K. FLEISCHMANN ET AL.

RESEARCH NOTE

Virtual gallery of the vegetation and flora of the Seychellles

KARL FLEISCHMANN*, PAULINE HÉRITIER, CYRILL MEUWLY, CHRISTOPH KÜFFER & PETER J. EDWARDS Geobotanical Institute, ETH Zürich, Zürichbergstrase 38, CH-8044 Zürich, Switzerland; * corresponding author: [email protected]

Summary 1 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- graphs. 2 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. 3 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) 4 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- tions/periodicals/bulletin.html

Keywords: conservation, endemism, island flora, plant invasion, Seychelles, vegetation types. Nomenclature: Friedmann (1994).

Bulletin of the Geobotanical Institute ETH (2003), 69, 57–64

Introduction The Seychelles archipelago consists of about fore had an extremely long time to develop a hundred granite and coralline islands near independently from that of the rest of the the equator in the Western Indian Ocean world, mainly through natural evolutionary (Fleischmann et al. 1996). These islands prob- processes, leading to a high level of ende- ably split from Gondwana some 65 million mism. The unique status of the granite islands years ago and have been isolated from conti- of the Seychelles as oceanic islands of conti- nents ever since. The Seychelles flora there- nental origin, and the phytogeographical im-

Bulletin of the Geobotanical Institute ETH, 69, 57–64 57 VIRTUAL GALLERY OF THE VEGETATION AND FLORA OF THE SEYCHELLLES portance of the islands as combining African, •Propagules dispersed by animals. Animal- Madagascan and Indo-Malaysian elements in dispersed seeds are typically fleshy berries, their flora make it a region of great floristic relatively small in size, and variously colo- interest. The fact that at the time of the first red. The dispersers of greatest importance human settlement on Mahé in the 1770’s the in the Seychelles are fruit-eating birds and flora had evolved continuously and without bats. Prominent amongst introduced spe- human interaction for many millions of years, cies with bird-dispersed fruits are Cinnamo- certainly adds to the outstanding status of the mum verum, Psidium cattleianum and Clide- Seychelles’ island vegetation. In fact the Sey- mia hirta. Species using animals or wind as chelles have been identified as a biodiversity dispersal mechanisms (i.e. Paraserianthes f.) hotspot by Conservation International and as are capable of quickly invading native eco- a centre of plant diversity by the WWF and systems in areas remote from where the IUCN. adults themselves are planted. As for Cin- One of the major threats to the native spe- namomum v. and Psidium c. an additional cies and forests of the Seychelles is the ram- attribute making these plants even worse is pant spread of a number of alien plant spe- that they can reproduce vegetatively as well cies across the islands (Fleischmann 1997); as by seeds. the most invasive ones are Cinnamomum • High fecundity. Species that produce many verum, Psidium cattleianum, Clidemia hirta, seeds per plant each year can invade new Merremia peltata and Paraserianthes falca- habitat patches more rapidly than can most taria. These plants displace the distinctive native plants that produce relatively few native flora of the Seychelles, resulting in the seeds (Peters 2001). For example, Cinna- loss of diverse native forests. The situation in momum v. and Clidemia h. (the latter is now the Seychelles is particularly serious because the subject of a control effort by state and there are several rare, endemic species like private organizations) produce large num- Medusagyne oppositifolia, Secamone schimpe- bers of seeds, so that their populations can riana, Vateriopsis seychellarum etc. which are increase very rapidly, which partially ac- fated to extinction following the invasion of a counts for the great threat they pose to the great variety of introduced organisms. It is Seychelles’ forests. generally accepted that invasive alien species •Fast growth: Fast-growing plants that may have a competitive or reproductive ad- quickly reach maturity will be more inva- vantage over native species (Parendes 2000). sive and harder to control than slower- Besides this, the introduction of certain plant growing plants. An outstanding example species may promote further change be- of the importance of this phenomenon is cause they affect ecosystem processes. Inva- Clidemia h. which was first seen on Mahé sive species can influence nitrogen availabil- island in 1993 (Gerlach 1993). Since then ity by changing litter quantity and quality, single plants have been found all over the rates of N2-fixation, or rates of nitrogen loss island. By competing with native species (Evans et al. 2001; Anderegg & Wiederkehr in gaps, Clidemia h. invasion has the po- 2001). A variety of biological attributes of tential to alter forest regeneration (Peters plants serve to make them invasive, but in 2001). the Seychelles three are of primary impor- In order to prevent fundamental changes to tance. the indigenous and endemic vegetation of the

