Pacific Island Ecosystems at Risk (PIER)

Report on invasive species in Micronesia

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Dangerous species not known to be in Micronesia

Species that are invasive elsewhere and likewise invasive in Micronesia

Species that are not known to be invasive elsewhere but which have spread or appear to be spreading in Micronesia

Species that are mentioned or listed as weedy or invasive elsewhere and are common or weedy in Micronesia

Native and naturalized species exhibiting aggressive behavior

Strategies for dealing with invasive species


All islands








Plans for the future

Appendix 1  Selected references and additional reading

Appendix 2  Species by category


Observations on invasive plant species in Micronesia


James C Space and Marjorie Falanruw


Report to the Pacific Islands Committee, Council of Western State Foresters

February 23, 1999


U.S.D.A. Forest Service

Pacific Southwest Research Station

Institute of Pacific Islands Forestry

Honolulu, Hawai‘i, USA



Observations on invasive plant species in Micronesia (1)

James C Space and Marjorie Falanruw (2)

As requested by the Pacific Islands Committee, Council of Western State Foresters, we conducted a survey of selected Micronesian islands for invasive plant species. The objectives were three-fold: (1) To identify species on the islands that are presently causing problems; (2) to identify species that, even though they are not presently a major problem, could spread to other islands where they are not present, potentially causing problems; and (3) to look for invasive species known to cause problems in ecosystems similar to the islands visited. This report is based on perceptions gained from a three-week trip from July 19 to August 6, 1998, to the islands of Saipan and Tinian (Commonwealth of the Northern Mariana Islands); Peleliu, Babelthaup and Koror (Republic of Palau); Pohnpei and Yap (Federated States of Micronesia) and Guam.

The topic of invasive species is complex and it is difficult to predict the behavior of species introduced into new areas under different combinations of environmental parameters and degrees of disturbance of native plant communities. For a more in-depth discussion of invasive species some selected references are given in Appendix 1. "Plant Invaders" by Cronk and Fuller gives a concise and readable account of the problem of invasive species and their management.

During our visit we consulted with local experts familiar with plant pests as well as academic experts at the University of Guam and the Northern Marianas College. We also had access to a number of reference works, including Stone’s "Flora of Guam;" Fosberg, Sachet and Oliver's geographical checklists of plants of Micronesia; checklists for a number of islands prepared by David Lorence and Tim Flynn of the National Tropical Botanical Garden based on Fosberg et al and supplemented by their observations during several trips to Micronesia; and lists of invasive species by Dr. Muniappan of the University of Guam. Our thanks to all who helped us with this survey.

For convenience, we have grouped invasive species occurring in or of threat to Micronesian islands in five categories:

1.  Species that are invasive elsewhere in similar ecosystems but were not seen on our visit and are not listed in the literature as being present in Micronesia (82 species).
2.  Species that are invasive elsewhere and are also invasive in Micronesia (13 species).
3.  Species that are not known to be particularly invasive elsewhere but are invasive in Micronesia (3 species).
4.  Species that are invasive or weedy elsewhere and are common or weedy in Micronesia (117 species).
5.  Native species that exhibit aggressive behavior (16 species).

These species are listed in Appendix 2. In addition, lists by location and a summary of information about each species are located on a World Wide Web site,

There are numerous species that are invasive weeds in gardens and pastures, but don’t seem to pose a particular threat to native wildland ecosystems. These species are not included.

1. Dangerous species not known to be in Micronesia

While there are already a number of serious weed species in Micronesia, some other major pests have not yet arrived. The worst of these include the following:

Miconia calvescens (the purple plague), which has caused serious damage to the ecosystem of Tahiti in French Polynesia. It has also escaped in Hawai‘i and is the subject of an intensive and costly eradication effort there. Recently it was discovered in Queensland, Australia.

Passiflora tarminiana (banana poka, formerly known as P. mollissima), a smothering vine that is a problem in Hawai‘i and New Zealand.

Rubus species (blackberries and raspberries), many of which are pests (absent in Micronesia with the exception of R. moluccanus, which occurs on Kosrae).

Tibouchina herbacea (glorybush or cane ti), another species that is a major problem in Hawai‘i.

