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Papers presented at the workshop

Watershed management and sustainable mountain development

Presented by
Mette Wilkie
on behalf of FORC, FAO Forestry Department

Watershed Management

Watershed management in small islands is particularly important for a number of reasons:

• The watersheds are reservoirs of biological diversity (a high percentage of endemic species are found in the Pacific islands and many of these are found in the forested parts of watersheds).

• Small islands are highly dependent on local water resources.

• Distances between the upper catchment and the sea are often very short, which means that processes in uplands impact directly on coastal areas.

Watershed problems in the sub-region include: flash floods, landslides, prolonged droughts and soil erosion as a result of irrational land-use including cultivation on steep slopes, deforestation and forest degradation.

These problems result in:

• Water scarcity.

• Sedimentation (rivers, ports, shipping lanes, mangroves, seagrass beds and coral reefs).

• Water pollution including saltwater intrusion.

• Decrease in fisheries.

• Decrease in tourism and trade.

Watershed management needs to take into consideration a number of ecological, social and economic factors and conditions. These include exposure to natural disasters, upland-lowland linkages, land tenure systems, weak and/or fragile economies and the need for equitable and sustainable development.

The need for integrated and participatory watershed management is, therefore, evident.

FAO has been providing support to watershed rehabilitation and management in the Pacific at the sub-regional as well as the national level (e.g., Samoa, following Cyclone Val in 1991).

FAO’s support to watershed management and sustainable mountain development after UNCED has been based on the follow-up to Chapter 13 of Agenda 21 “Management of fragile ecosystems: sustainable mountain development”. Additional information about FAO’s watershed management programme can be found on the Internet at

Mountain Issues: Broadening Perceptions and Realities

Forestry: Provision of wood and non-wood goods and services.

Agriculture: High dependence on agriculture. Erosion problems.

Water: 60 % of the freshwater in humid areas and up to 95% of the freshwater supply in semi-arid and arid areas available in watersheds originates in mountain areas. Potential for hydropower.

Biodiversity: High due to variation in altitude.

People: High cultural diversity and high level of indigenous knowledge.

Economy and trade: Difficult access.

Tourism and recreation: 15-20% of tourists visiting mountain areas account for US$70-90 billion per year.

Fragile areas: Natural and man-induced hazards.

Marginality and poverty: Often characterise mountain populations.

Opportunities: Large, based on diversity in culture, resources and indigenous knowledge. But due to fragility a strong need for integrated sustainable management of the existing resources and for people’s participation.

Many issues cross national borders and mountain issues have thus become an international concern.

The FAO Mountain Programme


• FAO’s Traditional Role – land, water conservation and technical support.

• Cooperation in watershed management and sustainable mountain development (i.e. EFC Working Party).

• Recent work has integrated participatory approach to watershed management, environmental and social issues.

• Input in the preparatory process of UNCED.

• Task Manager for Chapter 13 of Agenda 21 and Lead Agency for the International Year of Mountains.


• Generating and strengthening knowledge about the ecology and sustainable development of mountain ecosystems.

• Promoting integrated watershed development and alternative livelihood opportunities.

• Hub for FAO mountain-related sustainable development issues.

Principal Roles

• Promotion and co-ordination of FAO mountain-related activities.

• Conduct normative work in sustainable mountain development and watershed management.

• Develop field programme activities in cooperation with countries.

• In-house coordination through the establishment of the Inter-Departmental Working Group on Mountains.

• Chapter 13 Task Manager role.

• Lead agency for the International Year of Mountains – 2002.

Main Components

• Information generation and dissemination.

• Institutional arrangements and networking.

• Raising awareness.

• Capacity building.

• Field Programme support and collaboration.

• Co-ordination of in-house and external implementation of Chapter 13.

The International Year of Mountains 2002

The United Nations has proclaimed 2002 as the International Year of Mountains (IYM) to increase international awareness of the global importance of mountain ecosystems. It assigned the Food and Agriculture Organization (FAO) the role of lead agency in collaboration with governments, NGOs and other UN organizations


• Kyrgyz Initiative.

• ECOSOC Resolution.

• UNGA Resolution - 1998 FAO designated Lead Agency.


• To increase awareness of and knowledge about mountain ecosystems and their overriding importance in providing strategic services and products for the well being of rural and urban peoples.

• To promote and defend the cultural heritage of mountain communities.

• To promote conservation and sustainable development of mountain resources for present and future generations.

Key considerations for the International Year of Mountains 2002:

• Chapter 13 context.

• More than a celebration.

• Awareness raising plus concrete action.

• Part of long-term process.

• Advantage of lead time.

Additional information:

Additional information on mountains and the International Year of Mountains can be found in the FAO Concept paper on the IYM (copies distributed) and at the following Internet sites:

FAO’s home page:

The official IYM 2002 web site:

Forestry and agroforestry alien trees as invasive plants in the Pacific Islands1

Dr. Jean-Yves Meyer, Plant Ecologist & Field Botanist
Délégation à la Recherche, B. P. 20981, Papeete, Tahiti, French Polynesia


Jean-Pierre Malet, Forestry Officer
Service du Développement Rural, B. P. 4 Taiohae, Nuku Hiva, French Polynesia


Reforestation with introduced alien ("exotic") forestry and agroforestry trees increased significantly in the Pacific Islands during the last 50-80 years. The use of alien species was justified by the need for fast-growing plants that were resistant to drought, fire or poor soil conditions and easy to propagate by seed. The main purposes of introduction were for timber, fuelwood and soil erosion control. Other species were planted for nitrogen fixation, animal fodder, as poles and living fences, to provide shelter and windbreaks, and secondarily for ornament, food, medicinal use, essence oil and other purposes. About 40 forestry and agroforestry tree species (excluding fruiting and ornamental trees) are now considered to be invasive in the Pacific Islands, Leucaena leucocephala being the most common invader in nearly all the island groups. The fast-growing aggressive colonizers such as Acacia spp., Albizia spp., Castilla elastica, Cecropia spp., Cordia alliodora, Paraserianthes spp., Prosopis spp., Spathodea campanulata, Tecoma stans and Triplaris spp. are now widespread in secondary vegetation, including forestry plantations. A few of them are even found in undisturbed native forest (e.g. Chrysobalanus icaco). Other naturalized species are considered as potential invaders because of their invasiveness in other tropical islands or countries (e.g. Cedrela odorata, Cinchona succirubra or Ochroma pyramidale). Because of their large size, their tendency to form dense stands, and their significant impacts on ecosystem processes, these alien tree species constitutes a potential threat to Pacific islands biodiversity. Modern silviculture should assess the risk of disseminating invasive alien trees and recommend traditional agroforestry or forestry using native species.


Le reboisement avec des arbres introduits (“exotiques”) en foresterie et agroforesterie a augmenté de façon significative dans les îles du Pacifique dans les 50-80 dernières années. L’utilisation d’espèces étrangères a été justifiée par la demande en plantes à croissance rapide résistantes à la sécheresse, au feu, aux sols pauvres, et facile à propager par graines. Les principaux buts d’introduction étaient comme bois de charpente ou d’œuvre, bois de chauffe et lutte contre l’érosion du sol. D’autres espèces ont été plantées pour la fixation d’azote, comme fourrages pour animaux, poteaux de clôture et tuteurs vivants, arbres d’ombrage et de protection contre le vent, et secondairement comme plantes ornementales, alimentaires, médicinales, à essence, et pour d’autres utilisations. Environ 40 espèces d’arbres forestiers et agroforestiers (excluant les arbres fruitiers et ornementaux) sont actuellement considérés comme des espèces envahissantes dans les îles du Pacifique, Leucaena leucocephala étant l’envahisseur le plus commun dans presque tous les groupes d’îles. Les colonisateurs agressifs à croissance rapide comme Acacia spp., Albizia spp., Castilla elastica, Cecropia spp., Cordia alliodora, Paraserianthes spp., Prosopis spp., Spathodea campanulata, Tecoma stans et Triplaris spp. sont maintenant abondants en végétation secondaire, incluant les plantations forestières. Quelques uns d’entre eux sont même trouvés en forêt naturelle non perturbée (e.g. Chrysobalanus icaco). D’autres espèces naturalisées sont considérées comme des envahisseurs potentiels en raison de leur caractère envahissant dans d’autres îles ou pays tropicaux (e.g. Cedrela odorata, Cinchona succirubra ou Ochroma pyramidale). En raison de leur grande taille, de leur tendance à former des couverts denses, et de leurs impacts significatifs sur le fonctionnement des écosystèmes, ces arbres constituent une menace potentielle pour la biodiversité des îles du Pacifique. La sylviculture moderne devrait évaluer le risque de dissémination d’arbres étrangers envahissants, et recommender une foresterie et agroforesterie traditionnelles utilisant des espèces indigènes.


