Assessing the Status of the Pitcairn Island Flora - An Intergrated Approach to Conservation
S. Waldren - Trinity College Botanic Garden, Dublin 6, Ireland. N. Kingston - Trinity College Botanic Garden, Dublin 6, Ireland. P. Bingelli - School of Applied and Biological Sciences, University of Ulster, Northern Ireland. J. Starmer - University of Guam Marine Laboratory, Mangilao, Guam 96923, USA. J. Warren - Conservation & Quarantine Officer, Pitcairn Island, South-Central Pacific Ocean.
Home | Contents | Abstract | Introduction | Synopsis of the Flora | Status of the Flora | Vegetation Communities | Conservation Issues | Conclusions | Acknowledgements |
References | Table 1 | Table 2 | Table 3 | Appendix | Figure Legends
Remote Pitcairn Island has a depauperate, but none the less interesting vascular plant flora. The floristic relationships are with the rest of Polynesia to the west, with some representation of southern and eastern Polynesian elements. A recent survey of the island produced at least eight new records and two possibly undescribed species; the total indigenous vascular flora numbers some 80 taxa of which ten are thought to be endemic. Threat numbers and IUCN threat categories have been assigned to all native taxa; several are very rare, existing in small or highly fragmented populations. Apart from the stochastic problems of small population size, the main threat to the native flora is the spread of invasive exotic plant species; despite this alien threat, some areas of native forest still remain, mostly in the more-remote southern part of the island. The floristic and vegetation distribution data available for Pitcairn are now probably more complete than for most other Pacific islands, and they have facilitated the development of conservation priorities. The co-operation between government agencies, local communities and external scientific advice provides a useful practical approach to conservation that can hopefully be applied elsewhere in the Pacific.
The Pitcairn Group of islands, a British Overseas Territory, occupy the south-eastern extremity of Polynesia. The group consists of two atolls, Oeno and Ducie, the raised atoll or makatea island of Henderson, and the 'high' island of Pitcairn. Oeno, Henderson and Ducie all originated from the same lithospheric hotspot, while the much younger Pitcairn originated from a separate, parallel hotspot lineation (Spencer, 1989). The eruption of Pitcairn caused the lithospheric flexure that resulted in the uplift of Henderson (Blake, 1995). For further details of the geological history of the island group, see Spencer (1995). The islands are exceptionally remote, and form the south-eastern extremity of the Malesian phytogeographic region of van Balgooy (1974). As a result of this remoteness from source islands which lie to the west, the flora and fauna of these islands is relatively depauperate.
Botanical interest in the group centers on the World Heritage Site of Henderson, which contains an almost intact vegetation cover with very few non-native species (Waldren et al., 1999) and several endemic higher plant taxa (Waldren, Florence & Chepstow-Lusty, 1995a; Florence, Waldren & Chepstow-Lusty, 1995). Pitcairn shows considerable disturbance from Polynesian settlers and the 'Bounty' mutineers and their descendants but still contains endemic higher plant taxa (Florence et al., 1995) and remnants of native forest (Waldren et al., 1995b). There have been relatively few specific plant collecting missions to Pitcairn (Göthesson, 1997), the most important being by R.A. Young in 1898 (see Maiden, 1901), H. Ross between 1931 and 1935 (see St. John, 1987), H. St. John and F.R. Fosberg in 1934 (see St. John, 1987), I.T. Twyford in 1955 (see Göthesson, 1997), W.H. Lintott in 1956/57 (see Göthesson, 1997), and J. Florence, S. Waldren and AJ. Chepstow-Lusty in 1991 (see Florence et al., 1995). Several smaller collections have also been made (see Gothesson, 1997), however very few of these involved visits by professional botanists, and little attention has previously been given to the conservation status of the Pitcairn flora. During the Sir Peter Scott Commemorative Expedition to the Pitcairn Islands 1991-1992 (Benton, 1995) only one week was spent collecting on Pitcairn, mostly in adverse weather; this brief visit indicated the threatened or uncertain status of many of the native vascular plants (Waldren et al., 1995a).
