Report on invasive plant species in the Cook Islands

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Introduction

Dangerous species not known to be in the Cook Islands

Species that are known or listed as being weedy or invasive elsewhere and are common, weedy or cultivated in the Cook Islands

Native species (or Polynesian introductions) exhibiting aggressive behavior.

Strategies for dealing with invasive species

Recommendations

Appendix 1.  Species by category

Appendix 2.  Other invasive plant species, mostly ruderal weeds or of agricultural concern, seen or reported to be present in the Cook Islands

Appendix 3.  Invasive species present in American Samoa, Fiji, French Polynesia, Hawai‘i, Samoa or Tonga but not present in the Cook Islands

Appendix 5.   Invasive and potentially invasive species present on Aitutaki

Appendix 6.   Invasive and potentially invasive species present on ‘Atiu

Appendix 7.   Invasive and potentially invasive species present on Mangaia

Appendix 8.   Invasive and potentially invasive species present on Mau‘ke

Appendix 9.   Invasive and potentially invasive species present on Miti‘aro

Appendix 10.   Invasive and potentially invasive species reported to be present on other Cook Islands

Appendix 11.  Invasive and potentially invasive species present on other southern Cook Islands but not on Rarotonga

Appendix 12.  Invasive and potentially invasive species present on other southern Cook Islands but not on Aitutaki

Appendix 13.  Invasive and potentially invasive species present on other southern Cook Islands but not on ‘Atiu

Appendix 14.  Invasive and potentially invasive species present on other southern Cook Islands but not on Mangaia

Appendix 15.  Invasive and potentially invasive species present on other southern Cook Islands but not on Ma‘uke

Appendix 16.  Invasive and potentially invasive species present on other southern Cook Islands but not on Miti‘aro

Appendix 17.  Invasive and potentially invasive species present on southern Cook Islands but not reported to be present on the northern Cook Islands

Appendix 18.  Scientific name synonyms

Appendix 19.  Background material and references

Report to the Government of the Cook Islands on Invasive Plant Species of Environmental Concern

James C. Space and Tim Flynn ⁽¹⁾

The Government of the Cook Islands 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 previously conducted in Micronesia, American Samoa, Niue, Samoa and Tonga. The survey was carried out from 11 March through 1 April 2002. The islands of Rarotonga, Aitutaki, ‘Atiu, Mangaia, Ma‘uke and Miti‘aro were surveyed. Species reported by the Cook Islands Natural Heritage Project were used for the other islands (Manuae, Manihiki, Nassau, Palmerston, Penrhyn, Pukapuka, Rakahanga, Suwarrow and Takutea) as well as for some of the uncommon cultivated species on the surveyed islands.

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 the Cook Islands, 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 19, References), and comprehensive data on the location and relative abundance of species furnished by the Cook Islands Natural Heritage Project. 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 the Cook Islands have been grouped into four categories:

1. 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 the Cook Islands (208 species).

2. Species that are invasive or potentially invasive in the Cook Islands (66 species).

3. Species that are invasive or weedy elsewhere and are common, weedy or cultivated in the Cook Islands (143 species).

4. Native species (or Polynesian introductions) that exhibit aggressive behavior (4 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 Ministry of Agriculture.

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 the Cook Islands

The Cook Islands is fortunate that a number of troublesome species have yet to reach the country. These are listed in Appendix 1, Table 1. The following 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.

Two rubber trees, Castilla elastica (Panama rubber tree) and Funtumia elastica (African rubber tree), are very invasive in Samoa. Birds spread the seeds of Castilla while those of Funtumia are wind-borne "parachute" seeds.

Chromolaena odorata (Siam weed) is a highly invasive pan-tropical weed. It will likely show up in the Cook Islands 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.

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. It readily spreads vegetatively through cuttings and, if fruit is present, by birds and probably pigs.

Cordia alliodora (Ecuador laurel, salmwood) was introduced to Samoa, Tonga and Vanuatu as a forestry tree and has proven invasive in these locations (Tolfts, 1997). It should not be introduced to the Cook Islands.

Clerodendrum quadriloculare (bronze-leaved clerodendrum) is an attractive yard plant and is commonly planted for that purpose on many islands in the Pacific. 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 (Koster’s curse) is a serious problem in Hawai‘i and other locations, including American Samoa, Samoa, Fiji, the Solomon Islands and Vanuatu. This is a very serious weed of the forest understory.

Elaeocarpus angustifolius [=grandis] (blue fig, blue marble tree, quandong), a native of Australia, is a forestry tree that is invading intact and secondary forests in Samoa.

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.

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 from Hawai‘i or Tahiti.

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. 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 shows indications of naturalizing) and reported to be planted in French Polynesia and Fiji as well.

Piper auritum (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.

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 Hawai‘i and present in New Caledonia, the Solomon Islands and Vanuatu as well. A number of other Rubus species are invasive. In Hawai‘i, 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 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.

Solanum torvum (prickly solanum, devil's fig) is a large spiny species favoring disturbed areas and fields that forms dense, impenetrable thickets. Birds spread its seeds. It is a pest species in French Polynesia and Tonga and is rapidly spreading in Samoa.

Some potentially invasive grass species are not yet present in the Cook Islands, including:

• Imperata cylindrica, a very invasive species elsewhere and a problem for agriculture as well as the environment. It is present in Australia and New Zealand as well as New Caledonia, Papua New Guinea, Solomon Islands, Vanuatu, Wallis and Futuna. Several infestations in Micronesia (Palau and Yap) are presently subjects of eradication programs.
   