58 Bulletin of the Geobotanical Institute ETH, 69, 57–64 K. FLEISCHMANN ET AL.

Seychelles an ongoing commitment to con- to carefully describe and document their trolling invasive alien species is required. This present condition as a reference for future commitment is based on scientific research conservation measures. The purpose of this which provides a wider perspective on the article is (a) to give a brief account of the his- problem of invasion by alien species, and a toric development of the Seychelles flora and rational basis for habitat management (i.e. the (b) to describe its main vegetation types with control of this invasion). It has become obvi- characteristic plant species. This description ous that the protection of land in itself will not is illustrated by photographs available in elec- be sufficient to save the habitats. Since most tronic form. A similar account was given by areas of the Seychelles are heavily infested Francis Friedmann (1987) in his book “Flow- with alien plants, the crucial question is: what ers and Trees of the Seychelles”. This book can be done to save the remaining, intact na- comprises a selection of remarkable pictures tive forests? To address this question, several of the Seychelles flora on the granite islands, research projects in the field of conservation including typical habitats and beautiful sce- and invasion biology have been conducted nes. Unfortunately, this work is now out of through the Geobotanical Institute in Zürich print and cannot be re-printed in the original over the last eleven years. form because many of the original pictures Despite the wide scale destruction of the were destroyed by fire. Therefore, this contri- original island vegetation, there are sites bution and the associated “virtual gallery” where at least some of the original elements of with photographs of prominent plants and the natural flora have been preserved. On typical vegetation types is intended to be a Mahé and Silhouette there are still substantial small substitute of what is no longer available. areas of humid high-altitude forests and inselbergs containing a rich endemic flora. Luckily, relatively few of the endemic plant The Seychelles flora and its history species are so far known to have become ex- Thanks to a large number of contributors and tinct on all islands (Carlstroem 1996). How- the rather restricted area of the land, the flora ever, the fact that populations of many en- of the Seychelles is at present rather well demic and threatened species are extremely known and we have a fairly good knowledge small is a serious concern. For many of these of the conservation status of most species. species, especially those of the ancient forests The original flora of the granite islands was at intermediate altitude, the situation is critical rather poor with approximately 250 species since their natural habitats no longer exist. of indigenous flowering plants of which about These species (e.g. Medusagyne oppositifolia) 34% (84 taxa) are supposed to have been en- will never survive without human interfer- demic. There are also about 80 fern species ence. It is most likely that the displacement of growing on the islands, several of which are the native flora through competition with in- supposed to be endemic to the Seychelles vasive exotic taxa will reduce biodiversity (Fleischmann 1997). through the altering of the physical environ- While most oceanic islands have received ment, increased erosion and perhaps the dis- their flora predominantly by long-distance ruptive effects on nutrient recycling. (i.e. 1000 km) dispersal, the native flora of the Given the critical status of the last remnants Seychelles probably derived predominantly of native Seychelles vegetation, it is essential from ancestors which were already present

