R esearch n ote virtual gallery of the vegetation and flora of the Seychellles

Yüklə 106.23 Kb.
PDF просмотр
ölçüsü106.23 Kb.

K. F







Bulletin of the Geobotanical Institute ETH69, 







Virtual gallery of the vegetation and flora of the Seychellles





*, P




, C









 & P


 J. E


Geobotanical Institute, ETH Zürich, Zürichbergstrase 38, CH-8044 Zürich, Switzerland;

* corresponding author: fleischmann@geobot.umnw.ethz.ch


The Seychelles archipelago consists of about

a hundred granite and coralline islands near

the equator in the Western Indian Ocean

(Fleischmann et al. 1996). These islands prob-

ably split from Gondwana some 65 million

years ago and have been isolated from conti-

nents ever since. The Seychelles flora there-



  The Seychelles archipelago has been identified as a biodiversity hotspot by interna-

tional conservation agencies. One of the major threats to the Seychelles native species

and forests is the rampant spread of a large number of invasive alien plant species. As a

basis and reference for conservation measures, the native flora and some vegetation

types of granite islands of the Seychelles are briefly described and illustrated with photo-



  The original flora of the granite islands was rather poor with approximately 250 spe-

cies of indigenous flowering plants of which about 34% (84 taxa) are supposed to be or

to have been endemic to the Seychelles. About 80 fern species grow on the islands,

several of which are considered endemic.


  The main natural vegetation types are: coastal plateau, lowland and coastal forests,

mangrove forest, riverine forest, intermediate forest, mountain mist forest, glacis type

vegetation (inselbergs)


  A collection of photographs of plant species and vegetation types from the Seychelles

(‘virtual gallery’ can be viewed or downloaded at www.geobot.umnw.ethz.ch/publica-



 conservation, endemism, island flora, plant invasion, Seychelles, vegetation



 Friedmann (1994).

Bulletin of the Geobotanical Institute ETH

 (2003), 69, 57–64

fore had an extremely long time to develop

independently from that of the rest of the

world, mainly through natural evolutionary

processes, leading to a high level of ende-

mism. The unique status of the granite islands

of the Seychelles as oceanic islands of conti-

nental origin, and the phytogeographical im-






















Bulletin of the Geobotanical Institute ETH, 69, 


portance of the islands as combining African,

Madagascan and Indo-Malaysian elements in

their flora make it a region of great floristic

interest. The fact that at the time of the first

human settlement on Mahé in the 1770’s the

flora had evolved continuously and without

human interaction for many millions of years,

certainly adds to the outstanding status of the

Seychelles’ island vegetation. In fact the Sey-

chelles have been identified as a biodiversity

hotspot by Conservation International and as

a centre of plant diversity by the WWF and


One of the major threats to the native spe-

cies and forests of the Seychelles is the ram-

pant spread of a number of alien plant spe-

cies across the islands (Fleischmann 1997);

the most invasive ones are Cinnamomum

verum, Psidium cattleianum, Clidemia hirta,

Merremia peltata

  and  Paraserianthes falca-


  These plants displace the distinctive

native flora of the Seychelles, resulting in the

loss of diverse native forests. The situation in

the Seychelles is particularly serious because

there are several rare, endemic species like

Medusagyne oppositifolia, Secamone schimpe-

riana, Vateriopsis seychellarum

 etc. which are

fated to extinction following the invasion of a

great variety of introduced organisms. It is

generally accepted that invasive alien species

may have a competitive or reproductive ad-

vantage over native species (Parendes 2000).

Besides this, the introduction of certain plant

species may promote further change be-

cause they affect ecosystem processes. Inva-

sive species can influence nitrogen availabil-

ity by changing litter quantity and quality,

rates of N


-fixation, or rates of nitrogen loss

(Evans et al. 2001; Anderegg & Wiederkehr

2001). A variety of biological attributes of

plants serve to make them invasive, but in

the Seychelles three are of primary impor-


• Propagules dispersed by animals. Animal-

dispersed seeds are typically fleshy berries,

relatively small in size, and variously colo-

red. The dispersers of greatest importance

in the Seychelles are fruit-eating birds and

bats. Prominent amongst introduced spe-

cies with bird-dispersed fruits are Cinnamo-

mum verum, Psidium cattleianum

 and Clide-

mia hirta.