Introduction of weeds (e.g. grasses such as Chloris spp., Panicum spp., and Paspalum spp., vines such as Merremia spp., or spiny shrubs such as Mimosa spp.) may be sometimes accidental as seed contaminants (hidden among ship’s ballast, or carried in fodder), whereas introduction of alien invasive trees are mainly deliberate, as ornamental plants (in botanic gardens, plant nurseries and by private gardeners) or for agriculture, forestry and agroforestry. Of the 184 highly invasive woody plants worldwide compiled by P. Binggeli (1996), 34 tree species (18%) were introduced for forestry purposes. Agriculture and forestry follow as the next most significant sources of invasive plants in the Hawaiian Islands (C. W. Smith 1985).

The aim of this short paper is to illustrate the importance of alien invasive tree species introduced in the Pacific Islands for forestry or agroforestry purposes. Our purpose is not to blame past “unwise” introductions, but rather to raise awareness of the threat caused by current cultivation and future introduction of actual or potential invasive plant species in island ecosystems, which are famous for their unique but fragile native biota.

This paper deals only with introduced alien (or “exotic”, i.e. non-native, non-indigenous) trees, which are defined as relatively large, perennial, woody plants with a single main trunk. They comprise small trees (>5-10 m in height), medium-sized trees (>10-30 m) and large trees (> 30 m up to 40 m). Invasive woody shrubs (< 5 m) are excluded, e.g. the thorny Acacia farnesiana (Leguminosae), Rubus spp. (Rosaceae), Lantana camara (Verbenaceae), or the aggressive ornamentals Rose myrtle Rhodomyrtus tomentosa (Myrtaceae) and Brazilian pepper Schinus terebinthifolius (Anacardiaceae).

Forestry trees are tree species planted mainly for timber (construction and furniture), fuelwood and other wood products (e.g. woodcarving, cabinet-making, matchsticks, etc.). Agroforestry trees are any tree species used in agriculture other than exclusively for wood production; such uses include nitrogen fixation, animal fodder, poles and living fences, shelters and windbreaks, and secondarily for medicinal use, ornament, essence oil, food sources, etc. (see Table 1). Invasive tree species initially introduced exclusively for their fruits (or fruiting trees), such as pond-apple Annona glabra (Annonaceae), shoebutton ardisia Ardisia elliptica (Myrsinaceae), strawberry guava Psidium cattleianum (Myrtaceae), common guava Psidium guava (Myrtaceae), rose-apple Syzygium jambos (Myrtaceae), and Indian jujube Ziziphus mauritiana (Rhamnaceae) are not included in this paper, as well as invasive ornamental trees such as Miconia calvescens (Melastomataceae), Chinese banyan Ficus microcarpa (Moraceae) or octopus tree Schefflera actinophylla (Araliaceae).

The Pacific Islands included in this study are small tropical island countries or states, including Hawaii, but excluding the large continental islands of New Zealand, Papua New Guinea and the Solomon Islands. A preliminary list of the main invasive plant species in the Pacific Islands can be found in a recently published technical report (Meyer 2000). This list is neither exhaustive nor definitive, as alien plant species continue to be introduced and some previous introductions may have not yet been recorded.

Why are forestry and agroforestry trees good invaders?

The reason for the success of alien forestry and agroforestry tree species in the Pacific Islands may be explained by the following bio-ecological characteristics:

• Well-adapted to the climate because their native range (e.g. tropical America, Africa, Asia, Malaysia) has a similar rainfall and temperature regime;

• Fast-growing species considered as pioneer trees in their native range (e.g. Cedrela odorata and Ochroma pyramidale, 1-5 m height increase/year for Cecropia spp., 2-7 m height increase/year for Trema spp., up to 5 m height increase and 15 cm diameter increase/year for Paraserianthes falcataria). They are good colonizers of large open areas (forest clearings, pastures) and small-scale forest openings (riverbanks, trail- and road-sides, treefall gaps and forest edges). Legume trees (e.g. Albizia spp. and Paraserianthes spp.) and other species such as Myrica faya have faster growth due to a symbiotic association with nitrogen-fixing organisms;

• Prolific seed or fruit production (e.g. 800 000 seeds/kg for Casuarina equisetifolia; 200 000-300 000 seeds/kg for Toona ciliata; 100 000 seeds/kg for Grevillea robusta; 50 000-70 000 seeds/kg for Cedrela odorata; 100 000 fruits produced by a mature tree for Cinnamomum camphora);

• Long-distance dispersal of seeds by wind (e.g. winged seeds of Spathodea campanulata, Tecoma stans and Triplaris spp.; small hairy seeds of Alstonia macrophylla) or active dispersal of their fleshy fruits by birds (e.g. Citharexylum spinosum, Myrica faya and Cinnamomum camphora whose seed germination is facilitated by bird ingestion, possibly removing inhibitors in the fruit) or by flying foxes and bats (Melia azedarach in Australia, Muntingia calabura in the Northern Mariana Islands, Cecropia peltata in Costa Rica);

• Tolerance to drought (e.g. Acacia spp., Prosopis spp.) and salinity (e.g. Casuarina spp., Albizia lebbeck), flooding or poor soil conditions (e.g. Acacia confusa, Chrysobalanus icaco);

• Fire resistant (e.g. Acacia mearnsii, Cinnamomum camphora (which resprouts from the roots after burning and flowers in less than two years after a high intensity fire). Melaleuca spp., Melia azedarach, Leucaena leucocephala and Toona ciliata resprout from the base after high intensity fires);

• Resistant to insects, especially termites (e.g. Cordia alliodora, Syncarpia glomulifera and Toona ciliata);

• Coppice/sucker easily after being cut (e.g. Leucaena leucocephala, Prosopis spp.);

• Long viability of seeds in the soil (e.g. Cinnamomum camphora, whose seeds remain viable for 3 years). The seeds remain dormant in the soil awaiting disturbance to trigger germination;

• Large soil seed bank (e.g. 20 000 seeds/m² for Acacia mearnsii);

• Longevity of trees (e.g. 100-200 years for Toona ciliata, 70-100 years for Melia azedarach, more than 100 years for Cinnamomum camphora and up to 500 years in its native habitat);

• Large and widespread planting as timber crops (e.g. Myrica faya or Grevillea robusta, with 2.2 million trees planted between 1919 and 1959 in Hawaii) or multi-purpose tree species (e.g. Leucaena leucocephala, Prosopis spp.).

Ecological impacts of alien forestry and agroforestry trees

• Large size compared to other invasive shrubs, vines and herbs;

• Form dense, closed-canopy, nearly monospecific stands that shade out other species, and/or compete for water and sunlight, suppressing growth and regeneration of understorey plants;

• Produce allelopathic substances reducing the growth or inhibiting the establishment of other plant species (e.g. Cinnamomum camphora, Grevillea robusta, Myrica faya and Syzygium spp.);

• Poisonous to animals (e.g. Melia azedarach seeds are poisonous to dogs and man and reported to cause death of pigs and fowl; Pangium edule, whose large seeds are poisonous; the seeds of Leucaena leucocephala contain a toxic amino acid (mimosine) with injurious effects to horses and cattle);

• Alteration of the natural ecosystem processes such as the water regime, nutrient cycling and soil erosion (the superficial roots of Albizia lebbeck or Paraserianthes falcataria favour landslides on steep slopes; the root system of Albizia saman competes for water with cultivated plants; the fast-growing Cedrela odorata, Muntingia calabura, Toona ciliata or Spathodea campanulata are very susceptible to strong winds).

