Insular environmental change; climate-forced and system-driven

Abstract

Vegetation dynamics since the last glacial maximum in small oceanic islands and in continental settings are compared. We selected the islands of Minorca (Western Mediterranean), Tenerife (Eastern Atlantic), the Azores (Central Atlantic) and Mauritius (Indian Ocean) and compared pollen-based dynamics with selected continental areas of southern Italy, the Atlas mountains, northwest Africa, and the East African mountains. We identified potential areas where plant diversity is conserved during unfavourable periods serving as refugial areas. Most pollen records from small oceanic islands with a low topography show, as far as the pollen records reach, stable forest compositions suggesting floral diversity is lodged within a mosaic-like structure. In mountainous islands data point to an altitudinal distribution of plant diversity and to altitudinal migration of plants as a response to climate change. In Mauritius we registered at 11.4 cal. ka a climate-forced change in forest composition which triggered a cascade of species turnover events considered as system-driven. In the small islands discussed we identified areas with a high potential to provide on a long-term shelter to insular floral diversity, thus serving as a refugium: 1) gallery forest located along the drainage system (topography constrained), 2) cloud forest located at the elevation where atmospheric moisture condensates and cloud formation takes place (sea surface temperature and atmospheric lapse rate constrained), 3) and deeply incised valleys, connecting diversity between all available elevations, where relatively humid conditions prevail such as the barrancos in Tenerife and the deeply incised valleys in Mauritius (geomorphology and sea-level constrained)