MODELING THE EFFECTS OF CLIMATE-CHANGE ON THE GROWTH OF BRACKEN (PTERIDIUM-AQUILINUM) IN BRITAIN

1. A mechanistic, physiological model has been developed to describe t he yearly growth cycle of bracken, and it has been adapted to run usin g nationally available meteorological data. 2. The model (COBRA-X) pre dicts the equilibrium biomass of bracken stands under mean climatic co nditions for Great Britain based on a grid of 40-km squares.3. Estimat es from the model were similar to data collected in the field, althoug h at present it is not known whether discrepancies can be attributed t o limitations of the model, differences caused by the scale of availab le meteorological data or deviations of the stands from equilibrium va lues. 4. The model predicts that bracken biomass is limited by differe nt environmental factors in different regions of Great Britain. It can also be used to predict the effects of changing climate on bracken st ands. 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 difficult ies in extrapolating predictions from the stand scale to the countrywi de scale are outlined. Some solutions are put forward for bracken whic h may provide a methodology for other species.