Pacific Island Ecosystems at Risk (PIER)
Report on invasive plant species in Samoa
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Dangerous species not known to be in Samoa
Species that are invasive or have the potential to become so in Samoa
Species that are known or listed as being weedy or invasive elsewhere and are common, weedy or cultivated in Samoa
Native species (or Polynesian introductions) exhibiting aggressive behavior.
Strategies for dealing with invasive species
Appendix 1. Invasive species of environmental concern
Appendix 2. Other invasive plant species, mostly ruderal weeds or of agricultural concern
Appendix 3. Invasive species present in American Samoa, the Cook Islands, Fiji, French Polynesia, Hawai‘i or Tonga but not present in Samoa
Appendix 4. Invasive species of environmental concern by location
Appendix 5. Presence of invasive species of environmental concern within Samoa
Appendix 6. Scientific name synonyms
Appendix 7. Background material and references
Report to the Government of Samoa on Invasive
Plant Species of Environmental Concern
James C. Space and Tim Flynn
U.S.D.A. Forest Service
Pacific Southwest Research Station
Institute of Pacific Islands Forestry
Honolulu, Hawaii, USA
26 November 2002
James C. Space and Tim Flynn (1)
The Government of Samoa requested assistance from the US Department of Agriculture, Forest Service, Institute of Pacific Islands Forestry, to conduct a survey of invasive plant species of environmental concern, similar to surveys conducted in Micronesia, American Samoa, the Cook Islands, Niue and Tonga. The survey was carried out from 21 January through 1 February 2002. Only the main islands of Upolu and Savai‘i were surveyed. It is unlikely that additional species would be found on the Aleipata islands or the islands of Apolima and Manono. If fact, if past experience can be a guide, these somewhat isolated islands will have fewer invasive species than the main islands. Review of papers by Whistler (1983) and Ogle (2001) describing their findings on the Aleipata Islands would seem to bear out this hypothesis.
The objectives of the survey were to: (1) identify plant species presently causing problems to natural and semi-natural ecosystems; (2) identify species that, even though they are not presently a major problem, could spread more widely or are known to be problem species elsewhere; (3) confirm the absence of species that are a problem elsewhere and, if introduced to Samoa, could be a threat there; and (4) make appropriate recommendations.
During our visit local experts(1) showed us sites of known infestations. We also had available copies of botanical surveys conducted in the past (see Appendix 7, References), particularly those conducted by Dr. Arthur Whistler. The intent was only to conduct an overall survey and not an exhaustive survey of the weed flora of the islands. Additional surveys of individual species, sensitive areas or the other islands can and should be conducted as needed. This report summarizes our findings and makes some suggestions for further action.
Invasive species occurring in or of threat to Samoa have been grouped into four categories:
Species that are invasive elsewhere in similar ecosystems but were not seen on our visit and are not reported in the literature as being present in Samoa (264 species).
Species that are invasive or potentially invasive in the Samoa (49 species).
Species that are invasive or weedy elsewhere and are common, weedy or cultivated in Samoa (106 species).
Native species (or Polynesian introductions) that exhibit aggressive behavior (1 species).
These species are listed in Appendix 1. Additional information about each species is located on an Internet site, http://www.hear.org/pier/, and on the PIER-CD, copies of which have been made available to the Ministries of Lands, Surveys and Environment and Agriculture, Forestry, Fisheries and Meteorology.
There are a number of other species that are mostly invasive weeds in gardens, fields, and pastures and along roadsides and don’t seem to pose any particular threat to natural or semi-natural ecosystems. While we did not specifically survey for them, a list of these species, compiled from the literature as well as field observations, is included in Appendix 2.
1. Dangerous species not known to be in Samoa
Samoa is fortunate that a number of troublesome species have yet to reach the country. These are listed in Appendix 1, Table 1. The following list summarizes the worst of these. These species should receive high priority for exclusion from entry into the country and promptly evaluated for eradication if found to be present.
Cecropia obtusifolia is an invasive tree species that is a problem in Hawai‘i and the Cook Islands (Rarotonga). Cecropia peltata, a similar species is invasive in French Polynesia.
Chromolaena odorata (Siam weed) is a highly invasive pan-tropical weed. It will likely show up in Samoa at some point in time and should be promptly eradicated if found. It has tiny, wind-dispersed seeds that can also travel on boots, clothing or used cars or equipment. Biological controls are available but are most effective in open areas, less so in shaded stands. This species would be a major problem for agriculture as well.
Cryptostegia grandiflora (rubber vine, India rubber vine) is a climbing vine that has become a serious problem in northeastern Queensland, Australia. It is present in New Caledonia and Fiji.
Hiptage benghalensis (hiptage) is a problem species in Hawai‘i and is reported to be a very invasive species on La Réunion and Mauritius. The seeds are wind-dispersed and it also can reproduce from cuttings.
Macfadyena unguis-cati (cat’s claw climber) is an aggressive vine that climbs trees and also forms a dense mat on the ground. Control is difficult because it has tuberous roots and reproduces from pieces and cuttings. It is a problem species in Hawai‘i. It is cultivated as an ornamental in Australia, was observed on Niue and is reported to be moderately invasive in New Caledonia (Meyer, 2000).
Maesopsis eminii (musizi, umbrella tree) is a large African tree that has been introduced into other countries as a timber tree. Fruit-eating birds (and possibly fruit bats) spread its seed and it has become a problem in a number of countries. It was introduced as a timber tree to Fiji, where it is starting to naturalize.
Melaleuca quinquenervia (cajeput, paper bark tree) is a native of eastern Australia, New Guinea and New Caledonia. It produces large quantities of wind-dispersed seeds and reproduces profusely after fire or other disturbance. It is a major problem in the State of Florida (US) and is present in Fiji, French Polynesia (Tahiti) and Hawai‘i.
Miconia calvescens (the purple plague, velvetleaf) is undoubtedly the most destructive invasive plant in the Pacific. It has been a disaster to the forest ecosystem of Tahiti in French Polynesia and has subsequently spread to other islands in French Polynesia (Meyer and Florence, 1996). It has also escaped in Hawai‘i and is the subject of an intensive and costly eradication effort there. It recently was discovered in Queensland, Australia, where an eradication project is also under way. This species is an attractive garden plant and might be introduced this way or as tiny seeds on shoes or used equipment.
Other members of the Melastomataceae family (including Arthrostemma ciliatum, Heterocentron subtriplinervium, Medinilla magnifica, Medinilla venosa, Melastoma candidum, Melastoma sanguineum, Memecylon floribundum, Ossaea marginata, Oxyspora paniculata and Tetrazygia bicolor) that are not native or present in the Cook Islands should also be excluded.
Passiflora tarminiana (banana poka, banana passionfruit), a smothering vine that is a problem in Hawai‘i and New Zealand, is also absent. It can smother the forest canopy when the sub-canopy vegetation is disturbed. Passiflora rubra is very invasive in the Cook Islands. Other Passiflora species not already present (Passiflora alata, Passiflora caerulea, Passiflora coccinea, Passiflora pulchella, Passiflora suberosa, etc.) should also be excluded.
Pimenta dioica (allspice, pimento) is an invasive forest tree. The seeds are bird-dispersed. It is widespread in Tonga (‘Eua), planted in Hawai‘i (where it is naturalizing) and reported to be planted in French Polynesia and Fiji as well.
Pithecellobium dulce (Madras thorn) is a thorny tree that is a problem species in Hawai‘i and is present in New Caledonia, Fiji and French Polynesia (cultivated). The seeds are bird-dispersed.
All Rubus species (raspberries, blackberries, thimbleberries, brambles) should be excluded. These include Rubus alceifolius, invasive in Australia (Queensland) and La Réunion; Rubus moluccanus, a serious pest of the Mascarine Islands and present in Australia, Fiji, New Caledonia and the Solomon Islands and Rubus rosifolius, very invasive in French Polynesia and Hawaii and present in New Caledonia, the Solomon Islands and Vanuatu as well. A number of other Rubus species are invasive. In Hawaii, R. argutus (prickly Florida blackberry) and R. niveus (hill or Mysore raspberry) are problems. Introduced Rubus species (in particular, R. niveus) are a major problem in the Galapagos Islands. Some other species that should be excluded are R. ellipticus, R. glaucus and R. sieboldii. In general, where Rubus species are not present on tropical islands, they should not be introduced. If already introduced, they should be evaluated as candidates for eradication. The vines form thorny thickets and the fruits are widely dispersed by birds.