A more detailed survey of the vegetation and flora was undertaken in 1997, when the four senior authors spent ten weeks on Pitcairn. The aims of this expedition were to document and assess the status of the indigenous flora, map vegetation communities, assess the status of invasive species, and collect arthropods (also understudied on Pitcairn in 1991-1992). The information gained has been used to formulate conservation guidelines for the island, in consultation with the Island Council and the Conservation and Quarantine Officer. We were fortunate that our visit coincided with a programme to eradicate rats from the island, which required the construction of a network of trails for bait laying. This enabled us to visit almost all parts of the island, the first time such detailed botanical exploration has occurred on Pitcairn. This paper summarises our knowledge of the flora and its conservation status, and describes some of the conservation priorities and initiatives that have resulted from the 1997 expedition.
The total vascular plant flora amounts to some 80 taxa; to this must be added at least 50 fully naturalised taxa, and many other deliberate introductions. At least eight new records for the island were made in 1997. Some had clearly been overlooked (e.g. Trichomanes tahitense, Ophioglossum reticulatum and O. nudicaule) as they occur in well-botanised sites known to have been visited previously. Some represent first collections of taxa previously thought to occur, such as Psydrax odoratum; this is remarkable, as the islanders have long used the species as a Christmas tree. Psydrax was listed (as Canthium odoratum) in an unpublished list of H. St. John's Pitcairn collections seen by SW, although St. John claimed subsequently that the species did not occur on Pitcairn (Göthesson, 1997). Other taxa were collected from parts of the island which have probably not been visited by botanists, much of the southern side of Pitcairn is very steep and rough with difficult access. Some of the latter still require accurate identification, and it is possible that they may represent new endemic species; these include a distinct but highly localised Peperomia sp. (Peperomiaceae), and a possible Elatostema sp. (Urticaceae) which is restricted to cliffs in an almost inaccessible valley.
Florence et al. (1995) listed nine vascular plants endemic to Pitcairn. The Peperomia sp. and Elatostema sp. referred to above might possibly be added to this list. The distribution of all endemic, local or rare plants was mapped; some sample distributions are shown in figure 2. There are clear centres of local diversity in the valleys away from the settlement, including Faute and McCoy's Valleys, Tautama and Brown's Water. The latter site, despite being densely shaded by the invasive Syzygium jambos, is of exceptional interest; fourteen of the twenty Pitcairn pteridophytes occur there, in addition to the endemic Peperomia pitcairnensis.
Some of the naturalised taxa are invasive and present threats to the native flora. The most notorious is Lantana camara, which forms dense thickets and is well known as a weed elsewhere. Syzygium jambos was originally planted for fuel wood, but the plants are now very large and the branches have spread laterally in places to form a monospecific canopy under which few native species will grow. Although seed germination is apparently high, fruit dispersal is probably limited to movement by rats and by rolling down slope under gravity. Other problem species include Canna indica, which forms dense stands in some open valley floors, Sorghum sudanense which is widespread along tracks and in disturbed areas, Passiflora maliformis and Crinum asiaticum in coastal situations. Some taxa known to be invasive elsewhere currently exist in relatively low numbers including Carpobrotus sp. and Leucaena leucocephala. As already stated, the flora of Pitcairn is relatively impoverished compared to high islands further west which are the main sources for colonisation. The remoteness of Pitcairn and the small size of the island doubtless contribute to this impoverishment. Figure 3 shows some of the biogeographic affinities of the flora, we have grouped the data into broad categories to allow comparison: clearly this represents a very preliminary overview of Pitcairn phytogeography.
The flora of Pitcairn is clearly derived from that of Polynesia to the west, about half of the taxa are endemic to the broad area of Polynesia. A small number of taxa are restricted to eastern Polynesia (Pitcairn group, Gambiers, Marquesas, Hawai'i), and somewhat more are restricted to southern Polynesian group (mainly Austral Islands, but extending to New Zealand). One of the latter also occurs in S. America. Henderson, by comparison, has a greater proportion of eastern and southern Polynesian floristic elements (S. Waldren, unpublished data). Less than half of the Pitcairn flora also occurs on nearby Henderson, and many of these are littoral species; this probably highlights the different ecological niches available on the two islands. In general, there are few affinities with Easter Island to the east, all examples being pteridophytes. Most of the endemic taxa have relatives elsewhere in southern, central or eastern Polynesia.