 Species using animals or wind as

dispersal mechanisms (i.e. Paraserianthes f.)

are capable of quickly invading native eco-

systems in areas remote from where the

adults themselves are planted. As for Cin-


  v.  and  Psidium  c.  an additional

attribute making these plants even worse is

that they can reproduce vegetatively as well

as by seeds.

• High fecundity. Species that produce many

seeds per plant each year can invade new

habitat patches more rapidly than can most

native plants that produce relatively few

seeds (Peters 2001). For example, Cinna-

momum v.

 and Clidemia h. (the latter is now

the subject of a control effort by state and

private organizations) produce large num-

bers of seeds, so that their populations can

increase very rapidly, which partially ac-

counts for the great threat they pose to the

Seychelles’ forests.

• Fast growth: Fast-growing plants that

quickly reach maturity will be more inva-

sive and harder to control than slower-

growing plants. An outstanding example

of the importance of this phenomenon is

Clidemia h.

 which was first seen on Mahé

island in 1993 (Gerlach 1993). Since then

single plants have been found all over the

island. By competing with native species

in gaps, Clidemia h.  invasion has the po-

tential to alter forest regeneration (Peters


In order to prevent fundamental changes to

the indigenous and endemic vegetation of the

K. F







Bulletin of the Geobotanical Institute ETH, 69, 



Seychelles an ongoing commitment to con-

trolling invasive alien species is required. This

commitment is based on scientific research

which provides a wider perspective on the

problem of invasion by alien species, and a

rational basis for habitat management (i.e. the

control of this invasion). It has become obvi-

ous that the protection of land in itself will not

be sufficient to save the habitats. Since most

areas of the Seychelles are heavily infested

with alien plants, the crucial question is: what

can be done to save the remaining, intact na-

tive forests? To address this question, several

research projects in the field of conservation

and invasion biology have been conducted

through the Geobotanical Institute in Zürich

over the last eleven years.

Despite the wide scale destruction of the

original island vegetation, there are sites

where at least some of the original elements of

the natural flora have been preserved. On

Mahé and Silhouette there are still substantial

areas of humid high-altitude forests and

inselbergs containing a rich endemic flora.

Luckily, relatively few of the endemic plant

species are so far known to have become ex-

tinct on all islands (Carlstroem 1996). How-

ever, the fact that populations of many en-

demic and threatened species are extremely

small is a serious concern. For many of these

species, especially those of the ancient forests

at intermediate altitude, the situation is critical

since their natural habitats no longer exist.

These species (e.g. Medusagyne oppositifolia )

will never survive without human interfer-

ence. It is most likely that the displacement of

the native flora through competition with in-

vasive exotic taxa will reduce biodiversity

through the altering of the physical environ-

ment, increased erosion and perhaps the dis-

ruptive effects on nutrient recycling.

Given the critical status of the last remnants

of native Seychelles vegetation, it is essential

to carefully describe and document their

present condition as a reference for future

conservation measures. The purpose of this

article is (a) to give a brief account of the his-

toric development of the Seychelles flora and

(b) to describe its main vegetation types with

characteristic plant species. This description

is illustrated by photographs available in elec-

tronic form. A similar account was given by

Francis Friedmann (1987) in his book “Flow-

ers and Trees of the Seychelles”. This book

comprises a selection of remarkable pictures

of the Seychelles flora on the granite islands,

including typical habitats and beautiful sce-

nes. Unfortunately, this work is now out of

print and cannot be re-printed in the original

form because many of the original pictures

were destroyed by fire. Therefore, this contri-

bution and the associated “virtual gallery”

with photographs of prominent plants and

typical vegetation types is intended to be a

small substitute of what is no longer available.

The Seychelles flora and its history

Thanks to a large number of contributors and

the rather restricted area of the land, the flora

of the Seychelles is at present rather well

known and we have a fairly good knowledge

of the conservation status of most species.

The original flora of the granite islands was

rather poor with approximately 250 species

of indigenous flowering plants of which about

34% (84 taxa) are supposed to have been en-

demic. There are also about 80 fern species

growing on the islands, several of which are

supposed to be endemic to the Seychelles

(Fleischmann 1997).