Cecropia obtusifolia and C. peltata, invasive tree species that are a problem in Hawai‘i and French Polynesia, respectively.

In general, all grasses, members of the Melastomataceae family, and Ligustrum, Passiflora or Rubus species not already present should be suspect and should be proven benign before they are allowed to be introduced.

A number of other invasive species that are problems elsewhere and could potentially cause problems in Micronesia are listed in Appendix 2, Table 1. These species should be seriously considered for exclusion through plant quarantine and, if establishment is detected, promptly evaluated for eradication. Additional species will be added to this list if they are determined to be a potential threat.

2. Species that are invasive elsewhere and likewise invasive in Micronesia

Some known troublemakers have been introduced into Micronesia and are causing problems (see Appendix 2, Table 2). Those that have been introduced and spread widely on some islands, but are not yet widespread throughout Micronesia, include the following:

Antigonon leptopus (chain of hearts) is very prevalent on Guam. Occasional cultivated specimens were seen on Pohnpei.

Coccinia grandis (ivy or scarlet gourd), a smothering vine, is out of hand and showing potential for serious damage to the forests of Saipan. The vines form such dense cover that the forest underneath is completely shaded out and destroyed. It is also common on Guam and what is purported to be a horticultural variety has been introduced into Pohnpei.

Melinis minutiflora (molasses grass) is both invasive and causes a serious fire hazard,

Imperata cylindrica (cogon grass) has been introduced to Yap and has spread over 78 acres near the old airport. It has been evaluated and eradication recommended. Grasses that looked suspiciously like Imperata were seen on Palau and Saipan. Swarbrick (1997) lists it as present in Palau. Fosberg et al (1987) list I. cylindrica as being present in Saipan, Tinian and Guam and I. conferta as being present in Saipan, Tinian, Rota, Guam, Palau and Yap.

Clidemia hirta (Koster’s curse) is present on Palau and American Samoa. It is localized on Palau, and should be evaluated for possible control measures. It is a problem species in Hawai‘i.

Pennisetum setaceum (fountain grass) has been introduced on Guam. This species is a major problem in Hawai’i. P. polystachion and P. purpureum have spread, especially on Guam and Saipan, and are spreading on other islands.

Rubus moloccanus (Molucca bramble) is recorded as being present on Kosrae. This species is a serious pest on the Mascarene Islands in the Indian Ocean.

A number of other species such as Chromaeolena odorata (Siam weed), Lantana camera, Leucaena leucocephala (tangan-tangan), and Mimosa diplotricha [=invisa] (giant sensitive plant) are already widespread where they have been introduced. About the only alternative for these pests is to introduce appropriate biological control agents, when available, and try to prevent introduction to any islands where they are not yet present.

3. Species that are not known to be invasive elsewhere but which have spread or appear to be spreading in Micronesia

A few species, which have not been particularly invasive elsewhere, are problems or potential problems in Micronesia (Appendix 2, Table 3).

Clerodendrum quadrilocularae is suspicious because it appears to have the ability to invade intact or relatively intact native forests. A dense, monospecific understory of this species was seen growing in full shade beneath the forest canopy in Pohnpei, making it a likely candidate to invade intact or only slightly disturbed native forest stands.

Elaeis guineensis (African oil palm) is spreading on Pohnpei, particularly on drier sites.

Timonius timon (liberal) is widespread on the islands of Peleliu and Angaur, Republic of Palau. It is reported to be present in Koror, but this was not confirmed by us.

4. Species that are mentioned or listed as weedy or invasive elsewhere and are common or weedy in Micronesia

A 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 severely disturbed sites, although some species, particularly alien trees, are gradually spreading 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, since there is often a long lag time between introduction and when a species begins to cause serious impacts. These species (listed in Appendix 2, Table 4) should be seriously evaluated for inter-island quarantine to confine them to the islands where they are presently located.