The intensive period of field work in 1997 has enabled more accurate threat status to be assigned to the flora of Pitcairn. The status of several of the rarer and endemic taxa was assessed by population survey. Threat numbers were assigned to all native species based on modifications of the approaches of Rabinowitz et al. (1986) and Curtis & McGough (1987). The following criteria and scores were used to assess threat number:
Population size (estimated or recorded effective population size):
1000+ individuals 0 501-1000 individuals 1 101-500 individuals 2 51-100 individuals 3 11-50 individuals 4 5-10 individuals 5 1-4 individuals 6
The class intervals selected weights the scores in favour of smaller populations.
For mapping, the island was divided into 250 X 250 m squares, and species were recorded from 75 of these squares. The scores were calculated by expressing the number of squares in which a taxon was recorded as proportion of the 75 squares possible (p), and converting this by a cubic function standardised to give a maximum score of 4:
The cubic function weights the scores in favour of taxa that occurred in few grid squares.
Attractiveness: Usefulness: Taxon not obviously attractive 0 Taxon with no known or potential uses locally 0 Taxon with attractive foliage or flowers 1 Taxon with some potential or minor use 1 Taxon representing an important local resource 2
Remoteness: Accessibility: Taxon generally occurring in populations remote from tracks or settlement 0 Access to all populations very difficult 0 Taxon with at least some populations moderately close to trackways 1 Easy access to all populations 1 Taxon with the majority of populations close to trackways and habitation 2
Accessibility and remoteness define the potential of humans to interfere with populations: remote populations occur in sites that are rarely likely to be visited, while inaccessible populations are difficult to reach (on cliffs, for example) though not necessarily remote.
Habitat specificity: Habitat vulnerability: Taxon occurs in a variety of habitats 0 At least some of the habitats in which the taxon occurs are stable 0 Taxon occurs in a moderate habitat range 1 Habitats somewhat unstable or threatened 1 Taxon restricted to a narrow habitat range Taxon occurs in habitats which are unlikely to persist in present form (including vulnerability due to invasive species) 4
Threat number was calculated for each taxon by summing the scores for each category. The categories of population size, geographic distribution and habitat vulnerability have been given a greater weighting in calculating the threat score, and attractiveness and accessibility have been down weighted. The maximum threat score under this method was 22, with a minimum of zero. Table 1 lists all taxa with a threat score of 11 or greater and their corresponding IUCN threat category on Pitcairn; full data are given in appendix 1. In general there is overall agreement between the threat score and the IUCN category. When the latter are ranked from Lowest Risk (rank 1), to Critically Endangered (rank 4), the threat score and category rank were highly correlated (Spearman's Rank Correlation coefficient, 0.878). Note that threat scores could not be calculated for extinct taxa, as data on their habitat and distribution were unknown.
Despite the apparent relationship between threat score and IUCN category, there were some anomalies. For example, cf. Elatostema sp. with a threat number of only 11.0 was assigned Critically endangered by the IUCN categories, while Cyathea medullaris with a slightly higher threat score of 11.4 was only classified as Vulnerable. This is probably because the Elatostema exists in small numbers on a small area of very remote cliffs, while the Cyathea is more widespread but occurs in easily reached locations and has some potential for exploitation. We consider that the threat score gives a truer reflection of the overall extinction threat on Pitcairn. Moreover, the threat score can be used to prioritise conservation action on Pitcairn, particularly when these data are considered together with the range of the taxon outside of Pitcairn. Waldren et al. (1995a) have already pointed out that very large and stable populations may occupy a small but stable area of occurrence with a very low risk of extinction, yet must still be assigned as endangered or critically endangered if the latest IUCN categories are used. Generally, the most threatened taxa on Pitcairn are those that occur in very small and geographically restricted populations. The main threats to the Pitcairn flora include critically small population size, highly restricted range, lack of seed dispersal agents, and invasion by exotic species.
We were unable to add a category on regeneration because this was impossible to assess for some taxa. However, we are aware that regeneration is a problem for some taxa. No seedlings of Homalium taypau were seen during our visit, but it is not clear whether this reflects a lack of seed set or the requirement for a specialised regeneration niche. Some species, including Xylosma suaveolens and Psydrax odoratum, clearly set viable seed but lack a dispersal agent on Pitcairn. Berries of these taxa fell beneath parent trees where cohorts of seedlings and saplings could often be found, these fruits would normally be dispersed by birds as on nearby Henderson Island (Brooke & Jones, 1995). The population status of some of the most threatened endemic taxa was assessed in some detail.