• Melinis minutiflora (molasses grass), a species that is both invasive and can cause a serious fire hazard. It has fostered the establishment of fire regimes on many islands where it has been introduced (D’Antonio and Vitousek, 1992)
   

• A number of other grass species of various degrees of invasiveness, including Andropogon gayanus, Andropogon glomeratus, Andropogon virginicus, Cenchrus brownii, Cenchrus ciliaris, Chloris radiata, Cortaderia jubata, Digitaria insularis, Echinochloa polystachya, Hymenachne amplexicaulis, Hyparrhenia rufa, Ischaemum polystachyum, Ischaemum rugosum, Ischaemum timorense, Microlaena stipoides, Panicum repens, Paspalum fimbriatum, Pennisetum clandestinum, Pennisetum polystachyon, Saccharum spontaneum, Sacciolepis indica, Schizachyrium condensatum, Sorghum halepense ⁽³⁾ , Sporobolus elongatus and Tripsacum latifolium. 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 the Cook Islands 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, Fiji, French Polynesia, Hawai‘i, Samoa and Tonga but are not present in the Cook Islands are listed in Appendix 3. These species would be of high risk of introduction from air and ship traffic between these points and the Cook Islands.

2. Species that are invasive or have the potential to become so in the Cook Islands

A number of known invasive plants that cause serious problems in similar ecosystems have been introduced into the Cook Islands (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.

Acacia mangium (ākasia, mangium) has been widely planted on Mangaia and is naturalizing. It is also present on Rarotonga, ‘Atiu and Ma‘uke, where it also naturalizes. It has the potential to become much more widespread, particularly on ‘Atiu and Mangaia, where large numbers of seedlings and saplings were seen.

Other acacias spreading on Mangaia include Acacia aulacocarpa and Acacia crassicarpa.

A large block of Acacia crassicarpa is planted adjacent to the old airfield on Ma‘uke and is spreading rapidly. In addition, Acacia glauca [=Acacia curassavica] is also spreading on Ma‘uke. It is a small tree or shrub that forms dense thickets.

Acacia crassicarpa is spreading on ‘Atiu as well.

Adenanthera pavonina (kōviriviri, mata kōviriviri, tavara (Mangaia), pitipiti‘o (‘Atiu), coral bean tree), invasive in forests throughout the Pacific, is already widespread (and is not native) in the Cook Islands. 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 the Cook Islands 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.

Ardisia crenata (hen's eyes, Hilo holly) is reported present in cultivation on Rarotonga (Bill Sykes, pers. com.). This is a dangerous species with bird-dispersed seeds. It is present in Fiji and Hawai‘i and is on the list of plants barred from importation into French Polynesia.

Ardisia elliptica (venevene tinitō, shoebutton ardisia) is widespread throughout Rarotonga and is present to a lesser extent on Mangaia. There are scattered populations on Aitutaki and Ma‘uke. It grows well in the forest understory and crowds out other species. Birds (and children), which eat the fruit, are a major factor in its spread. It is a problem species in Hawai‘i, French Polynesia, Samoa and Florida (US). This species shows every sign of becoming a major component of the ecosystems of the islands where it is present.

Cardiospermum grandiflorum (kopūpū takaviri?, balloon vine), an invasive vine, is present only on Rarotonga, where it is already widespread. It is invasive in Australia and Hawai‘i. On Rarotonga, it teams up with Mikania micrantha to climb and sometimes overtop vegetation.

Cecropia obtusifolia (rau-māniota, trumpet tree, guarumo) is a very invasive tree species on Rarotonga (it is a problem in Hawai‘i as well). Birds disperse its seeds.

Cestrum nocturnum (tiare ariki-va‘ine, ariki-va‘ine, night-flowering cestrum) is quite prevalent and invasive on Rarotonga and Mangaia. It’s another species with bird-spread seeds and could become even more widespread. Cestrum diurnum (ariki-va‘ine, day cestrum) is also present and equally invasive on Mangaia.

Cyperus involucratus [=alternifolius] (umbrella sedge) is an invader of streamsides on Rarotonga and wet areas on Aitutaki. This species is often used as an ornamental plant.

Erigeron karvinskianus (Mexican daisy, seaside daisy, daisy fleabane), reported by Bill Sykes to be present in cultivation on Rarotonga, is a major problem on Kauai and is spreading elsewhere in Hawai‘i. It is also a serious weed on La Réunion.

Eugenia uniflora (venevene, menemene (Mangaia), Surinam cherry) was mostly seen in cultivation on Rarotonga, but on Mangaia it is spreading in the forest understory. It is growing along the road up the hill from Ureia on Aitutaki and a few examples were seen on Miti‘aro. A number of patches were noted on Ma‘uke. It is reported present on ‘Atiu by the Cook Islands Natural Heritage Project but was not seen. Fruit-eating birds probably spread the seeds.

Falcataria moluccana [=Paraserianthes falcataria] (‘ārapitia, Moluccca albizia) is widespread on Rarotonga, Aitutaki, ‘Atiu, Mangaia and Ma‘uke. This species has become common on many Pacific islands.

Flemingia macrophylla was seen naturalizing on both Rarotonga and Mangaia, mostly along roadsides, and a single cultivated plant was seen on Ma‘uke. F. strobilifera (luck plant, wild hops) is present on Rarotonga and ‘Atiu. Both of these species are prolific seed producers and have the potential to become a much more serious problem.

A number of patches of Hedychium coronarium (kōpī teatea, re‘a teatea, white ginger) were seen on Rarotonga and occasional plants, usually in cultivation, on ‘Atiu, Mangaia, Ma‘uke and Miti‘aro. H. flavescens (re‘a rengarenga, yellow ginger) was seen on ‘Atiu and it and H. gardnerianum (kōpī, kahili ginger) are reported to be present in cultivation elsewhere by the Cook Islands Natural Heritage Project. These species can be invasive in the forest understory, particularly in moist areas, and are difficult to control. They 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 the Cook Islands.

Hyptis pectinata (miri tītā (‘Atiu), mint weed) is a ubiquitous weed on roadsides and in disturbed areas on Rarotonga, Aitutaki, ‘Atiu, Mangaia and Miti‘aro.

