Rain forest vegetation of 'Eua Island, Kingdom of Tonga

New Zealand Journal of Botany, 1996, Vol. 34: 65-77 65
0028-825X/96/3401-065 $2.50/0 © The Royal Society of New Zealand 1996

Rain forest vegetation of 'Eua Island, Kingdom of Tonga

DONALD R. DRAKE ridges and shrub-dominated vegetation of cliffs and
Biology Department rocky shores, were sampled semi-quantitatively and
Georgia Southern University are also described.
Landrum Box 8042
Statesboro, GA 30460, USA Keywords 'Eua; Pacific Islands; rain forest;
Present address: School of Biological Sciences, Tonga; flora; vegetation
Victoria University of Wellington, P. O. Box
600, Wellington, New Zealand INTRODUCTION

W. ARTHUR WHISTLER The Kingdom of Tonga consists of two parallel
TIMOTHY J. MOTLEY chains of islands that run roughly north and south,
between 15-23° S latitude and 173-176° W longi-
Botany Department tude in the South Pacific Ocean (Fig. 1). The
University of Hawai'i sparsely-inhabited western chain consists of rela-
Honolulu, HI 96822, USA tively young, active, mainly andesitic volcanoes up
to 1030 m a.s.l. The densely-inhabited eastern chain
CLYDE T. IMADA consists of older, raised limestone islands up to
Botany Department 312 m a.s.l.
Bernice P. Bishop Museum
P.O.Box 19000-A To date, there have been few published descrip-
Honolulu, HI 96817, USA tions of the vegetation of Tonga. Uhe (1974) and
Sykes (1981) have described the vegetation of the
Abstract The indigenous vegetation of 'Eua Is- volcanic islands of Niuafo'ou and Late, respectively.
land, Tonga, is described and a species list presented. The coastal communities of several small islets in
Quantitative data were collected from 40 forest plots the Tongatapu (Stoddart 1975; Ellison 1990) and
in which all vascular plant species were recorded and Ha'apai (Woodroffe 1983) groups have been de-
the diameters of all stems > 5 cm dbh were meas- scribed. Palmer (1988) surveyed the least disturbed
ured. Plot classification, based on basal area data, relictual stand of inland forest on the limestone is-
identified six forest types, two coastal and four in- land of Tongatapu. Straatmans (1964) and Sykes
land, which reflect an elevational sequence from the (1978) have published brief, qualitative descriptions
coast to the island's summit (312 m a.s.l.). A polar of the vegetation of'Eua, which is Tonga's highest,
ordination, based on basal area data, arranged plots oldest, and least disturbed large, limestone island.
from the four inland forest types in a sequence from Whistler (1992) has reviewed the vegetation of Sa-
low to high elevation along one ordination axis, and moa and Tonga.
from more mature to less mature along a second axis.
Species richness increased with elevation. Several Although 'Eua has long been reputed to support
additional, non-forest vegetation types, including the richest, most unique forest in Tonga (Sykes
fern- and grass-dominated vegetation of inland 1978), no detailed, quantitative description of 'Eua's
forest vegetation has ever been published. The rapid
B95023 rate of forest clearing on 'Eua has recently begun to
Received 17 May 1995; accepted 27 October 1995 threaten its remaining stands of indigenous forest
(Allen 1990), increasing the need for such a descrip-
tion for scientific and conservation purposes. The
purpose of this study was to describe the composi-
tion and distribution of the indigenous vegetation of

66 New Zealand Journal of Botany, 1996, Vol. 34

Vava'u Group N 1). East of the ridge, a series of steep cliffs, inter-
Late ';"** rupted by narrow terraces, leads to the coast. Much
1 of the terraced relief is the result of periodic, geo-
logic uplifting of the island. Hoffmeister (1932)
Ha'apai Group 'Eua Island mapped five physiographic provinces on 'Eua: 1) the
eastern terraces and coastal region, 2) the eastern
• ,\ fit/ / I ridge, 3) the dissected, western slope of the eastern
ridge, 4) the western ridge and central valley, and
. •. • * fJ \\ 5) the western slope terraces and coastal region.

o 'A Although most of its surface is covered by lime-
Tolua ... .' stone, 'Eua is unique among Tonga's limestone is-
lands in that its core consists of volcanic rocks, and
« •. these form exposed outcrops along the eastern ridge
and eastern cliffs (Hoffmeister 1932; Bryan et al.
Tongatapu Group / 1972). Overlying the core, and forming additional
outcrops along the eastern ridge and its margins, is
^ 1 "Eua \ a layer of Eocene foraminiferal and algal limestones.
Overlying the Eocene limestones on the eastern ridge
3/ , 12 ml and its western slopes are Miocene submarine tuffs
and tuffaceous limestone. Late Tertiary coral reef
I \\ //f I i 4 (1 limestone comprises the bulk of the western ridge
(I j and central valley, and forms minor terraces along
both coasts. Quaternary andesitic tephra forms a
\ \ ^ \i 5 \ \J layer up to 2 m thick over most of the island, except
V. 4 in steep areas where it has been removed by erosion.
• 21°25- \ 2) i
Most soils are derived from the young andesitic
\s tephra with or without additional volcanic alluvium
from older tephras (Wilde & Hewitt 1983). Deeply-
\ {0 1 2 3 km weathered soils from the tuffs comprising the core
174P55-Vr are found where the core forms outcrops along the
eastern ridge. Volcanic and calcareous parent mate-
Fig. 1 Map of the major islands of Tonga and of the rials combine to form colluvial soils on steep slopes
five physiographic provinces on 'Eua (after Hoffmeister and at the bases of cliffs. Elsewhere, calcareous
1932) : 1) the eastern terraces and coastal region, 2) the materials are not involved in soil formation, except
eastern ridge, 3) the dissected, western slope of the east- as unconsolidated sand along the coasts. Develop-
ern ridge, 4) the western ridge and central valley, and ment of distinct soil horizons decreases, and
5) the western slope terraces and coastal region. evidence of continual soil development due to down-
slope movement increases, with increasing steepness
'Eua. A summary of the preliminary analysis of the of slope. The majority of'Eua's soils are alfisols and
data (Drake et al. 1990) was supplied to the Tongan mollisols, with inceptisols on the steep (> 30°) slopes
Government and was used as a basis for establish- and entisols (coralline sands) along some coasts
ing a national park on 'Eua in 1992. (Wilde & Hewitt 1983).