Bulletin of the Geobotanical Institute ETH, 69, 57–64 59 VIRTUAL GALLERY OF THE VEGETATION AND FLORA OF THE SEYCHELLLES on the Seychelles microcontinent 65 million varieties), and in the Hypoxidiaceae (Hypoxi- years ago when the archipelago was about to dia rhizophylla, Hypoxidia mahensis) (Carl- split up from Gondwanaland. Few species in stroem 1996). the Seychelles have seeds that are adapted to The present flora of the Seychelles is rela- long-distance dispersal. Before the arrival of tively homogeneous (Carlstroem 1996). No humans, only a minor part of the native flora, differences in morphological characters were mainly in the coastal zone and in the wet- observed between populations on different is- lands, had probably arrived by long-distance land (Fleischmann, personal observation). dispersal. However, it is still possible that genetic differ- As can be expected from the geological his- entiation exists among the different island tory of the area, the native flora of the Sey- populations; this could be revealed by genetic chelles includes elements of African, Mada- analyses. gascan and Indo-Malaysian origin, with the latter being the most prominent (Cox & Moor 1996). A considerable proportion of the en- Natural vegetation types on the granite demic species are probably relict elements islands from an ancient widespread Gondwana-flora Although a full documentation of the original which became extinct on the mainlands but vegetation types of Seychelles is lacking, survived in the Seychelles. Many primitive some conclusions can be drawn from the characters have been preserved in relict spe- present vegetation, in combination with old cies such as Medusagyne oppositifolia and written records. The following vegetation Psathura seychellarum (Procter 1974). types have been identified on the granite is- After the ice age a period of submergence lands. followed when the Seychelles microcontinent was reduced from a more or less continuous COASTAL PLATEAU land mass of 43’000 km2 to scattered islands We only have very scarce reports on the com- with a total area of about 245 km2 (Stoddart position of the shore vegetation from the ear- 1984). This dramatic reduction in land area lier records, which mainly noted the more undoubtedly must have been accompanied important timber trees. The exploitation of by massive extinctions in the flora. The spe- the trees of the beach crest as well as the con- cies occurring in the lowlands would have struction of sea walls, land reclamation, con- been especially affected. This theory is sup- struction of houses, coconut plantations, etc. ported by the fact that the main part of the have all contributed to the alteration of the endemic species are found at intermediate original coastal vegetation. Our knowledge and high altitudes, whereas only two species about the original composition is therefore are confined to the coastal zone. limited (Sauer 1967). During the long period of isolation of the By the time the first settlers arrived on the islands, evolution may have slowly given rise Seychelles the shores were fringed with coco- to new plant species like Lodoicea maldivica nut palms which were believed to have grown (Edwards et al. 2002). Groups of taxa which from nuts cast up by the sea. Other trees men- have probably evolved after the isolation of tioned from the shores in the earlier reports the Seychelles microcontinent exist within were Casuarina equisetifolia, Terminalia catap- genera like Gastonia (three species and three pa, Calophyllum inophyllum, Cordia subcor-