Lantana camara (tātarāmoa, tātarāmoa papa‘ā, lantana) is a component of the weed vegetation on Rarotonga but it does not seem to be a major problem there. However, on ‘Atiu it is vigorous and widespread.

Leucaena leucocephala (nito, mara‘inu, leucaena) is common, as on most Pacific islands, but it is not as big a problem in the Cook Islands as in some other locations. Interestingly, it is not present (or is very rare) on Aitutaki and Miti‘aro, as it was not seen on those islands.

Melia azedarach (tīra, Chinaberry) is common on Mangaia and also present on Rarotonga, Aitutaki, ‘Atiu, Ma‘uke and Miti‘aro. This small tree produces large amounts of bird-spread seed. It is a problem species in Hawai‘i and on some of the islands of French Polynesia.

Merremia peltata is a fairly recent introduction to Aitutaki (Bill Sykes reports collecting it in 1974) but is now quite widespread. It is considered a native or an early introduction throughout much of the Pacific, but its behavior on Aitutaki is a good example of why it should not be introduced to other islands.

Mikania micrantha (pōkutekute, mile-a-minute weed), a smothering vine, is a major invasive species on a number of Pacific islands. It 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. It is widespread on Rarotonga and ‘Atiu, less so on Aitutaki. There are only a few patches at present on Miti‘aro and a single small area on Ma‘uke.

Mimosa diplotricha [=invisa] (pikika‘a papa‘ā (Aitutaki), 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, Fiji, French Polynesia (Society Islands), New Caledonia, Niue, Papua New Guinea, Solomon Islands and Vanuatu). It became established some time ago on Aitutaki, the only island where it is present in the Cook Islands. A biological agent was introduced and has been effective in reducing flower production but the plant is still spreading. Mimosa pudica (pikika‘a, sensitive plant), a smaller plant with only small prickles, is common throughout the Cook Islands as a component of the weedy vegetation of roadsides and other disturbed areas. It is not common on Mangaia and Miti‘aro and local programs are under way to keep it under control. It is limited to two locations on ‘Atiu.

Panicum maximum (tinikarāti, Guinea grass, buffalograss) is a troublesome grass in the Cook Islands, 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.

Pennisetum purpureum (‘erepani (‘Atiu), elephant grass, napier grass, merker grass) has recently become established on Rarotonga, ‘Atiu and Mangaia. It is a very large grass that forms dense stands that can exclude other vegetation. It is one of the most invasive weeds in Papua New Guinea. An attempt is being made to eradicate it on Mangaia.

Pennisetum setaceum (fountain grass) has been recorded on Rarotonga by the Cook Islands Natural Heritage Project. This grass species is a major problem in Hawai‘i and is also present in Australia, Fiji, French Polynesia and New Caledonia. It is often sold as an ornamental through seed catalogues.

There are extensive areas of a running bamboo (Phyllostachys sp., probably P. bissetii per Bill Sykes, pers. com.) on Mangaia. Running bamboos spread by rhizomes and can form extensive, dense stands that are extremely difficult to control. Long-range spread is by cuttings or pieces. Bill Sykes (pers. com.) also reports Phyllostachys nigra in cultivation on Rarotonga.

While not as invasive as Pimenta dioica (absent from the Cook Islands), Pimenta racemosa (bay tree, bay rum tree) is becoming well established on most of the southern group of islands except Aitutaki. It is especially prevalent on Ma‘uke. However, on ‘Atiu we only saw two specimens (both in cultivation), one in Ngatiarua village and one at the ‘Atiu Motel.

Psidium cattleianum (tūava papa‘ā, strawberry guava) is a small tree that forms dense thickets. It is a major problem species in a number of Pacific island ecosystems including Hawai‘i and Tahiti as 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. It is present on Rarotonga, Mangaia and Miti‘aro and has undoubtedly not yet reached its full potential on these islands. On Ma‘uke a single specimen was pointed out to us growing at Government House. It is reported present on ‘Atiu by the Cook Islands Natural Heritage Project but was not seen.

Psidium guajava (tūava, guava) is very common on all the islands visited, particularly in abandoned fields. This is a major invasive species in Tonga and 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 the Cook Islands and may, over time, become even more widespread.

Spathodea campanulata (kō‘ī‘ī, mimi, pātītī vai, African tulip tree) is fairly common as an ornamental tree and is naturalized on Rarotonga, Aitutaki and ‘Atiu. It is reported present by the Cook Islands Natural Heritage Project but was not seen on Ma‘uke. It is a major problem in Fiji, the Hawaiian Islands and several 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. The possibility of biological control is being investigated in Fiji.

Stachytarpheta cayennensis [=urticifolia] (tiāki (Miti‘aro), blue rat’s tail) is very common in the Cook Islands 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. On Ma‘uke, Stachytarpheta jamaicensis is also present in the area around the reservoir and on Aitutaki it is very common around the airport. It is usually most prevalent in open areas.

Syzygium cumini (pistati, ka‘ika, paramu (Aitutaki), Java plum) is a serious invader in the Cook Islands. Fruit-eating birds and possibly also pigs spread the seeds. It is reported to be a very invasive species on Raiatea, French Polynesia. The trees produce prolific fruit, resulting in numerous seedlings. It is already widespread on Rarotonga, Aitutaki, ‘Atiu, Mangaia and Ma‘uke. It appears to be still limited in extent on Miti‘aro (on the road to Takaue and Mangarei), but it won’t be long before it will be beyond effective control.

Tithonia diversifolia (pua renga, tiare rengarenga (Aitutaki), kavakava, pua renga (Ma‘uke), tree marigold, Mexican sunflower) is widespread in disturbed areas of Aitutaki, Mangaia and Ma‘uke. It is also present on Rarotonga and ‘Atiu.

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 or control because of their invasive potential. Others should be monitored for possible future action, if necessary.