While most oceanic islands have received

their flora predominantly by long-distance

(i.e. 1000 km) dispersal, the native flora of the

Seychelles probably derived predominantly

from ancestors which were already present






















Bulletin of the Geobotanical Institute ETH, 69, 


on the Seychelles microcontinent 65 million

years ago when the archipelago was about to

split up from Gondwanaland. Few species in

the Seychelles have seeds that are adapted to

long-distance dispersal. Before the arrival of

humans, only a minor part of the native flora,

mainly in the coastal zone and in the wet-

lands, had probably arrived by long-distance


As can be expected from the geological his-

tory of the area, the native flora of the Sey-

chelles includes elements of African, Mada-

gascan and Indo-Malaysian origin, with the

latter being the most prominent (Cox & Moor

1996). A considerable proportion of the en-

demic species are probably relict elements

from an ancient widespread Gondwana-flora

which became extinct on the mainlands but

survived in the Seychelles. Many primitive

characters have been preserved in relict spe-

cies  such as Medusagyne oppositifolia  and

Psathura seychellarum

 (Procter 1974).

After the ice age a period of submergence

followed when the Seychelles microcontinent

was reduced from a more or less continuous

land mass of 43’000 km


 to scattered islands

with a total area of about 245 km



1984). This dramatic reduction in land area

undoubtedly must have been accompanied

by massive extinctions in the flora. The spe-

cies occurring in the lowlands would have

been especially affected. This theory is sup-

ported by the fact that the main part of the

endemic species are found at intermediate

and high altitudes, whereas only two species

are confined to the coastal zone.

During the long period of isolation of the

islands, evolution may have slowly given rise

to new plant species like Lodoicea maldivica

(Edwards et al. 2002). Groups of taxa which

have probably evolved after the isolation of

the Seychelles microcontinent exist within

genera like Gastonia (three species and three

varieties), and in the Hypoxidiaceae (Hypoxi-

dia rhizophylla, Hypoxidia mahensis

) (Carl-

stroem 1996).

The present flora of the Seychelles is rela-

tively homogeneous (Carlstroem 1996). No

differences in morphological characters were

observed between populations on different is-

land (Fleischmann, personal observation).

However, it is still possible that genetic differ-

entiation exists among the different island

populations; this could be revealed by genetic


Natural vegetation types on the granite


Although a full documentation of the original

vegetation types of Seychelles is lacking,

some conclusions can be drawn from the

present vegetation, in combination with old

written records. The following vegetation

types have been identified on the granite is-






We only have very scarce reports on the com-

position of the shore vegetation from the ear-

lier records, which mainly noted the more

important timber trees. The exploitation of

the trees of the beach crest as well as the con-

struction of sea walls, land reclamation, con-

struction of houses, coconut plantations, etc.

have all contributed to the alteration of the

original coastal vegetation. Our knowledge

about the original composition is therefore

limited (Sauer 1967).

By the time the first settlers arrived on the

Seychelles the shores were fringed with coco-

nut palms which were believed to have grown

from nuts cast up by the sea. Other trees men-

tioned from the shores in the earlier reports

were Casuarina equisetifolia, Terminalia catap-

pa, Calophyllum inophyllum, Cordia subcor-

K. F







Bulletin of the Geobotanical Institute ETH, 69, 




  It has been much discussed whether

Terminalia catappa, Casuarina equisetifolia


Cocos nucifera

 were brought to the Seychelles

by the first people visiting the islands or

whether they were present before the first ar-

rival of humans. Certainly they were already

widely spread by this time, and they now

form an integral part of the coastal vegetation.

The dominant shrub on the beach crests

today is Scaevola sericea.  Other common

shore-line trees are Cocos nucifera, Calo-

phyllum inophyllum, Hernandia nymphaeifo-

lia, Hibiscus tiliaceus, Barringtonia asiatica,

Guettarda speciosa

  and Cordia subcordata, in

the past frequently mixed with Tournefortia

argentea, Suriana maritima

  and  Sophora to-


Scramblers and creeping plants are

common in the shore vegetation. Most spe-

cies growing along the coast are species com-

mon to the shores of most tropical islands and

the endemic flora has never played an impor-

tant role on the littoral.









