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Floristic composition and distributionof coastal vegetation in Chuuk island, Federated States of Micronesia
南太平洋海域調査研究報告
No.53（pattern
201３年２月）
OCCASIONAL PAPERS No.53（February 2013）

Floristic composition and distribution pattern of coastal vegetationin Chuuk island, Federated States of Micronesia
KAWANISHI Motohiro
Faculty of Education, Kagoshima University
Abstract
The distribution pattern of the coastal vegetation that is closely related to the plant
diversity of the islands was surveyed in Chuuk islands, Micronesia. In consequence of
TWINSPAN, which is the classification method of plant communities, six communities
were classified as 1) Mangrove, 2) Vigna marina - Bidens pilosa var. radiata community, 3)
Scaevola taccada - Heliotropium foertherianum community, 4) Thespesia populnea - Pandanus
community, 5) Hibiscus tiliaceus - Derris trifoliate community, 6) Enhalus acoroides (Seagrass) community. Mangrove forest was mainly established on a salty swamp locatedon the small river mouth or coastline. V. marina - B. pilosa var. radiata community, S.
taccada - H. foertherianum community, and T. populnea - Pandanus. community establishedon the sandy seashore. And, the H. tiliaceus - D. trifoliate community was observed
around the rocky coast. Vegetation patterns on an island differ among three islands.
Mangrove and H. tiliaceus - D. trifoliate community established in Weno and Romanumisland, but not in Piis. This pattern seems to be the effect of the geology of the island, i.e.,base-rock type may relate to habitat formation in the coastal area. On the other hand,
V. marina - B. pilosa var. radiata community that includes many invader plants wasestablished only around the town in Weno island. This community may depend on theindustrial human activity. To recognize the mechanisms of formation of vegetation on
islands, we need to clarify several environment factors related to geology, sociology,
and economy.
Keywords: coastal vegetation, invader species, mangrove, plant community, species
richness

Introduction
The coastal vegetation that is established in the boundary between the sea andland is one of the major elements of island landscape. In general, the growth of manykinds of plants is restricted in the coastal environment i.e. high salinity, poor soil,
wind damage and ground instability. Therefore, the species composition of the coastal
plant community often is very simple. On the other hand, the species compositionand structure of the coastal plant communities vary among the topographical or
geographical conditions. Therefore, the distribution pattern of the coastal vegetation
would be closely related to the plant diversity of the islands.
Muller-Dombois & Fosberg (1998) reported ten categories of vegetation in
Micronesia, 1: Mangrove vegetation, 2: Strand vegetation, 3: Vegetation on the coral

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KAWANISHI Motohiro

atolls and low coral islands, 4: Vegetation on raised coral or elevated limestone,
5: Vegetation on coastal plains, including swamp forests, 6: Lowland rain forests,
7: Montane rain forests and cloud forest, 8: Dwarf vegetation on open crests, 9:
Vegetation on open crests, 9: Vegetation of rough lava flows, 10:“Savanna,”or
grassland, vegetation.
The general vegetation of the Caroline Islands consists of natural broad-leaved
evergreen trees and planted trees (e.g. coconuts, breadfruits, and mango). Micronesian
Economic surveys in 1946 reported that the coconut (Cocos nucifera) and bread fruits(Artocarpus incisus) were planted broadly on coral islands and coastal strips of volcanicislands (Muller-Dombois & Fosberg 1998). In the Chuuk islands, the forests on the
gentle slope were mostly cut, and coconuts and bread-fruits were planted broadly inthe cultivated site (Kanehira 1933). Like above, there are some reports of vegetationin Micronesia. However, the vegetation pattern of small coral islands or small volcanicislands in one atoll has not been shown. I will compare the species composition of
the coastal plants in the Chuuk islands, and discuss the ecological character and thediversity of the coastal vegetation.
Study site
We surveyed a series of neighboring plant communities along a coastline in Chuukstates, Federated States of Micronesia. The study site was located in the three islands
in Chuuk atoll, i.e. Piis, Romanum and Weno (Fig.1).

Fig. 1 Map of Chuuk atoll and studied island, Weno, Romanum, and Piis.