Acacia farnesiana (titima, Ellington curse, klu, sweet acacia) is present on Rarotonga and Aitutaki. This thorny shrub is a pest in Fiji, French Polynesia, New Caledonia, Solomon Islands and Vanuatu.

A few examples of Asparagus setaceus (remu, ornamental asparagus) and A. densiflorus (asparagus fern, sprengeri fern) were seen. These were in cultivation on Rarotonga, ‘Atiu and Miti‘aro but an example of Asparagus setaceus was seen in the wild on Mangaia. 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 of both are bird-dispersed and they may spread vegetatively through root tubers. They are commonly sold as ornamentals. Where they are only in cultivation they could be easily eradicated and future imports prohibited.

Bryophyllum pinnatum [=Kalanchoë pinnata] (ngāngā‘ere toka, life plant) was seen only in cultivation on Rarotonga and Aitutaki but on Mangaia escaped plants were seen reproducing along the roadside at a number of locations. This species reproduces vegetatively, is shade tolerant and can be invasive on the forest floor.

Cinnamomum verum (cinnamon) was found to be very invasive in our surveys of American Samoa and Samoa. It is also present in Fiji, French Polynesia and Hawai‘i. In the Cook Islands it is locally naturalized on Rarotonga and Miti‘aro (Teukovero). Given its observed ability to invade forests in the Samoas, this species may well become a serious pest on these islands.

Clerodendrum chinense (pitate māma‘o, Honolulu rose) is a shade-tolerant species. It primarily reproduces from root suckers and can form dense thickets, crowding out other species. It was only seen on Rarotonga. It should be excluded from the other islands or eradicated if it becomes established, as this species is considered a serious plant pest wherever it has become established throughout the Pacific.

Cryptostegia madagascariensis (Madagascar rubber vine) is a climbing vine that is reported by the Cook Islands Natural Heritage Project to be cultivated in the Cook Islands. A closely related species, C. grandiflora, has become a serious problem in northeastern Queensland, Australia and is also present in New Caledonia and Fiji. C. madagascariensis may have similar potential.

Dieffenbachia seguine (spotted dieffenbachia or dumb cane), a common house and yard plant, was seen in cultivation on Rarotonga, ‘Atiu and Mangaia and is reportedly present on Ma‘uke (Bill Sykes, pers. com.). This species has become a problem in American Samoa and Samoa and is reportedly present in Fiji and French Polynesia. Where found outside of cultivation this species should be removed, as it reproduces vegetatively and can thrive in the dense shade of an intact native forest canopy, particularly in stream bottoms and other moist areas, crowding out other species.

Dissotis rotundifolia (dissotis, pink lady) is reported by the Cook Islands Natural Heritage Project to be present but rare in cultivation on both Rarotonga and Ma‘uke. Serious infestations of this species were seen in Samoa where it forms dense mats, shading out low-growing species and occasionally even climbing over shrubs and small trees. The species is also found in American Samoa (Tutuila) as well as Fiji, French Polynesia and Hawai‘i.

Egeria densa (egeria, leafy elodea, dense waterweed) is reported by the Cook Islands Natural Heritage Project to be present in Rarotonga. This is a serious aquatic weed, commonly becoming established through dumping of aquarium plants. Once established, spread is mainly through broken-off pieces.

Eichhornia crassipes (riri vai, water hyacinth) is reported present by the Cook Islands Natural Heritage Project in Rarotonga and Mangaia. 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.

Quite a few examples of Epipremnum pinnatum cv. 'Aureum' [=Scindapsus aureus] (‘ara (Ma‘uke), pothos, money plant) were seen on Rarotonga and Mangaia. It is also present on Aitutaki and reported to be present on Ma‘uke. This species can invade the forest understory and climb trees. It reproduces vegetatively from cuttings and pieces and it is usually spread by the dumping of garden waste.

Gmelina arboreca is spreading on ‘Atiu but its extent presently seems to be limited. Bill Sykes (pers. com.) reports that it is also present on Rarotonga, but it was not seen during this survey and its status there is unknown.

Lonicera japonica (pitate papa‘ā, mangamangā rima (Ma‘uke), Japanese honeysuckle) was seen in cultivation on Rarotonga and ‘Atiu. It is also reported by the Cook Islands Natural Heritage Project to be present in cultivation on Mangaia and Ma‘uke. 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.

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). It was seen in cultivation on Rarotonga and has the potential to join the weedy vines Cardiospermum grandiflorum and Mikania micrantha as a serious pest on Rarotonga.

Merremia tuberosa (wood rose), a climbing, smothering vine, is notable for its aggressive behavior on Niue and is also a problem species in Hawai‘i. It was seen on Rarotonga and may be planted as an ornamental elsewhere.

Odontonema tubaeforme (fire spike, cardinal flower) was seen to a limited extent in the wild on Rarotonga and Mangaia. This species is invasive at a number of locations in moist forests in Samoa. Although it primarily spreads by vegetative means, it is a problem species due to its ability to invade the understory.

Passiflora foetida (love-in-a-mist) was not seen although the Cook Islands Natural Heritage Project reports isolated collections on Rarotonga. It is very invasive on most Pacific islands.

Bill Sykes (pers. com.) reports that Pistia stratiotes (water lettuce, tropical duckweed) is present on Rarotonga. This is another aquatic plant that can form dense mats in waterways.

Pluchea carolinensis (sour bush) is reported by the Cook Islands Natural Heritage Project to have been collected on Penrhyn Island. This species is a widespread pest species in Hawai‘i, commonly invading almost every habitat type. The seeds are spread by wind and possibly by birds. Pluchea indica is likewise present on Penrhyn. Bill Sykes says that both species were apparently accidentally introduced to Motu Moananui at the time that American engineers built the airstrip in the Second World War.

An example of Schefflera actinophylla (octopus tree, umbrella tree) was seen in cultivation in Avarua, Rarotonga (in front of the CITC center). It has bird-dispersed fruits and is invasive in Hawai‘i, Micronesia and French Polynesia.

