Geob. Kapitel 6 Ms76

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 international 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 photographs. 2 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 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.

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