Climate

STUDY AREA 'Eua lies within the south-east tradewind zone, and
winds blow from the easterly quadrant 65-75% of
Geology and soils the time. Mean annual rainfall is approximately
'Eua is a high island, roughly 81 km2 in area, whose 2700 mm, of which roughly 2A falls during the wet
surface rises gradually from the west coast as a se- season of November to April (Thompson 1986).
ries of distinct terraces, to a high eastern ridge with There is little seasonal variation in temperature.
a maximum elevation of 312 m a.s.l. (Hoffmeister Sykes (1978) has remarked that the microclimate
1932; Bryan et al. 1972; Wilde & Hewitt 1983) (Fig. near the summit ridge appears cooler and moister
than that at lower elevations.

Drake et al.—Forest vegetation of 'Eua Island, Tonga 67

METHODS 3

Data collection 15

In June and July 1990, forest vegetation was sam- 30
pled in forty 600 m2 plots (mainly 20 x 30 m), each
located in a stand of forest representative of that 31 VI —»
found in the surrounding area. Stands that had obvi-
ously been disturbed by humans were avoided. For 2
each plot, the precise location (on topographic map
and aerial photo), elevation, aspect, slope, substrate 18
(bare sand, limestone, volcanic soil), and canopy 35
height were determined and all vascular plant spe-
cies were recorded. A species list is presented in 26
Appendix I. For all trees, diameters of all stems >
5 cm diameter at breast height (dbh) were measured. 6'
For individuals < 5 cm dbh, as well as shrubs, herbs, 23
epiphytes, and lianas, a Braun-Blanquet semi-
quantitative estimate of cover was made for each 24
species in each of several strata: shrub (c. 1 —3(—5)
m), ground cover (< 1.0 m), epiphyte, and liana 5
(Mueller-Dombois & Ellenberg 1974). Braun-
Blanquet, semi-quantitative cover estimates were 7
also made in seven 600 m2 plots in non-forest veg- 8
etation. Detailed notes on species distribution and
forest composition were also compiled for sites not 16
sampled quantitatively. Most of the plots were lo-
cated in the most extensive tracts of undisturbed 19 V —
forest along the eastern coast and terraces, the east-
ern ridge, and the steep ravines of the western slope 22
of the eastern ridge. A few additional plots were
located in smaller, disjunct stands of indigenous 28
vegetation scattered throughout the island.
29
33

37

38

40.

4
20

21 —
32 IV
9
13

14
17

12 III —
27

10
11

26 II •
34

39

25'~r •

Level 3 0 100 200300

Elevation (m)

Data analysis Fig. 2 Dendrogram derived from two-way indicator spe-
cies analysis (TWINSPAN) classification of 40 forest
Relative basal area data for the 86 tree species re- plots, using relative basal area of tree species. Roman
corded in the 40 plots that were sampled quantita- numerals represent the following vegetation types: I.
tively were analysed using two-way indicator species Excoecaria-Tournefortia coastal forest, II. Hernandia-
analysis (TWINSPAN, Hill 1979) to identify species Terminalia coastal forest, III. Maniltoa-Pleiogynium low-
associations. Relative basal area data for 35 inland land rain forest, IV. Myristica lowland rain forest, V.
forest plots were also analysed using a Bray-Curtis Calophyllum mixed upland rain forest, VI. Calophyllum-
polar ordination (ORDIFLEX, Gauch 1979) to iden- Garcinia upland rain forest. The elevational range over
tify gradients in species composition. The five which each type occurs is indicated at the right.
coastal forest plots on coralline sands and raised
limestone benches were excluded from the ordina- RESULTS
tion because their dissimilarity to the 35 inland plots
resulted in poor separation among the inland plots. TWINSPAN identified six ecologically interpretable
End points of the first axis were the two plots that groups of plots at the third level of classification,
were most dissimilar to each other; end points of the with the three largest groups being divided into three
second axis were the two remaining plots that were additional subtypes at the fourth level (Fig. 2). One
most dissimilar to each other and had first axis scores plot (no. 34), containing a large, outlying coastal tree,
between 40 and 60. was misclassified by TWINSPAN and, in the com-
munity descriptions below, is grouped based on its

68 New Zealand Journal of Botany, 1996, Vol. 34

position in the ordination. In general, TWINSPAN occurs in the canopy in places. The subcanopy is
ordered the plots into groups reflecting a topographic overwhelmingly dominated by Neisosperma
sequence from the coast to the summit ridge. Char- oppositifolium, which can occasionally exceed
acteristics of the six community types and their 50 cm dbh, plus lesser amounts of Cordia
variants are outlined below. In the following descrip- subcordata (only on the northwest coast), and
tions, species within a given stratum are listed in Grewia crenata. A lower stratum contains Pandanus
order of decreasing relative basal area (trees) or tectorius, Xylosma simulans, Cycas rumphii, and
Braun-Blanquet cover values (smaller species). For Vavaea amicorum. The only common terrestrial herb
the dominant species, mean relative basal area (rba) is the fern Phymatosorus grossus, and epiphytes are
and maximum dbh are given in parentheses (% rba, rare. Lianas are sparse, the most common ones be-
diam. cm). ing Epipremnum pinnatum, Hoya australis, Fara-
daya amicorum, and Jasminum didymum.