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Floristic composition and distribution pattern of coastal vegetation in Chuuk island, Federated States of Micronesia

Weno is the capital and commercial center of Chuuk. This volcanic island has anarea of over 18 km2, and a high mountain (Mt. Tonoken, 370 m a.s.l) in the centerof the island. Coastal habitats on the west side of the island are mostly changed byindustrial activity, because relatively large towns are on the north-west side of theisland (Galbraith et al. 2000). In contrast, Piis is a very small and flat coral island on theatoll. The length of the island is about 1km. Romanum is also a small island of about 1.5
km in length. The terrace-like ground surface with sedimentary rock was observed on
the north-side of the island. On the other hand, the low-land at the south-side of islandis plain of coral sand with swamp.
Methods
In this study, the vegetation on the coast line was comprehended. The habitat
types on the coastline include sandy seashore, rocky coast, and salty swamp, and small
sea wall.
We obtained vegetational data (43 plot) using the phytosociological method (BraunBlanquet 1964), to recognize the species composition of the vascular plants in the
coastal vegetation of the island. The surveys were conducted in August 2011. The
plot area ranged from 20 m2 (2 × 10m) to 100 m2 (10 × 10m) because the study plot
be set to correspond to the width of the habitat. The location of the individual plot
was a typical point of the vegetation type. The community types were classified by
TWINSPAN (two-way indicator analysis) using a computer program PC-ORD ver.5(MjM software design).
To recognize the correspondence among the habitat types and the coastal
vegetation, ground conditions were surveyed at each plot during a vegetation survey.
Micro-landform, sediment (or base rock), and artificial structures were recorded byvisual observation in each quadrat.

Results and discussion
1. Plant community type
TWINSPAN classification (Fig. 2) showed strong divisions forming at the firstlevel (eigenvalues = 1.000), a group B with Enhalus acoroides as an indicator species
containing plots characterized by sea grass species, and another large group A include
the various community types.
At a second level of division (eigenvalues = 0.8069), the plots that have theindicator species Rhizophora mucronata and Sonneratia alba (A1) were separated fromthe others (A2) characterized by Vigna marina and Thespesia populnea. The formergroup was composed by the plot of Mangrove forest. On the other hand, the lattergroups include the various seashore vegetation.
At a third level of division (eigenvalues = 0.5869) the plots containing the indicatorspecies of Derris trifoliata (A22) were separated from the others.
At a fourth level of division (eigenvalues = 0.4809), the plots with the indicatorspecies Ipomoea pes-caprae and Leucaena leucocephala (A21-1) were separated fromthe other groups (A21-2) containing two groups derived from the final division,
characterized by Scaevola taccada (A21-21) and Thespesia populnea and Phymatosorus

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Fig. 2 T
 WINSPAN classification for 43 plots of coastal vegetation in Chuuk island.
Species name shown in dendrogram is indicator species of each divisionlevel.

scolopendria (A21-22).
In consequence of TWINSPAN as above mentioned, six communities wereclassified and are named as follows:
1) Mangrove (A1)
2) Vigna marina - Bidens pilosa var. radiata community (A21-1)
3) Scaevola taccada - Heliotropium foertherianum community (A21-21)
4) Thespesia populnea - Pandanus community (A21-22)
5) Hibiscus tiliaceus - Derris trifoliate community (A22)6) Enhalus acoroides (Sea grass) community (B)Floristic composition and occurrence of these communities are shown in Table 1 and 2,
respectively.
1) Mangrove
This community is mainly established on the salty swamp located on the small
river mouth or coastline of the large volcanic islands such as Weno and Romanum but
not in Piis island (Fig. 3, Table 2). This community mainly consists of Rhizophoraceae
trees (Rhizophora mucronata, Bruguiera gymnorhiza, Rhizophora apiculata), and Sonneratiaalba, Excoecaria agallocha (Species group A1, Table 1). Species diversity would be
relatively low because many species such as Avicennia marina, Xylocarpus granatum, andLumnitzera littorea that occur in well-developed Mangrove vegetation in Micronesia(Muller-Dombois & Fosberg 1998) were absent in the study site.
The canopy height of mangrove forest in the study area did not reach 10m high inevery site although mature forests reach the 30-40m high like in the Pohnpei Island(Cole et al. 1999). The mangrove forests on both islands seem affected by strong
human activity.

