Climate change is supposed to be a serious threat to the endemic flora and ecosystems of oceanic islands. Precise knowledge on precipitation change is missing due to high uncertainties in global climate models impeding their transfer to small-scaled and topography-depending complex island-specific climate conditions. Mountainous oceanic islands in the subtropics have a particular diverse climate because they are exposed to trade winds: They contain a high variability moisture conditions and and develop a prominent trade wind cloud layer.
We developed for our ECOPOTENTIAL model island system La Palma (Canary Islands/Spain) different precipitation scenarios to investigate potential future distribution changes of endemic species: (1) a divergence of precipitation extremes (dry areas get dryer, wet areas wetter), (2) a decrease of the mean annual precipitation (due to an increase in altitude of the trade wind cloud layer) and a scenario with (3) less precipitation for high elevations and more precipitation for low elevations (due to a decrease in altitude of the trade wind cloud layer). We combined these three scenarios with two temperature predictions based on RCP trajectories 4.5 and 8.5, respectively. Then, we calculated species distributions based on the current climate and projected them using the different scenarios. Furthermore, we analyzed potential distances between current and future areas of similar environmental conditions on the island scale.
Our study exemplifies the potential threats of climate change that native and endemic plant species are exposed to on small and isolated oceanic islands. Although buffered by the surrounding ocean, climate change will severely impact endemic species in island systems. This might present an overlooked danger to global biodiversity because range-restricted endemics on islands contribute substantially to global biodiversity.