I. Excoecaria-Tournefortia coastal forest is found at III. Maniltoa-Pleiogynium lowland rain forest occurs
elevations < 5 m a.s.l. on raised limestone substrates only in the north-western quarter of the island along
that lack sand or soil. It exists in small, disjunct the western slope terraces and coastal region. This
patches that combine to form a narrow band along vegetation begins at the landward edge of the litto-
the coast, though they rarely extend more than 20 m ral forest, where sand or exposed limestone gives
inland. There is often no beach along the seaward way to volcanic soils overlying limestone, and con-
margin of these forest patches, and therefore expo- tinues inland up to elevations of 60 m, on slopes
sure to waves and salt spray, particularly during ranging from 11-20°.
storms, must be great. Species richness is low.

Excoecaria agallocha (48%, 69 cm) and Tourne- Here Myristica hypargyraea and Neisosperma

fortia argentea (syn. Argusia argentea) (40%, oppositifolium, the dominant species of lowland rain

75 cm) dominate the canopy. Both are multi- forests over the rest of the island (see below), are

stemmed trees that reach a height of 12 m. Hibiscus completely absent. Instead, the dominant species are

tiliaceus, another multi-stemmed tree, forms a some- Maniltoa grandiflora (49%, 56 cm) and Pleiogynium

what lower middle stratum, which often includes timoriense (17%, 56 cm). Other large trees (> 35 cm

Neisosperma oppositifolium, Schleinitzia insularum, dbh) include Sapindus vitiensis and Aleurites

and Morinda citrifolia. The shrub stratum contains moluccana. The subcanopy contains Chionanthus

scattered individuals of Bikkia tetrandra, Wollas- vitiensis, Xylosma simulans, Vavaea amicorum, and

tonia biflora, Clerodendrum inerme, and Scaevola Diospyros samoensis. A lower stratum contains

sericea, all of which are much more abundant in the Cryptocarya hornei, Cycas rumphii, Memecylon

strand vegetation (type VII) on the seaward margin vitiense, Micromelum minutum, Rhamnella vitiensis,

of this forest. Terrestrial herbs, epiphytes, and lianas and the shrub Graptophyllum insularum. The most

are rare. common terrestrial herb is Asplenium polyodon.

Lianas comprise 29% of the species in the flora and

II. Hernandia-Terminalia coastal forest is found at are abundant, especially Entada phaseoloides,
elevations < 5 m a.s.l. on sand substrates. Although Jasminum simplicifolium, Alyxia stellata, Jasminum
this forest is somewhat sheltered behind sand didymum, Gynochtodes epiphytica, and Malaisia
beaches and strand vegetation, it is presumably scandens.

strongly influenced by salt spray, and occasionally

by large storms such as cyclone 'Ofa, which had IV. Myristica lowland rain forest begins at the land-

obviously disturbed the understory of many littoral ward edge of the coastal forest, where sand or ex-

forest sites in January 1990. Species richness is posed limestone gives way to volcanic soils

greater than in the Excoecaria-Tournefortia coastal overlying limestone, and continues inland up to el-

forest. evations of 110 m, on slopes ranging from 0-33° or

The upper canopy is dominated by Hernandia more. It is found along the eastern slopes and ter-

nymphaeifolia (31%, 90 cm) and/or Terminalia races, western slope terraces, and coastal region,

catappa (25%, 122 cm). Other common, large (> everywhere except in the north-western quarter of

40 cm dbh) canopy trees include Terminalia the island.

litoralis, Guettarda speciosa, Planchonella grayana, Myristica hypargyraea (53%, 97 cm) is the over-

Schleinitzia insularum, Hibiscus tiliaceus, Myristica whelming dominant in this forest type, where no

hypargyraea, and Pisonia grandis; Cocos nucifera other species averages more than 13% rba. It is a

Drake et al.—Forest vegetation of 'Eua Island, Tonga 69

large tree, reaching a height of 25 m, and is usually Vavaea amicorum, Cryptocarya turbinata,

present in all size classes. Occasional large (> 40 cm Hedycarya dorstenioides, and Psychotria carnea,

dbh) individuals of Pleiogynium timoriense, and large amounts of the shrub Macropiper

Maniltoa grandiflora, Guettarda speciosa, puberulum. The herb layer is well-developed, and is

Canarium harveyi, Diospyros samoensis, dominated by the ferns Tectaria dissecta, Christella

Planchonella grayana, and Calophyllum neo- parasitica, Pteris comans, and Arachnoides aristata;

ebudicum are also scattered through this forest type. the ground orchid Corymborkis veratnfolia is also

The subcanopy contains Neisosperma oppositifolium common. Asplenium australasicum is occasionally

and Xylosma simulans. A lower stratum often in- present as an epiphyte. Lianas comprise 23% of the

cludes Diospyros samoensis, Hibiscus tiliaceus, flora and are extremely abundant, especially Entada

Citronella samoensis, Cycas rumphii, and the shrub phaseoloides, Alyxia bracteolosa, Embelia vaupelii,

Macropiper puberulum. Herbaceous species are Jasminum simplicifolium, Connarus sp. nov., Epi-

uncommon, with little cover. Asplenium austral- premnum pinnatum, Melodinus vitiensis, Jasminum

asicum is occasionally present as an epiphyte. Lianas didymum, and Gynochtodes epiphytica.

comprise 25% of the flora, the most abundant spe- In places, this forest type appears to be in a state
cies being Faradaya amicorum, Connarus sp. nov., of recovery from some past disturbance, and here the
Epipremnum pinnatum, Alyxia bracteolosa, Entada leading dominants are either Dendrocnide harveyi
phaseoloides, Jasminum simplicifolium, Gyno- (55%, 95 cm) with Bischofiajavanica (24%, 56 cm)
chtodes epiphytica, and Jasminum didymum. (plots 7 and 8), or Rhus taitensis alone (65%, 99 cm)