The lowland forests originally covered the

mountain sides up to about 200–300 m. The

coastal plains were originally described as be-

ing covered by magnificent trees reaching up

to 20–25 m, with a circumference of 4–5 m

and with very straight trunks. The trees were

spaced at 2.5–3.5 m from each other with

hardly any branches for the first 15–20 m.

Species like Terminalia catappa, Casuarina equi-

setifolia, Intsia bijuga, Calophyllum inophyllum,

Heritiera littoralis, Mimusops seychellarum,

Vateriopsis seychellarum, Syzygium wrightii


Cordia subcordata

 were described as common

in this zone in the first records. Palm trees,

especially  Phoenicophorium borsigianum, Ne-

phrosperma vanhoutteana

 and Deckenia nobilis

were also mentioned from the original low-

land forests, especially on dry ridges. The spe-

cies composition of the woods of Silhouette

was described as being the same but smaller.

The islands of Cousin, Cousine and Aride

were apparently never well wooded and were

described as covered by scrubland even in the

first records from Malavoise 1786–87 (Carl-

stroem 1996).

The primary lowland flora was apparently

composed partly of endemic species as well

as indigenous species more widely spread on

most islands in the Indian Ocean; however, it

is obvious that the endemic species played a

less important role in the lowland vegetation

than at the higher elevations.





Near the sea level were also the mangrove

swamps dominated by the same six species of

mangrove trees that occur today, with Avi-

cennia marina

 and Rhizophora mucronata be-

ing the most prominent at present. The ex-

posed open sea coasts have never been colo-

nised by mangroves. Hence the mangrove

have always been found only on the more

tranquil lagoon shores. The earliest settlers

reported extensive areas covered with almost

impenetrable mangroves, especially along the

East coast of Mahé. All species known from

the mangrove swamps have a wide distribu-

tion and no endemic species are known to

occur in this vegetation type.





The vegetation along most rivers in the Sey-

chelles was much affected by human activities

and there is little information on riverine for-

ests to be found in the literature. Most of the

remaining river forests are composed of palm

trees, especially Phoenicophorium borsigianum,

Verschaffeltia splendida,

  frequently associated

with Barringtonia racemosa and Pandanus bal-


 at the lower altitudes. Possibly Vateriopsis


 also formed part of this commu-

nity. There also seems to be a constant asso-






















Bulletin of the Geobotanical Institute ETH, 69, 


ciation of Pandanus hornei  and  Verschaffeltia






From 200 to 500 m there was an intermediate

forest zone. These forests were rich in species

and had a high canopy at least occasionally

reaching up to 30–40 m. The big trees were

spaced at approximately 9–10-m intervals,

and the trunks were very straight. The forest

at intermediate altitudes was the one richest

in endemic species; endemics made up the

main part of the vegetation. These forests

have now been almost entirely cut down and

most of the remaining areas have been heavily

invaded by exotic species or have been

planted with exotic forest trees. Areas with

intermediate forests with at least remnants of

the high canopy are now very rare in the Sey-

chelles. Most of the remaining forests have

been combed through for timber and most

suitable tall trees have been cut down. It is

therefore difficult to judge what the species

composition in these forests was like and evi-

dence of its former appearance can only be

gained from much modified scattered

patches. Our best knowledge of the vegeta-

tion from the intermediate altitudes comes

from the exposed rocky areas and some river

ravines which have served as sanctuaries for

much of the flora.

At drier sites the intermediate forests have

probably been dominated by the endemic

palm trees associated with Campnosperma

seychellarum, Diospyros seychellarum, Meme-

cylon eleagni, Excoecaria benthamiana, Para-

genipa wrightii, Erythroxylon seychellarum,

Syzygium wrightii, Canthium bibracteatum,

Soulamea terminalioides,

 etc., whereas forests

at more humid sites were dominated by

Northea hornei, Dillenia ferruginea, Vateriopsis

seychellarum, Grisollea thomassetii, Pouteria

obovata, Campnosperma seychellarum,

 and Gas-

tonia crassa

  (Bwa Bannann). Palms were of

only minor importance in the forests of the

more humid type. There were also large

stands of screwpines (Pandanaceae). Tree

ferns (Cyathea seychellarum ) have been de-

scribed as a common feature in the humid in-

termediate forests and along the river ravines.