We were especially interested in observing the behavior of Acacia species, since many of them have a reputation for invasiveness. In Micronesia, the most commonly planted acacias are A. auriculiformis, A. confusa and A. mangium. Only a few areas of naturally occurring seedlings of Acacia were observed on the trip; however, abundant seedlings have been reported in areas planted to Acacia on Guam and Palau. Although these species do not seem to be a problem in Micronesia at present, they should be evaluated and serious thought should be given before other species of acacia or other exotic trees are introduced. There would seem to be little reason to introduce new species or to plant them where they are not already present, since many exotic trees are invasive. Even though they may spread only gradually, eventually there is a significant effect on native ecosystems. A special case may be Guam, where getting anything to persist in the face of repeated fires is a problem. But even there, whether or not any tree species can survive repeated, high-frequency fires is problematical.

A number of species of acacia were planted in a now-abandoned Institute of Pacific Islands Forestry species trial in Yap. One species was observed to be sending up new plants from root suckers; it would probably be best to eliminate this species before it spreads further. Cedrela odorata (cigar box or Mexican cedar) and Cordia alliodora (laurel) have been introduced in species trials on Yap and possibly on other islands. Both of these species are known to be invasive elsewhere (C. odorata in the Galapagos and South Africa, C. alliodora in the Galapagos and Vanuatu). These and any other plantings should be closely monitored for spread or, if there is no further need for them, eliminated.

There are a number of other introduced trees that, left to their own devices, are gradually spreading in the vicinity of, into or through native forests. These include Adenanthera pavonina (coral bean tree), Albizia lebbeck (siris-tree), Ceiba pentandra (kapok), Melaleuca quinquenervia (paperbark), Paraserianthes falcataria [Falcataria moluccana] (Molucca albizia, also known as tuhke kerosene on Pohnpei), Samanea saman (monkeypod), Spathodea campanulata (African tulip tree), and Tecoma stans (yellow-bells).

A wide variety of introduced grasses have become established, the most aggressive of which include the bur grasses, Cenchrus brownii and Cenchrus echinatus; Cynodon dactylon (Bermuda grass), Ischaemum rugosum (muraina grass) and other Ischaemum spp.; Paspalum spp., including P. conjugatum (Hilo grass), P. dilatatum (Dallis grass), P. fimbriatum, and P. urvillei (Vasey grass); Pennisetum polystachion (mission grass); Pennisetum pupureum (elephant or napier grass) and Sorghum halepense (Johnson grass).

Other widespread weedy species include Bidens pilosa (beggar's tick) and Wedelia [Sphagneticola] trilobata.

A number of other species present to some degree in Micronesia have bad reputations elsewhere. These should be monitored for invasive behavior and evaluated for quarantine. They include bamboos (Bambusa and other bamboo species), Cestrum nocturnum (night-flowering cestrum), Delairea odorata [Senecio mikanioides] (German ivy), Eichhornia crassipes (water hyacinth), Eriobotrya japonica (loquat), gingers (Hedychium spp.), Melia azedarach (Chinaberry), Passiflora spp. (passion fruits, granadillas, and related species), Pluchea indica (Indian fleabane), Pluchea carolinensis (sourbush), Psidium cattleianum (strawberry guava), Psidium guajava (guava), Ricinus communis (castor bean), Schinus terebinthifolius (Christmasberry), Syzygium cumini (Java or jambolan plum), Syzygium jambos (rose apple), Thunbergia spp. (various vines) and Tithonia diversifolia (tree marigold).

5. Native and naturalized species exhibiting aggressive behavior

Some native species (or early introductions) exhibit characteristics that could make them problem species if they are introduced to islands where they are not present.

Probably the native species with the most aggressive behavior is Merremia peltata, (a smothering vine), particularly on Palau, Yap, Kosrae and Pohnpei. This species often aggressively expands into areas that are disturbed.

Heterospathe elata (palma brava) palms continue to spread in ravines and slopes of central Guam.

The grass Ischaemum polystachyum is very prevalent along roadsides and in disturbed areas, particularly on Pohnpei. Sword grass (Miscanthus floridulus) is especially common, sometimes in fairly pure stands on volcanic soils on Guam. It is also present in the Northern Marianas, Chuuk, Pohnpei and Kosrae as well as American Samoa.

While most of these species are widespread in Micronesia, they should not be introduced where not already present. For example, Merremia peltata is not known to be present in the Northern Marianas and, given its aggressive behavior elsewhere, it certainly should be excluded.

