Changes to plant distributions in Britain

Species distributions always have and will change, and there are a number of controlling factors involved in their overall distribution. Climate is considered one of the strongest drivers of changes to species distributions, and due to historical climate change, has played an important part in current species distributions. A large number of species have changed their distributions in the past century, which can largely be attributed to current anthropogenic climate change. This study uses the Botanical Society of Britain and Ireland (BSBI) vascular plant database to explore changes which are occurring to native plant species distributions in Britain. Studies are carried out to assess how and where plant species distributions are changing. Initially the northern range margin of southerly distributed native plant species were used to determine if there was a poleward shift as would be expected with a warming climate. Results show that, unlike animal species which have advanced north, plant species are not advancing towards the pole and a large number are in fact retracting at their northern edge. This is a clear indication that although the climate is changing, other factors are having a stronger influence on many plant species distributions in Britain. As it is known historically that plant species will follow climate change it is likely that human disturbance such as agricultural intensification and urbanisation are stronger drivers of distribution changes in Britain. Natural dispersal mechanisms are no longer facilitating spread in a large number of species due to these barriers. However, human mediated dispersal may become the main disperser in the future by carrying seeds beyond their natural range. There is however evidence that Bee orchids (Ophrys apifera Huds.), a species which is wind dispersed, with seeds carried on currents due to the dust like seeds, are successful in spreading and have in recent years been occurring in a broader range of habitats to where they are considered to traditionally occur. This is likely to be an example of a species that is benefiting from the warmer climate and has facilitated its spread into previously un-colonised areas. Therefore I conclude that at present the majority of species distributions used in this study have not responded to climate as expected due to other anthropogenic factors, however humans may become the most important disperser, facilitating species spread into new locations and some species may start to infill in their range and spread by natural means if propagules are easily dispersed long distances.