Schinus terebinthefolius (Christmas-berry, Brazilian pepper) is reportedly present, possibly in cultivation, but was not seen. It is a major problem species in Hawai‘i was well as Florida (US) and the Indian Ocean islands of La Réunion and Mauritius. The fruits are very attractive to birds, aiding its spread. It is present, though uncommon, in American Samoa (Tutuila) as well as in French Polynesia (Tahiti) and New Caledonia (Îles Loyauté). It should be excluded or, if found, evaluated for prompt eradication.
A number of potentially invasive grass species are not yet present in Samoa, including:
A number of other grass species of various degrees of invasiveness, including Andropogon gayanus, Andropogon glomeratus, Andropogon virginicus, Arundo donax, Cenchrus brownii, Cenchrus ciliaris, Chloris radiata, Cortaderia jubata, Cortaderia selloana, Cynodon dactylon, Digitaria insularis, Echinochloa polystachya, Hymenachne amplexicaulis, Hyparrhenia rufa, Ischaemum polystachyum, Ischaemum rugosum, Ischaemum timorense, Melinis repens, Microlaena stipoides, Panicum repens, Paspalum fimbriatum, Paspalum urvillei, Paspalum scrobiculatum, Pennisetum clandestinum, Pennisetum polystachyon, Phylostachys nigra, Schizachyrium condensatum, Sorghum halepense, Sporobolus elongatus, Tripsacum latifolium and Urochloa [=Brachiaria] mutica. Grasses are easily introduced as contaminants in imported seed, imported sand and gravel or on used machinery, and by their nature tend to be invasive.
The best indicator that a species might be invasive is the fact that it is invasive elsewhere. However, each island ecosystem is unique and invasiveness cannot be predicted with certainty. A good strategy is to be extremely cautious and exclude these and other species known to be invasive or weedy elsewhere (although the best strategy is to exclude all species not shown by risk assessment to be of acceptable risk). The known problem species that have the potential to cause problems in tropical island ecosystems and are not yet present in Samoa are listed in Appendix 1, Table 1. These species should be excluded through plant quarantine and, if establishment is detected, promptly evaluated for eradication. In addition, species that are reported to be present in American Samoa, the Cook Islands, Fiji, French Polynesia, Hawai‘i and Tonga but are not present in Samoa are listed in Appendix 3. These species would be of high risk of introduction from air and ship traffic between these points and Samoa.
2. Species that are invasive or have the potential to become so in Samoa
A number of known invasive plants that cause trouble in similar ecosystems have been introduced into Samoa (Appendix 1, Table 2). Some of these are already causing problems while others are not. Some are cultivated plants that have not (yet) escaped and their potential for causing damage is so far unknown. However, one of the best predictors of invasiveness is the behavior of the species elsewhere, and these are known troublemakers.
Invasive species already widespread in Samoa
A number of invasive species are already widespread in Samoa. Eradication or extensive control is out of the question for these species, but they may still warrant control in sensitive, natural and protected areas such as the national parks and reserves.
Adenanthera pavonina (lopa, la‘au lopa, coral bean tree), invasive in secondary forests throughout the Pacific, is becoming widespread (and is not native) in Samoa. It is also quite invasive in American Samoa. Trees produce large quantities of seed and the tree will grow on a variety of soils. It has undoubtedly not yet reached its full potential in Samoa and in the future may become a major component of forested ecosystems. Although the seeds are eaten and many people consider it native, it was introduced from Southeast Asia and Malesia. Coral bean has the ability to overtop many native trees and eventually form monospecific stands.
Albizia chinensis (tamaligi uliuli, tamaligi ena‘ena Chinese albizia, silktree) is exceptionally widespread in Samoa, much more so than any other location visited so far in the Pacific. This is an excellent example of how a tree that seems to be a minor problem elsewhere can become a major invader, given time and the right conditions. Based on its behavior in Samoa, other Pacific islands should pay more attention to the invasiveness of this species.
Ardisia elliptica (togo vao, shoebutton ardisia) is widespread in the Vailima Reserve, the Alaoa area and perhaps elsewhere above Apia as well. It crowds out other species in the forest understory. The specimens we saw had prolific fruit. Birds, which eat the fruit, are a major factor in its spread. It is a problem species in Hawai‘i, French Polynesia and in Florida (US). It is now so widespread that it is probably beyond control, except locally.
Two rubber trees, Castilla elastica (pulu mamoe, Panama rubber tree) and Funtumia elastica (pulu vao, African rubber tree), are very invasive. Birds spread the seeds of Castilla while those of Funtumia are wind-borne "parachute" seeds. While already widespread, these two species will become an even bigger problem in the future, judging from the number of seedlings and young trees seen.
Cestrum nocturnum (teine o le po, ali‘i o le po, night-flowering cestrum) is quite prevalent and weedy. It’s another species with bird-spread seeds and could become even more widespread.
Cinnamomum verum (tinamoni, tigamoni, cinnamon) was found to be very invasive in our survey of American Samoa and shows similar characteristics in Samoa. Unfortunately, in Samoa it appears to have been present longer or more widely planted, and is therefore more widespread. It is also present in the Cook Islands (Rarotonga), Fiji, French Polynesia and Hawai‘i.
Clerodendrum chinense (losa Honolulu, losa Onolulu, Honolulu rose) is a shade-tolerant species. It primarily reproduces from root suckers and can form dense thickets, crowding out other species.
Clerodendrum quadriloculare (losa, losa Fiti, bronze-leaved clerodendrum) is widespread, although mostly in cultivation. The species is an attractive yard plant and is commonly planted for that purpose. It is notorious for being a prolific producer of root suckers and, in fact, the plant is easily propagated by means of root cuttings. It is a potential problem because of its ability to invade intact or relatively intact native forests. It has become widespread on Pohnpei, Federated States of Micronesia. In Hawai‘i it is becoming a problem ornamental, producing numerous root suckers that appear some distance from the parent plant.
Clidemia hirta (la‘au lau mamoe, Koster’s curse) is a serious problem species in Hawai‘i and other locations, including Fiji, the Solomon Islands and Vanuatu. It is widespread both in American Samoa and Samoa. This is a very serious weed of the forest understory on a number of tropical islands.
Cordia alliodora (kotia, Ecuador laurel, salmwood) was introduced to Samoa as a forestry tree. It was similarly introduced into Vanuatu and has become a pest there (Tolfts, 1997) as well as in Tonga. It is spreading where it is present in Samoa and will, over time, undoubtedly become a major component of Samoa’s forests.
A number of large infestations of Dieffenbachia seguine (spotted dieffenbachia or dumb cane), a common house and yard plant, were noted in the Vailima Reserve and elsewhere, particularly in stream bottoms and other moist areas. This species has become a problem in American Samoa and is reportedly present in the Cook Islands, Fiji and French Polynesia. Where found in natural areas this species should be removed, as it reproduces vegetatively and can thrive in the dense shade of an intact native forest canopy, crowding out other species.
Extensive areas of Dissotis rotundifolia (dissotis, pink lady) were seen on both Upolu and Savai‘i, the worst infestations seen so far in the Pacific. It forms dense mats, shading out other species, occasionally even climbing over small shrubs. The species is also found in American Samoa (Tutuila) as well as Fiji, French Polynesia and Hawai‘i.
Elaeocarpus angustifolius [=grandis] (sapatua, siapoatua, siapatua, blue fig, blue marble tree, quandong), a native of Australia, is a forestry tree that is invading intact and secondary forests in Samoa.
Falcateria moluccana [=Paraserianthes falcataria] (tamaligi paepae [tamaligi palagi on American Samoa], Moluccca albizia) is not as widespread as on many Pacific islands, its place largely taken by a similar species, Albizia chinensis. It is much more extensively naturalized on Tutuila, American Samoa and Tahiti, French Polynesia.
Patches of two species of ginger, Hedychium coronarium (teuila paepae, white ginger) and H. flavescens (teuila, yellow ginger), are common. These species are invasive in the forest understory and difficult to control. These species have become extensively established in Hawai‘i, where they are a major problem. Unless controlled, these species will probably become even more common over time in Samoa.