Some examples of forestry and agroforestry actual and potential invasive alien trees in the Pacific Islands

Acacia confusa Merr.

Introduced into the Hawaiian islands around 1915 by the Board of Agriculture and Forestry, and by the Hawaiian Sugar Planter’s Association, now widely naturalized on all of the main islands of this archipelago (Wagner et al. 1999). Considered as one of the 86 main invasive species in Hawaii (C.W. Smith 1985).

Acacia nilotica (L.) Willd. ex Del. (Leguminosae). Prickly acacia, Nile acacia, babul.

Currently considered as “an extremely valuable source of fuel, gum, small timber, fodder, tannin and honey in tropical Africa and the Indian subcontinent. It is very drought tolerant, withstands extreme temperature and grows fast under favourable soil irrigation” ( Known to be a serious plant invader in Australia, “a very serious threat” in Rodrigues Island (Kell 1997: 13) and a cultivated escape in the Galápagos Islands (McMullen 1999). Also considered a potential invader in New Caledonia where it is “widely naturalized” on one coastal site (Gargominy et al. 1996, p. 391).

Alstonia macrophylla Wall ex G. Don (Apocynaceae).

Introduced for reforestation in the Seychelles Islands and naturalized: “it must be expected that this species will spread and threaten the native species” (Friedman 1994, p. 465). Newly naturalized in Hawaii (Wagner et al. 1999) where it may constitute a potential invader.

Castilla (Castilloa) elastica M. Sessé (Moraceae). Panama or Mexican rubber tree.

“A tree reaching a height of 45 to 150 feet, source of the rubber balls Columbus saw” (Mabberley 1997, p. 233). Originally planted as an experimental crop in Western Samoa for its abundant milky sap used as rubber, then “naturalized in the wild, abundant in the lowlands in Upolu” (Parham 1972, p. 106). Now considered a dominant invasive plant in Samoa, “one of the few alien tree species that has become naturalized in Samoa ... it should not be promoted or encouraged” (Thaman & Whistler 1996, p. 73). Introduced and naturalized in French Polynesia, especially on the island of Moorea, where it has spread in the Opunohu valley since the 1980s (Florence 1997). Planted in the 1930s in the vicinity of the village of Taiohae on the island of Nuku Hiva (Marquesas Islands); noted as rare in 1987, it is now rapidly spreading in Tectona grandis and Swietenia sp. forestry plantations (Meyer & Malet, unpublished data, June 2000). Also planted and naturalized on the island of Mayotte (Indian Ocean) where “there is a highly invaded area near the agronomic experimental station of Dembéi” (C. Mas, personal communication, 2000).

Cecropia peltata L. (Cecropiaceae). Trumpet tree.

Planted as a shelter tree for coffee or cocoa plantations (Koohafkan & Lilin 1989). Originally planted in the botanical garden of Papeari on the island of Tahiti in 1926 (Meyer 1998), first collected on the island of Raiatea in 1937 (Florence 1997), now a dominant invader in low-elevation mesic habitats of all the islands of the Society Islands, French Polynesia. A similar species, Cecropia obtusifolia, is a dominant invader in Hawaii and in the Cook Islands (Meyer 2000).

Chrysobalanus icaco L. (Chrysobalanaceae). Coco plum, icaco, fat-pork.

A widespread coastal small tree, usually 3-6 m tall, but up to 10 m (Morean 1991). It ranges from subtropical Florida through the Caribbean, Jamaica and Central America to eastern South America and western Africa (Prance, 1970). Introduced in the early 1900s in the Seychelles to control erosion, and recommended for reforestation because it was considered as “an extremely hardy shrub which grows on the poorest soils. Very useful for afforestation. Reproduced itself well from seeds and is strongly recommended for growing in areas overrun with bracken ferns or gazontrail which it will keep in check, though it is easy to bring up other trees through thickets of this species” (Gibson 1938, p. 17). “The successful cultivation of the species in Trinidad augurs well for its potential cultivation and for landscapes” (Morean 1991, p. 708). It is now particularly abundant on the island of Mahé on degraded slopes at low elevation where it forms impenetrable thickets. Now considered as “a serious plant invader in the Seychelles” (Friedman 1994, p. 246).

First introduced to the botanical garden of Papeari on the island of Tahiti in 1922, now highly invasive on the Temehani plateaus in the island of Raiatea between 425 and 560 m elevation (Meyer 1998). Also spreading on Fatu Hiva (Marquesas Islands) where it has been planted along a trail between 600 and 660 m elevation (Meyer, unpublished data, February 2000). Commonly planted in the town of Papeete and along roadsides in Tahiti as an ornamental. In Fiji, it was presumably introduced as an ornamental, “growing in the Suva botanical gardens in 1948 and had been abundantly naturalized in Southeastern Viti Levu prior to that date” (A. C. Smith 1985, p. 44), now common along roadsides near sea-level, on the upper edges of beaches and in thickets on the inner margin of mangrove swamps.

Cinchona pubescens Vahl (synonym C. succirubra) (Rubiaceae). Red quinine tree.

Cultivated for the quinine of commerce in many tropical countries and islands, it was planted by foresters in Hawaii (Wagner et al. 1999). One of the most invasive plants in the Galápagos (McMullen 1999) and in Jamaica: “two other invaders of Blue Mountains forests are Cinchona pubescens and C. officinalis, native of Andean cloud forests. They were brought to the Jamaican garden that bears their names [Cinchona botanical garden] as a source of quinine in the 19th century” (Sauer 1988. pp. 86-87). Between 1945 and 1950, more than 10 000 trees were planted in Tahiti on the Taravao plateau at about 400 m elevation by the Agriculture Department (Pétard, 1986). Naturalized since the 1980s on the same site, a large tree has been found in nearly pristine cloud forest at 950 m elevation above the plateau (Meyer, unpublished data).

Cinnamomum camphora T. Nees & C. Eberm (Lauraceae). Camphor tree.

Introduced to Australia in 1822, by 1900-1920 widespread on the coast, especially in Sydney garden and public lands. Extensively naturalized, particularly over the past 30 years, in coastal areas on better soils where it often hinders the regeneration of native rainforest species and along gullies generally associated with catchment disturbance. Tendency to form monocultures, excluding native vegetation” (Benson & McDougall 1997). Considered as a moderate invader in Hawaii (Meyer 2000).

Cinnamomum verum J. Presl. (synonym C. zeylanicum) (Lauraceae). Cinnamon tree.

Introduced in 1772 on Mahé Island (Seychelles) as a spice. “Birds had spread seed from the garden into natural habitats on the rugged granitic islands. The species thrived and multiplied, its commercial value not being recognized until after 1900 when heavy exploitation of the stands began for export. However, it resprouts vigorously after cutting and remains a common permanent member of the flora in both artificially modified and remote natural habitats” (Sauer 1988). “Today it is both a useful tree because of its economical activity and noxious because it threaten the remnants of the native vegetation where it is thriving” (Friedman 1994, p. 70). Invasive in the Samoa Islands, the Cook Islands and the Federated States of Micronesia (Meyer 2000).

Citharexylum caudatum L. (Verbenaceae). Fiddlewood.

First introduced to Hawaii by the Hawaiian Sugar Planter’s Association in 1931, now naturalized and rapidly spreading in the Manoa valley on the island of Oahu (Wagner et al. 1999). It has been used extensively as an innocuous landscape tree in Hawaii and is rapidly becoming a problem. A related species cultivated as a garden ornamental, C. spinosum (synonym C. fruticosum), is naturalized in Fiji near sea level and is considered to be invasive (Meyer 2000).

Cordia alliodora (Ruiz & Pav.) Oken (Boraginaceae).