In places (plots 9, 14), this forest type appears to (plots 6, 23, and 24). Where present, these species

be in a state of recovery from some past disturbance; combine to form > 65% of the relative basal area,

here the leading dominant is Dendrocnide harveyi though they are absent from all smaller size classes,

(57%, 112 cm). Dendrocnide harveyi saplings do not which are instead dominated by the other tree spe-

occur in the understory beneath a closed canopy of cies common to the Calophyllum mixed forest.

mature trees. Myristica hypargyraea is codominant

in the upper stratum and abundant in the lower strata. VI. Calophyllum-Garcinia upland rain forest occurs

on volcanic soils overlying limestone, at elevations

V. Calophyllum mixed upland rain forest occurs on of 190-300 m, on slopes of 5 ^ 0 ° . It is found up-

volcanic soils overlying the limestone of the upper slope of the Calophyllum mixed forest and reaches

eastern terraces, the western slope of the eastern its greatest development mainly on the steep slopes

ridge, and upper portions of the ridge and ravine near the summit of the eastern ridge.

system of the central valley, at elevations of 100- Here, in contrast to the Calophyllum mixed for-

180(-240) m, on slopes of 2-45°. The tree strata are est below, the upper canopy is more strongly and

quite rich here, and no one species comprises, on consistently dominated by Calophyllum neo-

average, more than 12% of the relative basal area in ebudicum (27%, 76 cm), which is typically repre-

this forest. Of the 15 plots classified into this type, sented in all size classes. Other common large (>

eight different species were the leading dominant in 40 cm dbh) trees include Neonauclea forsteri,

at least one plot, and no one species was the leading Homalium whitmeeanum, Canarium harveyi, Podo-

dominant in more than three plots. carpus pallidus, Dysoxylum tongense, Elaeocarpus

The most consistently abundant large tree is Calo- graeffei, Hernandia moerenhoutiana, Myristica

phyllum neo-ebudicum (11%, 91 cm); it is present hypargyraea, and Rhus taitensis. The subcanopy is

in all plots, reaches a height of 35 m, and is typically almost completely dominated by Garcinia myrtifolia

represented in all size classes. Dysoxylum tongense (15%, 32 cm), which can occur at densities of more

(12%, 171 cm) is the most common co-dominant, than 50 trees per plot; it is consistently represented

and is present in 80 % of the plots. Other common in all size classes. The lower stratum contains

canopy species (> 50 cm dbh) are Elattostachys Vavaea amicorum and the shrubs Macropiper

falcata, Canarium harveyi, Myristica hypargyraea, puberulum, Ixora calcicola, Cordylinefruticosa, and

Alphitonia zizyphoides, Maniltoa grandiflora, Neo- Phaleria glabra. The herbaceous layer is well-de-

nauclea forsteri, Semecarpus vitiensis, Litsea veloped and the most common elements are the ferns

mellifera, and Dysoxylum forsteri. The subcanopy Arachnoides aristata, Pteris comans, Schizaea

contains large amounts of Diospyros samoensis, dichotoma, and Christella parasitica. Asplenium

Cryptocarya hornei, Garcinia myrtifolia, and australasicum and Robiquetia bertholdii are com-

Citronella samoensis. The lower stratum includes mon epiphytes. Lianas are extremely abundant,

70 New Zealand Journal of Botany, 1996, Vol. 34

especially Faradaya amicorum, Smilax vitiensis,
Alyxia bracteolosa, Jasminum simplicifolium,
Freycinetia urvilleana, Alyxia stellata, Hoya
australis, and Embelia vaupelii.

In places (plots 2, 18, 35) where this forest type
appears to be in a state of recovery from some past
disturbance, the leading dominants are Alphitonia
zizyphoides (33%, 76 cm) and Elattostachys falcata
(11 %, 48 cm). These are absent from the smaller size
classes, which are instead dominated by the other
tree species common to Calophyllum-Garcinia for-
est. Alphitonia zizyphoides is less common outside
disturbed upland forest, but E. falcata is often present
in low numbers throughout the upland rain forest.

Other types of vegetation, sampled semi-quantita-
tively, include:

VII. Strand vegetation: The species composition of

the strand vegetation, like that of the adjacent coastal

forest, is determined largely by the substrate. Sea- Fig. 3 Bray-Curtis polar ordination of 35 inland forest
ward of the Excoecaria-Tournefortia coastal forest, plots of 'Eua, using relative basal area of tree species.
and elsewhere on other bare, raised limestone Roman numerals represent the following vegetation types:
benches, the vegetation consists of a shrubby layer III. Maniltoa-Pleiogynium lowland rain forest, IV.

dominated by Bikkia tetrandra, Scaevola sericea, Myristica lowland rain forest, V. Calophyllum mixed up-

Clerodendrum inerme, and Wollastonia biflora, with land rain forest, VI. Calophyllum-Garcinia upland rain
a ground layer of succulent species such as Pemphis forest.

acidula, Sesuvium portulacastrum, and the parasitic

vine Cassythafiliformis. Seaward of the Hernandia- IX. Monospecific clonal stands: At lower and mid-
Terminalia coastal forest, on sand, trees include dle elevations, Hibiscus tiliaceus often forms exten-
scattered individuals of Cocos nucifera, Tournefortia sive (> 1000 m2), nearly monospecific stands that
argentea, Acacia simplex, and Sophora tomentosa. appear to have arisen through clonal growth. The
The most common shrubs are Scaevola sericea and stands are characterised by numerous stems grow-
Wollastonia biflora, and the ground layer contains ing in many planes and creating dense thickets. At
Ipomoea pes-caprae. On some sandy shores, the tree middle and high elevations, multi-stemmed, clonal
individuals of the banyan Ficus obliqua occasion-
Schleinitzia insularum forms small, monospecific ally cover areas in excess of 1000 m2, to the exclu-
stands.
sion of most other woody species. The upper

