Stretching from the Arctic to the South Pacific through the Atlantic, Amazonia, Antarctica and Indian Ocean, the 28 European Overseas Territories present both a remarkable and vulnerable biodiversity. Typically tropical islands, they are generally small in size with limited resources; they are often isolated and exposed to tropical cyclones and sea level rise. These insular ecosystems are particularly rich, with significant endemism rates, but they are also extremely fragile and often highly deteriorated. Therefore, their resilience to new aggressions is limited. Furthermore, island economies strongly rely on the quality of their natural environment. Notably through tourism, fishing and subsistence farming, a degradation of their environment could deeply affect local communities. Mountain areas do not represent a significant proportion of these territories but some of them shelter unique and threatened biodiversity: sub-Alpine forests in French Polynesia (the only ones in the South Pacific region), high altitude rainforests and mountain forest on Reunion Island, laurel forests in Macaronesia, etc.