Pacific Island Ecosystems at Risk (PIER)

Report on invasive species on Kosrae, Federated States of Micronesia

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Dangerous species not known to be on Kosrae

Species that are invasive elsewhere and are likewise invasive or have the potential to become so on Kosrae

Species that are mentioned or listed as weedy or invasive elsewhere and are cultivated, common or weedy on Kosrae

Native species (or early introductions) exhibiting aggressive behavior

Strategies for dealing with invasive species


Appendix 1. References

Appendix 2.  Species by category

Appendix 3. Invasive species present in Guam, Pohnpei or Hawai'i but not present in Kosrae

Appendix 4. Scientific name synonyms


Invasive plant species on Kosrae, Federated States of Micronesia


James C Space, Barbara Waterhouse, Julie S. Denslow, Duane Nelson and

Erick E. Waguk


U.S.D.A. Forest Service

Pacific Southwest Research Station

Institute of Pacific Islands Forestry

Honolulu, Hawai‘i, USA


22 December 2000



14 April 2000

Invasive plant species on Kosrae, Federated States of Micronesia

James C Space, Barbara Waterhouse, Julie S. Denslow, Duane Nelson and Erick E. Waguk(1)

This is a continuation of the survey of islands in Micronesia and American Samoa for invasive plant species requested by the Pacific Islands Committee, Council of Western State Foresters. A survey of other Micronesian islands was conducted in 1998 and was discussed in a previous report(2). This report is based on a survey of the island of Kosrae, Federated States of Micronesia, from 24 to 28 March 2000. The objectives, as with the previous survey, were three-fold: (1) To identify plant species on the islands that are presently causing problems to natural and semi-natural ecosystems; (2) to identify species that, even though they are not presently a major problem, could spread more widely or spread to other islands where they are not present, potentially causing problems; and (3) to confirm the absence of species that are a problem elsewhere and, if introduced to Kosrae, could be a threat there.

During our visit local experts showed us sites of known infestations. We also had available copies of various botanical and weed surveys conducted in the past (see Appendix 1, References). A visit of such short duration does not permit an exhaustive survey of the weed flora of the island. However, the intent was to conduct an overall survey. Additional surveys of individual species or sensitive areas can and should be conducted as needed. This report summarizes our findings and makes some suggestions for further action.

For convenience and to be consistent with the Micronesia report, invasive species occurring in or of threat to Kosrae 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 on Kosrae (352 species).
2.  Species that are invasive elsewhere and are also invasive or potentially invasive on Kosrae (12 species).
3.  Species that are invasive or weedy elsewhere and are cultivated, common or weedy on Kosrae (48 species).
4.  Native species (or early introductions) that exhibit aggressive behavior (9 species).

These species are listed in Appendix 2. Additional information about each species is located on a World Wide Web site,, and on the PIER-CD.

There are a number of other species that are invasive weeds in gardens, fields, and pastures and along roadsides but don’t seem to pose a particular threat to wildland ecosystems. These species are not included.

1. Dangerous species not known to be on Kosrae

Perhaps because of its location "off the beaten path", many invasive species have yet to reach Kosrae. These are listed in Appendix 2, Table 1. The worst of these include the following:

Antigonon leptopus (chain of hearts). This climbing vine has become a widespread pest on Guam and there are isolated plants in cultivation on Pohnpei. Traffic between Guam, Pohnpei and Kosrae and the fact that this is a pretty flower that people like to plant in their gardens makes this species a potential threat to Kosrae.

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

Cinnamomum verum (cinnamon), found to be very invasive in American Samoa and elsewhere. It is present on Pohnpei.

Clidemia hirta (Koster’s curse), a serious problem species in Hawai’i and in other locations. In Micronesia it is only present in Palau, but would be a serious problem if introduced as it grows well in the shade of closed forests.

Coccinia grandis (ivy or scarlet gourd), a smothering vine that is showing potential for serious damage to the forests of 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 a horticultural variety is present on Pohnpei. The proximity of the plant on Pohnpei and Guam poses a threat to Kosrae.

Two rubber trees, Funtumia elastica (African rubber tree) and Castilla elastica (Panama rubber tree), species that have proven very invasive in Samoa. While not known to be present in Micronesia (Castilla elastica is present in Hawai‘i) and thus posing a lesser threat, their invasive nature makes these species prime candidates for prompt eradication if found.

Eichhornia crassipes (water hyacinth), present on Guam and Pohnpei and a threat to Kosrae’s rivers and wetlands.

The Hyptis species, H. capitata, H. pectinata and H. suaveolens. Kosrae is presently free of these invasive plants. H. capitata is present on Pohnpei, though, and could pose a threat to Kosrae.