Coprosma rapensis var. benefica
This dioecious taxon was originally described as an endemic species but is now considered to be a variety of the Rapa species, although it is still poorly known. Only 12 plants of Coprosma were located on Pitcairn, most were very widely scattered (Fig. 2a). Of these, only one male was positively identified, although some of the indeterminate plants may prove to be male. As most of the isolated female plants were setting fruit, this suggests that we may have under-recorded the taxon, or that pollination is highly efficient over considerable distances, or that the taxon is agamospermous. More studies of this taxon are clearly needed, including comparison with the Rapa plant. We were able to successfully propagate Coprosma by cuttings taken with a heel and treated with rooting hormone. As the largest plant blew down in a storm while we were on Pitcairn, there is urgent need to replicate all remaining genotypes of this highly threatened taxon.
C. cumingii is endemic to Pitcairn, and occurs in a highly restricted range. The main population is at Brown's Water, on or adjacent to a cliff face in an area some 60 by 20 m (Fig. 2b). This cliff face is almost directly below a main track, and any widening of the track may cause significant disturbance to the site. In 1997 a single plant was located in a different valley approximately 500 m from the main population, the first time this species has ever been recorded outside of Brown's Water. In addition to its highly restricted area of occupancy, the population size is very small, with only 26 reproductive plants (Fig 4).
This giant terrestrial fern is an imposing and attractive species, with fronds up to 4 m long. It occurs in a number of scattered populations on the island (Fig. 2c; Table 2) and most of these are small. The leaf scars left as fronds senesce are prominant; recent scars on plants at Browns Water are often much smaller than older ones, suggesting that plants formerly produced larger fronds than at present. However, there is good evidence of regeneration in several populations, both from detached 'stipules' and from sporophyte production from gametophytes. However, many of the newly formed sporophytes at Brown's Water are on steep unstable slopes and it is questionable whether they will survive to maturity. Although currently described as an endemic taxon, the relationship of this species to relatives in the Society Islands and elsewhere is unclear. There is a need for detailed taxonomic appraisal of Polynesian Angiopteris.
This fern was originally described as the endemic Athyrium pitcairnense by Copeland, but is now considered to be part of the widespread D. harpeodes. The species occurs as very small isolated populations or scattered plants (Fig. 2d; Table 3), probably representing severe fragmentation. Further detailed systematic study of the Pitcairn material is needed; if there is any change in its taxonomic rank the taxon will be in urgent need of conservation action. The examples above give some indication of the threats to the native flora, and the clear need to link systematic and conservation studies.
Vegetation communities were mapped by eye from the main ridges and vantage points on the island. Vegetation was also recorded in 83 10 x 10 m quadrats, these were positioned to sample the major vegetation types and as far as possible all indigenous vascular plant taxa at least once; detailed analyses of these data will be published elsewhere. Several distinct communities can be recognised, these are mapped in figure 5. Most of the better areas of remaining native forest occur on the more-remote southern side of the island and at higher altitudes. The best areas of remaining native forest are dominated by the endemic Homalium taypau, often in association with Metrosideros collina, and with a rich ground layer of pteridophytes. Smaller remnants of lower altitude Hibiscus tileaceus forest occurs at Tautama and Pulau.
The small size of Pitcairn has resulted in improved floristic and vegetation community data being available for the whole island, and there are probably few if any other Pacific islands where the distribution of higher plants and their communities is known in such detail. While greater information is still needed for the bryophytes and lichens, these baseline data allow informed conservation priorities to be set. Some recommended conservation priorities will be outlined below, but before doing so it is important to realize that conservation is a management process requiring input of resources and manpower. With a current population of less than 40, manpower for conservation activities is critically limiting on Pitcairn.
It is impossible to dissociate conservation from development, especially as there is a clear need to encourage families to remain on Pitcairn and to encourage those that have left (most for New Zealand or Norfolk Island) to return. Minimum viable human population size may prove to be the critical factor limiting conservation on Pitcairn. Conservation activities clearly need to be integrated with ways to improve the socio-economic conditions on Pitcairn. One development which may well help to stimulate the local economy and reduce the remoteness of Pitcairn, is the proposed construction of an airstrip. This would provide more rapid international access for tourists, trade and islanders via French Polynesia. Ironically, if the airstrip can be sited away from important plant areas on Pitcairn, and if quarantine controls can be improved and enforced, the provision of an airstrip may be of great assistance to conservation activities.