Much of the dry ridges with a shallow soil

have been described as having a Mimusops /


  dominated forest type. This kind

of vegetation is now only to be found as scat-

tered remnants on rocky outcrops. The cree-

per Merremia peltata and the only recently es-

tablished Clidemia hirta have started to heav-

ily invade the lowland- and intermediate for-

ests on Mahé.







High altitude forest originally covered most

land above 400–500 m in the Seychelles. On

mainland tropical mountains, mist forest is

typically found at altitudes of between 2000

and 3500 m, but on steep small islands like

the Seychelles mist forests develop at much

lower altitudes. The transition into the mist

forest zone is gradual and depends greatly on

local conditions. In many places the transition

between the intermediate and high altitude

forests have been obscured by the dominance

of exotic vegetation, which grows from sea

level to the highest elevations, making the

transition less obvious. The conditions at the

high altitudes are more humid and a moun-

tain mist forest develops where the annual

rainfall is well over 3000 cm yr


. These areas

are often enshrouded in low clouds.

Even these high altitude areas have suffered

from heavy cutting of selected trees, so there

are only a few relict stands of primeval forest

left. The remaining areas, however, give us an

idea of its former appearance. The remnants

of high altitude forest are still dominated by

native species, giving an idea of the original

K. F







Bulletin of the Geobotanical Institute ETH, 69, 



structure of this forest type. The mountain

mist forest is rich in mosses, lichens, filmy

ferns and epiphytic orchids. Tree ferns (Cya-

thea seychellarum

) are a common feature of

this forest type. Climbers like Schefflera


 were described as a characteristic

feature in the past but are now much less

common. The trees in the mist forest exhibit a

reduced tree stature and increased stem den-

sity compared to forests of lower lying areas.

As a result of the cutting of the best timber

trees in the canopy, the second-story trees of-

ten form a new lower canopy today which is

lower than the original. However, big trees

can still be found at undisturbed sites at

higher altitudes indicating that the canopy

was previously up to about 15 m tall with a

circumference of more than 2 m. Northea hor-


 was, and still is, the dominant species of

the canopy of this zone. It commonly occurs

with  Pandanus seychellarum  and with a sec-

ond-story vegetation of Roscheria melano-

chaetes, Gastonia crassa, Psychiotria pervillei,

etc. In the original forest at the higher alti-

tudes endemic species dominated the vegeta-

tion. The total number of endemic species in

the mist forest is, however, lower than at the

intermediate altitudes.










On the granite islands of the Seychelles there

is a vegetation element which cannot be re-

lated to altitude. This vegetation type, com-

prising vegetation growing on solitary, often

monolithic rocks or parts of mountain sys-

tems which rise abruptly from their surround-

ings, is locally called “glacis-type” vegetation.

The term “glacis” is French and means

“steep, rocky slope”. Glacis are freely ex-

posed precambrian rock outcrops, which in

geomorphological terms are known as insel-

bergs. On the Seychelles they occur through-

out the above-mentioned habitats from the

seashore to the mountain tops. Extreme

edaphic and climatic conditions (high degree

of insolation combined with high evaporation

rates) exert an strong selective pressure re-

sulting in a vegetation that is very different

from the surroundings. Soil which accumu-

lates in pockets and fissures of the rock con-

sists largely of coarse quartz sand with vari-

able amounts of peaty organic matter. If the

peat cover is destroyed by clearing of the veg-

etation or fire the underlying bare rock is ex-

posed. These factors have given rise to a veg-

etation type which is characterised by an out-

standing degree of endemism, locally as high

as 96 %. Taxa typically growing on inselbergs

are Pandanus multispicatus, Memecylon elea-

gni, Mimusops seychellarum, Excoecaria ben-

thamiana, Soulamea terminalioides

  and on

just a few locations the very rare Medusagyne


Virtual gallery

A collection of photographs of typical vegeta-

tion types and their characteristic plant spe-

cies is given under http://www.geobot.umnw.


(on this web page, select “Electronic Appen-

dices”, and there “App. 2003-7”).