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Floristic composition and distribution pattern of coastal vegetation in Chuuk island, Federated States of Micronesia

Table 1 V egetation table of coastal vegetation in Weno, Romanum, and Piis island.
Six community types are derived from TWINSPAN (see Fig. 2). The value ofeach species are frequency of appearance and range of dominance-scalein parentheses.

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Table 2 E xistence pattern of costal vegetation in Weno, Romanum, and Piis island.
Community types are derived from TWINSPAN (see Fig. 2). Existence ofthe community type are shown as *.

A2 type communities (A21-1, A21-21, A21-22, and A22) distributed on theterrestrial habitat along the coastline and characterized by Cocos nucifera, Hernandia
nymphaeifolia, Phymatosorus scolopendria and so on. The community type of A21 (A21-1,
A21-21, A21-22) and A22 were characterized by species group A21 (e.g. Vigna marina,
Lepturus repens, Pemphis acidula), and the species group A22 (e.g. Barringtonia asiatica,

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Floristic composition and distribution pattern of coastal vegetation in Chuuk island, Federated States of Micronesia

Fig. 3 Mangrove forest (Romanum island).

Derris trifoliate, Hibiscus tiliaceus) respectively. The former communities established on
the sandy seashore of three islands. The latter was observed on the rocky coast of
Romanum and Weno Island.
2) Vigna marina - Bidens pilosa var. radiata community
This is occupied by a shrub (e.g. Leucaena leucocephala, Thespesia populnea) and vine
(Vigna marina, Ipomoea pes-caprae) and many herbaceous plants. This community ismainly established on the artificial coast on Weno island (Fig. 4), and includes many
invader species, such as Bidens pilosa var. radiate, Ipomoea littoralis, Panicum maximum,
Polygala paniculata, Senna occidentalis, Stachytarpheta jamaicensis, Vernonia cinerea,
Cenchrus echinatus (Space et al. 2000).

Fig. 4 Vigna
marina - Bidens pilosa var. radiata community (Weno island). Left:
Leucaena leucocephala and Ipomoea pes-caprae dominated type. Right:
Vigna marina and Panicum maximum dominated type.

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KAWANISHI Motohiro

3) Scaevola taccada - Heliotropium foertherianum community
This would be one of the natural vegetations on the sandy seashore in Chuuk (Fig.
5). Some shrub species such as Heliotropium foertherianum, Scaevola taccada, Terminalia
samoensis with vines; Canavalia cathartica, Vigna marina, Triumfetta procumbens distributeto the front side of the Cocos plantation. In addition, coastal herbs Chamaesyce atoto,
Thuarea involute, and Crinum sp. were observed in this community characteristically.

Fig. 5 Scaevola taccada - Heliotropium foertherianum community (Piis island).

4) Thespesia populnea - Pandanus community (A21-22)
This community was established on the similar habitat of Scaevola taccada Heliotropium foertherianum community (Fig. 6). Large trees such as Thespesia populnea,
Hernandia nymphaeifolia, Terminalia catappa, and Pandanus sp. dominated and form a
relatively higher canopy than the S. taccada - H. foertherianum community (Table 2).

Fig. 6 Thespesia populnea - Pandanus community (Romanum island).

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Floristic composition and distribution pattern of coastal vegetation in Chuuk island, Federated States of Micronesia

5) Hibiscus tiliaceus - Derris trifoliate community (A22)
Hibiscus tiliaceus, Barringtonia asiatica, Macaranga carolinensis, and many tree species
comprise this forest community. The richness of forest floor herbs (e.g. Nephrolepis,
Procris pedunculata) and epiphytic plants (e.g. Asplenium) are relatively high. This typewas observed on the rocky coast of Romanum and Weno island.
6) Enhalus acoroides (Sea grass) community (B)This consists of one or some kinds of sea-grass such as Enhalus acoroides. Thisgrass community was established in the shallow sea bottom (Fig. 7).

Fig. 7 Enhalus acoroides community: seagrass vegetation (Piis island).

