Plant species cannot escape climate change but may be less vulnerable than previously thought (Briefing 3.3)

Its rich and unique flora makes the Mediterranean region a hotspot of global biodiversity, including many wild progenitors of important crop species. Since water availability is the key limiting abiotic factor in these ecosystems, the main impact of climate change is expected to result from changing rainfall patterns, namely an increasing frequency of dry years, rather than from raising temperatures or CO2 levels. Even small changes in precipitation are believed to have a large impact and pose a major threat to plant diversity. However, Mediterranean and arid ecosystems are already now characterized by their large intra-annual precipitation variability. Therefore plant species growing there must be adapted to a wide range of conditions and may thus be more resilient to climatic shifts than commonly thought. It was our objective to find out to what extent the diverse plant communities are really threatened by climate change and which species are the most vulnerable. This knowledge will help developing efficient management strategies and to target investment into conservation to those actions that are most urgently needed and effective. Our study suggests that escaping climate change via seed dispersal is no option. Thus, species will have to deal with changing conditions or go extinct. The changes projected until 2065 are well within the conditions under which most species can maintain positive population growth. However, increasing frequencies of dry years have a negative effect and further changes will eventually increase extinction risk. If it comes to that, populations from arid and semiarid areas are likely to be more threatened than the ones from more humid areas, for which we could not find a direct link between population performance and rainfall. This implies that any effort to restrict climate change to the unavoidable minimum is worth fighting for since the magnitude of change will make the difference between survival and extinction of species