Hemigraphis alternata (suipi, metal leaf, red ivy), introduced as an ornamental, was seen at several locations (for example, in the Vailima Reserve and at the trail entrance in O le Pupu Pue National Park) where it forms dense low stands, excluding other species. It is shade tolerant and does well in the forest understory. Two other species with the potential for similar behavior are Tradescantia spathacea (oyster plant, boat plant, boat lily, Moses in a boat) and T. zebrina (wandering jew). These species were seen planted as ornamentals in Samoa. On other Pacific islands they have escaped into the forest understory. All of these plants are commonly spread through the dumping of garden cuttings.
Hyptis pectinata (vao mini, mint weed) is a ubiquitous weed of roadsides and disturbed areas.
Kyllinga polyphylla (tuise tele, tuise Fiti, Navua sedge) is also very common on roadsides, pastures and disturbed areas.
Leucaena leucocephala (lusina, pepe, fua pepe, leucaena) is common, as on most Pacific islands, but it is not as big a problem in Samoa as it is in some other locations.
Mikania micrantha (fue saina, mile-a-minute weed), a smothering vine, is spread both by seed (dispersed by wind or in clothing or hair of animals) and vegetatively from broken stem fragments. Each node of the stem can produce roots. This species is becoming widespread throughout the Pacific and is a major pest wherever it occurs.
Mimosa diplotricha [=invisa] (la‘au fefe palagi, vao fefe palagi, giant sensitive plant) is a particularly nasty plant covered with thorns, forming dense tangles that are difficult to walk through. It is present in a number of South Pacific locations (American Samoa, Cook Islands (Aitutaki), Fiji, French Polynesia (Society Islands), New Caledonia, Niue, Papua New Guinea, Solomon Islands and Vanuatu) and appears to have become established fairly recently in Samoa. However, it is already well beyond any hope of eradication. Based on its behavior on other Pacific islands, it will become much more prevalent in Samoa in years to come, undoubtedly becoming a major pest plant. A biological control agent is available. Mimosa pudica (vao fefe, tuitui, vao tuitui, sensitive plant), a smaller plant with only small prickles, is common throughout Samoa as a component of the weedy vegetation of roadsides and other disturbed areas.
Odontonema tubaeforme (totoe, fire spike, cardinal flower) is invasive at a number of locations on both Upolu and Savai‘i. It is a serious problem due to its ability to invade the understory. While it is present on a number of Pacific islands, the infestations seen in Samoa are the worst seen to date.
Panicum maximum (vao kini, Guinea grass, buffalograss) is the most troublesome non-native grass in Samoa, as on many Pacific islands. It forms dense stands up to 2 m tall. The seeds are dispersed by wind and it can survive long periods of drought. It spreads by seed and locally from underground rhizomes.
Psidium guajava (ku‘ava, guava) is common, but nothing like the dense stands seen in Tonga. This is a major invasive species in the Galapagos Islands and a problem in French Polynesia (Marquesas Islands), New Caledonia, Hawai‘i and Fiji as well. Frugivorous birds, as well as rats and feral pigs, disperse the seeds. It will continue to be a weedy component of the vegetation in Samoa and may, over time, become much more widespread.
Solanum torvum (lapiti, prickly solanum, devil’s fig) is a large spiny species of disturbed areas and fields that forms dense, impenetrable thickets. Its seeds are bird-spread, and it has probably not yet reached its full potential in Samoa. A leaf-eating chrysomelid beetle, Leptinotarsa undecimlineata, is reported to be host-specific and might be a useful control agent. (Waterhouse and Norris, 1987). Landowners should be encouraged to control the plants on their land.
Spathodea campanulata (African tulip tree) is fairly common as an ornamental tree. It is a major problem in Fiji, the Hawaiian Islands and some other places. The seeds are wind-dispersed and it also propagates from root suckers and cuttings. Large trees do not stand up well to wind. Further planting of this species should be discouraged and existing trees monitored for spread. The possibility of biological control is being investigated in Fiji.
Stachytarpheta cayennensis [=urticifolia] (mautofu tai, mautofu vao, mautofu fualanumoana, blue rat’s tail) is very common in Samoa as it is throughout the Pacific. While mostly a pest in open areas, it can invade into the forest, particularly when there has been disturbance.
Invasive species of limited extent
The following species are limited in extent or have recently become established. Some of them are only in cultivation and could be eradicated at minimal cost. Others are more widespread, but are high priority candidates for eradication because of their invasive potential. Others should be monitored for possible future action, if necessary.
A few examples of Asparagus setaceus (ornamental asparagus) and Asparagus densiflorus (asparagus fern, sprengeri fern) were seen, all in cultivation. On several islands in Tonga, the thorny vines of Asparagus setaceus have become established in the forest understory, climbing into the canopy. Asparagus densiflorus has recently been found to be rather widespread in Hawai‘i on the island of Kauai. There it is spreading along roadsides and invading secondary forest and seems to have the ability to withstand herbicide treatments used to control vegetation along roads. The seeds are bird-dispersed, and both may be spread vegetatively through root tubers. They are commonly sold as ornamentals. Since few examples are present in Samoa, they could easily be eradicated and future imports prohibited.
Carludovica palmata (Panama hat plant) was seen both cultivated and as small naturalized populations in the Vailima Reserve and the Alaoa area. It has the potential to spread more widely in the forest understory.
Cedrela odorata (cigar box cedar, Mexican cedar, Spanish cedar) has been introduced to Samoa as a timber species. It is invasive in South Africa.
Coccinia grandis (ivy or scarlet gourd) is a smothering vine that is a serious problem on Saipan. The vines climb over trees and form such dense cover that the forest underneath is completely shaded out and destroyed. It is also invasive in Guam and Hawai‘i and is reportedly present in Fiji and Vanuatu. It is a vegetable commonly used in southeastern Asian cooking and the plant is often introduced for that reason. A single plant was found on the Alaoa Road just off the cross-island road across from the R. L. Stevenson estate. Although this was a female plant (the species is dioecious) and not setting fruit, all that it would take would be the introduction of a male plant in the vicinity and fruit production would begin. In any case, the plant is still dangerous, as it has managed to become widespread on Guam even only one sex is present there. It readily spreads vegetatively through cuttings and, if fruit is present, by birds and probably pigs.
Eichhornia crassipes (water hyacinth) was seen in drainage ditches in Apia. Water hyacinth is a well-known problem worldwide in freshwater lakes, ponds, marshes, ditches, canals and slow-moving streams. It reproduces both by seed and vegetatively. It was reported to have been much more common in the past (per Bill Cable) and it would be desirable to complete its eradication.
Epipremnum pinnatum cv. 'Aureum' [=Scindapsus aureus] (pothos, money plant) was seen in the Vailima Botanical Garden. This species can invade the forest understory and climb trees. It is closely related to a native plant but is not native to Samoa. Since it only reproduces vegetatively from cuttings and pieces, it will be all right to retain it in the botanical garden, if desired, but cuttings should be disposed of properly. Any infestation found growing in the forest should be eliminated.
Flemingia macrophylla was seen naturalizing along the road west of A‘opo on Savai‘i. It was seen naturalizing in American Samoa as well. If this is the only area and it is limited in extent, this species should be a candidate for eradication. Flemingia strobilifera (luck plant, wild hops) was seen on a previous visit to Upolu. This species is a prolific seed producer and can form dense thickets. It is invasive in French Polynesia and Hawai‘i and is beginning to naturalize in Tonga. It has the potential to become a serious problem.
A single specimen of Grevillea robusta (silk oak) was noted at the watershed nursery, Vailima. This tree is commonly introduced as an ornamental and for forestry plantings. It has become a pest in Hawai‘i and is naturalized and starting to spread on the island of Rurutu in the Austral Archipelago, French Polynesia. If this is the sole specimen, it should be eliminated; if it has been planted for elsewhere it should be monitored for spread.
Hevea brasiliensis (Brazilian rubber tree, Para rubber tree) is a third rubber tree present in Samoa. It was seen along the road to Vaipouli College, Savai‘i, but may be planted elsewhere according to Bill Cable. This species is reported to be naturalizing on Christmas Island (Indian Ocean). Given Samoa’s bad experience to date with rubber trees, this one should be monitored closely for spread (or eliminated).
Lantana camera (latana, lantana) appears to be quite well under control on both islands. Most of the specimens seen were ornamentals in gardens (although we were told it was illegal to grow it).
A Ligustrum plant (L. sinense?) was noted in cultivation in a yard across from the Island Rock 2 Video store on the cross-island road, just beyond the Malua Printing Press building, Apia. Privets are notorious invaders and it would be desirable to eradicate this example and exclude them from the country in the future.
