hut which had been cleared of native vegetation. The station (1984), no exotic plants or animals arc allowed to be seedlings of these imported plants thus had a chance to ger imported. minate. and to compete with the native species, just when Apart from potatoes, all the plants introduced to Gough the fronds of Histiopteris incisa were dying down in the au Island which later became naturalised, were brought in unin tumn. The rapid spring growth and dense cover of Histiopte tentionally. To the end of 1984. only eight species of \'ascu ris must be important in preventing seedlings of alien plants lar plant~ had become naturalised: establishing themselves near the weather station. where Stellaria media much seed must be a!.:cidentally imported. :-.Jone of the Rumex obtusifolius above five species seen at the rnag:netometer hut was also Plamago major present aronnd the weather stmion, where the cover of His Sonchus oleraceus tiopteris and Scirpus remained little disturbed in 19R4. Agrostis stolonifera Holcus lanatus Poa mmua Present size and characteristics of the alien Poa pratensis flora A further 10 species were then (or had previously been) The total flora of introduced vascular plants so far recorded restricted to the vicinity of the old huts in The Glen, and/or from Oough Island thus consists of 23 species of flowering the immediate vicinity of the weather station in Transvaal plants. These can be divided according to their performance Bay: and range on the island, into three groups: *Cerastium fontanum Eight naturalised specie~ which reproduce freely. and Plantago lanceolata have been present at several places on the island for at least 'Verbena bmwriensis 10 years: Solanum tuberosum Sonchus asper Stellaria media ~ Agrostis castellana Rumex obwsifolius Agrostis lachnamha Plantago major Agmstis tenuis Sonchus ofcraceus Agwstis stofomfera Dactyli.~ glomerata *Rumex acetose!la Holcus lanatus Poa annua Four of these species (marked *) have been collected only Poa pratmsis once at one site, and have not been seen again at that site or elsewhere, although sought by the author during visits in Oc Five adventive species. which have been found in several tober 1976 and 1984 and in May 1968. Sonchus asper may be place~ on the island on a number of different occasions, but more widespread on the island, but confused with Soncfr,t.l" which do not seem to spread from these situations. This oleraceus; and the various species of Agrostis may be con group includes persi~tent cultivated plants: fused with A. stolomfera. Both Sonclws oleraceus and Plamago lanceolatli Agrostis stolonifera are widespread on the island. Hypocfwc Solanum wberosum ris glabra, allegedly collected at The Glen landing in 1904 Sonclws asper (Rudmose Brown 1905) is now thought to be an erroneow, Agrostis tenuis identification of Sonclws oleraceus (Groves 1981, p. 366). Dactylis glomerata A further five species of alien vascular plants were found in October !984, growing near the new magnetomcter hut. 10 Casual species, which have been found only once. m bc~idc the stream supplying drinking water to the weather one place on the island: ~tation: Cerastium fontanwn 0401 Conyzafloribundus (flcabane, Kleinskraalhan~) R.ttmex acctose!la (agg.) G402 Lactuca serriola (wild lettuce, wildc slaai) Oenothera indecora G403 Senecio burchellii (Molteno disease Senecio. Cony;;a floribunda Burchell"s senecio) Lactttca serriola 0404 Lolium multiflorwn (rye grass, raaigras) Senecio burcheffii 0405 Oenothera indecora (evening primrose, nagblom) Agrostis caste/lana Agrostis {ac/uwmha These plants were all pulled out by a working party on 27 Loliwn multijlorum October, when only Conyza had mature fruits and showed V erbma bonariensis signs of active spread, with yonng seedlings scattered around the new hut. The two wft-woody shrubs (Senecio burchel!ii With the very small amount of botanical investigation of and Oenothera indecora) were then np to half a metre or Gough Island. this can only be the mo~t tentative grouping more tall, and spreading vegetatively, but Lactuca and Lo of the total alien flora. Some casual species may become ad lium were scarce, and appeared less aggressive. These five ventive or even fully natnralised in future. and members of species are all common weeds in South Africa (Ilenderson & any group may become temporarily or permanently extinct Anderson 1966). '11tcir seeds probably arrived on Gough Is- on the island (e.g. ?Rumex acetosella, Verbena /Jonariensis). S. Air. J. Antarct. Res., Vol. 16, No. 3, 1986 97
Table 1 Remote islands of the Southern HemiSJihere, 35- 55' S. latitude. Basic geographical data, with indications of the degree to which their native ecosystems h:we been affected by human activities. Data dral\n largely from Clark & Dingwall (1985). {Figures in brackets indicate no permanent scll~sustaining human poJmlation)
~ > ~ ~' " ] " s ~ "
ATLANTJC' OCEA~