Sesbania grandiflora (hummingbird tree, scarlet wisteria tree) is cultivated as an ornamental but has the potential to naturalize, as it is doing in American Samoa and Samoa. It is present in cultivation on Rarotonga and Mangaia.

Setaria palmifolia (palmgrass) is reported to be in cultivation on Rarotonga (Bill Sikes (pers. com.) reports finding it in a garden in Avarua). This grass is very invasive in Samoa, Tahiti and Hawai‘i and is on the New Zealand noxious weed list. Wind or birds distribute its seeds.

Solanum capsicoides (poro‘iti taratara, cockroach berry, devil’s apple, soda apple) is reported by the Cook Islands Natural Heritage Project to be present on Rarotonga and Ma‘uke and was seen in cultivation of ‘Atiu. Although small, it is quite spiny and is not a desirable addition to the vegetation of these islands. It produces large amounts of small, tomato-like fruit that can be used in making ‘ei. Spread may be by birds, pigs or humans. This species is rapidly becoming established on Tonga.

Syngonium angustatum (arrowhead plant, goosefoot plant), a climbing aroid, is mostly cultivated in the Cook Islands, but escapes were noted on Rarotonga, Aitutaki, Mangaia and Ma‘uke. 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 is often spread from dumped garden cuttings. It is a problem species in American Samoa, is widespread in Hawai‘i and is quite invasive in Niue.

A rather large infestation of Tephrosia candida (white tephrosia) was found in the area of the dump on Mangaia. There is a small infestation on Miti‘aro along the road in Takaue. It is quite common on ‘Atiu and Ma‘uke and was seen in several places on Aitutaki (most notably on Piraki).

We were directed to cultivated specimens of Tibouchina urvilleana (glorybush, lasiandra, princess flower) on Rarotonga by Gerald McCormack of the Cook Islands Natural Heritage Project. This species is a major problem in Hawai‘i, forming dense thickets in moist habitats.

Wedelia [=Sphagneticola] trilobata (wedelia, Singapore daisy) has become a serious pest on many Pacific islands (Thaman, 1999) as well as in Australia. 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. It is present on Rarotonga and ‘Atiu.

3. Species that are known or listed as being weedy or invasive elsewhere and are common, weedy or cultivated in the Cook Islands

A large number of other common, weedy or cultivated 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 forest 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, if necessary.

Anacardium occidentale (kātū, cashew) was seen naturalizing on Ma‘uke and ‘Atiu. This is the first time we have observed this species naturalizing in the Pacific. It is reported to be naturalized in Western Australia.

Antigonon leptopus (chain of hearts, coral vine,), a climbing vine often planted as an ornamental, is a widespread pest on Guam. Only a few examples, in cultivation, were seen in the Cook Islands.

The aquatic mosquito fern, Azolla filiculoides (species identified by Bill Sykes, pers. com.), was noted in taro patches, ponds and slow-moving water on Rarotonga, Mangaia and Ma‘uke and may be present on the other islands of the southern group as well.

Bauhinia monandra (pine (Rarotonga), pīpī (Aitu), pī (Ma‘uke and Miti‘aro), orchid tree) is quite prevalent on Rarotonga and is also present on the other islands visited. It is quite weedy on Aitutaki and Ma‘uke.

Carludovica palmata (Panama, Panama hat plant) was seen in cultivation on Rarotonga and ‘Atiu. This species was found naturalizing in the forest understory on Upolu, Samoa, and thus has the potential to be an invasive plant on other tropical islands.

Crotalaria micans [=anagyroides] (crotalaria), a large species (up to 3 m tall), is quite prevalent in disturbed areas on Mangaia.

Hemigraphis alternata (metal leaf, red ivy) was seen in cultivation. This species can naturalize and forms dense low stands, excluding other species, if it escapes cultivation. 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, Moses in a boat) and T. zebrina (wandering jew). These species were mostly seen planted as ornamentals in the Cook Islands, but on Ma‘uke large areas Tradescantia spathacea are growing in the forest understory, on rocks, etc. (similar behavior was noted on Niue). Tradescantia zebrina is also common outside of cultivation on Ma‘uke (a notable example is the area around Vaitango Cave). It is common for these species to escape into the forest understory on Pacific islands. They are usually spread through the dumping of garden cuttings.

Indigofera suffruticosa (‘initiko, indigo) is established in some areas on Rarotonga, Aitutaki, ‘Atiu, Mangaia and Ma‘uke and is likely to become more common. It is a major weed species in Tonga.

Jasminum grandiflorum (pītate (Ma‘uke)) is present on ‘Atiu, Ma‘uke and the other high islands of the Southern Cooks. It is largely in cultivation, but specimens were seen outside of obvious cultivation on Ma‘uke. It appears to be spreading only vegetatively, but its ability to persist and form dense clumps is of concern.

Murraya paniculata (tiare ‘ānani, orange jessamine, satin-wood, Chinese box) is a hedge and ornamental plant. It has bird-dispersed seeds and thus the ability to spread. This species has mostly been extirpated from the Cook Islands, however, because it allegedly caused allergies. In Asia, Murraya paniculata is the preferred host of the insect pest Diaphorina citri, the citrus psyllid. The psyllid is the vector for the serious disease "huanglongbing".

Ocimum gratissimum (miri tītā, miri tutae puaka, miri nganga‘ere, miri tupapaku, miri papa‘ā, miri taratoni, wild basil) is present on all the islands surveyed. However, it is particularly prevalent in disturbed areas on Rarotonga, ‘Atiu and Ma‘uke.

Passiflora rubra (pōkutekute (‘Atiu), red passionfruit) is present on cliffs, along roadsides and in disturbed areas on all the islands visited. On Ma‘uke it is subject to a control program. In the Pacific, it is only reported to be present in the Cook Islands.

