Histoire de l'invasion d'une plante introduite, Miconia calvescens, dans une île polynésienne, Tahiti

Abstract

Miconia calvescens DC (Melastomataceae), a forest understory shrub native of central America was introduced into Tahiti in 1937 due to its ornemental attributes. For about thirty years, it was found near gardens, in secondary forests or as a primary forest understory shrub. Ever since, it's distribution extends from the lowland up to the midland wet forests, bringing about the extinction of several endemic species. It occupies 75 % of the island's surface area, most parts of Moorea island, and is fast spreading on other islands of the Society archipelago. Hazardously dispersed, it starts off by penetrating Tahitian forests which are marked by the small height of their emergent trees. It then gradually reaches the forest cover, outgrows the emergents and makes up a monospecific canopy which now dictates new understory microclimatic conditions incompatible with the ecological requirements of indigenous species. Considering several parameters, some which are intrinsic to the island's ecosystem and others to climatic conditions or to species biology, this paper demonstrates that the fragility of an island's ecosystem towards allochton plants is related not only to fundamental parameters such as forest structure and reproduction biology but is also dependant on hazardous events such as climatic perturbation or the involuntary introduction of a bird...