Native to tropical America, it is used as a shade tree in coffee plantations and produces good timber used in construction and furniture. Brought to Vanuatu as a timber tree in 1980 and promoted by the Forestry Department for the next 10-15 years assisted by aid programmes from several countries (Tolfts 1997). It is a pioneer species that has spread in pastures in Vanuatu, creating dense thickets. “Cordia is a classic case of introduction with the best of intentions of an organism, which then fails to live up to expectations and ends up as a nuisance: expensive, if not impossible, to eradicate” (Tolfts 1997, p. 13). Introduced and naturalized in the Seychelles, planted at the botanical garden in Mahé, “it is possible that it will disseminate more in the future” (Friedman 1994, p. 505). Also planted and naturalized in the Galápagos Islands (McMullen 1999) and in Tonga.

Funtumia elastica (Preuss) Stapf (Apocynaceae). African rubber tree.

“Commercially valuable tree in regrowth of forest after felling timber trees” (Mabberley 1997, p. 291). “Western Samoa’s worst pest which now dominates the secondary forests of western Upolu (Whistler 1994).

Grevillea robusta A. Cunn. ex R. Br. (Proteaceae). Silky oak, silver oak.

The timber is used for cabinetwork because of the silky and oak-like grain of the wood, cultivated to shelter coffee plantations (Mabberley 1997). Planted as an ornamental street-tree in Hawaii because of its particularly attractive orange blossoms (Neal 1965). “The tree grows quickly, sometimes 100 feet high or more, resists drought, and affords shade. In Hawaii, it thrives between sea level and 4,000 feet ... it is one of the 12 best trees for reforestation. In December 1938, 105,000 trees were planted in government forest reserves of the islands. The seeds are exceptionally light and, each seed being surrounded by a membranous wing, they are carried for miles by the wind. They can germinate in bare, rocky soil, and so the tree is found self-sown here and there in native Hawaiian forests” (Neal 1965: 320). Planted in more than 40 forest reserves on five main Hawaiian islands (Cuddihy & Stone 1990). One of the main forest plantation trees in New Caledonia and Tonga (Waterhouse 1997). Planted and naturalized in French Polynesia on the island of Rurutu (Austral Islands) where it is now spreading (Meyer, unpublished data, 1999).

Leucaena leucocephala (Lam.) de Wit (Leguminosae). Wild tamarind, lead tree.

“A leguminous species that flourishes in tropical lowland areas… Fuelwood, livestock forage, poles, and pulpwood are among the species’ most useful by-products. In addition, the tree’s rapid growth makes it an excellent choice for live fences and erosion control” ( The typical example of a multi-purpose tree cultivated for various purposes such as fodder, firewood, erosion control, soil improvement and shade for coffee, rubber or cocoa plantations. Now widely naturalized, it sometimes forms the dominant element of the vegetation in most of the Pacific Islands groups.

Maesopsis eminii Engl. (Rhamnaceae). Musizi.

A fast-growing large tree known to be a dominant invasive tree in Tanzania, also naturalized in Puerto Rico (Binggeli 1993). Planted in Fiji as a timber tree (Waterhouse 1997), now naturalized (M. K. Charan, Forestry Department, personal communication, 2000), and thus a potential invader.

Melia azedarach L. (Meliaceae). White cedar, pride of India, Indian lilac, Chinaberry.

A serious invader in South Africa and Florida, it is also considered an invasive plant in Hawaii (C. W. Smith 1985) where it was first planted as a shade tree. Introduced in French Polynesia on the islands of Tahiti and Moorea (Society Islands), naturalized on the islands of Raivavae, Rurutu and Tubuai (Austral Islands) along roadsides and in the lowlands (Meyer, unpublished data), invasive on the islands of Mangareva, Akamaru, Taravai (Gambier Islands) where it was planted to shelter coffee plantations (Meyer 1998).

Muntingia calabura L. (Tiliaceae). Calabura, jam tree, Jamaican cherry, Panama cherry.

A fast-growing small tree, up to 10 m in height, usually 4-5 m, introduced and naturalized in Guam, Nauru and the Mariana Islands where “it thrives on limestone soils in open fields, forest edges and roadsides” (Raulerson & Rinehart 1991, p. 98). Planted as an ornamental and used as firewood, this species is very sensitive to strong winds, which uproot the trees.

Ochroma pyramidale (Lam.) Urban (syn. O. lagopus) (Bombacaceae). Balsa, down tree, cork tree, corkwood.

A large, fast-growing tree native to tropical America, found in clearings and known as “the world’s lightest commercial timber used for insulation in refrigerators, model aeroplanes, architect’s models” (Mabberley 1997, p. 497). Widely planted in Papua New Guinea (Waterhouse 1997). In the Galápagos Islands, “it was introduced in 1940 as an experiment. The trees had reached a height of 30 m by 1964 and were considered too large to provide quality wood (Wiggins & Porter, 1971). So the experiment failed, but the trees remained to grow, reproduced, and took over a considerable part of the forest near Bella Vista” (Schofield 1973, p. 49). “In Hawaii it is sometimes planted for reforestation, not for ornament” (Neal 1965, p. 573). Naturalized and spreading in disturbed habitats on the island of Fatu Hiva (Marquesas Islands) up to 560 m elevation (Meyer, unpublished data, February 2000).

Paraserianthes falcataria (L.) I. Nielsen (syn. Albizia falcataria) (Leguminosae). Moluccana, batai wood.

Large tree used as a shade tree for coffee in many parts of the world and considered as “the world’s fastest growing tree” (Mabberley 1997, p. 529). It grows very rapidly even on nutrient-poor soils (C. W. Smith 1985), and spreads rapidly because its pods are dispersed by wind. Invasive in Hawaii, the Federated States of Micronesia, French Polynesia and the Seychelles Islands. “This proliferation is noxious, not only because they consume a lot of water and contributed certainly to decrease the water course debit but also because they compete with native species in the remnant of natural forests ... the falling down of old or not well-rooted Albizia destroy native plants in the understorey, the treefall gaps are rapidly colonized by Albizia and other exotics” (Friedman 1994, pp. 271-272). A dominant or moderate invader in the Cook Islands, French Polynesia, Guam, Hawaii and the Federated States of Micronesia (Meyer 2000).

Spathodea campanulata P. Beauv. (Bignoniaceae). African tulip tree.

Planted as an ornamental and often as a living fence or boundary marker in Tonga. The timber is occasionally used as firewood (Thaman & Whistler 1996). Introduced in the 1930s in Samoa and now naturalized and very common in some areas (Parham 1972). Considered to be a moderate or dominant plant invader in Hawaii, Fiji and French Polynesia (Meyer 2000).

Syncarpia glomulifera (Sm) Niedenzu (synopnym S. laurifolia) (Myrtaceae). Turpentine wood.

“In Fiji, probably a recent introduction by the Department of Forestry as a potential reforestation species” (A. C. Smith 1985, p. 298). In Hawaii, “at least 83,000 trees have been planted by state foresters on all of the main islands. It has been reported as reproducing and escaped at least in the Kamakou reserve on the island of Molokai” (Wagner et al. 1999, p. 948). Planted in Tahiti, and sparingly naturalized above the botanical garden in Papeari, considered as a potential invader (Meyer 1998).

Syzygium cumini (Myrtaceae). Java plum, jambolan.

“Timber occasionally used in light construction, good firewood, one of the main sources of fuel in the Marquesas” (Thaman & Whistler 1996). A dominant invader in French Polynesia and Hawaii (Meyer 2000). Forms dense forests that shade out all the other plants, especially on the islands of Raiatea (Society Islands) and Hiva Oa (Marquesas Islands) where it is spreading in montane native forests up to 1 200 m elevation (Meyer 1998).

Tecoma stans (L.) Juss ex. Kunth (synonym Stenolobium stans) (Bignoniaceae). Yellow elder, yellow bells.

A serious invader in South Africa. First introduced to Tahiti as a garden ornamental in 1845, than planted for soil protection (Soroquere et al., 1991) and as a shelter tree (and for stakes) in vanilla plantations. Now a dominant invader in the Society, Marquesas and Austral Islands (French Polynesia). Also widely naturalised in the Cook Islands, Federated States of Micronesia, Guam, New Caledonia (Meyer 2000), and Hawaii where it is sparingly naturalized in dry and mesic habitats (Wagner et al., 1999) but not yet considered an invasive plant.