37' Tri 51-~2' ~-alklando c.20 \2()\)() 7115 .".5 mctawdiment,_ pcrighwi,] 2 21J(Hl 163 92 Britain: :-.-1<"1 t~land' muob altered hJ 'hcep gmling. pent cutting & tiring.: intact ceo'J"C"'' on 'mall uff,horc ;,]et' c\rgenlill<' 53-55- South Georgia 1 + + 3756 ::!93--l 2.1 mctmed!mcnt,. 1cce,,p (l) (?21J+) 16.19 llritain" 1-kadland 19H4 Vegetation altered h; introduced reino.lccr: b1rd> rcdu<.:ed h\ 1ab: >mall i INDIA:-. OCEAN Amsterdmu- St. l'a111 2 62 lJ11 13.3 ~oung •olcanic. hot 'l""!nJ!' (1) (,·30) France l Mnrion- l'rince Edward 2 .14+ JJ3(} 'i.t }OUng IOic,HHC. lava n""' (1) (c.21J) 381--l S. Afric,o Grcmmcn 1982 Cab on Marion de~aqatcd w.1h1rd'· Prince Fd\\ard lmk altered Crozct Group 5(MJ HIYII (I) (< 20) France 1-'cral c;ll' and rodcnh on'""'" "lamh: nthe" prohahl) free of introduced plant, or aninH•I''' --l~o Kerguelen I<+ c.7(}!1(\ IH311 --l.l lt>lcamc.iccc,op.gl 53' lleard & :\lacdonalJ 2 1.2 "cti\e \Uic~no. ic~cap H.O Keaf:C 19H2 Mimmallmrnan impact. no cwtic planh natur"li~ed PAC"IFIC OCEAt" Chatharn Group ' 1973 270 11.2 <>Id volcanic 7()() New Zealand Richnrd; 1977 Bount) Group ,. 10 SH r ]() )!.lanitc i"\lct' a •. J rock> t).(j Ton >mall Ill c.on;- lan<.l vcgctalir>n: largd) unmodilicd 50 1 +~ 411::! c.H \Olcanic Ne" Zealand Apparent I) unmodified. dc,pitc earlier fer.tlli\cqoc~. no rab ~H' Sn""" 3 3 152 c.ll gr ~~- Aacklan 5-I :'l-hocr1uarie ll'J ~3:' ~.7 old\olcanic.rcccntuplift (\) (15) -1-1~4 Rabbit>.'"" and rah mnrhfied \cgctatmn and bird hfe: control; r)n r.,bhit< rcducrng numhc" The natura!i~cd and advcntive elements include no trees, Cyperw· congesws shrubs, lianes or other woody species, and no scramblers, C)•perw> rowndus large tussock-formers or geophytcs with spreading rhizomes Sporobolus capense - and no pteridophytes. Most of the naturalised and adven Cynodon dactylon tive plants are opportunist forbs and grasses which thrive in Paspalwn dilarawm unstable habitats, and all except some species of Agrostis Digitaria sanguinalis and the potatoe~ are native to Europe, but are now common Eleusine indica weeds with widespread ranges in the temperate zones of These five species of grasses naturalised on Tristan, all be both Northern and Southern Hemispheres. long to genera which are recorded as having C4 photosyn All of the eight naturalised and five adventiyc species on thetic pathways elsewhere (Hatterslcy 1983 & pers. comm., Gough Island belong to genera with tricarboxylic acid (C3) Vogel et al. 1978). Both the above Cyperus specimens rrom carbon pathways in photosynthesk This contrasts with some Tristan have the Kranz-anatomy typical of C4 plants. None of the more aggressive naturalised ~pedes on the lowlands of of the naturalised, adventive or casual species so far found Tristan da Cunha, where the volunteer alien plants include: on Gough Island belong to genera with C4 puthways else- 98 s. Afr. T. Nav. Antarkt., Deel16, No. 3, 1986 where. Specimens of the new arrivals Senecio burchellii and chyle lavas on Nightingale, contains collophane nodules Oenothera indecora do not have the leaf anatomy typical of (Oilier 1984) indicating that eutrophication of the island C4 plants. Amongst the native flora of the entire Tristan peats there by scabird excreta is a long-standing feature of Gough Group, only the large coastal tussock grass Spanina that island. The same is undoubtedly true of Gough Island. arundinacea has so far been found to have the typical C4 leaf The overall effects of eutrophication of the Holocene peats anatomy. on Gough Island by the enormous numbers of seabirds which still breed there today, must be considerable. Alien plants from the temperate zones that are well adapted to Disturbance of the native ecosystems on growth on wet orgunic soils in situations polluted by live Gough Island: enhanced opportunities for the stock might therefore establish and spread widely on Gough establishment of introduced plants Island, if introduced. In addition to this continuous natural eutrophication of It has long been assumed that even in the "disharrnonic" both soil and water, and the disturbance of native vegetation ecosystems typical of oceanic islands (Car!quist 1974), some by breeding seabirds and sea mammals, episodic and severe disturbance of their vegetation is essential if introduced disruption of the native vegetation results from peat plants are to establish themselves in competition with native avalanching in the steep terrain. Peat act-"Umulates rapidly in species (Elton 1958, Wace 1967, Byrne 1980). Such disturb the wet temperate climate of Gough Island, and sodden peat ance may be natural, or brought about directly or indirectly avalanches down the steep slopes during heavy rains. The by human activities. The major historical events leading to resulting scars in the peat and vegetation cover are a con the disturbance of the native ecosystem~ in all the islands of spicuous feature of the fern bush and wet heath in the Glens, the Tristan - Gough Group were summarised by Wace & and in some of the tussock-covered precipices around the Holdgate (1976). On Gough Island, parties of sealers, pros