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The Conservatoire Botanique National de Mascarin - Plant Conservation in Action on La Réunion Island (Indian Ocean)

Volume 3 Number 7 - February 2001

Jean-Yves Meyer

The tropical high volcanic island of La Réunion, being formed 2.1 million years ago, and located about 150 km west of Mauritius and 780 km east of Madagascar, is the largest (2,512 sq. km) and the highest (3,069 m in elev.) of all the oceanic islands in the Indian Ocean. Although relatively poorly known compared to nearby Mauritius or the Seychelles, the native flora of La Réunion appears to be relatively rich. About 240 fern species and more than 500 flowering plant species have been described from the island. Among the flowering plants, about 160 species are strictly endemic to La Réunion (species-level endemism of nearly 30 %), and 6 endemic genera are recognized. The uniqueness of La Réunion’s native biota lies in its great diversity of vegetation types, ranging from littoral vegetation and lowland semi-dry forests, to low- and mid- elevation wet (or rain-) forests, montane wet (or cloud-) forests, and ericoid vegetation on the highest summits of Piton des Neiges (3,069 m) and Piton de la Fournaise (2,631 m), a still active volcano.

As in most islands, the plant diversity of La Réunion is highly threatened, mainly by habitat destruction and fragmentation caused by human activities (the island was uninhabited until colonization in the late sixteenth and early seventeenth centuries; the population grew from about 250,000 inhabitants in 1950 to 600,000 in 1990, and is currently estimated at 710,000). Additional threats include over-harvesting of natural resources (especially endemic tree ferns of the genus Cyathea, terrestrial and epiphytic orchids, and palms of the genus Acanthophoenix), combined with habitat disturbances and severe invasion by alien plants. More than 620 naturalized plants have been recorded in La Réunion, of which about 60 species are considered to be highly invasive in almost intact native forests. A total of 61 native and endemic plant species have been legally protected by a national decree in February 1987, 94 belong to the most threatened categories defined by IUCN (Ex/E, E, V, R) and 6 are extinct in the wild (according to the 1997 Red List of Threatened Plants, (Walter & Gillett (eds) 1998), but nearly 250 could be considered as threatened which is one-third of the entire native flora (unpublished data) . However, unlike Mauritius Is. where less than 3% of the native forest is left, La Réunion has kept about 30% of its nearly pristine habitats, mainly in the mid- and high elevation humid vegetation types. Therefore, the prospect for conservation of some of these rare endemic species in their natural range holds promise.

The Conservatoire Botanique National de Mascarin (CBNM) was originally created in 1986 under the name “Conservatoire et Jardin Botanique de Mascarin”. A 12.5 ha-garden, the CBNM is located at an elevation of 500 m, on the leeward side of La Réunion above the town of Saint-Leu. It belongs to a network of 8 National Botanical Conservatories whose five main missions (1- inventory and study of the native flora; 2- in situ conservation; 3- ex situ conservation; 4- information and expertise for local authorities; 5- public education) are defined and approved by the French Ministry of Environment. CBNM is currently the only Conservatoire in the French tropical overseas departments and territories (which includes the islands of Martinique, Guadeloupe, French Polynesia, New Caledonia, Wallis & Futuna, and the region of French Guiana in Tropical America). Until 1996, the main goal of CBNM was primarily focussed on ex situ conservation; the cultivation and the propagation of rare and threatened plants endemic to La Réunion ("60% of the endangered flora of Réunion has been successfully rescued and established in cultivation in the garden”, BGCNews 1(4), June 1989), and also of the other Mascarene islands (namely Mauritius and Rodrigues) and Madagascar. Now, CBNM is becoming more involved in the management and monitoring of species and populations in their natural habitats, including the study and control of invasive plants which are recognized as one of the major threats to island native floras, and are also of growing importance for botanic gardens (BGCNews 3(1), December 1998). Ex situ propagation is considered as the last lifebuoy of a species on the verge of extinction (as quoted by the late J.-P. Galland who founded the network of National Botanical Conservatories in France in 1988), and a tool for in situ conservation programmes (reintroduction, population reinforcement in the wild, habitat restoration).