Aside from the integration of such development activities with conservation objectives, several other conservation priorities have been formulated by consultation with the Island Council, the Island Administration and the Island Conservation & Quarantine Officer. These priorities have categorised into short, medium and long term goals, and have been set out in a short draft policy document that we hope will prove acceptable to all parties concerned. Some of the main recommendations are outlined below.
Several protected areas have been suggested on Pitcairn, including areas of high local biodiversity (e.g. Brown's Water), good remaining native forest habitat (Faute Valley, upper McCoy's Valley), a forestry and timber reserve (St Pauls), cultural reserves (Tautama) and provision of a reserve with guided trails (The Hollow/Garnet's Ridge). If these areas can be adequately protected, they would conserve most of the vascular plant diversity and forest resources on Pitcairn. Most of these sites are relatively remote and are not used for other purposes, the exceptions being St Pauls which has been extensively planted with forestry trees, and Brown's Water which is an important watershed very close to a major trackway. One of the major problems in securing conservation of these areas is removing the threat of invasive species and controlling soil erosion.
Control of invasive species is one of the main priorities for conservation action. Some invasive species, including Lantana camara, Sorghum sudanense and Canna indica, are so widespread that their removal is presently impractical. It would be useful to remove such species from particularly sensitive areas, as for example where Lantana is invading the largest colony of Angiopteris chauliodonta, but their removal from large areas would result in rapid soil erosion. More effort should be concentrated on eradication of species such as Leucaena leucocephala which currently exist in small populations, but which are known to be invasive elsewhere. Removal of small areas of Syzygium jambos is feasible and this should be concentrated initially on the upper slopes and in areas where there are currently few trees, such as St Pauls and Faute Valley. Initial efforts to remove Syzygium will involve cutting and controlled chemical treatment of stumps. Small patches will be removed based on current practices used on Norfolk Island (P. Stephenson, pers. comm.). However, it will be essential that the vegetation cover is rapidly re-established to reduce any effects of soil erosion and this might be aided by establishment of plants propagated in nursery conditions. The potential for introducing biological control agents for the main invasive species requires urgent investigation.
The threat numbers described above allow candidate species for recovery programmes to be objectively prioritised. The endemic taxa Coprosma rapensis var. benefica and Ctenitis cumingii are in most urgent need of recovery action. We have successfully propagated Coprosma by cuttings of semi-ripe wood, and due to the low population number it is essential that all remaining genotypes are replicated. The species occurs in degraded areas and there will be an on-going requirement for the management of this taxon. Initially this should take the form of mixed plantings of different individuals in the vicinity of the existing specimens, this will hopefully lead to increased outcrossing. New individuals must also be raised from seed, and the parentage of all individuals tracked. These propagation methods can be carried out in the new nursery being set up on Pitcairn. We have collected tissue samples from all known individuals for molecular analysis; this will facilitate progeny testing and tracking of parentage.
Conservation and recovery of Ctenitis cumingii requires a different approach. Potentially many thousands of plants can be raised from spores, provided the potential problems of cross contamination can be avoided. The main difficulty will be to avoid severely damaging the population while collecting material for propagation, and to establish young sporophytes in suitable habitats outside of Brown's Water. Some potential locations exist for translocation on the southern side of Pitcairn in deep gullies at Tautama and Faute Valley; however, detailed microclimate studies of the sites and of the autecology of the Ctenitis in cultivation should be undertaken before large scale translocation experiments are attempted.
Provision of a Nursery
Following discussions in 1997, the Island Council has secured funding to establish a small nursery on Pitcairn. This will act as a source of material to revegetate small areas cleared of invasive species, provide propagated material of local plant resources, and provide the facilities needed for the Conservation Officer to undertake species recovery work. Clearly, there will be a need for on-going advice and consultation, but the Conservation Officer has already attended a period of training at the Royal Botanic Gardens, Kew, and we are hopeful that future scientific visits to Pitcairn can substantially contribute to the operations of the nursery. The provision of this nursery is an example of close co-operation between a small local community and outside scientific advisors: we see this co-operative approach as an essential means of forwarding conservation objectives while providing empowerment of local communities.
