Self-incompatibility will slow climate driven northward shift of two dominants of calcareous grasslands

Calcareous grasslands are considered as hotspots of plant and invertebrate diversity but little is known about the potential of their main dominants to migrate as a response to climate change. Although it is generally acknowledged that climate warming will allow plant species to expand their ranges northwards and upwards, not all restrictions on dispersal may be climate dependent. We assessed dispersal limitations in Bromopsis erecta and Brachypodium pinnatum, two dominant grasses of calcareous grasslands in Central Europe and southern England. Both species are known to spread rapidly in the absence of disturbance and are thus expected to have major impacts on species diversity and ecosystem functioning of northern calcareous grasslands. Pollination experiments showed that seed production in B. erecta, and we suspect also in B. pinnatum, at the northern range margin is climatically limited, which suggests that the species will be able to produce seeds outside their current distribution under climate warming. Self-incompatibility, on the other hand, is likely to considerably slow northward migration, as isolated founder populations may be unable to set seed, especially since calcareous grasslands are sparse and fragmented. Our results have important practical implications for managers attempting to slow the spread of these potential dominants, and also for those trying to encourage the northward migration of rare self-incompatible species in response to climate change.