VIII. Cliff vegetation: The upper cliffs of the east- branches of the banyans support large numbers of
ern ridge are covered in many places by a smooth the fern Asplenium australasicum.

canopy of wind-swept vegetation, 3-5 m high. Com-
mon species include Diospyros elliptica, Citronella X. Toafa (treeless) vegetation: Toafa vegetation
samoensis, Maesa tongensis, Badusa corymbifera, occurs on deeply weathered soils on exposed, vol-
Maytenus vitiensis, and many others. At lower eleva- canic ridges. Although the exact composition of the
tions, where the eastern cliffs are very steep and toafa patches varies from place to place, the physi-
relatively exposed to salt spray, the vegetation is ognomy is very consistent. A mixture of grasses,
open-canopied and dominated by Pandanus pteridophytes, and scattered woody species forms an
tectorius, and, in the south-east, by Pritchardia upper stratum 0.5—1.5 m tall, beneath which numer-
pacifica. Where the cliffs are less steep, though still ous herbaceous and semi-woody species are found.
exposed to spray, there is a low forest of Hibiscus Common species include the grasses Miscanthus
tiliaceus, Myristica hypargyraea, Neisosperma floridulus and Paspalum conjugatum, the pterido-
oppositifolium, Pandanus tectorius, Terminalia phytes Dicranopteris linearis, Sphaerostephanos
catappa, Schleinitzia insularum, and Cycas rumphii. unitus, and Lycopodium cernuum, and the woody

Drake et al.—Forest vegetation of 'Eua Island, Tonga 71

<50 100-149 200-249 20

50-99 150-199 >249 10
0 50 100 150 200 250 300
Elevation (m) Elevation (m)

M. hypargyraea C. neo-ebudicum Fig. 5 Regression of species richness (number of vas-
cular plant species per 600 m2 plot) vs. plot elevation for
Fig. 4 Basal area of two dominant species of trees the 40 forest plots on 'Eua.
(Myristica hypargyraea and Calophyllum neo-ebudicum)
at various elevations. (Community types IV, V, and VI,
only; number of plots = 3, 3, 6, 10, 7, and 3, from left to
right).

DISCUSSION

'Eua supports a variety of plant communities; some

are relatively widespread throughout Western Poly-

species Wikstroemiafoetida, Alphitonia zizyphoides, nesia, while others may be found nowhere else in the

Psidium guajava, and Melastoma denticulatum. The Pacific.
mean number of species in five 600 m2 plots was In general, 'Eua's coastal vegetation is similar to

26.4. that found in strand habitats throughout the tropical

South Pacific. Species such as Hernandia nymphaei-

Trends folia, Terminalia spp., Tournefortia argentea, and

Results of the ordination corresponded well with the Scaevola sericea are common coastal dominants
TWINSPAN analysis. Three of the major inland elsewhere in Tonga (Stoddart 1975; Woodroffe
communities were spread, with little overlap, along 1983; Ellison 1990), as well as in Nauru and Kiribati
the first axis (Fig. 3). An exception was one inland (Thaman 1992), Tuvalu (Woodroffe 1986, 1991),
community (Maniltoa-Pleiogynium lowland forest), Wallis, Futuna, and Alofi (Morat & Veillon 1985),
which appeared at the center of the ordination, be- Fiji (Garnock-Jones 1978; Kirkpatrick & Hassall
cause it lacked the dominant species of the plots that 1981; Ash 1992), Samoa (Whistler 1980, 1983),
formed the end points. Tokelau (Parham 1971), and the Cook Islands (Mer-
lin 1991; Franklin & Merlin 1992). In contrast,
The first axis score was positively correlated with Excoecaria agallocha appears to be of limited im-
elevation (first axis ordination score = 0.24 x plot portance outside Tonga.
elevation (m) + 15.3, n = 35, r2 = 0.52, P < 0.001).

This trend is further illustrated by the shift in domi- Similarly, the treeless, toafa vegetation dominated

nance from Myristica hypargyraea to Calophyllum by ferns (e.g., Dicranopteris linearis) and grasses

neo-ebudicum with increasing elevation in commu- (e.g., Miscanthus floridulus) frequently noted on

nities IV, V, and VI (Fig. 4). Species richness in the 'Eua(Straatmans 1964; Sykes 1978; Whistler 1992)

forest plots increased with increasing elevation (n = is also common on poor, volcanic soils elsewhere in
40, r2 = 0.38, P < 0.001; Fig. 5), with plots near the the South Pacific. It occurs in Vanuatu (Schmid

summit of the eastern ridge having approximately 1975), Wallis, Futuna, and Alofi (Morat & Veillon

twice as many species as occurred in plots near sea 1985), Fiji (Garnock-Jones 1978; Ash 1992), Samoa

level. The second ordination axis appeared to cor- (Whistler 1980), the Cook Islands (Sykes 1978;

respond to degree of disturbance, with vegetation Merlin 1985,1991), and the Society Islands (Fosberg

subtypes judged to be recovering from some past 1992).

disturbance occurring high on the second axis, and 'Eua's secondary forests share many pioneer spe-

older stands occurring lower (Fig. 3). cies with disturbed forests of other islands. For ex-

72 New Zealand Journal of Botany, 1996, Vol. 34

ample, Alphitonia zizyphoides, Rhus taitensis, and similarity to that of nearby volcanic or low coral is-