Pitcairn Island has a small but now well studied flora. The distribution of vascular plants across the island is now known in detail, the status and threats to the flora have been assessed, and the patterns of vegetation communities have been described. The provision of these baseline floristic and vegetation community data enables objective conservation priorities to be set: these priorities are essential in a remote location such as Pitcairn, which has limited financial and manpower resources available for conservation activities. Further study of the ecological interactions and processes involved in the relatively simple Pitcairn vascular flora are now required, as this should be of benefit in understanding these processes on other, more complex and biologically diverse islands elsewhere in the Pacific. Finally, we see the close co-operation between scientists, local people and government agencies as an important and essential step forward in furthering the conservation of biological diversity on this planet.
It is a pleasure for SW, NK, PB & JS to acknowledge warm friendship, hospitality, interest and logistic support that the people of Pitcairn Island provided. We thank the Island Council and Pitcairn Island Administration for permission to visit Pitcairn and collect specimens and for logistic support from New Zealand; especially thanks to the Pitcairn Island Administrator Leon Salt. We thank Graham Wragg and Ed Saul for marine transport with the RV Te Manu, assisted by crew member Thalia Sachtleben, and additionally for their support and suggestions in the field. Thanks to Brian Bell and his team at Wildlife Management International who provided field support in numerous ways, not least by cutting a series of trails; thanks especially to Dave and Chazz for their plant hunting exploits. Financial support was generously provided by the UK Foreign & Commonwealth Office, The Linnean Society of London, the Royal Geographic Society, Trinity College Dublin Association & Trust, the Royal Horticultural Society, the Systematic Association, the Merlin Trust, the Percy Sladen Memorial Fund, the Oleg Polunin Trust. We are also grateful for the support provided by Air New Zealand, Air Tahiti and Skye Instruments. JW thanks the UK Darwin Initiative for funding his training visit to Royal Botanic Gardens, Kew.
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Table 1. Pitcairn Island taxa with a threat score of 11 (half the maximum value) or greater, and their corresponding IUCN threat categories and criteria used to assign the categories. Asterisks denote taxa endemic to Pitcairn
Taxon Threat Score IUCN Category Criteria Argusia argentea 17.8 CR B1,D Osteomeles anthyllidifolia 17.3 CR B1,D Coprosma rapensis var. benefica* 16.5 CR B1,D Ctenitis cumingii* 16.2 CR B1,D Ipomoea macrantha 16.0 CR D Celtis pacifica 15.8 CR B1,D Pisonia umbellifera 15.3 EN D Jasminum didymum 15.0 CR D Hernandia sonora 14.5 EN D Diplazium harpeodes 14.0 CR D Ipomoea littoralis 13.8 CR B1,D Angiopteris chauliodonta* 13.4 EN D Lepidium bidentatum 12.8 CR B1 Xylosma suaveolens 12.6 CR D Caesalpinia major 12.5 EN D Dianella intermedia 12.2 CR D Guettarda speciosa 12.2 CR D Psydrax odorata 12.1 EN D Hibiscus sp. 11.9 EN D Peperomia sp.*? 11.7 CR D Adiantum hispidulum 11.6 EN D Cyathea medullaris 11.4 V D cf. Elatostema sp.*? 11.0 CR D Lycopodium cernuum 11.0 V D
Locality Number of individuals Fertile Mature sterile Immature Juvenile Faute Valley 9 0 0 0 0 Below Garnets Ridge 13 1 7 5 0 Below Parlver Valley Ridge 25 0 0 0 0 Below Big Ridge 272 114 17 110 31 Brown's Water (upper) 410 8 36 263 103 Brown's Water (lower) 43 2 2 31 8 Total 772 125 62 409 142
Locality Total Juvenile Medium Mature sterile Fertile Top of Faute Valley 1 0 0 0 1 Above McCoy's Valley 1 0 0 0 1 Below Big Ridge 0 2 0 2 14 Tautama 1 0 0 0 1 Brown's Water 5 0 0 2 1 Aute Valley, far end* 5 0 0 0 5 * Type locality for Athyrium pitcairnense Copel. (=D. harpeodes)
Pitcairn Island vascular plant taxa and recommended local IUCN category. Threat score is the sum of the score for population size (Popn. size), number of localities (Localities), potential use (Useful.), remoteness (Remote) and accessibility (Access) of populations, habitat vulnerability (Vulner.) and specificity (Specific.): descriptions of these codes are given in the text. Endemic taxa are noted with a asterisk.