Miconia calvescens (the purple plague), which has caused serious damage to the ecosystem of Tahiti and had spread to several other islands in French Polynesia. It has also escaped in Hawaii and is the subject of an intensive and costly eradication effort there. Recently it was discovered in Queensland, Australia. It is an attractive garden plant and might be introduced this way or as tiny seeds on shoes or used equipment.

A number of grass species, including:

Mimosa diplotricha [=invisa](giant sensitive plant) and Mimosa pudica (sensitive plant) are both absent from Kosrae but present on Pohnpei and Guam. Mimosa diplotrichais a particularly nasty plant as it is covered with thorns and forms dense tangles that are difficult to walk through. Mimosa pudica, a smaller plant with only small prickles, can form dense mats. Kosrae is at high risk for invasion by both these plants.

Momordica charantia (bitter-melon), a member of the cucumber family, is a climbing vine and its fruit can be the host for fruit flies. It is present on Pohnpei, Chuuk and Guam.

Passiflora foetida is present on Kosrae, but several invasive members of this invasive genus are absent, including:

Piper auritum (eared pepper, locally called "false sakau"), recently introduced to Pohnpei. This species suckers profusely and produces many small seeds that are spread by birds, rodents and bats. An attempt is being made to eradicate it on Pohnpei. It was introduced into Pohnpei as a new form of sakau, but is worthless in this regard.

Pithecellobium dulce (Madras thorn), on all the other major Micronesian islands but apparently not yet present on Kosrae.

Psidium cattleianum (strawberry guava), a small tree that forms dense thickets, is a major problem species in Hawai‘i, Tahiti and elsewhere. It is present on Pohnpei and thus is a serious threat to Kosrae.

Spathodea campanulata (African tulip tree), a commonly planted ornamental present on Pohnpei, Chuuk and Guam. This tree has become a major problem in Fiji, the Hawaiian Islands and some other places. It was not seen on Kosrae and it would be good to exclude it from the island.

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

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 an even better strategy, now being adopted by countries such as Australia and New Zealand, is to exclude all species not shown by risk analysis to be of negligible risk). Known problem species that have the potential to cause problems in tropical island ecosystems and are not yet present on Kosrae are listed in Appendix 2, Table 1. These species should be excluded through plant quarantine and, if establishment is detected, promptly evaluated for eradication. In addition, species that are present in Guam, Pohnpei and Hawai‘i but are not present on Kosrae are listed in Appendix 3. There is high risk of introduction of these species because of air and ship traffic between these points and Kosrae.

2. Species that are invasive elsewhere and are likewise invasive or have the potential to become so on Kosrae

Some known invasive plants that are causing trouble in similar ecosystems have been introduced into Kosrae (Appendix 2, Table 2). Some of them 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.

Adenanthera pavonina (the coral bean tree), invasive in secondary forests and already widespread on Kosrae.

Chromolaena odorata (Siam weed), a highly invasive pan-tropical weed. It will likely become even more widespread over time. Biological controls are available that are effective in open areas, less so in shaded stands. On Kosrae it is likely to follow new developments such as roads.

Clerodendrum quadriloculare is suspicious because it appears to have the ability to invade intact or relatively intact native forests. This species is notorious for being a prolific producer of root suckers and in fact the plant is easily propagated by means of root cuttings. A dense, monospecific understory of this species was seen growing in full shade beneath the forest canopy on Pohnpei, making it a likely candidate to invade intact or only slightly disturbed native forest stands. Specimens observed on Kosrae were cultivated ones in yards, but this species should be monitored for possible naturalization. If so, naturalized populations should be promptly eradicated.

Dieffenbachia seguine (spotted Dieffenbachia or dumb cane) appears to be mostly an ornamental at present on Kosrae. However, this is potentially a very bothersome species, as it reproduces vegetatively and can thrive in the dense shade of an intact native forest canopy.

Hedychium coronarium (white ginger) can be an invader of swampy areas and wet forests and appears to have escaped from cultivation on Kosrae.

Mikania micrantha (mile-a-minute weed) is apparently a fairly recent introduction, as it is not yet widespread. It is very invasive in some locations in the Pacific and should be evaluated for possible eradication or control.

Occasional trees of Paraserianthes falcataria [Falcataria moluccana] (Molucca albizia) were seen. This species has the potential, over time, of spreading widely through the forest (as can be seen on Pohnpei). Further planting should be discouraged. If this is not a desired species, emphasis could be given to cutting the existing trees.

Syngonium angustatum, a climbing aroid, is probably another escape from cultivation. Like Dieffenbachia maculata, it has the ability to spread in the deep shade of intact forests. It is difficult to eradicate by hand as it is able to reproduce from a single node and bits and pieces of the stems or roots are easily overlooked.