60 Bulletin of the Geobotanical Institute ETH, 69, 57–64 K. FLEISCHMANN ET AL. data. It has been much discussed whether was described as being the same but smaller. Terminalia catappa, Casuarina equisetifolia and The islands of Cousin, Cousine and Aride Cocos nucifera were brought to the Seychelles were apparently never well wooded and were by the first people visiting the islands or described as covered by scrubland even in the whether they were present before the first ar- first records from Malavoise 1786–87 (Carl- rival of humans. Certainly they were already stroem 1996). widely spread by this time, and they now The primary lowland flora was apparently form an integral part of the coastal vegetation. composed partly of endemic species as well The dominant shrub on the beach crests as indigenous species more widely spread on today is Scaevola sericea. Other common most islands in the Indian Ocean; however, it shore-line trees are Cocos nucifera, Calo- is obvious that the endemic species played a phyllum inophyllum, Hernandia nymphaeifo- less important role in the lowland vegetation lia, Hibiscus tiliaceus, Barringtonia asiatica, than at the higher elevations. Guettarda speciosa and Cordia subcordata, in the past frequently mixed with Tournefortia MANGROVE FOREST argentea, Suriana maritima and Sophora to- Near the sea level were also the mangrove mentosa. Scramblers and creeping plants are swamps dominated by the same six species of common in the shore vegetation. Most spe- mangrove trees that occur today, with Avi- cies growing along the coast are species com- cennia marina and Rhizophora mucronata be- mon to the shores of most tropical islands and ing the most prominent at present. The ex- the endemic flora has never played an impor- posed open sea coasts have never been colo- tant role on the littoral. nised by mangroves. Hence the mangrove have always been found only on the more LOWLAND AND COASTAL FORESTS tranquil lagoon shores. The earliest settlers The lowland forests originally covered the reported extensive areas covered with almost mountain sides up to about 200–300 m. The impenetrable mangroves, especially along the coastal plains were originally described as be- East coast of Mahé. All species known from ing covered by magnificent trees reaching up the mangrove swamps have a wide distribu- to 20–25 m, with a circumference of 4–5 m tion and no endemic species are known to and with very straight trunks. The trees were occur in this vegetation type. spaced at 2.5–3.5 m from each other with hardly any branches for the first 15–20 m. RIVERINE FOREST Species like Terminalia catappa, Casuarina equi- The vegetation along most rivers in the Sey- setifolia, Intsia bijuga, Calophyllum inophyllum, chelles was much affected by human activities Heritiera littoralis, Mimusops seychellarum, and there is little information on riverine for- Vateriopsis seychellarum, Syzygium wrightii and ests to be found in the literature. Most of the Cordia subcordata were described as common remaining river forests are composed of palm in this zone in the first records. Palm trees, trees, especially Phoenicophorium borsigianum, especially Phoenicophorium borsigianum, Ne- Verschaffeltia splendida, frequently associated phrosperma vanhoutteana and Deckenia nobilis with Barringtonia racemosa and Pandanus bal- were also mentioned from the original low- fouri at the lower altitudes. Possibly Vateriopsis land forests, especially on dry ridges. The spe- seychellarum also formed part of this commu- cies composition of the woods of Silhouette nity. There also seems to be a constant asso-

Bulletin of the Geobotanical Institute ETH, 69, 57–64 61 VIRTUAL GALLERY OF THE VEGETATION AND FLORA OF THE SEYCHELLLES ciation of Pandanus hornei and Verschaffeltia tonia crassa (Bwa Bannann). Palms were of splendida. only minor importance in the forests of the more humid type. There were also large INTERMEDIATE FOREST stands of screwpines (Pandanaceae). Tree From 200 to 500 m there was an intermediate ferns (Cyathea seychellarum) have been de- forest zone. These forests were rich in species scribed as a common feature in the humid in- and had a high canopy at least occasionally termediate forests and along the river ravines. reaching up to 30–40 m. The big trees were Much of the dry ridges with a shallow soil spaced at approximately 9–10-m intervals, have been described as having a Mimusops / and the trunks were very straight. The forest Excoecaria dominated forest type. This kind at intermediate altitudes was the one richest of vegetation is now only to be found as scat- in endemic species; endemics made up the tered remnants on rocky outcrops. The cree- main part of the vegetation. These forests per Merremia peltata and the only recently es- have now been almost entirely cut down and tablished Clidemia hirta have started to heav- most of the remaining areas have been heavily ily invade the lowland- and intermediate for- invaded by exotic species or have been ests on Mahé. planted with exotic forest trees. Areas with intermediate forests with at least remnants of MOUNTAIN MIST FOREST the high canopy are now very rare in the Sey- High altitude forest originally covered most chelles. Most of the remaining forests have land above 400–500 m in the Seychelles. On been combed through for timber and most mainland tropical mountains, mist forest is suitable tall trees have been cut down. It is typically found at altitudes of between 2000 therefore difficult to judge what the species and 3500 m, but on steep small islands like composition in these forests was like and evi- the Seychelles mist forests develop at much dence of its former appearance can only be lower altitudes. The transition into the mist gained from much modified scattered forest zone is gradual and depends greatly on patches. Our best knowledge of the vegeta- local conditions. In many places the transition tion from the intermediate altitudes comes between the intermediate and high altitude from the exposed rocky areas and some river forests have been obscured by the dominance ravines which have served as sanctuaries for of exotic vegetation, which grows from sea much of the flora. level to the highest elevations, making the At drier sites the intermediate forests have transition less obvious. The conditions at the probably been dominated by the endemic high altitudes are more humid and a moun- palm trees associated with Campnosperma tain mist forest develops where the annual seychellarum, Diospyros seychellarum, Meme- rainfall is well over 3000 cm yr-1. These areas cylon eleagni, Excoecaria benthamiana, Para- are often enshrouded in low clouds. genipa wrightii, Erythroxylon seychellarum, Even these high altitude areas have suffered Syzygium wrightii, Canthium bibracteatum, from heavy cutting of selected trees, so there Soulamea terminalioides, etc., whereas forests are only a few relict stands of primeval forest at more humid sites were dominated by left. The remaining areas, however, give us an Northea hornei, Dillenia ferruginea, Vateriopsis idea of its former appearance. The remnants seychellarum, Grisollea thomassetii, Pouteria of high altitude forest are still dominated by obovata, Campnosperma seychellarum, and Gas- native species, giving an idea of the original