Taxon Popn. size Localities Attract. Useful. Remote Access. Vulner. Specific. Threat Score IUCN Category Criteria Abutilon pitcairnense* Ex/CR Adiantum hispidulum 3 3.11 1.0 1 1 0.5 1 1 11.6 EN D Alyxia scandens 3 3.54 0 0 1 0.5 1 1 10.0 EN D Angiopteris chauliodonta* 2 2.85 1.0 2 1 0.5 2 2 13.4 EN D Apium prostratum 0 1.58 0 1 0 0.5 0 2 5.1 LR lc Arachnoides aristata 1 1.67 0.5 0 1 1.0 2 2 9.2 V D Argusia argentea 6 3.84 0.5 2 1 0.5 2 2 17.8 CR B1,D Asplenium nidus 2 1.85 1.0 0 1 0.5 1 0 7.3 V D Asplenium obtusatum 0 1.58 0.5 0 1 0 0 2 5.1 LR lc Asplenium shuttleworthianum 0 1.05 0.5 0 0 0 0 2 3.5 LR lc Bidens mathewsii* 1 1.58 0.5 1 1 0.5 2 1 8.6 V D Caesalpinia major 4 3.54 0 0 2 1.0 2 0 12.5 EN D Capparis cordifolia Ex/CR Celtis pacifica 6 3.84 0 1 1 1.0 2 1 15.8 CR B1,D Cerbera manghas 2 2.60 0.5 2 1 0.5 1 0 9.6 EN D Chamaesyce sparrmannii 0 2.60 0 0 1 0 0 0 3.6 LR lc Christella parasitica 0 0.21 0 0 2 1.0 3 0 6.2 LR lc Cocculus ferrandianus 2 3.69 0 0 0 0.5 0 1 7.2 V D Coprosma rapensis var. benefica* 5 3.54 0 0 2 1.0 4 1 16.5 CR B1,D Ctenitis cumingii* 4 3.69 0 0 2 0.5 4 2 16.2 CR B1,D Ctenitis sp. 2 2.37 0.5 0 1 0.5 2 2 10.4 V D Cyathea medullaris 2 1.41 1.0 1 1 1.0 2 2 11.4 V D Cyclophyllum barbatum 2 2.26 0 2 1 0.5 2 1 10.8 V D Davallia solida 0 0.12 0.5 1 2 1.0 2 0 6.6 LR lc Dianella intermedia 5 3.69 0.5 0 1 0.0 1 1 12.2 CR D Dicranopteris linearis 1 1.41 0 1 2 1.0 1 1 8.4 V D Diplazium harpeodes 4 2.98 0.5 1 1 0.5 2 2 14.0 CR D Doodia media 0 1.85 0.5 0 1 0.5 1 0 4.8 LR lc Elatostemma sp. 4 3.54 0.5 0 0 0.0 1 2 11.0 CR D Eugenia reinwardtiana 2 2.05 0 1 2 0.5 0 1 8.5 V D Glochidion comitum* 1 0.81 0 2 1 0.5 2 0 7.3 V D Glochidion pitcairnense 1 0.44 0 2 1 0.5 2 0 6.9 V D Guettarda speciosa 4 2.15 1.0 2 1 0.0 2 0 12.2 CR D Halorhagis cf. stokesii 2 3.25 0 0 0 0.0 1 2 8.3 V D Hernandia sonora 4 2.49 0 1 2 1.0 2 2 14.5 EN D Hibiscus sp. 4 3.39 1.0 0 1 0.5 1 1 11.9 EN D Hibiscus tiliaceus 2 0.70 0.5 1 2 1.0 1 1 9.2 V D Homalium taypau* 0 0.09 0 2 2 1.0 2 1 8.1 LR nt Ipomoea littoralis 4 3.84 1.0 0 1 1.0 1 2 13.8 CR B1,D Ipomoea macrantha 4 3.54 0.5 0 2 1.0 3 2 16.0 CR D Jasminum didymum 4 3.54 1.0 2 0 0.5 3 1 15.0 CR D Lepidium bidentatum 3 3.84 0.5 1 1 0.5 1 2 12.8 CR B1 Lepturus repens 3 3.39 0 0 1 0.5 1 1 9.9 EN D Loxoscaphe gibberosum 1 1.26 1.0 1 0 1.0 1 1 