Lonicera japonica (Japanese honeysuckle) was seen in cultivation on Savai‘i. This species is a serious pest in a number of countries and is on the New Zealand noxious weed list and banned from sale in that country. It can be spread both by birds and cuttings, but may be mostly a threat at higher elevations on tropical islands.
Merremia tuberosa (wood rose), a climbing, smothering vine, is notable for its aggressive behavior on Niue. It is also a problem species in Hawai‘i. It was seen at Asau, Savai‘i and may be planted as an ornamental elsewhere.
Piper auritum (‘ava Tonga, eared pepper, also called "false kava") has been introduced to Pacific islands as a fast-growing form of kava, but it is worthless in this regard. It is becoming widespread in Tonga and is presently subject of an eradication campaign on the island of Pohnpei, Federated States of Micronesia. It has also been introduced into Hawai‘i but the local kava growers association is working with the authorities to eradicate it there as well. See also SPC Pest Alert No. 19, False Kava. This species suckers profusely and produces many small seeds that can be spread by birds, rodents and bats and can also be introduced into new areas on machinery. Locally, it spreads by suckers, forming large clumps. Piper auritum was seen at scattered locations on both islands. This appears to be quite a dangerous species, both from the standpoint of invasiveness and as a threat to the ‘ava industry.
Psidium cattleianum (ku‘ava, strawberry guava) is a small tree that forms dense thickets. It is a major problem species in a number of island ecosystems including Hawai‘i and Tahiti well as La Réunion and Mauritius in the Indian Ocean. Varieties with red and yellow fruits are known. Birds and pigs (and possibly fruit bats as well) disperse the seeds. There is an infestation that apparently has been there for some time off the cross-island road at Malololelei. This is an extremely dangerous species.
Several examples of Schefflera actinophylla (octopus tree) were seen in cultivation. It has bird-dispersed fruits and is invasive in Hawai‘i, Micronesia and French Polynesia.
Sesbania grandiflora (sepania, hummingbird tree, scarlet wisteria tree) is mostly cultivated as an ornamental but seems to be naturalizing, as was also observed in American Samoa.
Vigorous, monospecific stands of the grass Setaria palmifolia (vao ‘ofe‘ofe, palmgrass, short pitpit) were seen in the Vailima Reserve and the Alaoa area. Wind or birds distribute its seeds. It is invasive in Tahiti and Hawai‘i and is on the New Zealand noxious weed list.
Solanum capsicoides was seen at Asau on Savai‘i. Although small, it is quite spiny and would not be a desirable addition to the vegetation of Samoa. It produces large amounts of small, tomato-like fruit. Spread may be by birds or pigs or by humans who use the fruit in lei making. It is becoming widespread on Tonga.
Syngonium angustatum (arrowhead plant, goosefoot plant), a climbing aroid, is mostly cultivated in Samoa, but some escapes were noted (Vailima). This species has the ability to spread in the deep shade of intact forests, forming a dense mat on the forest floor as well as climbing trees. It is difficult to eradicate as it is able to reproduce from a single node and bits and pieces of the stems or roots are easily overlooked. It spreads from dumped cuttings. It is a problem species in American Samoa, is widespread in Hawai‘i and is quite invasive in Niue. It spreads vegetatively so should be controlled outside of cultivation.
Tephrosia candida was found spreading along the main road near the A‘opo sawmill on Savai‘i. It is becoming well established on a number of the southern Cook Islands and there is every indication that it will be a pest species.
Isolated specimens of Tibouchina urvilleana (glorybush, lasiandra, princess flower) were seen near the top of the cross-island road on Upolu. This species, along with its close relative Tibouchina herbacea, is a major problem in Hawai‘i.
Toona ciliata (tuna, Australian red cedar, toon) has been introduced as a forestry tree. This species has wind-dispersed seeds and should be closely monitored for invasiveness.
Wedelia [Sphagneticola] trilobata (Singapore daisy) has become a serious pest on many Pacific islands (Thaman, 1999) as well as in Australia. It is planted and naturalizing at a number of locations throughout Samoa. It forms dense mats along roadsides and in disturbed areas and is a problem in agriculture. Control by chemical means is difficult and mechanical removal often leaves numerous nodes that freely root and rapidly spread. Eradication involves several visits to the site for follow-up action.
3. Species that are known or listed as being weedy or invasive elsewhere and are common, weedy or cultivated in Samoa
A large number of other common or weedy introduced species were noted. Many of these species, which might best be termed aggressive weeds, are mostly prevalent along roadsides or on disturbed sites, although some species, particularly alien trees, can gradually spread into forested ecosystems. In the case of vines and plants that form dense ground cover, the regeneration of native species can be inhibited. Some of these species could become a problem in the future, since there is often a long lag time between introduction and when a species begins to cause serious impacts. These species (listed in Appendix 1, Table 3) should be monitored for spread and possible control measures, if necessary.
Antigonon leptopus (chain of hearts), a climbing vine often planted as an ornamental, is a widespread pest on Guam. Only a few examples, mostly in cultivation, were seen on Samoa.
Bryophyllum delagoense [=Kalanchoë tubiflora] (chandelier plant) was seen in cultivation. It reproduces vegetatively and can be invasive on the forest floor.
Calliandra calothyrsus (kaliana, powderpuff, red calliandra) is used in plantings for watershed stabilization. It should be monitored for spread.
Cyperus involucratus [=alternifolius] (umbrella sedge) was mostly seen in cultivation. It can be an invader in wet areas.
Indigofera suffruticosa (la‘au mageso, indigo) is established in some areas and is likely to become more common. It is a major weed species in Tonga.
Murraya paniculata (orange jessamine, satin-wood, Chinese box) is cultivated as a hedge and ornamental plant. It has bird-dispersed seeds and thus the ability to spread. In Asia, M. paniculata is the preferred host of the insect pest Diaphorina citri, the citrus psyllid. The psyllid is the vector for the serious disease "citrus greening".
Passiflora foetida (love-in-a-mist) is widespread. It is quite prevalent on most Pacific islands.
Ricinus communis (lama palagi, lama papalagi, castor bean) is very common along roadsides and in disturbed places.
Tecoma stans (yellow bells, yellow-elder, yellow trumpetbush) is a serious invader of disturbed areas in Tonga and French Polynesia. It grows in dense stands, commonly with other weedy species. The seeds are wind-dispersed.
Some exotic tree species that have been introduced to Samoa include Acacia auriculiformis (earleaf acacia), Acacia mangium (mangium), Bauhinia monandra (orchid tree), Ceiba pentandra (kapok), Delonix regia (flame tree), Gliricidia sepium (mother of cacao, quickstick), Samanea saman (monkeypod) and Thevetia peruviana (yellow oleander). These species often naturalize and are more or less successful depending on local conditions.
In addition to Panicum maximum and Setaria palmifolia, a number of introduced grasses are established, including Axonopus compressus (carpetgrass), Axonopus fissifolius (narrow-leaved carpetgrass), Bothriochloa bladhii, (blue grass, Australian beardgrass), Cenchrus echinatus (tuitui, vao tuitui, bur grass); Chloris barbata, (swollen fingergrass), Digitaria ciliaris (fingergrass, smooth crabgrass), Digitaria violascens (smooth crabgrass, violet crabgrass), Eleusine indica (fahitalo, lau ta‘a ta‘a, ta‘a ta‘a, goosegrass), Paspalum conjugatum (vaolima matafao, vaolima papalagi, T grass), Paspalum dilatatum (dallis grass), Paspalum paniculatum (Russell river grass, galmarra grass), Pennisetum purpureum (vao povi, elephant grass, napier grass, merker grass), Saccharum spontaneum (vao tolo, wild cane, false sugarcane), Sacciolepis indica (glenwood grass), Setaria pumila (foxtail), Sporobolus indicus (smutgrass, wiregrass, Indian dropseed) and Urochloa [=Brachiaria] subquadripara (green summer grass). Bamboos (Bambusa spp.) are also present.