Toona ciliata M. Roemer (synonym Cedrella toona, Toona australis) (Meliaceae). Toon, Australian cedar, red cedar.

Planted in Western Samoa, Niue, Tonga and the Solomon Islands (Waterhouse 1997). It has light, durable wood used for furniture and in construction but is very susceptible to drought or wind damage (Thaman & Whistler 1996). In Hawaii, it was extensively planted, primarily in forested areas and now naturalized in mesic to wet disturbed habitats (Wagner et al. 1999), and is considered a potential invader (C. W. Smith 1985).

Triplaris weigeltiana (Rchb.) Kintze (synonym T. surinamensis) (Polygonaceae).

Naturalized in French Polynesia, on the island of Tahiti, between 10-300 m elevation. It forms dense stands with numerous seedlings (Meyer, unpublished data). It is also invasive in South Africa. “I am seeking information about Triplaris americana and its potential to escape cultivation. We seem to have a problem at the Durban Botanic Garden and surround” (Richard Boon, e-mail dated 3 June 2000 to the discussion forum Aliens-L on the Internet).

The case of Pinus spp. and Eucalyptus spp. in the Pacific Islands

In Australia, New Zealand and especially South Africa, invasive pines cause significant problems for managers of grazing lands, watersheds and protected areas (Richardson 1998a, 1999). In Hawaii, at least four species (Pinus caribaea, P. patula, P. pinaster and P. radiata) are considered to be invasive (C.W. Smith 1985). The Caribbean pine, Pinus caribaea, is one of the most common forestry tree species in the Pacific Islands, widely planted in the Cook Islands, Fiji, New Caledonia, Papua New Guinea, Solomon Islands, Tonga, Vanuatu, Wallis & Futuna and French Polynesia (Waterhouse, 1997). It is well known to naturalize in open and disturbed areas, producing many seedlings in French Polynesia as well as in New Caledonia (Gargominy et al., 1996). According to local foresters in French Polynesia, Pinus caribaea and Eucalyptus spp. are only found on open degraded lands after fires or landslides (W. Tetuanui, personal communication, 2000). The ecological impact of large, monospecific Caribbean pine plantations in the Pacific Islands is not known. In New Caledonia, it is one of the few alien species that is able to colonize ultrabasic soils with native vegetation (Meyer 2000).

Over 90 species of Eucalyptus have been planted in forestry plantings in Hawaii; 30 of them are now naturalized, but only one species, the blue gum (E. globulus) is considered to be a potential invader (C. W. Smith 1985). This tree, up to 70 m tall, “has been extensively planted and spreading or at least regenerating from seed” (Wagner et al. 1999, p. 949). In Haiti, Eucalyptus is not recommended for agroforestry because “it compete with the cultures for water, and it eliminates the understorey. It is to be avoided on steep slopes when there is a risk of erosion” (Koohafkan & Lilin 1989: 75).

Conclusions: conflict of interest between foresters and conservationists ?

This study is an attempt to demonstrate that several introduced tree species considered as beneficial by agronomists or foresters have (or may have) a negative impact on natural or semi-natural ecosystems. For example, there seems to be a clear conflict between the agroforestry value of Leucaena leucocephala and its deleterious impact on the environment. In the Marquesas Islands (French Polynesia), local foresters have noted that dense stands of Leucaena have caused the extirpation of native trees traditionally used as carving wood, such as Thespesia populnea (Malvaceae) and Cordia subcordata (Boraginaceae).

Forestry and agroforestry programs were developed in the Pacific Islands during the last 50-80 years in response to poverty, soil erosion and fuelwood shortages using fast-growing non-native plant species that were resistant to drought, fire or poor soil conditions and easy to propagate by seed (a set of bio-ecological characteristics that makes these tree species pre-adapted to be “good invaders”). Aid agencies worldwide, including FAO, ACIAR (Australia) and CIRAD (France) and NGOs (such as the “New Forest Project”) still encourage the use of exotic species in reforestation projects. For example, the invasive species Acacia mearnsii, A. nilotica, Paraserianthes falcataria, Leucaena leucocephala, Melia azedarach, Grevillea robusta, Muntingia calabura and Cinnamomum camphora are all recommended in the 1987 catalogue of forestry tree species by the Technical Center for Tropical Forestry of New Caledonia (Anonymous 1987).

However, the web site of the “New Forest Project” and the “World Seed Program”, which recommend and distribute tree seeds of Leucaena leucocephala, Prosopis juliflora and Acacia spp. for agroforestry and local reforestation projects in the tropics, specifies that “some of these species can be very invasive if not used carefully, replacing much of the local and native vegetation… Therefore, the introduction of a new species must be done with careful consideration for possible effects on native vegetation and with proper management of the tree introduced”.

In the same way, J. W. Turnbull (ACIAR) emphasizes in his book on multi-purpose Australian trees and shrubs that “attention is particularly drawn to potentially undesirable characteristics of some species. Fast-growing aggressive trees and shrubs are often appropriate for cultivation in areas experiencing severe fuelwood shortage or where there is serious erosion. However, under some environmental conditions these species have the potential to be invasive and to spread into areas where they are not wanted. Such species should be introduced with care and their performance monitored closely” (Turnbull 1986).

Even the neem tree (also called nim or margosa), Azadirachta indica Adr. Juss. (Meliaceae), considered “one of the world’s most useful trees” (Mabberley 1997) must be planted carefully: “Widely introduced to Haiti since the 1960s as shade trees along the roads… the nim is an invasive species not to be used for agroforestry” (Koohafkan & Lilin 1989).

National or regional development plans should take invasive tree species into account. Modern silviculture should assess the risk of disseminating invasive trees and recommend either traditional agroforestry or forestry using native tree species. For instance, the German Development Service (DED) is supporting efforts to preserve indigenous trees in watershed reforestation in the Philippines (

The importance of early control of invasive species also needs to be brought to the attention of managers because large number of introduced species may still be in a lag phase i.e. the time lag between establishment and population explosion. For instance, Acacia albida, planted in the Marquesas Islands by the Forestry Department in French Polynesia, was rapidly destroyed by foresters because of its similar noxious habit with the aggressive thorny shrub Acacia farnesiana (P. Labadie, pers. comm. 2000).


Anonymous. 1987. Catalogue des Semences d’Espèces Forestières. Centre Technique Forestier Tropical, Service des Forêts et du Patrimoine Naturel, Section semences, Nouméa.

Binggeli, P. 1993. Biological invasion by Maesopsis eminii in the Usambara forests, Tanzania. Opera Bot. 121: 229-235.

Binggeli, P. 1996. A taxonomic, biogeographical and ecological overview of invasive woody plants. Journal of Vegetation Science 7: 121-124.

Benson, D. & McDougall, L. 1997. Ecology of Sydney Plant Species. Part 5. Dicotyledon. Families Flacourtiaceae to Myrsinaceae. Cunninghamia 5(2).

Cronk, Q. C. B. & Fuller, J. L. 1995. Plant Invaders. The threat to natural ecosystems. Chapman & Hall, London.

Cuddihy, L. W. & Stone, C. P. 1990. Alteration of Native Hawaiian Vegetation. Effects of Humans, Their Activities and Introductions. University of Hawaii Cooperative National Park Resources Studies Unit, Honolulu.

Florence, J. 1997. Flore de la Polynésie française, Volume 1. Editions de l’ORSTOM, Paris.

Friedmann, F. 1994. Flore des Seychelles. Dicotylédones. Editions de l’ORSTOM, Paris.

Gargominy, O., Bouchet, P., Pascal, M., Jaffré, T. & Tourneur J.-C. 1996. Conséquences des introductions d’espèces animales et végétales sur la biodiversité en Nouvelle-Calédonie. Rev. Ecol. (Terre Vie) 51: 375-402.

