EVALUATION OF A BRACKEN (PTERIDIUM-AQUILINUM (L) KUHN) GROWTH-MODEL IN PREDICTING THE EFFECTS OF CONTROL STRATEGIES ACROSS A RANGE OF CLIMATIC ZONES IN GREAT-BRITAIN

A nationwide bracken control experiment provided data over a three-yea r period for testing the accuracy of a bracken growth model (BRACON). Objective assessments of model validity identified the model as a reas onably accurate predictor of bracken stand dynamics given the range of environmental conditions currently prevailing in Great Britain, in re lation to (1) cutting regimes and (2) spraying asulam. Ranking of trea tment efficacy at individual sites was closely reflected in model pred ictions. Predicted response of the rhizome system to cutting treatment s underestimated bracken resilience. Failure to consider the consequen ces of frond regrowth in the latter portion of the growing season as a means to offsetting energy loss was identified as a potential explana tion for this discrepancy. The role of the model as a practical manage ment tool is discussed with particular reference to relating model pre dictions, based upon generalised environmental data (40km x 40km grid cells), to bracken management at individual sites.