Elattostachys falcata are among the dominants on lands. Thus, 'Eua's forests differ from those of the

the relatively young volcanic island of Late, and the volcanic islands in Tonga, such as Late. Sykes

latter two are dominant in the last relictual stand of (1981) noted Casuarina equisetifolia, Alphitonia

inland forest on the limestone island of Tongatapu zizyphoides, Elattostachys falcata, and Rhus taitensis

(Palmer 1988). Straatmanns (1964) first described as dominant and Calophyllum neo-ebudicum as com-

the dynamic relationship among 'Eua's canopy trees. mon on Late; in contrast, Myristica hypargyraea,

He noted that seedlings of A. zizyphoides, R. taiten- Maniltoa grandiflora, Dysoxylum spp., and Garcinia

sis, and E. falcata did not grow in dense forest, myrtifolia were absent.

whereas seedlings of Calophyllum neo-ebudicum Even among raised limestone islands, 'Eua is
and Myristica hypargyraea did. In addition, A. zizy-
phoides, R. taitensis, and E. falcata, together with relatively unique in its combination of great eleva-
Dendrocnide harveyi and Bischofia javanica, are tion (312 m a.s.l.), large surface area (81 km2), age
important components of secondary forests in (Eocene), sharp relief, deep andesitic soils, and vol-
canic core. Only 'Uta Vava'u in northern Tonga has
Vanuatu (Schmid 1975), Wallis, Futuna, and Alofi the proper combination of biogeographic position,
(Morat & Veillon 1985), and Samoa (Whistler size (95 km2), elevation (210 m), and andesitic soils
1980).
over limestone (Orbell et al. 1985) to potentially

In contrast to the secondary forests, 'Eua's old- support rain forest vegetation similar to 'Eua's.

growth inland rain forests bear little similarity to However, 'Uta Vava'u's vegetation is quite distinct

those of other regional islands. Several factors may because many of the dominant species of 'Eua's

account for the uniqueness of 'Eua's rain forests. forests are rare or absent there (J. Franklin & D.

Because the number of plant taxa in the Pacific gen- Drake unpubl. data). Given the uniqueness of'Eua's

erally decreases with increasing distance from rain forest vegetation, the Tongan Government de-

Malesian source areas (van Balgooy 1971; Fosberg serves praise for the foresight they have demon-

1984; Stoddart 1992), nearly every island or small strated through their ongoing efforts to protect a large

archipelago has a somewhat unique flora and, there- tract of it in a national park.

fore, vegetation. Large islands north and west of

Tonga contain many of the dominant species of

'Eua's mature rain forest, however, these species are

not dominant in these richer forests. For example, ACKNOWLEDGMENTS
Samoa's Syzygium lowland forest is dominated by
Syzygium inophylloides (uncommon on 'Eua), but This study was funded by a grant from the Pacific Islands
also contains substantial amounts of two Tongan Development Program and the Program on the Environ-
dominants, Myristica hypargyraea and Calophyllum ment of the East-West Center in Honolulu, Hawaii. The
neo-ebudicum (Whistler 1992). In upland forests on Tongan Government, including the Ministry of Agricul-
Mt. Korobaba, Fiji, Calophyllum neo-ebudicum and ture, Forestry, and Fisheries and the Ministry of Lands
and Surveys facilitated our efforts throughout the project.

Garcinia myrtifolia are common, but not dominant M. Pomelile, M. Thomas, M. Sau, and K. Siakumi pro-
(Kirkpatrick & Hassall 1985). Islands east of Tonga, vided valuable assistance in the field. The manuscript
such as the Cook Islands, simply lack many of the benefitted greatly from the critical comments of J. Ash,
Tongan dominants (Merlin 1985, 1991; Franklin & J. Franklin, F. Kell, A. McGee, and an anonymous re-
Merlin 1992). Stoddart (1992) states that "there is viewer.

no more dramatic biogeographic boundary in the

Pacific than that between the southern Cooks and the

southern Tongan islands." This discontinuity is at

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APPENDIX I Hymenophyllaceae
Trichomanes humile, I
List of vascular plants recorded in the Trichomanes saxifragoides, I
Lindsaeaceae
vegetation samples Sphenomeris chinensis, I
Lycopodiaceae
Since there is no recent treatment of the spermatophyte Lycopodium cernuum, hiku 'i pusi, I
flora of Tonga, nomenclature follows several sources. Marattiaceae
Smith (1979, 1981, 1985, 1988, 1991) treats nearly all of Angiopteris evecta, hulufe vai, I
the spermatophyte species. For species not treated by Polypodiaceae
Smith, the most recent treatment from among Yuncker Drynaria rigidula, I
(1959), Wagner et al. (1990), or Whistler (1991) is Phymatosorus grossus, I
followed. Nomenclature for pteridophytes follows Sykes Pyrrosia adnascens, I
(1978). Tongan names are from Yuncker (1959), Sykes Psilotaceae
(1978), Whistler (1991), and the present study. Voucher Psilotum nudum, I
specimens are deposited in the personal collection of A. Schizaeaceae
Whistler at the University of Hawai'i (UHAW). Schizaea dichotoma, masalu ngaue, I
Key: E = endemic, I = indigenous, P = Polynesian Thelypteridaceae
introduction, A = post-European introduction. Christella parasitica, I
Sphaerostephanos decadens, I
PTERIDOPHYTES Sphaerostephanos invisus, I
Adiantaceae Sphaerostephanos unitus, I
Pteris comans, I Vittariaceae
Pteris ensiformis, I Antrophyum plantagineum, I
Pteris tripartita, I
Aspidiaceae GYMNOSPERMS
Arachnoides aristata, hulufe leisi, I Cycadaceae
Tectaria dissecta, I Cycas rumphii, longolongo, I
Tectaria latifolia, I Podocarpaceae
Aspleniaceae Podocarpus palliduSy uhiuhi, E
Asplenium australasicum, hakato, I
Asplenium marattioides, I DICOTYLEDONS
Asplenium polyodon, I Acanthaceae
Loxoscaphe gibberosum, hulufe leisi, I Graptophyllum insularum, I
Athyriaceae Aizoaceae
Diplazium harpeodes, I Sesuvium portulacastrum, I
Blechnaceae Amaranthaceae
Blechnum orientale, I Achyranthes aspera, tamatama, I or P
Cyatheaceae Deeringia amaranthoides, I
Sphaeropteris lunulata, ponga, I Anacardiaceae
Davalliaceae Pleiogynium timoriense, tangato, I
Davallia solida, kulutuma, I Rhus taitensis, tavahi, I
Nephrolepis hirsutula, hulufe, I Semecarpus vitiensis, olahi, I
Dennstaedtiaceae Apiaceae
Microlepia speluncae, I Centella asiatica, tono, A
Gleicheniaceae
Dicranopteris linearis, kahiva'e, I