Gibson, H. S. 1938. A report on the forests of the granitic islands of the Seychelles. (unpublished report)

Mabberley, D. J. 1997. The Plant-Book. A portable dictionary of the vascular plants. Second Edition. Cambridge University Press, Cambridge.

Kell, S. 1997. Alien plant invasions on Rodrigues Island (Indian Ocean). Aliens 5: 13-14.

Koohafkan, A. P. & Lilin Ch. 1989. Arbres et arbustes de Haïti. Utilisation des espèces ligneuses en conservation des sols et en aménagement des bassins versants. Centre de formation en aménagement des bassins versants GCP/HAI/SWI. Organisation des Nations Unies pour l’Alimentation et l’Agriculture (FAO)/Ministère de l’Agriculture, des Ressources Naturelles et du Développement Rural, Port-au-Prince, Haiti.

Maclet, J. N. undated. Les Arbres de la Polynésie française utilisables pour leur bois. Service de l’Agriculture et des Eaux et Forêts, N°44/Agri/PE, Tahiti (unpublished report).

Maclet, J. N. 1958. Liste préliminaire des plantes d’intérêt économique et des principales plantes adventices existant en Polynésie française. Section Documentation-Recherche, juillet-août 1958. Service de l’Agriculture et des Eaux et Forêts, N°47/Agri/PE, Tahiti (unpublished report).

McMullen, C. K. 1999. Flowering Plants of the Galapagos. Cornell University Press, Ithaca and London.

Meyer, J.-Y. 1998. Mécanismes et gestion des invasions biologiques par des plantes introduites dans des forêts naturelles à Hawai’i et en Polynésie française : une étude de cas. Rapport d’étude post-doctorale, Délégation à la Recherche/University of Hawaii at Manoa, (unpublished report).

Meyer, J.-Y. 2000. Preliminary review of the invasive plants in the Pacific islands (SPREP Member Countries). Pp. 85-114 in Sherley, G. (tech. ed.), Invasive species in the Pacific. A technical review and regional strategy. South Pacific Regional Environmental Program, Apia.

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Parham, B . E. V. 1972. Plants of Samoa. New Zealand Department of Scientific and Industrial Research, Wellington.

Pétard, P. 1986. Quelques plantes utiles de Polynésie française et raau Tahiti. Editions Haere Po No Tahiti, Papeete.

Prance, G. T. 1970. The genera of Chrysobalanaceae in the Southeastern United States. Journal of the Arnold Arboretum 89: 521-528.

Raulerson, I. & Rinehart A. 1991. Trees and Shrubs of the Northern Mariana Islands. Coastal Resources Management, Office of the Governor, Saipan.

Richardson, D. M. 1998a. Invasive alien trees: the price of forestry. World Conservation, IUCN, Double issue 4/97-1/98: 14-15.

Richardson, D. M. 1998b. Forestry trees as invasive aliens. Conservation Biology 12(1): 18-26.

Richardson, D. M. 1999. Commercial forestry and agroforestry as sources of invasive alien trees and shrubs. Pp 237-257 in T. Sandlung et al. (eds.), Invasive Species and Biodiversity Management. Kluwer Academic Publishers, Dodrecht.

Sauer, J. D. 1988. Plant Migration. The Dynamics of Geographic Patterning in Seed Plant Species. University of California Press, Berkeley.

Schofield, E. K. 1973. Galápagos Flora: the Threat of Introduced Plants. Biological Conservation 5(1): 48-51.

Smith, A. C. 1985. Flora Vitiensis. A New Flora of Fiji. Vol. 3. Pacific Tropical Botanical Garden, Lawai.

Smith, C. W. 1985. Impact of alien plants on Hawai’i’s native biota. Pp 180-250 in C. P. Stone & J. M. Scott (eds.), Hawai’i’s Terrestrial Ecosystems Preservation and Management. University of Hawaii Cooperative National Park Resource Studies Unit, Honolulu.

Soroquere, G. & Mondon G. 1979. Liste des principaux végétaux ligneux de la Polynésie française. Déc. 1979 (unpublished report).

Thaman, R. R. & Whistler, W. A. 1996. A review of uses and status of trees and forests in land-use systems in Samoa, Tonga, Kiribati and Tuvalu with recommendations for future action. UNDP/FAO, South Pacific Forestry Development Programme, Suva.

Tolfts, A. 1997. Cordia alliodora: the best laid plans…Aliens 6 (Pacific Issue): 12-13.

Turnbull, J. W. (ed.) 1986. Multipurpose Australian Trees and Shrubs. ACIAR, Canberra.

Wagner, W. L., Herbst, D. R. & Sohmer, S. H. 1999. Manual of the Flowering Plants of Hawaii. Revised Edition. University of Hawaii Press/Bishop Museum Press, Honolulu.

Waterhouse, D. F. 1997. The Major Invertebrate Pests and Weeds of Agriculture and Plantation Forestry in the Southern & Western Pacific. ACIAR, Canberra.

Whistler, W. A. 1994. Botanical inventory of the proposed Tutuila and Ofu units of the National Park of American Samoa. University of Hawaii Coop. Nat. Park. Res. Studies Unit, Tech. Report 87, Honolulu.

Whistler, W. A. 1998. Weeds of Samoa. Aliens 7: 8-9.

Table 1. List of some forestry and agroforestry alien invasive trees in the Pacific Islands

Scientific name


Common English names

Country of origin

Max. height

Introduction purposes & other uses

Acacia confusa

Leguminosae Mimosoideae


Philippines, Taiwan

15 m


Acacia mearnsii

Leguminosae Mimosoideae

black wattle

SE Aust.

20 m

Fuel, Tan, Pole

Acacia nilotica

Leguminosae Mimosoideae

prickly acacia, Nile acacia, babul

Trop. Afr.

10 m

Tan, Gum, Timb, Fodd, Med, Bee

Adenanthera pavonina



red sandalwood

SE Asia, Malaysia, Aust.

25 m


Albizia chinensis




SE Asia

20 m

Wood, Timb, Shad, Nit

Albizia lebbeck



East Indian walnut, siris

Trop. Asia

25 m

Wood, Timb, Shad, Nit

Albizia (= Samanea) saman



rain tree, monkey pod, saman tree

Trop. Amer.

25 m

Orn, Shad, Nit, Wood

Alstonia macrophylla




15 m


Castilla (= Castilloa) elastica


Panama rubber

C. Amer

20 m


Casuarina glauca


swamp oak, saltmarsh ironwood



Casuarina equisetifolia


common ironwood, Australian pine

SE Asia

20 m

Soil, Nit

Cecropia peltata +

C. obtusifolia


trumpet tree

Trop. Amer.

20 m

Timb, Shad, Med, Wood

Cedrela odorata


West Indian cedar, Mexican cedar

Trop. Amer.

35 m

Timb, Wood

Chrysobalanus icaco


coco plum, Icaco

Trop. America, West Indies, Florida

10 m

Orn, Soil, Fru, Med

Cinchona succirubra (= C. pubescens)


red quinine tree

S. Amer.

15 m

Med, Timb

Cinnamomum camphora



China, Taiwan, Japan

15 m

Med, Ess, Timb, Spic, Oil, Wind

Cinnamomum verum (= C. zeylanicum)



Sri Lanka, SW India

15 m

Spic, Timb

Citharexylum spinosum + C. caudatum



West Indies

15 m

Frui, Timb

Cordia alliodora


Equador laurel, salmwood, cypre

Trop. Amer.

20 m

Timb, Wood, Shad, Fru, Orn

Funtumia elastica


African rubber tree

Trop. Afr.



Grevillea robusta


silky oak, silk oak, silver oak

E. Aust.

40 m

Timb, Shad, Orn, Wood , Bee, Wind

Leucaena leucocephala (= L. glauca)



lead tree, wild tamarind

Trop Amer

20 m

Fuel, Fod, Soil, Nit, Gree, Wind, Timb, Med, Nit, Shad

Maesopsis eminii



Trop. Afr.