Other weedy species include Bidens pilosa (beggar’s tick), Chamaecrista nictitans (partridge pea, Japanese tea senna), Clerodendrum buchananii (red clerodendrum, pagoda-flower), Clerodendrum paniculatum (pagoda flower), Costus speciosus (crepe ginger), Crassocephalum crepidoides (fualele, thickhead, fireweed), Cyperus rotundus (mumuta, nut grass, nutsedge), Kyllinga nemoralis (ta‘a ta‘a, ta‘a ta‘a vili taliga, matie upo‘o, matie Tahiti, mo‘u upo‘onui, mo‘u upo‘o, tuise, white kyllinga), Leonurus japonicus (Lion’s tail), Macroptilium atropurpureum (siratro, purple bushbean), Momordica charantia (bitter-melon), Ocimum gratissimum (la’au sauga, wild basil), Orthosiphon aristatus (‘ava pusi, cat’s whiskers), Pueraria montana var. lobata (a'a, kudzu), Ruellia prostrata (vao uli, black weed, bell weed), Sambucus mexicana (elderberry, Mexican elder), Sanseveria trifasciata (bowstring hemp, mother-in-law’s tongue), Senna [=Cassia] tora (vao pinati, peanut weed), Solenostemon [=Plectranthus] scutellarioides (pate, patiale, la‘au fai sei, coleus), Thunbergia alata (black-eyed susan vine) and Thunbergia fragrans (white lady, white thunbergia, sweet clock-vine).
Species that are cultivated or of limited extent but have the potential to become more widespread include Abelmoschus moschatus (‘aute toga, fau tagaloa, fua samasama, musk mallow), Allamanda cathartica (yellow trumpet vine), Calliandra surinamensis (Surinamese stickpea), Duranta erecta (golden dewdrop), Heliconia spp., Nymphaea spp. (waterlily), Schefflera arboricola (dwarf brassia, dwarf schefflera), Senna [=Cassia] alata (fa‘i lafa, la‘au fai lafa, candle bush), Syzygium jambos (seasea papalagi, malabar plum, rose apple), Thevetia peruviana (be-still tree, yellow oleander, lucky nut) and Tithonia diversifolia (tree marigold).
Some additional invasive plant species, mostly ruderal weeds or of agricultural concern, seen or reported to be present, are listed in Appendix 2.
4. Native species (or Polynesian introductions) exhibiting aggressive behavior
Merremia peltata (fue lautetele, merremia) is quite invasive along forest edges and wherever there has been disturbance. It is not known whether this species is native or an early introduction to Polynesia, but it is reported here as a native species. Local people say that it was once uncommon, but this may just be because there is now substantially more disturbed area that provides suitable habitat. In any case, whether native or not, it is certainly an aggressive vine, not only in Samoa but on other Pacific islands as well.
Chrysopogon aciculatus (mutia tai, mutia vao, Mackie's pest, lovegrass) and Miscanthus floridulus (fiso, ‘u, swordgrass) are aggressive native grasses.
Strategies for dealing with invasive species
It was not our purpose to perform a review of quarantine operations and other methodologies for excluding and managing invasive species. The Samoa Quarantine Improvement Project and the planning effort presently underway will undoubtedly address many of these areas in more depth. Rather, the following strategies are a summary of general principles that have proven effective in dealing with exotic plant pests. For a more in-depth treatment of the principles of invasive species management the publication "Invasive alien species: a toolkit of best prevention and management practices" is available.
Samoa has laws and regulations in place that deal with quarantine and new introductions. The first line of defense against invasive species, and the most cost-effective, is to keep them out. Control at ports of entry is essential, and those concerned with the protection of natural ecosystems must work closely with plant protection and quarantine officials to combat known and potential invasive plant species. Plant quarantine officers should be familiar with both agricultural pests and those that threaten wildland ecosystems. At a minimum, a list of known noxious species to be excluded should be developed and exclusion of these species should be backed by the force of law and regulation. Better yet is to utilize the "precautionary principle" (now used by Australia and New Zealand and under serious consideration by a number of other counties) to exclude all alien species not shown to be of acceptable risk. Risk assessment and management techniques can be used to assess the likelihood and effects of possible introductions and to develop exclusion and eradication strategies. Samoa is fortunate to have effective quarantine measures in place and operating.
In the case of new introductions, the ability to take prompt action is essential, as expanding infestations soon become uneconomical to control. Provision for emergency response procedures and funds to deal with immediate problems should be in place.
Samoa is to be commended for setting up an invasive species committee. Close and immediate coordination and cooperation between various government departments and other entities is essential when an invasive species problem is encountered, especially when there is a need to move quickly to eradicate an introduced species. Such a committee can be effective both for long-term strategic actions, such as review and strengthening of relevant laws and regulations, as well as short-term tactical and operational problems, such as action when a new species is found to have been introduced. In addition to its management plan, the committee should also draw up a prioritized action plan. This would include critical areas to be protected and species subject to control or eradication as well as which governmental agency would take the lead in control or eradication measures. Time, money and people are always in limited supply and must be directed to the places where they will do the most good. Economic analysis can be used to assess the costs and benefits of management strategies and prioritize action. Some recommendations are made below as to possible actions against some individual plant species, but these should be tested against available resources and other priorities.
Education of the public about the danger of introductions and encouraging the use of native species needs to continue. People should be encouraged to take responsible actions such as following quarantine regulations, not dumping garden cuttings in the woods and reporting suspicious plants. There are many instances where an invasive plant started out as a pretty flower planted in a yard or garden. Public service announcements on television or radio can be used and "wanted" posters can be prepared for critical species. Education of schoolchildren is especially important, as this is the most impressionable age. Children can also have a notable effect on the actions of their parents. Prompt follow-up to public reports and inquiries is essential to maintain the credibility of a public education program.
The public also needs to understand that the immediate eradication of a small area of a problem species, even if it involves the use of pesticides, may be better than living with a problem species forever. There are many instances where you hear people say, "I wish we'd taken action when this pest was first noticed". It may even be worthwhile to take people to a place where they can be shown the full extent of the problem if the infestation is allowed to spread so that they will understand, accept and support eradication. For example, anyone visiting Tahiti would very likely come away convinced that Miconia calvescens is an ecological disaster and that it should be prevented from becoming established on other Pacific islands. The public should be informed and involved in any proposed control or eradication actions.
Local nurseries, botanical gardens or plant importers can be sources of new introductions. A positive approach is to work together to develop a "white list" of both native and non-native species that the public can be encouraged to plant. Likewise, home gardening associations and other village and local groups can perform an important education function for their members in what species to avoid and can assist in reporting infestations of invasive plants.
Foresters, conservation officers, extension agents and others that spend time in the field should be alert to new species that exhibit invasive behavior. Often, these species first show up in urban or farm areas because they are usually introduced by people and tend to first become established on farms or in gardens and disturbed areas. Suspicious plant species should be promptly reported. Periodically scheduled surveys can also be conducted for new or expanding infestations. An evaluation should be conducted for any new species that appears to be invasive or is known to be invasive elsewhere. Assistance by an expert who is familiar with the species and methods for its eradication or control should be requested if needed. Prompt action is essential, since once a species becomes widespread, control or eradication can be extremely costly or impossible. Assistance is also available on-line from experts through the Pacific Pestnet list-server.
Since most land in Samoa is privately owned, the ability of government to require the control of noxious species on private or customary lands or to take action on private lands if the landowner cannot be located or does not take prompt action is essential. New Zealand and some of its town councils have strong laws and regulations that can be used as models.
Although Samoa has laws, regulations and procedures in place to deal with quarantine and new introductions, these are presently under review as part of the Samoa Quarantine Improvement Project.
In addition to the above general strategies, we offer the following specific recommendations:
Make every effort to keep out all the species listed in Appendix 1, Table 1. All of these are known invasive species elsewhere, and there is no sense in running the risk that they will act the same in Samoa. As we are able to gather information on other species that might threaten tropical island ecosystems we will add them to the database. For those with Internet access, additional information and new listings can be found at http://www.hear.org/pier/. The information is also available on the PIER-CD for local use. Assistance from experts in identifying and managing invasive species can also be obtained by subscribing and posting inquiries to the Pacific Pestnet list server.
Take special measures to keep out the species listed in Table A, to monitor for their occurrence and to eradicate them immediately if found. These are all well-documented problem species that have had a major impact on natural ecosystems elsewhere. The potential impact of these species, if they are introduced and become established, is very severe.