2. Distribution pattern of coastal plant community
Although some endemic species of Chuuk, such as Maniltoa yokotai (Kaneh.) Hosok.,
Garcinia ponapensis var. trukensis (Kaneh.) Fosberg, Mischocarpus guillauminii Kaneh., andSemecarpus kraemeri Lauterb., have been known (Kanehira 1933), especially species inphytogeography, species like these did not occur in coastal vegetation. Many coastal
species observed in the study sites have a broad distribution area around the Pacific.
For example, Sonneratia alba and Rhizophora mucronata in Mangrove, and Scaevola
taccada, Hernandia sonora, Cassytha filiformis, Thespesia populnea, Hibiscus tiliaceus interrestrial coast vegetation reach to the Ryukyu Islands, Japan.
Vegetation pattern on the islands differs among these three islands. The mangroveand Hibiscus tiliaceus - Derris trifoliate community is established on Weno and Romanumislands, but not in Piis (Table 2). This pattern seems to be affected by the geologyof the island, i.e., the base-rock type may relate to soil the condition or habitat
formation in coastal areas. On the other hand, the Vigna marina - Bidens pilosa var.
radiata community was established only on Weno island. The floristic character of thiscommunity is high dominant and rich with invader plants (except for crop plants).
The establishment of this community may depend on human activity, because invader
plants invade the open site that has been created artificially. However, this community

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is absent in the coastal habitat on the village side of Piis and Romanum even thoughland-use seems strong and frequent. Therefore, the establishment of this community
may be affected by the activity style of the people (traditionally or industrially?). To
recognize the mechanisms of the formation of vegetation on an island, we need toclarify several environment factors related to geology, sociology, and economy.
References
BRAUN-BLANQUET, J. 1964. Pflanzensoziologie, 3 Aufl. Springer, Wien.
COLE T.G., EWELA K.C., DEVOEA N.N. (1999) Structure of mangrove trees and forests
in Micronesia. Forest Ecology and Management 117: 95-109.
G ALBRAITH K., B ENDURE G., F RIARY N. (2000) Micronesia 4 th ed. Lonely planet
publications, Australia.
KANEHIRA R. (1933) Flora Micronesica. Inoue-shoten, Tokyo.
MULLER-DOMBOIS D., FOSBERG F.R. (1998) Vegetation of the tropical pacific islands.
Springer-Verlag. New York.
SPACE J.C., WATERHOUSE B., DENSLOW J.S., NELSON D., MAZAWA T.R. (2000) Invasiveplant species in Chuuk, Federated States of Micronesia. USDA Forest Service,
Honolulu, Hawaii, USA, 41 pp.

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Floristic composition and distribution pattern of coastal vegetation in Chuuk island, Federated States of Micronesia＜要約＞
ミクロネシア，チューク諸島において，島の植生の分布パターンと多様性を明らかにすることを目的とし，ウエノ（Weno）島，ロマヌム島（Romanum），ピース島（Piis）
において海岸植生の調査を行った。海岸植生は，1)マングローブ，2)ハマアズキ（Vigna marina）－オオバナノセンダングサ（Bidens pilosa var. radiata）群落，3)クサトベラ（Scaevola taccada）－モンパノキ（Heliotropium foertherianum）群落，4)サキ
シマハマボウ（Thespesia populnea）－パンダヌス（Pandanus）群落，5)オオハマボウ（Hibiscus tiliaceus）－シイノキカズラ（Derris trifoliate）群落，6)ウミショウブ（Enhalus
acoroides）群落の6群落に区分された。マングローブは主に小河川の河口や海岸の塩生湿地に成立していた。一方，ハマアズキ－オオバナノセンダングサ群落，クサトベラ－
モンパノキ群落，サキシマハマボウ－パンダヌス群落は砂浜に，オオハマボウ－シイノ
キカズラ群落は主に岩石海岸に成立していた。ウミショウブ群落は浅い海底に成立していた。このような分布パターンは各島の地質，地形的要因と関連していると考えられた。
また，砂浜に成立している群落のうち，外来種を多く含むハマアズキ－オオバナノセン
ダングサ群落は，都市の発達したウエノ島のみで確認されたことから，人間活動も海岸
植生の種組成に大きく影響を及ぼしていることが予想された。島の植生の形成メカニズ
ムを理解するためには，地質・地形的要因および人間活動に関する要因が植生に及ぼす影響を明らかにする必要がある。

Chuukの海岸植生。ココヤシとともに様々な樹木，草本が海岸植生を形成している。
写真はRomanum島のサキシマハマボウ－パンダヌス群落