40 m


Melaleuca quinquenervia

+ M. leucadendra


paper bark

E. Aust., SE New Guinea, New Cal

25 m

Oil, Wind

Melia azedarach


white cedar, pride of India, Indian lilac, Chinaberry, Persian lilac

Asia, Aust.

25 m

Timb, Orn, Shad, Wood

Muntingia calabura


calabura, jam tree, Jamaican cherry

Trop. Amer

10 m

Fuel, Wind, Bee, Orn, Fru, Fibr

Myrica faya


firetree, fayatree


15 m

Soil, Nit, Orn, Fru

Ochroma pyramidale (= O. lagopus)


balsa, down tree, cork tree

Trop. Amer.

30 m

Timb, Wood, Can

Pangium edule


football fruit


40 m

Oil, Med, Wood, Fru

Paraserianthes (= Albizia) falcactaria

Leguminosae Mimosoideae

Moluccana, Molucca

Malaysia, New Guinea

40 m

Fuel, Soil, Timb, Can, Shad

Pithecellobium dulce



Madras thorn, Manila tamarind

C. Amer.

15 m

Shad, Wind, Oil, Fuel, Fru, Tan

Prosopis juliflora + P. pallida



mesquite, algaroba

S. Amer.

20 m

Fuel, Fodd, Fru, Bee, Med, Pol, Fodd

Spathodea campanulata


African tulip tree, flame tree

Trop. Afr.

25 m

Timb, Orn, Shad

Syncarpia glomulifera (= S. laurifolia)


turpentine wood

NE Austr.

30 m

Timb, Wind, Shad, Wood

Syzygium cumini


jambolan, Java plum


20 m

Fru, Tan, Fuel, Wind, Timb

Tecoma stans


yellow elder, yellow bells

Florida, Trop Amer.

10 m

Orn, Pol, Med

Toona ciliata (= T. australis) (= Cedrela toona)


toon, Australian cedar, red cedar

Indomal. + Aust.

30 m

Wood, Timb, Orn, Shad, Fuel

Triplaris americana + T. weigeltiana (surinamensis)



Trop. Amer.

35 m


Purpose of introduction & other uses (according to various sources)

Bee = beekeeping/apiculture (honey)

Boat = boat/canoe/ship building

Ess = Essence oil and perfumery

Fibr = Fibres and cordage ;

Fru = fruit, juice, syrup, jelly, jam, chutney

Fuel = fuelwood/firewood and charcoal

Fodd = animal fodder/livestock forage

Gree = green manure

Gum = Gum arabic substance, rubber and resin

Med = medicinal, insecticidal and pharmaceutical, antibacterial, narcotic, alkaloids, tonic drink

Nit= Nitrogen fixing

Oil = oil source

Orn = ornamental (gardens)

Pol = Poles, posts, and living fence

Shad = shade (streets and shelter for plantations)

Soil = soil erosion control, sand stabilization

Spic = Spice and condiment

Tan = Tanins/tanbark

Timb = timber for construction and furniture

Wind = windbreak and hedges

Wood = woodcraft (carving), cabinetmaking, marquetry, boxes and matchsticks

Table 2. Pacific islands and other tropical countries where the tree species is considered to be invasive or potentially invasive

Scientific name

Pacific Islands

Other tropical countries invaded

Acacia confusa



Acacia mearnsii


Mascarene Is., New Zealand, South Africa

Acacia nilotica

New Caledonia

Australia, Rodrigues Is., South Africa

Adenanthera pavonina

FSM, Guam, Nauru, Niue, Palau


Albizia chinensis

Hawaii, Samoa

E. Africa

Albizia lebbeck

Guam, Hawaii, New Caledonia, Northern Mariana


Albizia (= Samanea) saman

Niue, Fiji, Samoa


Alstonia macrophylla



Castilla elastica

French Polynesia, Samoa


Casuarina glauca


Florida, New Zealand

Casuarina equisetifolia

French Polynesia, Hawaii

Florida, Mascarenes, Seychelles, S. Africa

Cecropia peltata + C. obtusifolia

Cook Is., French Polynesia, Hawaii, New Caledonia

Haïti, Malaysia, Trop. Africa

Cedrela odorata

Hawaii, New Cal., Yap

E. Africa, Galapagos

Chrysobalanus icaco

Fiji, French Polynesia


Cinchona succirubra

(= C. pubescens)

French Polynesia

Galapagos Is., Jamaica, St-Helena

Cinnamomum camphora


Australia, Florida, S. Africa

Cinnamomum verum

(= C. zeylanicum)

Cook, Hawai’i, Samoa

Mayotte, Seychelles

Citharexylum caudatum + C. spinosum (fruticosum)

Hawaii, Fiji


Cordia alliodora


Galapagos Is.

Funtunia elastica



Grevillea robusta

French Polynesia, Hawaii


Leucaena leucocephala

(= L. glauca)

most Pacific Islands

Florida, Mascarenes, Puerto Rico, Seychelles, Singapore,

Maesopsis eminii


E. Africa, India, Puerto Rico

Melaleuca quinquenervia + M. leucadendra

FSM, Guam, Hawaii


Melia azedarach

French Polynesia, Hawaii

Florida, Galapagos, S. Africa, E. Africa,

Muntingia calabura

Guam, Nauru, Northern Mariana Is.


Myrica faya



Ochroma pyramidale

(= O. lagopus)

French Polynesia

Galapagos Is.

Pangium edule



Paraserianthes (= Albizia) falcataria

Cook Is., French Polynesia, FSM, Hawaii, Guam, Palau

Seychelles, Singapore

Pithecellobium dulce

Hawaii, Fiji

Australia, Puerto Rico

Prosopis pallida + P. juliflora


Arabia, Ascension, Australia, Haiti, Mascarenes, Puerto Rico, S. Africa

Spathodea campanulata

French Polynesia, Hawaii

E. Africa, New Guinea, Singapore

Syncarpia glomulifera (= S. laurifolia)

French Polynesia, Hawaii


Syzygium cumini

French Polynesia, Hawaii

S. Africa

Tecoma stans

French Polynesia

Haiti, S. Africa

Toona ciliata (= Cedrela toona)


S. Africa

Triplaris americana

+ T. weigletiana

French Polynesia

S. Africa

Invasive plants threatening Pacific ecosystems: The Pacific Islands Ecosystems at Risk Project2

James C. Space
USDA Forest Service


The ever-accelerating rate of biotic invasion is a major element of human-induced global change. Exotic plant species, in particular, pose a well confirmed and increasing danger to ecosystem integrity, especially on islands. The purpose of this project is to provide information and assistance to the people of the Pacific islands to help them prevent the establishment of invasive plant species. Surveys have been conducted of the major US and US-associated Pacific islands (excluding Hawai'i) and the island of Niue. The results have been provided as individual reports as well as an easy-to-use database of known and potential invasive species of threat to the islands. Assistance has been provided in the development of warning posters and the evaluation of a problem species on the island of Pohnpei. Training in the identification and management of invasive species is being provided and a risk assessment system is being evaluated.


Island ecosystems, because of their isolation and evolutionary history, are particularly susceptible to invasion by introduced species. Some plant invasions on Pacific islands are having profound impacts. Miconia calvescens, a fast-growing tree native to tropical America, has virtually overwhelmed native ecosystems on the islands of Tahiti and Moorea in French Polynesia, and threatens to do the same in Hawaii. The introduction of alien grasses onto Pacific islands, including Hawaii, has changed fire regimes by increasing fuel loads and altering fire frequency, intensity, and size. This now threatens catastrophic change to forest and woodland communities, disruption of ecosystem processes, and extirpation of some endemic plants and animals. One of the world’s worst weeds, Imperata cylindrica, has been introduced onto the island of Yap, Federated States of Micronesia, and poses a real threat to its native ecosystems unless eradicated.

While these examples are illustrative, weed threats and impacts in most Pacific island ecosystems have been poorly documented and evaluated. The Pacific Islands Committee of the Council of Western State Foresters called for a “…comprehensive evaluation of the effects of introduced species in island ecosystems, especially impacts on endemic trees and forests.” This project is in response to that request.

