Recent climate projections indicate substantial environmental alterations in oceanic island regions during the 21st century, setting up profound threats to insular floras. Inherent characteristics of island species and ecosystems (e.g. small population sizes, low habitat availability, isolated evolution, low functional redundancy) cause a particular vulnerability. Strong local anthropogenic pressures interact with climate change impacts and increase threats. Owing to the high degree of endemism in their floras, a disproportionally high potential for global biodiversity loss originates from climate change impacts on oceanic islands. We reviewed a growing body of research, finding evidence of emerging climate change influences as well as high potentials of future impacts on insular species and ecosystems. Threats from global climate change are not evenly distributed among the world's oceanic islands but rather vary with intrinsic (e.g. island area, structure, age and ecological complexity) and extrinsic factors (regional character, magnitude and rate of climatic alterations, local human influences). The greatest flora vulnerabilities to climate change impacts can be expected on islands of small area, low elevation and homogeneous topography. Islands of low functional redundancies will particularly suffer from high rates of co-modifications and co-extinctions due to climate-change-driven disruptions of ecological interactions. High threat potentials come from synergistic interactions between different factors, especially between climatic changes and local anthropogenic encroachments on native species and ecosystems. In addition, human responses to climate change can cause strong indirect impacts on island floras, making highly populated islands very vulnerable to secondary (derivative) effects. We provide an integrated overview of climate change-driven processes affecting oceanic island plants and depict knowledge gaps and uncertainties. The suitability of oceanic islands and their ecosystems for potential research on the field of climate change ecology is highlighted and implications for adequate research approaches are given.
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