Describing vegetation succession after bracken control: Evaluation of the REBRA model

The initial response of ground flora within bracken control experimental plots at a study site in Breckland, East Anglia was monitored in order to provide test data for a model (REBRA), which predicts vegetation succession after bracken control. The accuracy of model predictions for vegetation response at the community level was considered using multivariate analysis. Differences between vegetation assemblages were dominated by bracken litter and frond cover, with the hierarchy of treatment consistent between field observations and model predictions. Cutting once yearly exhibited the most limited vegetation response to management, whereas cutting twice yearly created the greatest change in the plant communities relative to untreated bracken. Spraying with asulam was an intermediate strategy with plant communities reverting to undesirable vegetation types after initial success in bracken control. Three factors responsible for discrepancies between recorded and predicted vegetation communities were identified: (1) bryophyte species which formed a consistent component of the recorded vegetation throughout the study were unable to be incorporated into model predictions; (2) model predictions for reduction in bracken litter cover as a consequence of experimental treatment were under-estimated considerably; (3) following cutting treatments, competition arising from frond regrowth in the latter portion of the growing season and subsequent litter inputs were not considered within the model. Despite these confounding factors, the model appeared, within this limited evaluation, to be a potentially valuable tool in formulating management strategies to better direct succession after bracken control.