Strategies for dealing with invasive species

The first line of defense against invasive species is to keep them out. Control at ports of entry is essential, and land management officials should work closely with their plant protection and quarantine officials to make them aware of known and potential invasive species. Plant quarantine officers are familiar with many agricultural pests, but they may not be aware of pests that threaten wildland ecosystems. In cooperation with the plant quarantine organization, a list of noxious species to be excluded should be developed, and exclusion of these species should be backed by the force of law and regulation. Risk assessment and management techniques can be used to assess the likelihood and effects of possible introductions and to develop exclusion and eradication strategies.

Education of the public about the danger of introductions and encouraging the use of native species is helpful. What may just be a pretty flower to be planted in the yard or garden can turn out to be an invasive species. It is particularly important to work with local nurseries and botanical gardens, as these are often the source of new introductions. A positive approach is to develop a "white list" of both native and non-native species that the public can be encouraged to plant.

Land managers 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 become established in disturbed areas. Suspicious plant species should be promptly reported. A formal evaluation should be requested for any new species that appears to be invasive or is known to be invasive elsewhere. This evaluation should be by an expert who is familiar with the species and methods for its eradication or control and can recommend further action. Prompt action is essential, since once a species becomes widespread, control or eradication can be extremely costly or impossible.

It is also very helpful to have laws and regulations in place to aid in dealing with new introductions. This includes the ability of government to require the control of noxious species on private lands, or to take action on private lands if the landowner cannot be located or does not take prompt action. Provision for emergency funds to deal with immediate problems should also be in place. Model laws and regulations can be obtained from states and countries that have implemented them.

All Micronesian governments are encouraged to take advantage of the Federal assistance programs in dealing with invasive species problems. Cost-share funding is available to provide locally available expertise in forest health protection to land management agencies. Often this is in the form of an agreement with a local college or university to provide the necessary assistance. Experts are also on call from the Forest Service’s Forest Health Protection staff, or they can arrange for expert consultation. Finally, cost-share funding can be provided to deal with forest health problems, including plant pests, under the Cooperative Forestry and Hawaii Tropical Forestry Recovery acts. Funding is subject to recommendations resulting from a professional evaluation of the problem and the overall availability of funds. Funding also tends to be prioritized based on an evaluation of cost-effectiveness, so rapid eradication of a pest species while it is still confined to a small area would undoubtedly take precedence over the chronic problem of a species that has escaped control.


In addition to the above strategies, we offer the following specific recommendations:

All islands:








While we did not visit Kosrae on this trip, Rubus moloccanus (Molucca bramble) is recorded as being present. This species is a serious pest and should be evaluated for control or possible eradication.

Plans for the future

This cursory survey has probably identified many of the major known and potential plant threats to Micronesian wildland ecosystems. However, due to limitations of time and funding, only selected islands could be visited, and only a few days spent on each. On-the-ground land managers, on the other hand, can see what is going on in their islands every day. We encourage reports to the authors of species we have missed, as well as new or suspicious species. We also welcome contributions of information to the database and web site and correction of erroneous information.

Priority for future work will be to: (1) Visit the rest of the major Micronesian islands and American Samoa to survey them for invasive species; (2) visit adjacent areas with similar ecosystems to survey for invasive species that might be transferred to Micronesia or American Samoa; (3) publish a hard-copy edition of the information for those who do not have Internet access; (4) continue to sponsor publication of public information leaflets and warning posters both in English and local languages; and (5) continue to maintain and update the data base and web site, contribute information to other international data bases, and encourage those with relevant information to contribute to ours.

We welcome inquiries on species that are suspicious or are causing problems so that we can help you keep them out of Micronesia and American Samoa. It has been our pleasure to assist you in protecting your island ecosystems.

Appendix 1  Selected references and additional reading

Appendix 2  Species by category

(1)  Prepared for the meeting of the Pacific Islands Committee, Council of Western State Foresters, Majuro, Republic of the Marshall Islands, February 22-26, 1999.

(2)  Formerly Director, Pacific Southwest Research Station, USDA Forest Service (now retired) and Research Biologist, Institute of Pacific Islands Forestry, USDA Forest Service.

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This page updated 11 March  2000.