62 Bulletin of the Geobotanical Institute ETH, 69, 57–64 K. FLEISCHMANN ET AL. structure of this forest type. The mountain seashore to the mountain tops. Extreme mist forest is rich in mosses, lichens, filmy edaphic and climatic conditions (high degree ferns and epiphytic orchids. Tree ferns (Cya- of insolation combined with high evaporation thea seychellarum) are a common feature of rates) exert an strong selective pressure re- this forest type. Climbers like Schefflera sulting in a vegetation that is very different procumbens were described as a characteristic from the surroundings. Soil which accumu- feature in the past but are now much less lates in pockets and fissures of the rock con- common. The trees in the mist forest exhibit a sists largely of coarse quartz sand with vari- reduced tree stature and increased stem den- able amounts of peaty organic matter. If the sity compared to forests of lower lying areas. peat cover is destroyed by clearing of the veg- As a result of the cutting of the best timber etation or fire the underlying bare rock is ex- trees in the canopy, the second-story trees of- posed. These factors have given rise to a veg- ten form a new lower canopy today which is etation type which is characterised by an out- lower than the original. However, big trees standing degree of endemism, locally as high can still be found at undisturbed sites at as 96%. Taxa typically growing on inselbergs higher altitudes indicating that the canopy are Pandanus multispicatus, Memecylon elea- was previously up to about 15 m tall with a gni, Mimusops seychellarum, Excoecaria ben- circumference of more than 2 m. Northea hor- thamiana, Soulamea terminalioides and on nei was, and still is, the dominant species of just a few locations the very rare Medusagyne the canopy of this zone. It commonly occurs oppositifolia. with Pandanus seychellarum and with a sec- ond-story vegetation of Roscheria melano- chaetes, Gastonia crassa, Psychiotria pervillei, Virtual gallery etc. In the original forest at the higher alti- A collection of photographs of typical vegeta- tudes endemic species dominated the vegeta- tion types and their characteristic plant spe- tion. The total number of endemic species in cies is given under http://www.geobot.umnw. the mist forest is, however, lower than at the ethz.ch/publications/periodicals/bulletin.html intermediate altitudes. (on this web page, select “Electronic Appen- dices”, and there “App. 2003-7”). GLACIS TYPE VEGETATION (INSELBERGS) This Appendix consists of a text part, which On the granite islands of the Seychelles there provides a concise compendium of the most is a vegetation element which cannot be re- important vegetation types, and a total of 74 lated to altitude. This vegetation type, com- photographs, which can be accessed from the prising vegetation growing on solitary, often text through hyperlinks. Most plant species monolithic rocks or parts of mountain sys- mentioned in the two preceding sections of tems which rise abruptly from their surround- this article are represented in the virtual gal- ings, is locally called “glacis-type” vegetation. lery. The photographs can be viewed on the The term “glacis” is French and means screen and downloaded as jpg files. They “steep, rocky slope”. Glacis are freely ex- have been produced by Karl Fleischmann, posed precambrian rock outcrops, which in Pauline Héritier and Cyrill Meuwly during geomorphological terms are known as insel- field work in 2001–2002. They can be used bergs. On the Seychelles they occur through- freely for teaching and scientific purposes, out the above-mentioned habitats from the provided that the full source is indicated.

