Like all oceanic islands, Europa is a hard-to-reach destination for plants that do not have their own means of travel. Marine currents, wind, birds are the only means of passive dissemination that allow the arrival of seeds, cuttings .. on these isolated lands. But Europa is a rebel to colonization: recent emergence of land (quaternary), unfavorable marine currents, sub-arid climate, coral limestone substrate eroded in lapiaz, absence of evolved soils have singularly limited the plant population ... Few elected among the plants have thus solved this implacable insular equation: to arrive, to germinate, to implant itself, that is to say to grow and to reproduce ... The natural population in vascular plants does not exceed forty species ...
The man, especially on the occasion of his sustainable settlements on the island (exploitation of Sisal in the early twentieth, installation of the weather station, airstrips and military camp) brought with him an almost equal contingent of introduced plants.
Following short visits by botanists and naturalists to Europa, 46 species of vascular plants have been observed for almost a century (the first data date back to 1904). The Europa 2006 mission has made it possible to inventory nearly 70 species in total (ie about 25 new ones for the island, more precise figures depending on the examination of a certain number of critical plants) and to correct certain preliminary determinations. In addition, it allowed to discover the first two ferns of the island (2 species of Ophioglossus). But above all, it allowed the first description and monograph of the island's vegetation (202 phytosociological surveys and numerous vegetation transects), from which we can extract the following essential features:
- low diversity of plants, but a wide variety of habitats, including barnacles and brackish steppes
- strong affinities of the natural flora of Europa with the flora of the subarid regions of Tuléar which had to constitute the source of the natural vegetation of the island; probable influences of other Scattered Islands in plant introductions, particularly at the current runway;
- good general state of conservation, with the exception of the sub-interior forests of Euphorbia stenoclada, which have suffered considerably from fire and clearing;
- threats of plant invasions seemingly weak and currently limited to areas disturbed by human occupation, current impact of goats still difficult to identify, but probably stronger on anthropized spaces than on natural vegetation ...
Vincent BOULLET