3. Species that are mentioned or listed as weedy or invasive elsewhere and are cultivated, common or weedy in Kosrae

A large number of other cultivated, 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 2, Table 3) should be monitored for spread and possible control, if necessary.

Potentially invasive tree species include Acacia auriculiformis (earleaf acacia), Bauhinia monandra (orchid tree), Ceiba pentandra (kapok), Moringa oleifera (horseradish tree), Samanea saman (monkeypod), and Tecoma stans (yellow bells).

Dissotis rotundifolia (dissotis) is quite prevalent in shaded areas and waterways.

A number of introduced grasses have become established, including Bothriochloa bladhii, Cenchrus echinatus (bur grass); Chloris radiata (plush-grass, radiate fingergrass), Digitaria ciliaris (fingergrass, smooth crabgrass); Eleusine indica (goose grass), Paspalum conjugatum (Hilo grass), Pennisetum polystachion (mission grass) and Pennisetum purpureum (elephant or napier grass). Pennisetum polystachion may be a new introduction as it was only seen at the airport and near the Catholic church.

Other widespread weedy species include Blechum pyramidata (blackweed) and Desmanthus virgatus, possibly a recent introduction.

Passiflora foetida (love-in-a-mist) is common but not overly aggressive.

Desmodium tortuosum (Spanish clover or Florida beggar weed) was noted at four sites.

Stachytarpheta jamaicensis was widespread but Stachytarpheta cayennensis [urticifolia] (blue rat's tail) has apparently not yet arrived—be on the lookout for it.

Wedelia [Sphagneticola trilobata (Singapore daisy) is a widespread pest, as on most Pacific islands.

4. Native species (or early introductions) exhibiting aggressive behavior

Some native species (or early introductions) exhibit aggressive characteristics. These species are listed in Appendix 2, Table 4.

Merremia peltata (pul) is quite invasive any place there is disturbance.

Rubus moluccanus (kohkihl) has a very bad reputation for invasiveness on tropical islands (Mauritius, La Reunion) but is considered native on Kosrae (Fosberg, 1979). It is widespread but does not seem to be causing major problems.

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 plant protection and quarantine officials to make them aware of known and potential invasive plant species. Plant quarantine officers are familiar with most agricultural pests, but they may not be aware of some of the 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. Better yet is to go to the approach recently adopted by Australia and under serious consideration by a number of other countries. That is to exclude all alien species not shown to be of negligible 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.

Education of the public about the danger of introductions and encouraging the use of native species can be helpful. People need to understand why they should follow the quarantine regulations, why they shouldn’t dump garden cuttings in the woods, and why they should report suspicious plants. What may just be a pretty flower to be planted in a yard or garden can turn out to be an invasive 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.

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 herbicides, 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 a problem if the infestation is allowed to spread so that they will 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 also be encouraged to report suspicious plants. Funding can be requested to prepare information folders or "wanted" posters. Prompt follow-up to public reports is essential to maintain credibility.

It is particularly important to work with any local plant importers, as these are often 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.

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 and tend to first become established 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 and Aliens list-servers

Laws and regulations should be reviewed to make sure they are adequate to deal 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.

The Federated States of Micronesia and Kosrae State governments are encouraged to take advantage of the Federal assistance programs in dealing with invasive plant species. Cost-share funding is available to provide locally available expertise in forest health protection. 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 requested 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 economic 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:

Since there is so much traffic to Kosrae from Guam and Hawai‘i, where many of these species are present, it would be highly desirable to institute special measures to prevent introduction of invasive species from these sources. At a minimum, quarantine officers should be alert to people who might have been in the woods or rural areas in Guam or Hawai‘i, especially on the Big Island of Hawai‘i, and inspect their shoes or boots for seeds. Any trucks or equipment coming from Hawai‘i that have been used in rural areas must be power washed or steam cleaned. Warning posters should be produced to alert the public and encourage reporting of any introductions. Any infestations picked up from public reporting or scouting should be promptly eradicated before the plants set seed.

Appendix 1. References

Appendix 2.  Species by category

Appendix 3. Invasive species present in Guam, Pohnpei or Hawai'i but not present in Kosrae

Appendix 4. Scientific name synonyms

(1)  Former Director, Pacific Southwest Research Station, USDA Forest Service (now retired); Botanist, Australian Quarantine and Inspection Service; Research Ecologist/Team Leader, Institute of Pacific Islands Forestry, USDA Forest Service; Forest Health Coordinator, Institute of Pacific Islands Forestry, USDA Forest Service and State Forester, Kosrae State, FSM, respectively.

(2)  Space, James C. and Marjorie Falanruw (1999). Observations on invasive plant species in Micronesia. Report prepared for the meeting of the Pacific Islands Committee, Council of Western State Foresters, Majuro, Republic of the Marshall Islands, February 22-26, 1999.

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This page updated 14 January 2001.