This Appendix consists of a text part, which

provides a concise compendium of the most

important vegetation types, and a total of 74

photographs, which can be accessed from the

text through hyperlinks. Most plant species

mentioned in the two preceding sections of

this article are represented in the virtual gal-

lery. The photographs can be viewed on the

screen and downloaded as jpg files. They

have been produced by Karl Fleischmann,

Pauline Héritier and Cyrill Meuwly during

field work in 2001–2002. They can be used

freely for teaching and scientific purposes,

provided that the full source is indicated.






















Bulletin of the Geobotanical Institute ETH, 69, 


It is the authors’ hope that a wider apprecia-

tion of the beauty and uniqueness of the Sey-

chelles flora, as reflected by the photographs

in the virtual gallery, will stimulate further

research aimed at protecting these plants

against increasing human disturbance and al-

ien plant invasions.


Karsten Rohweder and Hans-Heini Vogel

skilfully supported us in constructing the vir-

tual gallery. We also thank Sabine Güsewell

and an anonymous referee for helpful com-

ments on the manuscript.


Anderegg, M. & Wiederkehr, F. (2001) Problems


  Paraserianthes falcataria on Mahé, Sey-


  Master’s Thesis, Geobotanical Institute

ETH, Zürich.

Carlstroem, A. (1996) Endemic and threatened plant

species on the granite Seychelles.

  Report to the

Ministry of Foreign Affairs, Division of Environ-

ment, Seychelles.

Cox, C.B. & Moor, P.D. (1996) Biogegography, an

ecological and evolutionary approach.


Science, Oxford.

Edward, P.J., Kollmann, J. & Fleischmann, K.

(2002) Life history evolution in Lodoicea maldi-


 Nordic Journal of Botany, 22, 227–237.

Evans, R.D., Rimer, R. & Sperry, L. (2001) Exotic

plant invasions. Ecological Applications, 11, 1301–


Fleischmann, K., Porembski, S., Biedinger, N. &

Barthlott, W. (1996) Inselbergs in the sea: Vegeta-

tion of granite outcrops on the islands of Mahé,

Praslin and Silhouette (Seychelles). Bulletin of the

Geobotanical Institute ETH,

 62, 61–74.

Fleischmann, K. (1997) Invasion of alien woody

plants on the islands of Mahé and Silhouette,

Seychelles. Journal of Vegetation Science, 8, 5–12.

Friedmann, F. (1987) Flowers and trees of Seychelles.

ORSTOM, Paris.

Gerlach, J. (1993) Invasive Melastomataceae in

Seychelles. Phelsuma, 1, 18–38.

Peters, H.A. (2001) Clidemia hirta  invasion at the

Pasoh Forest Reserve: An unexpected plant in-

vasion in an undisturbed tropical forest. Bio-


 33, 60–68.

Parendes, L.A. & Jones, J.A. (2000) Role of light

availability and dispersal in exotic plant invasion

along roads and streams in the H. J. Andrews

Experimental Forest, Oregon. Conservation Biol-


 14, 64–75.

Procter, J. (1974) The endemic flowering plants of

the Seychelles: an annotated list. Candollea, 29,


Robertson, S.A. (1989) Flowering plants of Sey-


 Royal Botanic Gardens, Kew.

Sauer, J.D. (1967) Plants and man on the Seychelles

coast. A study in historical biogeography.

 The Uni-

versity of Wisconsin Press, Madison, London.

Stoddart, D.R. (1984) Biogeography and Ecology of

the Seychelles Islands.

 Monographiae Biologicae,

Boston & Lancaster.

Whittaker, R.J. (1998) Island Biogeography. Oxford

University Press, Oxford.

Received 11 April 2003

Revised version accepted 1 July 2003

Electronic Appendix

Appendix 1.

  Typical vegetation types of the

Seychelles (classified according to altitude)

and their characteristic plant species, with

hyperlinks to colour photographs.

The Appendix can be downloaded at



(select ‘Electronic Appendices’, App. 2003–7).

Verilənlər bazası müəlliflik hüququ ilə müdafiə olunur ©azkurs.org 2016
rəhbərliyinə müraciət

    Ana səhifə