Since 1996, a team of young scientists (aged between 26-31 years), all native to the island and trained at the Université de La Réunion, has been recruited by the current director of CBNM, D. Lucas. The team includes a field botanist (H. Thomas), a field-data collector (J-M Pausé), an ex situ conservation specialist (F. Picot), a database/GIS specialist (E. Picard), a vegetation mapping/invasive plant specialist (C. Lavergne) and three gardeners working in the botanic garden and the greenhouse (J. Ferrar, H. Fossy, B. Ellama). S. Françoise is the head of the “Service scientifique” which is based at the CBNM in the Laboratoire Thérésien Cadet, named in honour of a La Réunion-born plant ecologist (1937-1987) whose tremendous work on the island’s flora and vegetation is still considered an important reference. The three other departments of the CBNM are the “Service du tourisme” (tourism dept), the “Service éducatif” (education dept), and the “Service de gestion et d’aménagement du parc” (garden planning and management dept), with a total of about 40 employees.

Among the achieved and on-going conservation programmes, are:

  • the setting up of permanent plots in mid-elevation wet forests for long-term study of plant diversity and vegetation dynamics;
  • field surveys & botanical investigations, which have resulted in a significant increase in the number of locations for rare endemics (such as the highly endangered Ruizia cordata, Sterculiaceae, from one known location to five, or Carissa xylopicron, Apocynaceae);
  • assessment of natural areas of high conservation value for their protection or sustainable management by local authorities;
  • the setting up of an electronic database (called “Banque de données Mascarine”) on threatened endemic plants, including their geographical locations (using MapInfo software) and demographic structure for each population;
  • a recovery programme of an endangered and protected plant species (Lomatophyllum macrum, Liliaceae) with in situ population reinforcement (or restocking);
  • a detailed vegetation mapping project using high-technology tools (GIS/GPS, hand-computer I-pac), and 1:25 000 aerial colour photographs and Infra-Red photographs;
  • the study of the seed germination and reproductive biology of endemic plants such as the rare tristylous liana Hugonia serrata (Linaceae), or the lavaflow pioneer shrub Antirhea borbonica (Rubiaceae), in collaboration with the Université de La Réunion.

Future projects include:

  • the publication of an atlas of 15 protected plant species which are considered highly endangered in La Réunion (based on the “Mascarine” database), with their status, present and past distribution;
  • seed-storage of threatened endemic plants in the Laboratoire Thérésien Cadet, and the creation of an arboretum (field genebank) in the gardens of CBNM;
  • a strong collaboration with the Université de La Réunion on population genetics of rare endemic plants, and on an invasive plant study and management programme (called “INVABIO”) funded by the French Ministry of Environment;
  • the setting up a “Green List” of native and endemic plants for replanting on a wider scale in urban areas, as an alternative to the cultivation of potential or known invasive species, and in order to reduce pressure on plants in the wild.

Research and conservation programmes are approved by the CBNM scientific committee chaired by Dr. Dominique Strasberg (Lecturer at the Laboratory of Plant Biology and Physiology, Université de La Réunion). The committee, which meets once a year, is composed of 15 members, including scientists (in the fields of conservation biology, plant ecology, plant pathology, genetics, botany, ornithology), managers (foresters), and other local personalities (a naturalist, school teacher, curator of the museum of natural history). Researchers come from La Réunion (Université de La Réunion, CIRAD-Forêt), France (CEFE-CNRS Montpellier, Université de Toulouse), Mauritius (Mauritian Wildlife Foundation), and Madagascar (Parc botanique de Tsimbazaza).

Information/education of the public (both local people and tourists, children and adults) plays an important role for the CBNM, and the scientific team is contributing to this effort by making posters, giving talks, training a network of about 60 local “botanistes amateurs” on plant identification, and promoting nature conservation.

The CBNM is viewed as a conservation tool for local and French authorities, and a link between theoreticians (researchers) and practitioners (land managers, foresters,horticulturists) on La Réunion. The necessity of working with local communities, nature protection groups and other institutions involved in nature conservation (The Ornithological Society, The Natural History Museum, The Insectarium) is essential in a country where ecotourism has dramatically increased.

To conclude with a more personal thought, being an islander myself (native to Tahiti, French Polynesia), and having spent 5 years in La Réunion in the 80’s, I am deeply convinced that the young local scientific team of the CBNM is a “un gage d’avenir” (a future token) for La Réunion island’s native biota conservation.