7.3 V D Lycium sandwichense 2 1.85 0 0 1 0.0 1 2 7.8 V D Lycopodium cernuum 1 3.54 0.5 1 2 1.0 1 1 11.0 V D Metrosideros collina 1 0.44 1.0 1 2 1.0 2 1 9.4 V D Morinda myrtifolia 0 1.26 0 0 1 1.0 2 1 6.3 LR nt Myrsine aff. niauensis* Ex/CR Nasturtium sarmentosum 2 3.54 0 0 0 0.5 1 1 8.0 V D Nephrolepis biserrata 1 1.67 0 0 1 1.0 0 1 5.7 V D Nephrolepis cordifolia 0 0.44 1.0 0 1 1.0 1 1 5.4 LR lc Nephrolepis hirsutula 0 0.01 0.5 0 1 1.0 0 0 2.5 LR lc Ophioglossum nudicaule 2 3.54 0 0 0 1.0 2 2 10.5 EN D Ophioglossum reticulatum 2 3.54 0 0 0 1.0 2 2 10.5 V D Osteomeles anthyllidifolia 6 3.84 1.0 0 2 0.5 2 2 17.3 CR B1,D Pandanus tectorius 0 0.03 0.5 1 2 1.0 0 0 4.5 LR lc Pemphis acidula Ex/CR Peperomia blanda 0 1.58 0.5 0 0 0.5 0 0 2.6 LR lc Peperomia pitcairnense* 2 1.95 0.5 0 0 0.5 0 1 5.9 V D Peperomia rapensis 2 2.60 0.5 0 0 0.5 1 1 7.6 V D Peperomia sp. 4 3.69 0.5 0 0 0.5 1 2 11.7 CR D Phymatosorus commutatus 1 1.58 0.5 1 0 1.0 2 2 9.1 V D Phymatosorus powellii 0 2.05 1.0 1 1 1.0 2 2 10.0 LR lc Phymatosorus scolopendria 0 0.00 0 1 2 1.0 0 0 4.0 LR lc Pisonia umbellifera 4 3.25 0 1 1 1.0 3 2 15.3 EN D Pneumatopteris costata 1 1.05 0.5 0 1 1.0 1 1 6.5 V D Portulaca lutea 0 1.33 0.5 0 1 0.5 0 1 4.3 LR lc Procris pedunculata 5 3.84 0 0 0 0.0 0 2 10.8 CR D Psilotum nudum 0 1.19 0.5 0 1 1.0 1 1 5.7 LR nt Psydrax odorata 2 2.60 0.5 2 1 1.0 2 1 12.1 EN D Pyrrosia serpens 0 0.61 0 0 2 0.5 0 0 3.1 LR lc Samolus cf. repens 3 3.69 0 0 0 0.0 1 2 9.7 CR B1 Scaevola sericea 4 3.25 0 0 1 0.5 1 1 10.8 EN D Sesuvium portulacastrum 1 2.05 0 0 1 0.5 0 1 5.5 V D Taeniophyllum fasciola 0 1.58 0 0 1 0.0 0 2 4.6 LR lc Trichomanes endlicherianum 2 3.11 0.0 0 1 0.5 1 2 9.6 V D Trichomanes tahitense 2 2.98 0 0 1 0.5 1 2 9.5 V D Vittaria elongata 2 2.26 0.5 0 1 0.5 1 2 9.3 EN D Xylosma suaveolens 4 2.60 0 1 0 1.0 2 2 12.6 CR D
- Figure 2. Distribution of selected Pitcairn vascular plants: (a) Coprosma rapensis var. benefica, (b) Ctenitis cumingii, (c) Angiopteris chauliodonta, (d) Diplazium harpeodes. The figure shows the 250 x 250 m recording grid used.
- Figure 3. Biogeographic affinities of the Pitcairn Island vascular plant flora.
- Figure 4. Size class frequency for Ctenitis cumingii.
- Figure 5. Vegetation communities of Pitcairn Island.
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