Table A. Priority species for exclusion from Samoa
Common Names (abridged)
Cecropia obtusifolia trumpet tree, guarumo Cecropiaceae Hawai'i, Cook Islands Cecropia peltata trumpet tree Cecropiaceae French Polynesia Chromolaena odorata Siam weed, triffid weed Asteraceae Australia, Micronesia, Papua New Guinea, Philippines, Southeast Asia Coccinia grandis ivy gourd, scarlet-fruited gourd Cucurbitaceae Hawai‘i Saipan Cryptostegia grandiflora rubber vine, India rubber vine, Palay rubbervine Asclepiadaceae Australia Hiptage benghalensis hiptage Malpighiaceae Hawai'i, La Réunion, Mauritius Imperata cylindrica blady grass, cogon grass Poaceae Australia, New Zealand, Micronesia, New Caledonia, Papua New Guinea, Philippines, Solomon Islands, Southeast Asia, Vanuatu Macfadyena unguis-cati cat's-claw climber Bignoniaceae Hawai'i, Niue, New Caledonia Maesopsis eminii umbrella tree, musizi Rhamnaceae Fiji Melaleuca quinquenervia melaleuca, cajeput, paper bark tree, punk tree Myrtaceae Hawai‘i, US (Florida) Miconia calvescens miconia, velvetleaf, purple plague, bush currant Melastomataceae French Polynesia, Hawai'i Passiflora tarminiana banana poka, banana passionfruit, bananadilla Passifloraceae Hawai'i Pennisetum setaceum fountain grass Poaceae Hawai'i, Fiji Pimenta dioica pimento, allspice, sipaisi (Tonga) Myrtaceae Hawai‘i, Tonga Pithecellobium dulce Madras thorn, Manila tamarind Fabaceae Hawai'i, Fiji, French Polynesia Pluchea carolinensis sour bush Asteraceae Hawai'I, Tonga Rubus species raspberries, blackberries, brambles Rosaceae Hawai'i, French Polynesia, etc. Schinus terebinthifolius Christmas-berry, Brazilian pepper Anacardiaceae Hawai'i, US (Florida) Tibouchina herbacea glorybush, cane ti, tibouchina Melastomataceae Hawai'i All all other grass species not already present Poaceae pan-tropical All all other non-native melastomes Melastomataceae Hawai'i, etc.
Note: Appendix 1, Table 1 is a complete list of invasive and potentially invasive species of environmental concern not yet present in Samoa. Appendix 2,
Table 1 contains a list of other invasive species not reported to be present in Samoa.
Extraordinary measures need to be employed against Miconia calvescens because its effect on Samoa’s ecosystems would be so devastating if introduced. At a minimum, quarantine officers should be alert to people who might have been in the woods or rural areas in French Polynesia (particularly the islands of Tahiti, Moorea, Raiatea and Tahaa) or Hawai‘i (especially the island of Hawai‘i), and inspect their shoes or boots for seeds. Any trucks or equipment coming from French Polynesia or Hawai‘i, particularly those that have been used in rural areas, must be power washed or steam cleaned. Any infestations picked up from public reporting or scouting should be promptly eradicated before the plants set seed.
Be very cautious in introducing new grasses, as many of them are aggressive invaders. Also, grass seed is invariably contaminated with other, possibly invasive, grasses or weeds.
The species listed in Table B, seen or reported to be only in cultivation, should be closely monitored for spread or, better yet, eradicated if there are few examples, as they are also well-documented invasives elsewhere. They may behave similarly in Samoa if they escape cultivation.
Table B. Cultivated species of possible threat to Samoa
Common Names (abridged)
Anacardium occidentale cashew, cashew nut; ‘apu ‘initia (Samoa) Anacardiaceae
Cook Islands (Ma'uke), Jamaica, Mozambique, South Africa, Western Australia Antigonon leptopus Mexican creeper, chain-of-love, hearts on a chain, coral bells, coral vine Polygonaceae
Guam Asparagus densiflorus asparagus fern, sprengeri fern, smilax, regal fern Liliaceae
Hawai‘i Asparagus setaceus ornamental asparagus, climbing asparagus fern, plumosa Liliaceae
Tonga, Lord Howe Island Bryophyllum delagoense chandelier plant Crassulaceae
Hawai‘i Coccinia grandis ivy gourd, scarlet-fruited gourd Cucurbitaceae
Hawai‘i, Saipan Grevillea robusta silk oak, silky oak, he oak, silver oak, spider flower Proteaceae
French Polynesia (Rurutu) Ligustrum spp. privet Oleaceae
Hawai‘i, Mauritius, La Réunion Murraya paniculata orange jessamine, satin-wood, Chinese box, Hawaiian mock orange Rutaceae
French Polynesia, Hawai‘i; host to citrus psyllid Schefflera actinophylla octopus tree, umbrella tree, ivy palm Araliaceae
French Polynesia, Hawai‘i, Micronesia Tradescantia spathacea oyster plant, boat plant, boat lily, moses in a boat Commelinaceae
Cook Islands (Ma'uke), Niue Tradescantia zebrina wandering zebrina, wandering jew, inchplant Commelinaceae
Cook Islands (Ma'uke), Galapagos Islands
Quite a large number of invasive species are already widespread. These
Adenanthera pavonina, Ardisia
elliptica, Albizia chinensis,
Castilla elastica, Cestrum nocturnum,
Cinnamomum verum, Clerodendrum
chinense and C. quadriloculare,
Clidemia hirta, Dissotis
rotundifolia, Elaeocarpus angustifolius,
Falcataria moluccana, Funtumia
elastica, Hedychium flavescens,
Hyptis pectinata, Kyllinga
polyphylla, Leucaena leucocephala,
Merremia peltata, Mikania
micrantha, Mimosa diplotricha,
Odontonema tubaeforme, Panicum maximum,
Psidium guajava, Setaria
palmifolia and Stachytarpheta cayennensis.
About all that can be done with these species is to discourage further
planting and control them as needed on a local basis. However,
Clerodendrum chinense and
Setaria palmifolia appear to only be present on
Upolu and it may be feasible to prevent their establishment on Savai‘i or to
eradicate them from that island if there are only isolated infestations.
Table C shows the most serious invasive plant species in Samoa and summarizes recommendations for their management. In many cases, more detailed information and recommendations follow the table.
