The flora of Reunion Island is like other intertropical oceanic islands the result of a slow and selective immigration (native species*) and speciation process which, although only recent on the geological time scale, are at the origin of an important endemism.
For lack of own means of locomotion, the natural dissemination of plants is inevitably passive: by ocean currents (sea), winds or cyclones (air), or by birds (animals). Isolated in the middle of the Indian ocean, Reunion Island has always been a destination difficult to reach! Only a few species were able to complete the journey and establish themselves. The original vegetation is based on the nearest continental zones (nearly 70% of the flora comes from Madagascar and East Africa).
The spontaneous flora of Reunion Island currently** comprises 1730 species of vascular plants, of which 1478 spermatophytes*** (85,4%) and 252 "pteridophytes" (14,6%). They are divided into:
- 848 native species (86 of which only likely native), which is about half (49%) of the spontaneous flora. Among these species:
- 237 (28 %) are only endemic to Reunion Island,
- 153 (18 %) are regionally endemic, also growing in the other Mascareignes islands (Mauritius and Rodrigues),
- 458 (54 %) are simply native species, which can also be found in their country of origin,
- 829 exotic species*, which is approximately the other half (48 %),
- 53 cryptogenic* species 3 %.
The native flora of the island may present a relatively reduced plant diversity, it offers a high endemicity (28.0% for the strict endemism and 46.6% for the total endemism), awarding it with an important patrimonial value worldwide. Reunion Island has thus been recognised as one of the 25 hotspots of biodiversity in the world.
Human settlement during the middle of the 17th century enriched the flora of the island with an exotic component that would gradually play a more and more important role in the development of the society on Reunion Island. The wide range of usage (agricultural, forestry, economic, medicinal, ornamental,...) and an always increasing flow of goods and services lead to the intentional or unintentional introduction of several thousands of species from tempered tropical zones all over the world. A certain amount of these species now pose a real threat to the native flora.
Insularity and micro-endemicity make the native flora more fragile and vulnerable, enhancing the risk of extinction and the biodiversity crisis on the oceanic islands.
The alteration and destruction of habitats has had the most destructive impact on the biodiversity of the island. Although the process has slowed down considerably under the combined action of an association of vigilants and a proactive policy for the preservation of native habitats and the conservation of native biodiversity, native vegetation continues to shrink here and there.
Human disturbances (fires, wild grazing and the planting of crops in high mountain areas, plantations under trees, wild camping, the opening of paths, overcrowding, …) are contemporary examples that illustrate the more global problem of biological invasions by introduced species. The International Union for Conservation of Nature (IUCN) considers these invasions to be the third factor responsible for the loss of biodiversity, after the destruction of habitats and the overexploitation of species.
Today, 256 species on Reunion Island are considered to be endangered (according to IUCN criteria), or strictly spoken 30,7% of the native flora. 125 of these endangered species are now in acute danger of extinction (at least in nature).
Consequently, Reunion Island finds itself in the middle of sustainable development projects.
Knowledge of native flora and habitats along with their fragility is an asset that should contribute to preservation.
The challenge of a touristic development towards respect for the natural environment of Reunion Island, requires the involvement of everyone in saving a unique heritage in the world.
* Characterisation of vegetation:
- native species have arrived in a natural way on the island.
- endemic species are native species that have evolved into a new species, growing naturally in a certain place.
- exotic species have been introduced by man, coming from other countries.
- cryptogenic species are potentially native, but have an unclear origin due to lacking evidence.
- invasive species are exotic species whose growth and development have practically become uncontrollable, posing a severe threat to the native species.
** According to the 2008 version of the Index, published by "le Conservatoire Botanique National de Mascarin".
*** Spermatophytes are plants that produce seeds instead of spores such as mosses, lichens and fungi, but very little is known about them on the island.
Article by "le Conservatoire Botanique National de Mascarin"