Bulletin of the Geobotanical Institute ETH, 69, 57–64 63 VIRTUAL GALLERY OF THE VEGETATION AND FLORA OF THE SEYCHELLLES

It is the authors’ hope that a wider apprecia- Peters, H.A. (2001) Clidemia hirta invasion at the tion of the beauty and uniqueness of the Sey- Pasoh Forest Reserve: An unexpected plant in- chelles flora, as reflected by the photographs vasion in an undisturbed tropical forest. Bio- tropica, 33, 60–68. in the virtual gallery, will stimulate further Parendes, L.A. & Jones, J.A. (2000) Role of light research aimed at protecting these plants availability and dispersal in exotic plant invasion against increasing human disturbance and al- along roads and streams in the H. J. Andrews ien plant invasions. Experimental Forest, Oregon. Conservation Biol- ogy, 14, 64–75. Procter, J. (1974) The endemic flowering plants of the Seychelles: an annotated list. Candollea, 29, Acknowledgements 345–387. Robertson, S.A. (1989) Flowering plants of Sey- Karsten Rohweder and Hans-Heini Vogel chelles. Royal Botanic Gardens, Kew. skilfully supported us in constructing the vir- Sauer, J.D. (1967) Plants and man on the Seychelles tual gallery. We also thank Sabine Güsewell coast. A study in historical biogeography. The Uni- and an anonymous referee for helpful com- versity of Wisconsin Press, Madison, London. ments on the manuscript. Stoddart, D.R. (1984) Biogeography and Ecology of the Seychelles Islands. Monographiae Biologicae, Boston & Lancaster. Whittaker, R.J. (1998) Island Biogeography. Oxford References University Press, Oxford. Anderegg, M. & Wiederkehr, F. (2001) Problems with Paraserianthes falcataria on Mahé, Sey- Received 11 April 2003 chelles. Master’s Thesis, Geobotanical Institute Revised version accepted 1 July 2003 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. Blackwell Science, Oxford. Edward, P.J., Kollmann, J. & Fleischmann, K. (2002) Life history evolution in Lodoicea maldi- vica. Nordic Journal of Botany, 22, 227–237. Evans, R.D., Rimer, R. & Sperry, L. (2001) Exotic plant invasions. Ecological Applications, 11, 1301– 1310. Electronic Appendix Fleischmann, K., Porembski, S., Biedinger, N. & Barthlott, W. (1996) Inselbergs in the sea: Vegeta- Appendix 1. Typical vegetation types of the tion of granite outcrops on the islands of Mahé, Praslin and Silhouette (Seychelles). Bulletin of the Seychelles (classified according to altitude) Geobotanical Institute ETH, 62, 61–74. and their characteristic plant species, with Fleischmann, K. (1997) Invasion of alien woody hyperlinks to colour photographs. plants on the islands of Mahé and Silhouette, Seychelles. Journal of Vegetation Science, 8, 5–12. The Appendix can be downloaded at Friedmann, F. (1987) Flowers and trees of Seychelles. ORSTOM, Paris. http://www.geobot.umnw.ethz.ch/publica- Gerlach, J. (1993) Invasive Melastomataceae in tions/periodicals/bulletin.html Seychelles. Phelsuma, 1, 18–38. (select ‘Electronic Appendices’, App. 2003–7).

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