Table C. Summary of major invasive species present in Samoa with recommendations for their management
Common Names (abridged)
Comments and recommendations
|Adenanthera pavonina||Coral bean tree, red sandalwood tree, red bead tree; lopa, la‘au lopa (American Samoa, Samoa and Tonga)||Fabaceae||Widespread and very invasive; control in sensitive and natural areas, such as Tafua.|
|Albizia chinensis||Chinese albizia, silktree; tamaligi uliuli, tamaligi ena‘ena||Fabaceae||Widespread; control in sensitive and natural areas.|
|Ardisia elliptica||shoebutton ardisia; togo vao (Samoa)||Myrsinaceae||Widespread in Vailima Reserve, Alaoa and probably other areas above Apia; control in sensitive and natural areas.|
|*†Asparagus densiflorus||asparagus fern||Liliaceae||Only a few examples seen, all in cultivation; eradication recommended (a pest species in Hawai‘i)|
|*†Asparagus setaceus||ornamental asparagus, climbing asparagus fern, plumosa||Liliaceae||Only a few examples seen, all in cultivation; eradication recommended (a pest species in Tonga)|
|†Carludovica palmata||Panama hat plant||Cyclanthaceae||Cultivated and small infestations in Vailima reserve and Alaoa. Evaluate for eradication.|
|Castilla elastica||Panama rubber tree, Mexican rubber tree, uletree; pulu mamoe (American Samoa and Samoa)||Moraceae||Widespread and very invasive; control in sensitive and natural areas.|
|Cedrela odorata||cigar box cedar, Mexican cedar, West Indian cedar, Spanish cedar||Meliaceae||Monitor for possible spread.|
|Cestrum nocturnum||night-flowering cestrum, night-flowering jasmine, queen (or lady) of the night; teine o le po, ali‘i o le po (American Samoa and Samoa)||Solanaceae||Very invasive species. Control or eradicate in sensitive and natural areas such as Vailima Reserve.|
|Cinnamomum verum||cinnamon tree; tinamoni, tigamoni (American Samoa and Samoa)||Lauraceae||Widespread and very invasive; control in sensitive and natural areas.|
|Clerodendrum chinense||Honolulu rose; losa Honolulu, losa onolulu (American Samoa and Samoa)||Verbenaceae||Widespread and very invasive; discourage further planting, control in sensitive and natural areas, consider eradication on or exclusion from Sava‘i.|
|Clerodendrum quadriloculare||bronze-leaved clerodendrum; losa, losa Fiti (American Samoa and Samoa)||Verbenaceae||Widespred, mostly in cultivation; discourage further planting, control locally as needed.|
|Clidemia hirta||Koster’s curse, la‘au lau mamoe (Samoa)||Melastomataceae||Widespread and very invasive; control in sensitive and natural areas.|
|*Coccinia grandis||ivy gourd, scarlet-fruited gourd||Cucurbitaceae||Plant in cultivation noted on Alaoa Road across from Robert Lewis Stevenson estate. Female plant not setting seed. A serious pest on Guam and Saipan and in Hawai‘i. Eradicate.|
|Cordia alliodora||laurel, Ecuador laurel, salmwood, Spanish elm kotia (Samoa)||Boraginaceae||Very invasive in Tonga and Vanuatu; consider discontinuing planting; monitor spread, control in sensitive and natural areas.|
|Dieffenbachia seguine||dieffenbachia, dumb cane||Araceae||Very invasive in wet areas and will invade under the forest canopy. A number of infestations noted; control in sensitive or natural areas such as Vailima Reserve.|
|Dissotis rotundifolia||dissotis, Spanish shawl, pink lady||Melastomataceae||Widespread; worst infestations of this species seen so far in the Pacific. Control in sensitive and natural areas.|
|Eichhornia crassipes||water hyacinth||Pontederiaceae||Need to control or possibly eradicate in waterways and wetlands.|
|Elaeocarpus angustifolius||blue fig, blue marble tree; sapatua, siapoatua, siapatua (American Samoa and Samoa)||Elaeocarpaceae||Widespread; control in sensitive and natural areas.|
|Epipremnum pinnatum cv. 'Aureum'||pothos, money plant||Araceae||Noted in Vailima Botanical Garden. Can invade forest understory. Monitor for spread and control outside of cultivation as needed.|
|Falcataria moluccana||Molucca albizia; tamaligi palagi (American Samoa); tamaligi paepae (Samoa)||Fabaceae||Will invade widely over time. Widespread, control in sensitive and natural areas.|
|*†Flemingia macrophylla||Fabaceae||Seen along road west of A'opo. If only area a priority candidate for eradication.|
|*†Flemingia strobilifera||luck plant, wild hops||Fabaceae||Not seen on this visit but noted previously. Eradication recommended if not yet widespread.|
|Funtumia elastica||African rubber tree, silkrubber; pulu vao (Samoa)||Apocynaceae||Widespread and very invasive; control in sensitive and natural areas.|
|Grevillea robusta||silk oak, silky oak, he oak, silver oak, spider flower||Proteaceae||May have been introduced as a forestry tree. Has wind-dispersed seeds and is invasive in French Polynesia. Evaluate for eradication if not widespread (seen at watershed nursery, Vailima).|
|Hevea brasiliensis||Brazilian rubber tree, Para rubber tree||Euphorbiaceae||Along road to Vaipouli College, Savai'i. Monitor for invasiveness.|
|Hedychium coronarium||white ginger; teuila paepae (American Samoa and Samoa)||Zingiberaceae||Invasive in forest understory and difficult to control. Consider for eradication in sensitive areas.|
|Hedychium flavescens||yellow ginger; teuila (Samoa)||Zingiberaceae||Invasive in forest understory and difficult to control. Control in sensitive and natural areas.|
|Hemigraphis alternata||metal leaf; red ivy; suipi (American Samoa and Samoa)||Acanthaceae||Often planted as an ornamental and spread by cuttings. Control as needed in areas outside of cultivation.|
|Hyptis pectinata||mint weed; vao mini (Samoa)||Lamiaceae||Widespread, but mostly a weed of roadsides and disturbed areas.|
|Kyllinga polyphylla||Navua sedge; tuise tele, tuise Fiti (Samoa)||Cyperaceae||Widespread, but mostly a weed of roadsides and disturbed areas.|
|Lantana camara||lantana; latana (American Samoa and Samoa)||Verbenaceae||Appears to be quite well under control. Monitor for new infestations in the wild and control as needed. Consider eradication.|
|Leucaena leucocephala||leucaena, wild tamarind, lead tree; fua pepe (American Samoa and Samoa); lusina (Samoa);||Fabaceae||Widespread and invasive; control in sensitive and natural areas Discourage further planting.|
|*†Ligustrum sp.||privet||Oleaceae||One example seen (across from Island Rock 2 Video store on cross-island road, just beyond Malua Printing Press building, Apia); eradication recommended.|
|*†Lonicera japonica||Japanese honeysuckle, Hall’s honeysuckle||Caprifoliaceae||One example seen on Savai'i; eradication recommended.|
|Merremia peltata||merremia; fue lautetele (American Samoa and Samoa)||Convolvulaceae||Widespread; control in sensitive and natural areas.|
|Merremia tuberosa||wood rose, Spanish arborvine, yellow morning-glory||Convolvulaceae||Monitor for invasiveness (seen at Asau, Savai'i) or eliminate.|
|Mikania micrantha||mile-a-minute weed, Chinese creeper, American rope, bittervine; fue saina (American Samoa and Samoa)||Asteraceae||Widespread and very invasive, particularly along roadsides and disturbed areas.|
|Mimosa diplotricha||English: giant sensitive plant, nila grass; vao fefe palagi (American Samoa and Samoa), la'au fefe palagi (Samoa)||Fabaceae||Very invasive and already widespread. Will undoubtedly become much more prevalent. Biological control agent available and its introduction should be investigated. Control as needed.|
|Odontonema tubaeforme||fire spike, cardinal flower; totoe (Samoa)||Acanthaceae||Invasive in a number of locations; control in sensitive and natural areas such as Vailima Reserve.|
|Panicum maximum||Guinea grass, green panic, buffalograss; vao kini (American Samoa and Samoa)||Poaceae||A problem grass in Samoa as on many Pacific islands|
|*Piper auritum||eared pepper, anise piper, Veracruz pepper; 'ava Tonga (Samoa)||Piperaceae||Seen at a number of locations, most apparently planted. This species has become widespread on Tonga. Eradication recommended.|
|*Psidium cattleianum||strawberry guava, cherry guava, Cattley guava, Chinese guava; ku‘ava (Samoa)||Myrtaceae||Infestation just off cross-island road at Malololeleli. A serious pest in Hawai'i and elsewhere. Eradication strongly recommended.|
|Psidium guajava||guava; ku‘ava (American Samoa and Samoa)||Myrtaceae||Can be quite invasive. Control locally as needed.|
|†Schefflera actinophylla||octopus tree, umbrella tree, ivy palm; French: arbre ombelle||Araliaceae||Can be quite invasive. Examples seen were in cultivation. Eradication recommended.|
|Sesbania grandiflora||hummingbird tree, sesban, scarlet wisteria tree; sepania (Samoa)||Fabaceae||Although mostly in cultivation, appears to be naturalizing. Evaluate for control or eradication.|
|Setaria palmifolia||palmgrass, short pitpit, hailans pitpit, broadleaved bristlegrass; vao ‘ofe‘ofe (Samoa)||Poaceae||Becoming widespread in Vailima Reserve, Alaoa and probably other areas above Apia. Control locally as needed, exclude from Savai‘i.|
|*†Solanum capsicoides||cockroach berry, devil’s apple, soda apple||Solanaceae||This species, seen at Asau, Savai'i, is becoming widespread on Tonga. Eradication recommended.|
|Solanum torvum||prickly solanum, devil's fig, turkeyberry; lapiti (Samoa)||Solanaceae||Very invasive, particularly in pastures and disturbed areas. Control by landowners should be encouraged; investigate biological control.|
|Spathodea campanulata||African tulip tree; fa‘apasi (Samoa)||Bignoniaceae||Invasive and also doesn't stand up well to wind. Discourage further planting and work to eliminate from sensitive and natural areas, around houses and buildings, etc.|
|Stachytarpheta cayennensis||blue rat's tail, dark-blue snakeweed, false verbena, nettleleaf velvetberry; mautofu tai, mautofu vao, maatofu fualanumoana (American Samoa and Samoa)||Verbenaceae||Widespread along roadsides, trails and wherever there is disturbance.|
|Syngonium angustatum||arrowhead plant, goosefoot plant||Araceae||Can invade under forest canopy and is difficult to control. Control when found outside of cultivation.|
|*†Tephrosia candida||Fabaceae||Found along main road near the A'opo sawmill. Becoming a pest in the Cook Islands. An excellent candidate for eradication.|
|*†Tibouchina urvilleana||glorybush, lasiandra, princess flower||Melastomataceae||Very invasive in Hawai'i. Seen at one location (top of cross-island road). Eradicate as soon as possible.|
|Toona ciliata||Australian red cedar, toon; tuna (Samoa)||Meliaceae||Introduced forestry tree; monitor for invasiveness|
|Tradescantia spathacea||oyster plant, boat plant, boat lily, moses in a boat||Commelinaceae||Planted as an ornamental. Control outside of cultivation.|
|Tradescantia zebrina||wandering zebrina, wandering jew, inchplant||Commelinaceae||Planted as an ornamental. Control outside of cultivation.|
|*Spagneticola trilobata||wedelia, trailing daisy, Singapore daisy, creeping ox-eye||Asteraceae||A very invasive ornamental species that has not yet spread extensively. It would be desirable to eradicate or it will likely invade most roadsides and disturbed areas over time.|
*High priority for eradication
†Eradication can probably be accomplished at low cost
There appear to be only a few isolated infestations of the Panama hat
plant, Carludovica palmata, in the Vailima reserve and elsewhere. This
species should be evaluated for eradication.