Drake et al.—Forest vegetation of 'Eua Island, Tonga 75

Apocynaceae Stictocardia tiliifolia, A
Alyxia bracteolosa, kulu, I Dichapetalaceae
Alyxia stellata, maile, I Dichapetalum vitiense, kili, I
Cerbera odollam, toto, I Ebenaceae
Ervatamia obtusiuscula, te'ete'emanu, I Diospyros elliptica, kanume, I
Melodinus vitiensis, tuamea, I Diospyros major, mapa, I
Neisosperma oppositifolium, fao, I Diospyros samoensis, tutuna, kokau 'uli, I
Araliaceae Elaeocarpaceae
Meryta macrophylla, kulukulu, 1 Elaeocarpus graeffei, ma'ama'alava, I
Polyscias multijuga, tanetane vao, I Elaeocarpus sp. nov., E
Asclepiadaceae Elaeocarpus tonganus, ma'ama'alava, I
Hoya austra/is, laumatolu, I Euphorbiaceae
Hoya pottsii, I Aleurites moluccana, tuitui, P
Tylophora samoensis, I Bischofia javanica, koka, I
Asteraceae Chamaesyce atoto, I
Ageratum conyzoides, A Chamaesyce hirta, A
Bidenspilosa, fisi 'uli, A Croton microtiglium, I
Conyza bonariensis, A Drypetes vitiensis, I
Elephantopus mollis, A Excoecaria agallocha, feta'anu, I
Emilia sonchifolia, A Glochidion ramiflorum, malolo, I
Sonchus oleraceus, A Macaranga harveyana, loupata, I
Synedrella nodiflora, pakaka, A Omalanthus nutans, fonua mamala, I
Vernonia cinerea, fisi puna, A Phyllanthus amicorum, E
Wollastonia biflora, ate, I Flacourtiaceae
Barringtoniaceae Homalium whitmeeanum, I
Barringtonia asiatica, futu, I Xylosma simulans, filimoto, I
Boraginaceae Gesneriaceae
Tournefortia argentea, touhuni, I Cyrtandra samoensis, I
Cordia aspera, tou, I Goodeniaceae
Cordia subcordata, pua taukanave, I Scaevola sericea, ngahu, I
Burseraceae Hernandiaceae
Canarium harveyi, 'ai, I Hernandia moerenhoutiana, pipi tui, I
Caesalpiniaceae Hernandia nymphaeifolia, fotulona, I
Maniltoa grandiflora, tautau 'a manu, pekepeka, I Hippocrataceae
Campanulaceae Saiacia pachycarpa, I
Wahlenbergia marginata, I Icacinaceae
Caricaceae Citronella samoensis, olavai, I
Carica papaya, lesi, A Lauraceae
Cassythaceae Cryptocarya hornei, motou, I
Cassytha filiformis, fatai, I Cryptocarya turbinata, kakala 'uli, motou, I
Casuarinaceae Litsea mellifera, mamea, I
Casuarina equisetifolia, toa, I Loganiaceae
Celastraceae Fagraea berteroana, pua, I
Maytenus vitiensis, I Geniostoma rupestre, te'epilo 'a maui, I
Clusiaceae Loranthaceae
Calophyllwn inophyllum, feta'u, I Decaisnina forsteriana, topu'uno, kainikavea, I
Calophyllum neo-ebudicum, tamanu, I Lythraceae
Garcinia myrtifolia, feto'umaka, I Pemphis acidula, ngingie, I
Combretaceae Malvaceae
Lumnitzera littorea, I Abelmoschus moschatus, P
Terminalia catappa, telie, I Hibiscus tiliaceus, fau, I
Terminalia litoralis, telie 'a manu, I Sida rhombifolia, te'ehoosi, P
Connaraceae Thespesia populnea, milo, I
Connarus sp. nov., vavatu, E Meliaceae
Rourea minor, va'a 'uli, I Aglaia heterotricha, langakali vao, E
Convolvulaceae Dysoxylumforsteri, mo'ota hina, I
Ipomoea indica, fue 'ae puaka, I Dysoxylum tongense, mo'ota mea, mo'ota kula, E
Ipomoea macrantha, fue hina, I Vavaea amicorum, ahi vao, I
Ipomoea pes-caprae, fue kula, I Melastomataceae
Merremia peltata, fue mea, I Melastoma denticulatum, I
Operculina ventricosa, fue hina, A Memecylon vitiense, malamala 'a toa, I