Ricinus communis (tuitui papa‘ā, castor bean) is reported by the Cook Islands Natural Heritage Project to be present in cultivation on Rarotonga and Mangaia and was seen growing wild near the harbor on ‘Atiu. This is a weedy species on many Pacific islands, most particularly Samoa and Tonga. Its potential in the Cook Islands is unknown.

Naturalized clumps of Sanchezia parvibracteata were seen on Rarotonga and it was seen in cultivation on Aitutaki and ‘Atiu (‘Atiu Motel). Sanchezia speciosa was seen in cultivation on Rarotonga. Both of these are pest species in Australia, where they form dense thickets in moist areas. They reproduce vegetatively.

Senna tora (peanut weed) is widespread in fallow fields and other disturbed areas on Ma’uke.

Tecoma stans (tekoma, 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. It is present on Rarotonga, Aitutaki, ‘Atiu, Mangaia and Ma‘uke.

Some other exotic tree species that have been introduced to the Cook Islands include Acacia auriculiformis (ākasia, earleaf acacia), Acacia mearnsii (ākasia, black wattle, reported to be cultivated on Rarotonga), Albizia lebbeck (‘arapitia (Miti‘aro), rain tree), Cananga odorata (mata‘oi, perfume tree), Cedrela odorata (Mexican cedar), Ceiba pentandra (vavai, kapok), Coffea arabica (kaope, kaope Maori, coffee), Grevillea banksii (Banks grevillea), Grevillea robusta (silk oak), Gliricidia sepium (mother of cacao, quickstick), Pinus caribaea (paina papa‘ā, Caribbean pine), Syzygium jambos (ka‘ika papa‘ā, ka‘ika takataka, ka‘ika varani (Mangaia); ka‘ika (‘Atiu), malabar plum) and Thevetia peruviana (venevene, yellow oleander). These species can naturalize and are more or less successful depending on local conditions. For example, Acacia auriculiformis was seen naturalizing on Mangaia, Coffea arabica was seen naturalized on all the islands visited and Thevetia peruviana was seen naturalizing to a limited extent on both Mangaia and Miti‘aro. Pinus caribaea (Caribbean pine) has been widely planted on Mangaia and is naturalizing there and to some extent on ‘Atiu and Ma‘uke.

In addition to Panicum maximum, Pennisetum purpureum, Pennisetum setaceum and Setaria palmifolia, a number of other introduced grasses are established, including Arundo donax (giant reed), Axonopus compressus (carpetgrass), Axonopus fissifolius (narrow-leaved carpetgrass), Bothriochloa bladhii (blue grass, Australian beardgrass), Cenchrus echinatus (piripiri, parango (Ngaputoru), bur grass); Chloris barbata (swollen fingergrass), Chloris gayana (Rhodes grass), Cynodon dactylon, (matie, Burmuda grass), Cortaderia selloana (pampas grass, reported cultivated on Rarotonga), Digitaria ciliaris (fingergrass, smooth crabgrass), Digitaria violascens (smooth crabgrass, violet crabgrass), Eleusine indica (mauku mārōki‘aki‘a, goosegrass), Melinis repens (Natal grass), Paspalum conjugatum (mauku taravao, mauku katini, T grass), Paspalum dilatatum (dallis grass), Paspalum scrobiculatum [=orbiculare] (mātā, rice grass (perhaps indigenous or early introduction)), Paspalum paniculatum (matie manutai, Russell river grass, galmarra grass), Paspalum urvillei (tinikarāti, Vasey grass), Setaria pumila (foxtail, hairy-tail grass), Sporobolus indicus (smutgrass, wiregrass, Indian dropseed) (S. indicus var. capensis is also widespread per Bill Sykes, pers. com.), Stenotaphrum secundatum, Urochloa [Brachiaria] mutica (mauku puakatoro, para grass) and Urochloa [=Brachiaria] subquadripara (green summer grass). Bamboo (Bambusa vulgaris) is also present.

Other weedy species include Abelmoschus moschatus (vavai tara, ta‘uri‘au (Mangaia), musk mallow), Bidens pilosa (piripiri, piripiri kerekere, niroa (Aitutaki), kamika tuarongo (Mangaia), beggar’s tick), Centrosema pubescens (piriarero (Miti‘aro), centro), Clerodendrum buchananii (rākau tupopoku (‘Atiu), red clerodendrum, pagoda-flower), Commelina diffusa (mauku-vai, mauku ‘oro‘enua, mauku puakatoro, dayflower), Cyperus rotundus (ōniāni, mauku ‘ōniāni, ‘nut grass, nutsedge), Elephantopus mollis (tapuvae ‘erepani, tapuae ‘erepani, vaevae ‘erepani, elephant’s foot), Kyllinga nemoralis (neke ‘enua, white kyllinga), Leonurus japonicus (vavai tara (Miti‘aro), lion’s tail), Macroptilium atropurpureum (siratro, purple bushbean), Ruellia prostrata (tītā ‘aruru (Miti‘aro), black weed, bell weed) and Urena lobata (piripiri, vavai tara tītā (Ma‘uke), hibiscus burr).

Desmodium heterocarpon and Desmodium gangeticum are both common along roadsides at the very least on Mangaia and Ma‘uke and probably the other islands in the southern group (except Miti‘aro).

Gloriosa superba is naturalized on every island. All parts of the plant are considered to be extremely poisonous.

Additional species that are cultivated or of limited extent but have the potential to become more widespread include Allamanda cathartica (tiare rengarenga, pua, yellow trumpet vine), Calliandra surinamensis (Surinamese stickpea), Heliconia spp. (tiare pārata‘ito, heliconia), Nymphaea spp. (riri vai, waterlily), Sambucus mexicana (elderberry, Mexican elder) and Sanseveria trifasciata (riri, bowstring hemp, mother-in-law’s tongue).