The forestry trees Cedrela odorata and
Toona ciliata, along
with the rubber tree, Hevea brasiliensis, should be monitored for
possible invasiveness. The first two have been invasive elsewhere while the
nature of the third is unknown, although it is reported to be invasive on
Christmas Island (Indian Ocean).
Planting of Clerodendrum quadriloculare should be discouraged.
Several shade-loving species, including Dieffenbachia seguine,
Hemigraphis alternata and Syngonium
angustatum, have become
established in forested areas and several others, particularly
Epipremnum pinnatum cv. 'Aureum',
Tradescantia spathacea and
Tradescantia zebrina were
noted in cultivation. These species have the ability to crowd out other
species in the forest understory. They mostly reproduce vegetatively and the
most common method of spread is through the dumping of plants or cuttings.
Control action may be needed against infestations of Dieffenbachia seguine,
Hemigraphis alternata and Syngonium
angustatum in natural and
sensitive areas, such as the National Parks and Reserves. Eradication or
control when they appear outside of cultivation should be considered for the
others. The public should be encouraged, through education, not to dump garden
cuttings and waste.
Flemingia strobilifera and F. macrophylla are potentially problem species. Flemingia macrophylla was seen only along the road west of A‘opo on Savai‘i and should be considered for eradication. F. strobilifera was not seen but was noted on a previous visit, probably in cultivation. It should also be a candidate for eradication.
A specimen of Grevillea robusta was noted at the watershed nursery in Vailima. As this species has wind-dispersed seeds and is invasive elsewhere it should be closely monitored for spread or considered for eradication.
Scattered patches of Hedychium coronarium were seen. It is a possible candidate for eradication, depending on its extent, but in any case should be controlled where needed to prevent its establishment in the forest understory.
The owner should be requested to eliminate the single specimen of Ligustrum seen in cultivation in Apia. Any others found should also be eliminated and this species prohibited from importation.
Given its invasive nature on Niue, the specimen of Merremia tuberosa seen at Asau, Savai‘i, and any other examples found should be monitored for invasiveness or eliminated.
Introduction of the biological control agent for Mimosa diplotricha should be investigated.
Given its invasive tendencies, Piper auritum is likely to become even more widespread in the future. The species should be evaluated for control or eradication. Perhaps farmers and landowners could be encouraged or assisted to destroy it. A special effort should be made to eradicate this serious invader from all park or reserve lands.
Given its very invasive nature, high priority should be given to the eradication of the Psidium cattleianum infestation off the cross-island road at Malololelei.
Although Setaria palmifolia is undoubtedly beyond control in the areas of Upolu where it is already well established, it may be desirable to control this species in other areas where it is not present. It was not seen on Savai‘i, so it would be very desirable to exclude it from that island if it is not yet present.
The small, spiny Solanum capsicoides is an excellent candidate for eradication. It is likely to become a problem for agriculture if it becomes widespread.
The effectiveness and feasibility of introduction of the biological control agent for Solanum torvum should be investigated. In the meantime, control by landowners should be encouraged.
Planting of Spathodea campanulata as an ornamental should be discouraged and existing trees monitored for spread.
Although it primarily spreads by vegetative means, Tibouchina urvilleana is a dangerous species and high priority should be given to eradicating the isolated infestation at the top of the cross-island road.
There are areas such as O le Pupu Pue National Park where it may be desirable to set aside and maintain in natural condition selected areas as a heritage for future generations, for the protection of native biodiversity and tourism values and as an example of Samoa’s original forest cover. This will involve a continuous and long-term effort, even on a small scale, due to the continuing pressure from invading species. Keeping out shade-tolerant species that can invade closed forests is the biggest problem. Intact native forests are the most resistant to invasion and any measures that limit the amount of disturbance will help keep invasive species out.
Species listed in Appendix 1, Table 3 are pests and, although they may not be presently causing serious damage to natural ecosystems, they are certainly not desirable species. They should not be more widely distributed.
A number of species used in ornamental plantings are, at least to some degree, invasive. While many of these species have desirable ornamental or physical characteristics, planting exotics as opposed to native species is a policy question that needs to be carefully considered. Most species that naturalize to any extent will gradually spread throughout available and suitable habitat, given enough time. Existing plantings should be monitored for spread and new introductions should be carefully assessed to minimize risk. Risky ornamentals that could be eradicated at low cost include Asparagus setaceus and A. densiflorus, Coccinia grandis, Ligustrum sp., Lonicera japonica and Schefflera actinophylla.
Enforce steam cleaning or power washing of all used cars, trucks and equipment coming into Samoa. This is desirable not only from the standpoint of excluding invasive plants, but also insects and diseases. Especially suspect are roadbuilding machinery, military equipment and off-road vehicles. Inspectors should be especially vigilant to make sure used cars, trucks and equipment from Southeast Asia, Fiji, Hawai‘i and the Philippines are clean as many dangerous weeds are present in these locations. For instance, seeds of Chromolaena odorata can be transported in the radiators of used cars, trucks and other equipment.
Closely inspect boots, camping equipment and other materials for soil and seeds, particularly when they have been used in countries where Chromolaena odorata, Miconia calvescens, Mimosa diplotricha and other small-seeded species are present.
A risk-rating scheme would be useful in evaluating the various known and potential invasive species for their risk of introduction, spread and potential damage. The Institute of Pacific Islands Forestry is testing an adaptation of the Australian risk assessment system to the needs of the Pacific. If this proves to be satisfactory, our hope is to eventually rate all the species listed in the PIER database and provide this information to Pacific island countries. In the meantime, risk assessments can be performed on individual species to help evaluate their potential for invasion and spread.
The purpose of this survey was to give an overall assessment of the situation. In the short time available it was not possible to perform the evaluations that would be needed to justify control or eradication programs for individual species. For many species, therefore, our recommendations are provisional and must be subject to a more complete evaluation as to extent, invasiveness and the possibility of control or eradication. Technical assistance should be requested, if needed, to evaluate individual species.
Appendix 1. Invasive species of environmental concern
Appendix 2. Other invasive plant species, mostly ruderal weeds or of agricultural concern
Appendix 3. Invasive species present in American Samoa, the Cook Islands, Fiji, French Polynesia, Hawai‘i or Tonga but not present in Samoa
Appendix 4. Invasive species of environmental concern by location
Appendix 5. Presence of invasive species of environmental concern within Samoa
Appendix 6. Scientific name synonyms
Appendix 7. Background material and references
(1) Former Director, Pacific Southwest Research Station, USDA Forest Service (retired) and Herbarium Collections Manager, National Tropical Botanical Garden, respectively.
(2) We would like to express our sincere appreciation for the hospitality, assistance and support of the following members of the Ministries of Lands, Surveys and Environment and Agriculture, Forestry, Fisheries and Meteorology without whose help this survey would not have been possible: Faumuina S. V. Pati Liu, Seiuli Vaiinuupo Jungblut, Talie Foliga, Tuu’au Letaulau, Siosina Lui and A‘a Mauletana. Representatives from the National Park of American Samoa, Stassia Samuels and Tavita Togia, were able to join us for the survey. Finally, our thanks to Rob McKelleher, who did most of the work to set up the survey but, unfortunately, had to return to his position with Environment Australia prior to the beginning of the survey.
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