Accomplishments to date

Island surveys

While some work had previously been done in surveying the Pacific islands for agricultural weeds (Whistler 1988; Swarbrick 1997; Waterhouse 1997), little had been done on invasive plant species of environmental concern. Obviously, it is important to find out the nature and extent of the present threat. Perhaps even more important, from the standpoint of prevention, is to discover what is not present. The following surveys have been conducted to date:

• In August 1998, Jim Space and Marjorie Falanruw of the Institute of Pacific Islands Forestry (IPIF) conducted a survey of 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. A report on the situation in these islands (Space and Falanruw 1999) was furnished to the island governments and others.

• In August 1999, Jim Space and Tim Flynn (Curator of the Herbarium, National Tropical Botanical Garden) conducted a survey of invasive plant species in American Samoa. The main island, Tutuila, and the outer islands of Ofu, Olosega and Ta’u were visited. A report was prepared (Space and Flynn 2000).

• Jim Space, Julie Denslow and Duane Nelson of IPIF and Barbara Waterhouse of the Australian Quarantine and Inspection Service conducted surveys of Kosrae and Chuuk (Federated States of Micronesia) and Rota (Commonwealth of the Northern Mariana Islands) in April 2000. Reports have been furnished to the respective governments (Space et al. 2000).

• At the request of the Government of Niue, Jim Space and Tim Flynn surveyed that island in May of 2000. A report has been furnished to the Government of Niue (Space and Flynn 2000).

These surveys and reports let the island governments and concerned individuals and organizations know what species are present or absent on the islands and make recommendations, where appropriate, for management actions.

Some invasive species of serious environmental concern include Adenanthera pavonina (many islands), Antigonon leptopus (Guam), Chromolaena odorata (most Micronesian islands), Cinnamomum verum (the island of Tutuila in American Samoa), Clerodendrum quadriloculare (Micronesia and American Samoa), Clidemia hirta (American Samoa), Coccinia grandis (Saipan), Dieffenbachia maculata (Tutuila), Funtumia elastica (Tutuila), Imperata cylindrica (Yap, Palau, Saipan) as well as other grasses, Lantana camara (most islands), Leucaena leucocephala (most islands), Merremia peltata (Tutuila; native in most of Micronesia but still a pest there), Merremia tuberosa (Niue), Mikania micrantha (most islands), Mimosa invisa (Tutuila, Guam, Yap, Palau—fast becoming pan-tropical), Paraserianthes falcataria (Pohnpei, other islands), Piper auritum (Pohnpei), Psidium cattleianum (Pohnpei and Palau), Schinus terebinthifolius (Guam), Scindapsus aureus (Niue), Stachytarpheta urticifolia (almost all islands), Stizolobium pruriens (Saipan), Syngonium podophyllum (Tutuila, Niue), Timonius timon (Peleliu), Tradescanthia spathacea (Niue), Tradescanthia zebrina (Niue), and Wedelia trilobata (most islands). However, every island seems to be different and species that may be a problem one place may not be a problem elsewhere.

The PIER database

Information from the above surveys, supplemented by a review of the literature, has been compiled into a database. It can be accessed from the Internet at and is now available on CD. The information includes (where available) the plant’s identity (scientific and common names as well as a botanical description and photographs sufficient to positively identify it), growth form, area of origin, known or likely methods of introduction and spread, other countries or regions in which the weed is a pest, community types affected or potentially affected by invasion; assessment of the risk of introduction and potential for spread once introduced, methods of control or eradication (if feasible) and further references. Information is being shared with other databases, such as the International Union for the Conservation of Nature’s worldwide invasive species database presently under development.

This compilation provides quarantine organizations with a frequently updated master list of plants that would be desirable to exclude was well as the means to identify them. It provides land managers information to work with quarantine organizations in the exclusion of plant pests, identify plants found in the field, and help and references on potential ecological impacts and control and eradication measures. There are presently 327 plant species in the database.

Impact assessment of Piper auritum

Piper auritum has been introduced to the island of Pohnpei, Federated States of Micronesia, perhaps with the idea that it could be a faster-growing alternative to P. methysticum, which is used for making sakau (kava). It is not suitable for that purpose, but is a known invasive species that could become a major problem. Julie Denslow and Duane Nelson of IPIF produced an impact assessment with management alternatives for the Pohnpei State government to aid in their decisionmaking (Denslow and Nelson 2000)

Pest leaflets and warning posters

In cooperation with The Nature Conservancy, a database of invasive species on Pohnpei was prepared and pest leaflets for the ten worst invasive species were published in the Pohnpeian language to assist in management and control of invasive plant species on that island. Model warning posters have been developed for island governments to use when they wish to target a particular invasive species.

Future plans

While the original objective of surveying the US and US-associated Pacific Islands is complete, surveys of other Pacific island countries can be conducted if requested and if funding is available.

Duane Nelson of IPIF is working with the Secretariat of the Pacific Community and local colleges and governments to conduct training in the identification and management of invasive plant species.

On-the-ground assistance in the evaluation and control of incipient and established populations can be provided on request.

Dr. Julie Denslow of IPIF is looking at options for the development of a risk rating system appropriate to plant species threatening Pacific ecosystems.


Collaborators and cooperators in the project include the Hawaiian Ecosystems at Risk Project (HEAR), the National Tropical Botanical Garden, The Nature Conservancy, the Australian Quarantine and Inspection Service, the Bernice P. Bishop Museum (Hawai'i), the University of Hawai'i Department of Botany, the Secretariat of the Pacific Community (formerly the South Pacific Commission), the New Zealand Department of Conservation, the South Pacific Regional Environmental Programme, the ICUN Invasive Species Specialist Group and the Food and Agriculture Organization of the UN.


The first phase of the Pacific Island Ecosystems at Risk project is rapidly coming to a close with the completion of surveys of the US and US-associated Pacific islands and the production and distribution of information via the PIER web site and CD. The next phase will be to provide training and technical assistance when and where needed. Development of a reliable mechanism for assessing the risk of exotic species to natural ecosystems is a high priority. Surveys of other Pacific islands or island groups will be considered if requested and will likely be met with a favourable response.

Literature cited

Denslow, Julie S. and Duane Nelson. 2000. Impact assessment of Pier auritum Kunth on Pohnpei, FSM. Pacific Islands Forests and Trees 2(00):6-8.

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. 32 pp.

Space, James C. and Tim Flynn. 2000. Observations on invasive plant species in American Samoa. Report. 50 pp.

Space, James C. and Tim Flynn. 2000. Report to the Government of Niue on invasive plant species of environmental concern. 34 pp.

Space, James C., Barbara Waterhouse, Julie S. Denslow and Duane Nelson. 2000. Invasive plant species on Rota, Commonwealth of the Northern Mariana Islands. 31 pp.

Space, James C., Barbara Waterhouse, Julie S. Denslow, Duane Nelson and Thomas R. Mazawa. 2000. Invasive plant species in Chuuk, Federated States of Micronesia. 41 pp.

Space, James C., Barbara Waterhouse, Julie S. Denslow, Duane Nelson Erick E. Waguk. 2000. Invasive plant species on Kosrae, Federated States of Micronesia. 43 pp.

Swarbrick, John T. 1997. Weeds of the Pacific Islands. Technical paper No. 209. South Pacific Commission, Noumea, New Caledonia. 124 p.

Waterhouse, D.F. 1997. The major invertebrate pests and weeds of agriculture and plantation forestry in the Southern and Western Pacific. The Australian Centre for International Agricultural Research, Canberra. 69 pp.

Whistler, W. A. 1988. Checklist of the weed flora of western Polynesia. Technical Paper No. 194, South Pacific Commission, Noumea, New Caledonia. 69 pp.

1 Prepared for presentation at the FAO Workshop on Forestry Data Collection for the Pacific Region, 4-8 September 2000, Apia, Samoa.

2 Prepared by James C. Space for presentation at the FAO Workshop on Data Collection for the Pacific Region, Apia, Samoa, 4-8 September 2000.

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