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

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. Rather, the following strategies are general operational principles that have proven effective in dealing with exotic 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 on the internet (http://www.gisp.org/publications/toolkit/Toolkiteng.pdf) or the PIER-CD.

The Cook Islands has laws and regulations in place that deal with quarantine and new introductions. These are presently under review to see if they might need to be strengthened. 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.

The first line of defense against invasive species, and the most cost-effective, is to keep them out. The Cook Islands has quarantine measures in place and operating. Control at ports of entry is essential, and those concerned with the protection of natural ecosystems and quarantine must work closely together to combat known and potential invasive plant species. Plant quarantine officers should be familiar with both agricultural pests and those that threaten natural and semi-natural ecosystems. At a minimum, a list of known undesirable 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 risk assessment (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.

The Cook Islands is to be commended for establishing internal quarantine. As is typical, the main island of Rarotonga, which is the focal point of commerce and travel, has many more invasive species present than the outer islands. Maintaining and strengthening internal quarantine will do much to prevent the spread of unwanted species within the Cook Islands.

Many Pacific countries or individual islands have formed invasive species committees or working groups. 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 prevent introduction or to eradicate an introduced species. Such groups 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. Typically, an overall management plan is developed together with a prioritized action plan. Among other things, action planning addresses critical areas to protect, species subject to control or eradication and assignment of responsibility for specific 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. Some recommendations are made below as to possible management actions against some individual plant species, but these must be tested against available resources and local priorities.

Education of the public about the danger of introductions and encouraging the use of native and low-risk introduced species needs to continue. People need to be encouraged to take responsible actions such as following quarantine regulations, not dumping garden cuttings in the woods or along roadsides 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 problem species, even if it involves the use of pesticides, may be better than living with the impact 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 an infestation is allowed to spread so that they will understand, accept and support eradication. For example, anyone visiting Tahiti would very likely be convinced that Miconia calvescens is an ecological disaster and that it should be prevented from becoming established on other Pacific islands. The public must 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 exclude known invaders and to develop a "white list" of both native and non-native species that the public can be encouraged to plant. Likewise, local home gardening associations can perform an important education function for their members in what species to avoid.

Field-going personnel 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 in gardens, farms and disturbed areas. Suspicious plant species should be promptly reported and investigated. 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 and Aliens list-servers.

The Cook Islands is fortunate to have the Cook Islands Natural Heritage Project, which maintains an exhaustive and continuously updated database on both native and introduced species. This database provides baseline data on the species present in the Cook Islands and their location. The Project is a valuable resource for species identification, advice and training and should be utilized to its fullest.

Recommendations

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 the Cook Islands. New species and data are periodically added to the database. For those with Internet access, this information can be found at http://www.hear.org/pier/. The information is also available on the PIER-CD for local use and updates are mailed out about once a year. Assistance from experts in identifying and managing invasive species can also be obtained by subscribing and posting inquiries to the Pacific Pestnet and Aliens list-servers.
   

• 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.
   

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Table A. Priority species for exclusion from the Cook Islands

Scientific Name	Common Names (abridged)	Family	Invasive in:
Albizia chinensis	Chinese albizia, silktree	Fabaceae	Hawai’i, Samoa, Mauritius
Castilla elastica	Panama rubber tree	Moraceae	American Samoa, Hawai’i, French Polynesia, Samoa
Chromolaena odorata	Siam weed, triffid weed	Asteraceae	Australia, Micronesia, Papua New Guinea, Philippines, Southeast Asia
Clerodendrum quadriloculare	bronze-leaved clerodendrum	Verbenaceae	Micronesia
Clidemia hirta	Koster’s curse	Melastomataceae	American Samoa, Fiji, Hawai’i, Palau, Papua New Guinea, Samoa, Solomon Islands, Vanuatu
Coccinia grandis	ivy gourd, scarlet-fruited gourd	Cucurbitaceae	Saipan, Hawai’i
Cordia alliodora	Ecuador laurel	Boraginaceae	Tonga, Samoa, Vanuatu
Elaeocarpus angustifolius	blue marble tree	Elaeocarpaceae	Samoa
Funtumia elastica	African rubber tree	Apocynaceae	Samoa
Hiptage benghalensis	hiptage	Malpighiaceae	Hawai’i, Réunion, Mauritius
Imperata cylindrica	blady grass, cogon grass	Poaceae	Australia, New Zealand, Micronesia, New Caledonia, Papua New Guinea, Philippines, Solomon Islands, South-east Asia, Vanuatu
Kyllinga polyphylla	Navua sedge	Cyperaceae	Samoa
Ligustrum spp.	privet	Oleaceae	Mauritius, La Réunion
Maesopsis eminii	umbrella tree, musizi	Rhamnaceae	Fiji
Melaleuca quinquenervia	melaleuca, cajeput, paper bark tree, punk tree	Myrtaceae	US (Florida)
Melinis minutiflora	molassas grass	Poaceae	French Polynesia, Hawai’i
Miconia calvescens	miconia, velvetleaf, purple plague, bush currant	Melastomataceae	French Polynesia, Hawai’i
Mucuna pruriens	cow itch	Fabaceae	Saipan
Passiflora tarminiana	banana poka, banana passionfruit, bananadilla	Passifloraceae	Hawai’i
Pimenta dioica	allspice, pimento	Myrtaceae	Tonga (‘Eua)
Piper aduncum	spiked pepper	Piperaceae	Fiji, Papua New Guinea, Solomon Is.
Piper auritum	eared pepper, anise pepper, false kava	Piperaceae	Hawai’i, Pohnpei, Samoa, Tonga
Pithecellobium dulce	Madras thorn, Manila tamarind	Fabaceae	Hawai’i, Fiji, French Polynesia
Pluchea carolinensis	sour bush	Asteraceae	Hawai’i, Tonga (reported already present on Penrhyn)
Rubus species	raspberries, blackberries, brambles	Rosaceae	Hawai’i, French Polynesia, etc.
Schinus terebinthifolius	Christmas-berry, Brazilian pepper	Anacardiaceae	Hawai’i, US (Florida)
Solanum torvum	prickly solanum, devil’s fig	Solanaceae	French Polynesia, Samoa, Tonga
Tibouchina herbacea	glorybush, cane ti, tibouchina	Melastomataceae	Hawai’i
All grasses	all other grass species not already present	Poaceae	pan-tropical
All melastomes	all other melastomes	Melastomataceae	Hawai’i, etc.