76 New Zealand Journal of Botany, 1996, Vol. 34

Menispermaceae Pittosporum arborescens, masi kona, I
Pachygone vitiensis, I Pittosporum yunckeri, E
Mimosaceae Rhamnaceae
Acacia simplex, tatangia, I Alphitonia zizyphoides, toi, I
Adenanthera pavonina, A Colubrina asiatica, fiho'a, I
Entada phaseoloides, sipi, I Rhamnella vitiensis, I
Mimosa pudica, mateloi, A Rosaceae
Schleinitzia insularum, feifai, I Osteomeles anthyllidifolia, I
Monimiaceae Rubiaceae
Hedycarya dorstenioides, I Antirhea inconspicua, I
Moraceae Bikkia tetrandra, siale tafa, I
Ficus obliqua, 'ovava, I Cyclophyllum barbatum, I
Ficusprolixa, 'ovava, I Geophila repens, tono, I
Ficus scahra, masi 'ata, I Guettarda speciosa, puopua, I
Ficus tinctoria, masi 'ata, I Gynochtodes epiphytica, I
Malaisia scandens, hiehieapo, I Hedyotis foetida, I
Streblus anthropophagorum, I Ixora calcicola, ola, I
Myristicaceae Morinda citrifolia, nonu, I
Myristica hypargyraea, kotone, I Morinda myrtifolia, mamange, I
Myrsinaceae Mussaenda raiateensis, monomono 'a hina, 1
Discocalyx listeri, E Neonauclea forsteri, afa, I
Embelia vaupelii, I Psychotria carnea, I
Maesa tongensis, I Psychotria leiophylla, I
Myrtaceae Psydrax odorata, olamaka, I
Decaspermum fruticosum, nukonuka, I Spermacoce assurgens, 'aselemo, A
Psidium guajava, kuava, A Tarenna sambucina, manonu, I
Syzygium hrackenridgei, fekika vao, I Rutaceae
Syzygium dealatum, fekika vao, I Melicope retusa, I
Syzygium quadrangulatum, 1 Micromelum minutum, takafalu, I
Syzygium richii, heavula, I Santalaceae
Nyctaginaceae Santalum yasi, ahi, I
Pisonia grandis, puko, 1 Sapindaceae
Pisonia umbellifera, I Elattostachys falcata, ngatata, ngatata kula, I
Olacaceae Guioa lentiscifolia, E
Anacolosa lutea, I Harpullia arborea, filiamaama, I
Oleaceae Sapindus vitiensis, ngatata hina, I
Chionanthus vitiensis, 'afa, I Sapotaceae
Jasminum didymum, tutu 'uli, I Burckella richii, kau, I
Jasminum simplicifolium, tutu 'uli, I Planchonella garberi, kalaka, I
Onagraceae Planchonella grayana, kalaka, I
Ludwigia octovalvis, A Solanaceae
Oxalidaceae Capsicum frutescens, polo, polo fifisi, A
Oxalis corniculata, kihikihi, P Solanum amicorum, I
Papilionaceae Solanum mauritianum, pula, A
Canavalia cathartica, I Surianaceae
Canavalia sericea, fue veli, I Suriana maritima, ngingie, I
Desmodium triflorum, A Thymelaeaceae
Inocarpusfagifer, ifi, I or P Phaleria glabra, I
Mucuna gigantea, valai, I Wikstroemia foetida, lala vao, I
Pueraria lobata, aka, A Tiliaceae
Sophora tomentosa, lata, I Grewia crenata, fo'ui, I
Strongylodon sp. nov., matafu'i, I Triumfetta procumbens, I
Vigna marina, lautolu tahi, I Ulmaceae
Passifloraceae Celtis harperi, I
Passiflora maliformis, vaine tonga, A Trema cannabina, mangele, I
Passiflora subpeltata, A Urticaceae
Peperomiaceae Dendrocnide harveyi, salato, I
Peperomia tutuilana, I Pipturus argenteus, 'olonga, 1
Piperaceae Procris pedunculata, I
Macropiperpuberulum, kavakava'ulie, I Verbenaceae
Pittosporaceae Clerodendrum inerme, tutu hina, tutu tahi, I

Drake et al.—Forest vegetation of 'Eua Island, Tonga 77

Faradaya amicorum, fufula, I Liparis disepala, I
Lantana camara, talatala, A Malaxis latisegmenta, I
Premna serratifolia, volovalo, I Malaxis resupinata, I
Stachytarpheta urticifolia, hiku 'i kuma, A Phaius tankarvilleae, I
Violaceae Robiquetia bertholdii, I
Melicytus samoensis, I Spathoglottisplicata, lave'i moa, I
faeniophyllum fasciola, I
MONOCOTYLEDONS Pandanaceae
Agavaceae Freycinetia urvilleana, I
Cordyline fruticosa, I or P Pandanus tectorius, I
Furcraeafoetida, faumalila, A Poaceae
Araceae Botriochloa bladhii, A
Amorphophallus paeoniifolius, teve, P Chrysopogon aciculatus, matapekepeka, P
Epipremnum pinnatum, Alu, I Cyrtococcum oxyphyllum, P
Arecaceae Digitaria ciliaris, A
Cocos nucifera, niu, I Imperata conferta, I
Pritchardia pacijica, piu, I Ischaemum murinum, I
Commelinaceae Lepturus repens, I
Rhoeo spathacea, faina kula, A Miscanthus floridulus, kaho tonga, I
Cyperaceae Oplismenus compositus, mohuku laukofe, P
Fimbristylis cymosa, I Panicum decomposition, A
Fimbristylis ovata, I Paspalum conjugatum, vailima, A
Mariscus sumatrensis, A Paspalum vaginatum, A
Scleria polycarpa, mahelele, I Stenotaphrum micranthum, I
Dioscoreaceae Thuarea involuta, kefukefu, I
Dioscorea bulbifera, hoi, I Smilacaceae
Liliaceae Smilax vitiensis, matafu'i, I
Dianella aff. intermedia, lave'imoa, I Taccaceae
Orchidaceae Tacca leontopetaloides, mahoa'a, P
Corymborkis veratrifolia, I Zingiberaceae
Goodyera rubicunda, I Zingiber zerumbet, angoango, P
Hetaeria whitmeei, I