Modelling the effects of climate change on the growth of bracken (Pteridium aquilinum) in Britain

1. A mechanistic, physiological model has been developed to describe the yearly growth cycle of bracken, and it has been adapted to run using nationally available meteorological data. 2. The model (COBRA-X) predicts the equilibrium biomass of bracken stands under mean climatic conditions for Great Britain based on a grid of 40-km squares. 3. Estimates from the model were similar to data collected in the field, although at present it is not known whether discrepancies can be attributed to limitations of the model, differences caused by the scale of available meteorological data or deviations of the stands from equilibrium values. 4. The model predicts that bracken biomass is limited by different environmental factors in different regions of Great Britain. It can also be used to predict the effects of changing climate on bracken stands. Likely scenarios of climate change result in a large increase in bracken biomass in the north, especially in the highlands of central Scotland, but little change in England and Wales. 5. Certain difficulties in extrapolating predictions from the stand scale to the countrywide scale are outlined. Some solutions are put forward for bracken which may provide a methodology for other species.