coasts. Such "peatslips" take place repetitively, especially pectors and scientists have lived ashore intermittently since where fed by seepage of water from above, dislodging both c. 1800, and meteorological station personnel continuously rock and peat to the valley bottoms. Slopes swept by such since 1955. The hunting of fur seals, albatrosses, and other peatslips are rccolonised by both native and alien plants seabirds by sealers and the cultivation of vegetables at a few (Wace 1961). It is notable that the first seed colonists of places on the coasts have been the most important human the~c shallow peats and rocky surfaces are the alien grasses impacts on the native ecosystems in the island. Such activ Holcus !anaws and Agrostis stolonifera, and the dock Rumex ities have now ceased, and arc prohibited under the lease obtusifo!ius. Native colonists spread into the disturbed area agreement between Britain and South Africa. Shore parties by vegetative growth from the surrounding fernbush, and now rely on imported supplies for their sustenance, supple Histiopteris iiiCisa rapidly smothers these alien species by mented by locally caught fish and crustaceans. So far as is marginal ingrowth. Seedlings of the native Sparlina, Phylica known, no women have ever lived on Gough Island (and and Empetrum, and sporclings of Lycopodium, Blec!uwm very few have ever landed there), and no attempts have ever pemw-marina and other pteridophytes are the most conspic been made to establish a settled, self-sustaining, breeding uous of the native colonists away from the margins of the human population, with all the disturbance to the native peatslips. Peat avalanching is a most significant natural pro ecosystems which that would inevitably entail. cess disrupting and removing the mantle of peat and thus This paucity of direct human disturbance of the native presenting open habitats on mineral substratcs to colonising ecosystems by sustained activities such as agriculture. road plants, many of the most successful of which are introduced building or mining, is in marked contrast to the large scale species. Less spectacular peatslips take place naturally above und continuom natural disturbance of the native plant cover the fernbush up to the highest points of the island, but at due to the burrowing of enormous numbers of ground these higher altitudes, the conspicuous colonists of the dis nesting seabirds, the open nest-building of albatrosses, and turbed areas are native species ( Agrostis carmichaelii, Agros the colonial breeding of penguins and seals around the tis mage!lanicn, Grammitis magellanica, Lycopodium spp, coasts. Eutrophication of the peat, (leading to what would Hymenophyllum spp). be described as gross pollution of soils and soil water if it re sulted from human or domesticated animal excrc! Acknowledgements 3. Maintain botanical surveillance of Gough Island, especially in sites disturbed by human activities I am grateful to the National Geographic Society of Wash ington. USA: the South Africa n De pa rtme nt of Tran~port Alien plants will establish themselves on G o ugh Isla nd in a nd the So uth African Scie ntific Committee for Antarctic future. despite the best attempts to excl ude them by quaran Research. Trista n da Cunha administration. a nd Tristan In tine controls and to minimise disturbance of the native vege ve~tmc nt s Ltd .. for assista nce a~h ore a nd afloat. I tha nk Dr tation a nd peat ma ntles. It is therefore important to have Pa ul llatte rsley a nd Ms Jill Pate rson for assistance with the some people at the weather sta ti on. or visiting the isla nd ide ntificatio n of carbon pathway types in some Tristan and during the a nnual relief voyages. who have the botanical Gough Isla nd specimens. competence to identi fy plants, so that any intruding aliens can be detected and removed before they spread. References In October-November 1984, it was only by chance that ATKINSON. I. A. E. 19XS. The spread of commcnsal species of Rat one of the biologists ashore at the time knew the flora well IllS to oceanic islands and their effects o n island avifaunas. /111. enough to draw attention to the alien plants that were be Cntmr. Rird Pre5en•. Teclt . P11bl. 3· 35-R I coming esta blished around the magnetometer hut. No one BESTER . M.N .. BREYTENBACII. U.J . & WACE. N.M. 1985. else ashore at the time. and none o f the meteorological Gough Island rat im·estigation. Oct/ :-.lov t984- Report to South team. had e no ugh knowledge of fi eld botany to know which African Committee Antarctic Re~ca rc h . Preto ria (28 pp. type pla nts we re native and which alie n. If the intruding plants M:ript). had not been pulled out at the time. it is likely that Senecio 13YRNE. R. 1980. Man and the va ri able vulnerabili ty of island li fe burchellii (a decla red noxious weed thro ughout the Republic Atoll Res. 811/1. 2~0. of So uth Africa: Henderson & Anderson 1966, p. iv), and CARLOUIST . 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