The history and spread of bracken in Britain

Abstract

SynopsisBracken, Pleridium aquilinum, has long been present in Britain as part of the native flora. Before the arrival of man, Britain was a wooded and forested country, and in this vegetation bracken was an open woodland and forest margin species, which played only a relatively minor vegetational role. Its biology is such, however, that this plant is able to spread rapidly in response to removal of the forest canopy, developing into colonies which are much more ecologically aggressive and dominating than was the original habit of the plant when undisturbed.In open conditions, bracken also has a far greater spore output than in more shaded ones. It is able to establish anew from spores only in relatively virgin soil conditions, particularly those produced by burning of other vegetation. Burning also benefits established bracken by removal of its competitors, whilst heavy and selective grazing by sheep also slowly reduces the natural vegetation competition in favour of bracken's further spread.The history of the spread of bracken in Britain from palynological and historical evidence is reviewed in the light of this biology and, in particular, its spread as man has progressively removed the forest canopy,introduced steady heavy grazing pressure, and has burned, and continues to burn, vegetation.