Note: Appendix 1, Table 1 is a complete list of invasive and potentially invasive species not yet present in the Cook Islands.

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• Extraordinary measures need to be employed against Miconia calvescens because its effect on the Cook Islands’ 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 Taha‘a) 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 (although one plant of Asparagus setaceus was seen in the wild on Mangaia and the Ricinus communis seen at the harbor area on ‘Atiu appeared to be an escape), 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 the Cook Islands if they escape cultivation. They should also be subject to inter-island quarantine.

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Table B. Cultivated species of possible threat to the Cook Islands

Scientific Name	Common Names (abridged)	Family	Present on:	Invasive in:
Ardisia crenata	hen’s eyes, Hilo holly	Myrsinaceae	Rarotonga	Fiji, Hawai’i
Asparagus densiflorus	asparagus fern, sprengeri fern	Liliaceae	Rarotonga	Hawai’i
Asparagus setaceus	ornamental asparagus, climbing asparagus fern, remu (Cook Islands)	Liliaceae	Rarotonga, Aitutaki, ‘Atiu, Mangaia, Miti’aro, Palmerston**	Tonga, Lord Howe Island
Bryophyllum delagoense	chandelier plant	Crassulaceae	Rarotonga**	Hawai’i
Carludovica palmata	Panama hat plant, Panamā	Cyclanthaceae	Rarotonga, ‘Atiu	Samoa
Cedrela odorata	Mexican cedar	Meliaceae	Rarotonga, ‘Atiu	South Africa
Cortaderia selloana	silver pampas grass	Poaceae	Rarotonga*	Australia, New Zealand, US
Cryptostegia madagascariensis	rubber vine	Asclepiadaceae	Rarotonga*, Mangaia*, ‘Atiu*	Australia (Queensland)
Dieffenbachia seguine	dieffenbachia, dumb cane	Araceae	Rarotonga, ‘Atiu, Mangaia*, Ma’uke**, Penrhyn*	American Samoa, Samoa
Dissotis rotundifolia	pink lady	Melastomataceae	Rarotonga*, Ma’uke*	Samoa
Erigeron karvinkianus	Mexican daisy, seaside daisy, daisy fleabane	Asteraceae	Rarotonga	Hawai’i, La Réunion
Grevillea banksii	Banks grevillea	Proteaceae	Rarotonga**	Hawai’i
Grevillea robusta	silk oak	Proteaceae	Rarotonga, Mangaia*, ‘Atiu*	French Polynesia (Rurutu)
Hedychium flavescens	yellow ginger	Zingiberaceae	Rarotonga*, Mangaia*, ‘Atiu*, Ma’uke*	New Zealand, La Réunion
Hedychium gardnerianum	kahili ginger	Zingiberaceae	Rarotonga*, Mangaia	New Zealand, La Réunion
Lonicera japonica	Japanese honeysuckle, pitate papa‘ā	Caprifoliaceae	Rarotonga, Mangaia*, ‘Atiu, Ma’uke*	Australia, Hawai’i, New Zealand
Murraya paniculata	orange jessamine, tiare ‘ānani (Cook Islands)	Poaceae	Rarotonga (rare)*, Mangaia (rare)*, ‘Atiu (rare)	French Polynesia, Hawai’i; host to citrus psyllid
Pennisetum setaceum	fountain grass	Poaceae	Rarotonga*	Hawai’i, Canary Islands
Ricinus communis	castor bean, tuitui papa‘ā (Cook Islands)	Euphorbiaceae	Rarotonga*, Mangaia*, ‘Atiu	Hawai’i, Samoa, Tonga and elsewhere
Schefflera actinophylla	octopus tree, umbrella tree	Araliaceae	Rarotonga	French Polynesia, Hawai’i, Micronesia
Sesbania grandiflora	scarlet wisteria tree, sesban	Fabaceae	Rarotonga*, Mangaia	Samoa
Setaria palmifolia	palmgrass	Poaceae	Rarotonga**	Samoa, Hawai’i, Tahiti
Tibouchina urvilleana	princess flower, glorybush, lasiandra	Melastomataceae	Rarotonga	Hawai’i

*Not seen but reported present by the Cook Islands Natural Heritage Project.
**Not seen but reported present by Bill Sykes.

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• A number of invasive species are widespread on all the southern group of islands. These include Abelmoschus moschatus, Adenanthera pavonina, Bauhinia monandra, Bidens pilosa, Cenchrus echinatus, Coffea arabica, Commelina diffusa, Cyperus rotundus, Desmodium gangeticum, Desmodium heterocarpon, Elephantopus mollis, Kyllinga nemoralis, Melia azedarach, Ocimum gratissimum, Paspalum Conjugatum, Passiflora rubra, Psidium guajava, Ruellia prostrata, Stachytarpheta cayennensis and Tithonia diversifolia. About all that can be done with these species is to control them as needed on a local basis.
   

• Most invasive plant species are not yet present on all the islands of the southern group. Rarotonga has the most weedy species; there are significantly fewer on the outer islands. The Cook Islands has already established inter-island quarantine procedures. It is very important that this quarantine be maintained and strengthened to prevent the movement of invasive plants and other species between islands. Table C shows the species that should be subject to inter-island quarantine and, for use by the island quarantine officers, Appendices 11-16 show, for each island, the species that are not present there but are present on other islands in the southern group. Especially critical for inter-island quarantine are the major invasive species.